Mycobacterium tuberculosis exploits MPT64 to generate myeloid-derived suppressor cells to evade the immune system.

Mycobacterium tuberculosis (Mtb) is a smart and successful pathogen since it can persist in the intimidating environment of the host by taming and tuning the immune system. Mtb releases MPT64 (Rv1980c) protein in high amounts in patients with active tuberculosis (TB). Consequently, we were curious to decipher the role of MPT64 on the differentiating dendritic cells (DCs) and its relation to evading the immune system. We observed that pre-exposure of differentiating DCs to MPT64 (DC) transformed them into a phenotype of myeloid-derived suppressor cells (MDSCs). DC expressed a high level of immunosuppressive molecules PD-L1, TIM-3, nitric oxide (NO), arginase 1, IDO-1, IL-10 and TGF-β, but inhibited the production of pro-inflammatory cytokines TNF-α, IL-6 and IL-12. DC chemotaxis function was diminished due to the reduced expression of CCR7. DC promoted the generation of regulatory T cells (Tregs) but inhibited the differentiation of Th1 cells and Th17 cells. Further, high lipid and methylglyoxal content, and reduced glucose consumption by DC, rendered them metabolically quiescent and consequently, reduced DC ability to phagocytose Mtb and provided a safer shelter for the intracellular survival of the mycobacterium. The mechanism identified in impairing the function of DC was through the increased production and accumulation of methylglyoxal. Hence, for the first time, we demonstrate the novel role of MPT64 in promoting the generation of MDSCs to favor Mtb survival and escape its destruction by the immune system.