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

Dysregulated Tim-3 expression on natural killer cells is associated with increased Galectin-9 levels in HIV-1 infection

Background

Natural killer (NK) cells constitutively express high levels of Tim-3, an immunoregulatory molecule recently proposed to be a marker for mature and functional NK cells. Whether HIV-1 infection modulates the expression of Tim-3 on NK cells, or the levels of its ligand Galectin-9 (Gal-9), and how signaling through these molecules affects the NK cell response to HIV-1 remains inadequately understood.

Results

We analyzed Tim-3 and Gal-9 expression in a cohort of 85 individuals with early and chronic HIV-1 infection, and in 13 HIV-1 seronegative control subjects. HIV-1 infection was associated with reduced expression of Tim-3 on NK cells, which was normalized by HAART. Plasma concentrations of Gal-9 were higher in HIV-1-infected individuals than in healthy individuals. Interestingly, Gal-9 expression in immune cells was significantly elevated in early infection, with monocytes and dendritic cells displaying the highest expression levels, which correlated with HIV-1 viral loads. In vitro, Gal-9 triggered Tim-3 downregulation on NK cells as well as NK cell activation.

Conclusions

Our data suggest that high expression levels of Gal-9 during early HIV-1 infection can lead to enhanced NK cell activity, possibly allowing for improved early control of HIV-1. In contrast, persistent Gal-9 production might impair Tim-3 activity and contribute to NK cell dysfunction in chronic HIV-1 infection.

Galectin-9 protein is up-regulated in astrocytes by tumor necrosis factor and promotes encephalitogenic T-cell apoptosis

Demyelination and axonal damage in multiple sclerosis (MS) are thought to be a consequence of inflammatory processes that are perpetuated by activated glia and infiltrating leukocytes. Galectin-9 is a β-galactoside binding lectin capable of modulating immune responses and appears to be up-regulated in MS. However, its role in the pathogenesis of MS has yet to be determined. Here, we report that proinflammatory cytokines induce galectin-9 (Gal-9) expression in primary astrocytes and the mechanism by which TNF up-regulates Gal-9. Astrocytes did not express Gal-9 under basal conditions nor did IL-6, IL-10, or IL-13 trigger Gal-9 expression. In contrast, IL-1β, IFN-γ, and particularly TNF up-regulated Gal-9 in astrocytes. TNF-induced Gal-9 expression was dependent on TNF receptor 1 (TNFR1) as TNF failed to induce Gal-9 in TNFR1(-/-) astrocytes. Blockade of the JNK MAP kinase pathway with the JNK inhibitor SP600125 abrogated TNF-induced Gal-9, whereas p38 and MEK inhibitors had minimal effects. Furthermore, specific knockdown of c-Jun via siRNA in astrocytes before TNF treatment greatly suppressed Gal-9 transcription, suggesting that TNF induces astroglial Gal-9 through the TNF/TNFR1/JNK/cJun signaling pathway. Finally, utilizing astrocytes from Lgals9 mutant (Gal-9(-/-)) mice as well as a myelin basic protein-specific Tim-3(+) encephalitogenic T-cell clone (LCN-8), we found that conditioned medium from TNF-stimulated Gal-9(+/+) but not Gal-9(-/-) astrocytes increased the percentage of apoptotic encephalitogenic T-cells. Together, our results suggest that Gal-9 is induced in astrocytes by TNF via the JNK/c-Jun pathway and that astrocyte-derived Gal-9 may function as an immunoregulatory protein in response to ongoing neuroinflammation.

HIV infection deregulates Tim-3 expression on innate cells: combination antiretroviral therapy results in partial restoration

BACKGROUND

The Tim-3 receptor has been implicated as a negative regulator of adaptive immune responses and has been linked to T-cell dysfunction in chronic viral infections, such as HIV. Blocking Tim-3 has been proposed as a potential therapeutic intervention in HIV infection. However, a more detailed characterization of Tim-3 expression in the presence of HIV is required before such strategies can be considered.

METHODS

In this study, we investigate Tim-3 expression on innate immune cell subsets in chronic HIV-infected individuals pretherapy and posttherapy.

RESULTS

We report that, pretherapy, HIV infection is associated with elevated levels of Tim-3 on resting innate lymphocytes (NK, NKT, and γδ T cells), but not resting monocytes. In the absence of HIV infection, stimulation with an inflammatory stimulus resulted in decreased Tim-3 on monocytes and increased Tim-3 on NK, NKT, and γδ T cells. However, innate cells from HIV-infected donors were significantly less responsive to stimulation. Six months of combination antiretroviral therapy (cART) restored Tim-3 levels on resting NK cells but not NKT or γδ T cells. The responses of all subsets to inflammatory stimuli were restored to some extent with cART but only reached HIV-negative control levels in monocytes and NK cells.

DISCUSSION

These results demonstrate that, during HIV infection, Tim-3 expression on innate cells is dysregulated and that this dysregulation is only partially restored after 6 months of cART. Our findings suggest that Tim-3 is differentially regulated on innate immune effector cells, and have direct implications for strategies designed to block Tim-3-ligand interactions.

Immunogenic tumor cell death induced by chemoradiotherapy: molecular mechanisms and a clinical translation

Chemoradiotherapy can induce immunogenic cell death, triggering danger signals such as high-mobility group box 1 protein, and resulting in T-cell immunity. This concept can potentially be harnessed for clinical therapy to enhance tumor-specific immunity. There is however limited information to translate this theory directly in a clinical setting. In this review, we will discuss and summarize molecular and cellular mechanisms underlying immunogenic tumor cell death induced by chemoradiotherapy, with emphasis on a clinical translation.

Taming dendritic cells with TIM-3: another immunosuppressive strategy used by tumors

Evaluation of: Chiba S, Baghdadi M, Akiba H et al. Tumor-infiltrating DCs suppress nucleic acid-mediated innate immune responses through interactions between the receptor TIM-3 and the alarmin HMGB1. Nat. Immunol. 13, 832-842 (2012). The identification of TIM-3 expression on tumor-associated dendritic cells (TADCs) provides insight into another aspect of tumor-mediated immunosuppression. The role of TIM-3 has been well characterized on tumor-infiltrating T cells; however, its role on TADCs was not previously known. The current paper demonstrated that TIM-3 was predominantly expressed by TADCs and its interaction with the nuclear protein HMGB1 suppressed nucleic acid-mediated activation of an effective antitumor immune response. The authors were able to show that TIM-3 interaction with HMGB1 prevented the localization of nucleic acids into endosomal vesicles. Furthermore, chemotherapy was found to be more effective in anti-TIM-3 monoclonal antibody-treated mice or mice depleted of all DCs, which indicated that a significant role is played by TADCs in inhibiting tumor regression. Taken together, these findings identify TIM-3 as a potential target for inducing antitumor immunity in conjunction with DNA vaccines and/or immunogenic chemotherapy in clinical settings.

Functional diversity of microglia - how heterogeneous are they to begin with?

