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Abstract
SUMMARY Programmed death-1 (PD-1) is a cell surface molecule that regulates the adaptive immune response. Engagement of PD-1 by its ligands PD-L1 or PD-L2 transduces a signal that inhibits T-cell proliferation, cytokine production, and cytolytic function. While a great deal is known concerning the biologic roles PD-1 plays in regulating the primary immune response and in T-cell exhaustion, comparatively little is known regarding how PD-1 ligation alters signaling pathways. PD-1 ligation is known to inhibit membrane-proximal T-cell signaling events, while ligation of the related inhibitory molecule cytotoxic T-lymphocyte antigen-4 appears to target more downstream signaling pathways. A major obstacle to an in-depth understanding of PD-1 signaling is the lack of physiologic models in which to study signal transduction. This review focuses on: (i) signaling pathways altered by PD-1 ligation, (ii) factors recruited upon PD-1 phosphorylation, and (iii) exploring the hypothesis that PD-1 ligation induces distinct signals during various stages of immune-cell differentiation. Lastly, we describe models to dissect the function of the PD-1 cytoplasmic tail using primary cells in the absence of agonist antibodies.
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Affiliation(s)
- James L Riley
- Department of Pathology and Laboratory Medicine, Abramson Family Cancer Research Institute, The University of Pennsylvania, Philadelphia, PA, USA.
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52
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Fu Z, Li D, Jiang W, Wang L, Zhang J, Xu F, Pang D, Li D. Association of BTLA gene polymorphisms with the risk of malignant breast cancer in Chinese women of Heilongjiang Province. Breast Cancer Res Treat 2009; 120:195-202. [PMID: 19585237 DOI: 10.1007/s10549-009-0462-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Accepted: 06/27/2009] [Indexed: 02/03/2023]
Abstract
B and T lymphocyte attenuator (BTLA) is an immunoinhibitory receptor with the ability to deliver inhibitory signals for suppressing lymphocyte activation. To identify the influences of BTLA gene polymorphisms on the risk of sporadic breast cancer, a case-control study was conducted in women from northeast of China, Heilongjiang Province. We genotyped five SNPs (rs9288952, rs2931761, rs2633562, rs2705535 and rs1844089) in BTLA gene among exons and introns. Our research groups consist of 592 patients with breast cancer and 506 age/sex-matched healthy controls. Genotypes were determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and polymerase chain reaction with confronting two-pair primer (PCR-CTPP) methods. Data were analyzed using the chi-square test by EXCEL, SPSS and Haploview softwares. The frequencies of BTLA rs1844089 CT and rs2705535 AG were higher in patients than in controls (P = 0.0164; P = 0.0031), and rs1844089 CC, rs2705535 GG and rs9288952 CC genotypes had lower incidences in patients than in controls (P = 0.0483; P = 0.0098; P = 0.0400). The frequency of haplotype CAAAT was significantly higher in patients (P = 0.0112). Strong association was shown between five SNPs of BTLA gene and tumor size, estrogen receptor (ER), progesterone receptor (PR), C-erbB-2 and P53 statuses. Strong association was observed between tumor size, ER, PR, P53 and the CAGAT(P = 0.012), TAAGT(P = 0.0378), CAGAT(P = 0.0013), CAAGT(P = 0.0373) and CAAAT(P = 0.0306) haplotypes. These results primarily suggested that BTLA gene polymorphisms may affect the sporadic breast cancer risk and prognosis in Chinese women in northeast of Heilongjiang Province.
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Affiliation(s)
- Zhenkun Fu
- Department of Immunology, Harbin Medical University, 150081, Harbin, China.
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53
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Cai G, Freeman GJ. The CD160, BTLA, LIGHT/HVEM pathway: a bidirectional switch regulating T-cell activation. Immunol Rev 2009; 229:244-58. [DOI: 10.1111/j.1600-065x.2009.00783.x] [Citation(s) in RCA: 206] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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54
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Pentcheva-Hoang T, Corse E, Allison JP. Negative regulators of T-cell activation: potential targets for therapeutic intervention in cancer, autoimmune disease, and persistent infections. Immunol Rev 2009; 229:67-87. [PMID: 19426215 DOI: 10.1111/j.1600-065x.2009.00763.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The generation of productive adaptive immune responses depends on the antigen-specific activation of T and B cells. The outcome of T-cell receptor engagement is influenced by signals from both positive and negative regulatory molecules that can either activate or inhibit T-cell function. CD28 and cytotoxic T-lymphocyte antigen-4 are the prototypical members of an immunoglobulin domain-containing protein family that play important roles in the control of T-cell responses against infection, cancer, and in autoimmune disease. Although the precise molecular details of their functions are still under active investigation, tumors and chronic pathogens seem to have exploited these pathways to achieve immune evasion. Furthermore, malfunction of the inhibitory arm of the immune response appears responsible for the development of multiple autoimmune pathologies. As a result, the negative regulators of T-cell activation have become attractive targets for therapeutic intervention in cancer, chronic infection, and autoimmune disease. The application of findings from basic research has provided insight into the manipulation of these pathways in the clinic and offers promising strategies for the treatment of disease.
