Pasteurella haemolytica cytotoxin: relative susceptibility of bovine leucocytes.

An in vitro 51Cr-release assay was used to compare the susceptibility of various leucocytes from normal cattle to Pasteurella haemolytica cytotoxin. Neutrophils were found to be more sensitive than mammary or bronchoalveolar macrophages. Neutrophils induced with lipopolysaccharide (LPS) and mammary macrophages activated in vitro with LPS were as sensitive as homologous untreated cells. Bronchoalveolar macrophages from adult cows were significantly more resistant than those from calves. Sub-cytolytic concentrations of cytotoxin did not impair killing of para-influenza-3 virus infected MDBK cells by mammary macrophages.