A FUT2 gene common polymorphism determines resistance to rotavirus A of the P[8] genotype

Immune response and protective efficacy of the S particle presented rotavirus VP8* vaccine in mice

Rotaviruses cause severe diarrhea in infants and young children, leading to significant morbidity and mortality. Despite implementation of current rotavirus vaccines, severe diarrhea caused by rotaviruses still claims ∼200,000 lives of children with great economic loss worldwide each year. Thus, new prevention strategies with high efficacy are highly demanded. Recently, we have developed a polyvalent protein nanoparticle derived from norovirus VP1, the S particle, and applied it to display rotavirus neutralizing antigen VP8* as a vaccine candidate (S-VP8*) against rotavirus, which showed promise as a vaccine based on mouse immunization and in vitro neutralization studies. Here we further evaluated this S-VP8* nanoparticle vaccine in a mouse rotavirus challenge model. S-VP8* vaccines containing the murine rotavirus (EDIM strain) VP8* antigens (S-mVP8*) were constructed and immunized mice, resulting in high titers of anti-EDIM VP8* IgG. The S-mVP8* nanoparticle vaccine protected immunized mice against challenge of the homologous murine EDIM rotavirus at a high efficacy of 97% based on virus shedding reduction in stools compared with unimmunized controls. Our study further supports the polyvalent S-VP8* nanoparticles as a promising vaccine candidate against rotavirus and warrants further development.

Histo-Blood Group Antigen Phenotype Determines Susceptibility to Genotype-Specific Rotavirus Infections and Impacts Measures of Rotavirus Vaccine Efficacy

Background

Lewis and secretor histo–blood group antigens (HBGAs) have been associated with decreased susceptibility to P[8] genotype rotavirus (RV) infections. Efficacy of vaccines containing attenuated P[8] strains is decreased in low-income countries. Host phenotype might impact vaccine efficacy (VE) by altering susceptibility to vaccination or RV diarrhea (RVD). We performed a substudy in a monovalent RV vaccine (RV1) efficacy trial in Bangladesh to determine the impact of Lewis and secretor status on risk of RVD and VE.

Methods

In infants randomized to receive RV1 or no RV1 at 10 and 17 weeks with 1 year of complete active diarrheal surveillance, we performed Lewis and secretor phenotyping and genotyped the infecting strain of each episode of RVD.

Results

A vaccine containing P[8] RV protected secretors and nonsecretors similarly. However, unvaccinated nonsecretors had a reduced risk of RVD (relative risk, 0.53 [95% confidence interval, .36–.79]) mediated by complete protection from P[4] but not P[8] RVs. This effect reduced VE in nonsecretors to 31.7%, compared to 56.2% among secretors, and decreased VE for the overall cohort.

Conclusions

Host HBGA status may impact VE estimates by altering susceptibility to RV in unvaccinated children; future trials should therefore account for HBGA status.

Clinical Trials Registration

NCT01375647.

Unraveling the role of the secretor antigen in human rotavirus attachment to histo-blood group antigens

Rotavirus is the leading agent causing acute gastroenteritis in young children, with the P[8] genotype accounting for more than 80% of infections in humans. The molecular bases for binding of the VP8* domain from P[8] VP4 spike protein to its cellular receptor, the secretory H type-1 antigen (Fuc-α1,2-Gal-β1,3-GlcNAc; H1), and to its precursor lacto-N-biose (Gal-β1,3-GlcNAc; LNB) have been determined. The resolution of P[8] VP8* crystal structures in complex with H1 antigen and LNB and site-directed mutagenesis experiments revealed that both glycans bind to the P[8] VP8* protein through a binding pocket shared with other members of the P[II] genogroup (i.e.: P[4], P[6] and P[19]). Our results show that the L-fucose moiety from H1 only displays indirect contacts with P[8] VP8*. However, the induced conformational changes in the LNB moiety increase the ligand affinity by two-fold, as measured by surface plasmon resonance (SPR), providing a molecular explanation for the different susceptibility to rotavirus infection between secretor and non-secretor individuals. The unexpected interaction of P[8] VP8* with LNB, a building block of type-1 human milk oligosaccharides, resulted in inhibition of rotavirus infection, highlighting the role and possible application of this disaccharide as an antiviral. While key amino acids in the H1/LNB binding pocket were highly conserved in members of the P[II] genogroup, differences were found in ligand affinities among distinct P[8] genetic lineages. The variation in affinities were explained by subtle structural differences induced by amino acid changes in the vicinity of the binding pocket, providing a fine-tuning mechanism for glycan binding in P[8] rotavirus.

The interaction of viruses with host glycans has become an important topic in the study of enteric virus infectivity. This interaction modulates several aspects of the viral cycle, including viral attachment, which in most cases depends on the host glycobiology dictated by the secretor and Lewis genotypes. The capacity to synthesize secretory type-I antigen H (fucose-α1,2-galactose-β1,3-N-acetylglucosamine; H1) at the mucosae, dictated by the presence of one or two functional copies of the fucosyl-transferase FUT2 gene (secretor status), has been clearly linked to infectivity in important enteric viruses such as the noroviruses. However, a big controversy existed about the contribution of H1 antigen to infection in the leading cause of viral gastroenteritis in young children (rotavirus). It has not been until recently that epidemiological data evidenced a diminished incidence of rotavirus in non-secretor individuals unable to produce H1. In the present manuscript we offer the evidence that P[8] RV bind H1 via a binding site common for the P[II] RV genogroup and that the H1 precursor lacto-N-biose (galactose-β1,3-N-acetylglucosamine; LNB) is also bound to this pocket with diminished affinity. The P[8] VP8* structures show a marginal role for the L-fucose moiety from H1 in protein interaction. However, its presence provides conformational changes in the LNB moiety that increase the affinity of VP8* for the H1 ligand and would account for a stronger RV binding to mucosa in individuals expressing H1 (secretors). We thus offer a mechanistic explanation for the different incidence of P[8] RV infection in different secretor phenotypes.

Histo-Blood Group Antigens in Children with Symptomatic Rotavirus Infection

Group A rotaviruses are a major cause of acute gastroenteritis in children. The diversity and unequal geographical prevalence of rotavirus genotypes have been linked to histo-blood group antigens (HBGAs) in different human populations. In order to evaluate the role of HBGAs in rotavirus infections in our population, secretor status (FUT2+), ABO blood group, and Lewis antigens were determined in children attended for rotavirus gastroenteritis in Valencia, Spain. During three consecutive years (2013-2015), stool and saliva samples were collected from 133 children with rotavirus infection. Infecting viral genotypes and HBGAs were determined in patients and compared to a control group and data from blood donors. Rotavirus G9P[8] was the most prevalent strain (49.6%), followed by G1P[8] (20.3%) and G12P[8] (14.3%). Rotavirus infected predominantly secretor (99%) and Lewis b positive (91.7%) children. Children with blood group A and AB were significantly more prone to rotavirus gastroenteritis than those with blood group O. Our results confirm that a HBGA genetic background is linked to rotavirus P[8] susceptibility. Rotavirus P[8] symptomatic infection is manifestly more frequent in secretor-positive (FUT2+) than in non-secretor individuals, although no differences between rotavirus G genotypes were found.

FUT2 Genetic Variants and Reported Respiratory and Gastrointestinal Illnesses During Infancy

BACKGROUND

Fucosyltransferase 2 (FUT2) controls the production of digestive and respiratory epithelia of histo-blood group antigens involved in the attachment of pathogens. The aim of our study was to relate FUT2 variants to reported gastrointestinal and respiratory illnesses in infancy.

METHODS

In the Southampton Women's Survey, FUT2 genetic variants (single-nucleotide polymorphisms [SNPs] rs601338 and rs602662) were genotyped in 1831 infants and related to infant illnesses, after adjustment for sex, breastfeeding duration, and potential confounders.

