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Contents
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ix
Posttranscriptional Mechanisms Regulating the Inflammatory Response Georg Stoecklin and Paul Anderson 1. 2. 3. 4. 5. 6.
Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coordinate Regulation of Pro-Inflammatory Proteins . . . . . . . . . . . Control of mRNA Stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Translational Inhibition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Animal Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clinical Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 1 5 16 19 23 25 26
Negative Signaling in Fc Receptor Complexes Marc Dae¨ron and Renaud Lesourne 1. 2. 3. 4. 5.
Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fc Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Positive Signaling by Activating FcRs . . . . . . . . . . . . . . . . . . . . . . . Negative Signaling by Activating FcRs . . . . . . . . . . . . . . . . . . . . . . Negative Signaling by Inhibitory FcRs . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
v
39 40 44 50 60 70 74
c on t e n ts
vi
The Surprising Diversity of Lipid Antigens for CD1-Restricted T Cells D. Branch Moody 1. 2. 3. 4. 5. 6. 7. 8.
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction: From Molecules to Functions . . . . . . . . . . . . . . . . . . CD1 Protein Expression on Antigen-Presenting Cells . . . . . . . . . . Subcellular Lipid Antigen Processing Pathways. . . . . . . . . . . . . . . . 3-Dimensional Structures of CD1-b2-Microglobulin-Lipid Complexes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microbial Antigens and Infectious Disease . . . . . . . . . . . . . . . . . . . Self Antigens, Autoreactivity, and Autoimmune Disease . . . . . . . . . Synthetic Lipid Antigens and Prospects for Immunotherapy . . . . . Conclusion: Prospects for Immunotherapy . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
87 87 90 94 102 111 119 125 126 128
Lysophospholipids as Mediators of Immunity Debby A. Lin and Joshua A. Boyce Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. LPL Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Cell Surface Receptors for LPLs and Their Signaling Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Expression of LPA and S1P Receptors by Immune Cells and Their Functions in In Vitro Studies . . . . . . . . . . . . . . . . . . . . . 5. In Vivo Functions of LPLS in Immune Responses and Inflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Clinical Applications of S1P Receptor Agonists. . . . . . . . . . . . . . . . 7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
141 141 143 145 148 156 159 160 160
Systemic Mastocytosis Jamie Robyn and Dean D. Metcalfe 1. 2. 3. 4.
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mast Cell Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biology of Kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mastocytosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
169 169 170 184 193
c o nt e n t s 5. 6. 7. 8. 9.
Prognosis and Predictive Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supportive Care and Long-Term Management . . . . . . . . . . . . . . . . Future Therapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vii 209 209 216 218 220 220
Regulation of Fibrosis by the Immune System Mark L. Lupher, Jr. and W. Michael Gallatin 1. 2. 3. 4. 5. 6. 7.
Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fibrotic Disease Pathogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cellular Mediators of Fibrosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inflammatory Chemokines that Regulate Fibrosis. . . . . . . . . . . . . . The Role of Integrins in Regulating the Fibrotic Response . . . . . . Other Potential Targets for Anti-Fibrotic Therapy . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
245 245 246 249 261 264 268 270 273
Immunity and Acquired Alterations in Cognition and Emotion: Lessons from SLE Betty Diamond, Czeslawa Kowal, Patricio T. Huerta, Cynthia Aranow, Meggan Mackay, Lorraine A. DeGiorgio, Ji Lee, Antigone Triantafyllopoulou, Joel Cohen-Solal, and Bruce T. Volpe 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lupus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neuropsychiatric Lupus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanisms of NPSLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mouse Models of NPSLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peptide Reactivity of DNA-Reactive Antibodies . . . . . . . . . . . . . . . Presence of DWEYS-Reactive Antibodies in Murine and Human SLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Proteins Harboring the D/E W D/E Y S/G Concensus Sequence: Glutamate Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . Antibody-Mediated Neurotoxicity . . . . . . . . . . . . . . . . . . . . . . . . . . A Murine Model for Antibody-Mediated Neuronal Death . . . . . . . Antibody-Mediated Neurotoxicity in the Amygdala. . . . . . . . . . . . .
289 290 293 295 296 298 298 300 300 302 304 307
viii 12. 13. 14. 15. 16.
c on t e n ts Evidence that Antibodies Are Involved in NPSLE in Patients . . . . Anti-Peptide Antibody Activates Prolactin Secretion . . . . . . . . . . . . Anti-Peptide Antibodies and Manifestations of NP-SLE. . . . . . . . . Implications for SLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Implications for Human Pathobiology . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
308 309 310 310 311 311
Immunodeficiencies with Autoimmune Consequences Luigi D. Notarangelo, Eleonora Gambineri, and Raffaele Badolato Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Autoimmune Manifestations in Primary Immune Deficiencies: Relevance and Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. AIRE, Central Tolerance, and the Pathophysiology of Autoimmune Polyendocrinopathy. . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Defective AIRE Expression Explains the Pathophysiology of Autoimmunity in Omenn Syndrome . . . . . . . . . . . . . . . . . . . . . . . . 4. CD4þ CD25þ Regulatory T Cells and the Pathophysiology of IPEX (Immunodysregulation – Polyendocrinopathy – Enteropathy – X-Linked) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Concluding Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
321 322 324 337
346 357 359
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 Contents of Recent Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
Contributors
Numbers in parentheses indicate the pages on which the authors’ contributions begin.
Paul Anderson (1), Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts Cynthia Aranow (287), Department of Medicine, Columbia University Medical Center, New York, New York Raffaele Badolato (319), ‘‘Angelo Nocivelli’’ Institute for Molecular Medicine, Department of Pediatrics, University of Brescia, Brescia, Italy Joshua A. Boyce (141), Departments of Medicine and Pediatrics, Harvard Medical School, Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Boston, Massachusetts Joel Cohen-Solal (287), Department of Medicine, Columbia University Medical Center, New York, New York Marc Dae¨ron (39), Unite´ d’Allergologie Mole´ culaire et Cellulaire, De´partement d’Immunologie, Institut Pasteur, Paris, France Lorraine A. DeGiorgio (287), Department of Neurology and Neuroscience, The Burke Medical Research Institute, Weill Medical College of Cornell University, White Plains, New York Betty Diamond (287), Department of Medicine, Columbia University Medical Center, New York, New York W. Michael Gallatin* (245), ICOS Corporation, Bothell, Washington Eleonora Gambineri (319), Department of Pediatrics, University of Florence, Florence, Italy Patricio T. Huerta (287), Department of Neurology and Neuroscience, The Burke Medical Research Institute, Weill Medical College of Cornell University, White Plains, New York Czeslawa Kowal (287), Department of Medicine, Columbia University Medical Center, New York, New York *Current address: Frazier Healthcare Ventures, Seattle, Washington.
ix
x
c o n tr i b u t o rs
Ji Lee (287), Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York Renaud Lesourne (39), Unite´ d’Allergologie Mole´culaire et Cellulaire, De´partement d’Immunologie, Institut Pasteur, Paris, France Debby A. Lin (141), Department of Medicine, Harvard Medical School, and Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Boston, Massachusetts Mark L. Lupher, Jr. (245), ICOS Corporation, Bothell, Washington Meggan Mackay (287), Department of Medicine, Columbia University Medical Center, New York, New York Dean D. Metcalfe (169), Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland D. Branch Moody (87), Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts Luigi D. Notarangelo (319), ‘‘Angelo Nocivelli’’ Institute for Molecular Medicine, Department of Pediatrics, University of Brescia, Brescia, Italy Jamie Robyn (169), Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland Georg Stoecklin (1), Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts Antigone Triantafyllopoulou (287), Department of Medicine, Montefiore Medical Center, Bronx, New York Bruce T. Volpe (287), Department of Neurology and Neuroscience, The Burke Medical Research Institute, Weill Medical College of Cornell University, White Plains, New York
Posttranscriptional Mechanisms Regulating the Inflammatory Response Georg Stoecklin and Paul Anderson Division of Rheumatology, Immunology, and Allergy; Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
1. 2. 3. 4. 5. 6.
Abstract............................................................................................................. Coordinate Regulation of Pro‐Inflammatory Proteins ................................................. Control of mRNA Stability .................................................................................... Translational Inhibition......................................................................................... Animal Models ................................................................................................... Clinical Significance............................................................................................. Conclusions........................................................................................................ References .........................................................................................................
1 1 5 16 19 23 25 26
Abstract The inflammatory response is a complex physiologic process that requires the coordinate induction of cytokines, chemokines, angiogenic factors, effector‐ enzymes, and proteases. Although transcriptional activation is required to turn on the inflammatory response, recent studies have revealed that posttranscriptional mechanisms play an important role by determining the rate at which mRNAs encoding inflammatory effector proteins are translated and degraded. Most posttranscriptional control mechanisms function to dampen the expression of pro‐inflammatory proteins to ensure that potentially injurious proteins are not overexpressed during an inflammatory response. Here we discuss the factors that regulate the stability and translation of mRNAs encoding pro‐inflammatory proteins. 1. Coordinate Regulation of Pro‐Inflammatory Proteins In prokaryotes, the coordinate expression of genes encoding components of a metabolic pathway is often accomplished by expressing an mRNA transcript that encodes more than one protein. For example, the Lactose operon in Escherichia coli transcribes a single mRNA that encodes b‐galactosidase, permease, and transacetylase—proteins required for the utilization of lactose as a carbon source (Beckwith, 1967). Unlike their prokaryotic ancestors, processed eukaryotic transcripts generally encode a single protein. In eukaryotes, the coordinate expression of protein components of a complex functional program is accomplished by the use of regulatory nucleic acid sequences
1 advances in immunology, vol. 89 # 2006 Elsevier Inc. All rights reserved.
0065-2776/06 $35.00 DOI: 10.1016/S0065-2776(05)89001-7
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that determine rates of transcription, translation, and mRNA decay. Coordinate transcriptional control is accomplished by the selective use of promoter elements that are recognized by specific transcription factors. Activation of a transcription factor that turns on the expression of several genes involved in a common biological pathway can be sufficient to confer coordinate protein expression. One example is the heat shock response in which stress‐induced activation of heat shock factor 1 confers de novo transcription of mRNAs encoding several heat shock proteins (Voellmy, 2004). Mammalian cells have evolved posttranscriptional mechanisms that further coordinate the expression of proteins involved in a common cellular function. In some cases, regulation of mRNA stability and translation may be sufficient to coordinately regulate the expression of distinct functional classes of proteins. This appears to be the case in Saccharomyces cerevisiae in which gene array profiling has shown that mRNAs encoding subunits of complex structures such as proteasomes or ribosomes tend to have similar half‐lives (Wang et al., 2002). In many cases, posttranscriptional regulation is conferred by cis‐acting elements located in the 30 ‐untranslated region (30 UTR) of individual mRNAs. These regulatory elements recruit specific RNA‐binding proteins that, directly or indirectly, regulate mRNA translation and/or stability. A striking example of this type of regulation is provided by a family of Pumilio‐ Fem‐3‐binding factor (Puf) proteins. The Puf proteins bind to variants of a UGUR tetranucleotide motif found in the 30 UTR of selected mRNAs to regulate mRNA stability and/or translation (Wickens et al., 2002). In Saccharomyces cerevisiae, gene array profiling has revealed that Puf proteins can coordinately regulate the expression of mRNAs encoding proteins with a common function (Gerber et al., 2004). Thus, Puf1p and Puf2p were found to bind to mRNAs encoding membrane‐associated proteins, Puf3p binds to mRNAs encoding mitochondrial proteins, and Puf4p and Puf5p bind to mRNAs encoding nuclear proteins. Each Puf protein binds to a specific variant of the UGUR motif to confer specificity. These results strongly support the contention that RNA‐binding proteins coordinately regulate groups of mRNAs encoding proteins of a common function. This general mechanism has been referred to as a ‘‘post‐transcriptional operon’’ (Keene and Tenenbaum, 2002). The inflammatory response is an example of a functional program that requires the coordinate induction of proteins involved in a common function. During the inflammatory response, coordinate transcriptional control is accomplished by the selective use of promoter elements that are recognized by specific transcription factors. For example, the transcription factor Nuclear factor (NF)‐kB moves from the cytoplasm to the nucleus in T‐cells and macrophages that are exposed to inflammatory stimuli (Muller, 2001). Nuclear
P O S T T R A N S C R I P T I O N A L C O N T R O L O F I N F L A M M AT I O N
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NF‐kB binds to a nucleotide sequence element common to the promoters of several genes that encode inflammatory effector proteins (Muller, 2001). Although transcriptional activation is required for the synthesis of mRNA encoding inflammatory effector proteins, it does not determine the level of protein expression. Rather, it is the posttranscriptional regulation of mRNA stability and translation that determines levels of protein expression. Remarkably, mRNAs encoding proteins that regulate every facet of the inflammatory response are subject to these posttranscriptional control mechanisms. At the initiation phase of inflammation, Granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) primes neutrophils, macrophages, and dendritic cells for subsequent pro‐inflammatory action (Hamilton, 2002). Moreover, the expression of chemokines that recruit neutrophils, eosinophils, monocytes, and dendritic cells to sites of inflammation is strongly regulated at the posttranscriptional level. Effects on cellular recruitment are potentiated by the posttranscriptional regulation of the endothelial adhesion factor Vascular cell adhesion molecule (VCAM)‐1. During the effector phase of inflammation, the expression of pro‐inflammatory cytokines such as Tumor necrosis factor (TNF)a, Interleukin (IL)‐1b, IL‐6, and Interferon (IFN)g is also subject to posttranscriptional control. Excessive production of these cytokines orchestrates tissue damage in patients with inflammatory arthritis and inflammatory bowel disease. Proteases such as Matrix metalloprotease (MMP)‐9 and MMP‐ 13 participate in the tissue damage by breaking down components of the extracellular matrix. The effector phase is further exacerbated by enzymes that synthesize pro‐inflammatory mediators such as Cyclooxygenase (COX)‐2, 15‐Lipoxygenase (LO), and inducible Nitric oxide synthase (iNOS), which are also regulated at the level of mRNA stability and translation. Taken together, it is clear that posttranscriptional control mechanisms coordinately regulate multiple aspects of the inflammatory response. In general, these mechanisms conspire to dampen inflammation. This additional level of control may be required to prevent the pathological overexpression of proteins that are potentially injurious to the host. The synchronized anti‐inflammatory effects of these regulatory programs make them ideal targets for the development of anti‐ inflammatory drugs. In this review, we will focus on two mechanisms that regulate the fate of mRNAs in the cytoplasm: control of translation efficiency and control of mRNA stability. Although earlier steps (pre‐mRNA splicing, export of the mRNA from the nucleus into the cytoplasm) and later events (protein secretion, activation by proteolytic cleavage) are extensively regulated as well, they will not be discussed here. Table 1 lists pro‐inflammatory proteins whose expression is regulated at the level of translation or mRNA stability. Most of these proteins fall into one of three categories: cytokines, chemokines, and enzymes required for the synthesis of pro‐inflammatory mediators.
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Table 1 Pro‐Inflammatory Proteins Regulated at the Posttranscriptional Level mRNA
Mechanism
Element
References
Cytokines IL‐1b
mRNA stability
AREa
IL‐1F7b IL‐2
mRNA stability mRNA stability
CRDb ARE, JREc
IL‐3
mRNA stability
ARE
IL‐6
mRNA stability
ARE
IL‐11
mRNA stability
ARE
IL‐18 TNFa
mRNA stability mRNA stability, translation
n.d. ARE, CDEd
GM‐CSF
mRNA stability, translation
ARE
G‐CSF
mRNA stability
ARE, SLDEe
IFNb
mRNA stability
ARE, CRD
IFNg
mRNA stability
ARE
VEGF
mRNA stability
ARE, 50 UTR, CRD
MCP‐1 (CCL2) Eotaxin (CCL11) GROa (KC, CXCL1) GROb (MIP‐2, CXCL2) GROg (CXCL3) IL‐8 (CXCL8)
mRNA stability mRNA stability
n.d. ARE
(Pastore et al., 2005) (Atasoy et al., 2003)
mRNA stability
ARE
mRNA stability
ARE
mRNA stability mRNA stability
ARE ARE
IP‐10 (CXCL10)
mRNA stability
n.d.
(Biswas et al., 2003; Sirenko et al., 1997; Stoeckle, 1991) (Rousseau et al., 2002; Stoeckle, 1991) (Stoeckle, 1991) (Holtmann et al., 1999; Stoeckle, 1991; Winzen et al., 1999) (Vockerodt et al., 2005)
(Fenton et al., 1988; Sirenko et al., 1997) (Bufler et al., 2004) (Chen et al., 1998; Lindsten et al., 1989; Ogilvie et al., 2005) (Nair et al., 1994; Wodnar‐Filipowicz and Moroni, 1990) (Akashi et al., 1990; Neininger et al., 2002; Stoecklin et al., 2001; Winzen et al., 1999) (Bamba et al., 2003; Yang and Yang, 1994) (Bufler et al., 2004) (Brook et al., 2000; Carballo et al., 1998; Han et al., 1990; Stoecklin et al., 2003) (Carballo et al., 2000; Grosset et al., 2004; Koeffler et al., 1988; Shaw and Kamen, 1986) (Brown et al., 1996a; Koeffler et al., 1988; Putland et al., 2002) (Raj and Pitha, 1983; Whittemore and Maniatis, 1990) (Hodge et al., 2002; Lindsten et al., 1989; Mavropoulos et al., 2005) (Coles et al., 2004; Dibbens et al., 1999; Ikeda et al., 1995; Levy et al., 1998)
Chemokines
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Table 1 (Continued) mRNA
Mechanism
Element
References
Enzymes and other pro‐inflammatory proteins VCAM‐1
mRNA stability
n.d.
MMP‐9 MMP‐13 15‐LO iNOS
mRNA stability translation translation mRNA stability
ARE ARE DICE f ARE
COX‐2
mRNA stability, translation
ARE
(Croft et al., 1999; Iademarco et al., 1995) (Huwiler et al., 2003) (Yu et al., 2003) (Ostareck et al., 1997) (Di Macro et al., 2005; Rodriguez‐Pascual et al., 2000) (Dixon et al., 2003; Lasa et al., 2000; Mukhopadhyay et al., 2003; Ridley et al., 1998; Ristimaki et al., 1994)
a
ARE: AU‐rich element. CRD: coding region determinant of instability. c JRE: JNK response element. d CDE: constitutive decay element. e SLDE: stem‐loop destabilizing element. f DICE: differentiation control element. b
2. Control of mRNA Stability 2.1. mRNA Decay Mediated by the AU‐Rich Element Many of the pro‐inflammatory transcripts that are regulated at the posttranscriptional level have an adenine/uridine‐rich element (ARE) in their 30 UTR, which targets individual transcripts for rapid cytoplasmic degradation. AREs were initially discovered by their characteristic nucleotide pattern, and the high degree of sequence conservation between different mammalian species was an early indication of their important regulatory role (Caput et al., 1986). ARE‐mediated mRNA decay (AMD) was first demonstrated by Shaw and Kamen (1986), who inserted the ARE of GM‐CSF into the 30 UTR of a normally stable reporter mRNA (in this case a b‐globin transcript), and observed that it strongly reduced reporter gene expression by destabilizing the mRNA (Shaw and Kamen, 1986). Conversely, deletion of the ARE from the 30 UTR of IL‐3 or TNFa enhances gene expression by stabilizing the mRNA (Kontoyiannis et al., 1999; Stoecklin et al., 1994). Besides inducing AMD, quantitative analysis of TNFa reporter gene expression showed that the ARE also inhibits translation of the mRNA (Han et al., 1990). AREs are U‐rich sequences that contain several copies of a canonical AUUUA pentamer.
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According to a classification that takes into account deadenylation kinetics, the typical class II AREs of cytokine mRNAs (e.g., GM‐CSF, IL‐3, and TNFa) contain a cluster of 4–7 partially overlapping AUUUA pentamers within a U‐rich context (Chen and Shyu, 1995). Class I AREs (e.g., c‐myc, c‐fos) have fewer and more scattered AUUUA pentamers, while class III AREs (e.g., c‐jun) lack this motif. Class II AREs trigger a very rapid, asynchronous shortening of the poly‐A tail (processive deadenylation activity) prior to decay of the mRNA body, whereas class I and III AREs are associated with a less rapid, synchronous shortening of the poly‐A tail (distributive deadenylation activity) (Chen et al., 1995). For class II AREs, the AUUUA pentamers are of crucial importance, since point mutations within the pentamers efficiently abrogate AMD (Stoecklin et al., 1994). The extended UUAUUUAUU nonamer is the minimal sequence that can induce mRNA degradation (Lagnado et al., 1994; Zubiaga et al., 1995). This sequence is also the minimal binding site for tristetraprolin (TTP), an ARE‐binding protein required for AMD (see below). Compared to this minimal sequence, typical AREs are much longer (50–100 nucleotides), indicating that AREs of different mRNAs may vary with respect to their destabilizing activity, their ability to inhibit translation, and the regulatory mechanisms that control these activities. Since AREs were first discovered in cytokine transcripts, the biological importance of controlling mRNA stability has primarily been established in cells of the immune system. Nevertheless, AMD is a highly conserved regulatory mechanism that functions in yeast (Vasudevan and Peltz, 2001), trypanosomes (Quijada et al., 2002), Drosophila (Jing et al., 2005), and virtually all mammalian cell lines. Based on the frequency of AU‐rich sequences in the human genome, it has been estimated that 5–10% of all mRNAs may contain an ARE (Bakheet et al., 2003). Although experimental data is still needed to confirm this high estimate of functional AREs, it is clear that AMD is a general mechanism that regulates gene expression in most, if not all, eukaryotic cells. 2.2. The Different Roles of ARE‐Binding Proteins More than 20 different proteins that bind to AREs have so far been identified, but only a subset of them has been shown to influence the stability or translation efficiency of their target mRNAs. Table 2 gives an overview of ARE‐binding proteins (ARE‐BPs) that are known to have a regulatory function: TIA‐1, TIAR, FXR1P, and CUGBP2 inhibit the translation of ARE‐ mRNAs; HuR and YB1 stabilize ARE‐mRNAs; whereas AUF1, KSRP, RHAU, and the TTP/BRF family of proteins are involved in destabilizing ARE‐mRNAs.
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Table 2 ARE‐Binding Proteins ARE‐BP TIA‐1 TIAR FXRIP CUGBP2 HuR
Domains
Function
References
RRM (3)*
Inhibits translation
(Piecyk et al., 2000)
RRM (3) KH (2), RGG (1) RRM (3) RRM (3)
Inhibits translation Inhibits translation Inhibits translation Stabilizes mRNA
(Yu et al., 2003) (Garnon et al., 2005) (Mukhopadhyay et al., 2003) (Fan and Steitz, 1998; Lal et al., 2004; Peng et al., 1998; Wang et al., 2000) (Lal et al., 2004; Mazan‐Mamczarz et al., 2003) (Kullmann et al., 2002) (Capowski et al., 2001; Chen et al., 2000; Coles et al., 2004) (Lal et al., 2004; Loflin et al., 1999; Sarkar et al., 2003) (Xu et al., 2001) (Dean et al., 2002) (Chen et al., 2001; Gherzi et al., 2004) (Tran et al., 2004) (Carballo et al., 1998; Chen et al., 2001; Lai et al., 1999; Ming et al., 2001) (Lai et al., 2000; Stoecklin et al., 2000, 2002) (Lai et al., 2000)
Activates translation
YB1
CSD (1)
Inhibits translation Stabilizes mRNA
AUF1 (hnRNP D0)
RRM (2)
Destabilizes mRNA
AUF2 (CBF‐A) KSRP
RRM (2) KH (4)
Stabilizes mRNA Stabilizes mRNA Destabilizes mRNA
RHAU TTP (TIS11)
Helicase (1) C3H (2)
Destabilizes mRNA Destabilizes mRNA
BRF1 (TIS11b)
C3H (2)
Destabilizes mRNA
BRF2 (TIS11d)
C3H (2)
Destabilizes mRNA
*Designates the number of domains.
Genetic studies have provided evidence that the zinc finger proteins TTP, BRF1, and BRF2 play a central role in the degradation of ARE‐mRNAs. The TTP/BRF proteins bind to AREs with high specificity through their characteristic tandem C3H zinc finger domains (Blackshear, 2002; Varnum et al., 1991). The function of TTP was discovered by the study of TTP‐deficient mice, which develop generalized inflammatory symptoms that arise from increased levels of TNFa and GM‐CSF (Taylor et al., 1996). Cytokine overproduction in TTP/ mice is due to an increased stability of TNFa, GM‐CSF, and IL‐2 mRNAs (Carballo et al., 1998, 2000; Ogilvie et al., 2005). TTP normally binds to the ARE of these mRNAs and promotes their rapid degradation by targeting them to the cellular RNA degradation machinery (see below). Since TTP is mainly expressed in activated macrophages and T‐cells (Cao et al., 2004; Raghavan
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et al., 2001), its principal function appears to be the control of cytokine expression in the immune system. Yet TTP is also expressed in a variety of other tissues such as lung, liver, and intestine (Cao et al., 2004; Lu and Schneider, 2004), and may thus be involved in regulating other processes. BRF1 and BRF2 are homologues of TTP which share about 70% sequence identity in the highly conserved zinc finger domain, but differ substantially in the N‐ and C‐terminal domains (Varnum et al., 1991). BRF1‐deficient mice are not viable due to embryonic lethality at day 11 post‐fertilization, probably as a result of severe placental dysfunction (Stumpo et al., 2004). A mutant cell line generated by chemical mutagenesis and selected for a defect in AMD has provided evidence for the important role of BRF1 (Stoecklin et al., 2000, 2002). This mutant cell line lacks expression of BRF1 due to point mutations in both alleles, and is unable to rapidly degrade reporter transcripts containing the AREs of TNFa, GM‐CSF, IL‐2, IL‐3, and IL‐6 (Stoecklin et al., 2001). The results obtained with TTP/ mice and BRF1/ cells indicate that cytokine transcripts with class II AREs are subject to a common degradation pathway. Overexpression studies have shown that BRF2, the second homologue of TTP, can also induce AMD (Lai et al., 2000). Mice expressing an N‐terminally deleted form of the BRF2 protein are viable, but exhibit complete female infertility due to block of early embryonic development at the two‐cell stage (Ramos et al., 2004). Taken together, the data from the knock‐out mice reveal that TTP plays a critical and non‐redundant role in the immune system, whereas both BRF1 and BRF2 appear to be important regulators of embryonic development. It is noteworthy that prolonged overexpression of TTP and BRF1 causes apoptotic cell death in a variety of cell lines (Johnson and Blackwell, 2002; Johnson et al., 2000), indicating that the TTP/BRF family of proteins may target yet unidentified mRNAs. Characterizing the entire spectrum of mRNAs that are regulated by TTP/BRF will help to uncover biological processes for which posttranscriptional control of mRNA stability is relevant. Although enforced tethering of TTP to an mRNA that does not contain an ARE (through a heterologous RNA‐protein interaction) is sufficient to induce rapid degradation of the mRNA (Lykke‐Andersen and Wagner, 2005), it is clear that other ARE‐BPs are also required for destabilizing ARE‐mRNAs. KSRP was initially identified as an RNA‐binding protein that enhances splicing (Min et al., 1997), and later found to interact with the 30 UTR of IL‐2 transcripts (Chen et al., 2001). KSRP binds to different AREs (e.g., IL‐2, TNFa, c‐fos) through its KH domains, and simultaneously interacts with the exosome, a large complex of about ten 30 ‐50 exonucleases and associated helicases (Mitchell and Tollervey, 2000; Raijmakers et al., 2004). Importantly, KSRP was shown to be required for AMD both in vitro and in live cells (Chen et al., 2001; Gherzi et al., 2004). The helicase RHAU was identified as a protein that
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binds to the ARE of urokinase plasminogen activator (uPA) and also interacts with the exosome (Tran et al., 2004). RHAU accelerates degradation of uPA mRNA, but it is not clear whether RHAU facilitates the degradation of other ARE‐mRNAs as well. The ARE‐BP AUF1 was identified as an activity that destabilizes an ARE‐ containing RNA in vitro (Brewer, 1991; Zhang et al., 1993). The destabilizing role of AUF1 has been confirmed by studies using siRNA to suppress AUF1 expression (Lal et al., 2004; Raineri et al., 2004), as well as by overexpression studies (Loflin et al., 1999; Sarkar et al., 2003). Its ability to interact with the exosome may provide the mechanistic basis for its activity (Chen et al., 2001). At least one study, however, has indicated that overexpression of AUF1 can also cause stabilization of ARE‐containing reporter mRNAs (Xu et al., 2001). This apparent contradiction may arise from the fact that AUF1 is expressed as four different isoforms (Wagner et al., 1998), which can differ in their activity (Raineri et al., 2004). Interestingly, overexpression of AUF2, a close homologue of AUF1, also stabilizes an ARE‐mRNA (Dean et al., 2002). HuR and its neural‐specific homologues HuB, HuC, and HuD form the embryonic lethal abnormal visual (ELAV) family of RNA‐binding proteins, all of which have high affinity for AU‐ and U‐rich sequences (Antic and Keene, 1997; Ma et al., 1996). Various studies have shown that HuR, the ubiquitously expressed member of the ELAV family, stabilizes a large number of ARE‐ mRNAs, including transcripts containing the ARE of GM‐CSF, IL‐3, and VEGF (Fan and Steitz, 1998; Ford et al., 1999; Levy et al., 1998; Ming et al., 2001; Peng et al., 1998; Raineri et al., 2004). HuR is required for the induced expression of iNOS (Di Macro et al., 2005; Rodriguez‐Pascual et al., 2000), and has also been implicated in the stabilization of IL‐8, eotaxin, COX‐2, and MMP‐9 mRNA (Atasoy et al., 2003; Cok et al., 2003; Huwiler et al., 2003; Winzen et al., 2004). Class II AREs typically contain 4 to 7 AUUUA pentamers within a U‐rich sequence of 50 or more nucleotides. This contrasts with the fact that TTP requires only the nonameric sequence UUAUUUAUU for efficient binding (Blackshear et al., 2003a; Worthington et al., 2002), and that a single C3H zinc finger of BRF2 makes direct contact with just four nucleotides: UAUU (Hudson et al., 2004). This would indicate that physiological AREs are large enough to accommodate more than one, and perhaps several ARE‐BPs. A simple model would postulate that stabilizing proteins such as HuR compete with destabilizing proteins such as TTP or AUF1 for binding to the ARE, and thereby prevent decay of the mRNA. It appears, however, that HuR does not bind within the core region of class II AREs (which consists of clustered AUUUA pentamers), but to an auxiliary, mainly U‐rich region upstream of the core region (Chen et al., 2002; Winzen et al., 2004). Paradoxically, this
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auxiliary region both enhances the destabilizing activity of the ARE core region, and allows for stabilization of the mRNA by HuR. Such an upstream auxiliary region has been described for the AREs of c‐fos, TNFa, GM‐CSF, and IL‐8 (Chen et al., 2002; Stoecklin et al., 2001; Winzen et al., 2004). Very few studies have so far directly addressed the question whether ARE‐BPs bind individually to the ARE and compete for binding, or whether they bind cooperatively to form multi‐protein ARE‐mRNPs. One study found that KSRP and TTP together compete with HuR for binding to the Pitx2 mRNA (Briata et al., 2003). Using a genome‐wide approach, another study was able to distinguish between mRNAs that are simultaneously bound by both AUF1 and HuR, and mRNAs bound by the two proteins individually (Lal et al., 2004). Given the number of proteins which can bind to AREs (at least 20), and the fact that individual AREs differ quite considerably in their sequence, it is likely that each ARE recruits a different subset of ARE‐BPs, which together determine the stability and translation efficiency of that particular transcript. At present, we lack a broader understanding of the composition of specific ARE‐ mRNP complexes, and the changes these complexes may undergo when the degradation of the mRNA is activated or inhibited. 2.3. The Pathway of ARE‐mRNA Degradation In general, degradation of mRNAs in the cytoplasm is initiated by removal of the poly‐A tail, followed by exonucleolytic decay in the 30 ‐50 or the 50 ‐30 direction. At the 30 end, the mRNA is degraded through the exosome. At the 50 end, the 7‐methyl guanosine cap is removed by the decapping complex Dcp1/Dcp2, and the mRNA body is subsequently degraded by the 50 ‐30 exonuclease Xrn1 (Cougot et al., 2004b; Fillman and Lykke‐Andersen, 2005; Parker and Song, 2004). Dcp1/Dcp2 and Xrn1 form a larger complex with the Lsm1‐7 proteins, all of which are concentrated in small cytoplasmic foci termed processing bodies (Cougot et al., 2004a; Ingelfinger et al., 2002; van Dijk et al., 2002). Processing bodies are considered to be sites of mRNA degradation in the cytoplasm. In vitro decay studies have indicated that ARE‐mRNAs are degraded in the 30 ‐50 direction by the exosome (Chen et al., 2001), and one of the exosome components, Pm‐Scl‐75, was shown to directly bind to the ARE (Mukherjee et al., 2002). On the other hand, the ARE also stimulates decapping of the RNA in vitro (Gao et al., 2001). As illustrated in Fig. 1, the TTP/BRF family of proteins plays a central role in the degradation of ARE‐mRNAs. Both in vitro and when overexpressed in live cells, TTP enhances deadenylation of ARE‐ mRNA (Fig. 1A) (Lai et al., 1999, 2003). TTP and BRF1 further interact with both the exosome (Fig. 1B) and with components of the decapping/Xrn1 complex (Fig. 1C) (Chen et al., 2001; Gherzi et al., 2004; Lykke‐Andersen
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Figure 1 The TTP/BRF family of proteins plays a central role in the degradation of ARE‐mRNAs. (A) Cytoplasmic mRNA degradation is initiated by deadenylation. (B) 30 ‐50 decay is mediated by the exosome (green), a complex of exonucleases and helicases. (C) At the 50 end, the mRNA is decapped by Dcp1/2 (yellow), followed by Xrn1‐mediated 50 ‐30 degradation. These proteins form a larger complex with Lsm1‐7, and are concentrated in cytoplasmic processing bodies. (D) The RNA‐induced silencing complex (RISC, in blue) and microRNA 16 are also required for ARE‐ mRNA degradation. The zinc finger proteins TTP/BRF1 (red) bind with high affinity to the ARE and induce degradation of the mRNA by interacting with the exosome, the decapping/Xrn1 complex, and the RISC complex.
and Wagner, 2005). This suggests that TTP/BRF1 are capable of targeting ARE‐mRNAs to both decay pathways. We have recently shown that the 50 ‐30 pathway is indeed important for degrading ARE‐mRNAs (Stoecklin et al., 2005). Using siRNA to target individual components of both pathways, Xrn1 and Lsm1 were found to be essential for AMD, whereas exosome components are less important. TTP and BRF1 also colocalize with processing bodies, a further indication that AMD uses the 50 ‐30 pathway (Kedersha et al., 2005). A recent study by Jing and coworkers (2005) revealed that AMD is dependent on the RNA‐induced silencing complex (RISC) and the microRNA miR16 (Fig. 1D). TTP interacts with two proteins of the RISC complex, Argonaute 2 and 4, which in turn allows the microRNA miR16 to base‐pair with the ARE. Interestingly, Argonaute proteins also colocalize with processing bodies and mRNAs targeted by miRNAs become concentrated in these structures (Liu et al., 2005). These novel findings indicate that the ARE actually consist of a dual code: one part of the ARE serves to recruit RNA‐binding proteins which interact with the cellular degradation machinery, while another part of the ARE (or adjacent sequences) base‐pair with regulatory microRNAs, which may contribute to the sequence specificity of the destabilizing element. A challenge of future studies will be to break this code in a way that will allow
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us to predict for individual AREs which proteins bind to it, which microRNAs are associated, and what the functional consequences are for mRNA stability and translation efficiency. 2.4. Regulation of ARE‐mRNA Decay The ARE not only targets the mRNA for rapid degradation, but also allows the tight regulation of mRNA stability in response to extracellular cues. In a variety of cell types, many cytokine mRNAs have a very short half‐life (in the range of 10–30 minutes) in resting cells, effectively preventing cytokine protein production. Upon cell stimulation, the rapid induction of cytokine expression requires both transcriptional activation and stabilization of the mRNAs. In activated cells, cytokine mRNA half‐lives are in the range of several hours, which can easily account for a 10‐fold increase in protein production. In the post‐induction phase, ARE‐mRNAs are no longer stabilized and their degradation ensures rapid return to the low, usually undetectable levels of basal cytokine production. Thus, the dynamic regulation of mRNA stability is an important means by which cytokine levels are controlled in a time‐dependent manner. The following examples (listed in Table 1) document the general importance of this mode of posttranscriptional regulation. In T‐cells stimulated with anti‐CD3 and anti‐CD28 antibodies, or phorbol ester, induction of IL‐2, IFNg, TNFa, and GM‐CSF coincides with a marked increase in the stability of the corresponding mRNAs (Bickel et al., 1990; Lindsten et al., 1989). Stabilization of IL‐3 and GM‐CSF mRNA occurs in mast cells after treatment with calcium ionophores (Wodnar‐Filipowicz and Moroni, 1990), and GM‐CSF mRNA is likewise stabilized in stimulated eosinophils (Esnault and Malter, 1999). The production of IFNg in activated NK cells involves stabilization of the mRNA (Hodge et al., 2002; Mavropoulos et al., 2005). Macrophages produce a variety of cytokines and chemokines in response to activation by lipopolysaccharide (LPS), and mRNA stabilization contributes to the induction of IL‐1b, IL‐18, TNFa, GM‐CSF, Growth regulated oncogene (GRO)a and GROb expression (Biswas et al., 2003; Brook et al., 2000; Bufler et al., 2004; Carballo et al., 2000; Rousseau et al., 2002). In monocytes activated through adhesion, mRNAs encoding IL‐1b and GROa are stabilized (Sirenko et al., 1997). Regulation of ARE‐mRNA stability is not restricted to the cells of the immune system. Virally infected fibroblasts produce IFNb in the early phase of infection. During this phase, IFNb mRNA is stable, whereas rapid degradation of IFNb mRNA during the late phase accounts for the post‐induction turnoff of IFNb expression (Raj and Pitha, 1983; Whittemore and Maniatis, 1990). Stimulation of fibroblasts and other cell types with pro‐inflammatory
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cytokines such as TNFa or IL‐1 induces the production of various cytokines and chemokines. In these cells, mRNA stabilization contributes to the induced expression of IL‐6, IL‐11, G‐CSF, GM‐CSF, Macrophage chemoattractant protein (MCP)‐1, eotaxin, GROa, GROb, GROg, and IL‐8 (Akashi et al., 1990; Atasoy et al., 2003; Bamba et al., 2003; Koeffler et al., 1988; Pastore et al., 2005; Stoeckle, 1991; Yang and Yang, 1994). Expression of the adhesion molecule VCAM‐1 on endothelial cells and fibroblast‐like synoviocytes is induced by TNFa and IL‐4, and involves stabilization of the mRNA (Croft et al., 1999; Iademarco et al., 1995). Since VCAM‐1 is overexpressed in rheumatoid arthritis synovium (Morales‐Ducret et al., 1992), it may promote the inflammation by recruiting monocytes and lymphocytes to the affected joint. The inducible nitric oxide synthase (iNOS) enzyme is upregulated in many cell types in response to bacterial products or pro‐inflammatory cytokines, leading to the sustained production of nitric oxide (NO). NO is a diffusible molecule that has beneficial antimicrobial effects in the defense against pathogens, and acts as a potent messenger in regulating tissue perfusion, epithelial permeability, and the immune response. On the other hand, overproduction of NO can be detrimental as it is associated with tissue damage and chronic inflammation (Kolios et al., 2004; MacMicking et al., 1997). The induction of iNOS occurs both at the transcriptional level, and at the posttranscriptional level through stabilization of the mRNA (Carpenter et al., 2001; Di Macro et al., 2005; Lahti et al., 2003; Perez‐Sala et al., 2001; Rodriguez‐Pascual et al., 2000). Another important effector‐enzyme of the inflammatory response, COX‐2, is also regulated at the posttranscriptional level. In a variety of cell types, IL‐1 induces the expression of COX‐2 by a mechanism that involves stabilization of the mRNA (Ridley et al., 1998; Ristimaki et al., 1994), and the same is observed in LPS‐treated monocytes (Dean et al., 1999). Taken together, these examples demonstrate that mRNA stabilization is a general mechanism by which different cell types achieve proper expression of a large group of pro‐inflammatory proteins. In most cases, an ARE in the 30 UTR plays a pivotal role in regulating the stability of the mRNA. For this reason, a major effort in the field is to identify the molecular mechanisms by which ARE‐mRNAs are stabilized. Stabilization of ARE‐mRNAs is dependent upon the activation of different signal transduction pathways. In T‐cells and mast cells, activation of the c‐jun N‐terminal kinase (JNK) pathway is required for the stabilization of IL‐2 and IL‐3 mRNA (Chen et al., 1998; Ming et al., 1998). In NIH3T3 cells, the phosphatidylinositol 3‐kinase (PI3K) pathway contributes to ARE‐mRNA stabilization (Ming et al., 2001). Induction of iNOS was linked to protein kinase Cd activation and may also require the JNK pathway (Carpenter et al., 2001;
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Lahti et al., 2003). In most cases, however, the mitogen‐activated protein kinase p38 (p38‐MAPK) pathway plays a central role in stabilizing ARE‐ mRNAs. As shown in a variety of cell types, p38‐MAPK and the downstream MAPK‐activated protein kinase 2 (MK2) are required for the posttranscriptional induction of IL‐1b, IL‐3, IL‐6, IL‐11, TNFa, IFNg, GROa, GROb, IL‐8, IP‐10, and COX‐2 (Bamba et al., 2003; Brook et al., 2000; Dean et al., 1999; Holtmann et al., 1999; Kotlyarov et al., 1999; Lasa et al., 2000; Mavropoulos et al., 2005; Ming et al., 2001; Neininger et al., 2002; Ridley et al., 1998; Rousseau et al., 2002; Sirenko et al., 1997; Vockerodt et al., 2005; Winzen et al., 1999). Given that such a large number of pro‐inflammatory proteins are induced posttranscriptionally through the p38‐MAPK–MK2 axis, developing inhibitors of this pathway has been a major focus in the search for novel anti‐inflammatory drugs. Recent findings provide first insights into the molecular mechanism that links the p38‐MAPK–MK2 pathway to regulators of AMD. Again, the TTP/ BRF proteins appear to play a central role in this process. Both p38‐MAPK and MK2 phosphorylate TTP (Carballo et al., 2001; Mahtani et al., 2001; Zhu et al., 2001), and the direct phosphorylation of TTP by MK2 at serine 52 and serine 178 leads to complex formation between TTP and the adaptor protein 14‐3‐3 (Chrestensen et al., 2003; Johnson et al., 2002; Stoecklin et al., 2004). As a consequence of 14‐3‐3 binding, TTP activity is reduced and ARE‐mRNAs thereby stabilized (Stoecklin et al., 2004). Interestingly, the activity of BRF1 is also inhibited by phosphorylation and consecutive binding of 14‐3‐3 (Schmidlin et al., 2004). Although one study questions this model (Rigby et al., 2005), phosphorylation‐induced complex formation of the TTP/BRF proteins with 14‐3‐3 may be a general mechanism by which ARE‐mRNAs are stabilized. Another target of the p38‐MAPK pathway is the ARE‐BP hnRNP‐A0 (Rousseau et al., 2002). In LPS‐stimulated macrophages, MK2 phosphorylates hnRNP‐A0 at serine 84, but it is not clear whether this contributes to stabilization of ARE‐mRNAs. The anti‐inflammatory cytokine IL‐10 is a potent inhibitor of macrophage activation that reduces the expression of many cytokines (e.g., TNFa, IL‐1, IL‐6, GM‐CSF), several chemokines, and COX‐2 (Moore et al., 2001). Although most of the inhibitory effect of IL‐10 on the expression of cytokines appears to occur at the transcriptional level in a STAT3‐dependent manner (Takeda et al., 1999; Williams et al., 2004a), there is evidence that posttranscriptional mechanisms are also involved. In LPS‐treated macrophages, IL‐10 was found to reduce TNFa, IL‐1a, and IL‐1b mRNA levels without affecting their rates of transcription, indicating that IL‐10 accelerates the decay of these mRNAs (Bogdan et al., 1992). The suppressive effect of IL‐10 on TNFa expression requires the TNFa 30 UTR (Denys et al., 2002), and another study
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indicates that IL‐10 reduces the translation of TNFa through inhibition of the p38‐MAPK–MK2 pathway (Kontoyiannis et al., 2001). Moreover, IL‐10 was found to destabilize GROa (murine KC), GM‐CSF, and G‐CSF, as well as its own mRNA (Biswas et al., 2003; Brown et al., 1996b; Kishore et al., 1999). Given that some of these results are contradictory, the contribution of posttranscriptional mechanisms to the suppressive effect of IL‐10 remains a controversial issue (Williams et al., 2004b). 2.5. Non‐ARE Decay Elements The ARE is probably the most common element that regulates mRNA stability, yet other regulatory elements have been described in a number of mRNAs encoding pro‐inflammatory proteins. For example, TNFa contains a second, constitutive decay element (CDE) in the 30 UTR, located downstream of the ARE. As opposed to AMD, CDE‐mediated mRNA decay is not inhibited by stimulation of macrophages with LPS, nor by activation of the PI3K or p38‐MAPK pathways (Stoecklin et al., 2003). The CDE may thus serve as a safeguard element that maintains stringent control over TNFa production, thereby reducing the risk of accumulating potentially injurious TNFa levels. G‐CSF is another cytokine that contains in its 30 UTR two independent destabilizing elements: an ARE and the stem‐loop destabilizing element (SLDE). The SLDE, similar to the CDE of TNFa, prevents stabilization of G‐CSF mRNA under conditions where AMD is inhibited (Brown et al., 1996a; Putland et al., 2002). The induction of IL‐2 expression in stimulated T‐cells results from both transcriptional activation and posttranscriptional mRNA stabilization (Lindsten et al., 1989; Musgrave et al., 2004). In unstimulated cells, the ARE in the 30 UTR mediates rapid decay of IL‐2 mRNA. Stabilization of IL‐2 mRNA occurs in response to JNK activation and requires, besides the ARE, a JNK‐response element (JRE) in the 50 UTR of the transcript (Chen et al., 1998). Two proteins bind to the JRE, nucleolin and the cold shock domain (CSD) protein YB1, and both are required for stabilizing IL‐2 mRNA (Chen et al., 2000). Hypoxia‐induced expression of VEGF, a major angiogenic factor, is regulated at both transcriptional and posttranscriptional levels (Ikeda et al., 1995; Levy et al., 1996; Stein et al., 1995). Under normoxic conditions, VEGF mRNA is labile. Three distinct destabilizing elements mediate rapid decay of the VEGF transcript: an ARE in the 30 UTR, a coding region determinant of instability (CDR), and an element in the 50 UTR (Dibbens et al., 1999). Interestingly, the three elements can independently mediate rapid decay of a reporter transcript, yet all three elements together are required to allow the mRNA to be stabilized in response to hypoxia (Dibbens et al., 1999). The
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ARE‐BP HuR binds to the 30 UTR of VEGF mRNA and contributes to mRNA stabilization (Levy et al., 1998). A complex that contains YB1 and polypyrimidine tract binding protein (PTB) binds to two sites in the 50 UTR and one site in the 30 UTR, and participates in the stabilization of VEGF transcripts (Coles et al., 2004). These binding sites are very similar to the binding site of YB1 in the 50 UTR of IL‐2, indicating that YB1‐containing complexes may play a general role in stabilizing different mRNAs (Coles et al., 2004). YB1 was also found to enhance the stability of GM‐CSF mRNA, although in this case, YB1 appears to directly interact with the ARE of GM‐CSF (Capowski et al., 2001). The examples of TNFa, IL‐2, and VEGF illustrate that the ARE does not operate as an isolated element, but cooperates with other elements to achieve complex control over mRNA stability and translation. By recruitment of ARE‐ BPs together with other RNA‐binding proteins, multiple transcripts can be regulated specifically and expressed differentially according to cellular requirements and extracellular cues. We are still far away from understanding the complex interplay between the factors that contribute to the stability and translation efficiency of individual mRNAs. Future studies may reveal that combining non‐ARE regulatory elements with an ARE is a common mechanism of mRNAs that is regulated at the posttranscriptional level. 3. Translational Inhibition 3.1. Translational Silencing of ARE‐Transcripts Several RNA‐binding proteins repress the translation of mRNAs encoding proteins that regulate the inflammatory response. TIA‐1 and TIAR are closely related members of the RNA‐recognition motif (RRM) family of RNA‐binding proteins that inhibit the translation of TNFa transcripts in macrophages (Anderson and Kedersha, 2002a,b; Piecyk et al., 2000), but not in T lymphocytes (Saito et al., 2001). Although LPS‐activated macrophages derived from wild‐type and TIA‐1/ mice express similar amounts of TNFa transcripts, macrophages lacking TIA‐1 produce significantly more TNFa protein than wild‐type controls (Piecyk et al., 2000; Saito et al., 2001). In macrophages lacking TIA‐1, the percentage of TNFa transcripts found in polysomes is increased, suggesting that TIA‐1 functions as a translational silencer (Piecyk et al., 2000). The overexpression of TNFa protein in macrophages lacking TIA‐1 is strain dependent. TIA‐1/ macrophages derived from BALB/c mice produce 3–5 times more TNFa than wild‐type controls, whereas TIA‐1/ macrophages derived from C57BL/6 mice produce nearly 10 times more TNFa than wild‐type controls (Saito et al., 2001). Moreover, C57BL/6 mice
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spontaneously develop mild arthritis (Phillips et al., 2004). Thus, unidentified genetic modifiers determine whether TIA‐1/ mice develop arthritis. TIA‐1 similarly represses the translation of COX‐2 (Dixon et al., 2003), an enzyme that converts arachidonic acid into pro‐inflammatory prostaglandins (Sundy, 2001; Schnitzer and Hochberg, 2002). Pharmacologic inhibitors of COX‐2 are potent anti‐inflammatory agents that significantly reduce the severity of inflammatory arthritis (Schnitzer and Hochberg, 2002). The 30 UTR of COX‐2 transcripts contains an ARE that recruits a multimeric protein complex that includes TIA‐1, TIAR, hnRNP U, and HuR (Cok et al., 2003). TIA‐1 null fibroblasts express 2–3 times more COX‐2 and 2 times more prostaglandin E2 than wild‐type controls (Dixon et al., 2003). Moreover, the expression of COX‐ 2 in colon cancer‐derived cell lines is inversely correlated with the expression of TIA‐1 (Dixon et al., 2003). In colon cancer cell lines expressing abundant TIA‐1, sucrose gradient analysis shows that COX‐2 mRNA is concentrated in low‐density fractions that contain untranslated mRNPs (Dixon et al., 2003). These results suggest that TIA‐1 can coordinately repress the expression of TNFa and COX‐2 to dampen the inflammatory response. TIAR represses the translation of MMP‐13 (Yu et al., 2003), a TNFa‐ induced collagenase that has been implicated in pro‐inflammatory, angiogenic, and destructive processes within the joints of patients with rheumatoid arthritis (Konttinen et al., 1999; Moore et al., 2000; Vincenti and Brinckerhoff, 2002; Wernicke et al., 2002). Although the mechanism of TIAR‐induced translational silencing has not been investigated, the fact that TIAR/ macrophages, like TIA‐1/ macrophages, overexpress TNFa (Piecyk et al., 2000) suggests that TIA‐1 and TIAR use similar mechanisms to inhibit protein translation. Interestingly, a 17 amino acid peptide derived from an alternatively spliced TIAR exon enhances the expression of MMP‐13 (Yu et al., 2003), suggesting that this exon plays an important role in TIAR function. The ability of TIA‐1 and TIAR to coordinately regulate the expression of several pro‐inflammatory proteins supports the concept that posttranscriptional mechanisms play a major role in regulating the inflammatory response. CUGBP2, an RNA‐binding protein that is structurally related to HuR, has also been implicated in the translational silencing of ARE‐containing transcripts (Mukhopadhyay et al., 2003). CUGBP2 binds to two distinct AREs found in the 30 UTR of COX‐2 mRNA. Paradoxically, expression of recombinant CUGBP2 stabilizes luciferase reporter transcripts bearing the COX‐2 ARE, but reduces expression of the luciferase protein. Differential centrifugation analysis revealed that luciferase transcripts are excluded from polysomes in cells transfected with CUGBP2, but not CUGBP1 or HuR. Thus CUGBP2, like TIA‐1 and TIAR, appears to function by preventing its associated transcripts from
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moving to polysomes. It is not known whether CUGBP2, TIA‐1, and TIAR cooperate to repress the translation of ARE‐containing transcripts. The Fragile X‐related protein FXR1P has also been identified as a translational silencer that targets ARE‐containing transcripts (Garnon et al., 2005). The FXR family of RNA‐binding proteins (FMRP, FXR1P, and FXR2P) possesses two hnRNP K‐homology (KH) domains and an RGG box (Kaufmann et al., 2002). These proteins bind to both U‐rich and G‐rich sequences, and the RGG box allows FMRP to bind to the G‐quartet RNA motif (Darnell et al., 2001, 2004). Thus, the RNA specificity of the FXR proteins could be quite broad. FXR1P binds specifically to the ARE in the 30 UTR of TNFa mRNA, and FXR1P/ macrophages express approximately 2 times more TNFa than wild‐type macrophages (Garnon et al., 2005). Polysome profiles suggest that FXR1P, like TIA‐1 and TIAR, can exclude TNFa mRNA from polysomes. These results suggest that FXR1P, TIA‐1, and TIAR may work together to bring about translational silencing of TNFa transcripts. It remains to be determined whether FXR1P also represses the translation of additional pro‐inflammatory proteins. 3.2. Mechanisms of Translational Silencing Much of what we know about the mechanism of TIA‐1‐induced translational repression comes from studies of the general translational arrest triggered by environmental stress (e.g., heat, oxidative conditions, and energy deprivation) (Anderson and Kedersha, 2002a,b; Kedersha and Anderson, 2001). Stress‐ induced translational arrest is characterized by the activation of one or more members of a family of serine/threonine kinases (e.g., double‐stranded RNA‐ dependent protein kinase R, PKR‐like endoplasmic reticulum kinase, GCN2, and heme‐regulated inhibitor kinase) (Harding et al., 2000a,b; Sood et al., 2000; Williams, 1999). These kinases phosphorylate eIF2a, a component of the ternary complex that loads tRNAiMet onto the small ribosomal subunit to initiate protein synthesis (Dever, 2002). Phosphorylation of eIF2a inhibits protein translation by reducing the availability of active ternary complex (Krishnamoorthy et al., 2001). Under these conditions, TIA‐1 promotes the assembly of a non‐canonical translation‐initiation complex that is directed to discrete cytoplasmic foci known as stress granules (Anderson and Kedersha, 2002b; Kedersha et al., 1999, 2000, 2002). Like TIA‐1, the RNA‐binding proteins TIAR, FMRP, and FXR1P are concentrated at SGs, suggesting that these proteins might work together to bring about stress‐induced translational silencing. A non‐canonical translation initiation complex assembled during stress has reduced amounts of eIF2 and eIF5 (Kedersha et al., 2002). It is possible that the assembly of these non‐canonical translation initiation complexes contribute to
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the reduced translation of ARE‐containing transcripts mediated by TIA‐1, TIAR, and FXR1P. These complexes may be unable to recruit the large ribosomal subunit, preventing the assembly of polysomes. Although stress granules are visible only when large numbers of transcripts are simultaneously subjected to translational arrest, the underlying translational control mechanism (i.e., assembly of stalled initiation complexes) regulates protein expression in both stressed and unstressed cells (Anderson and Kedersha, 2002a,b). 3.3. Translational Silencing of Non‐ARE Transcripts The translational silencing of ARE‐containing transcripts has the potential to coordinately regulate the expression of multiple pro‐inflammatory proteins. Translational silencing also regulates the expression of non‐ARE‐containing transcripts encoding proteins that control the inflammatory response. A wellcharacterized example is the translational regulation of 15‐LO, an enzyme that participates in the conversion of arachidonic acid into either leukotriene A4 (LTA4) or lipoxin A4 (LXA4) (Kuhn et al., 2002). Whereas LTA4 is converted into LTB4, a potent pro‐inflammatory lipid, LXA4 is an anti‐inflammatory lipid that promotes the resolution of inflammation (Serhan, 2001). Because of this functional dichotomy, 15‐LO has both pro‐ and anti‐inflammatory effects in a variety of experimental systems (Kuhn et al., 2002). During erythrocyte maturation, the mRNA encoding 15‐LO is expressed in the early stages of erythropoiesis, but 15‐LO protein is only expressed at a late stage of maturation (van Leyen et al., 1998). The developmental stage‐specific expression of 15‐LO is achieved by translational silencing in early erythroid progenitors. Translational silencing of 15‐LO mRNA is dependent upon a differentiation control element (DICE) in the 30 UTR (Ostareck et al., 2001). mRNP K/E1 binds hnRNP K and hnRNP E1, which prevent the recruitment of 60S ribosomal subunits to the translation initiation complex (Ostareck et al., 2001). Thus, translational silencing by TIA‐1, TIAR, and hnRNP K/E1 may all involve the exclusion of the 60S ribosomal subunit from the initiation complex. The effect of translational regulation of 15‐LO on the production of pro‐ and anti‐inflammatory lipids remains to be determined. 4. Animal Models 4.1. TNFDARE Knock‐In Mice The importance of posttranscriptional pathways in the regulation of inflammation has been dramatically demonstrated in mutant mice lacking these regulatory controls. In general, posttranscriptional control mechanisms dampen
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the expression of pro‐inflammatory proteins, and thereby prevent the pathological overexpression of these potentially dangerous products. This is certainly true in the case of TNFa, in which transgene‐derived overexpression is sufficient to induce inflammatory arthritis (Keffer et al., 1991). The contribution of posttranscriptional mechanisms to the normal regulation of TNFa production was elegantly revealed by the analysis of knock‐in mice that lack the ARE in the 3’UTR of one of the TNFa alleles (TNFDARE). Macrophages and synovial fibroblasts from TNFDARE mice overexpress TNFa mRNA and protein, and these animals spontaneously develop inflammatory arthritis and inflammatory bowel disease (Kontoyiannis et al., 1999). Because the ARE has not been implicated in the transcriptional regulation of TNFa production, these results imply that posttranscriptional controls are essential for the prevention of spontaneous inflammatory disease. Importantly, the production of TNFa from TNFDARE macrophages is not affected by inhibitors of p38‐MAPK, confirming that the ARE is required for the ability of p38‐MAPK to stabilize and promote the translation of TNFa transcripts (Kontoyiannis et al., 1999). The development of inflammatory bowel disease in TNFDARE mice requires the function of CD8þ, but not CD4þ T lymphocytes (Kontoyiannis et al., 2002). The full spectrum of intestinal inflammation requires the Th1 cytokines IL‐12 and IFN‐g, but not the Th2 cytokine IL‐4 (Kontoyiannis et al., 2002). Restricted expression of TNFa by either macrophages or T lymphocytes is sufficient to induce intestinal inflammation (Kontoyiannis et al., 2002). Moreover, studies of bone marrow chimeras revealed that the presence of the TNFDARE mutation in either bone marrow‐derived or tissue stroma‐derived cells is sufficient to induce intestinal inflammation. It is therefore likely that redundant cellular pathways act downstream of TNFa to bring about intestinal inflammation. 4.2. TTP Knock‐Out Mice Studies of TNFDARE macrophages reveal that the ARE is a destabilizing element that promotes the degradation of TNFa transcripts. The decay of TNFa mRNA is dependent upon TTP, a zinc‐finger protein that targets ARE‐ containing transcripts to the mRNA degradation machinery (see Fig. 1). Mutant mice lacking TTP develop a syndrome of cachexia, arthritis, dermatitis, and autoimmunity that results from the pathological overexpression of TNFa (Taylor et al., 1996). The administration of neutralizing antibodies reactive with TNFa prevents all aspects of this syndrome, indicating that TNFa plays a central role in disease pathogenesis. The importance of TNFa was confirmed by breeding TTP‐deficient mice with mice lacking TNF‐Receptor (R)1 or TNFR2. Whereas TTP/ TNFR1/ mice did not develop cachexia or
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arthritis, TTP/ TNFR2/ developed more severe arthritis than mice lacking TTP alone (Carballo and Blackshear, 2001). Thus, TNFa binds to TNFR1 to bring about the pathological features of this syndrome. In contrast, interactions with TNFR2 may prevent pathology. TTP/ mice also develop bone marrow and peripheral blood granulopoiesis, suggesting that TTP may regulate the production of granulocyte growth and/or survival factors. Interestingly, this phenotype was preserved in TTP/ mice lacking TNFR1, TNFR2, or both TNF receptors, suggesting that granulopoiesis is not mediated by overexpressed TNFa. The mechanism of granulopoiesis remains to be determined. Unlike TNFDARE mice, TTP/ mice do not develop inflammatory bowel disease (Taylor et al., 1996). It is not surprising that the phenotypes of TNFDARE and TTP/ mice are different. TNFDARE macrophages lack the ability to bind to several ARE‐binding proteins, including the TTP homologues BRF1 and BRF2, or translational silencers such as TIA‐1 and FXR1P. Thus, the phenotype of TNFDARE mice is likely to be more severe than that of TTP/ mice. Because TNFa transgenic mice develop arthritis, but not inflammatory bowel disease (Keffer et al., 1991; Kollias, 2004), the level of TNFa expression may not be sufficient to explain why bowel inflammation is observed in the TNFDARE strain. It is possible that tissue‐specific regulation of TNFa expression determines whether there is inflammation in the joints, the intestines, or both. 4.3. TIA‐1 and TIAR Knock‐Out Mice On the Balb/c background, mice lacking TIA‐1 do not develop spontaneous inflammatory disease. When bred onto the C57Bl/6 background, however, TIA‐1/ mice develop mild non‐erosive arthritis (Phillips et al., 2004). Thus, genetic modifiers are important in determining the disease phenotype. Mutant mice lacking both TTP and TIA‐1 develop spontaneous inflammatory arthritis that is significantly more severe than the arthritis observed in mice lacking either TIA‐1 or TTP alone (Phillips et al., 2004). Although macrophages derived from TIA‐1/ TTP/ mice overexpress TNFa mRNA, they express less TNFa protein than TIA‐1/ or TTP/ macrophages (Phillips et al., 2004). Whether this results from defective nuclear export of TNFa transcripts, defective translation, or defective processing of TNFa protein remains to be determined. The source of arthritigenic cytokine in mice lacking both TIA‐1 and TTP appears to be an expanded population of neutrophils found in the bone marrow and peripheral blood. The marked increase in neutrophils in TTP/ bone marrow and peripheral blood is potentiated in mice that also lack TIA‐1. The mechanism whereby TIA‐1 and TTP cooperate to increase the maturation and/or survival of neutrophils is not known. Whereas wild‐type neutrophils produce little or no
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TNFa in response to LPS stimulation, neutrophils lacking TTP secrete significant amounts of TNFa in response to LPS (Phillips et al., 2004). It is therefore possible that neutrophils are an important source of this pro‐arthritic cytokine in mice lacking both TIA‐1 and TTP. Although neutrophils clearly contribute to the pathogenesis of arthritis (Edwards and Hallett, 1997; Pillinger and Abramson, 1995), our understanding of their precise contribution to the inflammatory process is incomplete. Neutrophils are the predominant cell type found in inflammatory synovial fluid (but not synovial pannus) derived from patients with rheumatoid arthritis. They are an important source of arachadonic acid‐derived inflammatory mediators (e.g., prostaglandins, leukotrienes, and lipoxins). In animal models of inflammatory arthritis, neutrophils are essential components of the inflammatory process (Jonsson et al., 2005; Lawlor et al., 2004; Wipke and Allen, 2001). The cooperative regulation of both neutrophil maturation and function by TIA‐1 and TTP suggests that these cells are a major source of inflammatory cytokine production in a subset of patients with rheumatoid arthritis. 4.4. G‐CSF and GM‐CSF Transgenic Mice The importance of neutrophils in inflammatory arthritis was dramatically demonstrated in mice lacking G‐CSF, an important regulator of neutrophil production. These mice exhibit impaired granulopoiesis and are protected from collagen‐induced arthritis (Lawlor et al., 2004). Moreover, administration of anti‐G‐CSF antibodies protects wild‐type mice from collagen‐induced arthritis (Lawlor et al., 2004). These results reveal that G‐CSF is required to produce the mature neutrophils which are essential effectors of synovitis. The 30 UTR of the G‐CSF mRNA encodes two regulatory elements that dampen the production of G‐CSF at the posttranscriptional level. Thus, G‐CSF may be one of the key cytokines whose posttranscriptional regulation can determine susceptibility to arthritis. Like G‐CSF, GM‐CSF contributes to the growth, differentiation, and function of granulocytes and macrophages. In both in vitro and in vivo studies, GM‐CSF has been shown to ‘‘prime’’ neutrophils and macrophages for their effector functions (Hamilton, 2002). In this capacity, GM‐CSF may play an important role in the inflammatory response. Consistent with this prediction, GM‐CSF/ mice are resistant to methylated BSA/IL‐1‐induced arthritis (Yang and Hamilton, 2001). Moreover, anti‐GM‐CSF antibodies reduce the severity of both collagen‐ and BSA/IL‐1‐induced arthritis (Cook et al., 2001; Yang and Hamilton, 2001). These results place GM‐CSF in the category of a pro‐inflammatory protein whose expression is regulated at the posttranscriptional level. The importance of posttranscriptional regulation of GM‐CSF
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production was demonstrated in transgenic mice expressing recombinant GM‐CSF with or without the 30 ARE under control of a CMV promoter. At embryonic day 14, the ARE‐deleted transcript, but not the ARE‐containing transcript, was expressed in all tissues in which the CMV promoter was active (Houzet et al., 2001). Mice with the ARE‐deleted construct exhibit increased proliferation of granulocytes and macrophages. Taken together, these results implicate GM‐CSF as an important pro‐inflammatory cytokine subject to posttranscriptional control. 5. Clinical Significance The coordinate regulation of pro‐inflammatory proteins by posttranscriptional control pathways suggests that components of these pathways may be attractive targets for drug development. Indeed, chemical inhibitors of p38‐MAPK potently reduce the expression of pro‐inflammatory proteins in activated macrophages, and strongly support a role for posttranscriptional control in the regulation of inflammation (Pargellis and Regan, 2003). p38‐MAPK inhibitors reduce the expression of pro‐inflammatory cytokines and chemokines such as TNFa, IL‐1b, IL‐6, IL‐8, and MCP‐1. These drugs also reduce the expression of pro‐inflammatory enzymes such as COX‐2, iNOS, MMP‐1, MMP‐3, MMP‐9, and MMP‐13, as well as endothelial adhesion molecules such as E‐selectin, intracellular adhesion molecule (ICAM)‐1, and VCAM‐1 that recruit inflammatory cells to the rheumatoid synovium (Westra et al., 2004a,b, 2005). These drugs also inhibit the development of inflammatory arthritis in different animal models of arthritis (Pargellis and Regan, 2003). Several pharmaceutical companies are testing p38‐MAPK inhibitors in clinical trials involving patients with rheumatoid arthritis. In phase I clinical trials, single dose administration of these agents has been well tolerated (Parasrampuria et al., 2003). If the safety profile of these drugs is acceptable, they could become important treatments for a variety of immune‐mediated inflammatory diseases. MK2, a specific substrate for p38‐MAPK, has also been implicated in the posttranscriptional regulation of pro‐inflammatory protein expression. Macrophages derived from mutant mice lacking MK2 overexpress TNFa, IFNg, IL‐1, IL‐6, and nitric oxide following LPS activation (Kotlyarov et al., 1999). Thus, MK2 inhibitors, similar to p38‐MAPK inhibitors, have the potential to coordinately reduce the expression of several classes of proteins with pro‐inflammatory activity. The effects of MK2 on mRNA stability and translation are complex and poorly understood. In macrophages lacking MK2, the half‐life of IL‐6 mRNA is reduced more than 10 fold, whereas the half‐ life of TNFa mRNA is essentially unchanged (Neininger et al., 2002).
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This could be due to the presence of a second decay element, the CDE, in the TNFa 30 UTR (Stoecklin et al., 2003). It remains to be determined whether differences in the spectrum of pro‐inflammatory proteins regulated by p38‐MAPK and MK2 will affect the clinical efficacy of these drugs. Comparative pre‐clinical and clinical evaluation of p38‐MAPK and MK2 inhibitors will be required to determine the potential for these drugs in the treatment of inflammation. A number of other compounds have also been shown to interfere with cytokine production at the posttranscriptional level. In macrophages, the radicicol analogue A inhibits IL‐1b, IL‐6, and TNFa production by accelerating mRNA decay in an ARE‐dependent manner (Kastelic et al., 1996). In monocytes, the cannabinoid ajulemic acid reduces LPS‐induced IL‐1b production, which may involve accelerated IL‐1b mRNA decay (Bidinger et al., 2003). In osteoblasts, a tetracycline derivative was shown to inhibit IL‐1b‐ induced IL‐6 production by accelerating decay of IL‐6 mRNA (Kirkwood et al., 2003). Thalidomide, once in use as a sedative but withdrawn from the market after its severe teratogenic effects were discovered, reduces TNFa and COX‐2 expression by accelerating the degradation of the corresponding mRNAs. Due to its anti‐inflammatory activity, thalidomide has been reintroduced for the treatment of erythema nodosum leprosum, aphtous stomatitis, Behcet syndrome, chronic cutaneous systemic lupus erythematosus, and graft‐versus‐host disease (Calabrese and Fleischer, 2000). Studies have also shown efficacy against aphthous ulcers and other HIV‐associated conditions including Kaposi sarcoma, as well as in the treatment of multiple myeloma. By interfering with posttranscriptional control mechanisms, these drugs have the capacity to dampen the expression of several pro‐inflammatory proteins simultaneously, and may therefore prove useful for the treatment of a variety of inflammatory conditions. The importance of posttranscriptional control mechanisms in the regulation of inflammation suggests that individual components of these regulatory pathways may influence disease susceptibility. Patients expressing single nucleotide polymorphisms that reduce the expression and/or function of TTP, TIA‐1, TIAR, and FXR1P could have an increased risk of developing inflammatory arthritis or inflammatory bowel disease. Sequence analysis has identified 13 polymorphisms in the coding regions of TTP and its two homologues BRF1 and BRF2 (Blackshear et al., 2003b). Six of these mutations would result in amino acid changes that could alter protein function. Another mutation was a dinucleotide substitution that would prevent splicing of the single intron in ZFP36L1, the gene encoding for BRF1. Analysis of lymphoblasts from this individual confirmed that the expression of ZFP36L1 mRNA was reduced by 50%. Case control association studies will be required to determine whether
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any of these gene polymorphisms are associated with increased susceptibility to immune‐mediated inflammatory disease. 6. Conclusions Posttranscriptional regulation of mRNA stability and translation are major determinants of pro‐inflammatory protein expression. An ARE in the 30 UTR of a large number of mRNAs encoding pro‐inflammatory proteins plays a central role by recruiting a specific set of ARE‐BPs, which exert their functions by (i) repressing translation of the bound mRNA, (ii) targeting the mRNA for rapid degradation, or (iii) stabilizing the mRNA in response to extracellular cues. In addition, non‐ARE elements participate in regulating stability and translation of certain mRNAs, and provide a further level of complexity. A molecular understanding of the underlying mechanisms will help to characterize new targets for the development of a next generation of anti‐inflammatory drugs. Genetic polymorphisms within the genes encoding posttranscriptional regulatory proteins are likely to identify individuals with enhanced susceptibility to immune‐mediated inflammatory diseases. As our understanding of posttranscriptional regulatory pathways is still rudimentary, this growing area of research will continue to provide important insights into the fundamental principles that determine gene expression. Much remains to be learned. It is not clear how posttranscriptional control pathways discriminate between the many transcripts that contain regulatory elements in their 30 UTRs. Gene array analysis of mRNAs that co‐precipitate with TIA‐1 or TIAR has revealed that these RNA‐binding proteins can associate with thousands of transcripts (Lopez de Silanes et al., 2005; M. Gorospe, personal communication). Yet functional studies suggest that the mRNAs regulated by these proteins may be much more restricted. It is likely that multiple RNA‐binding proteins expressed in individual cells work together to select mRNAs that are subject to post‐ transcriptional regulation. We know very little about how different ARE‐PBs cooperatively regulate mRNA stability and translation. The potential participation of microRNAs provides further opportunities for fine‐tuning the mRNA selection process. Defining the complex interplay of all factors associated with ARE and non‐ARE elements will help us to fully understand the posttranscriptional operon that governs the expression of pro‐inflammatory proteins. Acknowledgments We would like to thank Nancy Kedersha (Brigham and Women’s Hospital, Boston) for helpful comments on the manuscript. PA was supported by National Institute of Health grants AI‐33600 and AI‐50167.
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References Akashi, M., Loussararian, A. H., Adelman, D. C., Saito, M., and Koeffler, H. P. (1990). Role of lymphotoxin in expression of interleukin 6 in human fibroblasts. Stimulation and regulation. J. Clin. Invest. 85, 121–129. Anderson, P., and Kedersha, N. (2002a). Stressful initiations. J. Cell Sci. 115, 3227–3234. Anderson, P., and Kedersha, N. (2002b). Visibly stressed: The role of eIF2, TIA‐1, and stress granules in protein translation. Cell Stress Chaperones 7, 213–221. Antic, D., and Keene, J. D. (1997). Embryonic lethal abnormal visual RNA‐binding proteins involved in growth, differentiation, and posttranscriptional gene expression. Am. J. Hum. Genet. 61, 273–278. Atasoy, U., Curry, S. L., Lopez de Silanes, I., Shyu, A. B., Casolaro, V., Gorospe, M., and Stellato, C. (2003). Regulation of eotaxin gene expression by TNF‐alpha and IL‐4 through mRNA stabilization: Involvement of the RNA‐binding protein HuR. J. Immunol. 171, 4369–4378. Bakheet, T., Williams, B. R., and Khabar, K. S. (2003). ARED 2.0: An update of AU‐rich element mRNA database. Nucleic Acids Res. 31, 421–423. Bamba, S., Andoh, A., Yasui, H., Makino, J., Kim, S., and Fujiyama, Y. (2003). Regulation of IL‐11 expression in intestinal myofibroblasts: Role of c‐Jun AP‐1‐ and MAPK‐dependent pathways. Am. J. Physiol. Gastrointest. Liver Physiol. 285, G529–G538. Beckwith, J. R. (1967). Regulation of the lac operon. Recent studies on the regulation of lactose metabolism in Escherichia coli support the operon model. Science 156, 597–604. Bickel, M., Cohen, R. B., and Pluznik, D. H. (1990). Post‐transcriptional regulation of granulocyte‐ macrophage colony‐stimulating factor synthesis in murine T cells. J. Immunol. 145, 840–845. Bidinger, B., Torres, R., Rossetti, R. G., Brown, L., Beltre, R., Burstein, S., Lian, J. B., Stein, G. S., and Zurier, R. B. (2003). Ajulemic acid, a nonpsychoactive cannabinoid acid, induces apoptosis in human T lymphocytes. Clin. Immunol. 108, 95–102. Biswas, R., Datta, S., Gupta, J. D., Novotny, M., Tebo, J., and Hamilton, T. A. (2003). Regulation of chemokine mRNA stability by lipopolysaccharide and IL‐10. J. Immunol. 170, 6202–6208. Blackshear, P. J. (2002). Tristetraprolin and other CCCH tandem zinc‐finger proteins in the regulation of mRNA turnover. Biochem. Soc. Trans. 30, 945–952. Blackshear, P. J., Lai, W. S., Kennington, E. A., Brewer, G., Wilson, G. M., Guan, X., and Zhou, P. (2003a). Characteristics of the interaction of a synthetic human tristetraprolin tandem zinc finger peptide with AU‐rich element‐containing RNA substrates. J. Biol. Chem. 278, 19947–19955. Blackshear, P. J., Phillips, R. S., Vazquez‐Matias, J., and Mohrenweiser, H. (2003b). Polymorphisms in the genes encoding members of the tristetraprolin family of human tandem CCCH zinc finger proteins. Prog. Nucleic Acid Res. Mol. Biol. 75, 43–68. Bogdan, C., Paik, J., Vodovotz, Y., and Nathan, C. (1992). Contrasting mechanisms for suppression of macrophage cytokine release by transforming growth factor‐beta and interleukin‐10. J. Biol. Chem. 267, 23301–23308. Brewer, G. (1991). An AþU‐rich element RNA‐binding factor regulates c‐myc stability in vitro. Mol. Cell. Biol. 11, 2460–2466. Briata, P., Ilengo, C., Corte, G., Moroni, C., Rosenfeld, M. G., Chen, C. Y., and Gherzi, R. (2003). The Wnt/beta‐catenin–>Pitx2 pathway controls the turnover of Pitx2 and other unstable mRNAs. Mol. Cell 12, 1201–1211. Brook, M., Sully, G., Clark, A. R., and Saklatvala, J. (2000). Regulation of tumour necrosis factor alpha mRNA stability by the mitogen‐activated protein kinase p38 signalling cascade. FEBS Lett. 483, 57–61.
P O S T T R A N S C R I P T I O N A L C O N T R O L O F I N F L A M M AT I O N
27
Brown, C. Y., Lagnado, C. A., and Goodall, G. J. (1996a). A cytokine mRNA‐destabilizing element that is structurally and functionally distinct from A þ U‐rich elements. Proc. Natl. Acad. Sci. USA 93, 13721–13725. Brown, C. Y., Lagnado, C. A., Vadas, M. A., and Goodall, G. J. (1996b). Differential regulation of the stability of cytokine mRNAs in lipopolysaccharide‐activated blood monocytes in response to interleukin‐10. J. Biol. Chem. 271, 20108–20112. Bufler, P., Gamboni‐Robertson, F., Azam, T., Kim, S. H., and Dinarello, C. A. (2004). Interleukin‐1 homologues IL‐1F7b and IL‐18 contain functional mRNA instability elements within the coding region responsive to lipopolysaccharide. Biochem. J. 381, 503–510. Calabrese, L., and Fleischer, A. B. (2000). Thalidomide: Current and potential clinical applications. Am. J. Med. 108, 487–495. Cao, H., Tuttle, J. S., and Blackshear, P. J. (2004). Immunological characterization of tristetraprolin as a low abundance, inducible, stable cytosolic protein. J. Biol. Chem. 279, 21489–21499. Capowski, E. E., Esnault, S., Bhattacharya, S., and Malter, J. S. (2001). Y box‐binding factor promotes eosinophil survival by stabilizing granulocyte‐macrophage colony‐stimulating factor mRNA. J. Immunol. 167, 5970–5976. Caput, D., Beutler, B., Hartog, K., Thayer, R., Brown‐Shimer, S., and Cerami, A. (1986). Identification of a common nucleotide sequence in the 30 ‐untranslated region of mRNA molecules specifying inflammatory mediators. Proc. Natl. Acad. Sci. USA 83, 1670–1674. Carballo, E., and Blackshear, P. J. (2001). Roles of tumor necrosis factor‐alpha receptor subtypes in the pathogenesis of the tristetraprolin‐deficiency syndrome. Blood 98, 2389–2395. Carballo, E., Cao, H., Lai, W. S., Kennington, E. A., Campbell, D., and Blackshear, P. J. (2001). Decreased sensitivity of tristetraprolin‐deficient cells to p38 inhibitors suggests the involvement of tristetraprolin in the p38 signaling pathway. J. Biol. Chem. 276, 42580–42587. Carballo, E., Lai, W. S., and Blackshear, P. J. (1998). Feedback inhibition of macrophage tumor necrosis factor‐alpha production by tristetraprolin. Science 281, 1001–1005. Carballo, E., Lai, W. S., and Blackshear, P. J. (2000). Evidence that tristetraprolin is a physiological regulator of granulocyte‐macrophage colony‐stimulating factor messenger RNA deadenylation and stability. Blood 95, 1891–1899. Carpenter, L., Cordery, D., and Biden, T. J. (2001). Protein kinase Cdelta activation by interleukin‐ 1beta stabilizes inducible nitric‐oxide synthase mRNA in pancreatic beta‐cells. J. Biol. Chem. 276, 5368–5374. Chen, C.‐Y. A., and Shyu, A.‐B. (1995). AU‐rich elements: Characterization and importance in mRNA degradation. Trends Biochem. Sci. 20, 465–470. Chen, C. Y., Del Gatto‐Konczak, F., Wu, Z., and Karin, M. (1998). Stabilization of interleukin‐ 2 mRNA by the c‐Jun NH2‐terminal kinase pathway. Science 280, 1945–1949. Chen, C. Y., Gherzi, R., Andersen, J. S., Gaietta, G., Jurchott, K., Royer, H. D., Mann, M., and Karin, M. (2000). Nucleolin and YB‐1 are required for JNK‐mediated interleukin‐2 mRNA stabilization during T‐cell activation. Genes Dev. 14, 1236–1248. Chen, C. Y., Gherzi, R., Ong, S. E., Chan, E. L., Raijmakers, R., Pruijn, G. J., Stoecklin, G., Moroni, C., Mann, M., and Karin, M. (2001). AU Binding Proteins Recruit the Exosome to Degrade ARE‐Containing mRNAs. Cell 107, 451–464. Chen, C. Y., Xu, N., and Shyu, A. B. (1995). mRNA decay mediated by two distinct AU‐rich elements from c‐fos and granulocyte‐macrophage colony‐stimulating factor transcripts: Different deadenylation kinetics and uncoupling from translation. Mol. Cell. Biol. 15, 5777–5788. Chen, C. Y., Xu, N., and Shyu, A. B. (2002). Highly selective actions of HuR in antagonizing AU‐rich element‐mediated mRNA destabilization. Mol. Cell. Biol. 22, 7268–7278.
28
G E O R G S T O E C K L I N A N D PA U L A N D E R S O N
Chrestensen, C. A., Schroeder, M. J., Shabanowitz, J., Hunt, D. F., Pelo, J. W., Worthington, M. T., and Sturgill, T. W. (2004). MAPKAP kinase 2 phosphorylates tristetraprolin on in vivo sites including Ser 178, a site required for 14‐3‐3 binding. J. Biol. Chem. 279, 10174–1084. Cok, S. J., Acton, S. J., and Morrison, A. R. (2003). The proximal region of the 30 ‐untranslated region of cyclooxygenase‐2 is recognized by a multimeric protein complex containing HuR, TIA‐ 1, TIAR, and the heterogeneous nuclear ribonucleoprotein U. J. Biol. Chem. 278, 36157–36162. Coles, L. S., Bartley, M. A., Bert, A., Hunter, J., Polyak, S., Diamond, P., Vadas, M. A., and Goodall, G. J. (2004). A multi‐protein complex containing cold shock domain (Y‐box) and polypyrimidine tract binding proteins forms on the vascular endothelial growth factor mRNA. Potential role in mRNA stabilization. Eur. J. Biochem. 271, 648–660. Cook, A. D., Braine, E. L., Campbell, I. K., Rich, M. J., and Hamilton, J. A. (2001). Blockade of collagen‐induced arthritis post‐onset by antibody to granulocyte‐macrophage colony‐stimulating factor (GM‐CSF): Requirement for GM‐CSF in the effector phase of disease. Arthritis Res. 3, 293–298. Cougot, N., Babajko, S., and Seraphin, B. (2004a). Cytoplasmic foci are sites of mRNA decay in human cells. J. Cell Biol. 165, 31–40. Cougot, N., van Dijk, E., Babajko, S., and Seraphin, B. (2004b). ‘Cap‐tabolism’. Trends Biochem. Sci. 29, 436–444. Croft, D., McIntyre, P., Wibulswas, A., and Kramer, I. (1999). Sustained elevated levels of VCAM‐1 in cultured fibroblast‐like synoviocytes can be achieved by TNF‐alpha in combination with either IL‐4 or IL‐13 through increased mRNA stability. Am. J. Pathol. 154, 1149–1158. Darnell, J. C., Jensen, K. B., Jin, P., Brown, V., Warren, S. T., and Darnell, R. B. (2001). Fragile X mental retardation protein targets G quartet mRNAs important for neuronal function. Cell 107, 489–499. Darnell, J. C., Warren, S. T., and Darnell, R. B. (2004). The fragile X mental retardation protein, FMRP, recognizes G‐quartets. Ment. Retard. Dev. Disabil. Res. Rev. 10, 49–52. Dean, J. L., Brook, M., Clark, A. R., and Saklatvala, J. (1999). p38 mitogen‐activated protein kinase regulates cyclooxygenase‐2 mRNA stability and transcription in lipopolysaccharide‐treated human monocytes. J. Biol. Chem. 274, 264–269. Dean, J. L., Sully, G., Wait, R., Rawlinson, L., Clark, A. R., and Saklatvala, J. (2002). Identification of a novel AU‐rich‐element‐binding protein which is related to AUF1. Biochem. J. 366, 709–719. Denys, A., Udalova, I. A., Smith, C., Williams, L. M., Ciesielski, C. J., Campbell, J., Andrews, C., Kwaitkowski, D., and Foxwell, B. M. (2002). Evidence for a dual mechanism for IL‐10 suppression of TNF‐alpha production that does not involve inhibition of p38 mitogen‐activated protein kinase or NF‐kappa B in primary human macrophages. J. Immunol. 168, 4837–4845. Dever, T. E. (2002). Gene‐specific regulation by general translation factors. Cell 108, 545–556. Dibbens, J. A., Miller, D. L., Damert, A., Risau, W., Vadas, M. A., and Goodall, G. J. (1999). Hypoxic regulation of vascular endothelial growth factor mRNA stability requires the cooperation of multiple RNA elements. Mol. Biol. Cell 10, 907–919. Di Marco, S., Mazroui, R., Dallaire, P., Chittur, S., Tenenbaum, S. A., Radzioch, D., Marette, A., and Gallouzi, I. E. (2005). NF‐k B‐mediated MyoD decay during muscle wasting requires nitric oxide synthase mRNA stabilization, HuR protein, and nitric oxide release. Mol. Cell. Biol. 25, 6533–6545. Dixon, D. A., Balch, G. C., Kedersha, N., Anderson, P., Zimmerman, G. A., Beauchamp, R. D., and Prescott, S. M. (2003). Regulation of cyclooxygenase‐2 expression by the translational silencer TIA‐1. J. Exp. Med. 198, 475–481. Edwards, S., and Hallett, M. (1997). Seeing the wood for the trees: The forgotten role of neutrophils in rheumatoid arthritis. Immunol. Today 18, 320–324.
P O S T T R A N S C R I P T I O N A L C O N T R O L O F I N F L A M M AT I O N
29
Esnault, S., and Malter, J. S. (1999). Primary peripheral blood eosinophils rapidly degrade transfected granulocyte‐macrophage colony‐stimulating factor mRNA. J. Immunol. 163, 5228–5234. Fan, X. C., and Steitz, J. A. (1998). Overexpression of HuR, a nuclear‐cytoplasmic shuttling protein, increases the in vivo stability of ARE‐containing mRNAs. EMBO J. 17, 3448–3460. Fenton, M. J., Vermeulen, M. W., Clark, B. D., Webb, A. C., and Auron, P. E. (1988). Human pro‐ IL‐1 beta gene expression in monocytic cells is regulated by two distinct pathways. J. Immunol. 140, 2267–2273. Fillman, C., and Lykke‐Andersen, J. (2005). RNA decapping inside and outside of processing bodies. Curr. Opin. Cell Biol. 17, 326–331. Ford, L. P., Watson, J., Keene, J. D., and Wilusz, J. (1999). ELAV proteins stabilize deadenylated intermediates in a novel in vitro mRNA deadenylation/degradation system. Genes Dev. 13, 188–201. Gao, M., Wilusz, C. J., Peltz, S. W., and Wilusz, J. (2001). A novel mRNA‐decapping activity in HeLa cytoplasmic extracts is regulated by AU‐rich elements. EMBO J. 20, 1134–1143. Garnon, J., Lachance, C., Di Marco, S., Hel, Z., Marion, D., Ruiz, M. C., Newkirk, M. M., Khandjian, E. W., and Radzioch, D. (2005). Fragile X‐related protein FXR1P regulates proinflammatory cytokine tumor necrosis factor expression at the post‐transcriptional level. J. Biol. Chem. 280, 5750–5763. Gerber, A. P., Herschlag, D., and Brown, P. O. (2004). Extensive association of functionally and cytotopically related mRNAs with Puf family RNA‐binding proteins in yeast. PLoS Biol. 2, E79. Gherzi, R., Lee, K. Y., Briata, P., Wegmuller, D., Moroni, C., Karin, M., and Chen, C. Y. (2004). A KH domain RNA binding protein, KSRP, promotes ARE‐directed mRNA turnover by recruiting the degradation machinery. Mol. Cell 14, 571–583. Grosset, C., Boniface, R., Duchez, P., Solanilla, A., Cosson, B., and Ripoche, J. (2004). In vivo studies of translational repression mediated by the granulocyte‐macrophage colony‐stimulating factor AU‐rich element. J. Biol. Chem. 279, 13354–13362. Hamilton, J. A. (2002). GM‐CSF in inflammation and autoimmunity. Trends Immunol. 23, 403–408. Han, J., Brown, T., and Beutler, B. (1990). Endotoxin‐responsive sequences control cachectin/ tumor necrosis factor biosynthesis at the translational level. J. Exp. Med. 171, 465–475. Harding, H., Novoa, Y., Zhang, H., Zeng, R., Wek, M., Schapira, M., and Ron, D. (2000a). Regulated translation initiation controls stress‐induced gene expression in mammalian cells. Mol. Cell 6, 1099–1108. Harding, H. P., Zhang, Y., Bertolotti, A., Zeng, H., and Ron, D. (2000b). Perk is essential for translational regulation and cell survival during the unfolded protein response. Mol. Cell 5, 897–904. Hodge, D. L., Martinez, A., Julias, J. G., Taylor, L. S., and Young, H. A. (2002). Regulation of nuclear gamma interferon gene expression by interleukin 12 (IL‐12) and IL‐2 represents a novel form of posttranscriptional control. Mol. Cell. Biol. 22, 1742–1753. Holtmann, H., Winzen, R., Holland, P., Eickemeier, S., Hoffmann, E., Wallach, D., Malinin, N. L., Cooper, J. A., Resch, K., and Kracht, M. (1999). Induction of interleukin‐8 synthesis integrates effects on transcription and mRNA degradation from at least three different cytokine‐ or stress‐ activated signal transduction pathways. Mol. Cell. Biol. 19, 6742–6753. Houzet, L., Morello, D., Defrance, P., Mercier, P., Huez, G., and Kruys, V. (2001). Regulated control by granulocyte‐macrophage colony‐stimulating factor AU‐rich element during mouse embryogenesis. Blood 98, 1281–1288. Hudson, B. P., Martinez‐Yamout, M. A., Dyson, H. J., and Wright, P. E. (2004). Recognition of the mRNA AU‐rich element by the zinc finger domain of TIS11d. Nat. Struct. Mol. Biol. 11, 257–264.
30
G E O R G S T O E C K L I N A N D PA U L A N D E R S O N
Huwiler, A., Akool el, S., Aschrafi, A., Hamada, F. M., Pfeilschifter, J., and Eberhardt, W. (2003). ATP potentiates interleukin‐1 beta‐induced MMP‐9 expression in mesangial cells via recruitment of the ELAV protein HuR. J. Biol. Chem. 278, 51758–51769. Iademarco, M. F., Barks, J. L., and Dean, D. C. (1995). Regulation of vascular cell adhesion molecule‐1 expression by IL‐4 and TNF‐alpha in cultured endothelial cells. J. Clin. Invest. 95, 264–271. Ikeda, E., Achen, M. G., Breier, G., and Risau, W. (1995). Hypoxia‐induced transcriptional activation and increased mRNA stability of vascular endothelial growth factor in C6 glioma cells. J. Biol. Chem. 270, 19761–19766. Ingelfinger, D., Arndt‐Jovin, D. J., Luhrmann, R., and Achsel, T. (2002). The human LSm1‐7 proteins colocalize with the mRNA‐degrading enzymes Dcp1/2 and Xrnl in distinct cytoplasmic foci. RNA 8, 1489–1501. Jing, Q., Huang, S., Guth, S., Zarubin, T., Motoyama, A., Chen, J., Di Padova, F., Lin, S. C., Gram, H., and Han, J. (2005). Involvement of microRNA in AU‐rich element‐mediated mRNA instability. Cell 120, 623–634. Johnson, B. A., and Blackwell, T. K. (2002). Multiple tristetraprolin sequence domains required to induce apoptosis and modulate responses to TNFalpha through distinct pathways. Oncogene 21, 4237–4246. Johnson, B. A., Geha, M., and Blackwell, T. K. (2000). Similar but distinct effects of the tristetraprolin/TIS11 immediate‐early proteins on cell survival. Oncogene 19, 1657–1664. Johnson, B. A., Stehn, J. R., Yaffe, M. B., and Blackwell, T. K. (2002). Cytoplasmic localization of Tristetraprolin involves 14–3‐3‐dependent and ‐independent mechanisms. J. Biol. Chem. 277, 18029–18036. Jonsson, H., Allen, P., and Peng, S. L. (2005). Inflammatory arthritis requires Foxo3a to prevent Fas ligand‐induced neutrophil apoptosis. Nat. Med. 11, 666–671. Kastelic, T., Schnyder, J., Leutwiler, A., Traber, R., Streit, B., Niggli, H., Mac Kenzie, A., and Cheneval, D. (1996). Induction of rapid IL‐1 beta mRNA degradation in THP‐1 cells mediated through the AU‐rich region in the 30 UTR by a radicicol analogue. Cytokine 8, 751–761. Kaufmann, W. E., Cohen, S., Sun, H. T., and Ho, G. (2002). Molecular phenotype of Fragile X syndrome: FMRP, FXRPs, and protein targets. Microsc. Res. Tech. 57, 135–144. Kedersha, N., and Anderson, P. (2001). Stress granules: Sites of mRNA triage that regulate mRNA stability and translatability. Biochem. Soc. Trans 30, 963–969. Kedersha, N., Chen, S., Gilks, N., Li, W., Miller, I. J., Stahl, J., and Anderson, P. (2002). Evidence that ternary complex (eIF2‐GTP‐tRNA(i)(Met))‐deficient preinitiation complexes are core constituents of mammalian stress granules. Mol. Biol. Cell 13, 195–210. Kedersha, N., Cho, M. R., Li, W., Yacono, P. W., Chen, S., Gilks, N., Golan, D. E., and Anderson, P. (2000). Dynamic shuttling of TIA‐1 accompanies the recruitment of mRNA to mammalian stress granules. J. Cell Biol. 151, 1257–1268. Kedersha, N. L., Gupta, M., Li, W., Miller, I., and Anderson, P. (1999). RNA‐binding proteins TIA‐ 1 and TIAR link the phosphorylation of eIF‐2 alpha to the assembly of mammalian stress granules. J. Cell Biol. 147, 1431–1442. Kedersha, N., Stoecklin, G., Ayodele, M., Yacono, P., Lykke‐Andersen, J., Fitzler, M. J., Scheuner, D., Kaufman, R. J., Golan, D. E., and Andersen, P. (2005). Stress granules and processing bodies are dynamically linked sites of mRNP remodeling. J. Cell Biol. 169, 871–884. Keene, J. D., and Tenenbaum, S. A. (2002). Eukaryotic mRNPs may represent posttranscriptional operons. Mol. Cell 9, 1161–1167. Keffer, J., Probert, L., Cazlaris, H., Georgopoulos, S., Kaslaris, E., Kioussis, D., and Kollias, G. (1991). Transgenic mice expressing human tumour necrosis factor: A predictive genetic model of arthritis. EMBO J. 10, 4025–4031.
P O S T T R A N S C R I P T I O N A L C O N T R O L O F I N F L A M M AT I O N
31
Kirkwood, K., Martin, T., Andreadis, S. T., and Kim, Y. J. (2003). Chemically modified tetracyclines selectively inhibit IL‐6 expression in osteoblasts by decreasing mRNA stability. Biochem. Pharmacol. 66, 1809–1819. Kishore, R., Tebo, J. M., Kolosov, M., and Hamilton, T. A. (1999). Cutting edge: Clustered AU‐rich elements are the target of IL‐10‐mediated mRNA destabilization in mouse macrophages. J. Immunol. 162, 2457–2461. Koeffler, H. P., Gasson, J., and Tobler, A. (1988). Transcriptional and posttranscriptional modulation of myeloid colony‐stimulating factor expression by tumor necrosis factor and other agents. Mol. Cell. Biol. 8, 3432–3438. Kolios, G., Valatas, V., and Ward, S. G. (2004). Nitric oxide in inflammatory bowel disease: A universal messenger in an unsolved puzzle. Immunology 113, 427–437. Kollias, G. (2004). Modeling the function of tumor necrosis factor in immune pathophysiology. Autoimmun. Rev. 3(Suppl. 1), S24–S25. Kontoyiannis, D., Boulougouris, G., Manoloukos, M., Armaka, M., Apostolaki, M., Pizarro, T., Kotlyarov, A., Forster, I., Flavell, R., Gaestel, M., Tsichlis, P., Cominelli, F., and Kollias, G. (2002). Genetic dissection of the cellular pathways and signaling mechanisms in modeled tumor necrosis factor‐induced Crohn’s‐like inflammatory bowel disease. J. Exp. Med. 196, 1563–1574. Kontoyiannis, D., Kotlyarov, A., Carballo, E., Alexopoulou, L., Blackshear, P. J., Gaestel, M., Davis, R., Flavell, R., and Kollias, G. (2001). Interleukin‐10 targets p38 MAPK to modulate ARE‐ dependent TNF mRNA translation and limit intestinal pathology. EMBO J. 20, 3760–3770. Kontoyiannis, D., Pasparakis, M., Pizarro, T. T., Cominelli, F., and Kollias, G. (1999). Impaired on/off regulation of TNF biosynthesis in mice lacking TNF AU‐rich elements: Implications for joint and gut‐associated immunopathologies. Immunity 10, 387–398. Konttinen, Y. T., Salo, T., Hanemaaijer, R., Valleala, H., Sorsa, T., Sutinen, M., Ceponis, A., Xu, J. W., Santavirta, S., Teronen, O., and Lopez‐Otin, C. (1999). Collagenase‐3 (MMP‐13) and its activators in rheumatoid arthritis: Localization in the pannus‐hard tissue junction and inhibition by alendronate. Matrix Biol. 18, 401–412. Kotlyarov, A., Neininger, A., Schubert, C., Eckert, R., Birchmeier, C., Volk, H. D., and Gaestel, M. (1999). MAPKAP kinase 2 is essential for LPS‐induced TNF‐alpha biosynthesis. Nat. Cell Biol. 1, 94–97. Krishnamoorthy, T., Pavitt, G. D., Zhang, F., Dever, T. E., and Hinnebusch, A. G. (2001). Tight binding of the phosphorylated alpha subunit of initiation factor 2 (eIF2alpha) to the regulatory subunits of guanine nucleotide exchange factor eIF2B is required for inhibition of translation initiation. Mol. Cell. Biol. 21, 5018–5030. Kuhn, H., Walther, M., and Kuban, R. J. (2002). Mammalian arachidonate 15‐lipoxygenases structure, function, and biological implications. Prostaglandins Other Lipid Mediat. 68–69, 263–290. Kullmann, M., Gopfert, U., Siewe, B., and Hengst, L. (2002). ELAV/Hu proteins inhibit p27 translation via an IRES element in the p27 50 UTR. Genes Dev. 16, 3087–3099. Lagnado, C. A., Brown, C. Y., and Goodall, G. J. (1994). AUUUA is not sufficient to promote poly (A) shortening and degradation of an mRNA: The functional sequence within AU‐rich elements may be UUAUUUA(U/A)(U/A). Mol. Cell. Biol. 14, 7984–7995. Lahti, A., Jalonen, U., Kankaanranta, H., and Moilanen, E. (2003). c‐Jun NH2‐terminal kinase inhibitor anthra(1,9‐cd)pyrazol‐6(2H)‐one reduces inducible nitric‐oxide synthase expression by destabilizing mRNA in activated macrophages. Mol. Pharmacol. 64, 308–315. Lai, W. S., Carballo, E., Strum, J. R., Kennington, E. A., Phillips, R. S., and Blackshear, P. J. (1999). Evidence that tristetraprolin binds to AU‐rich elements and promotes the deadenylation and destabilization of tumor necrosis factor alpha mRNA. Mol. Cell. Biol. 19, 4311–4323.
32
G E O R G S T O E C K L I N A N D PA U L A N D E R S O N
Lai, W. S., Carballo, E., Thorn, J. M., Kennington, E. A., and Blackshear, P. J. (2000). Interactions of CCCH zinc finger proteins with mRNA. Binding of tristetraprolin‐related zinc finger proteins to Au‐rich elements and destabilization of mRNA. J. Biol. Chem. 275, 17827–17837. Lai, W. S., Kennington, E. A., and Blackshear, P. J. (2003). Tristetraprolin and its family members can promote the cell‐free deadenylation of AU‐rich element‐containing mRNAs by poly(A) ribonuclease. Mol. Cell. Biol. 23, 3798–3812. Lal, A., Mazan‐Mamczarz, K., Kawai, T., Yang, X., Martindale, J. L., and Gorospe, M. (2004). Concurrent versus individual binding of HuR and AUF1 to common labile target mRNAs. EMBO J. 23, 3092–3102. Lasa, M., Mahtani, K. R., Finch, A., Brewer, G., Saklatvala, J., and Clark, A. R. (2000). Regulation of cyclooxygenase 2 mRNA stability by the mitogen‐activated protein kinase p38 signaling cascade. Mol. Cell. Biol. 20, 4265–4274. Lawlor, K. E., Campbell, I. K., Metcalf, D., O’Donnell, K., van Nieuwenhuijze, A., Roberts, A. W., and Wicks, I. P. (2004). Critical role for granulocyte colony‐stimulating factor in inflammatory arthritis. Proc. Natl. Acad. Sci. USA 101, 11398–11403. Levy, A. P., Levy, N. S., and Goldberg, M. A. (1996). Post‐transcriptional regulation of vascular endothelial growth factor by hypoxia. J. Biol. Chem. 271, 2746–2753. Levy, N. S., Chung, S., Furneaux, H., and Levy, A. P. (1998). Hypoxic stabilization of vascular endothelial growth factor mRNA by the RNA‐binding protein HuR. J. Biol. Chem. 273, 6417–6423. Lindsten, T., June, C. H., Ledbetter, J. A., Stella, G., and Thompson, G. B. (1989). Regulation of lymphokine messenger RNA stability by a surface‐mediated T cell activation pathway. Science 244, 339–343. Liu, J., Valencia‐Sanchez, M. A., Hannon, G. J., and Parker, R. (2005). MicroRNA‐dependent localization of targeted mRNAs to mammalian P‐bodies. Nat. Cell Biol. 7, 719–723. Loflin, P., Chen, C. Y., and Shyu, A. B. (1999). Unraveling a cytoplasmic role for hnRNP D in the in vivo mRNA destabilization directed by the AU‐rich element. Genes Dev. 13, 1884–1897. Lopez de Silanes, I., Galban, S., Martindale, J. L., Yang, X., Mazan‐Mamczarz, K., Indig, F. E., Falco, G., Zhan, M., and Gorospe, M. (2005). Identification and functional outcome of mRNAs associated with RNA‐binding protein TIA‐1. Mol. Cell. Biol. 25, 9520–9531. Lu, J. Y., and Schneider, R. J. (2004). Tissue distribution of AU‐rich mRNA‐binding proteins involved in regulation of mRNA decay. J. Biol. Chem. 279, 12974–12979. Lykke‐Andersen, J., and Wagner, E. (2005). Recruitment and activation of mRNA decay enzymes by two ARE‐mediated decay activation domains in the proteins TTP and BRF‐1. Genes Dev. 19, 351–361. Ma, W.‐J., Cheng, S., Campbell, C., Wright, A., and Furneaux, H. (1996). Cloning and characterization of HuR, a ubiquitously expressed Elav‐like protein. J. Biol. Chem. 271, 8144–8151. MacMicking, J., Xie, Q. W., and Nathan, C. (1997). Nitric oxide and macrophage function. Annu. Rev. Immunol. 15, 323–350. Mahtani, K. R., Brook, M., Dean, J. L., Sully, G., Saklatvala, J., and Clark, A. R. (2001). Mitogen‐ activated protein kinase p38 controls the expression and posttranslational modification of tristetraprolin, a regulator of tumor necrosis factor alpha mRNA stability. Mol. Cell. Biol. 21, 6461–6469. Mavropoulos, A., Sully, G., Cope, A. P., and Clark, A. R. (2005). Stabilization of IFN‐gamma mRNA by MAPK p38 in IL‐12‐ and IL‐18‐stimulated human NK cells. Blood 105, 282–288. Mazan‐Mamczarz, K., Galban, S., Lopez de Silanes, I., Martindale, J. L., Atasoy, U., Keene, J. D., and Gorospe, M. (2003). RNA‐binding protein HuR enhances p53 translation in response to ultraviolet light irradiation. Proc. Natl. Acad. Sci. USA 100, 8354–8359.
P O S T T R A N S C R I P T I O N A L C O N T R O L O F I N F L A M M AT I O N
33
Min, H., Turck, C. W., Nikolic, J. M., and Black, D. L. (1997). A new regulatory protein, KSRP, mediates exon inclusion through an intronic splicing enhancer. Genes Dev. 11, 1023–1036. Ming, X. F., Kaiser, M., and Moroni, C. (1998). c‐jun N‐terminal kinase is involved in AUUUA‐ mediated interleukin‐3 mRNA turnover in mast cells. EMBO J. 17, 6039–6048. Ming, X. F., Stoecklin, G., Lu, M., Looser, R., and Moroni, C. (2001). Parallel and Independent Regulation of Interleukin‐3 mRNA Turnover by Phosphatidylinositol 3‐Kinase and p38 Mitogen‐ Activated Protein Kinase. Mol. Cell. Biol. 21, 5778–5789. Mitchell, P., and Tollervey, D. (2000). Musing on the structural organization of the exosome complex. Nat. Struct. Biol. 7, 843–846. Moore, B. A., Aznavoorian, S., Engler, J. A., and Windsor, L. J. (2000). Induction of collagenase‐3 (MMP‐13) in rheumatoid arthritis synovial fibroblasts. Biochim. Biophys. Acta 1502, 307–318. Moore, K. W., de Waal Malefyt, R., Coffman, R. L., and O’Garra, A. (2001). Interleukin‐10 and the interleukin‐10 receptor. Annu. Rev. Immunol. 19, 683–765. Morales‐Ducret, J., Wayner, E., Elices, M. J., Alvaro‐Gracia, J. M., Zvaifler, N. J., and Firestein, G. S. (1992). Alpha 4/beta 1 integrin (VLA‐4) ligands in arthritis. Vascular cell adhesion molecule‐1 expression in synovium and on fibroblast‐like synoviocytes. J. Immunol. 149, 1424–1431. Mukherjee, D., Gao, M., O’Connor, J. P., Raijmakers, R., Pruijn, G., Lutz, C. S., and Wilusz, J. (2002). The mammalian exosome mediates the efficient degradation of mRNAs that contain AU‐rich elements. EMBO J. 21, 165–174. Mukhopadhyay, D., Houchen, C. W., Kennedy, S., Dieckgraefe, B. K., and Anant, S. (2003). Coupled mRNA stabilization and translational silencing of cyclooxygenase‐2 by a novel RNA binding protein, CUGBP2. Mol. Cell 11, 113–126. Muller, C. W. (2001). DNA recognition by NF kappa B and STAT transcription factors. Ernst Schering Res. Found. Workshop 14, 3–166. Musgrave, B. L., Watson, C. L., Haeryfar, S. M., Barnes, C. A., and Hoskin, D. W. (2004). CD2‐ CD48 interactions promote interleukin‐2 and interferon‐gamma synthesis by stabilizing cytokine mRNA. Cell. Immunol. 229, 1–12. Nair, A. P., Hahn, S., Banholzer, R., Hirsch, H. H., and Moroni, C. (1994). Cyclosporin A inhibits growth of autocrine tumour cell lines by destabilizing interleukin‐3 mRNA. Nature 369, 239–242. Neininger, A., Kontoyiannis, D., Kotlyarov, A., Winzen, R., Eckert, R., Volk, H. D., Holtmann, H., Kollias, G., and Gaestel, M. (2002). MK2 targets AU‐rich elements and regulates biosynthesis of tumor necrosis factor and interleukin‐6 independently at different post‐transcriptional levels. J. Biol. Chem. 277, 3065–3068. Ogilvie, R. L., Abelson, M., Hau, H. H., Vlasova, I., Blackshear, P. J., and Bohjanen, P. R. (2005). Tristetraprolin down‐regulates IL‐2 gene expression through AU‐rich element‐mediated mRNA decay. J. Immunol. 174, 953–961. Ostareck, D., Ostareck‐Lederer, A., Shatsky, I., and Hentze, M. (2001). Lipoxygense mRNA silencing in erythroid differentiation: The 30 UTR regulatory complex controls 60S ribosomal subunit joining. Cell 104, 281–290. Ostareck, D. H., Ostareck‐Lederer, A., Wilm, M., Thiele, B. J., Mann, M., and Hentze, M. W. (1997). mRNA silencing in erythroid differentiation: hnRNP K and hnRNP E1 regulate 15‐lipoxygenase translation from the 30 end. Cell 89, 597–606. Parasrampuria, D. A., de Boer, P., Desai‐Krieger, D., Chow, A. T., and Jones, C. R. (2003). Single‐ dose pharmacokinetics and pharmacodynamics of RWJ 67657, a specific p38 mitogen‐activated protein kinase inhibitor: A first‐in‐human study. J. Clin. Pharmacol. 43, 406–413. Pargellis, C., and Regan, J. (2003). Inhibitors of p38 mitogen‐activated protein kinase for the treatment of rheumatoid arthritis. Curr. Opin. Investig. Drugs 4, 566–571. Parker, R., and Song, H. (2004). The enzymes and control of eukaryotic mRNA turnover. Nat. Struct. Mol. Biol. 11, 121–127.
34
G E O R G S T O E C K L I N A N D PA U L A N D E R S O N
Pastore, S., Mascia, F., Mariotti, F., Dattilo, C., Mariani, V., and Girolomoni, G. (2005). ERK1/2 regulates epidermal chemokine expression and skin inflammation. J. Immunol. 174, 5047–5056. Peng, S. S., Chen, C. Y., Xu, N., and Shyu, A. B. (1998). RNA stabilization by the AU‐rich element binding protein, HuR, an ELAV protein. EMBO J. 17, 3461–3470. Perez‐Sala, D., Cernuda‐Morollon, E., Diaz‐Cazorla, M., Rodriguez‐Pascual, F., and Lamas, S. (2001). Posttranscriptional regulation of human iNOS by the NO/cGMP pathway. Am. J. Physiol. Renal Physiol. 280, F466–F473. Phillips, K., Kedersha, N., Shen, L., Blackshear, P. J., and Anderson, P. (2004). Arthritis suppressor genes TIA‐1 and TTP dampen the expression of tumor necrosis factor alpha, cyclooxygenase 2, and inflammatory arthritis. Proc. Natl. Acad. Sci. USA 101, 2011–2016. Piecyk, M., Wax, S., Beck, A. R., Kedersha, N., Gupta, M., Maritim, B., Chen, S., Gueydan, C., Kruys, V., Streuli, M., and Anderson, P. (2000). TIA‐1 is a translational silencer that selectively regulates the expression of TNF‐alpha. EMBO J. 19, 4154–4163. Pillinger, M., and Abramson, S. (1995). The neutrophil in rheumatoid arthritis. Rheum. Dis. Clin. North Am. 21, 691–714. Putland, R. A., Sassinis, T. A., Harvey, J. S., Diamond, P., Coles, L. S., Brown, C. Y., and Goodall, G. J. (2002). RNA destabilization by the granulocyte colony‐stimulating factor stem‐loop destabilizing element involves a single stem‐loop that promotes deadenylation. Mol. Cell. Biol. 22, 1664–1673. Quijada, L., Guerra‐Giraldez, C., Drozdz, M., Hartmann, C., Irmer, H., Ben‐Dov, C., Cristodero, M., Ding, M., and Clayton, C. (2002). Expression of the human RNA‐binding protein HuR in Trypanosoma brucei increases the abundance of mRNAs containing AU‐rich regulatory elements. Nucleic Acids Res. 30, 4414–4424. Raghavan, A., Robison, R. L., McNabb, J., Miller, C. R., Williams, D. A., and Bohjanen, P. R. (2001). HuA and tristetraprolin are induced following T cell activation and display distinct but overlapping RNA binding specificities. J. Biol. Chem. 276, 47958–47965. Raijmakers, R., Schilders, G., and Pruijn, G. J. (2004). The exosome, a molecular machine for controlled RNA degradation in both nucleus and cytoplasm. Eur. J. Cell Biol. 83, 175–183. Raineri, I., Wegmueller, D., Gross, B., Certa, U., and Moroni, C. (2004). Roles of AUF1 isoforms, HuR and BRF1 in ARE‐dependent mRNA turnover studied by RNA interference. Nucleic Acids Res. 32, 1279–1288. Raj, N. B., and Pitha, P. M. (1983). Two levels of regulation of beta‐interferon gene expression in human cells. Proc. Natl. Acad. Sci. USA 80, 3923–3927. Ramos, S. B., Stumpo, D. J., Kennington, E. A., Phillips, R. S., Bock, C. B., Ribeiro‐Neto, F., and Blackshear, P. J. (2004). The CCCH tandem zinc‐finger protein Zfp36l2 is crucial for female fertility and early embryonic development. Development 131, 4883–4893. Ridley, S. H., Dean, J. L., Sarsfield, S. J., Brook, M., Clark, A. R., and Saklatvala, J. (1998). A p38 MAP kinase inhibitor regulates stability of interleukin‐1‐induced cyclooxygenase‐2 mRNA. FEBS Lett. 439, 75–80. Rigby, W. F., Roy, K., Collins, J., Rigby, S., Connolly, J. E., Bloch, D. B., and Brooks, S. A. (2005). Structure/Function Analysis of Tristetraprolin (TTP): p38 Stress‐Activated Protein Kinase and Lipopolysaccharide Stimulation Do Not Alter TTP Function. J. Immunol. 174, 7883–7893. Ristimaki, A., Garfinkel, S., Wessendorf, J., Maciag, T., and Hla, T. (1994). Induction of cyclooxygenase‐2 by interleukin‐1 alpha. Evidence for post‐transcriptional regulation. J. Biol. Chem. 269, 11769–11775. Rodriguez‐Pascual, F., Hausding, M., Ihrig‐Biedert, I., Furneaux, H., Levy, A. P., Forstermann, U., and Kleinert, H. (2000). Complex contribution of the 30 ‐untranslated region to the expressional
P O S T T R A N S C R I P T I O N A L C O N T R O L O F I N F L A M M AT I O N
35
regulation of the human inducible nitric‐oxide synthase gene. Involvement of the RNA‐binding protein HuR. J. Biol. Chem. 275, 26040–26049. Rousseau, S., Morrice, N., Peggie, M., Campbell, D. G., Gaestel, M., and Cohen, P. (2002). Inhibition of SAPK2a/p38 prevents hnRNP A0 phosphorylation by MAPKAP‐K2 and its interaction with cytokine mRNAs. EMBO J. 21, 6505–6514. Saito, K., Chen, S., Piecyk, M., and Anderson, P. (2001). TIA‐1 regulates the production of tumor necrosis factor alpha in macrophages, but not in lymphocytes. Arthritis Rheum. 44, 2879–2887. Sarkar, B., Xi, Q., He, C., and Schneider, R. J. (2003). Selective degradation of AU‐rich mRNAs promoted by the p37 AUF1 protein isoform. Mol. Cell. Biol. 23, 6685–6693. Schmidlin, M., Lu, M., Leuenberger, S. A., Stoecklin, G., Mallaun, M., Gross, B., Gherzi, R., Hess, D., Hemmings, B. A., and Moroni, C. (2004). The ARE‐dependent mRNA‐destabilizing activity of BRF1 is regulated by protein kinase B. EMBO J. 23, 4760–4769. Schnitzer, T. J., and Hochberg, M. C. (2002). COX‐2‐selective inhibitors in the treatment of arthritis. Cleve. Clin. J. Med. 69(Suppl. 1), SI20–SI30. Serhan, C. N. (2001). Lipoxins and aspirin‐triggered 15‐epi‐lipoxins are endogenous components of antiinflammation: Emergence of the counterregulatory side. Arch. Immunol. Ther. Exp. (Warsz) 49, 177–188. Shaw, G., and Kamen, R. (1986). A conserved AU sequence from the 30 untranslated region of GM‐ CSF mRNA mediates selective mRNA degradation. Cell 46, 659–667. Sirenko, O. I., Lofquist, A. K., De Maria, C. T., Morris, J. S., Brewer, G., and Haskill, J. S. (1997). Adhesion‐dependent regulation of an A þ U‐rich element‐binding activity associated with AUF1. Mol. Cell. Biol. 17, 3898–3906. Sood, R., Porter, A. C., Olsen, D. A., Cavener, D. R., and Wek, R. C. (2000). A mammalian homologue of GCN2 protein kinase important for translational control by phosphorylation of eukaryotic initiation factor‐2alpha. Genetics 154, 787–801. Stein, I., Neeman, M., Shweiki, D., Itin, A., and Keshet, E. (1995). Stabilization of vascular endothelial growth factor mRNA by hypoxia and hypoglycemia and coregulation with other ischemia‐induced genes. Mol. Cell. Biol. 15, 5363–5368. Stoeckle, M. Y. (1991). Post‐transcriptional regulation of gro alpha, beta, gamma, and IL‐8 mRNAs by IL‐1 beta. Nucleic Acids Res. 19, 917–920. Stoecklin, G., Colombi, M., Raineri, I., Leuenberger, S., Mallaun, M., Schmidlin, M., Gross, B., Lu, M., Kitamura, T., and Moroni, C. (2002). Functional cloning of BRF1, a regulator of ARE‐ dependent mRNA turnover. EMBO J. 21, 4709–4718. Stoecklin, G., Hahn, S., and Moroni, C. (1994). Functional hierarchy of AUUUA motifs in mediating rapid interleukin‐3 mRNA decay. J. Biol. Chem. 269, 28591–28597. Stoecklin, G., Lu, M., Rattenbacher, B., and Moroni, C. (2003). A constitutive decay element promotes tumor necrosis factor alpha mRNA degradation via an AU‐rich element‐independent pathway. Mol. Cell. Biol. 23, 3506–3515. Stoecklin, G., Mayo, T., and Anderson, P. (2005). ARE‐mRNA degradation requires the 50 ‐30 decay pathway. EMBO Rep. In Press. Stoecklin, G., Ming, X. F., Looser, R., and Moroni, C. (2000). Somatic mRNA turnover mutants implicate tristetraprolin in the interleukin‐3 mRNA degradation pathway. Mol. Cell. Biol. 20, 3753–3763. Stoecklin, G., Stoeckle, P., Lu, M., Muehlemann, O., and Moroni, C. (2001). Cellular mutants define a common mRNA degradation pathway targeting cytokine AU‐rich elements. RNA 7, 1578–1588. Stoecklin, G., Stubbs, T., Kedersha, N., Wax, S., Rigby, W. F., Blackwell, T. K., and Anderson, P. (2004). MK2‐induced tristetraprolin:14‐3‐3 complexes prevent stress granule association and ARE‐mRNA decay. EMBO J. 23, 1313–1324.
36
G E O R G S T O E C K L I N A N D PA U L A N D E R S O N
Stumpo, D. J., Byrd, N. A., Phillips, R. S., Ghosh, S., Maronpot, R. R., Castranio, T., Meyers, E. N., Mishina, Y., and Blackshear, P. J. (2004). Chorioallantoic fusion defects and embryonic lethality resulting from disruption of Zfp36L1, a gene encoding a CCCH tandem zinc finger protein of the Tristetraprolin family. Mol. Cell. Biol. 24, 6445–6455. Sundy, J. S. (2001). COX‐2 inhibitors in rheumatoid arthritis. Curr. Rheumatol. Rep. 3, 86–91. Takeda, K., Clausen, B. E., Kaisho, T., Tsujimura, T., Terada, N., Forster, I., and Akira, S. (1999). Enhanced Th1 activity and development of chronic enterocolitis in mice devoid of Stat3 in macrophages and neutrophils. Immunity 10, 39–49. Taylor, G. A., Carballo, E., Lee, D. M., Lai, W. S., Thompson, M. J., Patel, D. D., Schenkman, D. I., Gilkeson, G. S., Broxmeyer, H. E., Haynes, B. F., and Blackshear, P. J. (1996). A pathogenetic role for TNF alpha in the syndrome of cachexia, arthritis, and autoimmunity resulting from tristetraprolin (TTP) deficiency. Immunity 4, 445–454. Tran, H., Schilling, M., Wirbelauer, C., Hess, D., and Nagamine, Y. (2004). Facilitation of mRNA deadenylation and decay by the exosome‐bound, DExH protein RHAU. Mol. Cell 13, 101–111. van Dijk, E., Cougot, N., Meyer, S., Babajko, S., Wahle, E., and Seraphin, B. (2002). Human Dcp2: A catalytically active mRNA decapping enzyme located in specific cytoplasmic structures. EMBO J. 21, 6915–6924. van Leyen, K., Duvoisin, R. M., Engelhardt, H., and Wiedmann, M. (1998). A function for lipoxygenase in programmed organelle degradation. Nature 395, 392–395. Varnum, B. C., Ma, Q. F., Chi, T. H., Fletcher, B., and Herschman, H. R. (1991). The TIS11 primary response gene is a member of a gene family that encodes proteins with a highly conserved sequence containing an unusual Cys‐His repeat. Mol. Cell. Biol. 11, 1754–1758. Vasudevan, S., and Peltz, S. W. (2001). Regulated ARE‐mediated mRNA decay in Saccharomyces cerevisiae. Mol. Cell 7, 1191–1200. Vincenti, M. P., and Brinckerhoff, C. E. (2002). Transcriptional regulation of collagenase (MMP‐1, MMP‐13) genes in arthritis: Integration of complex signaling pathways for the recruitment of gene‐specific transcription factors. Arthritis Res. 4, 157–164. Vockerodt, M., Pinkert, D., Smola‐Hess, S., Michels, A., Ransohoff, R. M., Tesch, H., and Kube, D. (2005). The Epstein‐Barr virus oncoprotein latent membrane protein 1 induces expression of the chemokine IP‐10: Importance of mRNA half‐life regulation. Int. J. Cancer 114, 598–605. Voellmy, R. (2004). Transcriptional regulation of the metazoan stress protein response. Prog. Nucleic Acid Res. Mol. Biol. 78, 143–185. Wagner, B. J., De Maria, C. T., Sun, Y., Wilson, G. M., and Brewer, G. (1998). Structure and genomic organization of the human AUF1 gene: Alternative pre‐mRNA splicing generates four protein isoforms. Genomics 48, 195–202. Wang, W., Caldwell, M. C., Lin, S., Furneaux, H., and Gorospe, M. (2000). HuR regulates cyclin A and cyclin B1 mRNA stability during cell proliferation. EMBO J. 19, 2340–2350. Wang, Y., Liu, C., Storey, J., Tibshirani, R., Herschlag, D., and Brown, P. (2002). Precision and functional specificity in mRNA decay. Proc. Natl. Acad. Sci. USA 99, 5860–5865. Wernicke, D., Schulze‐Westhoff, C., Brauer, R., Petrow, P., Zacher, J., Gay, S., and Gromnica‐Ihle, E. (2002). Stimulation of collagenase 3 expression in synovial fibroblasts of patients with rheumatoid arthritis by contact with a three‐dimensional collagen matrix or with normal cartilage when coimplanted in NOD/SCID mice. Arthritis Rheum. 46, 64–74. Westra, J., Doornbos‐van der Meer, B., de Boer, P., van Leeuwen, M. A., van Rijswijk, M. H., and Limburg, P. C. (2004a). Strong inhibition of TNF‐alpha production and inhibition of IL‐8 and COX‐2 mRNA expression in monocyte‐derived macrophages by RWJ 67657, a p38 mitogen‐ activated protein kinase (MAPK) inhibitor. Arthritis Res. Ther. 6, R384–R392.
P O S T T R A N S C R I P T I O N A L C O N T R O L O F I N F L A M M AT I O N
37
Westra, J., Kuldo, J. M., van Rijswijk, M. H., Molema, G., and Limburg, P. C. (2005). Chemokine production and E‐selectin expression in activated endothelial cells are inhibited by p38 MAPK (mitogen activated protein kinase) inhibitor RWJ 67657. Int. Immunopharmacol. 5, 1259–1269. Westra, J., Limburg, P. C., de Boer, P., and van Rijswijk, M. H. (2004b). Effects of RWJ 67657, a p38 mitogen activated protein kinase (MAPK) inhibitor, on the production of inflammatory mediators by rheumatoid synovial fibroblasts. Ann. Rheum. Dis. 63, 1453–1459. Whittemore, L.‐A., and Maniatis, T. (1990). Postinduction turnoff of beta‐interferon gene expression. Mol. Cell. Biol. 64, 1329–1337. Wickens, M., Bernstein, D. S., Kimble, J., and Parker, R. (2002). A PUF family portrait: 30 UTR regulation as a way of life. Trends Genet. 18, 150–157. Williams, B. R. (1999). PKR; a sentinel kinase for cellular stress. Oncogene 18, 6112–6120. Williams, L., Bradley, L., Smith, A., and Foxwell, B. (2004a). Signal transducer and activator of transcription 3 is the dominant mediator of the anti‐inflammatory effects of IL‐10 in human macrophages. J. Immunol. 172, 567–576. Williams, L. M., Ricchetti, G., Sarma, U., Smallie, T., and Foxwell, B. M. (2004b). Interleukin‐10 suppression of myeloid cell activation—a continuing puzzle. Immunology 113, 281–292. Winzen, R., Gowrishankar, G., Bollig, F., Redich, N., Resch, K., and Holtmann, H. (2004). Distinct domains of AU‐rich elements exert different functions in mRNA destabilization and stabilization by p38 mitogen‐activated protein kinase or HuR. Mol. Cell. Biol. 24, 4835–4847. Winzen, R., Kracht, M., Ritter, B., Wilhelm, A., Chen, C. Y., Shyu, A. B., Muller, M., Gaestel, M., Resch, K., and Holtmann, H. (1999). The p38 MAP kinase pathway signals for cytokine‐induced mRNA stabilization via MAP kinase‐activated protein kinase 2 and an AU‐rich region‐targeted mechanism. EMBO J. 18, 4969–4980. Wipke, B. T., and Allen, P. M. (2001). Essential role of neutrophils in the initiation and progression of a murine model of rheumatoid arthritis. J. Immunol. 167, 1601–1608. Wodnar‐Filipowicz, A., and Moroni, C. (1990). Regulation of interleukin 3 mRNA expression in mast cells occurs at the posttranscriptional level and is mediated by calcium ions. Proc. Natl. Acad. Sci. USA 87, 777–781. Worthington, M. T., Pelo, J. W., Sachedina, M. A., Applegate, J. L., Arseneau, K. O., and Pizarro, T. T. (2002). RNA Binding Properties of the AU‐rich Element‐binding Recombinant Nup475/ TIS11/Tristetraprolin Protein. J. Biol. Chem. 277, 48558–48564. Xu, N., Chen, C. Y., and Shyu, A. B. (2001). Versatile role for hnRNP D isoforms in the differential regulation of cytoplasmic mRNA turnover. Mol. Cell. Biol. 21, 6960–6971. Yang, L., and Yang, Y. C. (1994). Regulation of interleukin (IL)‐11 gene expression in IL‐1 induced primate bone marrow stromal cells. J. Biol. Chem. 269, 32732–32739. Yang, Y. H., and Hamilton, J. A. (2001). Dependence of interleukin‐1‐induced arthritis on granulocyte‐macrophage colony‐stimulating factor. Arthritis Rheum. 44, 111–119. Yu, Q., Cok, S. J., Zeng, C., and Morrison, A. R. (2003). Translational repression of human matrix metalloproteinases‐13 by an alternatively spliced form of T‐cell‐restricted intracellular antigen‐ related protein (TIAR). J. Biol. Chem. 278, 1579–1584. Zhang, W., Wagner, B. J., Ehrenman, K., Schaefer, A. W., De Maria, C. T., Crater, D., De Haven, K., Long, L., and Brewer, G. (1993). Purification, characterization, and cDNA cloning of an AU‐rich element RNA‐binding protein, AUF1. Mol. Cell. Biol. 13, 7652–7665. Zhu, W., Brauchle, M. A., Di Padova, F., Gram, H., New, L., Ono, K., Downey, J. S., and Han, J. (2001). Gene suppression by tristetraprolin and release by the p38 pathway. Am. J. Lung Cell Mol. Physiol. 281, L499–L508. Zubiaga, A. M., Belasco, J. G., and Greenberg, M. E. (1995). The nonamer UUAUUUAUU is the key AU‐rich sequence motif that mediates mRNA degradation. Mol. Cell. Biol. 15, 2219–2230.
Negative Signaling in Fc Receptor Complexes Marc Dae¨ron and Renaud Lesourne Unite´ d’Allergologie Mole´culaire et Cellulaire, De´partement d’Immunologie, Institut Pasteur, Paris, France
1. 2. 3. 4. 5.
Abstract............................................................................................................. Fc Receptors ...................................................................................................... Positive Signaling by Activating FcRs ...................................................................... Negative Signaling by Activating FcRs..................................................................... Negative Signaling by Inhibitory FcRs..................................................................... Conclusion ......................................................................................................... References .........................................................................................................
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Abstract Cell activation results from the transient displacement of an active balance between positive and negative signaling. This displacement depends in part on the engagement of cell surface receptors by extracellular ligands. Among these are receptors for the Fc portion of immunoglobulins (FcRs). FcRs are widely expressed by cells of hematopoietic origin. When binding antibodies, FcRs provide these cells with immunoreceptors capable of triggering numerous biological responses in response to a specific antigen. FcR‐dependent cell activation is regulated by negative signals which are generated together with positive signals within signalosomes that form upon FcR engagement. Many molecules involved in positive signaling, including the FcRb subunit, the src kinase lyn, the cytosolic adapter Grb2, and the transmembrane adapters LAT and NTAL, are indeed also involved in negative signaling. A major player in negative regulation of FcR signaling is the inositol 5‐phosphatase SHIP1. Several layers of negative regulation operate sequentially as FcRs are engaged by extracellular ligands with an increasing valency. A background protein tyrosine phosphatase‐dependent negative regulation maintains cells in a «resting» state. SHIP1‐dependent negative regulation can be detected as soon as high‐affinity FcRs are occupied by antibodies in the absence of antigen. It increases when activating FcRs are engaged by multivalent ligands and, further, when FcR aggregation increases, accounting for the bell‐shaped dose‐ response curve observed in excess of ligand. Finally, F‐actin skeleton‐associated high‐molecular weight SHIP1, recruited to phosphorylated ITIMs, concentrates in signaling complexes when activating FcRs are coengaged with inhibitory FcRs by immune complexes. Based on these data, activating and inhibitory FcRs could be used for new therapeutic approaches to immune disorders.
39 advances in immunology, vol. 89 # 2006 Elsevier Inc. All rights reserved.
0065-2776/06 $35.00 DOI: 10.1016/S0065-2776(05)89002-9
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When sensitized with IgE antibodies, mouse mast cells and human basophils release granular mediators and secrete pro‐inflammatory cytokines and chemokines in response to stimulation by specific antigen. These biological responses depend on high‐affinity receptors for the Fc portion of IgE antibodies (FceRI) that are expressed by the two cell types (Ishizaka et al., 1970; Metzger et al., 1986; Prouvost‐Danon and Binaghi, 1970). For a given concentration of IgE used for sensitization, mediator release increases with the concentration of antigen used for challenge up to a maximum. Release then decreases as the concentration of antigen further increases (Dembo et al., 1978). Peritoneal mouse mast cells also degranulate when challenged by preformed IgG immune complexes (Prouvost‐Danon et al., 1966). IgG‐ induced responses depend on low‐affinity receptors for the Fc portion of IgG (FcgRIIIA) (Dae¨ron et al., 1992; Hazenbos et al., 1996) that bind immune complexes with a high avidity. Bone Marrow‐derived Mast Cells (BMMC) do not respond or respond very poorly to IgG immune complexes, although they express FcgRIIIA (Benhamou et al., 1990). Likewise, human blood basophils release no or little histamine in response to immune complexes (Van Toorenenbergen and Aalberse, 1981), although they express another type of low‐affinity IgG receptor (FcgRIIA) which can activate mast cells (Dae¨ron et al., 1995a). These observations have long been interpreted as resulting from an inefficient engagement of activating receptors by high concentrations of antigen or by IgG immune complexes. Actually, these experiments show that negative regulation occurs in Fc Receptor (FcR) complexes. One is an example of autonomous negative regulation of activating FcRs; others are examples of negative regulation by inhibitory FcRs. These examples were selected from studies of FcRs in mast cells and basophils. FcR‐ dependent negative signaling is not peculiar to these cells. Mast cells are, however, convenient models to study FcR signaling, and they will often be used as examples throughout this review. 1. Fc Receptors 1.1. FcRs, the Third Type of Immunoreceptors Receptors for the Fc portion of immunoglobulins are immunoreceptors of the third type. They ‘‘recognize’’ neither native antigens as B Cell Receptors (BCRs) do, nor the association of antigen‐derived peptides with Major Histocompatibility Complex molecules, as T Cell Receptors (TCRs) do, but antigen‐ antibody complexes. Even though they do not themselves bind to antigen, they enable cells to respond specifically to antigen. Antibodies indeed function as extracellular adapter molecules when their Fab and Fc portions bind
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simultaneously to specific epitopes on antigen and to FcRs on cell membrane, respectively. BCRs, TCRs, and FcRs are receptors for the three forms under which any given antigen can interact with and deliver signals to cells of the immune system. BCRs and TCRs are assigned specificity at an early stage during B and T cell differentiation through somatic DNA rearrangements. Combinations of variable gene segments determine the clonally restricted specificity of lymphocytes. Specificity persists over cell divisions, as it is transmitted to the progeny within a given clone. These unique features of lymphocytes have several consequences. Altogether, the lymphocytes of an individual can recognize virtually all antigens this individual can be exposed to. Their number being finite, only a small number of naı¨ve lymphocytes can respond to a given antigen. Lymphocytes therefore need first to undergo clonal expansion for significant numbers of cells expressing antigen receptors with any given specificity to be generated and to mount an adaptive immune response. In addition, B and T lymphocytes are not ready‐to‐work effector cells. They need to differentiate into antibody‐producing plasma cells and into helper, regulatory, or cytoxic T cells, respectively, before they can act on antigen. Unlike lymphocytes, large numbers of differentiated cells of hematopoietic origin are capable of exerting a variety of biological activities without needing to proliferate and/or to differentiate. These mostly myeloid cells are the primary effectors of innate immunity. They are equipped with pattern‐ recognition receptors which enable them to interact with structures borne or secreted by microorganisms, but they lack antigen receptors. Most myeloid cells, however, express FcRs. FcRs provide these cells with immunoreceptors and a bona fide immunological specificity. Antigen specificity is provided by antibodies that happen to be present in the environment and bind to FcRs. As these antibodies, polyclonal in nature, have different specificities, one FcR‐ expressing cell can respond specifically to a wide repertoire of different antigens. This repertoire can, theoretically, be as wide as that of the whole population of B cells. In the presence of specific antibodies, FcRs enroll in adaptive immunity, the many cells involved in innate immunity. Besides endowing them with specificity, FcRs can indeed generate intracellular signals which modulate their biological activities. Some FcRs activate, whereas others inhibit cellular responses. 1.2. Activating FcRs Most FcRs are activating receptors (Dae¨ron, 1997; Ravetch and Bolland, 2001; Ravetch and Kinet, 1991). Activating FcRs comprise receptors for IgA (FcaRI), IgE (FceRI), and IgG (FcgRI, FcgRIIA/C, FcgRIIIA, and FcgRIV).
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They include high‐affinity receptors (FcaRI, FceRI, FcgR, and FcgIV) which can bind monomeric immunoglobulins, and low‐affinity receptors (FcgRIIA/C and FcgRIIIA) which cannot, but which can bind multivalent antigen‐antibody complexes and immunoglobulin aggregates with a high avidity (Hulett and Hogarth, 1994). As a consequence, a proportion of high‐affinity FcRs are occupied in vivo, whereas low‐affinity FcRs remain free in spite of the high concentrations of immunoglobulins present in the extracellular milieu. With one exception in humans (FcgRIIA/C), activating FcRs are multi‐chain receptors composed by one immunoglobulin‐binding FcRa subunit and one (FcRg) or two (FcRg and FcRb) common transduction subunits. As for other immunoreceptors, the cell‐activating properties of FcRs depend on the presence of Immunoreceptor Tyrosine‐based Activation Motif(s) (ITAMs) in the intracytoplasmic domains of their transduction subunits (Reth, 1989). Activating FcRs are expressed by myeloid cells and by lymphoid cells with no classical antigen receptor (i.e., NK cells [Perussia et al., 1989] and intraepithelial g/d T cells of the intestine [Deusch et al., 1991; Sandor et al., 1992; Woodward and Jenkinson, 2001]). They are not expressed by mature T and B lymphocytes. Lymphocytes therefore do not express more than one type of antigen receptor, and activating FcRs do not interfere with lymphocyte activation triggered by clonally expressed antigen receptors. Interestingly, however, activating FcRs are transiently expressed by pre‐B and pre‐T cells, before they express a functional BCR or TCR, respectively (Sandor and Lynch, 1992). Low levels of FcgRIIIA were recently reported to be expressed on a subset of self‐specific murine CD8 T cells and to efficiently trigger antibody‐dependent cell‐ mediated cytotoxicity (Dhanji et al., 2005). Differing from other immunoreceptors, which induce both cell activation and proliferation, FcRs induce cell activation only. Activating FcRs do not induce unique biological responses, but biological activities that can be induced by other receptors in the same cell. 1.3. Inhibitory FcRs Inhibitory FcRs consist of one family of low‐affinity receptors for IgG, referred to as FcgRIIB (Dae¨ron, 1997; Ravetch and Bolland, 2001). FcgRIIB are single‐chain receptors, encoded by one gene named fcgr2b, which generates two (FcgRIIB1 and FcgRIIB2 in humans) or three (FcgRIIB1, FcgRIIB1’, and FcgRIIB2 in mice) isoforms of membrane receptors, by alternative splicing of sequences encoded by the first intracytoplasmic exon (Hibbs et al., 1986; Latour et al., 1996; Lewis et al., 1986; Ravetch et al., 1986). One distinctive feature of the fcgr2b gene is indeed that one exon encodes the transmembrane domain and three others the intracytoplasmic domain of FcgRIIB (in other FcR genes, a single exon encodes both the transmembrane
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and the intracytoplasmic domains) (Brooks et al., 1989; Hibbs et al., 1988). The inhibitory properties of FcgRIIB depend on an Immunoreceptor Tyrosine‐ based Inhibition Motif (ITIM) (Dae¨ron et al., 1995a), encoded by the third intracytoplasmic exon of the fcgr2b gene, and located in the intracytoplasmic domain of all murine and human FcgRIIB isoforms. FcgRIIB are expressed by myeloid and, with two exceptions, by lymphoid cells. The two exceptions are NK cells and resting T cells which express a variety of other inhibitory receptors involved in cell–cell interactions (Long, 1999). FcgRIIB can negatively regulate cell activation triggered by all ITAM‐containing receptors (Dae¨ron et al., 1995a) as well as cell proliferation triggered by growth factor receptors with an intrinsic kinase activity (Malbec et al., 1999). In order to exert their inhibitory properties, FcgRIIB must be co‐engaged with activating receptors by a common extracellular ligand at the surface of the same cell (Dae¨ron et al., 1995b). The specificity of negative regulation is therefore under the control of two antigen‐specific recognition processes: that of IgG antibodies which engage FcgRIIB and that of immunoreceptors with which FcgRIIB are coaggregated. 1.4. Activating and Inhibitory FcRs in Physiology and Pathology The aggregation of identical FcRs only (homo‐aggregation) is a rare situation in physiology. Even when cells express one type of FcR only (e.g., FcgRIIB in murine B cells, or FcgRIIIA in murine NK cells), immune complexes can co‐ engage FcRs with other immunoreceptors (BCRs in B cells, or NK Receptors on NK cells). Several FcRs are coaggregated when IgG immune complexes interact with cells that co‐express several FcgRs (FcgRI, FcgRIIB, and FcgRIIIA on macrophages or dendritic cells, for instance, or FcgRIIA and FcgRIIB on human B cells) or with cells that co‐express FcRs for several classes of antibodies (mouse mast cells, for instance, where IgG immune complexes can coaggregate FcgRs and FceRI‐bound IgE). Hetero‐aggregation, that is, the coaggregation of different types of FcRs or the coaggregation of FcRs with other immunoreceptors, is actually a rule, rather than an exception, under physiological conditions. Because there are FcRs for all antibody classes, because immune complexes contain more than one class of antibody, and because most cells express more than one type of FcRs, various combinations of FcRs can be engaged at the cell surface to form hetero‐aggregates with a non‐predetermined composition. FcRs can thus generate a variety of signaling complexes, depending on the relative proportion of receptors of the various types that are co‐engaged by immune complexes. The in vivo biological significance of FcgRIIB‐dependent negative regulation of activating FcR‐dependent physio‐pathological processes has been
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established using mice rendered deficient for FcgRIIB by homologous recombination (Ravetch and Bolland, 2001). Compared to wt mice, FcgRIIB‐ deficient mice were found to produce more antibodies (Takai et al., 1996), to exhibit exaggerated anaphylactic reactions and Arthus reactions of a higher intensity (Takai et al., 1996; Ujike et al., 1999), to be more susceptible to collagen‐induced arthritis (Kleinau et al., 2000; Yuasa et al., 1999), and, in the C57BL/6 background, to spontaneously develop Lupus‐like syndromes (Bolland and Ravetch, 2000). FcgRIIB were also shown to critically determine the protective effects of anti‐tumor therapeutic antibodies in a murine model of melanoma (Clynes et al., 1998), and of IVIG in a model of idiopathic thrombopenic purpura (Samuelsson et al., 2001). 2. Positive Signaling by Activating FcRs 2.1. Positive Signaling in Resting Cells Positive signals are generated even before immunoreceptors are engaged by extracellular ligands. This can be readily unraveled by treating cells with the tyrosine phosphatase inhibitor pervanadate. Pervanadate‐treated cells display an array of tyrosyl‐phosphorylated molecules, including immunoreceptors, indicating that protein tyrosine kinases are active in resting cells but that their substrates are constantly dephosphorylated by tyrosine phosphatases. It follows that cell activation results from a transient displacement of a physiological balance between positive and negative signals that controls cellular responses. Interestingly, the expression of multi‐subunit immunoreceptors such as BCRs was found to be required (and sufficient?) for intracellular signaling molecules to be phosphorylated in pervanadate‐treated cells (Wossning and Reth, 2004), suggesting that signaling complexes can be organized by immunoreceptors even in the absence of known extracellular ligands, but that positive signals emanating from such complexes are either insufficient to lead to cell activation or are dampened by an autonomous type of negative regulation of immunoreceptor signaling. The displacement of the constitutive balance between positive and negative signals that leads to biological responses primarily depends on extracellular ligands which engage surface receptors. 2.2. FcR Engagement and the Constitution of Signalosomes Activating FcRs trigger signals when aggregated by antibody and multivalent antigen. Dimerization was, long ago, shown to be the minimal degree of FceRI aggregation capable of generating activation signals sufficient for triggering
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mediator release by mast cells (Segal et al., 1977; Siraganian et al., 1975). Intracellular signals are generated within juxta‐membrane signaling complexes that assemble under FcR aggregates and form signalosomes. Signalosomes are transient structures which contain the signaling complexes generated at a given time and at a given location, in which signaling molecules can meet and interact with each other. These comprise receptors that are co‐engaged by common extracellular ligands, molecules that are recruited underneath, and molecules that are contained in subcellular compartments into which receptor aggregates translocate. Signalosomes are dynamic structures which evolve with time and with their intracellular location. Molecules are sequentially recruited first, as complexes build up and get organized around transmembrane adapters. Recruitment depends in part on inducible molecular changes, such as phosphorylation, on the generation of specific molecules, and on location or relocation of molecules into subcellular compartments. It is stabilized by cooperative interactions between molecules with several binding sites and by cytosolic adapters. The composition of signalosomes then rapidly changes as recruited enzymes meet substrates and act on them. Finally signalosomes are dismantled as signaling molecules are ubiquitinated and degraded by the proteasome. 2.3. Generation of Positive Signals by Activating FcRs An initial event in signal transduction by activating FcRs is the activation of src‐family protein tyrosine kinases. In resting cells, these kinases are maintained in an inactive state as a result of the phosphorylation of a regulatory C‐terminal tyrosine by the C‐terminal tyrosine Src kinase Csk (Okada et al., 1991). This confers the molecule a closed conformation that prevents substrates to have access to the catalytic site of the kinase (Cole et al., 2003). The regulatory tyrosine is dephosphorylated by the transmembrane protein tyrosine phosphatase CD45 (Burns et al., 1994; Thomas and Brown, 1999). Supporting a role of CD45 in FceRI signaling, CD45‐deficient mast cells displayed reduced IgE‐induced mediator release and CD45‐deficient mice were refractory to IgE‐induced systemic anaphylaxis (Berger et al., 1994). How CD45 becomes involved upon FcR receptor engagement is unclear. Whatever the mechanism, src kinases are activated and they can phosphorylate tyrosine residues in the ITAMs of FcR transduction subunits. In most cases, the responsible kinase is Lyn. Whether src kinases are constitutively associated with FcR subunits and transphosphorylate ITAMs upon FcR aggregation (Pribluda et al., 1994), or whether ITAMs are phosphorylated in lipid rafts, where src kinases are concentrated (Brown and London, 2000), upon translocation of FcR aggregates into these microdomains (Field et al., 1997) still
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needs to be clarified. In any case, phosphorylated ITAMs provide docking sites that mediate the recruitment of SH2 domain‐containing molecules, among which is the two‐SH2 domain‐containing protein tyrosine kinase Syk (Benhamou et al., 1993). Once recruited, Syk is tyrosyl‐phosphorylated by src kinases and it further auto‐phosphorylates (Kimura et al., 1996). This activates its catalytic activity. Syk then phosphorylates tyrosines in multiple molecules (Costello et al., 1996). Among these are the cytosolic adapter molecule SH2 domain‐containing Leukocyte Protein of 76 kDa (SLP‐76) (Hendricks‐Taylor et al., 1997; Kettner et al., 2003) and the raft‐associated transmembrane adapter Linker for Activation of T cells (LAT) (Wonerow and Watson, 2001). A parallel series of src kinase‐initiated events was described, following FceRI aggregation in mouse mast cells. Fyn was indeed found to tyrosyl‐ phosphorylate the cytosolic adapter Gab2, thus enabling its association with the p85 subunit of Phosphatidylinositol 3‐kinase (PI3K) via its SH2 domain, and the subsequent activation of the p110 catalytic subunit of this enzyme (Parravincini et al., 2002). PI3K generates phosphatidyl (3,4,5)tris‐phosphate [PI(3,4,5)P3] by adding a phosphate group at position 3 in phosphatidyl (4,5) bis‐phosphate. Several molecules that contain a Pleckstrin Homology (PH) domain are recruited to the membrane by PI(3,4,5)P3. 2.4. Organization of FcR Signaling Complexes by Adapter Proteins The many molecular interactions that occur in signalosomes generate signals that are organized by tyrosine‐rich adapter molecules which, when phosphorylated, function as scaffold proteins. These include cytosolic and transmembrane adapters. SLP‐76 is one such cytosolic adapter. Besides its N‐terminal SH2 domain, SLP‐76 contains a central proline‐rich region and multiple C‐terminal tyrosines (Jackman et al., 1995). Once phosphorylated, it binds to a variety of molecules including the exchange factor Vav (Tuosto et al., 1996) and other adapters such as Gads, Nck, and SLAP‐130 (Boerth et al., 2000). Based on studies of cells from SLP‐76‐deficient mice, SLP‐76 was shown to contribute to the activation of phospholipase C‐g (PLC‐g) and to the activation of Mitogen‐Activated protein (MAP) kinases (Pivniouk et al., 1999). Transmembrane adapters consist of a short extracellular domain, unlikely to bind extracellular ligands; a single transmembrane domain; and a long intracellular domain devoid of molecular interaction domains, but rich in tyrosine residues. When phosphorylated upon FcR engagement, these tyrosines function as inducible docking sites for cytosolic molecules having SH2 domains.
