The synergy of recombinant NSP4 and VP4 from porcine rotavirus elicited a strong mucosal response

Porcine rotavirus (PoRV) is one of the main pathogens causing diarrhea in piglets, and multiple genotypes coexist. However, an effective vaccine is currently lacking. Here, the potential adjuvant of nonstructural protein 4 (NSP4) and highly immunogenic structural protein VP4 prompted us to construct recombinant NSP486-175aa (NSP4*) and VP426-476aa (VP4*) proteins, combine them as immunogens to evaluate their efficacy. Results indicated that NSP4* enhanced systemic and local mucosal responses induced by VP4*. The VP4*-IgG, VP4*-IgA in feces and IgA-secreting cells in intestines induced by the co-immunization were significantly higher than those induced by VP4* alone. Co-immunization of NSP4* and VP4* also induced strong cellular immunity with significantly increased IFN-λ than the single VP4*. Summarily, the NSP4* as a synergistical antigen exerted limited effects on the PoRV NAbs elevation, but conferred strong VP4*-specific mucosal and cellular efficacy, which lays the foundation for the development of a more effective porcine rotavirus subunit vaccine.

Serological Humoral Immunity Following Natural Infection of Children with High Burden Gastrointestinal Viruses

Acute gastroenteritis (AGE) is a major cause of morbidity and mortality worldwide, resulting in an estimated 440,571 deaths of children under age 5 annually. Rotavirus, norovirus, and sapovirus are leading causes of childhood AGE. A successful rotavirus vaccine has reduced rotavirus hospitalizations by more than 50%. Using rotavirus as a guide, elucidating the determinants, breath, and duration of serological antibody immunity to AGE viruses, as well as host genetic factors that define susceptibility is essential for informing development of future vaccines and improving current vaccine candidates. Here, we summarize the current knowledge of disease burden and serological antibody immunity following natural infection to inform further vaccine development for these three high-burden viruses.

Dynamics of G2P[4] strain evolution and rotavirus vaccination: A review of evidence for Rotarix

Rotavirus (RV) gastroenteritis is a vaccine-preventable disease that creates high medical and economic burden in both developed and developing countries. Worldwide, more than 100 countries have introduced RV vaccines in their national immunization programs, and the remarkable impact of reducing the burden of severe childhood gastroenteritis has been unequivocally demonstrated. Currently, 2 oral vaccines (Rotarix, GSK and RotaTeq, Merck) are widely utilized. Recent temporary increases in the relative prevalence of G2P[4] RV strains have been observed in countries implementing RV vaccination. This comprehensive literature review aims to provide an insight on RV genotype evolution in the context of mass vaccination with Rotarix, particularly in the case of G2P[4]. In the post-vaccine era, strain surveillance data indicated temporal and spatial changes in countries both with and without RV vaccination programs. Annual fluctuations in G2P[4] prevalence seem to occur naturally, with no substantial differences between countries using Rotarix, RotaTeq or mixed vaccination programs. Moreover, Rotarix has been shown to be efficacious and effective against gastroenteritis caused by non-vaccine strains, including G2P[4]. These data indicate that shifts in RV genotype distribution are likely to constitute an inherent process of virus evolution to infect the human gut. Following RV vaccine introduction, incidences of RV gastroenteritis declined dramatically and mass vaccination will likely maintain this status, despite possible fluctuations in the relative distribution of genotypes. There is no conclusive evidence of unusual burst of new or vaccine-escape strains since global RV vaccines use. The emergence of strains with a potential to increase the current burden of RV disease should be continuously monitored and can only be established by exhaustive characterization of strains, including whole genomic sequencing. Given the natural fluctuations in RV strains over time, caution is advised when interpreting temporal changes in RV strain dynamics, as they could mistakenly be attributed to vaccination.

