Association with phagocytic inhibition of anti-Pseudomonas aeruginosa immunoglobulin G antibody subclass levels in serum from patients with cystic fibrosis.

Serum from cystic fibrosis patients colonized with Pseudomonas aeruginosa specifically inhibits phagocytosis of P. aeruginosa by alveolar macrophages. Serum was examined for P. aeruginosa lipopolysaccharide-specific immunoglobulin G (IgG) subclass levels (by enzyme-linked immunosorbent assay) and for the effect on macrophage phagocytosis (by radiolabeled P. aeruginosa uptake). Sera from cystic fibrosis patients with no known P. aeruginosa colonization history had negligible amounts of lipopolysaccharide-specific IgG and a mean phagocytic enhancement of 5%. The sera of normal volunteers also had negligible amounts of lipopolysaccharide-specific IgG. Serum from cystic fibrosis patients with P. aeruginosa respiratory tract infections had substantial titers (range, 1:20 to 1:1,280) of lipopolysaccharide-specific IgG2, IgG3, and IgG4 and a mean phagocytic inhibition of 56%. However, these patients had low or absent titers of lipopolysaccharide-specific IgG1. No consistent variation in the level of individual IgG subclasses in the sera of colonized patients was observed, as determined by radial immunodiffusion. The results suggest that during P. aeruginosa infection phagocytosis-inhibitory activity develops coincident with production of lipopolysaccharide-specific IgG subclasses.