Heightened Lung Bactericidal Activity in Mice after Aerosol Immunization with Re 595 Salmonella minnesota: Importance of Cellular rather than Humoral Factors

Intrapulmonary bactericidal activity was enhanced against aerosolized Serratia marcescens, Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus two weeks after aerosol immunization with Re 595 Salmonella minnesota. To define better this nonspecific stimulation of antibacterial lung defenses, mice were simultaneously challenged with S. aureus and S. marcescens up to 30 days after aerosol immunization with Re. Enhanced bactericidal activity against both organisms was noted, although activity against Serratia was more pronounced during the first week after immunization. Repetitive aerosol immunization with Re also resulted in enhanced bactericidal activity. Macrophages harvested from mice after aerosol immunization were “activated” by ultrastructural criteria and had enhanced intracellular bactericidal activity against S. aureus. Aerosol immunization also caused an increase in polymorphonuclear leukocytes in lung lavage fluid, which may have been important in activity against Serratia. Mice systemically immunized with Re developed high antibody titers in serum and lung washings but had no stimulation of lung antibacterial activity.