RESULTS

For FUT2 SNP rs601338, the risk ratios for ≥1 bout of diarrhea during ages 6-12 months and ages 12-24 months per additional risk (G) allele were 1.23 (95% confidence interval [CI], 1.08-1.4; P = .002) and 1.41 (95% CI, 1.24-1.61; P = 1.7 × 10-7), respectively; the risk ratio for ≥1 diagnosis of a lower respiratory illness (ie, pneumonia or bronchiolitis) during ages 12-24 months per additional G allele was 2.66 (95% CI, 1.64-4.3; P = .00007). Similar associations were found between rs602662 and gastrointestinal and respiratory illnesses, owing to the high linkage disequilibrium with rs601338 (R2 = 0.92). Longer breastfeeding duration predicted a lower risk of diarrhea, independent of infant FUT2 genotype.

CONCLUSIONS

We confirmed that FUT2 G alleles are associated with a higher risk of infant gastrointestinal illnesses and identified novel associations with respiratory illnesses. FUT2 locus variants need consideration in future studies of gastrointestinal and respiratory illnesses among infants.

Rotavirus infection beyond the gut

The landscape of rotavirus (RV) infection has changed substantially in recent years. Autoimmune triggering has been added to clinical spectrum of this pathology, which is now known to be much broader than diarrhea. The impact of RV vaccines in these other conditions is becoming a growing field of research. The importance of host genetic background in RV susceptibility has been revealed, therefore increasing our understanding of vaccine effectiveness and giving some clues about the limited efficacy of RV vaccines in low-income settings. Also, interaction of RV with intestinal microbiota seems to play a key role in the process of infection vaccine effect. This article reviews current findings on the extraintestinal impact of RV infection and their widening clinical picture, and the recently described mechanisms of host susceptibility to infection and vaccine effectiveness. RV infection is a systemic disease with clinical and pathophysiological implications beyond the gut. We propose an “iceberg” model for this pathology with almost hidden clinical implications away from the gastrointestinal tract and eventually triggering the development of autoimmune diseases. Impact of current vaccines is being influenced by host genetics and gut microbiota interactions and these factors must be taken into account in the development of public health programs.

Glycan binding patterns of human rotavirus P[10] VP8* protein

Background

Rotaviruses (RVs) are a major cause of acute children gastroenteritis. The rotavirus P [10] belongs to P[I] genogroup of group A rotaviruses that mainly infect animals, while the rotavirus P [10] was mainly identified from human infection. The rotavirus P [10] is an unusual genotype and the recognition pattern of cellular receptors remains unclear.

Methods

We expressed and purified the RV P [10] VP8* protein and investigated the saliva and oligosaccharide binding profiles of the protein. A homology model of the P [10] VP8* core protein was built and the superimposition structural analysis of P [10] VP8* protein on P [19] VP8* in complex with mucin core 2 was performed to explore the possible docking structural basis of P [10] VP8* and mucin cores.

Results

Our data showed that rotavirus P [10] VP8* protein bound to all ABO secretor and non-secretor saliva. The rotavirus P [10] could bind strongly to mucin core 2 and weakly to mucin core 4. The homology modeling indicated that RV P [10] VP8* binds to mucin core 2 using a potential glycan binding site that is the same to P [19] VP8* belonging to P[II] genogroup.

Conclusion

Our results suggested an interaction of rotavirus P [10] VP8* protein with mucin core 2 and mucin core 4. These findings offer potential for elucidating the mechanism of RV A host specificity, evolution and epidemiology.

FUT2 secretor genotype and susceptibility to infections and chronic conditions in the ALSPAC cohort

Background: The FUT2 (fucosyltransferase-2) gene determines blood group secretor status. Being homozygous for the inactive "non-secretor" rs601338(A) allele confers resistance to certain infections (e.g. Norovirus, Rotavirus) and susceptibility to others (e.g. Haemophilus influenza, Streptococcus pneumonia). Non-secretors also have an increased risk of type 1 diabetes and inflammatory bowel disease. We examined FUT2 genotype, infections and chronic conditions in a population-based cohort. Methods: We studied 7,582 pregnant women from the ALSPAC pregnancy cohort. Infections (measles, mumps, chicken pox, whooping cough, meningitis, herpes, gonorrhea and urinary infections) and chronic conditions (kidney disease, hypertension, diabetes, rheumatism, arthritis, psoriasis, hay fever, asthma, eczema and allergies) were self-reported. FUT2 secretor status was determined from the rs601338 genotype. ABO blood type was obtained from clinical records. Results: Overall, 1920 women (25.3%) were homozygous for the non-secretor allele (AA). Secretor status was associated with mumps, with 68% of non-secretors experiencing this infection, compared to 48% of secretors (RR, 1.40; 95% CI, 1.34-1.46). A weaker association was observed for measles infection (76% vs. 72%; RR, 1.05; 95% CI, 1.02-1.09). Non-secretors also experienced an increased risk of kidney disease (5.4% vs. 3.9%; RR, 1.39; 95% CI, 1.11-1.75). Independent of secretor status, AB blood type was a risk factor for mumps (RR 1.15; 95%CI, 1.03, 1.28 compared to type O). We found no evidence of interaction between secretor status and blood type.  For some conditions, including asthma and arthritis, FUT2 heterozygosity (GA) appeared to confer an intermediate phenotype. There was no strong evidence of association between secretor status and other infections or chronic conditions, although statistical power was limited for rare outcomes. Conclusion: Our results identify an association between FUT2 secretor status and self-reported kidney disease, and confirm a recently reported association with susceptibility to mumps infection. The clinical implications of these associations warrant further investigation.

Histo-blood group antigen-binding specificities of human rotaviruses are associated with gastroenteritis but not with in vitro infection

Human strains of rotavirus A (RVAs) recognize fucosylated glycans belonging to histo-blood group antigens (HBGAs) through their spike protein VP8*. Lack of these ligands due to genetic polymorphisms is associated with resistance to gastroenteritis caused by P[8] genotype RVAs. With the aim to delineate the contribution of HBGAs in the process, we analyzed the glycan specificity of VP8* proteins from various P genotypes. Binding to saliva of VP8* from P[8] and P[4] genotypes required expression of both FUT2 and FUT3 enzymes, whilst binding of VP8* from the P[14] genotype required FUT2 and A enzymes. We further defined a glycan motif, GlcNAcβ3Galβ4GlcNAc, recognized by P[6] clinical strains. Conversion into Lewis antigens by the FUT3 enzyme impaired recognition, explaining their lower binding to saliva of Lewis positive phenotype. In addition, the presence of neutralizing antibodies was associated with the presence of the FUT2 wild type allele in sera from young healthy adults. Nonetheless, in vitro infection of transformed cell lines was independent of HBGAs expression, indicating that HBGAs are not human RV receptors. The match between results from saliva-based binding assays and the epidemiological data indicates that the polymorphism of human HBGAs controls susceptibility to RVAs, although the exact mechanism remains unclear.

Glycan recognition in globally dominant human rotaviruses

Rotaviruses (RVs) cause life-threatening diarrhea in infants and children worldwide. Recent biochemical and epidemiological studies underscore the importance of histo-blood group antigens (HBGA) as both cell attachment and susceptibility factors for the globally dominant P[4], P[6], and P[8] genotypes of human RVs. How these genotypes interact with HBGA is not known. Here, our crystal structures of P[4] and a neonate-specific P[6] VP8*s alone and in complex with H-type I HBGA reveal a unique glycan binding site that is conserved in the globally dominant genotypes and allows for the binding of ABH HBGAs, consistent with their prevalence. Remarkably, the VP8* of P[6] RVs isolated from neonates displays subtle structural changes in this binding site that may restrict its ability to bind branched glycans. This provides a structural basis for the age-restricted tropism of some P[6] RVs as developmentally regulated unbranched glycans are more abundant in the neonatal gut.

Human rotaviruses (RV) bind to histo-blood group antigens (HBGA) for attachment, but how different viral genotypes interact with HBGA isn’t known. Here, Hu et al. report crystal structures of a prevalent and a neonate-specific RV in complex with HBGA and provide insights into glycan recognition and age-restricted tropism of RVs.