Phylogenetic comparison of the VP7, VP4, VP6, and NSP4 genes of rotaviruses isolated from children in Nizhny Novgorod, Russia, 2015-2016, with cogent genes of the Rotarix and RotaTeq vaccine strains

Group A rotaviruses (RVA) are one of the leading causes of gastroenteritis in young children worldwide. The introduction of universal mass vaccination around the world has contributed to a reduction in hospitalizations and outpatient visits associated with rotavirus infection. Continued surveillance of RVA strains is needed to determine long-term effects of vaccine introduction. In the present work, we carried out the analysis of the genotypic diversity of RVA strains isolated in Nizhny Novgorod (Russia) during the 2015-2016 epidemic season. Also we conducted a comparative analysis of the amino acid sequences of T-cell epitopes of wild-type and vaccine (RotaTeq and Rotarix) strains. In total, 1461 samples were examined. RVAs were detected in 30.4% of cases. Rotaviruses with genotype G9P[8] (40.5%) dominated in the 2015-16 epidemic season. Additionally, RVAs with the following genotypes were detected: G4P[8] (25.4%), G1P[8] (13%), G2P[4] (3.2%). Rotaviruses with genotypes G3P[9], G6P[9], and G1P[9] totaled 3%. The number of partially typed and untyped RVA samples was 66 (14.9%). The findings of a RVA of G6P[9] genotype in Russia were an original observation. Our analysis of VP6 and NSP4 T-cell epitopes showed highly conserved amino acid sequences. The found differences seem not to be caused by the immune pressure but were rather related to the genotypic affiliations of the proteins. Vaccination against rotavirus infection is not included in the national vaccination schedule in Russia. Monitoring of the genotypic and antigenic diversity of contemporary RVA will allow providing a comparative analysis of wild-type strains in areas with and without vaccine campaign.

Resurgence of Rotavirus Genotype G12 in St. Louis During the 2014-2015 Rotavirus Season

BACKGROUND

Rotaviruses are a leading cause of gastroenteritis. Rotavirus vaccination has dramatically reduced rotavirus occurrence; however, we have noticed mild to moderate recurrences in the St. Louis area in alternate years. In 2013, we found rotavirus genotype G12 to be the dominant strain in the St. Louis region. In this study, we again determined the distribution of genotypes and ascertained vaccine history in patients infected with rotavirus G12 during the 2014-15 season.

METHODS

Samples submitted to the St. Louis Children's Hospital Microbiology Laboratory were tested for rotavirus using an antigen assay. We determined the VP7 genotype using amplicon sequence analysis. We determined genome sequences using high-throughput sequencing. We evaluated rotavirus immunization records when available.

RESULTS

Of 30 typed viruses from 2014-15, 29 were G12 (97%). Whole-genome sequencing revealed few changes from G12 viruses analyzed in 2012-13. VP4 and VP7 sequences were >99% identical to previously sequenced G12 strains from St. Louis, and immune epitopes were conserved. Vaccination histories were available from 17 patients. Of these, 4 had been vaccinated, 3 had received incomplete vaccination or had a vaccine history that could not be confirmed, and 10 had not been vaccinated.

CONCLUSIONS

G12 re-emerged as the predominant rotavirus genotype in 2014-15, comprising a higher percentage of cases than in 2012-13. The majority of patients with G12 and available vaccination histories were unvaccinated. There was no genomic evidence to indicate that the G12 strains in St. Louis had evolved to escape vaccine protection. Our work emphasizes the need for continued surveillance.

NSP4 antibody levels in rotavirus gastroenteritis patients with seizures

BACKGROUND

Rotavirus nonstructural protein 4 (NSP4) has been suggested as a pathogen of rotavirus-associated seizures. We investigated pre-existing serum antibodies against NSP4 and VP6 (the most highly immunogenic rotavirus protein) in patients with rotavirus gastroenteritis and its correlation with the occurrence of seizures.

METHODS

With an enzyme-linked immunosorbent assay, IgG and IgA titers against NSP4 (genotype [A] and [B]) and VP6 were measured in acute-phase sera of 202 children aged 0.5-6.0 years with rotavirus gastroenteritis. The clinical characteristics and antibody levels were compared between patients with (seizure group) and without seizures (non-seizure group).

