Interaction between Pasteurella haemolytica and bovine alveolar macrophages: cytotoxic effect on macrophages and impaired phagocytosis.

Cultured bovine alveolar macrophages phagocytosed formalized 125I-labeled Pasteurella haemolytica organisms poorly when compared with uptake of an identical number of radiolabeled Yersinia enterocolitica organisms. The presence of immune serum enhanced uptake of P haemolytica, yet at high bacteria-to-macrophage ratios, a significant positive correlation existed between uptake and loss of cells from coverslips. This phenomenon was not observed with Y enterocolitica. While culture supernatant from P haemolytica either impaired phagocytosis or were cytotoxic to cultured macrophages, supernatant from Y enterocolitica did not show this effect. The observation of an apparent deterimental effect on bovine alveolar macrophages after uptake of P haemolytica may be used to explain events occurring in pneumonic pasteurellosis in cattle and may help in the development of immunizaiton techniques.