Letter: Complement components in cystic fibrosis.

Freshly obtained sera were assayed from 14 C.F. young adult patients (age 
18 - 33, 7 men and 7 women) and from 15 
control patients with bronchiectasis or chronic bronchitis in whom C.F. had 
been ruled out. In addition, the blood from 2 mothers (heterozygotes) 
of C.F. patients was assayed. The mean C3 level in the 
C.F. men was slightly lower than that in the male controls, 
whereas the C.F. women had a significantly higher mean level of 
C3 than did the female controls. The C3 level in the 
C.F. women was also significantly higher than that of the C.F. 
men (p < 0.01, t = 3.855 by the Student's t 
test). The female controls had slightly higher C3 levels than did 
the male controls, but this difference was not significant. Comparison of 
C3 levels from all of the C.F. subjects to the controls 
shows considerable overlap in values, especially in the men. These studies 
suggest that an assay of serum-C3 does not effectively distinguish C.F. 
subjects from patients with other types of chronic lung disease. However, 
the differences between C.F. women and C.F. men is interesting and 
deserves further attention. Our data from C.F. young adults do not 
fully confirm those reported by Conover et al., but it is 
possible that the experimental effects of carboxypeptidase B observed by Conover 
might result from action of the enzyme on the C.F. factor 
of serum, although its identity most likely is not C3a. 