P selectin (SELP) is a 140kDa protein that is stored in the alpha-granules of platelets and Weibel-Palade bodies of endothelial cells. SELP mediates rapid rolling of leukocyte rolling over vascular surfaces during the initial steps in inflammation through interaction with PSGL1. P selectin is a cell adhesion molecule on the surface of activated endothelial cells. Cellular adhesion molecules are a large family of proteins that attach the cytoskeleton and intracellular signaling cascades with the extracellular environment. SELP is a calcium-dependent receptor for myeloid cells that binds to sialylated forms of Lewis blood group carbohydrate antigens on neutrophils and monocytes. This protein redistributes to the plasma membrane during platelet activation and degranulation and mediates the interacton of activated endothelial cells or platelets with leukocytes.