Clearance of Pseudomonas aeruginosa from normal rat lungs after immunization with somatic antigens or toxin A

In a recent study we observed that in most Danish CF patients a period of approximately one year of intermittent colonization precedes the onset of chronic P. aeruginosa lung infection. An experimental model of acute P. aeruginosa pneumonia in normal rats was utilized to investigate the possibility of improving bacterial clearance by vaccination. Rats were immunized with either P. aeruginosa whole bacterial sonicate, O-polysaccharide toxin A conjugate, alginate toxin A conjugate or purified alginate. Saliva and serum samples were obtained to investigate the potential of different vaccines to induce local IgA and systemic IgM, IgG and IgA antibodies. In all immunized rats a significant (p < 0.05) rise in antibody titers against the vaccine components could be demonstrated in both saliva and serum. The macroscopic pathological changes observed at 6, 24 and 48 h after bacterial challenge included a pronounced inflammatory reaction in all groups of rats, whether vaccinated or not (p > 0.05). Approximately 99.5% of the initial inoculum was cleared within the first 6 h after challenge in all groups of rats (p > 0.77). Four weeks after challenge no bacteria could be cultured and no sign of previous inflammation could be demonstrated in any of the groups. The results of this study show that the inflammatory reaction and the natural capacity to clear bacteria in the lungs of normal rats are very efficient against P. aeruginosa and could not be improved by immunization.