Purification and some properties of a protein obtained from normal human plasma which inhibits the platelet aggregation induced by thrombotic thrombocytopenic purpura plasma

Plasma from patients with thrombotic thrombocytopenic purpura (TTP) caused the aggregation of washed human platelets, which was inhibited by preincubation with normal plasma. Using salt fractionation, ion exchange chromatography, and preparative agarose gel electrophoresis, we purified a protein from normal plasma which inhibited the platelet aggregation caused by TTP plasma. On SDS polyacrylamide gel, the purified inhibitor gave a single band with a M.W. of 150,000. The antiserum against the purified protein neutralized the activity of the inhibitor and formed an identical precipitin line against normal and TTP plasma.