CD61

CD61, also known as the integrin beta-3 subunit, is a cluster of differentiation marker encoded by the ITGB3 gene. It forms the platelet receptor αIIbβ3 together with integrin alpha IIb (CD41), and is a key component of the platelet glycoprotein IIb/IIIa complex (GPIIb/IIIa). This receptor is essential for platelet adhesion and aggregation.

The αIIbβ3 receptor is a heterodimer that binds several ligands, including fibrinogen, von Willebrand factor, and fibronectin. Upon platelet activation, inside-out signaling increases the affinity of αIIbβ3 for these ligands, enabling crosslinking of platelets and thrombus formation. Outside-in signaling through the receptor also promotes cytoskeletal rearrangement and platelet spreading, contributing to stable thrombus growth.

CD61 is most prominently expressed on platelets and their megakaryocyte precursors, with lower levels reported on some endothelial cells and other cell types. In laboratory practice, anti-CD61 antibodies are used to identify platelets and megakaryocytes in flow cytometry and immunohistochemistry.

Clinical relevance includes Glanzmann thrombasthenia, a rare inherited disorder caused by defects in the GPIIb/IIIa complex, leading to impaired platelet aggregation and mucocutaneous bleeding despite a normal platelet count. Pharmacologic blockade of the GPIIb/IIIa complex with monoclonal antibodies or small-molecule inhibitors (such as abciximab, eptifibatide, and tirofiban) can prevent thrombosis in high-risk settings but increases bleeding risk, limiting use to specific clinical indications.