Effects of thrombospondin purified by heparin affinity or ion-exchange chromatography on the alternative complement pathway.

Thrombospondin (TSP), a platelet glycoprotein, was purified from platelet supernatants applied sequentially to Sepharose 4B and heparin-agarose affinity columns. This TSP inhibited alternative pathway activity in serum as assessed by lysis of rabbit erythrocytes and contained bound heparin, a substance which is known to inhibit the alternative pathway. TSP purified by anion exchange chromatography did not contain heparin and was not inhibitory. Chromatography of this TSP over a heparin-agarose affinity column resulted in TSP which contained heparin and inhibited the alternative pathway. Purification of TSP by the standard technique of heparin affinity chromatography results in preparations which are contaminated with heparin.