| 1. |
- Ali, Syed Raza, et al.
(författare)
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Siglec-5 and Siglec-14 are polymorphic paired receptors that modulate neutrophil and amnion signaling responses to group B Streptococcus
- 2014
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 1540-9538 .- 0022-1007. ; 211:6, s. 1231-1242
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Tidskriftsartikel (refereegranskat)abstract
- Group B Streptococcus (GBS) causes invasive infections in human newborns. We recently showed that the GBS beta-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 beta-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.
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| 2. |
- Areschoug, Thomas, et al.
(författare)
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A Proline-Rich Region with a Highly Periodic Sequence in Streptococcal beta Protein Adopts the Polyproline II Structure and Is Exposed on the Bacterial Surface.
- 2002
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Ingår i: Journal of Bacteriology. - 0021-9193. ; 184:22, s. 6376-6383
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Tidskriftsartikel (refereegranskat)abstract
- Proline-rich regions have been identified in many surface proteins of pathogenic streptococci and staphylococci. These regions have been suggested to be located in cell wall-spanning domains and/or to be required for surface expression of the protein. Because little is known about these regions, which are found in extensively studied and biologically important surface proteins, we characterized the proline-rich region in one such protein, the beta protein of group B streptococci. The proline-rich region in beta, designated the XPZ region, has a proline at every third position, and the sequence is highly periodic in other respects. Immunochemical analysis showed that the XPZ region was not associated with the cell wall but was exposed on the bacterial surface. Moreover, characterization of a beta mutant lacking the XPZ region demonstrated that this region was not required for surface expression of the beta protein. Comparison of the XPZ region in different beta proteins showed that it varied in size but always retained the typical sequence periodicity. Circular dichroism spectroscopy indicated that the XPZ region had the structure of a polyproline II helix, an extended and solvent-exposed structure with exactly three residues per turn. Because of the three-residue sequence periodicity in the XPZ region, it is expected to be amphipathic and to have distinct nonpolar and polar surfaces. This study identified a proline-rich structure with unique properties that is exposed on the surface of an important human pathogen.
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| 3. |
- Areschoug, Thomas, et al.
(författare)
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Evasion of macrophage scavenger receptor A-mediated recognition by pathogenic streptococci
- 2008
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Ingår i: European Journal of Immunology. - : Wiley. - 1521-4141 .- 0014-2980. ; 38:11, s. 3068-3079
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Tidskriftsartikel (refereegranskat)abstract
- PRR recognize conserved structures on pathogenic microbes and are important for the defense against invading microorganisms. However, accumulating evidence indicates that many pathogens have evolved mechanisms to avoid recognition by PRR. One type of PRR is the macrophage scavenger receptor A (SR-A), which has been shown to play an important role in recognition and non-opsonic phagocytosis of pathogenic bacteria. The bacterial ligands for SR-A have been suggested to be LPS or lipoteichoic acid. Here, we use murine bone marrow-derived macrophages to analyze the role of SR-A in non-opsonic phagocytosis of two major Gram-positive pathogens, streptococcus agalactiae (group B streptococcus; GBS) and Streptococcus pyogenes. We show that the polysaccharide capsule of GBS and the surface M protein of S. pyogenes, two important virulence factors, prevent SR-A-mediated non-opsonic phagocytosis of streptococci. The sialic acid moiety of the GBS capsule was crucial for its ability to prevent recognition by SR-A. Moreover, we show that a ligand on GBS recognized by SR-A in the absence of capsule is the surface lipoprotein BIr. These findings represent the first example of a microbial strategy to prevent recognition by SR-A and suggest that bacterial surface proteins may be of importance as ligands for SR-A.
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| 4. |
- Areschoug, Thomas, et al.
(författare)
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Host-pathogen interactions in Streptococcus pyogenes infections, with special reference to puerperal fever and a comment on vaccine development.
