INHIBITORS OF ELASTASE IN AIRWAY LAVAGE SAMPLES FROM VENTILATED PRETERM HUMAN NEONATES

Surplus elastase released from neutrophils during lung injury is balan ced mainly by alpha(1)-protease inhibitor (alpha(1)-PI) and by two aci d-resistant inhibitors. The latter include mucus protease inhibitor (M PI, also named SLPI, BSI, ALP) and elastase-specific inhibitor (ESI or Elafin), but their functional role during the neonatal period has not yet been characterized precisely. The saline airway lavage samples fr om neonates intubated for respiratory distress were separated by centr ifugation into a cellular and a soluble, supernatant fraction and then analyzed. During the first 36 h of life (42 neonates, gestational age 24-40 wk), elastase activity was confined to the cellular fraction. T hirty percent of the acid-resistant inhibitors but almost no alpha(1)- PI, was cell-associated. In the soluble fraction, about 20-30% of the acid-resistant inhibitors was functionally active, but only about 10% of alpha(1)-PI was. In seven infants with a nosocomial infection and d eterioration during mechanical ventilation, only a very modest increas e in elastase activity was observed. However, the functional activity of the acid-resistant inhibitors was reduced in the soluble fraction, whereas total mass remained unchanged. A full assessment of protease a nd protease inhibitors should include the cellular and the soluble lav age compartments.