Generation of recombinant rotaviruses encoding a split NanoLuc peptide tag.

Recombinant viruses expressing fluorescent or luminescent reporter proteins are used to quantitate and visualize viral replication and transmission. Here, we used a split NanoLuc luciferase (NLuc) system comprising large LgBiT and small HiBiT peptide fragments to generate stable reporter rotaviruses (RVs). Reporter RVs expressing NSP1-HiBiT fusion protein were generated by placing an 11 amino acid HiBiT peptide tag at the C-terminus of the intact simian RV NSP1 open reading frame or truncated human RV NSP1 open reading frame. Virus-infected cell lysates exhibited NLuc activity that paralleled virus replication. The antiviral activity of neutralizing antibodies and antiviral reagents against the recombinant HiBiT reporter viruses were monitored by measuring reductions in NLuc expression. These findings demonstrate that the HiBiT reporter RV systems are powerful tools for studying the viral life cycle and pathogenesis, and a robust platform for developing novel antiviral drugs.

Evaluation on the efficacy and immunogenicity of recombinant DNA plasmids expressing S gene from porcine epidemic diarrhea virus and VP7 gene from porcine rotavirus.

Porcine rotavirus (PoRV) and porcine epidemic diarrhea virus (PEDV) usually co-infect pigs in modern large-scale piggery, which both can cause severe diarrhea in newborn piglets and lead to significant economic losses to the pig industry. The VP7 protein is the main coat protein of PoRV, and the S protein is the main structural protein of PEDV, which are capable of inducing neutralizing antibodies in vivo. In this study, a DNA vaccine pPI-2.EGFP.VP7.S co-expressing VP7 protein of PoRV and S protein of PEDV was constructed. Six 8-week-old mice were immunized with the recombinant plasmid pPI-2.EGFP.VP7.S. The high humoral immune responses (virus specific antibody) and cellular immune responses (IFN-γ, IL-4, and spleen lymphocyte proliferation) were evaluated. The immune effect through intramuscular injection increased with plasmid dose when compared with subcutaneous injection. The immune-enhancing effect of IFN-α adjuvant was excellent compared with pig spleen transfer factor and IL-12 adjuvant. These results demonstrated that pPI-2.EGFP.VP7.S possess the immunological functions of the VP7 proteins of PoRV and S proteins of PEDV, indicating that pPI-2.EGFP.VP7.S is a candidate vaccine for porcine rotaviral infection (PoR) and porcine epidemic diarrhea (PED).

Rotavirus Genotypes Circulating in Brazil Before and After the National Rotavirus Vaccine Program: A Review.

BACKGROUND: Rotavirus vaccines created the opportunity to control diarrhea in children. We describe the rotavirus genotypes before and after the rotavirus vaccine introduction in Brazil. METHODS: We reviewed the distribution of rotavirus genotypes in Brazil before and after vaccine introduction by searching publication. RESULTS: Eighty-six studies reported 6884 (15.2%) rotavirus episodes among 45,305 children. Rotavirus caused 22.4% and 11.6% of cases before and after vaccine introduction. G1P[8], G9P[8] and G2P[4] heterotypic strains were most common before and after vaccine introduction. CONCLUSIONS: The vaccines may have selected heterotypic strains in this highly vaccinated population.

Vitamin D3 supplementation alleviates rotavirus infection in pigs and IPEC-J2 cells via regulating the autophagy signaling pathway.

Vitamin D had an anti-infection effect and benefited to the intestinal health. Autophagy signaling pathway was regulated by vitamin D3 to inhibit the infection of human immunodeficiency virus type-1. Rotavirus (RV) was a major cause of the severe diarrheal disease in young children and young animals. Although evidence suggested that vitamin D3 attenuates the negative effects of RV infection via the retinoic acid-inducible gene I signaling pathway, little is known of its antiviral effect whether through the regulation of autophagy. The present study was performed to investigate whether vitamin D3 alleviates RV infection in pig and porcine small intestinal epithelial cell line (IPEC-J2) models via regulating the autophagy signaling pathway. RV administration increased the Beclin 1 mRNA abundance in porcine jejunum and ileum. 5000 IU/kg dietary vitamin D3 supplementation greatly up-regulated LC3-II/LC3-I ratios and PR-39 mRNA expression under the condition of RV challenged. The viability of IPEC-J2 was significantly inhibited by RV infection. Incubation with 25-hydroxyvitamin D3 significantly decreased the concentrations of RV antigen and non-structural protein 4 (NSP4), and up-regulated the mRNA expression of Beclin 1 and PR-39 in the RV-infected IPEC-J2 cells. And then, based on the 25-hydroxyvitamin D3 treatment and RV infection, LC3-II mRNA expression in cells was inhibited by an autophagy inhibitor 3-methyladenine (3-MA). Bafilomycin A1 (Baf A1, a class of inhibitors of membrane ATPases, inhibits maturation of autophagic vacuoles) treatment numerically enhanced the LC3-II mRNA abundance, but had no effect on NSP4 concentration. Furthermore, 25-hydroxyvitamin D3 decreased the p62 mRNA expression and increased porcine cathelicidins (PMAP23, PG1-5 and PR-39) mRNA expression in the RV-infected cells. Taken together, these results indicated that vitamin D3 attenuates RV infection through regulating autophagic maturation and porcine cathelicidin genes expression.

