The quantitative role of alternative pathway amplification in classical pathway induced terminal complement...

Area of Science:

• Immunology
• Complement System Biology
• Inflammation Research

Background:

• Complement activation, producing C5a and terminal C5b-9 complex (TCC), drives inflammation and tissue damage in autoimmune diseases.
• Complement plays a role in ischemia/reperfusion injury across multiple organs, with initial studies implicating classical/lectin pathways and later the alternative pathway.

Purpose of the Study:

• To investigate the hypothesis that alternative pathway amplification critically influences classical pathway-induced C5 activation.
• To elucidate the role of the alternative pathway in classical pathway-mediated complement activation using pathway-selective inhibitors.

Main Methods:

• Utilized pathway-selective inhibitory monoclonal antibodies (mAbs) to block the alternative pathway.
• Neutralization of factor D with mAb 166-32 in human serum to assess its impact on classical pathway activation.
• Measured C5a and TCC formation induced by solid-phase IgM and aggregated IgG.

Main Results:

• Selective blockade of the alternative pathway by neutralizing factor D inhibited over 80% of C5a and TCC formation.
• This inhibition occurred even when complement activation was initiated via the classical pathway (IgM and IgG stimuli).

Conclusions:

• Alternative pathway amplification significantly influences classical pathway-induced complement activation and subsequent mediator generation.
• Inhibition of the alternative pathway demonstrates therapeutic potential for conditions characterized by excessive complement activation.