IDO2 and psoriasis: To elucidate the mechanism by which IDO2 deficiency exacerbates IMQ-induced psoriasis-like skin inflammation, we next measured the concentration of tryptophan metabolites, including tryptophan, kynurenine, kynurenic acid, anthranilic acid, and 3-hydroxy anthranilic acid (3-HAA), in the ears of WT and IDO2 KO mice treated with vehicle or IMQ for 7 days, using high performance liquid chromatography (HPLC).