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Involvement of lipoprotein PpiA of Streptococcus gordonii in evasion of phagocytosis by macrophages

Authors

  • K. Cho,

    1. Department of Oral Microbiology and Immunology, Showa University School of Dentistry, Tokyo, Japan
    2. Department of Periodontology, Showa University School of Dentistry, Tokyo, Japan
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  • T. Arimoto,

    Corresponding author
    • Department of Oral Microbiology and Immunology, Showa University School of Dentistry, Tokyo, Japan
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  • T. Igarashi,

    1. Department of Oral Microbiology and Immunology, Showa University School of Dentistry, Tokyo, Japan
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    • This work is dedicated in fondest memory to Professor Takeshi Igarashi, whose influence as a mentor will be greatly missed, and without whom this work would not have been possible.
  • M. Yamamoto

    1. Department of Periodontology, Showa University School of Dentistry, Tokyo, Japan
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Correspondence: Takafumi Arimoto, Department of Oral Microbiology and Immunology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan Tel.: + 81 3 3784 8166; fax: + 81 3 3784 4105; E-mail: takafumi@dent.showa-u.ac.jp

Summary

Streptococcus gordonii is a commensal gram-positive bacterium that resides in the human oral cavity, and is one of the most common causes of infective endocarditis (IE). Bacterial surface molecules play an important role in establishing IE, and several S. gordonii proteins have been implicated in binding to host cells during the establishment of IE. In this study, we identified a putative lipoprotein, peptidyl-prolyl cis/trans isomerase (PpiA), and clarified its role in evasion of phagocytosis by macrophages. Attenuation of the gene encoding prolipoprotein diacylglyceryl transferase (Lgt) altered the localization of PpiA from the cell surface to the culture supernatant, indicating that PpiA is lipid-anchored in the cell membrane by Lgt. Both human and murine macrophages showed higher phagocytic activity towards ppiA and lgt mutants than the wild-type, indicating that the presence of PpiA suppresses phagocytosis of S. gordonii. Human macrophages treated with dextran sulfate had significantly impaired phagocytosis of S. gordonii, suggesting that class A scavenger receptors in human macrophages are involved in the phagocytosis of S. gordonii. These results provide evidence that S. gordonii lipoprotein PpiA plays an important role in inhibiting phagocytic engulfment and in evasion of the host immune response.

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