No abstract

Protective immunity against Mycobacterium tuberculosis (Mtb) requires IFNG. Besides, IFNG-mediated induction of autophagy suppresses survival of virulent Mtb in macrophage cell lines. We investigated the contribution of autophagy to the defense against Mtb antigen (Mtb-Ag) in cells from tuberculosis patients and healthy donors (HD). Patients were classified as high responders (HR) if their T cells produced significant IFNG against Mtb-Ag; and low responders (LR) when patients showed weak or no T cell responses to Mtb-Ag. The highest autophagy levels were detected in HD cells whereas the lowest quantities were observed in LR patients. Interestingly, upon Mtb-Ag stimulation, we detected a positive correlation between IFNG and MAP1LC3B-II/LC3-II levels. Actually, blockage of Mtb-Ag-induced IFNG markedly reduced autophagy in HR patients whereas addition of limited amounts of IFNG significantly increased autophagy in LR patients. Therefore, autophagy collaborates with human immune responses against Mtb in close association with specific IFNG secreted against the pathogen.

Mycobacterium tuberculosis (Mtb) causes nearly 10 millions of new tuberculosis disease cases annually. However, most individuals exposed to Mtb do not develop tuberculosis, suggesting the influence of a human genetic component. Here, we investigated the association of the rs2275913 SNP (G → A) from IL-17A and tuberculosis in Argentina by a case-control study. Furthermore, we evaluated in vitro the functional relevance of this SNP during the immune response of the host against Mtb and analyzed its impact on clinical parameters of the disease. We found an association between the AA genotype and tuberculosis resistance. Additionally, within the healthy donors population, AA cells stimulated with a Mtb lysate (Mtb-Ag) produced the highest amounts of IL-17A and IFN-γ, which further support the genetic evidence found. In contrast, within the tuberculosis patients population, AA Mtb-Ag stimulated cells showed the lowest immunological parameters and we evidenced an association between the AA genotype and clinical parameters of disease severity, such as severe radiological lesions and higher bacilli burden in sputum. Overall, our findings demonstrated that the AA genotype from the IL-17A rs2275913 SNP is positively associated with protection to active tuberculosis but related to higher disease severity in the Argentinean population.

During mycobacterial infection, macroautophagy/autophagy, a process modulated by cytokines, is essential for mounting successful host responses. Autophagy collaborates with human immune responses against Mycobacterium tuberculosis (Mt) in association with specific IFNG secreted against the pathogen. However, IFNG alone is not sufficient to the complete bacterial eradication, and other cytokines might be required. Actually, induction of Th1 and Th17 immune responses are required for protection against Mt. Accordingly, we showed that IL17A and IFNG expression in lymphocytes from tuberculosis patients correlates with disease severity. Here we investigate the role of IFNG and IL17A during autophagy in monocytes infected with Mt H37Rv or the mutant MtΔRD1. Patients with active disease were classified as high responder (HR) or low responder (LR) according to their T cell responses against Mt. IL17A augmented autophagy in infected monocytes from HR patients through a mechanism that activated MAPK1/ERK2-MAPK3/ERK1 but, during infection of monocytes from LR patients, IL17A had no effect on the autophagic response. In contrast, addition of IFNG to infected monocytes, increased autophagy by activating MAPK14/p38 α both in HR and LR patients. Interestingly, proteins codified in the RD1 region did not interfere with IFNG and IL17A autophagy induction. Therefore, in severe tuberculosis patients' monocytes, IL17A was unable to augment autophagy because of a defect in the MAPK1/3 signaling pathway. In contrast, both IFNG and IL17A increased autophagy levels in patients with strong immunity to Mt, promoting mycobacterial killing. Our findings might contribute to recognize new targets for the development of novel therapeutic tools to fight the pathogen.

Neutrophils infected with Mycobacterium tuberculosis (Mtb) predominate in tuberculosis patients' lungs. Neutrophils phagocytose the pathogen, but the mechanism of pathogen elimination is controversial. Macroautophagy/autophagy, a crucial mechanism for several neutrophil functions, can be modulated by immunological mediators. The costimulatory molecule SLAMF1 can act as a microbial sensor in macrophages being also able to interact with autophagy-related proteins. Here, we demonstrate for the first time that human neutrophils express SLAMF1 upon Mtb-stimulation. Furthermore, SLAMF1 was found colocalizing with LC3B + vesicles, and activation of SLAMF1 increased neutrophil autophagy induced by Mtb. Finally, tuberculosis patients' neutrophils displayed reduced levels of SLAMF1 and lower levels of autophagy against Mtb as compared to healthy controls.Altogether, these results indicate that SLAMF1 participates in neutrophil autophagy during active tuberculosis.

