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We previously reported that patients with multidrug‐resistant tuberculosis (MDR‐TB) showed low systemic and Mtb‐induced Th22 responses associated to high sputum bacillary load and severe lung lesions suggesting that Th22 response could influence the ability of these patients to control bacillary growth and tissue damage. In MDR‐TB patients, the percentage of IL‐22+ cells inversely correlates with the proportion of senescent PD‐1+ T cells. Herein, we aimed to evaluate the pathways involved on the regulation of systemic and Mtb‐induced Th22 response in MDR‐TB and fully drug‐susceptible TB patients (S‐TB) and healthy donors. Our results show that while IL‐1β and IL‐23 promote Mtb‐induced IL‐22 secretion and expansion of IL‐22+ cells, TGF‐β inhibits this response. Systemic and in vitro Mtb‐induced Th22 response inversely correlates with TGF‐β amounts in plasma and in PBMC cultures respectively. The number of circulating PD‐1+ T cells directly correlates with plasmatic TGF‐β levels and blockade of PD‐1/PD‐L1 signalling enhances in vitro Mtb‐induced expansion of IL‐22+ cells. Thus, TGF‐β could also inhibit Th22 response through upregulation of PD‐1 expression in T cells. Higher percentage of IL‐23+ monocytes was observed in TB patients. In contrast, the proportion of IL‐1β+ monocytes was lower in TB patients with bilateral lung cavities (BCC) compared to those patients with unilateral cavities (UCC). Interestingly, TB patients with BCC showed higher plasmatic and Mtb‐induced TGF‐β secretion than patients with UCC. Thus, high TGF‐β secretion and subtle differences in IL‐23 and IL‐1β expression could diminish systemic and in vitro Mtb‐induced Th22 response along disease progression in TB patients. [ABSTRACT FROM AUTHOR]

Tuberculosis (TB) is one of the world's most pernicious diseases mainly due to immune evasion strategies displayed by its causative agent Mycobacterium tuberculosis (Mtb). Blood monocytes (Mos) represent an important source of DCs during chronic infections; consequently, the alteration of their differentiation constitutes an escape mechanism leading to mycobacterial persistence. We evaluated whether the CD16+/CD16− Mo ratio could be associated with the impaired Mo differentiation into DCs found in TB patients. The phenotype and ability to stimulate Mtb-specific memory clones DCs from isolated Mo subsets were assessed. We found that CD16− Mos differentiated into CD1a+DC-SIGNhigh cells achieving an efficient recall response, while CD16+ Mos differentiated into a CD1a−DC-SIGNlow population characterized by a poor mycobacterial Ag-presenting capacity. The high and sustained phosphorylated p38 expression observed in CD16+ Mos was involved in the altered DC profile given that its blockage restored DC phenotype and its activation impaired CD16− Mo differentiation. Furthermore, depletion of CD16+ Mos indeed improved the differentiation of Mos from TB patients toward CD1a+DC-SIGNhigh DCs. Therefore, Mos from TB patients are less prone to differentiate into DCs due to their increased proportion of CD16+ Mos, suggesting that during Mtb infection Mo subsets may have different fates after entering the lungs. [ABSTRACT FROM AUTHOR]

During a chronic infection such as tuberculosis, the pool of tissue dendritic cells (DC) must be renewed by recruitment of both circulating DC progenitors and monocytes (Mo). However, the microenvironment of the inflammatory site affects Mo differentiation. As DC are critical for initiating a Mycobacterium tuberculosis-specific T-cell response, we argue that interference of M. tuberculosis with a correct DC generation would signify a mechanism of immune evasion. In this study, we showed that early interaction of γ-irradiated M. tuberculosis with Mo subverts DC differentiation in vitro. We found that irradiated M. tuberculosis effect involves (1) the loss of a significant fraction of monocyte population and (2) an altered differentiation process of the surviving monocyte subpopulation. Moreover, in the absence of irradiated M. tuberculosis, DC consist in a major DC-specific intercellular adhesion molecule 3-grabbing non-integrin receptor (DC-SIGNhigh)/CD86low and minor DC-SIGNlow/CD86high subpopulations, whereas in the presence of bacteria, there is an enrichment of DC-SIGNlow/CD86high population. Besides, this population enlarged by irradiated M. tuberculosis, which is characterized by a reduced CD1b expression, correlates with a reduced induction of specific T-lymphocyte proliferation. The loss of CD1molecules partially involves toll-like receptors (TLR-2)/p38 MAPK activation. Finally, several features of Mo, which have been differentiated into DC in the presence of irradiated M. tuberculosis, resemble the features of DC obtained from patients with active tuberculosis. In conclusion, we suggest that M. tuberculosis escapes from acquired immune response in tuberculosis may be caused by an altered differentiation into DC leading to a poor M. tuberculosis-specific T-cell response. [ABSTRACT FROM AUTHOR]

Although the role of natural killer (NK) cells in mycobacterial infections is unclear, it has been postulated that they contribute to protective immunity through the production of interferon (IFN)-γ. In this study, we evaluate the effect of interleukin (IL)-10, IL-15 and IL-18 on NK lytic activity through the expression of CD16, CD11a and CD69 molecules and the induction of IFN-γ production in patients with tuberculosis (TB) and healthy individuals (N). Our results showed an impairment of NK lytic activity and a gradual down-regulation of costimulatory and adhesion molecules on NK cells which were dependent on the severity of the disease. NK lytic activity was increased by exogenous IL-15 and IL-18 in both TB and N , and by neutralization of endogenous IL-10 only in TB; IL-15 and IL-18 increased CD69 receptor expression , while anti-IL-10 up-regulated CD16 and CD11a expression in TB. Mycobacterium tuberculosis reduced the number of intracellular adhesion molecule (ICAM)-1+ CD14+ cells, but in the presence of IL-15, IL-18 and anti-IL-10 its expression was up-regulated. In cells from TB patients, the observed effects of IL-15 and IL-18 on NK function were not dependent on IL-10 modulation of the surface expression of activator/adhesion molecules. In the absence of monocytes, IL-10 activated NK cells, suggesting an indirect effect on their function. Furthermore, in TB patients the depletion of monocytes increased the production of IFN-γ by NK cells. Therefore, monocytes from TB patients regulated the NK function involving IL-10 which, through an indirect mechanism, led to the down-regulation of costimulatory/adhesion molecules and/or IFN-γ production. [ABSTRACT FROM AUTHOR]