Involvement of lipoprotein PpiA ofStreptococcus gordoniiin evasion of phagocytosis by macrophages

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Streptococcus gordoniiis 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 severalS. gordoniiproteins have been implicated in binding to host cells during the establishment of IE. In this study, we identified a putative lipoprotein, peptidyl-prolylcis/transisomerase (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 towardsppiAandlgtmutants than the wild-type, indicating that the presence of PpiA suppresses phagocytosis ofS. gordonii. Human macrophages treated with dextran sulfate had significantly impaired phagocytosis ofS. gordonii, suggesting that class A scavenger receptors in human macrophages are involved in the phagocytosis ofS. gordonii. These results provide evidence thatS. gordoniilipoprotein PpiA plays an important role in inhibiting phagocytic engulfment and in evasion of the host immune response.

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