Immune complexes and complement abnormalities in patients with cystic fibrosis. Increased mortality associated with circulating immune complexes and decreased function of the alternative complement pathway.

Serum samples from 139 patients with cystic fibrosis (CF) were tested for complement abnormalities and circulating immune complexes (CIC). We found no consistent changes in whole complement activity. However, we found CIC in 29% of these patients and decreased activity of the alternative complement pathway (ACP) in 36%. During 5 yr of observation, mortality was much higher in patients whose sera contained CIC (p less than 0.001) or decreased ACP activity (p less than 0.01). Of patients with both abnormalities, 31% died; however, no deaths occurred in patients with normal ACP activity and negative tests for CIC (p less than 0.001). During a subsequent 2.5-yr period, 55% of patients greater than or equal to 21 yr old with both findings died. In contrast, no deaths occurred in older patients lacking this combination (p = 0.0062). Circulating immune complexes but not decreased ACP activity were an independent risk factor for death. Our findings support the hypothesis that humoral immune mechanisms may contribute to morbidity and mortality in CF.

The rabbit properdin system: I. Identification of a new factor and purification of rabbit properdin.

Pure preparations of rabbit properdin were obtained from rabbit serum by ion-exchange chromatography. These preparations functioned as properdin when they were measured with the zymosan assay or with a serum reagent selectively depleted of properdin by a specific immunoabsorbent. Properdin in these preparations was in its activated state. A new serum factor was required to measure properdin activity when purified preparations of rabbit properdin were tested with the zymosan assay. This factor was designated as ZBP, or zymosan-binding protein. ZBP appeared to be distinct from known components of the alternative complement pathway and the classical complement system, and it did not appear to be an immunoglobulin.