Promotion of tissue inflammation by the immune receptor Tim-3 expressed on innate immune cells

T cell/transmembrane, Ig, and mucin-3 allelic variants differentially recognize phosphatidylserine and mediate phagocytosis of apoptotic cells

T cell/transmembrane, Ig, and mucin (TIM) proteins, identified using a congenic mouse model of asthma, critically regulate innate and adaptive immunity. TIM-1 and TIM-4 are receptors for phosphatidylserine (PtdSer), exposed on the surfaces of apoptotic cells. Herein, we show with structural and biological studies that TIM-3 is also a receptor for PtdSer that binds in a pocket on the N-terminal IgV domain in coordination with a calcium ion. The TIM-3/PtdSer structure is similar to that of TIM-4/PtdSer, reflecting a conserved PtdSer binding mode by TIM family members. Fibroblastic cells expressing mouse or human TIM-3 bound and phagocytosed apoptotic cells, with the BALB/c allelic variant of mouse TIM-3 showing a higher capacity than the congenic C.D2 Es-Hba-allelic variant. These functional differences were due to structural differences in the BC loop of the IgV domain of the TIM-3 polymorphic variants. In contrast to fibroblastic cells, T or B cells expressing TIM-3 formed conjugates with but failed to engulf apoptotic cells. Together these findings indicate that TIM-3-expressing cells can respond to apoptotic cells, but the consequence of TIM-3 engagement of PtdSer depends on the polymorphic variants of and type of cell expressing TIM-3. These findings establish a new paradigm for TIM proteins as PtdSer receptors and unify the function of the TIM gene family, which has been associated with asthma and autoimmunity and shown to modulate peripheral tolerance.

TIM-3 and its regulatory role in immune responses

T cell immunoglobulin mucin-(TIM)-3 was first identified as a molecule specifically expressed on IFN-γ-secreting CD4(+) T helper 1 (Th1) and CD8(+) T cytotoxic (Tc1) cells in both mice and humans. TIM-3 acts as a negative regulator of Th1/Tc1 cell function by triggering cell death upon interaction with its ligand, galectin-9. This negative regulatory function of TIM-3 has now been expanded to include its involvement in establishing and/or maintaining a state of T cell dysfunction or "exhaustion" observed in chronic viral diseases. In addition, it is now appreciated that TIM-3 has other ligands and is expressed on other cell types, where it may function differently. Given that an increasing body of data support an important role for TIM-3 in both autoimmune and chronic inflammatory diseases in humans, deciphering the function of TIM-3 on different cell types during different immune conditions and how these can be regulated will be critical for harnessing the therapeutic potential of TIM-3 for the treatment of disease.

Galectin-9 significantly prolongs the survival of fully mismatched cardiac allografts in mice

BACKGROUND

The involvement of T-cell immunoglobulin mucin-3 (Tim-3) in the regulation of solid organ transplantation rejection is largely unknown. We used galectin-9 (Tim-3 ligand) to evaluate the effect and mechanisms of Tim-3/galectin-9 pathway in an allogeneic heart transplant model.

METHODS

The murine cardiac transplant model from BALB/c (H-2d) to C57BL/6 (H-2b) was built. The recipients were administered with galectin-9 for 7 days from day 1 or day 3 posttransplant. The complete cessation of cardiac contractility was defined as the observation endpoint. The effect of galectin-9 on cell proliferation was assessed by mixed lymphocyte reaction. Histology and immunohistochemistry were performed to estimate the severity of rejection. The phenotype and cytokine profile of lymphocytes were analyzed by flow cytometry.

RESULTS

In vitro, galectin-9 suppressed the proliferation of lymphocytes mixed lymphocyte reactions in a dose- and beta-galactoside-dependent manner. In vivo, galectin-9 treatment from day 1 to day 3 posttransplant achieved similar survival time of grafts (median survival time, 22.7+/-1.2 vs. 23.0+/-1.0 days). The prolonged survival time was associated with reduced infiltration of CD4 and CD8 lymphocytes in allografts. Furthermore, the intragraft transcriptional profiling in galectin-9-treated group showed reduction of IFN-gamma and IL-17 mRNA but elevation of Ebi-3 and galectin-9 mRNA. Flow cytometry analysis indicated that galectin-9 treatment reduced the ratio of T helper (Th) 1 and Th17 cells in the draining lymph nodes and peripheral blood.

CONCLUSIONS

A short-course administration of galectin-9 significantly prolonged the survival of fully allogeneic cardiac allografts, which was associated with the suppression of Th1 and Th17 immune responses.

