A Protein That Inhibits Surfactant in Respiratory Distress Syndrome

Abstract

A protein that interferes with surfactant function is present in the airways and alveoli of infants with respiratory distress syndrome (RDS). This inhibitor is also found in serum and amniotic fluid and presumably appears in the alveoli because of the abnormal protein leak present in the lungs of infants with RDS. This protein has a molecular weight of about 110,000 and is resistant to boiling or lipid extraction. As measured by radioimmunoassay, the ratio of inhibitor to phosphatidylcholine decreased from 8.1 ± 2.3 early in the course of RDS to 0.7 ± 0.1 on the day of extubation. The value at extubation was the same as that measured for preterm infants without RDS. The inhibitor to phosphatidylcholine ratio in airway samples from infants with RDS correlated significantly with simultaneously recorded PO₂/FiO₂ ratios and the peak inspiratory pressures used to normalized pCO₂ values. These results are consistent with the concept that the inhibitor contributes to surfactant dysfunction and thus the respiratory failure characteristic of RDS.