Complement components and activation in primary biliary cirrhosis.

Total complement activity was normal in 18 patients with primary biliary cirrhosis using two hemolytic assays capable of distinguishing between defects in classical and alternative pathways. Activation of the classical pathway was demonstrated in all patients by formation of complexes between C1r, C1s, and C1 inactivator. Large amounts of free C1q, not in complex with C1r and C1s, were demonstrated in the majority of patient sera. Furthermore, C4 levels were within the normal range or slightly subnormal. No evidence for alternative pathway activation was found. Increased mean levels of several complement components, in particular C1 inactivator, C2, C3, factor B, factor H, were noted. A significant correlation between these complement factors, derived mainly from the liver, and ceruloplasmin suggests that this elevation might be secondary to cholestasis. In contrast, no significant correlation with levels of early reacting acute phase reactants, immunoglobulins, or circulating immune complex-like material were observed. It is concluded that activation of the complement system by the classical pathway is common in patients with primary biliary cirrhosis.