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Mechanisms of GII.4 norovirus persistence in human populations.

Lindesmith LC, Donaldson EF, Lobue AD, Cannon JL, Zheng DP, Vinje J, Baric RS - PLoS Med. (2008)

Bottom Line: Individuals with defects in the FUT2 gene are termed secretor-negative, do not express the appropriate HBGA necessary for docking, and are resistant to Norwalk infection.Our data suggest that the surface-exposed carbohydrate ligand binding domain in the norovirus capsid is under heavy immune selection and likely evolves by antigenic drift in the face of human herd immunity.Variation in the capsid carbohydrate-binding domain is tolerated because of the large repertoire of similar, yet distinct HBGA carbohydrate receptors available on mucosal surfaces that could interface with the remodeled architecture of the capsid ligand-binding pocket.

View Article: PubMed Central - PubMed

Affiliation: University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA.

ABSTRACT

Background: Noroviruses are the leading cause of viral acute gastroenteritis in humans, noted for causing epidemic outbreaks in communities, the military, cruise ships, hospitals, and assisted living communities. The evolutionary mechanisms governing the persistence and emergence of new norovirus strains in human populations are unknown. Primarily organized by sequence homology into two major human genogroups defined by multiple genoclusters, the majority of norovirus outbreaks are caused by viruses from the GII.4 genocluster, which was first recognized as the major epidemic strain in the mid-1990s. Previous studies by our laboratory and others indicate that some noroviruses readily infect individuals who carry a gene encoding a functional alpha-1,2-fucosyltransferase (FUT2) and are designated "secretor-positive" to indicate that they express ABH histo-blood group antigens (HBGAs), a highly heterogeneous group of related carbohydrates on mucosal surfaces. Individuals with defects in the FUT2 gene are termed secretor-negative, do not express the appropriate HBGA necessary for docking, and are resistant to Norwalk infection. These data argue that FUT2 and other genes encoding enzymes that regulate processing of the HBGA carbohydrates function as susceptibility alleles. However, secretor-negative individuals can be infected with other norovirus strains, and reinfection with the GII.4 strains is common in human populations. In this article, we analyze molecular mechanisms governing GII.4 epidemiology, susceptibility, and persistence in human populations.

Methods and findings: Phylogenetic analyses of the GII.4 capsid sequences suggested an epochal evolution over the last 20 y with periods of stasis followed by rapid evolution of novel epidemic strains. The epidemic strains show a linear relationship in time, whereby serial replacements emerge from the previous cluster. Five major evolutionary clusters were identified, and representative ORF2 capsid genes for each cluster were expressed as virus-like particles (VLPs). Using salivary and carbohydrate-binding assays, we showed that GII.4 VLP-carbohydrate ligand binding patterns have changed over time and include carbohydrates regulated by the human FUT2 and FUT3 pathways, suggesting that strain sensitivity to human susceptibility alleles will vary. Variation in surface-exposed residues and in residues that surround the fucose ligand interaction domain suggests that antigenic drift may promote GII.4 persistence in human populations. Evidence supporting antigenic drift was obtained by measuring the antigenic relatedness of GII.4 VLPs using murine and human sera and demonstrating strain-specific serologic and carbohydrate-binding blockade responses. These data suggest that the GII.4 noroviruses persist by altering their HBGA carbohydrate-binding targets over time, which not only allows for escape from highly penetrant host susceptibility alleles, but simultaneously allows for immune-driven selection in the receptor-binding region to facilitate escape from protective herd immunity.

Conclusions: Our data suggest that the surface-exposed carbohydrate ligand binding domain in the norovirus capsid is under heavy immune selection and likely evolves by antigenic drift in the face of human herd immunity. Variation in the capsid carbohydrate-binding domain is tolerated because of the large repertoire of similar, yet distinct HBGA carbohydrate receptors available on mucosal surfaces that could interface with the remodeled architecture of the capsid ligand-binding pocket. The continuing evolution of new replacement strains suggests that, as with influenza viruses, vaccines could be targeted that protect against norovirus infections, and that continued epidemiologic surveillance and reformulations of norovirus vaccines will be essential in the control of future outbreaks.

