Description: The GR-P monoclonal antibody reacts with human CD42a, which is also known as glycoprotein IX (GPIX). CD42a is a 22-kDa transmembrane protein that is constitutively expressed on platelets and megakaryocytes. CD42a associates with CD42b, CD42c, and CD42d to form the GPIb-V-IX complex, which binds von Willebrand factor, an endothelial adhesion protein, to mediate platelet adhesion and activation. This binding results in platelet aggregation at sites of vascular injury. This receptor complex has also been demonstrated to bind thrombin, factors XI and XII, P-selectin, and Mac-1.