[Acquired hemophilia A due to factor VIIIC inhibitor: detection of circulating immune complexes containing factor...

In a 79-year-old, otherwise healthy woman who had developed multiple hematomas, laboratory tests revealed a factor VIII inhibitor (8.0 Bethesda units) which caused a decrease in factor VIIIC activity to 1%; factor VIIIR antigen and ristocetin cofactor activity were above normal values. Incubation of patient's plasma with a factor VIIIC sepharose immunoadsorbent partially removed the inhibitor, which was again detected in the IgG-containing eluate. In addition, immune complexes were found in the patient's serum. Whereas incubation of the serum with an immunoadsorbent containing rabbit antihuman factor VIIIR antibodies did not influence the titer of the immune complexes, 43% of which were removed by a rabbit antihuman factor VIIIC immunoadsorbent. This suggests that the factor VIIIC part only may be trapped by the inhibitor, leaving the factor VIIIR part of the molecule unchanged in circulation. This hypothesis is further supported by the fact that the amount of factor VIIIR antigen is likewise not diminished by incubation of patient's plasma with Raji cells.