FUT2 secretor genotype and susceptibility to infections and chronic conditions in the ALSPAC cohort

Background: The FUT2 (fucosyltransferase 2) gene encodes alpha (1,2) fucosyltransferase, which determines blood group secretor status. Being homozygous for the inactive "non-secretor" rs601338(A) allele appears to confer resistance to certain infections (e.g. Norovirus, Rotavirus and Helicobacter pylori) and susceptibility to others (e.g. Haemophilus influenza and Streptococcus pneumonia). Non-secretors also have an increased risk of type 1 diabetes and inflammatory bowel disease. We aimed to determine the association of the FUT2 secretor genotype with infections and chronic conditions in the population-based Avon Longitudinal Study of Parents and Children (ALSPAC). Methods: This study included 7,582 pregnant women from the ALSPAC pregnancy cohort. Personal history of infections (measles, mumps, chicken pox, whooping cough, cold sores, meningitis, genital herpes, gonorrhea and urinary infections) and chronic conditions (kidney disease, hypertension, diabetes, rheumatism, arthritis, psoriasis, hay fever, asthma, eczema and various allergies) were self-reported by standardized questionnaire. FUT2 secretor status was determined from the rs601338 genotype. Results: Overall, 1920 women (25.3%) were homozygous for the FUT2 non-secretor allele (AA). Secretor status was associated with mumps, with 68% of non-secretors experiencing this infection, compared to 48% of secretors (RR, 1.40; 95% CI, 1.34-1.46; p<0.0001). A weaker association was observed for measles infection (76% vs. 72%; RR, 1.05; 95% CI, 1.02-1.09; p=0.0008). Non-secretors also experienced a 39% increased risk of kidney disease (5.4% vs. 3.9%; RR, 1.39; 95% CI, 1.11-1.75; p=0.004). For some conditions, including gonorrhea and arthritis, FUT2 heterozygosity (GA) appeared to confer an intermediate phenotype. There was no strong evidence of association between FUT2 secretor status and other infections or chronic conditions, although statistical power was limited for rare outcomes. Conclusion: Our results identify an association between FUT2 secretor status and kidney disease, and confirm a recently reported association with susceptibility to mumps infection. The clinical implications of these associations warrant further investigation.

Human Milk Oligosaccharides as Promising Antivirals

Human milk oligosaccharides (HMOs) are diverse unconjugated carbohydrates that are highly abundant in human breast milk. These glycans are investigated in the context of exhibiting multiple functions in infant growth and development. They seem to provide protection against infectious diseases, including a number of poorly manageable viral infections. Although the potential mechanism of the HMO antiviral protection is rather broad, much of the current experimental work has focused on studying of HMO antiadhesive properties. HMOs may mimic structures of viral receptors and block adherence to target cells, thus preventing infection. Still, the potential of HMOs as a source for new antiviral drugs is relatively unexploited. This can be partly attributed to the extreme complexity of the virus-carbohydrate interactions and technical difficulties in HMO isolation, characterization, and manufacturing procedures. Fortunately, we are currently entering a period of major technological advances that have enabled deeper insights into carbohydrate mediated viral entry, rational selection of HMOs as anti-entry inhibitors, and even evaluation of individual synthetic HMO structures. Here, we provide an up-to-date review on glycan binding studies for rotaviruses, noroviruses, influenza viruses, and human immunodeficiency viruses. We also discuss the preventive and therapeutic potential of HMOs as anti-entry inhibitors and address challenges on the route from fundamental studies to clinical trials.

Infection's Sweet Tooth: How Glycans Mediate Infection and Disease Susceptibility

Glycans form a highly variable constituent of our mucosal surfaces and profoundly affect our susceptibility to infection and disease. The diversity and importance of these surface glycans can be seen in individuals who lack a functional copy of the fucosyltransferase gene, FUT2. Representing around one-fifth of the population, these individuals have an altered susceptibility to many bacterial and viral infections and diseases. The mediation of host-pathogen interactions by mucosal glycans, such as those added by FUT2, is poorly understood. We highlight, with specific examples, important mechanisms by which host glycans influence infection dynamics, including by: acting as pathogen receptors (or receptor-decoys), promoting microbial stability, altering the physical characteristics of mucus, and acting as immunological markers. We argue that the effect glycans have on infection dynamics has profound implications for many aspects of healthcare and policy, including clinical management, outbreak control, and vaccination policy.

Association analysis of the SNP (rs345476947) in the FUT2 gene with the production and reproductive traits in pigs

The FUT2 gene was considered as an important candidate for pathogenic infections, while the potential associations between this gene and the production and reproductive traits of pigs have not been explored. In this study, we detected the genetic variants of porcine FUT2 gene and analyzed the associations of the polymorphisms with FUT2 mRNA expression and production and reproductive traits (age at 100 kg, backfat thickness at 100 kg, eye muscle thickness, the number of newborn piglets, the number of weaned piglets, and birth weight) in 100 Large White sows. One single nucleotide polymorphism (SNP) (rs345476947, C→T) in the intron of FUT2 and three genotypes (TT, CT and CC) were determined. Association analysis revealed significant associations between this SNP with the number of newborn piglets and weaned piglets. Furthermore, individuals with the TT genotype had significantly higher numbers of newborn piglets and weaned piglets than those with the CC genotype (P < 0.05). Quantitative PCR analysis showed that FUT2 expression in individuals with CC genotype was significantly higher than those with TT and CT genotypes in the liver and lymph gland (P < 0.05) and higher than that of CT in the spleen, kidney, and duodenum (P < 0.05). These findings indicated that the TT genotype may be a favorable genotype for the reproductive traits of pigs. Our study revealed the genetic variants of the FUT2 gene and identified a promising candidate SNP (rs345476947) associated with the reproductive traits, which has the potential to be applied in selective breeding of pigs.

The Lewis A phenotype is a restriction factor for Rotateq and Rotarix vaccine-take in Nicaraguan children

Histo-blood group antigens (HBGAs) and the Lewis and secretor antigens are associated with susceptibility to rotavirus infection in a genotype-dependent manner. Nicaraguan children were prospectively enrolled in two cohorts vaccinated with either RotaTeq RV5 (n = 68) or Rotarix RV1 (n = 168). Lewis and secretor antigens were determined by saliva phenotyping and genotyping. Seroconversion was defined as a 4-fold increase in plasma IgA antibody titer 1 month after administration of the first dose of the vaccine. Regardless of the vaccine administered, significantly fewer of the children with Lewis A phenotype (0/14) seroconverted after receiving the first vaccine dose compared to 26% (45/175) of those with the Lewis B phenotype and 32% (15/47) of the Lewis negative individuals (P < 0.01). Furthermore, following administration of the RV1 vaccine, secretor-positive ABO blood group B children seroconverted to a significantly lesser extent (5%) compared to secretor-positive children with ABO blood groups A (26%) and O (27%) (P < 0.05). Other factors such as pre-vaccination titers, sex, breastfeeding, and calprotectin levels did not influence vaccine-take. Differences in HBGA expression appear to be a contributing factor in the discrepancy in vaccine-take and thus, in vaccine efficacy in different ethnic populations.

Decreased performance of live attenuated, oral rotavirus vaccines in low-income settings: causes and contributing factors

INTRODUCTION

Numerous studies have shown that the oral rotavirus vaccines are less effective in infants born in low income countries compared to those born in developed countries. Identifying the specific factors in developing countries that decrease and/or compromise the protection that rotavirus vaccines offer, could lead to a path for designing new strategies for the vaccines' improvement.

AREAS COVERED

We accessed PubMed to identify rotavirus vaccine performance studies (i.e., efficacy, effectiveness and immunogenicity) and correlated performance with several risk factors. Here, we review the factors that might contribute to the low vaccine efficacy, including passive transfer of maternal rotavirus antibodies, rotavirus seasonality, oral polio vaccine (OPV) administered concurrently, microbiome composition and concomitant enteric pathogens, malnutrition, environmental enteropathy, HIV, and histo blood group antigens.