Microglia serve in the surveillance and maintenance, protection and restoration of the central nervous system (CNS) homeostasis. By their parenchymal location they differ from other CNS-associated myeloid cells, and by origin as well as functional characteristics they are also–at least in part–distinct from extraneural tissue macrophages. Nevertheless, microglia themselves may not comprise a uniform cell type. CNS regions vary by cellular and chemical composition, including white matter (myelin) content, blood–brain barrier properties or prevailing neurotransmitters. Such a micromilieu could instruct as well as require local adaptions of microglial features. Yet even cells within circumscribed populations may reveal some specialization by subtypes, regarding house-keeping duties and functional capacities upon challenges. While diversity of reactive phenotypes has been established still little is known as to whether all activated cells would respond with the same program of induced genes and functions or whether responder subsets have individual contributions. Preferential synthesis of a key cytokine could asign a master control to certain cells among a pool of activated microglia. Critical functions could be sequestered to discrete microglial subtypes in order to avoid interference, such as clearance of endogenous material and presentation of antigens. Indeed, several and especially a number of recent studies provide evidence for the constitutive and reactive heterogeneity of microglia by and within CNS regions. While such a principle of “division of labor” would influence the basic notion of “the” microglia, it could come with the practival value of addressing separate microglia types in experimental and therapeutic manipulations.

Dysregulated expression of T cell immunoglobulin and mucin domain 3 is associated with the disease severity and the outcome of patients with spontaneous intracerebral hemorrhage

OBJECTIVES

We aimed to investigate the expression of T cell immunoglobulin and mucin domain 3 (Tim-3) on peripheral blood cells in spontaneous intracerebral hemorrhage (ICH) patients and to analyze its clinical significance.

DESIGN AND METHODS

Tim-3 expression on peripheral immunocytes from ICH patients and healthy volunteers was measured by flow cytometry. The correlation between Tim-3 expression and the clinical indices was estimated using linear regression.

RESULTS

Tim-3 expressions on peripheral CD3⁺ T cells and CD8⁺ T cells in ICH patients are significantly downregulated, while Tim-3 expressions on CD14⁺ monocytes and CD16⁺CD56⁺ NK cells are increased. Furthermore, Tim-3 expression on peripheral CD8⁺ cells was negatively correlated with the inflammatory response, the disease severity and the outcome of ICH patients. However, there was no relationship between Tim-3 expression and blood glucose concentration.

CONCLUSIONS

Altered expression of Tim-3 might play an important role in the pathogenesis of ICH, demonstrating that Tim-3 might be a novel candidate molecule for prognosis evaluation of ICH patients.

Galectin-9-mediated protection from allo-specific T cells as a mechanism of immune privilege of corneal allografts

The eye is an immune-privileged organ, and corneal transplantation is therefore one of the most successful organ transplantation. The immunosuppressive intraocular microenvironment is known as one of the mechanisms underlying immune privilege in the eye. T-cell immunoglobulin and mucin domain (Tim)-3 is a regulatory molecule for T-cell function, and galectin (Gal)-9 is a Tim-3 ligand. We investigated the role of this pathway in establishing the immune-privileged status of corneal allografts in mice. Gal-9 is constitutively expressed on the corneal epithelium, endothelium and iris-ciliary body in normal mouse eyes and eyes bearing surviving allografts, and Tim-3 was expressed on CD8 T cells infiltrating the allografts. Allograft survival in recipients treated with anti-Tim-3 monoclonal antibody (mAb) or anti-Gal-9 mAb was significantly shorter than that in control recipients. In vitro, destruction of corneal endothelial cells by allo-reactive T cells was enhanced when the cornea was pretreated with anti-Gal-9 mAb. Blockade of Tim-3 or Gal-9 did not abolish anterior chamber-associated immune deviation. We propose that constitutive expression of Gal-9 plays an immunosuppressive role in corneal allografts. Gal-9 expressed on corneal endothelial cells protects them from destruction by allo-reactive T cells within the cornea.

Galectin-9 functionally impairs natural killer cells in humans and mice

Galectin-9 is a pleiotropic immune modulator affecting numerous cell types of innate and adaptive immunity. Patients with chronic infection with either hepatitis C virus (HCV) or HIV have elevated circulating levels. Limited data exist on the regulation of natural killer (NK) cell function through interaction with galectin-9. We found that galectin-9 ligation downregulates multiple immune-activating genes, including eight involved in the NK cell-mediated cytotoxicity pathway, impairs lymphokine-activated killing, and decreases the proportion of gamma interferon (IFN-γ)-producing NK cells that had been stimulated with interleukin-12 (IL-12)/IL-15. We demonstrate that the transcriptional and functional changes induced by galectin-9 are independent of Tim-3. Consistent with these results for humans, we find that the genetic absence of galectin-9 in mice is associated with greater IFN-γ production by NK cells and enhanced degranulation. We also show that in the setting of a short-term (4-day) murine cytomegalovirus infection, terminally differentiated NKs accumulate in the livers of galectin-9 knockout mice, and that hepatic NKs spontaneously produce significantly more IFN-γ in this setting. Taken together, our results indicate that galectin-9 engagement impairs the function of NK cells, including cytotoxicity and cytokine production.

Rejection and regulation: a tight balance

PURPOSE OF REVIEW

Achieving allograft tolerance is the holy grail of transplantation. However, tolerance and rejection are two extreme ends of a scale that can be tipped in either direction. We review the novel effector and regulatory mechanisms involved and factors that tip the balance in favor of rejection or regulation.

RECENT FINDINGS

It is increasingly recognized that established T-cell phenotypes could change their commitments. New data point to the plasticity of Th17 cells in vivo with a reciprocal balance of Th17 cells and regulatory T cells (Tregs) driven by the local cytokine environment. Treg-cell profiles have been linked to acute and chronic allograft outcomes, and emerging data also indicate a novel role of a regulatory B-cell population. Current research efforts are looking into factors that tip the balance toward allograft tolerance by targeting cytokines, novel costimulatory pathways such as T-cell immunoglobulin mucin molecules, and components of innate immunity, particularly dendritic cells.

SUMMARY

The balance of effector and regulatory mechanisms contributing to allograft outcome is very complex. It is likely that targeting multiple pathways will be required to achieve tolerance. Further studies are warranted to define this balance and identify optimal combination of therapeutic interventions.

The influence of T cell Ig mucin-3 signaling on central nervous system autoimmune disease is determined by the effector function of the pathogenic T cells

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the CNS mediated by self-reactive, myelin-specific T cells. Both CD4(+) and CD8(+) T cells play important roles in the pathogenesis of MS. MS is studied using experimental autoimmune encephalomyelitis (EAE), an animal model mediated by myelin-specific T cells. T cell Ig mucin-3 (Tim-3) is a cell surface receptor expressed on CD4(+) IFN-γ-secreting Th1 cells, and triggering Tim-3 signaling ameliorated EAE by inducing death in pathogenic Th1 cells in vivo. This suggested that enhancing Tim-3 signaling might be beneficial in patients with MS. However, Tim-3 is also expressed on activated CD8(+) T cells, microglia, and dendritic cells, and the combined effect of manipulating Tim-3 signaling on these cell types during CNS autoimmunity is unknown. Furthermore, CD4(+) IL-17-secreting Th17 cells also play a role in MS, but do not express high levels of Tim-3. We investigated Tim-3 signaling in EAE models that include myelin-specific Th17, Th1, and CD8(+) T cells. We found that preventing Tim-3 signaling in CD4(+) T cells altered the inflammatory pattern in the CNS due to differential effects on Th1 versus Th17 cells. In contrast, preventing Tim-3 signaling during CD8(+) T cell-mediated EAE exacerbated disease. We also analyzed the importance of Tim-3 signaling in EAE in innate immune cells. Tim-3 signaling in dendritic cells and microglia did not affect the manifestation of EAE in these models. These results indicate that the therapeutic efficacy of targeting Tim-3 in EAE is dependent on the nature of the effector T cells contributing to the disease.

