Minimal role for the alternative pathway in complement activation by HIT immune complexes.

Background: Anti-platelet factor 4 (PF4)/heparin immune complexes that cause heparin-induced thrombocytopenia (HIT) activate complement via the classical pathway. Previous studies have shown that the alternative pathway of complement substantially amplifies the classical pathway of complement activation through the C3b feedback cycle.

Objectives: These studies sought to examine the contributions of the alternative pathway to complement activation by HIT antibodies.