Elevated expression of Tim-3 on CD8 T cells correlates with disease severity of pulmonary tuberculosis

The rs11684747 and rs55790676 SNPs of ADAM17 influence tuberculosis susceptibility and plasma levels of TNF, TNFR1, and TNFR2

Introduction

The proteolytic activity of A Disintegrin and Metalloproteinase 17 (ADAM17) regulates the release of tumor necrosis factor (TNF) and TNF receptors (TNFRs) from cell surfaces. These molecules play important roles in tuberculosis (TB) shaping innate immune reactions and granuloma formation.

Methods

Here, we investigated whether single nucleotide polymorphisms (SNPs) of ADAM17 influence TNF and TNFRs levels in 224 patients with active TB (ATB) and 118 healthy close contacts. Also, we looked for significant associations between SNPs of ADAM17 and ATB status. TNF, TNFR1, and TNFR2 levels were measured in plasma samples by ELISA. Four SNPs of ADAM17 (rs12692386, rs1524668, rs11684747, and rs55790676) were analyzed in DNA isolated from peripheral blood leucocytes. The association between ATB status, genotype, and cytokines was analyzed by multiple regression models.

Results

Our results showed a higher frequency of rs11684747 and rs55790676 in close contacts than ATB patients. Coincidentally, heterozygous to these SNPs of ADAM17 showed higher plasma levels of TNF compared to homozygous to their respective ancestral alleles. Strikingly, the levels of TNF and TNFRs distinguished participant groups, with ATB patients displaying lower TNF and higher TNFR1/TNFR2 levels compared to their close contacts.

Conclusion

These findings suggest a role for SNPs of ADAM17 in genetic susceptibility to ATB.

Association of tuberculosis risk with genetic polymorphisms of the immune checkpoint genes PDCD1, CTLA-4, and TIM3

The immune checkpoint proteins were reported to involve to host resistance to Mycobacteria tuberculosis (Mtb). Here, we evaluated 11 single nucleotide polymorphisms (SNPs) in PDCD1, CTLA4, and HAVCR2 genes between participants with and without TB infection. Genomic DNA isolated from 285 patients with TB and 270 controls without TB infection were used to perform the genotyping assay. Odds ratios were used to characterize the association of 11 SNPs with TB risk. In this study, the various genotypes of the 11 SNPs did not differ significantly in frequency between the non-TB and TB groups. When patients were stratified by sex, however, men differed significantly from women in genotype frequencies at HAVCR2 rs13170556. Odds ratios indicated that rs2227982, rs13170556, rs231775, and rs231779 were sex-specifically associated with TB risk. In addition, the combinations of rs2227982/rs13170556 GA/TC in men and the A-C-C haplotype of rs231775-rs231777-rs231779 in women were significantly associated with TB risk. Our results indicate that rs2227982 in PDCD1 and rs13170556 in HAVCR2 are associated with increased TB susceptibility in men and that the CTLA4 haplotype appears protective against TB in women.

Immune checkpoint modulating T cells and NK cells response to Mycobacterium tuberculosis infection

Many subversive mechanisms promote the occurrence and development of chronic infectious diseases and cancer, among which the down-regulated expression of immune-activating receptors and the enhanced expression of immune-inhibitory receptors accelerate the occurrence and progression of the disease. Recently, the use of immune checkpoint inhibitors has shown remarkable efficacy in the treatment of tumors in multiple organs. However, the expression of immune checkpoint molecules on natural killer (NK) cells by Mycobacterium tuberculosis (Mtb) infection and its impact on NK cell effector functions have been poorly studied. In this review, we focus on what is currently known about the expression of various immune checkpoints in NK cells following Mtb infection and how it alters NK cell-mediated host cytotoxicity and cytokine secretion. Unraveling the function of NK cells after the infection of host cells by Mtb is crucial for a comprehensive understanding of the innate immune mechanism of NK cells involved in tuberculosis and the evaluation of the efficacy of immunotherapies using immune checkpoint inhibitors to treat tuberculosis. In view of some similarities in the immune characteristics of T cells and NK cells, we reviewed the molecular mechanism of the interaction between T cells and Mtb, which can help us to further understand and explore the specific interaction mechanism between NK cells and Mtb.

Tim-3 expression is induced by mycobacterial antigens and identifies tissue-resident subsets of MAIT cells from patients with tuberculosis

Tissue-resident MAIT cells in tuberculous pleural effusions, the site of tuberculosis infection, were investigated in the study. Tim-3⁺CD69⁺CD103⁺ and CD39⁺CD69⁺CD103⁺ tissue-resident MAIT cell subsets were identified in tuberculous pleural effusions. Tim-3 expression in MAIT cells was greatly induced and CD39 expression was elevated following ex vivo stimulation with Mycobacterium tuberculosis antigens. Mycobacterial antigen-stimulated Tim-3⁺CD69⁺CD103⁺ tissue-resident MAIT cells had higher frequency of IFN-γ- and granzyme B-producing cells than Tim-3^-CD69⁺CD103⁺ subset, while CD39⁺CD69⁺CD103⁺ MAIT cells had similar frequency of IFN-γ-positive cells but higher ratio of granzyme B-producing cells than CD39^-CD69⁺CD103⁺ subset. Blocking of IL-2, IL-12p70 or IL-18 but not IL-15 led to significantly reduced expression of Tim-3 compared with isotype antibody control. In contrast, CD39 expression was not influenced by any of the cytokines tested. Tim-3⁺ MAIT cells had higher levels of lipid uptake and lipid content than Tim-3^- cells. It is concluded that Tim-3⁺CD69⁺CD103⁺ tissue-resident MAIT cells were elevated in tuberculous pleural effusions and had higher capacity to produce effector molecules of IFN-γ and granzyme B.