EXPERT COMMENTARY

We highlight two major factors that compromise rotavirus vaccines' efficacy: the passive transfer of rotavirus IgG antibodies to infants and the  co-administration of rotavirus vaccines with OPV. We also identify other potential risk factors that require further research because the data about their interference with the efficacy of rotavirus vaccines are inconclusive and at times conflicting.

Differences of Rotavirus Vaccine Effectiveness by Country: Likely Causes and Contributing Factors

Rotaviruses are a major cause of acute gastroenteritis in infants and young children worldwide and in many other mammalian and avian host species. Since 2006, two live-attenuated rotavirus vaccines, Rotarix^® and RotaTeq^®, have been licensed in >100 countries and are applied as part of extended program of vaccination (EPI) schemes of childhood vaccinations. Whereas the vaccines have been highly effective in high-income countries, they were shown to be considerably less potent in low- and middle-income countries. Rotavirus-associated disease was still the cause of death in >200,000 children of <5 years of age worldwide in 2013, and the mortality is concentrated in countries of sub-Saharan Africa and S.E. Asia. Various factors that have been identified or suggested as being involved in the differences of rotavirus vaccine effectiveness are reviewed here. Recognition of these factors will help to achieve gradual worldwide improvement of rotavirus vaccine effectiveness.

Genetic susceptibility to infectious diseases: Current status and future perspectives from genome-wide approaches

Genome-wide association studies (GWASs) have been widely applied to identify genetic factors that affect complex diseases or traits. Presently, the GWAS Catalog includes > 2800 human studies. Of these, only a minority have investigated the susceptibility to infectious diseases or the response to therapies for the treatment or prevention of infections. Despite their limited application in the field, GWASs have provided valuable insights by pinpointing associations to both innate and adaptive immune response loci, as well as novel unexpected risk factors for infection susceptibility. Herein, we discuss some issues and caveats of GWASs for infectious diseases, we review the most recent findings ensuing from these studies, and we provide a brief summary of selected GWASs for infections in non-human mammals. We conclude that, although the general trend in the field of complex traits is to shift from GWAS to next-generation sequencing, important knowledge on infectious disease-related traits can be still gained by GWASs, especially for those conditions that have never been investigated using this approach. We suggest that future studies will benefit from the leveraging of information from the host's and pathogen's genomes, as well as from the exploration of models that incorporate heterogeneity across populations and phenotypes. Interactions within HLA genes or among HLA variants and polymorphisms located outside the major histocompatibility complex may also play an important role in shaping the susceptibility and response to invading pathogens.

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Relatively few GWASs for infectious diseases were performed.

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Phenotype heterogeneity and case/control misclassification can affect GWAS power.

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Adaptive and innate immunity loci were identified in several infectious disease GWASs.

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Unexpected loci (e.g., lncRNAs) were also associated with infection susceptibility.

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GWASs should integrate host and pathogen diversity and use complex association models.

Detecting signatures of past pathogen selection on human HLA loci: are there needles in the haystack?

Human leucocyte antigens (HLAs) are responsible for the display of peptide fragments for recognition by T-cell receptors. The gene family encoding them is thus integral to human adaptive immunity, and likely to be under strong pathogen selection. Despite this, it has proved difficult to demonstrate specific examples of pathogen-HLA coevolution. Selection from multiple pathogens simultaneously could explain why the evolutionary signatures of particular pathogens on HLAs have proved elusive. Here, we present an individual-based model of HLA evolution in the presence of two mortality-causing pathogens. We demonstrate that it is likely that individual pathogen species causing high mortality have left recognizable signatures on the HLA genomic region, despite more than one pathogen being present. Such signatures are likely to exist at the whole-population level, and involve haplotypic combinations of HLA genes rather than single loci.

Genetic Susceptibility to Rotavirus Gastroenteritis and Vaccine Effectiveness in Taiwanese Children

The genetic susceptibility to and vaccine effectiveness against rotavirus gastroenteritis were different in distinct ethnic groups. The case-control study was aimed to evaluate the effectiveness of rotavirus vaccines and associations between the histo-blood group antigens and susceptibility to rotavirus infections in a Taiwanese population. Cases were children <18 years old who were hospitalized because of laboratory-confirmed rotavirus infection. Controls were healthy children matched to cases by age and gender. The secretor status and Lewis antigen and ABO types were determined by molecular methods. A total of 68 cases and 133 controls were included. Rotavirus immunization was recorded in 8 (12%) cases and 77 (58%) controls, indicating a vaccine effectiveness of 90.3% (95% confidence interval [CI], 78.1% - 95.7%). The secretor and Lewis-positive genotypes were independently associated with increased risk of rotavirus infections (matched odds ratio [mOR] 28.5, 95% CI 2.94-277, P = 0.003 and mOR 16.8, 95% CI 1.08-2601, P = 0.04, respectively). The distribution of ABO blood types did not differ significantly between cases and controls (P = 0.47). In conclusion, Taiwanese children with the secretor genotype and Lewis-positive genotype were at increased risk of moderate-to-severe rotavirus infections. The illness can be effectively prevented by immunization in this population.

Secretor and Salivary ABO Blood Group Antigen Status Predict Rotavirus Vaccine Take in Infants

Histo-blood group antigens (HBGAs) expressed on enterocytes are proposed receptors for rotaviruses and can be measured in saliva. Among 181 Pakistani infants in a G1P[8] rotavirus vaccine trial who were seronegative at baseline, anti-rotavirus immunoglobulin A seroconversion rates after 3 vaccine doses differed significantly by salivary HBGA phenotype, with the lowest rate (19%) among infants who were nonsecretors (ie, who did not express the carbohydrate synthesized by FUT2), an intermediate rate (30%) among secretors with non-blood group O, and the highest rate (51%) among secretors with O blood group. Differences in HBGA expression may be responsible for some of the discrepancy in the level of protection detected for the current rotavirus vaccines in low-income versus high-income settings.

Histo-blood group antigens as receptors for rotavirus, new understanding on rotavirus epidemiology and vaccine strategy

The success of the two rotavirus (RV) vaccines (Rotarix and RotaTeq) in many countries endorses a live attenuated vaccine approach against RVs. However, the lower efficacies of both vaccines in many low- and middle-income countries indicate a need to improve the current RV vaccines. The recent discovery that RVs recognize histo-blood group antigens (HBGAs) as potential receptors has significantly advanced our understanding of RV diversity, evolution and epidemiology, providing important new insights into the performances of current RV vaccines in different populations and emphasizing a P-type-based vaccine approach. New understanding of RV diversity and evolution also raises a fundamental question about the ‘Jennerian' approach, which needs to be addressed for future development of live attenuated RV vaccines. Alternative approaches to develop safer and more cost-effective subunit vaccines against RVs are also discussed.

FUT2 genotype influences lung function, exacerbation frequency and airway microbiota in non-CF bronchiectasis

OBJECTIVE

To assess whether FUT2 (secretor) genotype affects disease severity and airway infection in patients with non-cystic fibrosis bronchiectasis.

PARTICIPANTS

Induced sputum samples were obtained from 112 adult patients with high-resolution CT scan-proven bronchiectasis and at least two exacerbations in the previous year, as part of an unrelated randomised control trial.

OUTCOME MEASURES

Presence of null FUT2 polymorphisms were determined by gene sequencing and verified by endobronchial biopsy histochemical staining. Outcome measures were FEV1% predicted, exacerbation frequency, and bacterial, fungal and viral components of the microbiota (measured by culture independent approaches).

