Mechanistically, IAA upregulated the expression of key molecules 3’-phosphoadenosine 5’-phosphosulfate synthase 2 (Papss2) and solute carrier family 35 member B3 (Slc35b3) involved in mucin sulfation via AHR, thereby enhancing intestinal barrier function and ameliorating colitis. The gene discussed is MUC5AC; the disease is colitis.