CD31/PECAM-1

null CD31, or platelet endothelial cell adhesion molecule-1 (PECAM-1), is a 130 kDa transmembrane glycoprotein of the immunoglobulin superfamily expressed on endothelial cells, platelets, monocytes, neutrophils and subsets of T lymphocytes. Six extracellular Ig-like domains mediate homophilic binding at endothelial junctions, concentrating the molecule at intercellular borders where it governs vascular permeability and the transendothelial migration of leukocytes. CD31 also signals through cytoplasmic immunoreceptor tyrosine-based inhibitory motifs that temper integrin activation and platelet aggregation. Because of its dense expression on vascular endothelium, anti-CD31 staining is the standard method for quantifying microvessel density in tumor angiogenesis studies.