IFN-γ release assays (IGRAs) are better indicators of Mycobacterium tuberculosis infection than the tuberculin skin test (TST) in Bacillus Calmette–Guérin (BCG)-vaccinated populations. However, IGRAs do not discriminate active and latent infections (LTBI) and no gold standard for LTBI diagnosis is available. Thus, since improved tests to diagnose M. tuberculosis infection are required, we assessed the efficacy of several M. tuberculosis latency antigens. BCG-vaccinated healthy donors (HD) and tuberculosis (TB) patients were recruited. QuantiFERON-TB Gold In-Tube, TST and clinical data were used to differentiate LTBI. IFN-γ production against CFP-10, ESAT-6, Rv2624c, Rv2626c and Rv2628 antigens was tested in peripheral blood mononuclear cells. LTBI subjects secreted significantly higher IFN-γ levels against Rv2626c than HD. Additionally, Rv2626c peptide pools to which only LTBI responded were identified, and their cumulative IFN-γ response improved LTBI discrimination. Interestingly, whole blood stimulation with Rv2626c allowed the discrimination between active and latent infections, since TB patients did not secrete IFN-γ against Rv2626c, in contrast to CFP-10 + ESAT-6 stimulation that induced IFN-γ response from both LTBI and TB patients. ROC analysis confirmed that Rv2626c discriminated LTBI from HD and TB patients. Therefore, since only LTBI recognizes specific epitopes from Rv2626c, this antigen could improve LTBI diagnosis, even in BCG-vaccinated people.

Th17 lymphocytes, that produce IL17A, IL17F, and IL22, play a crucial role during the immune response against Mycobacterium tuberculosis (Mtb) infection. Whereas, the contribution of IL17A in immunity to tuberculosis is usually accepted, the role of IL17F has been scarcely studied so far. The aim of this work was to evaluate the existence of a potential association of the non-synonymous variant rs763780 SNP of the IL17F gene with human tuberculosis. Accordingly, by comparing healthy donors (HD) and tuberculosis patients (TB) populations we demonstrated an association between the C allele of the SNP and the susceptibility to tuberculosis disease in Argentina. Furthermore, we found that peripheral blood mononuclear cells (PBMCs) from individuals with a more effective immune response against Mtb secreted the highest levels of IL17F when stimulated with a lysate of Mtb (Mtb-Ag). Besides, we evidenced that Mtb-Ag-stimulated PBMCs from HD carrying the C variant of the SNP displayed the lowest IFNG secretion, proliferation index, and SLAM expression as compared to TT carriers. Moreover, Mtb-Ag-stimulated PBMCs from TB carrying the C allele produced the lowest levels of IFNG, the highest level of IL17A, and the minimum proliferation indexes as compared to TT TB, suggesting a relationship between the C allele and tuberculosis severity. In fact, TB carrying the C allele presented a more severe disease, with the highest bacilli burden in sputum. Together, our findings identify the IL17F rs763780 SNP as a biomarker of tuberculosis susceptibility and advanced disease severity in Argentina, suggesting that IL17F could be a critical cytokine in tuberculosis immunity.

Prostaglandin E2 (PGE2), an active lipid compound derived from arachidonic acid, regulates different stages of the immune response of the host during several pathologies such as chronic infections or cancer. In fact, manipulation of PGE2 levels was proposed as an approach for countering the Type I IFN signature of tuberculosis (TB). However, very limited information regarding the PGE2 pathway in patients with active TB is currently available. In the present work, we demonstrated that PGE2 exerts a potent immunosuppressive action during the immune response of the human host against Mycobacterium tuberculosis (Mtb) infection. Actually, we showed that PGE2 significantly reduced the surface expression of several immunological receptors, the lymphoproliferation and the production of proinflammatory cytokines. In addition, PGE2 promoted autophagy in monocytes and neutrophils cultured with Mtb antigens. These results suggest that PGE2 might be attenuating the excessive inflammatory immune response caused by Mtb, emerging as an attractive therapeutic target. Taken together, our findings contribute to the knowledge of the role of PGE2 in the human host resistance to Mtb and highlight the potential of this lipid mediator as a tool to improve anti-TB treatment.