Abstract
Group B Streptococcus (GBS) causes invasive infections in human newborns. We recently showed that the GBS β-protein attenuates innate immune responses by binding to sialic acid-binding immunoglobulin-like lectin 5 (Siglec-5), an inhibitory receptor on phagocytes. Interestingly, neutrophils and monocytes also express Siglec-14, which has a ligand-binding domain almost identical to Siglec-5 but signals via an activating motif, raising the possibility that these are paired Siglec receptors that balance immune responses to pathogens. Here we show that β-protein-expressing GBS binds to both Siglec-5 and Siglec-14 on neutrophils and that the latter engagement counteracts pathogen-induced host immune suppression by activating p38 mitogen-activated protein kinase (MAPK) and AKT signaling pathways. Siglec-14 is absent from some humans because of a SIGLEC14-null polymorphism, and homozygous SIGLEC14-null neutrophils are more susceptible to GBS immune subversion. Finally, we report an unexpected human-specific expression of Siglec-5 and Siglec-14 on amniotic epithelium, the site of initial contact of invading GBS with the fetus. GBS amnion immune activation was likewise influenced by the SIGLEC14-null polymorphism. We provide initial evidence that the polymorphism could influence the risk of prematurity among human fetuses of mothers colonized with GBS. This first functionally proven example of a paired receptor system in the Siglec family has multiple implications for regulation of host immunity.
© 2014 Ali et al.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Adult
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Amnion / immunology*
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Amnion / metabolism
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Amnion / microbiology
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Antigens, CD / genetics
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Antigens, CD / immunology*
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Antigens, CD / metabolism
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Antigens, Differentiation, Myelomonocytic / genetics
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Antigens, Differentiation, Myelomonocytic / immunology*
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Antigens, Differentiation, Myelomonocytic / metabolism
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Blotting, Western
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Cell Line, Tumor
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Cells, Cultured
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / immunology
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DNA-Binding Proteins / metabolism
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Female
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Gene Expression / drug effects
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Gene Expression / immunology
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Genotype
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Host-Pathogen Interactions / immunology
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Humans
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Infant, Newborn
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Lectins / genetics
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Lectins / immunology*
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Lectins / metabolism
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Lipopolysaccharides / immunology
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Lipopolysaccharides / pharmacology
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Monocytes / immunology
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Monocytes / metabolism
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Monocytes / microbiology
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Neutrophils / immunology*
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Neutrophils / metabolism
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Neutrophils / microbiology
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Phosphorylation
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Polymorphism, Genetic
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Pregnancy
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Proto-Oncogene Proteins c-akt / metabolism
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Receptors, Cell Surface / genetics
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Receptors, Cell Surface / immunology*
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Receptors, Cell Surface / metabolism
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction / immunology
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Streptococcal Infections / immunology*
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Streptococcal Infections / microbiology
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Streptococcus agalactiae / genetics
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Streptococcus agalactiae / immunology*
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Streptococcus agalactiae / physiology
Substances
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Antigens, CD
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Antigens, Differentiation, Myelomonocytic
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DNA-Binding Proteins
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Lectins
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Lipopolysaccharides
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Receptors, Cell Surface
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SIGLEC14 protein, human
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SIGLEC5 protein, human
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beta protein, Streptococcus
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Proto-Oncogene Proteins c-akt