Bovine pulmonary endothelial cell damage mediated by Pasteurella haemolytica pathogenic factors.

The in vitro effects of Pasteurella haemolytica components on bovine pulmonary endothelial monolayers were investigated to determine the relative role of individual bacterial factors in the pathogenesis of bovine pulmonary pasteurellosis. Bovine pulmonary endothelial monolayers were treated with P. haemolytica bacterial culture supernatant (CS) and P. haemolytica lipopolysaccharide. At 22 h postinoculation, the CS produced severe damage to the endothelial cells, indicated by high 51Cr release, extensive cellular detachment, and morphologic changes characterized by cell contraction, cytoplasmic blebbing, and loss of monolayer confluency. The neutralization of leukotoxin activity of the CS by heat inactivation was ineffective in decreasing the damage to endothelial cells; however, leukotoxin-neutralizing monoclonal antibody slightly diminished the toxic effect. P. haemolytica lipopolysaccharide by itself or as a supplement to CS produced endothelial cell damage similar to that of CS. The preincubation of CS dilutions (10(-1) and 10(-2)) or P. haemolytica lipopolysaccharide with polymyxin B almost completely eliminated cell toxicity. These studies show that P. haemolytica produces a soluble factor that is consistent with bacterial lipopolysaccharide and that is directly toxic to bovine pulmonary endothelial cells in vitro.