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Transmembrane adapters are of two types, depending on the presence, in their intracytoplasmic domain, of a juxtamembrane CxxC motif which targets them to lipid rafts. The Protein Associated with GEMs/Csk‐binding protein (PAG/Cbp), LAT, Non‐T cell Activation Linker/Linker of Activation for B cells (NTAL/LAB), and Lck‐Interacting Membrane protein (LIME) have such a palmitoylation site. The T cell Receptor‐Interacting Molecule (TRIM), SHP‐2‐Interacting Transmembrane adapter (SIT), and Linker of Activation for X cells (LAX) do not, and they are excluded from lipid rafts (Kliche et al., 2004; Togni et al., 2004). LAT was shown to support positive signaling triggered not only by TCR, but also by FceRI, and the mechanisms by which it concurs to mast cell activation and to T cell activation are thought to be similar. FceRI aggregation in BMMC from LAT/ mice triggered a reduced phosphorylation of SLP‐76 and of PLC‐g, resulting in a decreased Ca2þ mobilization and MAP Kinase activation and, ultimately, in a decreased release of preformed mediators and secretion of cytokines (Saitoh et al., 2000). FcRb/FcRg ITAMs and Syk were phosphorylated as in wt cells. These observations suggested that LAT primarily serves as a coupling molecule between immunoreceptors and intracellular signaling pathways leading to cellular responses (Sommers et al., 2004). LAT contains many tyrosines (9 in mice, 10 in humans) in its intracytoplasmic domain (Weber et al., 1998; Zhang et al., 1998a). It is tyrosyl‐phosphorylated by Syk following FceRI engagement, and serves as a scaffold molecule by providing multiple docking sites for additional SH2 domain‐containing cytosolic enzymes and adapters to be recruited. These include PLC‐g, protein tyrosine kinases of the Tec family, the p85 subunit of PI3K, exchange factors of the Vav family, and the adapters Gads, Grap, and Grb2 (Weber et al., 1998; Zhang et al., 1998a, 2000). Works based on mutational analysis of LAT identified critical tyrosine residues involved in the recruitment of these molecules in T cells (Zhang et al., 2000; Zhu et al., 2003). These were the four distal tyrosines (Y132, Y171, Y191, and Y226 in humans, and their homologues in mice Y136, Y175, Y195, and Y235). Specifically, Y132/136 was demonstrated as being the major binding site for PLC‐g, and the three distal tyrosines (Y171/175, Y191/195, and Y226/235) binding sites for Gads, Grap, and Grb2 (Zhang et al., 2000). The two sets of binding sites also contribute to the recruitment of other molecules such as SLP‐76 via Gads and they cooperate to stabilize the binding of molecules recruited by each other. A mutational analysis of the four distal tyrosines of LAT, in LAT/ BMMC reconstituted in vitro with wt or mutant LAT (Saitoh et al., 2003), confirmed that, once phosphorylated upon FceRI engagement, these residues play critical roles for FceRI signaling by recruiting the same set of signaling molecules in mast cells as in T cells.
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2.5. Intracellular Propagation of FcR Signals Molecules recruited and activated in signalosomes concur to the activation of metabolic pathways which propagate signals intracellularly up to the nucleus and back to the plasma membrane. Several pathways are used by activating FcRs. They are, with variations, the same as pathways used by other immunoreceptors. Some lead to the calcium response, while others lead to the activation of transcription factors. These pathways are not linear, but tightly interconnected. We will briefly underline only critical steps that either contribute to or are targets of negative regulation. The calcium response results from the recruitment and activation of PLC‐g1 and/or 2, depending on the cell type (Wang et al., 2000; Wen et al., 2002). The recruitment of PLC‐g involves the interaction of one of its SH2 domain with phosphorylated Y136 on LAT, and the interaction with the adapter Gads which binds to phosphorylated LAT terminal tyrosines. PLC‐g is also recruited to the membrane through the interaction of its PH domain with newly formed PI (3,4,5)P3. PLC‐g is subsequently activated as a result of the phosphorylation of specific tyrosine residues by Syk and by the Tec kinase Btk (Humphries et al., 2004), respectively. PLC‐g generates inositol (1,4,5)tris‐phosphate [IP(1,4,5) P3 or IP3] and Diacyl Glycerol (DAG). IP3 triggers an efflux of intracellular Ca2þ from the endoplasmic reticulum and, secondarily, an influx of extracellular Ca2þ. The result is a markedly increased intracellular Ca2þ concentration. Intracellular Ca2þ is critical for exocytosis in mast cells. It also activates calcineurin. This phosphatase dephosphorylates the Nuclear Factor of Activation for T cells (NF‐AT), which enables its translocation from the cytosol to the nucleus (Stankunas et al., 1999). DAG upregulates the catalytic activity of several among the many serine‐ threonine kinases of the Protein Kinase C (PKC) family. Following further activation as a result of the phosphorylation of several serine/threonine and tyrosine residues, PKCs phosphorylate a variety of substrates involved in the activation of MAP kinases (Kawakami et al., 1998) and of transcription factors (Turner and Cantrell, 1997), and in mast cell degranulation (Buccione et al., 1994). PKCs can also threonyl‐phosphorylate FcRg (Pribluda et al., 1997), which contributes to the activation of Syk (Swann et al., 1999). Another substrate of DAG‐activated PKCs is the serine Protein Kinase D (PKD) (Valverde et al., 1994). PKD is abundant in mast cells and, when activated upon FceRI engagement, it contributes to the regulation of transcriptional activity of NF‐kB (Johannes et al., 1998). NFkB activation was observed upon FceRI aggregation in mast cells (Hundley, Blood, 2004) and dendritic cells (Kraft et al., 2002), preceded by the seryl‐phosphorylation and degradation of IkB, and it was reported to be
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involved in the generation of several cytokines (Marquardt and Walker, 2000). NF‐kB was also activated in human monocytes (Drechsler et al., 2002) and mesangial cells (Duque et al., 1997), as a consequence of FcgRs and FcaRI aggregation, respectively. Three sets of MAP kinases are activated upon FcR engagement: Erk1/2, JNK, and p38 (Dong et al., 2002). Erk1/2 are the terminal effector kinases of the Ras pathway, JNK and p38, effector kinases of the rac pathway. Ras and Rac are small G proteins which are in an inactive form when associated with GDP, and in an active form when associated with GTP. The replacement of GDP by GTP on Ras and Rac depends on the exchange factors Sos and Vav, respectively (Cantrell, 1998; Downward, 1996). It initiates a cascade of serine/ threonine phosphorylations, the ultimate substrates of which are MAP kinases. Phosphorylated MAP kinases are translocated into the nucleus where they can phosphorylate transcription factors. These associate with NF‐AT to form a complex which can bind to specific sites in the promoter of cytokine genes and initiate their transcription. 2.6. Ligand Valency Influences FceRI‐Dependent Mast Cell Secretory Responses Several observations recently challenged the widely accepted concept that the binding of monomeric IgE to FceRI generates no detectable signal and no detectable response. An exposure of mast cells to IgE in the absence of antigen was indeed reported (1) to up‐regulate the expression of membrane FceRI (Hsu and MacGlashan, 1996; MacGlashan et al., 1997), (2) to increase the survival of mast cells in the absence of growth factors (Asai et al., 2001; Kawakami and Galli, 2002), and (3) to induce cytokine secretion (Kalesnikoff et al., 2001; Kohno et al., 2005; Pandey et al., 2004). The effect of monomeric IgE on mast cell survival and cytokine secretion was found to depend on the FcRg ITAM (Kohno et al., 2005), but not the upregulation of FceRI expression. The effect on receptor expression was shown to result from slowing down the removal of FceRI from the membrane and its subsequent degradation without affecting the rate of FceRI synthesis (Borkowski et al., 2001). As a consequence, FceRI accumulate on the mast cell membrane without requiring detectable intracellular signals. By contrast, the effects on mast cell survival and cytokine secretion were found to be restricted to anti‐DNP/TNP IgE, to vary markedly from one mAb IgE to another (Kitaura et al., 2005), and most importantly, to be inhibited by a monovalent hapten such as DNP‐lysine (Tanaka et al., 2005). These effects, therefore, must be understood as resulting from FceRI aggregation, whatever the mechanism, that is, to obey the general rule. Interestingly, however, quantitative variations of receptor aggregation were found to result in qualitative
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variation in cellular responses. A low level of FceRI aggregation, induced by incubating mast cells with IgE in the absence of (known) antigen, triggered intracellular signals leading to the secretion of IL‐3 or MCP‐1, but not to degranulation, whereas a high level of receptor aggregation, induced by incubating with multivalent antigen mast cells sensitized with the same IgE, triggered both degranulation and cytokine secretion (Gonzalez‐Espinosa et al., 2003; Kohno et al., 2005; Yamasaki et al., 2004). Molecular mechanisms that enable quantitative differences in receptor aggregation to produce qualitatively different responses remain to be elucidated. 3. Negative Signaling by Activating FcRs FcR‐dependent cell activation is negatively regulated by several inhibitory mechanisms generated by activating FcRs themselves. Some are triggered together with activation mechanisms by ITAM‐containing FcRs and contribute to their own, autonomous control. Others can be triggered by activating FcRs in the absence of detectable positive signals, although they depend on ITAMs, and can negatively regulate signaling triggered by other activating receptors expressed by the same cell. 3.1. Autonomous Negative Regulation of Activating FcRs When engaged by antibody and antigen, activating FcRs not only generate positive signals, but also negative signals. This autonomous negative regulation controls the intensity and duration of positive signals. Negative signaling depends on several mechanisms involving a variety of molecules. Interestingly, many among the proteins which contribute to negative regulation are the same as those which contribute to positive regulation. These include receptor subunits, protein tyrosine kinases, adapter molecules, and phosphatases. 3.1.1. FcRb The mast cell‐specific FcRb subunit was first understood to function as an amplifier of signals generated by FcRg upon FceRI aggregation (Adamczewski et al., 1995; Dombrowicz et al., 1998; Lin et al., 1996). Differing from mouse or rat FceRIa, which need to associate with both FcRg and FcRb in order to be expressed at the mast cell membrane, human FceRIa need to associate with FcRg only. As a consequence, FceRI can be expressed in human mast cells with or without FcRb. They can also be expressed by human monocytes, macrophages, and eosinophils, which do not express FcRb (Maurer et al., 1994), but not in corresponding murine cells. Signals triggered by FcRb‐
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associated FceRI were found to be of a higher intensity than signals triggered by FceRI associated with FcRg only (Dombrowicz et al., 1998). FcRb also enhances IgE‐induced allergic responses by up‐regulating the surface expression of FceRI (Donnadieu et al., 2003). Recently, however, FcRb was found to generate ITAM‐dependent negative signals. The FcRb ITAM has a unique feature. Compared to other ITAMs, the FcRb ITAM contains an additional tyrosine residue, in the 6‐residue sequence that separates the two canonical YxxL motifs:
Human Mouse
FcRg
FcRb
YTGLSTRNQETYETL YTGLNTRSQETYETL
YEELNIYSATYSEL YEELNVYSPIYSEL
Based on a mutational analysis, this additional tyrosine was shown to be involved in the negative regulation of IgE‐induced signals. The activation of the MAP kinases Erk and p38, the activation of NF‐kB, and, ultimately, the secretion of IL‐6, IL‐13, and TNF‐a were indeed enhanced when this residue was mutated into phenylalanine (Furumoto et al., 2004). No marked effect was observed on the activation of PLC‐g, the Ca2þ response, the generation of leukotrienes, and the release of b‐hexosaminidase, suggesting that this tyrosine is not critical in signal amplification. These altered responses were reminiscent of the phenotype of mast cells derived from Lyn‐deficient mice (Odom et al., 2004). Indeed, pull‐down experiments using beads coated with phosphopeptides corresponding to a wt or an altered FcRb ITAM showed that the additional tyrosine could mediate the binding of Lyn, and also of the SH2 domain‐containing inositol phosphatase SHIP1. Supporting an in vivo significance of this in vitro analysis, slightly less FcRb coprecipitated with Lyn, and SHIP1 was less phosphorylated following FceRI engagement, when the additional tyrosine was mutated in FcRb. FcRb may therefore contribute to the involvement of SHIP1 and to the recruitment of Lyn in FceRI signaling complexes. Increasing evidence supports the idea that this src family protein tyrosine kinase contributes to negative regulation of immunoreceptor signaling and, possibly, more than to positive regulation as originally thought. 3.1.2. Lyn The src‐family protein tyrosine kinase Lyn was shown to play a critical role in the initiation of IgE‐induced signal transduction in mast cells. Lyn was indeed demonstrated to be responsible for the phosphorylation of both FcRb and FcRg ITAMs upon FceRI aggregation and for the initial phosphorylation of
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Syk, when the latter has been recruited to the phosphorylated FcRg ITAM (Jouvin et al., 1994; Kihara and Siraganian, 1994; Scharenberg et al., 1995). Lyn was therefore considered first as a major player in positive signaling. When Lyn‐deficient mice became available, it became apparent that Lyn is involved in a variety of negative regulatory processes. B cells from Lyn/ mice were found to be hyper‐responsive to BCR engagement (Chan et al., 1997; Hibbs et al., 2002), and to IL‐4 stimulation (Janas et al., 1999). Lyn/ mast cells were also more responsive to proliferative signals delivered by IL‐3 or Stem Cell Factor (Hernandez‐Hansen et al., 2004). Importantly, Lyn/ mast cells were more responsive to FceRI‐dependent activation signals (Kawakami et al., 2000; Nishizumi and Yamamoto, 1997). As expected, IgE‐induced phosphorylation of FceRI ITAMs was reduced in Lyn/ BMMC (Kawakami et al., 2000; Kovarova et al., 2001). The phosphorylation of Csk‐binding protein (Cbp) was abrogated and, as a consequence, the coprecipitation of Csk with this scaffold adapter protein observed in wt mast cells was lost in Lyn/ mast cells. Noticeably, the catalytic activity of Fyn was increased in these cells, and hyperactive Fyn was phosphorylated on tyrosine 417, in the activation loop of the kinase. The hyper‐responsiveness of Lyn/ mast cells to IgE could be ascribed to this kinase as this phenotype was abrogated in BMMC derived from doubly deficient Lyn//Fyn/ mice (Odom et al., 2004). Altogether these data provided the following explanation to the negative role of Lyn in mast cell activation. In wt cells, Lyn phosphorylates Cbp which recruits Csk. Csk phosphorylates the regulatory tyrosines 508 and 528 of Fyn and thereby inhibits its catalytic activity (Odom et al., 2004). Interestingly, the phenotype of Lyn/ mice was reminiscent of an ‘‘allergic’’ phenotype which could not be accounted for by the hyper‐reactivity of mast cells only. As these mice grew older, they displayed an increased serum IgE concentration, an upregulation of FceRI expression on mast cells, increased numbers of peritoneal mast cells and eosinophils, and elevated levels of plasma histamine (Odom et al., 2004). Most of these allergy‐associated traits could be ascribed to a screwed isotypic switch toward IgE during B cell differentiation due to the hyper‐responsiveness of Lyn/ B cells to IL‐4, and to the consequences of an increased IgE serum concentration. Finally, besides its first recognized role in positive signaling by immunoreceptors, a critical role of Lyn kinase in negative signaling that dampens cell activation by these receptors must be considered. Whether Lyn primarily contributes to positive or to negative signaling may depend on the cell type and on engaged receptors. 3.1.3. LAT LAT has been first understood to organize signalosomes generated by activating receptors and to couple them with downstream signaling pathways leading
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to cellular responses (Sommers et al., 2004). LAT is critical for TCR signals involved in early T cell differentiation and, indeed, LAT‐deficient mice display an arrest in thymocyte development with a block in both TCRab and gd T cell differentiation (Zhang et al., 1999). Unexpectedly, knock‐in mice, expressing LAT with a single point mutation of the PLC‐g‐binding site (Y136F), displayed an aberrant T cell development characterized by a partial block in early T cell differentiation and polyclonal lymphoproliferative disorder, resulting in abnormally high numbers of CD4þ TCRab T cells that secreted abnormally high levels of TH2 cytokines in the periphery. As a consequence of this exaggerated TH2 polarization, serum IgG1 concentrations were 5000‐fold higher than in wild‐type mice, serum IgE concentrations were in the range of several mg/ml, instead of a few mg/ml, and peripheral tissues were massively infiltrated with eosinophils. The differentiation of TCRgd T cells was unaffected (Aguado et al., 2002; Sommers et al., 2002). Likewise, knock‐in mice bearing point mutations of the adapter‐binding three distal tyrosines of LAT (Y175F, Y195F, and Y235F) displayed a complete block in the differentiation of TCRab T cells and an abnormal differentiation of TCRgd T cells, also resulting in an exaggerated TH2 polarization and massive proliferation. As a result, IL‐4 secretion was increased, and the serum concentrations of IgG1 and IgE were 500‐ and 1000‐fold higher than in normal mice, respectively (Nun˜ez‐Cruz et al., 2003). Although they affect two distinct T cell lineages, respectively, the two types of LAT tyrosine mutations therefore seemed to inhibit a negative regulation that normally controls terminal T cell differentiation. This suggested that, besides positive signals, LAT might support negative signals that normally regulate terminal T cell differentiation and proliferation, and that this regulation, which differentially affects TCRab and TCRgd signaling, depends on distinct tyrosine residues. Our analysis of IgE‐induced biological responses of cultured mast cells derived from the same knock‐in mice led to the same conclusion for FceRI signaling. A systematic comparison of biologic responses observed in pairs of mutants enabled us to dissect the respective roles played by LAT tyrosines in mast cells (Malbec et al., 2004). As expected, Y136 and the three distal tyrosines differentially contributed to exocytosis and the secretion of cytokines, on the one hand, and to the generation or the activation of major cytosolic effectors such as intracellular Ca2þ and the terminal MAP kinases of the ras pathway, Erk1/2, on the other hand. Interestingly, mutations unraveled the existence of negative signals, generated by distinct LAT tyrosines. Thus Y136 had a negative effect on mediator release when Y175, 195, and 235 were mutated and, conversely, Y175, 195, and 235 had a negative effect when Y136 was mutated. Positive and negative signals generated by different segments of the LAT molecule are apparently additive. Thus, sequences containing the five proximal tyrosines
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could abrogate the negative effects of Y136 in the absence of the three distal tyrosines or the negative effects of the three distal tyrosines in the absence of Y136, observed on b‐hexosaminidase release in BMMC. Importantly, LAT can integrate positive and negative signals even when in a wt configuration. Thus, the four distal tyrosines together had a positive effect on b‐hexosaminidase release in BMMC, but of a lower magnitude than the intense positive effects of either Y136 alone or of the three distal tyrosines alone. These observations would be best explained if LAT could promote the assembly of a signaling complex composed of a mixture of intracellular molecules with antagonistic properties. 3.1.4. NTAL Another transmembrane adapter was recently cloned as a result of a search for the B cell homologue of LAT and was named Linker for activation of B cells (LAB) (Janssen et al., 2003). Because it is expressed not only by B cells, but also by monocytes, NK cells, mast cells, and platelets, this molecule was also named Non‐T cell Activation Linker (NTAL) (Brdicka et al., 2002). NTAL is encoded in humans by the WBSCR5 gene, on chromosome 7 (Brdicka et al., 2002; Martindale et al., 2000). It consists of a single polypeptide resembling LAT, with a short extracellular domain, a transmembrane domain with a potential palmitoylation CxxC motif, and a long intracytoplasmic domain containing nine tyrosine residues that are phosphorylated upon immunoreceptor engagement and provide multiple binding sites for SH2 domain‐containing molecules. Grb2, Sos, Gab1, and c‐Cbl indeed coprecipated with phosphorylated NTAL in monocytes and B cells (Brdicka et al., 2002). Differing from LAT, NTAL contains no PLC‐g binding site. When expressed in LAT‐deficient T cells, NTAL could partially restore TCR signaling (Koonpaew et al., 2004), and LAT/ mice expressing an NTAL transgene under the control of the CD2 promoter had a phenotype resembling that of LAT Y136F knock‐in mice (Janssen et al., 2004). Based on these observations, NTAL was proposed to play, in B cells, a similar role as the one LAT plays in T cells (Brdicka et al., 2002). Because mast cells co‐express LAT and NTAL and because FceRI signaling was reduced, but not abrogated in BMMC derived from LAT‐ deficient mice, the two adapters were thought to play complementary roles in mast cell activation. Surprisingly, the genetic deletion of NTAL resulted in increased, rather than diminished, IgE‐induced release of granular mediators and secretion of cytokines by mast cells (Volna et al., 2004; Zhu et al., 2004). The tyrosyl‐phosphorylation of Syk, LAT, and PLC‐g1 and 2 were increased, as well as the phosphorylation of the Erk, p38, and JNK MAP kinases in BMMC from NTAL‐deficient mice. The activity of PI3K, the concentration of PI
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(3,4,5)P3, the amount of IP3, and the Ca2þ response were also increased. NTAL therefore appears to negatively regulate FceRI signaling. The mechanism of inhibition still needs to be elucidated. Whether NTAL recruits an inhibitory molecule, such as a phosphatase, is one possibility that has not been convincingly demonstrated. Whether a competition between LAT and NTAL, which recruit a common set of adapter molecules, exists is supported by the observation that the phosphorylation of LAT is increased in the absence of NTAL (Volna et al., 2004) and that, reciprocally, the phosphorylation of NTAL is increased in the absence of LAT. The augmented phosphorylation of LAT in NTAL/ mast cells is likely to explain the increased phosphorylation of PLC‐g and its consequences on IP3 production and Ca2þ mobilization. Also, NTAL lacks a PLC‐g binding site, and the recruitment of PLC‐g by LAT requires the cooperative binding of several among the adapters that are recruited by both LAT and NTAL and that NTAL might sequester. Against the competition hypothesis, LAT and NTAL were found to reside in distinct lipid rafts on the plasma membrane (Volna et al., 2004). Whether these different microdomains could possibly merge during FceRI signaling, as it was suggested (Rivera, 2005), needs to be demonstrated. Interestingly, NTAL may not only generate negative signals, but also contribute to positive signals in mast cells. These could be observed in the absence of LAT. Inhibition of mediator release was indeed reported to be more pronounced in BMMC from LAT‐ and NTAL‐doubly deficient mice than in BMMC from LAT‐deficient mice (Volna et al., 2004; Zhu et al., 2004). A positive role of NTAL could be seen on Ca2þ responses in T and B lymphocytes (Brdicka et al., 2002; Janssen et al., 2004) and on Stem Cell factor‐ induced activation of human mast cells (Tkaczyk et al., 2004). A recent analysis performed in DT40 B cells proposed that, when recruiting Grb2, phosphorylated NTAL removes a Grb2‐dependent inhibitory effect on the BCR‐induced influx of extracellular Ca2þ (Stork et al., 2004). This inhibitory effect could be due to protein tyrosine phosphatases and inositol phosphatases which associate with Grb2 in different conditions. 3.1.5. Protein Tyrosine Phosp hatases Protein tyrosine phosphatases are thought to negatively regulate FcR signaling. Supporting evidence is, however, scarce. The SH2 domain‐containing Protein Tyrosine Phosphatase SHP‐1 has been implicated in FceRI signaling by using trapping mutants (Xie et al., 2000). SHP‐1 was reported to associate with the phosphorylated ITAM of FcgRIIA, Syk, the p85 subunit of PI3K, and Dok‐1, and to decrease the tysrosyl‐phosphorylation of intracellular proteins, upon FcgRIIA aggregation in the macrophage‐like THP‐1 cells (Ganesan
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et al., 2003). SHP‐1 also contains several consensus binding motifs for the SH2 domain of Grb2, and the inhibitory effect of Grb2‐SHP‐1 complexes was observed on cytokine receptor signaling (Minoo et al., 2004). The possible role of the second SH2 domain‐containing Protein Tyrosine Phosphatase SHP‐ 2 in the negative regulation of FcR‐dependent cell activation remains to be demonstrated. Several protein phosphatase devoid of SH2 domain were also found to be activated upon FceRI aggregation and to dephosphorylate ITAMs (Swieter et al., 1995). 3.1.6. Inositol Phosp hatases Inositol phosphatases, by contrast, play a prominent role in controlling FcR‐ dependent cell activation. The inositol 3‐phosphatase PTEN was involved in FcgR signaling as Akt and MAP kinase phosphorylation induced upon FcgRIIIA aggregation was enhanced in macrophages from PTEN/ mice, resulting in enhanced cytokine secretion (Cao et al., 2004). SHIP2 was tyrosyl‐ phosphorylated upon FcgRI engagement in THP‐1 cells or upon FcgRIIA engagement in human peripheral blood monocytes following upregulation by LPS, and it associated via its SH2 domain to the phosphorylated ITAM of this receptor (Pengal et al., 2003). Finally, SHIP1 was described to inhibit FcgRIIA‐dependent phagocytosis in THP‐1 cells (Nakamura et al., 2002), to coprecipitate with phosphorylated FcgRIIA, and to negatively regulate NFk‐ B‐mediated gene transcription during phagocytosis in human myeloid cells (Tridandapani et al., 2002). SHIP1 activity was reported to associate with the phosphorylated z subunit and to negatively regulate FcgRIIIA‐dependent ADCC in human NK cells (Galandrini et al., 2002). SHIP1 was found to bind in vitro to phosphopeptides corresponding to the FcRb ITAM (Kimura et al., 1997) and to interact with FcRb when examined by yeast triple hybrid assay (Osborne et al., 1996). The possible in vivo recruitment of this phosphatase in FceRI signaling complexes remains elusive as, so far, it was not reported to coprecipitate with FceRI, including the FcRb subunit, following receptor engagement in mast cells. SHIP1 was, however, understood to play a central regulatory role in the autonomous negative regulation of FceRI signaling. This conclusion was based on studies of SHIP1‐deficient mice. As they get older, SHIP1/ mice spontaneously develop a splenomegaly and a progressive lung infiltration by myeloid cells that leads to a waste syndrome and, ultimately, to a shortened life span. Their myeloid progenitor cells are hyper‐responsive to cytokines, such as IL‐3, and growth factors, such as Granulocyte/Macrophage Colony‐Stimulating Factor and Stem Cell Factor (Helgason et al., 1998). Interestingly, BMMC derived from SHIP1/ mice are hyper‐responsive not only to Stem Cell Factor‐, but also to IgE‐dependent
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stimulation. Such cells indeed release more b‐hexosaminidase than do BMMC derived from wt mice in response to FceRI aggregation by IgE and antigen. Supporting the conclusion that BMMC from SHIP1/ mice could respond to a lower degree of receptor aggregation, IgE anti‐DNP alone could trigger these cells, but not wt‐type cells, to release b‐hexosaminidase, as well as an array of cytokines. These antigen‐independent responses were inhibited by a monovalent hapten such as DNP‐lysine (Huber et al., 1998; Kalesnikoff et al., 2001). IgE‐induced increased degranulation was correlated with augmented and sustained Ca2þ mobilization and Erk1/2 activation. The phosphorylation of Shc, which associates constitutively to SHIP1, was reduced in the absence of SHIP1, but, surprisingly, FcRb phosphorylation was increased. Based on these data, SHIP1 was proposed to raise the threshold of FceRI aggregation needed to generate activation signals and to function as a ‘‘gatekeeper’’ of mast cell degranulation (Huber et al., 1998). SHIP1 is constitutively active. By contrast with SHPs, the phosphatase activity of SHIP1 is not up‐regulated when its SH2 domain binds to a tyrosyl‐phosphorylated motif, but when it is translocated close to the membrane (Bolland et al., 1998). The expression of a membrane‐targeted CD8‐SHIP1 chimera in COS cells constitutively induced a three‐fold higher enzymatic activity than the expression of a cytosolic form of SHIP1 (Phee et al., 2000). A simple explanation is that, under these conditions, SHIP1 is located close to its membrane substrate. SHIP1 removes 5‐phosphate groups in the inositol ring of 3‐phosphorylated inositides and phosphatidylinositides. Its substrates are inositol (1,3,4,5)tetrakis‐phosphate [I(1,3,4,5)P4] and PI(3,4,5)P3, which are hydrolyzed into inositol (1,3,4)tris‐phosphate and into phosphatidylinositol (3,4)bis‐phosphate, respectively (Damen et al., 1996). SHIP1 can therefore prevent PI(3,4,5)P3‐dependent critical upstream events leading to the Ca2þ response and, as a consequence, inhibit cell responses (Scharenberg and Kinet, 1998; Scharenberg et al., 1998). Another role of SHIP1 in autonomous negative regulation was recently unraveled. This regulation accounts for the bell‐shaped curve of mast cell activation as a function of antigen concentration. Inhibition of biological responses in excess of antigen is unique neither to FceRI nor to mast cells. It was long interpreted as resulting from a progressive decrease in receptor aggregation, due to a competition of high concentrations of antigen for efficiently crosslinking FceRI‐bound IgE (Dembo et al., 1978; Wofsy et al., 1978), although negative regulation had previously been hypothesized as an explanation, resulting from an excess of receptor aggregation (Magro and Alexander, 1974). Supporting experimental predictions deduced from a mathematical analysis (Delisi and Siraganian, 1979), recent works provided evidence that intracellular signals do not decrease, but increase, as the concentration of
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antigen increases. Thus, the tyrosyl‐phosphorylation of intracellular proteins in whole cell lysates and, more specifically, of FcRb and PLC‐g were of a higher magnitude in BMMC stimulated with supra‐optimal concentrations of antigen than in BMMC stimulated with an optimal antigen concentration. The secretory response decreases, however, because negative signals increase and become dominant over positive signals. Supporting this interpretation, the inducible tyrosyl‐phosphorylation of SHIP1 dose‐dependently increased with the concentration of antigen, even after supra‐optimal concentrations were reached. Most importantly, inhibition of secretion induced by an excess of antigen in mast cells derived from wt mice was abrogated in mast cells derived from SHIP1‐deficient mice (Gimborn et al., 2005). These data altogether indicate that SHIP1, possibly recruited by FcRb when heavily phosphorylated as a result of supra‐optimal receptor aggregation, is the effector of autonomous negative regulation of FceRI signaling that dampens mast cell activation in excess of ligand. 3.1.7. Cbl Finally, ubiquitination of receptors and signaling molecules, followed by proteasomal degradation, were shown to terminate cell activation. Thus, following FceRI engagement, FcRb and FcRg, as well as Syk, undergo rapid c‐Cbl‐ dependent E3 ligase‐mediated ubiquitination (Gimborn et al., 2005). Lyn also associates with c‐Cbl and is ubiquitinated and degraded in IgE‐activated mast cells (Kyo et al., 2003). Likewise, Syk and ZAP‐70 are ubiquitinated following FcgRIIIA engagement in human NK cells (Paolini et al., 2001). 3.2. Promiscuous Negative Regulation of Activating FcRs by FcaRI ITAM‐containing FcRs were recently demonstrated to have the ability of generating not only positive and negative signals which regulate each other, but also negative signals which can affect positive signals delivered by other activating FcRs in the same cell. FcaRI are such receptors. They bind monomeric IgA with a moderate affinity and dimeric IgA with a high avidity (Wines et al., 2001). FcaRI are encoded by genes of the Leukocyte Receptor Complex, on chromosome 19. They share with receptors encoded by this gene family a KIR‐type orientation, instead of an FcR‐type orientation of their extracellular domains (Herr et al., 2003). Although FcaRI can be expressed without, FcaRI associate with FcRg and, upon aggregation by IgA immune complexes, they trigger cell activation like other ITAM‐containing immunoreceptors. They are expressed by a variety of myeloid cells which contribute to inflammation (Monteiro and Van De Winkel, 2003).
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Surprisingly, the engagement of FcRg‐associated FcaRI by monomeric ligands—Fab fragments of mAbs against the extracellular domains of human FcaRI or human serum IgA—was found to negatively regulate the in vitro phagocytosis of IgG‐opsonized bacteria by human monocytes or IgE‐ dependent exocytosis in the rat mast cell line RBL‐2H3 transfected with cDNA encoding FcaRI. When administered intraperitoneally into human FcaRI transgenic mice, anti‐FcaRI Fab fragments also inhibited bronchial constriction and airway infiltration by inflammatory cells induced by IgE and antigen in a murine model of allergic asthma. Using chimeric molecules made of the a subunit of FcaRI the transmembrane domain of which had a point mutation preventing the association with FcRg and the intracytoplasmic domain of which was replaced by that of FcRg (FcaRI/FcRg chimeras) expressed in RBL transfectants, the authors demonstrated that inhibition depended on the FcRg ITAM, and that both tyrosines were required for inhibition. These tyrosines were phosphorylated following monovalent engagement of FcaRI/ FcRg chimeras, but to a much lower extent than following plurivalent engagement. Inhibition was a slow process, taking 6 hrs to be complete. Interestingly, inhibition induced by monovalent ligands was correlated with the coprecipitation of SHP‐1 with weakly phosphorylated FcaRI/FcRg chimeras. Indeed, SHP‐1 did not detectably coprecipitate with chimeras that were heavily phosphorylated following cell activation induced by multivalent ligands. Finally, the coprecipitation of SHP‐1 with FcaRI/FcRg chimeras was dose‐dependently inhibited by a MEK inhibitor, suggesting a positive role of Erk in SHP‐1 recruitment. Intriguingly, when engaged by monovalent Fab fragments of a mAb against the extracellular domain of FcgRIIB, FcgRIIB/FcRg chimeras failed to inhibit IgE‐induced mediator release in the same cells, suggesting that, beside the intracytoplasmic ITAM, the ligand and/or the extracellular domain of the chimera were critical for inhibition (Pasquier et al., 2005). Also, inhibition is unlikely to depend on the mere membrane recruitment of SHP‐1. IgE‐induced mediator release and intracellular signaling were indeed not impaired in RBL transfectants expressing FcgRIIB whose intracytoplasmic domain had been replaced by the catalytic domain of SHP‐1 (Hardre´‐Lie´nard and Dae¨ron, unpublished data). Whatever the mechanism of inhibition, these results have several important implications. First, they support the evidence that, although not able to fully activate cells, interactions of ITAM‐containing immunoreceptors with monovalent ligands can generate intracellular signals. Second, they indicate that FcaRI can generate either positive or negative signaling depending on extracellular ligands available (i.e., depending on whether IgA are in complexes with specific antigen or not). Whether other ITAM‐containing receptors may exert similar dual functions or whether it is a unique feature of FcaRI is not
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known. FceRI do not seem to inhibit cell activation by other ITAM‐containing receptors when occupied by monomeric IgE as they are under physiologic conditions. Third, they suggest that FcaRI may negatively regulate activation signals triggered by many other receptors. Negative regulation by ITAM‐ containing receptors apparently did not require that inhibitory and activating receptors be coaggregated at the cell surface. If this conclusion proves to be correct, one can expect that many biological responses be affected by monovalent ligand‐induced negative regulation by FcaRI. SHP‐1 can indeed inhibit most if not all activation processes triggered by receptors whose signaling depends on tyrosyl‐phosphorylation of proteins. Finally, these findings provide a possible explanation and molecular basis to the paradox that, although IgA receptors can activate inflammatory cells (Patry et al., 1995), IgA have long been known to have general anti‐inflammatory effects (Russell et al., 1997) and to the observation that selective IgA deficiencies are correlated with increased susceptibility to autoimmune and allergic diseases (Schaffer et al., 1991). 4. Negative Signaling by Inhibitory FcRs By contrast with FcaRI‐dependent negative regulation, FcgRIIB‐dependent negative regulation requires that the inhibitory receptors be coaggregated with activating receptors by a common extracellular ligand and affects cell signaling triggered by these receptors. 4.1. Inhibitory FcRs and ITIMs The inhibitory properties of FcgRIIB lie on the presence of an ITIM in their intracytoplasmic domain. First identified in FcgRIIB (Dae¨ron et al., 1995a), ITIMs were subsequently found in a large number of inhibitory receptors that control the biologic activities of hematopoietic cells (Long, 1999). Sequence alignments of these ITIMs made it possible to define ITIMs structurally. ITIMs consist of a sequence containing a single tyrosine (Y) followed by a hydrophobic residue (I, V, or L) at position Y þ 3 and preceeded by a less conserved hydrophobic residue at position Y 2 (Vivier and Dae¨ron, 1997). One consequence of the coaggregation of FcgRIIB with activating receptors is the phosphorylation of their ITIM. FcgRIIB are not tyrosyl‐ phosphorylated when aggregated at the cell surface. They become phosphorylated when they are coaggregated with activating immunoreceptors (D’Ambrosio et al., 1995) because these provide the src kinase which phosphorylates both ITAMs and ITIMs in receptor coaggregates (Malbec et al., 1998). Due to this peculiarity, FcgRIIB are not inhibitory in resting cells. They do not establish a threshold that must be overcome by activating receptors.
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They become functional ‘‘upon request’’ only, when cell activation has been launched. The phosphorylation of the FcgRIIB ITIM is indeed critical to initiate negative regulation. 4.2. The Recruitment of SHIP1 by FcgRIIB Inhibitory receptors carrying phosphorylated ITIMs (pITIMs) were shown to recruit SH2 domain‐containing cytosolic phosphatases that interfere with signals transduced by ITAM‐bearing receptors (Bolland and Ravetch, 1999). Four such phosphatases have been identified in mice and in humans: the two‐ SH2 domain‐containing Protein Tyrosine Phosphatases SHP‐1 and SHP‐2 and the single‐SH2 domain‐containing inositol 5‐phosphatases SHIP1 and SHIP2. Phosphorylated ITIMs differ from phosphorylated ITAMs by their specificity for SH2‐containing molecules. ITIMs recruit phosphatases only, whereas ITAMs recruit protein tyrosine kinases, adapter molecules, and phosphatases. FcgRIIB were found to differ from other ITIM‐containing receptors by being capable of recruiting SHIP1 and SHIP2. The FcgRIIB ITIM indeed has an affinity for the SH2 domain of SHIPs that other ITIMs lack. Our investigation of the bases of this unique specificity identified several parameters as being critical for SHIP1 to be recruited by FcgRIIB. 4.2.1 The Y þ 2 Leucine Determines the Affinity of the FcgRIIB ITIM for SHIP1/2 First of all, the affinity of FcgRIIB for SHIPs depends on a specific amino acid at position Y þ 2 in the ITIM. As expected from studies that established the molecular bases of the affinity of SH2 domains of other molecules for tyrosyl‐ phosphorylated peptides, the affinity of pITIMs for the SH2 domains of these phosphatases required the conservation of both the Y and the Y þ 3 residues. Synthetic peptides corresponding to pITIMs of all ITIM‐bearing molecules were found to bind SHP‐1 and SHP‐2 in vitro (Burshtyn et al., 1996; D’Ambrosio et al., 1995). The in vitro binding of SHP‐1 and SHP‐2 to the pITIMs of KIR2DL3 and FcgRIIB depends on the Y 2 residue (Ve´ly et al., 1997). Phosphorylated peptides corresponding to the FcgRIIB ITIM, but not phosphorylated peptides corresponding to the KIR2DL3 ITIMs, bound also SHIP1 and SHIP2 (Muraille et al., 2000; Ono et al., 1996). To identify the SHIP‐binding site in FcgRIIB, we exchanged residues between the FcgRIIB ITIM and the N‐terminal ITIM of KIR2DL3. Loss‐of‐function and gain‐of‐ function substitutions identified the Y þ 2 leucine, in the FcgRIIB ITIM, as determining the binding of both SHIP1 and SHIP2, but not the binding of SHP‐1 or SHP‐2. Conversely, the Y 2 isoleucine that determines the in vitro
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binding of SHP‐1 and SHP‐2 affected neither the in vitro binding nor the in vivo recruitment of SHIP1 or SHIP2 (Bruhns et al., 2000). One hydrophobic residue in the ITIM of FcgRIIB therefore determines the affinity for SHIPs. This residue is symmetrical to another hydrophobic residue that determines the affinity of all ITIMs for SHPs. It defines a SHIP‐binding site, distinct from a SHP‐binding site, which confers FcgRIIB their ability to recruit SHIP1 and SHIP2. 4.2.2. The Density of pITIM Determines the Selective Recruitment of SHIP1/2 by FcgRIIB Intriguingly, these two binding sites are not used in vivo. Although agarose beads coated with phosphorylated peptides corresponding to the FcgRIIB ITIM bind in vitro both SHIP1/2 and SHP‐1/2, phosphorylated FcgRIIB, recruit selectively SHIP1/2 in vivo (Fong et al., 1996; Muraille et al., 2000; Ono et al., 1996). When investigating the reasons for this discordance, we found that beads coated with low amounts of pITIM bound SHIP1, but not SHP‐1, i.e., they behaved in vitro like phosphorylated FcgRIIB in vivo. The same was found when examining the binding of pITIM‐coated beads to GST fusion proteins containing the SH2 domain of SHIP1 or the two SH2 domains of SHP‐1. The reason is that the affinity of the SH2 domain of SHIP1 is high enough for binding to pITIM‐coated beads, but not that of either the N‐ or the C‐terminal SH2 domain of SHP‐1 (Lesourne et al., 2001). SHP‐1 indeed requires its two SH2 domains to bind to two pITIMs that are close enough to enable a cooperative interaction. This condition is fulfilled in vitro when beads are coated with sufficient amounts of pITIMs or in vivo when two tandem pITIMs are present in the intracytoplasmic domain of inhibitory receptors such as KIR2DL3. The deletion (Bruhns et al., 1999) or the mutation (Burshtyn et al., 1996) of either ITIM indeed abrogated the ability of KIR2DL3 to recruit SHP‐1. This is not fulfilled by FcgRIIB when coaggregated with activating receptors. When trying to increase FcgRIIB phosphorylation in B cells and mast cells, we found that concentrations of extracellular ligands optimal for FcgRIIB phosphorylation failed to induce the recruitment of SHP‐1. SHP‐1 was, however, recruited by FcgRIIB when the receptors were hyperphosphorylated following cell treatment with pervanadate (Lesourne et al., 2001). These data suggest that, although it can be reached under non‐physiological conditions, a high enough level of FcgRIIB phosphorylation may not be reached, under physiological conditions, to enable the in vivo recruitment of SHP‐1. Whether a regulatory mechanism limits the phosphorylation of FcgRIIB and whether (pathological?) conditions that would lead to the hyperphosphorylation of FcgRIIB might enable the
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recruitment of SHP‐1 that would dephosphorylate signaling molecules are interesting possibilities that remain to be demonstrated. 4.2.3. The Recruitment of SHIP1 by FcgRIIB Requires the Cooperative Recruitment of Cytosolic Adapters Surprisingly, we found that, although sufficient for binding SHIP1 or SHIP2 in vitro, the FcgRIIB pITIM is not sufficient for the receptors to recruit these phosphatases in vivo. It is a general consensus that the FcgRIIB ITIM is both necessary and sufficient for inhibition of cell activation. The conclusion that it is necessary was based on the pioneer work by Amigorena and coworkers who showed that a 13‐amino acid deletion, which was later understood to encompass the ITIM, abrogated inhibition in B cells (Amigorena et al., 1992). A point mutation of the ITIM tyrosine also abrogated FcgRIIB‐dependent inhibition of mast cell and T cell activation (Dae¨ron et al., 1995a), and abolished (Muta et al., 1994) or reduced (Fong et al., 2000) the calcium response in B cells. The conclusion that the ITIM is sufficient was based on works by Muta and coworkers who showed that a chimeric molecule whose intracytoplasmic domain contained the murine FcgRIIB ITIM retained inhibitory properties in B cells (Muta et al., 1994). A C‐terminal deletion of the intracytoplasmic domain of murine FcgRIIB, which left the ITIM intact, however, prevented SHIP1 from being detectably coprecipitated, and reduced the inhibitory effect of FcgRIIB on BCR signaling (Fong et al., 2000). Our recent study showed that this C‐terminal sequence contains a second tyrosine‐based motif that mediates the recruitment of the cytosolic adapter proteins Grb2 and Grap via their SH2 domain and that contributes to the recruitment of SHIP1. The recruitment of the phosphatase indeed required an intact adapter‐binding motif and, conversely, the recruitment of adapters required an intact phosphatase‐binding motif. The reason is that Grb2 and Grap are constitutively associated with SHIP1 via their C‐terminal SH3 domain, and this association increases upon coaggregation of BCR with FcgRIIB. Grb2/Grap thus form a tri‐molecular complex with SHIP1 and FcgRIIB. This stabilizes the binding of the phosphatase to the ITIM and enables its recruitment by murine FcgRIIB. Supporting this conclusion, SHIP1 failed to coprecipitate with FcgRIIB, when tyrosyl‐phosphorylated upon coligation with BCR in mutant DT40 cells lacking both Grb2 and Grap (Isnardi et al., 2004). This requirement may not be peculiar to the interactions between FcgRIIB1, SHIP1, and Grb2. As discussed above, molecules that contain two SH2 domains require the cooperative binding of these two domains to two sequences containing phosphorylated tyrosines in order to be recruited in vivo. The recruitment of ZAP‐70 and Syk (Bu et al., 1995; Kurosaki et al., 1995), or SHP‐1 (Lesourne et al., 2001),
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required the conservation of their two SH2 domains and the conservation of the two tyrosines of ITAMs in immunoreceptors (Kimura et al., 1996) or of the two ITIMs in KIRs (Bruhns et al., 1999; Burshtyn et al., 1999), respectively. Moreover, molecules that contain a single SH2 domain were found to require the cooperation of other SH2 domain‐containing molecules in order to be recruited (Yamasaki et al., 2003). One can therefore propose that one SH2 domain alone may not be sufficient for enabling stable interactions between signaling molecules. 4.3. SHIP1 Accounts for FcgRIIB‐Dependent Negative Regulation 4.3.1. SHIP1 is Necessary and Sufficient for FcgRIIB‐Dependent Negative Regulation Once it has been stably recruited, SHIP1 is the effector of FcgRIIB‐ dependent negative regulation. Evidence supporting this conclusion is as follows. FcgRIIB‐dependent negative regulation was abolished in cultured mast cells derived from the bone marrow of SHIP1‐deficient mice (Malbec et al., 2001), but not in mast cells derived from the bone marrow of moth‐eaten mice which are deficient in SHP‐1 (Fong et al., 1996). FcgRIIB‐dependent inhibition of Ca2þ mobilization was abolished in SHIP1‐deficient chicken DT40 B cells, but not in SHP‐1‐deficient (Ono et al., 1997) or in SHP‐2‐ deficient (Isnardi et al., unpublished observation) DT40 cells. Noticeably, FcgRIIB‐dependent inhibition was only reduced in B cells from SHIP1‐ deficient mice (Brauweiler et al., 2000), possibly because SHIP‐2 could partially replace SHIP1. Although also present in mast cells, SHIP2 could, however, not mediate FcgRIIB‐inhibition in SHIP1‐deficient mast cells. Inhibition was also partially reduced in B cells from moth‐eaten mice (D’Ambrosio et al., 1995). One possible reason is that SHP‐1‐deficient B cells are constitutively hyper‐activated (Pani et al., 1995), which might make BCR‐dependent signaling more difficult to inhibit. These data indicate that SHIP1 is necessary for FcgRIIB‐dependent inhibition of mast cell activation and, most probably, of B cell activation. Evidence that SHIP1 is also sufficient is as follows. B cell (Ono et al., 1997) and mast cell (Malbec et al., 2001) activation were comparably inhibited when BCRs or FceRI were coaggregated with wt FcgRIIB or with FcgRIIB whose intracytoplasmic domain had been replaced by the catalytic domain of SHIP1. In an analysis of a series of FcgRIIB‐SHIP chimeras, we found that, when coaggregated with BCR in the FcgR‐deficient cell line IIA1.6, SHIP1 chimeras abolished IL‐2 secretion, Ca2þ mobilization, Akt phosphorylation, and Erk1/2 phosphorylation. Under the same conditions, SHIP2 chimeras inhibited Akt phosphorylation, but did not affect Erk1/2
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phosphorylation, Ca2þ mobilization, and IL‐2 secretion (Hardre´‐Lie´nard and Dae¨ron, unpublished data). 4.3.2. Two Effector Mechanisms Are Used By SHIP1 in FcgRIIB‐Dependent Negative Regulation SHIP1 mediates FcgRIIB‐dependent inhibition by at least two distinct mechanisms. One depends on its catalytic activity, the other does not. By dephosphorylating PI(3,4,5)P3, SHIP1 prevents the recruitment of PH domain‐containing molecules such as PKB/Akt. The serine/threonine phosphorylation of PKB/Akt observed following BCR or FceRI aggregation was indeed abrogated upon coaggregation of these immunoreceptors with FcgRIIB (Jacob et al., 1999; Malbec et al., 2001). PKB/Akt phosphorylation depends on the membrane translocation of PKB/Akt and of PDK1, the responsible kinase. Both contain one PH domain which targets both the substrate and the enzyme to PI(3,4,5)P3‐rich membrane regions. PKB/Akt phosphorylation is therefore an indirect means to estimate the amount of membrane PI(3,4,5)P3 (Carver et al., 2000). Supporting this approximation, when transfected into B cells, a GFP construct containing the PH domain of Akt that is diffusely distributed in the cytosol of resting cells, translocates to the membrane following BCR aggregation. This translocation was prevented when BCR were coaggregated with FcgRIIB (Astoul et al., 1999). PKB/Akt phosphorylation is critical for mechanisms that prevent apoptosis. Although useful to assess PI(3,4,5)P3 degradation, and although it was recently reported to promote IgG immune complex‐induced phagocytosis in murine macrophages (Ganesan et al., 2004), PKB/Akt is not known to be a major player in signaling pathways leading to cell activation. PLC‐g and Tec kinases are. Like PKB/Akt, PLC‐g and Tec kinases contain a PH domain which mediates or contributes to their membrane recruitment via PI(3,4,5)P3. When translocated to the membrane, Tec kinases are thought to be tyrosyl‐phosphorylated/activated by Lyn and, together with Syk, to phosphorylate PLC‐g. The mechanism by which SHIP1 can negatively regulate the activity of Tec kinases was recently documented. SHIP1, as well as SHIP2, were reported to bind preferentially to the Tec kinase itself, and to inhibit its activity. Binding occurs through the SH3 domain of Tec, and mutations of this domain generated a hyperactive form of Tec. Constitutively active Tec could also be generated by introducing mutations that targeted this kinase to the membrane. Since Tec activity is positively regulated by its membrane localization, mostly via its recruitment to PI(3,4,5)P3, it was proposed that, by hydrolyzing PI(3,4,5)P3, SHIP1/2 could prevent the membrane recruitment and, hence, the activation of Tec (Tomlinson et al., 2004). This explanation of the inhibition of Ca2þ responses observed upon coaggregation of FcgRIIB
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with immunoreceptors and the Fyn/Gab2/PI3K pathway that was described in mast cells (Parravincini et al., 2002) are not readily compatible. This Fyn‐ initiated pathway leads to the generation of PI(3,4,5)P3 by PI3K, whereas the Lyn/Syk/LAT/PLC‐g leads to Ca2þ mobilization. The mechanism of SHIP1‐ mediated FcgRIIB‐dependent inhibition of the Ca2þ response is more difficult to understand if the substrate of SHIP1 does not belong to the same pathway as that which leads to PLC‐g activation. These apparently conflicting data may be reconciled if one considers that bridges exist between the two pathways as suggested by the decreased phosphorylation of PLC‐g observed in Gab2/ mice (Gu et al., 2001). PLC‐g is indeed recruited both by PI(3,4,5)P3 and by LAT, as well as Btk, via Gads and SLP76. PI3K is recruited both by Gab2 and, via Gads, by LAT (Schraven et al., 1999). The coaggregation of FcgRIIB with immunoreceptors markedly inhibits the phosphorylation/activation of MAP kinases. SHIP1‐dependent PI(3,4,5)P3 degradation may affect the recruitment of the exchange factor Vav, which is translocated to the membrane via its PH domain, and the subsequent generation of Rac‐GTP that leads to the activation of JNK and p38. Inhibition of Erk1/2 activation also depends on SHIP1. It, however, does not depend on the phosphatase activity of the enzyme. SHIP has a tyrosine‐rich C‐terminal segment which contains NPXY motifs. It is constitutively tyrosyl‐phosphorylated. It is further phosphorylated following immunoreceptor‐dependent cell activation, and even further when recruited by FcgRIIB. The responsible kinase is thought to be Lyn. The phosphorylation of SHIP1 does not affect its enzymatic activity, but it confers this phosphatase the properties of an adapter molecule which can affect positive signals, independently of its catalytic activity. This conclusion stemmed from the observation that the adapter molecule Dok‐1 becomes heavily phosphorylated following the coaggregation of BCR with FcgRIIB in murine B cells (Tamir et al., 2000). Dok‐1 is a member of a family of adapter proteins that are tyrosyl‐phosphorylated upon engagement of a variety of cytokine receptors, growth factor receptors, and immunoreceptors. Dok phosphorylation depends on its membrane recruitment, and membrane‐targeted Dok‐1 was constitutively phosphorylated. Dok‐1 can be phosphorylated by Lyn or by Tec. Stem Cell factor‐induced Dok‐1 phosphorylation was, however, prevented in mast cells derived from Lyn/ mice, indicating that Lyn is primarily responsible for Dok‐1 phosphorylation in these cells (Liang et al., 2002). When tyrosyl‐phosphorylated, Dok‐1 recruits a variety of SH2 domain‐containing molecules including rasGAP which negatively regulates Ras activation. Dok‐1 contains an N‐terminal PH domain, a PTB domain, and a proline/tyrosine‐rich C‐terminal sequence. The role of Dok‐1 in FcgRIIB‐dependent negative regulation was analyzed using chimeric molecules made by replacing the intracytoplasmic domain of
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FcgRIIB by the PH and PTB domain‐containing N‐terminal half of Dok‐1 or the proline/tyrosine‐rich C‐terminal half of Dok‐1. SHIP1 coprecipitated with the N‐terminal Dok chimera, whereas rasGAP coprecipitated with the C‐terminal Dok chimera when chimeras were coaggregated with BCR (Tamir et al., 2000). Ras‐GAP contains an SH2, an SH3, another SH2, and a PH domain, followed by a catalytic domain which can enhance the auto‐catalytic activity of ras‐GTP. As a consequence, Ras‐GTP is converted into RasGDP, and the Ras pathway is extinguished. Indeed, Erk1/2 activation seen upon BCR aggregation was inhibited upon coaggregation of BCR with the C‐terminal Dok chimera, but not with the N‐terminal Dok chimera (Tamir et al., 2000). Based on these data, it was proposed that, when recruited by FcgRIIB and tyrosyl‐phosphorylated, SHIP1 recruits Dok‐1 via the PTB domain of the latter. Dok‐1 becomes tyrosyl‐phosphorylated and recruits rasGAP via the SH2 domain of the latter. rasGAP turns Ras off and prevents the activation of Erk1/2. Similar results were observed when FcgRIIB were coaggregated with FceRI in mast cells (Ott et al., 2002). Supporting this scenario, MAP kinase activation was enhanced in response to BCR aggregation, and inhibition of cell proliferation in response to the coaggregation of BCR with FcgRIIB was abolished in B cells from Dok‐1‐deficient mice (Yamanashi et al., 2000). 4.4. FcgRIIB Amplify the Autonomous Negative Regulation of Activating FcRs 4.4.1. FcgRIIB‐Dependent Negative Regulation of FceRI Signaling Does not Occur in Lipid Rafts Lipid rafts are cholesterol/glycosphygolipid‐rich membrane micro‐domains (Brown and London, 2000; Horejsi, 2003) that diffuse laterally within the plasma membrane (Pralle et al., 2000). They play a critical role in positive signaling by FceRI. Disruption of rafts, using cholesterol‐depleting drugs, dramatically decreases early phosphorylation events induced upon FceRI aggregation (Sheets et al., 1999). According to a current model, FceRI are excluded from rafts in resting mast cells, whereas signaling proteins that are covalently associated with saturated fatty acids, such as Lyn (Young et al., 2003) and LAT (Zhang et al., 1998b), are concentrated in these domains. Upon aggregation, a fraction of FceRI transiently translocate into rafts (Field et al., 1997), bringing FceRI and raft‐associated signaling proteins close to each other. Kono and coworkers reported that FcgRIIB can translocate into lipid rafts upon aggregation in RBL‐2H3 cells (Kono et al., 2002) and Aman and coworkers reported that, when coaggregated with BCRs in A20 lymphoma
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B cells, FcgRIIB recruited SHIP1 preferentially in low‐density detergent‐ resistant membrane compartments (Aman et al., 2000). We failed to observe a detectable translocation of FcgRIIB into lipid rafts, when coaggregated with FceRI. Actually the coaggregation of FcgRIIB with FceRI partially inhibited the translocation of FceRI into lipid rafts. The recruitment of SHIP1 by FcgRIIB is therefore not likely to take place in lipid rafts in mast cells. Because FcgRIIB are phosphorylated by the raft‐associated protein tyrosine kinase Lyn upon coaggregation with FceRI (Malbec et al., 1998), FcgRIIB may, however, transiently translocate into rafts where they are possibly phosphorylated. 4.4.2. FcgRIIB Associate with the Submembranous F‐Actin Skeleton When analyzing the contents of subcellular fractions prepared from RBL‐2H3 cells, we observed that FcgRIIB and SHIP1 were located in different subcellular compartments in resting cells. Following cell disruption in hypotonic buffer, differential centrifugation and solubilization of resulting fractions, most, if not all, FcgRIIB were indeed recovered in membrane fraction, whereas SHIP1 was recovered in the cytosolic and in the F‐actin skeleton fractions. The submembranous F‐actin skeleton, which connects F‐actin‐associated proteins with membrane proteins and phospholipids (Luna and Hitt, 1992), is another subcellular compartment. Unlike rafts, the submembranous F‐actin skeleton is not critical for FceRI‐dependent positive signaling. Rather, it seems to be involved in constitutive negative regulation of FceRI signaling. Indeed, drugs such as latrunculin, which prevent actin polymerization, enhance mast cell degranulation (Frigeri and Apgar, 1999). Interestingly, inhibition of degranulation observed in excess of antigen was markedly reduced in cells treated with latrunculin B, and actin could coprecipitate with SHIP1 in BMMC (Gimborn et al., 2005). Since FcgRIIB inhibit mast cell activation by recruiting SHIP1, the two molecules must meet somewhere. We found that, when coaggregated with FceRI, FcgRIIB heavily translocated into the F‐actin skeleton compartment. This translocation did not require that FcgRIIB be coaggregated with FceRI as FcgRIIB were similarly translocated upon aggregation by specific ligands. Surprisingly, it did not require either the intracytoplasmic domain of FcgRIIB as tail‐less FcgRIIB behaved similarly as intact receptors. Like FcgRIIB, FceRI were found in the membrane fraction in resting cells and, albeit in lower proportions, they dose‐dependently translocated into the F‐actin skeleton fraction when aggregated by IgE and antigen. The coaggregation with FcgRIIB did not increase but facilitated FceRI translocation which reached comparable levels at lower concentrations of antigen. Since tail‐less FcgRIIB
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could enhance the translocation of FceRI into the F‐actin skeleton fraction but failed to inhibit mast cell activation, when coaggregated with FceRI (Lesourne et al., 2005), this effect of FcgRIIB on FceRI cannot alone account for negative regulation. 4.4.3. FcgRIIB Concentrate SHIP1 Close to FceRI Signaling Complexes in the F‐Actin Skeleton Filamin 1 is an actin‐binding protein that was previously reported to associate with SHIP2 in platelets (Dyson et al., 2001, 2003). We found that SHIP1 and Filamin 1 were recovered in the same sub‐cellular fractions as SHIP1 and that SHIP1 coprecipitated with filamin 1 in unstimulated RBL‐2H3 cells. Noticeably, the high‐molecular weight isoform of SHIP1 was predominant in the F‐actin skeleton fraction and it preferentially coprecipitated with filamin 1, whereas the two main SHIP1 isoforms were equally distributed in the cytosolic fraction. SHIP2 was proposed to associate with filamin via its proline‐rich C‐terminal region that is conserved in high‐molecular weight isoforms of SHIP1, but is spliced out in low‐molecular weight isoforms. Interestingly, the high‐molecular weight isoform of SHIP1 also preferentially coprecipitated with phosphorylated FcgRIIB, following their coaggregation with FceRI. These data altogether suggested that FcgRIIB could recruit filamin‐bound SHIP1 in the submembranous F‐actin skeleton compartment. This possibility was examined in intact cells by confocal microscopy. Upon coaggregation, FcgRIIB and FceRI rapidly formed small FcR patches on the plasma membrane. Both SHIP1 and filamin 1, but not F‐actin, co‐patched with FcRs. As the size of patches enlarged with time, higher amounts of SHIP1 colocalized with FcR patches. Surprisingly, filamin 1, as well as F‐actin, were excluded from large FcR patches (Lesourne et al., 2005). Based on these data, we propose a dynamic model according to which the translocation of FcgRIIB into the cytoskeleton enables these receptors to meet filamin‐bound SHIP1. The high‐avidity cooperative interactions between SHIP1, Grb2, and FcgRIIB are likely to displace SHIP1 from filamin and to concentrate the phosphatase in FcR signaling complexes. Supporting this critical role of the cytoskeleton, FcgRIIB‐dependent negative regulation of IgE‐induced mediator release was markedly reduced in latrunculin B‐treated cells. As for the exclusion of filamin and F‐actin from large FcR patches, one may hypothesize that the increased local degradation of PI(3,4,5)P3 by SHIP1 might decrease the rate of actin polymerization. Actin is indeed constantly polymerized and depolymerized and actin polymerization depends on PI3K (Bhargavi et al., 1998). Finally, we propose that FcgRIIB negatively regulate FceRI signaling by two mechanisms. First, they facilitate the translocation of FceRI into the F‐actin skeleton
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compartment, thus enhancing SHIP1‐dependent constitutive negative regulation of FceRI at low antigen concentrations. Second, FcgRIIB concentrate SHIP1 in the vicinity of FceRI. Supporting this interpretation, SHIP1 readily coprecipitates with phosphorylated FcgRIIB but not with with FceRI. It follows that FcgRIIB act as amplifiers of SHIP1‐dependent constitutive negative regulation of FceRI signaling. 5. Conclusion FcRs are critical molecules of the immune system as they mediate most biological activities of the main effectors of the so‐called humoral immunity, that is, antibodies. Because they are ubiquitously expressed (mostly, but not only) by cells of hematopoietic origin, and because antibodies circulate in the blood stream, FcRs are involved in a wide array of biological activities in physiology. They also contribute to a variety of pathological processes. FcRs can trigger the release of potentially harmful—in some cases, life‐ threatening—inflammatory mediators, and induce destructive cytotoxic mechanisms, but (or therefore?) their activating properties are tightly controlled by regulatory mechanisms. As a consequence, immune responses are normally nonpathogenic. These regulatory mechanisms are primarily based on negative signaling that counterbalances positive signaling. Several levels of negative regulation can act on a given activating FcR. Negative regulation depends on different molecular mechanisms that may be used sequentially, depending on the conditions. A critical condition is the aggregation state of FcRs. Protein tyrosine phosphatase‐dependent negative regulation operates in resting cells when multi‐subunit FcRs are expressed on the plasma membrane and not yet engaged by any ligand (Fig. 1A). SHIP1‐ dependent negative regulation operates in mast cells whose FceRI are occupied by ‘‘monomeric’’ IgE (Fig. 1B). Unknown regulatory mechanisms account for the selective expression of some cytokine genes in mast cells exposed to IgE in the absence of antigen. Promiscuous SHP‐1‐dependent negative regulation is also triggered in cells whose FcaRI are occupied by monomeric IgA. Negative regulation involving multiple molecules that generate negative signals of different types operates as soon as positive signals are generated by activating FcRs. These include receptor subunits, kinases and phosphatases, and cytosolic and transmembrane adapter molecules. SHIP1 is a major player in the negative regulation that controls antigen‐induced IgE‐dependent mast cell activation (Fig. 1C). When further aggregated by supra‐optimal concentrations of ligand, FceRI associate with the F‐actin skeleton where the filamin 1‐bound high‐molecular weight isoform of SHIP1 resides. SHIP1 extinguishes positive signals and prevents mediator release. One, however, does not know
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which molecular interaction(s) enable its recruitment in FceRI signaling complexes (Fig. 1D). When they are co‐engaged by IgG immune complexes, FcgRIIB facilitate the association of FceRI with the F‐actin skeleton, and tyrosyl‐phosphorylated FcgRIIB recruit and concentrate high‐molecular weight SHIP1 in the signaling complex, where it dephosphorylates PI(3,4,5) P3, becomes C‐terminally tyrosyl‐phosphorylated, and recruits Dok‐1 (Fig. 1E). As consequences, both the Ca2þ response and the activation of MAP kinases are inhibited. Noticeably, negative signaling often uses molecules that are also involved in positive signaling. The ITAM‐containing FcR subunit FcRb generates positive signals that complement FcRg‐dependent signaling. It contributes to bring Lyn in the signalosome and, possibly SHIP1. Lyn phosphorylates not only FcR ITAMs and Syk, but also SHIP1, enabling this phosphatase to inhibit the Ras pathway via the sequential recruitment of Dok‐1 and rasGAP. Lyn phosphorylates also Cbp, enabling Csk to be recruited and to prevent Fyn from being activated and to lead to the activation of PI3K. Grb2 can be recruited via its SH2 domain by phosphorylated adapters such as LAT, NTAL, or Shc, in activating FcR signaling complexes and contribute to positive regulation, but also by FcgRIIB and contribute to negative regulation. It is constitutively associated, via its N‐terminal SH3 domain, with the exchange factor Sos which activates Ras, but also, via its C‐terminal SH3 domain, with SHIP1 which inhibits Ras. Grb2 can also interact, via its SH2 domain, with phosphorylated SHP‐1 which dephosphorylates signaling molecules. LAT is critical for positive TCR‐ and FcR‐dependent signaling but, as revealed by knock‐in mice expressing LAT with selective tyrosine mutations, it also contributes to generate negative signals. NTAL may function both as a LAT equivalent in B cells and as a LAT antagonist in mast cells and, in these cells, its overall dominant negative effect results from an integration of negative and positive signals. Noticeably, molecules involved in negative regulation such as SHP‐1 (Xie et al., 2000) and SHIP1 (Giallourakis et al., 2000) can also have positive effects when overexpressed. Finally, depending on the ligand valency—IgA alone or in complex with multivalent antigen—FcaRI, can either prevent or induce inflammatory responses. Altogether, data listed above lead to the conclusion that molecules have no biological functions, but biological properties only. What ultimately determines a ‘‘function’’ is the context in which a set of molecules interact in sequence with each other. This context depends on the organization of signaling complexes that transiently form and function in different subcellular compartments where different molecules reside or are translocated. As a consequence, and as learnt from the study of knock‐out mice, therapeutic approaches aiming at targeting any specific molecule can be expected to have
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Figure 1 Five levels of negative regulation in FcR complexes. Molecules in black are primarily involved in the generation of positive signals, molecules in red are primarily involved in the generation of negative signals, molecules in blue are involved in the generation of both positive and negative signals. (A) Positive and negative regulation in resting cells. Protein tyrosine kinases
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‘‘paradoxical’’ unwanted effects. An alternative is to act on the balance between positive and negative signaling in appropriate cells. Since most cells are constitutively equipped with both activating and inhibitory FcRs, these can be used as therapeutic tools. One way is to increase the expression of FcRs of one type or of the other. This is apparently what happens when intravenous immunoglobulins (IVIG) are administered and upregulate the expression of FcgRIIB (Bruhns et al., 2003). Another way is to bring more FcRs of one type into complexes of FcRs of the other type. In vitro and in vivo proofs of concepts were recently provided that one can favor negative regulation using bispecific synthetic molecules capable of co‐engaging FceRI and FcgRIIB on human mast cells and basophils, and reduce IgE‐dependent human mast cell activation (Tam et al., 2004), allergen‐induced systemic anaphylaxis, and airway hyper‐responsiveness in transgenic mice expressing human FceRI (Zhu et al., 2005). Similar approaches can be envisioned in other diseases requiring immune responses to be dampened. Conversely, other molecules can be tailored to favor positive regulation in pathological situations requiring immune responses to be boostered. For these approaches to develop and be mastered, further investigations are needed in order to understand what determines the ratio of activating and inhibitory FcRs expressed at the cell and protein tyrosine phosphatases constitutively phosphorylate and dephosphorylate, respectively, intracellular proteins. Possibly resulting activation signals do not lead to a detectable cellular reponse. (B) SHIP1 as a gatekeeper of mast cell activation. Positive signals triggered by IgE in the absence of antigen are constitutively negatively regulated by SHIP1. As a result, wt mast cells usually do not degranulate when sensitized with IgE and are not challenged with antigen, but SHIP1‐deficient mast cells do. (C) Negative signals generated together with positive signals by activating FcRs. Upon aggregation of activating FcRs by antibodies and multivalent antigens, both the Lyn/Syk/PLC‐g and the Fyn/Gab2/PI3K pathways are activated, leading to cell activation. These positive signals are counterbalanced by negative signals. By phosphorylating Cpb, Lyn enables Csk to be recruited and to inhibit Fyn. By phosphorylating SHIP1, Lyn enables Dok1 to be recruited and to inhibit Ras via rasGAP. SHIP1 is possibly recruited by phosphorylated FcRb. NTAL also negatively regulates FceRI signaling by not yet clear mechanisms. Biological responses of the cell results from the integration of these antagonistic signals. (D) Negative signals generated by activating FcRs in excess of ligand. When supra‐optimally engaged by an excess of ligand, FceRI aggregates associate with the F‐actin skeleton, where the high molecular isoform of SHIP1 is constitutively associated with Filamin 1. As a consequence, more SHIP1 is involved in negative regulation as indicated by its increased phosphorylation. The result is a dose‐dependent inhibition of degranulation. (E) Negative regulation by FcgRIIB. When coaggregated with FceRI, FcgRIIB are phosphorylated by Lyn, associate with the F‐actin skeleton, and recruit F‐actin‐associated SHIP1. The recruitment of SHIP1 involves the interactions of its SH2 domain with specific residues in the FcgRIIB phosphorylated ITIM and of its C‐terminal prolin‐rich region with the C‐terminal SH3 domain of Grb2 which, itself, binds to the phosphorylated C‐terminal tyrosine of FcgRIIB via its SH2 domain. FcgRIIB thus concentrate SHIP1 in FceRI signaling complex and, by inhibiting both the Ca2þ response and the activation of MAP Kinases, extinguish all cellular responses.
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surface, whether activating or inhibitory FcRs can be preferentially engaged by antibodies, how FcRs generate positive and negative signals, and how these signals are integrated within cells. Acknowledgments Our works discussed in this review were supported in part by the Institut National de la Sante´ et de la Recherche Me´dicale (INSERM), the Fondation pour la Recherche Me´dicale (FRM), the Association pour la Recherche sur le Cancer (ARC), and the Institut Pasteur. RL was the recipient of fellowships from the ARC and from the Socie´te´ Franc¸aise d’Allergologie et d’Immunologie Clinique (SFAIC).
References Adamczewski, M., Numerof, R. P., Koretzky, G. A., and Kinet, J. P. (1995). Regulation by CD45 of the tyrosine phosphorylation of high affinity IgE receptor b‐ and g‐chains. J. Immunol. 154, 3047–3055. Aguado, E., Richelme, S., Nunez‐Cruz, S., Miazek, A., Mura, A. M., Richelme, M., Guo, X. J., Sainty, D., He, H. T., Malissen, B., and Malissen, M. (2002). Induction of T helper type 2 immunity by a point mutation in the LAT adaptor. Science 296, 2036–2040. Aman, M. J., Walk, S. F., March, M. E., Su, H. P., Carver, D. J., and Ravichandran, K. S. (2000). Essential role for the C‐terminal noncatalytic region of SHIP in FcgRIIB1‐mediated inhibitory signaling. Mol. Cell. Biol. 20, 3576–3589. Amigorena, S., Bonnerot, C., Drake, J., Choquet, D., Hunziker, W., Guillet, J. G., Webster, P., Saute`s, C., Mellman, I., and Fridman, W. H. (1992). Cytoplasmic domain heterogeneity and functions of IgG Fc receptors in B‐lymphocytes. Science 256, 1808–1812. Asai, K., Kitaura, J., Kawakami, Y., Yamagata, N., Tsai, M., Carbone, D. P., Liu, F. T., Galli, S. J., and Kawakami, T. (2001). Regulation of mast cell survival by IgE. Immunity 14, 791–800. Astoul, E., Watton, S., and Cantrell, D. (1999). The dynamics of protein kinase B regulation during B cell antigen receptor engagement. J. Cell Biol. 145, 1511–1520. Benhamou, M., Bonnerot, C., Fridman, W. H., and Dae¨ron, M. (1990). Molecular heterogeneity of murine mast cell Fcg receptors. J. Immunol. 144, 3071–3077. Benhamou, M., Ryba, N. J., Kihara, H., Nishikata, H., and P., S. R. (1993). Protein tyrosine kinase p72syk in high‐affinity IgE receptor signaling. Identification as a component of pp72 and association with the receptor g chain after receptor aggregation. J. Biol. Chem. 268, 23318–23324. Berger, S. A., Mak, T. W., and Paige, C. J. (1994). Leukocyte common antigen (CD45) is required for immunoglobulin E‐mediated degranulation of mast cells. J. Exp. Med. 180, 471–476. Bhargavi, V., Chari, V. B., and Singh, S. S. (1998). Phosphatidylinositol 3‐kinase binds to profilin through the p85 a subunit and regulates cytoskeletal assembly. Biochem. Mol. Biol. Int. 46, 241–248. Boerth, N. J., Judd, B. A., and Koretzky, G. A. (2000). Functional association between SLAP‐130 and SLP‐76 in Jurkat T cells. J. Biol. Chem. 275, 5143–5152. Bolland, S., Pearse, R. N., Kurosaki, T., and Ravetch, J. V. (1998). SHIP modulates immune receptor responses by regulating membrane association of Btk. Immunity 8, 509–516. Bolland, S., and Ravetch, J. V. (1999). Inhibitory pathways triggered by ITIM‐containing receptors. Adv. Immunol. 72, 149–177.
N E G AT I V E S I G N A L I N G I N F C R E C E P T O R C O M P L E X E S
75
Bolland, S., and Ravetch, J. V. (2000). Spontaneous autoimmune disease in FcgRIIB‐deficient mice results from strain‐specific epistasis. Immunity 13, 277–285. Borkowski, T. A., Jouvin, M. H., Lin, S. Y., and Kinet, J. P. (2001). Minimal requirements for IgE‐ mediated regulation of surface FceRI. J. Immunol. 167, 1290–1296. Brauweiler, A., Tamir, I., Dal Porto, J., Benschop, R. J., Helgason, C. D., Humphries, R. K., Freed, J. H., and Cambier, J. C. (2000). Differential regulation of B cell development, activation, and death by the src homology 2 domain‐containing 50 inositol phosphatase (SHIP). J. Exp. Med. 191, 1545–1554. Brdicka, T., Imrich, M., Angelisova, P., Brdickova, N., Horvath, O., Spicka, J., Hilgert, I., Luskova, P., Draber, P., Novak, P., Engels, N., Wienands, J., Simeoni, L., Osterreicher, J., Aguado, E., Malissen, M., Schraven, B., and Horejsi, V. (2002). Non‐T cell activation linker (NTAL): A transmembrane adaptor protein involved in immunoreceptor signaling. J. Exp. Med. 196, 1617–1626. Brooks, D. G., Qiu, W. Q., Luster, A. D., and Ravetch, J. V. (1989). Structure and expression of human IgG FcRII (CD32). Functional heterogeneity is encoded by the alternatively spliced products of multiple genes. J. Exp. Med. 170, 1369–1386. Brown, D. A., and London, E. (2000). Structure and Function of Sphingolipid‐ and Cholesterol‐ rich Membrane Rafts. J. Biol. Chem. 275, 17221–17224. Bruhns, P., Marchetti, P., Fridman, W. H., Vivier, E., and Dae¨ron, M. (1999). Differential roles of N‐ and C‐terminal ITIMs during inhibition of cell activation by killer cell inhibitory receptors. J. Immunol. 162, 3168–3175. Bruhns, P., Samuelsson, A., Pollard, J. W., and Ravetch, J. V. (2003). Colony‐stimulating factor‐1‐ dependent macrophages are responsible for IVIG protection in antibody‐induced autoimmune disease. Immunity 18, 573–581. Bruhns, P., Ve´ly, F., Malbec, O., Fridman, W. H., Vivier, E., and Dae¨ron, M. (2000). Molecular basis of the recruitment of the SH2 domain‐containing inositol 5‐phosphatases SHIP1 and SHIP2 by FcgRIIB. J. Biol. Chem. 275, 37357–37364. Bu, J. Y., Shaw, A. S., and Chan, A. C. (1995). Analysis of the interaction of ZAP‐70 and Syk protein‐tyrosine kinases with the T‐cell antigen receptor by plasmon resonance. P.NA.S. 92, 5106–5110. Buccione, R., Di Tullio, G., Caretta, M., Marinetti, M. R., Bizzarri, C., Francavilla, S., Luini, A., and De Matteis, M. A. (1994). Analysis of protein kinase C requirement for exocytosis in permeabilized rat basophilic leukaemia RBL‐2H3 cells: A GTP‐binding protein(s) as a potential target for protein kinase C. Biochem. J. 298(Pt 1), 149–156. Burns, C. M., Sakaguchi, K., Appella, E., and Ashwell, J. D. (1994). CD45 regulation of tyrosine phosphorylation and enzyme activity of src family kinases. J. Biol. Chem. 269, 13594–13600. Burshtyn, D. N., Lam, A. S., Weston, M., Gupta, N., Warmerdam, P. A., and Long, E. O. (1999). Conserved residues amino‐terminal of cytoplasmic tyrosines contribute to the SHP‐1‐mediated inhibitory function of killer cell Ig‐like receptors. J. Immunol. 162, 897–902. Burshtyn, D. N., Scharenberg, A. M., Wagtmann, N., Rajogopalan, S., Berrada, K., Yi, T., Kinet, J.‐P., and Long, E. O. (1996). Recruitment of tyrosine phosphatase HCP by the killer cell inhibitory receptor. Immunity 4, 77–85. Cantrell, D. (1998). Lymphocyte signalling: A coordinating role for Vav? Curr. Biol. 8, R535–R538. Cao, X., Wei, G., Fang, H., Guo, J., Weinstein, M., Marsh, C. B., Ostrowski, M. C., and Tridandapani, S. (2004). The inositol 3‐phosphatase PTEN negatively regulates Fc g receptor signaling, but supports Toll‐like receptor 4 signaling in murine peritoneal macrophages. J. Immunol. 172, 4851–4857. Carver, D. J., Aman, M. J., and Ravichandran, K. S. (2000). SHIP inhibits Akt activation in B cells through regulation of Akt membrane localization. Blood 96, 1449–1456.
76
M A R C D A E¨ R O N A N D R E N A U D L E S O U R N E
Chan, V. W., Meng, F., Soriano, P., De Franco, A. L., and Lowell, C. A. (1997). Characterization of the B lymphocyte populations in Lyn‐deficient mice and the role of Lyn in signal initiation and down‐regulation. Immunity 7, 69–81. Clynes, R., Takechi, Y., Moroi, Y., Houghton, A., and Ravetch, J. V. (1998). Fc receptors are required in passive and active immunity to melanoma. Proc. Natl. Acad. Sci. USA 95, 652–656. Cole, P. A., Shen, K., Qiao, Y., and Wang, D. (2003). Protein tyrosine kinases Src and Csk: A tail’s tale. Curr. Opin. Chem. Biol. 7, 580–585. Costello, P. S., Turner, M., Walters, A. E., Cunningham, C. N., Bauer, P., Downward, J., and Tybulewicz, V. L. J. (1996). Critical role for the tyrosine kinase Syk in signalling through the high affinity IgE receptor of mast cells. Oncogene 13, 2595–2605. D’Ambrosio, D., Hippen, K. H., Minskoff, S. A., Mellman, I., Pani, G., Siminovitch, K. A., and Cambier, J. C. (1995). Recruitment and activation of PTP1C in negative regulation of antigen receptor signaling by FcgRIIB1. Science 268, 293–296. Dae¨ron, M. (1997). Fc Receptor Biology. Annu. Rev. Immunol. 15, 203–234. Dae¨ron, M., Bonnerot, C., Latour, S., and Fridman, W. H. (1992). Murine recombinant FcgRIII, but not FcgRII, trigger serotonin release in rat basophilic leukemia cells. J. Immunol. 149, 1365–1373. Dae¨ron, M., Latour, S., Malbec, O., Espinosa, E., Pina, P., Pasmans, S., and Fridman, W. H. (1995a). The same tyrosine‐based inhibition motif, in the intracytoplasmic domain of FcgRIIB, regulates negatively BCR‐, TCR‐, and FcR‐dependent cell activation. Immunity 3, 635–646. Dae¨ron, M., Malbec, O., Latour, S., Arock, M., and Fridman, W. H. (1995b). Regulation of high‐ affinity IgE receptor‐mediated mast cell activation by murine low‐affinity IgG receptors. J. Clin. Invest. 95, 577–585. Damen, J. E., Liu, L., Rosten, P., Humphries, R. K., Jefferson, A. B., Majerus, P. W., and Krystal, G. (1996). The 145‐kDa protein induced to associate with Shc by multiple cytokines is an inositol tetraphosphate and phosphatidylinositol 3,4,5‐trisphosphate 5‐phosphatase. Proc. Natl. Acad. Sci. USA 93, 1689–1693. Delisi, C., and Siraganian, R. P. (1979). Receptor cross‐linking and histamine release. II. Interpretation and analysis of anomalous dose‐response patterns. J. Immunol. 122, 2293–2299. Dembo, M., Goldstein, B., Sobotka, A., and Lichtenstein, L. (1978). Histamine release due to bivalent penicilloyl haptens: Control by the number of crosslinked IgE antibodies on the basophil plasma membrane. J. Immunol. 121, 354–358. Deusch, K., Pfeffer, K., Reich, K., Gstettenbauer, M., Daum, S., Luling, F., and Classen, M. (1991). Phenotypic and functional characterization of human TCR g dþ intestinal intraepithelial lymphocytes. Curr. Top. Microbiol. Immunol. 173, 279–283. Dhanji, S., Tse, K., and Teh, H. S. (2005). The low affinity Fc receptor for IgG functions as an effective cytolytic receptor for self‐specific CD8 T cells. J. Immunol. 174, 1253–1258. Dombrowicz, D., Lin, S., Flamand, V., Brini, A. T., Koller, B. H., and Kinet, J. P. (1998). Allergy‐ associated FcRb is a molecular amplifier of IgE‐ and IgG‐mediated in vivo responses. Immunity 8, 517–529. Dong, C., Davis, R. J., and Flavell, R. A. (2002). MAP kinases in the immune response. Annu. Rev. Immunol. 20, 55–72. Donnadieu, E., Jouvin, M. H., Rana, S., Moffatt, M. F., Mockford, E. H., Cookson, W. O., and Kinet, J. P. (2003). Competing functions encoded in the allergy‐associated FceRIb gene. Immunity 18, 665–674. Downward, J. (1996). Control of ras activation. Cancer Surv. 27, 87–100. Drechsler, Y., Chavan, S., Catalano, D., Mandrekar, P., and Szabo, G. (2002). FcgR cross‐linking mediates NF‐kappaB activation, reduced antigen presentation capacity, and decreased IL‐12 production in monocytes without modulation of myeloid dendritic cell development. J. Leukoc. Biol. 72, 657–667.
N E G AT I V E S I G N A L I N G I N F C R E C E P T O R C O M P L E X E S
77
Duque, N., Gomez‐Guerrero, C., and Egido, J. (1997). Interaction of IgA with Fc a receptors of human mesangial cells activates transcription factor nuclear factor‐kappa B and induces expression and synthesis of monocyte chemoattractant protein‐1, IL‐8, and IFN‐inducible protein 10. J. Immunol. 159, 3474–3482. Dyson, J. M., Munday, A. D., Kong, A. M., Huysmans, R. D., Matzaris, M., Layton, M. J., Nandurkar, H. H., Berndt, M. C., and Mitchell, C. A. (2003). SHIP‐2 forms tetrameric complex with filamin, actin, and GPIb‐IX‐V: Localization of SHIP‐2 to the activated platelet actin cytoskeleton. Blood 102, 940–948. Dyson, J. M., O’ Malley, C. J., Becanovic, J., Munday, A. D., Berndt, M. C., Coghill, I. D., Nandurkar, H. H., Ooms, L. M., and Mitchell, C. A. (2001). The SH2‐containing inositol polyphosphate 5‐phosphatase, SHIP‐2, binds filamin and regulates submembraneous actin. J. Cell Biol. 155, 1065–1079. Field, K. A., Holowka, D., and Baird, B. (1997). Compartmentalized Activation of the High Affinity Immunoglobulin E Receptor within Membrane Domains. J. Biol. Chem. 272, 4276–4280. Fong, D. C., Brauweiler, A., Minskoff, S. A., Bruhns, P., Tamir, I., Mellman, I., Dae¨ron, M., and Cambier, J. C. (2000). Mutational analysis reveals multiple distinct sites within Fcg receptor IIb that function in inhibitory signaling. J. Immunol. 165, 4453–4462. Fong, D. C., Malbec, O., Arock, M., Cambier, J. C., Fridman, W. H., and Dae¨ron, M. (1996). Selective in vivo recruitment of the phosphatidylinositol phosphatase SHIP by phosphorylated FcgRIIB during negative regulation of IgE‐dependent mouse mast cell activation. Immunol. Lett. 54, 83–91. Frigeri, L., and Apgar, J. R. (1999). The role of actin microfilaments in the down‐regulation of the degranulation response in RBL‐2H3 mast cells. J. Immunol. 162, 2243–2250. Furumoto, Y., Nunomura, S., Terada, T., Rivera, J., and Ra, C. (2004). The FceRIb immunoreceptor tyrosine‐based activation motif exerts inhibitory control on MAPK and IkappaB kinase phosphorylation and mast cell cytokine production. J. Biol. Chem. 279, 49177–49187. Galandrini, R., Tassi, I., Mattia, G., Lenti, L., Piccoli, M., Frati, L., and Santoni, A. (2002). SH2‐ containing inositol phosphatase (SHIP‐1) transiently translocates to raft domains and modulates CD16‐mediated cytotoxicity in human NK cells. Blood 100, 4581–4589. Ganesan, L. P., Fang, H., Marsh, C. B., and Tridandapani, S. (2003). The protein‐tyrosine phosphatase SHP‐1 associates with the phosphorylated immunoreceptor tyrosine‐based activation motif of FcgRIIa to modulate signaling events in myeloid cells. J. Biol. Chem. 278, 35710–35717. Ganesan, L. P., Wei, G., Pengal, R. A., Moldovan, L., Moldovan, N., Ostrowski, M. C., and Tridandapani, S. (2004). The serine/threonine kinase Akt Promotes Fc g receptor‐mediated phagocytosis in murine macrophages through the activation of p70S6 kinase. J. Biol. Chem. 279, 54416–54425. Giallourakis, C., Kashiwada, M., Pan, P. Y., Danial, N., Jiang, H., Cambier, J., Coggeshall, K. M., and Rothman, P. (2000). Positive regulation of interleukin‐4‐mediated proliferation by the SH2‐ containing inositol‐50 ‐phosphatase. J. Biol. Chem. 275, 29275–29282. Gimborn, K., Lessmann, E., Kuppig, S., Krystal, G., and Huber, M. (2005). SHIP down‐regulates FceRI‐induced degranulation at supraoptimal IgE or antigen levels. J. Immunol. 174, 507–516. Gonzalez‐Espinosa, C., Odom, S., Olivera, A., Hobson, J. P., Martinez, M. E., Oliveira‐Dos‐Santos, A., Barra, L., Spiegel, S., Penninger, J. M., and Rivera, J. (2003). Preferential signaling and induction of allergy‐promoting lymphokines upon weak stimulation of the high affinity IgE receptor on mast cells. J. Exp. Med. 197, 1453–1465. Gu, H., Saito, K., Klaman, L. D., Shen, J., Fleming, T., Wang, Y., Pratt, J. C., Lin, G., Lim, B., Kinet, J. P., and Neel, B. G. (2001). Essential role for Gab2 in the allergic response. Nature 412, 186–190.
78
M A R C D A E¨ R O N A N D R E N A U D L E S O U R N E
Hazenbos, L. W., Gessner, J. E., Hofhuis, F. M. A., Kuipers, H., Meyer, D., Heijnen, I. A. F. M., Schmidt, R. E., Sandor, M., Capel, P. J. A., Dae¨ron, M., van de Winkel, J. G. J., and Verbeek, J. S. (1996). Impaired IgG‐dependent anaphylaxis and Arthus reaction in FcgRIII (CD16) deficient mice. Immunity 5, 181–188. Helgason, C. D., Damen, J. E., Rosten, P., Grewal, R., Sorensen, P., Chappel, S. M., Borowski, A., Jirik, F., Krystal, G., and Humphries, R. K. (1998). Targeted disruption of SHIP leads to hemopoietic perturbations, lung pathology, and shortened life span. Genes Dev. 12, 1610–1620. Hendricks‐Taylor, L. R., Motto, D. G., Zhang, J., Siraganian, R. P., and Koretzky, G. A. (1997). SLP‐76 is a substrate of the high affinity IgE receptor‐stimulated protein tyrosine kinases in rat basophilic leukemia cells. J. Biol. Chem. 272, 1363–1367. Hernandez‐Hansen, V., Mackay, G. A., Lowell, C. A., Wilson, B. S., and Oliver, J. M. (2004). The Src kinase Lyn is a negative regulator of mast cell proliferation. J. Leukoc. Biol. 75, 143–151. Herr, A. B., Ballister, E. R., and Bjorkman, P. J. (2003). Insights into IgA‐mediated immune responses from the crystal structures of human FcaRI and its complex with IgA1‐Fc. Nature 423, 614–620. Hibbs, M. L., Bonadonna, L., Scott, B. M., McKenzie, I. F. C., and Hogarth, P. M. (1988). Molecular cloning of a human immunoglobulin G Fc receptor. Proc. Natl. Acad. Sci. USA 85, 2240–2244. Hibbs, M. L., Harder, K. W., Armes, J., Kountouri, N., Quilici, C., Casagranda, F., Dunn, A. R., and Tarlinton, D. M. (2002). Sustained activation of Lyn tyrosine kinase in vivo leads to autoimmunity. J. Exp. Med. 196, 1593–1604. Hibbs, M. L., Walker, I. D., Kirszbaum, L., Pietersz, G. A., Deacon, N. J., Chambers, G. W., McKenzie, I. F. C., and Hogarth, P. M. (1986). The murine Fc receptor for immunoglobulin: Purification, partial amino acid sequence, and isolation of cDNA clones. Proc. Natl. Acad. Sci. USA 83, 6980–6984. Horejsi, V. (2003). The roles of membrane microdomains (rafts) in T cell activation. Immunol. Rev. 191, 148–164. Hsu, C., and Mac Glashan, D. J. (1996). IgE antibody up‐regulates high affinity IgE binding on murine bone marrow‐derived mast cells. Immunol. Letters 52, 129–134. Huber, M., Helgason, C. D., Damen, J. E., Liu, L., Humphries, R. K., and Krystal, G. (1998). The src homology 2‐containing inositol phosphatase (SHIP) is the gatekeeper of mast cell degranulation. Proc. Natl. Acad. Sci. USA 95, 11330–11335. Hulett, M. D., and Hogarth, P. M. (1994). Molecular basis of Fc Receptor function. Adv. Immunol. 57, 1–127. Humphries, L. A., Dangelmaier, C., Sommer, K., Kipp, K., Kato, R. M., Griffith, N., Bakman, I., Turk, C. W., Daniel, J. L., and Rawlings, D. J. (2004). Tec kinases mediate sustained calcium influx via site‐specific tyrosine phosphorylation of the phospholipase Cg Src homology 2‐Src homology 3 linker. J. Biol. Chem. 279, 37651–37661. Ishizaka, K., Tomioka, H., and Ishizaka, T. (1970). Mechanism of passive sensitization. I. Presence of IgE and IgG molecules on human leukocytes. J. Immunol. 105, 1459–1467. Isnardi, I., Lesourne, R., Bruhns, P., Fridman, W. H., Cambier, J. C., and Dae¨ron, M. (2004). Two distinct tyrosine‐based motifs enable the inhibitory receptor FcgRIIB to cooperatively recruit the inositol phosphatases SHIP1/2 and the adapters Grb2/Grap. J. Biol. Chem. 279, 51931–51938. Jackman, J. K., Motto, D. G., Sun, Q., Tanemoto, M., Turck, C. W., Peltz, G. A., Koretzky, G. A., and Findell, P. R. (1995). Molecular cloning of SLP‐76, a 76‐kDa tyrosine phosphoprotein associated with Grb2 in T cells. J. Biol. Chem. 270, 7029–7032. Jacob, A., Cooney, D., Tridandapani, S., Kelley, T., and Coggeshall, K. M. (1999). FcgRIIb modulation of surface immunoglobulin‐induced Akt activation in murine B cells. J. Biol. Chem. 274, 13704–13710.
N E G AT I V E S I G N A L I N G I N F C R E C E P T O R C O M P L E X E S
79
Janas, M. L., Hodgkin, P., Hibbs, M., and Tarlinton, D. (1999). Genetic evidence for Lyn as a negative regulator of IL‐4 signaling. J. Immunol. 163, 4192–4198. Janssen, E., Zhu, M., Craven, B., and Zhang, W. (2004). Linker for activation of B cells: A functional equivalent of a mutant linker for activation of T cells deficient in phospholipase C‐g 1 binding. J. Immunol. 172, 6810–6819. Janssen, E., Zhu, M., Zhang, W., Koopnaw, S., and Zhang, W. (2003). LAB: A new membrane‐ associated adaptor molecule in B cell activation. Nature Immunol. 4, 117–123. Johannes, F. J., Horn, J., Link, G., Haas, E., Siemienski, K., Wajant, H., and Pfizenmaier, K. (1998). Protein kinase Cmu downregulation of tumor‐necrosis‐factor‐induced apoptosis correlates with enhanced expression of nuclear‐factor‐kappaB‐dependent protective genes. Eur. J. Biochem. 257, 47–54. Jouvin, M. H., Adamczewski, M., Numerof, R., Letourneur, O., Valle´, A., and Kinet, J. P. (1994). Differential control of the tyrosine kinases Lyn and Syk by the two signaling chains of the high affinity immunoglobulin E receptor. J. Biol. Chem. 269, 5918–5925. Kalesnikoff, J., Huber, M., Lam, V., Damen, J. E., Zhang, J., Siraganian, R. P., and Krystal, G. (2001). Monomeric IgE stimulates signaling pathways in mast cells that lead to cytokine production and cell survival. Immunity 14, 801–811. Kawakami, T., and Galli, S. J. (2002). Regulation of mast‐cell and basophil function and survival by IgE. Nat. Rev. Immunol. 2, 773–786. Kawakami, Y., Hartman, S. E., Holland, P. M., Cooper, J. A., and Kawakami, T. (1998). Multiple signaling pathways for the activation of JNK in mast cells: Involvement of Bruton’s tyrosine kinase, protein kinase C, and JNK kinases, SEK1 and MKK7. J. Immunol. 161, 1795–1802. Kawakami, Y., Kitaura, J., Satterthwaite, A. B., Kato, R. M., Asai, K., Hartman, S. E., Maeda‐ Yamamoto, M., Lowell, C. A., Rawlings, D. J., Witte, O. N., and Kawakami, T. (2000). Redundant and opposing functions of two tyrosine kinases, Btk and Lyn, in mast cell activation. J. Immunol. 165, 1210–1219. Kettner, A., Pivniouk, V., Kumar, L., Falet, H., Lee, J. S., Mulligan, R., and Geha, R. S. (2003). Structural requirements of SLP‐76 in signaling via the high‐affinity immunoglobulin E receptor (FceRI) in mast cells. Mol. Cell. Biol. 23, 2395–2406. Kihara, H., and Siraganian, R. P. (1994). Src homology 2 domains of Syk and Lyn bind to tyrosine‐ phosphorylated subunits of the high affinity IgE receptor. J. Biol. Chem. 269, 22427–22432. Kimura, T., Sakamoto, H., Apellea, E., and Siraganian, R. P. (1996). Conformational changes induced in the protein tyrosine kinase p72Syk by tyrosine phosphorylation or by binding of phosphorylatedimmunoreceptor tyrosine‐based activation motif peptides. Mol. Cell. Biol. 4, 1471–1478. Kimura, T., Sakamoto, H., Appella, E., and Siraganian, R. P. (1997). The negative signaling molecule SH2 domain‐containing inositol‐polyphosphate 5‐phosphatase (SHIP) binds to the tyrosine‐phosphorylated b subunit of the high affinity IgE receptor. J. Biol. Chem. 272, 13991–13996. Kitaura, J., Eto, K., Kinoshita, T., Kawakami, Y., Leitges, M., Lowell, C. A., and Kawakami, T. (2005). Regulation of Highly Cytokinergic IgE‐Induced Mast Cell Adhesion by Src, Syk, Tec, and Protein Kinase C Family Kinases. J. Immunol. 174, 4495–4504. Kleinau, S., Martinsson, P., and Heyman, B. (2000). Induction and suppression of collagen‐ induced arthritis is dependent on distinct fcg receptors. J. Exp. Med. 191, 1611–1616. Kliche, S., Lindquist, J. A., and Schraven, B. (2004). Transmembrane adapters: Structure, biochemistry and biology. Semin. Immunol. 16, 367–377. Kohno, M., Yamasaki, S., Tybulewicz, V. L., and Saito, T. (2005). Rapid and large amount of autocrine IL‐3 production is responsible for mast cell survival by IgE in the absence of antigen. Blood 105, 2059–2065.
80
M A R C D A E¨ R O N A N D R E N A U D L E S O U R N E
Kono, H., Suzuki, T., Yamamoto, K., Okada, M., Yamamoto, T., and Honda, Z. (2002). Spatial raft coalescence represents an initial step in FcgR signaling. J. Immunol. 169, 193–203. Koonpaew, S., Janssen, E., Zhu, M., and Zhang, W. (2004). The importance of three membrane‐ distal tyrosines in the adaptor protein NTAL/LAB. J. Biol. Chem. 279, 11229–11235. Kovarova, M., Tolar, P., Arudchandran, R., Draberova, L., Rivera, J., and Draber, P. (2001). Structure‐function analysis of Lyn kinase association with lipid rafts and initiation of early signaling events after Fce receptor I aggregation. Mol. Cell. Biol. 21, 8318–8328. Kraft, S., Novak, N., Katoh, N., Bieber, T., and Rupec, R. A. (2002). Aggregation of the high‐affinity IgE receptor FceRI on human monocytes and dendritic cells induces NF‐kB activation. J. Invest. Dermatol. 118, 830–837. Kurosaki, T., Johnson, S. A., Pao, L., Sada, K., Yamamura, H., and Cambier, J. C. (1995). Role of the Syk autophosphorylation site and SH2 domains in B cell antigen receptor signaling. J. Exp. Med. 182, 1815–1823. Kyo, S., Sada, K., Qu, X., Maeno, K., Miah, S. M., Kawauchi‐Kamata, K., and Yamamura, H. (2003). Negative regulation of Lyn protein‐tyrosine kinase by c‐Cbl ubiquitin‐protein ligase in FceRI‐mediated mast cell activation. Genes Cells 8, 825–836. Latour, S., Fridman, W. H., and Dae¨ron, M. (1996). Identification, molecular cloning, biological properties and tissue distribution of a novel isoform of murine low‐affinity IgG receptor homologous to human FcgRIIB1. J. Immunol. 157, 189–197. Lesourne, R., Bruhns, P., Fridman, W. H., and Dae¨ron, M. (2001). Insufficient Phosphorylation prevents FcgRIIB from recruiting the SH2 Domain‐Containing Protein Tyrosine Phosphatase SHP‐1. J. Biol. Chem. 6327–6336. Lesourne, R., Fridman, W. H., and Dae¨ron, M. (2005). Dynamic interactions of FcgRIIB with filamn‐bound SHIP1 amplify filamentous actin‐dependent negative regulation of FceRI signaling. J. Immunol. 174, 1365–1373. Lewis, V. A., Koch, T., Plutner, H., and Mellman, I. (1986). A complementary DNA clone for a macrophage‐lymphocyte Fc receptor. Nature 324, 372. Liang, X., Wisniewski, D., Strife, A., Shivakrupa, Clarkson, B., and Resh, M. D. (2002). Phosphatidylinositol 3‐kinase and Src family kinases are required for phosphorylation and membrane recruitment of Dok‐1 in c‐Kit signaling. J. Biol. Chem. 277, 13732–13738. Lin, S., Cicala, C., Scharenberg, A. M., and Kinet, J.‐P. (1996). The FceRIb subunit functions as an amplifier of FceRIg‐mediated cell activation signals. Cell 85, 985–995. Long, E. O. (1999). Regulation of immune responses through inhibitory receptors. Annu. Rev. Immunol. 17, 875–904. Luna, E. J., and Hitt, A. L. (1992). Cytoskeleton–plasma membrane interactions. Science 258, 955–964. Mac Glashan, D. W., Bochner, B. S., Adelman, D. C., Jardieu, P., Togias, A., and Lichtenstein, L. M. (1997). Serum IgE levels drives basophil and mast cell IgE receptor display. Int. Arch. Allergy Immunol. 113, 45–47. Magro, A. M., and Alexander, A. (1974). Histamine release: In vitro studies of the inhibitory region of the dose‐response curve. J. Immunol. 112, 1762–1765. Malbec, O., Fong, D., Turner, M., Tybulewicz, V. L. J., Cambier, J., C., Fridman, W. H., and Dae¨ron, M. (1998). FceRI‐associated lyn‐dependent phosphorylation of FcgRIIB during negative regulation of mast cell activation. J. Immunol. 160, 1647–1658. Malbec, O., Fridman, W. H., and Dae¨ron, M. (1999). Negative regulation of c‐kit‐mediated cell proliferation by FcgRIIB. J. Immunol. 162, 4424–4429. Malbec, O., Malissen, M., Isnardi, I., Lesourne, R., Mura, A.‐M., Fridman, W. H., Malissen, B., and Dae¨ron, M. (2004). Linker for activation of T cells integrates positive and negative signaling in mast cells. J. Immunol. 173, 5086–5094.
N E G AT I V E S I G N A L I N G I N F C R E C E P T O R C O M P L E X E S
81
Malbec, O., Schmitt, C., Bruhns, P., Krystal, G., Fridman, W. H., and Dae¨ron, M. (2001). The SH2 domain‐containing Inositol 5‐Phosphatase SHIP1 mediates cell cycle arrest by FcgRIIB. J. Biol. Chem. 276, 30381–30391. Marquardt, D. L., and Walker, L. L. (2000). Dependence of mast cell IgE‐mediated cytokine production on nuclear factor‐kappaB activity. J. Allergy. Clin. Immunol. 105, 500–505. Martindale, D. W., Wilson, M. D., Wang, D., Burke, R. D., Chen, X., Duronio, V., and Koop, B. F. (2000). Comparative genomic sequence analysis of the Williams syndrome region (LIMK1‐ RFC2) of human chromosome 7q11.23. Mamm. Genome. 11, 890–898. Maurer, D., Fiegiger, E., Reininger, B., Wolffwiniski, B., Jouvin, M.‐H., Kilgus, O., Kinet, J.‐P., and Stingl, G. (1994). Expression of a functional high affinity immunoglobulin E receptor (FceRI) on monocytes of atopic individuals. J. Exp. Med. 179, 745–750. Metzger, H., Alcaraz, G., Hohman, R., Kinet, J. P., Pribluda, V., and Quarto, R. (1986). The receptor with high affinity for immunoglobulin E. Annu. Rev. Immunol. 4, 419–470. Minoo, P., Zadeh, M. M., Rottapel, R., Lebrun, J. J., and Ali, S. (2004). A novel SHP‐1/Grb2‐ dependent mechanism of negative regulation of cytokine‐receptor signaling: Contribution of SHP‐1 C‐terminal tyrosines in cytokine signaling. Blood 103, 1398–1407. Monteiro, R. C., and Van De Winkel, J. G. (2003). IgA Fc receptors. Annu. Rev. Immunol. 21, 177–204. Muraille, E., Bruhns, P., Pesesse, X., Dae¨ron, M., and Erneux, C. (2000). The SH2 domain containing inositol 5‐phosphatase SHIP2 associates to the immunoreceptor tyrosine‐based inhibition motif of FcgRIIB in B cells under negative signalling. Immunol. Letters 72, 7–15. Muta, T., Kurosaki, T., Misulovin, Z., Sanchez, M., Nussenzweig, M. C., and Ravetch, J. V. (1994). A 13‐amino‐acid motif in the cytoplasmic domain of FcgRIIB modulates B‐cell receptor signalling. Nature 368, 70–73. Nakamura, K., Malykhin, A., and Coggeshall, K. M. (2002). The Src homology 2 domain‐ containing inositol 5‐phosphatase negatively regulates Fcg receptor‐mediated phagocytosis through immunoreceptor tyrosine‐based activation motif‐bearing phagocytic receptors. Blood 100, 3374–3382. Nishizumi, H., and Yamamoto, T. (1997). Impaired tyrosine phosphorylation and Ca2þ mobilization, but not degranulation, in lyn‐deficient bone marrow‐derived mast cells. J. Immunol. 158, 2350–2355. Nun˜ez‐Cruz, S., Aguado, E., Richelme, S., Chetaille, B., Mura, A.‐M., Richelme, M., Pouyet, L., Jouvin‐Marche, E., Xerri, L., Malissen, B., and Malissen, M. (2003). LAT regulates gd T cell homeostasis and differentiation. Nature Immunol. 4, 999–1008. Odom, S., Gomez, G., Kovarova, M., Furumoto, Y., Ryan, J. J., Wright, H. V., Gonzalez‐Espinosa, C., Hibbs, M. L., Harder, K. W., and Rivera, J. (2004). Negative regulation of immunoglobulin E‐dependent allergic responses by Lyn kinase. J. Exp. Med. 199, 1491–1502. Okada, M., Nada, S., Yamanashi, Y., Yamamoto, T., and Nakagawa, H. (1991). CSK: A protein‐ tyrosine kinase involved in regulation of src family kinases. J. Biol. Chem. 266, 24249–24252. Ono, M., Bolland, S., Tempst, P., and Ravetch, J. V. (1996). Role of the inositol phosphatase SHIP in negative regulation of the immune system by the receptor FcgRIIB. Nature 383, 263–266. Ono, M., Okada, H., Bolland, S., Yanagi, S., Kurosaki, T., and Ravetch, J. V. (1997). Deletion of SHIP or SHP‐1 reveals two distinct pathways for inhibitory signaling. Cell 90, 293–301. Osborne, M. A., Zenner, G., Lubinus, M., Zhang, X., Songyang, Z., Cantley, L. C., Majerus, P., Burn, P., and Kochan, J. P. (1996). The inositol 50 ‐phosphatase SHIP binds to immunoreceptor signaling motifs and responds to high affinity IgE receptor aggregation. J. Biol. Chem. 271, 29271–29278. Ott, V. L., Tamir, I., Niki, M., Pandolfi, P. P., and Cambier, J. C. (2002). Downstream of kinase, p62 (dok), is a mediator of FcgIIB inhibition of FceRI signaling. J. Immunol. 168, 4430–4439.
82
M A R C D A E¨ R O N A N D R E N A U D L E S O U R N E
Pandey, V., Mihara, S., Fensome‐Green, A., Bolsover, S., and Cockcroft, S. (2004). Monomeric IgE stimulates NFAT translocation into the nucleus, a rise in cytosol Ca2þ, degranulation, and membrane ruffling in the cultured rat basophilic leukemia‐2H3 mast cell line. J. Immunol. 172, 4048–4058. Pani, G., Kozlowski, M., Cambier, J. C., Mills, G. B., and Siminovitch, K. A. (1995). Identification of the tyrosine phosphatase PTP1C as a B cell antigen receptor‐associated protein involved in the regulation of B cell signaling. J. Exp. Med. 181, 2077–2084. Paolini, R., Molfetta, R., Piccoli, M., Frati, L., and Santoni, A. (2001). Ubiquitination and degradation of Syk and ZAP‐70 protein tyrosine kinases in human NK cells upon CD16 engagement. Proc. Natl. Acad. Sci. USA 98, 9611–6916. Parravincini, V., Gadina, M., Kovarova, M., Odom, S., Gonzalez‐Espinosa, C., Furumoto, Y., Saitoh, S., Samelson, L. E., O’ Shea, J. J., and Rivera, J. (2002). Fyn kinase initiates complementary signals required for IgE‐dependent mast cell degranulation. Nature Immunol. 3, 741–748. Pasquier, B., Launay, P., Kanamaru, Y., Moura, I. C., Pfirsch, S., Ruffie, C., Henin, D., Benhamou, M., Pretolani, M., Blank, U., and Monteiro, R. C. (2005). Identification of FcaRI as an inhibitory receptor that controls inflammation: Dual role of FcRg ITAM. Immunity 22, 31–42. Patry, C., Herblin, A., Lehven, A., Bach, J.‐F., and Monteiro, R. C. (1995). Fca receptors mediate release of tumour necrosis factor‐a and interleukine 6 by human monocytes following receptor aggregation. Immunology 86, 1–5. Pengal, R. A., Ganesan, L. P., Fang, H., Marsh, C. B., Anderson, C. L., and Tridandapani, S. (2003). SHIP‐2 inositol phosphatase is inducibly expressed in human monocytes and serves to regulate Fcg receptor‐mediated signaling. J. Biol. Chem. 278, 22657–22663. Perussia, B., Tutt, M. M., Qui, W. Q., Kuziel, W. A., Tucker, P. W., Trinchieri, G., Bennett, M., Ravetch, J. V., and Kumar, V. (1989). Murine natural killer cells express functional Fcg receptor II encoded by the FcgRa gene. J. Exp. Med. 170, 73–86. Phee, H., Jacob, A., and Coggeshall, K. M. (2000). Enzymatic activity of the Src homology 2 domain‐containing inositol phosphatase is regulated by a plasma membrane location. J. Biol. Chem. 275, 19090–19097. Pivniouk, V. I., Martin, T. R., Lu‐Kuo, J. M., Katz, H. R., Oettgen, H. C., and Geha, R. S. (1999). SLP‐76 deficiency impairs signaling via the high‐affinity IgE receptor in mast cells. J Clin Invest 103, 1737–1743. Pralle, A., Keller, P., Florin, E. L., Simons, K., and Horber, J. K. (2000). Sphingolipid‐ cholesterol rafts diffuse as small entities in the plasma membrane of mammalian cells. J. Cell Biol. 148, 997–1008. Pribluda, V. S., Pribluda, C., and Metzger, H. (1994). Transphosphorylation as the mechanism by which the high affinity receptor for IgE is phosphorylated upon aggregation. Proc. Nat. Acad. Sci. USA 91, 11246–11250. Pribluda, V. S., Pribluda, C., and Metzger, H. (1997). Biochemical evidence that the phosphorylated tyrosines, serines, and threonines on the aggregated high affinity receptor for IgE are in the immunoreceptor tyrosine‐based activation motifs. J. Biol. Chem. 272, 11185–11192. Prouvost‐Danon, A., and Binaghi, R. (1970). In vitro sensitization of mouse peritoneal mast cells with reaginic antibody. Nature 228, 66–68. Prouvost‐Danon, A., Queiroz‐Javierre, M., and Silva‐Lima, M. (1966). Passive anaphylactic reaction in mouse peritoneal mast cells in vitro. Life Sci. 5, 1751. Ravetch, J. V., and Bolland, S. (2001). IgG Fc receptors. Annu. Rev. Immunol. 19, 275–290. Ravetch, J. V., and Kinet, J. P. (1991). Fc Receptors. Annu. Rev. Immunol. 9, 457–492. Ravetch, J. V., Luster, A. D., Weinshank, R., Kochan, J., Pavlovec, A., Portnoy, D. A., Hulmes, J., Pan, Y. C. E., and Unkeless, J. C. (1986). Structural heterogeneity and functional domains of murine Immunoglobulin G Fc receptors. Science 234, 718–725.
N E G AT I V E S I G N A L I N G I N F C R E C E P T O R C O M P L E X E S
83
Reth, M. G. (1989). Antigen receptor tail clue. Nature 338, 383–384. Rivera, J. (2005). NTAL/LAB and LAT: A balancing act in mast‐cell activation and function. Trends Immunol 26, 119–122. Russell, M. W., Sibley, D. A., Nikolova, E. B., Tomana, M., and Mestecky, J. (1997). IgA antibody as a non‐inflammatory regulator of immunity. Biochem. Soc. Trans. 25, 466–470. Saitoh, S., Arudchandran, R., Manetz, T. S., Zhang, W., Sommers, C. L., Paul, E. Love, Rivera, J., and E., S. L. (2000). LAT is essential for FceRI‐mediated mast cell activation. Immunity 12, 525–535. Saitoh, S.‐I., Odom, S., Gomez, G., Sommers, C. L., Young, H. A., Rivera, J., and Samelson, L. E. (2003). The Four Distal Tyrosines Are Required for LAT‐dependent Signaling in FceRI‐ mediated Mast Cell Activation. J. Exp. Med. 198, 831–843. Samuelsson, A., Towers, T. L., and Ravetch, J. V. (2001). Anti‐inflammatory activity of IVIG mediated through the inhibitory Fc receptor. Science 291, 484–486. Sandor, M., Houlden, B., Bluestone, J., Hedrick, S. M., Weinstock, J., and Lynch, R. G. (1992). In vitro and in vivo activation of murine g/d T cells induces the expression of IgA, IgM, and IgG Fc receptors. J. Immunol. 148, 2363–2369. Sandor, M., and Lynch, R. G. (1992). Lymphocyte Fc receptors: The special case of T cells. Immunol. Today 14, 227–231. Schaffer, F. M., Monteiro, R. C., Volanakis, J. E., and Cooper, M. D. (1991). IgA deficiency. Immunodefic. Rev. 3, 15–44. Scharenberg, A. M., El‐Hillal, O., Fruman, D. A., Beitz, L. O., Li, Z., Lin, S., Gout, I., Cantley, L. C., Rawlings, D. J., and Kinet, J.‐P. (1998). Phosphatidylinositol‐3,4,5‐triphosphate (PtdIns‐ 3,4,5‐P3)/Tec kinase‐dependent calcium signaling pathway: A target for SHIP‐mediated inhibitory signals. EMBO J. 17, 1961–1972. Scharenberg, A. M., and Kinet, J. P. (1998). PtdIns‐3,4,5‐P3: A regulatory nexus between tyrosine kinases and sustained calcium signals. Cell 94, 5–8. Scharenberg, A. M., Lin, S., Cue´nod, B., Yamamura, H., and Kinet, J.‐P. (1995). Reconstitution of interactions between tyrosine kinases and the high affinity IgE receptor which are controlled by receptor clustering. EMBO J. 14, 3385–3394. Schraven, B., Marie‐Cardine, A., Hubener, C., Bruyns, E., and Ding, I. (1999). Integration of receptor‐mediated signals in T cells by transmembrane adaptor proteins. Immunol. Today 20, 431–434. Segal, D. M., Taurog, J. D., and Metzger, H. (1977). Dimeric immunoglobulin E serves as a unit signal for mast cell degranulation. Proc. Natl. Acad. Sci. USA 74, 2993–2997. Sheets, E. D., Holowka, D., and Baird, B. (1999). Critical role for cholesterol in Lyn‐mediated tyrosine phosphorylation of FceRI and their association with detergent‐resistant membranes. J. Cell Biol. 145, 877–887. Siraganian, R. P., Hook, W. A., and Levine, B. B. (1975). Specific in vitro histamine release from basophils by bivalent haptens: Evidence for activation by simple bridging of membrane‐bound antibodies. Immunochemistry 12, 149–155. Sommers, C. L., Park, C. S., Lee, J., Feng, C., Fuller, C. L., Grimberg, A., Hildebrand, J. A., Lacana, E., Menon, R. K., Shores, E. W., Samelson, L. E., and Love, P. E. (2002). A LAT mutation that inhibits T cell development yet induces lymphoproliferation. Science 296, 2040–2043. Sommers, C. L., Samelson, L. E., and Love, P. E. (2004). LAT: A T lymphocyte adapter protein that couples the antigen receptor to downstream signaling pathways. Bioessays 26, 61–67. Stankunas, K., Graef, I. A., Neilson, J. R., Park, S. H., and Crabtree, G. R. (1999). Signaling through calcium, calcineurin, and NF‐AT in lymphocyte activation and development. Cold Spring Harb. Symp. Quant. Biol. 64, 505–516.
84
M A R C D A E¨ R O N A N D R E N A U D L E S O U R N E
Stork, B., Engelke, M., Frey, J., Horejsi, V., Hamm‐Baarke, A., Schraven, B., Kurosaki, T., and Wienands, J. (2004). Grb2 and the non‐T cell activation linker NTAL constitute a Ca2þ‐ regulating signal circuit in B lymphocytes. Immunity 21, 681–691. Swann, P. G., Odom, S., Zhou, Y. J., Szallasi, Z., Blumberg, P. M., Draber, P., and Rivera, J. (1999). Requirement for a negative charge at threonine 60 of the FcRg for complete activation of Syk. J. Biol. Chem. 274, 23068–23077. Swieter, M., Berenstein, E. H., and Siraganian, R. P. (1995). Protein tyrosine phosphatase activity associates with the high affinity IgE receptor and dephosphorylates the receptor subunits, but not Lyn or Syk. J. Immunol. 155, 5330–5336. Takai, T., Ono, M., Hikida, M., Ohmori, H., and Ravetch, J. V. (1996). Augmented humoral and anaphylactic responses in FcgRII‐deficient mice. Nature 379, 346–349. Tam, S. W., Demissie, S., Thomas, D., and Dae¨ron, M. (2004). A bispecific antibody against human IgE and human FcgRII that inhibits antigen‐induced histamine release by human mast cells and basophils. Allergy 59, 772–780. Tamir, I., Stolpa, J. C., Helgason, C. D., Nakamura, K., Bruhns, P., Dae¨ron, M., and Cambier, J. C. (2000). The RasGAP‐binding protein p62dok is a Mediator of Inhibitory FcgRIIB Signals in B cells. Immunity 12, 347–358. Tanaka, S., Mikura, S., Hashimoto, E., Sugimoto, Y., and Ichikawa, A. (2005). Ca2þ influx‐ mediated histamine synthesis and IL‐6 release in mast cells activated by monomeric IgE. Eur. J. Immunol. 35, 460–468. Thomas, M. L., and Brown, E. J. (1999). Positive and negative regulation of Src‐family membrane kinases by CD45. Immunol. Today 20, 406–411. Tkaczyk, C., Horejsi, V., Iwaki, S., Draber, P., Samelson, L. E., Satterthwaite, A. B., Nahm, D. H., Metcalfe, D. D., and Gilfillan, A. M. (2004). NTAL phosphorylation is a pivotal link between the signaling cascades leading to human mast cell degranulation following Kit activation and FceRI aggregation. Blood 104, 207–214. Togni, M., Lindquist, J., Gerber, A., Kolsch, U., Hamm‐Baarke, A., Kliche, S., and Schraven, B. (2004). The role of adaptor proteins in lymphocyte activation. Mol. Immunol. 41, 615–630. Tomlinson, M. G., Heath, V. L., Turck, C. W., Watson, S. P., and Weiss, A. (2004). SHIP family inositol phosphatases interact with and negatively regulate the Tec tyrosine kinase. J. Biol. Chem. 279, 55089–55096. Tridandapani, S., Wang, Y., Marsh, C. B., and Anderson, C. L. (2002). Src homology 2 domain‐ containing inositol polyphosphate phosphatase regulates NF‐k B‐mediated gene transcription by phagocytic FcgRs in human myeloid cells. J. Immunol. 169, 4370–4378. Tuosto, L., Michel, F., and Acuto, O. (1996). p95vav associates with tyrosine‐phosphorylated SLP‐ 76 in antigen‐stimulated T cells. J. Exp. Med. 184, 1161–1166. Turner, H., and Cantrell, D. A. (1997). Distinct Ras effector pathways are involved in FceR1 regulation of the transcriptional activity of Elk‐1 and NFAT in mast cells. J. Exp. Med. 185, 43–53. Ujike, A., Ishikawa, Y., Ono, M., Yuasa, T., Yoshino, T., Fukumoto, M., Ravetch, J., and Takai, T. (1999). Modulation of immunoglobulin (Ig)E‐mediated systemic anaphylaxis by low‐affinity Fc receptors for IgG. J. Exp. Med. 189, 1573–1579. Valverde, A. M., Sinnett‐Smith, J., Van Lint, J., and Rozengurt, E. (1994). Molecular cloning and characterization of protein kinase D: A target for diacylglycerol and phorbol esters with a distinctive catalytic domain. Proc. Natl. Acad. Sci. USA 91, 8572–8576. Van Toorenenbergen, A. W., and Aalberse, R. C. (1981). IgG4 and passive sensitization of basophil leukocytes. Int. Arch. Allergy Appl. Immunol. 65, 432–440.
N E G AT I V E S I G N A L I N G I N F C R E C E P T O R C O M P L E X E S
85
Ve´ly, F., Olivero, S., Olcese, L., Moretta, A., Damen, J. E., Liu, L., Krystal, G., Cambier, J. C., Dae¨ron, M., and Vivier, E. (1997). Differential association of phosphatases with hematopoietic coreceptors bearing Immunoreceptor Tyrosine‐based Inhibition Motifs. Eur. J. Immunol. 27, 1994–2000. Vivier, E., and Dae¨ron, M. (1997). Immunoreceptor tyrosine‐based inhibition motifs. Immunol. Today 18, 286–291. Volna, P., Lebduska, P., Draberova, L., Simova, S., Heneberg, P., Boubelik, M., Bugajev, V., Malissen, B., Wilson, B. S., Horejsi, V., Malissen, M., and Draber, P. (2004). Negative regulation of mast cell signaling and function by the adptor LAB/NTAL. J. Exp. Med. 200, 1001–1013. Wang, D., Feng, J., Wen, R., Marine, J. C., Sangster, M. Y., Parganas, E., Hoffmeyer, A., Jackson, C. W., Cleveland, J. L., Murray, P. J., and Ihle, J. N. (2000). Phospholipase Cg2 is essential in the functions of B cell and several Fc receptors. Immunity 13, 25–35. Weber, J. R., Orstavik, S., Torgersen, K. M., Danbolt, N. C., Berg, S. F., Ryan, J. C., Tasken, K., Imboden, J. B., and Vaage, J. T. (1998). Molecular cloning of the cDNA encoding pp36, a tyrosine‐phosphorylated adaptor protein selectively expressed by T cells and natural killer cells. J. Exp. Med. 187, 1157–1161. Wen, R., Jou, S. T., Chen, Y., Hoffmeyer, A., and Wang, D. (2002). Phospholipase C g 2 is essential for specific functions of FceR and FcgR. J. Immunol. 169, 6743–6752. Wines, B. D., Sardjono, C. T., Trist, H. H., Lay, C. S., and Hogarth, P. M. (2001). The interaction of FcaRI with IgA and its implications for ligand binding by immunoreceptors of the leukocyte receptor cluster. J. Immunol. 166, 1781–1789. Wofsy, C., Goldstein, B., and Dembo, M. (1978). Theory of equilibrium binding of asymmetric bivalent haptens to cell surface antibody: Application to histamine release from basophils. J. Immunol. 593–601. Wonerow, P., and Watson, S. P. (2001). The transmembrane adapter LAT plays a central role in immune receptor signalling. Oncogene 20, 6273–6283. Woodward, J., and Jenkinson, E. (2001). Identification and characterization of lymphoid precursors in the murine intestinal epithelium. Eur. J. Immunol. 31, 3329–3338. Wossning, T., and Reth, M. (2004). B cell antigen receptor assembly and Syk activation in the S2 cell reconstitution system. Immunol. Lett. 92, 67–73. Xie, Z. H., Zhang, J., and Siraganian, R. P. (2000). Positive regulation of c‐Jun N‐terminal kinase and TNF‐a production but not histamine release by SHP‐1 in RBL‐2H3 mast cells. J. Immunol. 164, 1521–1528. Yamanashi, Y., Tamura, T., Kanamori, T., Yamane, H., Nariuchi, H., Yamamoto, T., and Baltimore, D. (2000). Role of the rasGAP‐associated docking protein p62Dok in negative regulation of B cell receptor‐mediated signaling. Gene Develop. 14, 11–16. Yamasaki, S., Ishikawa, E., Kohno, M., and Saito, T. (2004). The quantity and duration of FcRg signals determine mast cell degranulation and survival. Blood 103, 3093–3101. Yamasaki, S., Nishida, K., Sakuma, M., Berry, D., McGlade, C. J., Hirano, T., and Saito, T. (2003). Gads/Grb2‐Mediated Association with LAT Is Critical for the Inhibitory Function of Gab2 in T Cells. Mol. Cell. Biol. 23, 2515–2529. Young, R. M., Holowka, D., and Baird, B. (2003). A lipid raft environment enhances Lyn kinase activity by protecting the active site tyrosine from dephosphorylation. J. Biol. Chem. 278, 20746–20752. Yuasa, T., Kubo, S., Yoshino, T., Ujike, A., Matsumura, K., Ono, M., Ravetch, J. V., and Takai, T. (1999). Deletion of Fcg Receptor IIB Renders H‐2b Mice susceptible to Collagen‐induced Arthritis. J. Exp. Med. 189, 187–194.
86
M A R C D A E¨ R O N A N D R E N A U D L E S O U R N E
Zhang, W., Irvin, B. J., Trible, R. P., Abraham, R. T., and Samelson, L. E. (1999). Functional analysis of LAT in TCR‐mediated signaling pathways using a LAT‐deficient cell line. Int. Immunol. 11, 943. Zhang, W., Sloan‐Lancaster, J., Kitchen, J., Trible, R. P., and Samelson, L. E. (1998). LAT: The ZAP‐70 tyrosine kinase substrate that links T cell receptor to cellular activation. Cell 92, 83–92. Zhang, W., Trible, R. P., and Samelson, L. E. (1998). LAT palmitoylation: Its essential role in membrane microdomain targeting and tyrosine phosphorylation during T cell activation. Immunity 9, 239–246. Zhang, W., Trible, R. P., Zhu, M., Liu, S. K., McGlade, C. J., and Samelson, L. E. (2000). Association of Grb2, Gads and phospholipase C‐g1 with phosphorylated LAT tyrosine residues: Effect of LAT tyrosine mutations on T cell antigen receptor signaling. J. Biol. Chem. 275, 23335. Zhu, D., Kepley, C. L., Zhang, K., Terada, T., Yamada, T., and Saxon, A. (2005). A chimeric human‐ cat fusion protein blocks cat‐induced allergy. Nat. Med. 11, 446–449. Zhu, M., Janssen, E., and Zhang, W. (2003). Minimal requirements of tyrosine residues of linker for activation of T cells in TCR signaling and thymocyte development. J. Immunol. 170, 325–333. Zhu, M., Liu, Y., Koonpaew, S., Granillo, O., and Zhang, W. (2004). Positive and negative regulation of FceRI‐mediated signaling by the adaptor protein LAB/NTAL. J. Exp. Med. 200, 991–1000.
The Surprising Diversity of Lipid Antigens for CD1‐Restricted T Cells D. Branch Moody Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
1. 2. 3. 4. 5. 6. 7. 8.
Abstract............................................................................................................. Introduction: From Molecules to Functions ............................................................. CD1 Protein Expression on Antigen‐Presenting Cells ................................................ Subcellular Lipid Antigen Processing Pathways......................................................... 3‐Dimensional Structures of CD1‐b2‐Microglobulin‐Lipid Complexes .......................... Microbial Antigens and Infectious Disease ............................................................... Self Antigens, Autoreactivity, and Autoimmune Disease.............................................. Synthetic Lipid Antigens and Prospects for Immunotherapy........................................ Conclusion: Prospects for Immunotherapy ............................................................... References .........................................................................................................
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Abstract CD1 proteins have been conserved throughout mammalian evolution and function to present lipid antigens to T cells. Crystal structures of CD1‐lipid complexes show that CD1 antigen‐binding grooves are composed of four pockets and two antigen entry portals. This structural information now provides a detailed understanding of how CD1‐binding grooves capture a surprisingly diverse array of lipid ligands. CD1‐expressing APCs are able to acquire lipid antigens from their own pool of lipids and from exogenous sources, including microbial pathogens, bystander cells, or even the systemic circulation. CD1 proteins bind to certain antigens using high stringency loading reactions within endosomes that involve low pH, glycosidases, and lipid transfer proteins. Other antigens can directly load onto CD1 proteins using low stringency mechanisms that are independent of cellular factors. New evidence from in vivo systems shows that CD1‐restricted T cells influence outcomes in infectious, autoimmune, and allergic diseases. These studies lead to a broader view of the natural function of ab T cells, which involves recognition of both cellular proteins and lipids. 1. Introduction: From Molecules to Functions The discovery of the CD1 antigen presentation system represents an advance in immunology because it shows that T cells scan and respond to changes in the lipid content of target cells. The central questions in the study of
87 advances in immunology, vol. 89 # 2006 Elsevier Inc. All rights reserved.
0065-2776/06 $35.00 DOI: 10.1016/S0065-2776(05)89003-0
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CD1‐restricted T cells have unfolded in a very different way from those that led to the discovery of the major histocompatibility complex (MHC). The study of the MHC started by establishing the role of T cells in controlling viral infection and rejecting transplanted tissues (McDevitt and Benacerraf, 1969; Zinkernagel and Doherty, 1974) and represented a three‐decade‐long search for the molecules that mediate T cell activation (Garboczi et al., 1996; Garcia et al., 1996; Kappler et al., 1983; McIntyre and Allison, 1983; Oldstone et al., 1988). In contrast, detailed molecular information about CD1 proteins and CD1 genes was available for many years prior to the first evidence that CD1 proteins control the activation of T cells. McMichael and Milstein discovered CD1 proteins using the monoclonal antibody, NA1/34, which bound a protein on human thymocytes with an apparent molecular weight of 45 kilodaltons. The ligand bound by this antibody showed some biochemical similarities to the MHC class I protein, but could be distinguished by its lack of recognition by an MHC class I‐specific antibody, W6/32 (McMichael et al., 1979). Initially known as human thymocyte antigen‐1 (HTA‐1), this protein was renamed as the first cluster of differentiation antigen (CD1) because its discovery represented the first use of monoclonal antibodies to define a specific cell surface marker on human lymphocytes. Cellular studies showed that the CD1 heavy chain associates with b‐2 microglobulin to form heterodimers (Cotner et al., 1981; Terhorst et al., 1981). Subsequently, the five CD1 genes (CD1A, CD1B, CD1C, CD1D, CD1E) were cloned from human thymocytes and mapped to chromosome 1 (Calabi and Milstein, 1986). The first studies of CD1 function showed that human ab and gd T cell clones were directly reactive with CD1 in the sense that their activation could be blocked with antibodies against CD1 proteins, but the activation did not require an exogenous antigen (Porcelli et al., 1989). Shortly thereafter, it was found that antigens from microbial pathogens could be taken up into endosomes for processing reactions within human dendritic cells and that these microbial antigens were lipidic in nature (Beckman et al., 1994; Porcelli et al., 1992). Twenty‐five years after the discovery of CD1 proteins, current work in the field seeks to understand the precise functions of CD1‐ restricted T cells in influencing infectious, autoimmune, allergic, vascular, and neoplastic diseases. In considering the natural functions of CD1‐restricted T cells in immune response, two populations within the CD1‐restricted T cell repertoire have been recognized and categorized, based on whether or not they express conserved or diverse TCRs (Fig. 1). In general, CD1‐restricted T cells are capable of expressing diverse TCR a and b chains and recognize structurally diverse classes of lipid antigens. Within the larger CD1‐restricted T cell repertoire, NK T cells are an abundant and functionally important subset
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Figure 1 The larger repertoire of diverse CD1‐restricted T cells is composed of clones expressing TCRs with diverse structural elements, including differing TCR a‐ and b‐variable gene segments with varied N‐region additions. NK T cells are a large subpopulation of CD1‐restricted T cells that recognize CD1d and express conserved TCRs with an invariant TCR a chain and limited diversity of TCR Vb genes.
that expresses nearly invariant TCRs composed of a canonical a chain (Va14Ja18 in mice and Va24Ja18 in humans) paired with a limited number of b‐chains. The discovery of NK T cells involved the identification of T cells that lack CD4 and CD8 coreceptors, express Vb8‐containing TCRs and could be identified by staining C‐type lectins that are also found on NK cells such as NK1.1 (CD161) (Budd et al., 1987; Fowlkes et al., 1987). Separately, knockout of MHC class II proteins revealed a set of CD4þ T cells that express TCR a chains with limited diversity (Bendelac et al., 1994; Cosgrove et al., 1991). The molecular targets of recognition of NK T cells were solved in two key studies, which showed that CD1d expression on APCs was necessary for their activation (Bendelac, 1995) and that the CD1d‐mediated activation was greatly enhanced by treating APCs with synthetic glycolipids related in structure to a‐galactosyl ceramides (Kawano et al., 1997). The use of the term NK T cell to refer to CD1d‐restricted T cells with invariant TCRs persists for these historical reasons and because NK cells and NK T cells have some limited functional similarities. For example, both NK cells and NK T cells use T‐bet transcription factors (Townsend et al., 2004), expand in the presence of IL‐15 (Matsuda et al., 2002), and have at least some reliance on NK1.1 for activation (Exley et al., 1998). However, the primary activation signals for NK T cells involve TCRs and CD1d, not NK complex‐ encoded receptors. Further, many conventional T cells express NK1.1, and many CD1d‐restricted T cells with invariant TCR a chains do not express NK1.1 (Gumperz et al., 2002). The relative lack of sensitivity and specificity of NK1.1 and other NK complex‐encoded proteins for distinguishing NK T
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cells from MHC‐restricted T cells has led to the waning use of these markers as the primary defining features of NK T cells. Instead, NK T cells are identified by the presence of invariant TCR a chains and activation by CD1d in combination with glycolipid antigens (Fig. 1). This review of CD1‐restricted T cells follows the path of evolution of CD1 research—from molecular structures to in vivo studies—with emphasis on the newest advances in each area.
2. CD1 Protein Expression on Antigen‐Presenting Cells 2.1. Three Groups of CD1 Proteins The human CD1 locus encodes five genes: CD1A, CD1B, CD1C, CD1D, and CD1E (Calabi and Milstein, 1986). Prior to accumulation of any knowledge of the functions of CD1 proteins, a grouping system was proposed based on levels of amino acid sequence homology among the five members of the human CD1 family (Calabi et al., 1989). CD1a, CD1b, and CD1c were most homologous to one another and were designated as the group 1 isoforms. CD1d demonstrated the lowest overall homology to other CD1 proteins and was designated as the group 2 isoform. CD1e was similarly homologous to both groups, so it was not originally classified, but is now known as the group 3 isoform. Although this classification system was originally devised based on amino acid sequence, it remains useful because more detailed studies of gene regulation and CD1 function have generally, but not universally, found differing functions for group 1, group 2, and group 3 CD1 proteins. For example, each of the group 1 isoforms (CD1a, CD1b, CD1c) bind and present microbial lipid antigens to diverse CD1‐restricted T cells, whereas the group 2 isoform (CD1d) is more clearly associated with a function in activating invariant NK T cells. Because NK T cells generally function to regulate other cells, whereas diverse T cells are thought to have direct effector functions against cells with altered lipids, these differences in antigen profiles may also translate into differing functions in vivo. There are, however, exceptions to these apparently differing immunoregulatory and effector functions of group 1 and 2 CD1 proteins, as NK T cells have been recently found to directly recognize microbial lipids (Kinjo et al., 2005; Mattner et al., 2005), and T cells that are directly reactive to group 1 CD1 proteins regulate DC maturation (Vincent et al., 2003). The function of the group 3 isoform, CD1e, is distinct because it is not detected at the surface of APCs and does not function in antigen display (Angenieux et al., 2000, 2005). Instead, it functions in the processing and transfer of lipids to other CD proteins (de la Salle et al., 2005).
