Inhibitory activity of alpha 1-antitrypsin in infants with idiopathic respiratory distress syndrome.

In two groups of neonates serum concentrations of alpha-1-antitrypsin (1-AT) were determined by means of radial immunodiffusion, and 1-AT inhibitory capacity determinations were made using benzoyl-1-arginine-p-nitroanilide as a substrate. There were 66 children in the first group of neonates with idiopathic respiratory distress syndrome (IRDS), and 82 healthy children in the second group with birth weight and gestational and post natal ages similar to those of neonates with IRDS. In the latter, 1-AT concentration and inhibitory activity levels were lower than those found in healthy children; these differences were statistically significant. These findings explain both the retardation in the lysis of the hyaline membrane and the fact that a decrease in serum 1-AT levels elicits lung tissue damage by the action of proteolytic enzymes contained in leucocytes.