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

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 ( P pi A ), and clarified its role in evasion of phagocytosis by macrophages. Attenuation of the gene encoding prolipoprotein diacylglyceryl transferase ( L gt) altered the localization of P pi A from the cell surface to the culture supernatant, indicating that PpiA is lipid‐anchored in the cell membrane by L gt. Both human and murine macrophages showed higher phagocytic activity towards ppi A and lgt mutants than the wild‐type, indicating that the presence of P pi A 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 P pi A plays an important role in inhibiting phagocytic engulfment and in evasion of the host immune response.