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2.2. Evolutionary Conservation of CD1 CD1 proteins are expressed in every mammalian species that has been examined to date, including monkeys, horses, sheep, cows, rabbits, guinea pigs, rats, and mice. Because the human system was the first to be described, CD1 nomenclature designates non‐human sequences according to the human ortholog with which they share the highest level of overall sequence homology. When a species expresses more than one ortholog of a given human gene, each protein is given an arbitrary numerical designation. For example, guinea pigs express three CD1c orthologs (CD1c1, CD1c2, CD1c3), and rabbits express two orthologs of CD1a (CD1a1 and CD1a2) (Dascher et al., 1999; Hayes and Knight, 2001). This nomenclature reflects the fact that most mammalian species have larger numbers of CD1 genes, with mice and rats being the notable exceptions. Recent advances point to new insights in the evolutionary origins of the CD1 system. MHC class I and II molecules are conserved in bony and cartilaginous fish but are lacking in jawless fish. Based on fossil evidence that dates this split, MHC antigen‐presenting molecules are thought to have arisen approximately 500 million years ago, contemporaneously with recombinases that allowed production of rearranged TCRs, forming the basis of the acquired immune system (Laird et al., 2000). Sequence analyses of MHC I, MHC II, and CD1 genes show similar levels of relatedness (despite differences in domain organization), and it has been argued that these three families of antigen‐presenting molecules are derived from a single ancestral gene (Hughes, 1991; Porcelli, 1995). However, there has been controversy as to whether the CD1 system is an ancient branch of the adaptive immune system or evolved from MHC class I proteins under selective pressure over a relatively short span. For example, computer‐based homology analyses had predicted that CD1 may have diverged early in vertebrate evolution, whereas others suggested that divergence might have occurred later, perhaps even after the bird–mammal (synapsid–diapsid) split, approximately 300 million years ago (Hughes, 1991; Porcelli, 1995). Direct evidence that ancestral CD1 genes predate the bird–mammal divergence in the form of CD1 gene sequences in early vertebrates was lacking until recently. Two studies have independently isolated avian CD1 orthologs in chickens (Gallus gallus), which have sequence or structural homologies with mammalian CD1 genes (Miller et al., 2005; Salomonsen et al., 2005). Although the ability of these avian CD1 gene products to present antigens has not been analyzed, these chicken CD1 genes are predicted to encode proteins with requisitely high amino acid homology with mammalian CD1 proteins. Also, chicken CD1 proteins have hydrophobic amino acids in the predicted
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antigen‐binding domains. Importantly, both studies found that chicken CD1 genes are tightly linked with the MHC complex, providing the first example of direct linkage between CD1 and MHC genes. These studies indicate that the CD1 system predates evolution of mammalian species and more directly support prior arguments that CD1 and MHC genes diverged from a common ancestral gene. 2.3. Constitutive and Inducible Expression of CD1 on APCs With the exception of epithelial cells that line the gastrointestinal tract (Somnay‐Wadgaonkar et al., 1999; van de Wal et al., 2003), the expression of CD1 proteins is generally limited to hemopoietically derived cells with specialized functions in antigen presentation and immune response. All five human CD1 proteins are expressed on thymocytes at high levels (Calabi and Milstein, 1986). Most evidence suggests that thymocytes downregulate CD1 proteins prior to their exit to the periphery. However, there is some evidence for expression of CD1a and CD1c proteins on a small subset of T cells in the peripheral blood (Salamone et al., 2001a,b). B cells represent another effector population that constitutively expresses CD1 proteins at high levels. Although CD1c and CD1d are found on a minority of peripheral blood B cells, many studies of secondary lymphoid tissues show that these two isoforms are expressed on large numbers of B cells that localize to the interface of B cell‐ and T cell‐rich areas of secondary lymphoid tissues and co‐express markers of marginal zone B cells. In fact, formal analysis of patterns of CD1c and CD1d expression have found high correlation with localization to the marginal zone, such that CD1c and CD1d can be considered relatively specific markers of marginal zone B cells (Weller et al., 2004). Marginal zone B cells are positioned so that they can rapidly sample blood‐borne antigens, and new evidence indicates that the expression of CD1d at this site regulates Ig production in a way that can alter infection. For example, marginal zone B cells from CD1d‐ deficient mice produce lower levels of borrelia‐specific IgM than wild‐type mice, and passive transfer of IgM partially rescues the worsened infection seen in CD1d‐deficient mice infected by Borrelia burgdorferii and Borellia hermsii (Belperron et al., 2005; Kumar et al., 2000). In contrast to the apparently constitutive expression of CD1 on thymocytes, B cells, and epithelia, the patterns of expression of individual CD1 isoforms on myeloid cells are complex and change in response to cellular activation. CD1d proteins are expressed at low but consistently detectable levels on monocytes. In contrast, fresh human monocytes from peripheral blood lack expression of CD1a, CD1b, and CD1c, but can be induced to express these group 1 isoforms at high levels after treatment with GM‐CSF, IL‐4, and other factors that
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promote DC maturation (Porcelli et al., 1992; Sallusto and Lanzavecchia, 1994). Indeed, group 1 CD1 protein expression is increasingly used as a lineage marker that allows myeloid DCs to be distinguished from activated macrophages. However, modulation of CD1 expression on DCs has only recently come under study as a possible physiological means of regulating the functions of CD1‐restricted T cells, leading to the identification of molecular signals that turn off or on CD1 antigen presentation in DCs. One study has shown that infection of CD1‐expressing dendritic cells by Mycobacterium tuberculosis, a pathogen that makes several classes of CD1‐presented lipids, resulted in the complete loss of detectable CD1b proteins over a period of several days. Such downregulation of CD1 expression in vitro led to the speculation that this could represent a mechanism of immune evasion in vivo (Stenger et al., 1998b). However, similar studies of in vitro‐derived dendritic cells have found only partial or no downregulation of CD1 proteins in response to mycobacterial infection (Giuliani et al., 2001; Henderson et al., 1997). Also, studies testing the effect of Mycobacterium tuberculosis infection of fresh monocytes have found upregulation of CD1a, CD1b, and CD1c after infection. The mechanism of CD1 upregulation in response to mycobacteria involves lipid agonists of Toll‐like receptor 2 (TLR‐2), such as lipoarabinomannan, which promotes transcription and translation of group 1 CD1 proteins (Roura‐Mir et al., 2005b). A similar process likely occurs in vivo, as Mycobacterium leprae infection increases group 1 CD1 protein expression on DCs within the skin of patients with tuberculoid leprosy (Krutzik et al., 2005; Sieling et al., 1999). Also, group 1 CD1 proteins are expressed in peribronchial tissues and brochioalveolar lavage samples of tuberculosis patients (Buettner et al., 2005; Uehira et al., 2002). Thus, the dominant effect of mycobacteria is to generate a local inflammatory reaction that leads to increased expression of group 1 CD1 proteins on myeloid cells at sites of infection. New insights into the differential timing of expression of CD1a, CD1b, CD1c, CD1d, and CD1e on maturing myeloid DCs point to potentially distinct biological functions of each of the three groups of CD1 proteins. Kinetic measurements of group 1 CD1 induction at the cell surface in response to cytokines, TLR agonists, or mycobacterial lipids show that cell surface expression is first detected 2 days after activation, peaking at day 3. This delayed expression of group 1 CD1 proteins relates to the cellular mechanism of group 1 CD1 induction, which requires synthesis of new proteins, rather than redirected trafficking of pre‐formed proteins, as is the case with MHC class II (Roura‐Mir et al., 2005b). Certain stimuli that promote group 1 CD1 expression lead to the concurrent downregulation of CD1d and vice versa. For example, the upregulation of CD1d expression by agonists of
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the peroxisome proliferator activated receptor g (PPAR‐g) pathway is accompanied by decreased expression of CD1a (Szatmari et al., 2004), and mycobacterial cell wall products that increase group 1 CD1 expression decrease CD1d expression. The differing timing and opposite responses of group 1 and group 2 CD1 proteins imply distinct functions. Rapid activation of NK T cells over minutes to hours by constitutively expressed CD1d proteins is one criterion supporting the description of NK T cells as ‘‘lymphocytes of innate immunity’’ (Benlagha and Bendelac, 2000). In contrast, the delayed expression of group 1 CD1 proteins on DCs, as well as their regulation by antecedent activation of pattern recognition receptors of the innate immune system, are more in keeping with a slightly delayed pathogen recognition system that becomes effective during the transition from innate to adaptive immune responses. These new insights derived from in vitro studies of the agonists, receptors, and kinetics of expression of CD1 now form a rationale for further investigation of the dynamic patterns of expression of CD1 proteins in vivo. Given the clear evidence for cell‐type and activation‐dependent patterns of expression of CD1 proteins, there currently exists remarkably little information regarding signaling molecules, promoter elements, or transcriptional mechanisms that control CD1 expressions, at the surface of myeloid APCs. Agonists of TLRs and PPAR‐g both signal through nuclear factor kappa B (NFkB), implicating this signaling pathway in the control of CD1 expression. There has been some preliminary mapping of CD1 promoters, and new evidence shows that E26 transformation‐specific (ets) transcription factors control CD1d expression (Calabi et al., 1989; Geng et al., 2005). 3. Subcellular Lipid Antigen Processing Pathways New studies indicate that the loading of lipid antigens onto cellular CD1 proteins is regulated by vesicular ATPases, cell surface lectins, lipid transfer proteins, and other cellular cofactors with distinct patterns of expression within subcellular compartments of APCs. These studies are beginning to coalesce into models of coordinated subcellular pathways of lipid antigen processing. Whereas protein antigen processing centrally involves cleaving antigens to generate smaller peptides, lipid antigen processing is coming to be understood as a multi‐stage transfer process for moving relatively insoluble antigens through aqueous solutions for loading into the hydrophobic grooves of CD1 proteins. Viewed from this perspective, the trafficking of CD1 proteins through the secretory, cell surface, and endosomal pathways is not merely a means to disperse CD1 proteins throughout diverse lumenal compartments of APCs. Instead, the complex subcellular trafficking patterns offer a means to
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regulate the loading of differing subclasses of antigens into CD1 proteins and thereby influence the repertoire of lipids that are ultimately displayed to T cells. In particular, the routing of CD1 trafficking through late endosomes and lysosomes renders CD1 proteins able to capture antigens that cannot be captured within other cellular subcompartments. 3.1. CD1 Translation and Egress to the Cell Surface Leader sequences in the CD1 genes result in cotranslational insertion into the endoplasmic reticulum (ER), so that the a1, a2, and a3 portions of the heavy chain are inserted in the lumen, leaving 6 or more amino acids extending into the cytoplasm (cytoplasmic tails). The folding of CD1 heavy chains is regulated by calnexin and calreticulin and appears to be followed by rapid association with b‐2 microglobulin in the ER (Bauer et al., 1997; Huttinger et al., 1999; Kang and Cresswell, 2002a; Sugita and Brenner, 1994). Whether or not ER‐resident lipids associate with CD1 proteins during the initial folding process has not been directly assessed in cells, but there is indirect evidence that lipids promote CD1 folding. For example, addition of lipids to unfolded recombinant CD1 heavy chains increases the rate of folding and assembly with b‐2 microglobulin in vitro, likely due to the ability of the aliphatic hydrocarbon chains to stabilize the formation of the inner hydrophobic surface of the a1–a2 superdomain (Karadimitris et al., 2001). Further supporting this hypothesis, it has been possible to elute phosphatidylinositol‐containing lipids from cellular CD1d proteins, and some evidence indicates that lipid association occurs prior to transit of CD1 through the golgi apparatus (De Silva et al., 2002; Joyce et al., 1998). Microsomal triglyceride transfer protein (MTP), an ER‐resident protein with known function in assembling lipoprotein particles, has been recently shown to associate with CD1d, and MTP deletion results in reduced levels of NK T cells activation in vitro and in vivo (Brozovic et al., 2004; Dougan et al., 2005). This result implies that altered lipid transfer or loading onto CD1 within the secretory pathway affects the subsequent ability of cell surface CD1d proteins to regulate NK T cell activation. The ability of phosphatidylinositol and other endogenous lipids to load onto CD1 proteins early in their trafficking pathways has led to the speculation that these lipids might function as chaperones that are exchanged for exogenously acquired lipids in endosomes or subsequently encountered compartments, analogous to the mechanism by which MHC class II invariant chain peptide (CLIP) regulates loading of antigenic peptides. During golgi transit, CD1 proteins undergo N‐linked glycosylation at multiple sites so that mature CD1 proteins are decorated with three or more
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glycans. The trans‐golgi can be considered the point at which the trafficking patterns of each human CD1 proteins most clearly begin to diverge into separate pathways that lead to CD1 accumulation in endosomes via direct transport from the trans‐golgi or recycling from the cell surface. At least two mechanisms have been identified whereby sorting events at the trans‐golgi lead to direct transport of CD1 proteins to endosomal compartments. First, the cytoplasmic tail sequences of some CD1 proteins contain modified dileucine motifs, which generally promote sorting into vesicles that traffic to endosomes (Fig. 2). This role was first shown in human CD1d proteins, when mutagenesis of the modified dileucine motif in the cytoplasmic tail was shown to decrease steady state localization of CD1d proteins in endosomes (Rodionov et al., 1999, 2000). A second means of direct transport of CD1 proteins from the golgi to endosomes involves MHC class II‐invariant chain complexes, which have been detected in substoichiometric amounts in association with mouse CD1d (Jayawardena‐Wolf et al., 2001; Kang and Cresswell, 2002b). Although the precise mechanism of redirected trafficking is not yet known, the cytoplasmic tails of the MHC class II b‐chain and the invariant chain contain modified dileucine motifs (Fig. 2). Therefore, mouse CD1d proteins, which lack dileucine motifs, may nevertheless undergo dileucine‐based sorting using the tails of other proteins in heteromultimeric complexes. The recycling pathway involves rapid transport to the cell surface via the default secretory pathway, followed by regulated entry into the endosomal network via reinternalization. The relative proportions of CD1 proteins that reach endosomes by the direct and recycling pathways likely differs for each CD1 isoform. CD1e accumulates in the golgi apparatus at steady state and can be detected in smaller amounts in CD63‐expressing lysosomes with a multi‐lammellar appearance in electron micrographs. Because CD1e proteins have not been detected at the cell surface and do not mediate internalization of anti‐CD1e antibodies, CD1e appears to solely use direct transport from the trans‐golgi network to reach the endosomes (Angenieux et al., 2000, 2005). Human CD1e has a particularly long cytoplasmic tail, which contains a putative dileucine motif (Fig. 2), but the role of signaling sequences in the cytoplasmic tail has not yet been investigated. For other CD1 isoforms, the recycling pathway appears to be quantitatively dominant. This conclusion is supported by pulse‐chase studies showing that CD1b and CD1d proteins rapidly appear at the cell surface in a time frame typical of proteins in the secretory pathway (Briken et al., 2002; Jayawardena‐Wolf et al., 2001). Once CD1a, CD1b, CD1c, and CD1d proteins reach the surface, they recycle to varying extents to distinct subcompartments of the endosomal network.
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Figure 2 The cytoplasmic tails of CD1 proteins regulate intracellular trafficking. The cytoplasmically oriented sequences of transmembrane proteins are annotated for sequences that conform to YXXZ (bold) or modified dileucine motifs (underlined). The mechanism of action of YXXZ motifs is known to involve direct binding to the m‐subunit of adaptor protein (AP) complexes, which mediates packing of transmembrane cargo proteins into transport vesicles. Interspecies differences in trafficking of orthologous proteins are illustrated by human CD1d, which uses dileucine‐based sorting and YXXZ‐mediated interactions with AP‐2. Murine CD1d lacks an identifiable dileucine motif but has a YXXZ motif, which interacts with AP‐2 and AP‐3.
3.2. CD1 Recycling to Endosomes The internalization of CD1 proteins from the cell surface to the endosomal network is regulated by cytosolic adaptor protein complexes (AP), which bind to tyrosine‐containing amino acid sequence motifs in the cytoplasmic tails of CD1b, CD1c, and CD1d proteins. Adaptor protein complexes (AP‐1, AP‐2, AP‐3, AP‐4) are heterotetramers composed of two large (c, a, d, or paired
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with b1, b2, b3, or b4), one medium (m1, m2, m3, or m4), and one small (s1, s2, s3, s4) protein. The binding of AP complexes to transmembrane cargo proteins is mediated by the insertion of two amino acid residues from the cytoplasmic tail of cargo proteins, one tyrosine and one hydrophobic, into two clefts in the m‐subunit of AP complexes (Fig. 2). The spacing of these two interactions is favored when the tyrosine and hydrophobic residues are separated by two intervening amino acids (Ohno et al., 1995; Owen and Evans, 1998). Thus, AP‐interacting proteins can be recognized by the presence of a tyrosine‐containing sequence in their cytoplasmic tails, YXXZ, in which Y is a tyrosine, Z is a hydrophobic amino acid, and XX are any two amino acids that function as spacers. Although the intracellular distribution of AP complexes is somewhat overlapping, AP‐1 complexes localize to the trans‐golgi; AP‐2 complexes are abundant at the cell surface, and AP‐3 complexes are found in endosomal compartments (Bonifacino and Traub, 2003). These complexes localize to the cytoplasmic face of cellular membranes, where they regulate packaging of transmembrane proteins into transport vesicles and can be thought of as a network that influences the steady state intracellular localization of many cargo proteins. The functions of AP complexes in regulating the trafficking and antigen‐ presenting functions have been extensively studied for human and murine CD1 proteins. A clear function for the cytoplasmic tail in regulating CD1 localization was first shown for human CD1b using mutants that lacked the entire cytoplasmic tail (Sugita et al., 1996). Mutant CD1b proteins were found to have significantly reduced localization in MHC class II compartments (MIIC) at steady state, and this resulted in impairment of CD1b presentation of exogenously derived mycobacterial lipids to T cells (Jackman et al., 1998). Subsequently, it was found that the particular amino acids that comprise the YXXZ motif in human CD1b and mouse CD1d are capable of interacting with the m‐subunit of AP‐2 and AP‐3 complexes, whereas human CD1d and human CD1c only interact with the m‐subunit of AP‐2 (Briken et al., 2002; Elewaut et al., 2003; Sugita et al., 2002). Thus, human CD1b and mouse CD1d reinternalization appears to involve a two‐stage process in which AP‐2 complexes promote transport from the surface to endosomes, and then AP‐3 works within early endosomes to promote transport to late endosomes and lysosomes. In contrast, human CD1c and human CD1d undergo the first step involving reinternalization from the surface to endosomes, but lack AP‐3‐ mediated redistribution to late endosomes and lysosomes. Human CD1a has a short cytoplasmic tail lacking any discernable sorting motif, a feature which distinguishes human CD1a from other human CD1 isoforms as well as non‐human CD1a proteins (Fig. 2). This molecular analysis of AP complex interactions with tail motifs in various CD1 proteins predicts that human
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CD1b and mouse CD1d recycle to late endosomes most efficiently, followed by human CD1d, human CD1c, and human CD1a. Indeed, immunoelectron microscopic analysis of CD1 in multi‐lammellar compartments and multi‐color immunofluorescence analysis of CD1 colocalization bear out this prediction (Sugita et al., 1999). Thus, the apparent hierarchy of the degree of late endosomal localization among CD1 proteins can be largely accounted for by their known differences in interactions with AP‐2 and AP‐3 complexes. 3.3. CD1 Trafficking Controls Lipid Presentation Recycling from the cell surface to endosomes has important functional consequences for the ability of CD1 proteins to subsequently present lipid antigens at the cell surface. This conclusion is supported by many cellular studies in which lipid‐mediated T cell activation is abrogated by deleting endosomal targeting sequences located in CD1 tails, blocking trafficking by membrane fixation, or pharmacologically inhibiting acidification of endosomes. For example, reversal or blockade of endosomal acidification by treating APCs with concanamycin or chloroquine leads to a severe or complete loss of lipid‐ mediated T cell activation (Gilleron et al., 2004; Moody et al., 1999; Porcelli et al., 1992; Roberts et al., 2002; Sieling et al., 1995). In addition, CD1b proteins that have intact antigen‐binding domains, but lack cytoplasmic tail sequences for targeting to endosomes, fail to efficiently mediate T cell activation in response to mycolate antigens (Jackman et al., 1998). Similarly, deletion of the cytoplasmic tail of mouse CD1d, including the YXXZ motif, leads to the loss of activation and positive selection of NK T cells with invariant (Va14) TCRs (Chiu et al., 1999, 2002). The altered T cell activation seen in both types of studies likely occurs due to reduced levels of endosomal recycling and not other effects, because total cellular pools and cell surface density of CD1 proteins are generally maintained or increased after cytoplasmic tail deletion. In addition, alteration of endosomal trafficking by cytoplasmic tail mutation in mouse CD1d does not lead to the loss of ability to activate Va14 T cells, and human tail‐deleted CD1b retains its ability to present certain kinds of lipid antigens (Chiu et al., 1999; Moody et al., 2002). These studies have been interpreted to mean that altered CD1b or CD1d trafficking does not merely reduce the efficiency of presentation, but can meaningfully alter the subset of lipids that are displayed on the cell surface. Endosomal recycling also promotes T cell activation by CD1c‐presented mannosyl mycoketides and CD1a‐presented dideoxymycobactins (Sugita et al., 1999, 2000). However, recognition of these antigens is not absolutely dependent on intact recycling pathways, and fewer numbers of antigens presented
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by CD1a and CD1c have been studied, so it is not yet possible to draw generalizations about the role of recycling for these two isoforms. Although it is clear that passage through endosomes is important for presenting certain lipid antigens, it is not yet known whether the two means of access to endosomes, the direct and recycling pathways, have distinct or overlapping functions. Quantitatively, tyrosine motif‐mediated recycling from the surface appears dominant because the effects of deletion of dileucine motifs in CD1d and invariant chain are not clearly seen, unless the recycling pathway is also interrupted by mutation of tyrosine motifs (Jayawardena‐Wolf et al., 2001; Kang and Cresswell, 2002b). Also, the nearly complete loss of NK T cells after deletion of the CD1d tail implies that MHC class II‐invariant chain‐related mechanisms mediating endosomal delivery are not sufficient to rescue the functional defect in AP‐mediated recycling (Chiu et al., 2002). However, the precise localization and function of CD1 in the subcompartments of the late endosome–lysosome continuum are not yet fully understood. Therefore, it remains possible that these two cellular mechanisms may target CD1 proteins for subcompartments with distinct immunological functions. 3.4. Molecular Events in Endosomal Processing The targeting of CD1 proteins and antigens to endosomes leads to more efficient T cell activation, supporting the concept that endosomes represent a coordinated subcellular pathway that regulates antigen display. Whereas processing of protein antigens centrally involves covalent cleavage to generate peptides so they can fit within the groove of MHC‐encoded proteins, most known natural lipid antigens contain lipid tails that approximate the volume of their respective CD1 grooves. Thus, the cellular events involved in converting lipids to a recognizable form do not universally require modification of antigen structure through covalent cleavage. Instead, endosomal lipid antigen processing appears to be centrally concerned with transfer of relatively insoluble lipids through aqueous biological solutions to and from membranes, lipid‐ protein aggregates, and the hydrophobic groove found in CD1 proteins. Existing data support four separate, but not mutually exclusive events, which contribute to the generation of antigenic CD1 complexes within endosomes: concentration of lipids in proximity to CD1 proteins, acid‐mediated loading of lipids into the CD1 groove, glycosidase‐mediated trimming of glycans, and lipid‐binding protein‐mediated antigen transfer to CD1. CD1 proteins are expressed on myeloid DCs, Langerhans cells, B cells, and other professional APCs, which use receptor‐mediated and other mechanisms to concentrate certain classes of lipids within endosomes. Cell surface receptors that have been shown to mediate uptake and presentation of glycolipid
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antigens include two lectins, the mannose receptor and langerin, whose expression on DCs contributes to glycolipid‐mediated T cell activation (Hunger et al., 2004; Prigozy et al., 1997). In addition, new evidence shows that biotin‐specific B cell antigen receptors (BCR) can promote T cell recognition of biotinylated glycolipids, leading to the speculation that BCRs on glycolipid‐specific B cells might promote uptake and processing of natural glycolipid antigens (Lang et al., 2005). Also, a new study shows that deletion of expression of apolipoprotein E (apoE) affects presentation of bacterial antigens to diverse CD1‐restricted T cells and NK T cells (van den Elzen, et al., 2005). ApoE is expressed at high levels in endosomes and also functions as a major constituent of very low density lipoprotein (VLDL) particles in the bloodstream, where it mediates binding to the low density lipoprotein (LDL) receptors. Identification of lipoprotein pathways for antigen delivery provides a link between systemic circulation of lipids and their transport to APCs, illustrating how cellular pathways that had been previously known to control lipid metabolism also control immune recognition of lipids. In addition to these receptor‐mediated mechanisms, maturing DCs regulate macropinocytosis of antigen‐containing aggregates in ways that affect uptake of CD1‐presented lipid antigens (Roura‐Mir et al., 2005b). Last, lipids with particularly long alkyl chains preferentially accumulate in CD1b‐containing lysosomes via as yet undefined mechanisms (Moody et al., 2002). Collectively, these studies support the concept that the lumen of endosomes or perhaps the inner leaflet of endosomal membranes represents an antigen depot, where certain types of lipids accumulate to high local concentrations. These studies show how endosomes, in contrast to other subcellular compartments, are enriched for exogenously acquired lipids, including those that are selectively imported by pattern recognition receptors or phagocytosis triggered by direct encounter with pathogens. The ability of CD1 proteins to encounter distinct subsets of lipids during passage through endosomes may lead to their preferential display based on mass‐action, independent of any processes that increase the efficiency of antigen loading at this site. A second general mechanism by which endosomal cofactors promote lipid antigen recognition involves the acidic environment of late endosomes and lysosomes, which is maintained by vesicular ATPase proton pumps. The well documented ability of endosomal acidification inhibitors to block antigen processing may relate to the ability of low pH to partially denature CD1 proteins, as suggested by studies of recombinant CD1b binding with lipoarabinomannan and glucose monomycolate antigens (Ernst et al., 1998). These in vitro studies point to a model in which CD1 proteins remain in a closed conformation at neutral pH when moving through the secretory pathway, but open up to accept ligands, especially ligands with longer alkyl chains, as they
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traffic through late endosomes. Low pH may also indirectly promote antigen complex formation by activating pH‐dependent protein cofactors other than CD1, such as lipid transport proteins or hydrolases that act to alter the structure of endosomally localized antigens. Although lipases that might modify the lipid anchors of antigens in ways that affect binding to CD1 have not been identified, endosomally localized, pH‐dependent glycosidases can alter glycan structures to reveal TCR epitopes. For example, deletion of a‐galactosidase A prevents the conversion of synthetic digalactosyl‐a‐ceramides to antigenic monogalactosyl ceramides (Prigozy et al., 2001). Similarly, deletion of b‐hexosaminidase B reduces activation of NK T cells in vivo, by altering the self glycolipids present in endosomes (Zhou et al., 2004b). Last, certain lipid transfer proteins, including the saposin and apoE, localize to endosomes at relatively high concentrations, so that this environment may be particularly rich in lipid transfer proteins. Saposin lipid transfer proteins, also known as sphingolipid activator proteins, are a family of proteins that are derived from cleavage of the inactive precursor protein, prosaposin. At low pH, saposins bind to the inner leaflet of endosomal membranes, where they partially insert into the membrane causing local disruptions in lipid packing, which is thought to allow extraction of lipids into the lumen. Saposin family proteins play a key role in regulating the glycolipid transport and content, such that altered expression of saposins cause human lipid storage diseases (Sandhoff and Kolter, 2003). Deletion of prosaposin in mice or in human cells leads to decreased activation and positive selection of CD1‐restricted T cells both in vitro and in vivo (Kang and Cresswell, 2004; Winau et al., 2004; Zhou et al., 2004a). The observed loss of CD1‐restricted T cell function might result indirectly from the global alterations in endosomal glycolipid content that follow prosaposin deletion. However, in vitro studies show that saposins transport certain lipids between vesicles, providing evidence for an intermembrane antigen transport function, suggesting a direct role in antigen loading onto CD1 (Zhou et al., 2004b). ApoE is also expressed at high levels in endosomes, so that its effects in antigen recognition may relate to a dual role in mediating the capture of lipoprotein particles by LDL‐R and in solubilization of endosomally localized antigens (van den Elzen et al., 2005). 4. 3‐Dimensional Structures of CD1‐b2‐Microglobulin‐Lipid Complexes 4.1. Conserved Features of CD1 Structure Both CD1 and MHC class I are comprised of heavy chains of similar length, which are organized into three extracellular domains (a1, a2, and a3) and bind b‐2 microglobulin to form heterodimers in cells. The crystal structure of
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murine CD1d showed that the a1–a2 superdomain forms a hollow groove, which is delimited by two anti‐parallel a‐helices that sit atop six b‐strands, forming a b‐sheet. The three‐dimensional folding of mouse CD1 parallels that of MHC class I and II, such that it is possible to overlay the a‐carbon backbone traces and compare the structures of their antigen‐binding grooves (Zeng et al., 1997). However, several key features distinguish the overall architecture of the antigen‐binding grooves of CD1 from those found in MHC‐encoded antigen‐presenting molecules. First, CD1 grooves have a larger internal volume, which results in large part from a series of bulky amino acids at positions 18, 40, and 49 in the consensus sequence (Fig. 3). These residues are known as the a1 scaffold because their large side chains are positioned between the b‐sheet floor and the a1 helix, where they function to displace the a1 helix vertically. The scaffold creates greater depth for CD1 grooves, which are much larger (1350 to 2200 A˚3) than those found in MHC‐encoded antigen‐presenting molecules. The a1 scaffold has been observed in all CD1 proteins crystallized to date—murine CD1d, human CD1b, human CD1a, and human CD1d (Batuwangala et al., 2003; Gadola et al., 2002; Giabbai et al., 2005; Koch et al., 2005; Zajonc et al., 2003, 2005a,b; Zeng et al., 1997). Furthermore, bulky amino acids are present at consensus positions 18, 40, and 49 in most or all CD1 sequences in mammalian and avian species studied to date (Fig. 3). Thus, deep grooves represent a highly conserved feature of mammalian CD1 protein structure, which allow lipids to bind such that a substantial portion of the ligands lies within, rather than on top of, the a1–a2 superdomain. This mode of binding allows the aliphatic hydrocarbon chains of antigens to be extensively sequestered from the aqueous biological solutions that surround the CD1 protein. A second contrasting feature of CD1‐ and MHC‐binding grooves is the presence of non‐polar amino acids that are positioned at the inner surface of the CD1 groove. These amino acids form a nearly continuous hydrophobic surface that interacts with the aliphatic hydrocarbon chains of lipid ligands (Zeng et al., 1997). This situation contrasts with the polar and charged amino acids that allow for an extensive hydrogen bonding network and ionic interactions with peptide side chains with MHC groove surfaces. These differences in electrostatic topography of the grooves point to a basic difference in the chemical basis for ligand capture by CD1 and MHC antigen‐presenting molecules. Hydrophobic interactions, which predominate in CD1, generate binding force. Unlike salt bridges and hydrogen bonds, they do not require precise positioning of the individual chemical elements that constitute the binding pairs. Thus, any particular methylene unit within the alkyl chain can interact with nearly any point on the hydrophobic surface of CD1, and binding is optimized when the total number of hydrophobic interactions is maximized, as
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Figure 3 Functionally dominant amino acids near the antigen‐binding groove. This analysis aligns the a1 and a2 domains non‐human CD1 sequences based on a previously defined consensus
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would be the case when the lipid ligand fully occupies the groove. This contrasts with ionic and hydrogen bonding interactions which require that binding pairs be positioned at a discrete distance from its binding partner. Whereas MHC grooves are open for direct access to solvent throughout their length, interdomain interactions between the a1 and a2 helices close the superior margin of the groove at one end. In murine CD1d, this closure is formed by interdomain interactions between Leu66‐Thr167 and Phe70‐ Leu163 and can be thought of as a roof that encloses part of the superior aspect of the groove. This roof structure has been seen in crystal structures of murine CD1d, human CD1d, human CD1b, and human CD1a (Fig. 4), and the roof‐forming amino acids at consensus positions 66, 70, 162, and 166 are generally conserved in non‐human CD1 sequences (Fig. 3). Thus, whereas the MHC class I and II grooves are directly exposed to solvent over most of their 25 A˚ length, CD1 grooves are accessed by a smaller, 10 to 17 A˚ long gap. Because this gap is relatively small and connects the outer surface of CD1 to a large interior cavity, the main opening to the groove can be thought of as a portal. 4.2. CD1 Pockets and Portals A series of seven CD1‐lipid crystal structures were recently solved in a short time period, providing a wealth of new structural data that forms the basis for a standardized nomenclature of groove‐associated structures and sheds light on
sequence for human and mouse proteins (Porcelli, 1995), and shows ribbon and schematic diagrams of the CD1b‐phoshatidylinositol structure (Gadola et al., 2002). Amino acids are shown for those positions in the consensus sequence that form specialized structural features near the antigen‐binding groove as identified in crystal structures of human CD1a, human CD1b, human CD1d, or mouse CD1d proteins: a1 scaffold (bulky residues that raise the a1 helix), A0 roof (interdomain contacts involving leucine, isoleucine, threonine, or size‐conserved amino acids that close the superior margin of the A0 pocket), A0 pole (hydrophobic and bulky residues that form a vertical axis in the A0 pocket), A0 terminus (residues with side chains that are equal to or larger than valine and located near the inferior margin of the A0 pocket), C0 origin (small non‐aromatic residues that create a cavity forming the opening to the C0 pocket), C0 portal (two cysteine residues that form a disulfide bond to stabilize the C0 portal), and T0 tunnel (two glycine residues that create a cavity that forms the T0 tunnel). Grey shading identifies residues that are conserved in size or chemical characteristics as compared with residues that define the structural element in crystallized CD1 proteins. This analysis suggests that the a1 scaffold, the A0 roof, and the A0 pole are likely conserved in mammalian CD1 proteins, whereas other features are likely to be found in only certain CD1 isoforms
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Figure 4 CD1 antigen‐binding groove surfaces. Viewed from the superior aspect of the a‐helical surfaces of CD1, the antigen‐binding grooves of human CD1a, human CD1b, and murine CD1d proteins are rendered as transparent surfaces and shown with bound ligands. Ligands traverse a portal above the F0 pocket, whereas the top of the A0 pocket is covered by a roof‐like structure. Only CD1b has a second portal, the C0 portal, which connects the bottom of the groove with the outer, lateral surface of CD1b. All three grooves have an ovoid A0 pocket that encircles the A0 pole formed by phenylalanine at position 70 (F 70) and valine or cysteine at position 12 (V12, C12). Whereas the A0 pockets of CD1b and CD1d join directly with the F0 pocket (upper left corner), the A0 pocket of CD1a is terminated by a valine at position 28 (V28). This difference in structure allows the longer glucose monomycolate ligand to encircle the A0 pole of CD1b and exit to other pockets, whereas the terminus of the A0 pocket of CD1a places a limit on the length of alkyl chains that can bind in this groove. Groove surfaces are based on previous depictions or crystal structures of CD1‐ lipid complexes (Batuwangala et al., 2003; Giabbai et al., 2005; Moody et al., 2005; Zajonc et al., 2005b).
mechanisms of lipid antigen capture. These structures are CD1b bound to phosphatidylinositol (CD1b‐PI), CD1b‐GM2 ganglioside, CD1b‐glucose monomycolate, CD1a‐sulfatide, CD1a‐lipopeptide, CD1d‐phosphatidylcholine, and CD1d‐a‐galactosyl ceramide (Batuwangala et al., 2003; Gadola et al., 2002; Giabbai et al., 2005; Koch et al., 2005; Zajonc et al., 2003,
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2005a,b). One clear conclusion derived from these new studies is that the antigen‐binding grooves of CD1a (1300 A˚3), CD1d (1650 A˚3), and CD1b (2200 A˚3) differ significantly in volume, suggesting that each isoform is specialized for binding antigens with lipid anchors of differing size. The overall structures of CD1‐binding grooves are composed of up to six named component structures. In human CD1b, there are four pockets (A0 , C0 , F0, T0 ) and two portals (F0, C0 ), whereas human CD1a and mouse and human CD1d proteins have only two pockets (A0 , F0 ) and one portal (F0 ). Three of the pockets, A0 , C0 , and F0, take their names based on their positions relative to the A, C, and F pockets in MHC class I (Zeng et al., 1997). The fourth pocket, known as the T0 tunnel, is named for its location at the bottom of the CD1b groove, where it connects A0 and F0 pockets to form the A0T0 F0 superchannel (Fig. 3). Because all CD1 proteins studied to date have a roof structure above the A0 pocket, the main portal for ligand entry is positioned somewhat ectopically on the distal surface of CD1, above the F0 pocket, so it is known as the F0 portal (Figs. 3 and 4). In human CD1b, there is a second, smaller portal located beneath the a2 helix at the end of the C0 pocket and is known as the C0 portal (Figs. 3 and 4). The differing structures of CD1 antigen‐binding grooves can be understood by visualizing how these pockets and portals connect together in different ways. 4.2.1. F0 and A0 Pockets The main entrance to the grooves of CD1 proteins is the F0 portal, which is located at the top of the F0 pocket. The F0 pocket is a somewhat vertically oriented cavity, which serves to connect the outer, TCR‐binding surface of CD1 to the interior of the groove. The alkyl chains of antigens, which serve to anchor antigens into CD1 proteins, descend through the F0 pocket and then wind around the A0 pocket, an ovoid concavity positioned beneath the A0 roof. The A0 pocket is partially or completed bisected by the A0 pole, which is formed by larger, hydrophobic residues at positions 12 and 70 (Fig. 3). These amino acids form an axis around which the alkyl chains of antigens are wrapped. An A0 pole is present in all CD1 structures crystallized to date, and larger, non‐polar amino acids are generally conserved at these positions in most CD1 sequences, providing evidence for conservation of this structure among mammalian CD1 proteins (Fig. 3). A key difference among CD1 isoforms is the directionality and the degree to which alkyl chains can encircle the A0 pole. For example, the A0 pocket of CD1a is abruptly terminated, so that the A0 pocket is like a narrow bent tube with a terminus that does not allow long alkyl chains to protrude into other
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pockets (Fig. 4). This terminus creates a situation in which lipids of only a discrete length can fit within the pocket, leading to the description of the A0 pocket of CD1a as a ‘‘ruler’’ for alkyl chains (Zajonc et al., 2003). Supporting the hypothesis that CD1a selectively presents lipid antigens with a discrete chain length, lipopeptide analogs with alkyl chains that match the volume of the A0 pocket (C20) show higher potency for activating T cells than analogs with shorter (C18) alkyl chains (Moody et al., 2004; Zajonc et al., 2005b). The abrupt terminus of the A0 pocket in CD1a contrasts with the open‐ended A0 pockets of CD1b and CD1d, which connect directly to pockets within the groove. Also, glucose monomycolate and phosphatidylcholine traverse the donut‐shaped A0 pocket in opposite directions (Fig. 4), illustrating the more flexible ways in which CD1b and CD1d can bind lipids within the A0 pocket. The more interconnected nature of the A0 and F0 pockets in CD1 isoforms other than CD1a appears to allow binding of antigens whose lipid anchors vary more significantly in length. The particularly complex and interconnected nature of the pockets within CD1b led to the description of this groove as a ‘‘maze’’ for alkyl chains (Gadola et al., 2002). 4.2.2. The C0 Pocket and C0 Portal in CD1b CD1b has the largest and most complex groove structure of CD1 proteins studied to date. Whereas the grooves of other isoforms are completely enclosed so that the antigen‐binding cavity can be accessed only via the F0 portal, CD1b contains a second portal, the C0 portal, which takes its name from its location at the bottom of the C0 pocket (Gadola et al., 2002). The opening that forms the C0 portal is stabilized by a disulfide bond involving positions Cys131 and Cys145 in the consensus sequence. This pair of cysteines is not found in any other human or mouse CD1 isoform, suggesting that this is an isoform‐ specific adaptation of CD1b among human CD1 proteins (Fig. 3). The origin of the C0 pocket is created by a gap that results from the presence of a relatively small valine residue, compared to larger aromatic residues found at this position in other human CD1 isoforms (Fig. 3). The C0 pocket is open at both ends, so that it likely binds shorter lipids entirely within the pocket and allows longer lipids to protrude from the groove. Although crystal structures of CD1‐lipid complexes have not unambiguously depicted ligand density protruding through the C0 portal, CD1b is known to present antigens that match or exceed the volume of the CD1b groove (Gilleron et al., 2004; Moody et al., 2002). This leads to speculation that the C0 portal of CD1b functions as an escape hatch allowing presentation of antigen with particularly long alkyl chains.
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4.3. CD1 Isoform Specificity The apparent promiscuity with which a given CD1 protein can bind lipid anchors of differing structures has led to interesting controversies regarding the possible isoform‐specific antigen‐capturing functions of CD1 proteins. On the one hand, CD1a, CD1b, CD1c, and CD1d have distinct patterns of expression on and within APCs, implying distinct functions. Further, the obvious differences in size and shape of CD1a, CD1b, and CD1d antigen‐binding grooves strongly suggest that CD1 isoforms are specialized to bind distinct classes of lipid antigen (Fig. 4). On the other hand, chemical motifs that describe the structures of antigens that bind to one CD1 isoform but not to others have not yet been well established. For example, it is known that despite the large differences in size and shape seen in the CD1b and CD1d antigen‐binding grooves, both proteins can present sphingolipids and diacylglycerols with similar or identical lipid anchors, which have an overall length of C32–44 (Fischer et al., 2004; Gumperz et al., 2000; Joyce et al., 1998; Kawano et al., 1997; Shamshiev et al., 1999, 2000; Sieling et al., 1995). Similarly, sulfatide antigens are presented by human CD1a, CD1b, CD1c, and CD1d proteins (Shamshiev et al., 2002). These studies raise the possibility that each CD1 isoform might present essentially the same spectrum of antigens. A complete answer to this question of isoform‐specific binding motifs will require elution of lipids from cellular CD1 proteins and better methods to measure specific binding to CD1 proteins in vitro. Nevertheless, certain insights from molecular and cellular studies indicate that isoform‐specific patterns of antigen capture likely do exist. For example, CD1c‐presented dolichols and mycoketides have a single alkyl chain (Matsunaga et al., 2004; Moody et al., 2000), whereas most antigens presented by other CD1 isoforms have two. The hypothesis that CD1c may be specialized to present lipids with a single lipid anchor has not yet been proven. However, it already seems clear that the large size of the CD1b groove and the existence of the C0 portal as a functional escape hatch represent isoform‐specific adaptations that allow presentation of long chain (C80) antigens that cannot fit within the confines of CD1a or CD1d grooves. Secondly, even when two CD1 isoforms bind the same antigen, they may do so with differing molecular mechanisms, so that the antigens may differ in the overall hierarchy of antigens presented by each CD1 isoform. For example, CD1b and CD1d both present sphingolipids. However, a‐galactosyl ceramides occupy the full capacity of the CD1d groove (Zajonc et al., 2005a), whereas GM2 ganglioside occupies only two of the four pockets present in CD1b (Gadola et al., 2002). Consistent with the markedly differing mechanisms by which these CD1 proteins bind the same type of ceramide anchor, CD1d presents a‐galactosyl ceramides at much
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greater efficiency (nanomolar) than CD1b presents GM1 (micromolar) (Kawano et al., 1997; Shamshiev et al., 1999). 4.4. Functionally Dominant Aspects of CD1 Structure CD1 nomenclature and conventional analyses of relatedness among CD1 orthologs are based on overall levels of relatedness of proteins at the amino acid level. However, new information from CD1 crystal structures and functional studies have identified the particular amino acids that play dominant roles in CD1 function based on their abilities to mediate interactions with AP complexes or form the C0 portal, the T0 tunnel, and the terminus of the A0 pocket. Natural or experimentally induced point mutations in these functionally dominant positions lead to small changes in the overall sequence, but potentially large changes in the function of the protein. Figure 3 summarizes these functionally important amino acid positions, as determined from crystal studies of human and murine CD1 proteins, and then compares conservation of these residues among non‐human CD1 sequences. This analysis leads to questions about whether non‐human CD1 proteins that are denoted as orthologs of a given human CD1 isoform do indeed have the same or similar functions as their human counterparts. For example, the ability of human CD1b proteins to present particularly large lipids likely comes about in part due to the T0 tunnel, which results from two particularly small residues, glycines at positions 98 and 116 in the CD1 consensus sequence. These small amino acids leave a gap that forms the T0 tunnel and connects the A0 and F0 pockets to form a long A0T0 F0 superchannel. Whereas glycines are generally conserved at these positions among non‐human proteins that are designated as CD1b orthologs, guinea pig CD1b4 has larger valines at these positions and may therefore lack the T0 tunnel (Fig. 3). Likewise, the C0 portal contributes to the ability of human CD1b proteins to present large lipids. However, guinea pig CD1b4 and rabbit CD1b1 lack the cysteines at positions 131 and 145, suggesting that these proteins may lack an escape mechanism for larger alkyl chains. Thus, guinea pig CD1b4 provides an example of a protein that is designated as an ortholog of human CD1b based on its overall sequence, yet appears to lack key amino acids that form the structures that allow the groove in human CD1b to present lipids with long alkyl chains. Related to this, guinea pig CD1b3 might fail to capture lipids in late endosomes, as it is unique among CD1b orthologs in its lack of an identifiable tyrosine or dileucine endosomal targeting sequence (Fig. 2). These observations point to possible differences in function among guinea pig CD1b orthologs and might explain the basis of how this species retained a particularly large family of group 1 CD1 proteins (Dascher et al., 1999).
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Other questions arise from inspection of non‐conserved amino acids at functionally important positions in the consensus sequence. For example, non‐human CD1a sequences differ from human CD1a in key residues that are known to control antigen binding and endosomal trafficking. The valine at position 28 in human CD1a forms the terminus of the A0 pocket, which allows this pocket to bind lipids with a discrete chain length. Yet, the rabbit CD1a sequence at position 28 is more like that of human CD1b and mouse CD1d proteins, which use their open‐ended A0 pockets to interconnect with other pockets (Fig. 3). Similarly, human CD1a has been proposed to have a specialized function in surveying the content of early endosomes, based on the lack of endosomal targeting sequences in its cytoplasmic tail. However, non‐human human CD1a proteins have longer tails with putative endosomal localization sequences (Fig. 2). Although these questions related to the conservation of function in mammalian CD1a and CD1b proteins remain unanswered, the differential use of dileucine and tyrosine (YXXZ) motifs in the tails of CD1d orthologs provides a well documented example of how two species use distinct cellular mechanisms to promote recycling to late endosomes. Human, but not mouse CD1d has a dileucine motif that promotes steady state localization to endosomes (Rodionov et al., 1999, 2000). Conversely, the YXXZ motif in murine CD1d (YQDI) can interact with AP‐2 and AP‐3, whereas the human CD1d tail sequence (YQGV) binds only to the m‐subunit of AP‐2 (Elewaut et al., 2003; Sugita et al., 2002). One hypothesis is that this represents an unusual example of convergent evolution in which two closely related species evolved separate mechanisms to navigate into late endosomal compartments. Similarly, it has been proposed that the mouse CD1 system, which lacks an ortholog of CD1b, may have acquired point mutations that enable its YXXZ motif to allow CD1d binding to AP‐3, so that the mouse CD1d protein can sample lysosomal antigens in a way that is accomplished by CD1b in human systems (Dascher and Brenner, 2003). Both of these hypotheses emphasize the view that certain kinds of antigen processing reactions do not merely require antigen delivery to endosomes, but also require the particularly acidic environment ( pH 4.5) of late endosomes and lysosomes. 5. Microbial Antigens and Infectious Disease The range of known antigens presented by the CD1 system has grown rapidly in recent years. Whereas the early studies of CD1‐restricted T cells emphasized T cell activation by a‐galactosyl ceramide and several specialized lipids found only in mycobacteria, CD1 proteins have now been shown to mediate T cell activation in response to at least one example of most major classes
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of lipids found in mammalian cells, including phosphatidylinositols, glycosyl phosphatidylinositols, phosphatidylcholines, phosphatidylethanolamines, gangliosides, sulfatides, isoglobosides, and polyisoprenols. In addition, CD1 proteins present chemically diverse bacterial lipids such as mycolates, polyketides, acylated carbohydrates, and lipopeptides (Fig. 5). The apparent structural diversity of lipid antigens for the CD1 system is increasingly leading to the view that CD1 proteins do not solely present lipids with highly specialized structures or functions, but instead broadly sample the lipid content of cells for display. This in turn raises important practical questions about how CD1 proteins can bind to such structurally diverse ligands and how cells regulate the process by which different classes of self and foreign lipids compete for loading onto CD1. 5.1. Microbial Antigens The antigen presentation functions of CD1 were discovered through the study of human T cell responses to Mycobacterium tuberculosis. After isolation of T cell clones that respond to antigens presented by CD1a, CD1b, or CD1c, the stimulatory compounds were isolated and their structures identified as long chain, a‐branched, b‐hydroxy fatty acids known as mycolic acids (Beckman et al., 1994), lipoarabinomannans (Sieling et al., 1995), glucose monomycolates (Moody et al., 1997), mannosyl phosphomycoketides (Matsunaga et al., 2004; Moody et al., 2000), acylated sulfotrehaloses (Gilleron et al., 2004), and dideoxymycobactin lipopeptides (Moody et al., 2004) (Fig. 5). There is evidence that all of these lipids are made by mycobacterial species that infect mammals, and many of these antigens have been shown to correlate with or cause virulence. For example, mannosyl phosphomycoketides and acyl sulfotrehaloses are generally lacking in saprophytic mycobacteria, but are present in species capable of infecting cells (Domenech et al., 2004; Matsunaga et al., 2004). Deletion of pathways leading to the synthesis of mycobactin siderophores and dideoxymycobactin antigens reduce growth of M. tuberculosis in human cells (De Voss et al., 2000). Whereas most mycobacterial antigens are presented by group 1 CD1 proteins, there is new evidence that mycobacterial phosphatidylinositol mannosides (PIM) can bind to CD1d and activate NK T cells (Fischer et al., 2004). Two recent studies have provided convincing molecular evidence that NK T cells recognize structurally related, a‐linked sphingolipids from Sphingomonas capsulata, Sphingomonas paucimobilis, Sphingomonas yanoikuyae, or Ehrlichia muris (Kinjo et al., 2005; Mattner et al., 2005). Although is it not clear whether sphingomonas species, which have only rarely been shown to infect immunocompromised humans, are of clinical significance for human disease,
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Figure 5 Glycolipid stimulants of CD1‐restricted T cells. Human and mouse CD1 proteins are known to mediate T cell responses to structurally diverse classes of mammalian, microbial, and synthetic glycolipids.
this new insight is notable for several reasons. First, these naturally produced bacterial antigens have glucuronic or galacturonic acids that are in a‐anomeric linkage with the sphingosine base (Fig. 5). This a‐linkage represents a chemical feature that distinguishes these foreign lipids from most mammalian
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glycosyl ceramides, which typically are in b‐linkage to the sphingosine base. The difference in linkage serves to pivot the carbohydrate moiety into distinct positions. Therefore, the unusual a‐anomeric linkage plausibly serves as a chemical feature that allows these lipids to be recognized as foreign in comparison to mammalian sphingolipids that are otherwise similar in structure. In addition, this a‐linkage parallels a key feature of previously identified marine sponge‐derived a‐galactosyl ceramides, which are potent activators of NK T cells, but are not known to be produced by any organism that normally comes into contact with the mammalian immune system (Kawano et al., 1997). Therefore, identification of a‐linked sphingolipids in bacteria represents a step forward in identifying natural foreign antigens for NK T cells. Last, it is notable that the sphingomonas cell walls, unlike most gram negative bacteria, lack lipopolysaccharide (LPS) agonists of TLR‐4. This leads to the speculation that the invariant TCRs on NK T cells serve as a substitute for the well known means of innate activation through LPS and TLR‐4. In addition to these bacterial antigens for NK T cells, glycolipid stimulants of NK T cells have been identified from Leishmania, Trypanosoma, and Plasmodium species. CD1d knockout increases susceptibility of mice to infection by Leishmania donovani, and CD1‐tetramers loaded with lipophosphoglycan components of the outer cell wall of leishmania stain NK T cells, suggesting that activation by this antigen occurs through the TCR (Amprey et al., 2004). Glycosyl phosphatidylinositol anchors that resemble those found in Plasmodium and Trypanosoma species activate NK T cells in a CD1d‐dependent manner in vitro, and these glycolipids likewise bind to CD1d tetramers. In addition, under certain conditions, CD1d knockout can lead to altered B cell responses or outcomes of experimental models of malaria infection (Hansen et al., 2003a,b; Schofield et al., 1999). However, other studies have suggested that CD1d does not contribute to control of experimental infection with Plasmodium berghei (Molano et al., 2000) or activation of NK T cells (Procopio et al., 2002). In addition to the microbial compounds of known structure summarized in Fig. 5, CD1‐restricted T cells have been reported to be activated by a variety of bacteria, fungi, pathogenic protozoa, and viruses, although the precise structures of any antigenic compounds produced by these pathogens remain to be determined. 5.2. Diverse CD1‐Restricted T Cells in Infectious Disease In follow up to studies showing that human T cell clones could limit the in vitro growth of M. tuberculosis via cytolysis, granulysin, and g‐interferon (Stenger et al., 1997, 1998a), more recent studies have sought to detect lipid‐reactive T cells during in vivo infection. Because most or all antigens were presented by
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group 1 CD1 isoforms that lack orthologs in mice, in vivo studies were carried out with human patients with resolving subclinical M. tuberculosis infections (Agea et al., 2005; Moody et al., 2000; Ulrichs et al., 2003) or pulmonary tuberculosis (Gilleron et al., 2004). Each of these clinical studies found similar results. Fresh peripheral blood lymphocytes reactive against mannosyl phosphodolichols, mycolic acids, glucose monomycolates, or acyl sulfotrehaloses were not detectable in healthy controls, but were found in the majority of infected patients, with some evidence that they occur with high precursor frequency. These studies provide evidence that CD1‐ and lipid‐reactive T cells are activated during the acute phases of a human infectious disease and have prompted ongoing studies as to whether such responses persist such that they can be considered memory responses. Whether or not such lipid‐reactive T cells are protective against infection awaits further studies in animal models that express group 1 CD1 proteins. One study of guinea pigs, which express orthologs of human group 1 CD1 proteins, found that immunization with a mixture of lipid and protein antigens substantially reduces the size of pulmonary granulomata and provides some reduction in mycobacterial burden after challenge (Dascher et al., 2003). 5.3. NK T Cells and Infectious Disease CD1d and NK T cells have been implicated in affecting outcomes in response to a wide variety of infections by bacteria, viruses, fungi, and protozoa. Interpretation of the biological significance of these many findings hinges in part on certain aspects of study design relating to the antigens used and the means of deleting NK T cells. One general issue relates to experimental means to separately study the effects of invariant NK T cells with Va14Ja18 TCRs (previously known as Va14Ja281 TCRs) versus the larger repertoire of T cells that recognize CD1d, which includes T cells that do not express this particular TCR (varied NK T cells). The latter population was originally identified based on in vitro analysis of CD1d‐restricted T cells taken from mice and humans, and is receiving more scrutiny based on in vivo studies of infection showing that this population can mediate effects that are independent of invariant NK T cells (Behar and Cardell, 2000). CD1d deletion results in loss of both variable and invariant NK T cells. Invariant NK T cells can be selectively removed by germline deletion of the sequences containing the Ja18 segment (Kawano et al., 1997) or be selectively augmented by sorting for T cells that stain a‐galoctosyl ceramide‐loaded tetramers or antibodies against TCR a chains with the Va14 gene segment. Taking advantage of these methods, recent studies have suggested a role for variable NK T cells in mediating tissue damage in response to Coxsackie virus
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or hepatitis B virus (HBV) genes. In the former study, it was found that post‐ viral myocarditis was attenuated by CD1d deletion, but not Ja18 deletion, implicating variable NK T cells in causing the post‐infectious myocardial damage (Huber et al., 2003). Likewise, HBV gene‐mediated liver damage could be transferred by CD1d‐restricted cells that did not stain for Va14 or bind to a‐galactosyl ceramide‐loaded CD1d tetramers, implicating variable NK T cells in this model of hepatitis (Baron et al., 2002). A second general issue relates to outcomes of infection after treatment of animals with a particularly potent synthetic agonist of NK T cells, a‐galactosyl ceramide. Administration of this compound leads to systemically detectable levels of g‐interferon, a broadly acting anti‐microbial Th1 cytokine. It has long been speculated that a‐galactosyl ceramides are superagonists in the sense that they activate NK T cells more strongly than naturally occurring antigens for NK T cells. Recent studies have identified naturally occurring stimulants of NK T cells, including isoglobosides, sphingomonas‐derived ceramides, lipophosphoglycans, and phosphatidylinositol mannosides. Comparison of these lipids with synthetic a‐galacotsyl ceramides has generally found that naturally occurring antigens less potently activate NK T cells or mediate tetramer staining of NK T cells, as compared with a‐galactosyl ceramide (Amprey et al., 2004; Fischer et al., 2004; Kinjo et al., 2005; Mattner et al., 2005; Zhou et al., 2004b). Because a‐galactosyl ceramide appears to act much more strongly than natural antigens, evidence that a‐galactosyl ceramide mediates protection provides useful evidence supporting the use of this glycolipid as an immunotherapeutic agent, but does not necessarily imply a natural function for NK T cells in infection. For example, one study found that deletion of Va14Ja18 NK T cells does not affect the outcome of acute cytomegaloviral (CMV) infections, but administration of a‐galactosyl ceramide provides some protection (van Dommelen et al., 2003). The apparent differences in outcomes after these two experimental manipulations might be explained if NK T cells do indeed have an antiviral function, but the pathogen fails to provide a stimulus of comparable potency to that of a‐galactosyl ceramide. Several recent studies show that deletion of CD1d results in worsened outcomes of experimental viral infections. For example, deletion of CD1d or the combined deletion of NK and NK T cells leads to increased susceptibility to infections with intravaginal herpes simplex virus type 2 infections in mice (Ashkar and Rosenthal, 2003). Mouse infections with herpes simplex virus type 1 (HSV 1) are worsened in mice lacking either CD1d or the Ja14Va18 TCR, implicating a role for invariant NK T cells in the response (Grubor‐Bauk et al., 2003). Last, there is one case report of disseminated infection of a human with an attenuated strain of varicella zoster virus in a human with low levels of NK T
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cells (Levy et al., 2003). Collectively, these reports suggest that NK T cells can play a determinative role in infections with herpes viruses, a class of viruses that persist long term in mammalian hosts. Conversely, there is some evidence that CD1d and NK T cells do not affect outcomes in more acute infections with the SARS carona virus and lymphocytic choriomeningitis virus (Glass et al., 2004; Spence et al., 2001). 5.4. Virally Mediated Alterations in CD1 Expression Coupled to this evidence that CD1d protects against viral infections, there is new evidence that viruses modulate CD1 expression in ways that might lead to immune evasion. Kaposi sarcoma‐associated herpes virus (KSHV) downregulates cell surface CD1d expression via modulator of immune recognition (MIR)‐mediated reinternalization and ubiquitination (Sanchez et al., 2005). Similarly, the human immunodeficiency virus (HIV‐1) or other viral vectors expressing the HIV nuclear envelope factor (nef) gene partially downregulate human expression of CD1a and CD1d proteins on infected cells (Cho et al., 2005; Shinya et al., 2004). In both cases, nef‐mediated downregulation is lessened when the cytoplasmic tail of CD1 proteins is truncated, implicating altered trafficking as the mechanism of loss of cell surface CD1. This redirected trafficking of CD1 may be related to the previously known mechanism by which HIV nef induces downregulation of MHC class I by revealing a cryptic cytoplasmic tail sequence that interacts with adaptor protein complexes (Le Gall et al., 1998). However, the mechanisms involving CD1 and MHC class I are at least somewhat distinct, as MHC class I accumulates in the golgi, and CD1a loss appears to involve redirected transport to lysosomes. Given the emerging evidence that CD1d mediates protective responses during viral infections, especially herpes viruses, immune evasion through downregulation of CD1 expression is a plausible and interesting new concept. Understanding how partial downregulation of CD1 expression on the surface of infected cells translates into biologically meaningful immune evasion requires further work on several basic questions. Some evidence indicates that CD1 downregulation is a cell‐autonomous effect (Quaranta et al., 2002), raising questions about how viruses that persist in cells that do not normally express CD1 can transfer inhibitory effects to CD1‐expressing cells. Also, research into immune evasion by pathogens has in some cases outpaced work to determine whether CD1‐restricted T cells play a determinative role in infection. CD1 proteins and NK T cells are not uniformly active against all viruses, so strong support for active subversion of immune recognition must involve the search for evidence that CD1 proteins are determinative for the natural infectious process itself.
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5.5. Indirect Means of T Cell Activation by Glycolipids The primary means of activation of CD1‐restricted T cells involves direct contact of CD1‐lipid complexes with TCRs, as shown by experiments in which antigen‐dependent T cells can be stained with fluorescent, lipid‐loaded tetramers (Benlagha et al., 2000; Karadimitris et al., 2001; Matsuda et al., 2000). Also supporting this conclusion, truncated TCRs bind with high affinity to CD1‐lipid complexes, and TCR‐lipid‐CD1 complexes can be modeled based on the crystal structures of TCRs and CD1‐lipid complexes (Grant et al., 2002; Sidobre et al., 2002; Zajonc et al., 2005b). The strongest evidence that any given glycolipid functions as a cognate antigen that directly contacts the TCR is seen when (1) it activates T cells, (2) activation requires CD1 proteins, (3) purified CD1‐lipid complexes activate T cells, and (4) the lipid lacks adjuvant or mitogenic properties. Alpha‐galactosyl ceramide likely meets all of these criteria and can be considered to act as a cognate antigen, based on the ability of CD1d‐a‐galactosyl ceramide complexes to bind to and activate TCRs. Similarly, gangliosides, sulfatides, mycolates, and glucose monomycolates can stimulate T cells when added in complex with recombinant CD1 proteins, strongly pointing to the likelihood that their mechanism of action involves direct contact with variable regions of the TCR. Thus, many lipid stimulants of T cells act as classical cognate antigens in the sense that they provide stimulatory signals through the variable regions of the TCR. Several recent studies have shown that bacteria, bacterial lipids, or agonists of toll‐like receptors in ways that do not primarily involve TCR contact. Instead effects are mediated through increased CD1 expression, increases lipid antigen uptake, altered the production of endogenous lipids or secretion of activating cytokines by APCs (Brigl et al., 2003; De Libero et al., 2005; Krutzik et al., 2005; Mattner et al., 2005; Roura‐Mir et al., 2005b). These studies suggest bacterial lipids, especially those with the ability to agonize TLR‐2 or TLR‐4, may activate CD1‐restricted T cells by an indirect mechanism that requires two separate signals, APC activation combined with TCR‐CD1 contacts. For example, in vitro studies show that gram negative bacterial lipopolysaccharide leads to NK T cell activation through an indirect mechanism that involves TLR‐4‐mediated secretion of IL‐12 by myeloid APCs, rather than direct binding to CD1d and presentation to TCRs (Brigl et al., 2003). In fact, the failure of b‐hexosaminidase‐deficient mice to show NK T cell responses to LPS suggests that the role of LPS in vivo may involve stimulation of production of endogenous isogloboside antigens within the APC, rather than LPS‐ mediated contact with T cell receptors (Mattner et al., 2005). These new studies raise questions about whether some of the lipid stimulants depicted
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in Fig. 5 act mainly as cognate antigens for TCRs or function via indirect mechanisms by activating APCs. Further studies of the mechanisms of glycolipid‐mediated T cell activation have obvious importance for designing immunotherapies (Section 7) and may solve controversies relating to discordant results with the same glycolipid by different types of APCs. 6. Self Antigens, Autoreactivity, and Autoimmune Disease 6.1. Structures of Self Lipid Antigens Early studies of CD1‐mediated T cell activation showed that CD1‐autoreactive T cells could be selectively activated by CD1‐expressing APCs, but unlike T cells described in the prior section, did not require any exogenous or foreign lipid antigen (Porcelli et al., 1989). Such CD1 autoreactivity might have occurred as a result of TCR recognition of unliganded CD1 proteins or by CD1 proteins that were bound by endogenous self lipid antigens. Studies showing that GM1 ganglioside‐CD1b complexes can activate T cells provided more direct evidence for presentation of antigenic self lipids to T cells (Shamshiev et al., 1999, 2000). The ability of CD1 proteins to bind and present self lipids is now further supported by studies that have directly eluted phosphatidylinositols from CD1 and shown that they can activate NK T cells under certain circumstances (Gumperz et al., 2000; Joyce et al., 1998). In addition, sulfatides (Jahng et al., 2004; Shamshiev et al., 2002), ganglioside GD3 (Wu et al., 2003), phosphatidylethanolamine (Rauch et al., 2003), and other diacylglycerols (Agea et al., 2005) can lead to activation of human CD1‐ restricted T cells (Fig. 5). 6.2. Candidate Mechanisms for Regulating Responses to Self Antigens The identification of self cellular lipids as stimulants for CD1‐restricted T cells in vitro now raises basic questions about how T cell responses to self antigens are regulated in vivo. Although there is evidence for positive selection of NK T cells in the thymus (Benlagha et al., 2002), it is not yet known whether diverse CD1‐restricted T cells undergo negative selection in a process that is equivalent to mechanisms that are well established to control central tolerance in MHC‐restricted T cells (Wei et al., 2005). In fact, until recently there was little insight into the mechanisms of regulating autoreactivity to cellular lipids. However, new studies suggest several candidate mechanisms that could act in the periphery to regulate T cell stimulation by self lipids.
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6.2.1. Alterations of Self Lipid Antigen Production in Cells One possibility is that self lipid antigens with an ability to stimulate T cells are not constitutively synthesized, but instead are produced in response to activating stimuli. For example, a recent study has shown that knockout of a lysosome enzyme, b‐hexosaminidase b (Hex b), leads to loss of NK T cells in the periphery. Separately, it was found that isoglobotrihexosylceramide (iGb3), a mammalian glycolipid produced by this enzyme, can activate invariant NK T cells (Zhou et al., 2004b). Isoglobosides are known to exist in mammalian cells, but are not so abundant that their functions and cellular distributions are well understood. These findings now suggest that as yet unidentified upstream stimuli, which alter the production, intracellular localization, or loading of isogloboside lipids onto CD1d proteins, regulate the activation of NK T cells in vivo. 6.2.2. Adjuvants for CD1‐Restricted T Cells A second general possibility is that APCs require a second stimulus, in addition to self antigens bound in the groove, to optimally present lipid antigens to T cells. As discussed earlier, in vitro studies of antigen presentation and CD1 expression show that microbial cell wall products can alter levels of CD1 expression, rates of lipid antigen delivery to endosomes, and other factors that convert monocytes into competent antigen‐presenting cells (De Libero et al., 2005; Krutzik et al., 2005; Roura‐Mir et al., 2005b). Myeloid DCs and their precursors migrate widely among tissues and initiate T cell responses. In theory, a system that limits group 1 CD1 expression to those myeloid DC precursors that have directly encountered pathogens, and thereby received activating stimuli, may limit unwanted presentation of self lipid antigens in other situations. A recent study has shown that infection of human DCs with bacteria or treatment with bacterial products increases the ability of myeloid cells to present self gangliosides and sulfatides to CD1a‐ and CD1b‐restricted T cell clones, thereby highlighting the possibility that bacteria turn on pathways that lead to presentation of both self and foreign lipids (De Libero et al., 2005). 6.2.3. Regulation by Subcellular Antigen Processing Pathways A third possibility is that regulated mechanisms of antigen loading within endosomes can alter the spectrum of self and foreign lipids presented to T cells. This hypothesis can be considered by comparing emerging concepts in subcellular pathways of lipid antigen presentation with well‐established subcellular pathways of peptide presentation. To generate peptide antigens, nearly
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all proteins require cellular processing, which occurs in one of two distinct pathways, depending on whether peptides are generated in the endosomes or in the cytosol (Cresswell, 1994). The general cellular requirements for lipid antigen presentation differ from those of proteins in two important ways. First, individual lipid antigens presented by the CD1 system vary in the extent to which their recognition requires cellular processing, such that certain antigens absolutely require cellular processing and others can be readily recognized after binding to recombinant CD1 proteins at neutral pH. Secondly, most or all cellular cofactors for lipid antigen recognition identified to date act on antigens within the lumen of intracellular compartments, especially late endosomes. This leads to a model in which the separate pathways of lipid antigen presentation are defined in part based on the identity of the antigen and the stringency of its loading requirements, with most high‐stringency loading interactions occurring in endosomes (Table 1). The antigen‐binding domains of CD1 proteins remain topologically confined to lumenal compartments and cell surface of APCs, so most or all antigens likely contact the CD1 groove after delivery from the lumenal leaflet of membranes, intralumenal lipid‐protein complexes, intralumenal microbes, or, in the case of cell surface CD1 proteins, the outside of the cell. Thus, the total pool of antigens available for binding onto CD1 includes both endogenous self lipids that comprise the membranes or lumenal compartments of CD1‐expressing APCs and exogenous antigens taken up into endosomal compartments. Among these, certain types of lipid antigens appear to involve high stringency loading pathways in that they absolutely require cellular factors for loading onto CD1 proteins. These antigens include mycolic acids, lipoarabinomannan, glucose monomycolates with long alkyl chains (C80 GMM), and acylated sulfotrehaloses. The functional studies of the loading or recognition of these lipid antigens indicate that their loading takes place in acidic endosomes using mechanisms that involve low pH, receptor‐mediated delivery to endosomes, or lipid transfer systems involving saposins or apoE. Other lipid antigens readily bind to recombinant CD1 proteins at neutral pH in experimental systems using low stringency mechanisms. These antigens tend to be self lipids and have relatively short alkyl chains, such as phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine, ganglioside, sulfatide, and glucose monomycolate with short alkyl chains (C32 GMM) (Table 1). Many studies of the differing loading requirements of these antigens point to a general model in which high and low stringency loading interactions occur in distinct subcellular compartments. Under normal conditions, dynamically trafficking CD1 proteins are predicted to bind low stringency antigens in almost any lumenal compartment, including the ER, secretory pathway, cell
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Table 1 High and Low Stringency Pathways for Presentation of Lipids to T Cells High stringency Location
Endosomes
Representative antigens
mycolic acid, C80 glucose monomycolate, lipoarabinomannan acyl sulfotrehaloses, endogenous antigens for NK T cells No
Presentation by recombinant CD1 proteins at neutral pH Inhibition by fixation of APC membranes Inhibition by neutralization of APC endosomes Inhibition by endosomal targeting motif deletion in CD1 Potency of presentation Half‐life after antigen pulse References
Low stringency ER, Golgi, cell surface and endosomes Sulfatide, ganglioside, phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine C32 glucose monomycolate Yes
Yes
No
Yes
No
Yes
No
High (nanomolar)
Low (micromolar)
Long
Short
(Chiu et al., 1999; Gilleron et al., 2004; Jackman et al., 1998; Moody et al., 2002; Porcelli et al., 1992; Sieling et al., 1995)
(Agea et al., 2005; Joyce et al., 1998; Shamshiev et al., 1999, 2000, 2002)
Antigens can bring CD1b and CD1d proteins via stringent mechanisms that require endosomal cofactors or low pH or bind via non‐stringent mechanisms that likely occur in many cellular compartments.
surface, and endosomes. Such non‐selective interactions may lead to the capture of antigens based on their abundance, which might account for the elution of phosphatidylinositol‐containing compounds from cellular CD1d proteins (Joyce et al., 1998). When CD1 proteins enter the specialized endosomal microenvironment, they encounter antigens concentrated in this location by selective capture pathways and are loaded under more stringent conditions involving lipid transfer proteins, pH‐mediated CD1 denaturation, and other factors that selectively promote lipid exchange. Despite delay and greater complexity of cellular interactions that lead to loading of high
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stringency antigens, the studies summarized in Table 1 generally show that high stringency antigens have a greater potency for activating T cells (nanomolar) as compared with exogenously added low stringency antigens (micromolar). Further, some evidence suggests that high stringency antigens have longer half‐lives of binding to CD1 or activation of CD1‐restricted T cells (Moody et al., 2002). The general prediction of this model is that CD1 proteins bind and present many classes of self antigens. CD1 transit through endosomal compartments leads to acquisition of high affinity antigens, which skews the overall repertoire of subsequently displayed antigens toward those subclasses that enter the cells from the outside or have unusual chemical features (such as long chain length), which allow them to be retained within the groove. This may promote presentation of foreign antigens, if they are concentrated in endosomes by virtue of their entry into cells by phagocytosis or pattern recognition receptor‐mediated internalization and other mechanisms (Blander and Medzhitov, 2004; Hunger et al., 2004; Prigozy et al., 1997). Although this model is consistent with most published studies, certain missing information is the subject of ongoing study. Does CD1 randomly capture low stringency lipids, or are there dominant self antigens that serve a groove blocking function? Do lipid antigens generally undergo structural alterations in endosomes? Which endosomal cofactors are involved in the dynamic process of lipid insertion into the CD1 grooves? Also, it should be emphasized that the existence of high and low stringency loading pathways has been most clearly demonstrated for antigens presented by CD1b and CD1d, whereas much less information is available for CD1a and CD1c. 6.3. Autoimmune Recognition of Self Antigens The identification of mouse and human T cell clones that directly recognize CD1 proteins or ubiquitous self antigens raises the possibility that autoreactive T cells could mediate autoimmune injury in vivo. One model posits that activation of immunoregulatory NK T cells generally protects against autoimmunity and that loss or weakening of NK T cell immunoregulation leads to autoimmunity. This hypothesis is supported by several studies showing that patients with autoimmune disease have reduced total numbers of NK T cells or have NK T cells that are biased toward Th1 cytokine profiles (Sumida et al., 1995; van der Vliet et al., 2002; Wilson et al., 1998), although one study of human autoimmune diabetes patients has questioned these findings (Lee et al., 2002). Separately, deletion of CD1 or NK T cells generally worsens progression of autoimmune diabetes in animals (Duarte et al., 2004; Falcone et al., 2004; Naumov et al., 2001).
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A second type of model involves the hypothesis that diverse CD1‐restricted T cells might directly recognize lipids expressed within the target cells and that recognition leads to local tissue destruction. For example, sulfatides, which are expressed at particularly high levels in myelin, can be the targets of variable CD1d‐restricted T cells in vivo, and treatment of mice with sulfatides ameliorates experimental allergic encephalomyelitis (Jahng et al., 2004). Similarly, diverse CD1‐restricted T cells recognizing gangliosides, which are likewise expressed at high levels in myelin, have been detected in human patients with multiple sclerosis (Shamshiev et al., 1999). Also, studies of human patients with Grave’s disease and Hashimoto’s thyroiditis have identified autoreactive T cells that recognize CD1a and CD1c proteins and home to the thyroid gland (Roura‐Mir et al., 2005a). Because diverse CD1‐restricted T cells lack surface markers or structurally invariant TCRs that would allow direct tracking in vivo or ex vivo, it is not yet known whether such cells are more numerous in autoimmune disease patients versus normal controls. However, these studies do provide proof of concept that CD1 and self lipid recognition can occur at the site of autoimmune tissue destruction. 6.4. CD1 and Allergic Disease There is new evidence that activation of NK T cells contributes to the development of allergic diseases. One of the striking features of the function of NK T cells is that they are able to secrete large amounts of IL‐4 in a primary stimulation, in contrast to MHC‐restricted T cells. This led to the hypothesis that NK T cells function to provide a source of IL‐4 at early time points in immune response and could consequently polarize MHC‐restricted T cells towards Th2 differentiation pathways or otherwise regulate Th2 immune responses. The first studies of CD1 knockout in mice found that IL‐4 production, IgE responses, and other surrogates of Th2 immunity were generally intact in CD1d‐deficient mice, suggesting that NK T cells were not absolutely required for these particular outcomes (Chen et al., 1997; Smiley et al., 1997). However, the ability of NK T cells to secrete IL‐4 in large amounts has never been questioned, and more detailed studies of CD1d knockout mice now suggest a role for NK T cells in mouse models of asthma and some forms of allergic hypersensitivity reactions that are mediated by Th2 cytokines. A role of CD1d and NK T cells in a mouse model of OVA‐induced airways hyperreactivity was clearly shown in a study in which deletion of either CD1d or Va14Ja18þ T cells resulted in marked reduction of inflammation and airway responsiveness. Further, it was shown that reconstitution with NK T cells reversed the effects, as long as the transferred NK T cells were capable of secretion of IL‐4 or IL‐13 (Akbari et al., 2003). A role for CD1d knockout in
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worsening pulmonary airways disease has been confirmed in several other studies and has extended to models of ragweed‐induced pulmonary inflammation (Araujo et al., 2004; Bilenki et al., 2004; Lisbonne et al., 2003). Further, treatment of animals with a‐galactosyl ceramide results in increased levels of lung eosinophils, IgE, and IL‐4 (Kim et al., 2004). It is notable that effects of CD1d‐restricted NK T cells in animal models of airway hyperreactivity induced by pulmonary challenge with protein antigens are stronger than those seen with experiments carried out to assess IgE or other systemic measures of allergic inflammation, raising the possibility that NK T cells have particularly strong effects in the lung. In addition to these effects on murine NK T cells, pollen phospholipids that differ in structure from those found in mammalian cells can activate CD1‐restricted T cells in humans, and some evidence indicates that this effect correlates with seasonal allergy (Agea et al., 2005). 7. Synthetic Lipid Antigens and Prospects for Immunotherapy 7.1. T Cell Fine Specifity for Lipid Structure Based on emerging information about how the precise chemical features of antigens influence their recognition by T cells, it is now possible to design altered lipid ligands that activate T cells in ways that influence their cytokine profiles and other effector functions. Most structure‐function studies of lipid recognition have found that alteration of the carbohydrate or peptide moieties of antigens abrogate their ability to stimulate T cells. However, small changes in the overall chain length or saturation state of the alkyl units of CD1‐ presented antigens can preserve antigen recognition, while bypassing certain APC processing requirements or altering the potency or Th1–Th2 polarization properties of antigens. For example, mycobacterial glucose monomycolate antigens, normally produced with long (C80) alkyl chains, are presented by DCs after transport to endosomes. A version of glucose monomycolate that has the same carbohydrate structure, but a shorter C32 alkyl chain, is able to bypass the need for processing in endosomes so that it can be more efficiently presented by B cells that lack efficient mechanisms for uptake into endosomes (Moody et al., 2002). Similarly, several systems have shown that mono‐ or polyunsaturated fatty acids generally increase the potency of phosphatidylethanolamines, lipopeptides, and phosphatidylcholines for activating T cells (Agea et al., 2005; Moody et al., 2004; Rauch et al., 2003). It has been argued that the diunsaturated fatty acids that occur naturally in pollens are responsible for the increased responses compared to mammalian phosphatidylcholines that contain predominantly monounsaturated or saturated fatty acids.
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7.2. Synthesis of Altered Lipid Ligands The ability of the fine structure of the lipid moieties of antigens to influence T cell responses in vitro has facilitated efforts to design altered a‐galactosyl ceramides that produce desired immunological outcomes in vivo. The immunological properties of a‐linked ceramide lipids were initially identified by screening large chemical libraries for the ability of compounds to promote tumor regression. This screen identified marine sponge antigens, which served as the basis for synthesis of an a‐galactosyl ceramide with a C26:0 fatty acyl unit and a C18:0 sphingosine base. This synthetic compound likewise activates NK T cells and is known by the proprietary name, KRN 7000 (Kawano et al., 1997). Production of analogs with shorter fatty acyl and sphingosine bases, C24 and C9, respectively, resulted in a compound called OCH, a form of a‐galactosyl ceramide that causes NK T cells to secrete higher levels of IL‐4 and protects against experimental allergic encephalomyelitis in mice (Miyamoto et al., 2001). This effect, which has also been seen in mouse models of autoimmune diabetes, arthritis, and colitis, is related to the shorter alkyl chains, which appear to less effectively anchor the lipid to CD1d, resulting in faster off rates and altered TCR signaling (Chiba et al., 2004; Mizuno et al., 2004; Oki et al., 2004; Ueno et al., 2005). A separate approach validates the concept of synthesizing a‐galactosyl ceramides that preferentially stimulate Th2 cytokine secretion, as synthesis of an a‐galactosyl ceramide analog containing a C20:2 fatty acyl chain likewise allowed potent induction of IL‐4 by NK T cells in vitro and in vivo, as compared to KRN 7000 (Yu et al., 2005). 8. Conclusion: Prospects for Immunotherapy The isolation of natural antigens and synthesis of altered lipid antigens now offers a new means for immunotherapy, whereby CD1‐presented lipids are given as immunomodulatory agents that activate, deactivate, or polarize the responses of CD1‐restricted T cells. As evidence accumulates that lipid ligands of CD1 proteins alter outcomes in animal models of autoimmunity, infections, and cancer, CD1‐presented lipids are now being used as immunomodulatory agents in clinical trials of human diseases (Nieda et al., 2004). Many glycolipid antigens, including a‐galactosyl ceramides, are orally bioavailable, so that they could be readily administered in conventional oral formulations (Silk et al., 2004). Certain aspects of the basic biology of lipid synthesis and presentation suggest that lipid‐based immunotherapy could improve or complement existing approaches to immunization. The success of antigen‐specific T cell modulation by MHC‐presented peptides has been limited due to the diversity
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of human MHC protein structures, which requires design of peptides, which promiscuously bind to many MHC proteins. The lack of common or functionally important CD1 polymorphisms raises the prospect that lipid antigens would be presented similarly by individuals within genetically diverse human populations. Related to this, it has been argued that the low levels of allelic polymorphism in CD1 proteins results from the lack of rapid change in lipid structure over evolutionary time. Peptide antigens can escape detection by T cells with a single point mutation, which often disrupts TCR contact but does not have an appreciable affect on the overall function of the larger protein. In contrast, lipids and glycolipids are made by biosynthetic pathways involving multiple enzymes. Although changes in glycolipid structure can occur through genetic deletion of enzyme function, such changes usually alter the glycolipid in a more general way so that its overall function is lost. There is increasing evidence that CD1‐restricted T cells target mycobacterial lipids that have non‐redundant functions in growth or function as pathogenicity factors (Gilleron et al., 2004; Van Rhijn et al., 2005; Matsunaga et al., 2004). These observations are consistent with the hypothesis that pathogens cannot as readily form functionally intact escape mutants because the lipid antigens contribute directly to the ability to infect and persist in the host. Two types of lipid‐based immunotherapeutic strategies, which parallel the separate immunoregulatory and effector functions of diverse and invariant CD1‐restricted T cells (Fig. 1), are currently being developed. One strategy involves injection of a‐galactosyl ceramide or other agonists of NK T cells to promote cytokine release, leading to dendritic cell maturation and altered MHC‐restricted T cell activation. In this approach, glycolipids are considered adjuvants because the main effect of NK T cells involves activation of antigen‐ presenting function of DCs in mice (Fujii et al., 2003) and humans (Nieda et al., 2004). Concomitant treatment with conventional peptide antigens can focus the subsequent MHC‐restricted T cell response on a desired target tissue. For example, co‐administration of a‐galactosyl ceramide with HLA‐A2‐presented peptide antigens markedly increases the priming of CD8þ peptide‐specific T cells and promotes regression of melanoma tumors (Silk et al., 2004). A variant of this strategy has been used in animal models of Th1‐mediated autoimmune diseases. Altered lipid ligands increase the ratio of Th2/Th1 cytokines produced by NK T cells, which can downmodulate MHC‐restricted T cell function (Miyamoto et al., 2001; Van Kaer, 2005; Yu et al., 2005). A second strategy, which is just beginning to be developed, involves stimulating diverse CD1‐restricted T cells, which may directly carry out effector functions against those cells that express lipids that are selectively made by pathogens, tumors, or within tissues with specialized functions. This approach does not involve MHC‐restricted T cells and relies on the premise that human
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T cells can be activated to recognize lipid antigens with highly selective patterns of expression on a limited number of target cells. Some candidates already exist, as mycolates, sulfotrehaloses, and phosphomycoketides are found only in pathogens, and certain sphingolipids are somewhat selectively expressed in myelin (Fig. 5). Despite decades of work on tumor‐associated glycolipid targets of antibody responses, well‐defined tumor‐associated glycolipids presented by the CD1 system have not yet been extensively investigated. Because many of these antigens for diverse CD1‐restricted T cells are presented by inducibly expressed group 1 CD1 proteins, immunization strategies will likely involve glycolipid adjuvants to increase group 1 CD1 expression and function on myeloid DCs. These new therapeutic strategies derive from a simple observation, made about a decade ago, that human T cells are activated by both lipid and protein components of target cells. Acknowledgments The author thanks C. Anthony DeBono, Carme Roura‐Mir, Christopher Dascher, and Dirk Zajonc for analysis of CD1 sequence, design of CD1 schematics, and helpful discussions. This work is supported by the Pew Foundation Scholars in the Biomedical Sciences, the Cancer Research Institute, the Mizutani Foundation for Glycoscience, and the NIH (AI049313 and AR48632).
References Agea, E., Russano, A., Bistoni, O., Mannucci, R., Nicoletti, I., Corazzi, L., Postle, A. D., De Libero, G., Porcelli, S. A., and Spinozzi, F. (2005). Human CD1‐restricted T cell recognition of lipids from pollens. J. Exp. Med. 202, 295–308. Akbari, O., Stock, P., Meyer, E., Kronenberg, M., Sidobre, S., Nakayama, T., Taniguchi, M., Grusby, M. J., DeKruyff, R. H., and Umetsu, D. T. (2003). Essential role of NKT cells producing IL‐4 and IL‐13 in the development of allergen‐induced airway hyperreactivity. Nat. Med. 9, 582–588. Amprey, J. L., Im, J. S., Turco, S. J., Murray, H. W., Illarionov, P. A., Besra, G. S., Porcelli, S. A., and Spath, G. F. (2004). A subset of liver NK T cells is activated during Leishmania donovani infection by CD1d‐bound lipophosphoglycan. J. Exp. Med. 200, 895–904. Angenieux, C., Fraisier, V., Maitre, B., Racine, V., Van Der, W. N., Fricker, D., Proamer, F., Sachse, M., Cazenave, J. P., Peters, P., Goud, B., Hanau, D., Sibarita, J. B., Salamero, J., and de la Salle, H. (2005). The cellular pathway of CD1e in immature and maturing dendritic cells. Traffic 6, 286–302. Angenieux, C., Salamero, J., Fricker, D., Cazenave, J. P., Goud, B., Hanau, D., and de la Salle, H. (2000). Characterization of CD1e, a third type of CD1 molecule expressed in dendritic cells. J. Biol. Chem. 275, 37757–37764. Araujo, L. M., Lefort, J., Nahori, M. A., Diem, S., Zhu, R., Dy, M., Leite‐de‐Moraes, M. C., Bach, J. F., Vargaftig, B. B., and Herbelin, A. (2004). Exacerbated Th2‐mediated airway inflammation and hyperresponsiveness in autoimmune diabetes‐prone NOD mice: A critical role for CD1d‐ dependent NKT cells. Eur. J. Immunol. 34, 327–335.
LIPID ANTIGENS FOR CD1‐RESTRICTED T CELLS
129
Ashkar, A. A., and Rosenthal, K. L. (2003). Interleukin‐15 and natural killer and NKT cells play a critical role in innate protection against genital herpes simplex virus type 2 infection. J. Virol. 77, 10168–10171. Baron, J. L., Gardiner, L., Nishimura, S., Shinkai, K., Locksley, R., and Ganem, D. (2002). Activation of a nonclassical NKT cell subset in a transgenic mouse model of hepatitis B virus infection. Immunity 16, 583–594. Batuwangala, T., Shepard, D., Gadola, S. D., Gibson, K. J. C., Zaccai, N. R., Besra, G. S., Cerundolo, V., and Jones, E. Y. (2003). The crystal structure of human CD1b with a bound bacterial glycolipid. J. Immunol. 238, 2–2388. Bauer, A., Huttinger, R., Staffler, G., Hansmann, C., Schmidt, W., Majdic, O., Knapp, W., and Stockinger, H. (1997). Analysis of the requirement for beta 2‐microglobulin for expression and formation of human CD1 antigens. Eur. J. Immunol. 27, 1366–1373. Beckman, E. M., Porcelli, S. A., Morita, C. T., Behar, S. M., Furlong, S. T., and Brenner, M. B. (1994). Recognition of a lipid antigen by CD1‐restricted ab T cells. Nature 372, 691–694. Behar, S. M., and Cardell, S. (2000). Diverse CD1d‐restricted T cells: Diverse phenotypes, and diverse functions. Semin. Immunol. 12, 551–560. Belperron, A. A., Dailey, C. M., and Bockenstedt, L. K. (2005). Infection‐induced marginal zone B cell production of Borrelia hermsii‐specific antibody is impaired in the absence of CD1d. J. Immunol. 174, 5681–5686. Bendelac, A. (1995). Positive selection of mouse NK1þ T cells by CD1‐expressing cortical thymocytes. J. Exp. Med. 182, 2091–2096. Bendelac, A., Killeen, N., Littman, D. R., and Schwartz, R. H. (1994). A subset of CD4þ thymocytes selected by MHC class I molecules. Science 263, 1774–1778. Benlagha, K., and Bendelac, A. (2000). CD1d‐restricted mouse V alpha 14 and human V alpha 24 T cells: Lymphocytes of innate immunity. Semin. Immunol. 12, 537–542. Benlagha, K., Kyin, T., Beavis, A., Teyton, L., and Bendelac, A. (2002). A thymic precursor to the NK T cell lineage. Science 296, 553–555. Benlagha, K., Weiss, A., Beavis, A., Teyton, L., and Bendelac, A. (2000). In vivo identification of glycolipid antigen‐specific T cells using fluorescent CD1d tetramers. J. Exp. Med. 191, 1895–1903. Bilenki, L., Yang, J., Fan, Y., Wang, S., and Yang, X. (2004). Natural killer T cells contribute to airway eosinophilic inflammation induced by ragweed through enhanced IL‐4 and eotaxin production. Eur. J. Immunol. 34, 345–354. Blander, J. M., and Medzhitov, R. (2004). Regulation of phagosome maturation by signals from toll‐ like receptors. Science 304, 1014–1018. Bonifacino, J. S., and Traub, L. M. (2003). Signals for sorting of transmembrane proteins to endosomes and lysosomes. Annu. Rev. Biochem. 72, 395–447. Brigl, M., Bry, L., Kent, S. C., Gumperz, J. E., and Brenner, M. B. (2003). Mechanism of CD1d‐ restricted natural killer T cell activation during microbial infection. Nat. Immunol. 4, 1230–1237. Briken, V., Jackman, R. M., Dasgupta, S., Hoening, S., and Porcelli, S. A. (2002). Intracellular trafficking pathway of newly synthesized CD1b molecules. EMBO J. 21, 825–834. Brozovic, S., Nagaishi, T., Yoshida, M., Betz, S., Salas, A., Chen, D., Kaser, A., Glickman, J., Kuo, T., Little, A., Morrison, J., Corazza, N., Kim, J. Y., Colgan, S. P., Young, S. G., Exley, M., and Blumberg, R. S. (2004). CD1d function is regulated by microsomal triglyceride transfer protein. Nat. Med. 10, 535–539. Budd, R. C., Miescher, G. C., Howe, R. C., Lees, R. K., Bron, C., and MacDonald, H. R. (1987). Developmentally regulated expression of T cell receptor beta chain variable domains in immature thymocytes. J. Exp. Med. 166, 577–582.
130
D. BRANCH MOODY
Buettner, M., Meinken, C., Bastian, M., Bhat, R., Stossel, E., Faller, G., Cianciolo, G., Ficker, J., Wagner, M., Rollinghoff, M., and Stenger, S. (2005). Inverse correlation of maturity and antibacterial activity in human dendritic cells. J. Immunol. 174, 4203–4209. Calabi, F., Jarvis, J. M., Martin, L., and Milstein, C. (1989). Two classes of CD1 genes. Eur. J. Immunol. 19, 285–292. Calabi, F., and Milstein, C. (1986). A novel family of human major histocompatibility complex‐ related genes not mapping to chromosome 6. Nature 323, 540–543. Chen, Y. H., Chiu, N. M., Mandal, M., Wang, N., and Wang, C. R. (1997). Impaired NK1þ T cell development and early IL‐4 production in CD1‐deficient mice. Immunity 6, 459–467. Chiba, A., Oki, S., Miyamoto, K., Hashimoto, H., Yamamura, T., and Miyake, S. (2004). Suppression of collagen‐induced arthritis by natural killer T cell activation with OCH, a sphingosine‐ truncated analog of alpha‐galactosylceramide. Arthritis Rheum. 50, 305–313. Chiu, Y. H., Jayawardena, J., Weiss, A., Lee, D., Park, S. H., Dautry‐Varsat, A., and Bendelac, A. (1999). Distinct subsets of CD1d‐restricted T cells recognize self‐antigens loaded in different cellular compartments. J. Exp. Med. 189, 103–110. Chiu, Y. H., Park, S. H., Benlagha, K., Forestier, C., Jayawardena‐Wolf, J., Savage, P. B., Teyton, L., and Bendelac, A. (2002). Multiple defects in antigen presentation and T cell development by mice expressing cytoplasmic tail‐truncated CD1d. Nature Immunol. 3, 55–60. Cho, S., Knox, K. S., Kohli, L. M., He, J. J., Exley, M. A., Wilson, S. B., and Brutkiewicz, R. R. (2005). Impaired cell surface expression of human CD1d by the formation of an HIV‐1 Nef/ CD1d complex. Virology 337, 242–252. Cosgrove, D., Gray, D., Dierich, A., Kaufman, J., Lemeur, M., Benoist, C., and Mathis, D. (1991). Mice lacking MHC class II molecules. Cell 66, 1051–1066. Cotner, T., Mashimo, H., Kung, P. C., Goldstein, G., and Strominger, J. L. (1981). Human T cell surface antigens bearing a structural relationship to HLA antigens. Proc. Natl. Acad. Sci. USA 78, 3858–3862. Cresswell, P. (1994). Assembly, transport, and function of MHC class II molecules. [Review] [151 refs]. Ann. Rev. Immunol. 12, 259–293. Dascher, C. C., and Brenner, M. B. (2003). Evolutionary constraints on CD1 structure: Insights from comparative genomic analysis. Trends Immunol. 24, 412–418. Dascher, C. C., Hiromatsu, K., Naylor, J. W., Brauer, P. P., Brown, K. A., Storey, J. R., Behar, S. M., Kawasaki, E. S., Porcelli, S. A., Brenner, M. B., and LeClair, K. P. (1999). Conservation of a CD1 multigene family in the guinea pig. J. Immunol. 163, 5478–5488. Dascher, C. C., Hiromatsu, K., Xiong, X., Morehouse, C., Watts, G., Liu, G., McMurray, D. N., LeClair, K. P., Porcelli, S. A., and Brenner, M. B. (2003). Immunization with a mycobacterial lipid vaccine improves pulmonary pathology in the guinea pig model of tuberculosis. Int. Immunol. 15, 915–925. de la Salle, H., Mariotti, S., Angenieux, C., Gilleron, M., Garcia‐Alles, L. F., Malm, D., Berg, T., Paoletti, S., Maitre, B., Mourey, L., Salamero, J., Cazenave, J. P., Hanau, D., Mori, L., Puzo, G., and De Libero, G. (2005). Assistance of microbial glycolipid antigen processing by CD1e. Science 310, 1321–1324. De Libero, G., Moran, A. P., Gober, H. J., Rossy, E., Shamshiev, A., Chelnokova, O., Mazorra, Z., Vendetti, S., Sacchi, A., Prendergast, M. M., Sansano, S., Tonevitsky, A., Landmann, R., and Mori, L. (2005). Bacterial infections promote T cell recognition of self‐glycolipids. Immunity 22, 763–772. De Silva, A. D., Park, J. J., Matsuki, N., Stanic, A. K., Brutkiewicz, R. R., Medof, M. E., and Joyce, S. (2002). Lipid protein interactions: The assembly of CD1d1 with cellular phospholipids occurs in the endoplasmic reticulum. J. Immunol. 168, 723–733.
LIPID ANTIGENS FOR CD1‐RESTRICTED T CELLS
131
De Voss, J., Rutter, K., Schroeder, B. G., Su, H., Zhu, Y., and Barry, C. E. (2000). The salicylate‐ derived mycobactin siderophores of Mycobacterium tuberculosis are essential for growth in macrophages. Proc. Natl. Acad. Sci. USA 97, 1252–1257. Domenech, P., Reed, M. B., Dowd, C. S., Manca, C., Kaplan, G., and Barry, C. E., III (2004). The role of MmpL8 in sulfatide biogenesis and virulence of Mycobacterium tuberculosis. J. Biol. Chem. 279, 21257–21265. Dougan, S. K., Salas, A., Rava, P., Agyemang, A., Kaser, A., Morrison, J., Khurana, A., Kronenberg, M., Johnson, C., Exley, M., Hussain, M. M., and Blumberg, R. S. (2005). Microsomal triglyceride transfer protein lipidation and control of CD1d on antigen‐presenting cells. J. Exp. Med. 202, 529–539. Duarte, N., Stenstrom, M., Campino, S., Bergman, M. L., Lundholm, M., Holmberg, D., and Cardell, S. L. (2004). Prevention of diabetes in nonobese diabetic mice mediated by CD1d‐ restricted nonclassical NKT cells. J. Immunol. 173, 3112–3118. Elewaut, D., Lawton, A. P., Nagarajan, N. A., Maverakis, E., Khurana, A., Honing, S., Benedict, C. A., Sercarz, E., Bakke, O., Kronenberg, M., and Prigozy, T. I. (2003). The adaptor protein AP‐3 is required for CD1d‐mediated antigen presentation of glycosphingolipids and development of Valpha14i NKT cells. J. Exp. Med. 1133–1146. Ernst, W. A., Maher, J., Cho, S., Niazi, K. R., Chatterjee, D., Moody, DB, Besra, G. S., Watanabe, Y., Jensen, P. E., Porcelli, S. A., Kronenberg, M., and Modlin, R. L. (1998). Molecular interaction of CD1b with lipoglycan antigens. Immunity 8, 331–340. Exley, M., Porcelli, S., Furman, M., Garcia, J., and Balk, S. (1998). CD161 (NKR‐P1A) costimulation of CD1d‐dependent activation of human T cells expressing invariant V alpha 24 J alpha Q T cell receptor alpha chains. J. Exp. Med. 188, 867–876. Falcone, M., Facciotti, F., Ghidoli, N., Monti, P., Olivieri, S., Zaccagnino, L., Bonifacio, E., Casorati, G., Sanvito, F., and Sarvetnick, N. (2004). Up‐regulation of CD1d expression restores the immunoregulatory function of NKT cells and prevents autoimmune diabetes in nonobese diabetic mice. J. Immunol. 172, 5908–5916. Fischer, K., Scotet, E., Niemeyer, M., Koebernick, H., Zerrahn, J., Maillet, S., Hurwitz, R., Kursar, M., Bonneville, M., Kaufmann, S. H., and Schaible, U. E. (2004). Mycobacterial phosphatidylinositol mannoside is a natural antigen for CD1d‐restricted T cells. Proc. Natl. Acad. Sci. USA 101, 10685–10690. Fowlkes, B. J., Kruisbeek, A. M., Ton‐That, H., Weston, M. A., Coligan, J. E., Schwartz, R. H., and Pardoll, D. M. (1987). A novel population of T‐cell receptor alpha beta‐bearing thymocytes which predominantly expresses a single V beta gene family. Nature 329, 251–254. Fujii, S., Shimizu, K., Smith, C., Bonifaz, L., and Steinman, R. M. (2003). Activation of natural killer T cells by alpha‐galactosylceramide rapidly induces the full maturation of dendritic cells in vivo and thereby acts as an adjuvant for combined CD4 and CD8 T cell immunity to a coadministered protein. J. Exp. Med. 198, 267–279. Gadola, S. D., Zaccai, N. R., Harlos, K., Shepherd, D., Castro‐Palomino, J. C., Ritter, G., Schmidt, R. R., Jones, E. Y., and Cerundolo, V. (2002). Structure of human CD1b with bound ligands at 2.3 A, a maze for alkyl chains. Nature Immunol. 3, 721–726. Garboczi, D. N., Ghosh, P., Utz, U., Fan, Q. R., Biddison, W. E., and Wiley, D. C. (1996). Structure of the complex between human T‐cell receptor, viral peptide and HLA‐A2. Nature 384, 134–141. Garcia, K. C., Degano, M., Stanfield, R. L., Brunmark, A., Jackson, M. R., Peterson, P. A., Teyton, L., and Wilson, I. A. (1996). An alphabeta T cell receptor structure at 2.5 A and its orientation in the TCR‐MHC complex. Science 274, 209–219. Geng, Y., Laslo, P., Barton, K., and Wang, C. R. (2005). Transcriptional Regulation of CD1D1 by Ets Family Transcription Factors. J. Immunol. 175, 1022–1029.
132
D. BRANCH MOODY
Giabbai, B., Sidobre, S., Crispin, M. D., Sanchez‐Ruiz, Y., Bachi, A., Kronenberg, M., Wilson, I. A., and Degano, M. (2005). Crystal structure of mouse CD1d bound to the self ligand phosphatidylcholine: A molecular basis for NKT cell activation. J. Immunol. 175, 977–984. Gilleron, M., Stenger, S., Mazorra, Z., Wittke, F., Mariotti, S., Bohmer, G., Prandi, J., Mori, L., Puzo, G., and De Libero, G. (2004). Diacylated Sulfoglycolipids Are Novel Mycobacterial Antigens Stimulating CD1‐restricted T Cells during Infection with Mycobacterium tuberculosis. J. Exp. Med. 199, 649–659. Giuliani, A., Prete, S. P., Graziani, G., Aquino, A., Balduzzi, A., Sugita, M., Brenner, M. B., Iona, E., Fattorini, L., Orefici, G., Porcelli, S. A., and Bonmassar, E. (2001). Influence of Mycobacterium bovis bacillus Calmette Guerin on in vitro induction of CD1 molecules in human adherent mononuclear cells. Infect. Immun. 69, 7461–7470. Glass, W. G., Subbarao, K., Murphy, B., and Murphy, P. M. (2004). Mechanisms of host defense following severe acute respiratory syndrome‐coronavirus (SARS‐CoV) pulmonary infection of mice. J. Immunol. 173, 4030–4039. Grant, E. P., Beckman, E. M., Behar, S. M., Degano, M., Frederique, D., Besra, G. S., Wilson, I. A., Porcelli, S. A., Furlong, S. T., and Brenner, M. B. (2002). Fine specificity of TCR complementarity‐determining region residues and lipid antigen hydrophilic moieties in the recognition of a CD1‐lipid complex. J. Immunol. 168, 3933–3940. Grubor‐Bauk, B., Simmons, A., Mayrhofer, G., and Speck, P. G. (2003). Impaired clearance of herpes simplex virus type 1 from mice lacking CD1d or NKT cells expressing the semivariant V alpha 14‐J alpha 281 TCR. J. Immunol. 170, 1430–1434. Gumperz, J., Roy, C., Makowska, A., Lum, D., Sugita, M., Podrebarac, T., Koezuka, Y., Porcelli, S. A., Cardell, S., Brenner, M. B., and Behar, S. M. (2000). Murine CD1d‐Restricted T Cell Recognition of Cellular Lipids. Immunity 12, 211–221. Gumperz, J. E., Miyake, S., Yamamura, T., and Brenner, M. B. (2002). Functionally distinct subsets of CD1d‐restricted natural killer T cells revealed by CD1d tetramer staining. J. Exp. Med. 195, 625–636. Hansen, D. S., Siomos, M. A., Buckingham, L., Scalzo, A. A., and Schofield, L. (2003a). Regulation of murine cerebral malaria pathogenesis by CD1d‐restricted NKT cells and the natural killer complex. Immunity 18, 391–402. Hansen, D. S., Siomos, M. A., Koning‐Ward, T., Buckingham, L., Crabb, B. S., and Schofield, L. (2003b). CD1d‐restricted NKT cells contribute to malarial splenomegaly and enhance parasite‐ specific antibody responses. Eur. J. Immunol. 33, 2588–2598. Hayes, S. M., and Knight, K. L. (2001). Group 1 CD1 genes in rabbit. J. Immunol. 166, 403–410. Henderson, R. A., Watkins, S. C., and Flynn, J. L. (1997). Activation of human dendritic cells following infection with Mycobacterium tuberculosis. J. Immunol. 159, 635–643. Huber, S., Sartini, D., and Exley, M. (2003). Role of CD1d in coxsackievirus B3‐induced myocarditis. J. Immunol. 170, 3147–3153. Hughes, A. L. (1991). Evolutionary origin and diversification of the mammalian CD1 antigen genes. Mol. Biol. Evol. 8, 185–201. Hunger, R. E., Sieling, P. A., Ochoa, M. T., Sugaya, M., Burdick, A. E., Rea, T. H., Brennan, P. J., Belisle, J. T., Blauvelt, A., Porcelli, S. A., and Modlin, R. L. (2004). Langerhans cells utilize CD1a and langerin to efficiently present nonpeptide antigens to T cells. J. Clin. Invest 113, 701–708. Huttinger, R., Staffler, G., Majdic, O., and Stockinger, H. (1999). Analysis of the early biogenesis of CD1b: Involvement of the chaperones calnexin and calreticulin, the proteasome and b2‐microglobulin. Int. Immunol. 11, 1615–1623. Jackman, R. M., Stenger, S., Lee, A., Moody, D. B., Rogers, R. A., Niazi, K. R., Sugita, M., Modlin, R. L., Peters, P. J., and Porcelli, S. A. (1998). The tyrosine‐containing cytoplasmic tail of CD1b is essential for its efficient presentation of bacterial lipid antigens. Immunity 8, 341–351.
LIPID ANTIGENS FOR CD1‐RESTRICTED T CELLS
133
Jahng, A., Maricic, I., Aguilera, C., Cardell, S., Halder, R. C., and Kumar, V. (2004). Prevention of autoimmunity by targeting a distinct, noninvariant CD1d‐reactive T cell population reactive to sulfatide. J. Exp. Med. 199, 947–957. Jayawardena‐Wolf, J., Benlagha, K., Chiu, Y. H., Mehr, R., and Bendelac, A. (2001). CD1d endosomal trafficking is independently regulated by an intrinsic CD1d‐encoded tyrosine motif and by the invariant chain. Immunity 15, 897–908. Joyce, S., Woods, A. S., Yewdell, J. W., Bennink, J. R., De, S. A., Boesteanu, A., Balk, S. P., Cotter, R. J., and Brutkiewicz, R. R. (1998). Natural ligand of mouse CD1d1: Cellular glycosylphosphatidylinositol. Science 279, 1541–1544. Kang, S. J., and Cresswell, P. (2002a). Calnexin, calreticulin, and ERp57 cooperate in disulfide bond formation in human CD1d heavy chain. J. Biol. Chem. 277, 44838–44844. Kang, S. J., and Cresswell, P. (2002b). Regulation of intracellular trafficking of human CD1d by association with MHC class II molecules. EMBO J. 21, 1650–1660. Kang, S. J., and Cresswell, P. (2004). Saposins facilitate CD1d‐restricted presentation of an exogenous lipid antigen to T cells. Nat. Immunol. 5, 175–181. Kappler, J., Kubo, R., Haskins, K., White, J., and Marrack, P. (1983). The mouse T cell receptor: Comparison of MHC‐restricted receptors on two T cell hybridomas. Cell 34, 727–737. Karadimitris, A., Gadola, S., Altamirano, M., Brown, D., Woolfson, A., Klenerman, P., Chen, J. L., Koezuka, Y., Roberts, I. A., Price, D. A., Dusheiko, G., Milstein, C., Fersht, A., Luzzatto, L., and Cerundolo, V. (2001). Human CD1d‐glycolipid tetramers generated by in vitro oxidative refolding chromatography. Proc. Natl. Acad. Sci. USA 98, 3294–3298. Kawano, T., Cui, J., Koezuka, Y., Toura, I., Kaneko, Y., Motoki, K., Ueno, H., Nakagawa, R., Sato, H., Kondo, E., Koseki, H., and Taniguchi, M. (1997). CD1d‐restricted and TCR‐mediated activation of Va14 NKT cells by glycosylceramides. Science 278, 1626–1629. Kim, J. O., Kim, D. H., Chang, W. S., Hong, C., Park, S. H., Kim, S., and Kang, C. Y. (2004). Asthma is induced by intranasal coadministration of allergen and natural killer T‐cell ligand in a mouse model. J. Allergy Clin. Immunol. 114, 1332–1338. Kinjo, Y., Wu, D., Kim, G., Xing, G. W., Poles, M. A., Ho, D. D., Tsuji, M., Kawahara, K., Wong, C. H., and Kronenberg, M. (2005). Recognition of bacterial glycosphingolipids by natural killer T cells. Nature 434, 520–525. Koch, M., Stronge, V. S., Shepherd, D., Gadola, S. D., Mathew, B., Ritter, G., Fersht, A. R., Besra, G. S., Schmidt, R. R., Jones, E. Y., and Cerundolo, V. (2005). The crystal structure of human CD1d with and without alpha‐galactosylceramide. Nat. Immunol. 6, 819–826. Krutzik, S. R., Tan, B., Li, H., Ochoa, M. T., Liu, P. T., Sharfstein, S. E., Graeber, T. G., Sieling, P. A., Liu, Y. J., Rea, T. H., Bloom, B. R., and Modlin, R. L. (2005). TLR activation triggers the rapid differentiation of monocytes into macrophages and dendritic cells. Nat. Med. 11, 653–660. Kumar, H., Belperron, A., Barthold, S. W., and Bockenstedt, L. K. (2000). Cutting edge: CD1d deficiency impairs murine host defense against the spirochete, Borrelia burgdorferi. J. Immunol. 165, 4797–4801. Laird, D. J., De Tomaso, A. W., Cooper, M. D., and Weissman, I. L. (2000). 50 million years of chordate evolution: Seeking the origins of adaptive immunity. Proc. Natl. Acad. Sci. USA 97, 6924–6926. Lang, G. A., Illarionov, P. A., Glatman‐Freedman, A., Besra, G. S., and Lang, M. L. (2005). BCR targeting of biotin‐{alpha}‐galactosylceramide leads to enhanced presentation on CD1d and requires transport of BCR to CD1d‐containing endocytic compartments. Int. Immunol. 17, 899–908. Le Gall, S., Erdtmann, L., Benichou, S., Berlioz‐Torrent, C., Liu, L., Benarous, R., Heard, J. M., and Schwartz, O. (1998). Nef interacts with the mu subunit of clathrin adaptor complexes and reveals a cryptic sorting signal in MHC I molecules. Immunity 8, 483–495.
134
D. BRANCH MOODY
Lee, P. T., Putnam, A., Benlagha, K., Teyton, L., Gottlieb, P. A., and Bendelac, A. (2002). Testing the NKT cell hypothesis of human IDDM pathogenesis. J. Clin. Invest. 110, 793–800. Levy, O., Orange, J. S., Hibberd, P., Steinberg, S., LaRussa, P., Weinberg, A., Wilson, S. B., Shaulov, A., Fleisher, G., Geha, R. S., Bonilla, F. A., and Exley, M. (2003). Disseminated varicella infection due to the vaccine strain of varicella‐zoster virus, in a patient with a novel deficiency in natural killer T cells. J. Infect. Dis. 188, 948–953. Lisbonne, M., Diem, S., de Castro, K. A., Lefort, J., Araujo, L. M., Hachem, P., Fourneau, J. M., Sidobre, S., Kronenberg, M., Taniguchi, M., Van Endert, P., Dy, M., Askenase, P., Russo, M., Vargaftig, B. B., Herbelin, A., and Leite‐de‐Moraes, M. C. (2003). Cutting edge: Invariant V alpha 14 NKT cells are required for allergen‐induced airway inflammation and hyperreactivity in an experimental asthma model. J. Immunol. 171, 1637–1641. Matsuda, J. L., Gapin, L., Sidobre, S., Kieper, W. C., Tan, J. T., Ceredig, R., Surh, C. D., and Kronenberg, M. (2002). Homeostasis of V alpha 14i NKT cells. Nat. Immunol. 3, 966–974. Matsuda, J. L., Naidenko, O. V., Gapin, L., Nakayama, T., Taniguchi, M., Wang, C. R., Koezuka, Y., and Kronenberg, M. (2000). Tracking the response of natural killer T cells to a glycolipid antigen using CD1d tetramers. J. Exp. Med. 192, 741–754. Matsunaga, I., Bhatt, A., Young, D. C., Cheng, T. Y., Eyles, S. J., Besra, G. S., Briken, V., Porcelli, S. A., Costello, C. E., Jacobs, W. R., Jr., and Moody, D. B. (2004). Mycobacterium tuberculosis pks12 Produces a Novel Polyketide Presented by CD1c to T Cells. J. Exp. Med. 200, 1559–1569. Mattner, J., Debord, K. L., Ismail, N., Goff, R. D., Cantu, C., III, Zhou, D., Saint‐Mezard, P., Wang, V., Gao, Y., Yin, N., Hoebe, K., Schneewind, O., Walker, D., Beutler, B., Teyton, L., Savage, P. B., and Bendelac, A. (2005). Exogenous and endogenous glycolipid antigens activate NKT cells during microbial infections. Nature 434, 525–529. McDevitt, H. O., and Benacerraf, B. (1969). Genetic control of specific immune responses. Adv. Immunol. 11, 31–74. McIntyre, B. W., and Allison, J. P. (1983). The mouse T cell receptor: Structural heterogeneity of molecules of normal T cells defined by xenoantiserum. Cell 34, 739–746. McMichael, A. J., Pilch, J. R., Galfre, G., Mason, D. Y., Fabre, J. W., and Milstein, C. (1979). A human thymocyte antigen defined by a hybrid myeloma monoclonal antibody. Eur. J. Immunol. 9, 205–210. Miller, M. M., Wang, C., Parisini, E., Coletta, R. D., Goto, R. M., Lee, S. Y., Barral, D. C., Townes, M., Roura‐Mir, C., Ford, H. L., Brenner, M. B., and Dascher, C. C. (2005). Characterization of two avian MHC‐like genes reveals an ancient origin of the CD1 family. Proc. Natl. Acad. Sci. USA 102, 8674–8679. Miyamoto, K., Miyake, S., and Yamamura, T. (2001). A synthetic glycolipid prevents autoimmune encephalomyelitis by inducing TH2 bias of natural killer T cells. Nature 413, 531–534. Mizuno, M., Masumura, M., Tomi, C., Chiba, A., Oki, S., Yamamura, T., and Miyake, S. (2004). Synthetic glycolipid OCH prevents insulitis and diabetes in NOD mice. J. Autoimmun. 23, 293–300. Molano, A., Park, S. H., Chiu, Y. H., Nosseir, S., Bendelac, A., and Tsuji, M. (2000). Cutting edge: The IgG response to the circumsporozoite protein is MHC class II‐dependent and CD1d‐ independent: Exploring the role of GPIs in NK T cell activation and antimalarial responses. J. Immunol. 164, 5005–5009. Moody, D. B., Briken, V., Cheng, T. Y., Roura‐Mir, C., Guy, M. R., Geho, D. H., Tykocinski, M. L., Besra, G. S., and Porcelli, S. A. (2002). Lipid length controls antigen entry into endosomal and nonendosomal pathways for CD1b presentation. Nature Immunol. 3, 435–442. Moody, D. B., Reinhold, B. B., Guy, M. R., Beckman, E. M., Frederique, D. E., Furlong, S. T., Ye, S., Reinhold, V. N., Sieling, P. A., Modlin, R. L., Besra, G. S., and Porcelli, S. A. (1997). Structural requirements for glycolipid antigen recognition by CD1b‐restricted T cells. Science 278, 283–286.
LIPID ANTIGENS FOR CD1‐RESTRICTED T CELLS
135
Moody, D. B., Reinhold, B. B., Reinhold, V. N., Besra, G. S., and Porcelli, S. A. (1999). Uptake and processing of glycosylated mycolates for presentation to CD1b‐restricted T cells. Immunol. Lett. 65, 85–91. Moody, D. B., Ulrichs, T., Muhlecker, W., Young, D. C., Gurcha, S. S., Grant, E., Rosat, J. P., Brenner, M. B., Costello, C. E., Besra, G. S., and Porcelli, S. A. (2000). CD1c‐mediated T‐cell recognition of isoprenoid glycolipids in Mycobacterium tuberculosis infection. Nature 404, 884–888. Moody, D. B., Young, D. C., Cheng, T. Y., Rosat, J. P., Roura‐Mir, C., O’Connor, P. B., Zajonc, D. M., Walz, A., Miller, M. J., Levery, S. B., Wilson, I. A., Costello, C. E., and Brenner, M. B. (2004). T cell activation by lipopeptide antigens. Science 303, 527–531. Moody, D. B., Zajonc, D. M., and Wilson, I. A. (2005). Anatomy of CD1‐lipid antigen complexes. Nat. Rev. Immunol. 5, 387–399. Naumov, Y. N., Bahjat, K. S., Gausling, R., Abraham, R., Exley, M. A., Koezuka, Y., Balk, S. B., Strominger, J. L., Clare‐Salzer, M., and Wilson, S. B. (2001). Activation of CD1d‐restricted T cells protects NOD mice from developing diabetes by regulating dendritic cell subsets. Proc. Natl. Acad. Sci. USA 98, 13838–13843. Nieda, M., Okai, M., Tazbirkova, A., Lin, H., Yamaura, A., Ide, K., Abraham, R., Juji, T., Macfarlane, D. J., and Nicol, A. J. (2004). Therapeutic activation of Valpha24 þ Vbeta11 þ NKT cells in human subjects results in highly coordinated secondary activation of acquired and innate immunity. Blood 103, 383–389. Ohno, H., Stewart, J., Fournier, M. C., Bosshart, H., Rhee, I., Miyatake, S., Saito, T., Gallusser, A., Kirchhausen, T., and Bonifacino, J. S. (1995). Interaction of tyrosine‐based sorting signals with clathrin‐associated proteins. Science 269, 1872–1875. Oki, S., Chiba, A., Yamamura, T., and Miyake, S. (2004). The clinical implication and molecular mechanism of preferential IL‐4 production by modified glycolipid‐stimulated NKT cells. J. Clin. Invest 113, 1631–1640. Oldstone, M. B., Whitton, J. L., Lewicki, H., and Tishon, A. (1988). Fine dissection of a nine amino acid glycoprotein epitope, a major determinant recognized by lymphocytic choriomeningitis virus‐specific class I‐restricted H‐2Db cytotoxic T lymphocytes. J. Exp. Med. 168, 559–570. Owen, D. J., and Evans, P. R. (1998). A structural explanation for the recognition of tyrosine‐based endocytotic signals. Science 282, 1327–1332. Porcelli, S., Brenner, M. B., Greenstein, J. L., Balk, S. P., Terhorst, C., and Bleicher, P. A. (1989). Recognition of cluster of differentiation 1 antigens by human CD4‐CD8‐ cytolytic T lymphocytes. Nature 341, 447–450. Porcelli, S., Morita, C. T., and Brenner, M. B. (1992). CD1b restricts the response of human CD48 T lymphoyctes to a microbial antigen. Nature 360, 593–597. Porcelli, S. A. (1995). The CD1 family: A third lineage of antigen‐presenting molecules. Adv. Immunol. 59, 1–98. Prigozy, T. I., Naidenko, O., Qasba, P., Elewaut, D., Brossay, L., Khurana, A., Natori, T., Koezuka, Y., Kulkarni, A., and Kronenberg, M. (2001). Glycolipid antigen processing for presentation by CD1d molecules. Science 291, 664–667. Prigozy, T. I., Sieling, P. A., Clemens, D., Stewart, P. L., Behar, S. M., Porcelli, S. A., Brenner, M. B., Modlin, R. L., and Kronenberg, M. (1997). The mannose receptor delivers lipoglycan antigens to endosomes for presentation to T cells by CD1b molecules. Immunity 6, 187–197. Procopio, D. O., Almeida, I. C., Torrecilhas, A. C., Cardoso, J. E., Teyton, L., Travassos, L. R., Bendelac, A., and Gazzinelli, R. T. (2002). Glycosylphosphatidylinositol‐anchored mucin‐like glycoproteins from Trypanosoma cruzi bind to CD1d but do not elicit dominant innate or adaptive immune responses via the CD1d/NKT cell pathway. J. Immunol. 169, 3926–3933.
136
D. BRANCH MOODY
Quaranta, M. G., Tritarelli, E., Giordani, L., and Viora, M. (2002). HIV‐1 Nef induces dendritic cell differentiation: A possible mechanism of uninfected CD4(þ) T cell activation. Exp. Cell Res. 275, 243–254. Rauch, J., Gumperz, J., Robinson, C., Skold, M., Roy, C., Young, D. C., Lafleur, M., Moody, D. B., Brenner, M. B., Costello, C. E., and Behar, S. M. (2003). Structural features of the acyl chain determine self‐phospholipid antigen recognition by a CD1d‐restricted invariant NKT (iNKT) cell. J. Biol. Chem. 278, 47508–47515. Roberts, T. J., Sriram, V., Spence, P. M., Gui, M., Hayakawa, K., Bacik, I., Bennink, J. R., Yewdell, J. W., and Brutkiewicz, R. R. (2002). Recycling CD1d1 molecules present endogenous antigens processed in an endocytic compartment to NKT cells. J. Immunol. 168, 5409–5414. Rodionov, D. G., Nordeng, T. W., Kongsvik, T. L., and Bakke, O. (2000). The cytoplasmic tail of CD1d contains two overlapping basolateral sorting signals. J. Biol. Chem. 275, 8279–8282. Rodionov, D. G., Nordeng, T. W., Pedersen, K., Balk, S. P., and Bakke, O. (1999). A critical tyrosine residue in the cytoplasmic tail is important for CD1d internalization but not for its basolateral sorting in MDCK cells. J. Immunol. 162, 1488–1495. Roura‐Mir, C., Catalfamo, M., Cheng, T. Y., Marqusee, E., Besra, G. S., Jaraquemada, D., and Moody, D. B. (2005a). CD1a and CD1c activate intrathyroidal T cells during Graves’ disease and Hashimoto’s thyroiditis. J. Immunol. 174, 3773–3780. Roura‐Mir, C., Wang, L., Cheng, T. Y., Matsunaga, I., Dascher, C. C., Peng, S. L., Fenton, M. J., Kirschning, C., and Moody, D. B. (2005b). Mycobacterium tuberculosis Regulates CD1 Antigen Presentation Pathways through TLR‐2. J. Immunol. 175, 1758–1766. Salamone, M. C., Mendiguren, A. K., Salamone, G. V., and Fainboim, L. (2001a). Membrane trafficking of CD1c on activated T cells. J. Leukoc. Biol. 70, 567–577. Salamone, M. C., Rabinovich, G. A., Mendiguren, A. K., Salamone, G. V., and Fainboim, L. (2001b). Activation‐induced expression of CD1d antigen on mature T cells. J. Leukoc. Biol. 69, 207–214. Sallusto, F., and Lanzavecchia, A. (1994). Efficient presentation of soluble antigen by cultured human dendritic cells is maintained by granulocyte/macrophage colony‐stimulating factor plus interleukin 4 and downregulated by tumor necrosis factor alpha. J. Exp. Med. 179, 1109–1118. Salomonsen, J., Sorensen, M. R., Marston, D. A., Rogers, S. L., Collen, T., van Hateren, A., Smith, A. L., Beal, R. K., Skjodt, K., and Kaufman, J. (2005). Two CD1 genes map to the chicken MHC, indicating that CD1 genes are ancient and likely to have been present in the primordial MHC. Proc. Natl. Acad. Sci. USA 102, 8668–8673. Sanchez, D. J., Gumperz, J. E., and Ganem, D. (2005). Regulation of CD1d expression and function by a herpesvirus infection. J. Clin. Invest. 115, 1369–1378. Sandhoff, K., and Kolter, T. (2003). Biosynthesis and degradation of mammalian glycosphingolipids. Philos. Trans. R. Soc. Lond. B Biol. Sci. 358, 847–861. Schofield, L., McConville, M. J., Hansen, D., Campbell, A. S., Fraser‐Reid, B., Grusby, M. J., and Tachado, S. D. (1999). CD1d‐restricted immunoglobulin G formation to GPI‐anchored antigens mediated by NKT cells. Science 283, 225–229. Shamshiev, A., Donda, A., Carena, I., Mori, L., Kappos, L., and De Libero, G. (1999). Self glycolipids as T‐cell autoantigens. Eur. J. Immunol. 29, 1667–1675. Shamshiev, A., Donda, A., Prigozy, T. I., Mori, L., Chigorno, V., Benedict, C. A., Kappos, L., Sonnino, S., Kronenberg, M., and De Libero, G. (2000). The ab T cell response to self‐ glycolipids shows a novel mechanism of CD1b loading and a requirement for complex oligosaccharides. Immunity 13, 255–264. Shamshiev, A., Gober, H. J., Donda, A., Mazorra, Z., Mori, L., and De Libero, G. (2002). Presentation of the same glycolipid by different CD1 molecules. J. Exp. Med. 195, 1013–1021. Shinya, E., Owaki, A., Shimizu, M., Takeuchi, J., Kawashima, T., Hidaka, C., Satomi, M., Watari, E., Sugita, M., and Takahashi, H. (2004). Endogenously expressed HIV‐1 nef down‐regulates
LIPID ANTIGENS FOR CD1‐RESTRICTED T CELLS
137
antigen‐presenting molecules, not only class I MHC but also CD1a, in immature dendritic cells. Virology 326, 79–89. Sidobre, S., Naidenko, O. V., Sim, B. C., Gascoigne, N. R., Garcia, K. C., and Kronenberg, M. (2002). The V alpha 14 NKT cell TCR exhibits high‐affinity binding to a glycolipid/CD1d complex. J. Immunol. 169, 1340–1348. Sieling, P. A., Chatterjee, D., Porcelli, S. A., Prigozy, T. I., Mazzaccaro, R. J., Soriano, T., Bloom, B. R., Brenner, M. B., Kronenberg, M., and Brennan, P. J. (1995). CD1‐restricted T cell recognition of microbial lipoglycan antigens. Science 269, 227–230. Sieling, P. A., Jullien, D., Dahlem, M., Tedder, T. F., Rea, T. H., Modlin, R. L., and Porcelli, S. A. (1999). CD1 expression by dendritic cells in human leprosy lesions: Correlation with effective host immunity. J. Immunol. 162, 1851–1858. Silk, J. D., Hermans, I. F., Gileadi, U., Chong, T. W., Shepherd, D., Salio, M., Mathew, B., Schmidt, R. R., Lunt, S. J., Williams, K. J., Stratford, I. J., Harris, A. L., and Cerundolo, V. (2004). Utilizing the adjuvant properties of CD1d‐dependent NK T cells in T cell‐mediated immunotherapy. J. Clin. Invest. 114, 1800–1811. Smiley, S. T., Kaplan, M. H., and Grusby, M. J. (1997). Immunoglobulin E production in the absence of interleukin‐4‐secreting CD1‐dependent cells. Science 275, 977–979. Somnay‐Wadgaonkar, K., Nusrat, A., Kim, H. S., Canchis, W. P., Balk, S. P., Colgan, S. P., and Blumberg, R. S. (1999). Immunolocalization of CD1d in human intestinal epithelial cells and identification of a beta2‐microglobulin‐associated form. Int. Immunol. 11, 383–392. Spence, P. M., Sriram, V., Van Kaer, L., Hobbs, J. A., and Brutkiewicz, R. R. (2001). Generation of cellular immunity to lymphocytic choriomeningitis virus is independent of CD1d1 expression. Immunology 104, 168–174. Stenger, S., Hanson, D. A., Teitelbaum, R., Dewan, P., Niazi, K. R., Froelich, C. J., Ganz, T., Thoma‐Uszynski, S., Melian, A., Bogdan, C., Porcelli, S. A., Bloom, B. R., Krensky, A. M., and Modlin, R. L. (1998a). An antimicrobial activity of cytolytic T cells mediated by granulysin. Science 282, 121–125. Stenger, S., Mazzaccaro, R. J., Uyemura, K., Cho, S., Barnes, P. F., Rosat, J. P., Sette, A., Brenner, M. B., Porcelli, S. A., Bloom, B. R., and Modlin, R. L. (1997). Differential effects of cytolytic T cell subsets on intracellular infection. Science 276, 1684–1687. Stenger, S., Niazi, K. R., and Modlin, R. L. (1998b). Down‐regulation of CD1 on antigen‐ presenting cells by infection with Mycobacterium tuberculosis. J. Immunol. 161, 3582–3588. Sugita, M., and Brenner, M. B. (1994). An unstable beta 2‐microglobulin: Major histocompatibility complex class I heavy chain intermediate dissociates from calnexin and then is stabilized by binding peptide. J. Exp. Med. 180, 2163–2171. Sugita, M., Cao, X., Watts, G. F., Rogers, R. A., Bonifacino, J. S., and Brenner, M. B. (2002). Failure of trafficking and antigen presentation by CD1 in AP‐3‐deficient cells. Immunity 16, 697–706. Sugita, M., Grant, E. P., van Donselaar, E., Hsu, V. W., Rogers, R. A., Peters, P. J., and Brenner, M. B. (1999). Separate pathways for antigen presentation by CD1 molecules. Immunity 11, 743–752. Sugita, M., Jackman, R. M., van Donselaar, E., Behar, S. M., Rogers, R. A., Peters, P. J., Brenner, M. B., and Porcelli, S. A. (1996). Cytoplasmic tail‐dependent localization of CD1b antigen‐ presenting molecules to MIICs. Science 273, 349–352. Sugita, M., van Der, W., Rogers, R. A., Peters, P. J., and Brenner, M. B. (2000). CD1c molecules broadly survey the endocytic system. Proc. Natl. Acad. Sci. 97, 8445–8450. Sumida, T., Sakamoto, A., Murata, H., Makino, Y., Takahashi, H., Yoshida, S., Nishioka, K., Iwamoto, I., and Taniguchi, M. (1995). Selective reduction of T cells bearing invariant Va24JaQ antigen receptor in patients with systemic sclerosis. J. Exp. Med. 182, 1163–1168.
138
D. BRANCH MOODY
Szatmari, I., Gogolak, P., Im, J. S., Dezso, B., Rajnavolgyi, E., and Nagy, L. (2004). Activation of PPARgamma specifies a dendritic cell subtype capable of enhanced induction of iNKT cell expansion. Immunity 21, 95–106. Terhorst, C., van Agthoven, A., Le Clair, K., Snow, P., Reinherz, E. L., and Schlossman, S. F. (1981). Biochemical studies of the human thymocyte cell surface antigens T6, T9 and T10. Cell 23, 771–780. Townsend, M. J., Weinmann, A. S., Matsuda, J. L., Salomon, R., Farnham, P. J., Biron, C. A., Gapin, L., and Glimcher, L. H. (2004). T‐bet regulates the terminal maturation and homeostasis of NK and Valpha14i NKT cells. Immunity 20, 477–494. Uehira, K., Amakawa, R., Ito, T., Tajima, K., Naitoh, S., Ozaki, Y., Shimizu, T., Yamaguchi, K., Uemura, Y., Kitajima, H., Yonezu, S., and Fukuhara, S. (2002). Dendritic cells are decreased in blood and accumulated in granuloma in tuberculosis. Clin. Immunol. 105, 296–303. Ueno, Y., Tanaka, S., Sumii, M., Miyake, S., Tazuma, S., Taniguchi, M., Yamamura, T., and Chayama, K. (2005). Single dose of OCH improves mucosal T helper type 1/T helper type 2 cytokine balance and prevents experimental colitis in the presence of valpha14 natural killer T cells in mice. Inflamm. Bowel. Dis. 11, 35–41. Ulrichs, T., Moody, D. B., Grant, E., Kaufmann, S. H., and Porcelli, S. A. (2003). T‐cell responses to CD1‐presented lipid antigens in humans with Mycobacterium tuberculosis infection. Infect. Immun. 71, 3076–3087. van de Wal, Y., Corazza, N., Allez, M., Mayer, L. F., Iijima, H., Ryan, M., Cornwall, S., Kaiserlian, D., Hershberg, R., Koezuka, Y., Colgan, S. P., and Blumberg, R. S. (2003). Delineation of a CD1d‐restricted antigen presentation pathway associated with human and mouse intestinal epithelial cells. Gastroenterology 124, 1420–1431. van den Elzen, P., Garg, S., Leon, L., Brigl, M., Leadbetter, E., Gumperz, J., Dascher, C., Cheng, T., Iaiaronov, P., Besra, G., Kent, S. C., Moody, D. B., Michael, B., and Brenner, M. B. (2005). An apolipoprotein mediated pathway of exogenous lipid antigen presentation. Nature 437, 906–910. van der Vliet, H. J., von Blomberg, B. M., Hazenberg, M. D., Nishi, N., Otto, S. A., van Benthem, B. H., Prins, M., Claessen, F. A., van den Eertwegh, A. J., Giaccone, G., Miedema, F., Scheper, R. J., and Pinedo, H. M. (2002). Selective decrease in circulating V alpha 24 þ V beta 11 þ NKT cells during HIV type 1 infection. J. Immunol. 168, 1490–1495. van Dommelen, S. L., Tabarias, H. A., Smyth, M. J., and Degli‐Esposti, M. A. (2003). Activation of natural killer (NK) T cells during murine cytomegalovirus infection enhances the antiviral response mediated by NK cells. J. Virol. 77, 1877–1884. Van Kaer, L. (2005). alpha‐Galactosylceramide therapy for autoimmune diseases: Prospects and obstacles. Nat. Rev. Immunol. 5, 31–42. Van Rhijn, I., Zajonc, D. M., Wilson, I. A., and Moody, D. B. (2005). Presentation of lipopeptide antigens to T cells. Curr. Opin. Immunol., in press. Vincent, M. S., Gumperz, J. E., and Brenner, M. B. (2003). Understanding the function of CD1‐ restricted T cells. Nat. Immunol. 4, 517–523. Wei, D. G., Lee, H., Park, S. H., Beaudoin, L., Teyton, L., Lehuen, A., and Bendelac, A. (2005). Expansion and long‐range differentiation of the NKT cell lineage in mice expressing CD1d exclusively on cortical thymocytes. J. Exp. Med. 202, 239–248. Weller, S., Braun, M. C., Tan, B. K., Rosenwald, A., Cordier, C., Conley, M. E., Plebani, A., Kumararatne, D. S., Bonnet, D., Tournilhac, O., Tchernia, G., Steiniger, B., Staudt, L. M., Casanova, J. L., Reynaud, C. A., and Weill, J. C. (2004). Human blood IgM ‘‘memory’’ B cells are circulating splenic marginal zone B cells harboring a prediversified immunoglobulin repertoire. Blood 104, 3647–3654.
LIPID ANTIGENS FOR CD1‐RESTRICTED T CELLS
139
Wilson, S. B., Kent, S. C., Patton, K. T., Orban, T., Jackson, R. A., Exley, M., Porcelli Schatz, D. A., Atkinson, M. A., Balk, S. P., Strominger, J. L., and Hafler, D. A. (1998). Extreme Th1 bias of invariant Valpha24JalphaQ T cells in type 1 diabetes. Nature 391, 177–181. Winau, F., Schwierzeck, V., Hurwitz, R., Remmel, N., Sieling, P. A., Modlin, R. L., Porcelli, S. A., Brinkmann, V., Sugita, M., Sandhoff, K., Kaufmann, S. H., and Schaible, U. E. (2004). Saposin C is required for lipid presentation by human CD1b. Nat. Immunol. 5, 169–174. Wu, D. Y., Segal, N. H., Sidobre, S., Kronenberg, M., and Chapman, P. B. (2003). Cross‐ presentation of Disialoganglioside GD3 to Natural Killer T Cells. J. Exp. Med. 198, 173–181. Yu, K. O., Im, J. S., Molano, A., Dutronc, Y., Illarionov, P. A., Forestier, C., Fujiwara, N., Arias, I., Miyake, S., Yamamura, T., Chang, Y. T., Besra, G. S., and Porcelli, S. A. (2005). Modulation of CD1d‐restricted NKT cell responses by using N‐acyl variants of alpha‐galactosylceramides. Proc. Natl. Acad. Sci. USA 102, 3383–3388. Zajonc, D. M., Cantu, C., Mattner, J., Zhou, D., Savage, P. B., Bendelac, A., Wilson, I. A., and Teyton, L. (2005a). Structure and function of a potent agonist for the semi‐invariant natural killer T cell receptor. Nat. Immunol. 6, 810–818. Zajonc, D. M., Crispin, M. D., Bowden, T. A., Young, D. C., Cheng, T. Y., Hu, J., Costello, C. E., Rudd, P. M., Dwek, R. A., Miller, M. J., Brenner, M. B., Moody, D. B., and Wilson, I. A. (2005b). Molecular mechanism of lipopeptide presentation by CD1a. Immunity 22, 209–219. Zajonc, D. M., Elsliger, M. A., Teyton, L., and Wilson, I. A. (2003). Crystal structure of CD1a in complex with a sulfatide self antigen at a resolution of 2.15 A. Nat. Immunol. 4, 808–815. Zeng, Z., Castan˜o, A. R., Segelke, B. W., Stura, E. A., Peterson, P. A., and Wilson, I. A. (1997). Crystal structure of mouse CD1: An MHC‐like fold with a large hydrophobic binding groove. Science 277, 339–345. Zhou, D., Cantu, C., III, Sagiv, Y., Schrantz, N., Kulkarni, A. B., Qi, X., Mahuran, D. J., Morales, C. R., Grabowski, G. A., Benlagha, K., Savage, P., Bendelac, A., and Teyton, L. (2004). Editing of CD1d‐bound lipid antigens by endosomal lipid transfer proteins. Science 303, 523–527. Zhou, D., Mattner, J., Cantu, C., III, Schrantz, N., Yin, N., Gao, Y., Sagiv, Y., Hudspeth, K., Wu, Y. P., Yamashita, T., Teneberg, S., Wang, D., Proia, R. L., Levery, S. B., Savage, P. B., Teyton, L., and Bendelac, A. (2004). Lysosomal glycosphingolipid recognition by NKT cells. Science 306, 1786–1789. Zinkernagel, R. M., and Doherty, P. C. (1974). Restriction of in vitro T cell‐mediated cytotoxicity in lymphocytic choriomeningitis within a syngeneic or semiallogeneic system. Nature 248, 701–702.
Lysophospholipids as Mediators of Immunity Debby A. Lin* and Joshua A. Boyce{ *Department of Medicine, Harvard Medical School, and Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Boston, Massachusetts { Departments of Medicine and Pediatrics, Harvard Medical School, Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Boston, Massachusetts Abstract............................................................................................................. Introduction ....................................................................................................... LPL Synthesis .................................................................................................... Cell Surface Receptors for LPLs and Their Signaling Pathways ................................... Expression of LPA and S1P Receptors by Immune Cells and Their Functions in In Vitro Studies .................................................................................................. 5. In Vivo Functions of LPLS in Immune Responses and Inflammation............................ 6. Clinical Applications of S1P Receptor Agonists ......................................................... 7. Summary ........................................................................................................... References .........................................................................................................
1. 2. 3. 4.
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Abstract Lysophospholipids (LPLs) are lipid‐derived signaling molecules exemplified by lysophosphatidic acid (LPA) and sphingosine 1‐phosphate (S1P). Originally identified as serum‐associated growth factors, these mediators now are known to signal through a family of diverse G protein‐coupled receptors (GPCRs). Virtually all cells that participate in the immune response express multiple receptors for LPLs. The development of antibody reagents that recognize the receptors for each LPL and the derivation of receptor‐selective agonists and receptor‐null mouse strains have provided insights into the widely diverse functions of LPLs in immune responses, particularly the role of S1P in lymphocyte trafficking. This review focuses on the biology of the LPLs as these molecules relate to functional regulation of immune cells in vitro and to the regulation of integrated immune responses in vivo. 1. Introduction Lysophospholipids (LPLs) are lipid signaling molecules that derive from cell membrane‐associated precursors. They can be generated rapidly by cells in response to a variety of perturbations, are abundant in normal biologic fluids, and have broad and potent actions. The two major classes of LPLs, lysoglycerolphospholipids and lysosphingophospholipids, are exemplified by
141 advances in immunology, vol. 89 # 2006 Elsevier Inc. All rights reserved.
0065-2776/06 $35.00 DOI: 10.1016/S0065-2776(05)89004-2
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Figure 1 Chemical structures of LPA (A) and S1P (B). The structure of LPA 18:2, the most abundant molecular species of LPA in biologic fluids, is depicted. Other molecular species include both unsaturated (16:1, 18:1) and saturated (12:0, 14:0, 16:0, and 18:0) members.
lysophosphatidic acid (LPA) and sphingosine 1‐phosphate (S1P), respectively. These structurally related lipids are defined by the absence of one fatty acid from one of two potential acylation positions on a glycerol backbone (Fig. 1). Originally recognized as serum‐associated growth factors for endothelial cells, both LPA and S1P serve diverse functions in the growth, motility, and differentiation of a wide array of cells. High affinity receptors exist for each ligand, and genetic strategies for targeted deletion of some of these receptors have revealed critical functions for LPA in neurodevelopment (Contos et al., 2000) and for S1P in the development of the vascular system (Liu et al., 2000). The recognition that these receptors are widely expressed by the cells responsible for both innate and adaptive immune responses and the development of receptor‐selective agonists and receptor‐null mouse strains have permitted studies of the functions of these endogenous mediators in immunity and inflammation in vivo. A comprehensive understanding of these functions for each LPL in immunity is emerging, especially the recognition of a prominent role for S1P in the homeostatic control of lymphocyte migration. Moreover, the fact that LPA stimulates a range of responses from lymphocytes, eosinophils, macrophages, and mast cells in vitro suggests that it has additional functions in vivo in the induction or amplification of immune or inflammatory responses. This review summarizes the functional characteristics of the LPLs in immunity and inflammation, with particular emphasis on LPA and S1P, their receptors, the putative functions of each mediator, the validated role of S1P in lymphocyte homing, and prospects for therapeutic development.
