Factor VIII coagulant activity and factor VIII-like antigen: independent molecular entities.

Factor VIII coagulant activity (VIII(C)) and the von Willebrand's disease antigen (Factor VIII-like antigen, vW-Ag) are biologically linked, and it has been suggested that they reside on the same molecule. However, insolubilized human isoantibody to VIII(C) and rabbit antiserum containing antibodies to VIII(C) and vW-Ag differentially bind and remove these entities from plasma, thus physically segregating one from the other. These findings indicate that Factor VIII coagulant activity resides on a molecule distinct from that expressing the von Willebrand's antigen.