RESULTS

The non-seizure and seizure groups comprised 173 and 29 patients, respectively. Age, sex, hospital stay, presence of fever, white blood cell counts, C-reactive protein, vaccine status, IgG/IgA titers for VP6, and IgA titers for both NSP4s did not differ between the groups. The seizure group showed a lower level of IgG against NSP4 [A] (184.5 vs. 163.0 U/mL; P = 0.03) and NSP4 [B] (269.0 vs. 196.0 U/mL; P = 0.02). Delayed sampling time from the onset of gastroenteritis symptoms (3 vs. 2 days; P = 0.02) and lower serum sodium level (133.4 vs. 136.3 mEq/L; P < 0.01) were observed in the seizure group. Even after adjusting these factors, anti-NSP4 [A] IgG (OR 2.56 per 100 U/mL increment; 95% CI, 1.20-5.26, P = 0.01) and anti-NSP4 [B] IgG (OR 1.51 per 100 U/mL-increment; 95% CI, 1.04-2.22, P = 0.03) were independently associated with protection against seizures.

CONCLUSIONS

Serum anti-NSP4 IgG might protect rotavirus-associated seizures.

Molecular characterisation of the NSP4 gene of group A human rotavirus G2P[4] strains circulating in São Paulo, Brazil, from 1994 and 2006 to 2010

Group A human rotaviruses (HuRVA) are causative agents of acute gastroenteritis. Six viral structural proteins (VPs) and six nonstructural proteins (NSPs) are produced in RV-infected cells. NSP4 is a diarrhoea-inducing viral enterotoxin and NSP4 gene analysis revealed at least 15 (E1-E15) genotypes. This study analysed the NSP4 genetic diversity of HuRVA G2P[4] strains collected in the state of São Paulo (SP) from 1994 and 2006-2010 using reverse transcription-polymerase chain reaction, sequencing and phylogenetic analysis. Forty (97.6%) G2P[4] strains displayed genotype E2; one strain (2.4%) displayed genotype E1. These results are consistent with the proposed linkage between VP4/VP7 (G2P[4]) and the NSP4 (E2) genotype of HuRVA. NSP4 phylogenetic analysis showed distinct clusters, with grouping of most strains by their genotype and collection year, and most strains from SP were clustered together with strains from other Brazilian states. A deduced amino acid sequence alignment for E2 showed many variations in the C-terminal region, including the VP4-binding domain. Considering the ability of NSP4 to generate host immunity, monitoring NSP4 variations, along with those in the VP4 or VP7 protein, is important for evaluating the circulation and pathogenesis of RV. Finally, the presence of one G2P[4]E1 strain reinforces the idea that new genotype combinations emerge through reassortment and independent segregation.

Impact of vaccination on the molecular epidemiology and evolution of group A rotaviruses in Latin America and factors affecting vaccine efficacy

Despite high rotavirus (RV) vaccine coverage (∼83%) and good effectiveness (∼77%) against RV-diarrhea hospitalization, RV is still contributing to the burden of diarrhea that persists in hospital settings in several Latin American countries, where RV vaccination is being implemented. Due to the extensive genomic and antigenic diversity, among co-circulating human RV, a major concern has been that the introduction of RV vaccination could exert selection pressure leading to higher prevalence of strains not included in the vaccines and/or emergence of new strains, thus, reducing the efficacy of vaccination. Here we review the molecular epidemiology of RV in Latin America and explore issues of RV evolution and selection in light of vaccination. We further explore etiologies behind the large burden of diarrhea remaining after vaccination in some countries and discuss plausible reasons for vaccine failures.

Rotavirus VP6 preparations as a non-replicating vaccine candidates

Rotavirus (RV) structural proteins VP4 and VP7, located on the surface of viral particles, elicit neutralizing antibodies (Abs) and are therefore considered to be important components of RV vaccines. However, despite inducing neutralizing Abs, limits of cross-neutralizing activity and lack of full correlation with protection limit the usefulness of these proteins as protective agents against RV disease. VP6 protein, which forms the middle layer of RV particles, is discussed as an alternative vaccine candidate since it can induce cross-protective immune responses against different RV strains although the Ab raised is not neutralizing. This report reviews different functions of VP6 that can lead to considering it as an alternative vaccine against RV disease.

