Conflicting reports exist in the literature concerning the primary mechanism for heparin's inhibition of C1 hemolytic function. We provide evidence here that heparin's most effective inhibition is mediated through interaction with and potentiation of C1-INH. The molecular nature of the interaction between heparin and the C1-INH molecule is evidenced by an anodal shift in the electrophoretic mobility of C1-INH upon the addition of heparin.l We also demonstrate that C3 and C4 conversions in normal human serum by classical pathway activators such as heat-aggregated IgG are inhibited by addition of heparin, yet heparin does not prevent similar C3 conversion in serum depleted of C1-INH Heparin's inhibitory action is restored to C1-INH-depleted serum by the addition of purified C1-INH.
Complement Activation Complement C1 Inactivator Proteins