Persistent elevation of plasma osteopontin levels in HIV patients despite highly active antiretroviral therapy

In human immunodeficiency virus (HIV) infection, not only HIV itself but also systemic immune activation plays a role in the disease progression to acquired immune deficiency syndrome (AIDS). The systemic immune activation may be present even during highly active antiretroviral therapy (HAART). An increased expression of osteopontin, a proinflammatory cytokine, during HAART was reported in lymph nodes of HIV infected individuals. Osteopontin is also known to be involved in the pathogenesis of various HAART-induced diseases. Here, we measured osteopontin and other inflammatory markers such as neopterin and galectin-9 using serially collected plasma from patients with HIV/AIDS to find novel markers for immune activation. Four AIDS patients complicated with various opportunistic infections and one acute HIV patient were studied. Osteopontin levels (normal levels: < 820 ng/ml) were elevated in all the patients (1,178-2,450 ng/ml). Likewise, galectin-9 levels (normal levels: < 46 pg/ml) were elevated in all patients (> 130 pg/ml), with the exceptionally high level in the acute HIV patient (4,196 pg/ml). Neopterin levels (normal ranges: 2-8 pmol/L) were elevated in four patients (21-99 pmol/L). After HAART, the levels of galectin-9 and neopterin apparently decreased, whereas the levels of osteopontin did not decrease. Thus, the high levels of osteopontin were sustained despite the clinical improvement. Fisher exact probability test showed that the mode of the changes was different between osteopontin and galectin-9, and between osteopontin and neopterin (p = 0.024). We therefore propose that the plasma osteopontin is a useful marker of immune activation during HAART and HAART-induced side effects.

Galectin-9 ameliorates immune complex-induced arthritis by regulating Fc gamma R expression on macrophages

Galectin-9 up-regulated Fc gamma RIIb expression of mouse peritoneal macrophages in vitro but down-regulated Fc gamma RIII expression. Galectin-9-treated macrophages stimulated with immune complexes (IC) produced less TNFalpha and IL-1 beta but more IL-10 than PBS-treated macrophages. Macrophage enhancing effects on IC-induced C5a and neutrophil chemotactic activity were also diminished for galectin-9-treated macrophages. In galectin-9-treated mice, the severity of IC-induced arthritis was reduced, as were pro-inflammatory cytokine levels in inflamed joints and serum C5a. Fc gamma RIIb expression of macrophages from galectin-9-treated mice was up-regulated, whereas Fc gamma RIII expression was down-regulated. Macrophages from galectin-9-treated mice produced less TNFalpha and IL-1 beta but more IL-10 than PBS-treated mice. Disease severity of galectin-9-transgenic mice was milder than wild-type mice, whereas that of galectin-9-deficient mice was exaggerated. Furthermore, macrophage Fc gamma RIIb expression in galectin-9-deficient mice was down-regulated, while Fc gamma RIII expression was up-regulated. These results suggest that galectin-9 suppresses IC-induced inflammation partly by regulating Fc gamma R expression on macrophages.

Galectin-9 is a high affinity IgE-binding lectin with anti-allergic effect by blocking IgE-antigen complex formation

Galectin (Gal)-9 was first described as an eosinophil chemoattractant. With the progress in research, Gal-9 has come to be known as a versatile immunomodulator that is involved in various aspects of immune regulations, and the entire picture of the function still remains elusive. To uncover as-yet unknown activity of Gal-9, we have been examining the effect of the protein in various disease animal models. Here we show that Gal-9 attenuated asthmatic reaction in guinea pigs and suppressed passive-cutaneous anaphylaxis in mice. These results indicate the mast cell stabilizing effect of Gal-9. In vitro studies of mast cell degranulation involving RBL-2H3 cells demonstrated that Gal-9 suppressed degranulation from the cells stimulated by IgE plus antigen and that the inhibitory effect was completely abrogated in the presence of lactose, indicating lectin activity of Gal-9 is critical. We found that Gal-9 strongly and specifically bound IgE, which is a heavily glycosylated immunoglobulin, and that the interaction prevented IgE-antigen complex formation, clarifying the mode of action of the anti-degranulation effect. Gal-9 is expressed by several mast cells including mouse mast cell line MC/9. The fact that immunological stimuli of MC/9 cells augmented Gal-9 secretion from the cells implies that Gal-9 is an autocrine regulator of mast cell function to suppress excessive degranulation. Collectively, these findings shed light on a novel function of Gal-9 in mast cells and suggest a beneficial utility of Gal-9 for the treatment of allergic disorders including asthma.