TIM3 expression by leukemic and non-leukemic myeloblasts

BACKGROUND

T-cell immunoglobulin mucin-3 (TIM3) has recently been described as an acute myeloid leukemia (AML) stem cell antigen expressed on leukemic myeloblasts, but not on normal hematopoietic stem cells. TIM3 is also expressed by monocytes, natural killer cells, and several T cell subsets; however, normal myeloblasts have not been well-characterized or compared to AML. A specific flow cytometric marker capable of separating leukemic myeloblasts from non-neoplastic myeloblasts would be diagnostically useful, especially in the post-chemotherapy setting.

METHODS

TIM3 myeloblast expression was assessed in 69 bone marrow and/or peripheral blood specimens, including 27 AML and 42 non-neoplastic cases (20 with a recent history of chemotherapy). TIM3 median fluorescence intensity (MFI) was evaluated within myeloblast, monocyte, T cell, and natural killer cell populations.

RESULTS

The median percentage of myeloblasts positive for TIM3 was lower in non-neoplastic specimens without a history of recent chemotherapy (50.3%) as compared to AML (71.4%), but not significantly different as compared to non-leukemic myeloblasts in the post-chemotherapy setting (72.4%). Mean myeloblast TIM3 MFI was higher in AML myeloblasts and non-leukemic myeloblasts in the post-chemotherapy setting as compared to non-neoplastic myeloblasts in cases lacking a history of chemotherapy. Mean monocyte, natural killer cell, and T-cell TIM3 MFI remained relatively constant in varied clinical settings.

CONCLUSIONS

We confirm that leukemic myeloblasts overexpress TIM3 as compared to non-neoplastic controls; however, high levels of expression may also be seen among non-leukemic myeloblasts in the post-chemotherapy setting. This overlap limits the diagnostic utility of TIM3 as a specific marker of neoplasia.

TIM-3 does not act as a receptor for galectin-9

T cell immunoglobulin and mucin protein 3 (TIM-3) is a type I cell surface protein that was originally identified as a marker for murine T helper type 1 cells. TIM-3 was found to negatively regulate murine T cell responses and galectin-9 was described as a binding partner that mediates T cell inhibitory effects of TIM-3. Moreover, it was reported that like PD-1 the classical exhaustion marker, TIM-3 is up-regulated in exhausted murine and human T cells and TIM-3 blockade was described to restore the function of these T cells. Here we show that the activation of human T cells is not affected by the presence of galectin-9 or antibodies to TIM-3. Furthermore, extensive studies on the interaction of galectin-9 with human and murine TIM-3 did not yield evidence for specific binding between these molecules. Moreover, profound differences were observed when analysing the expression of TIM-3 and PD-1 on T cells of HIV-1-infected individuals: TIM-3 was expressed on fewer cells and also at much lower levels. Furthermore, whereas PD-1 was preferentially expressed on CD45RA⁻CD8 T cells, the majority of TIM-3-expressing CD8 T cells were CD45RA⁺. Importantly, we found that TIM-3 antibodies were ineffective in increasing anti-HIV-1 T cell responses in vitro, whereas PD-L antibodies potently reverted the dysfunctional state of exhausted CD8 T cells. Taken together, our results are not in support of an interaction between TIM-3 and galectin-9 and yield no evidence for a functional role of TIM-3 in human T cell activation. Moreover, our data indicate that PD-1, but not TIM-3, is a promising target to ameliorate T cell exhaustion.

Inhibitory costimulatory receptors are a hallmark of exhausted T cells, which accumulate during chronic infection with viruses like HIV-1. Recently, TIM-3 was described as functional receptor on exhausted human T cells. Galectin-9 was reported as an inhibitory ligand for TIM-3 on murine T cells, but it was not known whether galectin-9 has a role in human T cell activation processes. We have found that the activation of human T cells is not affected by the presence of galectin-9 or antibodies to TIM-3. Furthermore, we demonstrate that galectin-9 does not serve as a ligand of human or murine TIM-3. Analysis of T cells of HIV-infected individuals regarding the expression of TIM-3 and PD-1 demonstrates that TIM-3 is expressed on fewer cells and also at much lower levels. In fact, TIM-3 expression characterizes a T cell population that is distinct from the PD-1 expressing exhausted T cells. Our results indicate that PD-1, but not TIM-3, is a promising target to ameliorate T cell exhaustion.

The nature of activatory and tolerogenic dendritic cell-derived signal II

Dendritic cells (DCs) are central in maintaining the intricate balance between immunity and tolerance by orchestrating adaptive immune responses. Being the most potent antigen presenting cells, DCs are capable of educating naïve T cells into a wide variety of effector cells ranging from immunogenic CD4⁺ T helper cells and cytotoxic CD8⁺ T cells to tolerogenic regulatory T cells. This education is based on three fundamental signals. Signal I, which is mediated by antigen/major histocompatibility complexes binding to antigen-specific T cell receptors, guarantees antigen specificity. The co-stimulatory signal II, mediated by B7 family molecules, is crucial for the expansion of the antigen-specific T cells. The final step is T cell polarization by signal III, which is conveyed by DC-derived cytokines and determines the effector functions of the emerging T cell. Although co-stimulation is widely recognized to result from the engagement of T cell-derived CD28 with DC-expressed B7 molecules (CD80/CD86), other co-stimulatory pathways have been identified. These pathways can be divided into two groups based on their impact on primed T cells. Whereas pathways delivering activatory signals to T cells are termed co-stimulatory pathways, pathways delivering tolerogenic signals to T cells are termed co-inhibitory pathways. In this review, we discuss how the nature of DC-derived signal II determines the quality of ensuing T cell responses and eventually promoting either immunity or tolerance. A thorough understanding of this process is instrumental in determining the underlying mechanism of disorders demonstrating distorted immunity/tolerance balance, and would help innovating new therapeutic approaches for such disorders.

T cell Ig mucin-3 promotes homeostasis of sepsis by negatively regulating the TLR response

Sepsis is an excessive inflammatory condition with a high mortality rate and limited prediction and therapeutic options. In this study, for the first time, to our knowledge, we found that downregulation and/or blockade of T cell Ig and mucin domain protein 3 (Tim-3), a negative immune regulator, correlated with severity of sepsis, suggesting that Tim-3 plays important roles in maintaining the homeostasis of sepsis in both humans and a mouse model. Blockade and/or downregulation of Tim-3 led to increased macrophage activation, which contributed to the systemic inflammatory response in sepsis, whereas Tim-3 overexpression in macrophages significantly suppressed TLR-mediated proinflammatory cytokine production, indicating that Tim-3 is a negative regulator of TLR-mediated immune responses. Cross-talk between the Tim-3 and TLR4 pathways makes TLR4 an important contributor to Tim-3-mediated negative regulation of the innate immune response. Tim-3 signaling inhibited LPS-TLR4-mediated NF-κB activation by increasing PI3K-AKT phosphorylation and A20 activity. This negative regulatory role of Tim-3 reflects a new adaptive compensatory and protective mechanism in sepsis victims, a finding of potential importance for modulating innate responses in these patients.

