The MAIT cell response to controlled oral enterotoxigenic E. coli challenge

Mucosa-associated invariant T (MAIT) cells recognize conserved microbial antigens presented by the non-polymorphic MR1 molecules and play important roles in barrier immunity. Enterotoxigenic E. coli (ETEC) is a major cause of diarrheal disease especially among children in lower-income countries. Here we investigate the potential role of MAIT cells in ETEC infection using samples from a human experimental ETEC challenge study. MAIT cells were activated with elevated function and proliferation in blood on day 7 after challenge, reflected both at protein and transcript levels, a pattern most evident among individuals who developed mild to severe diarrhea (MSD). The MSD-positive group had elevated expression of CCR9 and α4β7 on MAIT cells and experienced expansion of the peripheral MAIT cell pool at day 28 after challenge. Finally, the size of the MAIT cell pool correlated with MSD disease severity score. These findings indicate that MAIT cells respond to ETEC infection in a way associated with the development of symptomatic disease.