Lectin-like factor and co-factor in serum from cystic fibrosis heterozygotes

Previous attempts to use an assay for a serum lectin-like factor as a carrier test for the cystic fibrosis gene have not been successful because food intake and effects of serum storage have interfered. A revised method for detecting the lectin-like factor employs the serum IgM fraction, rather than whole serum, separated on an S-300 Sephacryl gel filtration column. Elevated lectin titers were found in 95 percent of 43 obligate heterozygotes, 89 percent of patients with cystic fibrosis, 64 percent of siblings of patients with cystic fibrosis, and 5 percent of 60 control subjects. Lectin activity was shown to be associated with the IgM fraction of serum and to result from the binding of a low-molecular-weight co-factor to IgM. Unbound co-factor was also detected in a serum fraction from 81 percent of the heterozygotes and 88 percent of the cystic fibrosis homozygotes, and in a urine fraction from nine patients with cystic fibrosis who had positive serum lectin activity, but not in any urine sample from heterozygous subjects. The presence of co-factor in the urine of cystic fibrosis homozygotes suggests higher serum levels of this agent that spill over into the urine. Intravenous antibiotic therapy removes the lectin and co-factor from blood and urine for variable periods of time, suggesting a beneficial effect of antibiotics in cystic fibrosis apart from their antibacterial action. Detection of the lectin and co-factor are useful in screening for cystic fibrosis carriers, although the somewhat subjective biologic assay requires much experience to achieve reliability.