Anti-Pseudomonas aeruginosa IgG subclass titers in patients with cystic fibrosis: correlations with pulmonary function, neutrophil chemotaxis, and phagocytosis.

To explore possible mechanisms for the association between elevated immunoglobulin levels and lower pulmonary function in cystic fibrosis patients, we measured serum IgG subclass levels and anti-P. aeruginosa IgG subclass titers and correlated levels with neutrophil phagocytosis and chemotaxis. Serum was obtained from 13 cystic fibrosis patients colonized with the same serotype of P. aeruginosa, 12 noncolonized patients, and 12 normal volunteers. All anti-P. aeruginosa IgG subclass titers were elevated in serum from colonized patients. IgG3 level and anti-P. aeruginosa IgG3 titer were inversely correlated with pulmonary function. Phagocytosis of P. aeruginosa by neutrophils correlated with serum IgG3 level and was increased by opsonization with serum from colonized patients. Chemotactic index was increased in serum from colonized patients and inversely correlated with pulmonary function chest roentgenogram score. Chemotactic index directly correlated with anti-P. aeruginosa IgG3 titer and serum IgG3. These data demonstrate that cystic fibrosis patients with increased IgG3 levels are in poorer clinical condition and that their serum enhances neutrophil function. Such patients may have increased pulmonary inflammation with subsequent lung damage.