Influence Of High Molecular Weight Factor VIII On The Expression Of Factor VIII Procoagulant Activity

Abstract

The relationship of the high molecular weight (HMW) moiety and low molecular weight (LMW) moiety of factor VIII in expressing procoagulant activity (VIII C) was studied. LMW VIII C was prepared by immunoadsorbent chromatography; HMW VIII was prepared by chromatographing hemophilic cryo- precipitate in 4% agarose. The LMW VIII C obtained by immunoadsorbent chromatography gave higher VIII C values when tested in the one stage partial thromboplastin time (PTT) system using von Willebrand’s disease plasma as substrate than using hemophilic plasma as substrate. This finding was shown to be due to the VIII related antigen (VIIIR:Ag) in the substrate plasmas. When the VIIIR:Ag was removed from the hemophilic substrate plasma by immuno-adsorption, the VIII C values obtained for the LMW VIII C were higher. Also, adding purified HMW VIII to the von Willebrand’s disease substrate plasma resulted in lower VIII C values for the LMW VIII C in the PTT system.When the LMW VIII C was tested in the two stage assay, all VIII C was adsorbed to A1(0H)3. The adsorption of the LMW VIII C was prevented by mixing it with hemophilic plasma. From normal undiluted plasma only 5-21% of VIII C and no VIII related antigen were adsorbed to A1(OH)3, but after activation of the factor VIII of normal plasma by small amounts of thrombin, most of the VIII C was adsorbed. No VIII related antigen was adsorbed after activation.Nevertheless, when unadsorbed LMW VIII C was assayed by the two stage method both with and without HMW VIII or VIIIR:Ag, the results were the same.Our studies suggest that VIIIR:Ag prevents to some extent the activation of LMW VIII C. LMW VIII C that is not bound or protected by VIIIRiAg is adsorbed from plasma by A1(0H)3. These findings may help explain the differences for VIII C found in some patients and certain clinical circumstances with the one and two stage assays.