TIM genes: a family of cell surface phosphatidylserine receptors that regulate innate and adaptive immunity

Summary: The TIM (T cell/transmembrane, immunoglobulin, and mucin) gene family plays a critical role in regulating immune responses, including allergy, asthma, transplant tolerance, autoimmunity, and the response to viral infections. The unique structure of TIM immunoglobulin variable region domains allows highly specific recognition of phosphatidylserine (PtdSer), exposed on the surface of apoptotic cells. TIM-1, TIM-3, and TIM-4 all recognize PtdSer but differ in expression, suggesting that they have distinct functions in regulating immune responses. TIM-1, an important susceptibility gene for asthma and allergy, is preferentially expressed on T-helper 2 (Th2) cells and functions as a potent costimulatory molecule for T-cell activation. TIM-3 is preferentially expressed on Th1 and Tc1 cells, and generates an inhibitory signal resulting in apoptosis of Th1 and Tc1 cells. TIM-3 is also expressed on some dendritic cells and can mediate phagocytosis of apoptotic cells and cross-presentation of antigen. In contrast, TIM-4 is exclusively expressed on antigen-presenting cells, where it mediates phagocytosis of apoptotic cells and plays an important role in maintaining tolerance. TIM molecules thus provide a functional repertoire for recognition of apoptotic cells, which determines whether apoptotic cell recognition leads to immune activation or tolerance, depending on the TIM molecule engaged and the cell type on which it is expressed.     

Defective de novo thymocyte maturation in cyclosporin A (CsA)-induced autoimmunity: expression of costimulatory and activation molecules

Lethally x-irradiated Lewis rats, reconstituted with syngeneic bone marrow and transiently treated with CsA for 4 weeks, will develop an autoimmune disease about 2–3 weeks after cessation of CsA therapy. CsA-induced autoimmunity is a thymus-dependent and T cell-mediated autoimmune disease. CsA is thought to generate autoreactive T cells by interference with negative selection in the thymus; x-irradiation is required to eliminate the peripheral autoregulatory T cell circuit. In this study we re-evaluate the effect of CsA on thymic atrophy and thymocyte maturation. Subsequently we examine the expression of costimulatory and activation molecules (CD2, CD5, CD11a, CD11b, CD25, CD28, CD43, CD54, OX-40, RT-1A, RT-1B and RT-1D) during distinct maturational stages in order to detect possible clues to the observed effects of CsA on thymocyte maturation and selection. The results revealed that CsA blocks maturation of double-positive TCR^int to double-positive TCR^high thymocytes and preferentially inhibits the development of mature CD4 single-positive thymocytes. Furthermore, CsA administration resulted in a reduced expression of the costimulatory CD2 molecule. Although it is a matter of debate whether this defective CD2 expression is involved in the aberrant maturation and selection of thymocytes, it is speculated that reduced costimulation via CD2 may influence differentiation into distinct T cell subsets.     

T细胞免疫球蛋白粘蛋白域基因多态性与哮喘关系的研究进展

哮喘是儿童时期最常见的慢性呼吸道变应性疾病,近些年来在全球范围有逐渐增加的趋势。大多数成年期哮喘由儿童哮喘发展而来,其病因既受环境因素的影响,又有明显的遗传倾向,是一种复杂的多基因遗传性疾病。人类的TIM基因家族有3个,即:TIM-1、TIM-3和TIM-4,定位于染色体5q33.2,此区域是哮喘的主要遗传易感位点之一。本文就TIM基因家族多态性与哮喘近年来的研究进展做一综述。     

