Enterococcus faecalis Capsular Polysaccharide Serotypes C and D and Their Contributions to Host Innate Immune Evasion

• Published in: Infection and Immunity Vol. 77; no. 12; pp. 5551 - 5557
• Main Authors: Thurlow, Lance R, Thomas, Vinai Chittezham, Fleming, Sherry D, Hancock, Lynn E
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.12.2009; American Society for Microbiology (ASM)
• Subjects: Animals; Antibiotic resistance; Bacterial Capsules - immunology; Bacterial Capsules - physiology; Bacteriology; Biological and medical sciences; Capsular polysaccharides; Cell Line; Complement; Complement C3 - immunology; Complement C3 - metabolism; Enterococcus faecalis; Enterococcus faecalis - immunology; Enterococcus faecalis - pathogenicity; Fundamental and applied biological sciences. Psychology; Host Response and Inflammation; Immune response; Infection; Lipopolysaccharides - immunology; Lipoteichoic acid; Macrophages; Macrophages - immunology; Macrophages - microbiology; Mice; Microbiology; Miscellaneous; Opsonin Proteins - immunology; opsonophagocytosis; Phagocytosis - immunology; Protein Binding; Serotypes; Teichoic Acids - immunology; Tumor necrosis factor-a; Tumor Necrosis Factor-alpha - immunology; Tumor Necrosis Factor-alpha - secretion; virulence factors; Virulence Factors - immunology; Virulence Factors - physiology; Microorganism capsule; Enterococcus faecalis; Streptococcaceae; Lactic acid bacteria; Microbiology; Bacteria; Micrococcales; Natural immunity; Immune evasion; Serotype; Polysaccharide
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00576-09

It has become increasingly difficult to treat infections caused by Enterococcus faecalis due to its high levels of intrinsic and acquired antibiotic resistance. However, few studies have explored the mechanisms that E. faecalis employs to circumvent the host innate immune response and establish infection. Capsular polysaccharides are important virulence factors that are associated with innate immune evasion. We demonstrate, using cultured macrophages (RAW 264.7), that capsule-producing E. faecalis strains of either serotype C or D are more resistant to complement-mediated opsonophagocytosis than unencapsulated strains. We show that differences in opsonophagocytosis are not due to variations in C3 deposition but are due to the ability of capsule to mask bound C3 from detection on the surface of E. faecalis. Similarly, E. faecalis capsule masks lipoteichoic acid from detection, which correlates with decreased tumor necrosis factor alpha production by cultured macrophages in the presence of encapsulated strains compared to that in the presence of unencapsulated strains. Our studies confirm the important role of the capsule as a virulence factor of E. faecalis and provide several mechanisms by which the presence of the capsule influences evasion of the innate immune response and suggest that the capsule could be a potential target for developing alternative therapies to treat E. faecalis infections.