Rotavirus disease and vaccination: impact on genotype diversity

Temporal and spatial fluctuations in the genotype distribution of human rotaviruses are continuously observed in surveillance studies. New genotypes, such as G9 and G12, have emerged and spread worldwide in a very short time span. In addition, reassortment events have the potential to contribute substantially to genetic diversity among human and animal rotaviruses. With the recent introduction of the two rotavirus vaccines, RotaTeq and Rotarix, in many countries, it appears that the total number of hospitalizations due to rotavirus infections is being reduced, at least in developed countries that implemented a universal immunization program. However, continued surveillance is warranted, especially regarding the long-term effects of the vaccines. No data analyses are available to clarify whether rotavirus vaccine introduction would allow other rotavirus P and G genotypes, which are not covered by the current vaccines, to emerge into the human population and fill the apparent gap. This kind of data analysis is essential, but its interpretation is hampered by natural and cyclical genotype fluctuations.

Rotavirus vaccines and pathogenesis: 2008

PURPOSE OF REVIEW

Rotaviruses cause life-threatening gastroenteritis in children throughout the world. The burden of disease has resulted in the development of two live, attenuated vaccines that are now licensed in many countries. This review summarizes new data on these vaccines, their effectiveness, and remaining challenges including new data on the rotavirus enterotoxin, a potential antiviral target.

RECENT FINDINGS

Live attenuated rotavirus vaccines are used to protect infants against severe rotavirus-induced gastroenteritis and, RotaTeq, a pentavalent bovine-based vaccine, and, Rotarix, a monovalent human rotavirus, are now currently licensed in many countries. Initial results of the licensed RotaTeq vaccine have been promising in the USA and results of immunogenicity and efficacy in developing countries are expected soon. However, universal vaccine implementation is challenging due to age limitations on administration of these vaccines. Chronic rotavirus infections in immunocompromised children may remain a problem and require the development of new treatments including antiviral drugs. Increasing data on the mechanisms of action of the rotavirus enterotoxin highlight this pleiotropic protein as a good target as well as a unique calcium agonist.

SUMMARY

Rotavirus is now a commonly occurring vaccine-preventable disease among children in developed countries and hopefully this also will soon be true for developing countries. Future studies will determine whether other methods of prevention, such as nonreplicating vaccines and antiviral drugs, will be needed to treat disease in immunocompromised children.

Anti-NSP4 antibody can block rotavirus-induced diarrhea in mice

BACKGROUND

Rotavirus infection is the most common cause of infectious diarrhea and gastroenteritis among children worldwide. The viral proteins (VP), especially VP4- and VP7-induced neutralizing antibodies, were considered to be critical in protective immunity to rotavirus disease. However, whether the antibody to rotavirus nonstructural protein 4 (NSP4) protects against rotavirus-induced diarrhea directly is not completely clear, especially for the protective time course.

MATERIALS AND METHODS

To obtain direct evidence, 12-day-old ICR mice were treated with NSP4 and entire rotavirus to induce diarrhea.

RESULTS

Both NSP4 and rotavirus-treated mice developed diarrhea, which was accompanied by histological changes in the small intestine compared to age-matched control mice. Anti-NSP4 antibody demonstrated protection against both entire rotavirus-induced diarrhea and NSP4-induced diarrhea. The histological changes in the small intestinal were reversible. These data show that early intervention with anti-NSP4 antibody can prevent rotavirus-induced diarrhea in mice; late intervention with anti-NSP4 antibody could halt diarrhea progression in mice.

CONCLUSIONS

Our findings demonstrate for the first time that administration of anti-NSP4 antibody is effective both prior to and during the time course of rotavirus infection. These observations extend our knowledge of rotavirus infection and its therapeutic options.

Design of a multiplex nested PCR for genotyping of the NSP4 from group A rotavirus

A novel PCR method was developed to discriminate amongst genotypes A-C of the rotavirus non-structural protein 4 (NSP4). Genotype-specific primers were designed that correctly identified the NSP4 genotype when evaluated as a multiplex PCR with cell culture adapted rotavirus strains. Rotavirus strains B223 SGIG6P6[1], NCDV SGIG6P6[1] and SA11 SGIG3P5B[2] were used as control for NSP4 genotype A; A34 SGIG5P14[23], Gottfried SGIIG4P2B[6] and Wa SGIIG1P1A[8] for NSP4 genotype B; RRV SGIG3P5B[3] for NSP4 genotype C. Subsequently, the same set of specific primers was used to genotype a set of 77 Swedish clinical samples. The results showed that all human clinical samples analyzed belong to the NSP4 genotype B and the VP6 subgroup II.

