BACKGROUND The interrelationship between human airway epithelium and complement proteins may affect airway defence, airway function, and airway epithelial integrity. A study was undertaken to determine (1) whether unstimulated human bronchial epithelium generates complement proteins and expresses cell membrane complement inhibitory proteins (CIP) and (2) whether stimulation by proinflammatory cytokines affects the generation of complement and expression of cell membrane CIP by these cells.

RESULTS Unstimulated human bronchial epithelial cell line BEAS-2B in serum-free medium generates complement C3 (mean 32 ng/10⁶ cells/72 h, range 18–52) but not C1q and C5, and expresses cell membrane DAF, MCP, and CD59. Interleukin (IL)-1α (100 U/ml/72 h) and tumour necrosis factor (TNF-α; 1000 U/ml/72 h) increased generation of C3 up to a mean of 78% and 138%, respectively, above C3 generation by unstimulated cells. DAF was the only cell membrane CIP affected by cytokine stimulation. Interferon (IFN)-γ (10 U/ml/72 h) and TNF-α (1000 U/ml/72 h) increased DAF expression up to a mean of 116% and 45%, respectively, above that in unstimulated cells. MCP and CD59 expression was not consistently affected by IL-1α, TNF-α, or IFN-γ.

CONCLUSIONS Local generation of complement C3 and expression of cell membrane CIP by human bronchial epithelium and its modulation by proinflammatory cytokines might be an additional regulatory mechanism of local airway defence and may affect airway function and epithelial integrity in health and disease.