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Infection and Immunity, December 2002, p. 6524-6533, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.6524-6533.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Antimicrobial Peptides from Human Platelets{dagger}

Yi-Quan Tang,1 Michael R. Yeaman,2,3 and Michael E. Selsted1,4*

Departments of Pathology,1 Microbiology and Molecular Genetics, College of Medicine, University of California Irvine, Irvine, California 92697,4 Department of Medicine, School of Medicine, University of California Los Angeles Medical Center, Los Angeles, California 90509,2 St. John's Cardiovascular Research Center, Harbor-UCLA Research and Education Institute, Torrance, California 905023

Received 25 March 2002/ Returned for modification 28 May 2002/ Accepted 6 August 2002

Platelets share structural and functional similarities with granulocytes known to participate in antimicrobial host defense. To evaluate the potential antimicrobial activities of platelet proteins, normal human platelets were stimulated with human thrombin in vitro. Components of the stimulated-platelet supernatants were purified to homogeneity by reversed-phase high-performance liquid chromatography. Purified peptides with inhibitory activity against Escherichia coli ML35 in an agar diffusion antimicrobial assay were characterized by mass spectrometry, amino acid analysis, and sequence determination. These analyses enabled the identification of seven thrombin-releasable antimicrobial peptides from human platelets: platelet factor 4 (PF-4), RANTES, connective tissue activating peptide 3 (CTAP-3), platelet basic protein, thymosin ß-4 (Tß-4), fibrinopeptide B (FP-B), and fibrinopeptide A (FP-A). With the exception of FP-A and FP-B, all peptides were also purified from acid extracts of nonstimulated platelets. The in vitro antimicrobial activities of the seven released peptides were further tested against bacteria (E. coli and Staphylococcus aureus) and fungi (Candida albicans and Cryptococcus neoformans). Each peptide exerted activity against at least two organisms. Generally, the peptides were more potent against bacteria than fungi, activity was greater at acidic pHs, and antimicrobial activities were dose dependent. Exceptions to these observations were observed with PF-4, which displayed a bimodal dose-response relationship in microbicidal assays, and Tß-4, which had greater activity at alkaline pHs. At concentrations at which they were individually sublethal, PF-4 and CTAP-3 exerted synergistic microbicidal activity against E. coli. Collectively, these findings suggest a direct antimicrobial role for platelets as they are activated to release peptides in response to trauma or mediators of inflammation.

* Corresponding author. Mailing address: Department of Pathology, College of Medicine, University of California, Irvine, CA 92697-4800. Phone: (949) 824-2350. Fax: (949) 824-2346. E-mail: meselste{at}uci.edu.

Editor: V. J. DiRita

{dagger} For a commentary on this article, see page 6515 in this issue.

Infection and Immunity, December 2002, p. 6524-6533, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.6524-6533.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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