Table 1.

AhR Endogenous Ligands.

AhR Ligand	Source	Function	Reference
Tryptamine	Microbiota	Decreases TH17	[79]
Indole-3-aldehyde	Microbiota	Increases IL-22	[30]
Indole-3-acetic acid	Microbiota	Induces COX-2	[80]
Indole propionic acid	Microbiota	Suppresses CNS and Gut inflammation	[28,81]
Indoxyl-3-sulfate	Microbiota/Host cells	Suppresses CNS Inflammation	[63]
Skatole	Microbiota	IEC death	[82]
l-kynurenine	Host cells	Antimicrobial activites, increases IDO1 and TGF-β	[76,83]
Kynurenic acid	Host cells	Tumor cell migration	[84]
Xanthurenic acid	Host cells	Tumor cell migration	[84]
Cinnabarinic acid	Host cells	Increases IL-22	[85]
FICZ	Photo-oxidation	Enhances TH17 differentiation	[10]
Indirubin	Plant/Host cells	Increases CYP1A1	[86]
Indigo	Plant/Host cells	Protects against HFD-induced glucose dysregulation	[86,87,88]
ITE	Porcine Lung	Reduces IL-6 and TNF-α	[75]