Immunological Characterization of Factor VIII Autoantibodies in Patients with Acquired Hemophilia A in the Presence or Absence of Underlying Disease

The development of a factor VIII autoantibody results in a severe hemorrhagic diathesis known as acquired hemophilia A. Underlying pathologies, such as autoimmune disease or chronic inflammatory disease, are observed in about half of the patients. We have investigated a total of 16 cases with acquired hemophilia A and divided the patients into two groups according to the presence or absence of other clinical conditions. Group A comprised nine cases with no detectable associated pathology. Group B consisted of seven cases with other clinical diagnoses. Significant levels of factor VIII activity (FVIII:C) and factor VIII antigen (FVIII:Ag) were detected in Group A and the pattern of FVIII:C inactivation was characteristic of Type 2 inhibitors. In contrast, no FVIII:C was detected in Group B and, in five of seven cases, the inhibitory pattern was Type 1. IgG₄ antibody subclass specificity was dominant in both groups. IgG1 antibody reactivity was higher in Group B than in Group A. Our results suggested a close relationship between the presence of underlying disease and immunological and coagulation characteristics in acquired hemophilia A.