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2. LPL Synthesis LPLs arise as a consequence of mobilization of cell membrane‐associated precursors, both by homeostatic mechanisms and during activation responses. The synthetic pathways for each ensure the production of LPA and S1P, respectively, at quantities sufficient to maintain concentrations of each mediator close to the micromolar range in the extracellular fluid (Pages et al., 2001; Yatomi et al., 1997). These pathways are detailed below. 2.1. LPA LPA circulates at high (low micromolar) concentrations in normal serum. It is bound by serum albumin (Tigyi and Miledi, 1992), which is a high‐capacity but low‐affinity carrier for LPA, and gelsolin (Goetzl et al., 2000a), which has less capacity but higher affinity and specificity. It is likely that these carriers regulate the presentation, strength, and duration of receptor activation by LPA. Several molecular species of LPA, including both unsaturated (16:1, 18:1, and 18:2) and saturated (12:0, 14:0, 16:0, and 18:0) forms, are present in serum, with LPA 18:2 being the most abundant form (Fig. 1). The existence of multiple pathways for LPA production (Pages et al., 2001) (Fig. 2) likely reflects the importance of LPA in cell homeostasis. Although some LPA may be generated at inner membrane leaflets by phospholipase D, most LPA is likely produced at the outer membrane leaflet or extracellularly from LPA precursor, lysophosphatidylcholine (LPC). LPC is generated from phosphatidyl choline (PC) on the leaflets of cell membranes through the actions of extracellular (secretory) phospholipase A2 (sPLA2) enzymes, such as group IIA
Figure 2 Pathways for LPA synthesis. Platelets are the dominant source of LPA in vivo. PC is converted to lysophosphatidyl choline (LPC) by secretory phospholipase A2 (sPLA2), phospholipase A1 (PLA1), or lecithin‐cholesterol acyltransferase (LCAT). LPA can then be produced directly from LPC via lysoPLD (also known as autotaxin) or can be converted directly from PA. LPA is hydrolyzed to monoacylglycerol MAG by lipid phosphate phosphatases.
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PLA2. Platelets comprise the major source of LPC (and thus, of LPA) in normal serum (Sano et al, 2002); experimental depletion of platelets in rats decreases serum LPC concentrations by roughly half (Aoki et al., 2002). Other cells that can provide LPC (or that generate and secrete small quantities of LPA directly) include fibroblasts, adipocytes (which secrete LPA in response to stimulation with adrenergic agonists) (Pages et al., 1999), and potentially mononuclear phagocytes (which can also express sPLA2). The sources of LPC suggest mechanisms that may enhance LPA generation in diverse tissue injury, possibly to induce inflammation and/or initiate tissue healing through growth factor‐like activities. Furthermore, group IIA PLA2 is inducible in some cell types by interleukin (IL)‐1b, which suggests a mechanism by which LPA levels can increase during inflammation (Degousee et al., 2001). LPC can also be converted from membrane‐associated PC by phosphatidic acid‐specific PLA1, and it can be liberated by lecithin‐cholesterol acyltransferase from PC bound to serum lipoproteins (Aoki et al., 2002), thereby comprising a potential extracellular reservoir. Although both adipocytes and platelets can directly generate and release small amounts of LPA from endogenous enzymatic metabolism of LPC when they are activated by physiologic agonists, most extracellular LPA is likely converted from extracellular LPC by a serum‐ associated lysophospholipase D (lysoPLD), known also as autotaxin, which was originally identified as a serum factor that facilitated the chemotaxis of ovarian tumor cells. Lipoprotein‐bound LPC is constitutively in serum at concentrations approaching 100 mM (Aoki et al., 2002). Ovarian cancer cells generate especially large quantities of LPA, which is a potent autocrine growth factor for these cells (Xu et al., 1995b). An alternate pathway for LPA production involves conversion of phosphatidic acid (PA) directly to LPA by low molecular weight sPLA2 (Pages et al., 2001). Recently, sphingomyelinase D, which is an ecto‐enzyme of ticks and Corynebacterium species, has been identified as a virulence factor that converts host‐derived LPC to LPA (van Meeteren et al., 2004). In this instance, the local overproduction of LPA is pathogenetic and initiates regional inflammation and thrombosis. This finding suggests that LPA may initiate the innate immune response in vivo. The strength and duration of LPA‐mediated signaling is likely controlled by membrane‐associated lipid phosphate phosphatases, which hydrolyze LPA into monoacyl glyceride (MAG) (Smyth et al., 2003). 2.2. S1P Whereas LPA is generated predominantly in the extracellular compartment, S1P (which is present in physiologic fluids in a concentration range similar to that of LPA) is generated intracellularly, and its presence in the serum reflects
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its release from the cells of origin. The cellular sources of S1P include platelets (Yatomi et al., 1997) and resident tissue mast cells (Jolly et al., 2004). S1P synthesis begins with the conversion of endogenous membrane‐derived sphingomyelin to ceramide (Cer) by sphingomyelinase, then to sphingosine (Sph) by ceremidase, which is converted to S1P via phosphorylation by one of two Sph kinases (SphK1 or SphK2) (Olivera and Spiegel, 2001) (Fig. 3). SphK1 translocates to the cell membrane of activated mast cells by a mechanism requiring the actions of PLD. Once synthesized, S1P serves both intracellular and extracellular signaling functions (Spiegel and Milstein, 2000). Intracellular S1P binds putative endoplasmic reticulum‐associated receptors to facilitate the release of intracellular stores of calcium into the cytosol during cell activation, accounting for a portion of intracellular calcium flux in mast cells (Melendez and Khaw, 2002) and macrophages (Melendez et al., 1998). S1P is also released by mast cells and platelets into the extracellular space where, like LPA, it is carried by albumin and is typically found in high nanomolar to low micromolar concentrations. Signaling initiated by S1P is limited by its dephosphorylation by two S1P phosphatases (Mandala, 2001) or an S1P lyase (Zhou and Saba, 1998), and it is counterbalanced by antagonistic signaling induced by Cer and Sph (see below). 3. Cell Surface Receptors for LPLs and Their Signaling Pathways 3.1. Receptors LPLs were initially recognized as serum constituents with growth factor‐like activity that were susceptible to inhibition by pertussis toxin (PTX), suggesting that these actions were mediated by specific G protein‐coupled receptors (GPCRs) coupled to Gi/o family proteins. In the late 1990s, a group of eight homologous GPCRs known as endothelial differentiation and growth (Edg) receptors was identified. Of these, three (initially designated the Edg‐2, Edg‐ 4, and Edg‐7 receptors) selectively bind LPA with high affinity (low nM concentration range); these receptors are now designated the LPA1, LPA2, and LPA3 receptors, respectively (An et al., 1998a; Bandoh et al., 1999; Hecht et al., 1996). An orphan GPCR (p2y9/GPR23) recently was shown to bind LPA selectively and with high affinity when expressed by transfection in a cell line (Noguchi et al., 2003). This putative fourth LPA receptor (now termed the LPA4 receptor) shares little sequence homology with the Edg family members, being more closely related to the purinergic (P2Y) receptor family members that recognize extracellular nucleotides. In some cell types, LPA‐mediated effects on cell growth were found to be independent of GPCRs. This observation was explained by the demonstration that LPA can also function as a transcellular agonist for the nuclear peroxisome proliferator‐activated receptor gamma
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Figure 3 Pathway for S1P synthesis. Sphingomyelin is converted to Cer by sphingomyelinase. Cer is converted to Sph by ceramidase. Sph is phosphorylated by SphK1/2 to produce S1P, which is in turn dephosphorylated by S1P phosphatase.
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(PPAR‐g) (McIntyre et al., 2003). In a model of atherosclerosis in rats, PPAR‐g was central to LPA‐induced neointima formation (Zhang et al., 2004). A total of five Edg receptors (Edg‐1, Edg‐5, Edg‐3, Edg‐6, and Edg‐8) selectively bind S1P with high affinity and specificity; these receptors are also designated the S1P1, S1P2, S1P3, S1P4, and S1P5 receptors, respectively (An et al., 1997; Graeler et al., 1998; Hla and Maciag, 1990; Im et al., 2000; Okazaki et al., 1993; Yamaguchi et al., 1996). An additional orphan receptor, GPR63, binds S1P with low affinity (Niedernberg et al., 2003). The existence of multiple receptors for S1P (as well as LPA) implies that the functions for each mediator may be considerably diverse. Such diversity is further suggested by the observation that S1P receptors can also form homo‐ and heterodimers (van Brocklyn et al., 2002), a process that expands the repertoire of signaling processes initiated by other GPCR systems. 3.2. Signaling and G Proteins Each receptor for LPA and S1P induces biologic responses by initiating signaling events through G protein subunits. When expressed by transfection into heterologous cell lines, LPA1 receptors primarily couple to PTX‐sensitive Gi family proteins (An et al., 1998b) and potently stimulate cell growth through Ras‐dependent activation of mitogen‐activated protein kinase (MAPK) cascades. LPA2 associates with G12/13, prominently stimulating the Rho/Ras/Rac GTPases (Moolenaar, 1999; Radeff‐Huang et al., 2004); this event is critical to stimulating cell motility through effects on the actin cytoskeleton. In some cell types, LPA2 receptors stimulate calcium flux in part by inducing intracellular generation of S1P by SphK1 (Young et al., 2000), suggesting a potential mechanism for cross‐talk among these respective LPLs. LPA3 receptors induce calcium flux using Gq proteins that stimulate phospholipase C (PLC) (Radeff‐Huang et al., 2004). The LPA4 receptor differs sharply from the Edg‐type LPA receptors in its ability to stimulate the accumulation of cAMP in transfected cells (Noguchi et al., 2003), likely reflecting coupling to Gs family proteins. GPCRs exhibiting this property induce ligand‐initiated signaling events that inhibit secretory functions of activated leukocytes and that counteract contractile responses in smooth muscle cells. Studies with transfected cells show that S1P1 receptors signal exclusively through Gi proteins (Windh et al., 1999), whereas S1P2 and S1P3 receptors signal using Gi, Gq, and G12/13 (Pyne and Pyne, 2000). Xenopus oocytes exhibited S1P‐induced calcium flux when transfected with either the S1P2 or the S1P3 receptor, but not with the S1P1 receptor (Ancellin and Hla, 1999). Although studies in transfectants indicate that each receptor has preferences for specific G proteins, there is strong evidence that each LPA receptor can couple to two or three different G proteins when
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naturally expressed on primary cells. These findings further validate the diversity of signaling events and biologic responses to LPA and S1P. 4. Expression of LPA and S1P Receptors by Immune Cells and Their Functions in In Vitro Studies The receptors for LPA and S1P are broadly expressed on cell types of the immune system, including monocytes (Lee et al., 2002), B‐ and T‐lymphocytes (Girkontaite et al., 2004; Goetzl et al., 2000b), dendritic cells (DCs) (Idzko et al., 2002), mast cells (Bagga et al., 2004), natural killer (NK) cells (Maghazachi, 2003), neutrophils (Itagaki et al., 2005), and eosinophils (Roviezzo et al., 2004). The sections below outline the receptor‐mediated functions that have been identified for each cell type in vitro. 4.1. Lymphocytes Although transformed human T cells were reported to express several Edg receptor family members, the profile of these receptors expressed by primary human T cells is more limited. Jurkat leukemic T cells responded to LPA in vitro by migrating through an experimental connective tissue‐like barrier, accompanied by enhanced generation of matrix metalloproteases (Zheng et al., 2001). Freshly isolated human CD4þ T cells from peripheral blood predominantly express mRNA encoding the LPA2 receptor (Goetzl et al., 2000b), along with the corresponding protein. The generation of IL‐2 that is induced by stimulation of these primary cells with a combination of antibodies against CD3 and CD28 is decreased in a dose‐dependent manner when these cells are treated with LPA. The suppression of mitogen‐induced IL‐2 generation and decreased migration in response to LPA were both reproduced by activating LPA2 receptor‐selective monoclonal antibodies. Interestingly, no LPA receptors were identified on the CD8þ cells isolated from the same individuals in this study, and these cells did not respond functionally to LPA. Human CD4þ lymphocytes stimulated ex vivo with either a mitogenic lectin or with anti‐ CD3/anti‐CD28 exhibited inducible expression of the LPA1 receptor, accompanied by suppressed expression of the LPA2 receptor (Zheng et al., 2000). These changes in the receptor profile of CD4þ T cells were accompanied by striking corresponding changes in their functional responses to LPA. Specifically, LPA no longer induced chemotaxis itself and inhibited chemotaxis to exogenous chemokines; however, it stimulated (rather than suppressed) IL‐2 production. These in vitro experiments indicate that LPA receptor expression in CD4þ T cells is regulated dynamically by activation and suggest that naı¨ve T cells may respond initially to LPA as a chemoattractant and an inhibitor of mitogen‐induced IL‐2 production. It is tempting to speculate that
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the transition to effector T cell state upon arrival at the site of antigen presentation may be accompanied by a loss of LPA‐induced chemotaxis and migrational arrest, but LPA may amplify the effector function of T cells (i.e., IL‐2 production) at this stage. In contrast to the suppressive effects of LPA on the production of IL‐2 by freshly isolated human CD4þ T cells, LPA stimulated Jurkat T cells for calcium flux, proliferation, and IL‐2 production (Xu et al., 1995a). Similarly, immortalized human B lymphoblasts responded to LPA with calcium flux, MAPK activation, and immunoglobulin production (Rosskopf et al., 1998), whereas LPA induced calcium flux and chemotaxis of cultured human Th1 and Th2 cells (Wang, L. et al., 2004). In a separate study, LPA (1 mM) reduced the proliferation of mouse CD4þ and CD8þ T cells by 16% and 11%, respectively, in response to the combination of stimulatory antibodies to CD3 and CD28 (Dorsam et al., 2003). LPA has also been reported to inhibit apoptosis of a human T lymphoblast cell line (Goetzl et al., 1999). Since recently derived mice lacking LPA1 and LPA2 receptors have yet to be subjected to a rigorous analysis of immune function, the true physiologic role of LPA in T cell trafficking and function in vivo has yet to be determined. Like LPA, S1P mediates multiple biologic functions of both mouse and human lymphocytes, although, unlike LPA, these effects are not limited to the CD4þ subset. Mouse C57BL/6 T cells express S1P1 and S1P4 receptors (Graeler and Goetzel, 2002), while human peripheral blood T cells express S1P1, S1P3, S1P4, and S1P5 receptors (Jin et al., 2003a). At low nanomolar concentrations well within the physiologic range in normal serum, S1P is chemotactic for cultured mouse splenic T cells across a Matrigel membrane (Graeler and Goetzl, 2002). S1P at similarly low concentrations also augmented chemotaxis of mouse T cells to the chemokines CCL‐21 and CCL‐5, but it inhibited chemotaxis to these ligands when it was present at high nanomolar‐ to‐micromolar levels. These observations suggest the potential for differential modulatory effects of S1P on lymphocyte trafficking that depend on regional S1P concentrations. The direct effects of S1P on chemotaxis were reproduced in rat HTC4 cells that were transfected with S1P1 receptors, but not those transfected with S1P4 receptors, suggesting that the former receptor was the most crucial for chemotactic function. Both the enhancing and inhibitory effects of S1P were blocked by T cell activation through the T cell receptor (Graeler et al., 2002). This maneuver downregulates the expression of both the S1P1 and S1P4 receptors, while simultaneously upregulating the expression of S1P3 and S1P5 in cultured human peripheral blood T cells (Jin et al., 2003a). The activation‐dependent downregulation of the S1P1 receptor is transient and recovers in mouse T cells by a mechanism that is dependent on protein kinase (PK) C e and AP‐1 transcriptional activity (Graeler et al., 2003). Thus, as is the
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case for LPA, the response of T cells to S1P is dynamic and regulated in part by inducible changes in the levels and repertoire of expressed receptors, particularly that of the S1P1 receptor. These findings likely reflect events that are reproduced in vivo as demonstrated by models of lymphocyte trafficking (see below). Lymphocytes isolated from humans and mice exhibit responses to S1P in vitro in addition to chemotaxis. At relatively high (0.1–10 mM) concentrations, S1P inhibited the proliferation of human peripheral blood T cells induced by a combination of stimulating antibodies directed against CD3 and CD28, by stimulation with PMA/ionomycin, or by co‐culture with antigen‐loaded DCs. The inhibitory effects of S1P on PMA/ionomycin stimulation could be blocked by pre‐treatment of the cells with PTX. These findings imply the involvement of a Gi‐coupled S1P receptor family member, whereas PTX did not interfere with the effect of S1P on proliferation induced by anti‐CD3/anti‐CD28 or stimulation with DCs (Jin et al., 2003a). At slightly lower doses (0.01–1 mM), S1P inhibited the proliferation of splenic CD4þ and CD8þ T lymphocytes from C57BL/6 mice that occurred in response to stimulation with anti‐CD3/ anti‐CD28 or anti‐CD3 plus IL‐7 (Dorsam et al., 2003). Thus S1P has the potential to interfere with the proliferation of both human and mouse T cells and can do so by both Gi/o‐dependent and ‐independent signaling pathways. S1P (1–10 mM) also amplifies the production of IL‐2 and interferon (IFN)‐g by human T cells stimulated by anti‐CD3/anti‐CD28. This costimulatory effect was inhibited by either exogenous Sph or Cer (Jin et al., 2003a). S1P also enhances IL‐10 production by mouse CD4þ CD25þ regulatory T cells, facilitating the capacity of these cells to suppress IL‐2 production and proliferation of CD4þ CD25 T cells (Wang, W. et al., 2004). In another study, S1P decreased the production of IFN‐g and IL‐4, but not that of IL‐2, by antigen receptor‐stimulated CD4þ T cells from C57BL/6 mice. S1P inhibition of IFN‐g production was dependent on S1P1 receptor expression (Dorsam et al., 2003). Thus S1P either can directly augment the secretion of certain cytokines by lymphocytes or can also suppress lymphocyte functions, depending on context and (likely) on the profile of S1P receptors expressed by a given lymphocyte cell population. Since this repertoire is dynamically regulated, it is not surprising that the nature of the responses to S1P by lymphocytes in vitro vary from study to study. 4.2. Natural Killer Cells Human NK cells that are stimulated with IL‐2 express the LPA1, LPA2, and LPA3 receptors. Stimulation of these primed NK cells with LPA induced a chemotactic response in vitro that was inhibited by pre‐treatment of the cells
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with PTX. LPA and PA induced calcium flux and modestly augmented IFN‐g production by NK cells (Jin et al., 2003b). Whereas S1P receptors were not profiled in this study and S1P did not induce chemotaxis of these activated NK cells, in another study human NK cells expressed S1P1, S1P4, and S1P5 receptors and responded chemotactically to S1P in a PTX‐sensitive manner (Kveberg et al., 2002). Thus, like lymphocytes, NK cells express a diverse profile of LPA and S1P receptors and exhibit responses to these ligands that can be modulated by activation. The role of NK cells in anti‐tumor immunity raises the possibility that LPLs may provide an innate stimulus for the recruitment of NK cells to sites of tumor invasion. These studies also suggest the existence of additional functions for LPLs in anti‐viral immunity. 4.3. Dendritic Cells DCs, the most potent antigen‐presenting cells, can be differentiated from human monocytes in vitro. The addition of LPC, the precursor of LPA, to cultured human peripheral blood monocytes augmented their differentiation into mature DCs and was associated with extracellular signal‐regulated kinase (ERK) MAPK phosphorylation. In a mixed lymphocyte reaction, the LPC‐ treated monocytes enhanced the production of IL‐2 and IFN‐g by T cells. The effect of LPC on CD86 expression was partially inhibited by PTX and BN52021, an antagonist of the platelet‐activating factor receptor (Coutant et al., 2002). During antigen processing, maturing DCs undergo tightly coordinated changes in cell surface phenotype and responses to endogenous chemoattractants so as to facilitate their migration to regional lymph nodes. Although both immature and mature human DCs express mRNA transcripts for LPA1, LPA2, and LPA3 receptors (Panther et al., 2002) as well as for S1P1, S1P2, S1P3, and S1P4 receptors (Idzko et al., 2002), the responses of DCs to LPA and S1P change substantially as the cells mature. Both LPA and S1P elicited PTX‐sensitive calcium flux, actin polymerization, and chemotaxis in immature DCs. These chemotactic responses were lost after the cells were stimulated with lipopolysaccharide (LPS) to induce their maturation. However, both LPA and S1P (at high nanomolar/low micromolar range concentrations) inhibited the LPS‐mediated generation of IL‐12 and TNF‐a by DCs, and augmented their production of IL‐10 in a PTX‐insensitive manner (Idzko et al., 2002; Panther et al., 2002; Renkl et al., 2004). The changes in cytokine profile were associated with a reduced ability of these LPS‐stimulated DCs to polarize T cells toward the production of IFN‐g. Both the selective S1P receptor agonist FTY720 and its phosphorylated analogue, FTY720‐P, inhibited the chemotactic response of immature and mature DCs to S1P. Furthermore, mature DCs treated with FTY720 and FTY720‐P exhibited reduced IL‐12
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production and increased IL‐10 production. T cells co‐cultured with these DCs shifted from a Th1 to a Th2 cytokine profile (Muller et al., 2005). Collectively, these observations suggest that either LPA or S1P could favor polarization of T cells toward a pro‐allergic phenotype during the development of adaptive immunity through effects mediated by DCs. 4.4. Monocytes/Macrophages Peripheral blood monocytes and/or tissue macrophages in mice, humans, and rats all express receptors for LPA and S1P (Duong et al., 2004; Hornuss et al., 2001). Mouse peritoneal macrophages express the LPA1, S1P1, and S1P3 receptors. Stimulation of these mouse macrophages with LPA or S1P upregulated their expression of IL‐1b and TNF‐a transcripts and protein, and downregulated IL‐2 transcription (Lee et al., 2002). Human monocytes, macrophages, and the Mono Mac 6 (MM6) monocytic cell line express mRNA transcripts for LPA1, LPA2, S1P1, S1P2, and S1P4. Both LPA and S1P in nanomolar range concentrations stimulated calcium flux in LPS‐activated MM6 cells via a PLC and Gi pathway (Fueller et al., 2003). An important role for the S1P3 receptor in the localization of MOMA1þ metallophilic macrophages and endothelial cells within mouse splenic marginal sinus zones has been recognized in studies of mice lacking this receptor (Girkontaite et al., 2004). 4.5. Granulocytes Human peripheral blood eosinophils express mRNA encoding both LPA1 and LPA3 receptors. At low micromolar range concentrations, LPA induced chemotaxis, actin cytoskeletal rearrangement, CD11b upregulation, and oxidative burst by human eosinophils. These responses were sensitive to inhibition by PTX and were blocked by a dual‐selective antagonist of the LPA1 and LPA3 receptors, diacylglycerol pyrophosphate (Idzko et al., 2004). Human eosinophils also express S1P1 receptors and, to a lesser extent, S1P2 and S1P3 receptors. Importantly, ex vivo stimulation of human eosinophils with S1P sharply upregulated their expression of the mRNA encoding the critical chemokine receptor CCR3, as well as that of the CCR3 ligand RANTES (Roviezzo et al., 2004). Thus both S1P and LPA may induce or modify patterns of eosinophil recruitment in certain contexts. This possibility is supported by the observation that the injection of S1P induces recruitment of eosinophils into the footpads of rats (Roviezzo et al., 2004). Like eosinophils, human peripheral blood neutrophils respond to both LPA and S1P. LPA induced calcium flux and oxidative burst from neutrophils, neither of which was inhibited by PTX, thus suggesting a potential alternative
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pathway for neutrophil activation (Itagaki et al., 2005). However, local anesthetics have been shown to inhibit LPA‐induced chemotaxis and priming of neutrophils (Fischer et al., 2001), which may be important for their anti‐ inflammatory effects. LPA also stimulates neutrophil degranulation, in part through enhanced PLD activity (Tou and Gill, 2005). In an in vivo model, inhalation of LPA by guinea pigs increased eosinophil and neutrophil numbers in bronchoalveolar lavage fluid as well as superoxide production (Hashimoto et al., 2003). In contrast, other studies have shown that LPA inhibits the neutrophil metabolic burst after stimulation of the cells with fMLP and phorbol 12‐myristate 13‐acetate (PMA) (Chettibi et al., 1994). S1P stimulates calcium flux in human neutrophils independently of GPCRs and instead acts through store‐operated calcium entry channels (Itagaki and Hauser, 2003). Inhibition of SphK led to diminished neutrophil chemotaxis in vitro. In a rat model of hemorrhagic shock, SphK inhibition also decreased both CD11b expression, a marker of neutrophil activation, and lung injury as measured by permeability to dye (Lee et al., 2004). 4.6. Mast Cells Mast cells reside in perivascular spaces in all organs and are ideally situated to receive LPL signals from the vasculature. Human mast cells derived in vitro from umbilical cord blood express transcripts encoding all four LPA receptors (Bagga et al., 2004), and exhibit cytofluorographic expression of LPA1, LPA2, and LPA3 receptors (Lin and Boyce, 2005). In an in vitro model culture system for mast cell development from human cord blood‐derived progenitor cells, LPA potently stimulated the proliferation of mast cells, providing a synergistic signal with the obligate mast cell growth factor, stem cell factor (SCF). At peak concentrations (5 mM), LPA increased mast cell numbers by 10‐fold and strongly enhanced the formation of secretory granules and the expression of alpha and beta tryptases. PTX blocked LPA‐induced proliferation virtually completely (Bagga et al., 2004) and partly interfered with LPA‐induced calcium fluxes (Lin and Boyce, 2005) (Fig. 4). Whereas unprimed human mast cells did not generate cytokines or chemokines in response to LPA, mast cells primed with the Th2 cytokine IL‐4 produced abundant quantities of the chemokines macrophage inflammatory protein (MIP)‐1b, monocyte chemotactic protein (MCP)‐1, and IL‐8. The IL‐4‐dependent priming upregulated expression of mitogen‐activated protein kinase‐kinase, permitting LPA to induce strong phosphorylation of ERK. Interestingly, whereas LPA‐dependent proliferation was completely blocked by a dual LPA1/LPA3 receptor‐selective antagonist VPC32179, this compound did not affect LPA‐mediated chemokine generation, which instead was mimicked by fatty alcohol phosphate‐12, a
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Figure 4 Effect of LPA on mast cell growth and activation. LPA induces mast cell proliferation synergistically with SCF and stimulates tryptase expression through a pathway involving PPAR‐g, LPA1, and/or LPA3. In contrast, LPA induces chemokine (MIP‐1b, MCP‐1, and IL‐8) production through LPA2 receptors, and this production depends on IL‐4 priming and MAPK phosphorylation. KIT, c‐kit tyrosine kinase.
selective agonist of the LPA2 receptor. Thus LPA may both support reactive mastocytosis (a feature observed in several disease states) and may also serve as an amplifier of mucosal inflammation where mast cell hyperplasia is mediated by a Th2 cytokine‐based mechanism. Cer, Sph, and S1P exert complex and generally opposing effects on mast cell activation, a phenomenon referred to as the ‘‘sphingolipid rheostat’’ (Olivera and Rivera, 2005). Whereas the addition of exogenous Cer or Sph to mouse bone marrow‐derived mast cells (BMMCs) in vitro induces apoptosis (Itakura et al., 2002), S1P promotes proliferation and effector functions (Jolly et al., 2004; Prieschl et al., 1999) (Fig. 5). Exogenous Sph inhibited MAPK activation and the generation of leukotrienes and cytokines by BMMCs classically activated by cross‐linkage of the high‐affinity Fc receptor for IgE (FceRI) but had minimal effect on cell degranulation. The addition of S1P reversed Sph‐ induced inhibition of activation. A rat mast cell line, RBL‐2H3, produced MIP‐1b and MCP‐1 in response to stimulation with exogenous S1P. The mouse mast cell line CPII responded to stimulation with exogenous S1P with exocytosis and leukotriene secretion, as well as with TNF‐a production when S1P was provided in conjunction with ionomycin (Prieschl et al., 1999).
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Figure 5 Effect of S1P on mast cell activation. Antigen/IgE crosslinking of FcRI on mast cells activates SphK1 via a PLD‐dependent pathway to produce S1P. S1P acts intracellularly to induce Ca2þ release from the endoplasmic reticulum, which is necessary for exocytosis. S1P also acts extracellularly on S1P2 receptors to mediate calcium release via PLC/IP3, and on S1P1 to mediate antigen‐directed chemotaxis. The ability of mast cells to secrete S1P in response to activation suggests a potential mechanism for lymphocyte recruitment in allergic disease.
Although the receptor(s) responsible were not identified in these studies, both BMMCs and RBL‐2H3 cells express both S1P1 and S1P2 receptors, but do not express S1P3, S1P4, and S1P5 receptors. In addition to the paracrine effects already discussed, S1P also regulates mast cell activation in an autocrine manner. FcRI‐induced activation of CPII cells, BMMCs, and cultured human mast cells results in the generation and/or secretion of S1P. In human and mouse BMMCs, FcRI cross‐linkage induced the translocation of SphK1 to the cell membrane, a necessary prerequisite to S1P generation (Choi et al., 1996; Jolly et al., 2004; Melendez and Khaw, 2002). SphK1 required activation of PLD in human mast cells, and S1P production was in turn required for the calcium flux and exocytosis that occurred in response to FcRI cross‐linkage, presumably through the effects of S1P actions at the endoplasmic reticulum to liberate intracellular stores of calcium. Endogenous S1P generation was also required for optimal exocytosis of granule contents by BMMCs; however, this event reflected transactivation of the S1P2 receptor by secreted S1P, rather than intracellular actions (Jolly et al., 2004). Additionally, transactivation of the S1P1 receptor was required for migration of BMMCs toward antigen in this study, based on RNA interference
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with the pertinent receptors. Collectively, these studies support the likely importance of the Cer/Sph/S1P rheostat in the autocrine regulation of activation‐induced mast cell signaling and establish clearly distinct functions for the S1P1 and S1P2 receptors. Moreover, the ability of activated mast cells to secrete S1P in response to activation may have implications for chemotaxis of lymphocytes and other S1P‐responsive cells in allergic responses. 5. In Vivo Functions of LPLS in Immune Responses and Inflammation 5.1. LPA Recent studies have addressed LPA‐mediated functions in inflammation using direct challenges. The intranasal administration of LPA to immunologically naı¨ve C57BL/6 mice resulted in increased MIP‐2 and neutrophil recruitment in BAL fluid (Cummings et al., 2004). These effects were attributed to stimulatory effects on bronchial epithelial cells, since this same study demonstrated that LPA induced IL‐8 production in human bronchial epithelial cells that was dependent on NF‐kB transcription and protein kinase C‐d. The injection of LPA into the perivascular tissues of rat carotid arteries induced the formation of neointima, accompanied by local proliferation of macrophages (Zhang et al., 2004). These events were attributed to activation of PPAR‐g. Although no studies have specifically addressed the role of any specific LPA receptor in immunity or inflammation, the availability of mouse strains that lack LPA1 receptors (which have defective forebrain development), LPA2 receptors (which are phenotypically normal), or both receptors should permit such investigations (Contos et al., 2002). 5.2. S1P In contrast to the relatively limited information concerning the role of LPA in immune function in vivo, an abundant amount of literature supports the role of S1P. Intravenously administered S1P induced a rapid lymphopenia in experimental animals, an effect attributed to the sequestration of both T cells and B cells in secondary lymphoid organs. Thymocytes acquire S1P1 receptor expression during their maturation into CD4þ and CD8þ lymphocytes (Matloubian et al., 2004). Constitutive levels of S1P in the blood are sufficient to induce the egress of these naı¨ve T cells into the circulation. S1P1 receptor expression is then cyclically modulated, being down‐regulated in the blood, subsequently upregulated in the secondary lymphoid tissues, and then down‐modulated once again with transit to the lymph (Lo et al., 2005) (Fig. 6).
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Figure 6 Regulation of lymphocyte trafficking by S1P1 receptor signaling. S1P1 receptor expression is acquired during thymic development by single positive CD4þ or CD8þ T cells. Lymphocytes migrate into the blood and then to secondary lymphoid organs where the relatively low levels of S1P allow upregulation of S1P1 expression. S1P1 signaling facilitates lymphocyte egress into lymph. The administration of FTY720 downregulates S1P1 receptor expression and inhibits lymphocyte egress from thymus and lymphoid organs.
Both antigen‐induced and S1P‐induced stimulation of lymphocytes likely account for the down‐modulation of S1P1 receptor expression in the peripheral blood. The down‐modulation of S1P1 receptor expression likely permits chemokine‐dependent migration of T cells to regional lymph nodes, a process that requires the function of endogenously generated cysteinyl leukotrienes and the leukotriene‐specific multidrug transporter (Honig et al., 2003; Yopp et al., 2004). The acquisition of the S1P1 receptor during T cell development in the thymus and its re‐acquisition by mature lymphocytes in the lymph nodes permits S1P to promote egress of nascent T cells from the thymus and induce the re‐circulation of mature T cells from the secondary lymphoid organs, respectively. Whereas S1P1 receptor deficiency caused embryonic lethality due to a defect in the development of the microvasculature (Liu et al., 2000), mice with conditional deletion of the S1P1 receptor exhibited thymic hyperplasia due to retention of CD4þ and CD8þ T cells in the thymus (Allende et al., 2004). Moreover, the adoptive transfer of fetal liver‐derived hematopoietic progenitor cells from S1P1 receptor‐deficient mice into lethally irradiated recipient mice resulted in sequestration of T lymphocytes in the thymus and lymph nodes (Matloubian et al., 2004). Conversely, the transfer of T cells from mice transgenically over‐expressing S1P1 receptors resulted in increased numbers of T cells in the circulation and decreased numbers in the lymph nodes (Graeler et al., 2005). In transgenic cells, S1P1 surface expression was reduced in the blood and lymph and increased in spleen and lymph nodes (Lo et al., 2005). In studies of S1P1 receptor‐null mice, T lymphocytes and precursors could enter the thymus and peripheral lymphoid tissues but could not leave (Allende et al., 2004; Matloubian et al., 2004). Collectively, these
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studies support a major role for the S1P1 receptor in the regulation of T cell trafficking and indicate that the expression of this receptor is dynamically regulated in vivo. The ability of systemically administered S1P to elicit lymphopenia is similar to that of 2‐amino‐2‐(2‐[4‐octylphenyl]ethyl)‐1,3‐propanediol (FTY720) (Adachi et al., 1995), an immunosuppressant isolated from the fungus Isaria sinclairii, which induced profound lymphopenia in rats. The systemic administration of S1P, FTY720, or FTY720‐P induced sequestration of lymphocytes in peripheral lymphoid tissues (Brinkmann et al., 2002; Mandala et al., 2002), but did not affect the numbers of myelomonocytic cells. These similarities were explained by the subsequent recognition that FTY720 and FTY720‐P are potent agonists at all S1P receptors except for the S1P2 receptor (Brinkmann et al., 2002; Mandala et al., 2002). This discovery greatly accelerated the acquisition of knowledge about the physiologic functions of S1P. In in vitro studies, FTY720 crosses cell membranes and is phosphorylated by SphK2 to a greater extent than by SphK1, although much less efficiently than is Sph. FTY720 also inhibits the phosphorylation of Sph by SphK2 to a greater extent than by SphK1 (Paugh et al., 2003). In studies of rat HTC4 cells engineered to express S1P receptor subtypes, the administration of FTY720 caused pronounced internalization and degradation of the S1P1, S1P2, and S1P5 receptors but did not affect the expression of S1P3 or S1P4 receptors (Graeler and Goetzl, 2004). Systemically administered FTY720 depleted both T and B lymphocytes in thoracic duct, peripheral blood, and spleen (Brinkmann et al., 2002; Chiba et al., 1998; Mandala et al., 2002). FTY720‐induced lymphocyte homing to secondary lymphoid organs depends on CD49d, CD62L, and CD11a, as indicated by experiments with specific antibody blockade (Chiba et al., 1998). FTY720 also strikingly inhibits thymocyte egress from thymus (Matloubian et al., 2004). Indeed, systemically administered FTY720 induces equal depletion of naı¨ve and effector/memory T cells from the peripheral circulation. Many of the bioactive effects of FTY720 and its phosphorylated metabolite reflect its capacity to induce striking internalization and subsequent down‐modulation of S1P receptors, particularly that for S1P1. The administration of S1P, FTY720, or FTY720‐P to wild‐type mice sharply down‐modulates S1P1 receptor expression in vivo (Matloubian et al., 2004), thus arresting emigration of nascent CD4þ and CD8þ lymphocytes from the thymus while preventing the recirculation of mature T cells from the regional nodes. Another S1P receptor agonist, 2‐amino‐4-4‐heptyloxyphenyl‐2‐methylbutanol (Kiuchi et al., 2000), also inhibits thymic egress, which is accompanied by loss of CD69 on CD4þ and CD8þ thymocytes in C57BL/6 mice (Rosen et al., 2003). Thus, T lymphopenia induced by S1P receptor agonists relates directly to the requirement for S1P1 receptor signaling at two distinct developmental stages in T cells.
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S1P receptor agonism induced the migration of splenic B cells from the marginal zone into lymphoid follicles of mice. Based on studies of S1P1‐ deficient fetal liver chimeric mice, B cell localization to the marginal zone of the spleen depends on S1P1 (Cinamon et al., 2004). Activated B cells from C57BL/6 mice modified to overexpress S1P1 demonstrated decreased localization to the white pulp of the spleen compared to control cells. Treatment of the mice with FTY720 restored trafficking of the B cells to the white pulp. In studies of S1P3 null and reconstituted mice, S1P3 expression was required for normal migration and organization of splenic marginal sinus B lymphocytes (Girkontaite et al., 2004). Thus B cell lymphopenia induced by FTY720 reflects the arrest of normal S1P‐induced migration patterns in the spleen, which in turn reflect contributions from both the S1P1 and S1P3 receptors. 6. Clinical Applications of S1P Receptor Agonists Studies in animal models demonstrate that FTY720 is a potently immunosuppressant in vivo, with beneficial effects on allograft survival and in autoimmune disease models. FTY720 promoted skin graft survival in MHC incompatible rats. This effect was attributed to the redistribution of lymphocytes to the peripheral lymphoid organs rather than to transplanted tissues (Chiba et al., 1998, 1999). Such altered lymphocyte trafficking could have a potentially beneficial effect. In a mouse model, FTY720 diminished graft‐ versus‐host disease without affecting graft‐versus‐leukemia, due to lymphocyte migration into lymph nodes rather than tissues (Kim et al., 2003). In a mouse model of experimental autoimmune encephalitis, the administration of FTY720 or FTY720‐P resulted in clinical improvement (Webb et al., 2004). Furthermore, the administration of FTY720 prevented pulmonary inflammation induced by allergen challenge in mice that received adoptive transfer of antigen‐specific Th1 or Th2 cell clones, and abrogated antigen‐induced airway hyperresponsiveness (Sawicka et al., 2003). These observations in mice collectively support the therapeutic potential of S1P receptor agonism in organ transplantation, autoimmunity, and allergic diseases. Importantly, and in contrast to other immunosuppressive drugs, FTY720 has been reported not to impair immunity to specific pathogens. FTY720 (0.3 mg/kg) did not inhibit cell‐mediated or antibody responses in mice infected with lymphocytic choriomeningitis virus or vesicular stomatitis virus (Pinschewer et al., 2000). FTY720 did not alter IL‐4 and IFN‐g production by T cells, IgG production by B cells, or T cell proliferation responses in mixed‐lymphocyte reactions or after TCR stimulation (Brinkmann et al., 2001). However, in other studies, FTY720 diminished the immune response against specific antigens. FTY720 reduced the number of antigen‐specific CD4þ T cells in the draining lymph
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nodes and peripheral blood of mice after antigen challenge. This effect was attributed to reduced recirculation of naı¨ve and antigen‐specific T cells from lymph nodes, rather than inhibition of T cell proliferation (Xie et al., 2003). FTY720 also reduced the production of high‐affinity IgG1 antibodies against the T‐cell‐dependent antigen, alum‐precipitated nitrophenyl acetyl conjugated to chicken g‐globulin, in immunized mice. Antibody responses to the T cell‐ independent antigen, nitrophenyl‐Ficoll, were not affected. FTY720 (at doses <1 mM) did not inhibit B cell activation or proliferation in response to mitogens in vitro, but FTY720 (1mg/kg) was associated with a 50% reduction in germinal center B cell numbers in mice (Han et al., 2004). Despite these potential concerns, FTY720 shows promise for use as an immunosuppressant in humans. In a phase I trial, the oral administration of FTY720 (0.5–3.5 mg) induced a dose‐dependent, reversible peripheral lymphopenia (Budde et al., 2002). In a phase 2a clinical trial, FTY720 (2.5 mg) was as effective as mycophenolate mofetil when used with cyclosporine to prevent acute renal transplant rejection (Tedesco‐Silva et al., 2004). These observations are encouraging evidence for therapeutic promise. 7. Summary The functional modulation of a wide array of cell types involved in the immune response by LPLs likely indicates an ancient and strongly conserved component of the immune system. The development of receptor‐selective agonists and receptor‐null mouse strains has already led to profound insights into mechanisms by which S1P controls lymphocyte trafficking and to a promising treatment modality in humans. The ubiquitous nature of LPA and the potency of its bioactivities in vitro suggest that equally remarkable functions for this mediator in the immune response will be uncovered. It seems likely that these insights will lead to further therapeutic development for a broad range of human inflammatory and allergic diseases, as well as for the prevention of transplant rejection. References Adachi, K., Kohara, T., Nakao, N., Arita, M., Chiba, K., Mishina, T., Sasaki, S., and Fujita, T. (1995). Design, synthesis and structure‐activity relationships of 2‐substituted 2‐amino‐1,3‐propanediols: Discovery of a novel immunosuppressant, FTY720. Bioorg. Med. Chem. Lett. 5, 853–856. Allende, M. L., Dreier, J. L., Mandala, S., and Proia, R. L. (2004). Expression of the sphingosine 1‐phosphate receptor, S1P1, on T‐cells controls thymic emigration. J. Biol. Chem. 279, 15396–15401.
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An, S., Bleu, T., Huang, W., Hallmark, O. G., Coughlin, S. R., and Goetzl, E. J. (1997). Identification of cDNAs encoding two G protein‐coupled receptors for lysosphingolipids. FEBS Lett. 417, 279–282. An, S., Bleu, T., Hallmark, O. G., and Goetzl, E. J. (1998a). Characterization of a novel subtype of human G protein‐coupled receptor for lysophosphatidic acid. J. Biol. Chem. 273, 7906–7910. An, S., Bleu, T., Zheng, Y., and Goetzl, E. J. (1998b). Recombinant human G protein‐coupled lysophosphatidic acid receptors mediate intracellular calcium mobilization. Mol. Pharm. 54, 881–888. Ancellin, N., and Hla, T. (1999). Differential pharmacological properties and signal transduction of the sphingosine 1‐phosphate receptors EDG‐1, EDG‐3, and EDG‐5. J. Biol. Chem. 274, 18997–19002. Aoki, J., Taira, A., Takanezawa, Y., Kishi, Y., Hama, K., Kishimoto, T., Mizuno, K., Saku, K., Taguchi, R., and Arai, H. (2002). Serum lysophosphatidic acid is produced through diverse phospholipase pathways. J. Biol. Chem. 277, 48737–48744. Bagga, S., Price, K. S., Lin, D. A., Friend, D. S., Austen, K. F., and Boyce, J. A. (2004). Lysophosphatidic acid accelerates the development of human mast cells. Blood 104, 4080–4087. Bandoh, K., Aoki, J., Hosono, H., Kobayashi, S., Kobayashi, T., Murakami, M. K., Tsujimoto, M., Arai, H., and Inoue, K. (1999). Molecular cloning and characterization of a novel human G‐protein‐coupled receptor, EDG7, for lysophosphatidic acid. J. Biol. Chem. 274, 27776–27785. Brinkmann, V., Chen, S., Feng, L., Pinschewer, D., Nikolova, Z., and Hof, R. (2001). FTY720 alters lymphocyte homing and protects allografts without inducing general immunosuppression. Transplant. Proc. 33, 530–531. Brinkmann, V., Davis, M. D., Heise, C. E., Albert, R., Cottens, S., Hof, R., Bruns, C., Prieschl, E., Baumruker, T., Hiestand, P., Foster, C. A., Zollinger, M., and Lynch, K. R. (2002). The immune modulator FTY720 targets sphingosine 1‐phosphate receptors. J. Biol. Chem. 277, 21453–21457. Budde, K, Schmouder, R. L., Brunkhorst, R., Nashan, B., Lucker, P. W., Mayer, T., Choudhury, S., Skerjanec, A., Kraus, G., and Neumayer, H. H. (2002). First human trial of FTY720, a novel immunomodulator, in stable renal transplant patients. J. Am. Soc. Nephrol. 13, 1073–1083. Chettibi, S., Lawrence, A. J., Stevenson, R. D., and Young, J. D. (1994). Effect of lysophosphatidic acid on motility, polarization and metabolic burst of human neutrophils. FEMS Immunol. Med. Microbiol. 9, 271–281. Chiba, K., Yanagawa, Y., Masubuchi, Y., Kataoka, H., Kawaguchi, T., Ohtsuki, M., and Hoshino, Y. (1998). FTY720, a novel immunosuppressant, induces sequestration of circulating mature lymphocytes by acceleration of lymphocyte homing in rats. I. FTY720 selectively decreases the number of circulating mature lymphocytes by acceleration of lymphocyte homing. J. Immunol. 160, 5037–5044. Chiba, K., Yanagawa, Y., Kataoka, H., Kawaguchi, T., Ohtsuki, M., and Hoshino, Y. (1999). FTY720, a novel immunosuppressant, induces sequestration of circulating lymphocytes by acceleration of lymphocyte homing. Transplant. Proc. 31, 1230–1233. Choi, O. H., Kim, J. H., and Kinet, J. P. (1996). Calcium mobilization via sphingosine kinase in signaling by the FcRI antigen receptor. Nature 380, 634–636. Cinamon, G., Matloubian, M., Lesneski, M. J., Xu, Y., Low, C., Lu, T., Proia, R. L., and Cyster, J. G. (2004). Sphingosine 1‐phosphate receptor 1 promotes B cell localization in the splenic marginal zone. Nat. Immunol. 5, 713–720. Contos, J. J., Fukushima, N., Weiner, J. A., Kaushal, D., and Chun, J. (2000). Requirement for the lpA1 lysophosphatidic acid receptor gene in normal suckling behavior. Proc. Natl. Acad. Sci. USA 97, 13384–13389. Contos, J. J., Ishii, I., Fukushima, N., Kingsbury, M. A., Ye, X., Kawamura, S., Brown, J. H., and Chun, J. (2002). Characterization of lpa2 (Edg4) and lpa1/lpa2 (Edg2/Edg4) lysophosphatidic
162
DEBBY A. LIN AND JOSHUA A. BOYCE
acid receptor knockout mice: Signaling deficits without obvious phenotypic abnormality attributable to lpa2. Mol. Cell. Biol. 22, 6921–6929. Coutant, F., Perrin‐Cocon, L., Agaugue, S., Delair, T., Andre, P., and Lotteau, V. (2002). Mature dendritic cell generation promoted by lysophosphatidylcholine. J. Immunol. 169, 1688–1695. Cummings, R., Zhao, Y., Jacoby, D., Spannhake, E. W., Ohba, M., Garcia, J. G. N., Watkins, T., He, D., Saatian, B., and Natarajan, V. (2004). Protein kinase Cd mediates lysophosphatidic acid‐ induced NF‐kB activation and interleukin‐8 secretion in human bronchial epithelial cells. J. Biol. Chem. 279, 41085–41094. Degousee, N., Stefanski, E., Lindsay, T. F., Ford, D. A., Shahani, R., Andrews, C. A., Thuerauf, D. J., Glembotski, C. C., Nevalainen, T. J., Tischfield, J., and Rubin, B. B. (2001). p38 MAPK regulates group IIa phospholipase A2 expression in interleukin‐1beta‐stimulated rat neonatal cardiomyocytes. J. Biol. Chem. 276, 43842–43849. Dorsam, G., Graeler, M. H., Seroogy, C., Kong, Y., Voice, J. K., and Goetzl, E. J. (2003). Transduction of multiple effects of sphingosine 1‐phosphate (S1P) on T cell functions by the S1P1 G protein‐coupled receptor. J. Immunol. 171, 3500–3507. Duong, C. Q., Bared, S. M., Abu‐Khader, A., Buechler, C., Schmitz, A., and Schmitz, G. (2004). Expression of the lysophospholipid receptor family and investigation of lysophospholipid‐ mediated responses in human macrophages. Biochim. Biophys. Acta 1682, 112–119. Fischer, L. G., Bremer, M., Coleman, E. J., Conrad, B., Krumm, B., Gross, A., Hollmann, M., Mandell, G., and Durieux, M. E. (2001). Local anesthetics attenuate lysophosphatidic acid‐ induced priming in human neutrophils. Anesth. Analg. 92, 1041–1047. Fueller, M., Wang, D. A., Tigyi, G., and Siess, W. (2003). Activation of human monocytic cells by lysophosphatidic acid and sphingosine‐1‐phosphate. Cell Signal. 15, 367–375. Girkontaite, I., Sakk, V., Wagner, M., Borggrefe, T., Tedford, K., Chun, J., and Fischer, K.‐D (2004). The sphingosine‐1‐phosphate (S1P) lysophospholipid receptor S1P3 regulates MAdCAM‐1þ endothelial cells in splenic marginal sinus organization. J. Exp. Med. 200, 1491–1501. Goetzl, E. J., Kong, Y., and Mei, B. (1999). Lysophosphatidic acid and sphingosine 1‐phosphate protection of T cells from apoptosis in association with suppression of Bax. J. Immunol. 162, 2049–2056. Goetzl, E. J., Lee, H., Azuma, T., Stossel, T. P., Turck, C. W., and Karliner, J. S. (2000a). Gelsolin binding and cellular presentation of lysophosphatidic acid. J. Biol. Chem. 275, 14573–14578. Goetzl, E. J., Kong, Y., and Voice, J. K. (2000b). Cutting edge: Differential constitutive expression of functional receptors for lysophosphatidic acid by human blood lymphocytes. J. Immunol. 164, 4996–4999. Graeler, M. H., Bernhardt, G., and Lipp, M. (1998). EDG6, a novel G‐protein‐coupled receptor related to receptors for bioactive lysophospholipids, is specifically expressed in lymphoid tissue. Genomics 53, 164–169. Graeler, M., Shankar, G., and Goetzl, E. J. (2002). Cutting edge: Suppression of T cell chemotaxis by sphingosine 1‐phosphate. J. Immunol. 169, 4084–4087. Graeler, M., and Goetzl, E. J. (2002). Activation‐regulated expression and chemotactic function of sphingosine 1‐phosphate receptors in mouse splenic T cells. FASEB J. 16, 1874–1878. Graeler, M. H., and Goetzl, E. J. (2004). The immunosuppressant FTY720 downregulates sphingosine 1‐phosphate G protein‐coupled receptors. FASEB J. 18, 551–553. Graeler, M. H., Kong, Y., Karliner, J. S., and Goetzl, E. J. (2003). Protein kinase C dependence of the recovery from downregulation of S1P1 G protein‐coupled receptors of T lymphocytes. J. Biol. Chem. 278, 27737–27741. Graeler, M. H., Huang, M.‐C., Watson, S., and Goetzl, E. J. (2005). Immunological effects of transgenic constitutive expression of the type 1 sphingosine 1‐phosphate receptor by mouse lymphocytes. J. Immunol. 174, 1997–2003.
LY S O P H O S P H O L I P I D S A S M E D I AT O R S O F I M M U N I T Y
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Han, S., Zhang, X., Wang, G., Guan, H., Garcia, G., Li, P., Feng, L., and Zheng, B. (2004). FTY720 suppresses humoral immunity by inhibiting germinal center reaction. Blood 104, 4129–4133. Hashimoto, T., Yamashita, M., Ohata, H., and Momose, K. (2003). Lysophosphatidic acid enhances in vivo infiltration and activation of guinea pig eosinohils and neutrophils via a Rho/Rho‐ associated protein kinase‐mediated pathway. J. Pharmacol. Sci. 91, 8–14. Hecht, J. H., Weiner, J. A., Post, S. R., and Chun, J. (1996). Ventricular zone gene‐1 (vzg‐1) encodes a lysophosphatidic acid receptor expressed in neurogenic regions of the developing cerebral cortex. J. Cell Biol. 135, 1071–1083. Hla, T., and Maciag, T. (1990). An abundant transcript induced in differentiating human endothelial cells encodes a polypeptide with structural similarities to G‐protein‐coupled receptors. J. Biol. Chem. 265, 9308–9313. Honig, S. M., Fu, S., Mao, X., Yopp, A., Gunn, M. D., Randolph, G. J., and Bromberg, J. S. (2003). FTY720 stimulates multidrug transporter‐ and cysteinyl leukotriene‐dependent T cell chemotaxis to lymph nodes. J. Clin. Invest. 111, 627–637. Hornuss, C., Hammermann, R., Fuhrmann, M., Juergens, U. R., and Racke, K. (2001). Human and rat alveolar macrophages express multiple EDG receptors. Eur. J. Pharmacol. 429, 303–308. Idzko, M., Panther, E., Corinti, S., Morelli, A., Ferrari, D., Herouy, Y., Dichmann, S., Mockenhaupt, M., Gebicke‐Haerter, P., Di Virgilio, F., Girolomoni, G., and Norgauer, J. (2002). Sphingosine 1‐phosphate induces chemotaxis of immature dendritic cells and modulates cytokine‐release in mature human dendritic cells for emergence of Th2 immune responses. FASEB J. 16, 625–627. Idzko, M., Laut, M., Panther, E., Sorichter, S., Durk, T., Fluhr, J. W., Herouy, Y., Mockenhaupt, M., Myrtek, D., Elsner, P., and Norgauer, J. (2004). Lysophosphatidic acid induces chemotaxis, oxygen radical production, CD11b up‐regulation, Ca2þ mobilization, and actin reorganization in human eosinophils via pertussis toxin‐sensitive G proteins. J. Immunol. 172, 4480–4485. Im, D. S., Heise, D. E., Ancellin, H., O’Dowd, B. F., Shei, G. J., Heavens, R. P., Rigby, M. R., Hla, T., Mandala, S., McAllister, G., George, S. R., and Lynch, K. R. (2000). Characterization of a novel sphingosine‐1‐phosphate receptor, EDG‐8. J. Biol. Chem. 275, 14281–14286. Itagaki, K., and Hauser, C. J. (2003). Sphingosine 1‐phosphate, a diffusible calcium influx factor mediating store‐operated calcium entry. J. Biol. Chem. 278, 27540–27547. Itagaki, K., Kannan, K. B., and Hauser, C. J. (2005). Lysophosphatidic acid triggers calcium entry through a non‐store‐operated pathway in human neutrophils. J. Leukoc. Biol. 77, 181–189. Itakura, A., Tanaka, A., Aioi, A., Tonogaito, H., and Matsuda, H. (2002). Ceramide and sphingosine rapidly induce apoptosis of murine mast cells supported by interleukin‐3 and stem cell factor. Exp. Hematol. 30, 272–278. Jin, Y., Knudsen, E., Wang, L., Bryceson, Y., Damaj, B., Gessani, S., and Maghazachi, A. A. (2003a). Sphingosine 1‐phosphate is a novel inhibitor of T‐cell proliferation. Blood 101, 4909–4915. Jin, Y., Knudsen, E., Wang, L., and Maghazachi, A. A. (2003b). Lysophosphatidic acid induces human natural killer cell chemotaxis and intracellular calcium mobilization. Eur. J. Immunol. 33, 2083–2089. Jolly, P. S., Bektas, M., Olivera, A., Gonzalez‐Espinoza, C., Proia, R. L., Rivera, J., Milstien, S., and Spiegel, S. (2004). Transactivation of sphingosine‐1‐phosphate receptors by FcRI triggering is required for normal mast cell degranulation and chemotaxis. J. Exp. Med. 199, 959–970. Kim, Y.‐M., Sachs, T., Asavaroengchai, W., Bronson, R., and Sykes, M. (2003). Graft‐versus‐host disease can be separated from graft‐versus‐lymphoma effects by control of lymphocyte trafficking with FTY720. J. Clin. Invest. 111, 659–669. Kiuchi, M., Adachi, K., Kohara, T., Minoguchi, M., Hanano, T., Aoki, Y., Mishina, T., Arita, M., Nakao, N., Ohtsuki, M., Hoshino, Y., Teshima, K., Chiba, K., Sasaki, S., and Fujita, T. (2000).
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DEBBY A. LIN AND JOSHUA A. BOYCE
Synthesis and immunosuppressive activity of 2‐substituted 2‐aminopropane‐1,3‐diols and 2‐aminoethanols. J. Med. Chem. 43, 2946–2961. Kveberg, L., Bryceson, Y., Inngjerdigen, M., Rolstad, B., and Maghazachi, A. A. (2002). Sphingosine 1‐phosphate induces the chemotaxis of human natural killer cells: Role for heterotrimeric G proteins and phosphoinositide 3 kinases. Eur. J. Immunol. 32, 1856–1864. Lee, C., Xu, D.‐Z., Feketeova, E., Kannan, K. B., Yun, J. K., Deitch, E. A., Fekete, Z., Livingston, D. H., and Hauser, C. J. (2004). Attenuation of shock‐induced acute lung injury by sphingosine kinase inhibition. J. Trauma 57, 955–960. Lee, H., Liao, J.‐J., Graeler, M., Huang, M.‐C., and Goetzl, E. J. (2002). Lysophospholipid regulation of mononuclear phagocytes. Biochim. Biophys. Acta 1582, 175–177. Lin, D. A., and Boyce, J. A. (2005). 1L‐4 regulates MEK expression required for lysophoasphatidic acid‐mediated chemokine generation by human mast cells. J. Immunol. 175, 5430–5438. Liu, Y., Wada, R., Yamashita, T., Mi, Y., Deng, C. X., Hobson, J. P., Rosenfeldt, H. M., Nava, V. E., Chae, S. S., Lee, M. J., Liu, C. H., Hla, T., Spiegel, S., and Proia, R. L. (2000). Edg‐1, the G protein‐coupled receptor for sphingosine‐1‐phosphate, is essential for vascular maturation. J. Clin. Invest. 106, 951–961. Lo, C. G., Xu, Y., Proia, R. L., and Cyster, J. G. (2005). Cyclical modulation of sphingosine‐ 1‐phosphate receptor 1 surface expression during lymphocyte recirculation and relationship to lymphoid organ transit. J. Exp. Med. 201, 291–301. Maghazachi, A. A. (2003). G protein‐coupled receptors in natural killer cells. J. Leukoc. Biol. 74, 16–24. Mandala, S. M. (2001). Sphingosine‐1‐phosphate phosphatases. Prostaglandins Other Lipid Mediat. 64, 143–156. Mandala, S., Hajdu, R., Bergstrom, J., Quackenbush, E., Xie, J., Milligan, J., Thornton, R., Shei, G. J., Card, D., Keohane, C., Rosenbach, M., Hale, J., Lynch, C. L., Rupprecht, K., Parsons, W., and Rosen, H. (2002). Alteration of lymphocyte trafficking by sphingosine‐1‐phosphate receptor agonists. Science 296, 346–349. Matloubian, M., Lo, C. G., Cinamon, G., Lesneski, M. J., Xu, Y., Brinkmann, V., Allende, M. L., Proia, R. L., and Cyster, J. G. (2004). Lymphocyte egress from thymus and peripheral lymphoid organs is dependent on S1P receptor 1. Nature 427, 355–360. McIntyre, T. M., Pontsler, A. V., Silva, A. R., St. Hilaire, A., Xu, Y., Hinshaw, J. C., Zimmerman, G. A., Hama, K., Aoki, A., Arai, H., and Prestwich, G. D. (2003). Identification of an intracellular receptor for lysophosphatidic acid (LPA): LPA is a transcellular PPAR‐g agonist. Proc. Natl. Acad. Sci. USA 100, 131–136. Melendez, A. J., and Khaw, A. K. (2002). Dichotomy of Ca2þ signals triggered by different phospholipids pathways in antigen stimulation of human mast cells. J. Biol. Chem. 277, 17255–17262. Melendez, A., Floto, R. A., Cameron, A. J., Gillooly, D. J., Harnett, M. M., and Allen, J. M. (1998). A molecular switch changes the signaling pathway used by the Fc gamma RI antibody receptor to mobilize calcium. Curr. Biol. 8, 210–221. Moolenaar, W. H. (1999). Bioactive lysophospholipids and their G protein‐coupled receptors. Exp. Cell Res. 253, 230–238. Muller, H., Hofer, S., Kaneider, N., Neuwirt, H., Mosheimer, B., Mayer, G., Konwalinka, G., Heufler, C., and Tiefenthaler, M. (2005). The immunomodulator FTY720 interferes with effector functions of human monocyte‐derived dendritic cells. Eur. J. Immunol. 35, 533–545. Niedernberg, A., Tunaru, S., Blaukat, A., Ardati, A., and Kostenis, E. (2003). Sphingosine 1‐ phosphate and dioleoylphosphatidic acid are low affinity agonists for the orphan receptor GPR63. Cell Signal. 15, 435–446.
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Noguchi, K., Ishii, S., and Shimizu, T. (2003). Identification of p2y9/GPR23 as a novel G protein‐ coupled receptor for lysophosphatidic acid, structurally distant from the Edg family. J. Biol. Chem. 278, 25600–25606. Okazaki, H., Ishizaka, N., Sakurai, T., Kurokawa, K., Goto, K., Kumada, M., and Takuwa, Y. (1993). Molecular cloning of a novel putative G protein‐coupled receptor expressed in the cardiovascular system. Biochem. Biophys. Res. Commun. 190, 1104–1109. Olivera, A., and Rivera, J. (2005). Sphingolipids and the balancing of immune cell function: Lessons from the mast cell. J. Immunol. 174, 1153–1158. Olivera, A., and Spiegel, S. (2001). Sphingosine kinase: A mediator of vital cellular functions. Prostaglandins Other Lipid Mediat. 64, 123–134. Pages, C., Valet, P., Jeanneton, O., Zakaroff‐Girard, A., Barbe, P., Record, M., Wolf, C., Chevy, F., Lafontan, M., and Saulnier‐Blache, J. S. (1999). Alpha2‐adrenergic receptor‐ mediated release of lysophosphatidic acid by adipocytes: A paracrine signal for preadipocyte growth. Lipids 34, S79. Pages, C., Simon, M.‐F., Valet, P., and Saulnier‐Blache, J. S. (2001). Lysophosphatidic acid synthesis and release. Prostaglandins Other Lipid Mediat. 64, 1–10. Panther, E., Idzko, M., Corinti, S., Ferrari, D., Herouy, Y., Mockenhaupt, M., Dichmann, S., Gebicke‐Haerter, P., Di Virgilio, F., Girolomoni, G., and Norgauer, J. (2002). The influence of lysophosphatidic acid on the functions of human dendritic cells. J. Immunol. 169, 4129–4135. Paugh, S. W., Payne, S. G., Barbour, S. E., Milstien, S., and Spiegel, S. (2003). The immunosuppressant FTY720 is phosphorylated by sphingosine kinase type 2. FEBS Lett. 554, 189–193. Pinschewer, D. D., Ochsenbein, A. F., Odermatt, B., Brinkmann, V., Hengartner, H., and Zinkernagel, R. M. (2000). FTY720 immunosuppression impairs effector T‐cell peripheral homing without affecting induction, expansion, and memory. J. Immunol. 164, 5761–5770. Prieschl, E., Csonga, R., Novotny, V., Kikuchi, G., and Baumruker, T. (1999). The balance between sphingosine and sphingosine‐1‐phosphate is decisive for mast cell activation after Fc receptor I triggering. J. Exp. Med. 190, 1–8. Pyne, S., and Pyne, N. (2000). Sphingosine 1‐phosphate signaling via the endothelial differentiation gene family of G‐protein‐coupled receptors. Pharmacol. Ther. 88, 115–131. Radeff‐Huang, J., Seasholtz, T. M., Matteo, R. G., and Brown, J. H. (2004). G protein mediated signaling pathways in lysophospholipid induced cell proliferation and survival. J. Cell Biochem. 92, 949–966. Renkl, A., Berod, L., Mockenhaupt, M., Idzko, M., Panther, E., Termeer, C., Elsner, P., Huber, M., and Norgauer, J. (2004). Distinct effects of sphingosine‐1‐phosphate, lysophosphatidic acid and histamine in human and mouse dendritic cells. Int. J. Mol. Med. 13, 203–209. Rosen, H., Alfonso, C., Surh, C. D., and McHeyzer‐Williams, M. (2003). Rapid induction of medullary thymocyte phenotypic maturation and egress inhibition by nanomolar sphingosine 1‐phosphate receptor agonist. Proc. Natl. Acad. Sci. USA 100, 10907–10912. Rosskopf, D., Daelman, W., Busch, S., Schurks, M., Hartung, K., Kribben, A., Michel, M. C., and Siffert, W. (1998). Growth factor‐like action of lysophosphatidic acid on human B lymphoblasts. Am. J. Physiol. 274, C1573–C1582. Roviezzo, F., Del Galdo, F., Abbate, G., Bucci, M., D’Agostino, B., Antunes, E., De Dominicis, G., Parente, L., Rossi, F, Cirino, G., and De Palma, R. (2004). Human eosinophil chemotaxis and selective in vivo recruitment by sphingosine‐1‐phosphate. Proc. Natl. Acad. Sci. USA 101, 11170–11175. Sano, T., Baker, D., Virag, T., Wada, A., Yatomi, Y., Kobayashi, T., Igarishi, Y., and Tigyi, G. (2002). Multiple mechanisms linked to platelet activation result in lysophosphatidic acid and sphingosine 1‐phosphate generation in blood. J. Biol. Chem. 277, 21197–21206.
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Sawicka, E., Zuany‐Amorim, C., Manlius, C., Trifilieff, A., Brinkmann, V., Kemeny, D. M., and Walker, C. (2003). Inhibition of Th1‐ and Th2‐mediated airway inflammation by the sphingosine 1‐phosphate receptor agonist FTY720. J. Immunol. 171, 6206–6214. Smyth, S. S., Sciorra, V. A., Sigal, Y. J., Pamuklar, Z., Wang, Z., Xu, Y., Prestwich, G. D., and Morris, A. J. (2003). Lipid phosphate phosphatases regulate lysophosphatidic acid production and signaling in platelets: Studies using chemical inhibitors of lipid phosphate phosphatase activity. J. Biol. Chem. 278, 43214–43223. Spiegel, S., and Milstien, S. (2000). Sphingosine‐1‐phosphate: Signaling inside and out. FEBS Lett. 476, 55–57. Tedesco‐Silva, H., Mourad, G., Kahan, B. D., Boira, J. G., Weimar, W., Mulgaonkar, S., Nashan, B., Madsen, S., Charpentier, B., Pellet, P., and Vanrenterghem, Y. (2004). FTY720, a novel immunomodulator: Efficacy and safety results from the first phase 2A study in de novo renal transplantation. Transplantation 77, 1826–1833. Tigyi, G., and Miledi, R. (1992). Lysophosphatidates bound to serum albumin activate membrane currents in Xenopus oocytes and neurite retraction in PC12 pheochromocytoma cells. J. Biol. Chem. 267, 21360–21367. Tou, J. S., and Gill, J. S. (2005). Lysophosphatidic acid increases phosphatidic acid formation, phospholipase D activity and degranulation by human neutrophils. Cell. Signal. 17, 77–82. van Brocklyn, J. R., Behbahani, B., and Lee, N. H. (2002). Homodimerization and heterodimerization of S1P/EDG sphingosine 1‐phosphate receptors. Biochim. Biophys. Acta 1582, 89–93. van Meeteren, L. A., Frederiks, F., Giepmans, B. N., Pedrosa, M. F., Billington, S. J., Jost, B. H., Tambourgi, D. V., and Moolenaar, W. H. (2004). Spider and bacterial sphingomyelinases D target cellular lysophosphatidic acid receptors by hydrolyzing lysophosphatidylcholine. J. Biol. Chem. 279, 10833–10836. Wang, L., Knudsen, E., Jin, Y., Gessani, S., and Maghazachi, A. A. (2004). Lysophospholipids and chemokines activate distinct signal transduction pathways in T helper 1 and T helper 2 cells. Cell. Signal. 16, 991–1000. Wang, W., Graeler, M. H., and Goetzl, E. J. (2004). Physiological sphingosine 1‐phosphate requirement for optimal activity of mouse CD4þ regulatory T cells. FASEB J. 18, 1043–1045. Webb, M., Tham, C. S., Lin, F. F., Lariosa‐Willingham, K., Yu, N., Hale, J., Mandala, S., Chun, J., and Rao, T. S. (2004). Sphingosine 1‐phosphate receptor agonists attenuate relapsing‐remitting experimental autoimmune encephalitis in SJL mice. J. Neuroimmunol. 153, 108–121. Windh, R. T., Lee, M. J., Hla, T., An, S., Barr, A. J., and Manning, D. R. (1999). Differential coupling of the sphingosine 1‐phosphate receptors Edg‐1, Edg‐3, and H218/Edg‐5 to the G(i), G(q), and G(12) families of heterotrimeric G proteins. J. Biol. Chem. 274, 27351–27358. Xie, J. H., Nomura, N., Koprak, S. L., Quackenbush, E. J., Forrest, M. J., and Rosen, H. (2003). Sphingosine‐1‐phosphate receptor agonism impairs the efficiency of the local immune response by altering trafficking of naı¨ve and antigen‐activated CD4þ T cells. J. Immunol. 170, 3662–3670. Xu, Y., Casey, G., and Mills, G. B. (1995a). Effect of lysophospholipids on signaling in the human Jurkat T cell line. J. Cell. Physiol. 163, 441–450. Xu, Y., Gaudette, D. C., Boynton, J. D., Frankel, A., Fang, X. J., Sharma, A., Hurteau, J., Casey, G., Goodbody, A., and Mellors, A. (1995b). Characterization of an ovarian cancer activating factor in ascites from ovarian cancer patients. Clin. Cancer Res. 1, 1223–1232. Yatomi, Y., Igarashi, Y., Yang, L., Hisano, N., Qi, R., Asazuma, N., Satoh, K., Ozaki, Y., and Kume, S. (1997). Sphingosine‐1‐phosphate, a bioactive sphingolipid abundantly stored in platelets, is a normal constituent of human plasma and serum. J. Biochem. (Tokyo) 121, 969–973. Yamaguchi, F., Tokuda, M., Hatase, O., and Brenner, S. (1996). Molecular cloning of the novel human G protein‐coupled receptor (GPCR) gene mapped on chromosome 9. Biochem. Biophys. Res. Commun. 227, 608–614.
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Yopp, A. C., Fu, S., Honig, S. M., Randolph, G. J., Ding, Y., Krieger, N. R., and Bromberg, J. S. (2004). FTY720‐enhanced T cell homing is dependent on CCR2, CCR5, CCR7, and CXCR4: Evidence for distinct chemokine compartments. J. Immunol. 173, 855–865. Young, K. W., Bootman, M. D., Channing, D. R., Lipp, P., Maycox, P. R., Meakin, J., Challiss, R. A., and Nahorski, S. R. (2000). Lysophosphatidic acid‐induced Ca2þ mobilization requires intracellular sphingosine 1‐phosphate production. Potential involvement of endogenous EDG‐4 receptors. J. Biol. Chem. 275, 38532–38539. Zhang, C., Baker, D. L., Yasuda, S., Makarova, N., Balazs, L., Johnson, L. R., Marathe, G. K., McIntyre, T. M., Xu, Y., Prestwich, G. D., Byun, H. S., Bittman, R., and Tigyi, G. (2004). Lysophosphatidic acid induces neointima formation through PPARgamma activation. J. Exp. Med. 199, 763–774. Zheng, Y., Voice, J. K., Kong, Y., and Goetzl, E. J. (2000). Altered expression and functional profile of lysophosphatidic acid receptors in mitogen‐activated human blood T lymphocytes. FASEB J. 14, 2387–2389. Zheng, Y., Kong, Y., and Goetzl, E. J. (2001). Lysophosphatidic acid receptor‐selective effects on Jurkat T cell migration through a Matrigel model basement membrane. J. Immunol. 166, 2317–2322. Zhou, J., and Saba, J. D. (1998). Identification of the first mammalian sphingosine phosphate lyase gene and its functional expression in yeast. Biochem. Biophys. Res. Commun. 242, 502–507.
Systemic Mastocytosis Jamie Robyn and Dean D. Metcalfe Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland
1. 2. 3. 4. 5. 6. 7. 8. 9.
Abstract............................................................................................................. Introduction ....................................................................................................... Mast Cell Biology................................................................................................ Biology of Kit ..................................................................................................... Mastocytosis ....................................................................................................... Prognosis and Predictive Factors ............................................................................ Treatment .......................................................................................................... Supportive Care and Long‐Term Management.......................................................... Future Therapy................................................................................................... Conclusions........................................................................................................ References .........................................................................................................
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Abstract Systemic mastocytosis is a fascinating disease with diverse clinical features. There have been numerous advances in understanding the basis of clinical manifestations of this disease and of its molecular pathogenesis in the last several decades. The development of methods to study mast cell biology using cell culture and murine models has proven invaluable in this regard. Clarification of the roles of mast cells in various biological processes has expanded our understanding of their importance in innate immunity, as well as allergy. New diagnostic methods have allowed the design of detailed criteria to assist in distinguishing reactive mast cell hyperplasia from systemic mastocytosis. Variants and subvariants of systemic mastocytosis have been defined to assist in determining prognosis and in management of the disease. Elucidation of the roles of the Kit receptor tyrosine kinase and signal transduction pathway activation has contributed to development of potential targeted therapeutic approaches that may prove useful in the future. 1. Introduction 1.1. Historical In 1869 Nettleship and Tay described a two‐year‐old patient with brown lesions that wheeled after scratching, and this proved to be the first published description of urticaria pigmentosa (UP) (Nettleship, 1869). Mast cells were first described by a young medical student, Paul Ehrlich, in his doctoral thesis in 1878, and
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were thought to be over‐nourished connective tissue cells, due to their dense cytoplasmic granules (Ehrlich, 1878). Ehrlich named them ‘‘matzellen’’ from the German word meaning to chew or masticate. The term mastocytosis was first used in 1936 by Sezary (Sezary and Chauvillon, 1936). Not until 1887 were mast cells noted to be present in UP skin lesions (Unna, 1887). In 1949 Ellis described an autopsy of a one‐year‐old infant who died as a result of diffuse organ infiltration by mast cells, the first reported case of systemic mastocytosis (SM) (Ellis, 1949). A number of classification schemes have been devised and modified since 1988 in attempts to facilitate diagnostic, prognostic, and treatment decisions (Travis et al., 1988a). The criteria currently used for the diagnosis of SM were established in 2000 by a World Health Organization classification derived from the Year 2000 Mast Cell Disease Symposium Consensus Conference, a meeting that brought together nearly 50 clinicians, pathologists, and investigators whose primary interest was SM (Valent et al., 2001a). 1.2. Epidemiology Mastocytosis is a rare disease, with a reported male‐to‐female ratio of 1 to 1:3. There are an estimated 20,000–30,000 affected individuals in the United States. Although patients from all ethnic backgrounds have been found to have the disease, mastocytosis is more frequently reported in Caucasians. Mastocytosis may occur at any age including infancy and may be present at birth. Cutaneous mastocytosis (CM) involves only the skin while systemic mastocytosis (SM) is characterized by involvement of at least one extra‐cutaneous organ. 1.3. Genetic Factors Although there are more than 50 cases of familial cutaneous mastocytosis reported, the majority of patients report no family history of mastocytosis (Chang et al., 2001). While systemic mastocytosis in adults is most often associated with acquired somatic mutations in codon 816 of the c‐Kit gene, most easily detected in cutaneous lesions or bone marrow aspirates, familial cutaneous mastocytosis does not appear to be associated with codon 816 c‐Kit mutations. A case series of four patients with familial telangiectasia macularis eruptive persitans (TMEP) affecting three generations has been reported (Chang et al., 2001). Another case report describes two siblings with inherited neurosensory deafness and cutaneous mastocytosis (Trevisan et al., 2000). 2. Mast Cell Biology Mast cells, playing a key role in the elicitation of early and late‐phase IgE‐ mediated inflammatory reactions, are ancient immune effector cells. Mast cells are highly granulated, widely distributed, and are often found in connective and
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mucosal tissues where they are frequently located near blood vessels. Mast cells have been implicated in a large number of cellular processes including host defense in both acquired and innate immunity, allergic reactions, wound healing, fibrosis, angiogenesis, and autoimmune diseases. In contrast to other leukocytes, mast cells are long‐lived with an estimated life span of months (Valent, 1996). The study of human mast cells has been hampered by difficulties with purification of the cells from tissues. However, human mast cells can now be cultured from CD34þ cells derived from either peripheral blood or bone marrow, permitting in vitro studies of mast cell growth and differentiation (Kirshenbaum et al., 1992). Cells are cultured in serum‐free medium containing SCF, and the characteristics of cultured cells may be altered by the addition of cytokines such as IL‐4, IL‐6, and IL‐9. A pure population of mature human mast cells is obtained after approximately eight weeks of culture (Kirshenbaum et al., 1992). Several cell lines are available and have been useful for defining mast cell molecular biology. The HMC‐1 cell line established in 1988 from a patient with mast cell leukemia had been used for almost 13 years, despite two deficiencies which limit its usefulness (Butterfield et al., 1988). First, the HMC‐1 cell line is growth factor independent, unlike normal mast cells and, secondly, HMC‐1 cells exhibit inconsistent degranulation to IgE‐dependent signals. Two novel stem cell‐dependent cell lines, LAD 1 and LAD 2, were established from bone marrow aspirates from a patient with mast cell sarcoma/ leukemia in 2003 (Kirshenbaum et al., 2003). Both cell lines have ultrastructural features of human mast cells, do not exhibit activating mutations at codon 816 of c‐Kit, and both require SCF for growth. Mouse models have also played an invaluable role in the study of mast cell biology. The bone marrow origin of mast cells was shown by using the giant granules of beige mice as a marker (Kitamura et al., 2001). The study of W/Wv and Sl/Sld mice which lack mast cells led to the identification of the W locus as encoding c‐Kit receptor tyrosine kinase and the Sl locus as encoding stem cell factor (SCF), the ligand for c‐Kit receptor (Galli and Kitamura, 1987; Nakano et al., 1987). Indeed, SCF, a general hematopoietic growth factor, was found to be essential for mast cell proliferation and survival in these model systems. Mice homozygous for the ‘‘sash’’ mutation (W‐sh) have marked reduction of mast cell expression of Kit, but, unlike the KitW/KitW mice, are fertile (Lyon and Glenister, 1982). These mice have proved very useful for studies of mast cell function in vivo. 2.1. Origin of Mast Cells Mast cell progenitors are agranular, rare circulating cells expressing CD34þ, CD117þ, and CD13þ (Kirshenbaum et al., 1991; Rottem et al., 1994b). The first demonstration that mast cells were derived from bone marrow progenitors
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used mast cell‐deficient mice as a model (Kitamura et al., 1981). Normal murine marrow was introduced via transplantation into lethally irradiated mast cell‐deficient mice, and mast cells developed, confirming that mast cells are derived from pluripotential hematopoietic cells (Kitamura et al., 1981). The fact that mast cell progenitors in humans circulate as CD34þ mononuclear cells was shown by colony formation in response to SCF stimulation ex vivo (Rottem et al., 1994b). These progenitors may be distinguished from monocytes by lack of CD14 (lipopolysaccharide receptor). A more recent demonstration of the origin of human mast cells from hematopoietic stem cells has been shown by demonstration of donor genotype using a variable number of tandem repeat analysis after myeloablative bone marrow transplantation (Fodinger et al., 1994). Terminal differentiation of mast cells occurs in vascularized tissues under the influence of stem cell factor (SCF), in addition to other cytokines including IL‐6, IL‐9, and nerve growth factor (NGF) (Kirshenbaum et al., 1999; Metcalfe et al., 1997). Mast cell precursors leave the bone marrow to migrate via the blood into mucosal or connective tissues. Mast cells then undergo differentiation and maturation in extramedullary organs where they form secretory granules that stain metachromatically with basic dyes, and begin to express surface FcRI. Once in tissues, mast cells typically do not undergo further proliferation. The close relationship between mast cells and monocytes is supported by the demonstration that both cell types may be derived from progenitor cell populations that express CD34, CD117, and aminopeptidase N (CD13) (Kirshenbaum et al., 1999). In addition, lesional mast cells derived from patients with UP exhibit monocyte/macrophage markers by immunohistochemistry (Mirowski et al., 1990). Mast cells and basophils have long been debated to be derived from a common progenitor given their morphologic and functional similarities (Arock et al., 2002). Analysis of the lineage relationship between mast cells and basophils using the c‐Kit D816V mutation as a lineage marker revealed that mast cells and basophils do not share committed progenitors, arguing against the presence of a bilineage‐restricted progenitor for these two cell types (Kocabas et al., 2005). 2.2. Mast Cell Distribution and Heterogeneity Under normal conditions, mast cells are widely distributed in the body, being found throughout vascularized tissue. They are especially abundant on epithelial surfaces in the skin, respiratory tract, gastrointestinal tract, and genitourinary tract. However, there is some variation in mast cell numbers depending
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on the tissue. For example, mast cells are usually present in lymph node sinuses, but are virtually absent from the normal spleen. There are normally few mast cells in the liver sinusoids and the presence of intrasinusoidal liver mast cells is suggestive of SM (Horny and Valent, 2001). Mast cells have been found to be heterogeneous in phenotype and function. They exhibit histological heterogeneity based on cytoplasmic granule content, cell size, and susceptibility to pharmacologic agents. Thus, immune system associated and non‐immune system‐associated mast cell populations can be identified (Puxeddu et al., 2003). In humans, secretory granules of all mast cells contain tryptase, histamine, heparin, and chondroitin sulfate E. Human mast cells in the submucosal connective tissue (non‐immune system associated) stain intensely with dyes and express a tetrameric tryptase, a mast cell‐specific chymase, and carboxypeptidase A. They are sometimes referred to as ‘‘TC mast cells,’’ or MCTC. Increased numbers of MCTC are reported in fibrotic diseases, while their numbers are not increased in allergic or parasitic diseases or HIV infection (Galli et al., 1995). Mast cells in the mucosa (immune system associated) stain less intensely with dyes and express tryptase but not carboxypeptidase and are sometimes referred to as ‘‘T mast cells’’ or MCT. MCT are increased in allergic and parasitic diseases and decreased in the gastrointestinal mucosa in HIV‐infected individuals (Church and Levi‐ Schaffer, 1997). In fact, variable amounts of both of these mast cell subtypes are present within any given tissue, and specific environmental influences regulating the differentiation into one subtype or the other are poorly understood. A third mast cell phenotype, the ‘‘MCc cell’’ that contains only chymase, has also been described (Li et al., 1996). 2.3. Development and Proliferation of Mast Cells Numerous studies have shown that mast cell differentiation, proliferation, survival, and activation are critically dependent on stem cell factor (SCF). Studies of mouse strains W/Wv and Sl/Sld with mutations in c‐Kit and SCF, respectively, and which are deficient in mast cells, provided evidence that SCF is essential for murine mast cell development (Galli and Kitamura, 1987; Kitamura et al., 2001; Zsebo et al., 1990). The development of mast cells from CD34þ progenitors has been shown to be absolutely dependent on stem cell factor (Kirshenbaum et al., 1991; Valent et al., 1992). Both in vitro‐derived and ex vivo‐isolated mast cells have been shown to undergo rapid apoptosis if SCF is removed from the culture medium (Mekori et al., 2001). Recent studies demonstrate that SCF promotes mast cell survival via inactivation of the FOXO3a transcription factor and downregulation and phosphorylation of its target, Bim, a pro‐apoptotic protein (Moller et al., 2005).
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Other cytokines that may be involved in mast cell development include IL‐3, IL‐4, and IL‐9. Specific cytokines, however, have been shown to vary in their effects on human and murine mast cells. Interleukin 3 (IL‐3) was initially identified as a soluble, lymphocyte‐derived growth factor capable of promoting and sustaining murine mast cell growth (Ihle et al., 1983). Interleukin 3 and stem cell factor are the principal cytokines that promote murine mast cell proliferation, and mouse bone marrow‐derived mast cells were obtained using IL‐3 for nearly two decades following discovery of this cytokine effect in a number of laboratories (Ihle et al., 1983). IL‐3, however, has minimal direct effects on human mast cell proliferation and, in fact, IL‐3 dominantly elicits the development of basophils along with esoinophils from human progenitors (Kirshenbaum, 2000). Interestingly, SCF and IL‐3 act through a number of common signal transduction pathways including PI3‐K, the RAS‐MAP kinases, Janus kinase, and JAK/STAT pathways (Lennartsson et al., 2005). Using a similar approach, IL‐4 was identified as a growth factor that is synergistic with IL‐3 in promoting murine mast cell growth (Smith and Rennick, 1986). In human studies, however, IL‐4 inhibited SCF‐dependent differentiation of fetal liver‐derived mast cell progenitors when added during the first week of culture (Nilsson et al., 1994b; Oskeritzian et al., 1999), but not after two weeks (Oskeritzian et al., 1999). Seven‐week‐old cord blood‐ derived mast cells were significantly reduced one day after addition of IL‐4 (Oskeritzian et al., 1999a). In contrast, IL‐4 was shown to enhance proliferation of mature human intestine‐derived mast cells in synergy with SCF (Bischoff et al., 1999). It is unclear why more mature cord blood‐derived human mast cells in contrast with fetal liver and intestinal counterparts are so sensitive to the effects of IL‐4 (Kirshenbaum, 2000). IL‐4 has also been shown to promote apoptosis of mast cells under some conditions (Oskeritzian et al., 1999). A polymorphism in the gene for the IL‐4 receptor a chain resulting in increased activity has been shown to be associated with a less aggressive mastocytosis phenotype (Daley et al., 2001). A recent analysis using high‐resolution tracking of cell division revealed that exposure of human mast cells to IL‐4, IL‐5, and interferon‐g during growth and differentiation generally downregulated mast cell number, while IL‐4 increased mature mast cell division and degranulation (Kulka and Metcalfe, 2005). A number of other cytokines have been found to promote or augment murine mast cell proliferation or differentiation including IL‐9 and nerve growth factor (Matsuda et al., 1991; Rottem et al., 1994a). The effect of thrombopoietin (TPO) on human mast cell growth and development was explored by culturing human hematopoietic progenitors in the presence of TPO alone or in combination with SCF. TPO alone or in combination with SCF was shown to support growth of a unique population
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of CD117low/CD110þ mast cells (Kirshenbaum et al., 2005). Granulocyte‐ macrophage colony stimulating factor (GM‐CSF), on the other hand, inhibits development of mast cells from both murine and human marrow (Metcalfe et al., 1997). The importance of transcription factor activity in mast cell development and maturation was revealed by analysis of mi/mi mice (Hodgkinson et al., 1993). Mice of mi/mi genotype exhibit decreased tissue mast cells. These mice manifest a number of additional phenotypes including microphthalmia, depletion of pigment in hair and eyes, and osteoporosis. The Mi gene encodes mi transcription factor (MITF), a member of the basic helix‐loop‐helix‐leucine zipper family of transcription factors. The mi mutant MITF is defective in DNA‐binding activity (Morii et al., 1994). 2.4. Mast Cell Activation Following IgE‐mediated FcRI aggregation, mast cells release preformed mediators such as histamine; generate lipid‐derived substances such as leukotrienes; and synthesize and release growth factors and cytokines (Table 1) (Metcalfe et al., 1997). Antigen‐dependent ligation of FcRI‐bound IgE on the surface of mast cells is the principal mechanism of activation of the cell and release of preformed proinflammatory mediators as well as the generation of new mediators. Surface expression of FcRI is correlated with the serum level of IgE. Mast cells can also be activated by a variety of non‐IgE‐driven signals including physical trauma, heat, toxins, small peptides including substance P, calcitonin gene‐related peptide, and chemokines such as macrophage inflammatory protein‐1a and monocyte chemo‐attractant protein 1 (Mekori and Metcalfe, 2000). The suggestion that mast cells could be activated by non‐IgE‐dependent mechanisms was initially proposed due to a murine model where IgE‐deficient mice presented manifestations of anaphylaxis (Oettgen et al., 1994). Further data from rodent and human mast cells has revealed that IgG receptors (FcgR) can either induce or inhibit mast cell activation, responses which appear to depend on which receptors are engaged and the subsequent signaling pathways activated. Murine mast cells are known to express low affinity receptors for IgG including Fcg RIIb1, FcgRIIb2, and FcgRIII (Benhamou et al., 1990; Katz et al., 1990). Aggregation of FcgRI on human mast cells following exposure to interferon‐g promotes mediator release (Okayama et al., 2000). Three important classes of mediators (biogenic amines, lipid mediators, and cytokines) were upregulated and/or released by mast cells upon aggregation of FcgRI. In addition, there appeared to be qualitative differences for some cytokines released as a result of FcgRI aggregation compared to FcRI,
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Table 1 Mast Cell Mediators Mediators
Biological effects
Possible sequelae
Preformed Histamine
Heparin Tryptase
Chymase
Vasodilation, increased vascular permeability, gastric hypersecretion, bronchoconstriction Anti‐coagulant, inhibition of platelet aggregation Endothelial cell activation, fibrinogen cleavage, mitogenic for smooth muscle cells Conversion of angiotensin I to II, lipoprotein degradation
Hypotension, flushing urticaria, abdominal pain, diarrhea Excessive bleeding, elevated PTT Osteoporosis/osteopenia
Transient hypertension
Newly Synthesized Increased vascular permeability, bronchoconstriction Vasodilation, bronchoconstriction
Flushing, urticaria
Growth and survival of mast cells
Mast cell hyperplasia Fatigue, weight loss
TGF‐b IL‐5 IL‐6
Activation of vascular endothelial cells, cachexia, fatigue Fibrosis Eosinophil growth factor Growth and survival of mast cells
IL‐16
Lymphocyte accumulation
Leukotrienes Prostaglandins
Bronchospasm, hypotension
Cytokines SCF TNF‐a
Fibrosis Eosinophilia Fever, bone pain, osteoporosis/osteopenia Focal lymphoid aggregates
suggesting that selected responses of mast cells may be preferentially generated through FcgRI, especially in an IFN‐g‐rich environment (Okayama et al., 2001; Tkaczyk et al., 2002). FcgRIIb, on the other hand, when colligated with FcRI or Kit, inhibits murine mast cell degranulation (Daeron et al., 1995). Human and rodent mast cells do not constitutively express FcgRI, but expression has been shown to be induced following IFN‐g treatment of human mast cells (Okayama et al., 2000). Responses appear to be species‐ and/or mast cell phenotype‐dependent. In CD34þ‐derived human mast cells, interferon‐g exposure results in FcgRI upregulation, while FcgRII is expressed but not upregulated and FcgRIII is not expressed. In contrast, in murine mast cells, both FCgRII and FCgRIII receptors are expressed but FcgRI is not (Tkaczyk et al., 2004). Aggregation of FcgRI on human mast cells promotes mediator release in a manner which is similar to that observed following FcRI aggregation, while aggregation of FcgRIIb in murine mast cells fails to influence
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mediator release unless co‐ligated with FcRI. In this case, signaling events downregulate antigen‐dependent mediator release. These divergent responses have been shown to be a result of different motifs contained within the cytosolic tails of the signaling subunits of these receptors (Tkaczyk et al., 2004a). Nitric oxide, a cell‐derived radical generated largely by cells of the innate immune system, is known to suppress mast cell activation (Coleman, 2002). Recent studies show that Fos and Jun are key nitric oxide‐regulated components of antigen‐induced mast cell cytokine production (Davis et al., 2004). 2.5. Functions of Mast Cells In addition to classic IgE‐mediated immediate hypersensitivity allergic responses, mast cells have been implicated in a variety of biological processes including innate immunity, angiogenesis, and coagulation. In vitro and murine studies have been used to help define functional roles for mast cells. Current evidence supports a role for mast cells in host defense against microorganisms and a regulatory function in both the TH1‐ and TH2‐type inflammatory response. Mast cells may also stimulate connective tissue repair and maintain the vasculature. Convincing proof for involvement of MCs in specific immunologic responses in vivo has been challenging since many mast cell mediators are also produced by other cell types. In addition, many mediators released by mast cells have diverse and sometimes opposing biological effects, causing further difficulty with clarifying the roles of these substances (Mekori and Metcalfe, 2000). 2.5.1. Allergy Mast cells are known to be central effector cells in the elicitation of both early and late‐phase IgE‐mediated allergic inflammatory reactions (Metcalfe et al., 1997). The diverse range of biological effects of mast cell mediators which are released upon mast cell activation account for the central role of these cells in acute allergic reactions and chronic allergic inflammation (Mekori and Metcalfe, 1999). High affinity receptor for IgE (FcRI) on mast cells binds allergen‐specific IgE in an essentially irreversible fashion (Isersky et al., 1979). Mast cell activation and degranulation occur when the cell‐bound IgE interacts with a specific allergen leading to immediate hypersensitivity reactions. Mast cells also produce a variety of lymphokines and lipid mediators, contributing to the late or chronic phase reaction. Enhancing effects occur in many allergic patients who have elevated serum IgE antibody levels. Binding of monomeric IgE to high‐affinity receptor, in the
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absence of allergen‐induced receptor aggregation, upregulates expression of FcRI on the cell surface (MacGlashan et al., 1999). In addition, monomeric IgE binding suppresses mast cell apoptosis (Asai et al., 2001). The role of mast cells in recruitment of neutrophil and mononuclear cells in IgE‐induced late allergic responses has been verified by the use of mast cell‐ deficient mice (Wershil et al., 1991, 1996). Delayed cellular infiltration in response to IgE in these mice is likely the result of loss of effects of mast cell products such as TNF‐a on endothelial cells (Wershil et al., 1996). Leukocyte recruitment to sites of inflammation is influenced by release of chemoattractants IL‐8 and IL‐16 by mast cells (Compton et al., 1998; Moller et al., 1993; Rumsaeng et al., 1997). Activated mast cells or medium derived from them has been shown to induce T cell adhesion associated with upregulation of VCAM‐1 and ICAM‐1. This effect is neutralized by anti‐TNF‐a antibody (Meng et al., 1995). Studies in mast cell‐deficient mice have demonstrated that mast cells in specific models of inflammation can amplify acute inflammatory responses. Mast cell reconstitution was shown to normalize TNF‐a levels and neutrophil mobilization in mast cell‐deficient mice, and this response was shown to be dependent on IgG Fc receptors (Zhang et al., 1992). 2.5.2. Innate Immunity Mast cells have been clearly implicated in innate immune responses to bacterial pathogens. Direct evidence became available in studies of mouse models of Klebsiella pneumonia‐induced peritonitis and cecal ligation and puncture (CLP) where mice with normal mast cell numbers survived while mast cell‐ deficient mice succumbed to bacterial challenge (Echtenacher et al., 1996; Malaviya et al., 1996). Furthermore, when mast cells were selectively reconstituted into the peritoneal cavity, the ability to overcome infection was restored. In addition, treatment with stem cell factor improved the survival of mast cell‐deficient mice in the CLP model (Maurer et al., 1998). Another study using C3‐deficient mice has shown that mast cell degranulation and bacterial clearance in acute peritonitis is complement‐dependent (Prodeus et al., 1997). The roles of mast cells in innate immunity are partly mediated through direct recruitment of effector cells by release of mediators such as histamine, proteases, leukotrienes, and various chemokines and cytokines including TNF and IL‐6 (Marshall and Jawdat, 2004; Mekori and Metcalfe, 2000). Much progress has been made towards defining mechanisms by which innate immunity is mobilized. Toll‐like receptors (TLRs) are known to play a critical role in host defense. Both human and rodent mast cells have been shown to express TLR‐1,TLR‐2, TLR‐4, and TLR‐6 mRNAs and respond to lipopolysaccharide and peptidoglycan by producing GM‐CSF, TNF‐a, IL‐1b, IL5, IL13,
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and leukotriene C4 (McCurdy et al., 2003; Varadaradjalou et al., 2003). Studies in TLR‐deficient mice have shown that murine mast cells respond to LPS through TLR‐4 and to peptidoglycan through TLR‐2 (McCurdy et al., 2001; Supajatura et al., 2001, 2002). Human mast cells have also been shown to express TLR‐3 (Kulka et al., 2004). Furthermore, both murine and human mast cells were shown to produce type I interferons following exposure to double‐stranded RNA and/or virus, the former through interaction with TLR‐ 3 (Kulka et al., 2004). These results suggest that mast cells can contribute to innate immune responses to viral infection via this mechanism (Kulka et al., 2004). Other possible mechanisms involved in mast cell activation in innate immunity are via complement fixation, FMLP receptors, mannose‐binding protein, and other lectin‐like receptor molecules (Marshall and Jawdat, 2004). 2.5.3. Angiogenesis Mast cells have been linked to neovascularization during hemangioma formation, wound healing, and ovulation (Levi‐Schaffer and Piliponsky, 2003). Factors known to be important in angiogenesis include vascular endothelial growth factor (VEGF), basic fibroblast growth factor (FGF), and platelet‐derived growth factor (PDGF) (Risau, 1997). In most pathological processes, angiogenesis is accompanied by inflammation. Most inflammatory cells have been shown to produce VEGF including human neutrophils, lymphocytes, macrophages, and eosinophils (Gaudry et al., 1997; Horiuchi and Weller, 1997; Iijima et al., 1996; Perez‐Ruiz et al., 1999). Mast cells, as well, have been implicated in regulation of angiogenesis in a variety of pathologic conditions and have been shown to secrete angiogenic factors including VEGF and FGF (Azizkhan et al., 1980; Boesiger et al., 1998; Folkman, 1985; Grutzkau et al., 1998; Qu et al., 1998a,b). The human mast cell leukemia cell line can constitutively express and secrete three isoforms of VEGF (Grutzkau et al., 1998). A direct role of mast cells in inducing angiogenesis was shown in a chick embryo in vivo model. Convincing evidence that mast cell mediators were responsible for this effect was shown by addition of anti‐FGF and anti‐VEGF which reduced the angiogenic response (Ribatti et al., 2001). In addition, mast cell mediators such as heparin, histamine, tryptase, TGF‐b,TNF‐a, and IL‐8 have been shown to have pro‐angiogenic properties (Church and Levi‐Schaffer, 1997; Norrby, 1997). 2.5.4. Coagulation Mast cells are known to be an important source of heparin, which prevents coagulation by acting as a co‐factor of anti‐thrombin III. Mast cells may express and release significant amounts of fibrinolytic TPA, and TPA has been shown by immunohistochemistry to be present in
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mast cell granules (Sillaber et al., 1999). These anticoagulant effects may be clinically relevant in certain instances of cutaneous and systemic mastocytosis associated with hemorrhagic blisters and gastrointestinal bleeding (Smith et al., 1987b). Number studies support the idea that mast cell recruitment and activation may play roles in local thrombolysis and prevention of coagulation. Mast cells produce an array of vasoactive substances which can interact directly with vascular endothelial cells, influencing permeability of the vessel walls. Mast cell‐deficient mice are more susceptible to lethal thrombogenic stimuli than normal mice (Kitamura et al., 1986). B‐tryptase is capable of degrading fibrinogen (Schwartz et al., 1985); however, recent studies show that the anticoagulant activity of tryptase/heparin complex is attributable exclusively to the associated heparin (Samoszuk et al., 2003). Tryptase, however, is also capable of activating pro‐urokinase (Stack and Johnson, 1994). Chymase secreted by mast cells inactivates thrombin (Pejler and Karlstrom, 1993). 2.6. Mast Cell Mediators The two principal types of inflammatory mediators associated with mast cells are preformed mediators including histamine, neutral proteases (tryptase), and proteoglycans (heparin, chondroitin sulfates), and newly formed mediators including arachidonic acid metabolites (leukotrienes, prostaglandins); TNF; and interleukins 4, 5, and 6. Also synthesized and released by mast cells are specific cytokines and chemokines. (Table 1) (Escribano et al., 2002). Several mediators including histamine are released from MCs in response to aggregation of high‐affinity IgE receptors, activation through complement receptors, or activation by cytokines (Valent et al., 2003a). Other mediators such as tryptase are both constitutively released and secreted after activation. Mediators such as histamine and tryptase are capable of regulating T cell function, as manifested by differential effects on cytokine production (Jutel et al., 2001). 2.6.1. Secretory Granule Mediators 2.6.1.1. Tryptase Mast cell tryptase is a neutral serine protease with a molecular weight of 134 kDa and is the most abundant protein produced by human mast cells. There are two main types of mast cell tryptase, alpha and beta, which have approximately 90% sequence identity. The genes encoding alpha and beta tryptase are found on chromosome 16p13.3 (Payne and Kam, 2004). Approximately 25% of individuals lack a gene for a‐tryptase (Schwartz et al., 2003; Soto et al., 2002). B‐tryptases are classified into subtypes bI‐, bII‐, and
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bIII‐tryptases while a‐tryptases are classified as aI‐ and aII‐tryptases (Payne and Kam, 2004). Mature B‐tryptase is stored in secretory granules as an enzymatically active tetramer in a complex with heparin proteoglycan until mast cells are activated to degranulate and release the complex (Schwartz et al., 2003). There is a structural requirement for heparin to bridge tryptase monomers to form enzymatically active tryptase tetramers (Hallgren et al., 2001). The mechanisms regulating tryptase activity are incompletely understood since the enzyme is resistant to classic biological inhibitors of serine proteases (Alter et al., 1990). Reduced proteolytic activity may occur when the enzyme diffuses away from sites where pH is acidic (Schwartz and Irani, 2000). The biological function of tryptase is not clearly defined but it appears to play roles in inflammation, enhancement of vasopermeability, and airway smooth muscle hyperreactivity. Tryptase has the ability to cleave a variety of extracellular substrates including fibronectin, vasoactive intestinal peptide, and kininogens and is a potent growth factor for epithelial cells and fibroblasts. Mast cell tryptase can activate protease activated receptors (PAR), which are G‐protein‐coupled receptors, which, in turn, trigger intracellular signaling. PARs are expressed by a variety of cell types including airway epithelial and smooth muscle cells, vascular smooth muscle cells, type II pneumocytes, enterocytes, and sensory neurons (Payne and Kam, 2004). Tryptase induces IL‐6 and IL‐8 release in eosinophils by the MAPK/activator protein pathway (Temkin et al., 2002). Tryptase levels in blood have been used as indicators of mast cell numbers and mast cell activation. A number of immunoassays are available for tryptase. An early tryptase immunoassay used the G5 mAb for capture which detects BII tryptase with 10‐fold higher sensitivity than alpha‐1‐protryptase, and a goat polyclonal anti‐tryptase antibody for detection (Schwartz, 2001). This assay proved useful for detecting elevated serum tryptase after anaphylaxis. However, a very sensitive immunofluorescent assay is available that detects both alpha and beta tryptase, is thought to reflect total mast cell burden, and is elevated in patients with systemic mastocytosis (Schwartz, 2001). A study of tryptase levels in patients with biopsy‐proven SM demonstrated levels of total tryptase >20 ng/ml, while normal subjects had levels <14 ng/ml (Payne and Kam, 2004). 2.6.1.2. Heparin Mast cell heparin stabilizes and regulates secretory granule proteases, as described above. In addition, it binds to antithrombin III, inhibiting activation of the clotting cascade. Heparin binding also regulates and stabilizes cytokines and growth factors. Binding of heparin to fibroblast growth factor‐2 may affect angiogenesis and wound healing (Escribano et al., 2002;
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Nugent and Iozzo, 2000). Biological effects mediated by heparin include bleeding diathesis, osteopenia, and osteoporosis. 2.6.1.3. Histamine Histamine is a major mediator which is synthesized and stored within secretory granules of FcRIþ cells (Escribano et al., 2002). The myriad biological effects of histamine are mediated through activation of three receptors, H1, H2, and H3. H1 receptors are present on vascular and perivascular as well as epithelial cells. H2 receptors are found on epithelial cells in the gastrointestinal tract and H3 receptors are located in the brain and gastrointestinal tract. Histamine is one of the primary mediators contributing to vascular permeability and vascular instability, bronchospasm, edema, pruritis, and flushing as well as neurological effects including headache. Histamine also contributes to gastric hypersecretion causing abdominal pain, gastric hypersecretion, and subsequent peptic ulceration (Cherner et al., 1988). 2.6.1.4. Chymase Chymase is a 30 kDa chymotrypsin‐like serine endopeptidase which converts angiotensin I to angiotensin II (Caughey et al., 2000). Chymase is encoded on chromosome 14 and was originally purified from human skin (Caughey et al., 2000). The vasoconstrictive properties of angiotensin II produced by chymase activity may contribute to transient hypertension during mast cell activation reactions. 2.6.1.5. Carboxypeptidase A Human mast cell carboxypeptidase A is a 32 kDa protein belonging to a family of metalloexopeptidases and was originally purified from lung and skin mast cells (Goldstein et al., 1989). Carboxypeptidase A cleaves COOH‐terminal aromatic and aliphatic amino acid residues and converts angiotensin I to angiotensin II (Goldstein et al., 1989). 2.6.2. Membrane‐Derived Lipid Mediators 2.6.2.1. Prostaglandin D2 (PGD2) Human mast cells derived from a variety of tissues have substantial capacity to synthesize PGD2 (Escribano et al., 2002). Receptors for PGD2 are found on vascular and perivascular cells. Effects of PGD2 include induction of bronchoconstriction, production of vasodilation, increased vasopermeability upon injection, and inhibition of platelet aggregation (Morrow et al., 1994). Flushing in response to niacin is mediated by PGD2 (Escribano et al., 2002). 2.6.2.2. Cysteinyl Leukotrienes Human mast cells exhibit wide variation in the production of the cysteinyl leukotrienes (Benyon et al., 1989). The effects of cysteinyl leukotrienes (LTC4, LTD4, and LTE4) include increase of vascular
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permeability and induction of bronchoconstriction (Arm and Lee, 1993; Joris et al., 1987; Penrose et al., 1992). Upon inhalation, LTC4 and LTD4 induce bronchoconstriction in normal subjects with a 1000‐fold greater potency than histamine (Holgate et al., 1996). The cysteinyl leukotrienes also induce long‐ lasting wheal and flare responses in human skin (Joris et al., 1987; Penrose et al., 1992) and may also mediate abdominal symptoms in patients with SM (Escribano et al., 2002). 2.6.2.3. Platelet‐Activating Factor (PAF) Platelet activating factor associates with platelets, neutrophils, mast cells, eosinophils, endothelial cells, and epithelial cells (Escribano et al., 2002). Inhaled PAF causes bronchospasm in both normal subjects and asthmatics. PAF is 1000 times more potent than histamine at inducing increased vasopermeability in humans (Barnes et al., 1988). 2.6.3. Cytokines Although human mast cells are known to be a source of multifunctional cytokines, there is little information available about how the production and release of cytokines is controlled in mast cells. Several of these cytokines that may contribute to mediator release symptoms in SM are described below. 2.6.3.1. Tumor Necrosis Factor Alpha (TNF) TNF was the first cytokine localized in mast cells (Gordon and Galli, 1990). Receptors for TNF are found on endothelial cells as well as other cell types. TNF can cause transmigration of leukocytes, as well as cachexia and vascular instability (Escribano et al., 2002). 2.6.3.2. Transforming Growth Factor Beta (TGF‐b) TGF‐b is released by murine BM‐derived mast cells following IgE stimulation (Gordon, 2000). TGF‐b is selectively induced by IL‐3 (Lee et al., 2001). Receptors for TGF‐b are present on many cell types. TGF‐b can mediate tissue fibrosis, abnormal bone remodeling, and osteopenia and can promote eosinophilia (Valent et al., 2003b). 2.6.3.3. Interleukins Interleukin receptors are present on leukocytes and other cell types. IL‐1, IL‐2, IL‐3, IL‐4, IL‐5, IL‐6, IL‐9, IL‐10, and IL‐13 are released by mast cells. IL‐4 is implicated in the regulation of IgE synthesis as well as in generation of the T‐helper cell phenotype (Pawankar et al., 1997). IL‐6 is produced by a variety of inflammatory cells, such as monocytes, macrophages, mast cells, activated T cells, and fibroblasts. In addition, IL‐6 has been found to be highly expressed by keratinocytes in psoriatic skin
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(Grossman et al., 1989). There is evidence that IL‐6, in the presence of SCF, may help to prevent mast cell apoptosis (Kambe et al., 2001). Levels of IL‐6 are elevated in the plasma of patients with systemic mastocytosis and have been shown to correlate with plasma tryptase levels (Brockow et al., 2002, 2005; Theoharides et al., 2002). Thus, although mutations in Kit may be a principal initiating factor in the pathogenesis of SM, additional factors including IL‐6 production could serve to augment these mutations, affecting the clinical presentation of the disease. For example, IL‐6 has been linked to the pathophysiology of osteoporosis (Jilka et al., 1992). 3. Biology of Kit 3.1. Introduction The v‐kit gene was identified in 1986 as an oncogene in the Hardy‐Zuckerman 4 feline sarcoma virus (Kitamura and Hirotab, 2004). C‐kit, the genomic counterpart, was identified a year later. C‐kit encodes a transmembrane protein which serves as the receptor for stem cell factor. It is expressed on a variety of cell types including mast cells, hematopoietic cells, melanocytes, germ cells, and interstitial cells of cajal. In the human, the gene for Kit ligand, SCF, is located on chromosome 12. SCF is produced primarily by stromal cells but also by fibroblasts, endothelial cells, keratinocytes, intestinal epithelial cells, mast cells, Sertoli’s cells, and granulosa cells (Akin and Metcalfe, 2004). 3.2. Structure of Kit Kit is a member of the subclass III receptor tyrosine kinases which includes platelet‐derived growth factor receptors alpha and beta, Flt3, and CSF1R (Fig. 1) (Kitamura and Hirotab, 2004). Kit is found on mast cells as well as other cells including melanocytes, germ cells, hematopoietic stem cells, and gastrointestinal stromal cells (Akin and Metcalfe, 2004). Kit (Fig. 1) consists of three domains: an extracellular domain comprised of five immunoglobulin‐like motifs (the first three of which bind Kit to its ligand, SCF); a single short transmembrane region; and a cytoplasmic region. The cytoplasmic region of the protein includes a split tyrosine kinase domain, where the majority of activating mutations are located. The region between the tyrosine kinase domain and the transmembrane region is known as the juxtamembrane domain and is known to regulate the enzymatic activity of the kinase domain. The juxtamembrane domain (JMD) is thought to regulate Kit activity by virtue of
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Figure 1 Cartoon illustrating the structure of the kit receptor tyrosine kinase. The position of the most common mutation (D816V) in the second catalytic domain and of a juxtamembrane mutation (V560G) are shown.
an inhibitory alpha helical structure (Ma et al., 1999). Mutations in this region relieve this inhibitory structure and render Kit constitutively active. 3.3. Functions of Kit Stimulation with ligand, SCF, results in activation of downstream signaling. SCF exists in homodimers and its binding to Kit causes receptor dimerization which, in turn, activates the intrinsic tyrosine kinase activity, leading to autophosphorylation of the receptor (Linnekin, 1999). Ig‐like domain 4 in the extracellular domain of Kit appears to mediate receptor–receptor interactions which stabilize the dimerization complex (Blechman et al., 1995). Cholesterol‐depletion experiments have revealed that lipid rafts are essential for the subsequent internalization of the Kit receptor (Jahn et al., 2002). Phosphorylated Kit then becomes a docking site for signal transduction, regulatory and adaptor proteins containing Src homology 2 (SH2) domains including phosphatidylinositol 3‐OH kinase (PI3K), Janus kinase 2 (JAK2),
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signal transducer and activator of transcription 1 and 5 (Stat 1 and 5), Lyn, adaptor proteins Grb 2 and 7, and phospholipase Cg (Lennartsson et al., 2005). Molecules involved in downstream signaling also include Ras, Raf‐1, and the mitogen‐activated protein kinase cascade. Recent studies of the crystal structure of Kit have revealed that the conformation of the kinase domain is similar in inactive and active receptor, suggesting that it may be simply the separation of receptor monomers that prevents ligand‐independent autophosphorylation (Mol et al., 2003). Signals through the Kit receptor are essential for development of erythrocytes, mast cells, melanocytes, germ cells, and interstitial cells of cajal. Pathologic features seen in mice deficient in Kit serve to illustrate the biological roles of this receptor. Kit‐deficient mice display macrocytic anemia, lack of hair pigmentation, sterility, and reduced number of gastrointestinal pacemaker cells (Jiang et al., 2004). Loss‐of‐function mutations in Kit in humans result in piebaldism, an autosomal dominant disease characterized by patches of white skin and hair (Spritz, 1994). Kit is expressed on hematopoietic stem and progenitor cells but is downregulated from the cell surface as differentiation occurs. Mast cells are an exception to this phenomenon and retain high surface expression of Kit. Kit signaling appears to be critical for a number of mast cell functions including promoting mast cell survival by suppressing apoptosis, promoting mast cell chemotaxis, inducing development and differentiation, and inducing activation and mediator release (Iemura et al., 1994; Irani et al., 1992; Mitsui et al., 1993; Nilsson et al., 1994a; Sperr et al., 1993; Valent et al., 1992). 3.4. Kit Signaling Signaling through the Kit receptor involves multiple proteins and some of the more relevant pathways are described below (for a recent review see Lennartsson (Lennartsson et al., 2005)). 3.4.1. Phosphatidylinsoitol 30 Kinases (PI3K) PI3K is a second messenger generating enzyme involved in mitogenesis and ligand‐mediated receptor internalization and trafficking, and implicated in many other aspects of cell signaling including cell survival and chemotaxis. Once activated via association of the SH2 domain of the regulatory subunit with phosphorylated receptors, PI3K is translocated to the plasma membrane where its substrates are located (Lennartsson et al., 2005). A number of studies designed to clarify the role of PI3K in signaling by generating mutations of the tyrosine residue 721 in Kit, suggest that the direct
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association of Kit and PI3K contributes to—but is not required for—most SCF‐mediated responses (Blume‐Jensen et al., 1998; Hong et al., 2004; Kissel et al., 2000). However, studies in murine systems suggest that PI3K likely plays an important role in SCF‐mediated responses beyond that related to direct association with Kit, although further studies are required to clarify mechanisms involved (Fukao et al., 2002; Lennartsson et al., 2005; Lu‐Kuo et al., 2000; Tan et al., 2003). 3.4.2. JAK/STAT Janus kinases (JAKs) are nontransmembrane protein tyrosine kinases that are rapidly tyrosine phosphorylated and activated upon ligand binding to cytokine receptors. An important function of JAKs is activation of signal transducers and activators of transcription (STAT) proteins. STATs are a group of transcription factors which, after tyrosine and/or serine phosphorylation, translocate to the nucleus where they bind specific promoter elements and act to regulate expression of target genes. Many studies have documented activation of the JAK/STAT pathway by SCF (Brizzi et al., 1994; DeBerry et al., 1997; Gotoh et al., 1996; Ryan et al., 1997; Weiler et al., 1996). However, several studies have shown that SCF does not result in JAK/STAT activation, suggesting that there may be lineage‐specific differences in JAK/STAT activation (Jacobs‐Helber et al., 1997; Joneja et al., 1997; O’Farrell et al., 1996). Indeed, a recent study has demonstrated that JAK2 is important for SCF‐induced growth of Kitþ progenitor cells but is not critical for mast cell response to SCF (Radosevic et al., 2004). Another possible explanation for these disparate results may be related to experimental design. SCF‐induced activation of JAK is known to be very rapid and transient and this must be considered when choosing time points in experiments. Also, the presence of phosphatases in lysis buffer can result in rapid dephosphorylation of JAK2, necessitating the use of high levels of phosphatase inhibitors in in vitro experiments (Lennartsson et al., 2005). 3.4.3. Ras/Mitogen‐Activated Protein Kinase (MAP Kinase) Ras proteins are members of a family of GTPases that regulate growth of many cell types by acting as molecular switches which transduce signals from the extracellular environment to the cell interior. Ras proteins are regulated by cycling between an active GTP‐bound state and an inactive GDP‐bound state. Receptor binding by a variety of growth factors induces phosphorylation of son of sevenless (SOS), a guanine‐nucleotide exchange factor, which recruits the adaptor protein Grb2 which then binds SOS. The Grb‐2/SOS complex binds
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phosphorylated Kit resulting in translocation of SOS to membrane‐bound Ras‐ GDP. This results in conversion of RAS to the GTP‐bound state and activated Ras, then recruits Raf‐1 to the plasma membrane which, in turn, activates a series of downstream effectors including MAP kinases (Miyazawa et al., 1991). Mitogen‐activated protein kinases are a family of serine/threonine kinases activated through dual phosphorylation of serine and threonine motifs by a group of dual specificity kinases (Lennartsson et al., 2005). SCF has been shown to activate the RAS/MAPK pathway through multiple signaling components. A recent study showed that activation of the Ras‐MAPK pathway requires only an intact SFK binding site in Kit (Hong et al., 2004). Consistent with these results, knock‐in mice expressing a Kit receptor lacking the SFK binding site were unable to activate the MAPK cascade (Kimura et al., 2004). 3.4.4. SFK Pathway Src family kinases (SFKs) are non‐receptor tyrosine kinases that play key roles in cell morphology, motility, proliferation, and survival. There are at least 11 members of the Src‐family kinases in humans, including Blk, Brk, Fgr, Frk, Fyn, Hck, Lck, Lyn, Src, Srm, and Yes (Manning et al., 2002). Src was the first non‐receptor tyrosine kinase to be described. Src, Yes, and Fyn are expressed in a wide variety of cell types while the remaining family members are primarily expressed in hematopoietic cells (Manning et al., 2002). Activation of Kit causes a rapid increase in the activity of SFKs (Lennartsson et al., 2005). SFKs have been shown to be important for the ligand‐induced internalization of Kit (Broudy et al., 1999; Krystal et al., 1998; Linnekin et al., 1997). Lyn has been shown to associate with the juxtamembrane region of Kit and to have an important role in SCF‐induced chemotaxis in primary hematopoietic cells (Linnekin et al., 1997; O’Laughlin‐Bunner et al., 2001). Recent experiments examining effects of targeted changes in Kit have revealed that loss of SFK binding (kitY567F) causes defects primarily in lymphopoiesis while mice with kitY567F/Y569F had defects in mast cell development and pigmentation which were more severe than defects seen in mice with single mutations (Kimura et al., 2004). This would suggest that there is cooperation between tyrosine residues in activation of downstream signaling (Agosti et al., 2004). 3.4.5. Phospholipase Cg1 Phospholipase Cg (PLCg) plays a crucial role in initiation of signal transduction and is essential for growth factor‐induced motility and mitogenesis (Rottapel et al., 1991). PLCg has been shown to have a central role in SCF‐induced protection against apoptosis induced by either radiation or
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daunorubicin (Maddens et al., 2002; Plo et al., 2001). PLCg acts by generating two second messengers, diacylglyceral (DAG) and inositol 1,4,5 triphosphate (IP3) from phosphatidylinositol‐4,5‐biphosphate (Lennartsson et al., 2005). DAG binds and activates PKCs, while IP3 causes release of calcium from the endoplasmic reticulum. Association of PLCg with Kit is dependent on tyrosine residues 730 and 936 of the human receptor (Gommerman et al., 2000; Herbst et al., 1995). Several studies have shown that soluble SCF does not activate PLCg, whereas membrane‐bound SCF appears to activate this pathway (Gommerman et al., 2000; Koike et al., 1993; Kozawa et al., 1997; Trieselmann et al., 2003). These experimental results may be related to differences in the rate at which membrane‐bound and ‐soluble SCF internalize the receptor (Miyazawa et al., 1991, 1995; Yee et al., 1994). 3.4.6. Adapter Proteins Adaptor proteins are proteins which themselves lack enzyme activity but which serve as linking molecules to bring together two or more protein components. They lack catalytic domains but contain SH2 domains. Examples of this important class of molecule are growth factor receptor‐bound 2 (Grb2), growth factor receptor‐bound 10 (Grb10), Dok‐1, Gab2, and adaptor protein containing PH and SH2 domains (APS) (Lennartsson et al., 2005). The ability of these proteins to link together specific protein–protein interactions offers multiple versatile mechanisms to regulate signal transduction. Grb2 is a widely expressed adaptor protein which couples receptor tyrosine kinases to the Ras‐MAPK pathway. This occurs through association with the Ras guanine nucleotide exchange factor Sos and activated Kit has been shown to bind Grb2 (Lennartsson et al., 2005). ShcA is an adaptor protein that has been shown to interact with Grb2 upon phosphorylation. ShcA is therefore capable of recruiting Grb2 to receptors that lack direct Grb2 binding sites. Activation of Kit results in increased tyrosine phosphorylation of ShcA, which then correlates with the activation of the Ras‐MAPK pathway (Cutler et al., 1993; Lennartsson et al., 1999). 3.5. Regulators of Kit Signaling Kit is capable of potent activation of multiple signaling cascades necessitating multi‐faceted regulation of this pathway. An important feature of SCF is its capacity to synergize with ligands for the cytokine receptor super family members including GM‐CSF, IL‐3, and erythropoietin (Epo) (Lennartsson et al., 2005). However, the molecular mechanisms underlying these interactions remain to be elucidated. Several studies indicate that SCF does not alter the
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number or affinity of receptor for either GM‐CSF or IL‐3 (Hallek et al., 1992; Hendrie et al., 1991; Liu et al., 1994a). In general, GM‐CSF and SCF co‐ stimulation does not induce synergistic increases in Kit tyrosine phosphorylation (Lennartsson et al., 2005). Kit has been shown to physically interact with the EpoR and induces its phosphorylation (Wu et al., 1995). Negative regulation of the potent Kit receptor occurs through a variety of mechanisms. Protein kinase Cs (PKCs) are a large family of serine/threonine kinases important in regulating RTKs. Studies suggest that downregulation of Kit by PKCs occurs by several mechanisms. Studies using endothelial cells and fibroblasts transfected with c‐Kit suggest that activation of PKCs induces proteolytic release of the extracellular ligand‐binding domain of Kit and that PKC phosphorylation of serine residues in the kinase insert inhibits kinase activity via an unknown mechanism (Lennartsson et al., 2005). The hematopoeitic‐restricted Src homology 2 containing inosotol 50 ‐phosphatase (SHIP) acts as a negative regulator of myeloid proliferation. SCF stimulation of mast cells leads to phosphorylation of SHIP (Liu et al., 1994b). In bone marrow‐derived mast cells, SHIP prevents degranulation by IgE alone and limits production of inflammatory cytokines (Huber et al., 1998b; Huber et al., 1998a). Disruption of the SHIP gene has revealed that it negatively regulates mast cell degranulation (Huber et al., 1998b). Several lines of evidence suggest that tyrosine phosphatase, SHP1, is a negative regulator of Kit signaling. SHP1 interacts with the JMD of Kit (Kozlowski et al., 1998). Genetic experiments with moth‐eaten mice, which have a loss‐of‐function mutation in SHP1, suggest a negative role for SHP1 in Kit signaling (Lennartsson et al., 2005; Lorenz et al., 1996; Paulson et al., 1996; Shultz et al., 1993). SHP2, another SH2‐containing protein tyrosine phosphatase, has also been implicated as a negative regulator of Kit signaling, based on studies that show that SHP2 couples Kit to the RAs‐Raf‐MAP kinase pathway (Tauchi et al., 1994). SHP2 associates with murine Kit through phosphorylated tyrosine residue 567 following SCF stimulation (Kozlowski et al., 1998). Interestingly, mutations in Shp2 have been demonstrated to cause Noonan syndrome, which is associated with an increased risk of the myeloproliferative disorder juvenile myelomonocytic leukemia (JMML) (Tartaglia et al., 2001). Somatic mutations in SHP2 also occur in sporadic JMML and other leukemias, suggesting that mutations in this gene may play a broad role in hematologic malignancies (Loh et al., 2004; Tartaglia et al., 2003; tires‐Alj et al., 2004). 3.6. Kit Mutations in Human Diseases Heterozygous loss‐of‐function mutations cause the autosomal dominant disorder piebaldism characterized by white midline patches of hair and skin due to localized absence of melanocytes (Spritz, 1994). Mutations of Kit have been
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described in myeloproliferative disease, AML, GISTs, sinonasal lymphomas, and seminomas, in addition to SM. 3.6.1. Myeloproliferative Diseases (MPDs) Point mutations in exon 2 of c‐Kit were found in mononuclear cells in 3/25 patients with myeloproliferative disease (MPD) (one with chronic myeloid leukemia (CML) and two with myelofibrosis) (Nakata et al., 1995). The functional effects of these mutations have not yet been determined. 3.6.2. Acute Myelogenous Leukemia (AML) Wild‐type Kit is expressed in 80–90% of human acute myelogenous leukemias (AML). Approximately 30% of AML blasts co‐express Kit and SCF, a fact which has led to the hypothesis that an autocrine/paracrine loop may be involved in the pathobiology (Janowska‐Wieczorek et al., 2001). In contrast, Kit is rarely expressed in lymphoid leukemias. About 30% of cases of AML with inv (16) karyotype show deletions or insertions in exon 8 that encodes the extracellular domain of Kit (Gari et al., 1999). Mutations in codon 416 are involved in all of these cases; however, the functional significance of this mutation is unknown. The D816V mutation was demonstrated in 7 of 15 patients with AML M2 t (8:21) or AML M4 inv 16, so‐called core‐binding factor leukemias (Beghini et al., 2000). A recent study of 150 pediatric AML patients showed that 11% had Kit mutations and that 70% of core‐binding factor leukemias were associated with mutations in either Kit or Ras (Goemans et al., 2005). Interestingly, AML is also associated with mutations in the activation loop of a receptor tyrosine kinase, FLT3, which is closely related to Kit (Kelly and Gilliland, 2002). Overall, approximately 31% of AML patients have acquired mutations in FLT3 (Kelly and Gilliland, 2002; Kelly et al., 2002). These mutations occur as either internal tandem duplication in the juxtamembrane domain or point mutations in the kinase domain of Flt3 (Kelly et al., 2002). 3.6.3. Gastrointestinal Stromal Cell Tumors (GISTs) Gastrointestinal stromal cell tumors (GISTs) are rare tumors of the gastrointestinal tract that may occur from the esophagus to the rectum, but are most common in the gastric and small intestinal regions (Joensuu and Kindblom, 2004). Ninety percent of GISTs express Kit (Bono et al., 2004; Corless et al., 2004). Many sporadic GISTs have mutations in the juxtamembrane domain (JMD). Specifically, 57–71% are in exon 11 and 4–17% have mutations in exon 9 or 13 (Joensuu and Kindblom, 2004; Sattler and Salgia, 2004). Rarely, mutations in the tyrosine kinase (TK) domain have been found in GISTs. Mutations in the
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JMD domain are believed to be regulatory, acting through disruption of an inhibitory alpha helical structure (Ma et al., 1999). Approximately 10% of GISTs do not carry Kit mutations. A recent study showed that gain‐of‐function mutations in PDGFRa, also a member of the type III receptor tyrosine kinase family, were present in this subset of patients (Heinrich et al., 2003). Mutations were present at either the JMD or TK domain. Families with a germ line c‐Kit mutation at codon 557 or 559 in the JMD have been reported (Beghini et al., 2001; Maeyama et al., 2001; Robson et al., 2004). Multiple family members in these kindreds had GIST, hyperpigmentation, or cutaneous matocytosis. 3.6.4. Sinonasal Lymphomas Mutations in Kit have been reported in sinonasal natural killer/T cell lymphomas. However, the functional consequences of most of these mutations have not been determined. In one study, 71.4% (10/14) of Chinese cases and 22% (2/9) of Japanese cases had mutations at either exon 11 or 17 of c‐Kit. Furthermore, 7 out of 8 mutations in exon 17 occurred at codon 825 and 3 of 4 mutations in exon 11 occurred at codon 561 (Hongyo et al., 2000). A subsequent study of 20 cases from China revealed kit mutations in only 5% of cases (Hoshida et al., 2003). 3.6.5. Testicular Seminomas An appreciable proportion of testicular seminomas show gain‐of‐function mutations of Kit (Kemmer et al., 2004; Sakuma et al., 2003; Tian et al., 1999). Most are mutations in the TK‐II domain. The frequency and spectrum of Kit mutations was examined in 54 testicular seminomas (Kemmer et al., 2004). Of these, 25.9% contained mutations in exon 17, including 6 cases of D816V mutation, 3 cases of D816H, and 2 cases of Y823D. In transient transfection assays, mutants D816V, D816H, and Y823D showed constitutive phosphorylation of Kit in the absence of SCF, suggesting that these mutations may contribute to tumorigenesis. One case of a seminoma with a gain‐of‐ function mutation in the juxtamembrane domain of Kit has been reported (Sakuma et al., 2003). 3.6.6. Systemic Mastocytosis Several mutations in Kit have been identified in systemic mastocytosis (Table 2). The most commonly found mutation is a substitution of valine (V) for aspartate (D) at codon 816 (D816V), located in the tyrosine kinase domain. Tyrosine (Y) may also be substituted for aspartate (D816Y) (Nagata et al.,
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Table 2 Gene Mutations, Polymorphisms, and Karyotypic Abnormalities Identified in Patients with Systemic Mastocytosis Finding c‐kit D816V c‐kit D816Y c‐kit D816F c‐kit D816H c‐kit D820G c‐kit V560G c‐kit F522C c‐kit E839K c‐kit V530I c‐kit K5091 IL‐4Ra Q576R del 20 (q12)* þ9* T(8:21)*
Patient population
Estimated frequency (%)
All variants of SM (some CM)
>80%
CM, SM, SM‐AHNMD CM SM‐AHNMD ASM SM SM CM SM‐AML SM‐familial CM, ISM SM‐AHNMD SM‐AHNMD SM‐AHNMD
<5 <5 <5 <5 <5 <5 <5 <5 <5 NA <5 <5 <5
*These cytogenetic abnormalities are indicative of an AHNMD.
1995). These mutations lead to SCF‐independent activation of Kit which is thought to result in continued cell division and/or survival leading to mast cell hyperplasia. Other mutations occur less commonly in SM. The D816V‐activating mutation has been shown to enhance stem cell factor‐dependent chemotaxis (Taylor et al., 2001). Enhanced migration was demonstrated in both transfected Jurkat cells as well as circulating human mast cell precursors (Taylor et al., 2001). A novel germ line mutation has been recently identified in c‐Kit located within the sequence that codes for the transmembrane region of Kit (Akin et al., 2004). The substitution of phenylalanine (F) for cysteine (C) (Phe522Cys) was observed in a patient with skin manifestations typical of cutaneous mastocytosis. The bone marrow biopsy demonstrated an increase in mast cells that were of a mature morphology. This mutation conferred exquisite sensitivity to imatinib, a tyrosine kinase inhibitor that is also effective in gastrointestinal stromal tumors with juxtamembrane mutations in Kit. 4. Mastocytosis 4.1. General Mastocytosis is not a single well‐defined disorder but rather a disease characterized by multiple variants (Table 3) Mastocytosis is divided into distinct variants on the basis of clinical presentation, pathologic findings, and
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Table 3 WHO Systemic Mastocytosis Variants Variant term Cutaneous mastocytosis (CM)
Indolent systemic mastocytosis (ISM)
Systemic mastocytosis with an associated clonal hematologic non‐mast cell lineage disease (SM‐AHNMD)
Aggressive systemic mastocytosis (ASM) Mast cell leukemia (MCL) Mast cell sarcoma Extracutaneous mastocytoma
Subvariants Urticaria pigmentosa (UP) Maculopapular CM (MPCM) Diffuse CM (DCM) Mastocytoma of skin Smoldering SM Isolated bone marrow Mastocytosis SM‐AML SM‐MDS SM‐MPD SM‐CMML SM‐NHL Aleukemic MCL
prognosis. The most recent WHO consensus classification for mastocytosis is shown in Table 3. 4.2. Pathogenesis of Systemic Mastocytosis The first clue to the involvement of Kit signaling in the pathogenesis of SM was the finding that CD34þ cells from peripheral blood of SM patients when cultured in the presence of SCF produced a larger number of mast cells/CD34 cells than those from normal individuals (Rottem et al., 1994b). Based on this observation, a search for activating mutations in the SCF receptor led to the identification of a point mutation in the gene for c‐Kit which was subsequently identified in the peripheral blood, skin, and bone marrow in the majority of patients with SM (Nagata et al., 1995). This mutation, substituting a T for an A at nucleotide 2468 in c‐Kit mRNA, causes an Asp816 to Val substitution. This mutation was one of two mutations found to be present in the HMC‐1 cell line established from a patient with mast cell leukemia and was shown to cause ligand‐independent phosphorylation of Kit (Kanakura et al., 1994). Most patients with both indolent mastocytosis, as well as aggressive mastocytosis and mastocytosis with an associated hematologic disorder, were found to have D816V mutations in Kit (Nagata et al., 1995). Additional activating point mutations have been identified in some SM patients and rare mutations in other codons of Kit have been identified in other patients with SM (Table 2).
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Cytogenetic analysis has revealed a normal karyotype in the majority of patients with SM; however, a number of translocations have been described, most often in patients who have a myeloid disorder in addition to SM (Table 3) (Valent et al., 2005). Lineage analysis of SM samples demonstrated that the cell of origin in this disease is a pluripotent hematopoietic progenitor. The D816 V mutation was found in genomic DNA isolated from sorted peripheral blood T cells, B cells, and monocytes using single cell PCR (Yavuz et al., 2002). Most pediatric patients appear to lack the Asp816Val‐ and Asp816Tyr‐ activating mutations often found in adults with SM. A Gly839Lys mutation in Kit has been found in skin lesions of some pediatric patients with mastocytosis (Longley et al., 1999). Childhood onset disease tends to run a more benign course often with spontaneous remissions by puberty. However, there are pediatric‐age patients with mastocytosis that clinically resembles adult mastocytosis and in some of these patients a D816V mutation can be detected. Laser capture microdissection was used to demonstrate that mast cells, T cells, and B cells bearing the D816V mutation occur in clusters in the bone marrow of SM patients (Taylor et al., 2004). B cells within these clusters were shown to be oligoclonal using PCR for IgH VDJ gene rearrangements, suggesting that the cause for the clustering was not clonal proliferation (Taylor et al., 2004). Several recent studies have described mastocytosis‐like phenotypes associated with Ras dysregulation in mice (Guo et al., 2005; Wiesner et al., 2005). In one study, a transgenic line with NRASV12 driven by a tetracycline response element was shown to be responsible for initiation and maintenance of a disease mimicking aggressive systemic mastocytosis or mast cell leukemia, and which was manifested between two and four months of age in the animals (Wiesner et al., 2005). In another study, the expression of a constitutively active M‐Ras in murine bone marrow was sufficient to induce a malignant mastocytosis/mast cell leukemia in mice (Guo et al., 2005). The clinical relevance of mutated Ras genes remains to be explored. Aberrant surface expression of cell surface adhesion molecules has been demonstrated in most patients with SM. In particular, CD2 (LFA‐2) is an adhesion molecule which is not expressed on normal mast cells but is abnormally expressed on mast cells isolated from patients with SM. Mast cells are also known to express CD58 (LFA3), the natural ligand of CD2. There is speculation that this may contribute to cluster formation in SM. Whether aberrant surface molecule expression plays a pathogenetic role in SM is currently unknown. In a number of malignancies increased angiogenesis is thought to contribute to disease pathogenesis. Indeed, increased angiogenesis has been demonstrated
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by assessment of bone marrow microvascular density by CD34 immunohistochemistry in the marrow of patients with SM (Wimazal et al., 2002). In addition, expression of vascular endothelial growth factor in mast cell infiltrates was shown by immunohistochemistry and has been hypothesized to contribute to disease pathogenesis (Wimazal, 2002). The degree of clinical heterogeneity in patients with SM is not explained by the presence of the same activating mutation in the majority of patients. A number of possible explanations for clinical heterogeneity has been proposed (Metcalfe and Akin, 2001). First, polymorphisms may be present that influence expression of Kit‐activating mutations. Second, the Kit mutation may serve as an initial ‘‘permissive’’ mutation which requires additional mutations before overt SM develops. Secondary mutations may be simple point mutations in undefined genes or overt genetic instability affecting multiple loci. Gene expression analysis using bone marrow mononuclear cells from patients with SM compared to healthy controls revealed a highly consistent profile with 168 genes which were significantly up‐ or downregulated in patient samples (D’Ambrosio et al., 2003). Further analysis using this technology may be useful to identify candidate genes distinguishing patient groups showing divergent clinical behavior. 4.3. Diagnosis of Systemic Mastocytosis The diagnosis of mastocytosis is suspected by clinical presentation and established by histopathologic examination of an involved tissue, usually the bone marrow. Additional studies such as GI imaging, computed tomography, endoscopy, and bone scintography may be appropriate based on presenting symptoms. Histamine metabolites are often elevated in 24 h urine specimens in patients with systemic disease (Granerus et al., 1994; Keyzer et al., 1983). The test, however, appears to be neither more sensitive nor more specific than measurement of serum total tryptase. The most common clinical finding in patients with mastocytosis is the presence of typical skin lesions of urticaria pigmentosa (UP), which appear as fixed, dark red‐brown macules or papules. In patients without skin lesions, diagnosis of SM is often established after a bone marrow biopsy for unexplained anaphylaxis, organomegaly, peripheral blood abnormalities, or skeletal lesions. In addition to the bone marrow, other common sites of involvement in SM are spleen, liver, lymph nodes, and the gastrointestinal tract. The bone marrow, however, is the most common site of documented systemic involvement, followed by the spleen, liver, and lymph nodes (Lawrence et al., 1991; Parker, 2000; Travis et al., 1988a). The frequency of pathological involvement at sites other than bone marrow is not known because they are not routinely biopsied.
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Table 4 WHO Major and Minor Criteria for Diagnosis of SM Major Multifocal dense infiltrates of mast cells in bone marrow and/or other extracutaneous organs with at least 15 mast cells per aggregate and confirmed by special staining Minor 1. More than 25% of the mast cells in bone marrow aspirate smears or tissue biopsy sections are spindle shaped, immature, or display atypical morphology 2. Detection of a codon 816 c‐Kit point mutation or other kit mutation described in SM in blood, bone marrow, or lesional tissue 3. Mast cells in bone marrow, blood, or other lesional tissue expressing CD25 and/or CD2 4. Baseline serum total tryptase level of greater than 20 ng/ml (unless there is an associated clonal myeloid disorder, in which case this parameter is not valid) The diagnosis of SM may be made if one major and one minor criteria are present or if at least three minor criteria are present.
An increase in mast cells in hematopoietic tissues may be associated with reactive mast cell hyperplasia, myeloid disorders including myelodysplastic syndrome, or myeloproliferative syndrome as well as SM. Distinguishing these conditions by histological examination is not always straightforward. Criteria for the diagnosis of SM were established in 2000 by a World Health Organization classification derived from the Year 2000 Mast Cell Disease Symposium consensus conference (Valent et al., 2001a). They are divided into major and minor criteria (Table 4). In addition, the WHO has defined parameters to distinguish between indolent and more aggressive disease (Table 5). The development of new diagnostic methods has improved the study of SM with the most relevant contributions including immunohistochemistry, immunophenotyping using multiparapmetric flow cytometry, and molecular detection of mutations in c‐Kit. The major diagnostic criterion is established by demonstration of multi‐focal aggregates of mast cells, normally easily appreciated in mastocytosis marrow specimens, and usually found in peritrabecular or perivascular locations. Focal lesions often contain varying proportions of lymphocytes, fibroblasts, and eosinophils, in addition to mast cells (Horny and Kaiserling, 1988). It is recommended that suspected mast cell collections be confirmed by special stains. Stains used to demonstrate metachromatic granules include Giemsa or toluidine blue; however, fixation methods, particularly decalcification with acidified solution used for bone marrow biopsies, often significantly reduce or mask toluidine blue staining (Li, 2001). The most specific stain for mast cells is mast cell tryptase. Using anti‐tryptase monoclonal antibody (G3 or AA1) allows the demonstration of even very small mast cell infiltrates in
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Table 5 ‘‘B’’ and ‘‘C’’ Findings ‘‘B’’ findings 1. Bone marrow biopsy showing >30% infiltration by mast cells and or serum tryptase >200 ng/ml 2. Signs of dysplasia or myeloproliferation in non‐mast cell lineage but insufficient criteria for diagnosis of hematopoietic neoplasm by WHO criteria, with normal or slightly abnormal blood counts 3. Hepatomegaly with no impairment of liver function and/or splenomegaly without hypersplenism and/or palpable or visceral lymphadenopathy ‘‘C’’ findings 1. Bone marrow dysfunction manifested by one or more cytopenias (ANC < 1 109/L, Hb < 10 g/dl, or platelets <100 109/L) but no frank non‐mast cell lineage hematopoeitic disease 2. Hepatomegaly with impaired liver function, ascites, and/or portal hypertension 3. Skeletal involvement with large‐sized osteolysis and/or pathological fractures 4. Palpable splenomegaly with hypersplenism 5. Malabsorption with weight loss due to GI mast cell infiltrates
routinely processed paraffin sections (Horny et al., 1998; Valent et al., 2005; Walls et al., 1990) and is essential for the identification of atypical, hypogranulated, spindle‐shaped mast cells (Horny and Valent, 2001). Minor criteria include the presence of atypical spindle‐shaped mast cells. Normal mast cells by contrast have round or oval nuclei with a coarse chromatin pattern, and absent or inconspicuous nucleoli with cytoplasm that is densely packed with basophilic granules. Mast cells in SM may have indented nuclei which are eccentrically placed and/or irregularly distributed granules. Careful examination of the marrow is critical to exclude the presence of an associated clonal non‐mast cell lineage disease, which may include acute myeloid leukemia, a chronic myeloproliferative process, myelodysplasia, or a lymphoproliferative disease (Valent et al., 2001c, 2003a). Additional useful special stains in specific cases include iron stain (for ring sideroblasts), periodic acid Schiff (for PAS‐reactive erythroblasts), combined chloroacetate esterase/ butyrate esterase (for abnormal granulocytes or monocytes), peroxidase stain (for dysgranulopoiesis), and CD41 (for dysmegakaryopoiesis) (Li, 2001). Careful examination of the peripheral smear is also necessary to exclude a mast cell leukemia where mast cells may account for more than 10% of the peripheral white blood cells. The finding of unusually large numbers of mast cells in bone marrow aspirates may represent an aleukemic subtype of MC leukemia. The presence of mast cells with bi‐lobed or multi‐lobulated nuclei usually indicates an aggressive disease variant (Valent et al., 2001c).
