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Infection and Immunity, August 1999, p. 3768-3772, Vol. 67, No. 8
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Role of Phospholipase D in Pasteurella haemolytica Leukotoxin-Induced Increase in Phospholipase A2 Activity in Bovine Neutrophils

Zuncai Wang, Cyril R. Clarke,* and Kenneth D. Clinkenbeard

Department of Anatomy, Pathology, and Pharmacology, College of Veterinary Medicine, Oklahoma State University, Stillwater, Oklahoma 74078

Received 16 February 1999/Returned for modification 23 March 1999/Accepted 11 May 1999

The effects of Pasteurella haemolytica leukotoxin (LKT) on the activity of phospholipase D (PLD) and the regulatory interaction between PLD and phospholipase A2 (PLA2) were investigated in assays using isolated bovine neutrophils labeled with tritiated phospholipid substrates of the two enzymes. Exposure of [3H]lysophosphatidylcholine-labeled neutrophils to LKT caused concentration- and time-dependent production of phosphatidic acid (PA), the product of PLD. LKT-induced generation of PA was dependent on extracellular calcium. Both production of PA and metabolism of [3H]-arachidonate ([3H]AA)-labeled phospholipids by PLA2 were inhibited when ethanol was used to promote the alternative PLD-mediated transphosphatidylation reaction, resulting in the production of phosphatidylethanol rather than PA. The role of PA in regulation of PLA2 activity was then confirmed by means of an add-back experiment, whereby addition of PA in the presence of ethanol restored PLA2-mediated release of radioactivity from neutrophil membranes. Considering the involvement of chemotactic phospholipase products in the pathogenesis of pneumonic pasteurellosis, development and use of anti-inflammatory agents that inhibit LKT-induced activation of PLD and PLA2 may improve therapeutic management of the disease.

* Corresponding author. Mailing address: Department of Anatomy, Pathology, and Pharmacology, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK 74078. Phone: (405) 744-8093. Fax: (405) 744-5275. E-mail: clarke{at}okstate.edu.

Infection and Immunity, August 1999, p. 3768-3772, Vol. 67, No. 8
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.




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