Opsonophagocytic killing antibody to Pseudomonas aeruginosa mucoid exopolysaccharide in older noncolonized patients with cystic fibrosis.

The principal cause of morbidity and mortality in cystic fibrosis is persistent respiratory colonization with mucoid strains of Pseudomonas aeruginosa. To investigate possible mechanisms of resistance to this organism, we studied serum from 16 older (greater than or equal to 12 years) patients not colonized with mucoid P. aeruginosa, 11 older (greater than or equal to 14 years) colonized patients, 10 younger (less than or equal to 11 years) noncolonized patients, and 20 healthy adults. The samples from the older patients not colonized with mucoid P. aeruginosa contained antibody specific to the mucoid-exopolysaccharide antigen, which could mediate bacterial killing in conjunction with complement and white cells (titers of 4 to 80). These opsonophagocytic killing antibodies were not detected in samples from the 20 normal controls (P less than 0.0001 vs. noncolonized older patients) or 9 of 10 younger (less than or equal to 11 years) noncolonized patients (P = 0.0072 vs. noncolonized older patients). Although the patients with chronic colonization had higher titers of serum opsonophagocytic killing antibody than did the older noncolonized patients (P = 0.0005), these antibodies were not specific to the mucoid-exopolysaccharide antigen. We conclude that there is an association between mucoid-exopolysaccharide-specific opsonophagocytic killing antibody and a lack of detectable P. aeruginosa colonization in a subset of older, relatively healthy patients with cystic fibrosis.