Characterizing and correcting immune dysfunction in non-tuberculous mycobacterial disease

Non-tuberculous mycobacterial pulmonary disease (NTM-PD) is a chronic, progressive, and growing worldwide health burden associated with mounting morbidity, mortality, and economic costs. Improvements in NTM-PD management are urgently needed, which requires a better understanding of fundamental immunopathology. Here, we examine temporal dynamics of the immune compartment during NTM-PD caused by Mycobacterium avium complex (MAC) and Mycobactereoides abscessus complex (MABS). We show that active MAC infection is characterized by elevated T cell immunoglobulin and mucin-domain containing-3 expression across multiple T cell subsets. In contrast, active MABS infection was characterized by increased expression of cytotoxic T-lymphocyte-associated protein 4. Patients who failed therapy closely mirrored the healthy individual immune phenotype, with circulating immune network appearing to 'ignore' infection in the lung. Interestingly, immune biosignatures were identified that could inform disease stage and infecting species with high accuracy. Additionally, programmed cell death protein 1 blockade rescued antigen-specific IFN-γ secretion in all disease stages except persistent infection, suggesting the potential to redeploy checkpoint blockade inhibitors for NTM-PD. Collectively, our results provide new insight into species-specific 'immune chatter' occurring during NTM-PD and provide new targets, processes and pathways for diagnostics, prognostics, and treatments needed for this emerging and difficult to treat disease.

Characterization of multiple soluble immune checkpoints in individuals with different Mycobacterium tuberculosis infection status and dynamic changes during anti-tuberculosis treatment

BACKGROUND

Immune checkpoints are crucial for the maintenance of subtle balance between self-tolerance and effector immune responses, but the role of soluble immune checkpoints (sICs) in Mycobacterium tuberculosis (M. tb) infection remains unknown. We assessed the levels of multiple sICs in individuals with distinct M. tb infection status, and their dynamic changes during anti-tuberculosis treatment.

METHODS

We enrolled 24 patients with pulmonary tuberculosis, among which 10 patients were diagnosed with tuberculous pleurisy (TBP), 10 individuals with latent tuberculosis infection (LTBI), and 10 healthy volunteers from Wuxi Fifth People's Hospital and Huashan Hospital between February 2019 and May 2021. Plasma concentrations of thirteen sICs were measured at enrollment and during anti-tuberculosis treatment using luminex-based multiplex assay. sICs levels in tuberculous pleural effusion (TPE) and their relations to laboratory test markers of TPE were also assessed in TBP patients.

RESULTS

The circulating levels of sPD-1, sPD-L1, sCTLA-4, sBTLA, sGITR, sIDO, sCD28, sCD27 and s4-1BB were upregulated in tuberculosis patients than in healthy controls. A lower sPD-L1 level was found in LTBI individuals than in tuberculosis patients. In TBP patients, the levels of sPD-1, sPD-L2, sCD28, sCD80, sCD27, sTIM-3, sLAG-3, sBTLA, s4-1BB and sIDO increased significantly in TPE than in plasma. In TPE, sBTLA and sLAG-3 correlated positively with the adenosine deaminase level. sIDO and sCD80 correlated positively with the lactate dehydrogenase level and the percentage of lymphocytes in TPE, respectively. Meanwhile, sCD27 correlated negatively with the specific gravity and protein level in TPE. In tuberculosis patients, the circulating levels of sBTLA and sPD-L1 gradually declined during anti-tuberculosis treatment.

CONCLUSIONS

We characterized the changing balance of sICs in M. tb infection. And our results revealed the relations of sICs to laboratory test markers and treatment responses in tuberculosis patients, indicating that certain sICs may serve as potential biomarkers for disease surveillance and prognosis of tuberculosis.

