IDO1 and atherosclerosis: In addition to cytokines, a recent study implicated that IDO and IDO-catalyzed tryptophan metabolism were partly responsible for the Treg-mediated immune suppression and tolerance in the vascular tissues, which can mutually regulate one another to promote vascular tolerance and limit inflammation and atherosclerosis (135), since 3-hydroxyanthranilic acid generated in the kynurenine pathway shift the differentiation of Th effector cells toward a regulatory phenotype, thus lowering plasma lipids and decreasing atherosclerosis in Ldlr−/− mice (136).