The increase in Tregs may be due to the elevation in short-chain fatty acids (SCFAs; e.g., acetate, propionate, iso-buturate, iso-valeric and valeric) in the host gut following promoted A. muciniphila, which activates G protein-coupled receptor 43 (GPR43) and GPR41, thereby promoting Foxp3+Tregs in the host colon, relieving colitis and changing the composition of the gut microbiota (39). The gene discussed is FFAR2; the disease is colitis.