Alpha₁-Antitrypsin in the Respiratory-Distress Syndrome

The presence and severity of the idiopathic respiratory-distress syndrome in 34 newborn infants correlated with decreased serum levels of the protease enzyme inhibitor, alpha1-antitrypsin, as compared to 38 normal and sick neonates. These low levels were not the result of a circulating inhibitor or a genetic deficiency of alpha1-antitrypsin production. Serum levels of the inhibitor in survivors returned to normal during the recovery phase of the lung disease. Post-mortem immunofluorescent studies of the lungs of infants who did not survive showed that alpha1-antitrypsin was localized to the hyaline membranes. The intensity of immunofluorescence was comparable to that found for fibrin. The lowered serum level of alpha1-antitrypsin in the respiratory-distress syndrome may be accounted for by the incorporation of this protease inhibitor into the pulmonary hyaline membranes.