Figure 3.

Functional capacity of mucosal-associated invariant T (MAIT) cells and invariant natural killer T (iNKT) cells. Where subsets of MAIT or iNKT cells have been defined, characteristic cytokines, transcription factors, and/or surface markers, are illustrated. MAIT cells and iNKT cells exhibit overlapping functions, although a wider range of functions have been described for iNKT cells. In mice, distinct type 1 and type 17 MAIT and iNKT cell subsets have been identified. By contrast, human MAIT cells exhibit a mixed type 1/type 17 phenotype. Human iNKT cells secrete IFN-γ and IL-17 (only in vitro under pro-inflammatory conditions), but whether these cytokines are produced by distinct subsets, remains to be established. Unlike MAIT cells, iNKT cells also show type 2 functions, such as IL-4 secretion. In mice, IL-10-producing iNKT cells comprise a distinct subset with altered transcription factor expression. Human MAIT cells and iNKT cells can produce IL-10, and human IL-10-producing MAIT cells are enriched in adipose tissue, similar to mouse NKT10 cells. However, whether these IL-10-producing populations comprise distinct subsets, is currently unknown. Finally, multiple specialized subsets of iNKT cells have been identified in mice, including NKT_FH cells and iNKT_reg cells. Human iNKT cells with similar phenotypes and/or functions have also been identified (NKT_reg only in vitro), but analogous populations have yet to be described for MAIT cells.