Nonneutralizing IgM and IgG antibodies to von Willebrand factor-cleaving protease (ADAMTS-13) in a patient with thrombotic thrombocytopenic purpura.

Acquired thrombotic thrombocytopenic purpura (TTP) has been linked to severe deficiency of ADAMTS-13 activity caused by autoantibodies inhibitory to ADAMTS-13. We report data on a patient with confirmed TTP who had severely reduced ADAMTS-13 activity but showed no ADAMTS-13 inhibition in a widely used fluid phase activity assay. With a newly developed enzyme-linked immunosorbent assay, using immobilized recombinant ADAMTS-13, we found high titers of IgM and IgG antibodies that bound to ADAMTS-13, but did not neutralize protease activity.