Effects of sulphated polyanions on functions of complement factor H.

Heparin and two dextran sulphate preparations with a low or high average molecular mass (M(r) 5000 and 5 x 10(5), respectively) enhanced binding of radioactively labelled complement factor H to the complement protein C3b, coupled to Sepharose 4B, maximally 2.5-4-fold within a polyanion concn range of 12.5-400 micrograms/ml. Despite this, heparin or low molecular mass dextran sulphate had no effect on the activity of H as a cofactor of complement factor I, when C3b bound to Sepharose 4B was used as a substrate, and high molecular mass dextran sulphate inhibited. Heparin or low molecular mass dextran sulphate had also no effect on the decay-accelerating activity of factor H on the alternative pathway C3 convertase, C3b,Bb, and high molecular mass dextran sulphate inhibited this activity, too, regardless of whether Sepharose 4B or sheep erythrocytes were used as carriers of C3b,Bb. These results suggest strongly that fluid phase heparin or dextran sulphate do not inhibit activation of the alternative pathway of complement by augmenting functions of H.