At Once Friends and Foes

Mycobacterium tuberculosis (Mtb) is the causative agent of human tuberculosis (TB) disease. In chronic infections such as TB, consistent pro-inflammatory signalling promotes the generation of myeloid-derived suppressor cells (MDSCs). MDSCs are innate immune cells that are further divided into polymorphonuclear (PMN-MDSC) and monocytic (M-MDSC) subtypes on the basis of their morphology. These cells exert immunosuppressive effects on other immune cell types, thereby protecting the integrity of the lung tissue from damage caused by dysregulated Mtb. However, this comes at the expense of containing the Mtb infection. MDSCs’ unique double-edged role makes them an attractive target for host-directed TB therapeutics. This review aims to summarize current knowledge on the role of MDSCs in TB.