The intestinal microbiota and its fermentation products can influence immunity. Two recent studies report that treatment with microbiota-derived short-chain fatty acids (SCFAs) or with a mixture of 17 bacterial strains from the intestinal microbiota of a healthy individual promotes the expansion and the function of the colonic regulatory T ([T. sub. Reg]) cell population.

Smith et al. observed that the concentration of SCFAs in the gut is low in the absence of the microbiota. Strikingly, supplementation of germ-free or specific pathogen-free (SPF) mice with SCFAs increased the number of colonic [T. sub. Reg] cells and enhanced their expression of the transcription factor forkhead box P3 (Foxp3), interleukin-10 (Il10) and the gut-homing receptor G protein-coupled receptor 15 (Gpr15). These cells also showed enhanced suppressive activity in vitro. Moreover, supplementation with SCFAs was protective in a mouse model of colitis.