Complement activation by interaction of polyanions and polycations. III. Complement activation by interaction of multiple polyanious and polycations is the presence of C-reactive protein.

Interactions between heparin and protamine previously were found to result in activation of the complement (C) system. In the present investigation, this interaction was shown to result in the binding of purified C1, and this was markedly enhanced in the presence of C-reactive protein (CRP). CRP also enhanced C consumption during heparin-protamine interactions in whole serum, and in the presence of CRP depletion of C components C1-3 was observed. Similar C1 binding and C consumption in the presence of CRP were seen upon the interaction of multiple additional polyanions including DNA, ENA, hyaluronic acid, chondroitin sulfate, and dextran sulfate with the polycations protamine sulfate and poly-L-lysine. These effects were observed with CRP concentrations well within the range found in normal human sera and considerably less than those found in most acute phase sera. We suggest, therefore, C activation by polyanion-polycation interactions in the presence of CRP may be important to certain reactions of host defense and inflammation.