Interaction of factor VIII antigen in hemophilic plasmas with human antibodies to factor VIII.

By utilizing a simple modification of previous immunological assays, we have demonstrated that most, if not all, hemophilic plasmas contain antigen reactive with human antibodies directed against Factor VIII procoagulant activity (VIIIc). Antibodies developing in a nonhemophiliac patient and in a hemophiliac patient gave similar results. The VIIIc antigen so identified was removed from hemophilic plasmas with immobilized rabbit antibody which reacted with normal VIIIc and von Willebrand's disease antigen. These data suggest that there are greater antigenic similarities between normal and hemophilic Factor VIII than previously thought.