The central conclusion of this review is that MAIT cells are evolutionarily conserved rapid‐response units of the mucosal barrier that are activated by sensing microbial riboflavin metabolites, and subsequently secrete IFN‐γ, TNF‐α, IL‐17, and thereby exert cytotoxic effects, serving as the vanguard in the defense against bacterial/fungal infections. Here, TNF is linked to fungal infectious disease.