T-cell immunoglobulin- and mucin-domain-containing molecule 3 gene polymorphisms and prognosis of non-small-cell lung cancer

Lung cancer is the leading cause of death worldwide. Non-small-cell lung cancer (NSCLC) accounts for most of these cases. T-cell immunoglobulin- and mucin-domain-containing molecule 3 (TIM-3) has been established as a negative regulatory molecule and plays a critical role in immune tolerance. Studies have shown that polymorphisms in TIM-3 gene can be associated with various diseases. The aim of this study was to investigate whether polymorphisms in the TIM-3 gene were associated with susceptibility to NSCLC. Three polymorphisms in TIM-3 gene (-1516G/T, -574G/T, and +4259T/G) were identified by polymerase chain reaction-restriction fragment length polymorphism in 432 NSCLC patients and 466 healthy controls. Results showed that frequencies of TIM-3 +4259TG genotype for cases and controls were 10.9 and 4.1 %, respectively; subjects carrying the +4259TG genotype had a 2.81-fold increased risk of NSCLC compared to the wild-type genotype (P < 0.0001). The TIM-3 -1516G/T and -574G/T polymorphisms did not show any correlation with NSCLC. In addition, when analyzing the survival time of NSCLC patients with TIM-3 +4259T/G polymorphism, cases with +4259TG genotype had significantly shorter survival time compared to the wild-type patients (15.2 months vs. 26.7 months, P = 0.007). These results suggested polymorphism in TIM-3 gene is associated with increased susceptibility to NSCLC and could be used as prognostic factor for this malignancy.

Imbalanced expression of T-bet and T cell immunoglobulin mucin-3 in patients with aplastic anaemia

BACKGROUND

Activated T helper (Th)-1 CD4+ cells and their mediators are essential for pathogenesis processes in aplastic anaemia (AA). Recently, T-cell immunoglobulin and mucin domain 3 (Tim-3) molecules, a Th1-specific type 1 membrane protein, have been suggested to be important regulators of both Th1 proliferation and the development of tolerance. Moreover, T-box expressed in T cells (T-bet) is a major T cell transcription factor that regulates the expression of Th1 cytokine genes and plays a crucial role in T cell differentiation. The function of Tim-3 and its association with T-bet in the pathophysiology of AA remain unclear.

DESIGN AND METHODS

Plasma IL-18, IFN-γ and IL-4 levels were measured in patients with newly diagnosed AA (n = 29), AA in remission (n = 22) and healthy subjects (n = 30) via enzyme-linked immunosorbent assay (ELISA). CD4+ Tim-3+ cells were evaluated via flow cytometry and expressed as a percentage of the total number of CD4+ cells. Using real-time quantitative polymerase chain reaction (RT-PCR) and mRNA expression analysis the expression levels of Tim-3, IL-18, IFN-γ and T-box (T-bet) were examined in all subjects.

RESULTS

Tim-3 was expressed on CD4+T cells. The percentages of Tim-3 cells identified in newly diagnosed patients were significantly deceased compared with the controls. Meanwhile T-bet, IL-18 and IFN-γ levels were significantly elevated in patients, which resulted in an increased ratio of T-bet/Tim-3 expression levels in patients with active disease. During the remission stages, the levels of these cytokines were comparable with those observed in the healthy controls.

CONCLUSIONS

These results suggest that the imbalanced expression of Tim-3 and T-bet may play a role in the pathogenesis and course of AA, and the downregulation of T-bet/Tim-3 may represent a reasonable therapeutic strategy for AA treatment.

Tim-3/galectin-9 regulate the homeostasis of hepatic NKT cells in a murine model of nonalcoholic fatty liver disease

T cell Ig and mucin domain (Tim)-3 is well known to interact with its natural ligand, Galectin-9 (Gal-9), to regulate T cell function. However, little is known about the function of Tim-3/Gal-9 signaling in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) mediated by hepatic NKT cells that also express Tim-3. In the current study, we define the role and the mechanism of Tim-3/Gal-9 signaling in hepatic NKT cell regulation in a mouse model of diet-induced NAFLD. Adult male wild-type or CD1d knockout C57BL/6 mice were fed a high-fat diet to induce steatosis. Some of the mice also received one or a combination of Gal-9, anti-IL-15R/IL-15 mAb, rIL-15, α-galactosylceramide, and multilamellar liposomes containing Cl(2)MDP. The expression of Tim-3 and various markers reflecting cell proliferation, activation, cytokine production, and apoptosis was analyzed. Liver histology, steatosis grade, and hepatic triglyceride content were also evaluated. In the liver, Tim-3(+) NKT cells are in an activated state, and Gal-9 directly induces Tim-3(+) NKT cell apoptosis and contributes to the depletion of NKT cells in diet-induced steatosis. However, Gal-9 also interacts with Tim-3-expressing Kupffer cells to induce secretion of IL-15, thus promoting NKT cell proliferation. Exogenous administration of Gal-9 significantly ameliorates diet-induced steatosis by modulating hepatic NKT cell function. In summary, the Tim-3/Gal-9-signaling pathway plays a critical role in the homeostasis of hepatic NKT cells through activation-induced apoptosis and secondary proliferation and, thus, contributes to the pathogenesis of NAFLD.

Galectins in the Pathogenesis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a complex and common systemic autoimmune disease characterized by synovial inflammation and hyperplasia. Multiple proteins, cells, and pathways have been identified to contribute to the pathogenesis of RA. Galectins are a group of lectins that bind to β-galactoside carbohydrates on the cell surface and in the extracellular matrix. They are expressed in a wide variety of tissues and organs with the highest expression in the immune system. Galectins are potent immune regulators and modulate a range of pathological processes, such as inflammation, autoimmunity, and cancer. Accumulated evidence shows that several family members of galectins play positive or negative roles in the disease development of RA, through their effects on T and B lymphocytes, myeloid lineage cells, and fibroblast-like synoviocytes. In this review, we will summarize the function of different galectins in immune modulation and their distinct roles in RA pathogenesis.

TIM family proteins promote the lysosomal degradation of the nuclear receptor NUR77

T cell immunoglobulin and mucin domain (TIM) proteins are cell-surface signaling receptors in T cells and scavenger receptors in antigen-presenting cells and kidney tubular epithelia. Here, we demonstrated a function for TIM proteins in mediating the degradation of NUR77, a nuclear receptor implicated in apoptosis and cell survival. TIM proteins interacted with and mediated the lysosomal degradation of NUR77 in a phosphoinositide 3-kinase-dependent pathway. We also showed dynamic cycling of TIM-1 to and from the cell surface through clathrin-dependent constitutive endocytosis. Blocking this process or mutating the phosphatidylserine-binding pocket in TIM-1 abrogated TIM-1-mediated degradation of NUR77. In an in vitro model of kidney injury, silencing TIM-1 increased NUR77 abundance and decreased epithelial cell survival. These results show that TIM proteins may affect immune cell function and the response of the kidney to injury.