An Emerging Role of TIM3 Expression on T Cells in Chronic Kidney Inflammation

T cell immunoglobulin domain and mucin domain 3 (TIM3) was initially identified as an inhibitory molecule on IFNγ-producing T cells. Further research discovered the broad expression of TIM3 on different immune cells binding to multiple ligands. Apart from its suppressive effects on the Th1 cells, recent compelling experiments highlighted the indispensable role of TIM3 in the myeloid cell-mediated inflammatory response, supporting that TIM3 exerts pleiotropic effects on both adaptive and innate immune cells in a context-dependent manner. A large number of studies have been conducted on TIM3 biology in the disease settings of infection, cancer, and autoimmunity. However, there is a lack of clinical evidence to closely evaluate the role of T cell-expressing TIM3 in the pathogenesis of chronic kidney disease (CKD). Here, we reported an intriguing case of Mycobacterium tuberculosis (Mtb) infection that was characterized by persistent overexpression of TIM3 on circulating T cells and ongoing kidney tubulointerstitial inflammation for a period of 12 months. In this case, multiple histopathological biopsies revealed a massive accumulation of recruited T cells and macrophages in the enlarged kidney and liver. After standard anti-Mtb treatment, repeated renal biopsy identified a dramatic remission of the infiltrated immune cells in the tubulointerstitial compartment. This is the first clinical report to reveal a time-course expression of TIM3 on the T cells, which is pathologically associated with the progression of severe kidney inflammation in a non-autoimmunity setting. Based on this case, we summarize the recent findings on TIM3 biology and propose a novel model of CKD progression due to the aberrant crosstalk among immune cells.

Towards efficient immunotherapy for bacterial infection

The emergence of multiantibiotic-resistant bacteria, often referred to as superbugs, is leading to infections that are increasingly difficult to treat. Further, bacteria have evolved mechanisms by which they subvert the immune response, meaning that even antibiotic-sensitive bacteria can persist through antibiotic therapy. For these reasons, a broad range of viable therapeutic alternatives or conjunctions to traditional antimicrobial therapy are urgently required to reduce the burden of disease threatened by antibiotic resistance. Immunotherapy has emerged as a leading treatment option in cancer, and researchers are now attempting to apply this to infectious disease. This review summarizes and discusses the recent advances in the field and highlights current and future perspectives of using immunotherapies to treat bacterial infections.

Compromised Metabolic Reprogramming Is an Early Indicator of CD8+ T Cell Dysfunction during Chronic Mycobacterium tuberculosis Infection

The immunometabolic mechanisms underlying suboptimal T cell immunity in tuberculosis remain undefined. Here, we examine how chronic Mycobacterium tuberculosis (Mtb) and M. bovis BCG infections rewire metabolic circuits and alter effector functions in lung CD8⁺ T cells. As Mtb infection progresses, mitochondrial metabolism deteriorates in CD8⁺ T cells, resulting in an increased dependency on glycolysis that potentiates inflammatory cytokine production. Over time, these cells develop bioenergetic deficiencies that reflect metabolic “quiescence.” This bioenergetic signature coincides with increased mitochondrial dysfunction and inhibitory receptor expression and was not observed in BCG infection. Remarkably, the Mtb-triggered decline in T cell bioenergetics can be reinvigorated by metformin, giving rise to an Mtb-specific CD8⁺ T cell population with improved metabolism. These findings provide insights into Mtb pathogenesis whereby glycolytic reprogramming and compromised mitochondrial function contribute to the breakdown of CD8⁺ T cell immunity during chronic disease, highlighting opportunities to reinvigorate immunity with metabolically targeted pharmacologic agents.

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T cells from Mtb and BCG infections have unique metabolic and functional signatures

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Mitochondrial metabolism deteriorates in effector T cells as Mtb infection persists

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Metformin rejuvenates mitochondrial metabolism in T cells from Mtb-infected mice

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The breakdown of Mtb immunity during chronic disease is linked to immunometabolism

Elevated plasma sTIM-3 levels in patients with severe COVID-19

Background

The pathogenesis of coronavirus disease 2019 (COVID-19) is still incompletely understood, but it seems to involve immune activation and immune dysregulation.

Objective

We examined the parameters of activation of different leukocyte subsets in COVID-19–infected patients in relation to disease severity.

Methods

We analyzed plasma levels of myeloperoxidase (a marker of neutrophil activation), soluble (s) CD25 (sCD25) and soluble T-cell immunoglobulin mucin domain-3 (sTIM-3) (markers of T-cell activation and exhaustion), and sCD14 and sCD163 (markers of monocyte/macrophage activation) in 39 COVID-19–infected patients at hospital admission and 2 additional times during the first 10 days in relation to their need for intensive care unit (ICU) treatment.

Results

Our major findings were as follows: (1) severe clinical outcome (ICU treatment) was associated with high plasma levels of sTIM-3 and myeloperoxidase, suggesting activated and potentially exhausted T cells and activated neutrophils, respectively; (2) in contrast, sCD14 and sCD163 showed no association with need for ICU treatment; and (3) levels of sCD25, sTIM-3, and myeloperoxidase were inversely correlated with degree of respiratory failure, as assessed by the ratio of Pao₂ to fraction of inspired oxygen, and were positively correlated with the cardiac marker N-terminal pro-B–type natriuretic peptide.

Conclusion

Our findings suggest that neutrophil activation and, in particular, activated T cells may play an important role in the pathogenesis of COVID-19 infection, suggesting that T-cell–targeted treatment options and downregulation of neutrophil activation could be of importance in this disorder.

