The effect of specific immunization on pulmonary bacterial susceptibility was investigated in approximately 500 rats by defining the relationship of in vivo lung bacterial clearance and mortality to in vitro alveolar macrophage function.
Active immunization protected burned rats from the lethal effects of an aerosol exposure of Pseudomonas aeruginosa. Correlation of survival with lung bacterial clearance revealed that enhancement of the clearance mechanism takes place following immunization. The normal rat's defense mechanism was increased following immunization by activating the alveolar macrophages, thereby resulting in increased intracellular killing, 27% to 67%.
Following burning, the phagocytic ability of the alveolar macrophages of immunized rats increased approximately ten times, while intracellular killing remained constant. These in vitro studies indicate that the most significant single factor in determining a favorable outcome from aerosol exposure is phagocytosis by alveolar macrophages.