AHR and systemic sclerosis: Similarly, ligands of the aryl hydrocarbon receptor (AHR), specifically tryptophan metabolites [e.g., 2-(10 H-indole30-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) and FICZ], are capable of inhibiting TGF-β1-induced collagen I production in models of systemic sclerosis and thyroid eye disease (Woeller et al., 2016; Shi et al., 2020).