Regulation of immune response against Mycobacterium tuberculosis by the population of regulatory dendritic cells
On the background of a high level of genetic susceptibility to tuberculosis infection (TB), granulomatous reactions in the lung tissue fail to effectively isolate infection foci and rather result in diffuse pathology, confluence of granulomata and formation of necrotic zones. Uncontrolled inflammation severely affect breathing function of the lung. Thus, effective disease control requires a good balance between protective and pathogenic immune responses. Immature regulatory dendritic cells (DCreg) and regulatory T lymphocytes (Treg) represent a pool of important cellular regulators of inflammation. Earlier we have demonstrated that stromal lung cells support development of CD11b+CD11clowCD103- DCreg from their bone marrow-derived precursors in in vitro cultures. In addition, significantly larger population size and more rapid development of the lung CD4+Foxp3+ Treg cells characterize TB-resistant B6 mice compare to their TB-susceptible I/St counterparts. Here, we report that adoptive transfer of DCreg cells into TB-infected I/St mice is capable to enlarge the population of Treg cells in the lungs. This, in turn, attenuates lung pathology, decreases mycobacterial multiplication and diminishes lung infiltration with neutrophils, i.e., selectively restricts the population of cell largely responsible for TB pathogenesis. The key difference in lung pathology between DCreg recipients and control animals was the lack of tissue-destructive foci and necrotic zones in the former group. Meanwhile, the groups of mice did not differ in production of regulatory (IL-10 and TGF-β) and key inflammatory (IFNγ and IL-6) cytokines by lung cells. The latter result suggests that contact rather than secretory mechanisms underlie moderate attenuation of the TB process in the lungs of mice with an elevated lung Treg level, given that plethora of such mechanisms were described for Treg functioning. Although therapeutic effects were relatively weak, our results indicate that cell therapy approaches are applicable to regulation of lung tissue inflammation during TB course