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Complement components and activation in primary biliary cirrhosis
Insights
Primary biliary cirrhosis commonly activates the classical complement pathway, evidenced by specific protein complexes and elevated complement factors. This activation appears linked to cholestasis rather than immune complexes.
Area of Science:
- Immunology
- Hepatology
- Biochemistry
Background:
- Primary biliary cirrhosis (PBC) is a chronic liver disease with an autoimmune component.
- The role of the complement system in PBC pathogenesis is not fully understood.
- Understanding complement activation pathways may reveal therapeutic targets.
Purpose of the Study:
- To investigate complement system activation in patients with primary biliary cirrhosis.
- To determine whether classical or alternative complement pathways are involved.
- To explore the relationship between complement component levels and disease characteristics.
Main Methods:
- Analysis of total complement activity using two hemolytic assays.
- Detection of complement pathway activation through specific protein complex formation (C1r, C1s, C1 inactivator).
- Quantification of complement components (C1q, C4, C1 inactivator, C2, C3, factor B, factor H) and ceruloplasmin levels.
Main Results:
- Total complement activity was normal, but classical pathway activation was evident in all patients.
- Elevated levels of free C1q and several complement components (C1 inactivator, C2, C3, factor B, factor H) were observed.
- Increased complement factors correlated with ceruloplasmin, suggesting a link to cholestasis, not immune complexes.
Conclusions:
- Classical complement pathway activation is a common feature in primary biliary cirrhosis.
- Elevated complement component levels may be secondary to cholestasis.
- Further research into complement-mediated mechanisms in PBC is warranted.
Abstract:
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.