CD61, known as integrin b3 or glycoprotein IIIa (gpIIIa), is a 90 kD type I integral transmembrane glycoprotein. It is a member of integrin family that associates with platelet gpIIb (CD41) forming CD41/CD61 complex and associates with integrin aV (CD51) forming aV/b3 (CD51/CD61) integrin. CD41/CD61 is expressed on platelets and megakaryocytes, and plays a role in platelet activation and aggregation through interaction with fibrinogen, fibronectin, vWF, and other RGD-containing adhesion molecules. CD51/CD61 is expressed on platelets, osteoclasts, fibroblasts, macrophages, and some tumor cells involved in tumor metastasis and in adenovirus infection through binding to RGD motif ECM proteins.