Apoptotic signal transduction and T cell tolerance

The healthy immune system makes use of a variety of surveillance mechanisms at different stages of lymphoid development to prevent the occurrence and expansion of potentially harmful autoreactive T cell clones. Disruption of these mechanisms may lead to inappropriate activation of T cells and the development of autoimmune and lymphoproliferative diseases [such as multiple sclerosis, rheumatoid arthritis, lupus erythematosus, diabetes and autoimmune lymphoproliferative syndrome (ALPS)]. Clonal deletion of T cells with high affinities for self-peptide-MHC via programmed cell death (apoptosis) is an essential mechanism leading to self-tolerance. Referred to as negative selection, central tolerance in the thymus serves as the first checkpoint for the developing T cell repertoire and involves the apoptotic elimination of potentially autoreactive T cells clones bearing high affinity T cell receptors (TCR) that recognize autoantigens presented by thymic epithelial cells. Autoreactive T cells that escape negative selection are held in check in the periphery by either functional inactivation (“anergy”) or extrathymic clonal deletion, both of which are dependent on the strength and frequency of the TCR signal and the costimulatory context, or by regulatory T cells. This review provides an overview of the different molecular executioners of cell death programs that are vital to intrathymic or extrathymic clonal deletion of T cells. Further, the potential involvement of various apoptotic signaling paradigms are discussed with respect to the genesis and pathophysiology of autoimmune disease.     

The impact of the TIM gene family on tumor immunity and i mmunosuppression

Tumor immunoevasion is an advanced phase of cancer immunosurveillance in which tumor cells acquire the ability to circumvent host immune systems and exploit protumorigenic inflammation. T-cell immunoglobulin mucin （TIM） gene family members have emerged as critical checkpoint proteins that regulate multiple immune response phases and maintain immune homeostasis. Accumulating evidence demonstrates that tumor cells exploit TIM gene family members to evade immunosurveillance, whereas TIM gene family members facilitate the prevention of inflammation-related tumor progression. Thus, a comprehensive analysis to clarify the relative contributions of TIM gene family members in tumor progression may elucidate immunosurveillance systems in cancer patients.     

The role of ICOS and other costimulatory molecules in allergy and asthma

Activation and differentiation of T cells play a critical role in the pathogenesis of allergies and asthma. Upon encounter with specific antigen, naïve T helper precursor (ThP) cells become activated, an event that is regulated not only by engagement of the T cell receptor (TCR) with peptide presented in the context of MHC class II molecules, but also by a number of costimulatory signals. CD28 engagement by B7-1 and B7-2 on resting ThP cells provides a critical signal for initial cell cycle progression, interleukin-2 production and clonal expansion. However, in recent years, other related members of the immunoglobulin (Ig) family, such as inducible costimulatory molecules (ICOS) and the TNF receptor family members which include OX40, have also been demonstrated to play an important role in providing unique and complementary signals that regulate the outcome of immune responses. These positive costimulatory signals are counterbalanced by signals that dampen down immune responses and include CTLA-4, PD-1 and the recently described Ig superfamily members BTLA and TIM-3. This review discusses the role of these costimulatory signals and their potential involvement in the pathogenesis of asthma and allergic responses.     

Superantigen activation of CD4+ and CD8+ T cells from HIV-infected subjects: role of costimulatory molecules and antigen-presenting cells (APC)

T cell receptor (TCR) triggering via superantigens induces decreased proliferative responses and increased apoptosis in T cells from HIV-infected patients compared with controls. Our aim was to delineate the role of intrinsic T cell defects, of APC dysfunction and of cytokines and costimulatory signal dysregulation in the deficient responses of CD4⁺and CD8⁺ T cells from HIV⁺ subjects to the superantigen Staphylococcus enterotoxin A (SEA). Proliferation and IL-2Rα up-regulation on SEA-stimulated CD4⁺and CD8⁺T cells in whole blood were reduced in HIV⁺ subjects with CD4 counts < 500, compared with controls. Neither addition of IL-2, IL-12 or phorbol myristate acetate (PMA) nor neutralization of endogenous IL-10, tumour necrosis factor-alpha (TNF-α), TNF-β or transforming growth factor-beta (TGF-β) could restore the decreased activation by SEA. Possible intrinsic T cell defects were studied by presenting SEA on HLA-DR-transfected Chinese hamster ovary (CHO) cells, co-expressing LFA3 and/or CD80, to purified T cells. In this system CD8⁺T cells from most HIV⁺ patients were hyporesponsive with regard to IL-2 production, IL-2Rα up-regulation and proliferation, whereas clearly reduced responses were only shown in CD4⁺T cells from AIDS patients. Similarly, apoptosis was increased in CD8⁺T cells from all patients, but only in CD4⁺T cells from AIDS patients. During HIV infection, the responses to TCR triggering through SEA are deficient in both T cell subsets. The intrinsic defect appears earlier during disease progression in purified CD8⁺T than in CD4⁺T cells, it occurs in conjunction with both CD2 and CD28 costimulation, and it is correlated with increased levels of apoptosis.     

