Immunization against fatal experimental Klebsiella pneumoniae pneumonia

The ability of serospecific anti-capsular polysaccharide (CPS) antibody to prevent fatal Klebsiella pneumoniae pneumonia was evaluated in a rat lung model. Rats were immunized intramuscularly with 100 micrograms of purified serotype 2 CPS and challenged intrabronchially 14 days later with a serotype 2 strain of K. pneumoniae. Vaccination engendered high levels of serum anti-CPS antibody which afforded significant protection (P less than 0.01) against fatal pneumonia. Immunization promoted clearance of the challenge bacteria from the lungs and prevented bacteremia. Histological examination of lung tissue from infected control animals showed pronounced inflammatory cellular infiltrate in the alveolar spaces, intra- and peribronchial inflammation, and tissue necrosis. In contrast, pathological changes noted in lungs from immunized animals were restricted to infrequent intra- and peribronchial involvement.