Prognostic implications of circulating immune complexes and Pseudomonas aeruginosa-specific antibodies in cystic fibrosis.

We re-examined the role of circulating immune complexes (CIC) in cystic fibrosis, by their serial measurement in 16 patients who had advanced lung disease and persistent specific antibodies to Pseudomonas aeruginosa in their serum. CIC were detected by 125I C1q-BA (IgG + IgM-IC) and Raji RIA (IgG-IC), and IgA-IC by a modification of the Raji RIA method. Serum precipitins to Ps. aeruginosa were detected by crossed-immunoelectrophoresis (XIE) and antibodies to alkaline protease (AP), elastase (EL) and exotoxin-A (EA) of Ps. aeruginosa were detected by ELISA technique. CIC were positive in greater than 50% of the samples in 8 patients (group A) and in less than 25% in the other 8 (group B); follow-up averaged 22 mo in group A and 26 mo in group B. The numbers of precipitins to Pseudomonas were equally high, and levels of antibodies to AP, EL, and EA of Ps. aeruginosa were similarly positive, in the 2 groups. In group A the CIC were mostly IgG-IC by Raji RIA (76%) and IgA-IC, whereas in group B C1q-binding IC (79%) and IgA-IC were more prevalent than IgG-IC by Raji RIA. Four group A children died during follow-up, together with one group B child in whom the CIC level had suddenly risen precipitously. We postulate that a high level of CIC in association with persistent specific-antibody response to Ps. aeruginosa heralds a poor prognosis in cystic fibrosis.