The Tim3-galectin 9 pathway induces antibacterial activity in human macrophages infected with Mycobacterium tuberculosis

T cell Ig and mucin domain 3 (Tim3) is an inhibitory molecule involved in immune tolerance, autoimmune responses, and antiviral immune evasion. However, we recently demonstrated that Tim3 and Galectin-9 (Gal9) interaction induces a program of macrophage activation that results in killing of Mycobacterium tuberculosis in the mouse model of infection. In this study, we sought to determine whether the Tim3-Gal9 pathway plays a similar role in human pulmonary TB. We identified that pulmonary TB patients have reduced expression of Tim3 on CD14(+) monocytes in vivo. By blocking Tim3 and Gal9 interaction in vitro, we show that these molecules contribute to the control of intracellular bacterial replication in human macrophages. The antimicrobial effect was partially dependent on the production of IL-1β. Our results establish that Tim3-Gal9 interaction activates human M. tuberculosis -infected macrophages and leads to the control of bacterial growth through the production of the proinflammatory cytokine IL-1β. Data presented in this study suggest that one of the potential pathways activated by Tim3/Gal9 is the secretion of IL-1β, which plays a crucial role in antimicrobial immunity by modulating innate inflammatory networks.

TIM-3 regulates innate immune cells to induce fetomaternal tolerance

TIM-3 is constitutively expressed on subsets of macrophages and dendritic cells. Its expression on other cells of the innate immune system and its role in fetomaternal tolerance has not yet been explored. In this study, we investigate the role of TIM-3-expressing innate immune cells in the regulation of tolerance at the fetomaternal interface (FMI) using an allogeneic mouse model of pregnancy. Blockade of TIM-3 results in accumulation of inflammatory granulocytes and macrophages at the uteroplacental interface and upregulation of proinflammatory cytokines. Furthermore, TIM-3 blockade inhibits the phagocytic potential of uterine macrophages resulting in a build up of apoptotic bodies at the uteroplacental interface that elicits a local immune response. In response to inflammatory cytokines, Ly-6C(hi)G(neg) monocytic myeloid-derived suppressor cells expressing inducible NO synthase and arginase 1 are induced. However, these suppressive cells fail to downregulate the inflammatory cascade induced by inflammatory granulocytes (Ly-6C(int)G(hi)) and apoptotic cells; the increased production of IFN-γ and TNF-α by inflammatory granulocytes leads to abrogation of tolerance at the FMI and fetal rejection. These data highlight the interplay between cells of the innate immune system at the FMI and their influence on successful pregnancy in mice.

Galectin-1 for neuroprotection?

Classically activated microglia (M1) are believed to play a key role in neuronal degeneration in multiple sclerosis (MS). In this issue of Immunity, Starossom et al. (2012) show that Galectin-1 exerts a neuroprotective function through glycosylation-dependent inactivation with M1 cells.

Cell surface galectin-9 expressing Th cells regulate Th17 and Foxp3+ Treg development by galectin-9 secretion

Galectin-9 (Gal-9), a β-galactoside binding mammalian lectin, regulates immune responses by reducing pro-inflammatory IL-17-producing Th cells (Th17) and increasing anti-inflammatory Foxp3(+) regulatory T cells (Treg) in vitro and in vivo. These functions of Gal-9 are thought to be exerted by binding to receptor molecules on the cell surface. However, Gal-9 lacks a signal peptide for secretion and is predominantly located in the cytoplasm, which raises questions regarding how and which cells secrete Gal-9 in vivo. Since Gal-9 expression does not necessarily correlate with its secretion, Gal-9-secreting cells in vivo have been elusive. We report here that CD4 T cells expressing Gal-9 on the cell surface (Gal-9(+) Th cells) secrete Gal-9 upon T cell receptor (TCR) stimulation, but other CD4 T cells do not, although they express an equivalent amount of intracellular Gal-9. Gal-9(+) Th cells expressed interleukin (IL)-10 and transforming growth factor (TGF)-β but did not express Foxp3. In a co-culture experiment, Gal-9(+) Th cells regulated Th17/Treg development in a manner similar to that by exogenous Gal-9, during which the regulation by Gal-9(+) Th cells was shown to be sensitive to a Gal-9 antagonist but insensitive to IL-10 and TGF-β blockades. Further elucidation of Gal-9(+) Th cells in humans indicates a conserved role of these cells through evolution and implies the possible utility of these cells for diagnosis or treatment of immunological diseases.

The innate immune system in demyelinating disease

Demyelinating diseases such as multiple sclerosis are chronic inflammatory autoimmune diseases with a heterogeneous clinical presentation and course. Both the adaptive and the innate immune systems have been suggested to contribute to their pathogenesis and recovery. In this review, we discuss the role of the innate immune system in mediating demyelinating diseases. In particular, we provide an overview of the anti-inflammatory or pro-inflammatory functions of dendritic cells, mast cells, natural killer (NK) cells, NK-T cells, γδ T cells, microglial cells, and astrocytes. We emphasize the interaction of astroctyes with the immune system and how this interaction relates to the demyelinating pathologies. Given the pivotal role of the innate immune system, it is possible that targeting these cells may provide an effective therapeutic approach for demyelinating diseases.

Overexpression of galectin-9 in islets prolongs grafts survival via downregulation of Th1 responses

The differential activation of T helper (Th) cells and production of cytokines contribute to graft rejection or tolerance. In general, the Th1-type cytokines and cytotoxic T-cells are detected consistently in a host who is undergoing rejection, whereas Th2 responses are linked to a tolerance condition. Galectin-9 modulates Th1 cell immunity by binding to the T-cell immunoglobulin mucin-3 (Tim-3) molecule expressed on the Th1 cells. We investigate whether overexpression of galectin-9 in islets prolongs grafts survival in diabetic recipients. Islets were transduced with lentiviruses carrying galectin-9 and were then transplanted to streptozotocin-induced diabetic NOD/SCID recipients. The normoglycemic recipients then received splenocytes from diabetic NOD mice. Blood glucose concentration was monitored daily after adoptive transfer. The histology of the islet grafts and flow cytometric analyses were assessed at the end of the study. Overexpression of galectin-9 in islets prolonged graft survival in NOD/SCID mice after challenge with diabetogenic splenocytes (mean graft survival, 38.5 vs. 26.0 days, n=10, respectively; p=0.0096). The galectin-9-overexpressed grafts showed decreased infiltration of IFN-γ-producing CD4(+) and CD8(+) T-cells, but not of IL-17-producing CD4(+) T-cells. Strikingly, this islet-specific genetic manipulation did not affect the systemic lymphocyte composition, indicating that galectin-9 may regulate T-cell-mediated inflammation in situ. We demonstrate that galectin-9 protects grafts from Th1 and Tc1 cell-mediated rejections, suggesting that galectin-9 has preventive and/or therapeutic benefit in transplant therapy for autoimmune diabetes and may be applied further to the transplantation of other organs or tissues.