Structure of the extended diarrhea-inducing domain of rotavirus enterotoxigenic protein NSP4

Rotavirus nonstructural protein 4 (NSP4) is a multidomainal and multifunctional protein and is recognized as the first virus-encoded enterotoxin. Extensive efforts to crystallize the complete cytoplasmic tail (CT), which exhibits all the known biological functions, have been unsuccessful, and to date, the structure of only a synthetic peptide corresponding to amino acids (aa) 95-137 has been reported. Recent studies indicate that the interspecies-variable domain (ISVD) from aa 135 to 141 as well as the extreme C-terminus are critical determinants of virus virulence and the diarrhea-inducing ability of the protein. Among the five NSP4 genotypes identified, those belonging to genotypes A1, B and C possess either a proline at position 138 or a glycine at 140, while those of A2, D and E lack these residues in the ISVD, suggesting conformational differences in this region among different NSP4s. Here, we examined the crystallization properties of several deletion mutants and report the structure of a recombinant mutant, NSP4:95-146, lacking the N-terminal 94 and C-terminal 29 aa, from SA11 (A1) and I321 (A2) at 1.67 and 2.7 A, respectively. In spite of the high resolution of one of the structures, electron density for the C-terminal 9 residues could not be seen for either of the mutants, and the crystal packing resulted in the creation of a clear empty space for this region. Extension of the unstructured C-terminus beyond aa 146 hindered crystallization under the experimental conditions. The present structure revealed significant differences from that of the synthetic peptide in the conformation of amino acids at the end of the helix as well as the crystal packing owing to the additional space required to accommodate the un structured virulence-determining region. The crystal structure and secondary structure prediction of the NSP4:95-146 mutants from different genotypes suggest that the region C-terminal to aa 137 in all the NSP4 proteins is likely to be unstructured, and this might be of structural and biological functional significance.

Evaluation of serum antibody responses against the rotavirus nonstructural protein NSP4 in children after rhesus rotavirus tetravalent vaccination or natural infection

The immune response elicited by the rotavirus nonstructural protein NSP4 and its potential role in protection against rotavirus disease are not well understood. We investigated the serological response to NSP4 and its correlation with disease protection in sera from 110 children suffering acute diarrhea, associated or not with rotavirus, and from 26 children who were recipients of the rhesus rotavirus tetravalent (RRV-TV) vaccine. We used, as antigens in an enzyme-linked immunosorbent assay (ELISA), affinity-purified recombinant NSP4 (residues 85 to 175) from strains SA11, Wa, and RRV (genotypes A, B, and C, respectively) fused to glutathione S-transferase. Seroconversion to NSP4 was observed in 54% (42/78) of the children who suffered from natural rotavirus infection and in 8% (2/26) of the RRV-TV vaccine recipients. Our findings indicate that NSP4 evokes significantly (P < 0.05) higher seroconversion rates after natural infection than after RRV-TV vaccination. The serum antibody levels to NSP4 were modest (titers of < or = 200) in most of the infected and vaccinated children. A heterotypic NSP4 response was detected in 48% of the naturally rotavirus-infected children with a detectable response to NSP4. Following natural infection or RRV-TV vaccination, NSP4 was significantly less immunogenic than the VP6 protein when these responses were independently measured by ELISA. A significant (P < 0.05) proportion of children who did not develop diarrhea associated with rotavirus had antibodies to NSP4 in acute-phase serum, suggesting that serum antibodies against NSP4 might correlate with protection from rotavirus diarrhea. In addition, previous exposures to rotavirus did not affect the NSP4 seroconversion rate.

