ALLOANTIBODY FROM A PATIENT WITH SEVERE VON-WILLEBRAND-DISEASE INHIBITS VON-WILLEBRAND FACTOR-FVIII INTERACTION

The aim of this study was to analyze the ability of an alloantibody fr om a patient with severe von Willebrand disease (vWD) to interfere wit h the vWF domain for FVIII, to inhibit factor VIII (FVIII), and to com pare it with a rabbit polyclonal antibody. The vWF domain for binding to FVIII was assayed by a method previously described but using recomb inant FVIII (r-FVIII, Kogenate), which contains no vWF, instead of Hem ofil M (HM). Rabbit or human antibodies towards FVIII (FVIII-Ab) were analyzed using microtiter wells with immobilized r-FVIII through a mon oclonal anti-FVIII antibody and an ELISA method. IgG from plasma of a patient with hemophilia A and FVIII inhibitor was used as a positive c ontrol. Normal human and rabbit IgGs were included as negative control s. Human vWD alloantibody IgG and the rabbit anti-vWF antibody IgG rea cted with immobilized normal vWF, inhibiting its binding to r-FVIII in a dose-dependent manner, which suggests that it is specific. Normal h uman IgG fraction, as well as nonspecific rabbit IgG, did not interfer e with this binding at all. The monoclonal antibody used in this assay to immobilize vWF did not alter this interaction at all. Human vWD al loantibody IgG and the rabbit antibody against vWF showed a partial in hibitory activity to plasma FVIII as well as r-FVIII. The inhibition r eached a plateau with residual FVIII activity. FVIII-Ab were not detec ted in human alloantibody or in rabbit antibody preparations. In contr ast, hemophiliac FVIII inhibitor showed FVIII-AB. This human vWD alloa ntibody behaves like polyclonal heterologous antibodies, and their inh ibition of FVIII seems to be nonspecific due to a steric hindrance mec hanism, provided that both have no FVIII antibodies.