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Total serum tryptase levels over 20 ng/ml are considered a minor criteria for the diagnosis. The immunoassay of total tryptase in serum or plasma done in commercial diagnostic laboratories measures two related proteins, alpha and beta tryptase. The total serum typtase in normal individuals averages 5 ng/ml (Schwartz and Irani, 2000). Tryptase levels are useful in diagnosis as well as follow‐up of SM, although the absolute level of serum tryptase does not reliably predict disease severity (Akin and Metcalfe, 2002). The sensitivity of this assay as a diagnostic test is 83% with a specificity of >98% (Payne and Kam, 2004). Other surrogate markers used in the past include 24 h urine histamine, which appears to correlate with MC burden. However, serum tryptase was found to be a more sensitive indicator in one study (Granerus et al., 1994). Of note, some patients with myeloid neoplasms may also have total serum tryptase levels over 20 including myelodysplastic syndrome, acute myeloid leukemia, and myeloproliferative diseases (Sperr et al., 2001b; Valent et al., 1999). The WHO excludes serum tryptase as a minor criteria for diagnosis of SM if a myeloid neoplasm is also present. The immunophenotype of normal bone marrow mast cells as determined by multiparametric flow cytometry reveals the following: expression of CD9, CD44,CD45, CD33, activation markers (CD63, CD68), and CD117, while normal mast cells do not express CD2, CD14, CD15, CD16, CD25 or T and B cell‐related antigens (Escribano et al., 2004). The best surface marker for the detection of normal and pathologic MCs is CD117. Although it can be found on diverse cell types including CD34þ progenitor cells, NK cells, and neoplastic cells from a variety of myeloid neoplasms, mast cells express uniquely greater amounts of CD117 compared to these other cell types (Escribano et al., 2004). Bone marrow mast cells are normally present in low frequency (range 0.002 to 0.08%); however, additional markers help to uniquely identify mast cells such as CD45 low expression, strong CD33 expression, FcRI‐positivity, and CD34 negativity (Escribano et al., 2004). Application of multiparametric flow cytometry for the analysis of bone marrow mast cells from healthy controls and patients with mastocytosis show that CD2 and CD25 antigens are expressed on the surface of mast cells from the majority of patients with systemic disease and are not present on normal mast cells in bone marrow (Escribano et al., 2001). Both CD2 and CD25 have been shown to be consistently absent in normal mast cells, mast cells from reactive bone marrow specimens, and mast cells from patients suffering from other hematologic or non‐hematologic diseases, including B cell chronic lymphocytic leukemia, B cell non‐Hodgkin’s lymphoma, Waldenstrom’s macroglobulinemia, multiple myeloma, monoclonal gammopathy of undetermined significance, and myelodysplastic syndrome (Escribano et al., 1998; Pardanani et al., 2004b). Of these two antigens showing aberrant expression on mast cells
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from mastocytosis specimens, CD25 appears to be the most sensitive, specific, and easy to use (Escribano et al., 2004). A recent analysis of 33 patients with SM showed that, while CD25 was almost uniformly expressed, only 6 of 13 patients with indolent SM, 1 of 8 with aggressive SM, and none of 2 patients with either smoldering SM or mast cell leukemia expressed CD2 (Pardanani et al., 2004b). There are, however, rare exceptions to the finding of co‐expression of CD2 and CD25 on mast cells in SM. For example, the transmembrane mutation (F522C) associated with systemic mastocytosis was not associated with expression of CD2 and CD25 on bone marrow mast cells (Akin et al., 2004). The observation that c‐Kit activating mutations were present in a mast cell line (HMC‐1) (Furitsu et al., 1993) prompted investigation into the hypothesis that similar mutations might be present and involved in the pathogenesis of SM. Indeed, using a combination of single strand conformation polymorphism analysis (SSCP) followed by sequencing, the D816V mutation was identified in PBMCs in 4 out of 10 patients with SM, all of whom had an associated hematologic disorder, while the mutation was not detected in any of 67 control samples (Nagata et al., 1995). Subsequent studies have shown that the D816V mutation can be detected in the bone marrow in the majority of patients with SM (Longley et al., 1996, 1999; Sperr et al., 2002a). In 25% of 65 patients with SM the D816V mutation can also be detected in peripheral blood in addition to bone marrow samples (Worobec et al., 1998). Mastocytosis patients whose PBMCs were positive for the mutation were found to be more likely to have an associated hematologic disorder, as well as osteosclerosis and other disease‐specific findings (Worobec et al., 1998). The approach most commonly used for screening for the Kit D816V mutation is to reverse transcribe bone marrow mononuclear RNA into cDNA, followed by region‐specific PCR amplification and restriction fragment length polymorphism analysis (RFLP) for D816V Kit mutation (Fritsche‐Polanz et al., 2001). Cloning and sequencing of the coding region of c‐Kit should be performed in patients who meet criteria for SM where no D816V is detected. The following steps are useful in the initial screening of a patient with suspected SM. If SM is suspected on clinical grounds, the initial work‐up should include a baseline serum tryptase. In most patients with SM, the serum tryptase is >20 ng/ml. However, increases in serum tryptase are not specific for SM and may be found in patients with myeloid non‐MC lineage neoplasms including AML, CML, myelodysplastic syndrome, and myeloproliferative diseases including hypereosinophilic syndrome (Sperr et al., 2001b; Valent et al., 1999). If the serum tryptase is elevated, a bone marrow aspiration and biopsy should be performed. Bone marrow immunophenotyping and molecular analysis for the presence of the c‐Kit mutation D816V are useful as well,
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Table 6 Common Differential Diagnosis Benign cutaneous flushing Chronic urticaria Idiopathic anaphylaxis Carcinoid syndrome VIPoma Adrenal tumors MC hyperplasia (underlying conditions, including parasitic infections, tumors) Myelomastocytic leukemia, myelomastocytic cell spread in myelodysplastic syndromes Tryptase‐positive acute myeloid leukemia KIT‐positive acute myeloid leukemia with blasts expressing CD2 (FAB AML‐M4eo) Acute myeloid leukemia with aberrant expression of c‐kit point mutation Asp‐816‐Val Chronic myeloid leukemia with accumulation of tryptase‐positive cells Idiopathic myelofibrosis with focal accumulation of mast cells Acute or chronic basophilic leukemia with increase in mast cells Hypereosinophilic syndrome Immunocytoma with reactive focal increase in bone marrow mast cells Histiocytosis
since the WHO criteria use results from these studies to establish the diagnosis of SM. A complete blood count with differential, serum chemistries and liver function tests are usually obtained as part of the initial work‐up. Additional studies as suggested by clinical symptoms or findings on examination may include computerized tomography scans, gastrointestinal endoscopic evaluation, and/or ultrasound, plain X‐rays of the bone, and bone densitometry. It is important to note that most of the signs and symptoms of mastocytosis are non‐ specific and may be confused with other conditions. Some conditions that manifest similar symptoms and signs are listed in Table 6. In cases where AHNMD is suspected, cytogenetic studies should be performed to screen for chromosomal translocations, insertions, deletions, and chromosomal copy number changes associated with myeloid and lymphoid neoplasms. In patients with co‐existing eosinophilia, peripheral blood should be examined for the presence of the FIP1L1/PDGFRa fusion gene (Cools et al., 2003, 2004; Gilliland et al., 2004). 4.4. Clinical Spectrum 4.4.1. Cutaneous Mastocytosis In cutaneous mastocytosis (CM), by definition, mast cell infiltration is confined to the skin. CM usually develops in childhood, and isolated CM in adulthood is unusual (Wolff et al., 2001). The diagnosis is established by characteristic skin
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lesions and lack of signs or symptoms of SM. Assessment of a baseline serum tryptase should be performed and is usually found to be <20 ng/ml (Sperr et al., 2002b). There are three main forms of CM defined by the WHO: urticaria pigmentosa (UP), also called maculopapular cutaneous mastocytosis (MPCM); diffuse cutaneous mastocytosis (DCM); and mastocytoma of the skin (Hartmann and Henz, 2002; Wolff et al., 2001). A number of rare subvariants of UP have been described including telangiectasia macularis eruptive persistans (TMEP), a nodular and a plaque form (Wolff et al., 2001). UP is the most frequent form of CM and is observed in more than 90% of adult patients with ISM. The lesions of UP are maculopapular, small reddish‐ brown lesions that tend to be concentrated on the trunk, and usually spare areas exposed to sun. The prognosis of UP is good; however, some patients with CM have extensive skin involvement and accompanying mediator‐related symptoms requiring therapy. DCM is diagnosed almost exclusively in infants, although it sometimes persists into adult life. DCM is characterized by a diffuse mast cell infiltration of the dermis (Hartmann and Henz, 2002). TMEP is a rare form of mastocytosis seen most commonly in adults (Hartmann and Henz, 2002). The lesions are red‐brown, telangiectatic macules with irregular borders. The biopsy in cases of TMEP reveals increased numbers of perivascular mast cells. Nodular CM or mastocytoma appears as a sharply demarcated reddish‐ brown tumor most often located on the extremities (Hartmann and Henz, 2002). Mastocytomas may be either solitary or multiple. Irritation of a mastocytoma lesion may cause systemic symptoms such as flushing. 4.4.2. Systemic Mastocytosis Many of the symptoms of mastocytosis are caused by the release of preformed inflammatory mediators stored in mast cell granules, as well as newly formed inflammatory mediators produced following mast cell activation. Mediator‐ release‐related symptoms include flushing, pruritus, urticaria, nausea, vomiting, diarrhea, abdominal pain, headache, palpitations, dyspnea, and syncope (Escribano et al., 2002; Valent et al., 2005). Attacks are sometimes followed by lethargy that may last for several hours. Various neuropsychiatric symptoms have also been reported including headache, inability to concentrate, memory impairment, irritability, and personality changes (Valent et al., 2003b). The most frequently reported symptom in patients with systemic disease is pruritus (88%), followed by gastrointestinal (GI) symptoms (80%), and flushing (43%) (Cherner et al., 1988). Abdominal pain is the most common gastrointestinal symptom, followed by diarrhea, nausea, and vomiting.
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Table 7 Triggers of Mast Cell Degranulation Reactions Possible triggersa Venoms (insects, snakes) Polymers (dextran, gelatin) Physical stimuli (heat, cold, friction, sunlight) Drugs (examples) Aspirin and other NSAIDS,b thiamine, alcohol, narcotics, amphotericin B radiographic dyes,c and some drugs used in general anesthesia (inductors, muscle relaxants) Emotional factors (stress, anxiety) Miscellaneousd a
Triggers vary greatly from patient to patient. Patients with defined sensitivities should have these indicated on a Medic alert bracelet. b Aspirin and other NSIADS may induce mast cell degranulation in some patients and have proven to be well‐tolerated effective therapy in others. If patients have not taken these medications before, treatment should be initiated under close medical supervision. c If radiographic studies are needed, premedicate patients with H1 and H2 antihistamines and glucocorticoids. d In individual patients, foods, allergens, and other factors may act as triggers and once identified should be avoided.
Abdominal complaints may be a typical dyspeptic pain or a crampy lower abdominal pain. In some patients, attacks may be precipitated by stimuli (see Table 7) such as heat, cold, pressure, alcohol, and certain medications (e.g., opiates, aspirin), while in other patients triggers cannot be identified (Valent et al., 2005). In addition to mediator release, mast cells can cause symptoms related to organ infiltration. Hepatic and splenic involvement has been reported to occur in patients with all variants of systemic disease (Mican et al., 1995). In a case series of 26 patients, 45% of patients had hepatomegaly and 50% had splenomegaly (Webb et al., 1982). The most common liver abnormality is an elevated serum alkaline phosphatase, but transaminases may also be elevated. Elevated alkaline phosphatase has been associated with liver enlargement and extent of fibrosis, but may also be caused by bone involvement in some patients. Fractionation of alkaline phosphatase into isoenzymes should be done to clarify the enzyme source. The most serious complication of hepatic involvement in mastocytosis is portal hypertension and ascites, which result from mast cell infiltration and fibrosis. The most frequent finding on liver biopsy is increased portal fibrosis and prominent mast cell infiltrates in portal spaces (Horny et al., 1989). Inflammatory changes with focal necrosis or cirrhosis have also been reported (Jensen, 2000). Splenomegaly is more common in patients with aggressive mastocytosis. Histology shows a thickened capsule
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due to fibrosis with nodular areas in the parenchyma (Horny et al., 1992b). Extramedullary hematopoiesis may be evident as well. Mast cell infiltration shows two distinct patterns: diffuse infiltration involving the cords and sinuses in the red pulp and focal infiltration in the white pulp. Hematologic abnormalities may occur in patients with all subtypes of disease. Anemia is the most common abnormality, occurring in 30–50% of patients. Thrombocytopenia and leucopenia have been observed in 20–30%, while leukocytosis occurs in about 25%. Monocytosis occurs in about 15% of patients, while lymphocytosis and thrombocytosis occur rarely. Eosinophilia can be found in up to 40% of patients with SM, and this subset of disease is sometimes referred to as SM‐eo. It is important to distinguish this from FIP1L1/PDGFRa‐associated disease (myeloproliferative HES—discussed later) since effective treatment is available for the latter disease. In severe disease, mast cells may be found in peripheral blood. Often these have the appearance of atypical monocytes with scattered basophilic granules and dysplasia. Mast cell‐specific stains may aid in identification of these cells. Bone marrow infiltration with mast cells may induce bone changes that produce radiographically detectable lesions in up to 70% of patients (Parker, 2000) and associated abnormalities on bone scan (Avila et al., 1998). The most commonly reported radiographic abnormality is diffuse osteopenia. Both lytic and sclerotic lesions have also been described. Back pain secondary to osteoporosis with vertebral compression fractures may be a presenting feature of systemic mastocytosis (Rafii et al., 1983). Even in asymptomatic patients, radiographic changes may be seen including osteopenic, lytic, or sclerotic changes. Bone scans show multifocal abnormalities and may show diffuse increased uptake. Lymphadenopathy has been reported in up to 60% of patients with systemic mastocytosis (Horny et al., 1992a; Metcalfe, 1991b). Central or peripheral adenopathy may occur due to mast cell infiltration. Infiltration may be focal or diffuse with partial or total destruction of the normal architecture of the lymph node and with eosinophilia, fibrosis, and even extramedullary hematopoiesis associated with the infiltrates (Mekori, 2000). 4.4.2.1. Indolent Systemic Mastocytosis Indolent systemic mastocytosis (ISM) is the most frequently diagnosed variant of SM. The disease is characterized by extracutaneous mast cell hyperplasia with or without cutaneous involvement. ISM is typically not associated with significant organomegaly or organopathy and the prognosis tends to be favorable. Symptoms resulting from mediator‐ related mast cell degranulation are often the presenting complaint (Austen, 1992; Castells, 2004; Castells and Austen, 2002). Episodes of recurrent severe anaphylaxis have been described in some patients (Florian et al., 2005). Mast
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cell infiltrates can invariably be demonstrated in the bone marrow and may also be detected in other organs, including the liver, lymph nodes, spleen, and gastrointestinal tract (Horny et al., 1992a,b; Metcalfe, 1991b). In most cases, clonal mast cells express CD2 and/or CD25 surface markers and contain the c‐Kit mutation D816V (Feger et al., 2002; Longley et al., 1996, 1999). The serum tryptase concentrations are most often over 20 ng/ml (Schwartz, 2001; Sperr et al., 2002c). Smoldering mastocytosis is a subvariant of ISM (Akin et al., 2001; Hauswirth et al., 2002; Jordan et al., 2001; Valent et al., 2002). Patients with smoldering disease, by definition, manifest two or more ‘‘B findings’’ as defined by the WHO (Table 5). These ‘‘B findings’’ are bone marrow infiltration of greater than 30% mast cells (dense infiltrates), serum tryptase levels >200 ng/ml, signs of myelodysplasia, or myeloproliferation in the bone marrow without significant cytopenias, and palpable organomegaly (hepato‐, spleno‐, or lymphadenopathy) (Valent et al., 2001a). Although there is organ infiltration by mast cells or other neoplastic cells, impairment of organ function (‘‘C’’ findings) (Table 5) is not observed in patients with smoldering disease. Patients should be monitored carefully for signs of progression to another category of systemic disease as this subtype has an uncertain prognosis and a variable clinical course (Akin et al., 2001; Hauswirth et al., 2002; Jordan et al., 2001; Valent et al., 2002). 4.4.2.2. Aggressive SM Aggressive SM (ASM), a rare subvariant of SM, is characterized by a rapidly progressive course involving marrow infiltration followed by infiltration of the gastrointestinal tract, spleen, liver, and lymph nodes. According to WHO criteria, the presence of one or more ‘‘C findings’’ serves to distinguish ASM from ISM or SSM (Table 5). ASM is characterized by organopathy resulting from pathologic infiltration of various organs by neoplastic mast cells (Metcalfe, 1991a; Valent et al., 2001a, 2003a). Almost any organ may be involved but the most commonly affected are the bone marrow, liver, spleen, lymph nodes, and GI tract. Patients may demonstrate one or more of the following clinical characteristics (C findings): (1) bone marrow dysfunction with significant cytopenias; (2) impairment of liver function due to inflammatory cell infiltration (transaminitis, ascites, and/ or portal hypertension); (3) significant areas of osteolysis or severe diffuse osteopenia with pathologic fractures and, in some cases, elevated levels of serum calcium and alkaline phosphatase, as well as an elevated LDH; (4) malabsorption with weight loss due to infiltration of the gastrointestinal tract; and (5) splenomegaly with hypersplenism. In some cases, eosinophilia and lymphadenopathy may be prominent features, as well. Lymph node
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biopsies may show a hyperplastic process, suggestive of a lymphoproliferative disorder (Horny et al., 1992a; Mekori, 2000; Metcalfe, 1991b). The histology of the bone marrow in ASM may show a variable degree of infiltration. Bone marrow aspirates may reveal major mast cell atypia with a significant percentage (>20%) of mast cells exhibiting bi‐ or multi‐lobed nuclei (Sperr et al., 2001a). The serum tryptase, in some cases, may be very high, indicative of a high mast cell burden. In the majority of patients, bone marrow mast cells express CD2 and CD25 markers and the Kit D816V mutation is identified in some cases (Pignon et al., 1997; Valent et al., 2003a). 4.4.2.3. Systemic Mastocytosis with an Associated Hematologic Clonal Nonmast Cell Lineage Disorder (SM‐AHNMD) A significant proportion of patients with systemic mastocytosis (10–35%) develop an associated hematologic abnormality such as a myeloproliferative disease or myelodysplastic syndrome (Valent et al., 2001c). In order to establish the diagnosis, WHO criteria for both SM and AHNMD must be met. The associated disease is most often a myeloid disorder although lymphoproliferative diseases have been described (Horny et al., 1990, 2004; Lindner et al., 1992; Sperr et al., 2000; Travis et al., 1988a, b; Valent et al., 1999, 2001b). In one series, 18 out of 20 SM cases with AHNMDs were of myeloid origin (Horny et al., 2004). The spectrum of myeloid diseases occurring in this subtype of SM is broad and includes acute myelogenous leukemia, chronic myelomonocytic leukemia, chronic myeloid leukemia, essential thrombocythemia, polycythemia vera, and myelodysplastic syndrome (Hagen et al., 1998; Horny et al., 1997, 2004; Sperr et al., 1998; Valent et al., 2001d, 2003a). Lymphoid malignancies reported include non‐Hodgkins lymphoma, Hodgkin’s disease, multiple myeloma, and monoclonal gammopathy of unclear significance (Hagen et al., 1998; Meggs et al., 1985; Sperr et al., 2000). It is important to accurately determine the extent of systemic mastocytosis as well as the AHNMD, because the current therapeutic recommendation is to treat each disease as a separate entity. The prognosis in this category is determined primarily by the associated hematologic disorder and is often less favorable than in ISM. The molecular pathogenesis and relationship between ASM, SM‐AHNMD, and smoldering ISM remain unclear. In one series, c‐Kit point mutations were detected in 16 out of 20 cases of SM‐AHNMD (Horny et al., 2004). Whether the SM and AHNMD develop from the same neoplastic progenitor cell, or whether the disease represents the evolution of two separate clones that may evolve due to point mutations or genetic instability, requires further clarification. 4.4.2.4. Mast Cell Leukemia Mast cell leukemia (MCL) is extremely rare with a very short survival time (average 6.6 months, range 2–14 months)
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(Dalton et al., 1986; Noack et al., 2004; Travis et al., 1986). MCL is characterized by three features: (1) WHO criteria to diagnose SM are present, (2) mast cells represent more than 20% of all nucleated cells in bone marrow smears, and (3) there is multiorgan failure. The bone marrow typically shows a diffuse, dense infiltration by neoplastic mast cells, with normal bone marrow architecture almost completely replaced by pathological infiltrates. Mast cells are usually immature with blast‐like morphology, and often have multi‐lobed nuclei (Sperr et al., 2001a). Other clinical features include leukocytosis due to an increase in mast cells accompanied by anemia and thrombocytopenia, and a severe coagulation disorder manifested by loss of clotting factors and hyperfibrinolysis. In most cases, mast cells account for more than 10% of blood leukocytes (Dalton et al., 1986; Travis et al., 1986). In occasional patients, pancytopenia is found and mast cells account for less than 10% of blood leukocytes (aleukemic variant of MCL) (Valent et al., 2001a). Patients may complain of mediator‐related symptoms. However, ultimately, weight loss, bone pain, and organomegaly often occur. Extramedullary leukemic infiltrates are most frequently found in spleen (12/18), liver (11/18), and lymph nodes (5/18) (Noack et al., 2004). Often, multiorgan failure develops over weeks to months (Baghestanian et al., 1996; Efrati et al., 1957; Torrey et al., 1990). Serum tryptase levels are often significantly elevated, suggesting a high burden of mast cells. Most patients appear to have normal cytogenetics (Dalton et al., 1986; Le Cam et al., 1997; Noack et al., 2004; Pauls et al., 1999), but one case of a translocation between chromosomes 16 and 10 present in the cell line HMC‐1 derived from a patient with MCL has been described (Butterfield et al., 1988). Some patients with MCL have been found to have c‐Kit mutations at codon 816 (Travis et al., 1986). 4.4.2.5. Mast Cell Sarcoma (MCS) Mast cell sarcoma (MCS) is an exceedingly rare form of mastocytosis that has only been documented in a limited number of cases (Chott et al., 2003; Horny et al., 1986; Kojima et al., 1999). The disease is defined by a local destructive (sarcoma‐like) growth of a tumor consisting of highly atypical immature mast cells, similar in morphology to those seen in MCL. Tumors may be located at unusual organ sites including the larynx, ascending colon, and intracranial sites (Guenther et al., 2001; Horny et al., 1986; Kojima et al., 1999). A leukemic phase may occur in this disease variant (Horny et al., 1986). 4.4.2.6. Extracutaneous Mastocytoma Extracutaneous mastocytoma is a localized benign tumor consisting of mature mast cells. There is no systemic involvement as in MCS. Unlike mastocytomas of the skin, mastocytomas in extracutaneous organs are extremely rare. Most reported cases of this disease
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variant have involved the lungs (Kudo et al., 1988; Mylanus et al., 2000). An important differentiating feature of extracutaneous mastocytosis in comparison to MCS is the lack of an aggressive and destructive growth pattern. 4.4.2.7. Hypereosinophilic Syndrome and Mastocytosis A subgroup of patients with idiopathic hypereosinophilic syndrome (HES) have been described with elevated serum tryptase, dramatic male predominance, increased scattered atypical marrow mast cells, and imatinib‐responsiveness, often referred to as myeloproliferative HES (MP‐HES) (Klion et al., 2003, 2004). The question has arisen whether this disease is distinct from a primary mast cell disorder with eosinophilia (SM‐eo) (Bain, 2004b; Gilliland et al., 2004a; Klion et al., 2003; Pardanani et al., 2003b). The identification of the FIP1L1/ PDGFRa (F/P) fusion gene by nested RT‐PCR (unfortunately, the interstitial deletion that is responsible for generation of this fusion gene is not visible by standard cytogenetics) has provided a means to identify most but not all patients with this imatinib‐responsive disease (Cools et al., 2003; Gotlib et al., 2004). The presence of the FIP1L1/PDGFRa fusion gene is an accurate predictor of response to imatinib treatment (Gotlib et al., 2004). The majority of patients with FIP1L1/PDGFRa fusion genes treated with imatinib enter molecular remission, as defined by nested RT‐PCR assays (Gotlib et al., 2004; Klion et al., 2004). MP‐HES appears to be distinct from cases of mastocytosis accompanied by peripheral eosinophilia with codon 816 c‐Kit mutations, which, based on in vitro studies and limited clinical experience, are expected to be imatinib‐unresponsive. Certain clinical features in some patients with MP‐HES including endomyocardial fibrosis and mucosal ulcerations are not observed in SM‐eos, although there is clinical overlap in other cases (Bain, 2004a). Patients with systemic mastocytosis, in contrast, have clinical signs and symptoms of mast cell disease including mediator release symptoms, and manifest characteristic marrow pathology showing dense aggregates of mast cells or spindle‐shaped mast cells located in peritrabecular and perivascular locations. This is opposed to the diffusely scattered spindle‐shaped mast cells observed in MP‐HES (Castells, 2004; Horny and Valent, 2001, 2002). The majority of patients with SM‐eo have codon 816 c‐Kit mutations in bone marrow aspirate samples (Pardanani et al., 2003a). The FIP1L1/PDGFRa fusion gene has not been found to be present in this patient population (Pardanani et al., 2003b). Currently, differentiation of these entities for therapeutic reasons must be based on the combination of the above clinical and pathological distinctions as well as analysis for the F/P fusion gene and codon 816 c‐Kit mutations. As more information about these diseases is gathered, further clarification of the relationship between systemic mastocytosis and MP‐HES may be possible.
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5. Prognosis and Predictive Factors The prognosis for a given patient depends both on age of onset as well as category of disease. For instance, cutaneous mastocytoma in children usually has a favorable outcome and often regresses spontaneously around the time of puberty. Although the literature states that approximately 50% of children with UP experience complete regression of their disease by adolescence, an exact estimate is not available. In adults, CM rarely regresses and is often associated with SM. Patients who present with cutaneous disease, flushing, or limited extra‐cutaneous organ involvement usually have an indolent course and experience no impact of the disease on their survival. It is unusual to witness ISM progress to a more severe pattern, such as SM‐AHNMD or ASM. Patients in the indolent categories have a good prognosis. In most cases, patients with indolent disease gradually accrue more mast cells as symptoms progress. Such patients, however, are usually managed successfully for decades using medications that provide symptomatic relief. Patients with ASM have a much less optimistic prognosis and may survive for only a few years. The prognosis in cases of SM‐AHNMD usually depends on the course of the associated hematological non‐mast cell disease. MCL and MCS have the worst prognosis, with an average life expectancy of approximately 6 to12 months. A prospective univariate analysis of 46 patients with SM identified elevated lactate dehydrogenase (LDH) levels, late age of onset, and the presence of an associated hematologic disease as indicators of a less favorable prognosis (Lawrence et al., 1991). In multivariate analysis, late age of onset and elevated LDH remained predictive of a poor prognosis. A few studies have attempted to correlate surrogate disease markers to clinical severity and prognosis in SM. In a study of 29 patients with SM, IL‐ 6 levels correlated with disease category, severity of bone marrow pathology, organomegaly, and extent of skin involvement (Brockow et al., 2005). In another study, levels of soluble Kit and interleukin‐2‐receptor alpha chain were found to correlate with serum tryptase levels and bone marrow pathology (Akin et al., 2000). The presence of a polymorphism in the IL‐4 receptor (Q576R) was found more frequently in mastocytosis patients with disease limited to the skin, suggesting that this polymorphism may mitigate disease expression and confer a better prognosis (Daley et al., 2001). 6. Treatment Management of patients within all subtypes of mastocytosis includes counseling of patients and care providers, avoidance of factors triggering mediator release, treatment of acute episodes of systemic hypotension, management of chronic
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symptoms, and, in certain instances, cytoreductive therapy in an attempt to treat sequelae of organ infiltration by mast cells. 6.1. Management of Mediator‐Release Symptoms There are currently no generally effective mast cell ablative therapies or mast cell stabilizing drugs. Current treatments such as interferon and cladribine exhibit variable response rates and responses are often partial and/or unsustained (Casassus et al., 2002; Hauswirth et al., 2004; Kluin‐Nelemans et al., 2003). Imatinib use in patients with aggressive systemic mastocytosis who have codon 816 mutations is not recommended. Therefore, the treatment of mastocytosis is usually focused on symptomatic therapy. There is no evidence that symptomatic therapy alters the natural history of the disease. The choice of therapy is based on patient symptoms and on the category of the disease. A summary of mast cell mediator‐related symptoms and suggested medications for symptom management are listed in Table 8. The effects of histamine released from mast cells are mediated through H1, H2, and H3 receptors. Therefore, the mainstay of treatment for most patients with mastocytosis is antihistamines, although rarely is total relief of symptoms achieved. H1 antihistamines such as hydroxyzine and diphenhydramine are used to control tone and permeability of the vascular bed as well as smooth muscle tone (Valent et al., 2003b). In cases where sedation is a dose‐limiting side effect, newer non‐sedative antihistamines are useful. Addition of an H2 antihistamine such as ranitidine, cimetidine, or famotidine is sometimes useful to control pruritis and wheal formation in patients where H1 antihistamines alone are ineffective, and H2 antihistamines have been useful to manage gastritis and peptic ulcer disease secondary to excess gastric acid secretion. A proton pump inhibitor such as omeprazole may also help to decrease diarrhea in addition to controlling gastric acid hypersecretion (Valent et al., 2005). Anticholinergics are sometimes useful in controlling diarrhea (Achord and Langford, 1980). Aspirin has been used in some patients to treat flushing, tachycardia, and syncope. However, aspirin must be used with caution, as it may cause vascular collapse in some patients with mastocytosis and may also exacerbate peptic ulcer disease. Anti‐leukotrienes are effective in some patients in controlling symptoms of flushing, diarrhea, and abdominal cramping (Valent et al., 2005). Studies have suggested that oral cromolyn at fairly high doses may decrease abdominal symptoms and may be beneficial in relieving headaches and improving cognitive abilities (Alexander, 1985; Frieri et al., 1985; Horan et al., 1990; Soter et al., 1979). Malabsorption and ascites may be relieved by the use of steroids (Metcalfe, 1991a). Therapeutic doses of oral glucocorticoids (oral prednisone 40–60mg/day) usually result in symptom
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Table 8 Therapeutic Considerations Pruritis H1 and H2 antihistamines Consider topical glucocorticoids Consider PUVA for refractory symptoms Hypotension/anaphylaxis Intramuscular epinephrine For attempted prophylaxis in patients with frequent life‐threatening episodes consider scheduled H1 and H2 antihistamines þ/ glucocorticoids Recurrent flushing, abdominal pain, diarrhea H1 and H2 antihistamines, consider leukotriene antagonists, consider NSAIDS Peptic ulcer disease/GERD H2 antihistamines þ/ proton pump inhibitor Abdominal cramping H2 antihistamines þ/ leukotriene antagonists Diarrhea Proton pump inhibitor þ/ leukotriene antagonist þ/ anticholinergics Malabsorption Consider sodium cromolyn, consider glucocorticoids Ascites Glucocorticoids, consider portocaval shunt, consider cladribine or interferon‐a Osteopenia/osteosclerosis Calcium supplementation þ/ vitamin D Bisphosphonates Consider interferon‐a in severe osteoporosis at risk for pathologic fracture or radiation therapy for severe localized bone pain SM‐AHNMD Consider appropriate treatment of the associated non‐mast cell lineage disorder, if indicated Manage SM based on the extent of mast cell infiltration Smoldering SM Consider interferon‐a Consider splenectomy Aggressive SM Consider interferon‐a or cladribine Consider splenectomy Consider bone marrow transplantation if HLA‐matched sibling Consider investigational trial Supportive care for complications of pancytopenia (Continued)
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Table 8 (Continued) MCL Consider interferon‐a with polychemotherapy Consider investigational trial Supportive care for bleeding secondary to coagulopathy Mast cell sarcoma Consider interferon‐a with polychemotherapy Consider local radiation therapy Consider bone marrow transplantation if HLA‐matched sibling Consider investigational trial
improvement in about 10 to 21 days. Subsequently, steroids can sometimes be dose‐adjusted by a gradual taper to 15 to 20 mg every other day (Genovese et al., 1995; Marone et al., 1995). Patients with refractory ascites and portal hypertension represent a management challenge that is associated with a poor prognosis, although it has been suggested that certain patients may benefit from a porto‐caval shunt (Bonnet et al., 1987; Fonga‐Djimi et al., 1995). Musculoskeletal pain is seen in approximately 25% of patients with systemic disease (Valent et al., 2003b). While traditional pain relievers such as aspirin and NSAIDs may be effective, caution should be used in assuring that the patient is not aspirin sensitive. It is important to note that despite use of multiple medications, it may be difficult to adequately relieve symptoms in some patients. Diagnosis and management of osteoporosis must be considered when appropriate. Treatment should include calcium and vitamin D supplementation, estrogen replacement in postmenopausal women, and consideration of bisphosphonates (Valent et al., 2003b). Use of cytoreductive or radiation therapy has been advocated in certain patients with large osteolytic areas or fractures. Systemic hypotension may be seen in all categories of mastocytosis (Gonera et al., 1997; Horan and Austen, 1991; Walton, 1989). Acute therapy includes intramuscular epinephrine and support of hemodynamic function. Patients and caregivers should be instructed in the use of an auto‐injector (Epi‐Pen) for emergent situations and should have this available at all times. Wearing a medical alert bracelet or necklace is recommended. After receiving epinephrine, emergency medical services should be contacted since treatment of refractory hypotension and shock requires fluid resuscitative methods and additional pharmacologic intervention. The addition of both H1 and H2 antihistamines, along with glucocorticoids (in severe cases), is recommended to prevent or ameliorate a delayed response or further episodes of hypotension.
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6.2. Cytoreductive Therapies To date, no standard therapy for patients with ASM has been defined. Cytoreductive treatment should be considered in patients with SM who have severe osteoporosis and are at risk of pathologic fractures, in some cases of SM‐ AHNMD, and in patients with ASM and MCL (Table 8) (Escribano et al., 2002; Valent et al., 2003b, 2005). 6.2.1. Interferon Alpha (INF‐a) Interferons (IFNs) are a family of glycoproteins which have multiple effects on cytokine production and regulation of tumor oncogenes (reviewed in Clemens (Clemens, 2003)). The specific mechanism of anti‐tumor activity is unclear but IFNs are known to produce direct anti‐proliferative effects and to inhibit angiogenesis. Interferon‐a is physiologically produced by a variety of cells upon viral infection. Interferon‐a, a non‐leukemogenic cytotoxic agent, has demonstrated considerable efficacy in certain myeloproliferative disorders, including chronic myelogenous leukemia (The Italian Cooperative Study Group on Chronic Myelogenous Leukemia, 1994; Bonifazi et al., 2001; Hehlmann et al., 1994; Ohnishi et al., 1995, 1998). IFN‐a was first reported to show efficacy in a patient with aggressive mastocytosis (Kluin‐Nelemans et al., 1992). Subsequent reports in the literature have documented variable responses to treatment of systemic mastocytosis with INF‐a, often combined with glucocorticoids (Butterfield, 1998; Czarnetzki et al., 1994; Fiehn et al., 1995; Hennessy et al., 2004; Hubner et al., 1997; Kluin‐Nelemans et al., 1992; Lehmann et al., 1996; Pulik et al., 1994; Simon et al., 2004; Valent et al., 2003a; Weide et al., 1996; Worobec et al., 1996). INF‐a has been found to be efficacious in some patients to control pruritus, diarrhea, and abdominal pain (Czarnetzki et al., 1994; Kolde et al., 1995). Although INF‐a‐2b has not been found to significantly reduce the extent of mast cell infiltration of the bone marrow (Czarnetzki et al., 1994), some patients with mastocytosis and severe osteopenia unresponsive to other treatment may benefit from a trial of INF‐a (Lehmann et al., 1996; Weide et al., 1996). The current recommendation is to limit use of this agent to patients with high mast cell burden or with severe side effects of osteoporosis, such as collapse of vertebral bodies (Escribano et al., 2002). The formidable side effects of interferon including fever, myalgias, bone pain, anorexia, depression, and fatigue may limit use of this agent (Hauswirth et al., 2004). 6.2.2. 2‐Chlorodeoxyadenosine (2‐CDA) Cladribine or 2‐CDA is a purine nucleoside analogue which, when phosphorylated by deoxycytidine kinase, accumulates intracellularly as 2‐chlorodeoxyadenosine 50 triphosphate and inhibits DNA synthesis (Goodman et al., 2003). It
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is active against both resting and dividing lymphocytes. Cladribine is approved by the Food and Drug Administration for the treatment of hairy‐cell leukemia. It also has activity in CLL, NHL, Waldenstrom macroglubulinaemia, cutaneous T cell lymphoma, AML, and CML. The therapeutic activity of cladribine was first evaluated in a patient with interferon alpha‐resistant systemic mastocytosis (Tefferi et al., 2001). After four cycles of treatment with 2‐CDA, skin lesions resolved and there was marked reduction in bone marrow mast cell numbers. At one year follow‐up, the patient was free of clinical symptoms and the bone marrow biopsy revealed only minimal residual disease (Tefferi et al., 2001). Subsequent case reports have documented the successful use of cladribine in inducing clinical remissions in patients with more aggressive forms of mastocytosis (Escribano et al., 2002; Kluin‐Nelemans et al., 2003; Pardanani et al., 2004a). In a case series of nine patients who received six courses of therapy, all nine showed responses concerning symptoms and decreases in serum tryptase. None, however, achieved a complete response (Kluin‐ Nelemans et al., 2003). Side effects were mostly related to bone marrow suppression (Kluin‐Nelemans et al., 2003). Cladribine may prove to be a reasonable therapeutic approach in treating patients with aggressive forms of mastocytosis who have INF‐a resistant disease. Nevertheless, because cladribine may induce both pancytopenia and immunosuppression, and its potential oncogenicity remains largely unknown (Goodman et al., 2003), its use in aggressive forms of systemic mastocytosis should be approached with caution. 6.2.3. Other Chemotherapy A variety of chemotherapeutic regimens have been used in attempts to achieve control of symptoms and to control disease progression in ASM and SM‐AHNMD and MCL (reviewed in Worobec et al. (2000)). In general, patient responses depended on the prognosis of the underlying disease and most remissions were only partial and short‐lived (Schwartz et al., 1995). Cytoreductive drugs that have been used include cytosine arabinoside (ARA‐ C), doxorubicin, daunorubicin, and vincristine used alone or in combination (Travis et al., 1986; Valent et al., 2003a; Worobec, 2000). 6.2.4. Imatinib Tyrosine Kinase Inhibitor (STI571; GleevecW) Imatinib is a tyrosine kinase inhibitor that inhibits the kinase activity of c‐abl, bcr‐abl, and platelet‐derived growth factor receptor tyrosine kinases as well as Kit (Druker, 2004). Imatinib has proven effective for treatment of the chronic phase of chronic myelogenous leukemia, for myeloproliferative HES, and for treatment of most GIST patients that harbor c‐Kit mutations (Bono
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et al., 2004; Cools et al., 2004; Druker, 2004; Duensing et al., 2004; Klion et al., 2003, 2004). The sensitivity of Kit mutants to imatinib depends on the nature of the mutation. Imatinib has been shown to suppress proliferation of an HMC‐1 human mast cell line carrying the wild‐type codon at 816 but not the mutated 816 codon (Akin et al., 2003). Growth of COS cells expressing wild‐type Kit was inhibited by imatinib at 0.1 mM, but doses of imatinib as high as 10 mM did not suppress growth of COS cells expressing D816V mutated Kit (Ma et al., 2002). Imatinib has been reported to result in histologic or clinical responses in 5 out of 12 patients with systemic mastocytosis (Pardanani et al., 2003a). Although these patients were reported to lack a codon 816 or juxtamembrane mutation, it is not clear whether they had any distinguishing histopathologic changes in their bone marrow mast cells or carried other c‐Kit mutations. In fact, three of these patients showed dramatic and complete responses and had peripheral blood eosinophilia and other characteristics of patients with MP‐HES (Klion et al., 2003; Pardanani et al., 2003a). The FIP1L1/ PDGFRa fusion gene associated with imatinib‐responsive MP‐HES had not been described at the time of treatment of this case series of 12 patients (Cools et al., 2003). Additional limited clinical data corroborates in vitro studies suggesting that imatinib will prove to be ineffective in the majority of patients with SM associated with c‐Kit D816V mutations (Musto et al., 2004a,b). Imatinib, however, has been shown to dramatically decrease the bone marrow mast cell burden, serum tryptase level, and clinical symptoms in a patient with the (F522C) novel mutation in the transmembrane region of Kit (Akin et al., 2004). Therefore, this agent may be effective in patients with unusual mutations in Kit. 6.2.5. Cyclosporin A Cyclosporin A in combination with methylprednisolone has been reported to be of benefit in a patient with ASM (Kurosawa et al., 1999). However, in another patient with ASM, this treatment resulted in a partial response, and was associated with severe infectious complications (Escribano et al., 2002). 6.2.6. Splenectomy Splenectomy has been used in the management of patients with ASM or SM‐ AHNMD (Friedman et al., 1990; Grundfest et al., 1980; Smith et al., 1987a). In patients with massive splenomegaly, splenectomy decreases the mast cell burden and often improves cytopenias, facilitating the subsequent use of myelosuppressive agents if necessary. With splenectomy, survival has been reported to increase by an average of 12 months (Friedman et al., 1990).
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Splenectomy in patients with systemic mastocytosis should be considered a high‐risk surgical procedure for a variety of reasons. Some patients with SM have impaired liver function which may be associated with abnormal coagulation parameters, increasing the risk of bleeding peri‐operatively. In addition, the high body mast cell burden sometimes is associated with a massive release of mediators during surgery. Apart from an adequate anesthetic protocol, a careful study of blood coagulation parameters pre‐, intra‐, and post‐operatively is mandatory, with the replacement of deficient coagulation factors as necessary. In addition, serum tryptase should be carefully monitored throughout the peri‐surgical time period. 6.2.7. Bone Marrow Transplantation Bone marrow transplantation has traditionally been reserved for those patients with advanced and potentially fatal forms of SM‐AHNMD and ASM. There is limited experience with this procedure in SM. The reported responses have ranged from favorable with engraftment and prolongation of life, to poor in patients with advance disease, with transplant‐related complications such as graft‐versus host disease and death from infection (Fodinger et al., 1994; Przepiorka et al., 1998; Ronnov‐Jessen et al., 1991; Spyridonidis et al., 2004). Non‐myeloablative bone marrow transplantation has been performed in select patients. This treatment approach has proven to cause less transplant‐related mortality than myeloablative transplantation and is designed to take advantage of the graft versus tumor effect for further reduction of malignant cells (Barrett, 1997; Barrett and Childs, 2000; Barrett and Malkovska, 1996; Barrett and van, 1997). 7. Supportive Care and Long‐Term Management 7.1. Counseling of Patients and Providers Complete information about mastocytosis, including guidelines for avoidance of triggering factors and risks associated with systemic hypotension, should be given to patients and family members. Instructions to doctors and other care providers may also include information on pre‐medication for general anesthesia and radiologic studies with contrast media and inpatient treatment of anaphylaxis in patients at risk. Avoidance of known and possible triggering factors is a major goal in the management of mastocytosis. The exact percentage of patients at risk for significant systemic reactions is unknown. Despite this, it is generally accepted that the risk for systemic hypotension is higher than in the non‐mastocytosis population. Pharmacologic agents that may cause mast cell degranulation (Table 5) should be
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used with caution or after proper desensitization procedures when appropriate. It is advisable, whenever possible, to use a drug the patient has tolerated in the past. If a new medication is to be used, pre‐medication with H1 and H2 antihistamines should be considered, as well as administration of a test dose of the drug in an intensive care unit (ICU) or a monitored setting where skills in intubation and emergency treatment are available in order to prevent an adverse outcome should a systemic reaction occur. 7.2. General Anesthesia and Mastocytosis It is clear that some drugs used in general anesthesia may induce mast cell mediator release (Marone and Stellato, 1992; Stellato and Marone, 1995; Stellato et al., 1991). However, the exact incidence of serious reactions to general anesthesia in mastocytosis is not known. In addition, there appears to be a great variability in patient response to anesthesia. However, general anesthesia is generally considered a procedure with a greater risk of adverse events in patients with systemic mastocytosis. Severe reactions including systemic hypotension, anaphylactoid reactions, and coagulopathy, in some instances resulting in death, have been reported (Coleman et al., 1980; Greenblatt and Chen, 1990; Scott et al., 1983; Vaughan and Jones, 1998). A number of protocols aiming at preventing anesthetic complications have been proposed (Borgeat and Ruetsch, 1998; Worobec, 2000). Since b‐adrenergic blockers interfere with epinephrine, their use is generally contraindicated for patients with systemic mastocytosis undergoing surgery (reviewed in reference [Worobec, 2000]). A close communication between anesthesiologists, surgeons, and intensivists is mandatory in this situation. Samples to determine serum tryptase levels should be obtained and blood coagulation parameters monitored preoperatively and during surgery if suspected mast cell degranulation events occur. 7.3. Pregnancy in Systemic Mastocytosis Although our understanding of mastocytosis at the molecular level has increased dramatically over the past few decades, information regarding how mastocytosis may affect the clinical features and outcomes of pregnancy is limited. In a retrospective study of 87 female patients with the diagnosis of ISM, the clinical courses of 8 women with a total of 11 pregnancies have been reviewed (Worobec et al., 2000). These women were patients in the National Institutes of Health during the period from 1984 to 1998, although some had conceived before 1984. The most common symptoms reported by these patients were pruritus and/or flushing and abdominal symptoms. One patient required daily oral corticosteroids for treatment of malabsorption. In most
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cases, the only treatment required prior to pregnancy was H1 and H2 antihistamines. Half of these women required medication during pregnancy to control symptoms. A few patients experienced worsening symptoms during pregnancy and this tended to occur in the first and second trimesters. There were no life‐threatening manifestations of mastocytosis in the 11 pregnancies, either during labor or during the peripartum and postpartum periods. All infants had normal Apgar scores, although three had low birth weights. None of the children developed UP or systemic mastocytosis during the follow‐up period. The only adverse outcome in an infant was hydrocephalus at birth. 8. Future Therapy Since there is no specific treatment modality that is curative for mastocytosis, targeting of the constitutive kinase activity of mutated Kit in systemic mastocytosis has become a focus, as small molecular weight inhibitors of signal transduction become available for clinical use (Krause and Van Etten, 2005). As discussed earlier, imatinib inhibits autophosphorylation of Kit carrying a juxtamembrane mutation but does not appear to be efficacious for codon 816‐mutated Kit. Reports of resistance to kinase domain codon D816V mutations to imatinib have prompted in vitro studies designed to assay the efficacy of novel tyrosine kinase inhibitors. In one study, using the murine hematopoietic cell line, Ba/ F3, transformed with Kit D816V and D615Y, PKC412, a novel staurosporine‐ derived tyrosine kinase inhibitor, proved to inhibit autophosphorylation of Kit and activation of downstream effectors Stat5 and Stat3 (Growney et al., 2005b). PKC412 also caused growth inhibition of cells transformed with c‐Kit D816V and D816Y at an IC of 30–40 nM (Growney et al., 2005a). The clinical efficacy of PKC412 was assessed in a patient with MCL with an associated myelodysplastic/myeloproliferative disorder (Gotlib et al., 2005). The patient exhibited a partial response, but died after three months of therapy due to disease progression, suggesting that clinical efficacy of PKC412 may be limited by clonal evolution in the advanced leukemic phase of disease. Further studies aimed at assessing the clinical efficacy of this agent in aggressive systemic mastocytosis are in progress. Another novel agent, BMS‐354825, an orally available dual SRC/ABL kinase inhibitor, active against multiple imatinib‐resistant Bcr‐Abl isoforms, has shown efficacy in PHþ CML patients in chronic phase with hematologic progression or intolerance to imatinib in a phase I study (Sawyers et al., 2004; Shah et al., 2004b). The activity of BMS‐354825 was assessed using HMC‐1560 and HMC‐1560/816 carrying activating c‐Kit mutations in the juxtamembrane (560) and tyrosine kinase (816) domains, respectively (Shah et al.,
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2004a). BMS‐354825 led to growth inhibition of both cell lines with IC50 of <0.01 mM for the juxtamembrane mutant and 0.1–1 mM for the combined juxtamembrane and tyrosine kinase domain mutated cell line (Shah et al., 2004a). AMN107, another novel agent developed using a rational drug design strategy, shows 20‐fold improved affinity for wild‐type Bcr/Abl, translating into improved inhibitory activity against most of the common BCR‐ABL mutants (O’Hare et al., 2005). AMN107 shows affinity for Kit as well, although its improved binding affinity for Bcr/Abl is not seen with Kit (O’Hare et al., 2005). A novel tyrosine kinase inhibitor, MLN518, shown to be well‐tolerated in phase I clinical trials in AML, proved useful in inhibiting cell proliferation, phosphorylation of Kit and Stat3 in cell lines containing juxtamembrane, and kinase domain mutated Kit (Corbin et al., 2004). Two ATP‐based inhibitors, AP23464 and AP23848, proved to not disrupt hematopoetic cell growth at concentrations that inhibited activation loop mutants of Kit (Corbin et al., 2004). In a murine model, AP23848 inhibited the activation loop mutant Kit phosphorylation as well as tumor growth (Corbin et al., 2005). A novel NF‐kB inhibitor, IMD‐0354, has been shown to restrain factor‐ independent proliferation of several mast cell lines with kinase domain and juxtamembrane domain Kit mutations but does not affect growth of normal mast cells (Tanaka et al., 2005). Observations from this study suggest that compounds that interfere with NF‐kB signaling might prove to have therapeutic potential in SM. 17‐allylamino‐17‐demethoxygeldanamycin (17‐AAG) is a benzoquinoid ansamycin antibiotic, which binds to heat shock protein 90 (hsp90) and promotes the degradation of a variety of client proteins important in proliferation and survival of malignant cells. Treatment of the mast cell line HMC‐1.2 with 17‐ AAG showed significantly decreased levels of mutant Kit protein, Kit activity, and activity of downstream signaling molecules AKT and STAT3 following drug exposure (Fumo et al., 2004). In addition, neoplastic mast cells isolated from patients with mastocytosis were selectively sensitive to 17‐AAG compared to the mononuclear fraction, suggesting that 17‐AAG may be effective in the treatment of c‐Kit‐related diseases (Fumo et al., 2004). While some of these newly developed inhibitors have many hurdles to overcome before becoming clinically useful agents for systemic mastocytosis, the fact that understanding the molecular pathogenesis of CML has translated into the development of new treatments for this disease, demonstrates the speed at which drug development may occur in this setting. A potentially powerful approach in the future may prove to be combination therapy with targeted agents which have different mechanisms of action (O’Hare et al., 2005).
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9. Conclusions Systemic mastocytosis is a rare heterogeneous disorder characterized by many diverse signs and symptoms. The diagnosis and treatment of mast cell disease have been challenging clinicians for many years. Major advances have been made in the past two decades defining molecular abnormalities associated with this disease and delineating pathways involved in its pathogenesis. New diagnostic methods have been developed that have improved the ability to identify systemic mastocytosis and its variants. In addition, insights into mast cell biology have provided evidence for involvement of these cells in a variety of pathologic processes. Further studies aimed at identification of the molecular mechanisms underlying phenotypic diversity in systemic mastocytosis are in progress. The prospects of targeted therapy make further definition of mechanisms involved in disease pathogenesis critically important. Acknowledgment This work was supported by the Intramural Research Program of the NIAID at the NIH.
References Achord, J. L., and Langford, H. (1980). The effect of cimetidine and propantheline on the symptoms of a patient with systemic mastocytosis. Am. J. Med. 69, 610–614. Agosti, V., Corbacioglu, S., Ehlers, I., Waskow, C., Sommer, G., Berrozpe, G., Kissel, H., Tucker, C. M., Manova, K., Moore, M. A., Rodewald, H. R., and Besmer, P. (2004). Critical role for Kit‐ mediated Src kinase but not PI 3‐kinase signaling in pro T and pro B cell development. J. Exp. Med. 199, 867–878. Akin, C., Brockow, K., D’Ambrosio, C., Kirshenbaum, A. S., Ma, Y., Longley, B. J., and Metcalfe, D. D. (2003). Effects of tyrosine kinase inhibitor STI571 on human mast cells bearing wild‐type or mutated c‐Kit. Exp. Hematol. 31, 686–692. Akin, C., Fumo, G., Yavuz, A. S., Lipsky, P. E., Neckers, L., and Metcalfe, D. D. (2004). A novel form of mastocytosis associated with a transmembrane c‐Kit mutation and response to imatinib. Blood 103, 3222–3225. Akin, C., and Metcalfe, D. D. (2004). The biology of Kit in disease and the application of pharmacogenetics. J. Allergy Clin. Immunol. 114, 13–19. Akin, C., and Metcalfe, D. D. (2002). Surrogate markers of disease in mastocytosis. Int. Arch. Allergy Immunol. 127, 133–136. Akin, C., Schwartz, L. B., Kitoh, T., Obayashi, H., Worobec, A. S., Scott, L. M., and Metcalfe, D. D. (2000). Soluble stem cell factor receptor (CD117) and IL‐2 receptor alpha chain (CD25) levels in the plasma of patients with mastocytosis: Relationships to disease severity and bone marrow pathology. Blood 96, 1267–1273. Akin, C., Scott, L. M., and Metcalfe, D. D. (2001). Slowly progressive systemic mastocytosis with high masT cell burden and no evidence of a non‐masT cell hematologic disorder: An example of a smoldering case? Leuk. Res. 25, 635–638.
SYSTEMIC MASTOCYTOSIS
221
Alexander, R. R. (1985). Disodium cromoglycate in the treatment of systemic mastocytosis involving only bone. Acta Haematol. 74, 108–110. Alter, S. C., Kramps, J. A., Janoff, A., and Schwartz, L. B. (1990). Interactions of human mast cell tryptase with biological protease inhibitors. Arch. Biochem. Biophys. 276, 26–31. Arm, J. P., and Lee, T. H. (1993). Sulphidopeptide leukotrienes in asthma. Clin. Sci. (Lond.) 84, 501–510. Arock, M., Schneider, E., Boissan, M., Tricottet, V., and Dy, M. (2002). Differentiation of human basophils: An overview of recent advances and pending questions. J. Leukoc. Biol. 71, 557–564. Asai, K., Kitaura, J., Kawakami, Y., Yamagata, N., Tsai, M., Carbone, D. P., Liu, F. T., Galli, S. J., and Kawakami, T. (2001). Regulation of mast cell survival by IgE. Immunity. 14, 791–800. Austen, K. F. (1992). Systemic mastocytosis. N. Engl. J. Med. 326, 639–640. Avila, N. A., Ling, A., Metcalfe, D. D., and Worobec, A. S. (1998). Mastocytosis: Magnetic resonance imaging patterns of marrow disease. Skeletal Radiol. 27, 119–126. Azizkhan, R. G., Azizkhan, J. C., Zetter, B. R., and Folkman, J. (1980). Mast cell heparin stimulates migration of capillary endothelial cells in vitro. J. Exp. Med. 152, 931–944. Baghestanian, M., Bankl, H., Sillaber, C., Beil, W. J., Radaszkiewicz, T., Fureder, W., Preiser, J., Vesely, M., Schernthaner, G., Lechner, K., and Valent, P. (1996). A case of malignant mastocytosis with circulating mast cell precursors: Biologic and phenotypic characterization of the malignant clone. Leukemia 10, 159–166. Bain, B. (2004a). The idiopathic hypereosinophilic syndrome and eosinophilic leukemias. Haematologica 89, 133–137. Bain, B. J. (2004b). Relationship between idiopathic hypereosinophilic syndrome, eosinophilic leukemia, and systemic mastocytosis. Am. J. Hematol. 77, 82–85. Barnes, P. J., Chung, K. F., and Page, C. P. (1988). Platelet‐activating factor as a mediator of allergic disease. J. Allergy Clin. Immunol. 81, 919–934. Barrett, A. J. (1997). Mechanisms of the graft‐versus‐leukemia reaction. Stem Cells 15, 248–258. Barrett, A. J., and Malkovska, V. (1996). Graft‐versus‐leukaemia: Understanding and using the alloimmune response to treat haematological malignancies. Br. J. Haematol. 93, 754–761. Barrett, A. J., and van, R. F. (1997). Graft‐versus‐leukaemia. Baillieres Clin. Haematol. 10, 337–355. Barrett, J., and Childs, R. (2000). Non‐myeloablative stem cell transplants. Br. J. Haematol. 111, 6–17. Beghini, A., Peterlongo, P., Ripamonti, C. B., Larizza, L., Cairoli, R., Morra, E., and Mecucci, C. (2000). C‐kit mutations in core binding factor leukemias. Blood 95, 726–727. Beghini, A., Tibiletti, M. G., Roversi, G., Chiaravalli, A. M., Serio, G., Capella, C., and Larizza, L. (2001). Germ line mutation in the juxtamembrane domain of the kit gene in a family with gastrointestinal stromal tumors and urticaria pigmentosa. Cancer 92, 657–662. Benhamou, M., Bonnerot, C., Fridman, W. H., and Daeron, M. (1990). Molecular heterogeneity of murine mast cell Fc gamma receptors. J. Immunol. 144, 3071–3077. Benyon, R. C., Robinson, C., and Church, M. K. (1989). Differential release of histamine and eicosanoids from human skin mast cells activated by IgE‐dependent and non‐immunological stimuli. Br. J. Pharmacol. 97, 898–904. Bischoff, S. C., Sellge, G., Lorentz, A., Sebald, W., Raab, R., and Manns, M. P. (1999). IL‐4 enhances proliferation and mediator release in mature human mast cells. Proc. Natl. Acad. Sci. USA 96, 8080–8085. Blechman, J. M., Lev, S., Barg, J., Eisenstein, M., Vaks, B., Vogel, Z., Givol, D., and Yarden, Y. (1995). The fourth immunoglobulin domain of the stem cell factor receptor couples ligand binding to signal transduction. Cell 80, 103–113.
222
JAMIE ROBYN AND DEAN D. METCALFE
Blume‐Jensen, P., Janknecht, R., and Hunter, T. (1998). The kit receptor promotes cell survival via activation of PI 3‐kinase and subsequent Akt‐mediated phosphorylation of Bad on Ser136. Curr. Biol. 8, 779–782. Boesiger, J., Tsai, M., Maurer, M., Yamaguchi, M., Brown, L. F., Claffey, K. P., Dvorak, H. F., and Galli, S. J. (1998). Mast cells can secrete vascular permeability factor/vascular endothelial cell growth factor and exhibit enhanced release after immunoglobulin E‐dependent upregulation of fc epsilon receptor I expression. J. Exp. Med. 188, 1135–1145. Bonifazi, F., de, V. A., Rosti, G., Guilhot, F., Guilhot, J., Trabacchi, E., Hehlmann, R., Hochhaus, A., Shepherd, P. C., Steegmann, J. L., Kluin‐Nelemans, H. C., Thaler, J., Simonsson, B., Louwagie, A., Reiffers, J., Mahon, F. X., Montefusco, E., Alimena, G., Hasford, J., Richards, S., Saglio, G., Testoni, N., Martinelli, G., Tura, S., and Baccarani, M. (2001). Chronic myeloid leukemia and interferon‐alpha: A study of complete cytogenetic responders. Blood 98, 3074–3081. Bonnet, P., Smadja, C., Szekely, A. M., Delage, Y., Calmus, Y., Poupon, R., and Franco, D. (1987). Intractable ascites in systemic mastocytosis treated by portal diversion. Dig. Dis. Sci. 32, 209–213. Bono, P., Krause, A., von, M. M., Heinrich, M. C., Blanke, C. D., Dimitrijevic, S., Demetri, G. D., and Joensuu, H. (2004). Serum KIT and KIT ligand levels in patients with gastrointestinal stromal tumors treated with imatinib. Blood 103, 2929–2935. Borgeat, A., and Ruetsch, Y. A. (1998). Anesthesia in a patient with malignant systemic mastocytosis using a total intravenous anesthetic technique. Anesth. Analg. 86, 442–444. Brizzi, M. F., Zini, M. G., Aronica, M. G., Blechman, J. M., Yarden, Y., and Pegoraro, L. (1994). Convergence of signaling by interleukin‐3, granulocyte‐macrophage colony‐stimulating factor, and mast cell growth factor on JAK2 tyrosine kinase. J. Biol. Chem. 269, 31680–31684. Brockow, K., Akin, C., Huber, M., and Metcalfe, D. D. (2005). IL‐6 levels predict disease variant and extent of organ involvement in patients with mastocytosis. Clin. Immunol. 115, 216–223. Brockow, K., Akin, C., Huber, M., Scott, L. M., Schwartz, L. B., and Metcalfe, D. D. (2002). Levels of masT cell growth factors in plasma and in suction skin blister fluid in adults with mastocytosis: Correlation with dermal masT cell numbers and masT cell tryptase. J. Allergy Clin. Immunol. 109, 82–88. Broudy, V. C., Lin, N. L., Liles, W. C., Corey, S. J., O’Laughlin, B., Mou, S., and Linnekin, D. (1999). Signaling via Src family kinases is required for normal internalization of the receptor c‐Kit. Blood 94, 1979–1986. Butterfield, J. H. (1998). Response of severe systemic mastocytosis to interferon alpha. Br. J. Dermatol. 138, 489–495. Butterfield, J. H., Weiler, D., Dewald, G., and Gleich, G. J. (1988). Establishment of an immature mast cell line from a patient with mast cell leukemia. Leuk. Res. 12, 345–355. Casassus, P., Caillat‐Vigneron, N., Martin, A., Simon, J., Gallais, V., Beaudry, P., Eclache, V., Laroche, L., Lortholary, P., Raphael, M., Guillevin, L., and Lortholary, O. (2002). Treatment of adult systemic mastocytosis with interferon‐alpha: Results of a multicentre phase II trial on 20 patients. Br. J. Haematol. 119, 1090–1097. Castells, M., and Austen, K. F. (2002). Mastocytosis: Mediator‐related signs and symptoms. Int. Arch. Allergy Immunol. 127, 147–152. Castells, M. C. (2004). Mastocytosis: Classification, diagnosis, and clinical presentation. Allergy Asthma Proc. 25, 33–36. Caughey, G. H., Raymond, W. W., and Wolters, P. J. (2000). Angiotensin II generation by mast cell alpha‐ and beta‐chymases. Biochim. Biophys. Acta 1480, 245–257.
SYSTEMIC MASTOCYTOSIS
223
Chang, A., Tung, R. C., Schlesinger, T., Bergfeld, W. F., Dijkstra, J., and Kahn, T. A. (2001). Familial cutaneous mastocytosis. Pediatr. Dermatol. 18, 271–276. Cherner, J. A., Jensen, R. T., Dubois, A., O’Dorisio, T. M., Gardner, J. D., and Metcalfe, D. D. (1988). Gastrointestinal dysfunction in systemic mastocytosis. A prospective study 236. Gastroenterology 95, 657–667. Chott, A., Guenther, P., Huebner, A., Selzer, E., Parwaresch, R. M., Horny, H. P., and Valent, P. (2003). Morphologic and immunophenotypic properties of neoplastic cells in a case of mast cell sarcoma. Am. J. Surg. Pathol. 27, 1013–1019. Church, M. K., and Levi‐Schaffer, F. (1997). The human mast cell. J. Allergy Clin. Immunol. 99, 155–160. Clemens, M. J. (2003). Interferons and apoptosis. J. Interferon Cytokine Res. 23, 277–292. Coleman, J. W. (2002). Nitric oxide: A regulator of mast cell activation and mast cell‐mediated inflammation. Clin. Exp. Immunol. 129, 4–10. Coleman, M. A., Liberthson, R. R., Crone, R. K., and Levine, F. H. (1980). General anesthesia in a child with urticaria pigmentosa. Anesth. Analg. 59, 704–706. Compton, S. J., Cairns, J. A., Holgate, S. T., and Walls, A. F. (1998). The role of mast cell tryptase in regulating endothelial cell proliferation, cytokine release, and adhesion molecule expression: Tryptase induces expression of mRNA for IL‐1 beta and IL‐8 and stimulates the selective release of IL‐8 from human umbilical vein endothelial cells. J. Immunol. 161, 1939–1946. Cools, J., De Angelo, D. J., Gotlib, J., Stover, E. H., Legare, R. D., Cortes, J., Kutok, J., Clark, J., Galinsky, I., Griffin, J. D., Cross, N. C., Tefferi, A., Malone, J., Alam, R., Schrier, S. L., Schmid, J., Rose, M., Vandenberghe, P., Verhoef, G., Boogaerts, M., Wlodarska, I., Kantarjian, H., Marynen, P., Coutre, S. E., Stone, R., and Gilliland, D. G. (2003). A tyrosine kinase created by fusion of the PDGFRA and FIP1L1 genes as a therapeutic target of imatinib in idiopathic hypereosinophilic syndrome. N. Engl. J. Med. 348, 1201–1214. Cools, J., Stover, E. H., Wlodarska, I., Marynen, P., and Gilliland, D. G. (2004). The FIP1L1‐ PDGFRalpha kinase in hypereosinophilic syndrome and chronic eosinophilic leukemia. Curr. Opin. Hematol. 11, 51–57. Corbin, A. S., Demehri, S., Griswold, I. J., Wang, Y., Metcalf, C. A., III, Sundaramoorthi, R., Shakespeare, W. C., Snodgrass, J., Wardwell, S., Dalgarno, D., Iuliucci, J., Sawyer, T. K., Heinrich, M. C., Druker, B. J., and Deininger, M. W. (2005). In vitro and in vivo activity of ATP‐based kinase inhibitors AP23464 and AP23848 against activation‐loop mutants of Kit. Blood 106, 227–234. Corbin, A. S., Griswold, I. J., La, R. P., Yee, K. W., Heinrich, M. C., Reimer, C. L., Druker, B. J., and Deininger, M. W. (2004). Sensitivity of oncogenic KIT mutants to the kinase inhibitors MLN518 and PD180970. Blood 104, 3754–3757. Corless, C. L., Fletcher, J. A., and Heinrich, M. C. (2004). Biology of gastrointestinal stromal tumors. J. Clin. Oncol. 22, 3813–3825. Cutler, R. L., Liu, L., Damen, J. E., and Krystal, G. (1993). Multiple cytokines induce the tyrosine phosphorylation of Shc and its association with Grb2 in hemopoietic cells. J. Biol. Chem. 268, 21463–21465. Czarnetzki, B. M., Algermissen, B., Jeep, S., Haas, N., Nurnberg, W., Muller, K., and Kropp, J. D. (1994). Interferon treatment of patients with chronic urticaria and mastocytosis. J. Am. Acad. Dermatol. 30, 500–501. D’Ambrosio, C., Akin, C., Wu, Y., Magnusson, M. K., and Metcalfe, D. D. (2003). Gene expression analysis in mastocytosis reveals a highly consistent profile with candidate molecular markers. J. Allergy Clin. Immunol. 112, 1162–1170.
224
JAMIE ROBYN AND DEAN D. METCALFE
Daeron, M., Malbec, O., Latour, S., Arock, M., and Fridman, W. H. (1995). Regulation of high‐ affinity IgE receptor‐mediated mast cell activation by murine low‐affinity IgG receptors. J. Clin. Invest. 95, 577–585. Daley, T., Metcalfe, D. D., and Akin, C. (2001). Association of the Q576R polymorphism in the interleukin‐4 receptor alpha chain with indolent mastocytosis limited to the skin. Blood 98, 880–882. Dalton, R., Chan, L., Batten, E., and Eridani, S. (1986). Mast cell leukaemia: Evidence for bone marrow origin of the pathological clone. Br. J. Haematol. 64, 397–406. Davis, B. J., Flanagan, B. F., Gilfillan, A. M., Metcalfe, D. D., and Coleman, J. W. (2004). Nitric oxide inhibits IgE‐dependent cytokine production and Fos and Jun activation in mast cells. J. Immunol. 173, 6914–6920. DeBerry, C., Mou, S., and Linnekin, D. (1997). Stat1 associates with c‐Kit and is activated in response to stem cell factor. Biochem. J. 327(Pt 1), 73–80. Druker, B. J. (2004). Imatinib as a paradigm of targeted therapies. Adv. Cancer Res. 91, 1–30. Duensing, A., Heinrich, M. C., Fletcher, C. D., and Fletcher, J. A. (2004). Biology of gastrointestinal stromal tumors: KIT mutations and beyond. Cancer Invest. 22, 106–116. Echtenacher, B., Mannel, D. N., and Hultner, L. (1996). Critical protective role of mast cells in a model of acute septic peritonitis. Nature 381, 75–77. Efrati, P., Klajman, A., and Spitz, H. (1957). Mast cell leukemia? Malignant mastocytosis with leukemia‐like manifestations. Blood 12, 869–882. Ehrlich, P. (1878). Beitrage zur theoretic and praxis de histologischer farbung University of Leipzig, Leipzig, Germany. Ellis, J. M. (1949). Urticaria Pigmentosa: A report of a case with autopsy. Arch. Pathol. 48, 426. Escribano, L., Akin, C., Castells, M., Orfao, A., and Metcalfe, D. D. (2002). Mastocytosis: Current concepts in diagnosis and treatment. Ann. Hematol. 81, 677–690. Escribano, L., az‐Agustin, B., Bellas, C., Navalon, R., Nunez, R., Sperr, W. R., Schernthaner, G. H., Valent, P., and Orfao, A. (2001). Utility of flow cytometric analysis of mast cells in the diagnosis and classification of adult mastocytosis. Leuk. Res. 25, 563–570. Escribano, L., az‐Agustin, B., Lopez, A., Nunez, L. R., Garcia‐Montero, A., Almeida, J., Prados, A., Angulo, M., Herrero, S., and Orfao, A. (2004). Immunophenotypic analysis of mast cells in mastocytosis: When and how to do it. Proposals of the Spanish Network on Mastocytosis (REMA). Cytometry B Clin. Cytom. 58, 1–8. Escribano, L., Orfao, A., Villarrubia, J., az‐Agustin, B., Cervero, C., Rios, A., Velasco, J. L., Ciudad, J., Navarro, J. L., and San Miguel, J. F. (1998). Immunophenotypic characterization of human bone marrow mast cells. A flow cytometric study of normal and pathological bone marrow samples. Anal. Cell Pathol. 16, 151–159. Feger, F., Ribadeau, D. A., Leriche, L., Valent, P., and Arock, M. (2002). Kit and c‐Kit mutations in mastocytosis: A short overview with special reference to novel molecular and diagnostic concepts. Int. Arch. Allergy Immunol. 127, 110–114. Fiehn, C., Prummer, O., Gallati, H., Heilig, B., and Hunstein, W. (1995). Treatment of systemic mastocytosis with interferon‐gamma: Failure after appearance of anti‐IFN‐gamma antibodies. Eur. J. Clin. Invest. 25, 615–618. Florian, S., Krauth, M. T., Simonitsch‐Klupp, I., Sperr, W. R., Fritsche‐Polanz, R., Sonneck, K., Fodinger, M., Agis, H., Bohm, A., Wimazal, F., Horny, H. P., and Valent, P. (2005). Indolent systemic mastocytosis with elevated serum tryptase, absence of skin lesions, and recurrent severe anaphylactoid episodes. Int. Arch. Allergy Immunol. 136, 273–280. Fodinger, M., Fritsch, G., Winkler, K., Emminger, W., Mitterbauer, G., Gadner, H., Valent, P., and Mannhalter, C. (1994). Origin of human mast cells: Development from transplanted hematopoietic stem cells after allogeneic bone marrow transplantation. Blood 84, 2954–2959.
SYSTEMIC MASTOCYTOSIS
225
Folkman, J. (1985). Regulation of angiogenesis: A new function of heparin. Biochem. Pharmacol. 34, 905–909. Fonga‐Djimi, H. S., Gottrand, F., Bonnevalle, M., and Farriaux, J. P. (1995). A fatal case of portal hypertension complicating systemic mastocytosis in an adolescent. Eur. J. Pediatr. 154, 819–821. Friedman, B., Darling, G., Norton, J., Hamby, L., and Metcalfe, D. (1990). Splenectomy in the management of systemic mast cell disease 205. Surgery 107, 94–100. Frieri, M., Alling, D. W., and Metcalfe, D. D. (1985). Comparison of the therapeutic efficacy of cromolyn sodium with that of combined chlorpheniramine and cimetidine in systemic mastocytosis. Results of a double‐blind clinical trial. Am. J. Med. 78, 9–14. Fritsche‐Polanz, R., Jordan, J. H., Feix, A., Sperr, W. R., Sunder‐Plassmann, G., Valent, P., and Fodinger, M. (2001). Mutation analysis of C‐KIT in patients with myelodysplastic syndromes without mastocytosis and cases of systemic mastocytosis. Br. J. Haematol. 113, 357–364. Fukao, T., Yamada, T., Tanabe, M., Terauchi, Y., Ota, T., Takayama, T., Asano, T., Takeuchi, T., Kadowaki, T., Hata, J. J., and Koyasu, S. (2002). Selective loss of gastrointestinal mast cells and impaired immunity in PI3K‐deficient mice. Nat. Immunol. 3, 295–304. Fumo, G., Akin, C., Metcalfe, D. D., and Neckers, L. (2004). 17‐Allylamino‐17‐demethoxygeldanamycin (17‐AAG) is effective in down‐regulating mutated, constitutively activated KIT protein in human mast cells. Blood 103, 1078–1084. Furitsu, T., Tsujimura, T., Tono, T., Ikeda, H., Kitayama, H., Koshimizu, U., Sugahara, H., Butterfield, J. H., Ashman, L. K., and Kanayama, Y. (1993). Identification of mutations in the coding sequence of the proto‐oncogene c‐Kit in a human mast cell leukemia cell line causing ligand‐independent activation of c‐Kit product. J. Clin. Invest. 92, 1736–1744. Galli, S. J., and Kitamura, Y. (1987). Genetically masT cell‐deficient W/Wv and Sl/Sld mice. Their value for the analysis of the roles of mast cells in biologic responses in vivo. Am. J. Pathol. 127, 191–198. Galli, S. J., Tsai, M., Wershil, B. K., Tam, S. Y., and Costa, J. J. (1995). Regulation of mouse and human mast cell development, survival and function by stem cell factor, the ligand for the c‐Kit receptor. Int. Arch. Allergy Immunol. 107, 51–53. Gari, M., Goodeve, A., Wilson, G., Winship, P., Langabeer, S., Linch, D., Vandenberghe, E., Peake, I., and Reilly, J. (1999). c‐Kit proto‐oncogene exon 8 in‐frame deletion plus insertion mutations in acute myeloid leukaemia. Br. J. Haematol. 105, 894–900. Gaudry, M., Bregerie, O., Andrieu, V., El, B. J., Pocidalo, M. A., and Hakim, J. (1997). Intracellular pool of vascular endothelial growth factor in human neutrophils. Blood 90, 4153–4161. Genovese, A., Spadaro, G., Triggiani, M., and Marone, G. (1995). Clinical advances in mastocytosis. Int. J. Clin. Lab Res. 25, 178–188. Gilliland, G., Cools, J., Stover, E. H., Wlodarska, I., and Marynen, P. (2004). FIP1L1‐PDGFRalpha in hypereosinophilic syndrome and mastocytosis. Hematol. J. 5(Suppl. 3), S133–S137. Goemans, B. F., Zwaan, C., Miller, M., Zimmermann, M., Harlow, A., Meshinchi, S., Loonen, A. H., Hahlen, K., Reinhardt, D., Creutzig, U., Kaspers, G. J., and Heinrich, M. C. (2000). Mutations in KIT and RAS are frequent events in pediatric core‐binding factor acute myeloid leukemia. Leukemia 19, 1536–1542. Goldstein, S. M., Kaempfer, C. E., Kealey, J. T., and Wintroub, B. U. (1989). Human mast cell carboxypeptidase. Purification and characterization. J. Clin. Invest. 83, 1630–1636. Gommerman, J. L., Sittaro, D., Klebasz, N. Z., Williams, D. A., and Berger, S. A. (2000). Differential stimulation of c‐Kit mutants by membrane‐bound and soluble Steel Factor correlates with leukemic potential. Blood 96, 3734–3742. Gonera, R. K., Oranje, W. A., and Wolffenbuttel, B. H. (1997). Shock of unknown origin—think of mastocytosis!. Neth. J. Med. 50, 165–169.
226
JAMIE ROBYN AND DEAN D. METCALFE
Goodman, G. R., Beutler, E., and Saven, A. (2003). Cladribine in the treatment of hairy‐cell leukaemia. Best. Pract. Res. Clin. Haematol. 16, 101–116. Gordon, J. R. (2000). TGFbeta1 and TNFalpha secreted by mast cells stimulated via the FcepsilonRI activate fibroblasts for high‐level production of monocyte chemoattractant protein‐1 (MCP‐1). Cell Immunol. 201, 42–49. Gordon, J. R., and Galli, S. J. (1990). Mast cells as a source of both preformed and immunologically inducible TNF‐alpha/cachectin. Nature 346, 274–276. Gotlib, J., Berube, C., Growney, J. D., Chen, C. C., George, T. I., Williams, C., Kajiguchi, T., Ruan, J., Lilleberg, S. L., Durocher, J. A., Lichy, J. H., Wang, Y., Cohen, P. S., Arber, D., Heinrich, M. C., Neckers, L., Galli, S. J., Gilliland, D. G., and Coutre, S. E. (2000). Activity of the tyrosine kinase inhibitor PKC412 in a patient with mast cell leukemia with the D816V KIT mutation. Blood 106, 2865–2870. Gotlib, J., Cools, J., Malone, J. M., III, Schrier, S. L., Gilliland, D. G., and Coutre, S. E. (2004). The FIP1L1‐PDGFRalpha fusion tyrosine kinase in hypereosinophilic syndrome and chronic eosinophilic leukemia: Implications for diagnosis, classification, and management. Blood 103, 2879–2891. Gotoh, A., Takahira, H., Mantel, C., Litz‐Jackson, S., Boswell, H. S., and Broxmeyer, H. E. (1996). Steel factor induces serine phosphorylation of Stat3 in human growth factor‐dependent myeloid cell lines. Blood 88, 138–145. Granerus, G., Lonnqvist, B., and Roupe, G. (1994). No relationship between histamine release measured as metabolite excretion in the urine, and serum levels of mast cell specific tryptase in mastocytosis. Agents Actions 41 (Spec No), C127–C128. Greenblatt, E. P., and Chen, L. (1990). Urticaria pigmentosa: An anesthetic challenge. J. Clin. Anesth. 2, 108–115. Grossman, R. M., Krueger, J., Yourish, D., Granelli‐Piperno, A., Murphy, D. P., May, L. T., Kupper, T. S., Sehgal, P. B., and Gottlieb, A. B. (1989). Interleukin 6 is expressed in high levels in psoriatic skin and stimulates proliferation of cultured human keratinocytes. Proc. Natl. Acad. Sci. USA 86, 6367–6371. Growney, J. D., Clark, J. J., Adelsperger, J., Stone, R., Fabbro, D., Griffin, J. D., and Gilliland, D. G. (2005b). Activation mutations of human c‐KIT resistant to imatinib mesylate are sensitive to the tyrosine kinase inhibitor PKC412. Blood 106, 721–724. Grundfest, S., Cooperman, A. M., Ferguson, R., and Benjamin, S. (1980). Portal hypertension associated with systemic mastocytosis and splenomegaly. Gastroenterology 78, 370–373. Grutzkau, A., Kruger‐Krasagakes, S., Baumeister, H., Schwarz, C., Kogel, H., Welker, P., Lippert, U., Henz, B. M., and Moller, A. (1998). Synthesis, storage, and release of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) by human mast cells: Implications for the biological significance of VEGF206. Mol. Biol. Cell 9, 875–884. Guenther, P. P., Huebner, A., Sobottka, S. B., Neumeister, V., Weissbach, G., Todt, H., and Parwaresch, R. (2001). Temporary response of localized intracranial mast cell sarcoma to combination chemotherapy. J. Pediatr. Hematol. Oncol. 23, 134–138. Guo, X., Schrader, K. A., Xu, Y., and Schrader, J. W. (2005). Expression of a constitutively active mutant of M‐Ras in normal bone marrow is sufficient for induction of a malignant mastocytosis/ mast cell leukemia, distinct from the histiocytosis/monocytic leukemia induced by expression of activated H‐Ras. Oncogene 24, 2330–2342. Hagen, W., Schwarzmeier, J., Walchshofer, S., Zojer, N., Chott, A., Sillaber, C., Ackermann, J., Simonitsch, I., Buhring, H. J., Drach, J., Lechner, K., Horny, H. P., and Valent, P. (1998). A case of bone marrow mastocytosis associated with multiple myeloma. Ann. Hematol. 76, 167–174. Hallek, M., Druker, B., Lepisto, E. M., Wood, K. W., Ernst, T. J., and Griffin, J. D. (1992). Granulocyte‐macrophage colony‐stimulating factor and steel factor induce phosphorylation of
SYSTEMIC MASTOCYTOSIS
227
both unique and overlapping signal transduction intermediates in a human factor‐dependent hematopoietic cell line. J. Cell Physiol. 153, 176–186. Hallgren, J., Spillmann, D., and Pejler, G. (2001). Structural requirements and mechanism for heparin‐induced activation of a recombinant mouse mast cell tryptase, mouse mast cell protease‐ 6: Formation of active tryptase monomers in the presence of low molecular weight heparin. J. Biol. Chem. 276, 42774–42781. Hartmann, K., and Henz, B. M. (2002). Cutaneous mastocytosis—clinical heterogeneity. Int. Arch. Allergy Immunol. 127, 143–146. Hauswirth, A. W., Simonitsch‐Klupp, I., Uffmann, M., Koller, E., Sperr, W. R., Lechner, K., and Valent, P. (2004). Response to therapy with interferon alpha‐2b and prednisolone in aggressive systemic mastocytosis: Report of five cases and review of the literature. Leuk. Res. 28, 249–257. Hauswirth, A. W., Sperr, W. R., Ghannadan, M., Schernthaner, G. H., Jordan, J. H., Fritsche‐ Polanz, R., Simonitsch‐Klupp, I., Fodinger, M., Lechner, K., and Valent, P. (2002). A case of smoldering mastocytosis with peripheral blood eosinophilia and lymphadenopathy. Leuk. Res. 26, 601–606. Hehlmann, R., Heimpel, H., Hasford, J., Kolb, H. J., Pralle, H., Hossfeld, D. K., Queisser, W., Loffler, H., Hochhaus, A., and Heinze, B. (1994). Randomized comparison of interferon‐alpha with busulfan and hydroxyurea in chronic myelogenous leukemia. The German CML Study Group. Blood 84, 4064–4077. Heinrich, M. C., Corless, C. L., Duensing, A., McGreevey, L., Chen, C. J., Joseph, N., Singer, S., Griffith, D. J., Haley, A., Town, A., Demetri, G. D., Fletcher, C. D., and Fletcher, J. A. (2003). PDGFRA activating mutations in gastrointestinal stromal tumors. Science 299, 708–710. Hendrie, P. C., Miyazawa, K., Yang, Y. C., Langefeld, C. D., and Broxmeyer, H. E. (1991). Mast cell growth factor (c‐Kit ligand) enhances cytokine stimulation of proliferation of the human factor‐ dependent cell line, M07e. Exp. Hematol. 19, 1031–1037. Hennessy, B., Giles, F., Cortes, J., O’brien, S., Ferrajoli, A., Ossa, G., Garcia‐Manero, G., Faderl, S., Kantarjian, H., and Verstovsek, S. (2004). Management of patients with systemic mastocytosis: Review of M. D. Anderson Cancer Center experience. Am. J. Hematol. 77, 209–214. Herbst, R., Shearman, M. S., Jallal, B., Schlessinger, J., and Ullrich, A. (1995). Formation of signal transfer complexes between stem cell and platelet‐derived growth factor receptors and SH2 domain proteins in vitro. Biochemistry 34, 5971–5979. Hodgkinson, C. A., Moore, K. J., Nakayama, A., Steingrimsson, E., Copeland, N. G., Jenkins, N. A., and Arnheiter, H. (1993). Mutations at the mouse microphthalmia locus are associated with defects in a gene encoding a novel basic‐helix‐loop‐helix‐zipper protein. Cell 74, 395–404. Holgate, S. T., Bradding, P., and Sampson, A. P. (1996). Leukotriene antagonists and synthesis inhibitors: New directions in asthma therapy. J. Allergy Clin. Immunol. 98, 1–13. Hong, L., Munugalavadla, V., and Kapur, R. (2004). c‐Kit‐mediated overlapping and unique functional and biochemical outcomes via diverse signaling pathways. Mol. Cell Biol. 24, 1401–1410. Hongyo, T., Li, T., Syaifudin, M., Baskar, R., Ikeda, H., Kanakura, Y., Aozasa, K., and Nomura, T. (2000). Specific c‐Kit mutations in sinonasal natural killer/T cell lymphoma in China and Japan. Cancer Res. 60, 2345–2347. Horan, R. F., and Austen, K. F. (1991). Systemic mastocytosis: Retrospective review of a decade’s clinical experience at the Brigham and Women’s Hospital. J. Invest. Dermatol. 96, 5S–13S. Horan, R. F., Sheffer, A. L., and Austen, K. F. (1990). Cromolyn sodium in the management of systemic mastocytosis. J. Allergy Clin. Immunol. 85, 852–855.
228
JAMIE ROBYN AND DEAN D. METCALFE
Horiuchi, T., and Weller, P. F. (1997). Expression of vascular endothelial growth factor by human eosinophils: Upregulation by granulocyte macrophage colony‐stimulating factor and interleukin‐ 5. Am. J. Respir. Cell Mol. Biol. 17, 70–77. Horny, H. P., and Kaiserling, E. (1988). Lymphoid cells and tissue mast cells of bone marrow lesions in systemic mastocytosis: A histological and immunohistological study. Br. J. Haematol. 69, 449–455. Horny, H. P., Kaiserling, E., Campbell, M., Parwaresch, M. R., and Lennert, K. (1989). Liver findings in generalized mastocytosis. A clinicopathologic study. Cancer 63, 532–538. Horny, H. P., Kaiserling, E., Parwaresch, M. R., and Lennert, K. (1992a). Lymph node findings in generalized mastocytosis. Histopathology 21, 439–446. Horny, H. P., Kaiserling, E., Sillaber, C., Walchshofer, S., and Valent, P. (1997). Bone marrow mastocytosis associated with an undifferentiated extramedullary tumor of hemopoietic origin. Arch. Pathol. Lab Med. 121, 423–426. Horny, H. P., Parwaresch, M. R., Kaiserling, E., Muller, K., Olbermann, M., Mainzer, K., and Lennert, K. (1986). Mast cell sarcoma of the larynx. J. Clin. Pathol. 39, 596–602. Horny, H. P., Ruck, M., Wehrmann, M., and Kaiserling, E. (1990). Blood findings in generalized mastocytosis: Evidence of frequent simultaneous occurrence of myeloproliferative disorders. Br. J. Haematol. 76, 186–193. Horny, H. P., Ruck, M. T., and Kaiserling, E. (1992b). Spleen findings in generalized mastocytosis. A clinicopathologic study. Cancer 70, 459–468. Horny, H. P., Sillaber, C., Menke, D., Kaiserling, E., Wehrmann, M., Stehberger, B., Chott, A., Lechner, K., Lennert, K., and Valent, P. (1998). Diagnostic value of immunostaining for tryptase in patients with mastocytosis. Am. J. Surg. Pathol. 22, 1132–1140. Horny, H. P., Sotlar, K., Sperr, W. R., and Valent, P. (2004). Systemic mastocytosis with associated clonal haematological non‐mast cell lineage diseases: A histopathological challenge. J. Clin. Pathol. 57, 604–608. Horny, H. P., and Valent, P. (2001). Diagnosis of mastocytosis: General histopathological aspects, morphological criteria, and immunohistochemical findings. Leuk. Res. 25, 543–551. Horny, H. P., and Valent, P. (2002). Histopathological and immunohistochemical aspects of mastocytosis. Int. Arch. Allergy Immunol. 127, 115–117. Hoshida, Y., Hongyo, T., Jia, X., He, Y., Hasui, K., Dong, Z., Luo, W. J., Ham, M. F., Nomura, T., and Aozasa, K. (2003). Analysis of p53, K‐ras, c‐Kit, and beta‐catenin gene mutations in sinonasal NK/T cell lymphoma in northeast district of China. Cancer Sci. 94, 297–301. Huber, M., Helgason, C. D., Damen, J. E., Liu, L., Humphries, R. K., and Krystal, G. (1998a). The src homology 2‐containing inositol phosphatase (SHIP) is the gatekeeper of mast cell degranulation. Proc. Natl. Acad. Sci. USA 95, 11330–11335. Huber, M., Helgason, C. D., Scheid, M. P., Duronio, V., Humphries, R. K., and Krystal, G. (1998b). Targeted disruption of SHIP leads to Steel factor‐induced degranulation of mast cells. EMBO J. 17, 7311–7319. Hubner, C., Wedding, U., Strater, J., Limberg, B., and Stremmel, W. (1997). Clinical stable systemic mastocytosis with interferon alpha‐2b therapy. J. Intern. Med. 241, 529–533. Iemura, A., Tsai, M., Ando, A., Wershil, B. K., and Galli, S. J. (1994). The c‐Kit ligand, stem cell factor, promotes mast cell survival by suppressing apoptosis. Am. J. Pathol. 144, 321–328. Ihle, J. N., Keller, J., Oroszlan, S., Henderson, L. E., Copeland, T. D., Fitch, F., Prystowsky, M. B., Goldwasser, E., Schrader, J. W., Palaszynski, E., Dy, M., and Lebel, B. (1983). Biologic properties of homogeneous interleukin 3. I. Demonstration of WEHI‐3 growth factor activity, mast cell growth factor activity, p cell‐stimulating factor activity, colony‐stimulating factor activity, and histamine‐producing cell‐stimulating factor activity. J. Immunol. 131, 282–287.
SYSTEMIC MASTOCYTOSIS
229
Iijima, K., Yoshikawa, N., and Nakamura, H. (1996). Activation‐induced expression of vascular permeability factor by human peripheral T cells: A non‐radioisotopic semiquantitative reverse transcription‐polymerase chain reaction assay. J. Immunol. Methods 196, 199–209. Irani, A. M., Nilsson, G., Miettinen, U., Craig, S. S., Ashman, L. K., Ishizaka, T., Zsebo, K. M., and Schwartz, L. B. (1992). Recombinant human stem cell factor stimulates differentiation of mast cells from dispersed human fetal liver cells. Blood 80, 3009–3021. Isersky, C., Rivera, J., Mims, S., and Triche, T. J. (1979). The fate of IgE bound to rat basophilic leukemia cells. J. Immunol. 122, 1926–1936. Jacobs‐Helber, S. M., Penta, K., Sun, Z., Lawson, A., and Sawyer, S. T. (1997). Distinct signaling from stem cell factor and erythropoietin in HCD57 cells. J. Biol. Chem. 272, 6850–6853. Jahn, T., Seipel, P., Coutinho, S., Urschel, S., Schwarz, K., Miething, C., Serve, H., Peschel, C., and Duyster, J. (2002). Analysing c‐Kit internalization using a functional c‐Kit‐EGFP chimera containing the fluorochrome within the extracellular domain. Oncogene 21, 4508–4520. Janowska‐Wieczorek, A., Majka, M., Ratajczak, J., and Ratajczak, M. Z. (2001). Autocrine/paracrine mechanisms in human hematopoiesis. Stem Cells 19, 99–107. Jensen, R. T. (2000). Gastrointestinal abnormalities and involvement in systemic mastocytosis. Hematol. Oncol. Clin. North Am. 14, 579–623. Jiang, J., Paez, J. G., Lee, J. C., Bo, R., Stone, R. M., De Angelo, D. J., Galinsky, I., Wolpin, B. M., Jonasova, A., Herman, P., Fox, E. A., Boggon, T. J., Eck, M. J., Weisberg, E., Griffin, J. D., Gilliland, D. G., Meyerson, M., and Sellers, W. R. (2004). Identifying and characterizing a novel activating mutation of the FLT3 tyrosine kinase in AML. Blood 104, 1855–1858. Jilka, R. L., Hangoc, G., Girasole, G., Passeri, G., Williams, D. C., Abrams, J. S., Boyce, B., Broxmeyer, H., and Manolagas, S. C. (1992). Increased osteoclast development after estrogen loss: Mediation by interleukin‐6. Science 257, 88–91. Joensuu, H., and Kindblom, L. G. (2004). Gastrointestinal stromal tumors—a review. Acta Orthop. Scand. Suppl. 75, 62–71. Joneja, B., Chen, H. C., Seshasayee, D., Wrentmore, A. L., and Wojchowski, D. M. (1997). Mechanisms of stem cell factor and erythropoietin proliferative co‐signaling in FDC2‐ER cells. Blood 90, 3533–3545. Jordan, J. H., Fritsche‐Polanz, R., Sperr, W. R., Mitterbauer, G., Fodinger, M., Schernthaner, G. H., Christian, B. H., Gebhart, W., Chott, A., Lechner, K., and Valent, P. (2001). A case of ‘smoldering’ mastocytosis with high mast cell burden, monoclonal myeloid cells, and C‐KIT mutation Asp‐816‐Val. Leuk. Res. 25, 627–634. Joris, I., Majno, G., Corey, E. J., and Lewis, R. A. (1987). The mechanism of vascular leakage induced by leukotriene E4. Endothelial contraction. Am. J. Pathol. 126, 19–24. Jutel, M., Watanabe, T., Klunker, S., Akdis, M., Thomet, O. A., Malolepszy, J., Zak‐Nejmark, T., Koga, R., Kobayashi, T., Blaser, K., and Akdis, C. A. (2001). Histamine regulates T cell and antibody responses by differential expression of H1 and H2 receptors. Nature 413, 420–425. Kambe, M., Kambe, N., Oskeritzian, C. A., Schechter, N., and Schwartz, L. B. (2001). IL‐6 attenuates apoptosis, while neither IL‐6 nor IL‐10 affect the numbers or protease phenotype of fetal liver‐derived human mast cells. Clin. Exp. Allergy 31, 1077–1085. Kanakura, Y., Furitsu, T., Tsujimura, T., Butterfield, J. H., Ashman, L. K., Ikeda, H., Kitayama, H., Kanayama, Y., Matsuzawa, Y., and Kitamura, Y. (1994). Activating mutations of the c‐Kit proto‐ oncogene in a human mast cell leukemia cell line. Leukemia 8(Suppl. 1), S18–S22. Katz, H. R., Arm, J. P., Benson, A. C., and Austen, K. F. (1990). Maturation‐related changes in the expression of Fc gamma RII and Fc gamma RIII on mouse mast cells derived in vitro and in vivo. J. Immunol. 145, 3412–3417.
230
JAMIE ROBYN AND DEAN D. METCALFE
Kelly, L. M., and Gilliland, D. G. (2002). Genetics of myeloid leukemias. Annu. Rev. Genomics Hum. Genet. 3, 179–198. Kelly, L. M., Liu, Q., Kutok, J. L., Williams, I. R., Boulton, C. L., and Gilliland, D. G. (2002). FLT3 internal tandem duplication mutations associated with human acute myeloid leukemias induce myeloproliferative disease in a murine bone marrow transplant model. Blood 99, 310–318. Kemmer, K., Corless, C. L., Fletcher, J. A., McGreevey, L., Haley, A., Griffith, D., Cummings, O. W., Wait, C., Town, A., and Heinrich, M. C. (2004). KIT mutations are common in testicular seminomas. Am. J. Pathol. 164, 305–313. Keyzer, J. J., De Monchy, J. G., Van Doormaal, J. J., and Van, V. (1983). Improved diagnosis of mastocytosis by measurement of urinary histamine metabolites. N. Engl. J. Med. 309, 1603–1605. Kimura, Y., Jones, N., Kluppel, M., Hirashima, M., Tachibana, K., Cohn, J. B., Wrana, J. L., Pawson, T., and Bernstein, A. (2004). Targeted mutations of the juxtamembrane tyrosines in the Kit receptor tyrosine kinase selectively affect multiple cell lineages. Proc. Natl. Acad. Sci. USA 101, 6015–6020. Kirshenbaum, A. (2000). Regulation of mast cell number and function1. Hematol. Oncol. Clin. North Am. 14, 497–516. Kirshenbaum, A. S., Akin, C., Goff, J. P., and Metcalfe, D. D. (2005). Thrombopoietin alone or in the presence of stem cell factor supports the growth of KIT(CD117)low/ MPL(CD110)þ human mast cells from hematopoietic progenitor cells. Exp. Hematol. 33, 413–421. Kirshenbaum, A. S., Akin, C., Wu, Y., Rottem, M., Goff, J. P., Beaven, M. A., Rao, V. K., and Metcalfe, D. D. (2003). Characterization of novel stem cell factor responsive human mast cell lines LAD 1 and 2 established from a patient with mast cell sarcoma/leukemia; activation following aggregation of FcepsilonRI or FcgammaRI. Leuk. Res. 27, 677–682. Kirshenbaum, A. S., Goff, J. P., Kessler, S. W., Mican, J. M., Zsebo, K. M., and Metcalfe, D. D. (1992). Effect of IL‐3 and stem cell factor on the appearance of human basophils and mast cells from CD34þ pluripotent progenitor cells. J. Immunol. 148, 772–777. Kirshenbaum, A. S., Goff, J. P., Semere, T., Foster, B., Scott, L. M., and Metcalfe, D. D. (1999). Demonstration that human mast cells arise from a progenitor cell population that is CD34(þ), c‐Kit(þ), and expresses aminopeptidase N (CD13). Blood 94, 2333–2342. Kirshenbaum, A. S., Kessler, S. W., Goff, J. P., and Metcalfe, D. D. (1991). Demonstration of the origin of human mast cells from CD34þ bone marrow progenitor cells. J. Immunol. 146, 1410–1415. Kissel, H., Timokhina, I., Hardy, M. P., Rothschild, G., Tajima, Y., Soares, V., Angeles, M., Whitlow, S. R., Manova, K., and Besmer, P. (2000). Point mutation in kit receptor tyrosine kinase reveals essential roles for kit signaling in spermatogenesis and oogenesis without affecting other kit responses. EMBO J. 19, 1312–1326. Kitamura, Y., and Hirotab, S. (2004). Kit as a human oncogenic tyrosine kinase. Cell Mol. Life Sci. 61, 2924–2931. Kitamura, Y., Morii, E., Ogihara, H., Jippo, T., and Ito, A. (2001). Mutant mice: A useful tool for studying the development of mast cells. Int. Arch. Allergy Immunol. 124, 16–19. Kitamura, Y., Taguchi, T., Yokoyama, M., Inoue, M., Yamatodani, A., Asano, H., Koyama, T., Kanamaru, A., Hatanaka, K., and Wershil, B. K. (1986). Higher susceptibility of masT cell‐ deficient W/WV mutant mice to brain thromboembolism and mortality caused by intravenous injection of India ink. Am. J. Pathol. 122, 469–480. Kitamura, Y., Yokoyama, M., Matsuda, H., Ohno, T., and Mori, K. J. (1981). Spleen colony‐ forming cell as common precursor for tissue mast cells and granulocytes. Nature 291, 159–160.
SYSTEMIC MASTOCYTOSIS
231
Klion, A. D., Noel, P., Akin, C., Law, M. A., Gilliland, D. G., Cools, J., Metcalfe, D. D., and Nutman, T. B. (2003). Elevated serum tryptase levels identify a subset of patients with a myeloproliferative variant of idiopathic hypereosinophilic syndrome associated with tissue fibrosis, poor prognosis, and imatinib responsiveness. Blood 101, 4660–4666. Klion, A. D., Robyn, J., Akin, C., Noel, P., Brown, M., Law, M., Metcalfe, D. D., Dunbar, C., and Nutman, T. B. (2004). Molecular remission and reversal of myelofibrosis in response to imatinib mesylate treatment in patients with the myeloproliferative variant of hypereosinophilic syndrome. Blood 103, 473–478. Kluin‐Nelemans, H. C., Jansen, J. H., Breukelman, H., Wolthers, B. G., Kluin, P. M., Kroon, H. M., and Willemze, R. (1992). Response to interferon alfa‐2b in a patient with systemic mastocytosis. N. Engl. J. Med. 326, 619–623. Kluin‐Nelemans, H. C., Oldhoff, J. M., Van Doormaal, J. J., Van ’t Wout, J. W., Verhoef, G., Gerrits, W. B., van Dobbenburgh, O. A., Pasmans, S. G., and Fijnheer, R. (2003). Cladribine therapy for systemic mastocytosis. Blood 102, 4270–4276. Kocabas, C. N., Yavuz, A. S., Lipsky, P. E., Metcalfe, D. D., and Akin, C. (2005). Analysis of the lineage relationship between mast cells and basophils using the c‐Kit D816V mutation as a biologic signature. J. Allergy Clin. Immunol. 115, 1155–1161. Koike, T., Hirai, K., Morita, Y., and Nozawa, Y. (1993). Stem cell factor‐induced signal transduction in rat mast cells. Activation of phospholipase D but not phosphoinositide‐specific phospholipase C in c‐Kit receptor stimulation 2. J. Immunol. 151, 359–366. Kojima, M., Nakamura, S., Itoh, H., Ohno, Y., Masawa, N., Joshita, T., and Suchi, T. (1999). Mast cell sarcoma with tissue eosinophilia arising in the ascending colon. Mod. Pathol. 12, 739–743. Kolde, G., Sunderkotter, C., and Luger, T. A. (1995). Treatment of urticaria pigmentosa using interferon alpha. Br. J. Dermatol. 133, 91–94. Kozawa, O., Blume‐Jensen, P., Heldin, C. H., and Ronnstrand, L. (1997). Involvement of phosphatidylinositol 30 ‐kinase in stem‐cell‐factor‐induced phospholipase D activation and arachidonic acid release. Eur. J. Biochem. 248, 149–155. Kozlowski, M., Larose, L., Lee, F., Le, D. M., Rottapel, R., and Siminovitch, K. A. (1998). SHP‐1 binds and negatively modulates the c‐Kit receptor by interaction with tyrosine 569 in the c‐Kit juxtamembrane domain. Mol. Cell Biol. 18, 2089–2099. Krause, D. S., and Van Etten, R. A. (2005). Tyrosine kinases as targets for cancer therapy. N. Engl. J. Med. 353, 172–187. Krystal, G. W., DeBerry, C. S., Linnekin, D., and Litz, J. (1998). Lck associates with and is activated by Kit in a small cell lung cancer cell line: Inhibition of SCF‐mediated growth by the Src family kinase inhibitor PP1. Cancer Res. 58, 4660–4666. Kudo, H., Morinaga, S., Shimosato, Y., Noguchi, M., Mizutani, Y., Asamura, H., and Naruke, T. (1988). Solitary mast cell tumor of the lung. Cancer 61, 2089–2094. Kulka, M., Alexopoulou, L., Flavell, R. A., and Metcalfe, D. D. (2004). Activation of mast cells by double‐stranded RNA: Evidence for activation through Toll‐like receptor 3. J. Allergy Clin. Immunol. 114, 174–182. Kulka, M., and Metcalfe, D. D. (2005). High‐resolution tracking of cell division demonstrates differential effects of TH1 and TH2 cytokines on SCF‐dependent human mast cell production in vitro: Correlation with apoptosis and Kit expression. Blood 105, 592–599. Kurosawa, M., Amano, H., Kanbe, N., Igarashi, Y., Nagata, H., Yamashita, T., Kurimoto, F., and Miyachi, Y. (1999). Response to cyclosporin and low‐dose methylprednisolone in aggressive systemic mastocytosis. J. Allergy Clin. Immunol. 103, S412–S420. Lawrence, J. B., Friedman, B. S., Travis, W. D., Chinchilli, V. M., Metcalfe, D. D., and Gralnick, H. R. (1991). Hematologic manifestations of systemic mast cell disease: A prospective study of laboratory and morphologic features and their relation to prognosis. Am. J. Med. 91, 612–624.
232
JAMIE ROBYN AND DEAN D. METCALFE
Le Cam, M. T., Wolkenstein, P., Cosnes, A., Bocquet, H., Gaulard, P., Tulliez, M., Cordonnier, C., Roujeau, J. C., Bagot, M., and Revuz, J. (1997). Acute mast cell leukemia disclosed by vasomotor flushing. Ann. Dermatol. Venereol. 124, 621–622. Lee, C. G., Homer, R. J., Zhu, Z., Lanone, S., Wang, X., Koteliansky, V., Shipley, J. M., Gotwals, P., Noble, P., Chen, Q., Senior, R. M., and Elias, J. A. (2001). Interleukin‐13 induces tissue fibrosis by selectively stimulating and activating transforming growth factor beta(1). J. Exp. Med. 194, 809–821. Lehmann, T., Beyeler, C., Lammle, B., Hunziker, T., Vock, P., Olah, A. J., Dahinden, C., and Gerber, N. J. (1996). Severe osteoporosis due to systemic mast cell disease: Successful treatment with interferon alpha‐2B. Br. J. Rheumatol. 35, 898–900. Lennartsson, J., Blume‐Jensen, P., Hermanson, M., Ponten, E., Carlberg, M., and Ronnstrand, L. (1999). Phosphorylation of Shc by Src family kinases is necessary for stem cell factor receptor/ c‐Kit mediated activation of the Ras/MAP kinase pathway and c‐fos induction. Oncogene 18, 5546–5553. Lennartsson, J., Jelacic, T., Linnekin, D., and Shivakrupa, R. (2005). Normal and oncogenic forms of the receptor tyrosine kinase kit. Stem Cells 23, 16–43. Levi‐Schaffer, F., and Piliponsky, A. M. (2003). Tryptase, a novel link between allergic inflammation and fibrosis. Trends Immunol. 24, 158–161. Li, C. Y. (2001). Diagnosis of mastocytosis: Value of cytochemistry and immunohistochemistry. Leuk. Res. 25, 537–541. Li, L., Meng, X. W., and Krilis, S. A. (1996). Mast cells expressing chymase but not tryptase can be derived by culturing human progenitors in conditioned medium obtained from a human mastocytosis cell strain with c‐Kit ligand3. J. Immunol. 156, 4839–4844. Lindner, P. S., Pardanani, B., Angadi, C., and Frieri, M. (1992). Acute nonlymphocytic leukemia in systemic mastocytosis with biclonal gammopathy. J. Allergy Clin. Immunol. 90, 410–412. Linnekin, D. (1999). Early signaling pathways activated by c‐Kit in hematopoietic cells. Int. J. Biochem. Cell Biol. 31, 1053–1074. Linnekin, D., De Berry, C. S., and Mou, S. (1997). Lyn associates with the juxtamembrane region of c‐Kit and is activated by stem cell factor in hematopoietic cell lines and normal progenitor cells. J. Biol. Chem. 272, 27450–27455. Liu, L., Cutler, R. L., Mui, A. L., and Krystal, G. (1994a). Steel factor stimulates the serine/ threonine phosphorylation of the interleukin‐3 receptor. J. Biol. Chem. 269, 16774–16779. Liu, L., Damen, J. E., Cutler, R. L., and Krystal, G. (1994b). Multiple cytokines stimulate the binding of a common 145‐kilodalton protein to Shc at the Grb2 recognition site of Shc. Mol. Cell Biol. 14, 6926–6935. Loh, M. L., Vattikuti, S., Schubbert, S., Reynolds, M. G., Carlson, E., Lieuw, K. H., Cheng, J. W., Lee, C. M., Stokoe, D., Bonifas, J. M., Curtiss, N. P., Gotlib, J., Meshinchi, S., Le Beau, M. M., Emanuel, P. D., and Shannon, K. M. (2004). Mutations in PTPN11 implicate the SHP‐2 phosphatase in leukemogenesis. Blood 103, 2325–2331. Longley, B. J., Jr., Metcalfe, D. D., Tharp, M., Wang, X., Tyrrell, L., Lu, S. Z., Heitjan, D., and Ma, Y. (1999). Activating and dominant inactivating c‐KIT catalytic domain mutations in distinct clinical forms of human mastocytosis. Proc. Natl. Acad. Sci. USA 96, 1609–1614. Longley, B. J., Tyrrell, L., Lu, S. Z., Ma, Y. S., Langley, K., Ding, T. G., Duffy, T., Jacobs, P., Tang, L. H., and Modlin, I. (1996). Somatic c‐KIT activating mutation in urticaria pigmentosa and aggressive mastocytosis: Establishment of clonality in a human mast cell neoplasm. Nat. Genet. 12, 312–314. Lorenz, U., Bergemann, A. D., Steinberg, H. N., Flanagan, J. G., Li, X., Galli, S. J., and Neel, B. G. (1996). Genetic analysis reveals cell type‐specific regulation of receptor tyrosine kinase c‐Kit by the protein tyrosine phosphatase SHP1. J. Exp. Med. 184, 1111–1126.
SYSTEMIC MASTOCYTOSIS
233
Lu‐Kuo, J. M., Fruman, D. A., Joyal, D. M., Cantley, L. C., and Katz, H. R. (2000). Impaired kit‐ but not FcepsilonRI‐initiated mast cell activation in the absence of phosphoinositide 3‐kinase p85alpha gene products. J. Biol. Chem. 275, 6022–6029. Lyon, M. F., and Glenister, P. H. (1982). A new allele sash (Wsh) at the W‐locus and a spontaneous recessive lethal in mice. Genet. Res. 39, 315–322. Ma, Y., Cunningham, M. E., Wang, X., Ghosh, I., Regan, L., and Longley, B. J. (1999). Inhibition of spontaneous receptor phosphorylation by residues in a putative alpha‐helix in the KIT intracellular juxtamembrane region. J. Biol. Chem. 274, 13399–13402. Ma, Y., Zeng, S., Metcalfe, D. D., Akin, C., Dimitrijevic, S., Butterfield, J. H., McMahon, G., and Longley, B. J. (2002). The c‐KIT mutation causing human mastocytosis is resistant to STI571 and other KIT kinase inhibitors; kinases with enzymatic site mutations show different inhibitor sensitivity profiles than wild‐type kinases and those with regulatory‐type mutations. Blood 99, 1741–1744. MacGlashan, D., Jr., Lichtenstein, L. M., Kenzie‐White, J., Chichester, K., Henry, A. J., Sutton, B. J., and Gould, H. J. (1999). Upregulation of FcepsilonRI on human basophils by IgE antibody is mediated by interaction of IgE with FcepsilonRI. J. Allergy Clin. Immunol. 104, 492–498. Maddens, S., Charruyer, A., Plo, I., Dubreuil, P., Berger, S., Salles, B., Laurent, G., and Jaffrezou, J. P. (2002). Kit signaling inhibits the sphingomyelin‐ceramide pathway through PLC gamma 1: Implication in stem cell factor radioprotective effect. Blood 100, 1294–1301. Maeyama, H., Hidaka, E., Ota, H., Minami, S., Kajiyama, M., Kuraishi, A., Mori, H., Matsuda, Y., Wada, S., Sodeyama, H., Nakata, S., Kawamura, N., Hata, S., Watanabe, M., Iijima, Y., and Katsuyama, T. (2001). Familial gastrointestinal stromal tumor with hyperpigmentation: Association with a germ line mutation of the c‐Kit gene. Gastroenterology 120, 210–215. Malaviya, R., Ikeda, T., Ross, E., and Abraham, S. N. (1996). Mast cell modulation of neutrophil influx and bacterial clearance at sites of infection through TNF‐alpha. Nature 381, 77–80. Manning, G., Whyte, D. B., Martinez, R., Hunter, T., and Sudarsanam, S. (2002). The protein kinase complement of the human genome. Science 298, 1912–1934. Marone, G., Spadaro, G., and Genovese, A. (1995). Biology, diagnosis and therapy of mastocytosis. Chem. Immunol. 62, 1–21. Marone, G., and Stellato, C. (1992). Activation of human mast cells and basophils by general anaesthetic drugs. Monogr. Allergy 30, 54–73. Marshall, J. S., and Jawdat, D. M. (2004). Mast cells in innate immunity. J. Allergy Clin. Immunol. 114, 21–27. Matsuda, H., Kannan, Y., Ushio, H., Kiso, Y., Kanemoto, T., Suzuki, H., and Kitamura, Y. (1991). Nerve growth factor induces development of connective tissue‐type mast cells in vitro from murine bone marrow cells. J. Exp. Med. 174, 7–14. Maurer, M., Echtenacher, B., Hultner, L., Kollias, G., Mannel, D. N., Langley, K. E., and Galli, S. J. (1998). The c‐Kit ligand, stem cell factor, can enhance innate immunity through effects on mast cells. J. Exp. Med. 188, 2343–2348. McCurdy, J. D., Lin, T. J., and Marshall, J. S. (2001). Toll‐like receptor 4‐mediated activation of murine mast cells. J. Leukoc. Biol. 70, 977–984. McCurdy, J. D., Olynych, T. J., Maher, L. H., and Marshall, J. S. (2003). Cutting edge: Distinct Toll‐like receptor 2 activators selectively induce different classes of mediator production from human mast cells. J. Immunol. 170, 1625–1629. Meggs, W. J., Frieri, M., Costello, R., Metcalfe, D. D., and Papadopoulos, N. M. (1985). Oligoclonal immunoglobulins in mastocytosis. Ann. Intern. Med. 103, 894–895. Mekori, Y. A. (2000). Lymphoid tissues and the immune system in mastocytosis. Hematol. Oncol. Clin. North Am. 14, 569–577.
234
JAMIE ROBYN AND DEAN D. METCALFE
Mekori, Y. A., Gilfillan, A. M., Akin, C., Hartmann, K., and Metcalfe, D. D. (2001). Human mast cell apoptosis is regulated through Bcl‐2 and Bcl‐XL. J. Clin. Immunol. 21, 171–174. Mekori, Y. A., and Metcalfe, D. D. (1999). Mast cell‐T cell interactions. J. Allergy Clin. Immunol. 104, 517–523. Mekori, Y. A., and Metcalfe, D. D. (2000). Mast cells in innate immunity. Immunol. Rev. 173, 131–140. Meng, H., Tonnesen, M. G., Marchese, M. J., Clark, R. A., Bahou, W. F., and Gruber, B. L. (1995). Mast cells are potent regulators of endothelial cell adhesion molecule ICAM‐1 and VCAM‐1 expression. J. Cell Physiol. 165, 40–53. Metcalfe, D. D. (1991a). Classification and diagnosis of mastocytosis: Current status. J. Invest. Dermatol. 96, 2S–4S. Metcalfe, D. D. (1991b). The liver, spleen, and lymph nodes in mastocytosis. J. Invest. Dermatol. 96, 45S–46S. Metcalfe, D. D., and Akin, C. (2001). Mastocytosis: Molecular mechanisms and clinical disease heterogeneity. Leuk. Res. 25, 577–582. Metcalfe, D. D., Baram, D., and Mekori, Y. A. (1997). Mast cells. Physiol. Rev. 77, 1033–1079. Mican, J. M., Di Bisceglie, A. M., Fong, T. L., Travis, W. D., Kleiner, D. E., Baker, B., and Metcalfe, D. D. (1995). Hepatic involvement in mastocytosis: Clinicopathologic correlations in 41 cases. Hepatology 22, 1163–1170. Mirowski, G., Austen, K. F., Chiang, L., Horan, R. F., Sheffer, A. L., Weidner, N., and Murphy, G. F. (1990). Characterization of cellular dermal infiltrates in human cutaneous mastocytosis. Lab. Invest. 63, 52–62. Mitsui, H., Furitsu, T., Dvorak, A. M., Irani, A. M., Schwartz, L. B., Inagaki, N., Takei, M., Ishizaka, K., Zsebo, K. M., and Gillis, S. (1993). Development of human mast cells from umbilical cord blood cells by recombinant human and murine c‐Kit ligand. Proc. Natl. Acad. Sci. USA 90, 735–739. Miyazawa, K., Hendrie, P. C., Mantel, C., Wood, K., Ashman, L. K., and Broxmeyer, H. E. (1991). Comparative analysis of signaling pathways between mast cell growth factor (c‐Kit ligand) and granulocyte‐macrophage colony‐stimulating factor in a human factor‐dependent myeloid cell line involves phosphorylation of Raf‐1, GTPase‐activating protein and mitogen‐activated protein kinase. Exp. Hematol. 19, 1110–1123. Miyazawa, K., Williams, D. A., Gotoh, A., Nishimaki, J., Broxmeyer, H. E., and Toyama, K. (1995). Membrane‐bound Steel factor induces more persistent tyrosine kinase activation and longer life span of c‐Kit gene‐encoded protein than its soluble form. Blood 85, 641–649. Mol, C. D., Lim, K. B., Sridhar, V., Zou, H., Chien, E. Y., Sang, B. C., Nowakowski, J., Kassel, D. B., Cronin, C. N., and McRee, D. E. (2003). Structure of a c‐Kit product complex reveals the basis for kinase transactivation. J. Biol. Chem. 278, 31461–31464. Moller, A., Lippert, U., Lessmann, D., Kolde, G., Hamann, K., Welker, P., Schadendorf, D., Rosenbach, T., Luger, T., and Czarnetzki, B. M. (1993). Human mast cells produce IL‐8. J. Immunol. 151, 3261–3266. Moller, C., Alfredsson, J., Engstrom, M., Wootz, H., Xiang, Z., Lennartsson, J., Jonsson, J. I., and Nilsson, G. (2005). Stem cell factor promotes mast cell survival via inactivation of FOXO3a mediated transcriptional induction and MEK regulated phosphorylation of the pro‐apoptotic protein Bim. Blood 106, 1330–1336. Morii, E., Takebayashi, K., Motohashi, H., Yamamoto, M., Nomura, S., and Kitamura, Y. (1994). Loss of DNA binding ability of the transcription factor encoded by the mutant mi locus. Biochem. Biophys. Res. Commun. 205, 1299–1304. Morrow, J. D., Minton, T. A., Awad, J. A., and Roberts, L. J. (1994). Release of markedly increased quantities of prostaglandin D2 from the skin in vivo in humans following the application of sorbic acid. Arch. Dermatol. 130, 1408–1412.
SYSTEMIC MASTOCYTOSIS
235
Musto, P., Falcone, A., Sanpaolo, G., Bodenizza, C., and Carella, A. M. (2004a). Inefficacy of imatinib‐mesylate in sporadic, aggressive systemic mastocytosis. Leuk. Res. 28, 421–422. Musto, P., Falcone, A., Sanpaolo, G., Bodenizza, C., Perla, G., Minervini, M. M., Cascavilla, N., Dell’Olio, M., La, S. A., Mantuano, S., Melillo, L., Nobile, M., Scalzulli, P. R., Bisceglia, M., and Carella, A. M. (2004b). Heterogeneity of response to imatinib‐mesylate (glivec) in patients with hypereosinophilic syndrome: Implications for dosing and pathogenesis. Leuk. Lymphoma 45, 1219–1222. Mylanus, E. A., Wielinga, E. W., and van de Nes, J. A. (2000). A solitary manifestation of mastocytosis in the head and neck. Eur. Arch. Otorhinolaryngol. 257, 270–272. Nagata, H., Worobec, A. S., Oh, C. K., Chowdhury, B. A., Tannenbaum, S., Suzuki, Y., and Metcalfe, D. D. (1995). Identification of a point mutation in the catalytic domain of the protooncogene c‐Kit in peripheral blood mononuclear cells of patients who have mastocytosis with an associated hematologic disorder. Proc. Natl. Acad. Sci. USA 92, 10560–10564. Nakano, T., Kanakura, Y., Nakahata, T., Matsuda, H., and Kitamura, Y. (1987). Genetically mast cell‐deficient W/Wv mice as a tool for studies of differentiation and function of mast cells. Fed. Proc. 46, 1920–1923. Nakata, Y., Kimura, A., Katoh, O., Kawaishi, K., Hyodo, H., Abe, K., Kuramoto, A., and Satow, Y. (1995). c‐Kit point mutation of extracellular domain in patients with myeloproliferative disorders. Br. J. Haematol. 91, 661–663. Nettleship, P. (1869). Rare forms of urticaria. Br. Med. J. 2, 323. Nilsson, G., Butterfield, J. H., Nilsson, K., and Siegbahn, A. (1994a). Stem cell factor is a chemotactic factor for human mast cells. J. Immunol. 153, 3717–3723. Nilsson, G., Miettinen, U., Ishizaka, T., Ashman, L. K., Irani, A. M., and Schwartz, L. B. (1994b). Interleukin‐4 inhibits the expression of Kit and tryptase during stem cell factor‐dependent development of human mast cells from fetal liver cells. Blood 84, 1519–1527. Noack, F., Sotlar, K., Notter, M., Thiel, E., Valent, P., and Horny, H. P. (2004). Aleukemic mast cell leukemia with abnormal immunophenotype and c‐Kit mutation D816V. Leuk. Lymphoma 45, 2295–2302. Norrby, K. (1997). Mast cells and de novo angiogenesis: Angiogenic capability of individual masT cell mediators such as histamine, TNF, IL‐8 and bFGF. Inflamm. Res. 46(Suppl. 1), S7–S8. Nugent, M. A., and Iozzo, R. V. (2000). Fibroblast growth factor‐2. Int. J. Biochem. Cell Biol. 32, 115–120. O’Farrell, A. M., Ichihara, M., Mui, A. L., and Miyajima, A. (1996). Signaling pathways activated in a unique mast cell line where interleukin‐3 supports survival and stem cell factor is required for a proliferative response. Blood 87, 3655–3668. O’Hare, T., Walters, D. K., Deininger, M. W., and Druker, B. J. (2005). AMN107: Tightening the grip of imatinib. Cancer Cell 7, 117–119. O’Laughlin‐Bunner, B., Radosevic, N., Taylor, M. L., Shivakrupa, DeBerry, C., Metcalfe, D. D., Zhou, M., Lowell, C., and Linnekin, D. (2001). Lyn is required for normal stem cell factor‐ induced proliferation and chemotaxis of primary hematopoietic cells. Blood 98, 343–350. Oettgen, H. C., Martin, T. R., Wynshaw‐Boris, A., Deng, C., Drazen, J. M., and Leder, P. (1994). Active anaphylaxis in IgE‐deficient mice. Nature 370, 367–370. Ohnishi, K., Ohno, R., Tomonaga, M., Kamada, N., Onozawa, K., Kuramoto, A., Dohy, H., Mizoguchi, H., Miyawaki, S., and Tsubaki, K. (1995). A randomized trial comparing interferon‐alpha with busulfan for newly diagnosed chronic myelogenous leukemia in chronic phase. Blood 86, 906–916. Ohnishi, K., Tomonaga, M., Kamada, N., Onozawa, K., Kuramoto, A., Dohy, H., Mizoguchi, H., Miyawaki, S., Tsubaki, K., Miura, Y., Omine, M., Kobayashi, T., Naoe, T., Ohshima, T., Hirashima, K., Ohtake, S., Takahashi, I., Morishima, Y., Naito, K., Asou, N., Tanimoto, M.,
236
JAMIE ROBYN AND DEAN D. METCALFE
Sakuma, A., and Ohno, R. (1998). A long term follow‐up of a randomized trial comparing interferon‐alpha with busulfan for chronic myelogenous leukemia. The Kouseisho Leukemia Study Group. Leuk. Res. 22, 779–786. Okayama, Y., Hagaman, D. D., and Metcalfe, D. D. (2001). A comparison of mediators released or generated by IFN‐gamma‐treated human mast cells following aggregation of Fc gamma RI or Fc epsilon RI. J. Immunol. 166, 4705–4712. Okayama, Y., Kirshenbaum, A. S., and Metcalfe, D. D. (2000). Expression of a functional high‐ affinity IgG receptor, Fc gamma RI, on human mast cells: Upregulation by IFN‐gamma. J. Immunol. 164, 4332–4339. Oskeritzian, C. A., Wang, Z., Kochan, J. P., Grimes, M., Du, Z., Chang, H. W., Grant, S., and Schwartz, L. B. (1999). Recombinant human (rh)IL‐4‐mediated apoptosis and recombinant human IL‐6‐mediated protection of recombinant human stem cell factor‐dependent human mast cells derived from cord blood mononuclear cell progenitors. J. Immunol. 163, 5105–5115. Pardanani, A., Elliott, M., Reeder, T., Li, C. Y., Baxter, E. J., Cross, N. C., and Tefferi, A. (2003a). Imatinib for systemic masT cell disease. Lancet 362, 535–536. Pardanani, A., Hoffbrand, A. V., Butterfield, J. H., and Tefferi, A. (2004a). Treatment of systemic mast cell disease with 2‐chlorodeoxyadenosine. Leuk. Res. 28, 127–131. Pardanani, A., Ketterling, R. P., Brockman, S. R., Flynn, H. C., Paternoster, S. F., Shearer, B. M., Reeder, T. L., Li, C. Y., Cross, N. C., Cools, J., Gilliland, D. G., Dewald, G. W., and Tefferi, A. (2003b). CHIC2 deletion, a surrogate for FIP1L1‐PDGFRA fusion, occurs in systemic mastocytosis associated with eosinophilia and predicts response to imatinib mesylate therapy. Blood 102, 3093–3096. Pardanani, A., Kimlinger, T., Reeder, T., Li, C. Y., and Tefferi, A. (2004b). Bone marrow mast cell immunophenotyping in adults with mast cell disease: A prospective study of 33 patients. Leuk. Res. 28, 777–783. Parker, R. I. (2000). Hematologic aspects of systemic mastocytosis. Hematol. Oncol. Clin. North Am. 14, 557–568. Pauls, J. D., Brems, J., Pockros, P. J., Saven, A., Wagner, R. L., Weber, R., Metcalfe, D., and Christiansen, S. C. (1999). Mastocytosis: Diverse presentations and outcomes. Arch. Intern. Med. 159, 401–405. Paulson, R. F., Vesely, S., Siminovitch, K. A., and Bernstein, A. (1996). Signalling by the W/Kit receptor tyrosine kinase is negatively regulated in vivo by the protein tyrosine phosphatase Shp1. Nat. Genet. 13, 309–315. Pawankar, R., Okuda, M., Yssel, H., Okumura, K., and Ra, C. (1997). Nasal mast cells in perennial allergic rhinitics exhibit increased expression of the Fc epsilonRI, CD40L, IL‐4, and IL‐13, and can induce IgE synthesis in B cells. J. Clin. Invest. 99, 1492–1499. Payne, V., and Kam, P. C. (2004). Mast cell tryptase: A review of its physiology and clinical significance. Anaesthesia 59, 695–703. Pejler, G., and Karlstrom, A. (1993). Thrombin is inactivated by mast cell secretory granule chymase. J. Biol. Chem. 268, 11817–11822. Penrose, J. F., Gagnon, L., Goppelt‐Struebe, M., Myers, P., Lam, B. K., Jack, R. M., Austen, K. F., and Soberman, R. J. (1992). Purification of human leukotriene C4 synthase. Proc. Natl. Acad. Sci. USA 89, 11603–11606. Perez‐Ruiz, M., Ros, J., Morales‐Ruiz, M., Navasa, M., Colmenero, J., Ruiz‐del‐Arbol, L., Cejudo, P., Claria, J., Rivera, F., Arroyo, V., Rodes, J., and Jimenez, W. (1999). Vascular endothelial growth factor production in peritoneal macrophages of cirrhotic patients: Regulation by cytokines and bacterial lipopolysaccharide. Hepatology 29, 1057–1063.
SYSTEMIC MASTOCYTOSIS
237
Pignon, J. M., Giraudier, S., Duquesnoy, P., Jouault, H., Imbert, M., Vainchenker, W., Vernant, J. P., and Tulliez, M. (1997). A new c‐Kit mutation in a case of aggressive mast cell disease. Br. J. Haematol. 96, 374–376. Plo, I., Lautier, D., Casteran, N., Dubreuil, P., Arock, M., and Laurent, G. (2001). Kit signaling and negative regulation of daunorubicin‐induced apoptosis: Role of phospholipase Cgamma. Oncogene 20, 6752–6763. Prodeus, A. P., Zhou, X., Maurer, M., Galli, S. J., and Carroll, M. C. (1997). Impaired mast cell‐ dependent natural immunity in complement C3‐deficient mice. Nature 390, 172–175. Przepiorka, D., Giralt, S., Khouri, I., Champlin, R., and Bueso‐Ramos, C. (1998). Allogeneic marrow transplantation for myeloproliferative disorders other than chronic myelogenous leukemia: Review of forty cases1. Am. J. Hematol. 57, 24–28. Pulik, M., Lionnet, F., Petit, A., Genet, P., and Gaulier, A. (1994). Long‐term response to interferon‐alpha in a patient with systemic mastocytosis and chronic myelomonocytic leukemia. Am. J. Hematol. 47, 66. Puxeddu, I., Piliponsky, A. M., Bachelet, I., and Levi‐Schaffer, F. (2003). Mast cells in allergy and beyond. Int. J. Biochem. Cell Biol. 35, 1601–1607. Qu, Z., Huang, X., Ahmadi, P., Stenberg, P., Liebler, J. M., Le, A. C., Planck, S. R., and Rosenbaum, J. T. (1998a). Synthesis of basic fibroblast growth factor by murine mast cells. Regulation by transforming growth factor beta, tumor necrosis factor alpha, and stem cell factor. Int. Arch. Allergy Immunol. 115, 47–54. Qu, Z., Kayton, R. J., Ahmadi, P., Liebler, J. M., Powers, M. R., Planck, S. R., and Rosenbaum, J. T. (1998b). Ultrastructural immunolocalization of basic fibroblast growth factor in mast cell secretory granules. Morphological evidence for bfgf release through degranulation. J. Histochem. Cytochem. 46, 1119–1128. Radosevic, N., Winterstein, D., Keller, J. R., Neubauer, H., Pfeffer, K., and Linnekin, D. (2004). JAK2 contributes to the intrinsic capacity of primary hematopoietic cells to respond to stem cell factor. Exp. Hematol. 32, 149–156. Rafii, M., Firooznia, H., Golimbu, C., and Balthazar, E. (1983). Pathologic fracture in systemic mastocytosis. Radiographic spectrum and review of the literature. Clin. Orthop. Relat Res., 260–267. Ribatti, D., Crivellato, E., Candussio, L., Nico, B., Vacca, A., Roncali, L., and Dammacco, F. (2001). Mast cells and their secretory granules are angiogenic in the chick embryo chorioallantoic membrane1. Clin. Exp. Allergy 31, 602–608. Risau, W. (1997). Mechanisms of angiogenesis. Nature 386, 671–674. Robson, M. E., Glogowski, E., Sommer, G., Antonescu, C. R., Nafa, K., Maki, R. G., Ellis, N., Besmer, P., Brennan, M., and Offit, K. (2004). Pleomorphic characteristics of a germ line KIT mutation in a large kindred with gastrointestinal stromal tumors, hyperpigmentation, and dysphagia. Clin. Cancer Res. 10, 1250–1254. Ronnov‐Jessen, D., Lovgreen, N. P., and Horn, T. (1991). Persistence of systemic mastocytosis after allogeneic bone marrow transplantation in spite of complete remission of the associated myelodysplastic syndrome. Bone Marrow Transplant. 8, 413–415. Rottapel, R., Reedijk, M., Williams, D. E., Lyman, S. D., Anderson, D. M., Pawson, T., and Bernstein, A. (1991). The Steel/W transduction pathway: Kit autophosphorylation and its association with a unique subset of cytoplasmic signaling proteins is induced by the Steel factor. Mol. Cell. Biol. 11, 3043–3051. Rottem, M., Hull, G., and Metcalfe, D. D. (1994a). Demonstration of differential effects of cytokines on mast cells derived from murine bone marrow and peripheral blood mononuclear cells. Exp. Hematol. 22, 1147–1155.
238
JAMIE ROBYN AND DEAN D. METCALFE
Rottem, M., Okada, T., Goff, J. P., and Metcalfe, D. D. (1994b). Mast cells cultured from the peripheral blood of normal donors and patients with mastocytosis originate from a CD34þ/Fc epsilon RI‐ cell population. Blood 84, 2489–2496. Rumsaeng, V., Cruikshank, W. W., Foster, B., Prussin, C., Kirshenbaum, A. S., Davis, T. A., Kornfeld, H., Center, D. M., and Metcalfe, D. D. (1997). Human mast cells produce the CD4þ T lymphocyte chemoattractant factor, IL‐16. J. Immunol. 159, 2904–2910. Ryan, J. J., Huang, H., McReynolds, L. J., Shelburne, C., Hu‐Li, J., Huff, T. F., and Paul, W. E. (1997). Stem cell factor activates STAT‐5 DNA binding in IL‐3‐derived bone marrow mast cells. Exp. Hematol. 25, 357–362. Sakuma, Y., Sakurai, S., Oguni, S., Hironaka, M., and Saito, K. (2003). Alterations of the c‐Kit gene in testicular germ cell tumors. Cancer Sci. 94, 486–491. Samoszuk, M., Corwin, M., and Hazen, S. L. (2003). Effects of human mast cell tryptase on the kinetics of blood clotting. Thromb. Res. 109, 153–156. Sattler, M., and Salgia, R. (2004). Targeting c‐Kit mutations: Basic science to novel therapies. Leuk. Res. 28(Suppl. 1), S11–S20. Sawyers, C. L. S. N. P., Kantarjain, H. M., Donato, N., Nicoll, J., Bai, S. A., Huang, F., Clark, E., De Cillis, A. P., and Talpaz, M. (2004). Hematologic and cytogenetic responses in imatinib‐ resistant chronic phase chronic myeloid leukemia patients treated with the dual SRC//ABL kinase inhibitor. Blood 104, 1a. Schwartz, L. B. (2001). Clinical utility of tryptase levels in systemic mastocytosis and associated hematologic disorders. Leuk. Res. 25, 553–562. Schwartz, L. B., Bradford, T. R., Littman, B. H., and Wintroub, B. U. (1985). The fibrinogenolytic activity of purified tryptase from human lung mast cells. J. Immunol. 135, 2762–2767. Schwartz, L. B., and Irani, A. M. (2000). Serum tryptase and the laboratory diagnosis of systemic mastocytosis. Hematol. Oncol. Clin. North Am. 14, 641–657. Schwartz, L. B., Min, H. K., Ren, S., Xia, H. Z., Hu, J., Zhao, W., Moxley, G., and Fukuoka, Y. (2003). Tryptase precursors are preferentially and spontaneously released, whereas mature tryptase is retained by HMC‐1 cells, Mono‐Mac‐6 cells, and human skin‐derived mast cells. J. Immunol. 170, 5667–5673. Schwartz, L. B., Sakai, K., Bradford, T. R., Ren, S., Zweiman, B., Worobec, A. S., and Metcalfe, D. D. (1995). The alpha form of human tryptase is the predominant type present in blood at baseline in normal subjects and is elevated in those with systemic mastocytosis. J. Clin. Invest. 96, 2702–2710. Scott, H. W., Jr., Parris, W. C., Sandidge, P. C., Oates, J. A., and Roberts, L. J. (1983). Hazards in operative management of patients with systemic mastocytosis. Ann. Surg. 197, 507–514. Sezary, A., and Chauvillon, P. (1936). Dermographisme et mastocytose. Bull. Soc. Fr. Dermatol. Syph. 43, 359–361. Shah, N. P., Lee, F. Y., Sawyers, C. L., and Akin, C. (2004a). BMS‐354825 is a SRC/ABL inhibitor with high nanomolar activity against the Kit D816V mutation which drives systemic mastocytosis and is imatinib‐resistant. Blood 104, 228a. Shah, N. P., Tran, C., Lee, F. Y., Chen, P., Norris, D., and Sawyers, C. L. (2004b). Overriding imatinib resistance with a novel ABL kinase inhibitor. Science 305, 399–401. Shultz, L. D., Schweitzer, P. A., Rajan, T. V., Yi, T., Ihle, J. N., Matthews, R. J., Thomas, M. L., and Beier, D. R. (1993). Mutations at the murine moth‐eaten locus are within the hematopoietic cell protein‐tyrosine phosphatase (Hcph) gene. Cell 73, 1445–1454. Sillaber, C., Baghestanian, M., Bevec, D., Willheim, M., Agis, H., Kapiotis, S., Fureder, W., Bankl, H. C., Kiener, H. P., Speiser, W., Binder, B. R., Lechner, K., and Valent, P. (1999). The mast cell as site of tissue‐type plasminogen activator expression and fibrinolysis. J. Immunol. 162, 1032–1041.
SYSTEMIC MASTOCYTOSIS
239
Simon, J., Lortholary, O., Caillat‐Vigneron, N., Raphael, M., Martin, A., Briere, J., Barete, S., Hermine, O., and Casassus, P. (2004). Interest of interferon alpha in systemic mastocytosis. The French experience and review of the literature. Pathol. Biol. (Paris) 52, 294–299. Smith, C. A., and Rennick, D. M. (1986). Characterization of a murine lymphokine distinct from interleukin 2 and interleukin 3 (IL‐3) possessing a Tcell growth factor activity and a masTcell growth factor activity that synergizes with IL‐3. Proc. Natl. Acad. Sci. USA 83, 1857–1861. Smith, G. B., Gusberg, R. J., Jordan, R. H., and Kim, B. (1987a). Histamine levels and cardiovascular responses during splenectomy and splenorenal shunt formation in a patient with systemic mastocytosis. Anaesthesia 42, 861–867. Smith, T. F., Welch, T. R., Allen, J. B., and Sondheimer, J. M. (1987b). Cutaneous mastocytosis with bleeding: Probable heparin effect. Cutis 39, 241–244. Soter, N. A., Austen, K. F., and Wasserman, S. I. (1979). Oral disodium cromoglycate in the treatment of systemic mastocytosis. N. Engl. J. Med. 301, 465–469. Soto, D., Malmsten, C., Blount, J. L., Muilenburg, D. J., and Caughey, G. H. (2002). Genetic deficiency of human mast cell alpha‐tryptase. Clin. Exp. Allergy 32, 1000–1006. Sperr, W. R., Czerwenka, K., Mundigler, G., Muller, M. R., Semper, H., Klappacher, G., Glogar, H. D., Lechner, K., and Valent, P. (1993). Specific activation of human mast cells by the ligand for c‐Kit: Comparison between lung, uterus and heart mast cells235. Int. Arch. Allergy Immunol. 102, 170–175. Sperr, W. R., Escribano, L., Jordan, J. H., Schernthaner, G. H., Kundi, M., Horny, H. P., and Valent, P. (2001a). Morphologic properties of neoplastic mast cells: Delineation of stages of maturation and implication for cytological grading of mastocytosis. Leuk. Res. 25, 529–536. Sperr, W. R., Horny, H. P., Lechner, K., and Valent, P. (2000). Clinical and biologic diversity of leukemias occurring in patients with mastocytosis. Leuk. Lymphoma 37, 473–486. Sperr, W. R., Horny, H. P., and Valent, P. (2002a). Spectrum of associated clonal hematologic non‐ mast cell lineage disorders occurring in patients with systemic mastocytosis. Int. Arch. Allergy Immunol. 127, 140–142. Sperr, W. R., Jordan, J. H., Baghestanian, M., Kiener, H. P., Samorapoompichit, P., Semper, H., Hauswirth, A., Schernthaner, G. H., Chott, A., Natter, S., Kraft, D., Valenta, R., Schwartz, L. B., Geissler, K., Lechner, K., and Valent, P. (2001b). Expression of mast cell tryptase by myeloblasts in a group of patients with acute myeloid leukemia. Blood 98, 2200–2209. Sperr, W. R., Jordan, J. H., Fiegl, M., Escribano, L., Bellas, C., Dirnhofer, S., Semper, H., Simonitsch‐Klupp, I., Horny, H. P., and Valent, P. (2002b). Serum tryptase levels in patients with mastocytosis: Correlation with mast cell burden and implication for defining the category of disease. Int. Arch. Allergy Immunol. 128, 136–141. Sperr, W. R., Stehberger, B., Wimazal, F., Baghestanian, M., Schwartz, L. B., Kundi, M., Semper, H., Jordan, J. H., Chott, A., Drach, J., Jager, U., Geissler, K., Greschniok, A., Horny, H. P., Lechner, K., and Valent, P. (2002c). Serum tryptase measurements in patients with myelodysplastic syndromes. Leuk. Lymphoma 43, 1097–1105. Sperr, W. R., Walchshofer, S., Horny, H. P., Fodinger, M., Simonitsch, I., Fritsche‐Polanz, R., Schwarzinger, I., Tschachler, E., Sillaber, C., Hagen, W., Geissler, K., Chott, A., Lechner, K., and Valent, P. (1998). Systemic mastocytosis associated with acute myeloid leukaemia: Report of two cases and detection of the c‐Kit mutation Asp‐816 to Val. Br. J. Haematol. 103, 740–749. Spritz, R. A. (1994). Molecular basis of human piebaldism. J. Invest. Dermatol. 103, 137S–140S. Spyridonidis, A., Thomas, A. K., Bertz, H., Zeiser, R., Schmitt‐Graff, A., Lindemann, A., Waller, C. F., and Finke, J. (2004). Evidence for a graft‐versus‐masT cell effect after allogeneic bone marrow transplantation. Bone Marrow Transplant. 34, 515–519. Stack, M. S., and Johnson, D. A. (1994). Human mast cell tryptase activates single‐chain urinary‐ type plasminogen activator (pro‐urokinase). J. Biol. Chem. 269, 9416–9419.
