Letter: Complement components in cystic fibrosis.

Dr. Conover and his colleagues reported no difference in the haemolytic activity 
of serum complement components C1-C9 of cystic fibrosis (C.F.) patients, obligate 
heterozygotes, and normal controls. They also measured individual complement components by 
radial immunodiffusion and found a significant rise of C3 but no 
significant difference in C5 levels between these groups. Using immunodiffusion kits 
from the same manufacturer and freshly obtained sera, we have observed 
quite different findings. C5 was mildly elevated in 20 and more 
highly elevated in 25 of 56 C.F. patients, 2 to 29 
years of age. C5 was also elevated in 24 of 51 
parents of C.F. patients, 15 showing mild and 9 higher elevations, 
while 4 of 24 controls showed only mild elevation. No correlation 
was observed between serum-C5 levels, and the age, sex, clinical severity 
of disease (judged by Shwachman-Kulczyki scores), sputum bacterial colonisation, and mode 
of treatment of the C.F. patients. The elevation of C3 and 
C5 in a majority of patients with C.F. and obligate heterozygotes 
is very interesting and is suggestive of certain genetic defect(s) in 
the complement activation system in this autosomal recessive disorder. 