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Affiliation(s)
- Tsvetelina Pentcheva-Hoang
- Department of Immunology, Howard Hughes Medical Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA
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55
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Vendel AC, Calemine-Fenaux J, Izrael-Tomasevic A, Chauhan V, Arnott D, Eaton DL. B and T lymphocyte attenuator regulates B cell receptor signaling by targeting Syk and BLNK. THE JOURNAL OF IMMUNOLOGY 2009; 182:1509-17. [PMID: 19155498 DOI: 10.4049/jimmunol.182.3.1509] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
B and T lymphocyte attenuator (BTLA) functions as a negative regulator of T cell activation and proliferation. Although the role of BTLA in regulating T cell responses has been characterized, a thorough investigation into the precise molecular mechanisms involved in BTLA-mediated lymphocyte attenuation and, more specifically, its role in regulating B cell activation has not been presented. In this study, we have begun to elucidate the biochemical mechanisms by which BTLA functions to inhibit B cell activation. We describe the cell surface expression of BTLA on various human B cell subsets and confirm its ability to attenuate B cell proliferation upon associating with its known ligand, herpesvirus entry mediator (HVEM). BTLA associates with the BCR and, upon binding to HVEM, recruits the tyrosine phosphatase Src homology 2 domain-containing phosphatase 1 and reduces activation of signaling molecules downstream of the BCR. This is exemplified by a quantifiable decrease in tyrosine phosphorylation of the protein tyrosine kinase Syk, as measured by absolute quantification mass spectrometry. Furthermore, effector molecules downstream of BCR signaling, including the B cell linker protein, phospholipase Cgamma2, and NF-kappaB, display decreased activation and nuclear translocation, respectively, after BTLA activation by HVEM. These results begin to provide insight into the mechanism by which BTLA negatively regulates B cell activation and indicates that BTLA is an inhibitory coreceptor of the BCR signaling pathway and attenuates B cell activation by targeting the downstream signaling molecules Syk and B cell linker protein.
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Affiliation(s)
- Andrew C Vendel
- Department of Protein Chemistry, Genentech, Inc., South San Francisco, CA 94080, USA
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56
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Radhakrishnan Y, Maile LA, Ling Y, Graves LM, Clemmons DR. Insulin-like growth factor-I stimulates Shc-dependent phosphatidylinositol 3-kinase activation via Grb2-associated p85 in vascular smooth muscle cells. J Biol Chem 2008; 283:16320-31. [PMID: 18420583 DOI: 10.1074/jbc.m801687200] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Insulin-like growth factor-I (IGF-I) stimulates vascular smooth muscle cell proliferation and migration by activating both MAPK and phosphatidylinositol 3-kinase (PI3K). Vascular smooth muscle cells (VSMCs) maintained in 25 mm glucose sustain MAPK activation via increased Shc phosphorylation and Grb2 association resulting in an enhanced mitogenic response compared with cells grown in 5 mm glucose. PI3K plays a major role in IGF-I-stimulated VSMC migration, and hyperglycemia augments this response. In contrast to MAPK activation the role of Shc in modulating PI3K in response to IGF-I has not been determined. In this study we show that impaired Shc association with Grb2 results in decreased Grb2-p85 association, SHPS-1-p85 recruitment, and PI3K activation in response to IGF-I. Exposure of VSMCs to cell-permeable peptides, which contained polyproline sequences from p85 proposed to mediate Grb2 association, resulted in inhibition of Grb2-p85 binding and AKT phosphorylation. Transfected cells that expressed p85 mutant that had specific prolines mutated to alanines resulted in less Grb2-p85 association, and a Grb2 mutant (W36A/W193A) that attenuated p85 binding showed decreased association of p85 with SHPS-1, PI3K activation, AKT phosphorylation, cell proliferation, and migration in response to IGF-I. Cellular exposure to 25 mm glucose, which is required for Shc phosphorylation in response to IGF-I, resulted in enhanced Grb2 binding to p85, activation of PI3K activity, and increased AKT phosphorylation as compared with cells exposed to 5 mm glucose. We conclude that in VSMCs exposed to hyperglycemia, IGF-I stimulation of Shc facilitates the transfer of Grb2 to p85 resulting in enhanced PI3K activation and AKT phosphorylation leading to enhanced cell proliferation and migration.
