Javier O. Jurado

Programmed Death (PD)-1:PD-Ligand 1/PD-Ligand 2 Pathway Inhibits T Cell Effector Functions during Human Tuberculosis

Protective immunity against Mycobacterium tuberculosis requires the generation of cell-mediated immunity. We investigated the expression and role of programmed death 1 (PD-1) and its ligands, molecules known to modulate T cell activation, in the regulation of IFN-γ production and lytic degranulation during human tuberculosis. We demonstrated that specific Ag-stimulation increased CD3+PD-1+ lymphocytes in peripheral blood and pleural fluid from tuberculosis patients in direct correlation with IFN-γ production from these individuals. Moreover, M. tuberculosis-induced IFN-γ participated in the up-regulation of PD-1 expression. Blockage of PD-1 or PD-1 and its ligands (PD-Ls: PD-L1, PD-L2) enhanced the specific degranulation of CD8+ T cells and the percentage of specific IFN-γ-producing lymphocytes against the pathogen, demonstrating that the PD-1:PD-Ls pathway inhibits T cell effector functions during active M. tuberculosis infection. Furthermore, the simultaneous blockage of the inhibitory receptor PD-1 together with the activation of the costimulatory protein signaling lymphocytic activation molecule led to the promotion of protective IFN-γ responses to M. tuberculosis, even in patients with weak cell-mediated immunity against the bacteria. Together, we demonstrated that PD-1 interferes with T cell effector functions against M. tuberculosis, suggesting that PD-1 has a key regulatory role during the immune response of the host to the pathogen.

IL-17 and IFN-γ expression in lymphocytes from patients with active tuberculosis correlates with the severity of the disease

Th1 lymphocytes are crucial in the immune response against Mycobacterium tuberculosis. Nevertheless, IFN‐γ alone is not sufficient in the complete eradication of the bacteria, suggesting that other cytokines might be required for pathogen removal. Th17 cells have been associated with M. tuberculosis infection, but the role of IL‐17‐producing cells in human TB remains to be understood. Therefore, we investigated the induction and regulation of IFN‐γ and IL‐17 during the active disease. TB patients were classified as High and Low Responder individuals according to their T cell responses against the antigen, and cytokine expression upon M. tuberculosis stimulation was investigated in peripheral blood and pleural fluid. Afterwards, the potential correlation among the proportions of cytokine‐producing cells and clinical parameters was analyzed. In TB patients, M. tuberculosis induced IFN‐γ and IL‐17, but in comparison with BCG‐vaccinated healthy donors, IFN‐γ results were reduced significantly, and IL‐17 was markedly augmented. Moreover, the main source of IL‐17 was represented by CD4+IFN‐γ+IL‐17+ lymphocytes, a Th1/Th17 subset regulated by IFN‐γ. Interestingly, the ratio of antigen‐expanded CD4+IFN‐γ+IL‐17+ lymphocytes, in peripheral blood and pleural fluid from TB patients, was correlated directly with clinical parameters associated with disease severity. Indeed, the highest proportion of CD4+IFN‐γ+IL‐17+ cells was detected in Low Responder TB patients, individuals displaying severe pulmonary lesions, and longest length of disease evolution. Taken together, the present findings suggest that analysis of the expansion of CD4+IFN‐γ+IL‐17+ T lymphocytes in peripheral blood of TB patients might be used as an indicator of the clinical outcome in active TB.

Role Played by the Programmed Death-1-Programmed Death Ligand Pathway during Innate Immunity against Mycobacterium tuberculosis

Tuberculous pleurisy allows the study of specific cells at the site of Mycobacterium tuberculosis infection. Among pleural lymphocytes, natural killer (NK) cells are a major source of interferon gamma (IFN-gamma), and their functions are regulated by activating and inhibitory receptors. Programmed death-1 (PD-1), programmed death ligand 1 (PD-L1), and programmed death ligand 2 (PD-L2) are recognized inhibitory receptors in adaptive immunity, but their role during innate immunity remains poorly understood. We investigated the PD-1:PD-L1/PD-L2 pathway on NK cell effector functions in peripheral blood and pleural fluid from patients with tuberculosis. M. tuberculosis stimulation significantly up-regulated PD-1, PD-L1, and PD-L2 levels on NK cells. Interestingly, a direct correlation between PD-1 and IFN-gamma expression on NK cells was observed. Moreover, blockade of the PD-1 pathway markedly augmented lytic degranulation and IFN-gamma production of NK cells against M. tuberculosis. Furthermore, PD-1(+) NK cells displayed a diminished IFN-gamma mean fluorescence intensity, denoting the relevance of PD-1 on IFN-gamma regulation. Together, we described a novel inhibitory role played by PD-1:PD-L interactions in innate immunity in tuberculosis.

