A specific microbial metabolite influences the development of peripheral intraepithelial lymphocytes

Abstract

Abstract Peripheral CD4+CD8αα+TCRαβ+ intraepithelial lymphocytes (pIELs) are a specialised T cell population that are reduced in germ-free (GF) C57BL/6 mice and vary in frequency between SPF mice from different sources, indicating their development is dependent on the presence of intestinal microbes. The microbes and factors required for pIEL development, however, are not fully characterised. pIELs are closely associated with intestinal epithelial cells (IECs) that line the gastrointestinal tract, however the contribution of IECs in shaping pIEL development is not well defined. We investigated if microbial metabolites influence pIEL development, and whether this is mediated by microbe-IEC-pIEL interactions. In this study we used flow cytometry to characterise pIEL frequencies in GF mice administered different microbial metabolites, and in SPF mice from different colonies and animal facilities. qPCR of IEC RNA isolated from these mice and of metabolite-treated enteroids and MODE-K cells was performed to identify candidate genes expressed by IECs that may influence pIEL development. We identified a common bacterial metabolite that partially restores pIEL development in GF mice. pIEL frequency of SPF mice varied between different sources, and qPCR identified IEC expression of several T-cell-influencing cytokines that correlated with pIEL frequency in vivo. Our results indicate that a common microbial metabolite contributes to pIEL development, corresponding to metabolite-induced IEC expression of T-cell-influencing cytokines. Our work further elucidates the mechanisms of commensal microbe modulation of host tolerance, which may enable better strategies to prevent and treat intestinal infections and inflammation.