Complement in cystic fibrosis.

Complement components C3, C4, and C3A were estimated in 30 patients with cystic fibrosis aged 1 to 21 years (M:F = 16:14) and were compared with results in 40 healthy, age-matched subjects. The influences of the clinical score, sputum microbiology, and the patients' sex were also investigated. In contrast to most previous communications, this paper shows that, compared to the control group, a significant decrease of C3 (P less than 0.001) and C4 (P less than 0.02) was observed whereas C3A levels were not altered. There were no increases in complement. Shwachman-scores above or below 70 did not influence the complement levels, nor did exacerbations of the disease change the levels. No influence of the patients' sex could be shown. Pseudomonas aer. in the sputum was clearly associated with complement defects (14/18). Alternative-pathway involvement of complement activation could be demonstrated in 32%. The results make complement activation due to pulmonary infection most likely. The defects observed probably represent secondary changes.