Complement activation in primary biliary cirrhosis: an in vitro model.

Area of Science:

• Immunology
• Biochemistry

Background:

• Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by chronic inflammation and destruction of bile ducts.
• Evidence suggests the complement system, a crucial part of innate immunity, plays a role in PBC pathogenesis.

Purpose of the Study:

• To investigate the role of complement activation in primary biliary cirrhosis (PBC).
• To identify the specific components of the complement system involved and the potential triggers for its activation in PBC patients.

Main Methods:

• Analysis of C3dg concentrations in patient plasma to assess C3 activation.
• In vitro studies using patient serum and purified IgM to evaluate complement pathway activation (classical, alternative, lectin).
• Incubation of patient-derived IgM with normal and complement-deficient sera (e.g., C2-deficient) to pinpoint the responsible complement components.

Main Results:

• Elevated C3dg levels in PBC patients indicate in vivo C3 activation.
• Spontaneous C3 cleavage via the classical pathway observed in vitro, suggesting the presence of complement-activating substances in PBC serum.
• Purified IgM from PBC patients induced activation of C1, C4, and C3 (measured by C3dg formation) in normal serum.
• No C3 cleavage occurred when PBC-IgM was incubated with C2-deficient serum, confirming the classical pathway's involvement.

Conclusions:

• Complement activation, primarily through the classical pathway, is evident in vivo in PBC patients.
• An abnormal population of IgM antibodies in PBC patients appears to be responsible for initiating complement activation.
• These findings highlight the potential of targeting complement pathways for therapeutic interventions in PBC.