MR1 and infection: We observed rapid accumulation of pulmonary MAIT cells (defined as TCRβ+CD45.2+CD19− MR1-5-OP-RU tetramer+ cells, see Supplementary Fig. 2), which peaked around 5 days post-infection (dpi) (Fig. 1a, mean 2.6-fold increase from baseline, Kruskal–Wallis with post hoc Dunn’s P < 0.0001, n = 20, returning to baseline by day 7 (Fig. 1a, b)).