Diarrheagenic pathogens in adults attending a hospital in Singapore.

BACKGROUND: Singapore's diarrhoeal notification system is based on specific pathogens. Official data may thus be skewed towards notifiable diseases. Limited information is available on the profiles of aetiological agents responsible for acute gastroenteritis (AGE) cases, especially among the adult population. To understand the frequency and distribution of potential causative agents of diarrheal disease in Singapore, we screened adults' stool samples collected from a large public hospital. METHODS: The stool samples were screened for 18 diarrheagenic pathogens using a combination of commercial multiplex polymerase chain reaction (PCR), in-house singleplex PCR and immunochromatographic assays. One hundred adult faecal samples that were collected from October 2013 to January 2014 for routine diagnostic purposes and submitted for culture at Tan Tock Seng Hospital, Singapore were used. RESULTS: Pathogens were detected in 32% of the samples. The predominant organisms encountered were norovirus genogroup II (11%), Aeromonas spp. (9%) and Campylobacter spp. (5%). One sample was positive for both verocytotoxigenic E. coli (VTEC) and E. coli O157:H7. Two other samples were positive for VTEC only, and one other sample was positive for E. coli O157:H7 only. Astrovirus, C. perfringens, Shigella spp. and toxigenic C. difficile were each detected in 2% of the samples. Cryptosporidium parvum, Giardia lamblia, group A rotavirus, Salmonella spp. and Vibrio spp. were each detected in 1% of the samples. No L. monocytogenes, Y. enterocolitica, enteric adenovirus, or norovirus genogroup I were detected. CONCLUSION: Our preliminary findings suggest that pathogens causing non-notifiable diseases might have contributed considerably to the adult hospitalised AGE cases. However, as the samples were from an adult hospital, the data obtained may not be representative of the whole community. Thus, a larger study to collect clinical samples and risk exposure data from primary healthcare clinics and children hospital is planned for, to gain a more holistic perspective on the epidemiology of AGE in Singapore. A larger study may also offer valuable insights for improving the approach of microbiological surveillance of food, as well as strategizing inspection efforts along the food supply chain by public health authorities.

Engineering and expression of a human rotavirus candidate vaccine in Nicotiana benthamiana.

BACKGROUND: Human rotaviruses are the main cause of severe gastroenteritis in children and are responsible for over 500 000 deaths annually. There are two live rotavirus vaccines currently available, one based on human rotavirus serotype G1P[8], and the other a G1-G4 P[8] pentavalent vaccine. However, the recent emergence of the G9 and other novel rotavirus serotypes in Africa and Asia has prompted fears that current vaccines might not be fully effective against these new varieties. RESULTS: We report an effort to develop an affordable candidate rotavirus vaccine against the new emerging G9P[6] (RVA/Human-wt/ZAF/GR10924/1999/G9P[6]) strain. The vaccine is based on virus-like particles which are both highly immunogenic and safe. The vaccine candidate was produced in Nicotiana benthamiana by transient expression, as plants allow rapid production of antigens at lower costs, without the risk of contamination by animal pathogens. Western blot analysis of plant extracts confirmed the successful expression of two rotavirus capsid proteins, VP2 and VP6. These proteins assembled into VLPs resembling native rotavirus particles when analysed by transmission electron microscopy (TEM). Expression of the rotavirus glycoprotein VP7 and the spike protein VP4 was also tried. However, VP7 expression caused plant wilting during the course of the time trial and expression could never be detected for either protein. We therefore created three fusion proteins adding the antigenic part of VP4 (VP8*) to VP6 in an attempt to produce more appropriately immunogenic particles. Fusion protein expression in tobacco plants was detected by western blot using anti-VP6 and anti-VP4 antibodies, but no regular particles were observed by TEM, even when co-expressed with VP2. CONCLUSION: Our results suggest that the rotavirus proteins produced in N. benthamiana are candidates for a subunit vaccine specifically for the G9P[6] rotavirus strain. This could be more effective in developing countries, thereby possibly providing a higher overall efficacy for the existing vaccines. The production of rotavirus proteins in plants would probably result in lower manufacturing costs, making it more affordable for developing countries. Further investigation is required to evaluate the immunogenic potential of the VLPs and fusion proteins created in this study.