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Affiliation(s)
- Yashwanth Radhakrishnan
- Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA
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57
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De Trez C, Schneider K, Potter K, Droin N, Fulton J, Norris PS, Ha SW, Fu YX, Murphy T, Murphy KM, Pfeffer K, Benedict CA, Ware CF. The inhibitory HVEM-BTLA pathway counter regulates lymphotoxin receptor signaling to achieve homeostasis of dendritic cells. THE JOURNAL OF IMMUNOLOGY 2008; 180:238-48. [PMID: 18097025 DOI: 10.4049/jimmunol.180.1.238] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Proliferation of dendritic cells (DC) in the spleen is regulated by positive growth signals through the lymphotoxin (LT)-beta receptor; however, the countering inhibitory signals that achieve homeostatic control are unresolved. Mice deficient in LTalpha, LTbeta, LTbetaR, and the NFkappaB inducing kinase show a specific loss of CD8- DC subsets. In contrast, the CD8alpha- DC subsets were overpopulated in mice deficient in the herpesvirus entry mediator (HVEM) or B and T lymphocyte attenuator (BTLA). HVEM- and BTLA-deficient DC subsets displayed a specific growth advantage in repopulating the spleen in competitive replacement bone marrow chimeric mice. Expression of HVEM and BTLA were required in DC and in the surrounding microenvironment, although DC expression of LTbetaR was necessary to maintain homeostasis. Moreover, enforced activation of the LTbetaR with an agonist Ab drove expansion of CD8alpha- DC subsets, overriding regulation by the HVEM-BTLA pathway. These results indicate the HVEM-BTLA pathway provides an inhibitory checkpoint for DC homeostasis in lymphoid tissue. Together, the LTbetaR and HVEM-BTLA pathways form an integrated signaling network regulating DC homeostasis.
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Affiliation(s)
- Carl De Trez
- Division of Molecular Immunology, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037, USA
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58
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59
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Nelson CA, Fremont MD, Sedy JR, Norris PS, Ware CF, Murphy KM, Fremont DH. Structural Determinants of Herpesvirus Entry Mediator Recognition by Murine B and T Lymphocyte Attenuator. THE JOURNAL OF IMMUNOLOGY 2008; 180:940-7. [DOI: 10.4049/jimmunol.180.2.940] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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60
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Hurchla MA, Sedy JR, Murphy KM. Unexpected role of B and T lymphocyte attenuator in sustaining cell survival during chronic allostimulation. THE JOURNAL OF IMMUNOLOGY 2007; 178:6073-82. [PMID: 17475832 DOI: 10.4049/jimmunol.178.10.6073] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
B and T lymphocyte attenuator (BTLA; CD272) can deliver inhibitory signals to B and T cells upon binding its ligand herpesvirus entry mediator. Because CD28, CTLA-4, programmed death-1, and ICOS regulate the development of acute graft-vs-host disease (GVHD), we wished to assess if BTLA also played a role in this T cell-mediated response. In the nonirradiated parental-into-F1 model of acute GVHD, BTLA+/+ and BTLA-/- donor lymphocytes showed equivalent engraftment and expansion during the first week of the alloresponse. Unexpectedly, BTLA-/- donor T cells failed to sustain GVHD, showing a decline in surviving donor cell numbers beginning at day 9 and greatly reduced by day 11. Similarly, inhibition of BTLA-herpesvirus entry mediator engagement by in vivo administration of a blocking anti-BTLA Ab also caused reduced survival of donor cells. Microarray analysis revealed several genes that were differentially expressed by BTLA-/- and BTLA+/+ donor CD4+ T cells preceding the decline in BTLA-/- donor T cells. Several genes influencing Th cell polarization were differentially expressed by BTLA+/+ and BTLA-/- donor cells. Additionally, the re-expression of the IL-7Ralpha subunit that occurs in BTLA+/+ donor cells after 1 wk of in vivo allostimulation was not observed in BTLA-/- donor CD4+ cells. The striking loss of BTLA-/- T cells in this model indicates a role for BTLA activity in sustaining CD4+ T cell survival under the conditions of chronic stimulation in the nonirradiated parental-into-F1 GVHD.
