Circulating immune complexes in patients with cystic fibrosis.

Circulating immune complexes (CICs) were measured in the sera of clinically stable and acutely infected patients with cystic fibrosis (CF). Twenty CF patients were studied when clinically stable; and additional 18 patients were studied during an acute exacerbation of pulmonary infection as evidenced by fever, tachypnea, increased white blood cell count, increased sputum production, and acute chest x-ray film changes. Three methods for determining CICs were employed: polyethyelene glycol precipitation, a C1q phase assay, and the Raji cell radioimmune assay. Ten of 20 clinically stable CF patients had one or two positive assays for CICs; two of 20 had two positive assays. In contrast, 16 of 18 acutely infected CF patients had a positive CIC test, and 12 of these were positive with two or three of the assays employed. Serum C3 and C4 concentrations and total hemolytic complement activity did not correlate with the presence of CICs in either patient group. These findings suggest that immune complex formation may mediate some of the tissue damage characteristic of CF, although this usually does not involve intravascular complement activation.