Gamma-Delta T Cells Promote Oral Tolerance Via a Microbiota-Modulating Micro-RNA

Oral tolerance (OT) plays a critical role in maintaining the gut homeostatic environment. OT is defective in mice lacking microbiota or gamma-delta T cells (γδ-/-). We found that γδ-/- mice have an altered microbiota, including a decrease in Rumincoccus gnavus. Transfer of microbiota from γδ-/- mice to WT mice impaired OT, whereas transfer of WT microbiota or R. gnavus to γδ-/- mice restored OT. Restoration of OT was associated with increased IL-10 production by CX3CR1+ mononuclear phagocytes and Treg cells, and decreased Th17 cells. Fecal micro-RNAs can regulate the microbiota and we found that intestinal γδ T cells produced the miRNA let-7f and that oral administration of let-7f to γδ-/- mice increased R. gnavus and restored OT. Taken together, we demonstrate that the γδ T cell-selected microbiota is necessary and sufficient to promote OT, which is mechanistically linked to γδ T cell secretion of a microbiota-modulating miRNA.