The role of the T-cell costimulatory molecule Tim-1 in the immune response

Upon encountering antigen, CD4+ T-cells become activated and can differentiate into subsets with distinct functional characteristics. One of these subsets is the Th2 cell, which generates large amounts of interleukin (IL)-4, -5, -10 and -13 in response to a subsequent encounter with antigen. In the context of a protective immune response, Th2 cells promote immune cell activation, antibody production, and inflammatory responses that help clear infections. However, aberrant responses by Th2 cells can lead to debilitating allergic diseases such as asthma. Thus, a reasonable approach toward gaining novel insights into immunity and allergic disease is to define the mechanisms that control Th2 cell differentiation and mature Th2 cell function. Recent work suggests that a protein called Tim-1 (T-cell immunoglobulin and mucin protein-1) is expressed on CD4+ T-cells and plays a central role in regulating Th2 responses. Genetic analysis has linked polymorphisms in the human TIM1 gene to susceptibility to allergic disease, while studies involving mice have shown that ligation of Tim-1 promotes CD4+ T-cell activation. The signal transduction pathways downstream of Tim-1 are a relatively unexplored area. Continued study will undoubtedly reveal novel insights regarding the relationships between Tim-1, Th2 responses, and allergic disease.     

TIM2转基因细胞瘤苗对小鼠作用的初步研究

目的 观察小鼠TIM2转基因H22肝癌细胞瘤苗在小鼠体内的成瘤作用 ,初步研究其免疫原性.方法 构建TIM2基因真核表达载体pIRES2-EGFP - TIM2,脂质体法转染H22细胞,制备得到TIM2基因修饰的H22细胞瘤苗,建立小鼠肝癌移植瘤模型,观察其在小鼠体内的成瘤作用.结果 成功得到TIM2基因修饰的H22 细胞瘤苗,免疫接种小鼠后,可明显抑制小鼠体内肿瘤的发生和发展;给予H22-TIM2接种的小鼠CD4亚群、CD4/CD8比值显著高于H22-EGFP 细胞接种组、荷瘤对照组和正常对照组.结论 TIM2基因修饰H22细胞后,可显著降低H22细胞的体内成瘤性,抑制小鼠肿瘤生长,同时.在体内具有一定的免疫原性,为进一步探讨TIM2 在肿瘤生物治疗中的作用提供了初步的实验依据.     

Autoimmunity risk alleles in costimulation pathways

Summary:  The basis for susceptibility to common autoimmune diseases is a complex interplay between multiple genetic and environmental risk factors. We have now entered a new generation of genetic study designs which has not only furthered our understanding of the individual mechanisms involved in the common human autoimmune diseases but also has pointed towards common pathways. In this review we focus on costimulatory mechanisms with the most convincing association results in large collections of patients and control subjects. These include the genes encoding cytotoxic T-lymphocyte antigen-4, CD58, CD40, inducible T-cell costimulator ligand, CD244, CD226, tumor necrosis factor (TNF) (ligand) superfamily member 4, TNF superfamily member 15, and programmed cell death 1. The unbiased genome-wide association scans suggest that indeed immune related genes underlie the pathogenesis of human autoimmune disease with common involvement of costimulatory pathways. The identification of allelic variants associated with disease risk followed by understanding their functional outcomes and affected pathways provides a rationale approach for drug design.     