RESULTS

Patients were grouped by FUT2 loss-of-function genotype; categorised as non-secretors (n=27, sese), heterozygous secretors (n=54, Sese) or homozygous secretors (n=31, SeSe). FEV1% was significantly lower in SeSe patients compared with sese patients (mean 61.6 (SD 20.0) vs 74.5 (18.0); p=0.023). Exacerbation frequency was significantly higher in SeSe (mean count 5.77) compared with sese (4.07; p=0.004) and Sese (4.63; p=0.026) genotypes. The time until first exacerbation was significantly shorter in SeSe compared with Sese (HR=0.571 (95% CI 0.343 to 0.950); p=0.031), with a similar trend for sese patients (HR=0.577 (0.311 to 1.07); p=0.081). sese had a significantly reduced frequency of Pseudomonas aeruginosa-dominated airway infection (8.7%) compared with Sese (31%; p=0.042) and SeSe (36%; p=0.035). In contrast, fungal, viral and non-dominant bacterial components of the microbiome were not significantly different between FUT2 genotypes.

CONCLUSIONS

FUT2 genotype in patients with non-cystic fibrosis bronchiectasis was significantly associated with disease outcomes, with homozygous secretors exhibiting lower lung function, higher exacerbation number and a higher frequency of P. aeruginosa-dominated infection.

TRIAL REGISTRATION NUMBER

ACTRN12609000578202 (anzctr.org.au); Pre-results.

Genetic Susceptibility to Norovirus GII.4 Sydney Strain Infections in Taiwanese Children

BACKGROUND

A comprehensive evaluation of associations between the susceptibility to norovirus infections and histo-blood group antigens is not available in the Taiwanese population, in which the nonsecretor phenotype is absent.

METHODS

A 1:1 matched case-control study was conducted in northern Taiwan from February 2013 to December 2014 when an epidemic of norovirus infection occurred. Cases were children <18 years old who were hospitalized because of diarrhea and were found to have laboratory-confirmed norovirus infections. Controls were healthy children matched to the cases by age and gender. The norovirus genotype was determined by polymerase chain reaction sequencing of the VP1 gene. The secretor status, Lewis antigen and ABO type were determined by characterization of genetic polymorphisms in the FUT2, FUT3 and ABO genes, respectively.

RESULTS

A total of 147 case-control pairs were included. GII.4 Sydney strain was the major genotype and identified in 78.3% of the cases. The weak-secretor and Lewis-positive genotypes were less commonly identified in cases than in controls (5.4% vs. 23.1% and 79.6% vs. 89.8%, respectively). Multivariate analysis revealed that the secretor and Lewis-negative genotypes were both independent factors associated with increased risk of norovirus infections [matched odds ratio: 6.766, 95% confidence interval (CI): 2.649-17.285, P < 0.0001 and matched odds ratio: 3.071, 95% confidence interval [CI]: 1.322-7.084, P = 0.0085, respectively]. The ABO types were not significantly related to norovirus infections (P > 0.05).

CONCLUSION

The weak-secretor genotype and the Lewis antigen-positive genotype were both protective factors against severe norovirus gastroenteritis during the GII.4 Sydney strain epidemic in Taiwan.

Relevance of secretor status genotype and microbiota composition in susceptibility to rotavirus and norovirus infections in humans

Host genetic factors, such as histo-blood group antigens (HBGAs), are associated with susceptibility to norovirus (NoV) and rotavirus (RV) infections. Recent advances point to the gut microbiome as a key player necessary for a viral pathogen to cause infection. In vitro NoV attachment to host cells and resulting infections have been linked to interactions with certain bacterial types in the gut microbiota. We investigated the relationship between host genotype, gut microbiota, and viral infections. Saliva and fecal samples from 35 adult volunteers were analysed for secretor status genotype, the gut microbiota composition by 16S rRNA gene sequencing, and salivary IgA titers to NoV and RV. Higher levels of IgA against NoV and RV were related to secretor-positive status. No significant differences were found between the FUT2 genotype groups, although the multivariate analysis showed a significant impact of host genotype on specific viral susceptibilities in the microbiome composition. A specific link was found between the abundance of certain bacterial groups, such as Faecalibacterium and Ruminococcus spp., and lower IgA titers against NoV and RV. As a conclusion, we can state that there is a link between host genetics, gut microbiota, and susceptibility to viral infections in humans.

Acute Gastroenteritis Viruses

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Acute diarrhea is the leading cause of morbidity and second commonest cause of mortality in children <5 years old worldwide.

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Most acute diarrheal illnesses are caused by viruses.

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Noroviruses are the commonest cause of diarrhea in all age groups combined, and rotaviruses are still the leading cause of diarrhea for children <5 years old.

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Transmission is mainly by the fecal–oral route through person-to-person contact, contaminated food and water.

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Most cases of viral diarrhea are mild and self-limiting, but severe cases occur, leading to dehydration and death. Repeated episodes lead to malnutrition.

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Most cases can be managed at home with oral rehydration solutions and feeding a regular diet.

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Vaccines will be the best preventive measure. Only rotavirus vaccines are available.

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Breast-feeding, vitamin A supplementation and zinc significantly reduce the frequency and/or severity of diarrhea.

Shedding of porcine circovirus type 1 DNA and rotavirus RNA by infants vaccinated with Rotarix®

Thirty-three infants aged ∼2 months had serial stool samples collected after receipt of Rotarix® vaccine dose 1, and were assessed for shedding of porcine circovirus type 1 DNA and Rotavirus group A RNA by molecular methods. We did not find strong evidence that porcine circovirus type 1 replication occurred. Porcine circovirus type 1 genome with the same sequence as that in Rotarix® was detected in a few infants as late as day ≥ 13; while this timing could suggest there may have been replication and not just transient passage through the gastrointestinal tract, the lack of increase in copy number in any infant supports transient passage and there are inherent limitations to the results. We found that 21% of infants did not shed Rotarix® RVA RNA beyond the day 3 sample, which may suggest lack of vaccine virus replication. Of the infants in whom Rotarix RVA RNA shedding continued, peak copy numbers were reached on days 3-5 for ∼40%, and after day 5 in ∼60%, and shedding can be prolonged (≥ 45 days).

Epithelial glycosylation in gut homeostasis and inflammation

Intestinal epithelial cells apically express glycans, especially α1,2-fucosyl linkages, which work as a biological interface for the host-microbe interaction. Emerging studies have shown that epithelial α1,2-fucosylation is regulated by microbes and by group 3 innate lymphoid cells (ILC3s). Dysregulation of the gene (FUT2) encoding fucosyltransferase 2, an enzyme governing epithelial α1,2-fucosylation, is associated with various human disorders, including infection and chronic inflammatory diseases. This suggests a critical role for an interaction between microbes, epithelial cells and ILC3s mediated via glycan residues. In this Review, using α1,2-fucose and Fut2 gene expression as an example, we describe how epithelial glycosylation is controlled by immune cells and luminal microbes. We also address the pathophysiological contribution of epithelial α1,2-fucosylation to pathogenic and commensal microbes as well as the potential of α1,2-fucose and its regulatory pathway as previously unexploited targets in the development of new therapeutic approaches for human diseases.

Glycan Specificity of P[19] Rotavirus and Comparison with Those of Related P Genotypes

The P[19] genotype belongs to the P[II] genogroup of group A rotaviruses (RVs). However, unlike the other P[II] RVs, which mainly infect humans, P[19] RVs commonly infect animals (pigs), making P[19] unique for the study of RV diversity and host ranges. Through in vitro binding assays and saturation transfer difference (STD) nuclear magnetic resonance (NMR), we found that P[19] could bind mucin cores 2, 4, and 6, as well as type 1 histo-blood group antigens (HBGAs). The common sequences of these glycans serve as minimal binding units, while additional residues, such as the A, B, H, and Lewis epitopes of the type 1 HBGAs, can further define the binding outcomes and therefore likely the host ranges for P[19] RVs. This complex binding property of P[19] is shared with the other three P[II] RVs (P[4], P[6], and P[8]) in that all of them recognized the type 1 HBGA precursor, although P[4] and P[8], but not P[6], also bind to mucin cores. Moreover, while essential for P[4] and P[8] binding, the addition of the Lewis epitope blocked P[6] and P[19] binding to type 1 HBGAs. Chemical-shift NMR of P[19] VP8* identified a ligand binding interface that has shifted away from the known RV P-genotype binding sites but is conserved among all P[II] RVs and two P[I] RVs (P[10] and P[12]), suggesting an evolutionary connection among these human and animal RVs. Taken together, these data are important for hypotheses on potential mechanisms for RV diversity, host ranges, and cross-species transmission.

