Evidence that factor VIII and the ristocetin aggregating factor (VIIIRist) are separate molecular entities.

The most highly purified preparations of human factor VIII have at least three clearly defined properties. They shorten the clotting time of hemophilic plasma, an activity which will for convenience be referred to as VIIIcoag; they give a precipitin reaction with a rabbit antibody prepared against the preparation, a property referred to as the factor VIII related-antigen (VIIIR-Ag); and in the presence of the antibiotic, Ristocetin, they correct the defective aggregation of platelets found in von Willebrand's disease (1-4), an activity which will be referred to as VIIIRist. There are two prevailing concepts: (a) that each property represents a function of the same molecule, (b) that there is more than one molecule, each with one or more properties (5). The purpose of the experiments described below was to determine whether VIIIcoag, VIIIRist, and VIIIR-Ag reside on the same or on different molecules. The addition of a naturally occurring human factor VIII antibody known to be of the IgG class neutralizes ...