Hypergammaglobulinemia in cystic fibrosis. Role of Pseudomonas endobronchial infection.

Hypergammaglobulinemia, chronic endobronchial infection with Pseudomonas aeruginosa (PA), and the resulting systemic humoral immune response to PA are each associated with worsened clinical status and prognosis in patients with cystic fibrosis (CF). Major serum immunoglobulin isotype levels (IgG, IgA, IgM, and IgG1-4 subclasses) were measured in 31 CF patients and ten control subjects. Immunoglobulin levels were related to airway infection with PA and the resulting IgG antibody response against PA lipopolysaccharide (LPS). Hyperimmunoglobulinemia G was present with elevated IgG1 and IgG2 in 48 percent, IgG3 in 52 percent, and IgG4 in 42 percent of CF patients. The PA infection was associated with striking increases in IgG2. IgG2 levels correlated well with IgG2 antibodies to PA LPS (r = +0.70, p less than 0.001). However, even CF patients who were not infected with PA had an increased prevalence of high IgG3 (p less than 0.05) and IgG4 (p less than 0.01). The PA infection thus appears to be a major, but not the only factor causing hypergammaglobulinemia in CF.