Effect of 25-hydroxyvitamin D3 on rotavirus replication and gene expressions of RIG-I signalling molecule in porcine rotavirus-infected IPEC-J2 cells.

The study evaluated whether a 25-hydroxyvitamin D3 (25D3) supplementation decreases the replication of rotavirus by the retinoic acid-inducible gene I (RIG-I) signalling pathway in a porcine small intestinal epithelial cell line (IPEC-J2). The results show that IPEC-J2 cells express high baseline levels of 1α-hydroxylase (CYP27B1), which converts inactive 25D3 to the active 1,25-dihydroxyvitamin D3 (1,25D3). Porcine rotavirus (PRV) infection alone resulted in a significant increase in CYP27B1 mRNA, which augmented the production of active vitamin D. Physiological concentrations of 25D3 were found to decrease PRV replication in IPEC-J2 cells. RIG-I plays an important role in the recognition of double-stranded RNA virus by host cells. Upon recognition, RIG-I triggers a series of signalling molecules such as interferon-ß (IFN-ß) promoter stimulator 1 (IPS-1) leading to the expression of type I interferons (IFN-ß). Active 25D3 that was generated by PRV-infected IPEC-J2 cells led to an increased expression of toll-like receptors 3 (TLR3), RIG-I, IPS-1, IFN-ß and IFN-stimulated genes 15 (ISG15) with important innate immune functions. Inhibiting CYP27B1 also failed to increase RIG-I, IPS-1, IFN-ß and ISG15 mRNA expression. These observations suggest that 25D3 can directly inhibit PRV in IPEC-J2 cells, which requires this active form of vitamin D. The anti-rotavirus effect of 25D3 is mediated at least in part by RIG-I signalling pathways in IPEC-J2 cells.

Anti-rotavirus effects by combination therapy of stevioside and Sophora flavescens extract.

Anti-rotaviral activities of Sophora flavescens extract (SFE) and stevioside (SV) from Stevia rebaudiana Bertoni either singly or in various combinations were examined in vitro and in vivo using a porcine rotavirus G5[P7] strain. Combination of SFE and SV inhibited in vitro virus replication more efficiently than each single treatment. In the piglet model, SV had no effect on rotavirus enteritis, whereas SFE improved but did not completely cure rotaviral enteritis. Interestingly, combination therapy of SFE and SV alleviated diarrhea, and markedly improved small intestinal lesion score and fecal virus shedding. Acute toxicity tests including the piglet lethal dose 50, and body weight, organ weight and pathological changes for the combination therapy did not show any adverse effect on the piglets. These preliminary data suggest that the combination therapy of SV and SFE is a potential curative medication for rotaviral diarrhea in pigs. Determination of the efficacy of this combination therapy in other species including humans needs to be addressed in the future.

Anti-rotaviral effects of Glycyrrhiza uralensis extract in piglets with rotavirus diarrhea.

