The Idiotypic Characteristics of Human Antibodies to Factor VIII

We have prepared an antiidiotype antibody that specifically reacts with and inactivates a human autoantibody to factor VIII (VIll:C). The antiidiotype specificity of this rabbit anti-body was evident in solution. as specific inhibition of anti-Vlll:C activity. and in solid-phase studies. The antiidio-type antibody inhibited both plasma anti-Vlll:C and Fab’ fragments prepared from that plasma’s IgG. Although the antibody had a greater inhibitory effect on the anti-VIll:C H UMAN ANTIBODIES that inactivate factor VIII procoagulant activity (VIII:C, antihemo-philic factor) are detected in 5 % to 15 % of repeatedly transfused patients with severe classic hemophilia (he-mophilia A) and, less commonly, as autoantibodies that develop in individuals with previously normal hemostasis. ’ These antibodies, IgG in almost all cases