AHR and dermatitis: We also showed that IAld and indole but not IPA treatment increased tight junction expression (S4A–S4C Fig) but had no effects on E. coli growth (S5A–S5C Fig), indicating that induced AhR activation may account for inflammation limitations [16,18], Similar results have demonstrated that oral tryptophan-driven AhR ligands alleviated dermatitis [35] and EAE [21], suggesting that AhR activation by agonists from dietary sources may have systemic immunomodulatory effects.