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Murine Antisera Blockade of GII.4 VLP Binding to HBGAsAntisera collected from mice immunized against each GII.4 ORF2 were assayed for blockade of GII.4–1987- and GII.4–1997-H type 3, GII.4–2002a-Lea, and GII.4–2002-Ley interaction and the mean percentage of control binding calculated compared to the no-serum control. The floating bar plot shows the mean percentage of sera needed for BT50 for each antisera and each VLP; the mean titer is indicated by the line in the box. The upper and lower boundaries of the box represent the maximum and minimum values. Antisera groups that did not block 50% VLP–HBGA binding at the highest serum concentration tested (5%) were assigned an arbitrary value of 10%.*VLPs with significantly different BT50 titer compared to the homotypic antisera-VLP BT50 titer (p < 0.05, one-way ANOVA).
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pmed-0050031-g012: Murine Antisera Blockade of GII.4 VLP Binding to HBGAsAntisera collected from mice immunized against each GII.4 ORF2 were assayed for blockade of GII.4–1987- and GII.4–1997-H type 3, GII.4–2002a-Lea, and GII.4–2002-Ley interaction and the mean percentage of control binding calculated compared to the no-serum control. The floating bar plot shows the mean percentage of sera needed for BT50 for each antisera and each VLP; the mean titer is indicated by the line in the box. The upper and lower boundaries of the box represent the maximum and minimum values. Antisera groups that did not block 50% VLP–HBGA binding at the highest serum concentration tested (5%) were assigned an arbitrary value of 10%.*VLPs with significantly different BT50 titer compared to the homotypic antisera-VLP BT50 titer (p < 0.05, one-way ANOVA).

Mentions: Murine cross-reactive IgG data support the trend seen with human serum samples indicating clear serologic differences between the early and late GII.4 strains. To further test this hypothesis, blockade experiments were performed using mouse sera and BT50 values were compared. Antisera raised against GII.4–1987 and GII.4–1997 reacted similarly and effectively blocked both GII.4–1987 and −1997 interactions with H type 3, and both sera were unable to block GII.4–2002/2002a interaction with HBGA ligands (BT50 p < 0.01, one-way ANOVA; Figures 12 and S18). Conversely, antisera raised against GII.4–2002 or −2002a effectively blocked 2002/2002a interactions with HBGAs but were significantly less able to block GII.4–1987 (BT50 p < 0.05, one-way ANOVA) and GII.4–1997 (BT50 p < 0.01, one-way ANOVA) interactions with H type 3, again suggesting that the earlier strains share common blocking epitopes not found in the later Farmington Hills strains. GII.4–1987 and GII.4–1997 interaction with H type 3 was weakly blocked by sera against GII.4–2004 and GII.4–2005 (Figures 12 and S18). GII.4–2004 and GII.4–2005 sera efficiently blocked GII.4–2002-Ley interaction but were significantly less able to block GII.4–2002a interaction with Lea (BT50 p < 0.01 and p < 0.05, one-way ANOVA, respectively; Figure 12). In fact, GII.4–2002a-Lea interaction was not efficiently blocked by any sera except the GII.4–2002/2002a samples, supporting observations with human sera (Figure 12). Our inability to identify carbohydrates that efficiently bound GII.4–2004 and GII.4–2005 precluded the testing of sera from historic strains to block the binding of contemporary strains to HBGAs. None of the antisera generated to the GII.4 panel blocked NV-H type 3 interactions at any of the serum concentrations tested (unpublished data). These data support the hypothesis that not only does antigenic drift occur in the capsid region of GII.4 norovirus strains over time, but that the variation greatly influences the ability of preexisting herd immunity to neutralize extant strains, based on carbohydrate blockade assays.


