CD51 represents the 150 kDa integrin alphaV chain that associates with integrin beta3 (CD61) to form the CD51/CD61 vitronectin receptor on endothelial cells, certain activated leukocytes, NK cells, macrophages, neutrophils and platelets. CD51 is the most promiscuous integrin a subunit; it can form heterodimers with the beta1 (CD29), beta3 (CD61), beta5, beta6 and beta8 subunits in various tissues. CD51/CD61 acts as an activation-independent receptor for platelet attachment and spreading on vitronectin and other RGD-containing proteins, including matrix components. It also mediates leukocyte-endothelial cell adhesion via interaction with CD31.1-4