BACKGROUND: Since rotavirus is one of the leading pathogens that cause severe gastroenteritis and represents a serious threat to human and animal health, researchers have been searching for cheap, safe, and effective anti-rotaviral drugs. There is a widespread of interest in using natural products as antiviral agents, and among them, licorice derived from Glycyrrhiza spp. has exerted antiviral properties against several viruses. In this study, anti-rotaviral efficacy of Glycyrrhiza uralensis extract (GUE) as an effective and cheaper remedy without side-effects was evaluated in colostrums-deprived piglets after induction of rotavirus diarrhea. METHODS: Colostrums-deprived piglets were inoculated with porcine rotavirus K85 (G5P[7]) strain. On the onset of diarrhea, piglets were treated with different concentration of GUE. To evaluate the antiviral efficacy of GUE, fecal consistency score, fecal virus shedding and histological changes of the small intestine, mRNA expression levels of inflammation-related cytokines (IL8, IL10, IFN-ß, IFN-γ and TNF-α), signaling molecules (p38 and JNK), and transcription factor (NFκB) in the small intestine and spleen were determined. RESULTS: Among the dosages (100-400 mg/ml) administrated to animals, 400 mg/ml of GUE cured diarrhea, and markedly improved small intestinal lesion score and fecal virus shedding. mRNA expression levels of inflammation-related cytokines (IL8, IL10, IFN-ß, IFN-γ and TNF-α), signaling molecules (p38 and JNK), and transcription factor (NFκB) in the small intestine and spleen were markedly increased in animals with RVA-induced diarrhea, but dose- dependently decreased in GUE treated animals after RVA-induced diarrhea. CONCLUSIONS: GUE cures rotaviral enteritis by coordinating antiviral and anti-inflammatory effects. Therapy of this herbal medicine can be a viable medication for curing rotaviral enteritis in animals and humans.

Detection of rotavirus in food associated with a gastroenteritis outbreak in a mother and child sanatorium.

In the course of a rotavirus outbreak in a mother and child sanatorium 74 food samples from the sanatorium kitchen were taken and tested for rotavirus. Rotavirus particles were isolated from 25 g food samples by a simple method including ultrafiltration, originally designed for the detection of norovirus in various food matrices. Rotavirus was successfully detected in a sample of potato stew by conventional RT-seminested-PCR. Sequence comparison of the amplification products obtained from the potato stew and a stool sample from an infected child verified that the two viruses were identical.

Effective prophylaxis against rotavirus diarrhea using a combination of Lactobacillus rhamnosus GG and antibodies.

BACKGROUND: Rotavirus is a worldwide cause of infectious infantile diarrhea that claims over 600,000 lives annually. Recently, two new vaccine candidates have been developed but their efficacy in developing countries, still remains to be proven. Oral delivery of specific immunoglobulins provides passive immunity and is a fast acting treatment for rotavirus diarrhea. Probiotic bacteria have also gained considerable attention lately as treatment for rotavirus diarrhea. Here we report an evaluation of the therapeutic potential of different probiotics and their combination with anti - rotavirus antibodies in a mouse model of rotavirus diarrhea. RESULTS: Of the six probiotic bacteria tested, Lactobacillus rhamnosus strain GG had the strongest influence in reducing prevalence, duration and severity of diarrhea and was therefore chosen for combination treatment with immunoglobulins. The combination treatment reduced the diarrhea outcome measures significantly, prevented histopathological changes and reduced the virus load in the intestines. CONCLUSION: The advantages associated with immunoglobulins and probiotics based therapy is that the treatment provides a rapid therapeutic effect and is cost efficient. These components do not require special storage conditions and could potentially complement the rehydration therapy that is currently used.

Procedure for rapid concentration and detection of enteric viruses from berries and vegetables.

Several hepatitis A virus (HAV) and norovirus (NV) outbreaks due to consumption of berries and vegetables have been reported during recent years. To facilitate the detection of enteric viruses that may be present on different fresh and frozen products, we developed a rapid and sensitive detection method for HAV, NV, and rotavirus (RV). Initial experiments focused on optimizing the composition of the elution buffer, improving the viral concentration method, and evaluating the performance of various extraction kits. Viruses were extracted from the food surface by a direct elution method in a glycine-Tris (pH 9.5) buffer containing 1% beef extract and concentrated by ultrafiltration. Occasionally, PCR inhibitors were present in the processed berry samples, which gave relatively poor detection limits. However, this problem was overcome by adding a pectinase treatment in the protocol, which markedly improved the sensitivity of the method. After optimization, this concentration method was applied in combination with real-time reverse transcription-PCR (RT-PCR) using specific primers in various types of berries and vegetables. The average detection limits were 1 50% tissue culture infective dose (TCID(50)), 54 RT-PCR units, and 0.02 TCID(50) per 15 g of food for HAV, NV, and RV, respectively. Based on our results, it is concluded that this procedure is suitable to detect and quantify enteric viruses within 6 h and can be applied for surveillance of enteric viruses in fresh and frozen products.

Biotin-psolaren labeled cDNA amplicons for genotyping rotavirus strains by dot hybridization assay.

