MAIT cells recognize microbial antigens and are restricted to MR1 molecules. The stimulatory antigens are intermediate metabolites generated in the riboflavin pathway. Like other metabolic processes, the riboflavin pathway undergoes physiological adaptation according to bacterial growth conditions. We investigated whether this regulation can impact the production of MAIT antigens by bacteria present in the gut, in which growth competition and extreme survival conditions influence the adaptive capacities of local microbiota.

We cultivated bacteria with conditions that resemble different gut-like environments and tested the stimulatory capacity of purified bacterial antigens using a panel of human MAIT clones. We found that bacterial growth conditions significantly affect accumulation of MAIT-stimulatory metabolites and consequent MAIT cell activation.

Quantitative comparison of antigens present in bacteria associated with Inflammatory Bowel Disease showed important differences when compared to the normal gut, suggesting a potential mechanism of intestinal MAIT activation in this disease.