240
JAMIE ROBYN AND DEAN D. METCALFE
Stellato, C., de, P. A., Cirillo, R., Mastronardi, P., Mazzarella, B., and Marone, G. (1991). Heterogeneity of human mast cells and basophils in response to muscle relaxants. Anesthesiology 74, 1078–1086. Stellato, C., and Marone, G. (1995). Mast cells and basophils in adverse reactions to drugs used during general anesthesia. Chem. Immunol. 62, 108–131. Supajatura, V., Ushio, H., Nakao, A., Akira, S., Okumura, K., Ra, C., and Ogawa, H. (2002). Differential responses of mast cell Toll‐like receptors 2 and 4 in allergy and innate immunity. J. Clin. Invest 109, 1351–1359. Supajatura, V., Ushio, H., Nakao, A., Okumura, K., Ra, C., and Ogawa, H. (2001). Protective roles of mast cells against enterobacterial infection are mediated by Toll‐like receptor 4. J. Immunol. 167, 2250–2256. Tan, B. L., Yazicioglu, M. N., Ingram, D., McCarthy, J., Borneo, J., Williams, D. A., and Kapur, R. (2003). Genetic evidence for convergence of c‐Kit‐ and alpha4 integrin‐mediated signals on class IA PI‐3kinase and the Rac pathway in regulating integrin‐directed migration in mast cells. Blood 101, 4725–4732. Tanaka, A., Konno, M., Muto, S., Kambe, N., Morii, E., Nakahata, T., Itai, A., and Matsuda, H. (2005). A novel NF‐{kappa}B inhibitor, IMD‐0354, suppresses neoplastic proliferation of human mast cells with constitutively activated c‐Kit receptors. Blood 105, 2324–2331. Tartaglia, M., Mehler, E. L., Goldberg, R., Zampino, G., Brunner, H. G., Kremer, H., van, d.B., Crosby, A. H., Ion, A., Jeffery, S., Kalidas, K., Patton, M. A., Kucherlapati, R. S., and Gelb, B. D. (2001). Mutations in PTPN11, encoding the protein tyrosine phosphatase SHP‐2, cause Noonan syndrome. Nat. Genet. 29, 465–468. Tartaglia, M., Niemeyer, C. M., Fragale, A., Song, X., Buechner, J., Jung, A., Hahlen, K., Hasle, H., Licht, J. D., and Gelb, B. D. (2003). Somatic mutations in PTPN11 in juvenile myelomonocytic leukemia, myelodysplastic syndromes and acute myeloid leukemia. Nat. Genet. 34, 148–150. Tauchi, T., Feng, G. S., Marshall, M. S., Shen, R., Mantel, C., Pawson, T., and Broxmeyer, H. E. (1994). The ubiquitously expressed Syp phosphatase interacts with c‐Kit and Grb2 in hematopoietic cells. J. Biol. Chem. 269, 25206–25211. Taylor, M. L., Dastych, J., Sehgal, D., Sundstrom, M., Nilsson, G., Akin, C., Mage, R. G., and Metcalfe, D. D. (2001). The Kit‐activating mutation D816V enhances stem cell factor‐dependent chemotaxis 59. Blood 98, 1195–1199. Taylor, M. L., Sehgal, D., Raffeld, M., Obiakor, H., Akin, C., Mage, R. G., and Metcalfe, D. D. (2004). Demonstration that mast cells, T cells, and B cells bearing the activating kit mutation D816V occur in clusters within the marrow of patients with mastocytosis. J. Mol. Diagn. 6, 335–342. Tefferi, A., Li, C. Y., Butterfield, J. H., and Hoagland, H. C. (2001). Treatment of systemic masT cell disease with cladribine. N. Engl. J. Med. 344, 307–309. Temkin, V., Kantor, B., Weg, V., Hartman, M. L., and Levi‐Schaffer, F. (2002). Tryptase activates the mitogen‐activated protein kinase/activator protein‐1 pathway in human peripheral blood eosinophils, causing cytokine production and release. J. Immunol. 169, 2662–2669. The Italian Cooperative Study Group on Chronic Myeloid Leukemia (1994). Interferon alfa‐2a as compared with conventional chemotherapy for the treatment of chronic myeloid leukemia. N. Engl. J. Med. 330, 820–825. Theoharides, T. C., Boucher, W., and Spear, K. (2002). Serum interleukin‐6 reflects disease severity and osteoporosis in mastocytosis patients. Int. Arch. Allergy Immunol. 128, 344–350. Tian, Q., Frierson, H. F., Jr., Krystal, G. W., and Moskaluk, C. A. (1999). Activating c‐Kit gene mutations in human germ cell tumors. Am. J. Pathol. 154, 1643–1647.
SYSTEMIC MASTOCYTOSIS
241
tires‐Alj, M., Paez, J. G., David, F. S., Keilhack, H., Halmos, B., Naoki, K., Maris, J. M., Richardson, A., Bardelli, A., Sugarbaker, D. J., Richards, W. G., Du, J., Girard, L., Minna, J. D., Loh, M. L., Fisher, D. E., Velculescu, V. E., Vogelstein, B., Meyerson, M., Sellers, W. R., and Neel, B. G. (2004). Activating mutations of the noonan syndrome‐associated SHP2/PTPN11 gene in human solid tumors and adult acute myelogenous leukemia. Cancer Res. 64, 8816–8820. Tkaczyk, C., Okayama, Y., Metcalfe, D. D., and Gilfillan, A. M. (2004). Fcgamma receptors on mast cells: Activatory and inhibitory regulation of mediator release. Int. Arch. Allergy Immunol. 133, 305–315. Tkaczyk, C., Okayama, Y., Woolhiser, M. R., Hagaman, D. D., Gilfillan, A. M., and Metcalfe, D. D. (2002). Activation of human mast cells through the high affinity IgG receptor. Mol. Immunol. 38, 1289–1293. Torrey, E., Simpson, K., Wilbur, S., Munoz, P., and Skikne, B. (1990). Malignant mastocytosis with circulating mast cells. Am. J. Hematol. 34, 283–286. Travis, W. D., Li, C. Y., Bergstralh, E. J., Yam, L. T., and Swee, R. G. (1988a). Systemic mast cell disease. Analysis of 58 cases and literature review. Medicine (Baltimore) 67, 345–368. Travis, W. D., Li, C. Y., Hoagland, H. C., Travis, L. B., and Banks, P. M. (1986). Mast cell leukemia: Report of a case and review of the literature. Mayo Clin. Proc. 61, 957–966. Travis, W. D., Li, C. Y., Yam, L. T., Bergstralh, E. J., and Swee, R. G. (1988b). Significance of systemic mast cell disease with associated hematologic disorders. Cancer 62, 965–972. Trevisan, G., Pauluzzi, P., Gatti, A., and Semeraro, A. (2000). Familial mastocytosis associated with neurosensory deafness. J. Eur. Acad. Dermatol. Venereol. 14, 119–122. Trieselmann, N. Z., Soboloff, J., and Berger, S. A. (2003). Mast cells stimulated by membrane‐ bound, but not soluble, steel factor are dependent on phospholipase C activation. Cell Mol. Life Sci. 60, 759–766. Unna, P. G. (1887). Beitrage zur anatomic und pathogenese der urticaria simplex und pigmentosa. Mschr Prakt Dermatol, Suppl Dermatol Stud 3. Valent, P. (1996). Biology, classification and treatment of human mastocytosis. Wien. Klin. Wochenschr. 108, 385–397. Valent, P., Akin, C., Sperr, W. R., Escribano, L., Arock, M., Horny, H. P., Bennett, J. M., and Metcalfe, D. D. (2003a). Aggressive systemic mastocytosis and related mast cell disorders: Current treatment options and proposed response criteria. Leuk. Res. 27, 635–641. Valent, P., Akin, C., Sperr, W. R., Horny, H. P., Arock, M., Lechner, K., Bennett, J. M., and Metcalfe, D. D. (2003b). Diagnosis and treatment of systemic mastocytosis: State of the art. Br. J. Haematol. 122, 695–717. Valent, P., Akin, C., Sperr, W. R., Horny, H. P., and Metcalfe, D. D. (2002). Smoldering mastocytosis: A novel subtype of systemic mastocytosis with slow progression. Int. Arch. Allergy Immunol. 127, 137–139. Valent, P., Akin, C., Sperr, W. R., Mayerhofer, M., Fodinger, M., Fritsche‐Polanz, R., Sotlar, K., Escribano, L., Arock, M., Horny, H. P., and Metcalfe, D. D. (2005). Mastocytosis: Pathology, genetics, and current options for therapy. Leuk. Lymphoma 46, 35–48. Valent, P., Escribano, L., Parwaresch, R. M., Schemmel, V., Schwartz, L. B., Sotlar, K., Sperr, W. R., and Horny, H. P. (1999). Recent advances in mastocytosis research. Summary of the Vienna Mastocytosis Meeting 1998. Int. Arch. Allergy Immunol. 120, 1–7. Valent, P., Horny, H. P., Escribano, L., Longley, B. J., Li, C. Y., Schwartz, L. B., Marone, G., Nunez, R., Akin, C., Sotlar, K., Sperr, W. R., Wolff, K., Brunning, R. D., Parwaresch, R. M., Austen, K. F., Lennert, K., Metcalfe, D. D., Vardiman, J. W., and Bennett, J. M. (2001a). Diagnostic criteria and classification of mastocytosis: A consensus proposal. Leuk. Res. 25, 603–625.
242
JAMIE ROBYN AND DEAN D. METCALFE
Valent, P., Horny, H. P., Li, C. Y., Longley, B. J., Metcalfe, D. D., Parwaresch, R. M., and Bennett, J. M. (2001b). Mastocytosis. In ‘‘World Health Organization Classification of Tumours: Pathology and Genetics: Tumours of Haematopoietic and Lymphoid Tissues’’ (E. Jaffe, N. L. Harris, H. Stein, and J. W. Wardiman, Eds.), pp. 291–302. IARC Press, Lyon. Valent, P., Spanblochl, E., Sperr, W. R., Sillaber, C., Zsebo, K. M., Agis, H., Strobl, H., Geissler, K., Bettelheim, P., and Lechner, K. (1992). Induction of differentiation of human mast cells from bone marrow and peripheral blood mononuclear cells by recombinant human stem cell factor/ kit‐ligand in long‐term culture. Blood 80, 2237–2245. Valent, P., Sperr, W. R., Samorapoompichit, P., Geissler, K., Lechner, K., Horny, H. P., and Bennett, J. M. (2001c). Myelomastocytic overlap syndromes: Biology, criteria, and relationship to mastocytosis. Leuk. Res. 25, 595–602. Varadaradjalou, S., Feger, F., Thieblemont, N., Hamouda, N. B., Pleau, J. M., Dy, M., and Arock, M. (2003). Toll‐like receptor 2 (TLR2) and TLR4 differentially activate human mast cells. Eur. J. Immunol. 33, 899–906. Vaughan, S. T., and Jones, G. N. (1998). Systemic mastocytosis presenting as profound cardiovascular collapse during anaesthesia. Anaesthesia 53, 804–807. Walls, A. F., Bennett, A. R., McBride, H. M., Glennie, M. J., Holgate, S. T., and Church, M. K. (1990). Production and characterization of monoclonal antibodies specific for human mast cell tryptase. Clin. Exp. Allergy 20, 581–589. Walton, J. (1989). Mastocytosis/vasodilatory shock in a 25‐year‐old woman. J. Emerg. Nurs. 15, 356–357. Webb, T. A., Li, C. Y., and Yam, L. T. (1982). Systemic mast cell disease: A clinical and hematopathologic study of 26 cases. Cancer 49, 927–938. Weide, R., Ehlenz, K., Lorenz, W., Walthers, E., Klausmann, M., and Pfluger, K. H. (1996). Successful treatment of osteoporosis in systemic mastocytosis with interferon alpha‐2b. Ann. Hematol. 72, 41–43. Weiler, S. R., Mou, S., De Berry, C. S., Keller, J. R., Ruscetti, F. W., Ferris, D. K., Longo, D. L., and Linnekin, D. (1996). JAK2 is associated with the c‐Kit proto‐oncogene product and is phosphorylated in response to stem cell factor. Blood 87, 3688–3693. Wershil, B. K., Furuta, G. T., Wang, Z. S., and Galli, S. J. (1996). Mast cell‐dependent neutrophil and mononuclear cell recruitment in immunoglobulin E‐induced gastric reactions in mice. Gastroenterology 110, 1482–1490. Wershil, B. K., Wang, Z. S., Gordon, J. R., and Galli, S. J. (1991). Recruitment of neutrophils during IgE‐dependent cutaneous late phase reactions in the mouse is mast cell‐dependent. Partial inhibition of the reaction with antiserum against tumor necrosis factor‐alpha. J. Clin. Invest. 87, 446–453. Wiesner, S. M., Jones, J. M., Hasz, D. E., and Largaespada, D. A. (2005). A repressible transgenic model of NRAS oncogene driven mast cell disease in the mouse. Blood 106, 1054–1062. Wimazal, F., Jordan, J. H., Sperr, W. R., Chott, A., Dabbass, S., Lechner, K., Horny, H. P., and Valent, P. (2002). Increased angiogenesis in the bone marrow of patients with systemic mastocytosis. Am. J. Pathol. 160, 1639–1645. Wolff, K., Komar, M., and Petzelbauer, P. (2001). Clinical and histopathological aspects of cutaneous mastocytosis. Leuk. Res. 25, 519–528. Worobec, A. S. (2000). Treatment of systemic mast cell disorders. Hematol. Oncol. Clin. North Am. 14, 659–687, vii. Worobec, A. S., Akin, C., Scott, L. M., and Metcalfe, D. D. (2000). Mastocytosis complicating pregnancy 80. Obstet. Gynecol. 95, 391–395.
SYSTEMIC MASTOCYTOSIS
243
Worobec, A. S., Kirshenbaum, A. S., Schwartz, L. B., and Metcalfe, D. D. (1996). Treatment of three patients with systemic mastocytosis with interferon alpha‐2b. Leuk. Lymphoma 22, 501–508. Worobec, A. S., Semere, T., Nagata, H., and Metcalfe, D. D. (1998). Clinical correlates of the presence of the Asp816Val c‐Kit mutation in the peripheral blood mononuclear cells of patients with mastocytosis. Cancer 83, 2120–2129. Wu, H., Klingmuller, U., Besmer, P., and Lodish, H. F. (1995). Interaction of the erythropoietin and stem‐cell‐factor receptors. Nature 377, 242–246. Yavuz, A. S., Lipsky, P. E., Yavuz, S., Metcalfe, D. D., and Akin, C. (2002). Evidence for the involvement of a hematopoietic progenitor cell in systemic mastocytosis from single‐cell analysis of mutations in the c‐Kit gene. Blood 100, 661–665. Yee, N. S., Hsiau, C. W., Serve, H., Vosseller, K., and Besmer, P. (1994). Mechanism of downregulation of c‐Kit receptor. Roles of receptor tyrosine kinase, phosphatidylinositol 30 ‐kinase, and protein kinase C. J. Biol. Chem. 269, 31991–31998. Zhang, Y., Ramos, B. F., and Jakschik, B. A. (1992). Neutrophil recruitment by tumor necrosis factor from mast cells in immune complex peritonitis. Science 258, 1957–1959. Zsebo, K. M., Williams, D. A., Geissler, E. N., Broudy, V. C., Martin, F. H., Atkins, H. L., Hsu, R. Y., Birkett, N. C., Okino, K. H., and Murdock, D. C. (1990). Stem cell factor is encoded at the Sl locus of the mouse and is the ligand for the c‐Kit tyrosine kinase receptor. Cell 63, 213–224.
Regulation of Fibrosis by the Immune System Mark L. Lupher, Jr., and W. Michael Gallatin* ICOS Corporation, Bothell, Washington*Current address: Frazier Healthcare Ventures, Seattle, Washington.
1. 2. 3. 4. 5. 6. 7.
Abstract............................................................................................................. Introduction ....................................................................................................... Fibrotic Disease Pathogenesis................................................................................ Cellular Mediators of Fibrosis ............................................................................... Inflammatory Chemokines that Regulate Fibrosis...................................................... The Role of Integrins in Regulating the Fibrotic Response ......................................... Other Potential Targets for Anti‐Fibrotic Therapy ..................................................... Conclusions........................................................................................................ References .........................................................................................................
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Abstract Inflammation and fibrosis are two inter‐related conditions with many overlapping mechanisms. Three specific cell types, macrophages, T helper cells, and myofibroblasts, each play important roles in regulating both processes. Following tissue injury, an inflammatory stimulus is often necessary to initiate tissue repair, where cytokines released from resident and infiltrating leukocytes stimulate proliferation and activation of myofibroblasts. However, in many cases this drive stimulates an inappropriate pro‐fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro‐ inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Moreover, inflammatory cells have been shown to play contradictory roles in initiation, amplification, and resolution of fibrotic disease processes. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to be fully appreciated. In the following review, we discuss the fibrotic disease process from the context of the immune response to injury. We review the major cellular and soluble factors controlling these responses and suggest ways in which more specific and, hopefully, more effective therapies may be derived. 1. Introduction Inflammation and fibrosis are two inter‐related processes with many overlapping mechanisms. An inflammatory stimulus is often necessary to initiate *
Current address: Frazier Healthcare Ventures, Seattle, Washington.
245 advances in immunology, vol. 89 # 2006 Elsevier Inc. All rights reserved.
0065-2776/06 $35.00 DOI: 10.1016/S0065-2776(05)89006-6
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wound closure, where cytokines released from resident and infiltrating leukocytes stimulate proliferation and activation of myofibroblasts. However, in many cases this drive stimulates an inappropriate pro‐fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro‐inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Furthermore, some myofibroblasts appear to be of bone marrow origin, and can differentiate directly from circulating monocytes (i.e., fibrocytes). Moreover, inflammatory cells have been shown to play contradictory roles in initiation, amplification, and resolution of fibrotic disease processes. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to be fully appreciated. Therefore, the lines between the hematopoetic/immune system and the wound healing/fibrotic system are continually blurring. Given this, it is perhaps not surprising that broadly immunosuppressive drugs that may impact both pro‐ and anti‐fibrotic aspects of the immune system have been relatively ineffective in controlling fibrotic disease progression. However, there is hope that with a better understanding of the precise cellular and biochemical processes that inter‐relate inflammatory and fibrotic disease, more specific and effective therapies can be derived. In the following review we will first attempt to convey an understanding of the general processes involved in fibrotic disease initiation, progression, and resolution. Activation of the myofibroblast is critical for most (if not all) aspects of the fibrotic process. Second, we will discuss how the innate immune system contributes to and perhaps regulates these processes. Third, we will describe how the adaptive immune system can direct the innate response down pathways of resolution or fibrosis through production of TH1 or TH2 cytokines, respectively. Finally, we will look at therapeutic modalities in development and attempt to suggest potential new areas to explore based upon our current understanding of the inter‐relatedness of the inflammatory and fibrotic responses. 2. Fibrotic Disease Pathogenesis Fibrosis is a leading cause of morbidity and mortality and a key component of multiple diseases affecting millions of people worldwide including: liver cirrhosis; idiopathic pulmonary fibrosis; scleroderma; diabetic retinopathy and age‐related macular degeneration; diabetic nephropathy; glomerulosclerosis and IgA nephropathy; and congestive heart failure. There are currently no approved treatments that directly target the process of fibrosis despite this large unmet medical need. Fibrosis can best be described as an improperly regulated wound healing response, and is a normal reaction of tissues to injury (reviewed in [Martin,
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1997; Mutsaers et al., 1997]). This series of events is similar in most tissues including liver, lung, kidney, heart, and skin. Leakage of blood components at the injury site exposes platelets to extracellular matrix, triggering aggregation, clot formation, and haemostasis. In addition, the surrounding blood vessels constrict, reducing hemorrhage. Next, components derived from platelet degranulation cause vasodilation and increased permeability of nearby blood vessels; whereas, cleavage of fibrinogen by thrombin during the clotting cascade, together with fibronectin, holds the damaged tissues together in a provisional matrix. Inflammatory cells and later fibroblasts are recruited across this provisional matrix and migrate by chemotaxis to the site of injury. At early stages of wound healing, neutrophils are the most abundant inflammatory cell. As they degranulate and die, macrophages are recruited from circulation and the surrounding tissue and accumulate at the site of injury. Macrophages are vital for wound resolution and if their infiltration is blocked, healing is impaired (Leibovich and Ross, 1975). Macrophages and neutrophils act together to phagocytose debris and any invading microorganisms and are the source of many chemoattractants and growth factors (discussed later) which regulate the wound healing response. These factors are mitogenic and chemotactic for endothelial cells which surround the injury and form new blood vessels as they migrate towards its center as well as for T cells which become activated and secrete profibrotic cytokines. Additionally, fibroblasts migrate along the fibrin lattice into the wound and become activated into myofibroblasts. Fibroblasts can be derived from local mesenchymal pericytes, or be recruited from the bone marrow. Epithelial cells can also undergo epithelial‐mesenchymal transition (EMT), providing a continuous source of new fibroblasts (see Fig. 1). This complex mix of densely populated macrophages, myofibroblasts, T cells, and neovasculature embedded within a relatively loose matrix of hyaluronic acid, collagen, and fibronectin is called the granulation tissue. In the next phase, the now activated myofibroblasts produce and deposit large quantities of matrix proteins, predominantly types I and III collagen, which increases the tensile strength of the wound. Over time, the myofibroblasts contract the collagen lattice, reducing the size of the wound and bringing the wound margins closer together. During this process there is rapid synthesis and degradation of the matrix proteins called remodeling. In the remodeling phase the synthesis of new collagen exceeds the rate at which it is degraded such that the total amount of collagen continues to increase, resulting in scar formation. At the earliest stages, collagen III predominates, but at later stages it is replaced by collagen I. Although the wound may appear healed at this intermediate stage, chemical and structural changes are still occurring. Collagen fibrils become tightly packed and stabilized by the formation of inter‐ and intra‐molecular crosslinks.
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Figure 1 Mechanisms of fibrogenesis. During initial stages of tissue injury, polymorphonuclear leukocytes (PMN) and monocytes are recruited to the injury site. Cytokines such as TH1‐derived INF‐g, stimulate the differentiation of monocytes into M1 macrophages. PMN and M1 macrophages generate superoxides (O2) and TNF‐a, respectively, which can trigger apoptosis of surrounding tissue. Phagocytosis of apoptotic bodies (Apop) by monocytes or stimulation of monocytes by TH2‐derived IL‐13 or IL‐4 stimulates their differentiation into M2 macrophages. Similarly phagocytosis of apoptotic bodies by resident pericytes stimulates their differentiation into myofibroblasts. Pericytes can also be stimulated by M2 macrophage‐derived TGF‐b to differentiate into myofibroblasts. M2 macrophage‐derived TGF‐b may also stimulate endothelial cells to undergo endothelial‐to‐mesenchymal transition (EMT) to form additional myofibroblasts. Regardless of their origin, these activated myofibroblasts secrete large amounts of extracellular matrix including collagen 1. Integrin‐mediated contraction of this collagen matrix by the myofibroblasts leads to mechanical tension which by itself can also stimulate activation of fibroblasts (Fibro) to differentiate into myofibroblasts, thus amplifying the fibrogenic response.
Scar resolution is the final process in normal wound healing. This process occurs through a combination of reduced collagen synthesis and increased collagen degradation, coupled to regeneration of epithelial and endothelial layers over the resolving wound. The degradation of wound collagen and other matrix proteins is controlled by a variety of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) produced by the
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Figure 2 Mechanisms of fibrosis resolution. Infiltrating monocytes are stimulated to differentiate into M1 macrophages by TH1‐derived cytokines such as INF‐g. M1 macrophages secrete matrix metalloproteinases (MMPs) that degrade extracellular matrix and signal myofibroblasts to down‐ regulate tissue inhibitor of matrix metalloproteinases (TIMPs) as well as to undergo apoptosis (Apop). Decreased TIMP expression and myofibroblast apoptosis are required for resolution of fibrotic injury; however, the precise signaling events induced by M1 macrophages resulting in this response is currently unknown, but may involve TNF‐a, BMP‐7, HGF, and/or down‐regulation of avb3 binding.
granulocytes, macrophages, epidermal cells, and myofibroblasts recruited to the injury site. Thus, the wound healing process involves shifts in metabolic equilibrium, with an early increase in proteolytic activity, followed by a stimulation of deposition and then a resolution of the scar matrix (see Fig. 2). Any disruption in this equilibrium may result in excessive deposition of matrix components resulting in a destruction of normal tissue architecture and a compromise in tissue function; this disruption is termed fibrosis. Chronic inflammation is a common instigator, where repeated injury and repair can prevent resolution and drive the healing response to fibrosis. 3. Cellular Mediators of Fibrosis 3.1. The Origin and Role of the Myofibroblast in Fibrosis Myofibroblasts are generally believed to be the principal cell responsible for pathogenic deposition of extracellular matrix proteins within fibrotic tissue and the contraction of collagen matrix contributing to increased vascular pressure
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in the tissue and its associated morbidity in fibrotic disease. The ‘myofibroblast’ phenotype was first described by Gabbiani and coworkers in 1971 (Gabbiani et al., 1971) as fibroblastic cells located within granulation tissue which exhibited cytoplasmic microfilamentous processes. These microfilaments were later demonstrated to contain myosin and a‐smooth muscle (SM) actin, and a‐SM actin has become the most reliable marker of myofibroblastic cells (Gabbiani, 2003). A range of fibroblast‐to‐myofibroblast phenotypes exist in fibrotic lesions, from normal fibroblasts to those resembling SM cells. This range of phenotypes likely reflects different stages of transition between inactivated and ‘activated’ myofibroblasts in response to the combined action of three different pro‐fibrotic signals: (1) mechanical tension (Tomasek et al., 2002); (2) profibrotic cytokines such as transforming growth factor‐b (TGF‐b), interleukin‐13 (IL‐13), and IL‐4 (Desmouliere et al., 1993; Ronnov‐Jessen and Petersen, 1993; Wynn, 2004); and (3) EIII‐A fibronectin (George et al., 2000; Jarnagin et al., 1994; Serini et al., 1998). Presence of the differentiated myofibroblast is characteristic of nearly all fibrotic diseases. The myofibroblast population present in fibrotic lesions can be derived from multiple sources that may be inter‐related or tissue‐specific. The three main sources of myofibroblasts are (1) activation of circulating bone marrow‐derived ‘fibrocytes,’ potentially in all tissues (Abe et al., 2001); (2) resident epithelial‐ mesenchymal transition (EMT), mainly characterized in the kidney (Iwano et al., 2002), but likely occurring in other tissues as well (Kalluri and Neilson, 2003); and (3) ‘activation’ of resident pericytes such as stellate cells within the liver and pancreas and mesangial cells in the kidney (Bachem et al., 1998; Bissell, 1998; Demirci et al., 1996; Leyland et al., 1996; Reeves et al., 1996). Although there is the potential for a wide range of heterogeneity of myofibroblast phenotype due to differing lineages of the originating tissue fibroblast, it appears that the wound healing response has evolved to use common mechanisms of myofibroblast induction, and this has produced a relatively common phenotype in the resulting myofibroblast. This is fortuitous for anti‐fibrotic drug development as it implies that common targets may be identifiable which could yield drugs with application across multiple fibrotic diseases. For the purpose of reviewing their generalities, we will refer to all activated fibroblast populations as myofibroblasts for the remainder of this review, regardless of their tissue of origin (e.g., hepatic or pancreatic stellate cells, fibrocytes, mesangial cells, etc.). However, the reader is directed to some excellent reviews of the specific roll of EMT in kidney fibrosis (Kalluri and Neilson, 2003; Liu, 2004) and hepatic stellate cell activation in fibrotic liver disease (Bataller and Brenner, 2005; Bissell, 1998; Friedman, 1993) for a more thorough description of their subtle differences. The important role of the myofibroblast in fibrotic disease is emphasized by the fact that the majority of factors and functions specific to fibrogenesis and
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wound healing can be produced or controlled by the activated myofibroblast. For example, the most prominent feature of fibrosis is the fibrotic scar, due to excessive deposition of extracellular matrix components. Activation of myofibroblasts increases their secretion of types I, III, and IV collagens, fibronectin, laminin, and proteoglycans; some of which are increased by greater than 50‐ fold (Maher and McGuire, 1990). Contraction of collagen gels is also a prominent feature of activated myofibroblasts, which in vivo, likely contributes to hypertension within the tissue and its associated morbidity. For example, portal hypertension within the liver is a complication of cirrhosis likely controlled by the contraction of myofibroblasts and is a significant risk factor for esophageal varices (Rockey, 2003). Remodeling of the extracellular matrix due to its concomitant production and degradation during fibrogenesis is also a prominent feature of fibrotic disease that may be controlled by activated myofibroblasts (Arthur, 2000). During progression of fibrosis there is increased expression of MMPs (MMP‐2, MMP‐3, and MMP‐9) and to a larger extent, TIMPs (TIMP‐1 and TIMP‐2). Activated myofibroblasts express virtually all the key components required for matrix degradation including MMP‐2, MMP‐ 3, TIMP‐1, and TIMP‐2 (Arthur, 2000). Furthermore, resolving wound healing is associated with removal of activated myofibroblasts through apoptosis ((Saile et al., 1997); reviewed in (Gressner, 1998)). For example, myofibroblast apoptosis associated with reduced TIMP‐1 expression has been demonstrated during the recovery phase of experimentally induced liver injury (Iredale et al., 1998). Myofibroblasts may even be considered an active part of the innate immune system and display many functions and receptors in common with macrophages. Similar to macrophages, myofibroblasts can phagocytose apoptotic cells from wounded tissue and this process activates expression of TGF‐b and collagen I (Canbay et al., 2003). Activated myofibroblasts express MHC class I and II antigens, CD1b and CD1c, as well as co‐stimulatory molecules such as intracellular adhesion molecule 1 (ICAM‐1), CD40, and CD80 and can function as antigen presenting cells to T cells (Brennan et al., 1990; Hellerbrand et al., 1996; Knittel et al., 1999; Schwabe et al., 2001; Vinas et al., 2003). They also respond to pro‐inflammatory cytokines TNF‐a and IFN‐g by releasing the chemokine MCP‐1 (CCL2) (Marra et al., 1993). Moreover, myofibroblasts express innate immune system surveillance receptors such as mannose receptor, TLR‐2, TLR‐ 4, and CD14 and are stimulated by lipopolysaccharide (LPS) (Otte et al., 2003; Paik et al., 2003; Sprenger et al., 1997). CD40 in particular may play a major role in myofibroblast activation and recruitment of inflammatory amplification. Fibroblasts respond to CD40 ligation by increasing expression of ICAM‐1 and vascular cell adhesion molecule‐1 (VCAM‐1) and producing additional inflammatory mediators such as IL‐1, IL‐6, IL‐8, prostaglandins, and hyaluronate (Schwabe et al., 2001; Sempowski
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et al., 1997; Yellin et al., 1995). Also, blockade of CD40–CD40L interactions can protect mice from radiation pneumonitis and fibrosis and dramatically reduce lung pathology as evidenced by a limited influx of inflammatory cells, minimal collagen deposition, and reduced septal thickening (Adawi et al., 1998). Contraction of the collagen matrix may also be regulated by the myofibroblast. Myofibroblasts express the major collagen receptor a1b1 integrin in vivo and both a1b1 and a2b1 integrins upon in vitro culture (Racine‐Samson et al., 1997). Myofibroblasts from multiple tissues are capable of collagen gel contraction in vitro in an a1b1‐dependent fashion (Cook et al., 2002; Kagami et al., 2002; Racine‐Samson et al., 1997) (see also Section 5). Therefore, all three major features of active fibrotic disease, namely matrix production, remodeling, and contraction, can be regulated by activated myofibroblasts. In addition, myofibroblasts have the ability to recruit and stimulate the innate and adaptive immune response to amplify wound healing and fibrosis. For these reasons, the activated myofibroblast has become a prime target for therapeutic research. Study of the pathways leading to activation and regulation of myofibroblast function has revealed the prominent role that the immune system has in this process and identified additional potential therapeutic targets. 3.2. The Central Role of the Macrophage in Fibrosis The macrophage plays a very prominent role in fibrotic disease and regulates both pro‐ and anti‐fibrotic processes. Resident and/or infiltrating macrophages play a critical part in initiation of myofibroblast activation from precursor fibroblasts, stellate cells, and endothelial cells. Initial inflammatory macrophage recruitment to a wound site functions in debridement of necrotic and apoptotic tissue (Mutsaers et al., 1997). However, phagocytosis of apoptotic cells by inflammatory and/or resident macrophages results in a change in their phenotype from pro‐inflammatory to pro‐fibrotic by down‐regulating inflammatory cytokines and upregulating TGF‐b (Fadok et al., 1998). This TGF‐b production by resident and infiltrating macrophages may serve as the initiating event in myofibroblast activation from resident pericytes, activation of infiltrating fibrocytes, as well as stimulating EMT from resident epithelial cells. 3.2.1. TGF‐b In mammals, TGF‐b exists in three isotypes, TGF‐b1, ‐b2, and ‐b‐3, which have similar biological activities (Gorelik and Flavell, 2002). However, tissue fibrosis is mainly attributed to the TGF‐b1 isoform, and macrophages, both circulating and tissue‐derived, are the main cellular source (Bissell et al., 1995;
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Khalil et al., 1996; Letterio and Roberts, 1998). Indeed, it has been proposed that alveolar macrophages produce most of the active TGF‐b that is involved in the pathologic deposition of ECM in the bleomycin‐induced lung fibrosis model (Khalil et al., 1996). However, endothelial cells, epithelial cells, and myofibroblasts themselves can also produce TGF‐b (Bissell et al., 1995; Khalil et al., 1996; Letterio and Roberts, 1998), and such autocrine TGF‐b production may be sufficient for later stages of fibrosis progression. TGF‐b is one of the most pro‐fibrogenic cytokines known and is both necessary and sufficient for fibrotic disease induction and progression in many preclinical models. In animal models of lung fibrosis, collagen accumulation is preceded by increased TGF‐b expression (Coker et al., 1997; Santana et al., 1995; Sime et al., 1997; Westergren‐Thorsson et al., 1993). In addition, transgenic TGF‐b over‐expression in the liver resulted in fibrotic disease characterized by deposition of collagen around individual hepatocytes and within the space of Disse in a radiating linear pattern (Sanderson et al., 1995). Similarly, transient overexpression of active, but not latent, TGF‐b in the lung resulted in prolonged and severe interstitial and pleural fibrosis demonstrated by extensive deposition of collagen, fibronectin, and elastin, and by a significant increase in the number of lung myofibroblasts (Sime and O’Reilly, 2001; Sime et al., 1997). Conversely, when TGF‐b is inhibited in the rat bile duct ligation model or CCL4 model of fibrotic liver disease using a soluble TGF‐bR type II protein (sTGF‐bR), subsequent fibrosis is reduced (George et al., 1999; Yata et al., 2002). Using this system, collagen protein deposition in the liver was decreased by up to 55% even when the sTGF‐bR was administered four days after injury induction. Additionally, similar results were obtained in kidney and lung fibrotic disease models when TGF‐b is inhibited (Border et al., 1992; Fukasawa et al., 2004; Giri et al., 1993; McCormick et al., 1999; Sato et al., 2003; Wang et al., 1999). Importantly, TGF‐b inhibition was effective even when administered after disease induction (Fukasawa et al., 2004). Macrophages control the level of active TGF‐b mainly through regulation of both secretion and activation of latent TGF‐b, rather than at the level of transcription. In the cell, disulfide‐linked TGF‐b homodimers are kept in an inactive complex with latency‐associated protein (LAP). LAP is formed by cleavage of the amino terminus of the TGF‐b and normally forms a homodimer which non‐covalently associates with a homodimer of the mature, active TGF‐b. In this form, LAP prevents mature TGF‐b from binding its receptors and inducing active signaling. Dissociation of LAP is necessary for binding of TGF‐b to its receptors, and this dissociation process is catalyzed in vivo by a number of factors, including MMPs, avb6 integrin, plasmin, cathepsins, calpain, and thrombospondin (Gorelik and Flavell, 2002; Letterio and Roberts,
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1998; Munger et al., 1999). Following dissociation, TGF‐b signals are transduced by transmembrane serine/threonine kinase type I and type II receptors and intracellular mediators known as Smads (Massague, 2000). TGF‐b stimulation results in serine phosphorylation of Smad‐2 and Smad‐3 by the type 1 receptor, inducing formation of Smad‐2/3 heterodimers. The Smad‐2/3 heterodimers then associate with Smad‐4 and translocate to the nucleus, where they control the transcription of TGF‐b‐responsive genes such as collagen I and III and integrin‐linked kinase (ILK) (Li et al., 2003; Roberts et al., 2003). In vivo, both irradiation‐induced dermal fibrosis and unilateral ureteral obstruction (UUO)‐induced renal fibrosis are significantly reduced in Smad‐3 null mice (Flanders et al., 2002; Sato et al., 2003). Thus, one mechanism, whereby macrophages promote fibrosis is through production of TGF‐b which directly activates fibroblasts, epithelial cells, and pericytes to differentiate into collagen‐producing myofibroblasts. 3.2.2. PDGF Platelet‐derived growth factor (PDGF) produced mainly by macrophages is one of the most potent myofibroblast mitogens described (Bonner, 2004; Friedman and Arthur, 1989; Pinzani et al., 1989; Wong et al., 1994), and also functions as a chemoattractant and stimulant for collagen production and cell adhesion in myofibroblasts (Bonner, 2004). PDGF is a dimer of two chains selected from A, B, C, and D, which results in five potential isoforms, PDGF‐ AA, PDGF‐AB, PDGF‐BB, PDGF‐CC, and PDGF‐DD. PDGF‐AA and PDGF‐CC bind selectively to the PDGFRa, while PDGF‐AB and ‐BB isoforms bind and dimerize both PDGFRa and PDGFRb, and PDGF‐DD isoforms bind PDGFRb (Bonner, 2004). Both PDGF‐A, PDGF‐B and their receptors are induced in vivo during injury and fibrotic disease of the liver (Pinzani et al., 1994; Wong et al., 1994), lung (Martinet et al., 1986, 1987; Yi et al., 1996), kidney (Abboud, 1995; Iida et al., 1991), synovium (Rubin et al., 1988a), skin (Gay et al., 1989; Klareskog et al., 1990), and vasculature (Rubin et al., 1988b). Less is known about PDGF‐C and PDGF‐D, although the latter has been implicated in human obstructive nephropathy (Taneda et al., 2003). Since PDGF and its receptors are major mediators of myofibroblast growth and survival, it is predicted that PDGF or PDGF receptor inhibitors may be effective treatments of fibrotic disease. Indeed, treatment of rats with a PDGF‐B DNA‐aptamer antagonist or antibody prevented glomerulosclerosis and tubulointerstitial damage in a progressive mesangioproliferative glomerulonephritis model (Johnson et al., 1992; Ostendorf et al., 2001). Pirfenidone is an anti‐fibrotic agent with unknown biochemical target; however, it significantly inhibits PDGF‐stimulated hepatic myofibroblast proliferation in vitro and reduces hepatic fibrosis (Di Sario et al., 2002) and bleomycin‐induced
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lung fibrosis in vivo (Gurujeyalakshmi et al., 1999). Furthermore, small molecule inhibitors of PDGFR tyrosine kinase activity have shown significant activity in both lung (Rice et al., 1999) and liver fibrosis disease models (Yoshiji et al., 2005). 3.3. M1 and M2 Macrop hages Identification of the pro‐fibrotic phenotype of subsets of macrophages within fibrotic tissue has changed the way we perceive the role of macrophages in inflammation and fibrotic disease (Duffield, 2003; Goerdt and Orfanos, 1999). Macrophages can be functionally distinguished into two separate pools based upon cell surface phenotyping and route of activation. Classically activated macrophages (M1) are induced by TH1 lymphokines (INF‐g), bacterial and fungal cell wall components, or degraded matrix (Duffield, 2003; Goerdt and Orfanos, 1999; Pierce et al., 1996; Zhang et al., 1998). These same stimuli downregulate surface expression of the hemoglobin scavenger receptor CD163 (Buechler et al., 2000; Hogger et al., 1998). In contrast, alternatively activated macrophages (M2) are induced by TH2 lymphokines (IL‐4, IL‐13, IL‐10, and TGF‐b), phagocytosis of apoptotic cells, and corticosteroids (Goerdt and Orfanos, 1999; Stein et al., 1992; Duffield, 2003). M2 cells preferentially express the foreign antigen receptors of innate immunity, such as the macrophage mannose receptor, scavenger receptor type I, and CD163 (Geng and Hansson, 1992; Hogger et al., 1998; Mosser and Handman, 1992; Stein et al., 1992). M1 and M2 cells mediate contrasting and complementary functions in tissue fibrosis. M1 cells may play an obligatory role in initiation of the fibrotic response. First, M1 cells can induce apoptosis of surrounding tissue. As described above, subsequent phagocytosis of these apoptotic cells is a powerful stimulator of myofibroblast activation (Canbay et al., 2003). In the kidney, both mesangial and tubular cell apoptosis can be induced by macrophage membrane‐bound TNF‐a (Duffield et al., 2000, 2001). Second, M1 cells play important roles in matrix degradation through the direct and indirect production of MMPs. M1 cells display increased expression MMP‐9, MMP‐2 (gelatinases), MMP‐12 (metalloelastase), and MMP‐7 (matrilysin) (Gibbs et al., 1999; Song et al., 2000). M1 cells can also induce lung myofibroblasts to generate MMP‐13 (Mariani et al., 1998) and kidney myofibroblasts to produce MMP‐3 (Kitamura, 1998). Since the process of EMT is thought to be stimulated in part through the initial loss of basement membrane extracellular matrix contacts (Kalluri and Neilson, 2003; Liu, 2004), increased production of MMP‐9 and MMP‐2 by M1 cells may stimulate EMT during the initial inflammatory response.
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M1 cells may also play a role in resolution of fibrosis. Stimulation of the production of MMPs by M1 cells during later stages of fibrosis may shift the equilibrium towards degradation and play an important role in resolution of disease. Indeed, expression of the collagenases MMP‐1 and MMP‐13 predominate during the resolution phase of liver fibrosis (Iredale et al., 1998). Also, stimulation of apoptosis in myofibroblasts by M1 cells may contribute to their reduction during resolution of liver fibrosis (Iredale et al., 1998). In contrast, M2 cells appear to be highly pro‐fibrogenic and contribute to the remodeling phase of fibrotic disease where increased extracellular matrix deposition predominates. Indeed, M2 cells produce large amounts of TGF‐b, and complex matrix deposition is promoted when myofibroblasts are co‐ cultured with M2 cells (Erwig et al., 1998; Fadok et al., 1998; Mantovani et al., 2002; Song et al., 2000). In addition, M2 cells can induce myofibroblast proliferation through production of platelet‐derived growth factor (PDGF) and insulin‐like growth factor (IGF) (Pierce et al., 1989; Song et al., 2000). Moreover, M2 cells in healing wounds express high levels of transglutaminase, which crosslinks extracellular matrix proteins such as collagen, fibronectin, fibrinogen, and laminin, rendering them resistant to breakdown by proteases (Haroon et al., 1999a,b), and this may impede resolution of fibrotic injury (Issa et al., 2004). Further control of the process of matrix deposition during fibrosis by M1 and M2 cells may occur at the level of control of the pool of available free L‐ proline. Collagen synthesis is strictly dependent upon the availability of L‐ proline. M1 cells possess cytotoxic and antimicrobial effector functions based upon their expression of inducible nitric‐oxide synthase (iNOS) and its ability to produce nitric oxide (NO) (MacMicking et al., 1997). iNOS oxidizes the substrate L‐arginine to form NO and L‐citrulline. In contrast, M2 cells express the arginase‐1 (ARG1) enzyme which metabolizes L‐arginine into L‐ornithine and urea, and expression of iNOS vs. ARG1 appears to be mutually exclusive (Corraliza et al., 1995; Modolell et al., 1995; Munder et al., 1998). L‐ornithine in turn is the substrate for two additional enzymes, ornithine decarboxylase (ODC) and ornithine amino transferase (OAT). ODC generates polyamines which are necessary for cell growth and OAT generates L‐proline which is critical for collagen synthesis. Therefore, the presence of M1 vs. M2 cells at a site of fibrosis may affect the level of L‐proline available for collagen synthesis by myofibroblasts. Interestingly, fibroblasts themselves demonstrate similar patterns of iNOS and ARG1 expression when stimulated with TH1 vs. TH2 cytokines, respectively (Witte et al., 2002). The role of the macrophage in fibrogenesis has also been suggested by several studies in vivo. Early studies demonstrated that macrophage depletion using anti‐macrophage serum in a healing wound model resulted in reduced
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matrix production and fibrosis (Leibovich and Ross, 1975). In a more recent study of fibrotic kidney disease, tubular atrophy and interstitial fibrosis were significantly diminished when selectin‐dependent migration of macrophages into the kidney was blocked (Lange‐Sperandio et al., 2002). Additionally, depletion of alveolar macrophages greatly decreases collagen deposition in the lung following liposome‐encapsulated dichloromethylene diphosphonate administration (Zhang‐Hoover et al., 2000). In contrast, in the rat Thy1.1 glomerulonephritis model, the presence of macrophages within the kidney correlated with fewer myofibroblasts and resolution of the disease (De Heer et al., 1998; Westerhuis et al., 2000). However, these studies did not distinguish between M1 and M2 macrophage contributions and the stage at which they are acting. For example, blockade of M2 macrophages should decrease the fibrotic response, whereas the increased presence of M1 macrophages should correlate with disease resolution. An elegant and definitive study has recently confirmed the necessary role of M2 and M1 cells in the propagation and resolution, respectively, of liver fibrosis in vivo (Duffield et al., 2005). Duffield et al., has created a transgenic mouse model in which the selective depletion of macrophages can be temporally regulated. The investigators then used CCl4 to establish resolving liver fibrosis in the transgenic animals and determined the effect of macrophage depletion during the remodeling phase when injury and collagen deposition are still actively occurring, or during the resolution phase when further injury has been removed through cessation of CCl4 administration, and collagen levels are decreasing. Interestingly, removal of macrophages at these two time points had completely opposite effects on matrix deposition. In the first case, removal of macrophages during active remodeling reduced the level of matrix deposition, whereas in the second case removal of macrophages during resolution exacerbated matrix deposition. These results could be explained by the phenotype of the macrophages present within the fibrotic tissue at each time point. During the remodeling phase the macrophages present in the scar displayed an M2 phenotype whereas during the resolution phase the macrophages present in the scar displayed an M1 phenotype. These results are fully consistent with the conclusions above that M2 cells are profibrotic and M1 cells are involved in resolution of fibrotic injury. Left unanswered by this study is whether the two populations of macrophages are derived from the same source by transition of the early M2 cells into an M1 phenotype during resolution, or are the result of two different sources whereby the M2 cells leave (or die) and the M1 cells newly enter or become activated. In future studies it will be important to identify the signals necessary for the M1 cell transition and/or recruitment in order to resolve the fibrotic lesion.
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Taken together the data above are consistent with the concept that the macrophage/myofibroblast system is a tightly interrelated innate fibrotic response system to tissue injury. This system links innate inflammatory responses to activation of myofibroblasts and tissue healing. The ability of both these cell types to provide inter‐ and intra‐cellular amplification of initiating pro‐fibrotic events may help explain why certain anti‐inflammatory therapies have proven ineffective at controlling established fibrotic disease. In particular, corticosteroids which augment macrophage conversion to the M2 cell phenotype (Duffield, 2003) and stimulate macrophage production of PDGF‐B (Haynes and Shaw, 1992) may in fact do more to promote fibrosis than alleviate it. 3.4. Regulation of Fibrosis by T Helper 1 (TH1) and 2 (TH2) CD4þ T Cells Much as the adaptive immune system has evolved to take advantage of the innate immune system for many of its effector functions, an adaptive fibrotic response system also appears to have evolved to take advantage of the innate fibrotic response system described above. In many respects the traditional TH2 CD4þ T cell cytokine system plays a larger role as an initiator and amplifier of the innate fibrotic response system than as a suppressor of the TH1 CD4þ T cell response originally described (reviewed in [Chtanova and Mackay, 2001]). A variety of studies indicate that shifting the cytokine balance to a TH2 CD4þ T cell response involving IL‐4, IL‐5, and IL‐13 is strongly linked to the promotion of fibrotic disease (reviewed in [Wynn, 2004]). For example, TH2 inflammation is involved in the pathogenesis of fibrotic disorders such as hepatic fibrosis (Chiaramonte et al., 1999, 2001; Fallon et al., 2000; Hoffmann et al., 2000; Shi et al., 1997), pulmonary fibrosis (Gharaee‐Kermani and Phan, 1997; Majumdar et al., 1999; Wallace et al., 1995; Westermann et al., 1999), and systemic sclerosis (Hasegawa et al., 1997; Majumdar et al., 1999). T cells polarized in vitro to TH2 cells also induce lung fibrosis when passively transferred and activated in vivo (Wangoo et al., 2001). 3.4.1. IL‐4 Initially, IL‐4 was felt to be the primary pro‐fibrogenic cytokine produced by TH2 cells. Elevated levels of IL‐4 are found in the pulmonary interstitium of patients with cryptogenic fibrosing alveolitis, in the peripheral blood mononuclear cells of patients with periportal fibrosis, and in the bronchoalveolar lavage fluids of patients with idiopathic pulmonary fibrosis (IPF) (Booth et al., 2004; Emura et al., 1990; Wallace et al., 1995). In vitro, IL‐4 stimulates production of collagen types I and III and fibronectin from liver, lung, and scleroderma‐ derived fibroblasts (Doucet et al., 1998; Fertin et al., 1991; Tiggelman et al., 1995). Early in vivo studies seemed to confirm these in vitro results, as IL‐4
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blockade in models of liver and skin fibrosis inhibited deposition of extracellular matrix (Cheever et al., 1994; Le Moine et al., 1999; Ong et al., 1998). However, interpretation of these studies was complicated by the fact that IL‐ 13 levels are reduced when IL‐4 is inhibited (Cheever et al., 1994). Subsequent studies directly comparing the contribution of IL‐13 and IL‐4 in models of lung and liver fibrosis have demonstrated that IL‐13 may in fact be the dominant pro‐fibrotic TH2 cytokine (Chiaramonte et al., 1999; Fallon et al., 2000; Kolodsick et al., 2004). These studies compared IL‐4 null, IL‐13 null, and IL‐4/IL‐13 double‐null mice, and demonstrated that IL‐13 but not IL‐4 was required for the fibrotic response. Furthermore, IL‐4 over‐expression in the lung does not induce pulmonary fibrosis (Rankin et al., 1996), therefore IL‐4 is neither necessary nor sufficient for fibrosis in preclinical models in vivo. 3.4.2. IL‐13 Many of the pro‐fibrogenic effects of TH2 CD4þ T cells can be attributed to their production of IL‐13 (Wynn, 2004). In addition to its stimulation of macrophages to an M2 phenotype described above (Duffield, 2003), IL‐13 is also a potent stimulator of myofibroblast proliferation and collagen production in vitro (Chiaramonte et al., 1999; Doucet et al., 1998; Oriente et al., 2000). IL‐ 13 may play an additional role in fibrosis by indirectly activating TGF‐b through the upregulation of MMP‐9 and MMP‐12 which cleave the LAP‐ TGF‐b complex, thus releasing active TGF‐b (Lanone et al., 2002; Lee et al., 2001). In vivo, transgenic over‐expression of IL‐13 in murine airway causes subepithelial airway fibrosis (Zhu et al., 1999), and blockade of IL‐13 function inhibits development of hepatic fibrosis in murine schistosomiasis (Chiaramonte et al., 1999; Fallon et al., 2000) and development of lung fibrosis in both a murine fluorescein isothiocyanate model (Kolodsick et al., 2004) and bleomyocin model (Belperio et al., 2002). Moreover, IL‐13 has been implicated in the human pathogenesis of hepatic and lung fibrosis, systemic sclerosis, and nodular sclerosing Hodgkin’s disease (de Lalla et al., 2004; Hancock et al., 1998; Hasegawa et al., 1997; Ohshima et al., 2001). However, mechanistically it is unclear why IL‐13 would have greater fibrogenic activity than IL‐4. Both IL‐4 and IL‐13 can use the same IL‐4 receptor a chain and its associated signal transducer and activator of transcription protein 6 (STAT6) signaling pathway (Zurawski et al., 1993). Additionally, both cytokines induce fibroblasts from multiple tissues to produce collagen (Chiaramonte et al., 1999; Oriente et al., 2000; Saito et al., 2003). One possibility may simply be prevalence of expression, as IL‐13 levels often exceed IL‐4 levels in vivo by significant amounts (Wynn, 2004). Interestingly, active production of lung fibrosis can proceed in the absence of IL‐4Ra or STAT6 under certain
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conditions (Blease et al., 2002; Webb et al., 2003). In the latter case, subsequent deletion of IL‐13 responsive cells in STAT6 null mice blocked airway hyper‐responsiveness, but not pulmonary fibrosis (Blease et al., 2002). The mechanism whereby IL‐13 mediates its pro‐fibrotic effects is also still under debate and may vary by tissue. IL‐13 directly stimulates production of TGF‐b from M2 macrophages in fibrotic lung over‐expressing IL‐13, and fibrosis in this model was dependent upon TGF‐b and MMP9 (Lee et al., 2001). Notably, TGF‐b production and fibrosis in the IL‐13 transgenic mice could also be blocked by a null mutation in the IL‐11Ra chain (Chen et al., 2005), suggesting that IL‐13 stimulates IL‐11 production locally and this in turn drives fibrosis in the lung through TGF‐b. However, the above studies depend upon transgenic over‐expression of IL‐13. In contrast, when hepatic fibrosis is initiated by schistosomiasis, no effect on disease progression or collagen deposition was observed with blockade of TGF‐b, MMP9, or Smad‐ 3 (Kaviratne et al., 2004). IL‐13 injection in TGF‐b null animals markedly induced several genes involved in the fibrotic process including interstitial collagens, TIMP‐1, fibrillin, tanascin, and several MMPs (Kaviratne et al., 2004). Therefore, IL‐13 appears to have the capability of inducing TGF‐b‐ independent mechanisms of fibrosis. In this regard, it has also been shown that IL‐13 stimulates the expression of CD154 (CD40 ligand) on human lung fibroblasts (Kaufman et al., 2004), and the level of CD154 expression in human fibrotic lung tissue correlated strongly with the extent of fibrosis. Since lung myofibroblasts also express CD40 and are activated by its ligation (Schwabe et al., 2001; Sempowski et al., 1997; Yellin et al., 1995), amplification of the CD40/CD154 interaction may be another mechanism of IL‐13‐ mediated pro‐fibrotic responses. Also, IL‐13 is a potent inducer of several CC‐chemokines such as CCL2 (MCP‐1), CCL3 (MIP‐1a), CCL4 (MIP‐1b), CCL6 (C10), CCL11, CCL20 (MIP‐3a), and CCL22 (macrophage‐derived chemokine) (Belperio et al., 2002; Ma et al., 2004; Zhu et al., 2002). Blockade of CCL6 or chemokine receptor CCR2 diminishes fibrosis induction within the lung of IL‐13 transgenic mice (Ma et al., 2004; Zhu et al., 2002), suggesting additional ways in which IL‐13 may amplify inflammatory infiltration into a fibrotic foci (see also Section 4). 3.4.3. IFN‐g In contrast to TH2 responses, shifting the cytokine balance to a TH1 CD4þ T cell response involving interferon‐g (IFN‐g) or IL‐12 appears to be protective from fibrosis progression. IFN‐g downregulates the genes for TGF‐b and collagen 1 and inhibits the proliferation of fibroblasts (Narayanan et al., 1992). Indeed, IFN‐g was shown to be anti‐fibrotic in experimental models of hepatic, pulmonary. and renal fibrotic disease (Gurujeyalakshmi and Giri
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1995; Hoffmann et al., 2000; Oldroyd et al., 1999; Sime and O’Reilly, 2001), and similar responses have been observed with IL‐12 treatment (Keane et al., 2001; Wynn et al., 1995). These studies indicate that chronic inflammation does not always lead to fibrosis and that the magnitude of the fibrotic response can be strongly influenced by the nature of the T helper cell induced. However, application of this approach to human pulmonary fibrosis has met with mixed results so far (Raghu et al., 2004; Ziesche et al., 1999). In the study by Ziesche et al., 18 patients with IPF received either IFN‐g and prednisolone or prednisolone alone (Ziesche et al., 1999). Total lung capacity increased, the partial pressure of arterial oxygen improved, and the gene expression for TGF‐b and connective‐tissue growth factor (CTGF) decreased substantially in the IFN‐g treated patients, but not in the prednisolone‐alone group. However, a subsequent larger multicenter study by Raghu and coworkers in 330 IPF patients demonstrated no significant effect on the primary endpoints of improved pulmonary function, gas exchange, or the quality of life in the patients receiving IFN‐g (Raghu et al., 2004). Surprisingly, the authors did observe increased survival among patients who were compliant with the IFN‐g treatment, but given the lack of pulmonary function improvements, the exact mechanism behind the increased survival is unclear. It is possible that concurrent administration of prednisolone during these studies diminished the potential benefit of IFN‐g due to the steroid’s potential to further promote M2 macrophage differentiation. 4. Inflammatory Chemokines that Regulate Fibrosis Chemokines are potent chemoattractant peptides that may play important roles in the fibrogenic process by recruiting leukocytes and myofibroblasts to the site of injury. Several chemokines and their receptors have been shown to have critical roles in the development of fibrosis in specific animal models. In general, blockade of the TH2‐associated CC chemokines is protective from fibrosis, whereas blockade of the TH1‐associated CXC chemokines exacerbates fibrotic disease. However, there are also non‐TH1‐associated CXC chemokines (i.e., non‐IFN‐g inducible) which are pro‐angiogenic and pro‐fibrogenic (Strieter et al., 2002). 4.1. CC Chemokines A variety of TH2‐associated chemokines has been implicated in development of fibrotic disease. CCL2 is produced by activated myofibroblasts and is chemotactic for monocytes (Marra et al., 1993). Neutralization of CCL2 in a crescentic nephritis model of kidney fibrosis resulted in a dramatic decrease in
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both glomerular crescent formation and deposition of type I collagen (Lloyd et al., 1997). CCL3 is produced by macrophages and epithelial cells and is also chemotactic for monocytes. In the bleomycin‐induced lung fibrosis model, intratracheal challenge of CBA/J mice with bleomycin resulted in a significant time‐dependent increase in CCL3 protein levels both in whole‐lung homogenates and bronchoalveolar lavage fluid (Smith et al., 1994). Similar to CCL2 blockade above, passive immunization of bleomycin‐challenged mice with anti‐CCL3 antibodies significantly reduced pulmonary macrophage accumulation and fibrosis (Smith et al., 1994). Neutralization of CCL6 diminishes pulmonary fibrosis in IL‐13 over‐expressing transgenic mice (Ma et al., 2004), as well as in the bleomycin‐induced lung fibrosis model (Belperio et al., 2002). CCL17 is another TH2‐associated chemokine that is chemotactic for macrophages, and both CCL17 and its receptor CCR4 are overexpressed in the lung in the bleomycin‐induced lung fibrosis model (Belperio et al., 2004). Blockade of CCL17 in this model led to a significant reduction in pulmonary fibrosis (Belperio et al., 2004). In a complementary fashion, blockade of specific CC chemokine receptors also reduces fibrotic responses. For example, blockade of CCR1 (a receptor for CCL3) has been shown to reduce fibrosis in models of bleomycin‐induced lung fibrosis (Tokuda et al., 2000), chronic fungal allergic airway disease (Blease et al., 2000), and renal fibrosis following UUO (Anders et al., 2002; Eis et al., 2004), lupus nephritis (Anders et al., 2004), or adriamycin‐induced focal segmental glomerulosclerosis (Vielhauer et al., 2004). Blockade of CCR2 (a receptor for CCL2) has similarly been shown to reduce fibrosis in models of pulmonary fibrosis (Moore et al., 2001; Zhu et al. 2002). Interestingly, one mechanism by which CCR2 blockade may function in pulmonary fibrosis is by preventing specific recruitment of bone marrow‐derived fibrocytes via CCL2 (Moore et al., 2005). 4.2. CXC Chemokines The CXC chemokines also play significant roles in fibrosis development, through a mechanism that may involve control of angiogenesis. CXC chemokines can be divided into two groups based upon the presence or absence of a three amino acid Glu‐Leu‐Arg (ELR) motif at their amino‐terminus. The non‐ IFN‐g‐inducible CXC chemokines are all ELRþ and this group includes CXCL1 (GRO‐a), CXCL2 (GRO‐b), CXCL3 (GRO‐g), CXCL5 (ENA‐78), CXCL6 (GCP‐2), CXCL7 (NAP‐2), and CXCL8 (IL‐8). The TH1‐associated CXC chemokines (i.e., IFN‐g inducible) are all ELR and include CXCL9 (MIG), CXCL10 (IP‐10), and CXCL11 (I‐TAC) (Strieter et al., 2002). In addition to their roles in inflammation (Zlotnik and Yoshie, 2000), ELRþ
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CXC chemokines are potent promoters of angiogenesis, whereas ELR CXC chemokines are potent inhibitors of angiogenesis (Strieter et al., 1995). ELRþ CXC chemokines stimulate endothelial cell chemotaxis and proliferation in vitro, and stimulate angiogenesis in a cornea micropocket (CMP) assay in a CXCR2‐dependent manner (Addison et al., 2000). In vivo incisional wound healing is delayed in CXCR2 null mice and this correlates with decreased neovascularization (Devalaraja et al., 2000). In contrast, the ELR CXC chemokines all inhibit neovascularization in the CMP assay in response to either ELRþ CXC chemokines or vascular endothelial growth factor (VEGF) in a manner dependent upon endothelial expression of CXCR3 (Romagnani et al., 2001). Neovascularization has been demonstrated within the lungs of rats during bleomycin‐induced lung fibrosis in close association with areas of pulmonary fibrosis (Peao et al., 1994). This has been correlated in human IPF lung tissue where there were elevated levels of CXCL8 localized to pulmonary fibroblasts, elevated levels of CXCL5 localized to hyperplastic type II cells and macrophages, but decreased levels of CXCL10 relative to control subjects, suggesting an imbalance that favors net angiogenic activity (Keane et al., 1997, 2001). In addition, neutralizing antibodies to either CXCL8 or CXCL5 blocked angiogenesis in the CMP model stimulated by IPF samples (Keane et al., 1997, 2001). Similarly, CXCL2 and CXCL10 levels were found to be directly and inversely correlated with total lung hydroxyproline levels in the murine bleomycin‐induced lung fibrosis model (Keane et al., 1999a,b). Furthermore, blockade of CXCL2 by passive immunization with neutralizing antibodies or treatment with CXCL10 resulted in marked decreases in pulmonary fibrosis which was attributed to reductions in angiogenesis in the lung (Keane et al., 1999a). Together these data strongly suggest that lung fibrosis involves neovascularization regulated by CXC chemokine production. However, this may not tell the whole story, as a recent study investigating the effect of deletion of CXCR3 (the receptor for the IFN‐g‐inducible CXC chemokines CXCL9, CXCL10 and CXCL11) suggests additional mechanisms of action for TH1‐associated CXC chemokines in fibrotic lung disease (Jiang et al., 2004). First, the lung pathology in the CXCR3 null mice administered bleomycin was distinct from that observed following treatment of WT mice, and was very similar to the cystic honeycomb pattern observed in human IPF. Second, the progressive interstitial fibrosis present in the CXCR3 null mice occurred without changes in neutrophil or monocyte levels in the lungs, but with a selective decrease in CD8þ T cells and NK cells (Jiang et al., 2004). Increased fibrosis was associated with reduced early burst of IFN‐g production and decreased expression of CXCL10 after lung injury in CXCR3 null animals relative to controls. In addition, the increased fibrosis in CXCR3 null mice was significantly reversed by treatment with exogenous IFN‐g (Jiang et al., 2004).
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If IFN‐g was acting in this model to produce ELR CXC chemokines in order to suppress angiogenesis as suggested by Strieter and coworkers (Strieter et al., 2002), then treatment with IFN‐g in CXCR3 null mice should not have had any effect. However, since IFN‐g can rescue the phenotype induced by CXCR3 deficiency (Jiang et al., 2004), these data suggest that either other receptors for IFN‐g inducible CXC chemokines exist which can mediate the anti‐angiogenic effects of ELR CXC chemokines, or NK cell recruitment, rather than angiogenesis suppression, may in fact be the primary role of TH1‐associated, IFN‐g‐inducible CXC chemokines in pulmonary fibrosis. 5. The Role of Integrins in Regulating the Fibrotic Response Integrins are a large family of heterodimeric transmembrane proteins involved in cell–cell and cell–extracellular matrix interaction originally identified as antigens that increased expression following prolonged activation of T cells (Hemler, 1990). Each integrin molecule is composed of a single a subunit and a single b subunit. There are currently 18 identified a subunits, 8 specific b subunits, and 24 distinct integrin heterodimers, as certain a and b subunits allow for promiscuous heterodimerization. Integrins play central roles in modulating virtually every aspect of cell behavior, including migration, establishment of polarity, growth, survival, and differentiation. Integrin cytoplasmic domains bind directly to adaptor proteins which bind directly to cellular actin, allowing integrins to connect changes in cell shape or mechanical tension to signaling events that modify cellular behavior (Tomasek et al., 2002). Indeed, cell adhesion to extracellular matrix profoundly influences myofibroblast activation, differentiation, and proliferation in vitro (Bhowmick et al., 2001; Davis, 1988; Friedman et al., 1989; Gaca et al., 2003; Thannickal et al., 2003). As such, several integrin molecules have been directly and indirectly implicated in the regulation of wound healing and fibrotic disease (Sheppard, 2003). 5.1. a1b1 a1b1 integrin (also known as very late antigen‐1, VLA‐1) is one member of a family of four b1 integrin molecules that have been shown to bind to the extracellular matrix proteins collagen and laminin (Hemler and Lobb, 1995). The other b1 integrin collagen receptors include a2b1, a10b1, and a11b1. These four collagen receptors share overlapping but distinct expression profiles. They also appear to have distinct ligand preferences in vitro. For example, a1b1 has been shown to bind more effectively to type IV collagen than type I collagen while a2b1 binds to type I collagen better than to type IV collagen (Dickeson et al., 1999). Interestingly, a1b1 can signal via Shc into the MAP
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kinase pathway and thus can regulate cell proliferation following collagen ligation (Pozzi et al., 1998). Furthermore, b1 signaling may be required for TGF‐b‐mediated activation of the MAP kinase pathway leading to EMT (Bhowmick et al., 2001). a1b1 is expressed on several cell populations relevant to fibrotic disease, including microvascular endothelial cells, fibroblasts, and myofibroblasts (Racine‐Samson et al., 1997). It is also expressed on certain activated cells of the immune system including T cells, macrophages, and NK cells, but not on normal peripheral blood mononuclear cells (PBMC) (de Fougerolles et al., 2000). Despite this broad expression profile, a1 null mice are viable and fertile and initial characterization showed no overt phenotype, demonstrating that the molecule is not required for development (Gardner et al., 1996). However, subsequent studies have demonstrated a slight defect in the proliferation rate of dermal fibroblasts from a1 null mice resulting in hypocellularity within the skin (Pozzi et al., 1998). Two studies have investigated the effects of loss of a1b1 in wound healing. Gardner and coworkers followed up their earlier observations in the skin (above) by investigating full thickness incisional wound healing in wt and a1 null mice (Gardner et al., 1999). Although no differences were observed at day 7 after injury, by day 12, the distribution of collagen fibrils showed a variegated, nodular pattern in contrast to the even distribution in the wt animals. The second study by Ekholm and coworkers tested the regeneration of a fractured long bone in wt and a1 null animals (Ekholm et al., 2002). Although a1 null mice were able to heal, a significant reduction was detected in their capacity to make cartilaginous callus. These results correlated with a decreased proliferation rate in mesenchymal stem cells although proliferation of chondrocyte‐like cells was unaltered. Collectively, these results are consistent with a role for a1b1 in wound healing. a1b1 may also play a major role in liver fibrosis. For example, in vitro, an a1 mAb blocks liver myofibroblast adhesion to collagen and endothelin stimulation of myofibroblast contraction of collagen lattices (Bissell, 1998; Racine‐ Samson et al., 1997). a1b1 is also required for liver myofibroblast migration induced by TGF‐b1, EGF, or collagen I (Yang et al., 2003). In addition, a1b1 is the primary integrin expressed by liver myofibroblasts in vivo (Bissell, 1998; Racine‐Samson et al., 1997) and a1b1 can regulate matrix metalloproteinase (MMP) expression (Gardner et al., 1996; Lochter et al., 1999; Pozzi et al., 2000, 2002), thereby affecting collagen degradation. Thus, a1b1 has the potential to impact fibrotic disease progression in liver at multiple steps. a1b1 may also play a role in renal fibrotic disease. Alport syndrome is a genetic disorder characterized by progressive glomerulonephritis resulting in fibrosis of the kidneys and, ultimately, kidney failure (Cosgrove et al., 2000).
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Alport syndrome affects approximately 1 in 5000 people and is caused by mutations in the type IV collagen genes. This condition has been mimicked in mice by knocking out the gene of the alpha3 chain of type IV collagen (Alport mouse). Concomitant knockout of the a1b1 integrin in the ‘‘Alport mouse’’ delays onset of fibrosis (Cosgrove et al., 2000). In addition, inhibition of TGF‐b1 with a soluble receptor construct had a synergistic effect with the inactivation of a1 in slowing the onset and severity of glomerular disease. These results correlated with a dramatic decrease in the accumulation of myofibroblasts and macrophages in the tubular interstitium of double knockout mice (Sampson et al., 2001). Another report studying the effects of a1 expression in transfected glomerular mesangial cells showed that a1b1 expression levels influenced the cell growth, cell size, and collagen matrix remodeling ability of these cells (Kagami et al., 2000). Moreover, two studies demonstrate that anti‐a1b1 mAb can directly affect pathologic mesangial cell remodeling of extracellular matrix in progressive kidney disease in mice (Cook et al., 2002; Kagami et al., 2002). Collectively, these two studies demonstrated that blocking a1b1 mAb significantly decreased mesangial cell‐mediated collagen deposition, collagen gel contraction, production of serum creatinine, and increased survival, even when administered after the onset of measurable interstitial fibrosis. However, differing results have been noted in a recent study using adriamycin (ADR)‐induced nephropathy in a1‐deficient mice (Chen et al., 2004). In this study the authors observed an increase in collagen IV (but not collagen 1) production, and increased reactive oxygen generation in a1 null animals, resulting in increased mesangial cell death, although the distinctions between a1 null and a1 wt were minor at most time points. Collectively, these data are consistent with the concept that a1b1 may impact fibrotic disease progression at multiple stages. a1b1 expression on macrophages and T cells may influence M1 and M2 macrophage retention in the peripheral tissue, or subsequent expression of cytokines. a1b1 expression on myofibroblasts appears to play a critical role in their contractile activity in vitro and may represent their main collagen receptor for mediating collagen contraction in vivo, thereby impacting tissue architecture and local vascular tone. Finally, a1b1 regulation of MMP expression could impact the collagen remodeling ability of myofibroblasts and macrophages at sites of active fibrogenesis. 5.2. avb6 avb6 is another integrin molecule strongly implicated in the development and control of fibrotic disease (Sheppard, 2001). avb6 expression is restricted to epithelial cells and it functions in binding to the extracellular matrix proteins fibronectin, tenascin‐C, and vitronectin through the linear tripeptide sequence
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Arg‐Gly‐Asp (RGD) common to all av integrins. Initial studies analyzing the effects of heterologous expression of avb6 determined that it enhanced proliferation of cells in three‐dimensional culture and induced expression of MMP‐ 9 (Sheppard, 2001). However, significant interest in the role of avb6 in fibrotic disease stemmed from the unexpected phenotype in b6 null mice of significant inflammation in the lungs and skin (Huang et al., 1996), but a complete lack of pulmonary fibrosis in these animals upon challenge with bleomycin (Munger et al., 1999). Although the phenotype of the b6 null mice was reminiscent of the enhanced inflammation observed in TGF‐b1 null animals (Shull et al., 1992), no difference in expression of TGF‐b was observed between wt and b6 null animals after bleomycin treatment nor at baseline (Munger et al., 1999). Instead, the authors determined that similar to other av integrins (Munger et al., 1998), avb6 bound to the RGD sequence within the TGF‐b‐inactivating LAP protein. Unlike avb1 or avb5 binding, avb6 binding was a strong activator of TGF‐b function in cell culture. However, the conformational change in the TGF‐b/LAP complex induced by avb6 binding does not appear to release free active TGF‐b, thus providing a means for spatially restricted presentation of active TGF‐b (Munger et al., 1999). A useful secondary application of the b6 null mice has been in a comprehensive profile of the global gene expression in the lungs following bleomycin treatment in b6 null and wt mice (Kaminski et al., 2000). This study has allowed the distinction of genes involved in the inflammatory response to bleomycin from the genes that specifically contribute to the fibrotic response in a time‐dependent manner. 5.3. avb3 Just as integrins are implicated in controlling activation and propagation of the fibrotic process, they may also play a role in fibrosis resolution. Spontaneous resolution of liver fibrosis in rats coincides with decreased TIMP‐1 expression, enhanced MMP activity, and apoptosis of the activated myofibroblasts (Iredale et al., 1998; Issa et al., 2001), all of which may be regulated to a degree by integrin engagement. Although the natural trigger for hepatic myofibroblast apoptosis is currently unknown, endothelial cell survival in vitro and in vivo requires ligation of the integrin avb3 (Eliceiri and Cheresh, 2000). A recent study demonstrated that avb3 is expressed by rat and human liver myofibroblasts in vitro (Zhou et al., 2004). Blockade of avb3 function in these cells resulted in decreased proliferation, increased apoptosis, decreased TIMP‐1 expression, and increased MMP‐9 expression (Zhou et al. 2004). Therefore, these data suggest that avb3 may play a sensory role in recognizing degradation of extracellular matrix during resolution thus triggering apoptosis of myofibroblasts.
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5.4. ILK Integrin‐linked kinase (ILK) has recently been associated with the fibrotic process in the kidney downstream of TGF‐b (Li et al., 2003), and its expression appears to be both necessary and sufficient for the process of EMT leading to production of myofibroblasts from tubular epithelial cells. EMT appears to proceed in a step‐wise fashion involving four crucial events (Yang and Liu, 2001): (1) loss of epithelial adhesion properties mediated through E‐cadherin; (2) de novo expression of aSMA and actin reorganization; (3) disruption of tubular basement membrane (TBM); and (4) enhanced cell migration and invasion. ILK is a cytoplasmic serine/threonine protein kinase that interacts with the intracellular domains of integrins and numerous cytoskeleton‐ associated proteins (Wu and Dedhar, 2001). In an elegant series of experiments, Li and coworkers have demonstrated that ILK plays a major role in several of the events resulting in EMT (Li et al., 2003). First, ILK expression coincided with EMT induction in vivo in two models of chronic renal fibrosis, UUO, and diabetic injury. Second, ILK expression is induced by TGF‐b in tubular epithelial cells in vitro. Third, several of the events leading to EMT in vitro were induced by ILK over‐expression in epithelial cells, such as loss of E‐ cadherin expression, induction of fibronectin and MMP‐2 expression, and enhanced cell migration and invasion. Fourth, blockade of ILK function through expression of a dominant‐negative, kinase‐dead ILK prevented TGF‐b‐induced EMT. Fifth, inhibition of EMT in vitro and in vivo by hepatocyte growth hormone (HGF, see below) correlated with inhibition of ILK expression (Li et al., 2003). These studies are complemented by demonstration of ILK over‐expression in human patients with congenital nephritic syndrome associated with proteinuria (Kretzler et al., 2001), and in diabetic nephropathy patients at sites of mesangial expansion within the glomeruli in close association with fibronectin matrix deposition (Guo et al., 2001). Therefore, both in vitro and in vivo data suggest that ILK may serve as a very interesting new target for fibrotic disease therapy. 6. Other Potential Targets for Anti‐Fibrotic Therapy 6.1. CTGF Connective tissue growth factor (CTGF) is a cytokine that may act downstream of TGF‐b to regulate matrix metabolism and was first identified as a product of human umbilical vein endothelial cells that was chemotactic and mitogenic for fibroblasts (Bradham et al., 1991). CTGF is expressed by fibroblasts in the lesions but not normal adjacent tissue of patients with progressive systemic sclerosis, localized scleroderma, and keloids (Igarashi et al., 1996). CTGF
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mRNA is upregulated in lesions of crescentic glomerulonephritis, IgA nephropathy, focal and segmental glomerulosclerosis, and diabetic nephropathy (Ito et al., 1998; Riser et al., 2000). Normal human skin fibroblasts express CTGF in response to TGF‐b (Igarashi et al., 1993). Similar to TGF‐b, CTGF injected under the skin of mice induces a rapid and marked increase in connective tissue cells and ECM proteins (Frazier et al., 1996). Mesangial cells treated with human CTGF significantly increased fibronectin and collagen type I production (Riser et al., 2000). Importantly, TGF‐b‐stimulated fibroblast proliferation (Kothapalli et al., 1997, 1998) and collagen synthesis (Duncan et al., 1999) can be blocked with anti‐CTGF antibodies or by inhibition of CTGF synthesis, indicating that CTGF acts as a downstream mediator of certain TGF‐b effects. Finally, when TGF‐b transgenic mice were subtotally nephrectomized and treated with CTGF antisense oligodeoxynucleotide, they showed a reduction in mRNA levels of matrix molecules as well as proteinase inhibitors plasminogen activator inhibitor‐1 (PAI‐1) and TIMP‐1, as well as suppression of renal interstitial fibrosis (Okada et al., 2005). 6.2. HGF Hepatocyte growth factor (HGF) plays an important role in early kidney development and the conversion of nephrogenic mesenchyme to epithelial cells (Horster et al., 1999). EMT is essentially the reverse of this process. In the rat remnant kidney model, an increase in renal and systemic production of HGF coupled with an increase in renal c‐met (the HGF receptor) was observed (Liu et al., 2000). Administration of an anti‐HGF antibody in the model resulted in a rapid decrease in glomerular filtration rate and increased renal fibrosis. A marked increase in ECM accumulation and in aSMA‐positive cells was observed in both the interstitium and tubular epithelium of the antibody‐treated rats. In vitro studies demonstrated that rather than increase ECM synthetic rate in HCK cells, HGF markedly increased MMP‐9 protein expression and decreased the expression of tissue inhibitors of matrix metalloproteinase‐1 (TIMP‐ 1) and TIMP‐2 (Liu et al., 2000). These data suggested that HGF was involved in extracellular matrix degradation and may play a role in preservation of epithelial phenotypes perhaps by inhibiting the process of EMT. Subsequent studies demonstrated that HGF reversed virtually all phenotypic conversion stimulated by TGF‐b such that it restored E‐cadherin expression and suppressed aSMA, vimentin, and fibronectin expression (Yang and Liu, 2002). Additionally, treatment with recombinant HGF protein or its gene effectively blocked EMT in vivo and significantly reduced renal interstitial fibrosis in an obstructive nephropathy model (Yang and Liu, 2002; Yang et al., 2001). Interestingly, administration of HGF after injury induction effectively
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blocked further fibrotic injury, but did not reverse it (Yang and Liu, 2003). Mechanistically, HGF acts by inducing expression of the SnoN transcriptional corepressor of Smad, which in turn interacts with Smad‐2 and blocks the transactivation of Smad‐regulated genes, including ILK (Li et al., 2003). 6.3. BMP‐7 Bone morphogenic protein 7 (BMP‐7, also called OP‐1) is a member of the TGF‐b superfamily and an endogenous antagonist of TGF‐b induced signaling, including EMT in the kidney and other tissues (Zeisberg et al., 2003a,b). BMP‐7 signaling induces a subset of Smad proteins (Smad5) that antagonize the Smad2/3 heterodimers activated by TGF‐b, resulting in re‐expression of E‐ cadherin on tubular epithelial cells induced to undergo EMT. Importantly, Zeisberg et al., have demonstrated that systemic administration of recombinant BMP‐7 in mice with kidney fibrosis following UUO resulted in reversal of EMT and repair of damaged tubular structures with repopulation of healthy tubular epithelial cells associated with a return of renal function (Zeisberg et al., 2003b). The same laboratory also demonstrated that BMP‐7 can provide renal protection in models of diabetic nephropathy (Zeisberg et al., 2003b). 7. Conclusions Inflammation and fibrosis are two inter‐related conditions with many overlapping mechanisms. As we have observed above, an inflammatory stimulus is often necessary to initiate wound closure; however, in many cases this drive stimulates an inappropriate pro‐fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro‐inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying this process. M2 macrophages, TH2 T cells, and activated myofibroblasts have critical roles in fibrosis progression. In contrast, M1 macrophages and TH1 T cells play equally critical roles in fibrosis initiation and even more importantly in fibrosis resolution. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to being fully appreciated. To date, broadly immunosuppressive drugs (e.g., corticosteroids) have been largely ineffective in treating fibrotic disease. This may be due to the fact that these drugs impact both pro‐ and anti‐fibrotic leukocyte subsets. There is hope that with a better understanding of the precise cellular and biochemical processes that inter‐relate inflammatory and fibrotic responses, more specific and effective therapies can be derived. During the course of this review, we have attempted to provide a useful framework with which to discuss the inter‐relatedness of the immune system
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and fibrotic/wound‐healing system, in a relatively unbiased fashion. Cells of the immune system and soluble effector molecules produced by them play important roles in regulating initiation, propagation, and resolution of many types of fibrotic disease (see Table 1). However, it is important to note that the nature of the immune cell population changes during the course of fibrotic disease. These changes, such as macrophage transition from M1 to M2 and back to M1 phenotypes, are necessary for normal healing and disregulated during fibrotic disease. Therefore, a common opinion held by physicians who Table 1 Pro‐Fibrotic Mediators and the Cells that Express Them Pro‐fibrotic mediators: Myofibroblasts
M2 Macrophages
M1 Macrophages
TH2 Cells
TH1 Cells
Cytokines: IL‐4 IL‐5 IL‐13
X X X
Chemokines: CCL‐2 CCL‐3 CCL‐6 CCL‐17 CXCL2
X X ? ? ?
Growth Factors: TGF‐b PDGF IGF CTGF
X
X X X X
X X X X
X
Matrix Regulation: L‐Proline Collagen 1 TIMP‐1 TIMP‐2 MMP‐2 MMP‐9
X X
Integrins: a1b1 anb6 anb3
X X X
X
X
X
X
?
X, indicates expression of the given protein by the cell type. ?, indicates inferred or implied expression of the given protein by the cell type. For further descriptions of each protein, see text.
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treat fibrotic disease that inflammation plays a minor role during propagation and resolution of fibrotic disease may need to evolve in light of the more recent data cited here. We propose that immune cell populations (both macrophages and T‐cells) and the cytokines, growth factors, and chemokines they produce play a critical role in all aspects of the fibrotic process. Early studies using corticosteroids to imply that immune cells do not play a role in fibrotic disease ignore the positive activating effect these molecules have on the induction of the M2 macrophage phenotype. Therefore, in contemplating novel approaches to treat fibrotic disease we must be cognizant of the stage of disease the individual pathology presents to us and the likely role the immune system plays at that stage of disease in order to design appropriate targeted therapies. If used inappropriately, broad‐based anti‐inflammatory treatments are likely to suppress the very mediators of fibrosis resolution that we would like to promote (see Table 2). Although TGF‐b is an obvious target for inhibition in fibrotic disease, and several companies are actively pursuing both small molecule and biological inhibitors (de Gouville et al., 2005; Yata et al., 2002), we must keep in mind Table 2 Anti‐Fibrotic Mediators and the Cells that Express Them Anti‐fibrotic mediators: Myofibroblasts
M2 Macrophages
M1 Macrophages
TH2 Cells
TH1 Cells
Cytokines: INF‐g IL‐12 TNF‐a
X X X
Growth Factors: HGF BMP‐7
?
X ?
?
Matrix Remodeling: MMP‐2 MMP‐3 MMP‐7 MMP‐12 MMP‐13
X X
X X X
X
Chemokines: CCL‐2 CXCL‐10
X ?
X, indicates expression of the given protein by the cell type. ?, indicates inferred or implied expression of the given protein by the cell type. For further descriptions of each protein, see text.
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that TGF‐b is also one of the major anti‐inflammatory mediators controlling autoimmunity in highly antigen‐exposed tissues. For example, TGF‐b plays an important role in non‐disease settings preventing persistent inflammation in the lung (Letterio and Roberts, 1998; Roberts and Sporn, 1993). Thus, severe perivascular inflammation and death results when TGF‐b activity is blocked in the mouse lung (Gorelik and Flavell, 2000, 2002). Therefore, it is imperative that efforts targeting this pathway consider ways in which to separate out TGF‐b anti‐inflammatory activity from its pro‐fibrotic activity, perhaps by specifically targeting more downstream signaling mediators than the TGF‐b receptor tyrosine kinase itself. Some alternatives may be ILK (Li et al., 2003), ROCK (Nagatoya et al., 2002), or CTGF (Okada et al., 2005). Alternatively, TGF‐b signaling could be disrupted by using recombinant HGF or BMP‐7. However, caution should always be used, lest we inadvertently activate autoimmunity. New therapeutics that specifically target M2 vs. M1 macrophages may represent a more selective approach, thus, inhibiting the M2 macrophage during active fibrosis propagation or attempting to convert the M2 phenotype to the M1 phenotype in order to promote fibrosis resolution. One such method may be through specific inhibition of Arg1 activity; additional work in this area is warranted. Alternatively, specific inhibition of IL‐13 or the use of caspase inhibitors to block apoptotic cell production (Canbay et al., 2004; Valentino et al., 2003) may reduce the number and activity of M2 macrophages. Finally, a few words regarding the challenges of clinical development in this area are appropriate. Our current ability to clinically evaluate novel anti‐ fibrotic agents is impeded by a lack of validated surrogate clinical endpoints for fibrotic disease progression. Hardline endpoints currently required for drug approval by the FDA such as long‐term survival and 48‐week serial tissue biopsy are impractical for the earlier stage phase II clinical studies so critical to new therapy advancement. Although progress is being made in serum biomarker development and new non‐invasive imaging studies, more work is needed. Furthermore, their broad application across multiple fibrotic diseases is questionable. As we work towards our individual research goals, we must strive to never lose sight of the end goal of new effective therapy approval. The patients are desperately waiting, and many don’t have the luxury of time. References Abboud, H. E. (1995). Role of platelet‐derived growth factor in renal injury. Annu. Rev. Physiol. 57, 297–309. Abe, R., Donnelly, S. C., Peng, T., Bucala, R., and Metz, C. N. (2001). Peripheral blood fibrocytes: Differentiation pathway and migration to wound sites. J. Immunol. 166(12), 7556–7562.
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Adawi, A., Zhang, Y., Baggs, R., Rubin, P., Williams, J., Finkelstein, J., and Phipps, R. P. (1998). Blockade of CD40‐CD40 ligand interactions protects against radiation‐induced pulmonary inflammation and fibrosis. Clin. Immunol. Immunopathol. 89(3), 222–230. Addison, C. L., Daniel, T. O., Burdick, M. D., Liu, H., Ehlert, J. E., Xue, Y. Y., Buechi, L., Walz, A., Richmond, A., and Strieter, R. M. (2000). The CXC chemokine receptor 2, CXCR2, is the putative receptor for ELRþ CXC chemokine‐induced angiogenic activity. J. Immunol. 165(9), 5269–5277. Anders, H. J., Belemezova, E., Eis, V., Segerer, S., Vielhauer, V., Perez de Lema, G., Kretzler, M., Cohen, C. D., Frink, M., Horuk, R., Hudkins, K. L., Alpers, C. E., Mampaso, F., and Schlondorff, D. (2004). Late onset of treatment with a chemokine receptor CCR1 antagonist prevents progression of lupus nephritis in MRL‐Fas(lpr) mice. J. Am. Soc. Nephrol. 15(6), 1504–1513. Anders, H. J., Vielhauer, V., Frink, M., Linde, Y., Cohen, C. D., Blattner, S. M., Kretzler, M., Strutz, F., Mack, M., Grone, H. J., Onuffer, J., Horuk, R., Nelson, P. J., and Schlondorff, D. (2002). A chemokine receptor CCR‐1 antagonist reduces renal fibrosis after unilateral ureter ligation. J. Clin. Invest. 109(2), 251–259. Arthur, M. J. (2000). Fibrogenesis II. Metalloproteinases and their inhibitors in liver fibrosis. Am. J. Physiol. Gastrointest. Liver. Physiol. 279(2), G245–G249. Bachem, M. G., Schneider, E., Gross, H., Weidenbach, H., Schmid, R. M., Menke, A., Siech, M., Beger, H., Grunert, A., and Adler, G. (1998). Identification, culture, and characterization of pancreatic stellate cells in rats and humans. Gastroenterology 115(2), 421–432. Bataller, R., and Brenner, D. A. (2005). Liver fibrosis. J. Clin. Invest. 115(2), 209–218. Belperio, J. A., Dy, M., Burdick, M. D., Xue, Y. Y., Li, K., Elias, J. A., and Keane, M. P. (2002). Interaction of IL‐13 and C10 in the pathogenesis of bleomycin‐induced pulmonary fibrosis. Am. J. Respir. Cell Mol. Biol. 27(4), 419–427. Belperio, J. A., Dy, M., Murray, L., Burdick, M. D., Xue, Y. Y., Strieter, R. M., and Keane, M. P. (2004). The role of the Th2 CC chemokine ligand CCL17 in pulmonary fibrosis. J. Immunol. 173(7), 4692–4698. Bhowmick, N. A., Zent, R., Ghiassi, M., McDonnell, M., and Moses, H. L. (2001). Integrin beta 1 signaling is necessary for transforming growth factor‐beta activation of p38MAPK and epithelial plasticity. J. Biol. Chem. 276(50), 46707–46713. Epub 2001 Oct 5. Bissell, D. M. (1998). Hepatic fibrosis as wound repair: A progress report. J. Gastroenterol. 33(2), 295–302. Bissell, D. M., Wang, S. S., Jarnagin, W. R., and Roll, F. J. (1995). Cell‐specific expression of transforming growth factor‐beta in rat liver. Evidence for autocrine regulation of hepatocyte proliferation. J. Clin. Invest. 96(1), 447–455. Blease, K., Mehrad, B., Standiford, T. J., Lukacs, N. W., Kunkel, S. L., Chensue, S. W., Lu, B., Gerard, C. J., and Hogaboam, C. M. (2000). Airway remodeling is absent in CCR1‐/‐ mice during chronic fungal allergic airway disease. J. Immunol. 165(3), 1564–1572. Blease, K., Schuh, J. M., Jakubzick, C., Lukacs, N. W., Kunkel, S. L., Joshi, B. H., Puri, R. K., Kaplan, M. H., and Hogaboam, C. M. (2002). Stat6‐deficient mice develop airway hyperresponsiveness and peribronchial fibrosis during chronic fungal asthma. Am. J. Pathol. 160(2), 481–490. Bonner, J. C. (2004). Regulation of PDGF and its receptors in fibrotic diseases. Cytokine Growth Factor Rev. 15(4), 255–273. Booth, M., Mwatha, J. K., Joseph, S., Jones, F. M., Kadzo, H., Ireri, E., Kazibwe, F., Kemijumbi, J., Kariuki, C., Kimani, G., Ouma, J. H., Kabatereine, N. B., Vennervald, B. J., and Dunne, D. W. (2004). Periportal fibrosis in human Schistosoma mansoni infection is associated with low IL‐10, low IFN‐gamma, high TNF‐alpha, or low RANTES, depending on age and gender. J. Immunol. 172(2), 1295–1303.
R E G U L AT I O N O F F I B R O S I S B Y T H E I M M U N E S Y S T E M
275
Border, W. A., Noble, N. A., Yamamoto, T., Harper, J. R., Yamaguchi, Y., Pierschbacher, M. D., and Ruoslahti, E. (1992). Natural inhibitor of transforming growth factor‐beta protects against scarring in experimental kidney disease. Nature 360(6402), 361–364. Bradham, D. M., Igarashi, A., Potter, R. L., and Grotendorst, G. R. (1991). Connective tissue growth factor: A cysteine‐rich mitogen secreted by human vascular endothelial cells is related to the SRC‐induced immediate early gene product CEF‐10. J. Cell. Biol. 114(6), 1285–1294. Brennan, D. C., Jevnikar, A. M., Takei, F., and Reubin‐Kelley, V. E. (1990). Mesangial cell accessory functions: Mediation by intercellular adhesion molecule‐1. Kidney Int. 38(6), 1039–1046. Buechler, C., Ritter, M., Orso, E., Langmann, T., Klucken, J., and Schmitz, G. (2000). Regulation of scavenger receptor CD163 expression in human monocytes and macrophages by pro‐ and anti‐inflammatory stimuli. J. Leukoc. Biol. 67(1), 97–103. Canbay, A., Feldstein, A., Baskin‐Bey, E., Bronk, S. F., and Gores, G. J. (2004). The caspase inhibitor IDN‐6556 attenuates hepatic injury and fibrosis in the bile duct ligated mouse. J. Pharmacol. Exp. Ther. 308(3), 1191–1196. Epub 2003 Nov 14. Canbay, A., Taimr, P., Torok, N., Higuchi, H., Friedman, S., and Gores, G. J. (2003). Apoptotic body engulfment by a human stellate cell line is profibrogenic. Lab. Invest. 83(5), 655–663. Cheever, A. W., Williams, M. E., Wynn, T. A., Finkelman, F. D., Seder, R. A., Cox, T. M., Hieny, S., Caspar, P., and Sher, A. (1994). Anti‐IL‐4 treatment of Schistosoma mansoni‐infected mice inhibits development of T cells and non‐B, non‐T cells expressing Th2 cytokines while decreasing egg‐induced hepatic fibrosis. J. Immunol. 153(2), 753–759. Chen, Q., Rabach, L., Noble, P., Zheng, T., Lee, C. G., Homer, R. J., and Elias, J. A. (2005). IL‐11 receptor alpha in the pathogenesis of IL‐13‐induced inflammation and remodeling. J. Immunol. 174(4), 2305–2313. Chen, X., Moeckel, G., Morrow, J. D., Cosgrove, D., Harris, R. C., Fogo, A. B., Zent, R., and Pozzi, A. (2004). Lack of integrin alpha1beta1 leads to severe glomerulosclerosis after glomerular injury. Am. J. Pathol. 165(2), 617–630. Chiaramonte, M. G., Cheever, A. W., Malley, J. D., Donaldson, D. D., and Wynn, T. A. (2001). Studies of murine schistosomiasis reveal interleukin‐13 blockade as a treatment for established and progressive liver fibrosis. Hepatology 34(2), 273–282. Chiaramonte, M. G., Donaldson, D. D., Cheever, A. W., and Wynn, T. A. (1999). An IL‐13 inhibitor blocks the development of hepatic fibrosis during a T‐helper type 2‐dominated inflammatory response. J. Clin. Invest. 104(6), 777–785. Chtanova, T., and Mackay, C. R. (2001). T cell effector subsets: Extending the Th1/Th2 paradigm. Adv. Immunol. 78, 233–266. Coker, R. K., Laurent, G. J., Shahzeidi, S., Lympany, P. A., du Bois, R. M., Jeffery, P. K., and McAnulty, R. J. (1997). Transforming growth factors‐beta 1, ‐beta 2, and ‐beta 3 stimulate fibroblast procollagen production in vitro but are differentially expressed during bleomycin‐ induced lung fibrosis. Am. J. Pathol. 150(3), 981–991. Cook, H. T., Khan, S. B., Allen, A., Bhangal, G., Smith, J., Lobb, R. R., and Pusey, C. D. (2002). Treatment with an antibody to VLA‐1 integrin reduces glomerular and tubulointerstitial scarring in a rat model of crescentic glomerulonephritis. Am. J. Pathol. 161(4), 1265–1272. Corraliza, I. M., Soler, G., Eichmann, K., and Modolell, M. (1995). Arginase induction by suppressors of nitric oxide synthesis (IL‐4, IL‐10 and PGE2) in murine bone‐marrow‐derived macrophages. Biochem. Biophys. Res. Commun. 206(2), 667–673. Cosgrove, D., Rodgers, K., Meehan, D., Miller, C., Bovard, K., Gilroy, A., Gardner, H., Kotelianski, V., Gotwals, P., Amatucci, A., and Kalluri, R. (2000). Integrin alpha1beta1 and transforming growth factor‐beta1 play distinct roles in alport glomerular pathogenesis and serve as dual targets for metabolic therapy. Am. J. Pathol. 157(5), 1649–1659.
276
M A R K L . L U P H E R A N D W. M I C H A E L G A L L AT I N
Davis, B. H. (1988). Transforming growth factor beta responsiveness is modulated by the extracellular collagen matrix during hepatic into cell culture. J. Cell. Physiol. 136(3), 547–553. de Fougerolles, A. R., Sprague, A. G., Nickerson‐Nutter, C. L., Chi‐Rosso, G., Rennert, P. D., Gardner, H., Gotwals, P. J., Lobb, R. R., and Koteliansky, V. E. (2000). Regulation of inflammation by collagen‐binding integrins alpha1beta1 and alpha2beta1 in models of hypersensitivity and arthritis. J. Clin. Invest. 105(6), 721–729. de Gouville, A. C., Boullay, V., Krysa, G., Pilot, J., Brusq, J. M., Loriolle, F., Gauthier, J. M., Papworth, S. A., Laroze, A., Gellibert, F., and Huet, S. (2005). Inhibition of TGF‐beta signaling by an ALK5 inhibitor protects rats from dimethylnitrosamine‐induced liver fibrosis. Br. J. Pharmacol. 145(2), 166–177. De Heer, E., Prodjosudjadi, W., Davidoff, A., van der Wal, A., Bruijn, J. A., and Paul, L. C. (1998). Control of monocyte influx in glomerulonephritis in transplanted kidneys in the rat. Lab. Invest. 78(10), 1327–1337. de Lalla, C., Galli, G., Aldrighetti, L., Romeo, R., Mariani, M., Monno, A., Nuti, S., Colombo, M., Callea, F., Porcelli, S. A., Panina‐Bordignon, P., Abrignani, S., Casorati, G., and Dellabona, P. (2004). Production of profibrotic cytokines by invariant NKT cells characterizes cirrhosis progression in chronic viral hepatitis. J. Immunol. 173(2), 1417–1425. Demirci, G., Nashan, B., and Pichlmayr, R. (1996). Fibrosis in chronic rejection of human liver allografts: Expression patterns of transforming growth factor‐TGFbeta1 and TGF‐beta3. Transplantation 62(12), 1776–1783. Desmouliere, A., Geinoz, A., Gabbiani, F., and Gabbiani, G. (1993). Transforming growth factor‐ beta 1 induces alpha‐smooth muscle actin expression in granulation tissue myofibroblasts and in quiescent and growing cultured fibroblasts. J. Cell. Biol. 122(1), 103–111. Devalaraja, R. M., Nanney, L. B., Du, J., Qian, Q., Yu, Y., Devalaraja, M. N., and Richmond, A. (2000). Delayed wound healing in CXCR2 knockout mice. J. Invest. Dermatol. 115(2), 234–244. Di Sario, A., Bendia, E., Svegliati Baroni, G., Ridolfi, F., Casini, A., Ceni, E., Saccomanno, S., Marzioni, M., Trozzi, L., Sterpetti, P., Taffetani, S., and Benedetti, A. (2002). Effect of pirfenidone on rat hepatic stellate cell proliferation and collagen production. J. Hepatol. 37(5), 584–591. Dickeson, S. K., Mathis, N. L., Rahman, M., Bergelson, J. M., and Santoro, S. A. (1999). Determinants of ligand binding specificity of the alpha(1)beta(1) and alpha(2)beta(1) integrins. J. Biol. Chem. 274(45), 32182–32191. Doucet, C., Brouty‐Boye, D., Pottin‐Clemenceau, C., Canonica, G. W., Jasmin, C., and Azzarone, B. (1998). Interleukin (IL) 4 and IL‐13 act on human lung fibroblasts. Implication in asthma. J. Clin. Invest. 101(10), 2129–2139. Duffield, J. S. (2003). The inflammatory macrophage: A story of Jekyll and Hyde. Clin. Sci. (Lond.) 104(1), 27–38. Duffield, J. S., Erwig, L. P., Wei, X., Liew, F. Y., Rees, A. J., and Savill, J. S. (2000). Activated macrophages direct apoptosis and suppress mitosis of mesangial cells. J. Immunol. 164(4), 2110–2119. Duffield, J. S., Forbes, S. J., Constandinou, C. M., Clay, S., Partolina, M., Vuthoori, S., Wu, S., Lang, R., and Iredale, J. P. (2005). Selective depletion of macrophages reveals distinct, opposing roles during liver injury and repair. J. Clin. Invest. 115(1), 56–65. Duffield, J. S., Ware, C. F., Ryffel, B., and Savill, J. (2001). Suppression by apoptotic cells defines tumor necrosis factor‐mediated induction of glomerular mesangial cell apoptosis by activated macrophages. Am. J. Pathol. 159(4), 1397–1404. Duncan, M. R., Frazier, K. S., Abramson, S., Williams, S., Klapper, H., Huang, X., and Grotendorst, G. R. (1999). Connective tissue growth factor mediates transforming growth factor beta‐induced collagen synthesis: Downregulated by cAMP. FASEB J. 13(13), 1774–1786.
R E G U L AT I O N O F F I B R O S I S B Y T H E I M M U N E S Y S T E M
277
Eis, V., Luckow, B., Vielhauer, V., Siveke, J. T., Linde, Y., Segerer, S., De Lema, G. P., Cohen, C. D., Kretzler, M., Mack, M., Horuk, R., Murphy, P. M., Gao, J. L., Hudkins, K. L., Alpers, C. E., Grone, H. J., Schlondorff, D., and Anders, H. J. (2004). Chemokine receptor CCR1 but not CCR5 mediates leukocyte recruitment and subsequent renal fibrosis after unilateral ureteral obstruction. J. Am. Soc. Nephrol. 15(2), 337–347. Ekholm, E., Hankenson, K. D., Uusitalo, H., Hiltunen, A., Gardner, H., Heino, J., and Penttinen, R. (2002). Diminished callus size and cartilage synthesis in alpha1beta1 integrin‐deficient mice during bone fracture healing. Am. J. Pathol. 160(5), 1779–1785. Eliceiri, B. P., and Cheresh, D. A. (2000). Role of alpha v integrins during angiogenesis. Cancer J. 6(Suppl. 3), S245–S249. Emura, M., Nagai, S., Takeuchi, M., Kitaichi, M., and Izumi, T. (1990). In vitro production of B cell growth factor and B cell differentiation factor by peripheral blood mononuclear cells and bronchoalveolar lavage T lymphocytes from patients with idiopathic pulmonary fibrosis. Clin. Exp. Immunol. 82(1), 133–139. Erwig, L. P., Kluth, D. C., Walsh, G. M., and Rees, A. J. (1998). Initial cytokine exposure determines function of macrophages and renders them unresponsive to other cytokines. J. Immunol. 161(4), 1983–1988. Fadok, V. A., Bratton, D. L., Konowal, A., Freed, P. W., Westcott, J. Y., and Henson, P. M. (1998). Macrophages that have ingested apoptotic cells in vitro inhibit proinflammatory cytokine production through autocrine/paracrine mechanisms involving TGF‐beta, PGE2, and PAF. J. Clin. Invest. 101(4), 890–898. Fallon, P. G., Richardson, E. J., McKenzie, G. J., and McKenzie, A. N. (2000). Schistosome infection of transgenic mice defines distinct and contrasting pathogenic roles for IL‐4 and IL‐ 13: IL‐13 is a profibrotic agent. J. Immunol. 164(5), 2585–2591. Fertin, C., Nicolas, J. F., Gillery, P., Kalis, B., Banchereau, J., and Maquart, F. X. (1991). Interleukin‐4 stimulates collagen synthesis by normal and scleroderma fibroblasts in dermal equivalents. Cell Mol. Biol. 37(8), 823–829. Flanders, K. C., Sullivan, C. D., Fujii, M., Sowers, A., Anzano, M. A., Arabshahi, A., Major, C., Deng, C., Russo, A., Mitchell, J. B., and Roberts, A. B. (2002). Mice lacking Smad3 are protected against cutaneous injury induced by ionizing radiation. Am. J. Pathol. 160(3), 1057–1068. Frazier, K., Williams, S., Kothapalli, D., Klapper, H., and Grotendorst, G. R. (1996). Stimulation of fibroblast cell growth, matrix production, and granulation tissue formation by connective tissue growth factor. J. Invest. Dermatol. 107(3), 404–411. Friedman, S. L. (1993). Seminars in medicine of the Beth Israel Hospital, Boston. The cellular basis of hepatic fibrosis. Mechanisms and treatment strategies. N. Engl. J. Med. 328(25), 1828–1835. Friedman, S. L., and Arthur, M. J. (1989). Activation of cultured rat hepatic lipocytes by Kupffer cell conditioned medium. Direct enhancement of matrix synthesis and stimulation of cell proliferation via induction of platelet‐derived growth factor receptors. J. Clin. Invest. 84(6), 1780–1785. Friedman, S. L., Roll, F. J., Boyles, J., Arenson, D. M., and Bissell, D. M. (1989). Maintenance of differentiated phenotype of cultured rat hepatic lipocytes by basement membrane matrix. J. Biol. Chem. 264(18), 10756–10762. Fukasawa, H., Yamamoto, T., Suzuki, H., Togawa, A., Ohashi, N., Fujigaki, Y., Uchida, C., Aoki, M., Hosono, M., Kitagawa, M., and Hishida, A. (2004). Treatment with anti‐TGF‐beta antibody ameliorates chronic progressive nephritis by inhibiting Smad/TGF‐beta signaling. Kidney Int. 65(1), 63–74. Gabbiani, G. (2003). The myofibroblast in wound healing and fibrocontractive diseases. J. Pathol. 200(4), 500–503.
278
M A R K L . L U P H E R A N D W. M I C H A E L G A L L AT I N
Gabbiani, G., Ryan, G. B., and Majne, G. (1971). Presence of modified fibroblasts in granulation tissue and their possible role in wound contraction. Experientia 27(5), 549–550. Gaca, M. D., Zhou, X., Issa, R., Kiriella, K., Iredale, J. P., and Benyon, R. C. (2003). Basement membrane‐like matrix inhibits proliferation and collagen synthesis by activated rat hepatic stellate cells: Evidence for matrix‐dependent deactivation of stellate cells. Matrix. Biol. 22(3), 229–239. Gardner, H., Broberg, A., Pozzi, A., Laato, M., and Heino, J. (1999). Absence of integrin alpha1beta1 in the mouse causes loss of feedback regulation of collagen synthesis in normal and wounded dermis. J. Cell. Sci. 112(Pt. 3), 263–272. Gardner, H., Kreidberg, J., Koteliansky, V., and Jaenisch, R. (1996). Deletion of integrin alpha 1 by homologous recombination permits normal murine development but gives rise to a specific deficit in cell adhesion. Dev. Biol. 175(2), 301–313. Gay, S., Jones, R. E., Jr., Huang, G. Q., and Gay, R. E. (1989). Immunohistologic demonstration of platelet‐derived growth factor (PDGF) and sis‐oncogene expression in scleroderma. J. Invest. Dermatol. 92(2), 301–303. Geng, Y. J., and Hansson, G. K. (1992). Interferon‐gamma inhibits scavenger receptor expression and foam cell formation in human monocyte‐derived macrophages. J. Clin. Invest. 89(4), 1322–1330. George, J., Roulot, D., Koteliansky, V. E., and Bissell, D. M. (1999). In vivo inhibition of rat stellate cell activation by soluble transforming growth factor beta type II receptor: A potential new therapy for hepatic fibrosis. Proc. Natl. Acad. Sci. USA 96(22), 12719–12724. George, J., Wang, S. S., Sevcsik, A. M., Sanicola, M., Cate, R. L., Koteliansky, V. E., and Bissell, D. M. (2000). Transforming growth factor‐beta initiates wound repair in rat liver through induction of the EIIIA‐fibronectin splice isoform. Am. J. Pathol. 156(1), 115–124. Gharaee‐Kermani, M., and Phan, S. H. (1997). Lung interleukin‐5 expression in murine bleomycin‐induced pulmonary fibrosis. Am. J. Respir. Cell Mol. Biol. 16(4), 438–447. Gibbs, D. F., Warner, R. L., Warner, R. L., Weiss, S. J., Johnson, K. J., and Varani, J. (1999). Characterization of matrix metalloproteinases produced by rat alveolar macrophages. Am. J. Respir. Cell Mol. Biol. 20(6), 1136–1144. Giri, S. N., Hyde, D. M., and Hollinger, M. A. (1993). Effect of antibody to transforming growth factor beta on bleomycin induced accumulation of lung collagen in mice. Thorax 48(10), 959–966. Goerdt, S., and Orfanos, C. E. (1999). Other functions, other genes: Alternative activation of antigen‐presenting cells. Immunity 10(2), 137–142. Gorelik, L., and Flavell, R. A. (2000). Abrogation of TGFbeta signaling in T cells leads to spontaneous T cell differentiation and autoimmune disease. Immunity 12(2), 171–181. Gorelik, L., and Flavell, R. A. (2002). Transforming growth factor‐beta in T‐cell biology. Nat. Rev. Immunol. 2(1), 46–53. Gressner, A. M. (1998). The cell biology of liver fibrogenesis—an imbalance of proliferation, growth arrest and apoptosis of myofibroblasts. Cell Tissue. Res. 292(3), 447–452. Guo, L., Sanders, P. W., Woods, A., and Wu, C. (2001). The distribution and regulation of integrin‐ linked kinase in normal and diabetic kidneys. Am. J. Pathol. 159(5), 1735–1742. Gurujeyalakshmi, G., and Giri, S. N. (1995). Molecular mechanisms of antifibrotic effect of interferon gamma in bleomycin‐mouse model of lung fibrosis: Downregulation of TGF‐beta and procollagen I and III gene expression. Exp. Lung Res. 21(5), 791–808. Gurujeyalakshmi, G., Hollinger, M. A., and Giri, S. N. (1999). Pirfenidone inhibits PDGF isoforms in bleomycin hamster model of lung fibrosis at the translational level. Am. J. Physiol. 276(2 Pt. 1), L311–L318. Hancock, A., Armstrong, L., Gama, R., and Millar, A. (1998). Production of interleukin 13 by alveolar macrophages from normal and fibrotic lung. Am. J. Respir. Cell Mol. Biol. 18(1), 60–65.
R E G U L AT I O N O F F I B R O S I S B Y T H E I M M U N E S Y S T E M
279
Haroon, Z. A., Hettasch, J. M., Lai, T. S., Dewhirst, M. W., and Greenberg, C. S. (1999a). Tissue transglutaminase is expressed, active, and directly involved in rat dermal wound healing and angiogenesis. FASEB. J. 13(13), 1787–1795. Haroon, Z. A., Lai, T. S., Hettasch, J. M., Lindberg, R. A., Dewhirst, M. W., and Greenberg, C. S. (1999b). Tissue transglutaminase is expressed as a host response to tumor invasion and inhibits tumor growth. Lab. Invest. 79(12), 1679–1686. Hasegawa, M., Fujimoto, M., Kikuchi, K., and Takehara, K. (1997). Elevated serum levels of interleukin 4 (IL‐4), IL‐10, and IL‐13 in patients with systemic sclerosis. J. Rheumatol. 24(2), 328–332. Haynes, A. R., and Shaw, R. J. (1992). Dexamethasone‐induced increase in platelet‐derived growth factor (B) mRNA in human alveolar macrophages and myelomonocytic HL60 macrophage‐like cells. Am. J. Respir. Cell Mol. Biol. 7(2), 198–206. Hellerbrand, Wang, S. C., Tsukamoto, H., Brenner, D. A., and Rippe, R. A. (1996). Expression of intracellular adhesion molecule 1 by activated hepatic stellate cells. Hepatology 24(3), 670–676. Hemler, M. E. (1990). VLA proteins in the integrin family: Structures, functions, and their role on leukocytes. Annu. Rev. Immunol. 8, 365–400. Hemler, M. E., and Lobb, R. R. (1995). The leukocyte beta 1 integrins. Curr. Opin. Hematol. 2(1), 61–67. Hoffmann, K. F., Cheever, A. W., and Wynn, T. A. (2000). IL‐10 and the dangers of immune polarization: Excessive type 1 and type 2 cytokine responses induce distinct forms of lethal immunopathology in murine schistosomiasis. J. Immunol. 164(12), 6406–6416. Hogger, P., Dreier, J., Droste, A., Buck, F., and Sorg, C. (1998). Identification of the integral membrane protein RM3/1 on human monocytes as a glucocorticoid‐inducible member of the scavenger receptor cysteine‐rich family (CD163). J. Immunol. 161(4), 1883–1890. Horster, M. F., Braun, G. S., and Huber, S. M. (1999). Embryonic renal epithelia: Induction, nephrogenesis, and cell differentiation. Physiol. Rev. 79(4), 1157–1191. Huang, X. Z., Wu, J. F., Cass, D., Erle, D. J., Corry, D., Young, S. G., Farese, R. V., Jr., and Sheppard, D. (1996). Inactivation of the integrin beta 6 subunit gene reveals a role of epithelial integrins in regulating inflammation in the lung and skin. J. Cell. Biol. 133(4), 921–928. Igarashi, A., Nashiro, K., Kikuchi, K., Sato, S., Ihn, H., Fujimoto, M., Grotendorst, G. R., and Takehara, K. (1996). Connective tissue growth factor gene expression in tissue sections from localized scleroderma, keloid, and other fibrotic skin disorders. J. Invest. Dermatol. 106(4), 729–733. Igarashi, A., Okochi, H., Bradham, D. M., and Grotendorst, G. R. (1993). Regulation of connective tissue growth factor gene expression in human skin fibroblasts and during wound repair. Mol. Biol. Cell 4(6), 637–645. Iida, H., Seifert, R., Alpers, C. E., Gronwald, R. G., Phillips, P. E., Pritzl, P., Gordon, K., Gown, A. M., Ross, R., Bowen‐Pope, D. F., et al. (1991). Platelet‐derived growth factor (PDGF) and PDGF receptor are induced in mesangial proliferative nephritis in the rat. Proc. Natl. Acad. Sci. USA 88(15), 6560–6564. Iredale, J. P., Benyon, R. C., Pickering, J., McCullen, M., Northrop, M., Pawley, S., Hovell, C., and Arthur, M. J. (1998). Mechanisms of spontaneous resolution of rat liver fibrosis. Hepatic stellate cell apoptosis and reduced hepatic expression of metalloproteinase inhibitors. J. Clin. Invest. 102(3), 538–549. Issa, R., Williams, E., Trim, N., Kendall, T., Arthur, M. J., Reichen, J., Benyon, R. C., and Iredale, J. P. (2001). Apoptosis of hepatic stellate cells: Involvement in resolution of biliary fibrosis and regulation by soluble growth factors. Gut 48(4), 548–557. Issa, R., Zhou, X., Constandinou, C. M., Fallowfield, J., Millward‐Sadler, H., Gaca, M. D., Sands, E., Suliman, I., Trim, N., Knorr, A., Arthur, M. J., Benyon, R. C., and Iredale, J. P. (2004).
280
M A R K L . L U P H E R A N D W. M I C H A E L G A L L AT I N
Spontaneous recovery from micronodular cirrhosis: Evidence for incomplete resolution associated with matrix cross‐linking. Gastroenterology 126(7), 1795–1808. Ito, Y., Aten, J., Bende, R. J., Oemar, B. S., Rabelink, T. J., Weening, J. J., and Goldschmeding, R. (1998). Expression of connective tissue growth factor in human renal fibrosis. Kidney Int. 53(4), 853–861. Iwano, M., Plieth, D., Danoff, T. M., Xue, C., Okada, H., and Neilson, E. G. (2002). Evidence that fibroblasts derive from epithelium during tissue fibrosis. J. Clin. Invest. 110(3), 341–350. Jarnagin, W. R., Rockey, D. C., Koteliansky, V. E., Wang, S. S., and Bissell, D. M. (1994). Expression of variant fibronectins in wound healing: Cellular source and biological activity of the EIIIA segment in rat hepatic fibrogenesis. J. Cell. Biol. 127(6 Pt. 2), 2037–2048. Jiang, D., Liang, J., Hodge, J., Lu, B., Zhu, Z., Yu, S., Fan, J., Gao, Y., Yin, Z., Homer, R., Gerard, C., and Noble, P. W. (2004). Regulation of pulmonary fibrosis by chemokine receptor CXCR3. J. Clin. Invest. 114(2), 291–299. Johnson, R. J., Raines, E. W., Floege, J., Yoshimura, A., Pritzl, P., Alpers, C., and Ross, R. (1992). Inhibition of mesangial cell proliferation and matrix expansion in glomerulonephritis in the rat by antibody to platelet‐derived growth factor. J. Exp. Med. 175(5), 1413–1416. Kagami, S., Kondo, S., Urushihara, M., Loster, K., Reutter, W., Saijo, T., Kitamura, A., Kobayashi, S., and Kuroda, Y. (2000). Overexpression of alpha1beta1 integrin directly affects rat mesangial cell behavior. Kidney Int. 58(3), 1088–1097. Kagami, S., Urushihara, M., Kondo, S., Hayashi, T., Yamano, H., Loster, K., Vossmeyer, D., Reutter, W., and Kuroda, Y. (2002). Effects of anti‐alpha1 integrin subunit antibody on anti‐ Thy‐1 glomerulonephritis. Lab. Invest. 82(9), 1219–1227. Kalluri, R., and Neilson, E. G. (2003). Epithelial‐mesenchymal transition and its implications for fibrosis. J. Clin. Invest. 112(12), 1776–1784. Kaminski, N., Allard, J. D., Pittet, J. F., Zuo, F., Griffiths, M. J., Morris, D., Huang, X., Sheppard, D., and Heller, R. A. (2000). Global analysis of gene expression in pulmonary fibrosis reveals distinct programs regulating lung inflammation and fibrosis. Proc. Natl. Acad. Sci. USA 97(4), 1778–1783. Kaufman, J., Sime, P. J., and Phipps, R. P. (2004). Expression of CD154 (CD40 ligand) by human lung fibroblasts: Differential regulation by IFN‐gamma and IL‐13, and implications for fibrosis. J. Immunol. 172(3), 1862–1871. Kaviratne, M., Hesse, M., Leusink, M., Cheever, A. W., Davies, S. J., McKerrow, J. H., Wakefield, L. M., Letterio, J. J., and Wynn, T. A. (2004). IL‐13 activates a mechanism of tissue fibrosis that is completely TGF‐beta independent. J. Immunol. 173(6), 4020–4029. Keane, M. P., Arenberg, D. A., Lynch, J. P., 3rd, Whyte, R. I., Iannettoni, M. D., Burdick, M. D., Wilke, C. A., Morris, S. B., Glass, M. C., DiGiovine, B., Kunkel, S. L., and Strieter, R. M. (1997). The CXC chemokines, IL‐8 and IP‐10, regulate angiogenic activity in idiopathic pulmonary fibrosis. J. Immunol. 159(3), 1437–1443. Keane, M. P., Belperio, J. A., Arenberg, D. A., Burdick, M. D., Xu, Z. J., Xue, Y. Y., and Strieter, R. M. (1999a). IFN‐gamma‐inducible protein‐10 attenuates bleomycin‐induced pulmonary fibrosis via inhibition of angiogenesis. J. Immunol. 163(10), 5686–5692. Keane, M. P., Belperio, J. A., Burdick, M. D., Lynch, J. P., Fishbein, M. C., and Strieter, R. M. (2001a). ENA‐78 is an important angiogenic factor in idiopathic pulmonary fibrosis. Am. J. Respir. Crit. Care Med. 164(12), 2239–2242. Keane, M. P., Belperio, J. A., Burdick, M. D., and Strieter, R. M. (2001b). IL‐12 attenuates bleomycin‐induced pulmonary fibrosis. Am. J. Physiol. Lung. Cell Mol. Physiol. 281(1), L92–L97. Keane, M. P., Belperio, J. A., Moore, T. A., Moore, B. B., Arenberg, D. A., Smith, R. E., Burdick, M. D., Kunkel, S. L., and Strieter, R. M. (1999b). Neutralization of the CXC chemokine,
R E G U L AT I O N O F F I B R O S I S B Y T H E I M M U N E S Y S T E M
281
macrophage inflammatory protein‐2, attenuates bleomycin‐induced pulmonary fibrosis. J. Immunol. 162(9), 5511–5518. Khalil, N., Corne, S., Whitman, C., and Yacyshyn, H. (1996). Plasmin regulates the activation of cell‐associated latent TGF‐beta 1 secreted by rat alveolar macrophages after in vivo bleomycin injury. Am. J. Respir. Cell Mol. Biol. 15(2), 252–259. Kitamura, M. (1998). TGF‐beta1 as an endogenous defender against macrophage‐triggered stromelysin gene expression in the glomerulus. J. Immunol. 160(10), 5163–5168. Klareskog, L., Gustafsson, R., Scheynius, A., and Hallgren, R. (1990). Increased expression of platelet‐ derived growth factor type B receptors in the skin of patients with systemic sclerosis. Arthritis. Rheum. 33(10), 1534–1541. Knittel, T., Dinter, C., Kobold, D., Neubauer, K., Mehde, M., Eichhorst, S., and Ramadori, G. (1999). Expression and regulation of cell adhesion molecules by hepatic stellate cells (HSC) of rat liver: Involvement of HSC in recruitment of inflammatory cells during hepatic tissue repair. Am. J. Pathol. 154(1), 153–167. Kolodsick, J. E., Toews, G. B., Jakubzick, C., Hogaboam, C., Moore, T. A., McKenzie, A., Wilke, C. A., Chrisman, C. J., and Moore, B. B. (2004). Protection from fluorescein isothiocyanate‐ induced fibrosis in IL‐13‐deficient, but not IL‐4‐deficient, mice results from impaired collagen synthesis by fibroblasts. J. Immunol. 172(7), 4068–4076. Kothapalli, D., Frazier, K. S., Welply, A., Segarini, P. R., and Grotendorst, G. R. (1997). Transforming growth factor beta induces anchorage‐independent growth of NRK fibroblasts via a connective tissue growth factor‐dependent signaling pathway. Cell. Growth Differ. 8(1), 61–68. Kothapalli, D., Hayashi, N., and Grotendorst, G. R. (1998). Inhibition of TGF‐beta‐stimulated CTGF gene expression and anchorage‐independent growth by cAMP identifies a CTGF‐dependent restriction point in the cell cycle. FASEB. J. 12(12), 1151–1161. Kretzler, M., Teixeira, V. P., Unschuld, P. G., Cohen, C. D., Wanke, R., Edenhofer, I., Mundel, P., Schlondorff, D., and Holthofer, H. (2001). Integrin‐linked kinase as a candidate downstream effector in proteinuria. FASEB. J. 15(10), 1843–1845. Lange‐Sperandio, B., Cachat, F., Thornhill, B. A., and Chevalier, R. L. (2002). Selectins mediate macrophage infiltration in obstructive nephropathy in newborn mice. Kidney Int. 61(2), 516–524. Lanone, S., Zheng, T., Zhu, Z., Liu, W., Lee, C. G., Ma, B., Chen, Q., Homer, R. J., Wang, J., Rabach, L. A., Rabach, M. E., Shipley, J. M., Shapiro, S. D., Senior, R. M., and Elias, J. A. (2002). Overlapping and enzyme‐specific contributions of matrix metalloproteinases‐9 and ‐12 in IL‐13‐induced inflammation and remodeling. J. Clin. Invest. 110(4), 463–474. Le Moine, A., Flamand, V., Demoor, F. X., Noel, J. C., Surquin, M., Kiss, R., Nahori, M. A., Pretolani, M., Goldman, M., and Abramowicz, D. (1999). Critical roles for IL‐4, IL‐5, and eosinophils in chronic skin allograft rejection. J. Clin. Invest. 103(12), 1659–1667. Lee, C. G., Homer, R. J., Zhu, Z., Lanone, S., Wang, X., Koteliansky, V., Shipley, J. M., Gotwals, P., Noble, P., Chen, Q., Senior, R. M., and Elias, J. A. (2001). Interleukin‐13 induces tissue fibrosis by selectively stimulating and activating transforming growth factor beta(1). J. Exp. Med. 194(6), 809–821. Leibovich, S. J., and Ross, R. (1975). The role of the macrophage in wound repair. A study with hydrocortisone and antimacrophage serum. Am. J. Pathol. 78(1), 71–100. Letterio, J. J., and Roberts, A. B. (1998). Regulation of immune responses by TGF‐beta. Annu. Rev. Immunol. 16, 137–161. Leyland, H., Gentry, J., Arthur, M. J., and Benyon, R. C. (1996). The plasminogen‐activating system in hepatic stellate cells. Hepatology 24(5), 1172–1178. Li, Y., Yang, J., Dai, C., Wu, C., and Liu, Y. (2003). Role for integrin‐linked kinase in mediating tubular epithelial to mesenchymal transition and renal interstitial fibrogenesis. J. Clin. Invest. 112(4), 503–516.
282
M A R K L . L U P H E R A N D W. M I C H A E L G A L L AT I N
Liu, Y. (2004). Epithelial to mesenchymal transition in renal fibrogenesis: Pathologic significance, molecular mechanism, and therapeutic intervention. J. Am. Soc. Nephrol. 15(1), 1–12. Liu, Y., Rajur, K., Tolbert, E., and Dworkin, L. D. (2000). Endogenous hepatocyte growth factor ameliorates chronic renal injury by activating matrix degradation pathways. Kidney Int. 58(5), 2028–2043. Lloyd, C. M., Minto, A. W., Dorf, M. E., Proudfoot, A., Wells, T. N., Salant, D. J., and Gutierrez‐ Ramos, J. C. (1997). RANTES and monocyte chemoattractant protein‐1 (MCP‐1) play an important role in the inflammatory phase of crescentic nephritis, but only MCP‐1 is involved in crescent formation and interstitial fibrosis. J. Exp. Med. 185(7), 1371–1380. Lochter, A., Navre, M., Werb, Z., and Bissell, M. J. (1999). alpha1 and alpha2 integrins mediate invasive activity of mouse mammary carcinoma cells through regulation of stromelysin‐1 expression. Mol. Biol. Cell 10(2), 271–282. Ma, B., Zhu, Z., Homer, R. J., Gerard, C., Strieter, R., and Elias, J. A. (2004). The C10/CCL6 chemokine and CCR1 play critical roles in the pathogenesis of IL‐13‐induced inflammation and remodeling. J. Immunol. 172(3), 1872–1881. MacMicking, J., Xie, Q. W., and Nathan, C. (1997). Nitric oxide and macrophage function. Annu. Rev. Immunol. 15, 323–350. Maher, J. J., and McGuire, R. F. (1990). Extracellular matrix gene expression increases preferentially in rat lipocytes and sinusoidal endothelial cells during hepatic fibrosis in vivo. J. Clin. Invest. 86(5), 1641–1648. Majumdar, S., Li, D., Ansari, T., Pantelidis, P., Black, C. M., Gizycki, M., du Bois, R. M., and Jeffery, P. K. (1999). Different cytokine profiles in cryptogenic fibrosing alveolitis and fibrosing alveolitis associated with systemic sclerosis: A quantitative study of open lung biopsies. Eur. Respir. J. 14(2), 251–257. Mantovani, A., Sozzani, S., Locati, M., Allavena, P., and Sica, A. (2002). Macrophage polarization: Tumor‐associated macrophages as a paradigm for polarized M2 mononuclear phagocytes. Trends Immunol. 23(11), 549–555. Mariani, T. J., Sandefur, S., Roby, J. D., and Pierce, R. A. (1998). Collagenase‐3 induction in rat lung fibroblasts requires the combined effects of tumor necrosis factor‐alpha and 12‐lipoxygenase metabolites: A model of macrophage‐induced, fibroblast‐driven extracellular matrix remodeling during inflammatory lung injury. Mol. Biol. Cell 9(6), 1411–1424. Marra, F., Valente, A. J., Pinzani, M., and Abboud, H. E. (1993). Cultured human liver fat‐storing cells produce monocyte chemotactic protein‐1. Regulation by proinflammatory cytokines. J. Clin. Invest. 92(4), 1674–1680. Martin, P. (1997). Wound healing—aiming for perfect skin regeneration. Science 276(5309), 75–81. Martinet, Y., Bitterman, P. B., Mornex, J. F., Grotendorst, G. R., Martin, G. R., and Crystal, R. G. (1986). Activated human monocytes express the c‐sis proto‐oncogene and release a mediator showing PDGF‐like activity. Nature 319(6049), 158–160. Martinet, Y., Rom, W. N., Grotendorst, G. R., Martin, G. R., and Crystal, R. G. (1987). Exaggerated spontaneous release of platelet‐derived growth factor by alveolar macrophages from patients with idiopathic pulmonary fibrosis. N. Engl. J. Med. 317(4), 202–209. Massague, J. (2000). How cells read TGF‐beta signals. Nat. Rev. Mol. Cell. Biol. 1(3), 169–178. McCormick, L. L., Zhang, Y., Tootell, E., and Gilliam, A. C. (1999). Anti‐TGF‐beta treatment prevents skin and lung fibrosis in murine sclerodermatous graft‐versus‐host disease: A model for human scleroderma. J. Immunol. 163(10), 5693–5699. Modolell, M., Corraliza, I. M., Link, F., Soler, G., and Eichmann, K. (1995). Reciprocal regulation of the nitric oxide synthase/arginase balance in mouse bone marrow‐derived macrophages by TH1 and TH2 cytokines. Eur. J. Immunol. 25(4), 1101–1104.
R E G U L AT I O N O F F I B R O S I S B Y T H E I M M U N E S Y S T E M
283
Moore, B. B., Kolodsick, J. E., Thannickal, V. J., Cooke, K., Moore, T. A., Hogaboam, C., Wilke, C. A., and Toews, G. B. (2005). CCR2‐mediated recruitment of fibrocytes to the alveolar space after fibrotic injury. Am. J. Pathol. 166(3), 675–684. Moore, B. B., Paine, R., 3rd, Christensen, P. J., Moore, T. A., Sitterding, S., Ngan, R., Wilke, C. A., Kuziel, W. A., and Toews, G. B. (2001). Protection from pulmonary fibrosis in the absence of CCR2 signaling. J. Immunol. 167(8), 4368–4377. Mosser, D. M., and Handman, E. (1992). Treatment of murine macrophages with interferon‐ gamma inhibits their ability to bind leishmania promastigotes. J. Leukoc. Biol. 52(4), 369–376. Munder, M., Eichmann, K., and Modolell, M. (1998). Alternative metabolic states in murine macrophages reflected by the nitric oxide synthase/arginase balance: Competitive regulation by CD4þ T cells correlates with Th1/Th2 phenotype. J. Immunol. 160(11), 5347–5354. Munger, J. S., Harpel, J. G., Giancotti, F. G., and Rifkin, D. B. (1998). Interactions between growth factors and integrins: Latent forms of transforming growth factor‐beta are ligands for the integrin alphavbeta1. Mol. Biol. Cell 9(9), 2627–2638. Munger, J. S., Huang, X., Kawakatsu, H., Griffiths, M. J., Dalton, S. L., Wu, J., Pittet, J. F., Kaminski, N., Garat, C., Matthay, M. A., Rifkin, D. B., and Sheppard, D. (1999). The integrin alpha v beta 6 binds and activates latent TGF beta 1: A mechanism for regulating pulmonary inflammation and fibrosis. Cell 96(3), 319–328. Mutsaers, S. E., Bishop, J. E., McGrouther, G., and Laurent, G. J. (1997). Mechanisms of tissue repair: From wound healing to fibrosis. Int. J. Biochem. Cell Biol. 29(1), 5–17. Nagatoya, K., Moriyama, T., Kawada, N., Takeji, M., Oseto, S., Murozono, T., Ando, A., Imai, E., and Hori, M. (2002). Y‐27632 prevents tubulointerstitial fibrosis in mouse kidneys with unilateral ureteral obstruction. Kidney Int. 61(5), 1684–1695. Narayanan, A. S., Whithey, J., Souza, A., and Raghu, G. (1992). Effect of gamma‐interferon on collagen synthesis by normal and fibrotic human lung fibroblasts. Chest 101(5), 1326–1331. Ohshima, K., Akaiwa, M., Umeshita, R., Suzumiya, J., Izuhara, K., and Kikuchi, M. (2001). Interleukin‐13 and interleukin‐13 receptor in Hodgkin’s disease: Possible autocrine mechanism and involvement in fibrosis. Histopathology 38(4), 368–375. Okada, H., Kikuta, T., Kobayashi, T., Inoue, T., Kanno, Y., Takigawa, M., Sugaya, T., Kopp, J. B., and Suzuki, H. (2005). Connective tissue growth factor expressed in tubular epithelium plays a pivotal role in renal fibrogenesis. J. Am. Soc. Nephrol. 16(1), 133–143. Epub 2004 Dec 1. Oldroyd, S. D., Thomas, G. L., Gabbiani, G., and El Nahas, A. M. (1999). Interferon‐gamma inhibits experimental renal fibrosis. Kidney Int. 56(6), 2116–2127. Ong, C., Wong, C., Roberts, C. R., Teh, H. S., and Jirik, F. R. (1998). Anti‐IL‐4 treatment prevents dermal collagen deposition in the tight‐skin mouse model of scleroderma. Eur. J. Immunol. 28 (9), 2619–2629. Oriente, A., Fedarko, N. S., Pacocha, S. E., Huang, S. K., Lichtenstein, L. M., and Essayan, D. M. (2000). Interleukin‐13 modulates collagen homeostasis in human skin and keloid fibroblasts. J. Pharmacol. Exp. Ther. 292(3), 988–994. Ostendorf, T., Kunter, U., Grone, H. J., Bahlmann, F., Kawachi, H., Shimizu, F., Koch, K. M., Janjic, N., and Floege, J. (2001). Specific antagonism of PDGF prevents renal scarring in experimental glomerulonephritis. J. Am. Soc. Nephrol. 12(5), 909–918. Otte, J. M., Rosenberg, I. M., and Podolsky, D. K. (2003). Intestinal myofibroblasts in innate immune responses of the intestine. Gastroenterology 124(7), 1866–1878. Paik, Y. H., Schwabe, R. F., Bataller, R., Russo, M. P., Jobin, C., and Brenner, D. A. (2003). Toll‐like receptor 4 mediates inflammatory signaling by bacterial lipopolysaccharide in human hepatic stellate cells. Hepatology 37(5), 1043–1055. Peao, M. N., Aguas, A. P., de Sa, C. M., and Grande, N. R. (1994). Neoformation of blood vessels in association with rat lung fibrosis induced by bleomycin. Anat. Rec. 238(1), 57–67.
284
M A R K L . L U P H E R A N D W. M I C H A E L G A L L AT I N
Pierce, G. F., Mustoe, T. A., Lingelbach, J., Masakowski, V. R., Griffin, G. L., Senior, R. M., and Deuel, T. F. (1989). Platelet‐derived growth factor and transforming growth factor‐beta enhance tissue repair activities by unique mechanisms. J. Cell. Biol. 109(1), 429–440. Pierce, R. A., Sandefur, S., Doyle, G. A., and Welgus, H. G. (1996). Monocytic cell type‐specific transcriptional induction of collagenase. J. Clin. Invest. 97(8), 1890–1899. Pinzani, M., Gesualdo, L., Sabbah, G. M., and Abboud, H. E. (1989). Effects of platelet‐derived growth factor and other polypeptide mitogens on DNA synthesis and growth of cultured rat liver fat‐storing cells. J. Clin. Invest. 84(6), 1786–1793. Pinzani, M., Milani, S., Grappone, C., Weber, F. L., Jr., Gentilini, P., and Abboud, H. E. (1994). Expression of platelet‐derived growth factor in a model of acute liver injury. Hepatology 19(3), 701–707. Pozzi, A., LeVine, W. F., and Gardner, H. A. (2002). Low plasma levels of matrix metalloproteinase 9 permit increased tumor angiogenesis. Oncogene 21(2), 272–281. Pozzi, A., Moberg, P. E., Miles, L. A., Wagner, S., Soloway, P., and Gardner, H. A. (2000). Elevated matrix metalloprotease and angiostatin levels in integrin alpha 1 knockout mice cause reduced tumor vascularization. Proc. Natl. Acad. Sci. USA 97(5), 2202–2207. Pozzi, A., Wary, K. K., Giancotti, F. G., and Gardner, H. A. (1998). Integrin alpha1beta1 mediates a unique collagen‐dependent proliferation pathway in vivo. J. Cell Biol. 142(2), 587–594. Racine‐Samson, L., Rockey, D. C., and Bissell, D. M. (1997). The role of alpha1beta1 integrin in wound contraction. A quantitative analysis of liver myofibroblasts in vivo and in primary culture. J. Biol. Chem. 272(49), 30911–30917. Raghu, G., Brown, K. K., Bradford, W. Z., Starko, K., Noble, P. W., Schwartz, D. A., and King, T. E., Jr. (2004). A placebo‐controlled trial of interferon gamma‐1b in patients with idiopathic pulmonary fibrosis. N. Engl. J. Med. 350(2), 125–133. Rankin, J. A., Picarella, D. E., Geba, G. P., Temann, U. A., Prasad, B., DiCosmo, B., Tarallo, A., Stripp, B., Whitsett, J., and Flavell, R. A. (1996). Phenotypic and physiologic characterization of transgenic mice expressing interleukin 4 in the lung: Lymphocytic and eosinophilic inflammation without airway hyperreactivity. Proc. Natl. Acad. Sci. USA 93(15), 7821–7825. Reeves, H. L., Burt, A. D., Wood, S., and Day, C. P. (1996). Hepatic stellate cell activation occurs in the absence of hepatitis in alcoholic liver disease and correlates with the severity of steatosis. J. Hepatol. 25(5), 677–683. Rice, A. B., Moomaw, C. R., Morgan, D. L., and Bonner, J. C. (1999). Specific inhibitors of platelet‐derived growth factor or epidermal growth factor receptor tyrosine kinase reduce pulmonary fibrosis in rats. Am. J. Pathol. 155(1), 213–221. Riser, B. L., Denichilo, M., Cortes, P., Baker, C., Grondin, J. M., Yee, J., and Narins, R. G. (2000). Regulation of connective tissue growth factor activity in cultured rat mesangial cells and its expression in experimental diabetic glomerulosclerosis. J. Am. Soc. Nephrol. 11(1), 25–38. Roberts, A. B., Russo, A., Felici, A., and Flanders, K. C. (2003). Smad3: A key player in pathogenetic mechanisms dependent on TGF‐beta. Ann. NY Acad. Sci. 995, 1–10. Roberts, A. B., and Sporn, M. B. (1993). Physiological actions and clinical applications of transforming growth factor‐beta (TGF‐beta). Growth Factors 8(1), 1–9. Rockey, D. C. (2003). Vascular mediators in the injured liver. Hepatology 37(1), 4–12. Romagnani, P., Annunziato, F., Lasagni, L., Lazzeri, E., Beltrame, C., Francalanci, M., Uguccioni, M., Galli, G., Cosmi, L., Maurenzig, L., Baggiolini, M., Maggi, E., Romagnani, S., and Serio, M. (2001). Cell cycle‐dependent expression of CXC chemokine receptor 3 by endothelial cells mediates angiostatic activity. J. Clin. Invest. 107(1), 53–63. Ronnov‐Jessen, L., and Petersen, O. W. (1993). Induction of alpha‐smooth muscle actin by transforming growth factor‐beta 1 in quiescent human breast gland fibroblasts. Implications for myofibroblast generation in breast neoplasia. Lab. Invest. 68(6), 696–707.
R E G U L AT I O N O F F I B R O S I S B Y T H E I M M U N E S Y S T E M
285
Rubin, K., Terracio, L., Ronnstrand, L., Heldin, C. H., and Klareskog, L. (1988a). Expression of platelet‐derived growth factor receptors is induced on connective tissue cells during chronic synovial inflammation. Scand. J. Immunol. 27(3), 285–294. Rubin, K., Tingstrom, A., Hansson, G. K., Larsson, E., Ronnstrand, L., Klareskog, L., Claesson‐ Welsh, L., Heldin, C. H., Fellstrom, B., and Terracio, L. (1988b). Induction of B‐type receptors for platelet‐derived growth factor in vascular inflammation: Possible implications for development of vascular proliferative lesions. Lancet 1(8599), 1353–1356. Saile, B., Knittel, T., Matthes, N., Schott, P., and Ramadori, G. (1997). CD95/CD95L‐mediated apoptosis of the hepatic stellate cell. A mechanism terminating uncontrolled hepatic stellate cell proliferation during hepatic tissue repair. Am. J. Pathol. 151(5), 1265–1272. Saito, A., Okazaki, H., Sugawara, I., Yamamoto, K., and Takizawa, H. (2003). Potential action of IL‐ 4 and IL‐13 as fibrogenic factors on lung fibroblasts in vitro. Int. Arch. Allergy Immunol. 132(2), 168–176. Sampson, N. S., Ryan, S. T., Enke, D. A., Cosgrove, D., Koteliansky, V., and Gotwals, P. (2001). Global gene expression analysis reveals a role for the alpha 1 integrin in renal pathogenesis. J. Biol. Chem. 276(36), 34182–83418. Sanderson, N., Factor, V., Nagy, P., Kopp, J., Kondaiah, P., Wakefield, L., Roberts, A. B., Sporn, M. B., and Thorgeirsson, S. S. (1995). Hepatic expression of mature transforming growth factor beta 1 in transgenic mice results in multiple tissue lesions. Proc. Natl. Acad. Sci. USA 92(7), 2572–2576. Santana, A., Saxena, B., Noble, N. A., Gold, L. I., and Marshall, B. C. (1995). Increased expression of transforming growth factor beta isoforms (beta 1, beta 2, beta 3) in bleomycin‐induced pulmonary fibrosis. Am. J. Respir. Cell Mol. Biol. 13(1), 34–44. Sato, M., Muragaki, Y., Saika, S., Roberts, A. B., and Ooshima, A. (2003). Targeted disruption of TGF‐beta1/Smad3 signaling protects against renal tubulointerstitial fibrosis induced by unilateral ureteral obstruction. J. Clin. Invest. 112(10), 1486–1494. Schwabe, R. F., Schnabl, B., Kweon, Y. O., and Brenner, D. A. (2001). CD40 activates NF‐kappa B and c‐Jun N‐terminal kinase and enhances chemokine secretion on activated human hepatic stellate cells. J. Immunol. 166(11), 6812–6819. Sempowski, G. D., Chess, P. R., and Phipps, R. P. (1997). CD40 is a functional activation antigen and B7‐independent T cell costimulatory molecule on normal human lung fibroblasts. J. Immunol. 158(10), 4670–4677. Serini, G., Bochaton‐Piallat, M. L., Ropraz, P., Geinoz, A., Borsi, L., Zardi, L., and Gabbiani, G. (1998). The fibronectin domain ED‐A is crucial for myofibroblastic phenotype induction by transforming growth factor‐beta1. J. Cell. Biol. 142(3), 873–881. Sheppard, D. (2001). Integrin‐mediated activation of transforming growth factor‐beta(1) in pulmonary fibrosis. Chest 120(1 Suppl.), 49S–53S. Sheppard, D. (2003). Functions of pulmonary epithelial integrins: From development to disease. Physiol. Rev. 83(3), 673–686. Shi, Z., Wakil, A. E., and Rockey, D. C. (1997). Strain‐specific differences in mouse hepatic wound healing are mediated by divergent T helper cytokine responses. Proc. Natl. Acad. Sci. USA 94 (20), 10663–10668. Shull, M. M., Ormsby, I., Kier, A. B., Pawlowski, S., Diebold, R. J., Yin, M., Allen, R., Sidman, C., Proetzel, G., Calvin, D., et al. (1992). Targeted disruption of the mouse transforming growth factor‐beta 1 gene results in multifocal inflammatory disease. Nature 359(6397), 693–699. Sime, P. J., and O’Reilly, K. M. (2001). Fibrosis of the lung and other tissues: New concepts in pathogenesis and treatment. Clin. Immunol. 99(3), 308–319. Sime, P. J., Xing, Z., Graham, F. L., Csaky, K. G., and Gauldie, J. (1997). Adenovector‐mediated gene transfer of active transforming growth factor‐beta1 induces prolonged severe fibrosis in rat lung. J. Clin. Invest. 100(4), 768–776.
