MAIT cell development in mice and humans.

• In mice, MAIT cells develop into MAIT1 or MAIT17 subsets. • In mice, microbial metabolites travel to the thymus to mediate MAIT17 proliferation. • In humans, no distinct MAIT subsets exist. • Human MAIT cells are naive when exiting the thymus and become memory after birth. • MAIT cells are tissue resident memory cells located in specific tissues. MAIT cells arise in the thymus following rearrangement of a T cell receptor (TCR) reactive against microbial vitamin B2-derived metabolites presented by the MHC-Ib molecule, MR1. Mechanisms that are conserved in mammals ensure the frequent production of MR1-restricted TCRs and the intra-thymic differentiation of MR1-restricted thymocytes into effector cells. Upon thymic egress and migration into non-lymphoid tissues, additional signals modulate MAIT cell functions according to each local tissue environment. Here, we review the recent progress made towards a better understanding of the establishment of this major immune cell subset. [ABSTRACT FROM AUTHOR]