LDLR and metabolic syndrome: Interestingly, in one preclinical study using Ldlr−/− Pdcd−/− mice, not only atherosclerotic plaque size but also serum lipid levels were found to be higher compared to Ldlr−/− mice, suggesting that PD-1 deficiency further aggravates dyslipidemia [20], although in another preclinical study using hypercholesterolemic mice, serum lipid levels did not differ [13].