Monoclonal antibody Q90 recognizes human CD41, also called ITGA2B, GPIIb or integrin alpha chain 2b. It is predominantly expressed on platelets and plays a pivotal role in coagulation. CD41 associates with integrin β3 chain (GPIIa or CD61) to form the CD41/CD61 complex. This complex is a receptor for fibrinogen, vWF, fibronectin, vitronectin, thrombospondin, prothrombin and thrombospondin. The integrin receptor is required for platelet adhesion and aggregation. Per platelet there are approximately 60-80 thousand copies of the complex. CD41 has been considered a biomarker for megakaryocytes. Although there is increasing evidence that it also expressed during early hematopoiesis with low expression levels on cells with myeloid and lymphoid potential. Given its central role in haemostasis it has been considered an anti-thrombotic target with alternating success. Mutations in the genes of the CD41/CD61 complex are a cause of Glanzmann thrombasthenia leading to bleeding disorders. Furthermore, there are some associations with tumor metastasis.