CD61, also known as integrin β3 and glycoprotein IIIa (gpIIIa), is a 90 kD type I integral transmembrane glycoprotein. It is a member of the integrin family, associating with platelet gpIIb (CD41) to form CD41/CD61 complex and with integrin αV (CD51) to form αV/β3 (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 in extracellular matrix proteins.