Decay-accelerating factor (DAF) ~ is a membrane protein that inhibits amplification of the complement cascade on cell surfaces. By binding to C3b or C4b complement fragments that accidentally deposit on the cell membrane, DAF blocks the assembly of both the classical and alternative C3 and C5 convertases (1-3). In this manner, DAF protects host cells from damage by autologous complement. DAF is...

The alternative pathway of complement is regulated on the surface of homologous blood cells at the C3 amplification step by the membrane protein decay-accelerating factor, as well as by the plasma protein factor H. We have reported elsewhere that platelets from patients with paroxysmal nocturnal hemoglobinuria regulate the activity of the C3 convertase C3bBb, even though they lack decay-acceler...