This project will decipher how MAIT cell numbers or functions are influenced by the gut microbiota composition, and reciprocally, how MAIT cells regulate or control expansion of gut microbiota components competing with opportunistic or pathogenic bacteria or responsible for infections. Ultimately, this study will determine how and when gut microbiota and MAIT cell interactions are involved in the control of severe infectious or intestinal inflammatory events in high risk infants, an indispensable step to design predictive biomarkers and ultimately propose new therapeutic options.