Evidence of Pasteurella haemolytica linked immune complex disease in natural and experimental models

The pathogenesis of bovine pneumonic pasteurellosis is not completely under stood, and studies have not established that Pasteurella haemolytica Al (Ph l) virulence is exclusively responsible for the development of acute pulmon ary lesions. The purpose of this investigation was to determine if immune c omplex disease is involved in the pathogenesis of bovine pneumonic pasteure llosis. A retrospective immunohistologic study of lung tissue from natural cases of bovine pneumonic pasteurellosis (44) as performed, and immune comp lexes were observed in alveloar spaces and walls in 88% of these cases. To study this pathologic mechanism experimentally, groups of mice were immuniz ed with purified Phl outer membranes (OMs) or sham immunized on days 0 and 14. Mice were challenged intratracheally on day 24 with either live Phl or Phl OMs, and pulmonary lesions were assessed 24 h after challenge. Placebo immunized mice developed focal infiltrates of neutrophils and macrophages c entered around large caliber bronchi. Mice immunized with Phl OMs and chall enged with live Phl or OMs developed severe bronchointerstitial pneumonia w ith diffuse neutrophilic infiltration, focal necrosis, hemorrhage and edema , that is histologically similar to bovine pneumonic pasteurellosis. Immuno histology revealed flocculent aggregates of IgG and complement positive mat erial within alveolar spaces and walls from mice challenged with live Phl, and fine granular deposits of IgG and complement positive material were obs erved lining the alveolar walls from mice challenged with Phl OMs. Immunize d mice exhibited high serum IgG antibody titers to Ph1 outer membrane prote ins (OMPs). Results of this study suggest that immune complex disease plays a role in the pathogenesis of bovine pneumonic pasteurellosis. (C) 1999 Ac ademic Press.