Cystic fibrosis: the ciliary inhibitor is a small polypeptide associated with immunoglobulin G.

A small polypeptide within the molecular weight range of 6,000 to 11,000 
was found in immunoglobulin fractions from sera of cystic fibrosis homozygotes 
and heterozygotes. This factor appears to be responsible for interfering with 
ciliary activity in oyster gills. Since it can be dissociated from 
IgG without reductive cleavage it must be bound in a non-covalent 
manner. After its dissociation the IgG fractions from cystic fibrosis sera 
no longer inhibited ciliary activity. This finding explains the differences previously 
observed in the molecular weights of the ciliary inhibitor synthesized by 
cultured cells and that of sera from cystic fibrosis genotypes. 