Human alveolar macrophages synthesize active complement components C6, C7, and C8 in vitro

Area of Science:

• Immunology
• Cell Biology

Background:

• The complement system is crucial for innate immunity.
• Alveolar macrophages play a role in lung immunity.
• The synthesis of complement components by alveolar macrophages is not fully understood.

Purpose of the Study:

• To investigate the synthesis of complement proteins C6, C7, and C8 by human alveolar macrophages in vitro.
• To determine if these macrophages can assemble the terminal complement complex (TCC).

Main Methods:

• Serum-free culture of human alveolar macrophages.
• Incubation with agarose beads.
• Detection of complement proteins using polyclonal and monoclonal antibodies.
• Endotoxin stimulation of macrophages.

Main Results:

• Unstimulated macrophages synthesized C6.
• Endotoxin stimulation was required for C7 and C8 synthesis.
• Both stimulated and unstimulated macrophages produced C9 neoantigen, indicative of TCC formation.
• MCaE11 antibody was more sensitive in detecting C9 neoantigen.

Conclusions:

• Human alveolar macrophages synthesize active C6, C7, and C9.
• These components assemble into the TCC on agarose beads, requiring alternative pathway activation.
• Alveolar macrophages contribute to complement-mediated immunity in the lungs.