Galectin-9 is a high affinity IgE-binding lectin with anti-allergic effect by blocking IgE-antigen complex formation

Galectin (Gal)-9 was first described as an eosinophil chemoattractant. With the progress in research, Gal-9 has come to be known as a versatile immunomodulator that is involved in various aspects of immune regulations, and the entire picture of the function still remains elusive. To uncover as-yet unknown activity of Gal-9, we have been examining the effect of the protein in various disease animal models. Here we show that Gal-9 attenuated asthmatic reaction in guinea pigs and suppressed passive-cutaneous anaphylaxis in mice. These results indicate the mast cell stabilizing effect of Gal-9. In vitro studies of mast cell degranulation involving RBL-2H3 cells demonstrated that Gal-9 suppressed degranulation from the cells stimulated by IgE plus antigen and that the inhibitory effect was completely abrogated in the presence of lactose, indicating lectin activity of Gal-9 is critical. We found that Gal-9 strongly and specifically bound IgE, which is a heavily glycosylated immunoglobulin, and that the interaction prevented IgE-antigen complex formation, clarifying the mode of action of the anti-degranulation effect. Gal-9 is expressed by several mast cells including mouse mast cell line MC/9. The fact that immunological stimuli of MC/9 cells augmented Gal-9 secretion from the cells implies that Gal-9 is an autocrine regulator of mast cell function to suppress excessive degranulation. Collectively, these findings shed light on a novel function of Gal-9 in mast cells and suggest a beneficial utility of Gal-9 for the treatment of allergic disorders including asthma.

Attenuation of Th1 response through galectin-9 and T-cell Ig mucin 3 interaction inhibits autoimmune diabetes in NOD mice

Galectin-9 (gal-9), widely expressed in many tissues, regulates Th1 cells and induces their apoptosis through its receptor, T-cell Ig mucin 3, which is mainly expressed on terminally differentiated Th1 cells. Type 1 diabetes is a Th1-dominant autoimmune disease that specifically destroys insulin-producing beta cells. To suppress the Th1 immune response in the development of autoimmune diabetes, we overexpressed gal-9 in NOD mice by injection of a plasmid encoding gal-9. Mice treated with gal-9 plasmid were significantly protected from diabetes and showed less severe insulitis compared with controls. Flow cytometric analyses in NOD-T1/2 double transgenic mice showed that Th1-cell population in spleen, pancreatic lymph node and pancreas was markedly decreased in gal-9 plasmid-treated mice, indicating a negative regulatory role of gal-9 in the development of pathogenic Th1 cells. Splenocytes from gal-9 plasmid-treated mice were less responsive to mitogenic stimulation than splenocytes from the control group. However, adoptive transfer of splenocytes from gal-9-treated or control mice caused diabetes in NOD/SCID recipients with similar kinetics, suggesting that gal-9 treatment does not induce active tolerance in NOD mice. We conclude that gal-9 may downregulate Th1 immune response in NOD mice and could be used as a therapeutic target in autoimmune diabetes.

TIM-3 is expressed on activated human CD4+ T cells and regulates Th1 and Th17 cytokines

TIM-3 is a molecule selectively expressed on a subset of murine IFN-gamma-secreting T helper 1 (Th1) cells but not Th2 cells, and regulates Th1 immunity and tolerance in vivo. At this time little is known about the role of TIM-3 on human T cells. To determine if TIM-3 similarly identifies and regulates Th1 cells in humans, we generated a panel of mAb specific for human TIM-3. We report that TIM-3 is expressed by a subset of activated CD4(+) cells, and that anti-CD3/anti-CD28 stimulation increases both the level of expression as well as the number of TIM-3(+) T cells. We also find that TIM-3 is expressed at high levels on in vitro polarized Th1 cells, and is expressed at lower levels on Th17 cells. In addition, human CD4(+) T cells secreted elevated levels of IFN-gamma, IL-17, IL-2, and IL-6, but not IL-10, IL-4, or TNF-alpha, when stimulated with anti-CD3/anti-CD28 in the presence of TIM-3-specific, putative antagonistic antibodies. This was not mediated by differences in proliferation or cell death, but rather by induction of cytokines at the transcriptional level. These results suggest that TIM-3 is a negative regulator of human T cells and regulates Th1 and Th17 cytokine secretion.

Tolerogenic signals delivered by dendritic cells to T cells through a galectin-1-driven immunoregulatory circuit involving interleukin 27 and interleukin 10

Despite their central function in orchestrating immunity, dendritic cells (DCs) can respond to inhibitory signals by becoming tolerogenic. Here we show that galectin-1, an endogenous glycan-binding protein, can endow DCs with tolerogenic potential. After exposure to galectin-1, DCs acquired an interleukin 27 (IL-27)-dependent regulatory function, promoted IL-10-mediated T cell tolerance and suppressed autoimmune neuroinflammation. Consistent with its regulatory function, galectin-1 had its highest expression on DCs exposed to tolerogenic stimuli and was most abundant from the peak through the resolution of autoimmune pathology. DCs lacking galectin-1 had greater immunogenic potential and an impaired ability to halt inflammatory disease. Our findings identify a tolerogenic circuit linking galectin-1 signaling, IL-27-producing DCs and IL-10-secreting T cells, which has broad therapeutic implications in immunopathology.

