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Infect Immun, June 1998, p. 2791-2797, Vol. 66, No. 6
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Secretory Phospholipase A2 Is the Principal Bactericide for Staphylococci and Other Gram-Positive Bacteria in Human Tears

Xiao-Dan Qu1 and Robert I. Lehrer1,2,*

Department of Medicine1 and Molecular Biology Institute,2 UCLA School of Medicine, Los Angeles, California 90095-1690

Received 11 February 1998/Returned for modification 10 March 1998/Accepted 24 March 1998

We examined human tears for molecules that killed gram-positive bacteria. The principal mediator of bactericidal activity against staphylococci proved to be a calcium-dependent enzyme, secretory phospholipase A2. Whereas the concentration of secretory phospholipase A2 in the normal tear film exceeded 30 µg/ml, only 1.1 ng (<0.1 nM) of the enzyme per ml sufficed to kill Listeria monocytogenes and 15 to 80 ng/ml killed Staphylococcus aureus. Despite its efficacy against gram-positive bacteria, secretory phospholipase A2 lacked bactericidal activity against gram-negative organisms (Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa) when tested in the ionic environment of tears. Given the presence of secretory phospholipase A2 in tears, intestinal secretions, and leukocytes, this enzyme may play a substantial role in innate mucosal and systemic bactericidal defenses against gram-positive bacteria.

* Corresponding author. Mailing address: Department of Medicine, Box 951690, UCLA School of Medicine, Los Angeles, CA 90095-1690. Phone: (310) 825-5340. Fax: (310) 206-8766. E-mail: rlehrer{at}med1.medsch.ucla.edu.

Infect Immun, June 1998, p. 2791-2797, Vol. 66, No. 6
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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Copyright © 1998 by the American Society for Microbiology. All rights reserved.