Mucosal immunization with a ricin toxin B subunit-rotavirus NSP4 fusion protein stimulates a Th1 lymphocyte response

The castor-oil plant Ricinus communis A-B dimeric toxin B subunit (RTB) was genetically linked at its N-terminus with a 90 amino acid peptide from simian rotavirus SA-11 non-structural protein NSP4(90) and produced in Escherichia coli BL21 cells. Biologically active recombinant NSP4(90)-RTB fusion protein was shown to bind glycoprotein asialofetuin receptor molecules in an in vitro enzyme-linked immunosorbent assay (ELISA). Oral inoculation of the purified NSP4(90)-RTB ligand-antigen fusion protein delivered the chimeric protein to intestinal epidermal cells for mucosal immunization against rotavirus infection. Mice fed the NSP4(90)-RTB fusion protein generated higher humoral and intestinal antibody titers than mice inoculated with NSP4(90) alone. Titers of serum IgG2a antibodies were significantly higher than IgG1 titers suggesting a dominant Th1 lymphocyte immune response. ELISA measurement of cytokines secreted from splenocyte isolated from immunized mice confirmed NSP4(90)-RTB fusion protein stimulates a strong Th1 cell-mediated immune response. The experimental results demonstrate that the ricin toxin B subunit N-terminus can be used as a site for delivery of virus antigens to the gut associated lymphoid tissues for RTB-mediated immune stimulation of antiviral mucosal immune responses.

Humoral immune response to rotavirus NSP4 enterotoxin in Spanish children

The rotavirus non-structural protein 4 (NSP4) has been shown to play a crucial role in rotavirus-induced diarrhea, acting as a viral enterotoxin. It has also been demonstrated that antibody to NSP4 can reduce the severity of rotavirus-induced diarrhea in newborn mice. Two recombinant baculoviruses, expressing the NSP4 protein from the SA11 and Wa rotavirus strains, genotypes A and B, respectively, were used to produce and purify these glycoproteins, which were applied as antigen in an enzyme-linked immunosorbent assay (ELISA) to test the specific antibody response to NSP4 in human sera. Serum samples from 30 children convalescing from a rotavirus infection, from 54 healthy children under 5-years-old, and from 49 adults were tested to determine the presence of antibodies to the viral enterotoxin and to rotavirus structural proteins. Seventy percent of the sera from rotavirus-infected children showed an IgG antibody response to either one or both NSP4 proteins used in this study, although the response was weak. However, IgG antibodies towards either one or both NSP4 proteins were only detected in 26% of the non-convalescent healthy children and in only 18% of the adults. No serum IgA antibodies towards NSP4 were found in this study. IgG antibody recognition of the NSP4 protein from the SA11 and Wa rotavirus strains was not always heterotypic.

Single-chain variable fragment (scFv) antibodies against rotavirus NSP4 enterotoxin generated by phage display

The rotavirus non-structural NSP4 protein causes membrane destabilization as well as an increase in intracellular calcium levels in eukaryotic cells and induces diarrhea in young mice, acting as a viral enterotoxin. In this study the phage display technique was used to generate a panel of single-chain variable fragment (scFv) antibodies specific for the NSP4 protein of the human rotavirus strain Wa from a human semi-synthetic scFv library. After several rounds of panning and selection on NSP4 adsorbed to polystyrene tubes, individual scFv were isolated and characterised by fingerprinting and by sequencing the VH and VL genes. The isolated scFv antibodies specifically recognize NSP4 in enzyme immunoassay and in Western blot. Four truncated forms of the NSP4 protein were constructed which allowed us to map the binding region of the selected scFv antibodies to the C-terminal portion of NSP4. The isolated scFv antibodies constitute valuable tools to analyse the mechanisms of NSP4 functions.

Rotavirus-specific T-cell responses in young prospectively followed-up children

Rotavirus is a major cause of gastroenteritis in young children. Antibodies seem to protect against rotavirus infection but cell-mediated immune responses are probably also important for protection. We evaluated the development of T-cell responses to rotavirus in follow-up samples from 20 healthy children with an increased genetic risk for type 1 diabetes. Blood samples from 16 healthy adults were also available for the study. T-cell proliferation was analysed at 3-6 month intervals from the age of 3 months to the age of 4-5 years using the Wa strain of human rotavirus and the NCDV strain of bovine rotavirus as antigens. IgG and IgA antibodies to rotavirus were studied from simultaneously drawn plasma samples with EIA method using NCDV as an antigen. A total of 24 infections were revealed by antibody analysis. Sixteen children showed diagnostic increases in both IgG and IgA antibodies to rotavirus, while 5 children showed increases in IgA antibodies only and 3 in IgG only. Antibody rises were accompanied by T-cell responses to rotavirus (SI > 3) in 9 of the 24 cases. T-cell responses to purified or lysed human rotavirus were stronger after a rise in rotavirus antibodies than the responses before infection (P = 0.017 and 0.027, respectively). There was a correlation between T-cell responses to purified and lysed human rotavirus and NCDV. Strong T-cell responses to rotavirus were transient and the ability to respond usually disappeared in one year, but in all adults T-cell responses to rotavirus were strong implicating that several infections are needed to develop consistent, strong T-cell responsiveness.