T cell immunoglobulin-3 as a new therapeutic target for rheumatoid arthritis

T cell immunoglobulin-3 (Tim-3) is a surface molecule expressed on various cell types of the immune system which plays a central role in immune regulation. Recently, identification of galectin-9 (Gal-9) as a ligand for Tim-3 has established the Tim-3-Gal-9 pathway as an important regulator of Th1 immunity and induction of tolerance. The interaction of Tim-3 with Gal-9 induces cell death; the in vivo blockade of this interaction results in exacerbated autoimmunity and abrogation of tolerance in experimental models, thus establishing Tim-3 as a negative regulatory molecule. A number of previous studies have demonstrated that Tim-3 influences chronic autoimmune diseases, such as multiple sclerosis and systemic lupus erythematosus. In addition, an association between Tim-3 polymorphisms and susceptibility to several autoimmune diseases has been identified in various autoimmune diseases, including rheumatoid arthritis (RA). Recent work has focused on the role of Tim-3 in RA, and the results indicate that Tim-3 may represent a novel target for the treatment of RA. In this article we will discuss the Tim-3 pathway and the therapeutic potential of modulating the Tim-3 pathway in RA.

IL-1 signal affects both protection and pathogenesis of virus-induced chronic CNS demyelinating disease

Background

Theiler’s virus infection induces chronic demyelinating disease in mice and has been investigated as an infectious model for multiple sclerosis (MS). IL-1 plays an important role in the pathogenesis of both the autoimmune disease model (EAE) and this viral model for MS. However, IL-1 is known to play an important protective role against certain viral infections. Therefore, it is unclear whether IL-1-mediated signaling plays a protective or pathogenic role in the development of TMEV-induced demyelinating disease.

Methods

Female C57BL/6 mice and B6.129S7-Il1r1^tm1Imx/J mice (IL-1R KO) were infected with Theiler’s murine encephalomyelitis virus (1 x 10⁶ PFU). Differences in the development of demyelinating disease and changes in the histopathology were compared. Viral persistence, cytokine production, and immune responses in the CNS of infected mice were analyzed using quantitative PCR, ELISA, and flow cytometry.

Results

Administration of IL-1β, thereby rending resistant B6 mice susceptible to TMEV-induced demyelinating disease, induced a high level of Th17 response. Interestingly, infection of TMEV into IL-1R-deficient resistant C57BL/6 (B6) mice also induced TMEV-induced demyelinating disease. High viral persistence was found in the late stage of viral infection in IL-1R-deficient mice, although there were few differences in the initial anti-viral immune responses and viral persistent levels between the WT B6 and IL-1R-deficiecent mice. The initial type I IFN responses and the expression of PDL-1 and Tim-3 were higher in the CNS of TMEV-infected IL-1R-deficient mice, leading to deficiencies in T cell function that permit viral persistence.

Conclusions

These results suggest that the presence of high IL-1 level exerts the pathogenic role by elevating pathogenic Th17 responses, whereas the lack of IL-1 signals promotes viral persistence in the spinal cord due to insufficient T cell activation by elevating the production of inhibitory cytokines and regulatory molecules. Therefore, the balance of IL-1 signaling appears to be extremely important for the protection from TMEV-induced demyelinating disease, and either too much or too little signaling promotes the development of disease.

T-cell inhibitors: a bench-to-bedside review

Allergic contact dermatitis is the quintessential example of a delayed-in-time and T-cell-mediated immune response. In the last decade, many of the molecular events required to initiate (or block) such a response have been uncovered. Textbook and journal reviews have emphasized the costimulatory requirements, with less focus on the coinhibitory signals that are of equal importance in understanding this central event of adaptive immunity. To fill this gap, we offer a compendium of discoveries characterizing the ligand-receptor pairs inhibiting T-cell activation and of selected illnesses and therapeutic applications that illuminate their role in health and disease.

The role of TIM-containing molecules in airway disease and their potential as therapeutic targets

T cell immunoglobulin and mucin-domain (TIM)-containing molecules have emerged as promising therapeutic targets to correct abnormal immune function in several autoimmune and chronic inflammatory conditions. Despite the initial discovery linking TIM-containing molecules and the airway hyperreactivity regulatory locus in mice, there is a paucity of studies on the function of TIM-containing molecules in lung inflammatory disease. Initially, studies were limited to mice models of asthma. More recently however, TIM-containing molecules have been implicated in an ever-expanding list of airway conditions that includes pneumonia, tuberculosis, influenza, sarcoidosis, lung cancer, and cystic fibrosis. This present review discusses the role of TIM-containing molecules and their ligands in the lung, as well as their potential as therapeutic targets in airway disease.

Galectin-1 deactivates classically activated microglia and protects from inflammation-induced neurodegeneration

Inflammation-mediated neurodegeneration occurs in the acute and the chronic phases of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Classically activated (M1) microglia are key players mediating this process. Here, we identified Galectin-1 (Gal1), an endogenous glycan-binding protein, as a pivotal regulator of M1 microglial activation that targets the activation of p38MAPK-, CREB-, and NF-κB-dependent signaling pathways and hierarchically suppresses downstream proinflammatory mediators, such as iNOS, TNF, and CCL2. Gal1 bound to core 2 O-glycans on CD45, favoring retention of this glycoprotein on the microglial cell surface and augmenting its phosphatase activity and inhibitory function. Gal1 was highly expressed in the acute phase of EAE, and its targeted deletion resulted in pronounced inflammation-induced neurodegeneration. Adoptive transfer of Gal1-secreting astrocytes or administration of recombinant Gal1 suppressed EAE through mechanisms involving microglial deactivation. Thus, Gal1-glycan interactions are essential in tempering microglial activation, brain inflammation, and neurodegeneration, with critical therapeutic implications for MS.

Enhanced Tim3 activity improves survival after influenza infection

Influenza is a major cause of morbidity and mortality in the United States. Studies have shown that excessive T cell activity can mediate pneumonitis in the setting of influenza infection, and data from the 2009 H1N1 pandemic indicate that critical illness and respiratory failure postinfection were associated with greater infiltration of the lungs with CD8+ T cells. T cell Ig and mucin domain 3 (Tim3) is a negative regulator of Th1/Tc1-type immune responses. Activation of Tim3 on effector T cells has been shown to downregulate proliferation, cell-mediated cytotoxicity, and IFN-γ production, as well as induce apoptosis. In this article, we demonstrate that deletion of the terminal cytoplasmic domain of the Tim3 gene potentiates its ability to downregulate Tc1 inflammation, and that this enhanced Tim3 activity is associated with decreased phosphorylation of the TCR-CD3ζ-chain. We then show that mice with this Tim3 mutation infected with influenza are protected from morbidity and mortality without impairment in viral clearance or functional heterotypic immunity. This protection is associated with decreased CD8+ T cell proliferation and decreased production of inflammatory cytokines, including IFN-γ. Furthermore, the Tim3 mutation was protective against mortality in a CD8+ T cell-specific model of pneumonitis. These data suggest that Tim3 could be targeted to prevent immunopathology during influenza infection and demonstrate a potentially novel signaling mechanism used by Tim3 to downregulate the Tc1 response.

