A new elastase inhibitor from Streptococcus pneumoniae protects against acute lung injury induced by neutrophil granules

A neutrophil elastase-inhibitor isolated from lysed pneumococcal cells, as well as trypsin-digest peptides derived from this factor, were tested for their ability to suppress acute lung injury in mice treated with human neutrophil granule extracts. Injury was assessed by measuring pulmonary sequestration of circulating 125I-labeled albumin, lung water, and lung hemoglobin. Both the native inhibitor and the tryptic-peptides gave good protection when preincubated with granule extract for brief periods before intrapulmonary instillation. Lesser, but still significant, protection was observed in the absence of preincubation. Protection was not simply due to addition of exogenous proteins to the granule extract because substitution of goat immunoglobulin for pneumococcal fraction was ineffective. These results suggest that pneumococcal elastase-inhibitors, recently described by us, may play a role in minimizing lung injury during pneumococcal pneumonia.