CD4 and myocardial infarction: The PD-1–PD-L1 doublet is upregulated in myocardial injury patterns (such as myocardial ischemia and myocardial infarction), and the genetic deficiency of PD-1 increases atherosclerosis in hyperlipidemic mice by increasing the function of CD4+ and CD8+ T cell effector molecules and their abundance in plaques (Seijkens et al., 2018; Herrmann, 2020).