The costimulatory role of TIM molecules

SUMMARY

The T-cell immunoglobulin domain and mucin domain (TIM) family, including TIM-1, TIM-2, TIM-3, and TIM-4, is a relatively newly described group of molecules with a conserved structure and important immunological functions, including T-cell activation, induction of T-cell apoptosis and T-cell tolerance, and the clearance of apoptotic cells. TIM-1 costimulates T-cell activation and enhances cytokine production. In humans, TIM-1 also serves as a susceptibility gene for allergy and asthma. TIM-3, expressed on T cells and dendritic cells, regulates T-cell apoptosis and immune tolerance. By contrast, TIM-4, which is expressed primarily on antigen-presenting cells and which is a receptor for phosphatidylserine, regulates T-cell activation and tolerance, in part by mediating the uptake and engulfment of apoptotic cells. The TIM molecules thus have surprisingly broad activities affecting multiple aspects of immunology.

Autoimmune T cell responses in the central nervous system

Autoreactive T cell responses have a crucial role in central nervous system (CNS) diseases such as multiple sclerosis. Recent data indicate that CNS autoimmunity can be mediated by two distinct lineages of CD4+ T cells that are defined by the production of either interferon-gamma or interleukin-17. The activity of these CD4+ T cell subsets within the CNS influences the pathology and clinical course of disease. New animal models show that myelin-specific CD8+ T cells can also mediate CNS autoimmunity. This Review focuses on recent progress in delineating the pathogenic mechanisms, regulation and interplay between these different T cell subsets in CNS autoimmunity.

Human pregnancy up-regulates Tim-3 in innate immune cells for systemic immunity

Pregnant women have both the local immune tolerance at the maternal-fetal interface and the systemic immune defense against pathogens. To date, regardless of the extensive investigation on the maternal-fetal immune tolerance, the maintenance of systemic immune defense in pregnant women still remains poorly understood. In the present study, we demonstrate that the immunoregulatory molecule T cell Ig and mucin domain (Tim)-3 plays important roles in innate and adaptive immunity of human pregnancy. During pregnancy, Tim-3 is strikingly up-regulated in peripheral blood of pregnant women, most by monocytes but not by T or B cells. The increased IL-4/STAT6 signaling may contribute to such up-regulation of Tim-3. In turn, the increased Tim-3 enhances not only innate immunity but also Th1-associated immune responses of pregnant women against pathogens. In contrast, our clinical data show that abnormal Tim-3 expression level might be connected to the pregnancy loss. In conclusion, our data show in this study that an immune regulatory molecule Tim-3, by virtue of its up-regulation in innate immune cells in pregnant women, enhances both innate and adaptive immune responses. Nevertheless, the abnormality of Tim-3 in pregnant woman may be deleterious to normal pregnancy.

Radiolucency below the crown of mandibular horizontal incompletely impacted third molars and acute inflammation in men with diabetes

Although mandibular third molar has a high risk of infection extending any complications, the influence of diabetes on radiolucency and acute inflammation in pericoronitis remains unclear. The present study was to evaluate whether radiolucency below the crown is related to acute inflammation in mandibular horizontal incompletely impacted third molars and to review the records of 140 men more than 45 years with and without diabetes. The odds ratio of exhibiting acute inflammation was 3.38 (95% CI: 1.13-10.16, p < 0.05) and that of exhibiting severe acute inflammation was 15.38 (95% CI: 3.56-66.49, p < 0.0001), indicating an association of acute pericoronitis in diabetes. The frequency of radiolucency below the crown and below the root in diabetics was similar to that in nondiabetics. However, the odds ratio of exhibiting both radiolucency below the crown and acute inflammation under the diabetic condition was 4.85 (95% CI: 1.60-14.73, p < 0.01), whereas that of diabetics showing both radiolucency below the root and acute inflammation was 0.46 (95% CI: 0.06-3.74, p = 0.74). Radiolucency below the crown and acute inflammation were associated with diabetes, but that below root and acute inflammation were not associated with diabetes, indicating that the region below the crown carries susceptibility to acute pericoronitis, whereas the periodontium shows a protective effect against acute pericoronitis.

Turning 'sweet' on immunity: galectin-glycan interactions in immune tolerance and inflammation

The function of deciphering the biological information encoded by the glycome, which is the entire repertoire of complex sugar structures expressed by cells and tissues, is assigned in part to endogenous glycan-binding proteins or lectins. Galectins, a family of animal lectins that bind N-acetyllactosamine-containing glycans, have many roles in diverse immune cell processes, including those relevant to pathogen recognition, shaping the course of adaptive immune responses and fine-tuning the inflammatory response. How do galectins translate glycan-encoded information into tolerogenic or inflammatory cell programmes? An improved understanding of the mechanisms underlying these functions will provide further opportunities for developing new therapies based on the immunoregulatory properties of this multifaceted protein family.