286
M A R K L . L U P H E R A N D W. M I C H A E L G A L L AT I N
Smith, R. E., Strieter, R. M., Phan, S. H., Lukacs, N. W., Huffnagle, G. B., Wilke, C. A., Burdick, M. D., Lincoln, P., Evanoff, H., and Kunkel, S. L. (1994). Production and function of murine macrophage inflammatory protein‐1 alpha in bleomycin‐induced lung injury. J. Immunol. 153 (10), 4704–4712. Song, E., Ouyang, N., Horbelt, M., Antus, B., Wang, M., and Exton, M. S. (2000). Influence of alternatively and classically activated macrophages on fibrogenic activities of human fibroblasts. Cell. Immunol. 204(1), 19–28. Sprenger, H., Kaufmann, A., Garn, H., Lahme, B., Gemsa, D., and Gressner, A. M. (1997). Induction of neutrophil‐attracting chemokines in transforming rat hepatic stellate cells. Gastroenterology 113(1), 277–285. Stein, M., Keshav, S., Harris, N., and Gordon, S. (1992). Interleukin 4 potently enhances murine macrophage mannose receptor activity: A marker of alternative immunologic macrophage activation. J. Exp. Med. 176(1), 287–292. Strieter, R. M., Belperio, J. A., and Keane, M. P. (2002). CXC chemokines in angiogenesis related to pulmonary fibrosis. Chest 122(6 Suppl.), 298S–301S. Strieter, R. M., Polverini, P. J., Kunkel, S. L., Arenberg, D. A., Burdick, M. D., Kasper, J., Dzuiba, J., Van Damme, J., Walz, A., Marriott, D., et al. (1995). The functional role of the ELR motif in CXC chemokine‐mediated angiogenesis. J. Biol. Chem. 270(45), 27348–27357. Taneda, S., Hudkins, K. L., Topouzis, S., Gilbertson, D. G., Ophascharoensuk, V., Truong, L., Johnson, R. J., and Alpers, C. E. (2003). Obstructive uropathy in mice and humans: Potential role for PDGF‐D in the progression of tubulointerstitial injury. J. Am. Soc. Nephrol. 14(10), 2544–2555. Thannickal, V. J., Lee, D. Y., White, E. S., Cui, Z., Larios, J. M., Chacon, R., Horowitz, J. C., Day, R. M., and Thomas, P. E. (2003). Myofibroblast differentiation by transforming growth factor‐ beta1 is dependent on cell adhesion and integrin signaling via focal adhesion kinase. J. Biol. Chem. 278(14), 12384–12389. Epub 2003 Jan 16. Tiggelman, A. M., Boers, W., Linthorst, C., Sala, M., and Chamuleau, R. A. (1995). Collagen synthesis by human liver (myo)fibroblasts in culture: Evidence for a regulatory role of IL‐1 beta, IL‐4, TGF beta and IFN gamma. J. Hepatol. 23(3), 307–317. Tokuda, A., Itakura, M., Onai, N., Kimura, H., Kuriyama, T., and Matsushima, K. (2000). Pivotal role of CCR1‐positive leukocytes in bleomycin‐induced lung fibrosis in mice. J. Immunol. 164 (5), 2745–2751. Tomasek, J. J., Gabbiani, G., Hinz, B., Chaponnier, C., and Brown, R. A. (2002). Myofibroblasts and mechano‐regulation of connective tissue remodeling. Nat. Rev. Mol. Cell. Biol. 3(5), 349–363. Valentino, K. L., Gutierrez, M., Sanchez, R., Winship, M. J., and Shapiro, D. A. (2003). First clinical trial of a novel caspase inhibitor: Anti‐apoptotic caspase inhibitor, IDN‐6556, improves liver enzymes. Int. J. Clin. Pharmacol. Ther. 41(10), 441–449. Vielhauer, V., Berning, E., Eis, V., Kretzler, M., Segerer, S., Strutz, F., Horuk, R., Grone, H. J., Schlondorff, D., and Anders, H. J. (2004). CCR1 blockade reduces interstitial inflammation and fibrosis in mice with glomerulosclerosis and nephrotic syndrome. Kidney Int. 66(6), 2264–2278. Vinas, O., Bataller, R., Sancho‐Bru, P., Gines, P., Berenguer, C., Enrich, C., Nicolas, J. M., Ercilla, G., Gallart, T., Vives, J., Arroyo, V., and Rodes, J. (2003). Human hepatic stellate cells show features of antigen‐presenting cells and stimulate lymphocyte proliferation. Hepatology 38(4), 919–929. Wallace, W. A., Ramage, E. A., Lamb, D., and Howie, S. E. (1995). A type 2 (Th2‐like) pattern of immune response predominates in the pulmonary interstitium of patients with cryptogenic fibrosing alveolitis (CFA). Clin. Exp. Immunol. 101(3), 436–441.
R E G U L AT I O N O F F I B R O S I S B Y T H E I M M U N E S Y S T E M
287
Wang, Q., Wang, Y., Hyde, D. M., Gotwals, P. J., Koteliansky, V. E., Ryan, S. T., and Giri, S. N. (1999). Reduction of bleomycin induced lung fibrosis by transforming growth factor beta soluble receptor in hamsters. Thorax 54(9), 805–812. Wangoo, A., Sparer, T., Brown, I. N., Snewin, V. A., Janssen, R., Thole, J., Cook, H. T., Shaw, R. J., and Young, D. B. (2001). Contribution of Th1 and Th2 cells to protection and pathology in experimental models of granulomatous lung disease. J. Immunol. 166(5), 3432–3439. Webb, D. C., Mahalingam, S., Cai, Y., Matthaei, K. I., Donaldson, D. D., and Foster, P. S. (2003). Antigen‐specific production of interleukin (IL)‐13 and IL‐5 cooperate to mediate IL‐4Ralpha‐ independent airway hyperreactivity. Eur. J. Immunol. 33(12), 3377–3385. Westergren‐Thorsson, G., Hernnas, J., Sarnstrand, B., Oldberg, A., Heinegard, D., and Malmstrom, A. (1993). Altered expression of small proteoglycans, collagen, and transforming growth factor‐beta 1 in developing bleomycin‐induced pulmonary fibrosis in rats. J. Clin. Invest. 92(2), 632–637. Westerhuis, R., van Straaten, S. C., van Dixhoorn, M. G., van Rooijen, N., Verhagen, N. A., Dijkstra, C. D., de Heer, E., and Daha, M. R. (2000). Distinctive roles of neutrophils and monocytes in anti‐thy‐1 nephritis. Am. J. Pathol. 156(1), 303–310. Westermann, W., Schobl, R., Rieber, E. P., and Frank, K. H. (1999). Th2 cells as effectors in postirradiation pulmonary damage preceding fibrosis in the rat. Int. J. Radiat. Biol. 75(5), 629–638. Witte, M. B., Barbul, A., Schick, M. A., Vogt, N., and Becker, H. D. (2002). Upregulation of arginase expression in wound‐derived fibroblasts. J. Surg. Res. 105(1), 35–42. Wong, L., Yamasaki, G., Johnson, R. J., and Friedman, S. L. (1994). Induction of beta‐platelet‐ derived growth factor receptor in rat hepatic lipocytes during cellular activation in vivo and in culture. J. Clin. Invest. 94(4), 1563–1569. Wu, C., and Dedhar, S. (2001). Integrin‐linked kinase (ILK) and its interactors: A new paradigm for the coupling of extracellular matrix to actin cytoskeleton and signaling complexes. J. Cell. Biol. 155(4), 505–510. Epub 2001 Nov 5. Wynn, T. A. (2004). Fibrotic disease and the T(H)1/T(H)2 paradigm. Nat. Rev. Immunol. 4(8), 583–594. Wynn, T. A., Cheever, A. W., Jankovic, D., Poindexter, R. W., Caspar, P., Lewis, F. A., and Sher, A. (1995). An IL‐12‐based vaccination method for preventing fibrosis induced by schistosome infection. Nature 376(6541), 594–596. Yang, C., Zeisberg, M., Mosterman, B., Sudhakar, A., Yerramalla, U., Holthaus, K., Xu, L., Eng, F., Afdhal, N., and Kalluri, R. (2003). Liver fibrosis: Insights into migration of hepatic stellate cells in response to extracellular matrix and growth factors. Gastroenterology 124(1), 147–159. Yang, J., Dai, C., and Liu, Y. (2001). Systemic administration of naked plasmid encoding hepatocyte growth factor ameliorates chronic renal fibrosis in mice. Gene. Ther. 8(19), 1470–1479. Yang, J., and Liu, Y. (2001). Dissection of key events in tubular epithelial to myofibroblast transition and its implications in renal interstitial fibrosis. Am. J. Pathol. 159(4), 1465–1475. Yang, J., and Liu, Y. (2002). Blockage of tubular epithelial to myofibroblast transition by hepatocyte growth factor prevents renal interstitial fibrosis. J. Am. Soc. Nephrol. 13(1), 96–107. Yang, J., and Liu, Y. (2003). Delayed administration of hepatocyte growth factor reduces renal fibrosis in obstructive nephropathy. Am. J. Physiol. Renal. Physiol. 284(2), F349–F357. Yata, Y., Gotwals, P., Koteliansky, V., and Rockey, D. C. (2002). Dose‐dependent inhibition of hepatic fibrosis in mice by a TGF‐beta soluble receptor: Implications for antifibrotic therapy. Hepatology 35(5), 1022–1030. Yellin, M. J., Winikoff, S., Fortune, S. M., Baum, D., Crow, M. K., Lederman, S., and Chess, L. (1995). Ligation of CD40 on fibroblasts induces CD54 (ICAM‐1) and CD106 (VCAM‐1) upregulation and IL‐6 production and proliferation. J. Leukoc. Biol. 58(2), 209–216.
288
M A R K L . L U P H E R A N D W. M I C H A E L G A L L AT I N
Yi, E. S., Lee, H., Yin, S., Piguet, P., Sarosi, I., Kaufmann, S., Tarpley, J., Wang, N. S., and Ulich, T. R. (1996). Platelet‐derived growth factor causes pulmonary cell proliferation and collagen deposition in vivo. Am. J. Pathol. 149(2), 539–548. Yoshiji, H., Noguchi, R., Kuriyama, S., Ikenaka, Y., Yoshii, J., Yanase, K., Namisaki, T., Kitade, M., Masaki, T., and Fukui, H. (2005). Imatinib mesylate (STI‐571) attenuates liver fibrosis development in rats. Am. J. Physiol. Gastrointest. Liver. Physiol. 288(5), G907–G913. Epub 2004 Dec 23. Zeisberg, M., Bottiglio, C., Kumar, N., Maeshima, Y., Strutz, F., Muller, G. A., and Kalluri, R. (2003a). Bone morphogenic protein‐7 inhibits progression of chronic renal fibrosis associated with two genetic mouse models. Am. J. Physiol. Renal. Physiol. 285(6), F1060–F1067. Epub 2003 Aug 12. Zeisberg, M., Hanai, J., Sugimoto, H., Mammoto, T., Charytan, D., Strutz, F., and Kalluri, R. (2003b). BMP‐7 counteracts TGF‐beta1‐induced epithelial‐to‐mesenchymal transition and reverses chronic renal injury. Nat. Med. 9(7), 964–968. Zhang, Y., McCluskey, K., Fujii, K., and Wahl, L. M. (1998). Differential regulation of monocyte matrix metalloproteinase and TIMP‐1 production by TNF‐alpha, granulocyte‐macrophage CSF, and IL‐1 beta through prostaglandin‐dependent and ‐independent mechanisms. J. Immunol. 161(6), 3071–3076. Zhang‐Hoover, J., Sutton, A., van Rooijen, N., and Stein‐Streilein, J. (2000). A critical role for alveolar macrophages in elicitation of pulmonary immune fibrosis. Immunology 101(4), 501. Zhou, X., Murphy, F. R., Gehdu, N., Zhang, J., Iredale, J. P., and Benyon, R. C. (2004). Engagement of alphavbeta3 integrin regulates proliferation and apoptosis of hepatic stellate cells. J. Biol. Chem. 279(23), 23996–24006. Epub 2004 Mar 24. Zhu, Z., Homer, R. J., Wang, Z., Chen, Q., Geba, G. P., Wang, J., Zhang, Y., and Elias, J. A. (1999). Pulmonary expression of interleukin‐13 causes inflammation, mucus hypersecretion, subepithelial fibrosis, physiologic abnormalities, and eotaxin production. J. Clin. Invest. 103(6), 779–788. Zhu, Z., Ma, B., Zheng, T., Homer, R. J., Lee, C. G., Charo, I. F., Noble, P., and Elias, J. A. (2002). IL‐13‐induced chemokine responses in the lung: Role of CCR2 in the pathogenesis of IL‐13‐induced inflammation and remodeling. J. Immunol. 168(6), 2953–2962. Ziesche, R., Hofbauer, E., Wittmann, K., Petkov, V., and Block, L. H. (1999). A preliminary study of long‐term treatment with interferon gamma‐1b and low‐dose prednisolone in patients with idiopathic pulmonary fibrosis. N. Engl. J. Med. 341(17), 1264–1269. Zlotnik, A., and Yoshie, O. (2000). Chemokines: A new classification system and their role in immunity. Immunity 12(2), 121–127. Zurawski, S. M., Vega, F., Jr., Huyghe, B., and Zurawski, G. (1993). Receptors for interleukin‐13 and interleukin‐4 are complex and share a novel component that functions in signal transduction. EMBO. J. 12(7), 2663–2670.
Immunity and Acquired Alterations in Cognition and Emotion: Lessons from SLE Betty Diamond,* Czeslawa Kowal,* Patricio T. Huerta,{ Cynthia Aranow,* Meggan Mackay,* Lorraine A. DeGiorgio,{ Ji Lee,{ Antigone Triantafyllopoulou,} Joel Cohen‐Solal,* and Bruce T. Volpe{ *Department of Medicine, Columbia University Medical Center, New York, New York { Department of Neurology and Neuroscience, The Burke Medical Research Institute, Weill Medical College of Cornell University, White Plains, New York { Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York } Department of Medicine, Montefiore Medical Center, Bronx, New York
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
Abstract ........................................................................................................... Introduction ..................................................................................................... Lupus.............................................................................................................. Neuropsychiatric Lupus ...................................................................................... Mechanisms of NPSLE....................................................................................... Mouse Models of NPSLE ................................................................................... Peptide Reactivity of DNA‐Reactive Antibodies....................................................... Presence of DWEYS‐Reactive Antibodies in Murine and Human SLE ........................ Proteins Harboring the D/E W D/E Y S/G Concensus Sequence: Glutamate Receptors.......................................................................................... Antibody‐Mediated Neurotoxicity ......................................................................... A Murine Model for Antibody‐Mediated Neuronal Death ......................................... Antibody‐Mediated Neurotoxicity in the Amygdala................................................... Evidence that Antibodies Are Involved in NPSLE in Patients .................................... Anti‐Peptide Antibody Activates Prolactin Secretion................................................. Anti‐Peptide Antibodies and Manifestations of NP‐SLE............................................ Implications for SLE .......................................................................................... Implications for Human Pathobiology.................................................................... References .......................................................................................................
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Abstract Classic immunologic teaching describes the brain as an immunologically privileged site. Studies of neuroimmunology have focused for many years almost exclusively on multiple sclerosis, a disease in which inflammatory cells actually infiltrate brain tissue, and the rodent model of this disease, experimental allergic encephalitis. Over the past decade, however, increasingly, brain‐ reactive antibodies have been demonstrated in the serum of patients with numerous neurological diseases. The contribution these antibodies make to
289 advances in immunology, vol. 89 # 2006 Elsevier Inc. All rights reserved.
0065-2776/06 $35.00 DOI: 10.1016/S0065-2776(05)89007-8
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neuronal dysfunction has, in general, not been determined. Here, we describe recent studies showing that serum antibodies to the N‐methyl D‐asparate receptor occur frequently in patients with systemic lupus erythematosus and can cause alterations in cognition and behavior following a breach in the blood–brain barrier. 1. Introduction Autoantibodies can be found in the serum of patients with a number of diseases. Determining whether these antibodies are merely a marker of disease or contribute to disease pathogenesis has represented a continuing challenge to both the clinician and the biomedical scientist. While a beneficial effect of immunomodulatory therapy may suggest an immunological basis for disease pathogenesis, it often remains controversial whether the serum antibodies are the sole effector arm of the immune system or there might be an additional T cell component. Nonetheless, recent studies increasingly show that a large number of both neurological and psychiatric diseases are characterized by the presence of autoantibodies. The necessary evidence to implicate these antibodies in disease pathogenesis requires either an animal model or transfer of human serum to animals with resulting brain dysfunction. In diseases of the peripheral nervous system, antibodies can clearly contribute to neurological symptoms. For example, autoantibodies cause the muscle fatigue of myasthenia gravis (Lindstrom et al., 1998; Romi et al., 2005; Simpson, 1960). The best‐characterized antibodies in this disease bind to acetylcholine receptors at the neuromuscular junction and behave as a receptor antagonist preventing the effective synaptic transmission of acetylcholine. While the effector function of the autoantibodies in myasthenia gravis is clear, two important questions regarding these antibodies remain unanswered. Why do these antibodies arise? And why are they pathogenic in some individuals and not in others? This latter question was first asked by clinicians who recognized that the offspring of mothers with myasthenia gravis could be clinically unaffected despite having maternal anti‐acetylcholine receptor antibodies in their serum, and subsequently, when it was found that affected offspring could have asymptomatic mothers (Bartoccioni et al., 1986; Brueton et al., 2000; Lefvert and Osterman, 1983). In fact, transfer of an unaffected infant’s serum to a rabbit could cause symptoms of disease in the rabbit. These studies provided the earliest evidence that antibody‐mediated disease in the peripheral nervous system requires both potentially pathogenic autoantibodies and a vulnerable target organ. Another well‐studied autoimmune disease of the peripheral nervous system is Guillain‐Barre syndrome. This segmental demyelination of peripheral
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nerves is caused by macrophages; stripping of the myelin occurs about two weeks after even a clinically trivial infection, runs a variable course for about a month, and leaves equally variable residual peripheral neurological defects (Willison, 2005). One form of the disease is characterized by an ascending paralysis; a less common form affects the oculomotor apparatus and is accompanied by ataxia and a descending paralysis (Fisher, 1956). In this group of autoimmune acute inflammatory polyneuropathies, and the related acute motor and sensory axonal neuropathy, it is thought that the autoantibodies arise through molecular mimicry in response to infection by the microorganism campylobacter jejuni or Haemophilus influenza (Aspinall et al., 1994; Ju et al., 2004). Carbohydrate epitopes in the gangliosides within the myelin sheath have been demonstrated to have structural similarity to microbial glycans. As the antibodies recognize antigenic determinants present in both the peripheral and central nervous system, it is presumed that damage is limited to peripheral nerves because of the presence of the blood–brain barrier. The situation is more complex for diseases that are characterized by antibodies to antigens located exclusively or primarily within the central nervous system, as antibodies do not routinely penetrate brain tissue. In paraneoplastic syndromes, the autoantibody is generally reactive to the primary tumor and also with neurons in the central nervous system. The symptoms and signs of neurological impairment are distant from the primary tumor. For example, a paraneoplastic syndrome that occurs in individuals with breast, lung, or ovarian cancer is manifested as cerebellar ataxia (Cao et al., 1999; Peterson et al., 1992). Antibodies that bind to the tumor and to Purkinje cells in the cerebellum are present in the serum of these patients (Albert et al., 1998; Fathallah‐ Shaykh et al., 1991), and it is tempting to speculate that they play a role in cerebellar dysfunction, although the clinical toxicity may also depend on activated cellular immunity (Darnell and Posner, 2003; Sutton, 2002). Yet how these serum antibodies might gain access to cerebellar cells and how they alter cellular function is not known. Recently, a study of patients with Sydenham’s chorea, the neurological manifestation of rheumatic fever, has demonstrated the presence of serum antibodies that cause the activation of Ca2þ/calmodulin‐dependent protein kinase II (CaM kinase) in neurons (Kirvan et al., 2003). CaM kinase II is highly abundant in the brain and has been implicated in neurotransmitter synthesis and release and in learning and memory function (Chen et al., 1994; Silva et al., 1992). Antibodies activating CaM kinase II arise in patients with rheumatic fever through molecular mimicry; they cross‐react with the capsular polysaccharide of streptococci, the etiologic agent of this disease. The observation that the antibodies are present in symptomatic patients and disappear in the serum of convalescent patients, and further, that the antibodies are not
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present in patients with acute rheumatic fever without chorea, lends support to the hypothesis that they are of pathogenetic significance. Yet the mechanism by which the antibodies induce CaM kinase II activation, how they gain access to the brain, and their apparent tropism for neurons in the basal ganglia remains unresolved. Rasmussen’s encephalitis exemplifies the difficulty that exists in implicating autoantibody as a causative agent of disease. It is a rare, non‐familial focal seizure disorder caused by a circumscribed region of encephalitis (Rasmussen et al., 1958). Investigators raising antibodies to the GluR3 subunit of the a‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid receptor (AMPA) noted that several of the animals immunized with a GluR3 fusion protein developed seizures and demonstrated on neuropathological analysis bihemispheric encephalitis that bore resemblance to Rasmussen’s encephalitis (Rogers et al., 1994). Subsequent studies of the patients with epilepsy and Rasmussen’s syndrome revealed that several, but not all, had anti‐GluR3 antibodies, and one patient had a long lasting respite from seizures after plasmapheresis decreased the GluR3 antibodies (Mantegazza et al., 2002; Rogers et al., 1994; Wiendl et al., 2001). Further mechanistic studies have suggested that anti‐GluR3 antibody activates the complement cascade and that while there was some neuronal death, the preferred target was the astrocyte; blocking complement activation protected astrocytes from antibody‐mediated toxicity (Whitney and McNamara, 2000; Whitney et al., 1999). Since the anti‐ GluR3 antibody has no channel‐activating properties (Frassoni et al., 2001), the model for seizure pathogenesis is that inflammatory events resulting from complement‐mediated death of astrocytes, as well as the presumed neuronal toxicity of complement components, eventually destroys neurons and thereby generates a seizure focus. Among the unanswered questions regarding this disease are: Why are only cortical neurons affected? and What beyond the presence of the antibodies and complement is necessary for the disease phenotype, as animal models suggest that the anti‐GluR3 antibodies in the systemic circulation are not sufficient to produce disease? There are several reports of patients with movement disorders having serum antibodies that bind to the basal ganglia neurons, although again the question arises whether these antibodies are markers of disease or mediators of disease (Edwards et al., 2004). Patients with psychiatric diseases such as schizophrenia and autism, and patients with post‐streptococcal syndromes such as chorea, and perhaps even obsessive compulsive disorders have been reported to have anti‐neuronal antibodies to basal ganglia or Purkinje cells, (Bodner et al., 2001; Dinn et al., 2001; Kim et al., 2004; Morshed et al., 2001; Padmos et al., 2004; Perlmutter et al., 1999; Swedo et al., 1998; Snider and Swedo, 2004; Vojdani et al., 2004). In general, what has been missing from these reports is any
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mechanism for antibody entry into brain tissue or antibody‐mediated neuronal dysfunction. Furthermore, animal models demonstrating that antibodies from patients or antibodies with the same antigenic specificities as the antibodies present in patients can cause neurological or psychiatric disease have not yet been developed. Despite the many unanswered questions, the evidence is mounting that antibodies may contribute to altered neurological function, even in the central nervous system. Paradoxically, the most detailed mechanistic studies of this phenomenon have arisen from a serendipitous observation made in the course of studying anti‐DNA antibodies in the disease systemic lupus erythematosus. 2. Lupus Systemic lupus erythematosus (SLE) is an autoimmune disease that affects primarily women, with a female:male ratio of 9:1 (Alarcon et al., 1999; Manzi, 2001; Rivest et al., 2000). The age of onset is generally after puberty and, in women, before menopause, suggesting a hormonal component to the disease. Clinical manifestations are protean with tissue damage occurring in multiple target organs, including skin, kidneys, blood, brain, and less commonly lungs, liver, and heart (Hahn and Tsao, 2002; Winfield et al., 1977). The disease is thought to include a strong genetic component as well as an environmental trigger. Why different patients make autoantibodies of different antigenic specificity and why they develop different symptom complexes is an area of active investigation. One diagnostic criterion for lupus is the presence of anti‐nuclear antibodies in the serum. Essentially all lupus patients have anti‐nuclear antibodies. While these can be directed to a number of nuclear antigens, the most common antigenic specificity is double‐stranded DNA. Anti‐double‐stranded DNA antibodies, when they are present, are essentially diagnostic of lupus, as there is no other disease that is characterized by the presence of these antibodies. They occur in as many as 70% of patients but their frequency depends, in part, on the assay being used to measure them (Davidson and Diamond, 2001; Hahn, 1998). Anti‐DNA antibodies have been eluted from the skin and kidney of lupus patients (Hahn, 1998; Winfield et al., 1977). Whether they cause pathology in the skin is not determined because they are present in both lesional and non‐ lesional skin. It is clear, however, that anti‐DNA antibodies can contribute to renal disease in lupus. While many studies have shown a correlation between renal disease and anti‐DNA antibodies and a correlation between antibody titer and ongoing renal inflammation (Bootsma et al., 1997; Pearson and Lightfoot, 1981), two studies provided clear evidence of their causal relationship to
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kidney destruction. In one study, a transgenic mouse was generated expressing an anti‐DNA antibody lacking the transmembrane portion of the immunoglobulin heavy chain. Because there can be no tolerance induction of B cells producing this autoantibody in the absence of membrane immunoglobulin, the anti‐DNA antibody is secreted in high titer into the serum. Mice expressing this antibody developed a lupus‐like glomerulonephritis (Tsao et al., 1992). As the transgenic mice were not generated on a spontaneously autoimmune background and produced no other autoantibody, this study demonstrated that an anti‐DNA antibody could cause glomerulonephritis. This observation was confirmed in a second study in which B cell hybridomas producing anti‐DNA antibodies were injected into the peritoneal cavity of non‐autoimmune mice. These mice also developed glomerulonephritis, demonstrating again that the presence of a monoclonal anti‐DNA antibody can be sufficient to cause renal disease in an otherwise healthy host (Ehrenstein et al., 1995). Much has been written about the characteristics of pathogenic anti‐DNA antibodies. In general, they are of relatively high affinity for DNA and are likely to be cationic (Ebling and Hahn, 1980; Foster et al., 1993; Woitas and Morioka, 1996). They have no sequence specificity and are thought to bind to phosphate epitopes in the sugar backbone of double‐stranded DNA. There are two theories regarding the mechanism by which they deposit in glomeruli (Lefkowith and Gilkeson, 1996). One theory is that they bind DNA that is present as chromatin in the glomeruli (Garred et al., 2001; Morioka et al., 1994; Yasutomo et al., 2001). Chromatin is known to bind collagen in glomerular basement membrane; thus, anti‐DNA antibodies might bind to sequestered antigen in glomeruli. This theory is referred to as the ‘‘planted antigen’’ theory because first the chromatin is trapped in glomeruli and subsequently the antibody binds the chromatin (Budhai et al., 1996; Lefkowith and Gilkeson, 1996). The alternative theory, the ‘‘cross‐reactive antigen’’ theory, postulates that the antibodies bind directly to a cross‐reactive renal antigen. Anti‐DNA antibodies have, in fact, been shown to bind laminin, an actinin and heparan sulfate, all present in the glomerulus, and may have an even more extensive spectrum of cross‐reactive renal antigens (D’Andrea et al., 1996; Faaber et al., 1986; Jacob et al., 1985; Madaio et al., 1987; Mostoslavsky et al., 2001; Qureshi et al., 2000; Raz et al., 1989; Sabbaga et al., 1989; Zhao et al., 2005). It is important to state that there is growing evidence that not all kidneys are equally susceptible to anti‐DNA antibody‐mediated damage. There appears to be genetically determined target organ susceptibility or resistance to the effects of anti‐DNA antibodies, just as in myasthenia gravis (Morel et al., 2000). While anti‐DNA antibodies have now clearly been shown to cause tissue damage in lupus, the factors that lead to impaired immunologic self‐tolerance
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and to the production of these antibodies remain the subject of inquiry. These antibodies are cross‐reactive not only with other self‐antigens but have also been shown to cross‐react with a number of microbial antigens, both polysaccharide and protein, leading to the speculation that they may arise as part of the response to microbial infection. In particular, Epstein Barr virus and pneumococci have been studied as potential triggering antigens (Diamond and Scharff, 1984; Kowal et al., 1999; McClain et al., 2005; Wun et al., 2001). An alternative theory regarding their origin is that they represent an immune response to apoptotic cells in a host that is genetically predisposed to autoreactivity and may have a defect in the clearance of apoptotic debris (Bickerstaff et al., 1999; Cohen et al., 2002; Kaplan, 2004; Napirei et al., 2000; Pisetsky, 2004; Yasutomo et al., 2001). One possibility that has really not been explored is that the antibodies arise as an aberrant response to a non‐DNA, cross‐reactive self‐antigen. 3. Neuropsychiatric Lupus Increasingly, it is recognized that the central nervous system is affected in SLE, with studies showing between 25 and 60% of patients having central nervous system symptoms and an even higher percent displaying central nervous system pathology in imaging studies or on post mortem examination (Brey et al., 2002; Jennekens and Kater, 2002; McLaurin et al., 2005). As lupus patients live longer, consequent to more potent immunosuppressive therapy and an expanded number of antibiotics to treat the infectious complications of immunosuppression, it has become clear that the spectrum of central nervous system manifestations of lupus is broader than initially described, and that it contributes to increased mortality (Ginzler and Dvorkina, 2005; Scolding and Joseph, 2002). In 1999, a concensus document was prepared describing 19 neuropsychiatric manifestations of lupus (Table 1) (The American College of Rheumatology nomenclature, 1999). Since then, more and more studies have focused on describing the cognitive impairment that constitutes one of these 19 clinical manifestations (Kozora et al., 2004). The cognitive impairment is present in 20 to over 80% of patients depending on the patient cohort studied and the battery of neuropsychological assessments used to measure cognitive function (Brey and Petri, 2003). Most studies report greater than 50% prevalence. Affected individuals display poor memory function, with verbal memory most compromised, but visuospatial processing and psychomotor speed are also frequently impaired. Impairment can be transient, but is persistent in most patients. Interestingly, while the cognitive impairment increases with age and seems to increase with duration of disease, it does not correlate with disease activity (McLaurin et al., 2005).
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Table 1 Neuropsychiatric Syndromes Observed in Systemic Lupus Erythematosus Central nervous system
Aseptic meningitis Cerebrovascular disease Demyelinating syndrome Headache (including migraine and benign intracranial hypertension) Movement disorder (chorea) Myelopathy Seizure disorders Acute confusional state Anxiety disorder Cognitive dysfunction Mood disorder Psychosis
Peripheral nervous system
Acute inflammatory demyelinating polyradiculoneuropathy
(Guillain‐Barre syndrome) Autonomic disorder Mononeuropathy, single/multiplex Myasthenia gravis Neuropathy, cranial Plexopathy Polyneuropathy
Systemic lupus erythematosus affects the central and peripheral nervous system causing sensorimotor, cognitive, and emotional impairments.
4. Mechanisms of NPSLE Despite a growing awareness of the high prevalence of neuropsychiatric lupus and its significant contribution to a diminished quality of life for lupus patients, no pathophysiological explanation has yet emerged for most of the manifestations. Both vasculitis and thrombosis occur in the cerebral vasculature of lupus patients, but much pathology occurs in the absence of clinically apparent vasculitis or stroke. Imaging studies have identified both structural and functional abnormalities in many different anatomic regions of the brain although the relationship of the abnormality detected in an imaging study to an individual’s symptoms is often unclear (Abreu et al., 2005; Bosma et al., 2004; Huizinga et al., 2001; Steens et al., 2004). The potential mechanisms responsible for brain damage in SLE are multiple. As stated above, vasculitis occurs, although it is relatively infrequent (Devinsky et al., 1988; Johnson and Richardson, 1968). Thrombosis consequent to anti‐phospholipid antibodies or lupus anti‐coagulant
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(a misnomer because these antibodies are prothrombotic) is far more common, and results in microinfarcts throughout the brain (Crowther and Wisloff, 2005). Yet microinfarcts also cannot account for all the functional impairment or tissue pathology seen in SLE (Scolding and Joseph, 2002). Many lupus patients receive cytotoxic drugs and corticosteroids as part of a therapeutic regimen. Much has been written regarding the potential neurotoxicity of these agents. Cytotoxic drugs have been implicated in cognitive impairment in patients receiving cancer chemotherapy. These patients typically receive higher doses of medication and there is no knowledge yet regarding the potential neurotoxicity of these agents in the doses that are routinely given to lupus patients. While data exist in rodent models that corticosteroids may damage hippocampal neurons (Sapolsky, 1993), these experiments focused on the added effects of steroids on ischemic neuron loss or damage from seizures making it difficult to judge the effect of physiologic levels of steroids alone. Adrenalectomy led to decreased damage following ischemic challenge suggesting that steroids in conjunction with an ischemic insult have additive neurotoxic potential (Armanini et al., 1990; McEwen, 2002). It is clear, however, that the absence of steroids has a deleterious effect on hippocampal development (Sloviter et al., 1989), thus basal levels of steroids are required for development, plasticity, and survival, while elevated levels may exacerbate hippocampal neuron loss (Abraham et al., 2001; Reagan and McEwen, 1997). Aging increases vulnerability to a variety of stresses that follow disease, although clinical studies of middle‐aged and elderly patients who were treated for at least a year with steroids, and in subjects acutely treated with steroids, there were non‐significant changes in memory performance (Keenan et al., 1996; Schmidt et al., 1999). However, patients with elevated cortisol levels, as high as in Cushing’s disease, have decreased overall cognitive ability, especially in aged individuals (MacLullich et al., 2005; Starkman et al., 2001), but the appropriate control group is controversial and difficult to assemble. Thus, the exact degree of neuronal damage caused by long‐term steroid use remains controversial and may depend on the presence or absence of additional neuronal stresses. In lupus patients across all age groups, the epidemiologic data show no correlation of cognitive impairment with steroid dose or duration of steroid therapy (McLaurin et al., 2005). These epidemiologic observations have implications for the model presented below as they suggest that events other than disease flares and the accompanying increases in medication precipitate the decrements in cognitive function. Another symptom identified among the 19 NPSLE disease manifestations is mood disorder with a prevalence of 25–75% (Ainiala et al., 2001; Brey et al., 2002). Although less has been written regarding these mood disorders, recent studies using validated measures of mood disturbance revealed depression as
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the primary disorder (Omdal et al., 2005). Some investigators have suggested that cytokines can be neurotoxic (Hayley and Anisman, 2005). TNF, for example, can cause apoptosis of human fetal neurons in culture, but there are no in vivo data on the neurotoxicity of TNF and TNF levels may actually be low in many lupus patients. Finally, depression can alter cognitive performance and lupus patients often are depressed. While it is not clear whether depression is a response to a chronic, debilitating illness or whether depression is a manifestation of disease, it has been demonstrated that the cognitive impairment occurs even in the absence of depression; treatment of depression will uncover cognitive decline unrelated to mood disorder. Because lupus is a disease of autoantibodies, several studies have explored the presence of brain‐reactive antibodies. While neuron‐binding antibodies occur in lupus patients, their presence is not predictive of neuropathology and cannot account for the very high incidence of neuropathology. Antibodies to ribosomal P protein have been associated with psychosis in some studies, but not in others. How they might cause psychosis is not known. Antibodies that predispose to thrombosis clearly contribute to brain pathology, as stated above, but occur in only approximately one‐third of lupus patients. Many patients with NPSLE have no detectable prothrombotic antibodies. Thus, much brain dysfunction in lupus has no known pathogenetic mechanism. 5. Mouse Models of NPSLE There are several murine models of SLE. Both the NZB/W mouse and the MRL/ lpr mouse have been shown to have inflammatory lesions and tissue‐bound antibody in the brain. In addition, these mice display a cognitive impairment (Ballok et al., 2004; Borchers et al., 2000; Sakic et al., 1992). There has been little progress made, however, in identifying the basis for the inflammation that occurs in the brain. There are no data on the important autoantigenic specificities in the brain or on the relative role of Tcells and B cells in tissue damage. The models are, in fact, very difficult to study because of the multiple immune pathways that are simultaneously activated and because the immune activation in the brain can be seen even in very young mice. Thus, it is difficult to identify the sequence of events that ultimately leads to cognitive impairment. 6. Peptide Reactivity of DNA‐Reactive Antibodies For many years, we have been studying both the origins and the pathogenicity of anti‐DNA antibodies. In the course of these studies, we isolated a germ line‐ encoded anti‐DNA antibody, R4A, from a non‐spontaneously autoimmune mouse (Shefner et al., 1991). This antibody had the critical characteristic of a pathogenic anti‐DNA antibody as it is sequestered in glomeruli when
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administered to SCID mice. To investigate the structural basis of DNA binding, we performed site‐direct mutagenesis of this antibody, selectively altering arginines and other amino acids known to be critical to DNA binding in a number of DNA‐interacting proteins (Katz et al., 1994). One mutant of R4A, 52B3, differing by only three amino acids from the parental antibody, displayed one log greater apparent affinity for DNA. 52B3 had a glutamine instead of an arginine at residue 66, an alanine instead of a threonine at residue 82b, and a serine instead of an arginine at residue 83. The parental R4A antibody was deposited in the glomeruli when injected into SCID mice. Surprisingly, the 52B3 antibody failed to deposit in glomeruli. This suggested to us that R4A bound glomeruli through cross‐reactivity with a renal antigen. If R4A was sequestered in glomeruli because it bound DNA present in chromatin in the kidney, 52B3 should also have been sequestered in glomeruli. If R4A differed from 52B3 in fine antigenic specificity as well as in affinity for DNA, we reasoned we could identify antigens bound specifically by each antibody. We, therefore, decided to investigate the fine specificity of each antibody by screening a phage‐displayed peptide library. Each antibody recognized a unique peptide sequence. The peptide sequence D/EWD/EYS/G that was recognized by R4A is recognized whether it is comprised of L amino acids or D amino acids, suggesting that the antibody binds to the amino acid side chains, rather than to peptide bonds (Gaynor et al., 1997). Both the L and D peptides could inhibit the binding of R4A to double‐stranded DNA demonstrating that the peptides bound at or near the DNA binding site. Furthermore, when R4A was injected into a SCID mouse, the D peptide but not the L peptide blocked glomerular deposition. The L peptide does not bind R4A with a lower affinity; rather, it is subject to degradation by serum proteases. The D peptide could be detected in serum 24 h following intraperitoneal administration when there was no detectable L peptide remaining. Thus, the ability of the D peptide to inhibit glomerular immunoglobulin deposition in vivo appears to reflect its resistance to endogenous proteases and its resulting extended half‐life (Gaynor et al., 1997). To test whether the pentapeptide was a true double‐stranded DNA mimetope, we immunized mice with a decapeptide that had the pentapeptide sequence within it and that was octamerized on a polylysine backbone (Putterman and Diamond, 1998). Immunization of BALB/c mice, but not several other strains, with the octameric compound led to anti‐peptide and anti‐DNA reactivity and to glomerular immunoglobulin deposition and proteinuria. The antibody response in BALB/c mice is T cell dependent and Ed restricted (Khalil et al., 2001). The antibody response is primarily IgG1 but includes also IgG2a. Thus, we had identified a cross‐reactive antigen that was a double‐stranded DNA mimetope and could break self‐tolerance in BALB/c mice.
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7. Presence of DWEYS‐Reactive Antibodies in Murine and Human SLE The NZB/W mouse is a strain that spontaneously develops an SLE‐like glomerulonephritis mediated, in part, by the deposition of anti‐DNA antibodies. Studies have shown that a multiplicity of immunoglobulin variable region genes is employed to encode the polyclonal anti‐DNA response present in these mice (Marion et al., 1997). Despite the heterogeneity of variable region gene utilization, approximately 60% of the serum DNA reactivity was DWEYS pentapeptide inhibitable, suggesting much less heterogeneity in antigenic fine specificity. When preparations of human anti‐DNA antibodies isolated from the serum of 10 patients with lupus nephritis were examined for peptide binding, we found that all but one preparation had some peptide‐ inhibitable DNA reactivity. In half the preparations, over 75% of the DNA binding was DWEYS pentapeptide inhibitable. We, therefore, believed we had identified a frequent and important specificity in lupus patients (Sharma et al., 2003). Subsequent studies from a number of investigators have demonstrated that antibodies with specificity for the DWEYS peptide are present in the serum of approximately 50% of unselected lupus patients (Omdal et al., 2005; Sharma et al., 2003; Mackey et al., submitted; Lapteva et al., submitted). These antibodies are present only in patients with anti‐DNA antibodies. The observation is consistent with the presence of a subset of anti‐DNA antibodies in each patient displaying cross‐reactivity with the DWEYS peptide, although inhibition studies to formally prove cross‐reactivity have not been performed. 8. Proteins Harboring the D/E W D/E Y S/G Concensus Sequence: Glutamate Receptors A protein database revealed that several bacterial proteins harbor the concensus pentapeptide sequence. One of these, pneumococcal choline kinase, when injected into BALB/c mice in Complete Freund’s Adjuvant, will induce high serum titers of anti‐choline kinase, anti‐DNA antibodies (unpublished). Most interestingly, however, two self‐proteins also contained the concensus sequence, the NR2A and NR2B subunits of the N‐methyl D‐aspartate (NMDA) receptor. NMDA receptors are expressed on neurons throughout the brain. They consist of two NR1 subunits and two of any four NR2 subunits (a–d) (Kutsuwada et al., 1992). NR2A and NR2B are most abundantly expressed on neurons in the hippocampus, amygdala, anterior hypothalamus, and cerebellum (Collingridge et al., 1983; Huntley et al., 1994; Ozawa et al., 1998). During excitatory synaptic transmission, glutamate is released from presynaptic
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terminals and binds to receptors on the postsynaptic membrane, the most common of which are the AMPA receptors (Wenthold et al., 1996) and the NMDA receptors (Collingridge et al., 1983; Huntley et al., 1994; Ozawa et al., 1998). AMPA receptors mediate fast excitation through the influx of sodium into the postsynaptic cell, which results in rapid depolarization of the postsynaptic membrane. NMDA receptors mediate a slower and longer‐lasting excitation through the influx of calcium. Each subunit (NR2A or B) has a binding site for glutamate and several allosteric sites. Glycine is regarded as a partial agonist because it binds to a site on NR1 and enhances the response to glutamate (Kutsuwada et al., 1992). NMDA receptors are also voltage‐ dependent, becoming activated only during significant postsynaptic depolarization (Collingridge and Singer, 1990). In the resting state, the pore of the ionic channel formed by the NMDA receptor is blocked by magnesium, but during the depolarized state magnesium is forced out of the pore, allowing calcium to enter into the postsynaptic cell (Coan and Collingridge, 1985). NMDA receptors play a central role in synaptic plasticity, perhaps best studied in hippocampal neurons (Bliss and Collingridge, 1993; Collingridge et al., 2004; Dudek and Bear, 1992; Heynen et al., 2000; Lisman and Goldring, 1988; Malenka and Nicoll, 1999; Mulkey and Malenka, 1992). Activation of the NMDA receptor is responsible for long‐term potentiation (Bliss and Lomo, 1973), the mechanism for memory formation in the hippocampus. Mice with a targeted deletion of NR2A or of a targeted deletion of the NMDA receptor in the CA1 region of the hippocampus display impaired memory function (Huerta et al., 2000; Sakimura et al., 1995; Tsien et al., 1996). Thus, aberrant function of the NMDA receptor might contribute to cognitive impairment in lupus. The wide distribution of NMDA receptors in the brain raises the possibility of other potential clinically important interactions with this anti‐NR2 antibody. As an example, stimulation of the NMDA receptors in the anterior hypothalamus/diencephalon region leads to prolactin synthesis and secretion (Brann and Mahesh, 1997; Bregonzio et al., 2004; Kanasaki et al., 2002; Villalobos et al., 2002; Xia et al., 1996). Recent data suggests that activation of NMDA receptors in the amygdala down‐ regulate AMPA receptors (Kim et al., 2005), and downregulation of AMPA receptors alters the response to a fear‐conditioning paradigm (Rumpel et al., 2005). Overstimulation of the NMDA receptors, due to excessive glutamate binding, leads to an extremely high influx of calcium into the postsynaptic cell that, in turn, will cause neuronal dysfunction and death. It has become clear that the exact point of entry of calcium is a crucial factor in triggering excitotoxicity (Aarts and Tymianski, 2004; Aarts et al., 2002). Calcium entering into the postsynaptic spines, through extrasynaptic NMDA receptors, has a particularly
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deleterious effect because it overstimulates neuronal nitric oxide synthase (nNOS), an enzyme that produces nitric oxide and is found preferentially in the postsynaptic spines. The molecular cascade activated by nNOS that leads to cell death is only partially understood. Nitric oxide and superoxide anions poison mitochondria, which lead to the activation of poly (ADP‐ribose) polymerase‐1 (PARP‐1) and release of apoptosis‐inducing factor (AIF). It is not clear yet whether release of AIF is sufficient to cause apoptosis (Dawson and Dawson, 2004; Hong et al., 2004). While activation of extrasynaptic NMDA receptors, enriched for the NR2B subunit, causes apoptosis, the activation of synaptic NMDA receptors that have a greater representation of NR2A is less likely to cause excitotoxic death and may even be protective (Hardingham et al., 2002). Finally, NMDA receptor antagonists have been used in clinical trials in humans with some effectiveness (Reisberg et al., 2003). The FDA has approved memantine for the treatment of Alzheimer’s disease, and a small‐scale study suggested it may be effective in the treatment of depression also. Others have failed in the clinic as they have caused seizures or psychosis (Ellison, 1995). These failed trials are of interest because they suggest that disruption of normal NMDA receptor function might trigger two additional symptoms of NP‐SLE, and that there might be antibodies capable of inducing seizures or psychosis. The pentapeptide sequence is present in residues 283 to 287 in NR2A and 284 to 288 in NR2B, in the extracellular domain of the proteins. Three‐ dimensional modeling suggests that the peptide‐containing region is solvent exposed. Studies of NMDA receptor function have shown that zinc binds very near the site of the peptide and is thought to downmodulate the effects of ligand binding to the receptor. Immunoprecipitation experiments using the PC12 cell line demonstrated that the R4A antibody bound both the NR2A and NR2B subunits of the NMDA receptor (DeGiorgio et al., 2001). Studies of antibody binding to fragments derived from the extracellular domain show that the antibody binds a fragment consisting of amino acids 158 to 357, which includes the pentapeptide concensus sequence. 9. Antibody‐Mediated Neurotoxicity When the antibody is injected directly into the hippocampus of a living mouse, there is neuronal death at the site of the injection (Fig. 1). This also occurs when Fab’2 fragments are injected, demonstrating that complement activation or engagement of Fc receptors with subsequent activation of Fc receptor‐bearing cells is not necessary for the antibody‐ mediated cell death (DeGiorgio et al., 2001). In vitro studies of PC12 cells or cultured human fetal brain cells also demonstrated that the antibody
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Figure 1 Direct intracerebral injection of R4A causes neuron death. Micro‐stereotaxic injection of R4A into the CA 1 region of the hippocampus destroys CA 1 neurons compared to an IgG2b isotype control antibody injection. (top row cresyl violet 5X, middle row 40X). Bottom panels display Neu‐N staining of neurons, with loss of neurons in the R4A injected brain (40X).
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Figure 2 PC12 cells exposed to R4A and IgG2b isotype antibody. Apoptag identifies PC12 cells undergoing apoptosis.
mediates cell death and showed that incubation of brain cell cultures with antibody leads to intracellular expression of activated caspase 3 (Fig. 2). Thus, cell death occurs through an apoptotic pathway. Apoptosis is restricted to neurons, as microglial cells, astrocytes, and fibroblasts in the fetal brain culture do not undergo cell death. Anti‐peptide antibodies that are affinity purified from the serum of lupus patients display cross‐reactivity with double‐stranded DNA, as expected, and when injected into mouse hippocampus, also mediate neuronal death. Finally, antibodies present in the cerebrospinal fluid (CSF) of lupus patients also cause neuronal death. Our initial study was performed with CSF of a lupus patient who had experienced progressive cognitive decline over many years. The CSF contained antibodies to DNA and peptide and when injected into mouse brain caused neuronal apoptosis at the site of injection. When the CSF was diluted 1:100 and added to fetal brain cell cultures, neuronal death was also apparent. Thus, the CSF of a patient was demonstrated to have a concentration of antibodies to the NMDA receptor more than sufficient to cause neuronal death. Interestingly, when mice were sacrificed 48 h after injection of CSF, there was no evidence of an inflammatory response in the brain. 10. A Murine Model for Antibody‐Mediated Neuronal Death The studies demonstrating the neurotoxicity of these antibodies when injected directly into a brain led us to speculate that the anti‐NR2A and ‐NR2B antibodies present in the serum of lupus patients might be capable of causing cognitive impairment and memory loss (DeGiorgio et al., 2001). As we had shown, we could immunize mice with multimeric peptide (MAP‐peptide) and cause the mice to exhibit high titers of anti‐DNA, anti‐NR2 antibody capable
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of binding and activating the NMDA receptor. We, therefore, had a system in which to study whether brain pathology could result from high titers of circulating antibodies to the NMDA receptor. Brains of mice immunized with octameric peptide (MAP‐peptide) and possessing high titered anti‐NMDA receptor antibody in the serum are completely normal and indistinguishable from brains of mice immunized with the polylysine backbone only (MAP‐core). As expected, there is no detectable immunoglobulin present in the brains of these mice. Because the blood–brain barrier impedes the transit of immunoglobulin into brain tissue, we decided to breach the blood–brain barrier to determine if the serum antibody would be neurotoxic once it gained access to brain tissue. There is an expanding list of agents, including immunoglobulins, and conditions known to breach the blood–brain barrier (Abbott et al., 2003; Ballabh et al., 2004; Banks, 2001; Banks et al., 2001, 2002; Brines et al., 2000; Kuang et al., 2004; Mayhan, 2001). Prominent among these blood–brain barrier breaching agents are bacterial lipopolysaccharide (LPS), epinephrine, hypertension, and nicotine (Hawkins et al., 2004; Johansson, 1978, 1989; Johansson and Martinsson, 1979; Nukhet Turkel and Ziya Ziylan, 2004; Tuor et al., 2002, 1986; Xaio et al., 2001). We elected to study the impact of exposure to LPS and epinephrine in mice with anti‐NMDA receptor antibody. We reasoned that these agents would mimic infection and stress, respectively, conditions likely to be intermittently present in individuals with lupus. When mice were given LPS to open the blood–brain barrier, there was a penetration of immunoglobulin throughout the brain with binding of specific anti‐NR2 antibody to neurons in the hippocampus. By one week following LPS administration, there was a 25–30% reduction in the number of CA1 hippocampal neurons that was a result of neuronal apoptosis (Fig. 3). That number remained stable; at one month following LPS administration, there was no additional loss of neurons (Kowal et al., 2004). Furthermore, at one month there was no longer immunoglobulin detectable in the brain. Most surprisingly, there was no evidence of an inflammatory process in the brain, either one day following the breach of the blood–brain barrier or at any time up to one month following administration of LPS. There was no activation of resident astrocytes or microglial cells and no recruitment of blood‐borne inflammatory cells. Thus, it appeared in a situation modeling infection in a seropositive patient with lupus that damage occurred selectively in the hippocampus, without accompanying inflammation and through an excitotoxic mechanism. Mice with hippocampal neuron loss were examined for memory function. They failed to perform better than chance on the T maze and performed poorly also on a Morris water maze in which they had to use visual cues to
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Figure 3 Animals immunized with MAP‐peptide and exposed to subsequent treatment with LPS to open the blood–brain barrier display neuronal damage. Animals treated with LPS after immunization with MAP‐peptide display IgG binding to neurons of the hippocampus compared to animals immunized with MAP‐core and treated with LPS. In data not shown, unimmunized animals treated with LPS displayed no staining of cell bodies. Fluoro‐jade positivity, a marker of neuronal stress, and presence of activated caspase‐3, a marker of apoptosis, appear in neurons of animals immunized with MAP‐peptide and treated with LPS.
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Figure 4 Animals treated with memantine after immunization with MAP‐peptide and treatment with LPS demonstrate normal hippocampal histology and no activated caspase‐3 or fluoro‐jade reactivity. Insets demonstrate activated caspase‐3 and fluoro‐jade positive hippocampal neurons in animals following MAP‐peptide immunization and LPS administration treated with placebo instead of memantine.
remember where in the maze they had previously explored to expedite their discovery of a submerged platform. Mice with anti‐NR2 antibody that were not given LPS, and mice without specific antibody that were given LPS had no long‐term histopathological changes in the brain and no detectable memory impairment (Kowal et al., 2004). Thus, both neurotoxic antibody and a breach of the blood–brain barrier have to be present simultaneously to produce brain pathology and memory impairment. Mice with high titered anti‐NMDA receptor antibody that were given LPS were protected from neuronal damage if they were given memantine systemically at the time of the breach in the blood–brain barrier (Fig. 4). This observation again confirmed that neuronal death was mediated by the agonist properties of the antibody. Furthermore, the observation suggests a potential therapeutic modality, should it become apparent that lupus patients also experience excitotoxic damage from NMDA receptor binding antibodies. 11. Antibody‐Mediated Neurotoxicity in the Amygdala It is well established that epinephrine causes cerebral hypertension, with a greater increase in blood pressure and blood flow to the amygdala than to the hippocampus. It is thought that opening of the blood–brain barrier by epinephrine represents a mass action effect secondary to increased blood flow. Both the increased cerebral blood flow and the leakiness of the blood–brain barrier are transient, lasting only minutes after administration of the drug. Epinephrine alone causes no inflammatory response in the brain. When
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epinephrine was administered systemically to open the blood–brain barrier, the anti‐NR2 antibody selectively bound to and destroyed neurons in the amygdala. There was no evidence of damage to the hippocampus (Huerta et al., 2004). These mice displayed normal memory function, but failed to respond to fear‐ conditioning paradigms. They recognized neither the tone nor the context that were associated with a previous noxious stimulus, although their performance on a T maze was no different from that of control mice. Thus, a behavioral disorder as well as a cognitive deficit can be mediated by neuron‐specific antibody. In this paradigm also, we attempted to effect neuronal sparing with memantine. As expected, memantine protected neurons in the amygdala from antibody‐mediated excitotoxicity. We also were able to effect neuronal sparing by systemic administration of D isoform of the pentapeptide. This approach represents a better therapeutic modality than memantine, as peptide blocks the antibody itself and does not interfere with normal NMDA receptor function. Several critical additional observations have been made in these studies. Antibody‐mediated brain injury requires both the presence of neurotoxic antibody in the serum and an opening of the blood–brain barrier. The location of the damage depends on the agent used to open the blood–brain barrier. Neuronal damage can occur in the absence of an inflammatory response. These studies also help explain an observation that has been made regarding central nervous system dysfunction in lupus patients: that there is no relationship between disease activity and decreasing cognitive function or mood impairment. Clearly, the condition leading to opening of the blood–brain barrier could be cerebral vasculitis or some other manifestation of disease activity, but it could also be an insult unrelated to disease activity, such as infection or stress. 12. Evidence that Antibodies Are Involved in NPSLE in Patients It was apparent that murine antibodies with specificity for DNA and peptide could cause both cognitive and behavior changes in mice. The critical question was whether human antibodies with the same specificity could cause neuronal damage. To address this question, we first asked whether we could use human lupus serum to cause brain dysfunction in mice. When lupus serum with known high titered anti‐peptide reactivity was given intravenously to mice, followed by systemic administration of LPS, the mice experienced damage selectively to hippocampal neurons. When mice were given lupus serum lacking high‐titered anti‐peptide reactivity, followed by LPS administration, there was no detectable brain damage. Thus, lupus serum with anti‐peptide reactivity at an approximate 1:30 dilution in the circulation of the mice is still
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sufficiently high titered to cause neuronal damage, and exhibits the same regional specificity that was seen with mouse serum. We have obtained post mortem brains from five patients with lupus. In each case, it was possible to see endogenous antibody co‐localizing with antibody to the NMDA receptor. We also extracted immunoglobulin from one brain that we received as frozen tissue. The eluted protein had an immunoglobulin: albumin ratio of 15:1 confirming that it was tissue‐bound and not circulating antibody. The preparation bound both NR2 and double‐stranded DNA and when injected into the brain of living mice, caused neuronal apoptosis. 13. Anti‐Peptide Antibody Activates Prolactin Secretion In seemingly unrelated studies, we have been exploring hormonal modulation of the immune system and have demonstrated that mild elevations in serum prolactin, like those levels present in lupus patients, can lead to the survival and activation of autoreactive B cells. This phenomenon, which occurs only in mice of certain genetic backgrounds, appears to reflect upregulation of CD40 on B cells and CD40 ligand on T cells, leading to increase CD40 signaling in immature and transitional B cells and their consequent rescue from apoptosis (Peeva et al., 2003). Some 20–50% of lupus patients have mildly elevated serum prolactin levels, the etiology of which is not known. It has been generally understood that the prolactin secretion is under the inhibitory control of dopamine (Freeman et al., 2000). Recent data from a series of in vivo and in vitro experiments shows that NMDA receptors may directly affect the anterior pituitary and act as prolactin releasing factors, and on nuclei in the periventricular region to act on candidate prolactin‐ releasing factors like thyroid‐releasing hormone or vasopressin (Arslan et al., 1992; Brann and Mahesh, 1997; D’Aniello et al., 2000; Pampillo et al., 2002; Zelena et al., 2003). Other studies take advantage of the lack of a blood–brain barrier protection around the pituitary and anterior‐ventral hypothalamus, and demonstrate that acute administration of glutamate elicits a rapid rise in prolactin synthesis as well as release (Terry et al., 1981). We, therefore, speculated that antibody to the NMDA receptor might be responsible for the elevated prolactin present in a subset of patients. Interestingly, the anterior hypothalamus resides outside the blood–brain barrier and is, therefore, exposed to antibodies in the systemic circulation. GH4 cells are derived from the pituitary of rats. In preliminary studies, we have demonstrated that the R4A antibody modulates a luciferase reporter gene under regulation of a prolactin promoter in this cell line. We believe, therefore, that further in vitro and in vivo studies may demonstrate a relationship between anti‐peptide, anti‐DNA cross‐reactive antibodies, increased prolactin, and the consequent cascade of decreased B cell self tolerance.
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14. Anti‐Peptide Antibodies and Manifestations of NP‐SLE Attempts are underway to determine if the presence of anti‐DNA anti‐peptide antibodies in patients correlates with any manifestations of NP‐SLE. One study from Norway demonstrated a positive correlation with both memory impairment and depression (Omdal et al., 2005). The latter symptom is of interest because NMDA receptor antagonists have been reported to be successful therapy for depression in humans. Some of our own studies of lupus patients also suggest a relationship between anti‐NR2 antibody and depression. The critical studies, however, await an analysis of antibody titer in the cerebrospinal fluid, as we have clearly demonstrated in murine models that serum antibody alone is not sufficient to mediate brain disease. 15. Implications for SLE These studies suggest a mechanistic explanation for certain manifestations of NP SLE. Specifically, they suggest that the memory dysfunction present in a large number of patients may be antibody‐mediated and may occur in the absence of any tissue inflammation. Similarly, emotional disturbances may be antibody‐mediated and may also occur in the absence of an inflammatory response. The data also suggest why decrements in neurological function are not associated with disease flares. Decrements are likely to occur coincident with a loss of integrity of the blood–brain barrier. Since many insults besides lupus flare cause a breach in the barrier, decrements in cognitive function or in emotional appropriateness can be precipitated at times of disease quiescence so long as the antibody titers remain elevated. The subtle, progressive neurological impairment in lupus that may be caused by antibodies to brain antigens differs from other antibody‐mediated tissue damage in lupus, as two conditions, both antibody and a pathologic access to tissue antigen, are necessary for tissue damage to occur. Thus, persistent serologic activity in the absence of detectable tissue damage may not be innocuous in lupus patients as it constitutes a continued threat to the brain. A breach of the blood–brain barrier may occur with unpredictable timing. If this mechanism of brain damage occurs in lupus, and we believe it does, then maintaining the blood–brain barrier becomes a therapeutic goal. To date, the only drug that functions in this capacity is corticosteroid, which protects the integrity of the barrier. Less toxic agents performing that function would be highly desirable. Many questions regarding this model remain. Is this actually a correct model? How many different lupus autoantibodies have cross‐reactivities to brain antigens and function in a similar manner to antibodies to the NMDA
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receptor? What plasticity exists in the brain to repair antibody‐mediated damage? What is the explanation for transient impairments in function? Do different individuals have a different threshold for antibody‐mediated damage? What determines the regional specificity of antibody extravasation when different agents open the blood–brain barrier? If the model is correct, and we believe there is now an abundant amount of data supporting the model, addressing these questions becomes highly relevant and even urgent. 16. Implications for Human Pathobiology These studies suggest that antibodies may be involved in acquired alterations in cognitive performance and emotional response, aspects of human pathobiology not previously considered to be affected by the immune system. The fact that these changes occur in the absence of an inflammatory response has perhaps helped mask the involvement of the immune system. It is indeed highly probably that brain‐reactive antibodies are routinely made during the response to foreign antigen as brain antigens are sequestered behind the blood–brain barrier during negative selection of immature B cells. The particular antibody specificity that arises would depend in each case on the cross‐ reactive microbial antigen being targeted by the immune system. Thus, an individual might make a broad spectrum of brain‐reactive antibodies during the course of a lifetime, and whether any of these antibodies cause damage would be contingent on the fortuitous occurrence of a breach in the blood– brain barrier. This paradigm reveals the importance of the blood–brain barrier and implies that genetic or acquired porousness of the cerebral vasculature may expose the brain to toxicity even from a protective immune response. Our data show that both cognitive and emotional aspects of behavior can be altered by antibody. Our preliminary data suggest that antibodies can also affect the neuroendocrine axis. These observations would imply that the immune system can be destructive in covert ways, but perhaps can also be harnessed to therapeutic ends. If this paradigm proves correct, there are major implications for public health. References Aarts, M., Liu, Y., Liu, L., Besshoh, S., Arundine, M., Gurd, J. W., Wang, Y. T., Salter, M. W., and Tymianski, M. (2002). Treatment of ischemic brain damage by perturbing NMDA receptor‐ PSD‐95 protein interactions. Science 298, 846–850. Aarts, M. M., and Tymianski, M. (2004). Molecular mechanisms underlying specificity of excitotoxic signaling in neurons. Curr. Mol. Med. 4, 137–147. Abbott, N. J., Mendonca, L. L., and Dolman, D. E. (2003). The blood–brain barrier in systemic lupus erythematosus. Lupus 12, 908–915.
312
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Abraham, I. M., Harkany, T., Horvath, K. M., and Luiten, P. G. (2001). Action of glucocorticoids on survival of nerve cells: Promoting neurodegeneration or neuroprotection? J. Neuroendocrinol. 13, 749–760. Abreu, M. R., Jakosky, A., Folgerini, M., Brenol, J. C., Xavier, R. M., and Kapczinsky, F. (2005). Neuropsychiatric systemic lupus erythematosus: Correlation of brain MR imaging, CT, and SPECT. Clin. Imaging 29, 215–221. Ainiala, H., Loukkola, J., Peltola, J., Korpela, M., and Hietaharju, A. (2001). The prevalence of neuropsychiatric syndromes in systemic lupus erythematosus. Neurology 57, 496–500. Alarcon, G. S., Friedman, A. W., Straaton, K. V., Moulds, J. M., Lisse, J., Bastian, H. M., McGwin, G., Jr., Bartolucci, A. A., Roseman, J. M., and Reveille, J. D. (1999). Systemic lupus erythematosus in three ethnic groups: III. A comparison of characteristics early in the natural history of the LUMINA cohort. LUpus in MInority populations: NAture vs. Nurture. Lupus 8, 197–209. Albert, M. L., Darnell, J. C., Bender, A., Francisco, L. M., Bhardwaj, N., and Darnell, R. B. (1998). Tumor‐specific killer cells in paraneoplastic cerebellar degeneration. Nat. Med. 4, 1321–1324. Armanini, M. P., Hutchins, C., Stein, B. A., and Sapolsky, R. M. (1990). Glucocorticoid endangerment of hippocampal neurons is NMDA‐receptor dependent. Brain Res. 532, 7–12. Arslan, M., Pohl, C. R., Smith, M. S., and Plant, T. M. (1992). Studies of the role of the N‐methyl‐ D‐aspartate (NMDA) receptor in the hypothalamic control of prolactin secretion. Life Sci. 50, 295–300. Aspinall, G. O., Fujimoto, S., McDonald, A. G., Pang, H., Kurjanczyk, L. A., and Penner, J. L. (1994). Lipopolysaccharides from Campylobacter jejuni associated with Guillain‐Barre syndrome patients mimic human gangliosides in structure. Infect. Immun. 62, 2122–2125. Ballabh, P., Braun, A., and Nedergaard, M. (2004). The blood–brain barrier: An overview: Structure, regulation, and clinical implications. Neurobiol. Dis. 16, 1–13. Ballok, D. A., Woulfe, J., Sur, M., Cyr, M., and Sakic, B. (2004). Hippocampal damage in mouse and human forms of systemic autoimmune disease. Hippocampus 14, 649–661. Banks, W. A. (2001). Enhanced leptin transport across the blood–brain barrier by alpha 1‐adrenergic agents. Brain Res. 899, 209–217. Banks, W. A., Moinuddin, A., and Morley, J. E. (2001). Regional transport of TNF‐alpha across the blood–brain barrier in young ICR and young and aged SAMP8 mice. Neurobiol. Aging 22, 671–676. Banks, W. A., Terrell, B., Farr, S. A., Robinson, S. M., Nonaka, N., and Morley, J. E. (2002). Passage of amyloid beta protein antibody across the blood–brain barrier in a mouse model of Alzheimer’s disease. Peptides 23, 2223–2226. Bartoccioni, E., Evoli, A., Casali, C., Scoppetta, C., Tonali, P., and Provenzano, C. (1986). Neonatal myasthenia gravis: Clinical and immunological study of seven mothers and their newborn infants. J. Neuroimmunol. 12, 155–161. Bickerstaff, M. C., Botto, M., Hutchinson, W. L., Herbert, J., Tennent, G. A., Bybee, A., Mitchell, D. A., Cook, H. T., Butler, P. J., Walport, M. J., and Pepys, M. B. (1999). Serum amyloid P component controls chromatin degradation and prevents antinuclear autoimmunity. Nat. Med. 5, 694–697. Bliss, T. V., and Collingridge, G. L. (1993). A synaptic model of memory: Long‐term potentiation in the hippocampus. Nature 361, 31–39. Bliss, T. V., and Lomo, T. (1973). Long‐lasting potentiation of synaptic transmission in the dentate area of the anaesthetized rabbit following stimulation of the perforant path. J. Physiol. 232, 331–356. Bodner, S. M., Morshed, S. A., and Peterson, B. S. (2001). The question of PANDAS in adults. Biol. Psychiatry 49, 807–810.
I M M U N I T Y A N D A C Q U I R E D A LT E R AT I O N S
313
Bootsma, H., Spronk, P. E., Ter Borg, E. J., Hummel, E. J., de Boer, G., Limburg, P. C., and Kallenberg, C. G. (1997). The predictive value of fluctuations in IgM and IgG class anti‐dsDNA antibodies for relapses in systemic lupus erythematosus. A prospective long‐term observation. Ann. Rheum. Dis. 56, 661–666. Borchers, A., Ansari, A. A., Hsu, T., Kono, D. H., and Gershwin, M. E. (2000). The pathogenesis of autoimmunity in New Zealand mice. Semin. Arthritis Rheum. 29, 385–399. Bosma, G. P., Steens, S. C., Petropoulos, H., Admiraal‐Behloul, F., van den Haak, A., Doornbos, J., Huizinga, T. W., Brooks, W. M., Harville, A., Sibbitt, W. L., Jr., and van Buchem, M. A. (2004). Multisequence magnetic resonance imaging study of neuropsychiatric systemic lupus erythematosus. Arthritis Rheum. 50, 3195–3202. Brann, D. W., and Mahesh, V. B. (1997). Excitatory amino acids: Evidence for a role in the control of reproduction and anterior pituitary hormone secretion. Endocr. Rev. 18, 678–700. Bregonzio, C., Moreno, G. N., Cabrera, R. J., and Donoso, A. O. (2004). NMDA receptors in the medial zona incerta stimulate luteinizing hormone and prolactin release. Cell Mol. Neurobiol. 24, 331–342. Brey, R. L., Holliday, S. L., Saklad, A. R., Navarrete, M. G., Hermosillo‐Romo, D., Stallworth, C. L., Valdez, C. R., Escalante, A., del Rincon, I., Gronseth, G., Rhine, C. B., Padilla, P., and McGlasson, D. (2002). Neuropsychiatric syndromes in lupus: Prevalence using standardized definitions. Neurology 58, 1214–1220. Brey, R. L., and Petri, M. A. (2003). Neuropsychiatric systemic lupus erythematosus: Miles to go before we sleep. Neurology 61, 9–10. Brines, M. L., Ghezzi, P., Keenan, S., Agnello, D., de Lanerolle, N. C., Cerami, C., Itri, L. M., and Cerami, A. (2000). Erythropoietin crosses the blood–brain barrier to protect against experimental brain injury. Proc. Natl. Acad. Sci. USA 97, 10526–10531. Brueton, L. A., Huson, S. M., Cox, P. M., Shirley, I., Thompson, E. M., Barnes, P. R., Price, J., Newsom‐Davis, J., and Vincent, A. (2000). Asymptomatic maternal myasthenia as a cause of the Pena‐Shokeir phenotype. Am. J. Med. Genet. 92, 1–6. Budhai, L., Oh, K., and Davidson, A. (1996). An in vitro assay for detection of glomerular binding IgG autoantibodies in patients with systemic lupus erythematosus. J. Clin. Invest. 98, 1585–1593. Cao, Y., Abbas, J., Wu, X., Dooley, J., and van Amburg, A. L. (1999). Anti‐Yo positive paraneoplastic cerebellar degeneration associated with ovarian carcinoma: Case report and review of the literature. Gynecol. Oncol. 75, 178–183. Chen, C., Rainnie, D. G., Greene, R. W., and Tonegawa, S. (1994). Abnormal fear response and aggressive behavior in mutant mice deficient for alpha‐calcium‐calmodulin kinase II. Science 266, 291–294. Coan, E. J., and Collingridge, G. L. (1985). Magnesium ions block an N‐methyl‐D‐aspartate receptor‐mediated component of synaptic transmission in rat hippocampus. Neurosci. Lett. 53, 21–26. Cohen, P. L., Caricchio, R., Abraham, V., Camenisch, T. D., Jennette, J. C., Roubey, R. A., Earp, H. S., Matsushima, G., and Reap, E. A. (2002). Delayed apoptotic cell clearance and lupus‐like autoimmunity in mice lacking the c‐mer membrane tyrosine kinase. J. Exp. Med. 196, 135–140. Collingridge, G. L., Isaac, J. T., and Wang, Y. T. (2004). Receptor trafficking and synaptic plasticity. Nat. Rev. Neurosci. 5, 952–962. Collingridge, G. L., Kehl, S. J., and McLennan, H. (1983). Excitatory amino acids in synaptic transmission in the Schaffer collateral‐commissural pathway of the rat hippocampus. J. Physiol. 334, 33–46. Collingridge, G. L., and Singer, W. (1990). Excitatory amino acid receptors and synaptic plasticity. Trends Pharmacol. Sci. 11, 290–296.
314
BETTY DIAMOND ET AL.
Crowther, M. A., and Wisloff, F. (2005). Evidence based treatment of the antiphospholipid syndrome II. Optimal anticoagulant therapy for thrombosis. Thromb. Res. 115, 3–8. D’Andrea, D. M., Coupaye‐Gerard, B., Kleyman, T. R., Foster, M. H., and Madaio, M. P. (1996). Lupus autoantibodies interact directly with distinct glomerular and vascular cell surface antigens. Kidney Int. 49, 1214–1221. D’Aniello, G., Tolino, A., D’Aniello, A., Errico, F., Fisher, G. H., and Di Fiore, M. M. (2000). The role of D‐aspartic acid and N‐methyl‐D‐aspartic acid in the regulation of prolactin release. Endocrinology 141, 3862–3870. Darnell, R. B., and Posner, J. B. (2003). Paraneoplastic syndromes involving the nervous system. N. Engl. J. Med. 349, 1543–1554. Davidson, A., and Diamond, B. (2001). Autoimmune diseases. N. Engl. J. Med. 345, 340–350. Dawson, V. L., and Dawson, T. M. (2004). Deadly conversations: Nuclear‐mitochondrial cross‐talk. J. Bioenerg. Biomembr. 36, 287–294. DeGiorgio, L. A., Konstantinov, K. N., Lee, S. C., Hardin, J. A., Volpe, B. T., and Diamond, B. (2001). A subset of lupus anti‐DNA antibodies cross‐reacts with the NR2 glutamate receptor in systemic lupus erythematosus. Nat. Med. 7, 1189–1193. Devinsky, O., Petito, C. K., and Alonso, D. R. (1988). Clinical and neuropathological findings in systemic lupus erythematosus: The role of vasculitis, heart emboli, and thrombotic thrombocytopenic purpura. Ann. Neurol. 23, 380–384. Diamond, B., and Scharff, M. D. (1984). Somatic mutation of the T15 heavy chain gives rise to an antibody with autoantibody specificity. Proc. Natl. Acad. Sci. USA 81, 5841–5844. Dinn, W. M., Harris, C. L., McGonigal, K. M., and Raynard, R. C. (2001). Obsessive‐compulsive disorder and immunocompetence. Int. J. Psychiatry Med. 31, 311–320. Dudek, S. M., and Bear, M. F. (1992). Homosynaptic long‐term depression in area CA1 of hippocampus and effects of N‐methyl‐D‐aspartate receptor blockade. Proc. Natl. Acad. Sci. USA 89, 4363–4367. Ebling, F., and Hahn, B. H. (1980). Restricted subpopulations of DNA antibodies in kidneys of mice with systemic lupus. Comparison of antibodies in serum and renal eluates. Arthritis Rheum. 23, 392–403. Edwards, M. J., Trikouli, E., Martino, D., Bozi, M., Dale, R. C., Church, A. J., Schrag, A., Lees, A. J., Quinn, N. P., Giovannoni, G., and Bhatia, K. P. (2004). Anti‐basal ganglia antibodies in patients with atypical dystonia and tics: A prospective study. Neurology 63, 156–158. Ehrenstein, M. R., Katz, D. R., Griffiths, M. H., Papadaki, L., Winkler, T. H., Kalden, J. R., and Isenberg, D. A. (1995). Human IgG anti‐DNA antibodies deposit in kidneys and induce proteinuria in SCID mice. Kidney Int. 48, 705–711. Ellison, G. (1995). The N‐methyl‐D‐aspartate antagonists phencyclidine, ketamine and dizocilpine as both behavioral and anatomical models of the dementias. Brain Res. Rev. 20, 250–267. Faaber, P., Rijke, T. P., van de Putte, L. B., Capel, P. J., and Berden, J. H. (1986). Cross‐reactivity of human and murine anti‐DNA antibodies with heparan sulfate. The major glycosaminoglycan in glomerular basement membranes. J. Clin. Invest. 77, 1824–1830. Fathallah‐Shaykh, H., Wolf, S., Wong, E., Posner, J. B., and Furneaux, H. M. (1991). Cloning of a leucine‐zipper protein recognized by the sera of patients with antibody‐associated paraneoplastic cerebellar degeneration. Proc. Natl. Acad. Sci. USA 88, 3451–3454. Fisher, C. M. (1956). An unusual variant of acute idiopathic polyneuritis (syndrome of ophthalmoplegia, ataxia and areflexia). N. Engl. J. Med. 255, 57–65. Foster, M. H., Cizman, B., and Madaio, M. P. (1993). Nephritogenic autoantibodies in systemic lupus erythematosus: Immunochemical properties, mechanisms of immune deposition, and genetic origins. Lab. Invest. 69, 494–507.
I M M U N I T Y A N D A C Q U I R E D A LT E R AT I O N S
315
Frassoni, C., Spreafico, R., Franceschetti, S., Aurisano, N., Bernasconi, P., Garbelli, R., Antozzi, C., Taverna, S., Granata, T., and Mantegazza, R. (2001). Labeling of rat neurons by anti‐GluR3 IgG from patients with Rasmussen encephalitis. Neurology 57, 324–327. Freeman, M. E., Kanyicska, B., Lerant, A., and Nagy, G. (2000). Prolactin: Structure, function, and regulation of secretion. Physiol. Rev. 80, 1523–1631. Garred, P., Voss, A., Madsen, H. O., and Junker, P. (2001). Association of mannose‐binding lectin gene variation with disease severity and infections in a population‐based cohort of systemic lupus erythematosus patients. Genes Immun. 2, 442–450. Gaynor, B., Putterman, C., Valadon, P., Spatz, L., Scharff, M. D., and Diamond, B. (1997). Peptide inhibition of glomerular deposition of an anti‐DNA antibody. Proc. Natl. Acad. Sci. USA 94, 1955–1960. Ginzler, E. M., and Dvorkina, O. (2005). Newer therapeutic approaches for systemic lupus erythematosus. Rheum. Dis. Clin. North Am. 31, 315–328. Hahn, B. H. (1998). Antibodies to DNA. N. Engl. J. Med. 338, 1359–1368. Hahn, B. H., and Tsao, B. (2002). In ‘‘Dubois’ Lupus Erythematosus’’ (D. Wallace and B. H. Hahn, Eds.). Lippincott, Williams & Wilkins, Philadelphia. Hardingham, G. E., Fukunaga, Y., and Bading, H. (2002). Extrasynaptic NMDARs oppose synaptic NMDARs by triggering CREB shut‐off and cell death pathways. Nat. Neurosci. 5, 405–414. Hawkins, B. T., Abbruscato, T. J., Egleton, R. D., Brown, R. C., Huber, J. D., Campos, C. R., and Davis, T. P. (2004). Nicotine increases in vivo blood–brain barrier permeability and alters cerebral microvascular tight junction protein distribution. Brain Res. 1027, 48–58. Hayley, S., and Anisman, H. (2005). Multiple mechanisms of cytokine action in neurodegenerative and psychiatric states: Neurochemical and molecular substrates. Curr. Pharm. Des. 11, 947–962. Heynen, A. J., Quinlan, E. M., Bae, D. C., and Bear, M. F. (2000). Bidirectional, activity‐ dependent regulation of glutamate receptors in the adult hippocampus in vivo. Neuron. 28, 527–536. Hong, S. J., Dawson, T. M., and Dawson, V. L. (2004). Nuclear and mitochondrial conversations in cell death: PARP‐1 and AIF signaling. Trends Pharmacol. Sci. 25, 259–264. Huerta, P. T., Sun, L. D., Wilson, M. A., and Tonegawa, S. (2000). Formation of temporal memory requires NMDA receptors within CA1 pyramidal neurons. Neuron. 25, 473–480. Huerta, P. T., Kowal, C., Digiorgio, L. A., Volpe, B. T., and Diamond, B. (2004). Immunity and behavior: Antibodies alter emotion. Proceedings National Academy of Sciences (In press).. Huizinga, T. W., Steens, S. C., and van Buchem, M. A. (2001). Imaging modalities in central nervous system systemic lupus erythematosus. Curr. Opin. Rheumatol. 13, 383–388. Huntley, G. W., Vickers, J. C., and Morrison, J. H. (1994). Cellular and synaptic localization of NMDA and non‐NMDA receptor subunits in neocortex: Organizational features related to cortical circuitry, function and disease. Trends Neurosci. 17, 536–543. Jacob, L., Lety, M. A., Louvard, D., and Bach, J. F. (1985). Binding of a monoclonal anti‐DNA autoantibody to identical protein(s) present at the surface of several human cell types involved in lupus pathogenesis. J. Clin. Invest. 75, 315–317. Jennekens, F. G., and Kater, L. (2002). The central nervous system in systemic lupus erythematosus. Part 2. Pathogenetic mechanisms of clinical syndromes: A literature investigation. Rheumatology (Oxford) 41, 619–630. Johansson, B. B. (1978). Effect of an acute increase of the intravascular pressure on the blood– brain barrier: A comparison between conscious and anesthetized rats. Stroke 9, 588–590. Johansson, B. B. (1989). In ‘‘Implications of the Blood–Brain Barrier and its Manipulation’’ (E. A. Neuwelt, Ed.), Vol. 2, pp. 389–410. Plenum Publishing Co, New York.
316
BETTY DIAMOND ET AL.
Johansson, B. B., and Martinsson, L. (1979). Blood–brain barrier to albumin in awake rats in acute hypertension induced by adrenaline, noradrenaline or angiotensin. Acta Neurol. Scand. 60, 193–197. Johnson, R. T., and Richardson, E. P. (1968). The neurological manifestations of systemic lupus erythematosus. Medicine (Baltimore) 47, 337–369. Ju, Y. Y., Womersley, H., Pritchard, J., Gray, I., Hughes, R. A., and Gregson, N. A. (2004). Haemophilus influenzae as a possible cause of Guillain‐Barre syndrome. J. Neuroimmunol. 149, 160–166. Kanasaki, H., Yonehara, T., Yamamoto, H., Takeuchi, Y., Fukunaga, K., Takahashi, K., Miyazaki, K., and Miyamoto, E. (2002). Differential regulation of pituitary hormone secretion and gene expression by thyrotropin‐releasing hormone. A role for mitogen‐activated protein kinase signaling cascade in rat pituitary GH3 cells. Biol. Reprod. 67, 107–113. Kaplan, M. J. (2004). Apoptosis in systemic lupus erythematosus. Clin. Immunol. 112, 210–218. Katz, J. B., Limpanasithikul, W., and Diamond, B. (1994). Mutational analysis of an autoantibody: Differential binding and pathogenicity. J. Exp. Med. 180, 925–932. Keenan, P. A., Jacobson, M. W., Soleymani, R. M., Mayes, M. D., Stress, M. E., and Yaldoo, D. T. (1996). The effect on memory of chronic prednisone treatment in patients with systemic disease. Neurology 47, 1396–1402. Khalil, M., Inaba, K., Steinman, R., Ravetch, J., and Diamond, B. (2001). T cell studies in a peptide‐induced model of systemic lupus erythematosus. J. Immunol. 166, 1667–1674. Kim, M. J., Dunah, A. W., Wang, Y. T., and Sheng, M. (2005). Differential roles of NR2A‐ and NR2B‐containing NMDA receptors in Ras‐ERK signaling and AMPA receptor trafficking. Neuron 46, 745–760. Kim, S. W., Grant, J. E., Kim, S. I., Swanson, T. A., Bernstein, G. A., Jaszcz, W. B., Williams, K. A., and Schlievert, P. M. (2004). A possible association of recurrent streptococcal infections and acute onset of obsessive‐compulsive disorder. J. Neuropsychiatry Clin. Neurosci. 16, 252–260. Kirvan, C. A., Swedo, S. E., Heuser, J. S., and Cunningham, M. W. (2003). Mimicry and autoantibody‐mediated neuronal cell signaling in Sydenham chorea. Nat. Med. 9, 914–920. Kowal, C., DeGiorgio, L. A., Nakaoka, T., Hetherington, H., Huerta, P. T., Diamond, B., and Volpe, B. T. (2004). Cognition and immunity; antibody impairs memory. Immunity 21, 179–188. Kowal, C., Weinstein, A., and Diamond, B. (1999). Molecular mimicry between bacterial and self antigen in a patient with systemic lupus erythematosus. Eur. J. Immunol. 29, 1901–1911. Kozora, E., Ellison, M. C., and West, S. (2004). Reliability and validity of the proposed American College of Rheumatology neuropsychological battery for systemic lupus erythematosus. Arthritis Rheum. 51, 810–818. Kuang, F., Wang, B. R., Zhang, P., Fei, L. L., Jia, Y., Duan, X. L., Wang, X., Xu, Z., Li, G. L., Jiao, X. Y., and Ju, G. (2004). Extravasation of blood‐borne immunoglobulin G through blood–brain barrier during adrenaline‐induced transient hypertension in the rat. Int. J. Neurosci. 114, 575–591. Kutsuwada, T., Kashiwabuchi, N., Mori, H., Sakimura, K., Kushiya, E., Araki, K., Meguro, H., Masaki, H., Kumanishi, T., Arakawa, M., et al. (1992). Molecular diversity of the NMDA receptor channel. Nature 358, 36–41. Lapteva, T., Nowak, M., Yarboro, C. H., Takada, K., Roebuck, T., Weickert, T., Bleiberg, J., Rosentein, D., Pao, M., Patronas, N., Steele, S., Manzano, M., Van Der Veen, J., Lipsky, P. E., Marenco, S., Wosley, R., Volpe, B., Diamond, B., and Illei, G. G. AntiNMDAR antibodes, cognitive dysfunction and depression in SLC. Arthritis & Rheum. Submitted. Lefkowith, J. B., and Gilkeson, G. S. (1996). Nephritogenic autoantibodies in lupus: Current concepts and continuing controversies. Arthritis Rheum. 39, 894–903.
I M M U N I T Y A N D A C Q U I R E D A LT E R AT I O N S
317
Lefvert, A. K., and Osterman, P. O. (1983). Newborn infants to myasthenic mothers: A clinical study and an investigation of acetylcholine receptor antibodies in 17 children. Neurology 33, 133–138. Lindstrom, J. M., Seybold, M. E., Lennon, V. A., Whittingham, S., and Duane, D. D. (1998). Antibody to acetylcholine receptor in myasthenia gravis: Prevalence, clinical correlates, and diagnostic value. 1975. Neurology 51, 933 and 6 pages following. Lisman, J. E., and Goldring, M. A. (1988). Feasibility of long‐term storage of graded information by the Ca2þ/calmodulin‐dependent protein kinase molecules of the postsynaptic density. Proc. Natl. Acad. Sci. USA 85, 5320–5324. Mackay, M., Aranow, C., Roebuck‐Spenser, T., Bleiberg, J., Volpe, B., and Diamond, B. Submitted. MacLullich, A. M., Deary, I. J., Starr, J. M., Ferguson, K. J., Wardlaw, J. M., and Seckl, J. R. (2005). Plasma cortisol levels, brain volumes and cognition in healthy elderly men. Psychoneuroendocrinology 30, 505–515. Madaio, M. P., Carlson, J., Cataldo, J., Ucci, A., Migliorini, P., and Pankewycz, O. (1987). Murine monoclonal anti‐DNA antibodies bind directly to glomerular antigens and form immune deposits. J. Immunol. 138, 2883–2889. Malenka, R. C., and Nicoll, R. A. (1999). Long‐term potentiation—a decade of progress? Science 285, 1870–1874. Mantegazza, R., Bernasconi, P., Baggi, F., Spreafico, R., Ragona, F., Antozzi, C., Bernardi, G., and Granata, T. (2002). Antibodies against GluR3 peptides are not specific for Rasmussen’s encephalitis but are also present in epilepsy patients with severe, early onset disease and intractable seizures. J. Neuroimmunol. 131, 179–185. Manzi, S. (2001). Epidemiology of systemic lupus erythematosus. Am. J. Manag. Care 7, S474–S479. Marion, T. N., Krishnan, M. R., Desai, D. D., Jou, N. T., and Tillman, D. M. (1997). Monoclonal anti‐DNA antibodies: Structure, specificity, and biology. Methods 11, 3–11. Mayhan, W. G. (2001). Regulation of blood–brain barrier permeability. Microcirculation 8, 89–104. McClain, M. T., Heinlen, L. D., Dennis, G. J., Roebuck, J., Harley, J. B., and James, J. A. (2005). Early events in lupus humoral autoimmunity suggest initiation through molecular mimicry. Nat. Med. 11, 85–89. McEwen, B. S. (2002). Sex, stress and the hippocampus: Allostasis, allostatic load and the aging process. Neurobiol. Aging 23, 921–939. McLaurin, E. Y., Holliday, S. L., Williams, P., and Brey, R. L. (2005). Predictors of cognitive dysfunction in patients with systemic lupus erythematosus. Neurology 64, 297–303. Morel, L., Croker, B. P., Blenman, K. R., Mohan, C., Huang, G., Gilkeson, G., and Wakeland, E. K. (2000). Genetic reconstitution of systemic lupus erythematosus immunopathology with polycongenic murine strains. Proc. Natl. Acad. Sci. USA 97, 6670–6675. Morioka, T., Woitas, R., Fujigaki, Y., Batsford, S. R., and Vogt, A. (1994). Histone mediates glomerular deposition of small size DNA anti‐DNA complex. Kidney Int. 45, 991–997. Morshed, S. A., Parveen, S., Leckman, J. F., Mercadante, M. T., Bittencourt Kiss, M. H., Miguel, E. C., Arman, A., Yazgan, Y., Fujii, T., Paul, S., Peterson, B. S., Zhang, H., King, R. A., Scahill, L., and Lombroso, P. J. (2001). Antibodies against neural, nuclear, cytoskeletal, and streptococcal epitopes in children and adults with Tourette’s syndrome, Sydenham’s chorea, and autoimmune disorders. Biol. Psychiatry 50, 566–577. Mostoslavsky, G., Fischel, R., Yachimovich, N., Yarkoni, Y., Rosenmann, E., Monestier, M., Baniyash, M., and Eilat, D. (2001). Lupus anti‐DNA autoantibodies cross‐react with a glomerular structural protein: A case for tissue injury by molecular mimicry. Eur. J. Immunol. 31, 1221–1227. Mulkey, R. M., and Malenka, R. C. (1992). Mechanisms underlying induction of homosynaptic long‐term depression in area CA1 of the hippocampus. Neuron. 9, 967–975.
318
BETTY DIAMOND ET AL.
Napirei, M., Karsunky, H., Zevnik, B., Stephan, H., Mannherz, H. G., and Moroy, T. (2000). Features of systemic lupus erythematosus in Dnase1‐deficient mice. Nat. Genet. 25, 177–181. Nukhet Turkel, A., and Ziya Ziylan, Y. (2004). Protection of blood–brain barrier breakdown by nifedipine in adrenaline‐induced acute hypertension. Int. J. Neurosci. 114, 517–528. Omdal, R., Brokstad, K., Waterloo, K., Koldingsnes, W., Jonsson, R., and Mellgren, S. I. (2005). Neuropsychiatric disturbances in SLE are associated with antibodies against NMDA receptors. Eur. J. Neurol. 12, 392–398. Ozawa, S., Kamiya, H., and Tsuzuki, K. (1998). Glutamate receptors in the mammalian central nervous system. Prog. Neurobiol. 54, 581–618. Padmos, R. C., Bekris, L., Knijff, E. M., Tiemeier, H., Kupka, R. W., Cohen, D., Nolen, W. A., Lernmark, A., and Drexhage, H. A. (2004). A high prevalence of organ‐specific autoimmunity in patients with bipolar disorder. Biol. Psychiatry 56, 476–482. Pampillo, M., Theas, S., Duvilanski, B., Seilicovich, A., and Lasaga, M. (2002). Effect of ionotropic and metabotropic glutamate agonists and D‐aspartate on prolactin release from anterior pituitary cells. Exp. Clin. Endocrinol. Diabetes 110, 138–144. Pearson, L., and Lightfoot, R. W. Jr. (1981). Correlation of DNA‐anti‐DNA association rates with clinical activity in systemic lupus erythematosus (SLE). J. Immunol. 126, 16–19. Peeva, E., Michael, D., Cleary, J., Rice, J., Chen, X., and Diamond, B. (2003). Prolactin modulates the naive B cell repertoire. J. Clin. Invest. 111, 275–283. Perlmutter, S. J., Leitman, S. F., Garvey, M. A., Hamburger, S., Feldman, E., Leonard, H. L., and Swedo, S. E. (1999). Therapeutic plasma exchange and intravenous immunoglobulin for obsessive‐compulsive disorder and tic disorders in childhood. Lancet 354, 1153–1158. Peterson, K., Rosenblum, M. K., Kotanides, H., and Posner, J. B. (1992). Paraneoplastic cerebellar degeneration. I. A clinical analysis of 55 anti‐Yo antibody‐positive patients. Neurology 42, 1931–1937. Pisetsky, D. S. (2004). DNA as a marker of cell death in systemic lupus erythematosus. Rheum. Dis. Clin. North Am. 30, 575–587, x. Putterman, C., and Diamond, B. (1998). Immunization with a peptide surrogate for double‐ stranded DNA (dsDNA) induces autoantibody production and renal immunoglobulin deposition. J. Exp. Med. 188, 29–38. Qureshi, F., Yang, Y., Jaques, S. M., Johnson, M. P., Naparstek, Y., Ulmansky, R., and Schuger, L. (2000). Anti‐DNA antibodies cross‐reacting with laminin inhibit trophoblast attachment and migration: Implications for recurrent pregnancy loss in SLE patients. Am. J. Reprod. Immunol. 44, 136–142. Rasmussen, T., Olszewski, J., and Lloydsmith, D. (1958). Focal seizures due to chronic localized encephalitis. Neurology 8, 435–445. Raz, E., Brezis, M., Rosenmann, E., and Eilat, D. (1989). Anti‐DNA antibodies bind directly to renal antigens and induce kidney dysfunction in the isolated perfused rat kidney. J. Immunol. 142, 3076–3082. Reagan, L. P., and McEwen, B. S. (1997). Controversies surrounding glucocorticoid‐mediated cell death in the hippocampus. J. Chem. Neuroanat. 13, 149–167. Reisberg, B., Doody, R., Stoffler, A., Schmitt, F., Ferris, S., and Mobius, H. J. (2003). Memantine in moderate‐to‐severe Alzheimer’s disease. N. Engl. J. Med. 348, 1333–1341. Rivest, C., Lew, R. A., Welsing, P. M., Sangha, O., Wright, E. A., Roberts, W. N., Liang, M. H., and Karlson, E. W. (2000). Association between clinical factors, socioeconomic status, and organ damage in recent onset systemic lupus erythematosus. J. Rheumatol. 27, 680–684. Rogers, S. W., Andrews, P. I., Gahring, L. C., Whisenand, T., Cauley, K., Crain, B., Hughes, T. E., Heinemann, S. F., and McNamara, J. O. (1994). Autoantibodies to glutamate receptor GluR3 in Rasmussen’s encephalitis. Science 265, 648–651.
I M M U N I T Y A N D A C Q U I R E D A LT E R AT I O N S
319
Romi, F., Skeie, G. O., Gilhus, N. E., and Aarli, J. A. (2005). Striational antibodies in myasthenia gravis: Reactivity and possible clinical significance. Arch. Neurol. 62, 442–446. Rumpel, S., LeDoux, J., Zador, A., and Malinow, R. (2005). Postsynaptic receptor trafficking underlying a form of associative learning. Science 308, 83–88. Sabbaga, J., Line, S. R., Potocnjak, P., and Madaio, M. P. (1989). A murine nephritogenic monoclonal anti‐DNA autoantibody binds directly to mouse laminin, the major non‐collagenous protein component of the glomerular basement membrane. Eur. J. Immunol. 19, 137–143. Sakic, B., Szechtman, H., Keffer, M., Talangbayan, H., Stead, R., and Denburg, J. A. (1992). A behavioral profile of autoimmune lupus‐prone MRL mice. Brain Behav. Immun. 6, 265–285. Sakimura, K., Kutsuwada, T., Ito, I., Manabe, T., Takayama, C., Kushiya, E., Yagi, T., Aizawa, S., Inoue, Y., Sugiyama, H., et al. (1995). Reduced hippocampal LTP and spatial learning in mice lacking NMDA receptor epsilon 1 subunit. Nature 373, 151–155. Sapolsky, R. M. (1993). Potential behavioral modification of glucocorticoid damage to the hippocampus. Behav. Brain Res. 57, 175–182. Schmidt, L. A., Fox, N. A., Goldberg, M. C., Smith, C. C., and Schulkin, J. (1999). Effects of acute prednisone administration on memory, attention and emotion in healthy human adults. Psychoneuroendocrinology 24, 461–483. Scolding, N. J., and Joseph, F. G. (2002). The neuropathology and pathogenesis of systemic lupus erythematosus. Neuropathol. Appl. Neurobiol. 28, 173–189. Sharma, A., Isenberg, D., and Diamond, B. (2003). Studies of human polyclonal and monoclonal antibodies binding to lupus autoantigens and cross‐reactive antigens. Rheumatology (Oxford) 42, 453–463. Shefner, R., Kleiner, G., Turken, A., Papazian, L., and Diamond, B. (1991). A novel class of anti‐ DNA antibodies identified in BALB/c mice. J. Exp. Med. 173, 287–296. Silva, A. J., Paylor, R., Wehner, J. M., and Tonegawa, S. (1992). Impaired spatial learning in alpha‐ calcium‐calmodulin kinase II mutant mice. Science 257, 206–211. Simpson, J. A. (1960). Myasthenia gravis: A new hypothesis. Scot. Med. J. 5, 419036. Sloviter, R. S., Valiquette, G., Abrams, G. M., Ronk, E. C., Sollas, A. L., Paul, L. A., and Neubort, S. (1989). Selective loss of hippocampal granule cells in the mature rat brain after adrenalectomy. Science 243, 535–538. Snider, L. A., and Swedo, S. E. (2004). PANDAS: Current status and directions for research. Mol. Psychiatry 9, 900–907. Starkman, M. N., Giordani, B., Berent, S., Schork, M. A., and Schteingart, D. E. (2001). Elevated cortisol levels in Cushing’s disease are associated with cognitive decrements. Psychosom. Med. 63, 985–993. Steens, S. C., Admiraal‐Behloul, F., Bosma, G. P., Steup‐Beekman, G. M., Olofsen, H., Le Cessie, S., Huizinga, T. W., and Van Buchem, M. A. (2004). Selective gray matter damage in neuropsychiatric lupus. Arthritis. Rheum. 50, 2877–2881. Sutton, I. (2002). Paraneoplastic neurological syndromes. Curr. Opin. Neurol. 15, 685–690. Swedo, S. E., Leonard, H. L., Garvey, M., Mittleman, B., Allen, A. J., Perlmutter, S., Lougee, L., Dow, S., Zamkoff, J., and Dubbert, B. K. (1998). Pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections: Clinical description of the first 50 cases. Am. J. Psychiatry 155, 264–271. Terry, L. C., Epelbaum, J., and Martin, J. B. (1981). Monosodium glutamate: Acute and chronic effects on rhythmic growth hormone and prolactin secretion, and somatostatin in the undisturbed male rat. Brain Res. 217, 129–142. The American College of Rheumatology nomenclature and case definitions for neuropsychiatric lupus syndromes (1999). Arthritis Rheum. 42, 599–608.
320
BETTY DIAMOND ET AL.
Tsao, B. P., Ohnishi, K., Cheroutre, H., Mitchell, B., Teitell, M., Mixter, P., Kronenberg, M., and Hahn, B. H. (1992). Failed self‐tolerance and autoimmunity in IgG anti‐DNA transgenic mice. J. Immunol. 149, 350–358. Tsien, J. Z., Huerta, P. T., and Tonegawa, S. (1996). The essential role of hippocampal CA1 NMDA receptor‐dependent synaptic plasticity in spatial memory. Cell 87, 1327–1338. Tuor, U. I., Edvinsson, L., and McCulloch, J. (1986). Catecholamines and the relationship between cerebral blood flow and glucose use. Am. J. Physiol. 251, H824–H833. Tuor, U. I., McKenzie, E., and Tomanek, B. (2002). Functional magnetic resonance imaging of tonic pain and vasopressor effects in rats. Magn. Reson. Imaging 20, 707–712. Villalobos, C., Nunez, L., Faught, W. J., Leaumont, D. C., Boockfor, F. R., and Frawley, L. S. (2002). Calcium dynamics and resting transcriptional activity regulates prolactin gene expression. Endocrinology 143, 3548–3554. Vojdani, A., O’Bryan, T., Green, J. A., McCandless, J., Woeller, K. N., Vojdani, E., Nourian, A. A., and Cooper, E. L. (2004). Immune response to dietary proteins, gliadin and cerebellar peptides in children with autism. Nutr. Neurosci. 7, 151–161. Wenthold, R. J., Petralia, R. S., Blahos, J. II, and Niedzielski, A. S. (1996). Evidence for multiple AMPA receptor complexes in hippocampal CA1/CA2 neurons. J. Neurosci. 16, 1982–1989. Whitney, K. D., Andrews, P. I., and McNamara, J. O. (1999). Immunoglobulin G and complement immunoreactivity in the cerebral cortex of patients with Rasmussen’s encephalitis. Neurology 53, 699–708. Whitney, K. D., and McNamara, J. O. (2000). GluR3 autoantibodies destroy neural cells in a complement‐dependent manner modulated by complement regulatory proteins. J. Neurosci. 20, 7307–7316. Wiendl, H., Bien, C. G., Bernasconi, P., Fleckenstein, B., Elger, C. E., Dichgans, J., Mantegazza, R., and Melms, A. (2001). GluR3 antibodies: Prevalence in focal epilepsy but no specificity for Rasmussen’s encephalitis. Neurology 57, 1511–1514. Willison, H. J. (2005). The immunobiology of Guillain‐Barre syndromes. J. Peripher. Nerv. Syst. 10, 94–112. Winfield, J. B., Faiferman, I., and Koffler, D. (1977). Avidity of anti‐DNA antibodies in serum and IgG glomerular eluates from patients with systemic lupus erythematosus. Association of high avidity antinative DNA antibody with glomerulonephritis. J. Clin. Invest. 59, 90–96. Woitas, R. P., and Morioka, T. (1996). Influence of isoelectric point on glomerular deposition of antibodies and immune complexes. Nephron. 74, 713–719. Wun, H. L., Leung, D. T., Wong, K. C., Chui, Y. L., and Lim, P. L. (2001). Molecular mimicry: Anti‐DNA antibodies may arise inadvertently as a response to antibodies generated to microorganisms. Int. Immunol. 13, 1099–1107. Xaio, H., Banks, W. A., Niehoff, M. L., and Morley, J. E. (2001). Effect of LPS on the permeability of the blood–brain barrier to insulin. Brain Res. 896, 36–42. Xia, Z., Dudek, H., Miranti, C. K., and Greenberg, M. E. (1996). Calcium influx via the NMDA receptor induces immediate early gene transcription by a MAP kinase/ERK‐dependent mechanism. J. Neurosci. 16, 5425–5436. Yasutomo, K., Horiuchi, T., Kagami, S., Tsukamoto, H., Hashimura, C., Urushihara, M., and Kuroda, Y. (2001). Mutation of DNASE1 in people with systemic lupus erythematosus. Nat. Genet. 28, 313–314. Zelena, D., Makara, G. B., and Nagy, G. M. (2003). Effect of glutamate receptor antagonists on suckling‐induced prolactin release in rats. Endocrine 21, 147–152. Zhao, Z., Weinstein, E., Tuzova, M., Davidson, A., Mundel, P., Marambio, P., and Putterman, C. (2005). Cross‐reactivity of human lupus anti‐DNA antibodies with alpha‐actinin and nephritogenic potential. Arthritis Rheum. 52, 522–530.
Immunodeficiencies with Autoimmune Consequences Luigi D. Notarangelo,* Eleonora Gambineri,{ and Raffaele Badolato* *‘‘Angelo Nocivelli’’ Institute for Molecular Medicine, Department of Pediatrics, University of Brescia, Brescia, Italy { Department of Pediatrics, University of Florence, Florence, Italy Abstract............................................................................................................. 1. Autoimmune Manifestations in Primary Immune Deficiencies: Relevance and Mechanisms................................................................................... 2. AIRE, Central Tolerance, and the Pathophysiology of Autoimmune Polyendocrinopathy ........................................................................... 3. Defective AIRE Expression Explains the Pathophysiology of Autoimmunity in Omenn Syndrome........................................................................ 4. CD4þ CD25þ Regulatory T Cells and the Pathophysiology of IPEX (Immunodysregulation – Polyendocrinopathy – Enteropathy – X‐linked) ....................... 5. Concluding Remarks............................................................................................ References .........................................................................................................
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Abstract Far from being mutually exclusive, immunodeficiency and autoimmunity may occur simultaneously. During the last years, analysis of Autoimmune Polyendocrinopathy – Candidiasis – Ectodermal Dystrophy (APECED) and Immunodysregulation – Polyendocrinopathy – Enteropathy – X‐linked (IPEX), two rare monogenic forms of immunodeficiency associated with autoimmunity, has led to the identification of Auto Immune Regulator (AIRE) and Forkhead Box P3 (FOXP3), essential transcriptional regulators, involved in central tolerance and peripheral immune homeostasis, respectively. Characterization of the molecular and cellular mechanisms involved in APECED, and recognition that AIRE expression is sustained by effective thymopoiesis, has recently allowed to define that the autoimmunity of Omenn syndrome, a combined immunodeficiency due to defects of V(D)J recombination, also results from defective expression of AIRE. The implications of identification of the basis of autoimmunity in these rare forms of immunodeficiency have important implications for a better understanding of more common autoimmune disorders, and for development of novel therapeutic approaches.
321 advances in immunology, vol. 89 # 2006 Elsevier Inc. All rights reserved.
0065-2776/06 $35.00 DOI: 10.1016/S0065-2776(05)89008-X
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1. Autoimmune Manifestations in Primary Immune Deficiencies: Relevance and Mechanisms 1.1. Introduction The main function of the immune system is to preserve homeostasis. In vertebrates, this includes the ability to specifically recognize and react against non‐self antigens, thus counteracting harm associated with infections and tumors. At the same time, the immune system specifically recognizes self antigens that are tolerated. Failure to accomplish these functions leads to immune deficiency and autoimmunity, respectively. Based on this dichotomy, immune deficiency and autoimmunity have long been considered at opposite sides of the clinical immune response. However, careful analysis of the clinical features associated with congenital immunodeficiencies, and a better understanding of the molecular and cellular mechanisms involved in immunodeficiency and autoimmunity, has shown that, in fact, these conditions are often related. Importantly, the study of autoimmune manifestations associated with primary immune deficiencies (PID) has led to novel insights into the molecular pathophysiology of autoimmune reactions, which now also include exaggerated and harmful inflammatory responses. At the same time, while most autoimmune diseases in humans are of multifactorial origin, the study of rare single‐gene disorders that associate immunodeficiency and autoimmunity has shown the clinical relevance of specific events during development and function of immune cells which are essential to the preservation of immune homeostasis. 1.2. Primary Immunodeficiencies Associated with Autoimmunity Although the clinical hallmark of PID is represented by an increased susceptibility to infections, careful analysis of the clinical features associated with the various forms of PID has shown that many of them are also characterized by autoimmunity and/or aberrant inflammatory responses (Arkwright et al., 2002; Candotti et al., 2002; Etzioni, 2003). While autoimmune manifestations have been reported in various forms of PID, irrespective of the nature of the immune defect primarily involved in the disease (Table 1), the molecular and cellular mechanisms responsible for autoimmunity may vary in different forms of PID. In addition, several mechanisms may be involved even within the same form of PID. In particular, the notion that autoimmunity results from a failure of self‐tolerance applies only to some of the autoimmune manifestations associated with PID. For many other forms of PID, autoimmune manifestations do not reflect defects in deletion of autoreactive lymphocytes, or inefficient mechanisms of
Table 1 Autoimmunity and Other Manifestations of Immune Dysregulation in Primary Immune Deficiencies Main type of immune deficiency Humoral immune deficiencies
T cell/combined immune deficiencies
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Phagocytic cell defects Complement deficiency Immunodeficiency syndromes
Immunodeficiency disease
Autoimmune manifestations
X‐linked agammaglobulinemia Common variable immunodeficiency IgA deficiency DiGeorge syndrome PNP deficiency ADA deficiency SCID (other forms) Omenn syndrome MHC class I deficiency MHC class II deficiency CD40L or CD40 deficiency Chronic granulomatous disease C1q, C1r, C1s, C2, and C4 deficiency APECED
Arthritis, dermatomyositis, AHA, scleroderma Thrombocytopenia, AHA, IBD, arthritis, hepatitis, lungs granulomatosis
IPEX Wiskott‐Aldrich syndrome X‐linked lymphoproliferative disease FHL ALPS
Celiac disease, rheumatoid arthritis, SLE, alopecia, thyroiditis, IDDM ITP, arthritis, erythrodermia, cytopenias AHA AHA, IDDM, asthma, eczema Skin rash, infiltration of target organs by oligoclonal T cells, AHA Erythrodermia, enteropathy, multiple organs lymphoid infiltration Leukocytoclastic vasculitis, arthritis, Wegener‐like granulomatosis Sclerosing cholangitis, autoimmune cytopenias Sclerosing cholangitis, neutropenia IBD, granulomatous lesions of lungs, liver, and urinary tract SLE, nephritis Hypoparathyroidism, Addison disease, primary ovarian failure, IDDM, hepatitis Enteropathy, IDDM, eczema, autoimmune polyendocrinopathy AHA, vasculitis, IBD, arthritis, renal disease EBV‐associated hemophagocytic lymphohistiocytosis Virus‐associated hemophagocytic lymphohistiocytosis AHA, thrombocytopenia, neutropenia
AHA: autoimmune haemolytic anemia; IBD: inflammatory bowel disease; SLE: systemic lupus erythematosus; IDDM: insulin‐dependent diabetes mellitus; ITP: idiopathic thrombocytopenic purpura; PNP: purine nucleoside phosphorylase; ADA: adenosine deaminase; SCID: severe combined immune deficiency; MHC: major histocompatibility complex; CD40L: CD40 ligand; APECED: autoimmune polyendocrinopathy – candidiasis – ectodermal dystrophy; IPEX: immunodysregulation – polyendocrinopathy – enteropathy – X‐linked; EBV: Epstein‐Barr virus; FHL: familial hemophagocytic lymphohistiocytosis; ALPS: autoimmune lymphoproliferative syndrome.
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peripheral tolerance, but rather are the consequence of inability of the immune system to eliminate pathogens. This often leads to continuous and exaggerated inflammatory responses, which ultimately cause damage of bystander tissues. This mechanism is involved in the hemophagocytic syndromes that follow especially viral infections in patients with defects in T and NK cell‐mediated cytotoxicity, as typically observed in X‐linked lymphoproliferative disease, familial hemophagocytic lymphohistiocytosis, Chediak‐Higashi syndrome, and Griscelli disease (Clark and Griffiths, 2003). Increased inflammatory responses to bacterial microbes are probably involved in the granulomatous lesions associated with chronic granulomatous disease (Barton et al., 1998). Similarly, chronic stimulation by Cryptosporidium parvum or cytomegalovirus may result in sclerosing cholangitis in patients with hyper‐IgM syndrome due to CD40 ligand or CD40 deficiency (Notarangelo and Hayward, 2000), and in infants with Major Histocompatibility Complex class II deficiency (Saleem et al., 2000). Improper handling of pathogens (of viral and bacterial origin) is supposed to be responsible for the autoimmune manifestations of Wiskott‐Aldrich syndrome (Schurman and Candotti, 2003). Finally, impaired clearance of immune complexes is likely involved in the Systemic Lupus Erythematosus‐like forms associated with defects of early components of the complement classical pathway (Walport et al., 1997). Vis‐a`‐vis, with this heterogeneity, in this review we will focus our attention on monogenic disorders of central and peripheral tolerance that associate immunodeficiency and autoimmunity, such as Autoimmune Polyendocrinopathy – Candidiasis – Ectodermal Distrophy (APECED) and Immunodysregulation – Polyendocrinopathy – Enteropathy – X‐linked (IPEX), respectively. We will also discuss how characterization of the cellular and molecular bases of these rare disorders has been essential to a better understanding of the pathophysiology of other immunodeficiency disorders with autoimmunity, such as Omenn syndrome. These novel insights have far‐reaching implications for the pathophysiology of disorders of immune homeostasis and may lead to novel forms of therapeutic intervention. 2. AIRE, Central Tolerance, and the Pathophysiology of Autoimmune Polyendocrinopathy 2.1. Clinical and Immunological Features of APECED 2.1.1. Clinical Manifestations of APECED Autoimmune Polyendocrinopathy – Candidiasis – Ectodermal Distrophy (APECED) is a rare autosomal recessive organ‐specific autoimmune disorder that is characterized by a variable combination of (i) chronic mucocutaneous
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candidiasis, (ii) polyendocrinopathy and/or hepatitis, and (iii) dystrophy of dental enemal and nails (Ahonen et al., 1990; Halonen et al., 2002). Indeed, the triad of candidiasis, hypoparathyroidism, and adrenal failure constitutes the most typical presentation of the disease. The clinical diagnosis of APECED is established when a subject presents at least two of these major features, but, in the case of a sibling of an APECED patient, one feature is sufficient for suspecting the disease (Ahonen et al., 1990). Although APECED is generally a rare disease, it is more frequently observed in some selected populations, in particular among the Finns (incidence 1:25,000), Iranian Jews (1:9000), and Sardinians (1:14,400) (Aaltonen et al., 1994; Rosatelli et al., 1998; Zlotogora and Shapiro, 1992). The phenotype of APECED is extremely heterogeneous, varying from one single manifestation, usually candidiasis, up to nine different types of endocrine or dystrophic conditions (Halonen et al., 2002). In the majority of APECED patients, the first symptom to develop is mucocutaneous candidiasis, which is usually resistant to antimicrobial therapy and may recur throughout the patient’s life. Hypoparathyroidism is the second symptom to appear, often already in the second year of life. Finally, adrenocortical failure is usually identified after four years of age (Ahonen et al., 1990; Halonen et al., 2002). Definition of a genotype–phenotype correlation in APECED is difficult, since patients, even when from the same family, may present different clinical manifestations in variable sequence. Nevertheless, there are some exceptions to this rule, at least for some populations. In particular, candidiasis, which is observed in the vast majority of APECED patients, is rarely present among the Iranian Jewish patients, suggesting a specific genetic determinant of the APECED phenotype in this population (Zlotogora and Shapiro, 1992). Hypoparathyroidism is the most frequent endocrinopathy that is identified in APECED. It affects 88% of patients, on average (Ahonen et al., 1990; Halonen et al., 2002). Its incidence, as recently reported, varies greatly among sexes, being more common in females (98%) than in males (71%) (Gylling et al., 2003). Like hypoparathyroidism, also hypogonadism is more frequent in females (60% of APECED patients older than 13 years) than in males (14%), while other endocrinopathies such as adrenocortinal failure (observed in 72% of APECED patients), insulin‐dependent diabetes mellitus, and hypothyroidism do not seem to be influenced by sex (Table 2). APECED patients may also display numerous autoimmune manifestations affecting the gastrointestinal tract, including pernicious anemia due to vitamin B12 deficiency (13–15%), and intestinal malabsorption, with onset varying from 4 months to 21 years of age (Ahonen et al., 1990). Steathorrea and malabsorption are common presenting symptoms of gastrointestinal involvement, and may even mark the clinical onset of the disease (Ahonen et al., 1990).
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Table 2 Disease Manifestations in Patients with APECEDa Disease components Candidiasis Hypoparathyroidism Adrenal failure Alopecia Ovarian failure Vitiligo Hepatitis Kerathopathy Gastrointestinal dysfunction Vitamin B12 malabsorption Diabetes mellitus Hypothyroidism Growth hormone deficiency Testicular failure Oral carcinoma a
Percentage of patients affected 88.5 84.6 72.1 34.6 38.5 23.1 19.2 19.2 15.4 14.4 12.5 12.5 2.9 1.2 1.0
Modified from (Halonen et al., 2002).
Skin and other tissues of ectodermal origin are also frequently involved in APECED: alopecia is particularly common (29–36%) and may appear as early as five years of age, while vitiligo affects 13–26% of the cases, depending on the study. Pitted nails are another cutaneous symptom of the disease; in most cases, they reflect ectodermal dysplasia, because microbial culture of nail specimens are usually negative for fungi, and the lesions may heal spontaneously. However, in some cases, candida infection may play a role in the pathophysiology of the lesions, and specific antifungal therapy is then required to induce complete resolution (Ahonen et al., 1990). Evaluation of the clinical course of APECED in large cohorts of patients has shown that candidiasis has the highest occurrence in infancy, but its incidence slowly declines in following years. Conversely, hypoparathyroidism and adrenal insufficiency are usually detected during the first decade of life, and gonadal insufficiency is usually not observed before the second decade (Ahonen et al., 1990; Halonen et al., 2002). In addition to these most common APECED manifestations, the other manifestations of the disease, including alopecia, vitiligo, and gastrointestinal dysfunction, may continue to appear also in older patients. The immune deficiency of APECED is clinically marked by chronic candidiasis. Although this is usually confined to skin and mucosal tissues, a proportion of patients may develop severe lung disease.
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Overall, prospective analysis of APECED patients has shown that the recurrence of several endocrine and non‐endocrine autoimmune diseases leads to a poor quality of life in the vast majority of patients, without affecting long‐term survival. However, in a minority of APECED patients, acute adrenal insufficiency, with or without hypoparathyroidism, and fulminant hepatic failure have been registered as causes of death (Ahonen et al., 1990). Early identification of this genetic disease and strict follow‐up of endocrine and of other autoimmune symptoms help to prevent severe complications of the disease. 2.1.2. Autoantibodies Development of organ‐specific autoimmune manifestations is accompanied by the appearence of a variety of autoantibodies directed against enzymes or intracellular proteins (Betterle et al., 2002). Study of large cohorts of APECED patients has shown that the specificity and number of autoantibodies that can be detected is not affected by patients’ sex or age (Soderbergh et al., 2004). The majority of APECED subjects present from one to up to eight different types of autoantibodies, while a minority of them (8%) may not show detectable autoantibodies (Table 3). Lack of detectable autoantibodies is more common in patients whose clinical features are restricted to candidiasis and/or hypoparathyroidism, while autoantibodies are usually present in patients with other autoimmune manifestations, suggesting a correlation between antigen specificity and autoimmune reaction against the same organ (Soderbergh et al., 2004). In fact, most of the patients with adrenal insufficiency present circulating antibodies that recognize several steroidogenic enzymes, including 21‐hydroxilase (21‐OH), side‐chain cleavage enzymes (SCC), and 17alpha‐hydroxilase (17alpha‐OH). Two of these autoantibodies (21‐OH and SCC) are strongly associated with adrenocortical failure, being detected in 75% and 61% of APECED patients with Addison’s disease, while the anti‐17alpha‐OH has a lower predictive power as a risk factor (Soderbergh et al., 2004). However, the autoantibodies that are identified in APECED are not necessarily specific for each of the single clinical manifestations of the disease, but can be variably linked to other endocrinopathies as well. In fact, autoantibodies directed against SCC and/or 17alpha‐OH (that are often detected in patients with Addison’s disease) may also be present in APECED patients with hypogonadism (Soderbergh et al., 2004). Association has been reported between autoimmune hepatitis and the presence of autoantibodies directed against tryptophan hydroxilase (TPH) (Soderbergh et al., 2004), the cytochromes P450 1A2 (CYP1A2) and 2A6
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Table 3 Autoantibodies in Patients with APECEDa Autoantigen involved 21‐hydroxylase (21‐OH) Side‐chain cleavage enzyme (SCC) Aromatic l‐amino acid decarboxylase (AADC) Tryptophan hydroxylase (TPH) 17alpha‐hydroxylase (17alpha‐OH) Tyrosine hydroxylase (TH) Glutamic acid decarboxylase 65 (GAD65) Cytochrome P450 1A2 (CYP1A2) Protein IA‐2 (IA‐2) Calcium‐sensing receptor (CaSR)
Percentage of patients affected 66 52 51 45 44 40 38 8 7 0
a
Modified from (Soderbergh et al., 2004).
(CYP2A6), and aromatic L‐amino acid decarboxylase (AADC) (Clemente et al., 1997, 1998; Husebye et al., 1997; Perniola et al., 2000). However, recent studies suggest lack of correlation of anti‐CYP2A6 antibody with the disease and a low sensitivity of anti‐CYP1A2 antibodies, suggesting that anti‐ TPH antibodies are a more sensitive marker for autoimmune hepatitis (Obermayer‐Straub et al., 2001). TPH and GAD65 autoantibodies also have an independent correlation with intestinal dysfunction; in particular, each of them has been detected in 75% of APECED patients with this manifestation (Ekwall et al., 1998; Soderbergh et al., 2004). In patients with cutaneous autoimmune manifestations of APECED, such as alopecia or vitiligo, association with serum autoantibodies directed against the transcription factor SOX10 (Hedstrand et al., 2000), or against the enzyme tyrosine hydroxilase (Hedstrand et al., 2001), respectively, has been demonstrated, and might account for the pathophysiology of these conditions. Although more rare, hypopituitarism and growth arrest have also been observed in APECED patients. In such cases, circulating autoantibodies directed against hypothalamic‐hypophyseal structures have been occasionally detected, suggesting that these may be additional potential targets of autoimmune destruction (Arvanitakis and Knouss, 1973; Cocco et al., 2005; Franzese et al., 1999; Ward et al., 1999). Identification of the autoantigen(s) responsible for the development of hypoparathyroidism has been especially elusive. Descriptions of autoantibodies against parathyroid gland and epithelia have been controversial (Irvine and Scarth, 1969). Even the demonstration of antibodies against the extracellular domain of the Ca2þ‐sensing receptor (Li et al., 1996) has not been confirmed. Nevertheless, immunoflorescence and western blot analysis has
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shown that the serum from 37% of APECED patients contains antibodies that bind to the parathyroid gland tissue, but identification of the specific autoantigen(s) is still missing (Gylling et al., 2003). Finally, the presence of autoantibodies does not necessarily indicate a destructive autoimmune process leading to clinically active disease. In fact, reactivity against pancreatic islet cell antigens, including the major autoantigen glutamic acid decarboxylase 65 (GAD65) of insulin‐dependent diabetes mellitus, is detected in a large proportion of APECED patients (37–43%), but development of diabetes is observed only in a minority of these patients, suggesting that GAD65 antibodies have a low predictive value for development of diabetes in APECED (Gylling et al., 2000; Soderbergh et al., 2004). In contrast, autoantibodies against IA‐2 tyrosine phosphatase‐like protein (IA‐2) or insulin (IAA) have a strong association with IDDM, but a low sensitivity (Gylling et al., 2000; Soderbergh et al., 2004). 2.2. Molecular Genetics of APECED The gene responsible for APECED, known as AIRE (Auto Immune Regulator), was identified by positional cloning in 1997 on chromosome 21q22.3 (Nagamine et al., 1997; The Finnish–German APECED Consortium, 1997). The gene extends for approximately 13 kb, and is composed of 14 exons. Up to now, more than 40 APECED‐causing mutations and at least 6 polymorphisms have been identified in the coding and flanking regions of AIRE. These mutations are spread throughout the gene, but a few of them account for the majority of APECED patients identified among Caucasians (Bjorses et al., 2000a; Heino et al., 2001). Transition of the C nucleotide of a CpG dinucleotide leading to premature stop at codon 257 (R257X) is found in 83% of Finnish APECED chromosomes, but it has also been identified in other APECED patients of continental European nationality and/or ancestry (Bjorses et al., 2000a; Heino et al., 1999b, 2001; Scott et al., 1998; Wang et al., 1998). Another frequently occurring mutation is a deletion of 13 nucleotides (1094–1106del) that creates a premature termination at position 371 and a consequent loss of the last 73 amino acid residues. This mutation accounts for 70% of British and 53% of North American APECED alleles (Heino et al., 1999b; Pearce et al., 1998; Wang et al., 1998). Together, the R257X and the 1094–1106del mutations account for more than 70% of North American APECED patients (Wang et al., 1998). There have been numerous attempts to define whether such high frequency of mutant alleles is the consequence of a founder effect or may reflect recurrent mutations. The R257X mutation involves a CpG dinucleotide, a well‐known mutational hot spot, whereas the 1094–1106del may possibly
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arise from formation of hairpin structures because of imperfect inverted repeats near the mutation site (Scott et al., 1998). Therefore, these observations are suggestive of recurrent mutations being caused by mutational hot spots. To further support this hypothesis, the 1094–1106del mutation has been shown to be carried on different haplotypes of various APECED patients, as defined by analysis of microsatellites that flank the AIRE gene (Scott et al., 1998; Wang et al., 1998). On the other hand, it is still possible that divergence of current haplotypes from a common ancestral haplotype carrying the 1094– 1106 deletion might be the consequence of recombinational events which occurred in the recent past. It is interesting that almost all the Sardinian APECED patients are homozygous for a nonsense mutation resulting from transition of a C residue of a CpG dinucleotide that creates a premature stop in exon 3 at arginine 139 (R139X) (Rosatelli et al., 1998). This mutation is mostly associated with one single haplotype that is rarely found in healthy individuals from the same region, suggesting that this is a ‘‘private’’ mutation that probably occurred between 500 and 600 years ago (Meloni et al., 2002; Rosatelli et al., 1998). Another AIRE mutation with limited geographical distribution has been identified in Iranian Jewish APECED patients, who are known to have an elevated incidence of the disease. Almost all affected patients from this region carry a single homozygous nucleotide substitution in exon 2 (G374A), which leads to a tyrosine to cysteine substitution at position 85 (Y85C). Heterozygosity for the same mutant allele was detected in 1 of 35 unrelated Iranian Jewish subjects (Bjorses et al., 2000a). In contrast to other individual populations affected by APECED, Iranian Jewish subjects present a lower incidence of mucocutaneous candiasisis and of other symptoms related to ectodermal dystrophy, suggesting that this mutation is associated with a milder clinical phenotype (Bjorses et al., 2000a). 2.3. Cellular Expression of the AIRE Protein AIRE encodes a protein of 545 amino acids with a molecular weight of 58 kDa that mainly localizes in the cell nucleus, but it is also detectable at lower levels in the cytosol (Nagamine et al., 1997; The Finnish‐German APECED Consortium, 1997). The AIRE protein is characterized by conserved motifs that are typical of a transcriptional regulator. It is composed of a highly conserved 100 amino acid domain at the N‐terminus, known as the homogenously staining region (HSR), a nuclear localization signal (NLS) between amino acids 113 and 133, a putative DNA‐binding domain named ‘‘SAND,’’ two zinc fingers of plant homeodomain (PHD)‐type motifs that are structural components of several nuclear proteins, and four nuclear receptor‐binding LXXLL motifs (Fig. 1).
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Figure 1 Top: Schematic representation of the AIRE gene, and illustration of the mutations identified in patients with APECED. Open circles identify missense mutations; closed circles, nonsense mutations; open triangles, in‐frame deletions; closed triangles, out‐of‐frame deletions; closed squares, out‐of‐frame insertions; and asterisks, splice‐site mutations, respectively. Bottom: Schematic representation of the AIRE protein, with the main functional domains. Position of the most common mutations identified in APECED patients (Y85C, R139X, R257X, and C322fsX372) is shown.
In keeping with these findings, transfection of a tagged‐AIRE construct in cell lines, including COS‐1 and U937 cells, shows that most of the protein is detectable as speckled structures in the nucleus (Fig. 2), and are reminiscent of the nuclear dots that are observed in promyelocitic leukaemia cells (Bjorses et al., 2000a; Halonen et al., 2004; Heino et al., 1999a; Pitkanen et al., 2001; Rinderle et al., 1999). However, the AIRE protein is also detected in the cytoplasm, where it is organized in filamentous structures resembling intermediate filaments (Fig. 2), and co‐localizes with vimentin (Bjorses et al., 2000a; Halonen et al., 2004; Heino et al., 1999a; Pitkanen et al., 2001; Rinderle et al., 1999). Several APECED‐causing mutations that are permissive for protein expression have been shown to interfere with the subcellular localization of the protein. In particular, expression of the major Finnish mutation (R257X) leads to production of a 28 kDa protein that lacks the two PHD fingers and is detectable as filamentous and/or granular structures in the cytoplasm, but is undetectable in the nucleus (Bjorses et al., 2000a). In addition, analysis of the C1313del mutant, which disrupts the second PHD finger, shows that the
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Figure 2 Illustration of AIRE expression in AIRE‐transfected COS‐1 cells. Staining with anti‐ AIRE antibody shows delicate cytoplasmic filaments and nuclear dots.
protein is retained in the cytoplasm as well (Bjorses et al., 2000a). These observations suggest that both PHD fingers and the nuclear localization signal are required for the correct subcellular distribution of AIRE and its interaction with other nuclear proteins. Other AIRE mutations that are predicted to result in the synthesis of a prematurely truncated polypeptide lacking either one of the PHD finger domains also lead to prevalent expression in the cytoplasm (Bjorses et al., 2000a). It is noticeable that many missense mutations in the AIRE gene are located in exons 2 and 8, which encode for the HSR and PHD1 finger domains, respectively. This suggests that these domains are critically required for essential functions of the protein. The HSR domain is also present in the Sp100 and Sp140 proteins, and has been reported to be necessary for homodimerization of the protein (Pitkanen et al., 2000b; Sternsdorf et al., 1999). The common Iranian Jewish mutation (Y85C) is located in the four‐helix bundle of the HSR domain (Halonen et al., 2004; Pitkanen et al., 2000a). Transfection of this mutant and of other constructs with mutations in exons 1 and 2 leads to homogenous expression of AIRE protein in the cytoplasm and in the nucleus, but neither the nuclear dots, nor the cytoplasmic filaments can be observed (Bjorses et al., 2000a; Halonen et al., 2004). Indeed, study of homomultimerization of AIRE by a two‐hybrid system shows that the same missense mutations affecting the HSR domain severely reduce the homomultimerization ability of AIRE, and prevent ability of the mutant to interact with the wild‐type
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protein (Halonen et al., 2004; Meloni et al., 2005). Homodimerization of the protein is required for normal transcriptional activating property of AIRE, because inhibition of dimerization prevents transactivating activity of AIRE, as assessed by use of AIRE constructs carrying a copy of the gene fused to a heterologous binding domain in combination with the appropriate reporter gene (Bjorses et al., 2000b; Halonen et al., 2004; Pitkanen et al., 2000a). Characterization of the nuclear proteins and/or of DNA sequences that interact with AIRE is still a matter of debate. It has been shown that the common transcriptional coactivator CREB‐binding protein (CBP) interacts with AIRE in vitro, suggesting that CBP, and possibly other nuclear factors, might act as cofactors for increasing binding of AIRE to target genes (Pitkanen et al., 2000a). Subsequent studies by Kumar and coworkers (2001) have identified a DNA motif with specific binding activity for AIRE multimeric protein that might constitute a potential target for the three putative DNA binding domains (PHD fingers and SAND) of AIRE, but this observation has not been confirmed by other investigators. Heteronuclear nuclear magnetic spectroscopy, which has been used to determine the solution structure of the first PHD finger, has demonstrated that the AIRE‐PHD1 domain has a canonical PHD finger fold, including two coordinated zinc ions, which resemble RING finger domains with potential ubiquitylation activity (Bottomley et al., 2005). In addition to this structural evidence, Uchida and coworkers (2004) have shown that the first PHD finger domain of AIRE mediates ubiquitylation and has intrinsic E3 ligase activity. Moreover, APECED‐causing missense mutations located in the first PHD finger domain result in abrogation of the E3 ligase activity, while mutations in the second PHD finger only affect transactivating activity of the AIRE protein. It is likely that ubiquitylation activity of AIRE is important to regulate the steady‐state level of transcription factors that are present in the nucleus and/or in the cytoplasm, but the identity of these proteins is still unknown. 2.4. Immunobiology of AIRE 2.4.1. Distribution and Regulation of AIRE Expression In humans, AIRE expression is essentially restricted to lymphoid tissues, including thymus, lymph node, spleen, and fetal liver (Nagamine et al., 1997). This contrasts with what is observed in mice, in which Aire is widely expressed in numerous non‐hematopoietic organs, including adrenal glands, pancreas, intestine, liver, and kidney, suggesting a broader function of this regulatory factor in mouse (Halonen et al., 2001). In both species, however, the highest levels of AIRE are detected in thymic epithelial cells, where it
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concentrates in the nucleus to form the same dot‐like structures that are observed after AIRE expression in vitro (Heino et al., 1999a, 2000; Zuklys et al., 2000). Comparison of AIRE staining pattern in the thymus to cytokeratin staining of epithelial cells demonstrates that only a fraction of thymic epithelial cells express AIRE mRNA and protein (Heino et al., 1999a). In particular, AIRE is more expressed in a subset of thymic medullary epithelial cells that strongly express HLA class II antigens and the costimulatory molecules CD80, CD86, and CD40. This suggests that levels of AIRE protein are tightly regulated during maturation of medullary epithelial cells (Heino et al., 1999a). Isolation of medullary epithelial cells from murine thymi on the basis of the level of CD80 expression has shown a positive correlation between the intensity of Aire expression and CD80 levels, supporting the model that regulation of costimulary molecules increases in parallel with Aire mRNA levels in thymic epithelial cells (Derbinski et al., 2005). Analysis of AIRE expression in the thymic medulla shows that a minor proportion of AIRE‐expressing cells presents a dendritic morphology and lacks epithelial antigens. In fact, these cells express the cell surface markers typical of myeloid cells, such as CD11c and CD83 (Heino et al., 1999a). Moreover, monocytes and monocyte‐derived dendritic cells generated in culture with IL‐4, GM‐CSF, and TNF‐alpha also express AIRE, although at lower levels than thymic epithelial cells (Kogawa et al., 2002). Therefore, it is likely that AIRE expression by DCs may account for the low levels of AIRE expression that are observed in many lymphoid organs, including lymph nodes and spleen. Study of Aire expression during thymus ontogeny in mice has revealed that CD3 transgenic mice, which present a complete arrest at the early stage of thymocyte differentiation (CD44þ CD25þ) before appearance of CD4þ CD8þ double positive (DP) T cells, completely fail to express Aire (Zuklys et al., 2000). In contrast, RAGnull mutant mice, which present a block of thymocyte differentiation at the phase of CD4þ/CD8þ DP T cells, display detectable transcripts of Aire mRNA (Zuklys et al., 2000). On the basis of these observations it seems that AIRE expression in the thymus is strictly influenced by thymocyte differentiation and requires a precise spatial and temporal interaction between these two cell populations of thymus. In RelBnull thymi, the cortico‐medullary structure of the organ is completely subverted and there is a lack of Aire expression, even in the presence of normal mature epithelial cells (Heino et al., 1999a; Zuklys et al., 2000). Investigation of other animal models has shown that lymphotoxin‐alpha (LT‐alpha) might be important for the interaction between thymocytes and epithelial cells and for Aire expression, because LT‐a gene‐targeted mice are defective in Aire expression, but it is unclear whether the lymphotoxin
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beta receptor is required for this pathway (Boehm et al., 2003; Chin et al., 2003). 2.4.2. Animal Models of APECED Genetic disruption of the Aire gene by homologous recombination has provided a unique opportunity to investigate the function of Aire and to develop an animal model for APECED. Although mucocutaneous candidiasis and polyendocrinopathy have never been observed in the Airenull mice, these animals present other features of the human disease, including multiorgan lymphocyte infiltration and circulating autoantibodies (Anderson et al., 2002; Ramsey et al., 2002). The autoantibodies are directed against several organs, such as salivary glands, liver, exocrine pancreas, and their presence correlates with the lymphocyte infiltration in the same tissues (Anderson et al., 2002; Kuroda et al., 2005; Ramsey et al., 2002). Despite the humoral and cellular autoimmune manifestations, the Airenull mice present normal immunoglobulin levels, normal B and T subpopulations, and normal cytokine secretion in response to mitogens (Anderson et al., 2002; Kuroda et al., 2005; Ramsey et al., 2002). In addition, circulating lymphocytes from Airenull mice do not present any obvious defect in lymphocyte apoptosis, and in the expression of activation markers (CD25 and CD69), suggesting that Aire is not essential for functions of peripheral blood lymphocytes. Both the expression studies of AIRE and the role of thymus in central tolerance suggest that the most crucial function of AIRE is related to regulation of thymocyte differentiation and selection. Although thymi from Airenull mice are of normal size and show a normal architecture of the organ with a preserved cortico‐medullary demarcation, epithelial cells from Airenull mice present a striking reduction in the number of mRNA transcripts in comparison to cells of wild‐type animals, as assessed by microarray analysis (Anderson et al., 2002). Analysis of the genes that are downregulated in Airenull mice showed that the vast majority of them are ectopically expressed transcripts of tissue‐specific antigens, including preproinsulin, cythocrome P450 1A2, and many others. This observation prompted the authors to suggest that Aire expression by medullary epithelial cells is required to promote antigen presentation by medullary epithelial cells and subsequent negative selection of autoreactive T cells that are generated during TCR rearrangement (Anderson et al., 2002) (Fig. 3). Matching this observation, Liston and coworkers have demonstrated that Aire mutation causes a severe defect in the deletion of organ‐specific autoreactive T cell clones giving further support to the role of AIRE in the regulation of central tolerance (Liston et al., 2003).
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Figure 3 Schematic representation of the role of AIRE in central tolerance. Active thymopoiesis sustains AIRE expression by medullary thymic epithelial cells through a lymphotoxin‐a (LT‐a)‐ dependent mechanism that involves activation of the transcription factor NF‐kB.By poorly characterized mechanisms, AIRE induces expression of tissue‐specific antigens, which are presented to nascent T cells in the context of major histocompatibility complex (MHC) antigens. Autoreactive T cells, whose T cell receptor (TCR) is specific for the ectopically expressed tissue‐specific antigens, are deleted in the thymus.