Tumor-infiltrating DCs suppress nucleic acid-mediated innate immune responses through interactions between the receptor TIM-3 and the alarmin HMGB1

The mechanisms by which tumor microenvironments modulate nucleic acid-mediated innate immunity remain unknown. Here we identify the receptor TIM-3 as key in circumventing the stimulatory effects of nucleic acids in tumor immunity. Tumor-associated dendritic cells (DCs) in mouse tumors and patients with cancer had high expression of TIM-3. DC-derived TIM-3 suppressed innate immune responses through the recognition of nucleic acids by Toll-like receptors and cytosolic sensors via a galectin-9-independent mechanism. In contrast, TIM-3 interacted with the alarmin HMGB1 to interfere with the recruitment of nucleic acids into DC endosomes and attenuated the therapeutic efficacy of DNA vaccination and chemotherapy by diminishing the immunogenicity of nucleic acids released from dying tumor cells. Our findings define a mechanism whereby tumor microenvironments suppress antitumor immunity mediated by nucleic acids.

Galectins as self/non-self recognition receptors in innate and adaptive immunity: an unresolved paradox

Galectins are characterized by their binding affinity for β-galactosides, a unique binding site sequence motif, and wide taxonomic distribution and structural conservation in vertebrates, invertebrates, protista, and fungi. Since their initial description, galectins were considered to bind endogenous (“self”) glycans and mediate developmental processes and cancer. In the past few years, however, numerous studies have described the diverse effects of galectins on cells involved in both innate and adaptive immune responses, and the mechanistic aspects of their regulatory roles in immune homeostasis. More recently, however, evidence has accumulated to suggest that galectins also bind exogenous (“non-self”) glycans on the surface of potentially pathogenic microbes, parasites, and fungi, suggesting that galectins can function as pattern recognition receptors (PRRs) in innate immunity. Thus, a perplexing paradox arises by the fact that galectins also recognize lactosamine-containing glycans on the host cell surface during developmental processes and regulation of immune responses. According to the currently accepted model for non-self recognition, PRRs recognize pathogens via highly conserved microbial surface molecules of wide distribution such as LPS or peptidoglycan (pathogen-associated molecular patterns; PAMPs), which are absent in the host. Hence, this would not apply to galectins, which apparently bind similar self/non-self molecular patterns on host and microbial cells. This paradox underscores first, an oversimplification in the use of the PRR/PAMP terminology. Second, and most importantly, it reveals significant gaps in our knowledge about the diversity of the host galectin repertoire, and the subcellular targeting, localization, and secretion. Furthermore, our knowledge about the structural and biophysical aspects of their interactions with the host and microbial carbohydrate moieties is fragmentary, and warrants further investigation.

Tim-3 negatively regulates cytotoxicity in exhausted CD8+ T cells in HIV infection

Cytotoxic CD8⁺ T cells (CTLs) contain virus infections through the release of granules containing both perforin and granzymes. T cell ‘exhaustion’ is a hallmark of chronic persistent viral infections including HIV. The inhibitory regulatory molecule, T cell Immunoglobulin and Mucin domain containing 3 (Tim-3) is induced on HIV-specific T cells in chronic progressive infection. These Tim-3 expressing T cells are dysfunctional in terms of their capacities to proliferate or to produce cytokines. In this study, we evaluated the effect of Tim-3 expression on the cytotoxic capabilities of CD8⁺ T cells in the context of HIV infection. We investigated the cytotoxic capacity of Tim-3 expressing T cells by examining 1) the ability of Tim-3⁺ CD8⁺ T cells to make perforin and 2) the direct ability of Tim-3⁺ CD8⁺ T cells to kill autologous HIV infected CD4⁺ target cells. Surprisingly, Tim-3⁺ CD8⁺ T cells maintain higher levels of perforin, which was mainly in a granule-associated (stored) conformation, as well as express high levels of T-bet. However, these cells were also defective in their ability to degranulate. Blocking the Tim-3 signalling pathway enhanced the cytotoxic capabilities of HIV specific CD8⁺ T cells from chronic progressors by increasing; a) their degranulation capacity, b) their ability to release perforin, c) their ability to target activated granzyme B to HIV antigen expressing CD4⁺ T cells and d) their ability to suppress HIV infection of CD4⁺ T cells. In this latter effect, blocking the Tim-3 pathway enhances the cytotoxcity of CD8⁺ T cells from chronic progressors to the level very close to that of T cells from viral controllers. Thus, the Tim-3 receptor, in addition to acting as a terminator for cytokine producing and proliferative functions of CTLs, can also down-regulate the CD8⁺ T cell cytotoxic function through inhibition of degranulation and perforin and granzyme secretion.

Allograft rejection is restrained by short-lived TIM-3+PD-1+Foxp3+ Tregs

Tregs play a pivotal role in inducing and maintaining donor-specific transplant tolerance. The T cell immunoglobulin and mucin domain-3 protein (TIM-3) is expressed on many fully activated effector T cells. Along with program death 1 (PD-1), TIM-3 is used as a marker for exhausted effector T cells, and interaction with its ligand, galectin-9, leads to selective death of TIM-3+ cells. We report herein the presence of a galectin-9-sensitive CD4+FoxP3+TIM-3+ population of T cells, which arose from CD4+FoxP3+TIM-3- proliferating T cells in vitro and in vivo and were often PD-1+. These cells became very prominent among graft-infiltrating Tregs during allograft response. The frequency and number of TIM-3+ Tregs peaked at the time of graft rejection and declined thereafter. Moreover, these cells also arise in a tolerance-promoting donor-specific transfusion model, representing a pool of proliferating, donor-specific Tregs. Compared with TIM-3- Tregs, TIM-3+ Tregs, which are often PD-1+ as well, exhibited higher in vitro effector function and more robust expression of CD25, CD39, CD73, CTLA-4, IL-10, and TGF-β but not galectin-9. However, these TIM-3+ Tregs did not flourish when passively transferred to newly transplanted hosts. These data suggest that a heretofore unrecognized graft-infiltrating, short-lived subset of Tregs can restrain rejection.

Contrasting acute graft-versus-host disease effects of Tim-3/galectin-9 pathway blockade dependent upon the presence of donor regulatory T cells

T-cell immunoglobulin mucin-3 (Tim-3) is expressed on pathogenic T cells, and its ligand galectin-9 (gal-9) is up-regulated in inflamed tissues. When Tim-3(+) T cells encounter high gal-9 levels, they are deleted. Tim-3 is up-regulated on activated T cells during GVHD. Inhibition of Tim-3/gal-9 binding by infusion of a Tim-3-Ig fusion protein or Tim-3(-/-) donor T cells increased T-cell proliferation and GVHD lethality. When the Tim-3/gal-9 pathway engagement was augmented using gal-9 transgenic recipients, GVHD lethality was slowed. Together, these data indicate a potential for modulating this pathway to reduce disease by increasing Tim-3 or gal-9 engagement. Paradoxically, when Tim-3/gal-9 was inhibited in the absence of donor T-regulatory cells (Tregs), GVHD was inhibited. GVHD reduction was associated with decreased colonic inflammatory cytokines as well as epithelial barrier destruction. CD25-depleted Tim-3(-/-) donor T cells underwent increased activation-induced cell death because of increased IFN-γ production. To our knowledge, these studies are the first to show that although the absence of Tim-3/gal-9 pathway interactions augments systemic GVHD, concurrent donor Treg depletion paradoxically and surprisingly inhibits GVHD. Thus, although donor Tregs typically inhibit GVHD, under some conditions, such Tregs actually may contribute to GVHD by reducing activation-induced T-cell death.