Galectin-9 accelerates transforming growth factor beta3-induced differentiation of human mesenchymal stem cells to chondrocytes

Galectin-9 (Gal-9), a beta-galactoside binding lectin, plays a crucial role in innate and adaptive immunity. In the rat collagen-induced arthritis model, administration of Gal-9 induced repair of existing cartilage injury even when joints were already swollen with cartilage destruction. We thus attempted to explore the role of Gal-9 in chondrocyte differentiation utilizing human mesenchymal stem cell (MSC) pellet cultures. During chondrogenesis induced by transforming growth factor beta3 (TGFbeta3), MSCs strongly expressed endogenous Gal-9. Expression of Gal-9 peaked on day 14 and the neutralization of endogenous Gal-9 resulted in the reduced chondrogenesis, indicating possible involvement of Gal-9 in TGFbeta-mediated chondrogenesis. In pellets, addition of Gal-9 significantly enhanced TGFbeta3-induced chondrogenesis, as evidenced by increasing proteoglycan content, but not cell proliferation. In the absence of Gal-9, collagen expression by MSCs switched from type I to type II on 28 days after stimulation with TGFbeta3. When MSCs were co-stimulated with Gal-9, the class switch occurred on day 21. In addition, Gal-9 synergistically enhanced TGFbeta3-induced phosphorylation of Smad2, though Gal-9 did not itself induce detectable Smad2 phosphorylation. These results suggest that Gal-9 has a beneficial effect on cartilage repair in injured joints by induction of differentiation of MSCs into chondrocytes.

Immunoactivation in preeclampsia: Vdelta2+ and regulatory T cells during the inflammatory stage of disease

Recent data suggest a dominant role of the innate, rather than the adaptive immune system in pregnancy-related immunoregulation. gamma/delta T cells, that comprise a minor subpopulation of human peripheral blood lymphocytes, represent a link between the innate and the acquired immune systems. However little is known about how they function in preeclampsia, which is suggested to be associated with a Th1 predominant immune response. The aim of our study was to investigate the presence and phenotype of Vdelta2+ cells and of regulatory T cells in the pathogenesis of preeclampsia. Since Vdelta2+ T cell function has been shown to be altered in patients with preeclampsia we investigated the expression of perforin, Fas and TIM-3 by Vdelta2+ T cells and the possible role of activating and inhibitory NK cell receptors as well as of regulatory T cells. Vdelta2+ T cells of preeclamptic patients demonstrated an increased perforin and IFNgamma production, which could be explained by dysregulation of NK cell receptor expression. These Th1 polarized cells were less susceptible to apoptosis than Vdelta2+ T cells from healthy pregnant women. Our data suggest that activated Vdelta2+ T cells of preeclamptic women have an increased cytotoxic potential, which may be due to altered expression of NK cell inhibitory and activating receptors. In this study we report a series of observations, which taken together suggest the role of multiple pathways in generating an exaggerated systemic inflammatory response observed in the clinical stage of preeclampsia.

Dendritic cells: functional aspects of glycosylation and lectins

Dendritic cells (DC) direct immune responses either toward tolerance to a presented antigen or toward inflammatory reactions of effector cells. Many crucial cytokines and cell surface proteins have been identified in this process using gene expression profiling. However, it is becoming evident that important steps involve carbohydrate-protein interactions, which cannot be anticipated by gene expression profiling in most cases. These contacts are crucial for the uptake of certain antigens, migration, and homing, but also for infection by viruses. On one hand, DC use numerous C-type lectins, such as DC-SIGN, dectin-1, langerin, and DEC-205, for antigen uptake. Other lectins, such as CD83, siglecs, and galectins, may be involved in regulation of the immune response to a given antigen. On the other hand, cell surface glycosylation of DC themselves changes significantly depending on the environment and the functional state, generating different signals by altered glycans. Because DC occur at the interface between innate and acquired immunity, it may not be surprising that glycans and lectins play an important role in many biological functions of DC. In this review, we focus on glycobiological aspects of antigen uptake and processing, immune modulation, and viral infections in the context of DC biology.

Tim-3 mediates phagocytosis of apoptotic cells and cross-presentation

Phagocytes such as macrophages and dendritic cells (DCs) engulf apoptotic cells to maintain peripheral immune tolerance. However, the mechanism for the recognition of dying cells by phagocytes is not fully understood. Here, we demonstrate that T-cell immunoglobulin mucin-3 (Tim-3) recognizes apoptotic cells through the FG loop in the IgV domain, and is crucial for clearance of apoptotic cells by phagocytes. Whereas Tim-4 is highly expressed on peritoneal resident macrophages, Tim-3 is expressed on peritoneal exudate macrophages, monocytes, and splenic DCs, indicating distinct Tim-mediated phagocytic pathways used by different phagocytes. Furthermore, phagocytosis of apoptotic cells by CD8(+) DCs is inhibited by anti-Tim-3 mAb, resulting in a reduced cross-presentation of dying cell-associated antigens in vitro and in vivo. Administration of anti-Tim-3 as well as anti-Tim-4 mAb induces autoantibody production. These results indicate a crucial role for Tim-3 in phagocytosis of apoptotic cells and cross-presentation, which may be linked to peripheral tolerance.

