Platelet - Agglutinating Protein P 37 From a Thrombotic Thrombocytopenic Purpura Plasma Forms a Complex With Human Immunoglobulin

We have previously reported the purification of a 37-kd platelet-agglutinating protein (PAP p37) from the plasma of a patient with thrombotic thrombocytopenic purpura (TTP) that was shown to be present in a subset of TTP patients. The platelet agglutination induced by PAP p37 has been shown to be inhibited by lgG from normal human adults and the same TTP patient after recovery. To elucidate the mechanism of inhibition of lgG. the interaction between PAP p37 and IgG was studied. The complex formation was demonstrated by the binding of fluid-phase lgG from normal adults and the same TTP patient after recovery to adsorbed PAP by using an enzyme-linked immunosorbent assay. The binding was specific. concentration dependent. and saturable. lgG purified from a 5-month-old baby and the same TTP patient during active disease did not form complex with PAP p37. The IgG covalently cross-linked to