Inducible Costimulator: A Modulator of IFN-γ Production in Human Tuberculosis

Effective host defense against Mycobacterium tuberculosis requires the induction of Th1 cytokine responses. We investigated the regulated expression and functional role of the inducible costimulator (ICOS), a receptor known to regulate Th cytokine production, in the context of human tuberculosis. Patients with active disease, classified as high responder (HR) or low responder (LR) patients according to their in vitro T cell responses against the Ag, were evaluated for T cell expression of ICOS after M. tuberculosis-stimulation. We found that ICOS expression significantly correlated with IFN-γ production by tuberculosis patients. ICOS expression levels were regulated in HR patients by Th cytokines: Th1 cytokines increased ICOS levels, whereas Th2-polarizing conditions down-regulated ICOS in these individuals. Besides, in human polarized Th cells, engagement of ICOS increased M. tuberculosis IFN-γ production with a magnitude proportional to ICOS levels on those cells. Moreover, ICOS ligation augmented Ag-specific secretion of the Th1 cytokine IFN-γ from responsive individuals. In contrast, neither Th1 nor Th2 cytokines dramatically affected ICOS levels on Ag-stimulated T cells from LR patients, and ICOS activation did not enhance IFN-γ production. However, simultaneous activation of ICOS and CD3 slightly augmented IFN-γ secretion by LR patients. Together, our data suggest that the regulation of ICOS expression depends primarily on the response of T cells from tuberculosis patients to the specific Ag. IFN-γ released by M. tuberculosis-specific T cells modulates ICOS levels, and accordingly, ICOS ligation induces IFN-γ secretion. Thus, ICOS activation may promote the induction of protective Th1 cytokine responses to intracellular bacterial pathogens.

IFN-γ Production during Active Tuberculosis Is Regulated by Mechanisms That Involve IL-17, SLAM, and CREB

Interferon-gamma (IFN-gamma) is crucial for protection against Mycobacterium tuberculosis, and the transcription factor cAMP response element binding protein (CREB) increases IFN-gamma transcription. We determined whether the transmembrane receptor signaling lymphocyte activation molecule (SLAM) and interleukin-17 (IL-17) affect CREB phosphorylation and IFN-gamma production in persons with tuberculosis. When T cells from patients with tuberculosis were activated with M. tuberculosis, 80% of SLAM(+) T cells expressed phosphorylated CREB, and SLAM activation increased CREB phosphorylation and IFN-gamma production. In contrast, IL-17 down-regulated SLAM expression, CREB phosphorylation, and IFN-gamma production. Therefore, IL-17 and SLAM have opposing effects on IFN-gamma production through CREB activation in persons with tuberculosis.

Cross-Talk between CD31 and the Signaling Lymphocytic Activation Molecule—Associated Protein during Interferon-γ Production against Mycobacterium tuberculosis

Effective host defense against tuberculosis requires Th1 cytokine responses. We studied the regulation of interferon (IFN)- gamma production during tuberculosis by investigating the role of CD31, a receptor that attenuates T cell receptor signals. After antigen stimulation, CD3(+)CD31(+) blood lymphocytes decreased in healthy donors and in tuberculosis patients with robust Th1 responses to Mycobacterium tuberculosis and IFN- gamma was secreted only by CD31(-) T cells. In contrast, in patients with weak Th1 cytokine responses to M. tuberculosis, the level of CD3(+)CD31(+) lymphocytes was increased and IFN- gamma production was low. Furthermore, the inverse relationship between CD31 expression and IFN- gamma production was in contrast to signaling lymphocytic activation molecule (SLAM) expression, an IFN- gamma inducer in tuberculosis. Interestingly, CD31 bound to SLAM-associated protein (SAP), an IFN- gamma inhibitor in tuberculosis, and when CD31 and SAP were coexpressed in lymphocytes, their association inhibited the IFN- gamma response to M. tuberculosis. Thus, CD31, when binding to SAP, interferes with Th1 responses, suggesting that CD31 has a key regulatory role in the signaling pathway(s) leading to the IFN- gamma response to M. tuberculosis.

ICOS, SLAM and PD-1 expression and regulation on T lymphocytes reflect the immune dysregulation in patients with HIV-related illness with pulmonary tuberculosis

Tuberculosis (TB) continues to be the most frequent cause of illness and death from an infectious agent globally, and its interaction with HIV is having devastating effects. To investigate how HIV alters the immune response to Mycobacterium tuberculosis (Mtb), we assessed basal and Mtb‐induced proliferation, cytokine production, and expression of signalling lymphocytic activation molecule (SLAM), inducible costimulator (ICOS) and programmed death‐1 (PD‐1) on T lymphocytes from HIV‐positive individuals coinfected with TB, HIV‐positive subjects, TB patients and healthy donors (HD).

CD137 differentially regulates innate and adaptive immunity against Mycobacterium tuberculosis

Protective immunity against Mycobacterium tuberculosis is primarily mediated by the interaction of antigen‐specific T cells and antigen presenting cells, which often depends on the interplay of cytokines produced by these cells. Costimulatory signals represent a complex network of receptor–ligand interactions that qualitatively and quantitatively influence immune responses. Thus, here we investigated the function of CD137 and CD137L, molecules known to have a central role in immune regulation, during human tuberculosis (TB). We demonstrated that M. tuberculosis antigen stimulation increased both CD137 and CD137L expression on monocytes and NK cells from TB patients and healthy donors, but only up‐regulated CD137 on T lymphocytes. Blockage of the CD137 pathway enhanced the levels of interferon (IFN)‐γ and tumor necrosis factor (TNF)‐α produced by monocytes and NK against M. tuberculosis. In contrast, CD137 blockage significantly decreased the specific degranulation of CD8+ T cells and the percentage of specific IFN‐γ and TNF‐α producing lymphocytes against the pathogen. Furthermore, inhibition of the CD137 pathway markedly increased T‐cell apoptosis. Taken together, our results demonstrate that CD137:CD137L interactions regulate the innate and adaptive immune response of the host against M. tuberculosis.