{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Factor VIII (F VIII) is an essential clotting factor. The lack of normal F VIII causes Hemophilia A, an inherited bleeding disorder. FVIII is a glycoprotein procofactor synthesized and released into the bloodstream by the liver. In the circulating blood, it is mainly bound to von Willebrand factor (vWF, also known as Factor VIII-related antigen) to form a stable complex. Upon activation by thrombin or Factor Xa, it dissociates from the complex to interact with Factor IXa, the coagulation cascade. It is a cofactor to Factor IXa in the activation of Factor X, which, in turn, with its cofactor Factor Va, activates more thrombin. Thrombin cleaves fibrinogen into fibrin which polymerizes and crosslinks (using Factor XIII) into a blood clot."}]},{"type":"paragraph","children":[{"type":"text","value":"This antibody reacts with endothelial cells in normal, reactive, and neoplastic blood cells. F VIII antibody has helped to establish the endothelial nature of some lesions of disputed histogenesis, e.g., Kaposi`s Sarcoma and Cardiac Myxoma. Not all endothelial cells synthesize (or store) this molecule; therefore, it should not be\n surprising that not all tumors of endothelial differentiation (benign or malignant) react with this antigen."}]}]}