IMPORTANCE In this study, we found that our P[19] strain and other P[II] RVs recognize mucin cores and the type 1 HBGA precursors as the minimal functional units and that additional saccharides adjacent to these units can alter binding outcomes and thereby possibly host ranges. These data may help to explain why some P[II] RVs, such as P[6] and P[19], commonly infect animals but rarely humans, while others, such as the P[4] and P[8] RVs, mainly infect humans and are predominant over other P genotypes. Elucidation of the molecular bases for strain-specific host ranges and cross-species transmission of these human and animal RVs is important to understand RV epidemiology and disease burden, which may impact development of control and prevention strategies against RV gastroenteritis.

Functional and Structural Characterization of P[19] Rotavirus VP8* Interaction with Histo-blood Group Antigens

Rotaviruses (RVs) of species A (RVA) are a major causative agent of acute gastroenteritis. Recently, histo-blood group antigens (HBGAs) have been reported to interact with human RVA VP8* proteins. Human P[19] is a rare P genotype of porcine origin that infects humans sporadically. The functional and structural characteristics of P[19] VP8* interaction with HBGAs are unknown. In this study, we expressed and purified the VP8* proteins of human and porcine P[19] RVs. In oligosaccharide and saliva binding assays, P[19] VP8* proteins showed obvious binding to A-, B-, and O-type saliva samples irrespective of the secretor status, implying broad binding patterns. However, they did not display specific binding to any of the oligosaccharides tested. In addition, we solved the structure of human P[19] VP8* at 2.4 Å, which revealed a typical galectin-like fold. The structural alignment demonstrated that P[19] VP8* was most similar to that of P[8], which was consistent with the phylogenetic analysis. Structure superimposition revealed the basis for the lack of binding to the oligosaccharides. Our study indicates that P[19] RVs may bind to other oligosaccharides or ligands and may have the potential to spread widely among humans. Thus, it is necessary to place the prevalence and evolution of P[19] RVs under surveillance.

IMPORTANCE

Human P[19] is a rare P genotype of porcine origin. Based on phylogenetic analysis of VP8* sequences, P[19] was classified in the P[II] genogroup, together with P[4], P[6], and P[8], which have been reported to interact with HBGAs in a genotype-dependent manner. In this study, we explored the functional and structural characteristics of P[19] VP8* interaction with HBGAs. P[19] VP8* showed binding to A-, B-, and O-type saliva samples, as well as saliva of nonsecretors. This implies that P[19] has the potential to spread among humans with a broad binding range. Careful attention should be paid to the evolution and prevalence of P[19] RVs. Furthermore, we solved the structure of P[19] VP8*. Structure superimposition indicated that P[19] may bind to other oligosaccharides or ligands using potential binding sites, suggesting that further investigation of the specific cell attachment factors is warranted.

P[8] and P[4] Rotavirus Infection Associated with Secretor Phenotypes Among Children in South China

Rotaviruses are known to recognize human histo-blood group antigens (HBGAs) as a host ligand that is believed to play an important role in rotavirus host susceptibility and host range. In this study, paired fecal and saliva samples collected from children with viral gastroenteritis, as well as paired serum and saliva samples collected from the general population in south China were studied to evaluate potential association between rotavirus infections and human HBGA phenotypes. Rotavirus was detected in 75 (28%) of 266 fecal samples and P[8] rotaviruses were found to be the predominant genotype. The HBGA phenotypes of the rotavirus-infected children were determined through their saliva samples. Secretor statuses were found to correlate with the risk of rotavirus infection and all P[8]/P[4] rotavirus infected children were secretors. Accordingly, recombinant VP8* proteins of the P[8]/P[4] rotaviruses bound saliva samples from secretor individuals. Furthermore, correlation between serum P[8]/P[4]-specific IgG and host Lewis and secretor phenotypes has been found among 206 studied serum samples. Our study supported the association between rotavirus infection and the host HBGA phenotypes, which would help further understanding of rotavirus host range and epidemiology.

A genome-wide association meta-analysis of diarrhoeal disease in young children identifies FUT2 locus and provides plausible biological pathways

More than a million childhood diarrhoeal episodes occur worldwide each year, and in developed countries a considerable part of them are caused by viral infections. In this study, we aimed to search for genetic variants associated with diarrhoeal disease in young children by meta-analyzing genome-wide association studies, and to elucidate plausible biological mechanisms. The study was conducted in the context of the Early Genetics and Lifecourse Epidemiology (EAGLE) consortium. Data about diarrhoeal disease in two time windows (around 1 year of age and around 2 years of age) was obtained via parental questionnaires, doctor interviews or medical records. Standard quality control and statistical tests were applied to the 1000 Genomes imputed genotypic data. The meta-analysis (N = 5758) followed by replication (N = 3784) identified a genome-wide significant association between rs8111874 and diarrhoea at age 1 year. Conditional analysis suggested that the causal variant could be rs601338 (W154X) in the FUT2 gene. Children with the A allele, which results in a truncated FUT2 protein, had lower risk of diarrhoea. FUT2 participates in the production of histo-blood group antigens and has previously been implicated in the susceptibility to infections, including Rotavirus and Norovirus Gene-set enrichment analysis suggested pathways related to the histo-blood group antigen production, and the regulation of ion transport and blood pressure. Among others, the gastrointestinal tract, and the immune and neuro-secretory systems were detected as relevant organs. In summary, this genome-wide association meta-analysis suggests the implication of the FUT2 gene in diarrhoeal disease in young children from the general population.

Rotavirus infection and histo-blood group antigens in the children hospitalized with diarrhoea in China

To explore the association between rotavirus (RV) infection and histo-blood group antigens (HBGAs), a cross-sectional study was conducted in children hospitalized with diarrhoea in China from November 2014 to February 2015. In total, 424 sets of stool, saliva and buccal cell samples were collected. For the 125 RV-negative samples, 92% (104/125) were secretors/partial secretors, 8% (10/125) were non-secretors. Among the 299 RV-positive samples, 277 were P[8] and 22 were P[4]. All P[4] and P[8] positive individuals were secretors/partial secretors except for one P[8] (0.3%, 1/299), which was a non-secretor. These findings indicate that P[8] and P[4] RVs preferably infect secretors/partial secretors (p <0.001).

Rotavirus P[8] Infections in Persons with Secretor and Nonsecretor Phenotypes, Tunisia

To determine whether rotavirus infections are linked to secretor status, we studied samples from children in Tunisia with gastroenteritis. We phenotyped saliva for human blood group antigens and tested feces for rotavirus. Rotavirus was detected in 32/114 patients. Secretor genotyping showed that P[8] rotavirus infected secretors and nonsecretors, and infection correlated with presence of Lewis antigen.

Development and evaluation of two subunit vaccine candidates containing antigens of hepatitis E virus, rotavirus, and astrovirus

Hepatitis E virus (HEV), rotavirus (RV), and astrovirus (AstV) are important pathogens that transmit through a common fecal-oral route, causing hepatitis (HEV) and gastroenteritis (RV and AstV) respectively in humans. In this study, we developed and evaluated two subunit vaccine candidates that consisted of the same protruding or spike protein antigens of the three viruses in two formats, a fusion of the three antigens into one molecule (fused vaccine) vs. a mixture of the three free antigens together (mixed vaccine). Both vaccines were easily made via E. coli expression system. Mouse immunization experiments showed that the fused vaccine elicited significantly higher antibody responses against the three viral antigens than those induced by the mixed vaccine. In addition, the mouse post-immune antisera of the fused vaccine revealed significantly higher neutralizing titers against HEV infection in cell culture, as well as significantly higher 50% blocking titers (BT50) against RV VP8-HBGA receptor interactions than those of the post-immune antisera after immunization of the mixed vaccine. Thus, the fused vaccine is a promising trivalent vaccine candidate against HEV, RV, and AstV, which is worth for further development.

