Glycoepitopes of Staphylococcal Wall Teichoic Acid Govern Complement-mediated Opsonophagocytosis via Human Serum Antibody and Mannose-binding Lectin

Serum antibodies and mannose-binding lectin (MBL) are important host defense factors for host adaptive and innate immunity, respectively. Antibodies and MBL also initiate the classical and lectin complement pathways, respectively, leading to opsonophagocytosis. We have shown previously that Staphylococcus aureus wall teichoic acid (WTA), a cell wall glycopolymer consisting of ribitol phosphate substituted with alpha- or beta-O-N-acetyl-D-glucosamine (GlcNAc) and D-alanine, is recognized by MBL and serum anti-WTA IgG. However, the exact antigenic determinants to which anti-WTA antibodies or MBL bind have not been determined. To answer this question, several S. aureus mutants, such as alpha-GlcNAc glycosyltransferase-deficient S. aureus Delta tarM, beta-GlcNAc glycosyltransferase-deficient Delta tarS, and Delta tarMS double mutant cells, were prepared from a laboratory and a community-associated methicillin-resistant S. aureus strain. Here, we describe the unexpected finding that beta-GlcNAc WTA-deficient Delta tarS mutant cells (which have intact alpha-GlcNAc) escape from anti-WTA antibody-mediated opsonophagocytosis, whereas alpha-GlcNAc WTA-deficient Delta tarM mutant cells (which have intact beta-GlcNAc) are efficiently engulfed by human leukocytes via anti-WTA IgG. Likewise, MBL binding in S. aureus cells was lost in the Delta tarMS double mutant but not in either single mutant. When we determined the serum concentrations of the anti-alpha- or anti-beta-GlcNAc-specific WTA IgGs, anti-beta-GlcNAc WTA-IgG was dominant in pooled human IgG fractions and in the intact sera of healthy adults and infants. These data demonstrate the importance of the WTA sugar conformation for human innate and adaptive immunity against S. aureus infection.