Complement in cystic fibrosis.

Quantitative and functional assessments were made of both the classical and alternative pathways of complement activation in sera from 23 patients with cystic fibrosis. The classical pathway functioned similarly in patients and controls as measured by CH50 titre. Alternative pathway function, initiated in patient sera by incubation with inulin, was equal to that of controls as determined by cleavage of Factor B and C3, and by the consumption of terminal components. Factor B, however, was more readily activated in patient than in control sera. This rapid alteration of Factor B did not lead to accelerated or more extensive activation of the terminal complement components via the alternative pathway when assessed by C3 cleavage and the consumption of terminal components. Thus, a complement deficiency was not found. The importance of the easily activated Factor B is undefined.