GPIIbIIIa

GPIIbIIIa, also known as integrin αIIbβ3 or CD41/CD61, is a transmembrane receptor expressed on the surface of platelets and their precursor cells, megakaryocytes. It is the most abundant platelet integrin and functions as the final common pathway for platelet aggregation.

αIIbβ3 exists in a low-affinity state and, upon platelet activation, undergoes inside-out signaling that converts it to a high-affinity receptor for circulating ligands such as fibrinogen, von Willebrand factor, fibronectin, and vitronectin. When activated, αIIbβ3 binds these ligands and cross-links adjacent platelets, forming the platelet plug essential for primary hemostasis. Ligand binding often involves the RGD sequence and can be inhibited to prevent thrombosis.

It is a heterodimer composed of the αIIb subunit (ITGA2B) and the β3 subunit (ITGB3), encoded by ITGA2B and ITGB3 genes on chromosome 17. The receptor is a major platelet surface protein and is responsible for transducing signals that stabilize aggregation and thrombus growth.

Dysfunction or deficiency of GPIIbIIIa causes Glanzmann thrombasthenia, a rare autosomal recessive bleeding disorder characterized by mucocutaneous bleeding and absent or defective platelet aggregation despite normal platelet counts. Pharmacologically, GPIIbIIIa is a target for antiplatelet therapy; antagonists such as abciximab, eptifibatide, and tirofiban inhibit receptor function to prevent thrombus formation during acute coronary syndromes or percutaneous coronary interventions.