MAIT cells in the human oral mucosa are activated and perforinlow

Abstract

Abstract Mucosa-associated invariant T (MAIT) cells are a class of non-classical T lymphocytes defined by their invariant Vα7.2-containing MR1-restricted T cell receptor, as well as high expression of CD161. At present, the characteristics of MAIT cells in the oral mucosa are poorly defined. In this study, we have analyzed buccal biopsies and matched blood samples from a cohort of healthy volunteers. MAIT cells were present in the buccal mucosa, with a tendency to cluster around the basal layer, a region also found to contain a higher frequency of MR1-expressing antigen-presenting cells. The frequency of MAIT cells was similar in the buccal mucosa compared to matched peripheral blood, in contrast to other major T cell subsets. However, the buccal mucosal MAIT cells displayed a tissue resident activated profile, with high CD69, HLA-DR and PD-1 expression, as well as a skewed subset distribution with higher representation of CD4/CD8 double-negative cells and of CD8αα+ cells within the CD8+ subset. The Jα chain usage in the MAIT cell TCR was more variable in oral mucosal MAIT cells than in peripheral blood MAIT cells. Functionally, the oral mucosal MAIT cells had lower perforin levels, indicative of a lower cytolytic potential. Interestingly, aspects of the oral MAIT cell population were associated with life-style factors such as consumption of bacterially fermented milk products and alcohol intake. Together, these data show that MAIT cells form a part of the oral mucosal T cell compartment, where they exhibit a tissue-resident activated profile. Thus, MAIT cells are positioned in the oral cavity and equipped to handle resident microbiota as well as invading pathogens.