Protection against atherosclerosis by PD-1/PD-L1 is reflected in knockout mice presenting with enlarged plaques containing higher T-cell and macrophage numbers, increased Tumor Necrosis Factor alpha (TNFα) levels and T-cell activation by antigen presenting cells (APCs), and enhanced cytotoxic activity of CD8 T-cells, all of which increase inflammation and plaque formation (Figure 1A) (Gotsman et al., 2007; Bu et al., 2011). Here, PDCD1 is linked to atherosclerosis.