Circulating Monocyte-Like Myeloid Derived Suppressor Cells and CD16 Positive Monocytes Correlate With Immunological Responsiveness of Tuberculosis Patients.

Alterations of myeloid cell populations have been reported in patients with tuberculosis (TB). In this work, we studied the relationship between myeloid-derived suppressor cells (MDSC) and monocytes subsets with the immunological responsiveness of TB patients. Individuals with active TB were classified as low responders (LR-TB) or high responders (HR-TB) according to their T cell responses against a cell lysate of Mycobacterium tuberculosis (Mtb-Ag). Thus, LR-TB, individuals with severe disease, display a weaker immune response to Mtb compare to HR-TB, subjects with strong immunity against the bacteria. We observed that LR-TB presented higher percentages of CD16 positive monocytes as compared to HR-TB and healthy donors. Moreover, monocyte-like (M-MDSC) and polymorphonuclear-like (PMN-MDSC) MDSC were increased in patients and the proportion of M-MDSC inversely correlated with IFN-γ levels released after Mtb-Ag stimulation in HR-TB. We also found that LR-TB displayed the highest percentages of circulating M-MDSC. These results demonstrate that CD16 positive monocytes and M-MDSC frequencies could be used as another immunological classification parameter. Interestingly, in LR-TB, frequencies of CD16 positive monocytes and M-MDSC were restored after only three weeks of anti-TB treatment. Together, our findings show a link between the immunological status of TB patients and the levels of different circulating myeloid cell populations.

IFN-γ and IgG responses to Mycobacterium tuberculosis latency antigen Rv2626c differentiate remote from recent tuberculosis infection.

Tuberculin skin test (TST) and IFN-γ release assays are currently used to detect Mycobacterium tuberculosis (Mtb) infection but none of them differentiate active from latent infection (LTBI). Since improved tests to diagnose Mtb infection are required, we studied the immune response to Mtb latency antigen Rv2626c in individuals exposed to the bacteria during different periods. Tuberculosis patients (TB), TB close contacts (CC: subjects exposed to Mtb for less than three months) and healthcare workers (HW: individuals exposed to Mtb at least two years) were recruited and QuantiFERON (QFT) assay, TST and IFN-γ secretion to Rv2626c were analyzed. Twenty-two percent of the individuals assessed had discordant results between QFT and TST tests. Furthermore, QFT negative and QFT positive individuals produced differential levels of IFN-γ against Rv2626c, in direct association with their exposure period to Mtb. Actually, 91% of CC QFT negative subjects secreted low levels of IFN-γ to Rv2626c, whereas 43% of HW QFT negative people produced elevated IFN-γ amounts against Rv2626c. Conversely, 69% of CC QFT positive subjects didn´t produce IFN-γ to Rv2626c. Interestingly, a similar pattern of IgG anti-Rv2626c plasma levels was observed. Therefore, determination of IFN-γ and IgG levels against the dormancy antigen Rv2626c allows to identify established LTBI.

The IFNG rs1861494 Single Nucleotide Polymorphism Is Associated with Protection against Tuberculosis Disease in Argentina.

Interferon gamma (IFNG) plays a key role during Mycobacterium tuberculosis (Mtb) infection, and several polymorphisms located in its gene are associated with risk of tuberculosis in diverse populations. Nevertheless, the genetic resistance/susceptibility to tuberculosis in Argentina is unknown. The IFNG rs1861494 polymorphism (G→A) was reported to alter the binding of transcription factors to this region, influencing IFNG production. Using a case-control study, we found an association between the AA and AG genotypes and tuberculosis resistance (AA vs. GG: odds ratio (OR) = 0.235, p-value = 0.012; AG vs. GG: OR = 0.303, p-value = 0.044; AA vs. AG: OR = 0.776, p-value = 0.427; AA + AG vs. GG: OR = 0.270, p-value = 0.022). Moreover, Mtb-antigen stimulated peripheral blood mononuclear cells (PBMCs) from healthy donors and AA carriers secreted the highest amounts of IFNG in culture supernatants (p-value = 0.034) and presented the greatest percentage of CD4⁺IFNG⁺ lymphocytes (p-value = 0.035), in comparison with GG carriers. No association between the polymorphism and clinical parameters of tuberculosis severity was detected. However, our findings indicate that the rs1861494 single nucleotide polymorphism (SNP) could be considered as a biomarker of tuberculosis resistance in the Argentinean population.

Restimulation-induced T-cell death through NTB-A/SAP signaling pathway is impaired in tuberculosis patients with depressed immune responses.

Production of IFN-γ contributes to host defense against Mycobacterium tuberculosis (Mtb) infection. We previously demonstrated that Signaling lymphocytic activation molecule-associated protein (SAP) expression on cells from tuberculosis (TB) patients was inversely correlated with IFN-γ production. Here we first investigated the role of NK, T- and B-cell antigen (NTB-A)/SAP pathway in the regulation of Th1 response against Mtb. Upon antigen stimulation, NTB-A phosphorylation rapidly increases and afterwards modulates IFN-γ and IL-17 secretion. To sustain a healthy immune system, controlled expansion and contraction of lymphocytes, both during and after an adaptive immune response, is essential. Besides, restimulation-induced cell death (RICD) results in an essential homeostatic mechanism for precluding excess T-cell accumulation and associated immunopathology during the course of certain infections. Accordingly, we found that the NTB-A/SAP pathway was required for RICD during active tuberculosis. In low responder (LR) TB patients, impaired RICD was associated with diminished FASL levels, IL-2 production and CD25high expression after cell-restimulation. Interestingly, we next observed that SAP mediated the recruitment of the Src-related kinase FYNT, only in T cells from LR TB patients that were resistant to RICD. Together, we showed that the NTB-A/SAP pathway regulates T-cell activation and RICD during human TB. Moreover, the NTB-A/SAP/FYNT axis promotes polarization to an unfavorable Th2-phenotype.

A Mycobacterium tuberculosis Dormancy Antigen Differentiates Latently Infected Bacillus Calmette-Guérin-vaccinated Individuals.

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.