Antigenicity of the human R484-I508 A2 segment in HSQ-immunized hemophilia A mice. Plasma was obtained from hemophilia A mice immunized with HSQ and was assayed for inhibitory anti-fVIII antibodies against HSQ and HP9 by Bethesda assay (A) and anti-fVIII antibodies against MSQ and HM1 by ELISA (B), as described in “Materials and methods.” Each data pair corresponds to an individual mouse plasma sample.