Pulmonary recruitment of neutrophils and bacterial clearance in mice inoculated with aerosols of Pasteurella haemolytica or Staphylococcus aureus.

The aim of this investigation was to study in mice the correlation between numbers of phagocytic cells in the bronchoalveolar space and the pulmonary clearance of bacteria. White mice were exposed to aerosols of P. haemolytica or S. aureus in 3 different experimental replicates. Another group of mice was sham exposed to an aerosol of sterile phosphate buffered solution in a single replicate. Animals were sacrificed at various times postaerosolization. The numbers of neutrophils and alveolar macrophages in lung lavages and the pulmonary bacterial clearance rates were determined and statistically analyzed. No significant differences (P > 0.05) were observed in the rates of pulmonary clearance between the 2 genera of bacteria, but P. haemolytica had a significant (P < 0.05) replicate effect. The number of alveolar macrophages was not significantly affected by either bacteria or phosphate buffered solution. Exposure to P. haemolytica resulted in dramatic, significant (P < 0.01) but transient increases in neutrophils in the bronchoalveolar space as well as a significant (P < 0.01) increase in the weights of lung. The correlation between neutrophils and clearance was positive for P. haemolytica but negative for S. aureus. Thus both species of bacteria are rapidly eliminated from the lung despite a rather different cellular response.