The CD41 (HIP8) antibody recognizes a 140-kDa glycoprotein which is the ? subunit of the CD41/CD61 (GPIIb/IIIa, ?IIb(B)3) comple, Xenopus/Amphibian, called glycoprotein IIb (GPIIb). GPIIb is a calcium-dependent, no covalently associated heterodimer and contains a heavy chain (GPIIb?) and a light chain (GPIIb(B)) linked by a single disulfide bond. The CD41 antigen is strictly e, Xenopus/Amphibian,pressed on platelets and platelet precursors (megakaryocytes). The CD41/CD61 comple, Xenopus/Amphibian, is the receptor for fibrinogen, fibronectin and von Willebrand factor, and plays a central role in platelet activation and aggregation. The GPIIb/IIIa may be absent or strongly reduced in Glanzmann