Antigen-specific induction of CD4+CD8αα+ intraepithelial T lymphocytes byBacteroidetes species
The microbiome contributes to the development and maturation of the immune system1-3 In response to commensal bacteria, CD4+ T cells can differentiate into distinct functional subtypes with regulatory or effector functions along the intestine. Peripherally-induced Foxp3+-regulatory T cells (pTregs) maintain immune homeostasis at the intestinal mucosa by regulating effector T cell responses against dietary antigens and microbes4. Similarly to pTregs, a subset of small intestine intraepithelial lymphocytes CD4+CD8+ (CD4IELS) exhibit regulatory properties and promote tolerance against dietary antigens5. Development of CD4IELS from conventional CD4+ T cells or from Treg precursors depends on the microbiota5,6. However, the identity of the microbial antigens recognized by CD4IELs remains unknown. We identified species belonging to the Bacteroidetes phylum as commensal bacteria capable of generating CD4IEL from naive CD4+ T cells expressing the pTreg transnuclear (TN) monoclonal TCR6 as well as from polyclonal WT T cells. We found that {beta}-hexosaminidase, a widely conserved carbohydrate-metabolizing enzyme in the Bacteroidetes phylum, is recognized by TN T cells, which share their TCR specificity with CD4+ T cells found in the intraepithelial compartment of polyclonal specific-pathogen-free (SPF) mice. In a mouse model of colitis, {beta}-hexosaminidase-specific CD4IELs provided protection from ulceration of the colon and weight loss. Thus, a single T cell clone can recognize a variety of abundant commensal bacteria and elicit a regulatory immune response at the intestinal epithelial surface.