Galectin-9 increases Tim-3+ dendritic cells and CD8+ T cells and enhances antitumor immunity via galectin-9-Tim-3 interactions

A Tim-3 ligand, galectin-9 (Gal-9), modulates various functions of innate and adaptive immune responses. In this study, we demonstrate that Gal-9 prolongs the survival of Meth-A tumor-bearing mice in a dose- and time-dependent manner. Although Gal-9 did not prolong the survival of tumor-bearing nude mice, transfer of naive spleen cells restored a prolonged Gal-9-induced survival in nude mice, indicating possible involvement of T cell-mediated immune responses in Gal-9-mediated antitumor activity. Gal-9 administration increased the number of IFN-gamma-producing Tim-3(+) CD8(+) T cells with enhanced granzyme B and perforin expression, although it induced CD4(+) T cell apoptosis. It simultaneously increased the number of Tim-3(+)CD86(+) mature dendritic cells (DCs) in vivo and in vitro. Coculture of CD8(+) T cells with DCs from Gal-9-treated mice increased the number of IFN-gamma producing cells and IFN-gamma production. Depletion of Tim-3(+) DCs from DCs of Gal-9-treated tumor-bearing mice decreased the number of IFN-gamma-producing CD8(+) T cells. Such DC activity was significantly abrogated by Tim-3-Ig, suggesting that Gal-9 potentiates CD8(+) T cell-mediated antitumor immunity via Gal-9-Tim-3 interactions between DCs and CD8(+) T cells.

TIMs: central regulators of immune responses

Exhaustion of T cell responses during chronic viral infections has been observed in both mouse and man and has been attributed to up-regulation of PD-1 on the surface of exhausted T cells. In patients with chronic human HIV infection, T cell exhaustion leads to opportunistic infections associated with AIDS. However, not all the exhausted T cells express PD-1, suggesting that other molecules may be involved in the phenotype. A new study now demonstrates a central role for T cell immunoglobulin and mucin domain–containing protein-3 (TIM-3) in T cell exhaustion during chronic HIV infection and suggests that TIM-3 may be a novel therapeutic target in chronic viral diseases.

Blood diffusion and Th1-suppressive effects of galectin-9-containing exosomes released by Epstein-Barr virus-infected nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) is the third most frequent virus-associated human malignancy. How this tumor escapes immune recognition despite the expression of several viral antigens has remained poorly understood. Our previous in vitro studies have shown that NPC cells release exosomes containing high amounts of galectin-9, a ligand of the membrane receptor Tim-3, which is able to induce apoptosis in mature Th1 lymphocytes. Here, we sought to determine whether galectin-9-carrying exosomes were produced in NPC patients and whether such exosomes might play a role in the immune evasion of NPC cells. We report that galectin-9-containing exosomes are selectively detected in plasma samples from NPC patients and mice xenografted with NPC tumors. The incorporation into exosomes protects galectin-9 against proteolytic cleavage but retains its Tim-3-binding capacity. Importantly, NPC exosomes induce massive apoptosis in EBV-specific CD4(+) cells used as a model of target T cells. This effect is inhibited by both anti-Tim-3 and antigalectin-9 blocking antibodies. These results indicate that blocking galectin-9/Tim-3 interaction in vivo might alleviate the Th1-suppressive effect of NPC exosomes and sustain antitumoral T-cell responses and thereby improve clinical efficacy of immunotherapeutic approaches against NPC.

Tim-3 expression defines a novel population of dysfunctional T cells with highly elevated frequencies in progressive HIV-1 infection

Progressive loss of T cell functionality is a hallmark of chronic infection with human immunodeficiency virus 1 (HIV-1). We have identified a novel population of dysfunctional T cells marked by surface expression of the glycoprotein Tim-3. The frequency of this population was increased in HIV-1-infected individuals to a mean of 49.4 +/- SD 12.9% of CD8(+) T cells expressing Tim-3 in HIV-1-infected chronic progressors versus 28.5 +/- 6.8% in HIV-1-uninfected individuals. Levels of Tim-3 expression on T cells from HIV-1-infected inviduals correlated positively with HIV-1 viral load and CD38 expression and inversely with CD4(+) T cell count. In progressive HIV-1 infection, Tim-3 expression was up-regulated on HIV-1-specific CD8(+) T cells. Tim-3-expressing T cells failed to produce cytokine or proliferate in response to antigen and exhibited impaired Stat5, Erk1/2, and p38 signaling. Blocking the Tim-3 signaling pathway restored proliferation and enhanced cytokine production in HIV-1-specific T cells. Thus, Tim-3 represents a novel target for the therapeutic reversal of HIV-1-associated T cell dysfunction.

