Neuropathologic, phenotypic and functional analyses of Mucosal Associated Invariant T cells in Multiple Sclerosis

International audienceBackground: The involvement of Mucosal Associated Invariant T (MAIT) cells, which are anti-microbial semi-invariant T cells, remains elusive in Multiple Sclerosis (MS).Objective: Deciphering the potential involvement of MAIT cells in the MS inflammatory process. Methods: By flow cytometry, blood MAIT cells from similar cohorts of MS patients and healthy volunteers (HV) were compared for frequency, phenotype, activation potential after in vitro TCR engagement by bacterial ligands and transmigration abilities through an in vitro model of blood-brain barrier. MS CNS samples were also studied by immunofluorescent staining and quantitative PCR.Results and conclusion: Blood MAIT cells from relapsing-remitting MS patients and HV presented similar frequency , ex vivo effector phenotype and activation abilities. MAIT cells represented 0.5% of the total infiltrating T cells on 39 MS CNS lesions. This is low as compared to blood frequency (p b 0.001), but consistent with their low trans-migration rate. Finally, transcriptional over-expression of MR1-which presents cognate antigens to MAIT cells-and of the activating cytokines IL-18 and IL-23 was evidenced in MS lesions, suggesting that the CNS microenvi-ronment is suited to activate the few infiltrating MAIT cells. Taken together, these data place MAIT cells from MS patients as minor components of the inflammatory pathological process