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MESH Headings
- Animals
- Antibodies, Monoclonal/administration & dosage
- B-Lymphocyte Subsets/cytology
- B-Lymphocyte Subsets/immunology
- Cell Survival/immunology
- Chronic Disease
- Disease Models, Animal
- Graft Survival/immunology
- Graft vs Host Disease/immunology
- Graft vs Host Disease/metabolism
- Graft vs Host Disease/pathology
- Isoantigens/immunology
- Lymphocyte Activation/immunology
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C57BL
- Mice, Inbred MRL lpr
- Mice, Knockout
- Receptors, Immunologic/deficiency
- Receptors, Immunologic/genetics
- Receptors, Immunologic/immunology
- Receptors, Immunologic/physiology
- T-Lymphocyte Subsets/cytology
- T-Lymphocyte Subsets/immunology
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Affiliation(s)
- Michelle A Hurchla
- Department of Pathology and Center for Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, MO 63110, USA
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61
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Parry RV, Riley JL, Ward SG. Signalling to suit function: tailoring phosphoinositide 3-kinase during T-cell activation. Trends Immunol 2007; 28:161-8. [PMID: 17336157 DOI: 10.1016/j.it.2007.02.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Revised: 01/29/2007] [Accepted: 02/16/2007] [Indexed: 11/20/2022]
Abstract
Members of the CD28 family of co-receptors are crucial determinants of the outcome of T-cell activation. These receptors interact with ligands in the B7 family and either costimulate or co-inhibit signals through antigen-specific receptors. The T-cell-costimulatory molecules CD28 and inducible costimulator recruit and activate class 1A phosphoinositide 3-kinase (PI3K). Interestingly, the co-inhibitory molecules cytotoxic T lymphocyte antigen-4 and B and T lymphocyte attenuator also interact with class 1A PI3K. However, all co-inhibitory receptors share an ability to oppose activation of the key PI3K effector protein kinase B (also known as Akt). Recent evidence suggests that distinct mechanisms exist to limit Akt activation by different co-inhibitory receptors. This article examines how differential positive or negative regulation of the PI3K-Akt signalling pathway by CD28 family receptors enables functional differences between the receptors.
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Affiliation(s)
- Richard V Parry
- Inflammatory Cell Biology Laboratory, Department of Pharmacy and Pharmacology, University of Bath, Bath, UK.
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62
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Miletic AV, Sakata-Sogawa K, Hiroshima M, Hamann MJ, Gomez TS, Ota N, Kloeppel T, Kanagawa O, Tokunaga M, Billadeau DD, Swat W. Vav1 acidic region tyrosine 174 is required for the formation of T cell receptor-induced microclusters and is essential in T cell development and activation. J Biol Chem 2006; 281:38257-65. [PMID: 17050525 PMCID: PMC1876972 DOI: 10.1074/jbc.m608913200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Vav proteins are multidomain signaling molecules critical for mediating signals downstream of several surface receptors, including the antigen receptors of T and B lymphocytes. The catalytic guanine nucleotide exchange factor (GEF) activity of the Vav Dbl homology (DH) domain is thought to be controlled by an intramolecular autoinhibitory mechanism involving an N-terminal extension and phosphorylation of tyrosine residues in the acidic region (AC). Here, we report that the sequences surrounding the Vav1 AC: Tyr(142), Tyr(160), and Tyr(174) are evolutionarily conserved, conform to consensus SH2 domain binding motifs, and bind several proteins implicated in TCR signaling, including Lck, PI3K p85alpha, and PLCgamma1, through direct interactions with their SH2 domains. In addition, the AC tyrosines regulate tyrosine phosphorylation of Vav1. We also show that Tyr(174) is required for the maintenance of TCR-signaling microclusters and for normal T cell development and activation. In this regard, our data demonstrate that while Vav1 Tyr(174) is essential for maintaining the inhibitory constraint of the DH domain in both developing and mature T cells, constitutively activated Vav GEF disrupts TCR-signaling microclusters and leads to defective T cell development and proliferation.
