Affinity of factor 8 clotting activity for antigen detectable immunologically.

Abstract

IT has been shown1 that antibodies produced in the rabbit in response to immunization with human factor VIII are capable of reacting by precipitation with a human protein which seems to be related to factor VIII. This factor VIII-related antigen, in contrast to factor VIII clotting activity, may be detected in normal quantities in patients with haemophilia, but is usually reduced or absent in patients with von Willebrand's disease. The nature of the relationship between factor VIII-related antigen and factor VIII clotting activity is not well understood at present. It has been suggested that the factor VIII-related antigen might represent the factor VIII molecule, which in haemophiliacs is structurally incomplete1. Another hypothesis is that the antigen is a “von Willebrand's factor” which is normally complexed with factor VIII2. It is possible, therefore, that “purified” factor VIII may contain two separable substances, one of which is detectable as factor VIII-related antigen and the other as factor VIII clotting activity.