Pulmonary Elastase Activity in Response to Streptococcus pneumoniae and Pseudomonas aeruginosa

Abstract

Elastase activity generated during lung defense against aerobic bacteria was studied in an animal model. Bronchoalveolar lavage (BAL) fluid from hamsters inoculated with bacteria was assayed for elastase activity at 0, 2, 4, 6 and 8 h after inoculation using a synthetic substrate of elastase, succinyl-trialanine-nitroanilide (SLAPN). S. pneumoniae type 25 inoculation led to a peak elastase activity of 0.72 .+-. 0.27 .times. 10-3 units, not significantly different from baseline (0.41 .+-. 0.08 .times. 10-3 units) or saline control (0.33 .+-. 0.18 .times. 10-3 units). In contrast, inoculation with P. aeruginosa strain PAO-1 (a species known to produce elastase as well as other virulence factors) produced peak elastase activity of 3.0 .+-. 1.2 10-3 units in BAL fluids, significantly higher than either pneumococcus type 25 or saline control (P < 0.025). Inoculation with P. aeruginosa strain E-64, an isogenic mutant of PAO-1 that produces a nonfunctional elastase, led to peak levels similar to the PAO-1 strain, suggesting that the presence of bacterial elastase was not the primary factor in BAL fluid elastase activity. Total numbers of granulocytes in BAL fluid from pneumococcus-inoculated animals (144 .+-. 31 .times. 106) was significantly higher (P < 0.05) than from either the PAO-1 (74 .+-. 31 .times. 106) or E-64 (99 .+-. 27 .times. 106) strains of Pseudomonas. Use of selective enzyme inhibitors of elastase, DFP and disodium ethylenediaminetetraacetate, implied that the majority of elastase activity in BAL fluid was due to a serine protease, of which granulocytes elastase is the primary source. Elastase activity is present in BAL fluid after inoculation with some bacterial pathogens, the source of the elastase is lung granulocytes and there are bacterial species differences that result in different levels of elastase activity.