Ligand-dependent activation of AhR has been shown to abrogate colitis, a disease linked to changes of the gut microbiome homeostasis.7,9 More recently, bacterially derived molecules such as phenazines and indole derivates have been shown to work as AhR activators,9,10 which implies the existence of a possible microbiome-AhR communication. This evidence concerns the gene AHR and colitis.