Evidence of cytocidal effects of Pasteurella haemolytica on bovine peripheral blood mononuclear leukocytes.

Pasteurella haemolytica had a pronounced cytocidal effect on bovine mononuclear leukocytes. Mononuclear leukocytes separated from venous blood on Ficoll-diatrizoate and incubated with either P haemolytica or Escherichia coli showed a significantly greater percentage cell death than did cells incubated with Staphylococcus epidermidis or controls. Neither heat-killed nor x-irradiated P haemolytica caused a significant percentage cell death. The cytotoxic potential of P haemolytica was dose related in that cell death among mononuclear leukocytes increased as the ratio of bacteria-to-cells increased. Enriched monocyte cultures showed a higher and less variable rate of cell death than either enriched lymphocyte or mixed leukocyte cultures.