The frequency of mucosal-associated invariant T cells is selectively increased in dermatitis herpetiformis

Background/ObjectivesMucosal-associated invariant T (MAIT) cells are a novel subset of innate-like T-cells that are enriched in mucosal tissues. Their presence in human skin has only recently been recognised. We describe the expression of skin-tropic molecules on human skin MAIT cells at steady state and investigate their contribution to various dermatoses with known T-cell involvement. MethodsTo examine the expression of skin-tropic molecules by MAIT cells at steady state, we performed a flow cytometric analysis of blood and skin samples from healthy donors. To investigate any potential wider contribution of MAIT cells to skin disease, we examined psoriasis, alopecia areata and dermatitis herpetiformis biopsies using immunofluorescent staining to identify the proportion of T-cells expressing MAIT cell surface markers. ResultsWe found that MAIT cells constituted a small population of T-cells in normal human skin, similar to the percentage found in peripheral blood. Like other skin T-cells, skin MAIT cells expressed high levels of the skin-associated markers, cutaneous lymphocyte antigen and CD103. In psoriasis and alopecia areata the proportion of MAIT cells was similar to that found in normal skin, but in dermatitis herpetiformis it was significantly elevated. ConclusionsThe expression of skin-tropic molecules by skin MAIT cells is consistent with their resident status in normal human skin. Our results suggest that MAIT cells may play a role in the pathogenesis of dermatitis herpetiformis.