Tim-3: A co-receptor with diverse roles in T cell exhaustion and tolerance

T cell inhibitory co-receptors play a crucial role in maintaining the balance between physiologic immune responses and maladaptive ones. T cell immunoglobulin and mucin domain-containing-3 (Tim-3) is a unique inhibitory co-receptor in that its expression is chiefly restricted to interferon (IFN)γ-producing CD4⁺ and CD8⁺ T cells. Early reports firmly established its importance in maintaining peripheral tolerance in transplantation and autoimmunity. However, it has become increasingly clear that Tim-3 expression on T cells, together with other check-point molecules, in chronic infections and cancers can hinder productive immune responses. In this review, we outline what is currently known about the regulation of Tim-3 expression, its ligands and signaling. We discuss both its salutary and deleterious function in immune disorders, as well as the T cell-extrinsic and -intrinsic factors that regulate its function.

TIM3 comes of age as an inhibitory receptor

T cell immunoglobulin and mucin domain-containing protein 3 (TIM3), a member of the TIM family, was originally identified as a receptor expressed on interferon-γ-producing CD4⁺ and CD8⁺ T cells. Initial data indicated that TIM3 functioned as a 'co-inhibitory' or 'checkpoint' receptor, but due to the lack of a definable inhibitory signalling motif, it was also suggested that TIM3 might act as a co-stimulatory receptor. Recent studies have shown that TIM3 is part of a module that contains multiple co-inhibitory receptors (checkpoint receptors), which are co-expressed and co-regulated on dysfunctional or 'exhausted' T cells in chronic viral infections and cancer. Furthermore, co-blockade of TIM3 and programmed cell death 1 (PD1) can result in tumour regression in preclinical models and can improve anticancer T cell responses in patients with advanced cancers. Here, we highlight the developments in understanding TIM3 biology, including novel ligand identification and the discovery of loss-of-function mutations associated with human disease. In addition, we summarize emerging data from human clinical trials showing that TIM3 indeed acts as a 'checkpoint' receptor and that inhibition of TIM3 enhances the antitumour effect of PD1 blockade.

Immune checkpoint receptors: homeostatic regulators of immunity

Alcoholic liver disease (ALD) is an escalating global problem accounting for more than 3 million deaths annually. Bacterial infections are diagnosed in 25-47% of hospitalized patients with cirrhosis and represent the most important trigger for acute decompensation, multi-organ failure, septic shock and death. Current guidelines recommend intensive antibiotic therapy, but this has led to the emergence of multi-drug resistant bacteria, which are associated with increased morbidity and mortality rates. As such, there is a pressing need to explore new paradigms for anti-infective therapy and host-directed immunomodulatory therapies are a promising approach. Paradoxically, cirrhotic patients are characterised by heightened immune activity and exacerbated inflammatory processes but are unable to contend with bacterial infection, demonstrating that whilst immune effector cells are primed, their antibacterial effector functions are switched-off, reflecting a skewed homeostatic balance between anti-pathogen immunity and host-induced immunopathology. Preservation of this equilibrium physiologically is maintained by multiple immune-regulatory checkpoints and these feedback receptors serve as pivotal regulators of the host immunity. Checkpoint receptor blockade is proving to be effective at rescuing deranged/exhausted immunity in pre-clinical studies for chronic viral infection and sepsis. This approach has also obtained FDA approval for restoring anti-tumor immunity, with improved response rates and good safety profiles. To date, no clinical studies have investigated checkpoint blockade in ALD, highlighting an area for development of host-targeted immunotherapeutic strategies in ALD, for which there are no current specific treatment options. This review aims at framing current knowledge on immune checkpoints and the possibility of their therapeutic utility in ALD-associated immune dysfunctions.

TIM3 Mediates T Cell Exhaustion during Mycobacterium tuberculosis Infection

While T cell immunity initially limits Mycobacterium tuberculosis infection, why T cell immunity fails to sterilize the infection and allows recrudescence is not clear. One hypothesis is that T cell exhaustion impairs immunity and is detrimental to the outcome of M. tuberculosis infection. Here we provide functional evidence for the development T cell exhaustion during chronic TB. Second, we evaluate the role of the inhibitory receptor T cell immunoglobulin and mucin domain–containing-3 (TIM3) during chronic M. tuberculosis infection. We find that TIM3 expressing T cells accumulate during chronic infection, co-express other inhibitory receptors including PD1, produce less IL-2 and TNF but more IL-10, and are functionally exhausted. Finally, we show that TIM3 blockade restores T cell function and improves bacterial control, particularly in chronically infected susceptible mice. These data show that T cell immunity is suboptimal during chronic M. tuberculosis infection due to T cell exhaustion. Moreover, in chronically infected mice, treatment with anti-TIM3 mAb is an effective therapeutic strategy against tuberculosis.

