Anti-factor VIII antibodies from three hemophilia A patients were selectively isolated by immune complex formation and secondary precipitation with polyethylene glycol. These antibodies were characterized as IgG, with only one type of light chains (kappa) and a mixture of IgG3 and IgG4 heavy chains. This finding indicated that stable complexes of factor VIII and homologous anti-factor VIII antibodies could be obtained, and that the immunologic response to the infusion of homologous factor VIII was oligoclonal rather than monoclonal in these patients.

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