Immune complexes and humoral response to Pseudomonas aeruginosa in cystic fibrosis.

We studied the humoral immune status of 51 patients with cystic fibrosis (CF) as compared to 25 patients with other respiratory diseases (RD). CF patients had higher serum concentrations of IgG and IgA (p less than 0.001), C5, and CH50 (p less than 0.05), than did RD patients. Twenty-three % of CF patients had increased IgE concentrations. Of 32 CF and 1 RD patients colonized with mucoid Pseudomonas aeruginosa (PA), 91% had serum precipitins to PA, whereas no precipients were found in patients not colonized with mucoid PA. Fifty-one % of CF patients had circulating immune complexes detected by 125I-C1q binding (for CF patients mean values +/- SD, 14.5 +/- 12% versus 7.5 +/- 3.4% for RD patients; p less than 0.005). Complexes were correlated with higher serum IgA concentrations but not other immunoglobulins, complement components, response to PA, or pulmonary function at time of assay. Extra vascular formation of complexes was suggested by uniform absence of plasma C3 activation in vivo.