TLR4 and colitis: FMT and co-housing experiments reveal that predisposing gut microbiota is required for the enhanced susceptibility to colitis of TLR4−/− mice, and TLR4 knockout suppresses RORγt+ Treg cells to exacerbate colitis in a gut-microbiota-dependent manner; additionally, colonic RORγt+ Treg cell frequency is negatively correlated with colitis severity [108].