- 2004
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Ingår i: Vaccine. - : Elsevier BV. - 1873-2518 .- 0264-410X. ; 22 Suppl 1:Suppl 1, s. 9-14
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pyogenes (group A streptococcus) causes a variety of diseases, including acute pharyngitis, impetigo, rheumatic fever and the streptococcal toxic shock syndrome. Moreover, S. pyogenes was responsible for the classical example of a nosocomial infection, the epidemics of puerperal fever (childbed fever) that caused the death of numerous women in earlier centuries. The most extensively studied virulence factor of S. pyogenes is the surface M protein, which inhibits phagocytosis and shows antigenic variation. Recent data indicate that many M proteins confer phagocytosis resistance because the variable N-terminal region has non-overlapping sites that specifically bind two components of the human immune system, the complement inhibitor C4b-binding protein (C4BP) and IgA-Fc. Concerning puerperal fever, molecular and epidemiological analysis suggests that the S. pyogenes surface protein R28 may have played a pathogenetic role in these epidemics. This article summarizes the properties of M protein and the R28 protein and considers a potential problem encountered in connection with the use of animal models for vaccine development.
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| 5. |
- Areschoug, Thomas, et al.
(författare)
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Scavenger receptors: role in innate immunity and microbial pathogenesis.
- 2009
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Ingår i: Cellular Microbiology. - : Hindawi Limited. - 1462-5814 .- 1462-5822. ; 11, s. 1160-1169
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Tidskriftsartikel (refereegranskat)abstract
- Summary Accumulating evidence shows that many scavenger receptors (SR), including SR-A, MARCO and CD36, represent an important part of the innate immune defence by acting as pattern-recognition receptors (PRR), in particular against bacterial pathogens. Several SR are expressed on macrophages and dendritic cells, where they act as phagocytic receptors mediating non-opsonic phagocytosis of pathogenic microbes. Another important function of some SR is to act as co-receptors to TLRs, modulating the inflammatory response to TLR agonists. On bacteria, the SR ligands have commonly been reported to be LPS and LTA, but recent advances in the field indicate that bacterial surface proteins play a more important role as target molecules for SR than previously thought. Interestingly, recent data show that major pathogens, including Streptococcus pyogenes and the group B streptococcus (GBS), have evolved mechanisms to evade SR-mediated recognition. Moreover, intracellular pathogens, such as hepatitis C virus (HCV) and Plasmodium falciparum, utilize the SR to gain entry into host cells, focusing interest on the importance of SR also in the molecular pathogenesis of infectious diseases. This review highlights the complex interactions between SR and pathogenic microbes, and discusses the role of these interactions in host defence and microbial pathogenesis.
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| 6. |
- Areschoug, Thomas, et al.
(författare)
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Streptococcal beta protein has separate binding sites for human factor H and IgA-Fc.
- 2002
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 277:15, s. 12642-12648
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Tidskriftsartikel (refereegranskat)abstract
- The group B streptococcus (GBS) is the most important cause of life-threatening bacterial infections in newborn infants. Protective immunity to GBS infection is elicited by several surface proteins, one of which, the beta protein, is known to bind human IgA-Fc. Here, we show that the beta protein also binds human factor H (FH), a negative regulator of complement activation. Absorption experiments with whole human plasma demonstrated binding of FH to a GBS strain expressing beta protein, but not to an isogenic beta-negative mutant. This binding was due to a direct interaction between beta and FH, as shown by experiments with purified proteins. Inhibition tests and studies with beta fragments demonstrated that FH and IgA-Fc bind to separate and non-overlapping regions in beta. Heparin, a known ligand for FH, specifically inhibited the binding between beta and FH, suggesting that FH has overlapping binding sites for beta and heparin. Bacteria-bound FH retained its complement regulatory activity, implying that beta-expressing GBS may use bound FH to evade complement attack. The finding that beta protein binds FH adds to a growing list of interactions between human pathogens and complement regulatory proteins, supporting the notion that these interactions are of general importance in bacterial pathogenesis.
