Histopathology of the lung following intratracheal challenge with livePseudomonas aeruginosain intestinally immunized rats

This paper examines the histology of rat lungs following intestinal immunization with killed mucoid Pseudomonas aeruginosa and subsequent pulmonary challenge with live P. aeruginosa. The lungs of non-immune challenged rats developed a confluent haemorrhagic pneumonitis with degeneration and sloughing of the mucosa of the airways; perivascular infiltration with mononuclear cells was apparent 1-2 h post-challenge; some neutrophils were present by 2 h post-challenge; by 12 h post-challenge oedema and intra-alveolar haemorrhage were prominent and Gram-negative organisms were seen in large quantities. In contrast, immunized challenged animals showed a pronounced neutrophilic response 1-2 h post challenge; by 12 h post-challenge patchy abscesses were apparent with resolving inflammation and no organisms visible. The findings suggest that intestinal immunization prevents the development of fatal P. aeruginosa infections in the lung by accelerating the recruitment of polymorphonuclear neutrophils.