Revisiting the role of histo-blood group antigens in rotavirus host-cell invasion

Histo-blood group antigens as mediators of infections

The critical first step of a microbial infection is usually the attachment of pathogens to host cell glycans. Targets on host tissues are in particular the histo-blood group antigens (HBGAs), which are present in rich diversity in the mucus layer and on the underlying mucosa. Recent structural and functional studies have revealed significant new insight into the molecular mechanisms, explaining why individuals with certain blood groups are at increased risk of some infections. The most prominent example of blood-group-associated diseases is cholera, caused by infection with Vibrio cholerae. Many other microbial pathogens, for example Pseudomonas aeruginosa infecting the airways, and enterotoxigenic Escherichia coli (ETEC) causing traveler's diarrhea, also bind to histo-blood group antigens, but show a less clear correlation with blood group phenotype. Yet other pathogens, for example norovirus and Helicobacter pylori, recognize HBGAs differently depending on the strain. In all cases, milk oligosaccharides can aid the hosts' defenses, acting as natural receptor decoys, and anti-infectious therapy can be designed along similar strategies. In this review, we focus on important infections of humans, but the molecular mechanisms are of general relevance to a broad range of microbial infections of humans and animals.

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.

Epidemiology of Rotavirus in the Iranian Children: A Systematic Review and Meta-analysis

Rotavirus is associated with increased risk for severe diarrhea in infants and young children worldwide. This systematic review and meta-analysis was performed to determine the prevalence rate of rotavirus from different parts of Iran and provide an overall relative frequency (RF) for Iran. We performed a systematic literature review from several databases including PubMed, ISI Web of Science, Scopus, OVID, MAG IRAN, IranMedex, and Iranian Scientific Information Database. We searched the following keywords: "rotavirus," "rotavirus infection," "acute gastroenteritis," "diarrhea," "children," "infant," and "Iran." The purpose of this study was to report the prevalence of rotavirus with the application of meta-analysis. We selected 43 researches out of 1147 for our study. From all the samples, the pooled estimate of prevalence (95% confidence interval) =39.9% (0.396%-0.409%) were rotavirus positive. It should be noted that rotavirus infection's RF varied from 6.4% to 79.3% in Birjand and Tehran Provinces, respectively. Thereupon, it is divergent in different studies. According to our study result, rotavirus RF has a wide range in Iran and is associated with diarrhea in children. Thus, further researches should be taken to minimize the emergence and transmission of rotavirus.

A role for glycolipid biosynthesis in severe fever with thrombocytopenia syndrome virus entry

A novel bunyavirus was recently found to cause severe febrile illness with high mortality in agricultural regions of China, Japan, and South Korea. This virus, named severe fever with thrombocytopenia syndrome virus (SFTSV), represents a new group within the Phlebovirus genus of the Bunyaviridae. Little is known about the viral entry requirements beyond showing dependence on dynamin and endosomal acidification. A haploid forward genetic screen was performed to identify host cell requirements for SFTSV entry. The screen identified dependence on glucosylceramide synthase (ugcg), the enzyme responsible for initiating de novo glycosphingolipid biosynthesis. Genetic and pharmacological approaches confirmed that UGCG expression and enzymatic activity were required for efficient SFTSV entry. Furthermore, inhibition of UGCG affected a post-internalization stage of SFTSV entry, leading to the accumulation of virus particles in enlarged cytoplasmic structures, suggesting impaired trafficking and/or fusion of viral and host membranes. These findings specify a role for glucosylceramide in SFTSV entry and provide a novel target for antiviral therapies.

Virus-Bacteria Interactions: An Emerging Topic in Human Infection

Bacteria and viruses often occupy the same niches, however, interest in their potential collaboration in promoting wellness or disease states has only recently gained traction. While the interaction of some bacteria and viruses is well characterized (e.g., influenza virus), researchers are typically more interested in the location of the infection than the manner of cooperation. There are two overarching types of bacterial-virus disease causing interactions: direct interactions that in some way aid the viruses, and indirect interactions aiding bacteria. The virus-promoting direct interactions occur when the virus exploits a bacterial component to facilitate penetration into the host cell. Conversely, indirect interactions result in increased bacterial pathogenesis as a consequence of viral infection. Enteric viruses mainly utilize the direct pathway, while respiratory viruses largely affect bacteria in an indirect fashion. This review focuses on some key examples of how virus-bacteria interactions impact the infection process across the two organ systems, and provides evidence supporting this as an emerging theme in infectious disease.