The interaction properties of costimulatory molecules revisited

B7-1 and B7-2 are generally thought to have comparable structures and affinities for their receptors, CD28 and CTLA-4, each of which is assumed to be bivalent. We show instead (1) that B7-2 binds the two receptors more weakly than B7-1, (2) that, relative to its CTLA-4 binding affinity, B7-2 binds CD28 2- to 3-fold more effectively than B7-1, (3) that, unlike B7-1, B7-2 does not self-associate, and (4) that, in contrast to CTLA-4 homodimers, which are bivalent, CD28 homodimers are monovalent. Our results indicate that B7-1 markedly favors CTLA-4 over CD28 engagement, whereas B7-2 exhibits much less bias. We propose that the distinct structures and binding properties of B7-1 and B7-2 account for their overlapping but distinct effects on T cell responses.     

Regulatory T cells in human disease and their potential for therapeutic manipulation

Regulatory T cells are proposed to play a central role in the maintenance of immunological tolerance in the periphery, and studies in many animal models demonstrate their capacity to inhibit inflammatory pathologies in vivo. At a recent meeting [Clinical Application of Regulatory T Cells, 7-8 April 2005, Horsham, UK, organized by the authors of this review, in collaboration with the British Society for Immunology and Novartis] evidence was discussed that certain human autoimmune, infectious and allergic diseases are associated with impaired regulatory T-cell function. In contrast, evidence from several human cancer studies and some infections indicates that regulatory T cells may impair the development of protective immunity. Importantly, certain therapies, both those that act non-specifically to reduce inflammation and antigen-specific immunotherapies, may induce or enhance regulatory T-cell function. The purpose of this review was to summarize current knowledge on regulatory T-cell function in human disease, and to assess critically how this can be tailored to suit the therapeutic manipulation of immunity.     

Challenges in the pursuit of immune tolerance

Strategies for inducing immune tolerance are fundamentally similar across a spectrum of immune-mediated disorders, including allergic disease, autoimmunity, and rejection of allografts. In each case, the objective of establishing an immunoregulatory balance is challenged by variable upswings in effector cell populations and proinflammatory mediators of immunity, requiring careful, and innovative therapeutic intervention to restore stability. The Immune Tolerance Network, an international consortium sponsored by the National Institutes of Health, seeks to advance both the scientific understanding and the clinical success of immune therapies for these disorders, through an innovative and collaborative effort involving clinical trials and mechanistic studies. Over the last decade, scientists have evaluated cell-based ablation and deviation strategies in trials using lymphocyte-specific targeting, induction of host-donor hematopoietic chimerism, induction of antigen-specific immune regulation, and a variety of antigen desensitization approaches. In this article, we review some of the highlights of this experience and discuss the potential for progress, utilizing new insights into regulatory mechanisms and biomarker signatures of tolerance.     

Phenothiazine-induced increase in thyroid autoantigens and costimulatory molecules on thyroid cells: a pathophysiological mechanism for drug-induced autoimmunity?

We have previously demonstrated (J Immunol 1995; 154 :3593) that MHC class II antigens can be induced on thyroid epithelial cells (TEC) by alimemazine, a member of the phenothiazine group. Although this expression of MHC class II antigens on TEC confers the theoretical ability to behave as antigen-presenting cells (APC), the simultaneous expression of self antigens and co-receptor(s) must also occur for efficient presentation of self antigens. Therefore, we investigated whether alimemazine applied at pharmacologic doses would modify the expression of thyroid antigens, and simultaneously, the expression of intercellular adhesion molecule-1 (ICAM-1), B7, and LFA-1 co-receptors in human TEC in culture. Using polymerase chain reaction (PCR) amplification and Northern blot analysis, we showed that alimemazine induces increases in thyroglobulin (Tg) and thyroid-stimulating hormone receptor (TSH-R) cDNA, within the first 2 h following its addition. This phenomenon is followed 48 h later by an increase of Tg and TSH-R protein expression on the surface of TEC. Furthermore, increases in the expression of ICAM-1 and B7 co-receptors were concomitantly observed. These results suggest that alimemazine, a drug currently used in paediatrics, could play a role in the induction and perpetuation of thyroid autoimmune disorders by transforming TEC into functional APC.     