Galectin-9 expands unique macrophages exhibiting plasmacytoid dendritic cell-like phenotypes that activate NK cells in tumor-bearing mice

Galectin-9 (Gal-9) inhibits the metastasis of tumor cells by blocking their adhesion to endothelium and the extracellular matrix. In this study, we addressed the involvement of Gal-9 in anti-tumor activity. Gal-9 significantly prolonged the survival of B16F10 melanoma-bearing mice. Gal-9 increased the numbers of NK cells, CD8 T cells and macrophages in tumor-bearing mice. Gal-9-mediated anti-tumor activity was not induced in NK cell-, macrophage- and CD8 T cell-depleted mice. NK cells from Gal-9-treated mice, compared to PBS-treated mice, exhibited significantly higher cytolytic activity. Co-culture of naïve NK cells with macrophages from Gal-9-treated mice resulted in enhanced NK activity, although Gal-9 itself did not enhance the NK activity. We also found that Ly-6C(+)CD11b(+)F4/80(+) macrophages with plasmacytoid cell (pDC)-like phenotypes (PDCA-1 and B220) were responsible for the enhanced NK activity. These results provide evidence that Gal-9 promotes NK cell-mediated anti-tumor activity by expanding unique macrophages with a pDC-like phenotype.

Analysis of retinal cellular infiltrate in experimental autoimmune uveoretinitis reveals multiple regulatory cell populations

Experimental autoimmune uveoretinitis (EAU) is an animal model for human intraocular inflammatory disease. EAU is induced in B10.RIII mice by immunization with RBP-3 161-180 peptide and intraperitoneal pertussis toxin and is mediated by CD4(+) T cells that generate a clinically monophasic disease peaking approximately 2 weeks post-immunization. Collagenase digestion of retinal tissue allowed the quantification and characterization of leukocytes in the inflamed retina during disease progression. Using this method we identified three stages of disease. Initially there is a prodromal phase where we found significant changes in the number of leukocytes in the eye as early as 5 days post-immunization. This effect was, in part, non-antigen specific as a small increase in retinal leukocytes was also observed following immunization with OVA peptide. Following the prodrome there is a primary peak of infiltration including both CD4(+) T cells and CD11b(+) cells. This coincides with an early influx of neutrophils and is associated with a peak in IL-17-producing T cells. The neutrophils in the eye are CD11b(+) and Gr1(+) but can be distinguished from other myeloid cells by their high expression of Ly6G. The remaining CD11b(+)Gr1(+) cells can suppress proliferation and are analogous to myeloid derived suppressor cells which are found in tumors. The inflamed eye also contains a considerable proportion of FoxP3(+) regulatory cells. Following peak disease, the retina does not return to its pre-disease phenotype. Instead, fluctuations in infiltrating leukocyte numbers and changes to their relative composition continue, indicating that clinical recovery does not equate to the restoration of a normal retinal leukocyte population.

Multiple sclerosis and regulatory T cells

INTRODUCTION

Multiple sclerosis (MS) is a complex genetic disease characterized by chronic inflammation of the central nervous system (CNS). The pathology of MS is largely attributed to autoreactive effector T cells that penetrate the blood-brain barrier and become activated within the CNS. As autoreactive T cells are present in the blood of both patients with MS and healthy individuals, other regulatory mechanisms exist to prevent autoreactive T cells from causing immune disorders. Active suppression by regulatory T (Treg) cells plays a key role in the control of self-antigen-reactive T cells and the induction of peripheral tolerance in vivo. In particular, the importance of antigen-specific Treg cells in conferring genetic resistance to organ-specific autoimmunity and in limiting autoimmune tissue damage has been documented in many disease models including MS.

RESULTS

We have found that the frequency of Tregs in MS patients is unchanged from controls, but their function measured in vitro may be diminished, correlating with impaired inhibitory activity in vivo. This review discusses the immunopathology of MS with particular focus given to regulatory T cells and their potential for the development of new therapies to treat this disease.

TIM-1 and TIM-3 proteins in immune regulation

Over the last several years, there has been increasing interest in the role of proteins of the TIM (T cell immunoglobulin and mucin domain) family in regulating immune responses. Despite what the name suggests, proteins of this family function in a much more widespread manner than just on T cells, as we will discuss in this review. We therefore propose that the definition of TIM be adjusted to "transmembrane immunoglobulin and mucin".

New roles for TIM family members in immune regulation

Members of the TIM (T-cell immunoglobulin domain and mucin domain) protein family are emerging as important regulators of immune responses. As their names imply, the TIM proteins were originally thought to be T-cell-specific molecules that served mainly to regulate T-helper-cell responses. However, the recent discovery that antigen-presenting cells also express TIM molecules and the identification of new TIM-protein ligands has expanded the known roles of the TIM proteins in immune regulation.

