Investigations on the relationship of factor VIII related antigen, factor VIII procoagulant activity and Von Willebrand factor activity using insolubilized rabbit antiserum

Insolubilized rabbit antifactor VIII sera removed factor VIII activity and factor VIII related antigen almost completely from normal plasma. This reduction was accompanied by a parallel decrease of the factors correcting the abnormal platelet retention and ristocetin aggregation in Von Willebrand's Disease. This indicated that rabbit antifactor VIII sera are indeed directed not only against factor VIII but also against the correcting factors on the abnormal platelet retention and ristocetin aggregation in Von Willebrand's Disease. In fluid phase assays antifactor VIII sera inhibited factor VIII activity only partly. Non inhibitory antibodies may be responsible for this. Prolonged immunization of a rabbit with factor VIII resulted in an antiserum, which inhibited factor VIII activity very potently. This can be explained by assuming that the functional site of the factor VIII molecule has a very conservative structure that has little changed in the course of evolution