Song noted in his article that IDO activity in the blood positively correlates significantly with the progression of atherosclerosis (Song et al., 2017), and inhibiting IDO1 leads to more significant atherosclerotic lesions in ApoE−/− mice fed a high-fat diet (Polyzos et al., 2015), while treatment of Ldlr−/− mice with the tryptophan metabolite 3-hydroxycyanuric acid inhibits atherosclerosis by modulating lipid metabolism and inflammation (Zhang et al., 2012) is more evidence that activation of the KYN pathway can influence the pathological development of AS. Here, APOE is linked to atherosclerosis.