Although human antibodies to Factor VIII inactivate its procoagulant activity, they do not form immunoprecipitates when tested with this antigen. To understand this observation, we have examined the interaction of normal human Factor VIII with four high-titer human anti-Factor VIII, two from transfused hemophiliacs and two “spontaneous” antibodies from nonhemophilic individuals. An estimate of the size of complexes formed by these antibodies has been obtained by agarose gel filtration of mixtures of anti-Factor VIII with cryoprecipitate. Complexed anti-Factor VIII was detected by the method of Allain and Frommel: acid dissociation of complexes at pH 3.5.
John Lazarchick, Leon W. Hoyer