Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 12, 2000
Publication Date: N/A
The ruminant-specific leukotoxin (Lkt) from P. haemolytica is the major factor contributing to lung injury in bovine pneumonic pasteurellosis (BPP). Neutrophil migration into alveolar spaces and subsequent lysis of these neutrophils by native Lkt plays a pivotal role in the pathogenesis of lung injury in BPP. Arachidonic acid (AA) metabolites are known to mediate ecytolysis, besides being potent chemotactic agents for neutrophil migration. We found that native Lkt causes significant tritiated AA and LDH release in a concentration- and time-dependent manner. In contrast, mutant Lkt (lacking 344 amino acids in the N-terminal end) and lipopolysaccharide induce a lesser degree of AA and LDH release. Inhibitors of AA metabolism attenuated LDH release by >90% without affecting AA release. Native Lkt-induced AA, and LDH release were inhibited by pertussis toxin, inhibitors of cytosolic phospholipase A2 (cPLA2), phospholipase C (PLC), and protein kinase C (PKC), and by chelation of intracellular calcium. Moreover, western blot analysis revealed the presence of Gi-type G-proteins. This study demonstrates for the first time that Lkt-induced AA metabolites from cPLA2 contribute to cytolysis and that cPLA2 activity is regulated by Gi-type G-proteins, PLC, PKC, and calcium in bovine leukocytes. This invites speculation that therapeutic inhibition of cPLA2 activity may minimize lung damage in BPP by restoring neutrophil function and by attenuating neutrophil influx into alveolar spaces.