Immunologic Studies in von. Willebrand's Disease EVIDENCE THAT THE ANTIHEMOPHILIC FACTOR (AHF) PRODUCED AFTER TRANSFUSIONS LACKS AN ANTIGEN ASSOCIATED WITH NORMAL AHF AND THE INACTIVE MATERIAL PRODUCED BY PATIENTS WITH CLASSIC HEMOPHILIA

VIII) levels were measured by a standard coagulation assay and by an immunological technique before and serially after infusion of fresh frozen plasma or cryopre-cipitate into patients with von Willebrand's disease. Ini-tial levels of AHF, measured both as procoagulant and as antigen, were low. Immediately after transfusions, the rise in levels of AHF-like antigen was compatible with the quantity of antigen present in the infused plasma or cryoprecipitate. Thereafter, levels of antigen declined rapidly and reached preinfusion values in approximately 24 hr. In contrast, procoagulant activity remained ele-vated, and sometimes continued to rise, for longer periods of time. One possible explanation of this finding is that the AHF molecule produced by patients with von Wil-lebrand's disease, in response to transfusion of as yet unidentified factors, lacks the antigenic site associated with the normal AHF molecule or the inactive molecule produced by patients with hemophilia A. A preliminary report of these studies was presented at th