Tuberculosis is a leading cause of morbidity and mortality across the globe. Fortunately, most people infected with M. tuberculosis mount a protective immune response and only a small fraction develops active disease. Impairment of immunity late during the course of disease can lead to bacterial recrudescence; however, why immunity fails is poorly understood. We investigated whether T cell exhaustion develops and contributes to immunological impairment during disease. Our studies provide definitive evidence that CD4⁺ T cells become functionally exhausted early after infection, and subsequently, CD8⁺ T cells also show signs of dysfunction. T cell exhaustion in both subsets was associated with the expression of multiple inhibitory receptors. Exhausted T cells expressed TIM3 plus other inhibitory receptors (e.g., PD1, TIM3, Lag-3, and 2B4), TIM3⁺PD1⁺ T cells were more likely to be poor producers of IL-2, IFNγ, and TNF and instead produce IL-10. Evaluation of gene expression by Nanostring confirmed that TIM3⁺PD1⁺ T cells in the lungs of infected mice had a transcriptional profile characteristic of exhausted T cells. Thus, this phenotype identified T cells that were truly exhausted and correlates well with previously established paradigm that co-expression of TIM3 with other inhibitory receptors such as PD1 contributes to impairment of T cell function during chronic inflammatory conditions. Most importantly, treatment of chronically infected mice with blocking antibodies specific for TIM3 led to a significant gain in bacterial control. Treatment was associated with an increase in IL-2, IFNγ, and TNF production by T cells. Based on this key result, we infer that TIM3-mediated T cell exhaustion impairs host resistance to M. tuberculosis. Thus, these data suggest that blockade of inhibitory T cell signals has the potential to be a therapeutic strategy against tuberculosis. The data in our report significantly advances our current knowledge of the biology of TIM3, the role of inhibitory T cell receptors during chronic infection, and the pathogenesis of tuberculosis.

The emerging role of myeloid-derived suppressor cells in lung diseases

Myeloid-derived suppressor cells (MDSCs) are innate immune cells characterised by their potential to control T-cell responses and to dampen inflammation. While the role of MDSCs in cancer has been studied in depth, our understanding of their relevance for infectious and inflammatory disease conditions has just begun to evolve. Recent studies highlight an emerging and complex role for MDSCs in pulmonary diseases. In this review, we discuss the potential contribution of MDSCs as biomarkers and therapeutic targets in lung diseases, particularly lung cancer, tuberculosis, chronic obstructive pulmonary disease, asthma and cystic fibrosis.

Mucosal-associated invariant T cells from patients with tuberculosis exhibit impaired immune response

OBJECTIVES

To identify factors which regulate MAIT cell response to Mycobacterium tuberculosis antigens, and to investigate the role of MAIT cells in patients with active tuberculosis.

METHODS

Immune response of MAIT cells to M. tuberculosis antigens were compared between patients with active TB and healthy controls by flow cytometry and RNA sequencing.

RESULTS

IFN-γ response of MAIT cells to M. tuberculosis lysates was dramatically improved by signal 3 cytokine IL-15 (p = 0.0002). Patients with active TB exhibited highly reduced IFN-γ production in MAIT cells stimulated with M. tuberculosis lysates/IL-15 compared with healthy controls (p < 0.0001) and individuals with latent TB infection (p = 0.0008). RNA sequencing of flow-sorted MAIT cells from patients with TB and healthy controls identified numerous differentially expressed genes, and the expression of genes that encode IFN-γ, TNF-α, IL-17F, granulysin and granzyme B were all down-regulated in patients with TB. MAIT cells from patients with TB has significantly lower expression of γc receptor than those from healthy controls under condition of Mtb lysates/IL-15 stimulation (p = 0.0028). Blockade of both γc and IL-2Rβ receptors resulted in highly reduced frequency of IFN-γ-producing MAIT cells (79.4%) (p = 0.0011).

CONCLUSIONS

MAIT cells from patients with active TB exhibited impaired cytokine and cytotoxic response to M. tuberculosis antigens.

Elevated expression of T-bet in mycobacterial antigen-specific CD4(+) T cells from patients with tuberculosis

T-bet is a T-box transcriptional factor that controls the differentiation and effector functions of CD4 T cells. In this study, we studied the role of T-bet in regulating CD4(+) T cell immunity against tuberculosis (TB). T-bet expression in Mycobacterium tuberculosis antigen-specific CD4(+) T cells was significantly higher in patients with active TB than in individuals with latent TB infection (p<0.0001). Comparison of T-bet expression in TCM and TEM subsets showed that CD4(+)T-bet(+)M. tuberculosis antigen-specific CD4(+) T cells had significantly lower frequency of TCM (p=0.003) and higher frequency of TEM (p=0.003) than CD4(+)T-bet(-) cells. The expression of PD-1 in antigen-specific CD4(+) T cells was significantly higher in patients with TB than in individuals with latent TB infection (p=0.006). CD4(+)CD154(+)T-bet(+) T cells had significantly higher expression of PD-1 than CD4(+)CD154(+)T-bet(-) T cells (p=0.0028). It is concluded that T-bet expression might be associated with differentiation into effector memory cells and PD-1 expression in mycobacterial antigen-specific CD4(+) T cells.