Region-specific expression of immunoregulatory proteins on microglia in the healthy CNS

In accordance with a high degree of spatial organization in the central nervous system (CNS), most CNS diseases display a regional distribution. Although microglia have been established as key players in various CNS diseases, it is not yet clear whether microglia display region-specific properties. Therefore, this study aimed to evaluate the existence of distinct microglia phenotypes in various regions of the healthy, adult mouse CNS. Using ex vivo flow cytometric analysis surface expression of CD11b, CD40, CD45, CD80, CD86, F4/80, TREM-2b, MHCII, CXCR3, CCR9, and CCR7 were analyzed. Most of these immunoregulatory markers were found on microglia and showed significant region-specific differences in expression levels. These findings considerably corroborate the existence of immunological diversity among microglia in the healthy, unchallenged CNS of adult mice.

Protein-glycan interactions in the control of innate and adaptive immune responses

The importance of protein glycosylation in the migration of immune cells throughout the body has been extensively appreciated. However, our awareness of the impact of glycosylation on the regulation of innate and adaptive immune responses is relatively new. An increasing number of studies reveal the relevance of glycosylation to pathogen recognition, to the modulation of the innate immune system and to the control of immune cell homeostasis and inflammation. Similarly important is the effect of glycan-containing 'information' in the development of autoimmune diseases and cancer. In this review, we provide an overview of these new directions and their impact in the field of glycoimmunology.

Galectin-9 suppresses tumor metastasis by blocking adhesion to endothelium and extracellular matrices

We previously described an inverse correlation between galectin-9 (Gal-9) expression and metastasis in patients with malignant melanoma and breast cancer. This study verified the ability of Gal-9 to inhibit lung metastasis in experimental mouse models using highly metastatic B16F10 melanoma and Colon26 colon cancer cells. B16F10 cells transfected with a secreted form of Gal-9 lost their metastatic potential. Intravenous Gal-9 administration reduced the number of metastases of both B16F10 and Colon26 cells in the lung, indicating that secreted Gal-9 suppresses metastasis. Analysis of adhesive molecule expression revealed that B16F10 cells highly express CD44, integrin alpha1, alpha 4, alpha V, and beta1, and that Colon26 cells express CD44, integrin alpha2, alpha 5, alpha V, and beta1, suggesting that Gal-9 may inhibit the adhesion of tumor cells to vascular endothelium and the extracellular matrix (ECM) by binding to such adhesive molecules. Indeed, Gal-9 suppressed the binding of hyaluronic acid to CD44 on both B16F10 and Colon26 cells, and also suppressed the binding of vascular cell adhesion molecule-1 to very late antigen-4 on B16F10 cells. Furthermore, Gal-9 inhibited the binding of tumor cells to ECM components, resulting in the suppression of tumor cell migration. The present results suggest that Gal-9 suppresses both attachment and invasion of tumor cells by inhibiting the binding of adhesive molecules on tumor cells to ligands on vascular endothelium and ECM.

Galectins: structure, function and therapeutic potential

Galectins are a family of animal lectins that bind beta-galactosides. Outside the cell, galectins bind to cell-surface and extracellular matrix glycans and thereby affect a variety of cellular processes. However, galectins are also detectable in the cytosol and nucleus, and may influence cellular functions such as intracellular signalling pathways through protein-protein interactions with other cytoplasmic and nuclear proteins. Current research indicates that galectins play important roles in diverse physiological and pathological processes, including immune and inflammatory responses, tumour development and progression, neural degeneration, atherosclerosis, diabetes, and wound repair. Some of these have been discovered or confirmed by using genetically engineered mice deficient in a particular galectin. Thus, galectins may be a therapeutic target or employed as therapeutic agents for inflammatory diseases, cancers and several other diseases.

TIM-3 polymorphisms in type 1 diabetes families

TIM-3 is a transmembrane protein preferentially expressed on differentiated Th1 cells, which play a role in Th1-mediated diseases including type 1 diabetes. We investigated the role of the rs10515746 (A/C), rs1036199 (A/C), and rs10053538 (A/C) single nucleotide polymorphisms (SNPs) within the TIM-3 gene in 186 German type 1 diabetes families (558 individuals) and its interaction with human leukocyte antigen (HLA) high-risk haplotypes DQ2(DQA*0501-DQB*0201)-DQ8 (DQA*0301-DQB*0302). Alleles A, C, and A of the rs10515746 (A/C), rs1036199 (A/C), and rs10053538 (A/C) SNPs were found in a frequency of 20.4%, 19.0%, and 4.2%, respectively. Transmission analysis of these polymorphisms did not show any significant difference. Although in patients with HLA DQx/x (neither HLA DQ2 nor DQ8) an undertransmission of allele A (14.3% vs. 85.7%) of the rs10053538 (A/C) SNP and an overtransmission of allele A (66.7% vs. 33.3%) of the rs10515746 (A/C) SNP was observed, these associations did not remain statistically significant after correction for multiple comparisons. Although we found no association of TIM-3 with type 1 diabetes in the German population, we cannot discard a possible association in a larger size.