Heterogeneity in biological activity of human factor VIII antibodies.

Antibodies against factor VIII collected from six patients were studied for their effect on factor-VIII coagulant activity, Willebrand factor activity (WF) and factor-VIII-related antigen. The results demonstrate differences between individual antibodies; some acting primarily as anti factor VIII, others inhibiting both after VIII and WF. Differences in effect between plasma and serum indicate that the process of coagulation alters the interaction of these antibodies.