Regulation of T cell responses by the receptor molecule Tim-3

Tim-3 is a member of the T cell immunoglobulin and mucin domain (Tim) family of proteins, which are expressed by several cell types in the immune system, including CD4 and CD8 T cells activated under certain conditions. These molecules are generally thought to act as receptors for multiple ligands and thus to function by engaging intracellular signaling pathways in a ligand-dependent manner. In recent years, the function of the Tim-3 protein has been studied in some detail, particularly with respect to its role in the regulation of CD4 and CD8 T cell responses. Here, we review the structural features of Tim-3, known ligands for this molecule and the links established between Tim-3 and signal transduction pathways. In addition, we review the current literature regarding the role of Tim-3 in the regulation of effector responses by CD4 and CD8 T cells. Overall, findings published thus far strongly support the conclusion that Tim-3 functions to inhibit T cell responses, particularly under conditions involving chronic stimulation. Conversely, some reports have provided evidence that Tim-3 can stimulate T cells under conditions involving acute stimulation, suggesting that the role of Tim-3 may vary depending on context. Further study of Tim-3 is likely to advance our understanding of how CD4 and CD8 T cell responses are regulated and could uncover novel approaches for manipulating T cell function for therapeutic benefit.

Tuberculosis and HIV Coinfection

Tuberculosis (TB) and human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) constitute the main burden of infectious disease in resource-limited countries. In the individual host, the two pathogens, Mycobacterium tuberculosis and HIV, potentiate one another, accelerating the deterioration of immunological functions. In high-burden settings, HIV coinfection is the most important risk factor for developing active TB, which increases the susceptibility to primary infection or reinfection and also the risk of TB reactivation for patients with latent TB. M. tuberculosis infection also has a negative impact on the immune response to HIV, accelerating the progression from HIV infection to AIDS. The clinical management of HIV-associated TB includes the integration of effective anti-TB treatment, use of concurrent antiretroviral therapy (ART), prevention of HIV-related comorbidities, management of drug cytotoxicity, and prevention/treatment of immune reconstitution inflammatory syndrome (IRIS).

Orchestration of pulmonary T cell immunity during Mycobacterium tuberculosis infection: immunity interruptus

Despite the introduction almost a century ago of Mycobacterium bovis BCG (BCG), an attenuated form of M. bovis that is used as a vaccine against Mycobacterium tuberculosis, tuberculosis remains a global health threat and kills more than 1.5 million people each year. This is mostly because BCG fails to prevent pulmonary disease--the contagious form of tuberculosis. Although there have been significant advances in understanding how the immune system responds to infection, the qualities that define protective immunity against M. tuberculosis remain poorly characterized. The ability to predict who will maintain control over the infection and who will succumb to clinical disease would revolutionize our approach to surveillance, control, and treatment. Here we review the current understanding of pulmonary T cell responses following M. tuberculosis infection. While infection elicits a strong immune response that contains infection, M. tuberculosis evades eradication. Traditionally, its intracellular lifestyle and alteration of macrophage function are viewed as the dominant mechanisms of evasion. Now we appreciate that chronic inflammation leads to T cell dysfunction. While this may arise as the host balances the goals of bacterial sterilization and avoidance of tissue damage, it is becoming clear that T cell dysfunction impairs host resistance. Defining the mechanisms that lead to T cell dysfunction is crucial as memory T cell responses are likely to be subject to the same subject to the same pressures. Thus, success of T cell based vaccines is predicated on memory T cells avoiding exhaustion while at the same time not promoting overt tissue damage.

Mucosal-associated invariant T-cell function is modulated by programmed death-1 signaling in patients with active tuberculosis

RATIONALE

Mucosal-associated invariant T (MAIT) cells have been proven to play an important role in host defense against mycobacterial infection in animal infection models; however, the functional role of MAIT cells in patients with active tuberculosis (TB) is still largely unknown.

OBJECTIVES

To understand the clinical features and functions of MAIT cells in patients with active TB.

METHODS

MAIT cells were analyzed in patients with pulmonary TB, tuberculous pleurisy, and tuberculous peritonitis by flow cytometry. The functions of MAIT cells were compared between patients with active TB and healthy control subjects.

MEASUREMENTS AND MAIN RESULTS

The frequency of MAIT cells was significantly reduced both in peripheral blood from patients with active pulmonary TB (P < 0.0001) and in tuberculous pleural effusions compared with healthy control subjects but not in ascitic fluids from patients with tuberculous peritonitis. A comparison of bacillus Calmette-Guérin (BCG)-stimulated cytokine production showed that patients with active TB had significantly higher production of IFN-γ (P = 0.0034) and tumor necrosis factor (TNF)-α (P = 0.0399) compared with healthy control subjects. In contrast, when MAIT cells were stimulated with Escherichia coli, patients with active TB had significantly lower production of IFN-γ (P = 0.0007) and TNF-α (P = 0.0032). MAIT cells in patients with active TB exhibited elevated expression of programmed death-1 (PD-1) (P = 0.0015), and blockade of PD-1 signaling resulted in a significantly higher frequency of BCG-stimulated IFN-γ production in MAIT cells (P = 0.0178).