Blood Group Antigen Recognition via the Group A Streptococcal M Protein Mediates Host Colonization

Streptococcus pyogenes (group A streptococcus [GAS]) is responsible for over 500,000 deaths worldwide each year. The highly virulent M1T1 GAS clone is one of the most frequently isolated serotypes from streptococcal pharyngitis and invasive disease. The oral epithelial tract is a niche highly abundant in glycosylated structures, particularly those of the ABO(H) blood group antigen family. Using a high-throughput approach, we determined that a strain representative of the globally disseminated M1T1 GAS clone 5448 interacts with numerous, structurally diverse glycans. Preeminent among GAS virulence factors is the surface-expressed M protein. M1 protein showed high affinity for several terminal galactose blood group antigen structures. Deletion mutagenesis shows that M1 protein mediates glycan binding via its B repeat domains. Association of M1T1 GAS with oral epithelial cells varied significantly as a result of phenotypic differences in blood group antigen expression, with significantly higher adherence to those cells expressing H antigen structures compared to cells expressing A, B, or AB antigen structures. These data suggest a novel mechanism for GAS attachment to host cells and propose a link between host blood group antigen expression and M1T1 GAS colonization.

IMPORTANCE

There has been a resurgence in group A streptococcal (GAS) invasive disease, which has been paralleled by the emergence of the highly virulent M1T1 GAS clone. Intensive research has focused on mechanisms that contribute to the invasive nature of this serotype, while the mechanisms that contribute to host susceptibility to disease and bacterial colonization and persistence are still poorly understood. The M1T1 GAS clone is frequently isolated from the throat, an environment highly abundant in blood group antigen structures. This work examined the interaction of the M1 protein, the preeminent GAS surface protein, against a wide range of host-expressed glycan structures. Our data suggest that susceptibility to infection by GAS in the oral tract may correlate with phenotypic differences in host blood group antigen expression. Thus, variations in host blood group antigen expression may serve as a selective pressure contributing to the dissemination and overrepresentation of M1T1 GAS.

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.

Norovirus drug candidates that inhibit viral capsid attachment to human histo-blood group antigens

Human noroviruses are the leading causative agents of epidemic and sporadic viral gastroenteritis and childhood diarrhoea worldwide. Human histo-blood group antigens (HBGA) serve as receptors for norovirus capsid protein attachment and play a critical role in infection. This makes HBGA-norovirus binding a promising target for drug development. Recently solved crystal structures of norovirus bound to HBGA have provided a structural basis for identification of potential anti-norovirus drugs and subsequently performed in silico and in vitro drug screens have identified compounds that block norovirus binding and may thereby serve as structural templates for design of therapeutic norovirus inhibitors. This review explores norovirus therapeutic options based on the strategy of blocking norovirus-HBGA binding.

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.

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.

Substantial Receptor-induced Structural Rearrangement of Rotavirus VP8*: Potential Implications for Cross-Species Infection

Rotavirus-cell binding is the essential first step in rotavirus infection. This binding is a major determinant of rotavirus tropism, as host cell invasion is necessary to initiate infection. Initial rotavirus-cell interactions are mediated by carbohydrate-recognizing domain VP8* of the rotavirus capsid spike protein VP4. Here, we report the first observation of significant structural rearrangement of VP8* from human and animal rotavirus strains upon glycan receptor binding. The structural adaptability of rotavirus VP8* delivers important insights into how human and animal rotaviruses utilize the wider range of cellular glycans identified as VP8* binding partners. Furthermore, our studies on rotaviruses with atypical genetic makeup provide information expected to be critical for understanding the mechanisms of animal rotavirus gene emergence in humans and support implementation of epidemiologic surveillance of animal reservoirs as well as future vaccination schemes.

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.

6th European Rotavirus Biology Meeting, Dijon, France, 17–20 May 2015

The European Rotavirus Biology Meeting was established 12 years ago and takes place biannually. Approximately 100 scientists, medical doctors and students of biomedical sciences from 28 countries of five continents participated in this meeting, which was efficiently organized by Pierre Pothier and his staff. Their hospitality and inventive social program were highly appreciated. The aim of the meeting was to review and discuss new developments of rotavirus (RV) research, pathophysiology, immunology, molecular epidemiology and prevention.

Relative quantitation of multi-antennary N-glycan classes: combining PGC-LC-ESI-MS with exoglycosidase digestion

In the search for N-glycan disease biomarkers current glycoanalytical methods may not be revealing a complete picture of precious samples, and we may be missing valuable structural information that fall outside analysis windows.