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| 7. |
- Areschoug, Thomas
(författare)
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Surface proteins of pathogenic streptococci
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Streptococcus pyogenes (group A streptococcus) and the group B streptococcus (GBS) are two important human pathogens that cause different types of diseases and express different surface structures implicated in virulence. This thesis focuses on several surface proteins expressed by these pathogens, analyzing the biological function of these proteins and their ability to elicit protective immunity. R28 is a surface protein expressed by some strains of S. pyogenes isolated from cases of puerperal fever, suggesting that R28 may play a role in these infections. Molecular analysis of R28 showed that it is a novel member of a family of extremely repetitive surface proteins first identified through studies of the GBS proteins Rib and alfa. Like the Rib and alfa proteins, R28 was found to be a target for protective antibodies. Moreover, the R28 protein was found to act as an epithelial cell adhesin. Interestingly, the R28 and Rib proteins were shown to cross-react immunologically. This cross-reactivity was found to be surprisingly limited, but sufficient to confer cross-protective immunity between R28-expressing S. pyogenes strains and Rib-expressing GBS strains. Most GBS isolates express a polysaccharide capsule, which is the basis for serological typing of GBS. There are nine capsular serotypes of GBS, one of which, serotype V, has recently become increasingly important in GBS disease. Characterization of serotype V strains allowed identification of two novel GBS surface proteins, Fbs and “Rib-like”, which are targets for protective antibodies and therefore are interesting as possible components in a GBS vaccine. Interestingly, the “Rib-like” protein of type V strains was found to be closely related, if not identical, to the R28 protein of S. pyogenes. Both S. pyogenes and GBS express surface proteins that bind to the Fc part of human IgA. Little is known about the role of these interactions in pathogenesis. The IgA-binding proteins of S. pyogenes are M proteins, which are important virulence factors with antiphagocytic properties. The IgA-binding protein from GBS, the beta protein, is unrelated to the IgA-binding proteins from S. pyogenes. The binding site in IgA for the different streptococcal proteins was mapped to two hydrophobic loops in the Fc interdomain region. This region is also used by the human IgA-receptor CD89, an important mediator of IgA effector functions. In agreement with this result, the IgA-binding streptococcal proteins were found to inhibit binding of IgA to CD89. Thus, unrelated IgA-binding proteins from S. pyogenes and GBS bind the same region in IgA-Fc and may inhibit IgA effector function. The IgA-binding beta protein of GBS was found to contain a separate binding region for human factor H (FH), a plasma protein that regulates complement activation. Bacteria-bound FH retains its regulatory function, indicating that beta-expressing GBS may use FH to downregulate complement deposition and thereby inhibit phagocytosis.
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| 8. |
- Carlin, Aaron F., et al.
(författare)
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Group B Streptococcus suppression of phagocyte functions by protein-mediated engagement of human Siglec-5
- 2009
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 1540-9538 .- 0022-1007. ; 206:8, s. 1691-1699
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Tidskriftsartikel (refereegranskat)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. 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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| 9. |
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| 10. |
- Ghumra, Ashfaq, et al.
(författare)
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Structural requirements for the interaction of human IgM and IgA with the human Fc alpha/mu receptor
- 2009
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Ingår i: European Journal of Immunology. - : Wiley. - 1521-4141 .- 0014-2980. ; 39:4, s. 1147-1156
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Tidskriftsartikel (refereegranskat)abstract
- Here we unravel the structural features of human IgM and IgA that govern their interaction with the human Fc alpha/mu receptor (hFc alpha/mu R). Ligand polymerization status was crucial for the interaction, because hFc alpha/mu R binding did not occur with monomeric Ab of either class. hFc alpha/mu R bound IgM with an affinity in the nanomolar range, whereas the affinity for dimeric IgA (dIgA) was tenfold lower. Panels of mutant IgM and dIgA were used to identify regions critical for hFc alpha/mu R binding. IgM binding required contributions from both C mu 3 and C mu 4 Fc domains, whereas for dIgA, an exposed loop in the C alpha 3 domain was crucial. This loop, comprising residues Pro440-Phe443, lies at the Fc domain interface and has been implicated in the binding of host receptors Fc alpha RI and polymeric Ig receptor (pIgR), as well as IgA-binding proteins produced by certain pathogenic bacteria. Substitutions within the Pro440-Phe443 loop resulted in loss of hFc alpha/mu R binding. Furthermore, secretory component (SC, the extracellular portion of pIgR) and bacterial IgA-binding proteins were shown to inhibit the dIgA-hFc alpha/mu R interaction. Therefore, we have identified a motif in the IgA-Fc inter-domain region critical for hFc alpha/mu R interaction, and highlighted the multi-functional nature of a key site for protein-protein interaction at the IgA Fc domain interface.
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