Indeed, antibodies against flagellin are increased in IBS51 and Toll-like receptor 5 (Tlr5; the receptor for flagellin) signalling is impaired in Crohn’s disease.52 We find that mNFa neurons express Tlr5 and mPEPa neurons express Tlr4 (a receptor for the bacterial product lipopolysaccharide), suggesting that afferents of these subtypes contribute to defence mechanisms (including facilitating immune response) against bacterial penetration of the mucosal barrier. Here, TLR4 is linked to Crohn disease.