CD61 is the integrin beta3 subunit, a 105 kDa transmembrane glycoprotein expressed on platelets, megakaryocytes, and endothelial cells. Integrin beta3 associates with gpIIb (CD41) to form the CD41/CD61 complex that mediates platelet adhesion and aggregation. CD61 also associates with CD51 to form the alphaVbeta3 vitronectin receptor.1-5