A simple method to produce biotinylated probes by utilizing an amine-psoralen to conjugate an ester-biotin to nucleic acid molecules is described. It is simple, rapid, and well suited to label cDNA probes with any PCR-generated amplicon for hybridization assay. Its application to identify or to confirm the G and P genotypes of rotavirus-derived amplicons is described; however, it may be used to label amplicons of any origin. As an alternative or as a complementary test to either PCR-typing assay and/or sequencing, it should reduce considerably the laboratory costs required to genotype fully virus strains in large epidemiological surveys conducted in developing countries.

Transgenic plants for the production of veterinary vaccines.

The expression of antigens in transgenic plants has been increasingly used in the development of experimental vaccines, particularly oriented to the development of edible vaccines. Hence, this technology becomes highly suitable to express immunogenic proteins from pathogens. Foot and mouth disease virus, bovine rotavirus and bovine viral diarrhoea virus are considered to be the most important causative agents of economic loss of cattle production in Argentina, and they are thus optimal candidates for alternative means of immunization. Here, we present a review of our results corresponding to the expression of immunogenic proteins from these three viruses in alfalfa transgenic plants, and we discuss the possibility of using them for the development of plant-based vaccines.

Plant-synthesized E. coli CFA/I fimbrial protein protects Caco-2 cells from bacterial attachment.

A DNA fragment encoding the cholera toxin A2 subunit (CTA2) linked to the enterotoxigenic Escherichia coli (ETEC) colony forming fimbrial antigen CFA/I was inserted into a plant expression vector containing the cholera toxin B subunit (CTB) fused to the rotavirus enterotoxin 22 amino acid epitope NSP422. Anti-CFA/I antibodies recognized a single band of approximately 72-kDa in transformed potato tuber tissue consistent with CFA/I-CTA2 and CTB-NSP4 fusion protein assembly into a cholera holotoxin-like structure. Enzyme-linked immunosorbent assay (GM1 ELISA) indicated that the CFA/I-CTA2 fusion protein bound specific GM1 ganglioside membrane receptors and made up approximately 0.002% of the total soluble tuber protein. Oral immunization of BALB/c mice with transformed tuber tissues generated anti-CFA/I serum and intestinal IgG and IgA secretory antibodies. Attachment of ETEC H10407 to enterocyte-like Caco-2 human colon carcinoma cells incubated with antiserum from immunized mice was reduced by 15% in comparison with Caco-2 cells incubated with serum from unimmunized mice. Immunogold staining of bacterial preparations revealed deposition of gold particles on E. coli H10407 fimbria incubated with immune serum but not on fimbria treated with sera from unimmunized mice demonstrating the specificity of antibodies in the immune serum for binding to CFA/I protein containing fimbria. The protection against toxic E. coli binding to Caco-2 cells generated by antisera from mice immunized with plant-synthesized CFA/I antigen demonstrates the feasibility of plant-based multi-component vaccine protection against enterotoxigenic E. coli, rotavirus and cholera, three enteric diseases that together exert the highest levels of child morbidity and mortality in economically emerging countries.

RoXaN, a novel cellular protein containing TPR, LD, and zinc finger motifs, forms a ternary complex with eukaryotic initiation factor 4G and rotavirus NSP3.

Rotavirus mRNAs are capped but not polyadenylated, and viral proteins are translated by the cellular translation machinery. This is accomplished through the action of the viral nonstructural protein NSP3, which specifically binds the 3' consensus sequence of viral mRNAs and interacts with the eukaryotic translation initiation factor eIF4G I. To further our understanding of the role of NSP3 in rotavirus replication, we looked for other cellular proteins capable of interacting with this viral protein. Using the yeast two-hybrid assay, we identified a novel cellular protein-binding partner for rotavirus NSP3. This 110-kDa cellular protein, named RoXaN (rotavirus X protein associated with NSP3), contains a minimum of three regions predicted to be involved in protein-protein or nucleic acid-protein interactions. A tetratricopeptide repeat region, a protein-protein interaction domain most often found in multiprotein complexes, is present in the amino-terminal region. In the carboxy terminus, at least five zinc finger motifs are observed, further suggesting the capacity of RoXaN to bind other proteins or nucleic acids. Between these two regions exists a paxillin leucine-aspartate repeat (LD) motif which is involved in protein-protein interactions. RoXaN is capable of interacting with NSP3 in vivo and during rotavirus infection. Domains of interaction were mapped and correspond to the dimerization domain of NSP3 (amino acids 163 to 237) and the LD domain of RoXaN (amino acids 244 to 341). The interaction between NSP3 and RoXaN does not impair the interaction between NSP3 and eIF4G I, and a ternary complex made of NSP3, RoXaN, and eIF4G I can be detected in rotavirus-infected cells, implicating RoXaN in translation regulation.