These observations propose AIRE as an exclusive regulator of lymphocyte selection in the thymus. However, several observations argue in favor of additional factors involved in this phenomenon. In particular, a significant proportion of APECED patients carry mutations of the AIRE gene on one allele only, suggesting that other genetic loci influence central tolerance (Buzi et al., 2003; Heino et al., 2001; Wang et al., 1998). There is evidence that the effect of Aire on thymic expression of promiscuous genes is strictly subjected to a gene‐dosage effect. Loss of a single copy of Aire results in proportional reduction of insulin gene expression in thymic medulla, and increase in the number of autoreactive T cell clones that escape from thymic deletion (Liston et al., 2004). In addition, recent studies have directly suggested that AIRE is not the only gene that induces promiscuous gene expression in the thymus. In fact, mature CD80bright medullary epithelial cells express a broader array of promiscuous genes than those known to be regulated by Aire (Derbinski et al., 2005). Furthermore, Derbinski and coworkers have shown that maturation of medullary epithelial results in increased CD80 levels on the cell surface and in
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parallel upregulation of more than 300 mRNA transcripts, most of which are not affected by AIRE (Derbinski et al., 2005). Promiscuous genes that are expressed by medullary thymic epithelium present an uneven distribution in the mouse genome and tend to cluster on chromosomes. This has suggested that genomic clustering may be a mechanism by which coordinated regulation of genes expressed during thymocyte selection is achieved (Derbinski et al., 2005; Johnnidis et al., 2005). It is also possible that other ‘‘AIRE‐like’’ factors regulate promiscuous gene expression in medullary epithelial cells and participate with AIRE in the mechanism of central tolerance. In any case, characterization of the critical role played by AIRE in the control of central tolerance has opened the way to a better understanding of other autoimmune disorders, including some associated with PID characterized by defective thymopoiesis. 3. Defective AIRE Expression Explains the Pathophysiology of Autoimmunity in Omenn Syndrome 3.1. Omenn Syndrome: Clinical and Laboratory Features Omenn syndrome (OS) is a rare and severe form of combined immunodeficiency, characterized by early‐onset diffuse erythrodermia, lymphadenopathy, and hepato‐splenomegaly (Fig. 4A) (Omenn, 1965). Protracted diarrhea, generalized oedema, failure to thrive, and alopecia are also common findings in OS (Aleman et al., 2001). Typical laboratory features of OS include hypoprotidemia and hypogammaglobulinemia with increased serum IgE, defective antibody production, and marked eosinophilia. While the total lymphocyte count may vary from low to increased, analysis of lymphocyte subpopulations reveals a variable number of T cells, with absent or very few circulating B lymphocytes. The circulating T lymphocytes from OS patients are autologous (i.e., they do not reflect trans‐ uterine passage and expansion of maternally derived T cells in an immunocompromised fetus), and show a highly restricted T cell receptor (TCR) repertoire (Rieux‐Laucat et al., 1998; Signorini et al., 1999; Villa et al., 1998). In most cases, a selective expansion of CD4þ or—less frequently—of CD8þ cells is observed. Although the vast majority of OS patients show circulating T cells carrying the ab form of the TCR, accumulation of TCRGD cells has also been described (Brugnoni et al., 1997; de Saint Basile et al., 1991). Occasionally, OS patients present a predominance of TCRABþ CD4 CD8 cells (Wirt et al., 1989). In addition, T lymphocytes from OS patients carry activation markers (DR, CD30, CD25), are poorly responsive to mitogens, and tend to infiltrate target
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Figure 4 Panel A: Typical features of Omenn syndrome, with diffuse erythrodermia and oedema. Panel B: Skin section for an infant with Omenn syndrome, showing abundant lymphocytic infiltrate in the superficial derma and in the epidermis, associated with keratinocytes damage and several apoptotic bodies and abundant presence of eosinophils. (Courtesy: Prof. F. Facchetti)
organs (skin, gut, liver, and spleen) (Fig. 4B), thus contributing to the clinical manifestations of the disease (Brugnoni et al., 1997; Rieux‐Laucat et al., 1998; Signorini et al., 1999; Villa et al., 1998). The pathological findings observed in patients with OS are very similar to what is observed in some infants with severe combined immune deficiency (SCID) who develop graft‐versus‐host‐ like reactions following maternal T cell engraftment (Denianke et al., 2001). Analysis of the profile of cytokine secretion indicates that OS T lymphocytes are skewed towards a T‐helper 2 (Th2) phenotype (Chilosi et al., 1996; Schandene´ et al., 1993), thus accounting for the eosinophilia and the increased serum IgE levels. Architecture of lymphoid tissues is drastically altered in OS. Lymph nodes show absence of primary follicles and germinal centers, and an expansion of interdigitating reticulum cells in the paracortex (Facchetti et al., 1998; Martin et al., 1995). Lymphoid depletion is also apparent in the thymus, with lack of cortico‐medullary demarcation, and a reduced number of CD3þ cells (Signorini et al., 1999). In the absence of hematopoietic stem cell transplantation (HSCT), the disease is rapidly and uniformly fatal within the first few years of life. In a review of OS patients reported in the literature (1965–1999), 69% of the untransplanted infants with OS died within the first year of life (Aleman et al., 2001). Mortality is most often due to overwhelming infections and to metabolic disturbances associated with the severe autoimmune manifestations of the disease. Immune suppression with steroids and/or cyclosporin A has
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been shown to be effective in ameliorating the clinical conditions, while waiting for HSCT, which represents at present the only way to provide a definitive cure. We have recently reported an excellent long‐term survival (81.8%) in OS infants treated by HSCT, even with the use of matched unrelated donors or of partially‐matched related donors (Mazzolari et al., 2005b). 3.2. Molecular Pathophysiology of Omenn Syndrome The description of a family with OS in one sibling, and SCID with complete absence of T and B lymphocytes (T‐B‐SCID) in another sibling, suggested that OS may be a ‘‘leaky’’ form of T‐B‐SCID (de Saint Basile et al., 1991). In addition, the demonstration of a restricted TCR repertoire in OS, associated with a severe block in B cell differentiation, was indicative of a putative defect in V(D)J recombination (Rieux‐Laucat et al., 1998). This process is initiated by the lymphoid‐specific recombinase activating gene (RAG) proteins, which specifically recognize the recombination signal sequences (RSS) that flank the Variable (V), Diversity (D), and Joining (J) gene segments. The RAG proteins introduce a nick in the DNA double‐strand between a coding V, (D), or J element and the heptamer of its flanking RSS. The resulting free 30 ‐OH attacks the phosphodiester bond on the opposite strand, resulting in formation of covalently sealed hairpins at the coding ends. The recently identified Artemis protein (Moshous et al., 2001) is responsible for opening these coding end hairpins, and requires DNA‐dependent protein kinase catalytic subunit (DNA‐PKcs) for its activity (Ma et al., 2002). The process of DNA repair in V(D)J recombination is then completed by other proteins, including Ku70, Ku80, XRCC4, and DNA ligase IV. A few years ago, we showed that in most cases OS is due to hypomorphic mutations in the RAG1 or RAG2 (Villa et al., 1998). While null mutations in these genes are associated with T‐B‐SCID (Schwarz et al., 1996), hypomorphic mutations in the same genes, which impair, but do not completely abolish, the V(D)J recombination process, may lead to the OS phenotype. Several molecular mechanisms may account for defective (but not abolished) V(D)J recombination associated with hypomorphic mutations in the RAG genes detected in patients with OS. In particular, some missense mutations in the RAG1 nonamer binding domain (NBD) impair RSS recognition and cleavage (Villa et al., 1998). Another RAG1 common mutation (R561H) observed in patients with OS affects a region of the protein that mediates interaction with RAG2, whereas the Y912 substitution in the catalytic region is highly inefficient in DNA nicking (Santagata et al., 1999). Another common mutation in patients with OS is represented by a dinucleotide deletion (del nt 368–369) in the
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RAG1 gene. This mutation results in usage of a downstream translation initation site; the resulting N‐terminal deleted protein shows improper subcellular localization (Santagata et al., 2000). Among the RAG2 gene mutations associated with OS, most are located on one side of a predicted six‐bladed b‐propeller in the active core of the molecule (Callebaut et al., 1998; Gomez et al., 2000); in particular, the mutations associated with OS occur at the borders of the b‐propeller b‐strands, or within the loops that connect the various b‐strands, in regions that are more tolerant to substitutions. Also, these mutants have been shown to retain partial recombinational activity when tested in vitro (Gomez et al., 2000). While these findings of hypomorphic RAG mutations in patients with OS have been confirmed by several other groups, the impact of the gene defect onto clinical phenotype has been challenged. In particular, it has been recognized that the same missense mutations in either RAG1 or RAG2 genes may lead to different phenotypes, ranging from T‐B‐SCID to OS, and including atypical cases with some but not all features of OS (Corneo et al., 2001; Villa et al., 2001). These data indicate that the clinical and immunological phenotype of OS is possibly contributed by the following mechanisms, which are not mutually exclusive: (1) defective V(D)J recombination activity, due to RAG gene defects; (2) the existence of yet undefined modifier genes that may control expression of the RAG genes, or efficiency of the V(D)J recombination process; (3) epigenetic factors, which may affect the function of the RAG proteins, or may favor expansion of selected T cell clonotypes. As mentioned above, one of the typical features of OS is represented by the presence of a detectable number of circulating T lymphocytes, with virtual absence of B cells. While the observation that serum IgE levels are often increased in OS suggests that some B cell maturation occurs (possibly in the bone marrow), these data indicate that the RAG gene mutations differently affect the process of V(D)J recombination and cell differentiation in the T vs. B cell lineages. In particular, by studying TCR and immunoglobulin genes rearrangement, Noordzij and coworkers have shown that N‐terminal truncated RAG1 protein can direct TCR but not immunoglobulin gene rearrangements (Noordzij et al., 2000b). The same authors have also found that in most patients with RAG defects, the B cell differentiation is arrested at the transition from cytoplasmic Igm– pre‐B‐I cells to cytoplasmic Igmþ pre‐B‐II cells (Noordzij et al., 2000a). The hypothesis that RAG defects exert a stronger constraint onto immunoglobulin than TCR genes rearrangements is also supported by the observation that cross‐lineage TCR rearrangements are frequently detected in precursor B cell acute lymphoblastic leukaemia, whereas immunoglobulin gene rearrangements are rare in T cell acute lymphoblastic leukaemia (Szczepanski et al., 1999a,b).
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The notion that OS is indeed a syndrome, whose clinical phenotype reflects impaired, but not completely abolished thymopoiesis, has received support through the description of several OS patients in which no defects could be identified in the RAG1 or RAG2 genes (Aleman et al., 2001; Gennery et al., 2005; Wada et al., 2000). More recently, one patient was described, in which OS was due to ARTEMIS gene mutations (Ege et al., 2005). Interestingly, similar to that observed for null mutations in the RAG1 and RAG2 genes, severe mutations in ARTEMIS are also associated with a T‐B‐SCID phenotype (Moshous et al., 2001). Altogether, these data reinforce the notion that hypomorphic mutations in genes involved in V(D)J recombination may allow for residual T cell development, and thus possibly result in OS phenotype. 3.3. Unraveling the Molecular Basis of Immune‐Mediated Damage in Omenn Syndrome: Implications for Other Forms of T Cell Immunodeficiency with Autoimmunity 3.3.1. Autoimmunity in Omenn Syndrome is Sustained by Impaired Expression of AIRE and of Tissue‐Specific Transcripts in the Thymus Tissue infiltration by oligoclonal T cells is a hallmark of OS and leads to detrimental clinical consequences that mimic that observed in graft‐versus‐ host disease (erythrodermia, hepato‐splenomegaly, abnormalities of gut mucosa and chronic diarrhea, alopecia). During the last years, the mechanisms accounting for the expansion of selected T cell clonotypes in OS have been studied in detail. The notion that the diversity of TCR repertoire among tissue‐ infiltrating lymphocytes is different in various tissues suggests peripheral expansion of selected clonotypes in response to tissue‐restricted (auto)antigens (Signorini et al., 1999). Importantly, preferential usage of the same TCRBV chain has been found in different patients with OS. In particular, oligoclonal expansion of TCRBV14 has been documented in several patients with severe erythrodermia (Pirovano et al., 2003; Rieux‐Laucat et al., 1998; Signorini et al., 1999; Villa et al., 1998), suggesting that the same (auto)antigen may elicit peripheral expansion of selected clonotypes in different patients. However, the nature of the antigens that drive this peripheral expansion remains largely unknown. While the resemblance with clinical manifestations of graft‐versus‐host disease suggests autoantigen‐driven T cell proliferation, the possibility that exogenous antigens may initiate the process should also be considered. In particular, it has been recently reported that among three patients belonging to the same family with typical T‐B‐SCID due to RAG2 defect, one infant developed typical features of OS following a parainfluenza 3 virus infection
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(Dalal et al., 2005). It remains unclear whether the expansion of oligoclonal T cells in this patient reflected a direct response to the virus, or whether it represented a proliferative response to autoantigens, possibly sustained through a mechanism of molecular mimicry with virus‐specific antigens. In any case, this observation illustrates the interaction of genetic (RAG defect) and environmental (parainfluenza 3 virus) factors in determining the clinical and immunological phenotype of OS. In particular, it demonstrates that antigens may elicit clonal proliferation of T lymphocytes also in patients with OS. In view of defective V(D)J recombination, oligoclonal representation of T cells in OS may reflect disturbed and restricted thymopoiesis, in addition to (auto)antigen‐driven peripheral expansion. To address this issue, we have analyzed TCR repertoire and the sequence of productively rearranged TCR gene segments in OS thymocytes, and compared these data with similar data obtained on circulating and tissue‐infiltrating T cells from the same patients (Signorini et al., 1999). We have been able to show that while thymus from control infants shows a fully polyclonal TCR representation, predominance of few TCR clonotypes is present in the thymus from OS infants. The pattern and sequence of productively rearranged TCR gene segments is different in the thymus vs. other tissues, indicating that thymic oligoclonality does not simply reflect recirculation of expanded clonotypes, but rather is due to inability to generate a polyclonal repertoire. In addition, we have also shown that RAG gene defects in OS do not interfere with the process of N and P nucleotide insertions, and that they may cause only a marginal reduction in CDR3 length (Signorini et al., 1999). The critical role for residual V(D)J recombination activity in allowing production and expansion of selected TCR clonotypes has been recently confirmed by Wada and coworkers (2005). These authors have studied a patient with T‐B‐SCID due to RAG1 deficiency in which appearance of somatic second‐site mutations, capable of restoring the RAG1 reading frame, resulted in development of autologous, activated T cells with a highly restricted TCR repertoire, associated with clinical features of OS. Altogether, these data indicate that the autoimmune manifestations of OS are sustained by (auto)antigen‐specific T cell clonotypes, whose production reflects both an intrathymic restriction of TCR repertoire and a peripheral expansion. In spite of this, the mechanisms that account for the accumulation of such clonotypes have long remained obscure. In particular, it was not known whether the autoimmune manifestations of OS are due to altered central or peripheral tolerance. The studies performed on the role of AIRE in central tolerance and on the molecular pathophysiology of APECED have been essential to a better understanding of autoimmunity in OS.
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In particular, the notion that AIRE expression in the thymus is strictly influenced by thymocyte differentiation (through secretion of LT‐a) and requires a precise spatial and temporal interaction between nascent thymocytes and medullary thymic epithelial cells, has led to the hypothesis that impairment of T cell development (as observed in OS) may cause reduced AIRE expression and poor negative selection of newly generated autoreactive T cells in the thymus. To address this possibility, we have investigated AIRE expression in the thymus derived from controls, patients with OS, and patients with T‐B‐SCID due to RAG gene defects (Cavadini et al., 2005). As shown in Fig. 5, we have confirmed that in humans AIRE expression in the thymus is
Figure 5 Expression of AIRE in the thymus from a control subject (panel A), infant with Omenn syndrome (panel B), and a patient with T‐B‐SCID (panel C). Positive staining can be clearly appreciated in the normal thymus, in particular in the medulla, where epithelial cells show cytoplasmic and nuclear expression of AIRE (inset in panel A). Thymi from the Omenn syndrome patient and the infant with T‐B‐SCID show grossly abnormal architecture, with severe depletion of lymphoid cells, and lack of corticomedullary demarcation. In these thymi, expression of AIRE is absent or negligible.
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largely restricted to medullary thymic epithelial cells and to few myeloid dendritic cells. However, AIRE expression is markedly reduced in the thymus derived from OS or from T‐B‐SCID infants. Based on what was observed in Aire/ mice, we hypothesized and indeed demonstrated that low AIRE expression in the thymus from OS and SCID infants results in markedly reduced expression of tissue‐specific transcripts, such as insulin, cytochrome P450 1a2, and fatty acid binding protein (Fig. 6) (Cavadini et al., 2005). 3.3.2. Imp lications for Other Forms of T Cell Immunodeficiency with Autoimmunity The data on reduced expression of AIRE and of tissue‐specific transcripts in the thymus from patients with OS and with T‐B‐SCID have important implications for human immunopathology. They offer the first demonstration that, in humans as well as mice, AIRE expression in the thymus is tightly controlled by the efficiency of T cell development. However, they also indicate that regulation of AIRE expression by thymopoiesis occurs differently in mice and humans. In fact, while RAG mutations in humans are severely detrimental to AIRE expression, this is not the case in Ragnull mice (Zuklys et al., 2000).
Figure 6 Impaired AIRE expression in the thymus from patients with Omenn syndrome or with T‐B‐SCID results in defective expression of tissue‐specific transcripts. Semi‐quantitative evaluation (as measured by RT‐PCR) of the levels of transcripts for insulin, cytochrome p450, and fatty acid binding protein (FABP) in thymic extracts from two controls, two infants with Omenn syndrome, and one T‐B‐SCID infant is shown. Modified from (Cavadini et al., 2005).
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Furthermore, our data strongly support the notion that in OS the process of negative selection is impaired, as the result of inadequate expression of tissue‐ specific self‐antigens by medullary thymic epithelial cells. The few T cell clonotypes that may develop in infants with OS, in spite of defective V(D)J recombination, are likely to contain a proportion of autoreactive T cells, which upon maturation and thymic egression, may expand in peripheral tissues, upon contact with the specific autoantigen. The different clinical phenotype (OS vs. T‐B‐SCID) that may be observed in patients with RAG defects is justified by the residual V(D)J recombination activity detected in patients with OS, that allows for partial T cell development, which is, however, insufficient to sustain AIRE and ectopic transcripts expression, and thus causes impaired deletion of autoreactive T cells. In contrast, the complete block in the process of V(D)J recombination observed in patients with T‐B‐SCID prevents generation of autoreactive T cells, in spite of an equally defective expression of AIRE and of tissue‐specific transcripts. While these data strongly support the hypothesis that impairment of central tolerance plays a major role in the pathophysiology of OS, additional mechanisms might also be involved. In particular, a dysfunction of regulatory CD4þ T cells that express FOXP3 and are of thymic origin might also be postulated. However, we have found that FOXP3 is normally expressed by circulating CD4þ T cells derived from a series of patients with OS (Badolato and Notarangelo, unpublished observations). Importantly, recognition that AIRE expression is reduced in the thymus from patients with OS or with RAG‐deficient T‐B‐SCID suggests that a similar phenomenon may occur in other forms of PID with ineffective thymopoiesis, and contribute to possibly autoimmune manifestations. In particular, autoimmunity may be observed in patients with DiGeorge syndrome, a developmental defect of the thymus, heart, and parathyroid glands, and is more common among patients with pronounced deficiency of T cell development. Some of these patients with so‐called ‘‘complete’’ DiGeorge syndrome may develop clinical manifestations that may mimic OS, with generalized erythrodermia and lymphadenopathy (Sullivan, 2003). Also in such cases, reduced thymic output (as detected by a low number of T cell receptor excision circles) was associated with oligoclonal representation of circulating T cells (Markert et al., 2004; Pirovano et al., 2003). Immune dysregulation, including autoimmune haemolytic anemia, thrombocytopenia, insulin‐dependent diabetes mellitus, asthma, and skin rash, has also been reported in patients with combined immune deficiency due to adenosine deaminase deficiency (Notarangelo et al., 1992). Furthermore, autoimmune manifestations are particularly common (up to a third of all cases) among infants with purine nucleoside phosphorylase deficiency (Hershfield, 2004).
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Finally, dense lymphocytic infiltration in several target organs (gut, lung, bone, and soft tissues) has been reported in patients with mutations of the IL2RA gene, encoding for interleukin‐2 receptor a chain (Sharfe et al., 1997). Similar disturbances have been occasionally observed in patients with combined immune deficiency due to defects of the common g chain (gc), of JAK3, and of the interleukin‐7 receptor a chain gene (IL7RA), who showed evidence of lymphoproliferative disease, or developed oligoclonal and activated T lymphocytes (Frucht et al., 2001; Notarangelo and Giliani, unpublished observation). Although immune dysregulation in these cases may reflect abnormal function of CD4þ CD25þ regulatory T cells or pertubed peripheral immune homeostasis, the observation of thymic abnormalities (with impaired expression of CD1 on cortical thymocytes) in IL2RA deficiency and of profound defect of thymic output in gc and JAK3 deficiency suggests that inefficient presentation of self‐antigens to autoreactive T cells may contribute to the immunological and clinical phenotype. 4. CD4þ CD25þ Regulatory T Cells and the Pathophysiology of IPEX (Immunodysregulation – Polyendocrinopathy – Enteropathy – X‐linked) 4.1. IPEX Syndrome: Clinical and Laboratory Features 4.1.1. Introduction IPEX (OMIM: 304930) is a rare X‐linked recessive disorder of immune regulation resulting in overwhelming and systemic autoimmunity. The three most common clinical features are early onset insulin‐dependent diabetes mellitus, severe watery diarrhea, and dermatitis (Fig. 7A) that typically correlate with elevated titers of serum immunoglobulin E (IgE). Other clinical manifestations that have been described less consistently include thyroiditis, hemolytic anemia, thrombocytopenia, and nephropathy. The disease is rare, but retrospective data on clinical cases of early autoimmune enteritis associated with Type I diabetes, or of neonatal diabetes of unknown origin, suggest that the actual frequency of the disease may be underestimated (Marquis et al., 2002). In the majority of cases, affected males develop symptoms early in infancy and most die prematurely of either metabolic alterations due to intractable diarrhea or severe infections, which occur in some patients prior to the initiation of immune suppressive treatment. The animal model of IPEX, called scurfy mouse, is a natural mutant, described more than 40 years ago. Scurfy mice develop a severe lymphoproliferative disorder resulting from an inability of the immune system to properly regulate CD4þCD8 T cell activity. In these mice, autoaggressive phenomena and multiorgan infiltration, leading to death in a few weeks, are prominent features.
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Figure 7 Panel A: Severe psoriasiform erythrodermia in an infant with immunedysregulation – polyendocrinopathy – enteropathy – X‐linked (IPEX) syndrome. Panel B: Small‐bowel biopsy from an infant with IPEX, showing characteristic villous atrophy and lymphocytic infiltrates. Infiltrating lymphocytes are T cells, as indicated by staining with anti‐CD3 antibody. (Courtesy: Prof. F. Facchetti.)
IPEX and scurfy are caused by mutations of Forkhead Box P3 (FOXP3) gene, located on the X chromosome and encoding for a DNA‐binding protein. Previously, adoptive transfer experiments and CD4þCD8 T cell subset depletion studies had indicated that Scurfy and IPEX can be the result of immune dysregulation. More recent findings have revealed the crucial role of FOXP3 for CD4þCD25þ regulatory T cells (Treg) development and function, and consequently provided the most direct evidence of an alteration of the immune homeostasis in IPEX and its murine orthologue model. 4.1.2. Historical Aspects An early description of a syndrome similar to IPEX was reported by Meyer and coworkers (1970), who describe two brothers with absent islet cells, neonatal onset type I diabetes, enteropathy, and failure to thrive. Both brothers were affected by several severe infections (including fungal infections, thigh abscess, and discharge from ears) and died early in life. The mother had 10 brothers who had died of unknown causes in infancy, and a healthy sister, suggesting X‐linked inheritance. The first detailed report of the complete IPEX phenotype was published by Powell and coworkers (1982), who described an X‐linked syndrome in a large kindred in which 19 affected males in five generations experienced similar illnesses with variable onset and severity. In these patients, the disease was mostly characterized by intractable diarrhea, eczema, and endocrine abnormalities associated with various combinations of hemolytic anemia, thrombocytopenia, autoimmune hepatitis, collagen‐vascular
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disease, and infections. Satake and coworkers (1993) described a Japanese family in which two brothers and their maternal uncle suffered from autoimmune enteropathy with hemolytic anemia and polyendocrinopathy. Two of the boys died from severe diarrhea accompanied by total or subtotal intestinal villous atrophy. The third affected male showed the same symptoms and had circulating antibodies against enterocytes, but his condition improved when treated with immune suppressive drugs. Peake and coworkers (1996) reported the cases of four related males who presented with neonatal diabetes mellitus, intractable diarrhea, and exfoliative dermatitis with extremely high IgE serum levels. These patients died early in life, mainly of severe infections. Additional families were reported by Roberts and Searle (1995) and Di Rocco and Marta (1996). Also in these series, most of the affected males developed autoimmune phenomena within the first six months of life and died within the first year of life. Although isolated cases with the characteristic phenotype of the IPEX syndrome have been documented over many years, they had not been related to a single disorder nor linked to the scurfy mouse syndrome. One of the first suggestions that the human and mouse diseases might represent orthologue models came from linkage analysis which located the responsible locus of each disease to the synthenic pericentromeric region of the X chromosome (Xp11.23 to Xq21.1) (Ferguson et al., 2000; Means et al., 2000). Since the gene encoding the Wiskott‐Aldrich syndrome (WAS) protein also lies within this region, it was thought that IPEX could represent a variant of WAS. However, sequence of the WAS protein (WASP) gene was found to be normal in IPEX patients and carrier females (Bennett et al., 2000; Ferguson et al., 2000). Subsequently, combining genetic and physical mapping with large‐scale sequence analysis, Brunkow and coworkers (2000) identified the gene defective in scurfy mice, foxp3. The consequent association of the human IPEX syndrome with mutations in FOXP3, the human orthologue of the mouse gene, proved that these two syndromes are in fact homologous and distinct from Wiskott‐Aldrich syndrome (Bennett et al., 2001b; Chatila et al., 2000; Wildin et al., 2001). 4.1.3. Clinical Features of IPEX In recent years, several IPEX cases have been described (Gambineri et al., 2003; Ochs et al., 2005; Wildin et al., 2002). As more patients were documented, three basic features of symptoms were recognized (Table 4). Enteropathy was found to be present in every case of IPEX. The enteropathy consists of a severe refractory and life‐threatening diarrhea causing failure to thrive. The onset typically occurs
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Table 4 Clinical Features of IPEX Syndrome Basic Clinical and Laboratory Features Enteropathy Dermatitis
Endocrinopathy Elevated IgE
Watery diarrhea (rarely bloody) with villous atrophy Inflammatory bowel disease Eczema Erythroderma Psoriasiform dermatitis Alopecia Type I Diabetes Thyroid abnormalities Usually present
Other Clinical and Laboratory Features Hematologic
Renal Hepatic Lymphadenopathy Arthritis / Vasculitis Cytokines production Autoantibodies (Ab)
Coombs (þ) hemolytic anemia Autoimmune thrombocytopenia Autoimmune neutropenia Nephrosis or nephritis Autoimmune hepatitis Rare Rare Low IFN‐g May be present: AIE‐75 (Ab against gut and kidney specific antigen) Anti‐nuclear antibodies Antibodies against different organs (thyroid, pancreatic islets, erythrocytes, platelets, smooth muscle)
in early infancy with watery, and sometimes bloody, diarrhea. Characteristic severe villous atrophy and mucosal erosion with lymphocytic infiltrates of the submucosa or lamina propria are observed in small bowel biopsies (Fig. 7B), often leading to an incorrect diagnosis of inflammatory bowel disease. Other common features of the IPEX phenotype, present in nearly all cases, are skin disorders, primarily eczema, but also erythroderma and psoriasiform dermatitis. Alopecia and nail abnormalities have been described in one patient (Nieves et al., 2004). Endocrinopathy is also frequently observed in most but not all patients. The most common endocrine manifestation is early‐onset type I diabetes, frequently characterized by a difficult control of glycemia. Thyroid abnormalities include abnormal serum triiodothyronine and/or thyroxine levels, possibly associated with clinical evidence of hypo‐ or hyperthyroidism. Lymphocytic infiltrates, observed also in pancreas and thyroid, suggest that the pathology of these organs is the result of an inflammatory destruction by a T cell‐mediated autoimmune mechanism rather than of abnormal organogenesis.
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In addition to these recurrent features, other autoimmune manifestations may occur. Hematologic disorders such as Coombs’s positive hemolytic anemia, thrombocytopenia, and neutropenia are frequent. Less common manifestations include tubular nephropathy, hepatitis, arthritis, and/or lymphadenopathy, with or without hepato‐splenomegaly (Table 4). An increased risk of recurrent infections has been observed (Ferguson et al., 2000; Jonas et al., 1991; Kobayashi et al., 1999; Levy‐Lahad and Wildin, 2001; Peake et al., 1996; Powell et al., 1982; Roberts and Searle, 1995). It is still unclear whether the increased susceptibility to infections in IPEX patients reflects a primary defect in immune regulation or whether it is the consequence of a barrier defect. Severe enteropathy and eczema may in fact facilitate bacterial entry via the gut and skin. Finally, immunosuppressive therapy used to treat the disorder may also increase the risk of infections. The severity of infections typically varies from moderate infections of the upper respiratory or gastrointestinal tract, to severe and invasive infections such as sepsis, meningitis, and osteomyelitis. The most common infectious organisms are Enterococcus and Staphylococcus species, Cytomegalovirus, and Candida (Ochs et al., 2005). Interestingly, heterozygous females appear to be healthy even though X‐inactivation occurs randomly. The X chromosome inactivation analysis performed on one carrier female has demonstrated that both the normal and the mutated FOXP3 alleles are equally expressed in circulating T lymphocytes (Tommasini et al., 2002), thereby masking the disease by a compensatory mechanism. However, such analysis has been performed on total CD4þ cells. No data are available on the pattern of X chromosome inactivation in purified Treg cells. 4.1.4. Laboratory Findings There is not a significant commonality in the immune aberrations of IPEX patients, and the laboratory findings are not a remarkable aspect of the syndrome. Elevated IgE levels seem to be an important feature, and have been reported in the majority of patients; persistent or periodic eosinophilia has also been commonly described (Wildin et al., 2002). In contrast, IgG, M, and A levels are generally normal, although they may decrease over time due to a progressive loss of protein through the bowel caused by the enteropathy. Most patients generate a variety of autoantibodies against different organs including thyroid, pancreatic islets, erythrocytes, platelets, smooth muscle, and intestine. Autoantibodies to a novel 75 kDa gut and kidney‐specific antigen, AIE‐75, have been described in IPEX patients (Kobayashi et al., 1998, 1999). Antinuclear antibodies are either absent or present at low titer
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(Baud et al., 2001; Powell et al., 1982). The total lymphocyte count and T/B lymphocyte subsets are generally within the normal range (Baud et al., 2001; Di Rocco and Marta, 1996; Ferguson et al., 2000; Jonas et al., 1991; Peake et al., 1996). In one case, reported by Satake and coworkers (1993), CD4þ lymphocytes were elevated at birth, and predominantly naı¨ve; activation markers (HLA‐DRþ and CD25þ) increased over time, in association with clinical deterioration. The in vitro lymphocyte proliferation to mitogens and specific antigens is generally normal in most of the patients. Only one patient with increased responses to mitogens and enhanced IL‐2 production has been reported (Shigeoka et al., 1991). In a single family, one affected male had low T cell responses to mitogens, a second showed a poor response to immunization with diphteria and tetanus toxoid, and a third was found to have normal antibody responses to protein antigens, but defective response to pneumococcal polysaccharides (Ferguson et al., 2000), thus revealing a significant variability in the immune defect of IPEX patients even within the same family. Two reports have described increased response of peripheral mononuclear cells to in vitro activation, associated with production of high levels of Th2 cytokines and decreased production of the Th1 cytokine interferon‐g (IFN‐g) (Chatila et al., 2000; Nieves et al., 2004; Powell et al., 1982). Patients with IPEX have normal neutrophil function and normal complement levels. However, caution must be used when interpreting data regarding the immunological responses of IPEX patients since most are already on immunosuppressive treatment at the time of immunological evaluation. 4.1.5. Treatment In order to target T cell activation, the use of immunosuppressive agents such as cyclosporin A and FK506, either alone or in combination with steroids, constitute the best available choice for treatment of IPEX patients (Ferguson et al., 2000; Kobayashi et al., 1995, 2001). Most patients respond at least temporarily to immunosuppressive treatment with steroids and/or cyclosporin A, which may attenuate or delay the clinical course. However, these drugs often fail to sustain long‐term remission of symptoms. Use of rapamycin has been recently advocated as a possibly better alternative (Battaglia et al., 2005). In any case, chronic immunosuppression often leads to drug toxicity and increases the chance of severe or opportunistic infections. Use of rituximab (anti‐CD20 monoclonal antibody) has been reported in patients where autoantibody‐mediated symptoms are predominant. Supportive therapy with total parenteral nutrition, insulin, and blood transfusion is frequently required. Intravenous immunoglobulins are used in patients with evidence of primary or secondary antibody deficiency.
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Up to now, HSCT is the only effective cure for the disease. At least four cases of IPEX patients who received HSCY from an HLA identical sibling have been reported in the literature. One boy received HSCT at four months of age from his HLA‐identical sister, who was not a carrier (Baud et al., 2001). Remission began during the conditioning phase that consisted of anti‐ T‐lymphocyte globulin, busulfan, and cyclophosphamide, and continued after the transplant. Enteropathy, type I diabetes, and eczema were all resolved. The patient remained in a complete remission of symptoms for 29 months, despite the fact that only 20–30% of the T cells were of donor origin. Subsequently he developed a rapidly progressive haemophagocytic syndrome and died suddenly when he was nearly three years old. Two other affected males, reported by Wildin and coworkers (2002), received HSCT as a final choice after developing life‐threatening complications of long‐term immunosuppressant medications. Although both died from infectious complications of their transplants, their symptoms showed marked improvement. Recently, we performed transplantation of allogenic bone marrow from an HLA identical family member in a one‐year‐old boy with IPEX who failed therapy with steroids and cyclosporin A (Mazzolari et al., 2005a). The patient achieved a complete clinical and immunological remission of his diseases after transplantation and at 20 months after HSCT is still asymptomatic. Engraftment studies showed the presence of a stable, mixed host/donor chimerism throughout remission indicating that, despite previous unsuccessful attempts, partial chimerism is sufficient to obtain a complete rescue of IPEX, as also shown in a transplantation model in the scurfy mouse. This experience confirms that HSCT is so far the only effective and definitive cure for this otherwise fatal disease. 4.2. The Mouse Model for IPEX ‘‘Scurfy’’ is an X‐linked recessive mouse mutant which was first described in 1949 and that occurred spontaneously in a partially inbred strain of mice at the Oak Ridge National Laboratory (Russell, 1959). IPEX shares many phenotypic features with the scurfy mice. Affected mice tend to be smaller and appear sick early after birth. They present with X‐linked recessive inheritance of scaly skin, small‐thickened ears, marked runting secondary to diarrhea and malabsorption, progressive anemia, thrombocytopenia, leucocytosis, lymphadenopathy, and hepatosplenomegaly. Scurfy mice typically die by three to four weeks of age. The thymus is typically small for age, but has normal cellular architecture. There is massive infiltration of activated lymphocytes into the liver as well as into lymph nodes and spleen, which have abnormal cellular architecture. Previous studies in scurfy mice have demonstrated that the clinical phenotype
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is the result of immune dysregulation (Godfrey et al., 1991; Lyon et al., 1990). The lymphoproliferative disease is mediated by CD4þCD8 T lymphocytes constitutively activated in affected males, as suggested by spontaneous expression of activation markers (CD69, CD25, CD80, and CD86) and by increased levels of cytokine production. Although scurfy T cells are hyperresponsive to T cell receptor (TCR) ligation, they still require costimulation through CD28, even if at decreased intensity (Blair et al., 1994; Clark et al., 1999; Kanangat et al., 1996). Interestingly, T cell activation in scurfy mice is not downregulated by inhibitors of tyrosine kinases, such as the immune‐suppressant cyclosporine A (Clark et al., 1999). Both depletion and adoptive transfer experiments have indicated that CD4þ T cells are primarily responsible for the disease phenotype in mice. Moreover, Foxp3 overexpression studies carried out on different transgenic mice resulted in reduction of lymphoid organ size as well as of CD4þ T lymphocyte number. CD4þ T cells from these transgenic mice also display decreased proliferative responses and markedly diminished IL‐2 production following in vitro activation, indicating the crucial role played by Foxp3 in regulating their ability to respond to TCR‐mediated signals (Kasprowicz et al., 2003; Khattri et al., 2001). Recent works in murine models highlighted that Foxp3 is preferentially expressed in the CD4þCD25þ Treg cells and that these cells are absent in the scurfy mouse, strongly suggesting that the lack of Treg cells is most likely responsible for the defect observed in downregulation of T cell activation (Fontenot et al., 2003; Hori et al., 2003; Khattri et al., 2003). 4.3. Molecular and Cellular Pathophysiology of IPEX 4.3.1. Molecular Aspects of IPEX and Scurfy Brunkow and coworkers (2001) identified the gene defective in scurfy mice. The protein (scurfin) encoded by this gene, designated Foxp3 (FOXP3 in humans), is a member of the forkhead/winged‐helix family of transcriptional regulators and is highly conserved in humans. Scurfin has several interesting structural features including a proline‐rich domain at the N‐terminus, a zinc finger, and a leucine zipper, conserved structural motifs involved in protein– protein interactions located within the central portion, and a forkhead DNA‐ binding domain at the C‐terminus embracing a putative nuclear localization signal at the C‐terminal portion (Clark et al., 1993; Kaestner, Knochel, and Martinez, 2000; Qian and Costa, 1995). In most members of the FOX family of transcription factors, the forkhead domain is located near the amino terminus, but in Foxp3 the forkhead domain is uniquely positioned at the C terminus (amino acids residues 337–420) (Brunkow et al., 2001). Proteins bearing
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forkhead DNA‐binding motifs consist of a large family of related molecules that play diverse roles in enhancing or suppressing transcription from specific binding sites. Several members of this protein family are involved in cell lineage commitment and developmental differentiation. Two other members of Foxp subfamily, Foxp1 and Foxp2, have been shown to act as transcriptional repressors in the lung (Shu et al., 2001). At present there is very little understanding of the function of Foxp3 at the molecular level. Foxp3 binds DNA, localizes to the nucleus, and can act as a transcriptional repressor. In fact, as demonstrated by Khattri and coworkers (2001), the overexpression of scurfin in mice leads to a significant repression of the immune function, suggesting a possible role as a repressor of transcription in T cells. Moreover, identification of consensus forkhead binding domains nearby to Nuclear‐ Factor‐of‐Activated‐T cells (NFAT) transcription factor binding sites in the promoter of several cytokine genes, suggests a possible competition between NFAT and Foxp3 for the control of the expression of genes involved in T cell activation (Schubert et al., 2001). Based on these and other findings, it has also been proposed that Foxp3 is induced in different cell types as a general mechanism of negative immune regulation, through repression of multiple cytokines production. A recent study indicates how Foxp3 interacts with NF‐ kB and NFAT protein, and as a consequence, inhibits IL‐2, IL‐4, and IFN‐g production by CD4þ effector T cells (Bettelli et al., 2005). However, so far there is no clear evidence of Foxp3 target genes, and the mechanisms by which it controls transcription of target genes have not been completely characterized. The human FOXP3 gene is located at Xp11.23 and consists of 11 translated exons that encode a protein of 431 amino acids and 429 amino acids in mice, with a high level of evolutionary conservation (86% identity). FOXP3 is expressed at high levels in thymus, spleen, and lymph nodes. Analysis of the subpopulations of purified lymphocytes shows that FOXP3 is predominantly expressed in CD4þCD25þ Treg lymphocytes. In mice, Foxp3 is expressed at low levels in CD4þCD25 cells but not in CD8þ cells (Bennett et al., 2001b; Hori et al., 2003); human CD8þ cells can express FOXP3, although typically at lower levels (Cosmi et al., 2003; Walker et al., 2003). Identification of the genes responsible for IPEX and for the scurfy phenotype has allowed mutation analysis in the patients and in the murine model of the disease. The spontaneous scurfy mutation is the result of two base‐pair insertion leading to a frameshift and loss of the entire forkhead domain. Based on this finding, affected members from different families who suffer from a disease resembling IPEX were studied for mutation of the FOXP3 gene.
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Figure 8 Schematic representation of the FOXP3 gene, the encoded proteins, and of the mutations identified in patients with IPEX. Panel A: Representation of the FOXP3 gene. Exons are identied by solid boxes. Locations of the mutations identified in IPEX patients are also shown, and the correspondence between symbols and type of mutations is illustrated in the legend. Panel B: Linear organization of the functional domains of the FOXP3 protein. Panel C: Description of the mutations identified in IPEX patients. For each mutation, the genomic abnormality, and the corresponding effect on protein structure and sequence, are shown, along with appropriate quotations from the literature.
Mutations within the FOXP3 gene reported to date in different families are shown in Fig. 8. The majority of these are missense mutations within the C‐terminal forkhead DNA binding domain, but there are also mutations affecting the leucine zipper and the N‐terminal proline‐rich domain, demonstrating their importance for FOXP3 function (Bennett et al., 2001b; Chatila et al., 2000; Gambineri et al., 2003; Kobayashi et al., 2001; Wildin et al., 2001). In particular, the other mutations reported outside of the forkhead domain include one deletion in exon 2 at nucleotide 227 (Kobayashi et al., 2001; Owen et al., 2003), causing frame‐shift and early termination; two different deletions of 3‐bp each involving nucleotides 747–749 and 750–752 respectively, within exon 7, presumably altering the function of the leucine‐zipper domain (Chatila et al., 2000; Wildin et al., 2002); an A to G transition at position þ4 of intron 8 that causes exon 9 skipping, resulting in frame‐shift and early termination (Chatila et al., 2000); and two deletions that remove the stop codon and create
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products with C‐terminal extensions (Bennett et al., 2001b; Wildin et al., 2001). Phenotypically, every patient with one of these FOXP3 mutations has classic IPEX and the symptomatic differences are unremarkable. Two other mutations, one within an intron/exon splice junction and one in the first polyadenylation signal of the gene, tend to lead to a milder, late‐onset form of the disease (Bennett et al., 2001a; Gambineri et al., 2003). 4.3.2. CD4þCD25þ Regulatory T Cells Naturally arising CD4þCD25þ regulatory T cells are a CD4þ T cell subpopulation (5–10% of peripheral CD4þ T cells) that is highly specialized for suppressive function. These cells play a key role not only in maintenance of self‐tolerance, but also in the control of aberrant or excessive immune responses to invading or commensal microbes and to innocuous environmental substances (Levings and Roncarolo, 2005). Deficiency or dysfunction of these cells can be a cause of autoimmune or other inflammatory diseases in animals and humans. CD4þCD25þTreg cells are produced by normal thymus as a functionally distinct and mature T cell subpopulation and are not induced de novo from naı¨ve T cells after antigen exposure in the periphery. CD4þCD25þTreg cells constitutively express the CD25 molecule (IL‐2 receptor a‐chain), and are anergic. However, upon activation, they suppress proliferation and IL‐2 production by memory and naı¨ve CD4þ T cells, through a cell‐mediated and cytokine‐independent mechanism (Sakaguchi, 2004; Sakaguchi et al., 2001). Recent reports indicated that Treg cell‐mediated suppression can be overridden by large amounts of IL‐2 (Shevach, 2002). It should be noted that the concentration of IL‐2 present in the environment is a critical determinant of Treg cell function. In fact, IL‐2 is also required for CD4þCD25þ Treg cell suppressive activity, since this function can be abrogated in the presence of IL‐2 neutralizing antibody (de la Rosa et al., 2004; Thornton et al., 2004). Altogether, these data suggest the possibility of a regulatory network where the function of Treg cells is conditional on IL‐2 production by non‐regulatory T cells. Moreover, specific TCR stimulation is necessary for Treg function as shown by studies on TCR‐transgenic mice, which develop organ‐specific autoimmunity. In addition, Treg cells isolated from organ‐draining lymph nodes are more efficient in mediating protection against organ‐specific autoimmunity as compared to Treg cells found elsewhere (Fontenot and Rudensky, 2005; Green et al., 2002). Costimulatory signals mediated by CD28 engagement of CD80 and CD86 are also important in the generation of Treg cells in the thymus, and presumably play a role in survival of Treg cells in the periphery. In fact,
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CD4þCD25þ T reg cells are reduced in the absence of CD28–CD80 or CD28– CD86 interaction (Tai et al., 2005). Recent works in murine models have revealed the specific role of Foxp3 in development and function of CD4þCD25þ Treg cells. It has been demonstrated that Foxp3 is preferentially expressed in CD4þCD25þ Treg cells and that these cells are absent in the scurfy mouse, thus strongly suggesting that the absence of Treg cells is responsible for the lack of downregulation of effector lymphocytes in the scurfy mouse. Moreover, murine CD4þCD25 cells, if activated in vitro, do not express Foxp3 and do not acquire suppressor activity, despite the expression of CD25 on their surface (Fontenot et al., 2003; Hori et al., 2003; Khattri et al., 2003). In contrast, human CD4þCD25 cells can be activated in vitro to express FOXP3 and to suppress T cell proliferation (Walker et al., 2003). The importance of CD4þCD25þ Treg cells for the maintenance of immune homeostasis has been previously demonstrated by depletion of this subpopulation from healthy mice. These animals spontaneously develop various T cell‐mediated autoimmune diseases, such as thyroiditis, gastritis, and type I diabetes. Reconstitution of the depleted mice with CD4þCD25þ T cells promptly suppresses the development of multi‐ organ autoimmunity (Sakaguchi et al., 2001). Furthermore, retroviral transduction or transgenic expression studies of Foxp3 in murine CD4þCD25 T lymphocytes phenotypically and functionally converts them to Treg cells that are able to suppress proliferation of other T cells in vitro as well as to prevent the development of autoimmune diseases in vivo (Fontenot et al., 2003; Hori et al., 2003; Khattri et al., 2003). Based on these findings, FOXP3 seems to play a crucial role in the maintenance of the immune homeostasis, by controlling the development and function of CD4þCD25þ Treg cells. Thus, the scurfy mouse and the human disease IPEX constitute a significant model not only to better understand the developmental process and the mechanism of suppression mediated by CD4þCD25þ Treg cells, but also to elucidate how the function of these cells is modulated. 5. Concluding Remarks Far from being at the opposite ends of immunopathology, immune deficiency and autoimmunity may actually go hand‐in‐hand, both being examples of immune dysregulation. Careful analysis of autoimmune manifestations associated with PID has shown that they are heterogeneous in nature, ranging from organ‐specific autoimmunity to systemic manifestations. Furthermore, it has been appreciated that the mechanisms involved in autoimmunity associated with PID are also variable, and may be related to defective central or
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peripheral tolerance, inability to clear pathogens and extinguish inflammatory reactions, or inadequate removal of immune complexes. In spite of their rarity, PID continues to represent an extraordinary model to dissect human immunopathology. In particular, the study of two unique forms of PID with associated autoimmunity (APECED and IPEX) has revealed the crucial role played by transcriptional regulators in central and peripheral tolerance. These achievements have not only led to a better understanding of the molecular and cellular mechanisms underlying APECED and IPEX, but have allowed more accurate investigation of the basis of autoimmunity associated with other forms of PID as well. Thus, recognition that active thymopoiesis is essential for normal expression of AIRE and of tissue‐specific antigens in the thymus (both critical for induction of central tolerance), has led to the identification that failure in this mechanism is responsible for autoimmunity of Omenn syndrome, a combined immune deficiency with very severe immune dysregulation. It is likely that the same mechanism also applies to other forms of defective T cell development associated with autoimmunity, and complete DiGeorge syndrome in particular. On the other hand, detailed studies of patients with IPEX and of the murine model (the scurfy mouse) have revealed the critical role played by FOXP3, a transcriptional repressor of immune response, required for the generation of CD4þCD25þ regulatory T cells and peripheral immune homeostasis. Important studies on the murine model indicate that if Foxp3 is mutated, Treg cells cannot develop, thus causing autoimmune lymphoproliferative phenomena. Thus, IPEX/scurfy provides an ideal model to study immune dysregulation and the role played by regulatory T cells in controlling autoimmune and lymphoproliferative disease development. Further investigation of the structure, function, and regulation of the FOXP3 gene product will allow a better understanding of its role in generating regulatory T cells and will provide new insights in comprehending the mechanism of immune tolerance. Already at this stage, however, it is possible to envisage the use of Treg cells not only in the treatment of autoimmune diseases, but even to control alloreactivity (Hauben et al., 2005). Finally, characterization of the molecular and cellular defects that are responsible for these rare monogenic disorders of immunodeficiency associated with autoimmunity has important implications also for a better understanding of the more common autoimmune disorders, since they indicate two crucial steps (central tolerance and peripheral immune homeostasis), whose abnormalities may contribute to the multifactorial nature of most autoimmune diseases.
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Acknowledgments This work was partially supported by Ministero dell’Istruzione dell’Universita` e della Ricerca (MIUR)‐COFIN 2004, European Union (EUROPOLICY‐PID grant, SP23‐CT‐2005–006411), and MIUR‐Fondo per gli Investimenti della Ricerca di Base (FIRB) to L.D.N., by Fondazione Berlucchi to LDN, PF2003 from Min‐Salute to LDN and RB, Telethon Italia Grant No. GGP0485 to RB and to EG.
References Aaltonen, J., Bjorses, P., Sandkuijl, L., Perheentupa, J., and Peltonen, L. (1994). An autosomal locus causing autoimmune disease: Autoimmune polyglandular disease type I assigned to chromosome 21. Nat. Genet. 8, 83–87. Ahonen, P., Myllarniemi, S., Sipila, I., and Perheentupa, J. (1990). Clinical variation of autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy (APECED) in a series of 68 patients. N. Engl. J. Med. 322, 1829–1836. Aleman, K., Noordzij, J. G., de Groot, R., et al. (2001). Reviewing Omenn syndrome. Eur. J. Pediatr. 160, 718–725. Anderson, M. S., Venanzi, E. S., Klein, L., Chen, Z., Berzins, S. P., Turley, S. J., von Boehmer, H., Bronson, R., Dierich, A., Benoist, C., and Mathis, D. (2002). Projection of an immunological self shadow within the thymus by the aire protein. Science 298, 1395–1401. Arkwright, P. D., Abinun, M., and Cant, A. J. (2002). Autoimmunity in human primary immunodeficiency diseases. Blood 99, 2694–2702. Arvanitakis, C., and Knouss, R. F. (1973). Selective hypopituitarism. Impaired cell‐mediated immunity and chronic mucocutaneous candidiasis. JAMA: The Journal of the American Medical Association 225, 1492–1495. Barton, L. L., Moussa, S. L., Villar, R. G., and Hulett, R. L. (1998). Gastrointestinal complications of chronic granulomatous disease: Case report and literature review. Clin. Pediatr. 37, 231–236. Battaglia, M., Stabilini, A., and Roncarolo, M. G. (2005). Rapamycin selectively expands CD4þ CD25þ FoxP3þ regulatory T cells. Blood 105, 4743–4748. Baud, O., Goulet, O., Canioni, D., Le Deist, F., Radford, I., Rieu, D., Dupuis‐Girod, S., Cerf‐ Bensussan, N., Cavazzana‐Calvo, M., Brousse, N., Fischer, A., and Casanova, J. L. (2001). Treatment of the immune dysregulation, polyendocrinopathy, enteropathy, X‐linked syndrome (IPEX) by allogeneic bone marrow transplantation. N. Engl. J. Med. 344, 1758–1762. Bennett, C. L., Brunkow, M. E., Ramsdell, F., O’Briant, K. C., Zhu, Q., Fuleihan, R. L., Shigeoka, A. O., Ochs, H. D., and Chance, P. F. (2001a). A rare polyadenylation signal mutation of the FOXP3 gene (AAUAAA–>AAUGAA) leads to the IPEX syndrome. Immunogenetics 53, 435–439. Bennett, C. L., Christie, J., Ramsdell, F., Brunkow, M. E., Ferguson, P. J., Whitesell, L., Kelly, T. E., Saulsbury, F. T., Chance, P. F., and Ochs, H. D. (2001b). The immune dysregulation, polyendocrinopathy, enteropathy, X‐linked syndrome (IPEX) is caused by mutations of FOXP3. Nat. Genet. 27, 20–21. Bennett, C. L., Yoshioka, R., Kiyosawa, H., Barker, D. F., Fain, P. R., Shigeoka, A. O., and Chance, P. F. (2000). X‐Linked syndrome of polyendocrinopathy, immune dysfunction, and diarrhoea maps to Xp11.23‐Xq13.3. Am. J. Hum. Genet. 66, 461–468. Bettelli, E., Dastrange, M., and Oukka, M. (2005). Foxp3 interacts with nuclear factor of activated T cells and NF‐kappa B to repress cytokine gene expression and effector functions of T helper cells. Proc. Natl. Acad. Sci. USA 102, 5138–5143.
360
L U I G I D . N O TA R A N G E L O E T A L .
Betterle, C., Dal Pra, C., Mantero, F., and Zanchetta, R. (2002). Autoimmune adrenal insufficiency and autoimmune polyendocrine syndromes: Autoantibodies, autoantigens, and their applicability in diagnosis and disease prediction. Endocr. Rev. 23, 327–364. Bjorses, P., Halonen, M., Palvimo, J. J., Kolmer, M., Aaltonen, J., Ellonen, P., Perheentupa, J., Ulmanen, I., and Peltonen, L. (2000a). Mutations in the AIRE gene: Effects on subcellular location and transactivation function of the autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy protein. Am. J. Hum. Genet. 66, 378–392. Bjorses, P., Halonen, M., Palvimo, J. J., Kolmer, M., Aaltonen, J., Ellonen, P., Perheentupa, J., Ulmanen, I., and Peltonen, L. (2000b). Mutations in the AIRE gene: Effects on subcellular location and transactivation function of the autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy protein. Am. J. Hum. Genet. 66, 378–392. Blair, P. J., Bultman, S. J., Haas, J. C., Rouse, B. T., Wilkinson, J. E., and Godfrey, V. L. (1994). CD4 þCD8‐ T cells are the effector cells in disease pathogenesis in the scurfy (sf) mouse. J. Immunol. 153, 3764–3774. Boehm, T., Scheu, S., Pfeffer, K., and Bleul, C. C. (2003). Thymic medullary epithelial cell differentiation, thymocyte emigration, and the control of autoimmunity require lympho‐epithelial cross talk via LTbetaR. J. Exp. Med. 198, 757–769. Bottomley, M. J., Stier, G., Pennacchini, D., Legube, G., Simon, B., Akhtar, A., Sattler, M., and Musco, G. (2005). NMR structure of the first PHD finger of autoimmune regulator protein (AIRE1). Insights into autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy (APECED) disease. J. Biol. Chem. 280, 11505–11512. Brugnoni, D., Airo`, P., Facchetti, F., Blanzuoli, L., Ugazio, A. G., Cattaneo, R., and Notarangelo, L. D. (1997). In vitro cell death of activated lymphocytes in Omenn’s syndrome. Eur. J. Immunol. 27, 2765–2773. Brunkow, M. E., Jeffery, E. W., Hjerrild, K. A., Paeper, B., Clark, L. B., Yasayko, S. A., Wilkinson, J. E., Galas, D., Ziegler, S. F., and Ramsdell, F. (2001). Disruption of a new forkhead/winged‐ helix protein, scurfin, results in the fatal lymphoproliferative disorder of the scurfy mouse. Nat. Genet. 27, 68–73. Buzi, F., Badolato, R., Mazza, C., Giliani, S., Notarangelo, L. D., Radetti, G., Plebani, A., and Notarangelo, L. D. (2003). Autoimmune Polyendocrinopathy‐Candidiasis‐Ectodermal Dystrophy Syndrome: Time to review diagnostic criteria? J. Clin. Endocrinol. Metab. 88, 3146–3148. Callebaut, I., and Mornon, J. P. (1998). The VDJ recombination activating protein rag2 consists of a six‐bladed propeller and PHD finger‐like domain, as revealed by sequence analysis. Cell. Mol. Life 54, 880–891. Candotti, F., Notarangelo, L., Visconti, R., and O’Shea, J. (2002). Molecular aspects of primary immunodeficiencies: Lessons from cytokine and other signaling pathways. J. Clin. Invest. 109, 1261–1269. Cavadini, P., Vermi, W., Facchetti, F., Fontana, S., Nagafuchi, S., Mazzolari, E., Sediva, A., Marrella, V., Villa, A., Fischer, A., Notarangelo, L. D., and Badolato, R. (2005). AIRE deficiency in thymus of 2 patients with Omenn syndrome. J. Clin. Invest. 115, 728–732. Chatila, T. A., Blaeser, F., Ho, N., Lederman, H. M., Voulgaropoulos, C., Helms, C., and Bowcock, A. M. (2000). JM2, encoding a fork head‐related protein, is mutated in X‐linked autoimmunity‐ allergic disregulation syndrome. J. Clin. Invest. 106, R75–R81. Chilosi, M., Facchetti, F., Notarangelo, L. D., Romagnani, S., Del Prete, G., Almerigogna, F., De Carli, F., and Pizzolo, G. (1996). CD30 cell expression and abnormal soluble CD30 serum accumulation in Omenn’s syndrome: Evidence for a T helper‐2 mediated condition. Eur. J. Immunol. 26, 329–334.
IMMUNODEFICIENCIES WITH AUTOIMMUNITY
361
Chin, R. K., Lo, J. C., Kim, O., Blink, S. E., Christiansen, P. A., Peterson, P., Wang, Y., Ware, C., and Fu, Y. X. (2003). Lymphotoxin pathway directs thymic Aire expression. Nat. Immunol. 4, 1121–1127. Clark, K. L., Halay, E. D., Lai, E., and Burley, S. K. (1993). Co‐crystal structure of the HNF‐3/fork head DNA‐recognition motif resembles histone H5. Nature 364, 412–420. Clark, L. B., Appleby, M. W., Brunkow, M. E., Wilkinson, J. E., Ziegler, S. F., and Ramsdell, F. (1999). Cellular and molecular characterization of the scurfy mouse mutant. J. Immunol. 162, 2546–2554. Clark, R., and Griffiths, G. M. (2003). Lytic granules, secretory lysosomes, and disease. Curr. Opin. Immunol. 516–521. Clemente, M. G., Meloni, A., Obermayer‐Straub, P., Frau, F., Manns, M. P., and De Virgiliis, S. (1998). Two cytochromes P450 are major hepatocellular autoantigens in autoimmune polyglandular syndrome type 1. Gastroenterology 114, 324–328. Clemente, M. G., Obermayer‐Straub, P., Meloni, A., Strassburg, C. P., Arangino, V., Tukey, R. H., De Virgiliis, S., and Manns, M. P. (1997). Cytochrome P450 1A2 is a hepatic autoantigen in autoimmune polyglandular syndrome type 1. J. Clin. Endocrinol. Metab. 82, 1353–1361. Cocco, C., Meloni, A., Boi, F., Pinna, G., Possenti, R., Mariotti, S., and Ferri, G. L. (2005). Median eminence dopaminergic nerve terminals: A novel target in autoimmune polyendocrine syndrome? J. Clin. Endocrinol. Metab. 90, 4108–4111. Corneo, B., Moshous, D., Gungor, T., Wulfraat, N., Philippet, F. L., Le Deist, A., Fischer, A., and de Villartay, J. P. (2001). Identical mutations in RAG1 or RAG2 genes leading to defective V(D)J recombinase activity can cause either T‐B‐severe combined immune deficiency or Omenn syndrome. Blood 97, 2772–2776. Cosmi, L., Liotta, F., Lazzeri, E., Francalanci, M., Angeli, R., Mazzinghi, B., Santarlasci, V., Manetti, R., Vanini, V., Romagnani, P., Maggi, E., Romagnani, S., and Annunziato, F. (2003). Human CD8þCD25þ thymocytes share phenotypic and functional features with CD4þCD25þ regulatory thymocytes. Blood 102, 4107–4114. Dalal, I., Tabori, U., Bielorai, B., Golan, H., Rosenthal, E., Amariglio, N., Rechavi, G., and Toren, A. (2005). Evolution of T‐B‐SCID into Omenn syndrome phenotype following parainfluenza 3 virus infection. Clin. Immunol. 115, 70–73. de la Rosa, M., Rutz, S., Dorninger, H., and Scheffold, A. (2004). Interleukin‐2 is essential for CD4þCD25þ regulatory T cell function. Eur. J. Immunol. 34, 2480–2488. Denianke, K. S., Frieden, I. J., Cowan, M. J., Williams, M. L., and McCalmont, T. H. (2001). Cutaneous manifestations of maternal engraftment in patients with severe combined immunodeficiency: A clinicopathological study. Bone Marrow Transplant. 28, 227–233. Derbinski, J., Gabler, J., Brors, B., Tierling, S., Jonnakuty, S., Hergenhahn, M., Peltonen, L., Walter, J., and Kyewski, B. (2005). Promiscuous gene expression in thymic epithelial cells is regulated at multiple levels. J. Exp. Med. 202, 33–45. de Saint Basile, G., Le Deist, F., de Villartay, J. P., Cerf‐Bensussan, N., Journet, O., Brousse, N., Griscelli, C., and Fischer, A. (1991). Restricted heterogeneity of T lymphocytes in combined immunodeficiency with hypereosinophilia (Omenn’s syndrome). J. Clin. Invest. 87, 1352–1359. Di Rocco, M., and Marta, R. (1996). X linked immune dysregulation, neonatal insulin dependent diabetes, and intractable diarrhoea. Arch. Dis. Child Fetal Neonatal Ed. 75, F144. Ege, M., Ma, Y., Manfras, B., Kalwak, K., Lu, H., Lieber, M. R., Schwarz, K., and Pannicke, U. (2005). Omenn syndrome due to ARTEMIS mutations. Blood 105, 4179–4186. Ekwall, O., Hedstrand, H., Grimelius, L., Haavik, J., Perheentupa, J., Gustafsson, J., Husebye, E., Kampe, O., and Rorsman, F. (1998). Identification of tryptophan hydroxylase as an intestinal autoantigen. Lancet 352, 279–283.
362
L U I G I D . N O TA R A N G E L O E T A L .
Etzioni, A. (2003). Immune deficiency and autoimmunity. Autoimmunity Reviews 2, 364–369. Facchetti, F., Blanzuoli, L., Ungari, M., Alebardi, O., and Vermi, W. (1998). Lymph node pathology in primary combined immunodeficiency diseases. Springer Semin. Immunopathol. 19, 459–478. Ferguson, P. J., Blanton, S. H., Saulsbury, F. T., McDuffie, M. J., Lemahieu, V., Gastier, J. M., Francke, U., Borowitz, S. M., Sutphen, J. L., and Kelly, T. E. (2000). Manifestations and linkage analysis in X‐linked autoimmunity‐immunodeficiency syndrome. Am. J. Med. Genet. 90, 390–397. Fontenot, J. D., Gavin, M. A., and Rudensky, A. Y. (2003). Foxp3 programs the development and function of CD4þCD25þ regulatory T cells. Nat. Immunol. 4, 330–336. Fontenot, J. D., and Rudensky, A. Y. (2005). A well adapted regulatory contrivance: Regulatory T cell development and the forkhead family transcription factor Foxp3. Nat. Immunol. 6, 331–337. Franzese, A., Valerio, G., Di Maio, S., Iannucci, M. P., Bloise, A., and Tenore, A. (1999). Growth hormone insufficiency in a girl with the autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy. J. Endocrinol. Invest. 22, 66–69. Frucht, D. M., Gadina, M., Jagadees, G. J., Aksentijevic, I., Takata, K., Blessing, J., Nelson, J., Muul, L. M., Perham, T. G. M., Morgan, G., Gerritsne, E. J. A., Schumacher, R. F., Mella, P., Veys, P., Fleisher, T. A., Kaminsky, E. R., Notarangelo, L. D., O’Shea, J. J., and Candotti, F. (2001). Unexpected and variable phenotypes in a family with JAK3 deficiency. Genes Immun. 2, 422–432. Gambineri, E., Torgerson, T. R., and Ochs, H. D. (2003). Immune dysregulation, polyendocrinopathy, enteropathy, and X‐linked inheritance (IPEX), a syndrome of systemic autoimmunity caused by mutations of FOXP3, a critical regulator of T cell homeostasis. Curr. Opin. Rheumatol. 15, 430–435. Gennery, A. R., Hodges, E., Williams, A. P., Harris, S., Villa, A., Angus, B., Cant, A. J., and Smith, J. L. (2005). Omenn’s syndrome occurring in patients without mutations in recombinase activating genes. Clin. Immunol. 116, 246–256. Godfrey, V. L., Wilkinson, J. E., and Russell, L. B. (1991). X‐linked lymphoreticular disease in the scurfy (sf) mutant mouse. Am. J. Pathol. 138, 1379–1387. Gomez, C. A., Ptaszek, L. M., Villa, A., Bozzi, F., Sobacchi, C., Brooks, E. G., Notarangelo, L. D., Spanopoulou, E., Pan, Z. Q., Vezzoni, P., Cortes, P., and Santagata, S. (2000). Mutations in conserved regions of the predicted RAG2 kelch repeats block initiation of V(D)J recombination and result in primary immunodeficiencies. Mol. Cell. Biol. 20, 5653–5664. Green, E. A., Choi, Y., and Flavell, R. A. (2002). Pancreatic lymph node‐derived CD4(þ)CD25(þ) Treg cells: Highly potent regulators of diabetes that require TRANCE‐RANK signals. Immunity 16, 183–191. Gylling, M., Kaariainen, E., Vaisanen, R., Kerosuo, L., Solin, M. L., Halme, L., Saari, S., Halonen, M., Kampe, O., Perheentupa, J., and Miettinen, A. (2003). The hypoparathyroidism of autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy: Protective effect of male sex. J. Clin. Endocrinol. Metab. 88, 4602–4608. Gylling, M., Tuomi, T., Bjorses, P., Kontiainen, S., Partanen, J., Christie, M. R., Knip, M., Perheentupa, J., and Miettinen, A. (2000). ss‐cell autoantibodies, human leukocyte antigen II alleles, and type 1 diabetes in autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy. J. Clin. Endocrinol. Metab. 85, 4434–4440. Halonen, M., Eskelin, P., Myhre, A. G., Perheentupa, J., Husebye, E. S., Kampe, O., Rorsman, F., Peltonen, L., Ulmanen, I., and Partanen, J. (2002). AIRE mutations and human leukocyte antigen genotypes as determinants of the autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy phenotype. J. Clin. Endocrinol. Metab. 87, 2568–2574.
IMMUNODEFICIENCIES WITH AUTOIMMUNITY
363
Halonen, M., Kangas, H., Ruppell, T., Ilmarinen, T., Ollila, J., Kolmer, M., Vihinen, M., Palvimo, J., Saarela, J., Ulmanen, I., and Eskelin, P. (2004). APECED‐causing mutations in AIRE reveal the functional domains of the protein. Hum. Mutat. 23, 245–257. Halonen, M., Pelto‐Huikko, M., Eskelin, P., Peltonen, L., Ulmanen, I., and Kolmer, M. (2001). Subcellular location and expression pattern of autoimmune regulator (Aire), the mouse orthologue for human gene defective in autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED). J. Histochem. Cytochem. 49, 197–208. Hauben, E., Bacchetta, R., and Roncarolo, M. G. (2005). Utilizing regulatory T cells to control alloreactivity. Cytotherapy 7, 158–165. Hedstrand, H., Ekwall, O., Haavik, J., Landgren, E., Betterle, C., Perheentupa, J., Gustafsson, J., Husebye, E., Rorsman, F., and Kampe, O. (2000). Identification of tyrosine hydroxylase as an autoantigen in autoimmune polyendocrine syndrome type I. Biochem. Biophys. Res. Commun. 267, 456–461. Hedstrand, H., Ekwall, O., Olsson, M. J., Landgren, E., Kemp, E. H., Weetman, A. P., Perheentupa, J., Husebye, E., Gustafsson, J., Betterle, C., Kampe, O., and Rorsman, F. (2001). The transcription factors SOX9 and SOX10 are vitiligo autoantigens in autoimmune polyendocrine syndrome type I. J. Biol. Chem. 276, 35390–35395. Heino, M., Peterson, P., Kudoh, J., Nagamine, K., Lagerstedt, A., Ovod, V., Ranki, A., Rantala, I., Nieminen, M., Tuukkanen, J., Scott, H. S., Antonarakis, S. E., Shimizu, N., and Krohn, K. (1999a). Autoimmune regulator is expressed in the cells regulating immune tolerance in thymus medulla. Biochem. Biophys. Res. Commun. 257, 821–825. Heino, M., Peterson, P., Kudoh, J., Shimizu, N., Antonarakis, S. E., Scott, H. S., and Krohn, K. (2001). APECED mutations in the autoimmune regulator (AIRE) gene. Hum. Mutat. 18, 205–211. Heino, M., Peterson, P., Sillanpaa, N., Guerin, S., Wu, L., Anderson, G., Scott, H. S., Antonarakis, S. E., Kudoh, J., Shimizu, N., Jenkinson, E. J., Naquet, P., and Krohn, K. J. (2000). RNA and protein expression of the murine autoimmune regulator gene (Aire) in normal, RelB‐deficient and in NOD mouse. Eur. J. Immunol. 30, 1884–1893. Heino, M., Scott, H. S., Chen, Q., Peterson, P., Maebpaa, U., Papasavvas, M. P., Mittaz, L., Barras, C., Rossier, C., Chrousos, G. P., Stratakis, C. A., Nagamine, K., Kudoh, J., Shimizu, N., Maclaren, N., Antonarakis, S. E., and Krohn, K. (1999b). Mutation analyses of North American APS‐1 patients. Hum. Mutat. 13, 69–74. Hershfield, M. S. (2004). Combined immune deficiencies due to purine enzyme defects. In ‘‘Immunologic disorders in infants and children’’ (E. R. Stiehm, H. D. Ochs, and J. A. Winkelstein, Eds.), 5th Ed. pp. 480–504. W.B. Saunders, Philadelphia. Hori, S., Nomura, T., and Sakaguchi, S. (2003). Control of regulatory T cell development by the transcription factor Foxp3. Science 299, 1057–1061. Husebye, E. S., Gebre‐Medhin, G., Tuomi, T., Perheentupa, J., Landin‐Olsson, M., Gustafsson, J., Rorsman, F., and Kampe, O. (1997). Autoantibodies against aromatic L‐amino acid decarboxylase in autoimmune polyendocrine syndrome type I. J. Clin. Endocrinol. Metab. 82, 147–150. Irvine, W. J., and Scarth, L. (1969). Antibody to the oxyphil cells of the human parathyroid in idiopathic hypoparathyroidism. Clin. Exp. Immunol. 4, 505–510. Johnnidis, J. B., Venanzi, E. S., Taxman, D. J., Ting, J. P., Benoist, C. O., and Mathis, D. J. (2005). Chromosomal clustering of genes controlled by the aire transcription factor. Proc. Natl. Acad. Sci. USA 102, 7233–7238. Jonas, M. M., Bell, M. D., Eidson, M. S., Koutouby, R., and Hensley, G. T. (1991). Congenital diabetes mellitus and fatal secretory diarrhea in two infants. J. Pediatr. Gastroenterol. Nutr. 13, 415–425.
364
L U I G I D . N O TA R A N G E L O E T A L .
Kaestner, K. H., Knochel, W., and Martinez, D. E. (2000). Unified nomenclature for the winged helix/forkhead transcription factors. Genes Dev. 14, 142–146. Kanangat, S., Blair, P., Reddy, R., Daheshia, M., Godfrey, V., Rouse, B. T., and Wilkinson, E. (1996). Disease in the scurfy (sf ) mouse is associated with overexpression of cytokine genes. Eur. J. Immunol. 26, 161–165. Kasprowicz, D. J., Smallwood, P. S., Tyznik, A. J., and Ziegler, S. F. (2003). Scurfin (FoxP3) controls T‐dependent immune responses in vivo through regulation of CD4þ T cell effector function. J. Immunol. 171, 1216–1223. Khattri, R., Cox, T., Yasayko, S. A., and Ramsdell, F. (2003). An essential role for Scurfin in CD4þCD25þ T regulatory cells. Nat. Immunol. 4, 337–342. Khattri, R., Kasprowicz, D., Cox, T., Mortrud, M., Appleby, M. W., Brunkow, M. E., Ziegler, S. F., and Ramsdell, F. (2001). The amount of scurfin protein determines peripheral T cell number and responsiveness. J. Immunol. 167, 6312–6320. Kobayashi, I., Imamura, K., Kubota, M., Ishikawa, S., Yamada, M., Tonoki, H., Okano, M., Storch, W. B., Moriuchi, T., Sakiyama, Y., and Kobayashi, K. (1999). Identification of an autoimmune enteropathy‐related 75‐kilodalton antigen. Gastroenterology 117, 823–830. Kobayashi, I., Imamura, K., Yamada, M., Okano, M., Yara, A., Ikema, S., and Ishikawa, N. (1998). A 75‐kD autoantigen recognized by sera from patients with X‐linked autoimmune enteropathy associated with nephropathy. Clin. Exp. Immunol. 111, 527–531. Kobayashi, I., Kawamura, N., and Okano, M. (2001). A long‐term survivor with the immune dysregulation, polyendocrinopathy, enteropathy, X‐linked syndrome. N. Engl. J. Med. 345, 999–1000. Kobayashi, I., Nakanishi, M., Okano, M., Sakiyama, Y., and Matsumoto, S. (1995). Combination therapy with tacrolimus and betamethasone for a patient with X‐linked auto‐immune enteropathy. Eur. J. Pediatr. 154, 594–595. Kobayashi, I., Shiari, R., Yamada, M., Kawamura, N., Okano, M., Yara, A., Iguchi, A., Ishikawa, N., Ariga, T., Sakiyama, Y., Ochs, H. D., and Kobayashi, K. (2001). Novel mutations of FOXP3 in two Japanese patients with immune dysregulation, polyendocrinopathy, enteropathy, X linked syndrome (IPEX). J. Med. Genet. 38, 874–876. Kogawa, K., Nagafuchi, S., Katsuta, H., Kudoh, J., Tamiya, S., Sakai, Y., Shimizu, N., and Harada, M. (2002). Expression of AIRE gene in peripheral monocyte/dendritic cell lineage. Immunol. Lett. 80, 195–198. Kumar, P. G., Laloraya, M., Wang, C. Y., Ruan, Q. G., Davoodi‐Semiromi, A., Kao, K. J., and She, J. X. (2001). The autoimmune regulator (AIRE) is a DNA‐binding protein. J. Biol. Chem. 276, 41357–41364. Kuroda, N., Mitani, T., Takeda, N., Ishimaru, N., Arakaki, R., Hayashi, Y., Bando, Y., Izumi, K., Takahashi, T., Nomura, T., Sakaguchi, S., Ueno, T., Takahama, Y., Uchida, D., Sun, S., Kajiura, F., Mouri, Y., Han, H., Matsushima, A., Yamada, G., and Matsumoto, M. (2005). Development of autoimmunity against transcriptionally unrepressed target antigen in the thymus of Aire‐ deficient mice. J. Immunol. 174, 1862–1870. Levings, M. K., and Roncarolo, M. G. (2005). Phenotypic and functional differences between human CD4þCD25þ and type 1 regulatory T cells. Curr. Top. Microbiol. Immunol. 293, 303–326. Levy‐Lahad, E., and Wildin, R. S. (2001). Neonatal diabetes mellitus, enteropathy, thrombocytopenia, and endocrinopathy: Further evidence for an X‐linked lethal syndrome. J. Pediatr. 138, 577–580. Li, Y., Song, Y‐H., Rais, N., Connor, E., Schatz, D., Muir, A., and Maclaren, N. (1996). Autoantibodies to the extracellular domain of the calcium sensing receptor in patients with acquired hypoparathyroidism. J. Clin. Invest. 97, 910–914.
IMMUNODEFICIENCIES WITH AUTOIMMUNITY
365
Liston, A., Gray, D. H. D., Lesage, S., Fletcher, A. L., Wilson, J., Webster, K. E., Scott, H. S., Boyd, R. L., Peltonen, L., and Goodnow, C. C. (2004). Gene dosage‐limiting role of aire in thymic expression, clonal deletion, and organ‐specific autoimmunity. J. Exp. Med. 200, 1015–1026. Liston, A., Lesage, S., Wilson, J., Peltonen, L., and Goodnow, C. C. (2003). Aire regulates negative selection of organ‐specific T cells. Nat. Immunol. 4, 350–354. Lyon, M. F., Peters, J., Glenister, P. H., Ball, S., and Wright, E. (1990). The scurfy mouse mutant has previously unrecognized hematological abnormalities and resembles Wiskott‐Aldrich syndrome. Proc. Natl. Acad. Sci. USA 87, 2433–2437. Ma, Y., Pannicke, U., Schwarz, K., and Lieber, M. R. (2002). Hairpin opening and overhang processing by an Artemis/DNA‐dependent protein kinase complex in non‐homologous endjoining and V(D)J recombination. Cell 108, 781–794. Markert, M. L., Alexieff, M. J., Li, J., Sarzotti, M., Ozaki, D. A., Devlin, B. H., Sempowski, G. D., Rhein, M. E., Szabolcs, P., Hale, L. P., Buckley, R. H., Coyne, K. E., Rice, H. E., Mahaffey, S. M., and Skinner, M. A. (2004). Complete DiGeorge syndrome: Development of rash, lymphadenopathy, and oligoclonal T cells in 5 cases. J. Allergy Clin. Immunol. 113, 734–741. Marquis, E., Robert, J. J., Bouvattier, C., Bellanne‐Chantelot, C., Junien, C., and Diatloff‐Zito, C. (2002). Major difference in aetiology and phenotypic abnormalities between transient and permanent neonatal diabetes. J. Med. Genet. 39, 370–374. Martin, J. V., Willoughby, P. B., Giusti, V., Price, G., and Cerezo, L. (1995). The lymph node pathology of Omenn’s syndrome. Am. J. Surg. Pathol. 19, 1082–1087. Mazzolari, E., Forino, C., Fontana, M., D’Ippolito, C., Lanfranchi, A., Gambineri, E., Ochs, H., Badolato, R., and Notarangelo, L. D. (2005a). A new case of IPEX receiving bone marrow transplantation. Bone Marrow Transplant. 35, 1033–1034. Mazzolari, E., Moshous, D., Forino, C., DeMartiis, D., Offer, C., Lanfranchi, A., Giliani, S., Imberti, L., Pasic, S., Ugazio, A. G., Porta, F., and Notarangelo, L. D. (2005b). Hematopoietic stem cell transplantation in Omenn syndrome: A single‐center experience. Bone Marrow Transplant. 36, 107–114. Means, G. D., Toy, D. Y., Baum, P. R., and Derry, J. M. (2000). A transcript map of a 2‐Mb BAC contig in the proximal portion of the mouse X chromosome and regional mapping of the scurfy mutation. Genomics 65, 213–223. Meloni, A., Fiorillo, E., Corda, D., Perniola, R., Cao, A., and Rosatelli, M. C. (2005). Two novel mutations of the AIRE protein affecting its homodimerization properties. Hum. Mutat. 25, 319. Meloni, A., Perniola, R., Faa, V., Corvaglia, E., Cao, A., and Rosatelli, M. C. (2002). Delineation of the molecular defects in the AIRE gene in autoimmune polyendocrinopathy‐ candidiasis‐ectodermal dystrophy patients from Southern Italy. J. Clin. Endocrinol. Metab. 87, 841–846. Moshous, D., Callebaut, I., de Chasseval, R., Corneo, B., Cavazzana‐Calvo, M., Le Deist, F., Tezcan, I., Sanal, O., Bertrand, Y., Philippe, N., Fischer, A., and de Villartay, J. P. (2001). Artemis, a novel DNA double‐strand break repair/V(D)J recombination protein, is mutated in human severe combined immune deficiency. Cell 105, 177–186. Nagamine, K., Peterson, P., Scott, H. S., Kudoh, J., Minoshima, S., Heino, M., Krohn, K. J., Lalioti, M. D., Mullis, P. E., Antonarakis, S. E., Kawasaki, K., Asakawa, S., Ito, F., and Shimizu, N. (1997). Positional cloning of the APECED gene. Nat. Genet. 17, 393–398. Nieves, D. S., Phipps, R. P., Pollock, S. J., Ochs, H. D., Zhu, Q., Scott, G. A., Ryan, C. K., Kobayashi, I., Rossi, T. M., and Goldsmith, L. A. (2004). Dermatologic and immunologic
366
L U I G I D . N O TA R A N G E L O E T A L .
findings in the immune dysregulation, polyendocrinopathy, enteropathy, X‐linked syndrome. Arch. Dermatol. 140, 466–472. Noordzij, J. G., de Bruin‐Versteeg, S., Verkaik, N. S., Vossen, J. M. J. J., de Groot, R., Bernatowska, E., Langerak, A. W., van Gent, D. C., and van Dongen, J. J. M. (2000a). The immunophenotypic and immunogenotypic B cell differentiation arrest in bone marrow of RAG‐deficient SCID corresponds to residual recombination activities of mutated RAG proteins. Blood 100, 2145–2152. Noordzij, J. G., Verkaik, N. S., Hartwig, N. G., de Groot, R., van Gent, D. C., and van Dongen, J. J. M. (2000b). N‐terminal truncated RAG1 proteins can direct T cell receptor but not immunoglobulin gene rearrangements. Blood 96, 203–209. Notarangelo, L. D., Stoppoloni, G., Toraldo, R., Mazzolari, E., Coletta, A., Airo`, P., Bordignon, C., and Ugazio, A. G. (1992). Insulin‐dependent diabetes mellitus and severe atopic dermatitis in a child with adenosine deaminase deficiency. Eur. J. Pediatr. 151, 811–814. Notarangelo, L. D., and Hayward, A. R. (2000). X‐linked immunodeficiency with hyper‐IgM (XHIM). Clin. Exp. Immunol. 120, 399–405. Obermayer‐Straub, P., Perheentupa, J., Braun, S., Kayser, A., Barut, A., Loges, S., Harms, A., Dalekos, G., Strassburg, C. P., and Manns, M. P. (2001). Hepatic autoantigens in patients with autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy. Gastroenterology 121, 668–677. Ochs, H. D., Ziegler, S. F., and Torgerson, T. R. (2005). FOXP3 acts as a rheostat of the immune response. Immunol. Rev. 203, 156–164. Omenn, G. S. (1965). Familial reticuloendothleiosis with eosinophilia. N. Engl. J. Med. 273, 427–432. Owen, C. J., Jennings, C. E., Imrie, H., Lachaux, A., Bridges, N. A., Cheetham, T. D., and Pearce, S. H. (2003). Mutational analysis of the FOXP3 gene and evidence for genetic heterogeneity in the immunodysregulation, polyendocrinopathy, enteropathy syndrome. J. Clin. Endocrinol. Metab. 88, 6034–6039. Peake, J. E., McCrossin, R. B., Byrne, G., and Shepherd, R. (1996). X‐linked immune dysregulation, neonatal insulin dependent diabetes, and intractable diarrhoea. Arch. Dis. Child Fetal Neonatal Ed. 74, F195–F199. Pearce, S. H., Cheetham, T., Imrie, H., Vaidya, B., Barnes, N. D., Bilous, R. W., Carr, D., Meeran, K., Shaw, N. J., Smith, C. S., Toft, A. D., Williams, G., and Kendall‐Taylor, P. (1998). A common and recurrent 13‐bp deletion in the autoimmune regulator gene in British kindreds with autoimmune polyendocrinopathy type 1. Am. J. Hum. Genet. 63, 1675–1684. Perniola, R., Falorni, A., Clemente, M. G., Forini, F., Accogli, E., and Lobreglio, G. (2000). Organ‐ specific and non‐organ‐specific autoantibodies in children and young adults with autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy (APECED). Eur. J. Endocrinol. 143, 497–503. Pirovano, S., Mazzolari, E., Pasic, S., Alberini, A., Notarangelo, L. D., and Imberbti, L. (2003). Impaired thymic output and restricted T cell repertoire in two infants with immunodeficiency and early‐onset generalized dermatitis. Immunol. Lett. 86, 93–97. Pitkanen, J., Doucas, V., Sternsdorf, T., Nakajima, T., Aratani, S., Jensen, K., Will, H., Vahamurto, P., Ollila, J., Vihinen, M., Scott, H. S., Antonarakis, S. E., Kudoh, J., Shimizu, N., Krohn, K., and Peterson, P. (2000a). The autoimmune regulator protein has transcriptional transactivating properties and interacts with the common coactivator CREB‐binding protein. J. Biol. Chem. 275, 16802–16809. Pitkanen, J., Vahamurto, P., Krohn, K., and Peterson, P. (2001). Subcellular localization of the autoimmune regulator protein. Characterization of nuclear targeting and transcriptional activation domain. J. Biol. Chem. 276, 19597–19602.
IMMUNODEFICIENCIES WITH AUTOIMMUNITY
367
Pitkanen, J., Doucas, V., Sternsdorf, T., Nakajima, T., Aratani, S., Jensen, K., Will, H., Vahamurto, P., Ollila, J., Vihinen, M., Scott, H. S., Antonarakis, S. E., Kudoh, J., Shimizu, N., Krohn, K., and Peterson, P. (2000b). The autoimmune regulator protein has transcriptional transactivating properties and interacts with the common coactivator CREB‐binding protein. J. Biol. Chem. 275, 16802–16809. Powell, B. R., Buist, N. R., and Stenzel, P. (1982). An X‐linked syndrome of diarrhea, polyendocrinopathy, and fatal infection in infancy. J. Pediatr. 100, 731–737. Qian, X., and Costa, R. H. (1995). Analysis of hepatocyte nuclear factor‐3 beta protein domains required for transcriptional activation and nuclear targeting. Nucleic Acids Res. 23, 1184–1191. Ramsey, C., Winqvist, O., Puhakka, L., Halonen, M., Moro, A., Kampe, O., Eskelin, P., Pelto‐ Huikko, M., and Peltonen, L. (2002). Aire deficient mice develop multiple features of APECED phenotype and show altered immune response. Hum. Mol. Genet. 11, 397–409. Rieux‐Laucat, F., Bahadoran, P., Brousse, N., Selz, F., Fischer, A., Le Deist, F., and de Villartay, J. P. (1998). Highly restricted human T cell repertoire in peripheral blood and tissue‐infiltrating lymphocytes in Omenn’s syndrome. J. Clin. Invest. 102, 312–321. Rinderle, C., Christensen, H. M., Schweiger, S., Lehrach, H., and Yaspo, M. L. (1999). AIRE encodes a nuclear protein co‐localizing with cytoskeletal filaments: Altered subcellular distribution of mutants lacking the PHD zinc fingers. Hum. Mol. Genet. 8, 277–290. Roberts, J., and Searle, J. (1995). Neonatal diabetes mellitus associated with severe diarrhea, hyperimmunoglobulin E syndrome, and absence of islets of Langerhans. Pediatr. Pathol. Lab. Med. 15, 477–483. Rosatelli, M. C., Meloni, A., Devoto, M., Cao, A., Scott, H. S., Peterson, P., Heino, M., Krohn, K. J., Nagamine, K., Kudoh, J., Shimizu, N., and Antonarakis, S. E. (1998). A common mutation in Sardinian autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy patients. Hum. Genet. 103, 428–434. Russell, W. L., Russell, L. B., and Gower, J. S. (1959). Exceptional inheritance of a sex‐linked gene in the mouse explained on the basis that the X/O sex chromosome constitution is female. Proc. Natl. Acad. Sci. USA 45, 554–560. Sakaguchi, S. (2004). Naturally arising CD4þ regulatory t cells for immunologic self‐tolerance and negative control of immune responses. Annu. Rev. Immunol. 22, 531–562. Sakaguchi, S., Sakaguchi, N., Shimizu, J., Yamazaki, S., Sakihama, T., Itoh, M., Kuniyasu, Y., Nomura, T., Toda, M., and Takahashi, T. (2001). Immunologic tolerance maintained by CD25þ CD4þ regulatory T cells: Their common role in controlling autoimmunity, tumor immunity, and transplantation tolerance. Immunol. Rev. 182, 18–32. Saleem, M. A., Arkwright, P. D., Davies, E. G., Cant, A. J., and Veys, P. (2000). Clinical course of patients with major histocompatibility complex class II deficiency. Arch. Dis. Child 83, 356–359. Santagata, S., Besmer, E., Villa, A., Bozzi, F., Allingham, J. S., Sobacchi, C., Haniford, D. B., Vezzoni, P., Nussenzweig, M. C., Pan, Z. Q., and Cortes, P. (1999). The RAG1/RAG2 complex constitutes a 30 flap endonuclease: Implications for junctional diversita` in V(D)J and transpositional recombination. Mol. Cell 4, 1–20. Santagata, S., Gomez, C. A., Sobacchi, C., Bozzi, F., Abinun, M., Pasic, S., Cortes, P., Vezzoni, P., and Villa, A. (2000). N‐terminal RAG1 frameshift mutations in Omenn’s syndrome: Internal methionine usage leads to partial V(D)J recombination activity and reveals a fundamental role in vivo for the N‐terminal domains. Proc. Natl. Acad. Sci. USA 19, 14572–14577. Satake, N., Nakanishi, M., Okano, M., Tomizawa, K., Ishizaka, A., Kojima, K., Onodera, M., Ariga, T., Satake, A., Sakiyama, Y., et al. (1993). A Japanese family of X‐linked auto‐immune enteropathy with haemolytic anaemia and polyendocrinopathy. Eur. J. Pediatr. 152, 313–315. Schandene´, L., Ferster, A., Mascart‐Lemone, F., Crusiaux, A., Ge´rard, C., Marchant, A., Lybin, M., Velu, T., Sariban, E., and Goldman, M. (1993). T helper 2‐like cells and therapeutic effects of
368
L U I G I D . N O TA R A N G E L O E T A L .
interferon‐g in combined immunodeficiency with hypereosinophilia (Omenn’s syndrome). Eur. J. Immunol. 23, 56–60. Schubert, L. A., Jeffery, E., Zhang, Y., Ramsdell, F., and Ziegler, S. F. (2001). Scurfin (FOXP3) acts as a repressor of transcription and regulates T cell activation. J. Biol. Chem. 276, 37672–37679. Schurman, S. H., and Candotti, F. (2003). Autoimmunity in Wiskott‐Aldrich syndrome. Curr. Opin. Rheumatol. 15, 446–453. Schwarz, K., Gauss, G. H., Ludwig, L., Pannicke, U., Li, Z., Lindner, D., Friedrich, W., Seger, R. A., Hansen‐Hagge, T. E., Desiderio, S., and Lieber, M. R. (1996). RAG mutations in human B cell‐negative SCID. Science 274, 97–99. Scott, H. S., Heino, M., Peterson, P., Mittaz, L., Lalioti, M. D., Betterle, C., Cohen, A., Seri, M., Lerone, M., Romeo, G., Collin, P., Salo, M., Metcalfe, R., Weetman, A., Papasavvas, M. P., Rossier, C., Nagamine, K., Kudoh, J., Shimizu, N., Krohn, K. J., and Antonarakis, S. E. (1998). Common mutations in autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy patients of different origins. Mol. Endocrinol. 12, 1112–1119. Sharfe, N., Dadi, H. K., Shahar, M., and Roifman, C. M. (1997). Human immune disorder arising from mutation of the a chain of the interleukin‐2 receptor. Proc. Natl. Acad. Sci. USA 94, 3168–3171. Shevach, E. M. (2002). CD4þ CD25þ suppressor T cells: More questions than answers. Nat. Rev. Immunol. 2, 389–400. Shigeoka, A. O., Araneo, B., Carey, J., and Rallison, M. (1991). An X‐linked T cell activation syndrome and response to Cyclosporin A in one affected infant. Pediatr. Res. 29, 163A. Shu, W., Yang, H., Zhang, L., Lu, M. M., and Morrisey, E. E. (2001). Characterization of a new subfamily of winged‐helix/forkhead (Fox) genes that are expressed in the lung and act as transcriptional repressors. J. Biol. Chem. 276, 27488–27497. Signorini, S., Imberti, L., Pirovano, S., Villa, A., Facchetti, F., Ungari, M., Bozzi, F., Albertini, A., Ugazio, A. G., Vezzoni, P., and Notarangelo, L. D. (1999). Intrathymic restriction and peripheral expansion of the T cell repertoire in Omenn syndrome. Blood 94, 3468–3478. Soderbergh, A., Myhre, A. G., Ekwall, O., Gebre‐Medhin, G., Hedstrand, H., Landgren, E., Miettinen, A., Eskelin, P., Halonen, M., Tuomi, T., Gustafsson, J., Husebye, E. S., Perheentupa, J., Gylling, M., Manns, M. P., Rorsman, F., Kampe, O., and Nilsson, T. (2004). Prevalence and clinical associations of 10 defined autoantibodies in autoimmune polyendocrine syndrome type I. J. Clin. Endocrinol. Metab. 89, 557–562. Sternsdorf, T., Jensen, K., Reich, B., and Will, H. (1999). The nuclear dot protein sp100, characterization of domains necessary for dimerization, subcellular localization, and modification by small ubiquitin‐like modifiers. J. Biol. Chem. 274, 12555–12566. Szczepanski, T., Beishuizen, A., Pongers‐Willemse, M. J., Hahlen, K., van Wering, E. R., Wijkhuijs, A. G., Tibbe, G. J., de Bruijn, M. A., and van Dongen, J. J. (1999a). Cross‐lineage T cell receptor gene rearrangements occur in more than ninety percent of childhood precursor‐B acute lymphoblastic leukemias: Alternative PCR targets for detection of minimal residual disease. Leukemia 13, 196–205. Szczepanski, T., Pongers‐Willemse, M. J., Langerak, A. W., Harts, W. A., Wijkhuis, A. J., van Wering, E. R., and van Dongen, J. J. (1999b). Ig heavy chain gene rearrangements in T cell acute lymphoblastic leukaemia exhibit predominant DH6‐19 and DH‐27 gene usage, can result in complete V‐D‐J rearrangements, and are rare in T cell receptor alpha beta lineage. Blood 93, 4079–4085. Tai, X., Cowan, M., Feigenbaum, L., and Singer, A. (2005). CD28 costimulation of developing thymocytes induces Foxp3 expression and regulatory T cell differentiation independently of interleukin 2. Nat. Immunol. 6, 152–162.
IMMUNODEFICIENCIES WITH AUTOIMMUNITY
369
The Finnish‐German APECED Consortium (1997). An autoimmune disease, APECED, caused by mutations in a novel gene featuring two PHD‐type zinc‐finger domains. The Finnish‐German APECED Consortium. Autoimmune Polyendocrinopathy‐Candidiasis‐Ectodermal Dystrophy. Nat. Genet. 17, 399–403. Thornton, A. M., Donovan, E. E., Piccirillo, C. A., and Shevach, E. M. (2004). IL‐2 is critically required for the in vitro activation of CD4þCD25þ T cell suppressor function. J. Immunol. 172, 6519–6523. Tommasini, A., Ferrari, S., Moratto, D., Badolato, R., Boniotto, M., Pirulli, D., Notarangelo, L. D., and Andolina, M. (2002). X chromosome inactivation analysis in a female carrier of FOXP3 mutation. Clin. Exp. Immunol. 130, 127–130. Uchida, D., Hatakeyama, S., Matsushima, A., Han, H., Ishido, S., Hotta, H., Kudoh, J., Shimizu, N., Doucas, V., Nakayama, K. I., Kuroda, N., and Matsumoto, M. (2004). AIRE functions as an E3 ubiquitin ligase. J. Exp. Med. 199, 167–172. Villa, A., Santagata, S., Bozzi, F., Giliani, S., Frattini, A., Imberti, L., Benerini Gatta, L., Ochs, H. D., Schwarz, K., Notarangelo, L. D., Vezzoni, P., and Spanopoulou, E. (1998). Partial V(D)J recombination activity leads to Omenn syndrome. Cell 93, 885–896. Villa, A., Sobacchi, C., Notarangelo, L. D., Bozzi, F., Abinun, M., Abrahamsen, T. G., Arkwright, P. D., Baniyash, M., Brooks, E. G., Conley, M. E., Cortes, P., Duse, M., Fasth, A., Filipovich, A. M., Infante, A. J., Jones, A., Mazzolari, E., Muller, S. M., Pasic, S., Rechavi, G., Sacco, M. G., Santagata, S., Schroeder, M. L., Seger, R., Strina, D., Ugazio, A., Valiaho, J., Vihinen, M., Vogler, L. B., Ochs, H. D., Vezzoni, P., Friedrich, W., and Schwarz, K. (2001). V(D)J recombination defects in lymphocytes due to RAG mutations: Severe immunodeficiency with a spectrum of clinical presentations. Blood 97, 81–88. Wada, T., Takei, K., Kudo, M., Shimura, S., Kasahara, Y., Koizumi, S., Kawa‐Ha, K., Ishida, Y., Imashuku, S., Seki, H., and Yachie, A. (2000). Characterization of immune function and analysis of RAG gene mutations in Omenn syndrome and related disorders. Clin. Exp. Immunol. 119, 148–155. Wada, T., Toma, T., Okamoto, H., Kasahara, Y., Koizumi, S., Agematsu, K., Kimura, H., Shimada, A., Hayashi, Y., Kato, M., and Yachie, A. (2005). Oligoclonal expansion of T lymphocytes with multiple second‐site mutations leads to Omenn syndrome in a patient with RAG1‐deficient severe combined immunodeficiency. Blood 106, 2099–2101. Walker, M. R., Kasprowicz, D. J., Gersuk, V. H., Benard, A., Van Landeghen, M., Buckner, J. H., and Ziegler, S. F. (2003). Induction of FoxP3 and acquisition of T regulatory activity by stimulated human CD4þCD25 T cells. J. Clin. Invest. 112, 1437–1443. Walport, M. J., Davies, K. A., Morley, B. J., and Botto, M. (1997). Complement deficiency and autoimmunity. Ann. N. Y. Acad. Sci. 815, 267–281. Wang, C. Y., Davoodi‐Semiromi, A., Huang, W., Connor, E., Shi, J. D., and She, J. X. (1998). Characterization of mutations in patients with autoimmune polyglandular syndrome type 1 (APS1). Hum. Genet. 103, 681–685. Ward, L., Paquette, J., Seidman, E., Huot, C., Alvarez, F., Crock, P., Delvin, E., Kampe, O., and Deal, C. (1999). Severe autoimmune polyendocrinopathy‐candidiasis‐ectodermal dystrophy in an adolescent girl with a novel AIRE mutation: Response to immunosuppressive therapy. J. Clin. Endocrinol. Metab. 84, 844–852. Wildin, R. S., Ramsdell, F., Peake, J., Faravelli, F., Casanova, J. L., Buist, N., Levy‐Lahad, E., Mazzella, M., Goulet, O., Perroni, L., Bricarelli, F. D., Byrne, G., McEuen, M., Proll, S., Appleby, M., and Brunkow, M. E. (2001). X‐linked neonatal diabetes mellitus, enteropathy and endocrinopathy syndrome is the human equivalent of mouse scurfy. Nat. Genet. 27, 18–20.
370
L U I G I D . N O TA R A N G E L O E T A L .
Wildin, R. S., Smyk‐Pearson, S., and Filipovich, A. H. (2002). Clinical and molecular features of the immunodysregulation, polyendocrinopathy, enteropathy, X linked (IPEX) syndrome. J. Med. Genet. 39, 537–545. Wirt, D. P., Brooks, E. G., Vaidya, S., Klimpel, G. R., Waldmann, T. A., and Goldblum, R. M. (1989). Novel T‐lymphocyte population in combined immunodeficiency with features of graft versus host disease. N. Engl. J. Med. 321, 370–374. Zlotogora, J., and Shapiro, M. S. (1992). Polyglandular autoimmune syndrome type I among Iranian Jews. J. Med. Genet. 29, 824–826. Zuklys, S., Balciunaite, G., Agarwal, A., Fasler‐Kan, E., Palmer, E., and Hollander, G. A. (2000). Normal thymic architecture and negative selection are associated with Aire expression, the gene defective in the autoimmune‐polyendocrinopathy‐candidiasis‐ectodermal dystrophy (APECED). J. Immunol. 165, 1976–1983.
INDEX
A A0 pockets, 107–108 Acidification, 99, 101 Actin-binding proteins, 69 Activation. See also Cells caspase, 304 FcRs dependent cell, 39, 50, 56 FcR’s immunoglobulin, 41–42, 44–50 mast cell, 57, 72, 175–177 NFkB, 48–49 NMDA receptor, 301 T-cell, 88, 99, 101, 118–119 Acute myelogenous leukemia (AML), 191 Adaptor(s) molecules, 46 proteins, 46–49, 66, 97, 189 transmembrane, 46–47 Addison’s disease, 327 Adenine/uridine-rich element (ARE), 5–6 binding proteins, 6–10, 7 Class II, 9 classes of, 6 decay, 12–16 degradation, 10–15 mRNAs and, 5, 9, 12–15 silencing transcripts of, 16–18, 19 TNFD, 19–21 Adrenal insufficiency, 327 Aggregation allergen-induced receptor, 178 FcgRIIA, 43, 55–56 FcRs, 43–44 mast cell, 197 receptor, 49–50, 57 Aggressive systemic mastocytosis (ASM), 205–206 AIRE gene. See Auto Immune Regulator gene Akt phosphorylation, 64
Allergic disease, 124–125 Allergic encephalitis, 289 Alport syndrome, 265, 266 AMD. See ARE-mediated mRNA decay Amino acids functionally dominant, 104–105 non-conserved, 111 non-polar, 103 AML. See Acute myelogenous leukemia AMPTA receptors, 301 Amygdala, neurotoxicity in, 307–308 Angiogenesis cxc chemokine promotion of, 262–263 inflammation and, 179 mast cell, 179 Antibodies anti-DNA, 293, 294, 300 anti-peptide, 309, 310 auto-, 290, 328 brain and, 293 DNA-reactive, 298–299 DWEYS-reactive, 300 GluR3, 292 IgE, 40, 49, 51–52, 170 mediated toxicity of, 292, 302, 303, 304, 307–308 murine, 308 neuronal death of, 304–305, 306, 307 NPSLE and, 308–309 Anti-DNA antibodies, 293, 294, 300 Antigen(s). See also CD1 binding grooves, 103, 106 blocked processing of, 101 brain, 310–311 cross-reactive, 294 lipid, 87, 94, 100, 120, 121, 125 loading requirements of, 121
371
i nd e x
372 Antigen(s). See also CD1 (continued) microbial, 112–114 potential triggering, 295 processing pathways, 94–102, 120 protein, 94 range of known, 111–112 self, 119–125 T cell recognition by, 125 tissue-restricted, 341 Anti-peptide antibodies, 309, 310 AP complexes, 98 interacting proteins, 98 mediated recycling, 100 APCs, 92–94, 100, 246 APECED. See Autoimmune Polyendocrinopathy–CandidiasisEctodermal Distrophy ARE. See Adenine/uridine-rich element ARE-binding proteins (ARE-BPs), 6–10 ARE-mediated mRNA decay (AMD), 5 Argonaute proteins, 11 Artemis protein, 339 Arthritis, 22, 24 ASM. See Aggressive systemic mastocytosis ATPase proton pumps, 101 AU-rich element, 5–15 Auto Immune Regulator (AIRE) gene, 329, 332, 336 expression, 333–335, 337–346 genetic disruption of, 335 immunobiology of, 333–337 motif, 330 mutations of, 330, 335 protein, 330–333 reduced expression of, 344 thymus lymphocyte regulation by, 336, 343, 344 Autoantibodies, 290, 328 Autoimmune disease, 119–125, 290–291, 293–295 endocrine/non-endocrine, 327 hepatitis and, 327 infants and, 345 Autoimmune Polyendocrinopathy-CandidiasisEctodermal Distrophy (APECED). See also Finnish-German APECED Consortium animal models of, 335–337 autoantibodies in patients with, 328
clinical/immunological features of, 324–329 diabetes and, 325, 329 disease manifestations of, 326 homodimerization of, 333 homomultimerization ability of, 332–333 Iranian Jews and, 330, 332 molecular genetics of, 329–330, 342 mutations caused by, 331–332, 335 North American alleles of, 329 Autoimmunity, 322, 323, 324, 341–344 Autoreactive lymphocytes, 322, 324 Autoreactivity, 119–125 B B cell receptors (BCRs), 40–41, 44. See also Non-T cell Activation Linker/Linker of Activation for B-cells BALB/c mice, 300 Basophils human, 43 mast cells and, 172 BCRs. See B cell receptors Birds, mammals divergence with, 91–92 Blood brain barrier, 307, 309, 310 BMMC. See Bone marrow-derived Mast Cells BMP-7. See Bone morphogenic protein 7 Bone marrow transplantation, 216 Bone marrow-derived mast cells (BMMCs), 40, 52, 54, 56, 199 Bone morphogenic protein 7 (BMP-7), 270 Bone scintography, 196 Bowel disease. See Inflammation Brain. See also Blood brain barrier; Cerebral hypertension; Cognitive impairment antibody entry into, 293 antigens, 310–311 cultured human fetal cell of, 302, 304 immunoglobulin penetration of, 305 immunological privileges of, 289 microinfarcts, 297 multiple sclerosis influence on, 289 SLE damage to, 296, 310 thrombosis, 296 BRF proteins, 8, 10 C C0 pocket, 108 C0 portal, 108 Carboxypeptidase, 182 Caspase, activated, 304
index Cbl, 58 Cbp. See Csk-binding protein Cc chemokines, 261–262 CD1 proteins, 87–88 allergic disease and, 124–125 APCs and, 92–94 cytoplasmic tails of, 97 dendritic cells, 93 dominant aspects of, 110–111 downregulation, 117 endosomal recycling and, 97–99 evolutionary conservation of, 91–92 expression, 93, 100 genes, 88, 91, 95 golgi transit of, 95–96 grooves, 100, 103, 109 human, 90, 96, 110 internalization of, 97 isoforms, 90, 109–110 lipid crystal structures, 105–106 mammals and, 91 origins of, 91 pockets/portals, 105–107 promoters, 94 recycling of, 97–99 structure of, 102–105 T-cells, 88, 89, 113, 114–115, 120 thymocytes expressed by, 92 trafficking, 99–100 translation, 95–97 virally mediated alterations and, 117 CD1a proteins, 98 CD1b proteins, 108 CD1d-restricted T-cells, 89 CD1-restricted T-cells, 88, 89, 113, 114–115, 120 CD1-b2-Microglobulin-Lipid complexes, 102–111 CD4þ CD25þ regulatory T-cells, 346–357 CD40 amplification of, 260 role of, 251–252 CDE. See Constitutive decay element Cell(s). See also Mast cells activation, 39, 50, 56 AIRE expressing, 334 cultured human fetal brain, 302, 304 death, 304 dendritic, 93 differentiation of, 41
373 epithelial, 92 hemopoietic, 60 inflammatory, 247 mammal, 91–92 medullary epithelial, 334–337 myeloid, 58 NK T, 89, 94, 112, 114, 115–117 receptor surface of, 100 resting, 44, 60 THP-1, 55–56 Cerebellar ataxia, 291 Cerebral hypertension, 307 Cerebrospinal fluid (CSF), 304 Cg1, 188–189 Chemokines cc, 261–262 cxc, 262–264 inflammatory, 261–264 TH2-associated, 261–262 Chimeras FcgRIIB-SHIP, 64 N-terminal Dok, 67 Cholesterol-depleting drugs, 67 Cognitive impairment, 304 Cold shock domain (CSD) proteins, 15 Collagen degradation, 265 Colon cancer, 17 Complexes AP, 98 CD1-b2-Microglobulin-Lipid, 102–111 Major Histocompatibility, 40, 88 non-canonical translational initiation, 18–19 signaling, 46–49 Connective-tissue growth factor (CTGF), 261, 268–269 Constitutive decay element (CDE), 15 COX-2. See Cyclooxygenase-2 CREB-binding protein, 333 Cross-reactive antigen theory, 294 CSD protein, 15 CSF. See Cerebrospinal fluid Csk-binding protein (Cbp), 52 CTGF. See Connective-tissue growth factor CUGBP2, 17–18 Cushing’s disease, 297 Cutaneous mastocytosis, 201–202 Cxc chemokines, 262–264 Cyclooxygenase-2 (COX-2), 3, 17, 23 Cyclosporin A, 215 Cysteinyl leukotrienes, 182–183
374 Cytokine(s) arthritigenic, 21 IL-10 anti-inflammatory, 14 interfering with production of, 24 mast cell development and, 174 mRNAs, 12 neurotoxicity of, 298 overproduction, 7 pro-inflammatory, 3, 23 responsiveness to, 56 secretions of, 49 shifting balance of, 258 TGF-b, 253 transcripts, 6 Cytoplasmic tails, 97, 98 D Death antibody mediated neuronal, 304–305, 306, 307 cell, 304 Degradation ARE, 10–15 collagen, 265 matrix, 255 mRNA, 5–15, 20 Dermal fibroblasts, 265 D/EWD/EYS/G concensus sequence, 300–302 Diabetes, APECED and, 325, 329 DiGeorge syndrome, 345 Dimerization, 44–45 Disease allergic, 124–125 APECED manifestations of, 326 autoimmune, 119–125, 290–291, 293–295, 327, 345 bowel, 21, 24 Cushing’s, 297 infectious, 111–119 kidney, 293 myeloproliferative, 191 psychiatric, 292 Diversity (D) gene segments, 339 DNA-binding domain, 330 DNA-reactive antibodies, 298–299 Dok/Dok-1 phosphorylation, 66 Dopamine, prolactin secretion and, 309 Drugs, cholesterol-depleting, 67 DWEYS peptides, 300 DWEYS-reactive antibodies, 300
i nd e x E Ehrlich, Paul, 169 EMT. See Epithelial-mesenchymal transition Encephalitis, 289, 292 Endocrine/non-endocrine disease, 327 Endosomes acidification of, 99, 101 CD1 recycling to, 97–99 pathways of, 94 processing of, 100–102 recycling of, 97–99 Epithelial cells, 92, 334–337 Epithelial-mesenchymal transition (EMT), 250, 255 Epstein Barr virus, 295 Erk1/2 phosphorylation, 64 Extracutaneous mastocytoma, 207–208 F F0 pockets, 107–108 Fab fragments, 59 F-actin skeleton, 68–70 Fc portion of immunoglobulins (FcRs), 39. See also FcgRIIB activating, 41–42, 44–50 aggregation, 43–44 aggregation of identical, 43–44 dependent cell activation, 39, 50, 56 engagement, 44–45 inhibitory, 42–43, 60–70 ITAM-containing, 58 negative signaling by activating, 50–60 plasma membrane expression of, 72 receptors, 40–44 signaling complexes, 46–49 subunits of, 45 Fcgr2b gene, 42, 43 FcgRIIA, 43, 55–56 FcgRIIB, 42 dependent negative regulation, 64–67 immunoreceptor coaggregation with, 66 inhibitory properties of, 60, 64 lipid raft translocation of, 67–68 mast cell inhibition by, 68 phosphorylation, 62 SHIP1’s recruitment by, 61, 63–64 tail-less, 68–69 FcgRIIB1, 42 FcgRIIB10 , 42 FcgRIIB2, 42
index FcgRIIIA, 43 FcRg, 52 FcRb, 50–51, 57 FcRs. See Fc portion of immunoglobulins Fibroblasts dermal, 265 stimulation of, 12–13 Fibrogenesis, 248, 256 Fibrosis BMP-7 and, 270 cc chemokines and, 261–262 cellular mediators of, 249–261 CTGF for, 261, 268–269 cxc chemokines and, 262–264 fibrotic scar in, 251 hepatic, 254–255, 257, 259, 260, 265 HGF and, 269–270 increased, 263 inflammation and, 245 inflammatory chemokine regulation of, 261–264 integrin and, 264–268 kidney, 250, 260 lesions in, 250 lung, 254–255, 258, 259–260 M1 in, 256 macrophages in, 252–255 major features of, 252 myofibroblast’s role in, 249–252 pathogenesis of, 246–249 progression of, 251 resolution, 249 skin, 259 T helper regulation of, 258–261 TGF-b and, 252–254 therapy for, 268–270 Filamin 1, 69 Finnish-German APECED Consortium, 329 50 -30 pathways, 11 Flow cytometry, 199 FOXP3 gene, 354, 355, 358 Fragile X-related protein (FXRIP), 18 FRLP. See Restriction fragment length polymorphism analysis G Gastrointestinal stromal cell tumors (GISTs), 191–192 G-CSF, 22–23 GEMs/Csk-binding proteins, 47
375 Gene(s) array analysis, 25 CD1, 88, 91, 95 fcgr2b, 42, 43 FOXP3 (human), 354, 355, 358 mutations, 193 promiscuous, 336–337 segments, 339 study of, 7 GISTs. See Gastrointestinal stromal cell tumors GluR3 antibodies, 292 Glutamate receptors, 300–302 Glycosylation, 95–96 GM-CSF. See Granulocyte-macrophage colony-stimulating factor Golgi transit, 95–96 Granulocyte-macrophage colony-stimulating factor (GM-CSF), 3, 22–23, 56, 175 Grooves antigen binding, 103, 106 CD1 protein, 100, 103, 109 Guillain-Barre Syndrome, 290–291 H HCD1b-phosphatidylinositol, 104–105 Heat shock response, 2 Hematopoietic stem cell transplantation (HSCT), 338–339 Hemoglobin scavenger receptors, 255 Hemopoietic cells, 60 Heparin, 181–182 Hepatic fibrosis, 254–255, 257, 259, 260, 265 Hepatic growth factor (HGF), 269–270 Hepatitis, autoimmune, 327 HES. See Hypereosinophilic syndrome Heteronuclear nuclear magnetic spectroscopy, 333 HGF. See Hepatic growth factor Histamine, 182, 196, 210, 212 HIV-associated conditions, 24, 117 HSCT. See Hematopoietic stem cell transplantation Human(s) AIRE expression in, 333 basophils, 43 CD1 proteins in, 90, 96, 110 FOXP3 gene in, 354, 355, 358 immunocompromised, 112–113 kit and disease in, 190–193 mast cells, 171, 172, 173
376 Human(s) (continued) obstructive nephropathy, 254 RAG mutations in, 344 HuR, neural-specific homologues of, 9 Hypereosinophilic syndrome (HES), 208 Hypertension, cerebral, 307 Hypogammaglobulinemia, 337 Hypogonadism, 325 Hypoparathyroidism, 325, 326, 328 Hypopituitarism, 328 Hypoprotidemia, 337 I Idiopathic pulmonary fibrosis (IPF), 258, 263 IFNs. See Interferons IgE antibodies, 40, 49 inflammatory response mediated by, 170 mast cells signal transduction induced by, 51–52 IL-4, 258–259 IL-10 anti-inflammatory cytokine, 14 IL-13, 259–260 ILK. See Integrin-linked kinase Imatinib tyrosine kinase inhibitor (STI571), 214–215 Immune system adaptation of, 258 dysregulation, 345, 346 main function of, 322 mast cells and, 178–179 self-tolerance of, 294–295 TTP and, 8 Immunodeficiency autoimmunity associated, 322, 323, 324 T cell, 344–346 Immunodysregulation - Polyendocrinopathy Enteropathy - X-linked (IPEX) clinical/laboratory features of, 346–350 historical aspects of, 347–348 laboratory findings, 350–351 molecular/cellularpathophysiologyof,353–356 mouse model for, 352–353 treatment for, 351–352 Immunofluorescence, 328–329 Immunoglobulins. See Fc portion of immunoglobulins Immunomodulatory therapy, 290 Immunoreceptor Tyrosine-based Activation Motifs (ITAMs), 42, 45 FcRs, 58
i nd e x intracytoplasmic, 59 phosphorylation, 52, 55 receptors containing, 59–60 Immunoreceptor Tyrosine-based Inhibition Motif (ITIM), 43. See also pITIMs Immunoreceptors, 40–41 FcgRIIB’s coaggregation with, 66 ITAM-containing, 58 Immunosuppressive therapy, 295 Immunotherapy, 125–128 Inducible nitric oxide synthase (iNOS) enzyme, 13 Infants. See Autoimmune disease Infections. See Viral infections Inflammation angiogenesis and, 179 bowel disease and, 21, 24 cells of, 247 chemokines and, 261–264 exaggerated response of, 324 fibrosis and, 245 mast cell allergic, 177–178 mediators, 22, 202 Inflammatory response coordinate transcriptional control during, 2 dampening of, 3 IgE-mediated, 170 initial, 255 myeloid cells influence on, 58 thalidomide’s influence on, 24 Inhibition FcgRIIB, 60, 64 FcRs, 60–70 mechanics of, 59 receptor, 62 translational, 16–19 INOS enzyme. See Inducible nitric oxide synthase enzyme Inositol phosphatases, 56–58 Integrin a1b1, 264–266 kinases linked to, 254 avb3, 266–268 avb6, 266–267 Integrin-linked kinase (ILK), 254 Interferons (IFNs), 12, 213, 260 Interleukins, 183–184 IPEX. See Immunodysregulation Polyendocrinopathy - Enteropathy X-linked
index IPF. See Idiopathic pulmonary fibrosis Iranian Jews, APECED and, 330, 332 ITAMS. See Immunoreceptor Tyrosine-based Activation Motifs, 42 ITIM. See Immunoreceptor Tyrosine-based Inhibition Motif J JAK/STAT pathways, 174, 187 Jews (Iranian), APECED and, 330, 332 Joining (J) gene segments, 339 K Kaposi sarcoma-associated herpes virus (KSHV), 117 Kidney disease, 293 failure, 265 fibrosis, 250, 260 myofibroblasts, 255 Kinases, 46. See also Mitogen-activated protein kinases; Src family kinases integrin-linked, 254 PLC-g, 65 Tec, 65 tyrosine, 51 Kit biology of, 184–193 functions of, 185–186 human, 185, 190–193 screening for, 200 signaling, 186–190 structure of, 184–185 Knock-in mice, 19–20 Knock-out mice, 20–22 KSHV. See Kaposi sarcoma-associated herpes virus L LAP. See Latency associated protein LAT, 52–54, 55 Latency associated protein (LAP), 253–254 LAX. See Linker of Activation for X cells LDL. See Low density lipoprotein Leishmania donovani, 114 Leucine. See Y þ 2 leucine Leukemia. See Acute myelogenous leukemia; Mast cell leukemia Ligand valency, 49–50
377 Ligands lipid, 103, 126 monomeric, 59 Linker of Activation for X cells (LAX), 47 Lipid(s) acid-mediated loading of, 100 antigens, 87, 94, 100, 120, 121, 125 crystal structures of CD1, 105–106 ligands, 103, 126 mediators, 182–184 phosphatidylinositol-containing, 95, 106 presentation, 99–100 rafts, 67–68 self cellular, 119 T-cells mediation of, 99 transport proteins, 102 Low density lipoprotein (LDL), 101 LPS-activated macrophages, 16 LT-alpha. See Lymphotoxin-alpha Lung fibrosis, 254–255, 258, 259–260 myofibroblasts, 253 LXXLL motifs, 330, 331 Lymphocytes autoreactive, 322, 324 T, 337–338 Lymphotoxin-alpha (LT-alpha), 334 Lyn, 51–52 M M1 macrophages, 255–258 M2 macrophages, 255–258 Macrophage(s), 247 depletion, 256–257 fibrogenesis and, 248, 256 fibrosis and, 252–255 Guillain-Barre syndrome caused by, 290–291 IL-13 stimulation of, 259 LPS-activated, 16 M1/M2, 255–258 MK2 lacking in, 23 pro-fibrotic phenotype subsets of, 255 TGF-b and, 253 TNFDARE, 20 Major Histocompatibility Complex (MHC), 40, 88 Mammals birds divergence with, 91–92 CD1 proteins and, 91 cells, 91–92
378 MAP kinases, See Mitogen-activated protein kinases MAP-peptide. See Multimeric peptide Mast cell(s). See also Bone marrow-derived mast cells activation of, 57, 72, 175–177 aggregation of, 197 allergic inflammation and, 177–178 angiogenesis, 179 basophils and, 172 biology of, 170–184 bone marrow-derived, 40, 52, 54, 56, 199 coagulation, 179–180 cytokines involved with, 174 development/proliferation of, 173–175 differentiation, 173 distribution/heterogeneity, 172–173 FcgRIIB inhibition of, 68 functions of, 177 granulation, 176, 180, 203 histamine release from 51–52, 210, 212 human, 171, 172, 173 IgE-induced signal transduction in, 51–52 innate immunity and, 178–179 LAT tyrosines in, 53 mediators, 176, 180 mice deficient in, 172, 178 origin of, 40, 171–172 secretory responses of, 49–50 systemic mastocytosis and, 169 TC/MCTC, 173 Mast Cell Disease Symposium, 197 Mast cell leukemia (MCL), 206–207 Mast cell sarcoma (MCS), 207 Mastocytosis. See Cutaneous mastocytosis; Extracutaneous mastocytoma; Systemic mastocytosis Matrix degradation, 255 Matrix metalloproteinases (MMPs), 248–249, 265. See also Tissue inhibitors of metalloproteinases Matrix proteins, 247, 249 Matzfellen. See Mast cells MCL. See Mast cell leukemia MCS. See Mast cell sarcoma Mechanism(s) candidate, 119 effector, 65 receptor-mediated, 101 regulatory, 62
i nd e x translational silencing, 18–19 Mediator(s) antibody toxicity, 292, 302, 303, 304, 307–308 anti-fibrotic, 272 fibrosis cellular, 249–261 IL-13 as, 260 inflammatory, 22, 202 M1/M2 cell, 255 managing release symptoms of, 210 mast cell, 176, 180 membrane-derived lipid, 182–184 neurotoxicity antibody, 302, 303, 304 OS, 341–346 pro-fibrotic, 271 secretory granule, 180–182 T-cell, 99 Medullary epithelial cells, 334–337 Memory loss, 304 MHC class I proteins, 88, 100 MHC. See Major histocompatibility complex Mice BALB/c, 300 IPEX model for, 352–353 knock-in, 19–20 knock-out, 20–22 MAP-peptide immunized, 305 mast cell-deficient, 172, 178 maze tested, 305–306 NP SLE, 298 NZB/W, 300 transgenic, 22–23, 294 Microbial agents, 111–119, 324 MicroRNAs, 11 Mitogen-activated protein (MAP) kinases, 14, 46, 49, 51, 53, 56, 187–188, 304–305 MMPs. See Matrix metalloproteinases Monomeric ligands, 59 Mood disorders, 297–298 Motif(s) AIRE’s conserved, 330 consensus binding, 56 Immunoreceptor Tyrosine-based Activation, 42, 45, 52, 55 Immunoreceptor Tyrosine-based Inhibition, 43 isoform-specific binding, 109 LXXLL, 330, 331 modified dileucine, 96 PHD-type, 330
index RNA-recognition, 16 tyrosine mediated recycling, 100 UGUR, 2 MPDs. See Myeloproliferative diseases MRNA(s), 2 ARE-, 5, 9, 12–15 CDE-mediated decay of, 15 cytokine, 12 degradation of, 5–15, 20 encodings, 2 gene array analysis of, 25 half-life of, 12 preventing decay of, 9 stabilization of, 13, 25 TNFa, 20 transcripts, 1, 335 TTP/BRF regulation of, 8 YB1-containing complexes and, 16 Multimeric peptide (MAP-peptide), 304–305, 306 Multiple sclerosis, 289 Murine antibodies, 308 neuronal death and, 304–305, 306, 307 Mutations AIRE gene, 330, 335 APECED-causing, 331–332, 335 gene, 193 OS causing, 339–340 Myasthenia gravis, 290, 294 Mycobacterium leprae, 93 Mycobacterium tuberculosis, 93, 112, 114 Myeloid cells, 58 Myeloproliferative diseases (MPDs), 191 Myofibroblasts, 249–252 kidney, 255 lung, 253 N Nephropathy, human obstructive, 254 Neuroimmunology, 289 Neuronal death, 304–305, 306, 307 Neuropsychiatric systemic lupus erythematosus (NPSLE), 295–298, 308–309, 310–311. See also Systemic lupus erythematosus Neurotoxicity, 298, 302, 304, 307–308, 312 Neutrophils, 247 TTC-less, 22 wild-type, 21–22
379 NFkB activation, 48–49 NK T-cells, 89, 94, 112, 114, 115–117 N-linked glycosylation, 95–96 NMDA receptors, 300–302, 305, 308, 309 N-methyl D-aspartate receptors, 290 Non-T cell Activation Linker (NTAL), 54, 55 Non-T cell Activation Linker/Linker of Activation for B-cells (NTAL/LAB), 47 North American alleles, 329 NPSLE. See Neuropsychiatric systemic lupus erythematosus NTAL. See Non-T cell Activation Linker NTAL/LAB. See Non-T cell Activation Linker/ Linker of Activation for B-cells N-terminal deleted protein, 340 N-terminal Dok chimeras, 67 N-terminal kinase (JNK) pathway, 13 Nucleic acid sequences, 1–2 O Obsessive compulsive disorders, 292 Obstructive nephropathy, 254 Omenn Syndrome (OS) AIRE expression in, 343 autoimmunity in, 341–344 central tolerance and, 345 clinical laboratory features of, 337–339 immune-mediated damage in, 341–346 molecular pathophysiology of, 339–341 mutations caused by, 339–340 OS. See Omenn Syndrome P P13K. See Phosphatidylinositoil 30 kinases PAF. See Platelet-activating factor Paraneoplastic syndrome, 291 Pathway(s) 50 -3,0 11 antigen processing, 94–102, 120 decay, 11 deletion of, 112 downstream signaling, 52–53 endosomal, 94 high-stringency loading, 121, 122 JAK/STAT, 174, 187 lipid antigen, 121 low-stringency loading, 122 N-terminal kinase (JNK), 13 phosphatidylinositol 3-kinase, 13 postranscriptional, 19–20
380 Pathway(s) (continued) recycling, 96 secretory, 96, 101 subcellular antigen processing, 94–102, 120–123 Pattern reception receptors, 101 PDGF. See Platelet-derived growth factor Peptides. See also Antibodies DWEYS, 300 MAP-, 304–305 tyrosyl-phosphorylated, 61 PGD2. See Prostaglandin D2 PHD motifs, See Plant homeodomain-type motifs Phosphates, protein tyrosine, 55–56 Phosphatidylinositoil 30 kinases (P13K), 13, 186–187 Phosphatidylinositol-containing lipids, 95, 106 Phospholipase Cg1, 188–189 Phosphorylation Akt, 64 Cbp-binding protein, 52 Dok/Dok-1, 66 Erk1/2, 64 FcgPIIA, 55 FcgRIIB, 62 FcRg, 52 FcRb, 57 intracellular protein tyrosyl-, 58 ITAM’s, 52, 55 MAP kinase, 56 Shc, 57 SHIP1, 66 PID. See Primary immune deficiencies PITIMs, 62–63 PKC. See Protein Kinase C family PKD. See Protein Kinase D Plant homeodomain (PHD)-type motifs, 330 Planted antigen theory, 294 Platelet-activating factor (PAF), 183 Platelet-derived growth factor (PDGF), 254–255 PLC-g kinases, 65 Pockets A0 , 107–108 C0 , 108 F0, 107–108 protein, 105–107 Polyclonal lymphoproliferative disorder, 53 Prednisolone, 261
i nd e x Primary immune deficiencies (PID), 322, 323, 324 Pro-inflammatory cytokines, 3, 23 Pro-inflammatory proteins, 1–3, 4–5, 20, 22–23 Prolactin secretion, 309 Prostaglandin D2 (PGD2), 182 Protein(s). See also Auto Immune Regulator gene; Bone morphogenic protein 7; CD1 proteins; Zinc finger protein actin-binding, 69 adaptor, 46–49, 66, 97, 189 AIRE, 330–333 antigens, 94 AP-interacting, 98 ARE-binding, 6–10 Argonaute, 11 Artemis, 339 background, 39 BRF, 8, 10 CD1a, 98 CD1b, 108 CREB-binding, 333 CSD, 15 Csk-binding, 52 database, 300 Fragile X-related, 18 GEMs/Csk-binding, 47 human CD1, 90, 96, 110 inflammatory effector, 1 latency associated, 253–254 lipid transport, 102 matrix, 247, 249 MHC class I, 88, 100 N-terminal deleted, 340 pockets, 105–107 pro-inflammatory, 1–3, 4–5, 20, 22–23 Pumilio-Fem-3-binding factor (Puf), 2 RAG, 339, 340, 344 ras, 187–188 RNA-binding, 2, 11, 16, 17, 18 Saposin family, 102 src-family, 51 TTP/BRF family of, 10, 11 tyrosine phosphates, 55–56 tyrosyl phosphorylation of intracellular, 58 Protein Kinase C (PKC) family, 48 Protein Kinase D (PKD), 48 Proton pumps, 101 Psychiatric disease, 292 Pumilio-Fem-3-binding factor (Puf) proteins, 2
index R RAG proteins. See Recombinase Activating Gene proteins Ras proteins, 187–188 Rasmussen’s encephalitis, 292 Receptor(s). See also Immunoreceptors aggregation, 49–50, 57 allergen-induced, 178 AMPTA, 301 cc chemokine, 261, 262 cell surface, 100 cxc chemokine, 263 Fc, 40–44 glutamate, 300–302 hemoglobin scavenger, 255 inhibitory, 62 ITAM-containing, 59–60 LDL, 101 lymphotoxin beta, 334–335 mannose, 101 NMDA, 300–302, 305, 308, 309 N-methyl D-aspartate, 290 pattern reception, 101 toll-like, 178 ubiquitination of, 58 Recombinase Activating Gene (RAG) proteins, 339, 340, 344 Recombination signal sequences (RSS), 339 Recruitment SHIP1, 61, 63–64 ZAP-70, 63–64 Recycling AP-mediated, 100 CD1, 97–99 endosomal, 97–99 pathways, 96 tyrosine motif-mediated, 100 Resting cells, 44, 60 Restriction fragment length polymorphism analysis (FRLP), 200 Rheumatic fever, 291 RNA binding proteins, 2, 11, 16, 17, 18 micro, 11 RNA-recognition motif (RRM), 16 RSS. See Recombination signal sequences S SAND. See DNA-binding domain Saposin family proteins, 102
381 Scars fibrotic, 251 formation of, 247 resolution of, 248 Schistosomiasis, 260 SCID. See Severe Combined Immune Deficiency Scurfy, 353–356 Secretory granule mediators, 180–182 See Inducible nitric oxide synthase (iNOS) enzyme, 13 Self antigens, 119–125 Severe Combined Immune Deficiency (SCID), 338, 339 SFKs. See Src family kinases SH2 domain, 55, 56, 64 Shc phosphorylation, 57 SHIP1 activity, 56, 57 consensus binding motifs, 56 effector mechanisms, 65 FcgRIIB’s recruitment of, 61, 63–64 necessity of, 64 negative regulation, 39, 72 phosphorylation of, 66 SHP2-Interacting Transmembrane adapter (SIT), 47 Signaling complexes, 46–49 downstream, 52–53 kit, 186–190 negative, 50–60 Signalosomes constitution of, 44–45 LAT’s organization of, 52–53 molecules recruited for, 48 Single strand conformation polymorphism analysis (SSCP), 200 Sinonasal lymphomas, 192 SIT. See SHP-2-Interacting Transmembrane adapter SLE. See Systemic lupus erythematosus SLP-76, 46 SMAHNMD. See Systemic mastocytosis with associated clonal nonmast cell lineage disorder Spectroscopy. See Heteronuclear nuclear magnetic spectroscopy Splenectomy, 215–216 Src family kinases (SFKs), 188
i nd e x
382 Src-family proteins, 51 SSCP. See Single strand conformation polymorphism analysis Stem Cell Factor, 56, 66 STI571. See Imatinib tyrosine kinase inhibitor Sydenham’s chorea, 291 Systemic lupus erythematosus (SLE), 293–295, 296, 304, 310. See also Neuropsychiatric systemic lupus erythematosus Systemic mastocytosis. See also Cutaneous mastocytosis; kit; Mast cells; Mediators aggressive, 205–206 clinical spectrum, 201–208 counseling and, 216–217 diagnosis of, 196–201 epidemiology of, 170 gene mutations, polymorphisms, abnormalities in, 193 general anesthesia and, 217 genetic factors, 170 history of, 169–170 indolent, 204–205 mast cells and, 169 pathogenesis of, 194–196 pregnancy in, 217–218 prognosis/predictive factors for, 209 supportive care/management of, 216–218 symptoms, 202 therapy, 211–212, 213–216, 218–219 treatment of, 209–216 variants of, 194, 198 Systemic mastocytosis with associated clonal nonmast cell lineage disorder (SMAHNMD), 206 T T cell Receptor-Interacting Molecule (TRIM), 47 T Cell Receptors (TCRs), 40–41, 335 T helpers, 258–261 T lymphocytes, 337–338 T-cell(s) activation of, 88, 99, 101, 118–119 anti-CD3/anti-CD28 stimulation of, 12 antigens recognized by, 125 autoantigen-driven proliferation of, 341 autoimmunity, 344 autoreactive clones of, 335 CD1d-restricted, 89 CD1-restricted, 88, 89, 113, 114–115, 120
þ
þ
CD4 CD25 regulatory, 346–357 differentiation of, 53 fine specificity, 125 immunodeficiency, 344–346 LAT-deficient, 54 lipid mediation by, 99 maternal engraftment of, 338 NK, 89, 94, 112, 114, 115–117 oligoclonal, 341, 342 responses of, 87 TC/MCTC mast cells, 173 TCRs. See T Cell Receptors Tec kinases, 65 Telangiectasia macularis (TMEP), 170 Testicular seminomas, 192 TGF-b. See Transforming growth factor beta TH2-associated chemokines, 261–262 Thalidomide, 24 Theory cross-reactive antigen, 294 planted antigen, 294 Therapy fibrosis, 268–270 immuno-, 125–128 immunomodulatory, 290 immunosuppressive, 295 systemic mastocytosis, 211–212, 213–216, 218–219 THP-1 cells, 55–56 Thrombopoieten (TPO), 174–175 Thymocytes, CD1 expression of, 92 Thymus AIRE gene and, 336, 343, 344 oligoclonality of, 342 tissue-specific transcripts in, 341–344 TIA-1, 21–22 TIA-1/TIAR knock-out mice, 21–22 TIAR, 17, 21–22 TIMPs. See Tissue inhibitors of metalloproteinases Tissue inhibitors of metalloproteinases (TIMPs), 248–249. See also Matrix metalloproteinases TLRs. See Toll-like receptors TMEP. See Telangiectasia macularis TNF. See Tumor necrosis factor alpha TNFa mRNA, 20 TNFD Adenine/uridine-rich element, 19–21 TNFDARE knock-in mice, 19–20 Toll-like receptors (TLRs), 178
index Toxicity, antibody-mediated, 292 TPO. See Thrombopoieten Transcripts ARE-containing, 16–18, 19 cytokine, 6 mRNA, 1, 335 Transforming growth factor beta (TGF-b), 183, 252–254, 260 Translation CD1, 95–97 determing rates of, 2 Translational inhibition, 16–19 Translational silencing, 18–19 Transplantation, bone marrow, 216 TRIM. See T cell Receptor-Interacting Molecule Tryptase, 180–181 TTP knock-out mice, 20–21 TTP. See Zinc finger protein Tumor necrosis factor alpha (TNF), 3, 183 2-chlorodeoxyadenosine (2-CDA), 213–214 Tyrosine dephosphorylization of, 45 kinase, 51 LAT, 53 motif-mediated recycling, 100 phosphates, 55–56 Tyrosine phosphate proteins, 55–56 U UGUR motif, 2 UP. See Urticaria pigmentosa Urticaria pigmentosa (UP), 169
383 V Variable (V) gene segments, 339 Vascular cell adhesion molecule (VCAM)-1, 3, 13 Vascular endothelial growth factor (VEGF), 5, 179 Vasculitis, 296 VCAM-1. See Vascular cell adhesion molecule VEGF. See Vascular endothelial growth factor Viral infections, 88, 115–116, 117, 295, 324, 341–342 W Wounds healing of, 246–247 scar resolution and, 248 Y Y þ 2 leucine, 61–62 YB1-containing complexes, 16 Z ZAP-70, 63–64 Zinc finger protein (TTP) BRF proteins, 10, 11 function of, 7–8 immune system and, 8 knock-out mice, 20–21 mRNA regulation by, 8 neutrophils lacking, 22 TNFa mRNA and, 20
Contents of Recent Volumes
Volume 79 Neutralizing Antiviral Antibody Responses Rolf M. Zinkernagel, Alain Lamarre, Adrian Ciurea, Lukas Hunziker, Adrian F. Ochsenbein, Kathy D. McCoy, Thomas Fehr, Martin F. Bachmann, Ulrich Kalinke, and Hans Hengartner Regulation of Interleukin-12 Production in Antigen-Presenting Cells Xiaojing Ma and Giorgio Trinchieri Mechanisms of Signaling by the Hematopoietic-Specific Adaptor Proteins, SLP-76 and LAT and Their B Cell Counterpart, BLNK/SLP-65 Deborah Yablonski and Arthur Weiss Xenotransplantation David H. Sachs, Megan Sykes, Simon C. Robson, and David K. C. Cooper Regulation of Antibacterial and Antifungal Innate Immunity in Fruitflies and Humans Michael J. Williams Functional Heavy-Chain Antibodies in Camelidae Viet Khong Nguyen, Aline Desmyter, and Serge Muyldermans
Uterine Natural Killer Cells in the Pregnant Uterus Chau-Ching Liu and John Ding-E Young Index
Volume 80 Protein Degradation and the Generation of MHC Class I-Presented Peptides Kenneth L. Rock, Ian A. York, Tomo Saric, and Alfred L. Goldberg Proteoanalysis and Antigen Presentation by MHC Class II Molecules Paula Wolf Bryant, Ana-Maria Lennon-Dume´nil, Edda Fiebiger, Ce´cile Lagaudrie´re-Gesbert, and Hidde L. Ploegh Cytokine Memory of T Helper Lymphocytes Max Lo«hning, Anne Richter, and Andreas Radbruch Ig Gene Hypermutation: A Mechanism Is Due Jean-Claude Weill, Barbara Bertocci, Ahmad Faili, Said Aoufouchi, Ste´phane Frey, Annie De Smet, Se´bastian Storck, Auriel Dahan, Fre´de´ric Delbos, Sandra Weller, Eric Flatter, and Claude-Agne´s Reynaud
385
386 Generalization of Single Immunological Experiences by Idiotypically Mediated Clonal Connections Hilmar Lemke and Hans Lange
co n t en t s o f r e c e nt vo l um es Control of Autoimmunity by Naturally Arising Regulatory CD4þ T Cells S. Sakaguchi Index
The Aging of the Immune System B. Grubeck-Loebenstein and G. Wick Index
Volume 81 Regulation of the Immune Response by the Interaction of Chemokines and Proteases Jo Van Damme and Sofie Struyf Molecular Mechanisms of Host-Pathogen Interaction: Entry and Survival of Mycobacteria in Macrophages Jean Pieters and John Gatfield B Lymphoid Neoplasms of Mice: Characteristics of Naturally Occurring and Engineered Diseasse and Relationships to Human disorders Herbert Morse et al. Prions and the Immune System: A Journey Through Gut Spleen, and Nerves Adriano Aguzzi Roles of the Semaphorin Family in Immune Regulation H. Kikutani and A. Kumanogoh HLA-G Molecules: from Maternal-Fetal Tolerance to Tissue Acceptance Edgardo Carosella et al. The Zebrafish as a Model Organism to Study Development of the Immune System Nick Trede et al.
Volume 82 Transcriptional Regulation in Neutrophils: Teaching Old Cells New Tricks Patrick P. McDonald Tumor Vaccines Freda K. Stevenson, Jason Rice, and Delin Zhu Immunotherapy of Allergic Disease R. Valenta, T. Ball, M. Focke, B. Linhart, N. Mothes, V. Niederberger, S. Spitzauer, I. Swoboda, S.Vrtala, K. Westritschnic, and D. Kraft Interactions of Immunoglobulins Outside the Antigen-Combining Site Roald Nezlin and Victor Ghetie The Roles of Antibodies in Mouse Models of Rheumatoid Arthritis, and Relevance to Human Disease Paul A. Monach, Christophe Benoist, and Diane Mathis MUC1 Immunology: From Discovery to Clinical Applications Anda M. Vlad, Jessica C. Kettel, Nehad M. Alajez, Casey A. Carlos, and Olivera J. Finn Human Models of Inherited Immunoglobulin Class Switch Recombination and Somatic Hypermutation Defects (Hyper-IgM Syndromes) Anne Durandy, Patrick Revy, and Alain Fischer
c o nt e n ts o f re c e nt vo l um e s
387
The Biological Role of the C1 Inhibitor in Regulation of Vascular Permeability and Modulation of Inflammation Alvin E. Davis, III, Shenghe Cai, and Dongxu Liu
Volume 84
Index
Multitasking of Helix-Loop-Helix Proteins in Lymphopoiesis Xiao-Hong Sun
Volume 83 Lineage Commitment and Developmental Plasticity in Early Lymphoid Progenitor Subsets David Traver and Koichi Akashi The CD4/CD8 Lineage Choice: New Insights into Epigenetic Regulation during T Cell Development Ichiro Taniuchi, Wilfried Ellmeier, and Dan R. Littman CD4/CD8 Coreceptors in Thymocyte Development, Selection, and Lineage Commitment: Analysis of the CD4/CD8 Lineage Decision Alfred Singer and Remy Bosselut Development and Function of T Helper 1 Cells Anne O’Garra and Douglas Robinson Th2 Cells: Orchestrating Barrier Immunity Daniel B. Stetson, David Voehringer, Jane L. Grogan, Min Xu, R. Lee Reinhardt, Stefanie Scheu, Ben L. Kelly, and Richard M. Locksley Generation, Maintenance, and Function of Memory T Cells Patrick R. Burkett, Rima Koka, Marcia Chien, David L. Boone, and Averil Ma
Interactions Between NK Cells and B Lymphocytes Dorothy Yuan
Customized Antigens for Desensitizing Allergic Patients Fa¨tima Ferreira, Michael Wallner, and Josef Thalhamer Immune Response Against Dying Tumor Cells Laurence Zitvogel, Noelia Casares, Marie O. Pe¨quignot, Nathalie Chaput, Mathew L. Albert, and Guido Kroemer HMGB1 in the Immunology of Sepsis (Not Septic Shock) and Arthritis Christopher J. Czura, Huan Yang, Carol Ann Amella, and Kevin J. Tracey Selection of the T-Cell Repertoire: Receptor-Controlled Checkpoints in T-Cell Development Harald Von Boehmer The Pathogenesis of Diabetes in the NOD Mouse Michelle Solomon and Nora Sarvetnick
CD8þ Effector Cells Pierre A. Henkart and Marta Catalfamo
Index
An Integrated Model of Immunoregulation Mediated by Regulatory T Cell Subsets Hong Jiang and Leonard Chess
Volume 85
Index
Cumulative Subject Index Volumes 66–82
388
Volume 86 Adenosine Deaminase Deficiency: Metabolic Basis of Immune Deficiency and Pulmonary Inflammation Michael R. Blackburn and Rodney E. Kellems Mechanism and Control of V(D)J Recombination Versus Class Switch Recombination: Similarities and Differences Darryll D. Dudley, Jayanta Chaudhuri, Craig H. Bassing, and Frederick W. Alt
co n t en t s o f r e c e nt vo l um es The Integration of Conventional and Unconventional T Cells that Characterizes Cell-Mediated Responses Daniel J. Pennington, David Vermijlen, Emma L. Wise, Sarah L. Clarke, Robert E. Tigelaar, and Adrian C. Hayday Negative Regulation of Cytokine and TLR Signalings by SOCS and Others Tetsuji Naka, Minoru Fujimoto, Hiroko Tsutsui, and Akihiko Yoshimura Pathogenic T-Cell Clones in Autoimmune Diabetes: More Lessons from the NOD Mouse Kathryn Haskins
Isoforms of Terminal Deoxynucleotidyltransferase: Developmental Aspects and Function To-Ha Thai and John F. Kearney
The Biology of Human Lymphoid Malignancies Revealed by Gene Expression Profiling Louis M. Staudt and Sandeep Dave
Innate Autoimmunity Michael C. Carroll and V. Michael Holers
New Insights into Alternative Mechanisms of Immune Receptor Diversification Gary W. Litman, John P. Cannon, and Jonathan P. Rast
Formation of Bradykinin: A Major Contributor to the Innate Inflammatory Response Kusumam Joseph and Allen P. Kaplan Interleukin-2, Interleukin-15, and Their Roles in Human Natural Killer Cells Brian Becknell and Michael A. Caligiuri Regulation of Antigen Presentation and CrossPresentation in the Dendritic Cell Network: Facts, Hypothesis, and Immunological Implications Nicholas S. Wilson and Jose A. Villadangos Index
Volume 87 Role of the LAT Adaptor in T-Cell Development and Th2 Differentiation Bernard Malissen, Enrique Aguado, and Marie Malissen
The Repair of DNA Damages/Modifications During the Maturation of the Immune System: Lessons from Human Primary Immunodeficiency Disorders and Animal Models Patrick Revy, Dietke Buck, Franc,oise le Deist, and Jean-Pierre de Villartay Antibody Class Switch Recombination: Roles for Switch Sequences and Mismatch Repair Proteins Irene M. Min and Erik Selsing Index
Volume 88 CD22: A Multifunctional Receptor That Regulates B Lymphocyte Survival and Signal Transduction Thomas F. Tedder, Jonathan C. Poe, and Karen M. Haas
c o nt e n ts o f re c e nt vo l um e s
389
Tetramer Analysis of Human Autoreactive CD4-Positive T Cells Gerald T. Nepom
Dendritic Cell Biology Francesca Granucci, Maria Foti, and Paola Ricciardi-Castagnoli
Regulation of Phospholipase C-g2 Networks in B Lymphocytes Masaki Hikida and Tomohiro Kurosaki
The Murine Diabetogenic Class II Histocompatibility Molecule I-Ag7: Structural and Functional Properties and Specificity of Peptide Selection Anish Suri and Emil R. Unanue
Role of Human Mast Cells and Basophils in Bronchial Asthma Gianni Marone, Massimo Triggiani, Arturo Genovese, and Amato De Paulis A Novel Recognition System for MHC Class I Molecules Constituted by PIR Toshiyuki Takai
RNAi and RNA-Based Regulation of Immune System Function Dipanjan Chowdhury and Carl D. Novina Index