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Group B Streptococcus suppression of phagocyte functions by protein-mediated engagement of human Siglec-5.

Carlin AF, Chang YC, Areschoug T, Lindahl G, Hurtado-Ziola N, King CC, Varki A, Nizet V - J. Exp. Med. (2009)

Bottom Line: 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 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 beta protein, resulting in recruitment of SHP protein tyrosine phosphatases.We conclude that protein-mediated functional engagement of an inhibitory host lectin receptor promotes bacterial innate immune evasion.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093, USA.

ABSTRACT
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 beta 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 beta 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.

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GBS β protein effects on human neutrophil activation and killing. (A) Oxidative burst activity of neutrophils exposed to GBS WT, ΔBac mutant, and complemented mutant strains. (B) Production of NETs in response to GBS WT, ΔBac mutant, and complemented mutant strains. Bar, 50 µm. (C) Comparison of WT and ΔBac mutant GBS strains in induction of IL-8 transcript from human neutrophils. (D and E) Survival of GBS WT and ΔBac mutant strains upon coincubation with human neutrophils (D), with or without coincubation with anti–Siglec-5 Ab or control Ab (E). All experiments performed in triplicate and repeated three (A–C and E) or two (D) times with similar results. A representative experiment (A, C, and D) or pooled data (B and E) are shown. The error bars represent mean value ± SD.
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fig5: GBS β protein effects on human neutrophil activation and killing. (A) Oxidative burst activity of neutrophils exposed to GBS WT, ΔBac mutant, and complemented mutant strains. (B) Production of NETs in response to GBS WT, ΔBac mutant, and complemented mutant strains. Bar, 50 µm. (C) Comparison of WT and ΔBac mutant GBS strains in induction of IL-8 transcript from human neutrophils. (D and E) Survival of GBS WT and ΔBac mutant strains upon coincubation with human neutrophils (D), with or without coincubation with anti–Siglec-5 Ab or control Ab (E). All experiments performed in triplicate and repeated three (A–C and E) or two (D) times with similar results. A representative experiment (A, C, and D) or pooled data (B and E) are shown. The error bars represent mean value ± SD.

Mentions: Recently, we reported that GBS serotype III mimicry of host Sias allowed engagement of hSiglec-9, leading to reduced neutrophil phagocytosis, diminished oxidative burst, and impaired formation of neutrophil extracellular traps (NETs; Brinkmann et al., 2004), together promoting pathogen survival (Carlin et al., 2007). In this study, we performed additional neutrophil studies to ascertain how the newly discovered GBS β protein–mediated engagement of hSiglec-5 would affect these phagocyte functions. Compared with the isogenic ΔBac mutant, the WT GBS strain elicited a weaker oxidative burst (Fig. 5 A), triggered the release of fewer NETs (Fig. 5 B), and stimulated less transcription of IL-8 (Fig. 5 C) upon coincubation with human neutrophils. Moreover, the WT GBS strain showed increased survival versus the ΔBac mutant in a neutrophil killing assay (Fig. 5 D). Inhibition of β protein engagement of hSiglec-5 with an anti–hSiglec-5 monoclonal antibody increased neutrophil killing of GBS (Fig. 5 E). These findings indicated that β protein–expressing GBS strains can use this protein to suppress the innate immune function of phagocytic cells.


Group B Streptococcus suppression of phagocyte functions by protein-mediated engagement of human Siglec-5.

Carlin AF, Chang YC, Areschoug T, Lindahl G, Hurtado-Ziola N, King CC, Varki A, Nizet V - J. Exp. Med. (2009)

GBS β protein effects on human neutrophil activation and killing. (A) Oxidative burst activity of neutrophils exposed to GBS WT, ΔBac mutant, and complemented mutant strains. (B) Production of NETs in response to GBS WT, ΔBac mutant, and complemented mutant strains. Bar, 50 µm. (C) Comparison of WT and ΔBac mutant GBS strains in induction of IL-8 transcript from human neutrophils. (D and E) Survival of GBS WT and ΔBac mutant strains upon coincubation with human neutrophils (D), with or without coincubation with anti–Siglec-5 Ab or control Ab (E). All experiments performed in triplicate and repeated three (A–C and E) or two (D) times with similar results. A representative experiment (A, C, and D) or pooled data (B and E) are shown. The error bars represent mean value ± SD.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2722167&req=5

fig5: GBS β protein effects on human neutrophil activation and killing. (A) Oxidative burst activity of neutrophils exposed to GBS WT, ΔBac mutant, and complemented mutant strains. (B) Production of NETs in response to GBS WT, ΔBac mutant, and complemented mutant strains. Bar, 50 µm. (C) Comparison of WT and ΔBac mutant GBS strains in induction of IL-8 transcript from human neutrophils. (D and E) Survival of GBS WT and ΔBac mutant strains upon coincubation with human neutrophils (D), with or without coincubation with anti–Siglec-5 Ab or control Ab (E). All experiments performed in triplicate and repeated three (A–C and E) or two (D) times with similar results. A representative experiment (A, C, and D) or pooled data (B and E) are shown. The error bars represent mean value ± SD.
Mentions: Recently, we reported that GBS serotype III mimicry of host Sias allowed engagement of hSiglec-9, leading to reduced neutrophil phagocytosis, diminished oxidative burst, and impaired formation of neutrophil extracellular traps (NETs; Brinkmann et al., 2004), together promoting pathogen survival (Carlin et al., 2007). In this study, we performed additional neutrophil studies to ascertain how the newly discovered GBS β protein–mediated engagement of hSiglec-5 would affect these phagocyte functions. Compared with the isogenic ΔBac mutant, the WT GBS strain elicited a weaker oxidative burst (Fig. 5 A), triggered the release of fewer NETs (Fig. 5 B), and stimulated less transcription of IL-8 (Fig. 5 C) upon coincubation with human neutrophils. Moreover, the WT GBS strain showed increased survival versus the ΔBac mutant in a neutrophil killing assay (Fig. 5 D). Inhibition of β protein engagement of hSiglec-5 with an anti–hSiglec-5 monoclonal antibody increased neutrophil killing of GBS (Fig. 5 E). These findings indicated that β protein–expressing GBS strains can use this protein to suppress the innate immune function of phagocytic cells.

Bottom Line: 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 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 beta protein, resulting in recruitment of SHP protein tyrosine phosphatases.We conclude that protein-mediated functional engagement of an inhibitory host lectin receptor promotes bacterial innate immune evasion.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093, USA.

ABSTRACT
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 beta 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 beta 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.

Show MeSH
Related in: MedlinePlus