Table 1.

Classes of Ahr ligands.

Class of Molecule	Metabolites	Genes Activated	Effects (Ligand Dependent)
Tryptophan Metabolites	Kynurenine Kynurenic Acid Xanthurenic Acid Anthralinic Acid Quinolinic Acid Pinolinic Acid Cinnabarinic Acid 3-hydroxykynurenine 3-hydroxyanthralinic acid	CYP1A1/CYP1B1 AHRR IL-6 VEGFA PTGS2 IL-22 IDO1 TDO	Neurotoxic Effects B-cell & T-cell differentiation Development of intraepithelial lymphocytes Immune tolerance Enhanced epithelial barrier function Anti-inflammatory Intestinal homeostasis Gut motility Microbial composition Antimicrobial affects Mucosal barrier function Serotonin modulation
Dioxins	Polycyclic Aromatic hydrocarbons Benzatheracues Halogenated aromatic hydrocarbons
Dietary compounds	3-3-diindolemethane (DIM) Indole-3-carbinol Indole-3-acetonitrile Indole [3,2-b] carbazole 2-(indole-3-ylmethyl)-3,3-diindolymethane Herbs- Ginseng, gingko biloba, licorice
Microbial metabolites	Indole 3-hydroxyindole Indolealdehyde Tryptamine Indole acetic acid Tryptanthrin 3-methyl indole Indirubin Indigo Indole sulphate Malassezin
Photo-oxidative Trp metabolite	6-formylindole [3,2-b] Carbazole (FICZ)