Lentiviral gene transfer of CTLA4 generates B cells with reduced costimulatory properties

Peripheral T-cell (TC) tolerance can be induced by tolerogenic antigen-presenting cell (APC). A prerequisite is the reduction or blockade of B7 of APC. Besides dendritic cell, B cells can be used as APC. Here, we show the generation B cells with reduced B7 expression by lentiviral transduction of endoplasmic reticulum (ER)-directed CTLA4. Vectors coding for the human CTL4-Ig were used for the human B-cell line Raji. Transduction efficiency was over 90% (MOI = 3). For the murine B-cell line A20 and for primary mouse B cells, murine CTLA4 was used. We show that B cells with reduced B7 expression reduce the antigen (Ag) specific TC proliferation in vitro. B cells expressing an ER-directed CTLA4 may reduce Ag-specific immune responses.     

Intracellular signals of T cell costimulation

Ligation of T cell receptor （TCR） alone is insufficient to induce full activation of T lymphocytes. Additional ligand-receptor interactions （costimulation） on antigen presenting cells （APCs） and T cells are required. T cell costimulation has been shown to be essential for eliciting efficient T cell responses, involving all phases during T cell development. However, the mechanisms by which costimulation affects the function of T cells still need to be elucidated. In recent years, advances have been made in studies of costimulation as potential therapies in cancer, infectious disease as well as autoimmune disease. In this review, we discussed intracellular costimulation signals that regulate T cell proliferation, cell cycle progression, cytokine production, survival, and memory development. In general, the pathway of phosphoinositide-3 kinase （PI3K）/protein kinase B （PKB, also known as Akt）/nuclear factor κB （NF-κB） might be central to many costimulatory effects. Through these pathways, costimulation controls T-cell expansion and proliferation by maintenance of survivin and aurora B expression, and sustains long-term T-cell survival and memory development by regulating the expression of bcl-2 family members. Cellular ＆ Molecular Immunology. 2008;5（4）：239-247.     

Potential role of B7-1 and CD28 molecules in immunosuppression in leprosy

In order to understand the mechanism of unresponsiveness towards Mycobacterium leprae antigens in leprosy, we evaluated the role of M. leprae sonicate antigens in regulating the expression of the costimulatory molecules B7-1, CD28, intercellular adhesion molecule-1 (ICAM-1), LFA-1α, LFA-1β and Mac-1 on the lymphocytes of both leprosy patients and healthy subjects. It was observed that the expression of B7-1 and CD28 was significantly decreased but the levels of ICAM-1 and LFA-1α were increased in patients with untreated borderline leprosy (BL)/lepromatous leprosy (LL) disease. No remarkable change was noticed in the case of borderline tuberculoid (BT) leprosy or treated BL/LL patients. Further, a striking finding was that lymphocytes from healthy subjects cultured with a particularly high dose of M. leprae sonicate antigens down-regulated the expression of B7-1 and CD28 molecules, but up-regulated the display of ICAM-1 and LFA-1α. Furthermore, proliferation induced by M. leprae sonicate was inhibited only by anti-B7-1 antibody. Mycobacterium leprae antigen-induced suppression of the proliferation of lymphocytes of healthy volunteers and LL patients was reversed by culturing the lymphocytes with purified protein derivative (PPD). It may be concluded from the findings in this study that down regulation of B7-1 and CD28 in BL/LL leprosy patients may be responsible for a defective T cell signalling by the B7-1/CD28 pathway caused by M. leprae antigens. This may lead to clonal inactivation of M. leprae-reactive T cells, consequently the bacilli grow without restriction in macrophages.     

TIM family proteins and autoimmunity

Despite their relative novelty, a growing body of literature now demonstrates that T cell immunoglobulin and mucin domain (TIM) family proteins are important regulators of immunity. Not surprisingly, these proteins also play prominent roles in the control of auto-reactive immune responses. Thus, modulation of TIM protein function may prove to be a useful strategy to control autoimmune diseases.