Effects of activated complement components on enzyme secretion by macrophages

Area of Science:

• Immunology
• Cell Biology

Background:

• The complement system plays a crucial role in innate immunity.
• Complement component C3 is a central protein in complement activation.
• Macrophages are key immune cells involved in inflammation and tissue remodeling.

Purpose of the Study:

• To investigate the interaction of C3 cleavage products (C3b and C3a) with macrophages.
• To elucidate the mechanisms of lysosomal enzyme release induced by C3b and C3a.
• To explore the potential role of this interaction in chronic inflammation.

Main Methods:

• Cultured guinea-pig and mouse macrophages were treated with purified C3b and C3a.
• Lysosomal enzyme release was measured in the culture medium.
• Cell viability was assessed by lactate dehydrogenase release.
• Macrophage attachment to C3b was inhibited using anti-C3 Fab.
• Enzyme-mediated C3 cleavage by stimulated macrophages was analyzed.

Main Results:

• Both C3b and C3a induced dose- and time-dependent lysosomal enzyme release from macrophages.
• C3b-induced release was selective for hydrolases and did not cause cell death.
• C3a-induced release was associated with cell death (lactate dehydrogenase release).
• Inhibition of C3b attachment to macrophages reduced enzyme release.
• Macrophages released enzymes that could cleave C3, generating more C3b, creating an amplification loop.

Conclusions:

• C3b and C3a differentially modulate macrophage function, impacting enzyme release and cell viability.
• An autocrine amplification loop involving C3 cleavage by macrophage-derived enzymes may sustain inflammatory responses.
• This mechanism could explain the persistent inflammation and tissue damage observed in chronic inflammatory conditions.