Immunological analysis of acquired factor VIII inhibitor in a case with immunologic disorder.

Coagulation factor VIII inhibitor arising in a patient with autoimmune disease was immunologically analyzed. A 63-year-old man who had been diagnosed as suffering from polyarteritis nodosa was treated with prednisolone for 10 years. Severe bleeding tendency developed and coagulation studies demonstrated a high titer of inhibitor to factor VIII:C. As a result of immunological analysis, the inhibitor was found to be IgG type autoantibody having both kappa and lambda light chains. The subclasses were IgG1 and IgG4. The inhibitor recognized the COOH-terminal light chain (72-kDa thrombin fragment) on the factor VIII molecule as an epitope.