Alveolar macrophage and neutrophil interactions in Pasteurella haemolytica-induced endothelial cell injury.

Pasteurella haemolytica, the cause of fibrinous pleuropneumonia in cattle, produces extensive microvascular endothelial cell damage. This study investigated endothelial cell-leukocyte interactions by using a Millicell coculture assay system that modeled the bovine pulmonary alveolar defense system and showed that P. haemolytica-mediated endothelial cell damage was enhanced by the presence of alveolar macrophages, presumably due to soluble alveolar macrophage products. The alveolar macrophage-enhanced endothelial cell damage occurred regardless of the presence of anti-P. haemolytica immune serum; however, neutrophils and immune serum effectively prevented endothelial cell damage. These results suggest that alveolar macrophages are ineffective in controlling P. haemolytica growth and actually promote endothelial cell damage.