Ectopic expression of TIM-3 in lung cancers: a potential independent prognostic factor for patients with NSCLC

T-cell immunoglobulin- and mucin domain-3-containing molecule 3 (TIM-3) is a membrane protein expressed in various kinds of immune cells and plays a pivotal role in immune regulation. Recently, TIM-3 was reported to be expressed aberrantly in melanoma cells, contributing to the low adhesion ability of tumor cells and promoting the survival of melanoma cells. We investigated TIM-3 expression in non-small cell lung cancers (NSCLCs), and further analyzed whether the aberrant expression of TIM-3 is related to the prognosis for patients with lung cancer. Tumor tissue samples from 30 patients with NSCLC were involved. Results of immunohistochemical analysis showed that TIM-3 stained positive on tumor cells in 86.7% (26/30) patients with primary NSCLC. The TIM-3 expression in NSCLC tumor cells was correlated with histologic type and pathologic T classification of the disease (P < .05). More importantly, patients with TIM-3-positive tumor cells had a significantly shorter survival time than those with TIM-3-negative tumors. Multivariate analysis demonstrated the significant role of TIM-3 expression in tumor cells as an independent prognostic factor for patients with NSCLC (relative risk, 4.481; 95% confidence interval, 1.790-11.22; P = .0005). Our results suggest that the ectopic expression of TIM-3 in tumor cells may be a potential, independent prognostic factor for patients with NSCLC.

Increased bovine Tim-3 and its ligand expressions during bovine leukemia virus infection

The immunoinhibitory receptor T cell immunoglobulin domain and mucin domain-3 (Tim-3) and its ligand, galectin-9 (Gal-9), are involved in the immune evasion mechanisms for several pathogens causing chronic infections. However, there is no report concerning the role of Tim-3 in diseases of domestic animals. In this study, cDNA encoding for bovine Tim-3 and Gal-9 were cloned and sequenced, and their expression and role in immune reactivation were analyzed in bovine leukemia virus (BLV)-infected cattle. Predicted amino acid sequences of Tim-3 and Gal-9 shared high homologies with human and mouse homologues. Functional domains, including tyrosine kinase phosphorylation motif in the intracellular domain of Tim-3 were highly conserved among cattle and other species. Quantitative real-time PCR analysis showed that bovine Tim-3 mRNA is mainly expressed in T cells such as CD4⁺ and CD8⁺ cells, while Gal-9 mRNA is mainly expressed in monocyte and T cells. Tim-3 mRNA expression in CD4⁺ and CD8⁺ cells was upregulated during disease progression of BLV infection. Interestingly, expression levels for Tim-3 and Gal-9 correlated positively with viral load in infected cattle. Furthermore, Tim-3 expression level closely correlated with up-regulation of IL-10 in infected cattle. The expression of IFN-γ and IL-2 mRNA was upregulated when PBMC from BLV-infected cattle were cultured with Cos-7 cells expressing Tim-3 to inhibit the Tim-3/Gal-9 pathway. Moreover, combined blockade of the Tim-3/Gal-9 and PD-1/PD-L1 pathways significantly promoted IFN-γ mRNA expression compared with blockade of the PD-1/PD-L1 pathway alone. These results suggest that Tim-3 is involved in the suppression of T cell function during BLV infection.

Regulatory circuits mediated by lectin-glycan interactions in autoimmunity and cancer

Numerous regulatory programs have been identified that contribute to the restoration of homeostasis at the conclusion of immune responses and to safeguarding against the detrimental effects of chronic inflammation and autoimmune pathology. Malignant cells may usurp these pathways to create immunosuppressive networks that thwart antitumor responses. Herein we review the role of endogenous lectins (C-type lectins, siglecs, and galectins) and specific N- and O-glycans generated by the coordinated action of glycosyltransferases and glycosidases that together promote regulatory signals that control immune cell homeostasis. We also discuss the mechanisms by which glycan-dependent regulatory programs integrate into canonical circuits that amplify or silence immune responses related to autoimmunity and neoplastic disease.

Multiple sclerosis

Multiple sclerosis (MS) is a multifocal demyelinating disease with progressive neurodegeneration caused by an autoimmune response to self-antigens in a genetically susceptible individual. While the formation and persistence of meningeal lymphoid follicles suggest persistence of antigens to drive the continuing inflammatory and humoral response, the identity of an antigen or infectious agent leading to the oligoclonal expansion of B and T cells is unknown. In this review we examine new paradigms for understanding the immunopathology of MS, present recent data defining the common genetic variants underlying disease susceptibility, and explore how improved understanding of immune pathway disruption can inform MS prognosis and treatment decisions.

Tim-2 up-regulation and galectin-9-Tim-3 pathway activation in Th2-biased response in Schistosoma japonicum infection in mice

T cell immunoglobulin domain and mucin domain (Tim) family, a new gene that expresses on the surface of T cells, plays a critical role in regulation of T cells response. Previous data have shown that Tim-3 expressed on Th1 cells promotes itself apoptosis. Tim-2 is preferentially up-regulated during Th2 differentiation and functions as a potent costimulatory molecule for T-cell immunity. The present study aims to learn whether Tims are responsible for Th2-biased response evoked by Schistosoma japonicum infection. The expressions of Tim-2 and Tim-3 in spleen lymphocytes from S. japonicum-infected mice were examined, and the possible role of galectin-9-Tim-3 pathway in Th2-biased response triggered by schistosome infection was discussed. Our results showed that Tim-2 mRNAs were up-regulated in the spleen of schistosome-infected mice, which coincided with elevated IL-4 gene expression. Administration of galectin-9 significantly induced apoptosis of naïve spleen lymphocytes with down-regulation IFN-γexpression in vitro. Additionally, Tim-3-Fc fusion protein notably enhanced Th1 cells and decreased Th2 cells in vitro. Thus, we concluded that pro-apoptotic effects on Th1 population through galectin-9-Tim-3 pathway and the up-regulation of Tim-2 on Th2 cells might be critical to Th2-biased response of host with schistosomiasis japonica.

The role of coinhibitory signaling pathways in transplantation and tolerance

Negative costimulatory molecules, acting through so-called inhibitory pathways, play a crucial role in the control of T cell responses. This negative “second signal” opposes T cell receptor activation and leads to downregulation of T cell proliferation and promotes antigen specific tolerance. Much interest has focused upon these pathways in recent years as a method to control detrimental alloresponses and promote allograft tolerance. However, recent experimental data highlights the complexity of negative costimulatory pathways in alloimmunity. Varying effects are observed from molecules expressed on donor and recipient tissues and also depending upon the activation status of immune cells involved. There appears to be significant overlap and redundancy within these systems, rendering this a challenging area to understand and exploit therapeutically. In this article, we will review the literature at the current time regarding the major negative costimulation pathways including CTLA-4:B7, PD-1:PD-L1/PD-L2 and PD-L1:B7-1, B7-H3, B7-H4, HVEM:BTLA/CD160, and TIM-3:Galectin-9. We aim to outline the role of these pathways in alloimmunity and discuss their potential applications for tolerance induction in transplantation.