Cross-sectional and longitudinal studies of naturally occurring antibodies to Pseudomonas aeruginosa in cystic fibrosis indicate absence of antibody-mediated protection and decline in opsonic quality after infection.

Most patients with cystic fibrosis (CF) develop chronic endobronchial infection with mucoid Pseudomonas aeruginosa. It has been suggested that opsonic antibodies to the mucoid exopolysaccharide of P. aeruginosa protect older CF patients (> 12 years of age) who have remained free of colonization by this organism. Serum antibodies from chronically infected CF patients had greater total complement-dependent opsonic activity than did those of older noncolonized patients (P < .02), but when bound antibody was equalized, opsonic quality was greater for the latter group (P < .03). In longitudinal studies, antibody titers to mucoid P. aeruginosa rose greatly after initial infection, but opsonic quality declined (P = .002). Twenty CF patients who passed age 12 free of P. aeruginosa colonization developed chronic P. aeruginosa lung infection at ages 14-35 years. Thus, naturally occurring antibodies do not protect CF patients from P. aeruginosa infection, and opsonic quality of serum antibodies deteriorates as infection becomes established.