Some studies with a monoclonal antibody directed against human fibrinogen

Some properties of a monoclonal antibody generated against the fibrinogen component of a factor VIII preparation were investigated. The antibody bound with equal affinity in solid phase radioimmunoassays to fibrinogens isolated from both normal patients and patients with von Willebrand disease. It reacted in a sensitive immunoassay of plasma fibrinogen. The specificity of the antibody was confined to the parent molecule with no significant inhibition of fibrinogen binding by the fibrinogen degradation products (FDPs) X, Y, D, or E. The antibody had no significant effect on the activated partial thromboplastin time and prothrombin time of normal plasma. However, it prolonged the thrombin time as determined by the Clauss chronometric fibrinogen method. During fibrinogen lysis by plasmin immunoreactivity of fibrinogen to the antibody was lost at the same rate as the clottable fibrinogen content determined by the Clauss assay. The lack of reactivity of the antibody with FDPs makes it a suitable reagent for investigating plasmin activity as well as studying fibrinogen and fibrin. These findings suggest that the epitope of the antibody lies within the polar protruberance of the carboxy terminal end of the Aα chain of fibrinogen and is destroyed by plasmin cleavage.