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Affiliation(s)
- Ana V. Miletic
- From the Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, the
| | - Kumiko Sakata-Sogawa
- Research Unit for Single Molecule Immunoimaging, RIKEN Center for Allergy and Immunology, Yokohama, Kanagawa 230-0045, Japan, the
| | - Michio Hiroshima
- Research Unit for Single Molecule Immunoimaging, RIKEN Center for Allergy and Immunology, Yokohama, Kanagawa 230-0045, Japan, the
| | - Michael J. Hamann
- Department of Immunology and Division of Oncology Research, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, the
| | - Timothy S. Gomez
- Department of Immunology and Division of Oncology Research, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, the
| | - Naruhisa Ota
- Laboratory for Autoimmune Regulation, RIKEN Center for Allergy and Immunology, Yokohama, Kanagawa 230-0045, Japan, and the
| | - Tracie Kloeppel
- From the Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, the
| | - Osami Kanagawa
- Laboratory for Autoimmune Regulation, RIKEN Center for Allergy and Immunology, Yokohama, Kanagawa 230-0045, Japan, and the
| | - Makio Tokunaga
- Research Unit for Single Molecule Immunoimaging, RIKEN Center for Allergy and Immunology, Yokohama, Kanagawa 230-0045, Japan, the
- Structural Biology Center, National Institute of Genetics, and Department of Genetics, Graduate University for Advanced Studies, Mishima, Shizuoka 411-8540, Japan
| | - Daniel D. Billadeau
- Department of Immunology and Division of Oncology Research, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, the
| | - Wojciech Swat
- From the Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, the
- To whom correspondence should be addressed: Dept. of Pathology and Immunology, WA University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110. Tel.: 314-747-8886; Fax: 314-362-4096; E-mail:
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63
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Murphy KM, Nelson CA, Sedý JR. Balancing co-stimulation and inhibition with BTLA and HVEM. Nat Rev Immunol 2006; 6:671-81. [PMID: 16932752 DOI: 10.1038/nri1917] [Citation(s) in RCA: 229] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The interaction between B- and T-lymphocyte attenuator (BTLA), an inhibitory receptor whose extracellular domain belongs to the immunoglobulin superfamily, and herpesvirus-entry mediator (HVEM), a co-stimulatory tumour-necrosis factor receptor, is unique in that it is the only receptor-ligand interaction that directly bridges these two families of receptors. This interaction has raised many questions about how receptors from two different families could interact and what downstream signalling events might occur as a result of receptor ligation. As we discuss, recent studies show that engagement of HVEM with its endogenous ligand (LIGHT) from the tumour-necrosis factor family induces a powerful immune response, whereas HVEM interactions with BTLA negatively regulate T-cell responses.
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MESH Headings
- Animals
- Disease
- Humans
- Ligands
- Protein Binding
- Receptors, Immunologic/antagonists & inhibitors
- Receptors, Immunologic/chemistry
- Receptors, Immunologic/immunology
- Receptors, Tumor Necrosis Factor/antagonists & inhibitors
- Receptors, Tumor Necrosis Factor/chemistry
- Receptors, Tumor Necrosis Factor/classification
- Receptors, Tumor Necrosis Factor/immunology
- Receptors, Tumor Necrosis Factor, Member 14
- Receptors, Virus/antagonists & inhibitors
- Receptors, Virus/chemistry
- Receptors, Virus/classification
- Receptors, Virus/immunology
- Signal Transduction
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Affiliation(s)
- Kenneth M Murphy
- Department of Pathology and Centre for Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, 660 S. Euclid, St Louis, Missouri 63110, USA.
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64
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Gavrieli M, Sedy J, Nelson CA, Murphy KM. BTLA and HVEM Cross Talk Regulates Inhibition and Costimulation. Adv Immunol 2006; 92:157-85. [PMID: 17145304 DOI: 10.1016/s0065-2776(06)92004-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Recently a new inhibitory immunoglobulin domain-containing lymphocyte receptor was identified on the basis of its T helper 1 (T(H)1)-selective expression in murine T cell lines, which was named B and T lymphocyte attenuator (BTLA). Several groups have confirmed the initial characterization of BTLA as an inhibitory receptor, which was initially inferred from the mild increases in several parameters of BTLA-deficient mice. The initial expectation that BTLA would interact with a B7 family ligand, such as the B7x protein, was surprisingly overturned with the functional cloning of the actual BTLA ligand as herpesvirus entry mediator (HVEM). This was unexpected largely due to the fact that this interaction represents the convergence of two very different, although each quite extensive, families of receptors and ligands. The interaction of BTLA, which belongs to the CD28 family of the immunoglobulin superfamily, and HVEM, a costimulatory tumor-necrosis factor (TNF) receptor (TNFR), is quite unique in that it is the only receptor-ligand interaction that directly bridges these two families of receptors. This interaction has raised many questions about how receptors from two different families could interact and which are the signaling events downstream of receptor ligation. As we discuss here and recently demonstrated, HVEM interaction with BTLA serves to negatively regulate T cell responses, in contrast to the strong activation observed when HVEM engages its endogenous ligand from the TNF family. Finally, as studies of BTLA are just now beginning to extend beyond the initial characterizations, it is becoming clear that there are many complex issues remaining to be resolved, particularly potential polymorphisms that may engender disease susceptibility in the human.
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Affiliation(s)
- Maya Gavrieli
- Department of Pathology and Center for Immunology, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri, USA
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