Mucosal-activated invariant T cells do not exhibit significant lung recruitment and proliferation profiles in macaques in response to infection with Mycobacterium tuberculosis CDC1551

TB is a catastrophic infectious disease, affecting roughly one third of the world's population. Mucosal-associated invariant T (MAIT) cells are innate-like T cells that recognize vitamin B metabolites produced by bacteria, possess effector memory phenotype, and express tissue-homing markers driving migration to sites of infection. Previous research in both Mtb and HIV infections has shown that MAIT cells are depleted in the human periphery, possibly migrating to the tissue sites of infection. We investigated this hypothesis using rhesus macaques (RMs) with active TB, latent TB (LTBI), and SIV-coinfection to explore the effects of different disease states on the MAIT cell populations in vivo. Early in infection, we observed that MAIT cells increased in the blood and bronchoalveolar lavage fluid (BAL) of all infected RMs, irrespective of clinical outcome. However, the frequency of MAIT cells rapidly normalized such that they had returned to baseline levels prior to endpoint. Furthermore, following infection, the chemokines expressed on MAIT cells reflected a strong shift towards a Th1 phenotype from a shared Th1/Th17 phenotype. In conclusion, MAIT cells with enhanced Th1 functions migrating to the site of Mtb-infection. The anti-mycobacterial effector functions of MAIT cells, particularly during the early stages of Mtb infection, had been of interest in promoting protective long-term TB immunity. Our research shows, however, that they have relatively short-acting responses in the host.