This protein recognizes C4b and C3b fragments that condense; with cell-surface hydroxyl or amino groups when nascent C4b and C3b are; locally generated during C4 and c3 activation. Interaction of daf with; cell-associated C4b and C3b polypeptides interferes with their ability; to catalyze the conversion of C2 and factor B to enzymatically active; C2a and Bb and thereby prevents the formation of C4b2a and C3bBb, the; amplification convertases of the complement cascade.; Inhibits complement activation by destabilizing and preventing the; formation of C3 and C5 convertases, which prevents complement damage;.