CONCLUSIONS

MAIT-cell immune response to antigen stimulation in patients with active TB is regulated by PD-1, which could be a potential target for TB immunotherapy.

Tim-3 directly enhances CD8 T cell responses to acute Listeria monocytogenes infection

T cell Ig and mucin domain (Tim) 3 is a surface molecule expressed throughout the immune system that can mediate both stimulatory and inhibitory effects. Previous studies have provided evidence that Tim-3 functions to enforce CD8 T cell exhaustion, a dysfunctional state associated with chronic stimulation. In contrast, the role of Tim-3 in the regulation of CD8 T cell responses to acute and transient stimulation remains undefined. To address this knowledge gap, we examined how Tim-3 affects CD8 T cell responses to acute Listeria monocytogenes infection. Analysis of wild-type (WT) mice infected with L. monocytogenes revealed that Tim-3 was transiently expressed by activated CD8 T cells and was associated primarily with acquisition of an effector phenotype. Comparison of responses to L. monocytogenes by WT and Tim-3 knockout (KO) mice showed that the absence of Tim-3 significantly reduced the magnitudes of both primary and secondary CD8 T cell responses, which correlated with decreased IFN-γ production and degranulation by Tim-3 KO cells stimulated with peptide Ag ex vivo. To address the T cell-intrinsic role of Tim-3, we analyzed responses to L. monocytogenes infection by WT and Tim-3 KO TCR-transgenic CD8 T cells following adoptive transfer into a shared WT host. In this setting, the accumulation of CD8 T cells and the generation of cytokine-producing cells were significantly reduced by the lack of Tim-3, demonstrating that this molecule has a direct effect on CD8 T cell function. Combined, our results suggest that Tim-3 can mediate a stimulatory effect on CD8 T cell responses to an acute infection.

Involvement of CD244 in regulating CD4+ T cell immunity in patients with active tuberculosis

CD244 (2B4) is a member of the signaling lymphocyte activation molecule (SLAM) family of immune cell receptors and it plays an important role in modulating NK cell and CD8⁺ T cell immunity. In this study, we investigated the expression and function of CD244/2B4 on CD4⁺ T cells from active TB patients and latent infection individuals. Active TB patients had significantly elevated CD244/2B4 expression on M. tuberculosis antigen-specific CD4⁺ T cells compared with latent infection individuals. The frequencies of CD244/2B4-expressing antigen-specific CD4⁺ T cells were significantly higher in retreatment active TB patients than in new active TB patients. Compared with CD244/2B4-dull and -middle CD4⁺ T cells, CD244/2B4-bright CD4⁺ T cell subset had significantly reduced expression of IFN-γ, suggesting that CD244/2B4 expression may modulate IFN-γ production in M. tuberculosis antigen-responsive CD4⁺ T cells. Activation of CD244/2B4 signaling by cross-linking led to significantly decreased production of IFN-γ. Blockage of CD244/2B4 signaling pathway of T cells from patients with active TB resulted in significantly increased production of IFN-γ, compared with isotype antibody control. In conclusion, CD244/2B4 signaling pathway has an inhibitory role on M. tuberculosis antigen-specific CD4⁺ T cell function.

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-expressing CD4+ and CD8+ T cells in human tuberculosis (TB) exhibit polarized effector memory phenotypes and stronger anti-TB effector functions

T-cell immune responses modulated by T-cell immunoglobulin and mucin domain-containing molecule 3 (Tim-3) during Mycobacterium tuberculosis (Mtb) infection in humans remain poorly understood. Here, we found that active TB patients exhibited increases in numbers of Tim-3-expressing CD4⁺ and CD8⁺ T cells, which preferentially displayed polarized effector memory phenotypes. Consistent with effector phenotypes, Tim-3⁺CD4⁺ and Tim-3⁺CD8⁺ T-cell subsets showed greater effector functions for producing Th1/Th22 cytokines and CTL effector molecules than Tim-3⁻ counterparts, and Tim-3-expressing T cells more apparently limited intracellular Mtb replication in macrophages. The increased effector functions for Tim-3-expressing T cells consisted with cellular activation signaling as Tim-3⁺CD4⁺ and Tim-3⁺CD8⁺ T-cell subsets expressed much higher levels of phosphorylated signaling molecules p38, stat3, stat5, and Erk1/2 than Tim-3- controls. Mechanistic experiments showed that siRNA silencing of Tim-3 or soluble Tim-3 treatment interfering with membrane Tim-3-ligand interaction reduced de novo production of IFN-γ and TNF-α by Tim-3-expressing T cells. Furthermore, stimulation of Tim-3 signaling pathways by antibody cross-linking of membrane Tim-3 augmented effector function of IFN-γ production by CD4⁺ and CD8⁺ T cells, suggesting that Tim-3 signaling helped to drive stronger effector functions in active TB patients. This study therefore uncovered a previously unknown mechanism for T-cell immune responses regulated by Tim-3, and findings may have implications for potential immune intervention in TB.

