Cluster of Differentiation 31 (CD31) is also known as Platelet endothelial cell adhesion molecule (PECAM-1), is a 130-kDa transmembrane glycoprotein expressed by endothelial cells, platelets, macrophages and Kupffer cells, granulocytes, T / NK cells, lymphocytes, megakaryocytes, osteoclasts, neutrophils, certain tumors, and is the only known member of the CAM family on platelets. CD31 is found on the surface of platelets, monocytes, neutrophils, and some types of T-cells, and makes up a large portion of endothelial cell intercellular junctions. The encoded protein is a member of the immunoglobulin superfamily and is likely involved in leukocyte migration, angiogenesis, and integrin activation. CD31 plays a key role in removing aged neutrophils from the body. CD31 mediates the homotypic or heterotypic cell adhesion by binding to itself or the leukocyte integrin αvβ3, and thus plays a role in neutrophil recruitment in inflammatory responses, transendothelial migration of leukocytes, as well as in cardiovascular development. In addition, it has been shown that CD31 expression is up-regulated by LPS stimulation, and might function as a feedback negative regulator of LPS inflammatory response in macrophages.