A subset of follicular helper-like MAIT cells can provide B cell help and support antibody production in the mucosa.

Mucosal-associated invariant T (MAIT) cells are innate-like T lymphocytes that aid in protection against bacterial pathogens at mucosal surfaces through the release of inflammatory cytokines and cytotoxic molecules. Recent evidence suggests that MAIT cells can also provide B cell help. In this study, we describe a population of CXCR5 + T follicular helper (Tfh)–like MAIT cells (MAITfh) that have the capacity to provide B cell help within mucosal lymphoid organs. MAITfh cells are preferentially located near germinal centers in human tonsils and express the classical Tfh-associated transcription factor, B cell lymphoma 6 (BCL-6), the costimulatory markers inducible T cell costimulatory (ICOS) and programmed death receptor 1 (PD-1), and interleukin-21 (IL-21). We demonstrate the ability of MAIT cells to provide B cell help in vivo after mucosal challenge with Vibrio cholerae . Specifically, we show that adoptive transfer of MAIT cells into αβ T cell–deficient mice promoted B cell differentiation and increased serum V. cholerae –specific IgA responses. Our data demonstrate the capacity of MAIT cells to participate in adaptive immune responses and suggest that MAIT cells may be potential targets for mucosal vaccines.