The MAIT conundrum - how human MAIT cells distinguish bacterial colonization from infection in mucosal barrier tissues

Abstract

We review the recent human mucosal-associated invariant T (MAIT) cell literature to examine the signals that control MAIT cell activation. We discuss these signals in context of MAIT cell function in mucosal barrier tissues and address how MAIT cells avoid responding to commensal bacteria, while maintaining responsiveness to infections.

Keywords: Barrier tissue; Commensal bacteria; Cytokine; Effector function; Infection; Mucosal-associated invariant T cell (MAIT); T cell receptor.

Figure 1. Model of MAIT cell activation

A functional riboflavin synthesis pathway is found in commensal and pathogenic species, which can lead to MR1-dependent presentation of metabolites to MAIT cells. (A) A TCR signal alone is not sufficient to elicit robust effector function, thus commensal-derived antigen in the absence of additional inflammatory cues is not sufficient to elicit MAIT cell effector function (B) Proinflammatory cytokines including IL-12/15/18 are elicited following infection and synergize with the TCR signal to elicit robust effector function.