Epidemiology of rotavirus A diarrhea in Chókwè, Southern Mozambique, from February to September, 2011

Acute diarrhea disease caused by Rotaviruses A (RVA) is still the leading cause of morbidity and mortality in children ≤5 years old in developing countries. An exploratory cross-sectional study was conducted between February and September, 2011 to determine the proportion of acute diarrhea caused by RVA. A total of 254 stool specimens were collected from children ≤5 years old with acute diarrhea, including outpatients (222 children) and inpatients (32 children), in three local health centers in Chókwè District, Gaza Province, South of Mozambique. RVA antigens were detected using enzyme immunoassay (EIA); the RVA G (VP7) and P (VP4) genotypes were determined by RT-PCR or analysis sequencing. Sixty (24%) out of 254 fecal specimens were positive for RVA by EIA; being 58 (97%) from children ≤2 years of age. RVA prevalence peaks in June and July (coldest and drier months) and the G[P] binary combination observed were G12P[8] (57%); G1P[8] (9%); G12P[6] (6%); and 2% for each of the following genotypes: G1P[6], G2P[6] G4P[6], and G9P[8]. Non-Typeable (NT) G and/or P genotypes were observed as follows: G12P [NT] (6%); G1P [NT], G3P[NT] and GNTP[NT] (4%). Considering the different GP combinations, G12 represented 67% of the genotypes. This is the first data showing the diversity of RVA genotypes in Mozambique highlighting the epidemiological importance of these viruses in acute diarrhea cases in children ≤2 years old. In addition, these findings will provide a baseline data before the introduction of the RVA monovalent (Rotarix(®) ) vaccine in the National Immunization Program in September 2015. J. Med. Virol. 88:1751-1758, 2016. © 2016 Wiley Periodicals, Inc.

Diversity in Rotavirus-Host Glycan Interactions: A "Sweet" Spectrum

Interaction with cellular glycans is a critical initial step in the pathogenesis of many infectious agents. Technological advances in glycobiology have expanded the repertoire of studies delineating host glycan-pathogen interactions. For rotavirus, the VP8* domain of the outer capsid spike protein VP4 is known to interact with cellular glycans. Sialic acid was considered the key cellular attachment factor for rotaviruses for decades. Although this is true for many rotavirus strains causing infections in animals, glycan array screens show that many human rotavirus strains bind nonsialylated glycoconjugates, called histo-blood group antigens, in a strain-specific manner. The expression of histo-blood group antigens is determined genetically and is regulated developmentally. Variations in glycan binding between different rotavirus strains are biologically relevant and provide new insights into multiple aspects of virus pathogenesis such as interspecies transmission, host range restriction, and tissue tropism. The genetics of glycan expression may affect susceptibility to different rotavirus strains and vaccine viruses, and impact the efficacy of rotavirus vaccination in different populations. A multidisciplinary approach to understanding rotavirus-host glycan interactions provides molecular insights into the interaction between microbial pathogens and glycans, and opens up new avenues to translate findings from the bench to the human population.

The gut microbiota and inflammatory bowel disease

PURPOSE OF REVIEW

Inflammatory bowel diseases (IBDs) reflect the cooperative influence of numerous host and environmental factors, including those of elements of the intestinal immune system, the gut microbiota, and dietary habits. This review focuses on features of the gut microbiota and mucosal immune system that are important in the development and control of IBDs.

RECENT FINDINGS

Gut innate-type immune cells, including dendritic cells, innate lymphoid cells, and mast cells, educate acquired-type immune cells and intestinal epithelial cells to achieve a symbiotic relationship with commensal bacteria. However, perturbation of the number or type of commensal microorganisms and endogenous genetic polymorphisms that affect immune responses and epithelial barrier system can ultimately lead to IBDs. Providing beneficial bacteria or fecal microbiota transplants helps to reestablish the intestinal environment, maintain its homeostasis, and ameliorate IBDs.

SUMMARY

The gut immune system participates in a symbiotic milieu that includes cohabiting commensal bacteria. However, dysbiotic conditions and aberrations in the epithelial barrier and gut immune system can disrupt the mutualistic relationship between the host and gut microbiota, leading to IBDs. Progress in our molecular and cellular understanding of this relationship has yielded numerous insights regarding clinical applications for the treatment of IBDs.

Infection models of human norovirus: challenges and recent progress

Human norovirus (hNoV) infections cause acute gastroenteritis, accounting for millions of disease cases and more than 200,000 deaths annually. However, the lack of in vitro infection models and robust small-animal models has posed barriers to the development of virus-specific therapies and preventive vaccines. Promising recent progress in the development of a norovirus infection model is reviewed in this article, as well as attempts and efforts made since the discovery of hNoV more than 40 years ago. Because suitable experimental animal models for human norovirus are lacking, attractive alternatives are also discussed.

Association of elevated rotavirus-specific antibody titers with HBGA secretor status in Swedish individuals: The FUT2 gene as a putative susceptibility determinant for infection

The histo-blood group antigens (HBGAs) have recently been suggested to serve as attachment factors for rotavirus VP8* (P-genotype) in vitro and associated with susceptibility in vivo. We thus investigated whether rotavirus antibody titers and genotype specific neutralization titers correlate with HBGA status in Swedish individuals. We investigated the effect of inactivating mutations in the secretor FUT2 (rs601338) and Lewis FUT3 genes (rs28362459, rs3894326, rs812936 and rs778986) on serum IgG antibody titers and neutralizing antibody titers to rotavirus strains of the P[8] and P[6] genotypes in Swedish healthy blood donors and patients with IgA deficiency using genotyping, enzyme linked immunosorbent assay and a neutralization assay. Rotavirus-specific serum IgG and neutralizing antibody titers to the Wa strain (G1P[8]), but not to the ST3 (G4P[6]) strain, were significantly higher in secretors (with at least one functional FUT2 gene) than in non-secretors (P<0.001) (with homozygous nonsense mutation in the FUT2 gene). Thus, our results represent that secretors show elevated rotavirus specific serum antibodies, suggesting a higher susceptibility to rotavirus infections, as compared to non-secretors in Sweden.

The human milk oligosaccharide 2'-fucosyllactose modulates CD14 expression in human enterocytes, thereby attenuating LPS-induced inflammation

BACKGROUND

A major cause of enteric infection, Gram-negative pathogenic bacteria activate mucosal inflammation through lipopolysaccharide (LPS) binding to intestinal toll-like receptor 4 (TLR4). Breast feeding lowers risk of disease, and human milk modulates inflammation.

OBJECTIVE

This study tested whether human milk oligosaccharides (HMOSs) influence pathogenic Escherichia coli-induced interleukin (IL)-8 release by intestinal epithelial cells (IECs), identified specific proinflammatory signalling molecules modulated by HMOSs, specified the active HMOS and determined its mechanism of action.

METHODS

Models of inflammation were IECs invaded by type 1 pili enterotoxigenic E. coli (ETEC) in vitro: T84 modelled mature, and H4 modelled immature IECs. LPS-induced signalling molecules co-varying with IL-8 release in the presence or absence of HMOSs were identified. Knockdown and overexpression verified signalling mediators. The oligosaccharide responsible for altered signalling was identified.

RESULTS

HMOSs attenuated LPS-dependent induction of IL-8 caused by ETEC, uropathogenic E. coli, and adherent-invasive E. coli (AIEC) infection, and suppressed CD14 transcription and translation. CD14 knockdown recapitulated HMOS-induced attenuation. Overexpression of CD14 increased the inflammatory response to ETEC and sensitivity to inhibition by HMOSs. 2'-fucosyllactose (2'-FL), at milk concentrations, displayed equivalent ability as total HMOSs to suppress CD14 expression, and protected AIEC-infected mice.

