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¹ Department of Pediatrics, ² Department of Medicine, and ³ Department of Cellular and Molecular Medicine, ⁴ Glycobiology Research and Training Center, ⁵ Biomedical Sciences Graduate Program, and ⁶ Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA 92093
⁷ Department of Laboratory Medicine, Lund University, S-221 00 Lund, Sweden,
⁸ Rady Children's Hospital, San Diego, CA 92123

CORRESPONDENCE Victor Nizet: vnizet{at}ucsd.edu OR Ajit Varki: a1varki{at}ucsd.edu

Group B Streptococcus (GBS) is a leading cause of invasive bacterial infections in human newborns. A key GBS virulence factor is its capsular polysaccharide (CPS), displaying terminal sialic acid (Sia) residues which block deposition and activation of complement on the bacterial surface. We recently demonstrated that GBS Sia can bind human CD33-related Sia-recognizing immunoglobulin (Ig) superfamily lectins (hCD33rSiglecs), a family of inhibitory receptors expressed on the surface of leukocytes. We report the unexpected discovery that certain GBS strains may bind one such receptor, hSiglec-5, in a Sia-independent manner, via the cell wall–anchored β protein, resulting in recruitment of SHP protein tyrosine phosphatases. Using a panel of WT and mutant GBS strains together with Siglec-expressing cells and soluble Siglec-Fc chimeras, we show that GBS β protein binding to Siglec-5 functions to impair human leukocyte phagocytosis, oxidative burst, and extracellular trap production, promoting bacterial survival. We conclude that protein-mediated functional engagement of an inhibitory host lectin receptor promotes bacterial innate immune evasion.

© 2009 Carlin et al.
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