Antibody‐induced von willebrand syndrome: Inhibition of VIII VWF and VIII AGN with sparing of VIII AHF by the autoanti body

Abstract

Abstract Acquired von Willebrand syndrome is reported in a 16‐year‐old girl with systemic lupus erythematosus. Routine coagulation studies showed a normal platelet count, prolonged bleeding time, and abnormal glass bead retention. Factor VIII molecular complex respective activities were 8% for VIII AHF and undetectable for VIII VWF (ristocetin aggregation of washed platelets) and VIII AGN (electro‐immunodiffusion). In vitro, the patient's plasma exhibited an inhibitory activity against exogenous VIII AGN and VIII VWF but did not neutralize VIII AHF activity of control plasma, even after a two‐hour incubation at 37°C. This inhibitory activity was supported by the purified plasma IgG fraction. In vivo, following cryoprecipitate administration (20 units VIII AHF/kg), only 50% of the infused VIII AHF activity was recovered after 15 mn, and the original level was reached four hours later. Only a transient peak of VIII VWF activity was observed, and VIII AGN level did not increase at all after the infusion. After the start of prednisone therapy the three factor VIII related activities returned to normal levels in the following order: VIII AHF and VIII VWF (9‐12 days); VIII AGN (3 weeks). These findings could be explained by the formation of a short‐lived circulating immune complex between the antibody and the factor VIII molecular complex. In such an hypothesis the autoantibody would respect the site of VIII AHF activity and would mask the site reacting with anti VIII AGN heteroantibodies.