CONCLUSIONS

HMOSs and 2'-FL directly inhibit LPS-mediated inflammation during ETEC invasion of T84 and H4 IECs through attenuation of CD14 induction. CD14 expression mediates LPS-TLR4 stimulation of portions of the 'macrophage migration inhibitory factors' inflammatory pathway via suppressors of cytokine signalling 2/signal transducer and activator of transcription 3/NF-κB. HMOS direct inhibition of inflammation supports its functioning as an innate immune system whereby the mother protects her vulnerable neonate through her milk. 2'-FL, a principal HMOS, quenches inflammatory signalling.

Epidemiologic Association Between FUT2 Secretor Status and Severe Rotavirus Gastroenteritis in Children in the United States

IMPORTANCE

A genetic polymorphism affecting FUT2 secretor status in approximately one-quarter of humans of European descent affects the expression of histo-blood group antigens on the mucosal epithelia of human respiratory, genitourinary, and digestive tracts. These histo-blood group antigens serve as host receptor sites necessary for attachment and infection of some pathogens, including norovirus.

OBJECTIVE

We investigated whether an association exists between FUT2 secretor status and laboratory-confirmed rotavirus infections in US children.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter case-control observational study involving active surveillance at 6 US pediatric medical institutions in the inpatient and emergency department clinical settings. We enrolled 1564 children younger than 5 years with acute gastroenteritis (diarrhea and/or vomiting) and 818 healthy controls frequency matched by age and month, from December 1, 2011, through March 31, 2013.

MAIN OUTCOMES AND MEASURES

Paired fecal-saliva specimens were tested for rotavirus and for secretor status. Comparisons were made between rotavirus test-positive cases and healthy controls stratified by ethnicity and vaccination status. Adjusted multivariable analyses assessed the preventive association of secretor status against severe rotavirus gastroenteritis.

RESULTS

One (0.5%) of 189 rotavirus test-positive cases was a nonsecretor, compared with 188 (23%) of 818 healthy control participants (P < .001). Healthy control participants of Hispanic ethnicity were significantly less likely to be nonsecretors (13%) compared with healthy children who were not of Hispanic ethnicity (25%) (P < .001). After controlling for vaccination and other factors, children with the nonsecretor FUT2 polymorphism appeared statistically protected (98% [95% CI, 84%-100%]) against severe rotavirus gastroenteritis.

CONCLUSIONS AND RELEVANCE

Severe rotavirus gastroenteritis was virtually absent among US children who had a genetic polymorphism that inactivates FUT2 expression on the intestinal epithelium. We observed a strong epidemiologic association among children with rotavirus gastroenteritis compared with healthy control participants. The exact cellular mechanism behind this epidemiologic association remains unclear, but evidence suggests that it may be rotavirus genotype specific. The lower prevalence of nonsecretors among Hispanic children may translate to an enhanced burden of rotavirus gastroenteritis among this group. Our findings may have bearing on our full understanding of rotavirus infections and the effects of vaccination in diverse populations.

Human Intestinal Enteroids: a New Model To Study Human Rotavirus Infection, Host Restriction, and Pathophysiology

Human gastrointestinal tract research is limited by the paucity of in vitro intestinal cell models that recapitulate the cellular diversity and complex functions of human physiology and disease pathology. Human intestinal enteroid (HIE) cultures contain multiple intestinal epithelial cell types that comprise the intestinal epithelium (enterocytes and goblet, enteroendocrine, and Paneth cells) and are physiologically active based on responses to agonists. We evaluated these nontransformed, three-dimensional HIE cultures as models for pathogenic infections in the small intestine by examining whether HIEs from different regions of the small intestine from different patients are susceptible to human rotavirus (HRV) infection. Little is known about HRVs, as they generally replicate poorly in transformed cell lines, and host range restriction prevents their replication in many animal models, whereas many animal rotaviruses (ARVs) exhibit a broader host range and replicate in mice. Using HRVs, including the Rotarix RV1 vaccine strain, and ARVs, we evaluated host susceptibility, virus production, and cellular responses of HIEs. HRVs infect at higher rates and grow to higher titers than do ARVs. HRVs infect differentiated enterocytes and enteroendocrine cells, and viroplasms and lipid droplets are induced. Heterogeneity in replication was seen in HIEs from different patients. HRV infection and RV enterotoxin treatment of HIEs caused physiological lumenal expansion detected by time-lapse microscopy, recapitulating one of the hallmarks of rotavirus-induced diarrhea. These results demonstrate that HIEs are a novel pathophysiological model that will allow the study of HRV biology, including host restriction, cell type restriction, and virus-induced fluid secretion.

IMPORTANCE

Our research establishes HIEs as nontransformed cell culture models to understand human intestinal physiology and pathophysiology and the epithelial response, including host restriction of gastrointestinal infections such as HRV infection. HRVs remain a major worldwide cause of diarrhea-associated morbidity and mortality in children ≤5 years of age. Current in vitro models of rotavirus infection rely primarily on the use of animal rotaviruses because HRV growth is limited in most transformed cell lines and animal models. We demonstrate that HIEs are novel, cellularly diverse, and physiologically relevant epithelial cell cultures that recapitulate in vivo properties of HRV infection. HIEs will allow the study of HRV biology, including human host-pathogen and live, attenuated vaccine interactions; host and cell type restriction; virus-induced fluid secretion; cell-cell communication within the epithelium; and the epithelial response to infection in cultures from genetically diverse individuals. Finally, drug therapies to prevent/treat diarrheal disease can be tested in these physiologically active cultures.

Structural basis of glycan specificity in neonate-specific bovine-human reassortant rotavirus

Strain-dependent variation of glycan recognition during initial cell attachment of viruses is a critical determinant of host specificity, tissue-tropism and zoonosis. Rotaviruses (RVs), which cause life-threatening gastroenteritis in infants and children, display significant genotype-dependent variations in glycan recognition resulting from sequence alterations in the VP8* domain of the spike protein VP4. The structural basis of this genotype-dependent glycan specificity, particularly in human RVs, remains poorly understood. Here, from crystallographic studies, we show how genotypic variations configure a novel binding site in the VP8* of a neonate-specific bovine-human reassortant to uniquely recognize either type I or type II precursor glycans, and to restrict type II glycan binding in the bovine counterpart. Such a distinct glycan-binding site that allows differential recognition of the precursor glycans, which are developmentally regulated in the neonate gut and abundant in bovine and human milk provides a basis for age-restricted tropism and zoonotic transmission of G10P[11] rotaviruses.

Expanding diversity of glycan receptor usage by rotaviruses

Rotaviruses are major etiologic agents of severe gastroenteritis in human and animals, infecting the mature intestinal epithelium. Their attachment to host cell glycans is mediated through the virion spike protein. This is considered to be crucial for successful host cell invasion by rotaviruses. Recent studies have greatly expanded our understanding of the diversity of glycans commonly recognized by rotaviruses, to include the ganglioside GM1a and histo-blood group antigens. Here, these new findings are integrated with advances in knowledge of spike protein structure, rotavirus entry mechanisms and innate intestinal immunity to provide an overview of the variety of rotavirus glycan receptors and their roles in cell penetration, host tropism and pathogenesis.

Binding Patterns of Rotavirus Genotypes P[4], P[6], and P[8] in China with Histo-Blood Group Antigens

Rotaviruses (RVs) are an important cause of severe gastroenteritis in children. It has been found that RV may recognize the histo-blood group antigens (HBGAs) as ligands or receptors and bind HBGAs in a type-dependent manner. In this study, we investigated the binding specificity of VP8* proteins from human rotaviruses (RV) that are prevalent in China including genotypes P[4], P[6], and P[8]. Through the saliva- and oligosaccharide-based binding assays, we found that the VP8* proteins of P[4] and P[8] RV showed similar reactivity with the Le^b and H type 1 antigens, while P[6] RV weakly bound the Le^b antigen. These findings may facilitate further research into RV host specificity and vaccine development.