Mechanisms of GII.4 norovirus persistence in human populations.

Lindesmith LC, Donaldson EF, Lobue AD, Cannon JL, Zheng DP, Vinje J, Baric RS - PLoS Med. (2008)

Murine Antisera Blockade of GII.4 VLP Binding to HBGAsAntisera collected from mice immunized against each GII.4 ORF2 were assayed for blockade of GII.4–1987- and GII.4–1997-H type 3, GII.4–2002a-Lea, and GII.4–2002-Ley interaction and the mean percentage of control binding calculated compared to the no-serum control. The floating bar plot shows the mean percentage of sera needed for BT50 for each antisera and each VLP; the mean titer is indicated by the line in the box. The upper and lower boundaries of the box represent the maximum and minimum values. Antisera groups that did not block 50% VLP–HBGA binding at the highest serum concentration tested (5%) were assigned an arbitrary value of 10%.*VLPs with significantly different BT50 titer compared to the homotypic antisera-VLP BT50 titer (p < 0.05, one-way ANOVA).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2235898&req=5

pmed-0050031-g012: Murine Antisera Blockade of GII.4 VLP Binding to HBGAsAntisera collected from mice immunized against each GII.4 ORF2 were assayed for blockade of GII.4–1987- and GII.4–1997-H type 3, GII.4–2002a-Lea, and GII.4–2002-Ley interaction and the mean percentage of control binding calculated compared to the no-serum control. The floating bar plot shows the mean percentage of sera needed for BT50 for each antisera and each VLP; the mean titer is indicated by the line in the box. The upper and lower boundaries of the box represent the maximum and minimum values. Antisera groups that did not block 50% VLP–HBGA binding at the highest serum concentration tested (5%) were assigned an arbitrary value of 10%.*VLPs with significantly different BT50 titer compared to the homotypic antisera-VLP BT50 titer (p < 0.05, one-way ANOVA).
Mentions: Murine cross-reactive IgG data support the trend seen with human serum samples indicating clear serologic differences between the early and late GII.4 strains. To further test this hypothesis, blockade experiments were performed using mouse sera and BT50 values were compared. Antisera raised against GII.4–1987 and GII.4–1997 reacted similarly and effectively blocked both GII.4–1987 and −1997 interactions with H type 3, and both sera were unable to block GII.4–2002/2002a interaction with HBGA ligands (BT50 p < 0.01, one-way ANOVA; Figures 12 and S18). Conversely, antisera raised against GII.4–2002 or −2002a effectively blocked 2002/2002a interactions with HBGAs but were significantly less able to block GII.4–1987 (BT50 p < 0.05, one-way ANOVA) and GII.4–1997 (BT50 p < 0.01, one-way ANOVA) interactions with H type 3, again suggesting that the earlier strains share common blocking epitopes not found in the later Farmington Hills strains. GII.4–1987 and GII.4–1997 interaction with H type 3 was weakly blocked by sera against GII.4–2004 and GII.4–2005 (Figures 12 and S18). GII.4–2004 and GII.4–2005 sera efficiently blocked GII.4–2002-Ley interaction but were significantly less able to block GII.4–2002a interaction with Lea (BT50 p < 0.01 and p < 0.05, one-way ANOVA, respectively; Figure 12). In fact, GII.4–2002a-Lea interaction was not efficiently blocked by any sera except the GII.4–2002/2002a samples, supporting observations with human sera (Figure 12). Our inability to identify carbohydrates that efficiently bound GII.4–2004 and GII.4–2005 precluded the testing of sera from historic strains to block the binding of contemporary strains to HBGAs. None of the antisera generated to the GII.4 panel blocked NV-H type 3 interactions at any of the serum concentrations tested (unpublished data). These data support the hypothesis that not only does antigenic drift occur in the capsid region of GII.4 norovirus strains over time, but that the variation greatly influences the ability of preexisting herd immunity to neutralize extant strains, based on carbohydrate blockade assays.