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (Mtb) infection, remains a leading cause of morbidity and mortality worldwide. While CD4⁺ and CD8⁺ T-cell effector functions producing Th1 or cytotoxic cytokines are required to mount anti-mycobacterial immunity, insufficiency or failure to mount anti-mycobacterial effector functions by CD4⁺ and CD8⁺ T cells may lead to impaired immunity against TB. Therefore, it is important to elucidate functional characteristics and regulatory pathways for Mtb-specific CD4⁺ and CD8⁺ T cells during immune responses to Mtb infection. It was postulated that T-cell immunoglobulin and mucin domain-containing molecule 3 (Tim-3) might represent a T-cell exhaustion marker, and expression of Tim-3 on T cells may be linked to progressive loss of secretion of cytokines. Thus, Tim-3 expression on T cells might correlate with T-cell dysfunction and disease pathogenic events. However, T-cell immune responses modulated by Tim-3 in human TB disease remain poorly understood. Here, we found that up-regulation of Tim-3 expression in active human TB disease allows CD4⁺ and CD8⁺ T cells to mount stronger, but not impaired, anti-mycobacterium effector functions. This study therefore uncovers a previously unknown mechanism for T-cell immune responses regulated by Tim-3, and has an important implication for TB diagnostics and therapy.

Antigen-independent induction of Tim-3 expression on human T cells by the common γ-chain cytokines IL-2, IL-7, IL-15, and IL-21 is associated with proliferation and is dependent on the phosphoinositide 3-kinase pathway

T cell Ig mucin domain-containing molecule 3 (Tim-3) is a glycoprotein found on the surface of a subset of CD8(+) and Th1 CD4(+) T cells. Elevated expression of Tim-3 on virus-specific T cells during chronic viral infections, such as HIV-1, hepatitis B virus, and hepatitis C virus, positively correlates with viral load. Tim-3(+) cytotoxic T cells are dysfunctional and are unable to secrete effector cytokines, such as IFN-γ and TNF-α. In this study, we examined potential inducers of Tim-3 on primary human T cells. Direct HIV-1 infection of CD4(+) T cells, or LPS, found to be elevated in HIV-1 infection, did not induce Tim-3 on T cells. Tim-3 was induced by the common γ-chain (γc) cytokines IL-2, IL-7, IL-15, and IL-21 but not IL-4, in an Ag-independent manner and was upregulated on primary T cells in response to TCR/CD28 costimulation, as well as γc cytokine stimulation with successive divisions. γc cytokine-induced Tim-3 was found on naive, effector, and memory subsets of T cells. Tim-3(+) primary T cells were more prone to apoptosis, particularly upon treatment with galectin-9, a Tim-3 ligand, after cytokine withdrawal. The upregulation of Tim-3 could be blocked by the addition of a PI3K inhibitor, LY 294002. Thus, Tim-3 can be induced via TCR/CD28 costimulation and/or γc cytokines, likely through the PI3K pathway.

Tuberculosis and HIV co-infection

Tuberculosis (TB) and HIV co-infections place an immense burden on health care systems and pose particular diagnostic and therapeutic challenges. Infection with HIV is the most powerful known risk factor predisposing for Mycobacterium tuberculosis infection and progression to active disease, which increases the risk of latent TB reactivation 20-fold. TB is also the most common cause of AIDS-related death. Thus, M. tuberculosis and HIV act in synergy, accelerating the decline of immunological functions and leading to subsequent death if untreated. The mechanisms behind the breakdown of the immune defense of the co-infected individual are not well known. The aim of this review is to highlight immunological events that may accelerate the development of one of the two diseases in the presence of the co-infecting organism. We also review possible animal models for studies of the interaction of the two pathogens, and describe gaps in knowledge and needs for future studies to develop preventive measures against the two diseases.

Enhanced upper genital tract pathologies by blocking Tim-3 and PD-L1 signaling pathways in mice intravaginally infected with Chlamydia muridarum

Background

Although Tim-3 & PD-L1 signaling pathways play important roles in negatively regulating immune responses, their roles in chlamydial infection have not been evaluated.

Methods

Neutralization antibodies targeting Tim-3 and PD-L1 were used to treat mice. Following an intravaginal infection with C. muridarum organisms, mice with or without the dual antibody treatment were compared for live chlamydial organism shedding from the lower genital tract and inflammatory pathology in the upper genital tract.

Results

Mice treated with anti-Tim-3 and anti-PD-L1 antibodies displayed a time course of live organism shedding similar to that of mice treated with equivalent amounts of isotype-matched IgG molecules. The combined antibody blocking failed to alter either the lower genital tract cytokine or systemic humoral and cellular adaptive responses to C. muridarum infection. However, the antibody blocking significantly enhanced C. muridarum-induced pathologies in the upper genital tract, including more significant hydrosalpinx and inflammatory infiltration in uterine horn and oviduct tissues.

Conclusions

The Tim-3 and PD-L1-mediated signaling can significantly reduce pathologies in the upper genital tract without suppressing immunity against chlamydial infection, suggesting that Tim-3 and PD-L1-mediated negative regulation may be manipulated to attenuate tubal pathologies in women persistently infected with C. trachomatis organisms.