The outcome of PD-1 deficiency in Ldlr−/− mice was a net increase in vascular inflammation and atherosclerosis, suggesting that overwhelming CD4+ and CD8+ T cell activation could not be compensated by Treg-mediated immune modulation in hypercholesterolemic Ldlr−/−Pd1−/− mice. This evidence concerns the gene PDCD1 and atherosclerosis.