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Infection and Immunity, December 2004, p. 7212-7219, Vol. 72, No. 12
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.12.7212-7219.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

The pH 6 Antigen Is an Antiphagocytic Factor Produced by Yersinia pestis Independent of Yersinia Outer Proteins and Capsule Antigen

Xiao-Zhe Huang* and Luther E. Lindler

Department of Bacterial Diseases, Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Silver Spring, Maryland

Received 12 January 2004/ Returned for modification 2 March 2004/ Accepted 13 August 2004

The pH 6 antigen (pH 6 Ag; PsaA) of Yersinia pestis has been shown to be a virulence factor. In this study, we set out to investigate the possible function of Y. pestis PsaA in a host cell line, RAW264.7 mouse macrophages, in order to better understand the role it might play in virulence. Y. pestis KIM5 derivatives with and without the pCD1 plasmid and their psaA isogenic counterparts and Escherichia coli HB101 and DH5{alpha} carrying a psaA clone or a vector control were used for macrophage infections. Macrophage-related bacteria and gentamicin-resistant intracellular bacteria generated from plate counting and direct microscopic examinations were used to evaluate these RAW264.7 macrophage infections. Y. pestis psaA isogenic strains did not show any significant difference in their abilities to associate with or bind to mouse macrophage cells. However, expression of psaA appeared to significantly reduce phagocytosis of both Y. pestis and E. coli by mouse macrophages (P < 0.05). Furthermore, we found that complementation of psaA mutant Y. pestis strains could completely restore the ability of the bacteria to resist phagocytosis. Fluorescence microscopy following differential labeling of intracellular and extracellular Y. pestis revealed that significantly lower numbers of psaA-expressing bacteria were located inside the macrophages. Enhanced phagocytosis resistance was specific for bacteria expressing psaA and did not influence the ability of the macrophages to engulf other bacteria. Our data demonstrate that Y. pestis pH 6 Ag does not enhance adhesion to mouse macrophages but rather promotes resistance to phagocytosis.

* Corresponding author. Mailing address: Department of Bacterial Diseases, Division of Communicable Diseases and Immunology, WRAIR, 503 Robert Grant Ave., Silver Spring, MD 20910. Phone: (301) 319-9648. Fax: (301) 319-9123. E-mail: xiaozhe.huang{at}NA.AMEDD.ARMY.MIL.

Editor: J. B. Bliska

Infection and Immunity, December 2004, p. 7212-7219, Vol. 72, No. 12
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.12.7212-7219.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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