Bottom Line: Individuals with defects in the FUT2 gene are termed secretor-negative, do not express the appropriate HBGA necessary for docking, and are resistant to Norwalk infection.Our data suggest that the surface-exposed carbohydrate ligand binding domain in the norovirus capsid is under heavy immune selection and likely evolves by antigenic drift in the face of human herd immunity.Variation in the capsid carbohydrate-binding domain is tolerated because of the large repertoire of similar, yet distinct HBGA carbohydrate receptors available on mucosal surfaces that could interface with the remodeled architecture of the capsid ligand-binding pocket.

View Article: PubMed Central - PubMed

Affiliation: University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA.

ABSTRACT

Background: Noroviruses are the leading cause of viral acute gastroenteritis in humans, noted for causing epidemic outbreaks in communities, the military, cruise ships, hospitals, and assisted living communities. The evolutionary mechanisms governing the persistence and emergence of new norovirus strains in human populations are unknown. Primarily organized by sequence homology into two major human genogroups defined by multiple genoclusters, the majority of norovirus outbreaks are caused by viruses from the GII.4 genocluster, which was first recognized as the major epidemic strain in the mid-1990s. Previous studies by our laboratory and others indicate that some noroviruses readily infect individuals who carry a gene encoding a functional alpha-1,2-fucosyltransferase (FUT2) and are designated "secretor-positive" to indicate that they express ABH histo-blood group antigens (HBGAs), a highly heterogeneous group of related carbohydrates on mucosal surfaces. Individuals with defects in the FUT2 gene are termed secretor-negative, do not express the appropriate HBGA necessary for docking, and are resistant to Norwalk infection. These data argue that FUT2 and other genes encoding enzymes that regulate processing of the HBGA carbohydrates function as susceptibility alleles. However, secretor-negative individuals can be infected with other norovirus strains, and reinfection with the GII.4 strains is common in human populations. In this article, we analyze molecular mechanisms governing GII.4 epidemiology, susceptibility, and persistence in human populations.

Methods and findings: Phylogenetic analyses of the GII.4 capsid sequences suggested an epochal evolution over the last 20 y with periods of stasis followed by rapid evolution of novel epidemic strains. The epidemic strains show a linear relationship in time, whereby serial replacements emerge from the previous cluster. Five major evolutionary clusters were identified, and representative ORF2 capsid genes for each cluster were expressed as virus-like particles (VLPs). Using salivary and carbohydrate-binding assays, we showed that GII.4 VLP-carbohydrate ligand binding patterns have changed over time and include carbohydrates regulated by the human FUT2 and FUT3 pathways, suggesting that strain sensitivity to human susceptibility alleles will vary. Variation in surface-exposed residues and in residues that surround the fucose ligand interaction domain suggests that antigenic drift may promote GII.4 persistence in human populations. Evidence supporting antigenic drift was obtained by measuring the antigenic relatedness of GII.4 VLPs using murine and human sera and demonstrating strain-specific serologic and carbohydrate-binding blockade responses. These data suggest that the GII.4 noroviruses persist by altering their HBGA carbohydrate-binding targets over time, which not only allows for escape from highly penetrant host susceptibility alleles, but simultaneously allows for immune-driven selection in the receptor-binding region to facilitate escape from protective herd immunity.

Conclusions: Our data suggest that the surface-exposed carbohydrate ligand binding domain in the norovirus capsid is under heavy immune selection and likely evolves by antigenic drift in the face of human herd immunity. Variation in the capsid carbohydrate-binding domain is tolerated because of the large repertoire of similar, yet distinct HBGA carbohydrate receptors available on mucosal surfaces that could interface with the remodeled architecture of the capsid ligand-binding pocket. The continuing evolution of new replacement strains suggests that, as with influenza viruses, vaccines could be targeted that protect against norovirus infections, and that continued epidemiologic surveillance and reformulations of norovirus vaccines will be essential in the control of future outbreaks.

Show MeSH
Related in: MedlinePlus