Concentrations of alpha 1-proteinase inhibitor and alpha 2-macroglobulin in serum and lung secretions of intubated infants.

In order to determine the relative importance of the two proteinase inhibitors, alpha 1-proteinase inhibitor (alpha 1 PI) and alpha 2-macroglobulin (alpha 2M), in defending the infant lung against proteolytic attack, we measured concentrations of alpha 1PI and alpha 2M in both serum and lung secretions of infants intubated for respiratory insufficiency. In addition, we compared the concentration of each of the proteinase inhibitors in lung secretions with the serum concentrations of the proteinase inhibitor on the same day. Serum and secretions of all infants contained quantifiable levels of alpha 1PI. All serum samples had measurable amounts of alpha 2M. Ninety-two percent of the infants and 78% of all secretion samples tested contained alpha 2M. Molar ratios of alpha 1PI/albumin did not change as a function of gestational age in either serum or secretions. Serum alpha 2M/albumin also remained unchanged, but in lung secretions alpha 2M/albumin increased significantly with gestational age. With increasing postnatal age up to 44 days, mean levels of serum alpha 1PI, alpha 1PI/albumin, alpha 2M and alpha 2M/albumin increased. There was a greater increase in serum alpha 2M than in alpha 1PI as evidence by a decreasing molar ratio of alpha 1PI/alpha 2M with increasing postnatal age. In lung secretions, only alpha 1PI/albumin increased with postnatal age. Mean values for the molar ratio of alpha 1PI/alpha 2M in lung secretions ranged from 17 at 1-5 d to 22 at 11-44 d compared with the ratio of 200 reported for healthy adults (7).