MR1 and tuberculosis: Reduced frequencies of MAIT cells have been observed in the peripheral blood of active TB patients relative to healthy counterparts (5, 10, 21), and functional relevance for MAIT cells in controlling mycobacterial infection is supported by the finding that MR1-deficient mice have higher lung mycobacterial burden following aerosol challenge with M. bovis than MR1-sufficient counterparts (22).