Immune stimulation of lung bactericidal activity: evidence for both cellular and humoral participation after immunization with Serratia marcescens.

Mice were immunized by aerosol or by a parenteral route with Serratia marcescens, and subsequently challenged by aerosol with both Staphylococcus aureus and S. marcescens. After a single aerosol immunization, intrapulmonary bactericidal activity was initially enhanced against both organisms. Repetitive aerosol immunization caused the same initial response; however, after antistaphylococcal activity returned to normal, enhanced antiserratia activity was still demonstrable. Parenteral immunization was associated with increased in situ bactericidal activity against both organisms with more pronounced antiserratia activity. Intracellular bactericidal activity against S. aureus of lung phagocytes harvested from mice after aerosol immunization with serratia paralleled the above findings. Aerosol immunization also resulted in recruitment of polymorphonuclear leukocytes. These data suggested that macrophage activation, leukocyte recruitment, and local antibody are important contributing factors to heightened lung antibacterial activity after aerosol immunization with S. marcescens.