Synthesis of an HIV-1 Tat transduction domain-rotavirus enterotoxin fusion protein in transgenic potato.

A DNA fragment encoding a 12-amino acid (aa) HIV-1 Tat transduction peptide fused to a 90-aa murine rotavirus NSP4 enterotoxin protein (Tat-NSP4(90)) was transferred to Solanum tuberosum by Agrobacterium tumefaciens-mediated transformation. The fusion gene was detected in the genomic DNA of transformed plant leaf tissues by PCR DNA amplification. The Tat-NSP4(90 )fusion protein was identified in transformed tuber extracts by immunoblot analysis using anti-NSP4(90) and anti-Tat as the primary antibodies. Enzyme-linked immunosorbent assay results showed that the Tat-NSP4(90) fusion protein made up to 0.0015% of the total soluble tuber protein. The synthesis of Tat-NSP4(90) fusion protein in transformed potato tuber tissues demonstrates the feasibility of plant cell delivery of the HIV-1 Tat transduction domain as a carrier for non-specific targeting of fused antigens to the mucosal immune system.

Expression of rotavirus capsid protein VP6 in transgenic potato and its oral immunogenicity in mice.

Murine rotavirus gene six encoding the 41 kDa group specific capsid structural protein VP6 was stably inserted into the Solanum tuberosum genome by Agrobacterium tumefaciens mediated transformation. The molecular mass of plant synthesized VP6 capsid protein determined by immunoblot was similar to the size of both purified virus VP6 monomeric peptides and partially assembled virus-like particles. The amount of VP6 protein synthesized in transgenic potato leaf and tuber was determined by enzyme-linked immunosorbent assay to be approximately 0.01% of total soluble protein. Oral immunization of CD-1 mice with transformed potato tuber tissues containing VP6 capsid protein generated measurable titers of both anti-VP6 serum IgG and intestinal IgA antibodies. The presence of detectable humoral and intestinal antibody responses against the rotavirus capsid protein following mucosal immunization provides an optimistic basis for the development of edible plant vaccines against enteric viral pathogens.

A plant-based multicomponent vaccine protects mice from enteric diseases.

Cholera toxin (CT) B and A2 subunit complementary DNAs (cDNAs) were fused to a rotavirus enterotoxin and enterotoxigenic Escherichia coli fimbrial antigen genes and transferred into potato. Immunoblot and enzyme-linked immunosorbent assay (ELISA) results indicated that the fusion antigens were synthesized in transformed tuber tissues and assembled into cholera holotoxin-like structures that retained enterocyte-binding affinity. Orally immunized mice generated detectable levels of serum and intestinal antibodies against the pathogen antigens. Elevated levels of interleukin 2 (IL2) and interferon gamma (INFgamma) detected in immunogen-challenged spleen cells from the immunized mice indicated the presence of a strong Th1 immune response to the three plant-synthesized antigens. This result was supported by flow cytometry analysis of immunized mouse spleen cells that showed a significant increase in CD4+ lymphocyte numbers. Diarrhea symptoms were reduced in severity and duration in passively immunized mouse neonates following rotavirus challenge. The results suggest that food plants can function as vaccines for simultaneous protection against infectious virus and bacterial diseases.

Analysis of anti-rotavirus activity of extract from Stevia rebaudiana.

Anti-human rotavirus (HRV) activity of hot water extracts from Stevia rebaudiana (SE) was examined. SE inhibited the replication of all four serotypes of HRV in vitro. This inhibitory effect of SE was not reduced on the prior exposure of SE to HCl for 30 min at pH 2. Binding assay with radiolabeled purified viruses indicated that the inhibitory mechanism of SE is the blockade of virus binding. The SE inhibited the binding of anti-VP7 monoclonal antibody to HRV-infected MA104 cells. The inhibitory components of SE were found to be heterogeneous anionic polysaccharides with different ion charges. The component analyses suggested that the purified fraction named as Stevian with the highest inhibitory activity consists of the anionic polysaccharide with molecular weight of 9800, and contains Ser and Ala as amino acids. Analyses of sugar residues suggest uronic acid(s) as sugar components. It did not contain amino and neutral sugars and sulfate residues. These findings suggest that SE may bind to 37 kD VP7 and interfere with the binding of VP7 to the cellular receptors by steric hindrance, which results in the blockade of the virus attachment to cells.