PF4 and atherosclerosis: Platelets and platelet-derived factors play well-characterized roles in atherosclerosis initiation and progression70: 1) platelet adhesion to endothelium and formation of platelet-leukocyte heterotypic aggregates, enabling leukocyte transmigration; and 2) release of pro-inflammatory cytokines and chemokines, such as platelet factor 4 (PF4), by activated platelets and platelet-monocyte aggregates, activating ECs and innate immune cells.71