Monoclonal antibodies against the human factor VIII von Willebrand molecule: characterization and potential for screening of von Willebrand patients.

Two new monoclonal antibodies (M.Abs) 4F91C5 and 202D3 which are capable of inhibiting ristocetin cofactor activity have been raised against high molecular weight detergent denatured Factor VIII/von Willebrand preparations. Characterized in a simple solid phase radioimmune binding assay (RIA) the binding activity of the two M.Abs can be shown to be absorbed by normal plasma, and plasma from type A hemophilia patients but not by plasma from patients suffering from severe von Willebrand disease. Both monoclonal antibodies are capable of inhibiting strongly the FVIII.vWF associated ristocetin cofactor activity. Competition radioimmune assays have shown that the two monoclonal antibodies recognize different epitopes on the Factor VIII/vWF molecule. This has been confirmed by the differential binding of the two M.Abs observed to monkey plasma. Whilst inhibition curves for the two M.Abs with normal plasma and FVIII/vWF preparations in solid phase RIA are similar, quite different reactivities with commercially available F VIII preparations have been found. The high sensitivity of these reagents for the FVIII/vWF molecule and their ability to inhibit strongly the associated biological activity suggest the potential usefulness of these monoclonal antibodies as diagnostic reagents.