Decreased C4 complement component serum levels correlate with the degree of emphysema in patients with chronic bronchitis.

Patients with COPD who fulfill the diagnostic criteria of chronic bronchitis have been shown to exhibit lower serum levels of complement components C3 and C4 than healthy subjects, and this may indicate sustained complement activation as a result of recurrent respiratory tract infections. Since activation of complement leads to influx of inflammatory cells into the lung parenchyma with subsequent release of elastases and oxidants that cause damage to elastic lung tissue, we postulated that there might be a quantitative relationship between complement consumption and degree of elastic tissue destruction. In this study, we tried to investigate possible correlations between serum levels of C3 and C4 and degree of emphysema among patients with COPD of the bronchitic type.