Definitions of C3d
An inactivated fragment of complement 3b ( C3b). Factor H makes C3b susceptible to factor I ( formerly called KAF, C3bINF, or enzyme 3b inactivator) to form iC3b. Then factor I and a trypsin- like proteolytic enzyme further cleave iC3b into C3c and C3dg. Serum proteases degrade C3dg into complement 3d ( C3d) and C3g.