Protease inhibitor and defective proteolysis in cystic fibrosis.

Meconium specimens from 18 infants with cystic fibrosis (CF) had strong trypsin inhibitory activity (TIA). The same specimen, which contained increased quantities of undigested proteins, had normal concentrations of immunoreactive trypsin (IRT), but deficient trypsin catalytic activity (TCA). TIA was not detected in any specimen from non-CF infants who had high concentration of proteins comparable to that of CF infants. Subjecting meconium supernatant of CF infants to Sephadex G-75 gel filtration revealed that TCA was greatly enhanced in effluents after fractions were activated by porcine trypsin. TCA was present in the same fractions with IRT. The findings suggested that proteases were secreted into the intestinal lumen in CF infants prior to birth. Deficient proteolysis in the disease might be due to the presence of a trypsin inhibitor.