Co-immunization with an HIV-1 Tat transduction peptide-rotavirus enterotoxin fusion protein stimulates a Th1 mucosal immune response in mice

The cholera toxin B subunit (CTB) and a 12 aa HIV-1 Tat transduction peptide were genetically linked to a 90 aa peptide from the murine rotavirus non-structural enterotoxin protein (NSP4) for comparison of receptor directed and transduction peptide mediated antigen targeting to the gut associated lymphoid tissues for enhanced protection against rotavirus infection. Oral immunization with Tat-NSP4(90) fusion protein isolated from Escherichia coli generated detectable anti-NSP4(90) IgG titers in mice. CTB-NSP4(90) fusion protein stimulated higher serum IgG titers than CTB fused to a 22 aa immunodominant epitope NSP4(22) indicating the presence of additional immunogenic epitopes in the NSP4(90) peptide. Mice immunized with CTB-NSP4(22) stimulated high IgG2a antibody levels suggesting a dominant Th1 lymphocyte response. However, mice immunized with CTB-NSP4(90) generated similar levels of IgG1 and IgG2a suggesting equal stimulation of Th1 and Th2 responses. Mice co-immunized with CTB-NSP4(90) and Tat-NSP4(90) fusion proteins generated dominant IgG2a levels indicating that the two ligands co-operate to generate an increased Th1 response.

Antigenic analysis of nonstructural protein (NSP) 4 of group A avian rotavirus strain PO-13

In order to analyze the antigenic structure of nonstructural protein (NSP) 4 of group A avian rotavirus strain PO-13, 25 monoclonal antibodies (MAbs) against NSP4 expressed in Escherichia coli were produced. All MAbs reacted with NSP4 on Western blotting, indicating that they recognized sequential epitopes. To determine the antigenic sites (ASs) recognized by the produced MAbs, seven truncated NSP4s were expressed in E. coli. Western blotting analysis showed that there are at least four major ASs on PO-13 NSP4, designated as AS I located in amino acids (aa) 151 to 169, AS II (aa 136 to 150), AS III (aa 112 to 133) and AS IV (aa 1 to 24). Two MAbs reacted exclusively with AS III encompassing the region that has been reported to be an enterotoxin domain. MAbs against ASs II, III and IV reacted with all avian rotaviruses tested by indirect immunofluorescent antibody assays. MAbs against AS I reacted with turkey strains, Ty-1 and Ty-3, but not with a chicken strain, Ch-1. Nine of 11 MAbs against AS II cross-reacted with NSP4 of mammalian rotavirus strains with different NSP4 genotypes. These results suggest that AS II on NSP4 is widely conserved among a variety of rotaviruses.

Expression and purification of polyhistidine-tagged rotavirus NSP4 proteins in insect cells

The rotavirus nonstructural NSP4 protein, a transmembrane endoplasmic reticulum-specific glycoprotein, has been described as the first viral enterotoxin. Purified NSP4 or a peptide corresponding to NSP4 residues 114-135 induces diarrhea in young mice. NSP4 has a membrane-destabilizing activity and causes an increase in intracellular calcium levels and chloride secretion by a calcium-dependent signalling pathway in eucaryotic cells. In this study, four recombinant baculoviruses were generated expressing the rotavirus NSP4 glycoprotein from the human strains Wa and Ito, the porcine strain OSU, and the simian strain SA11, which belong to two different NSP4 genotypes, A and B. The recombinant glycoproteins, expressed as polyhistidine-tagged molecules, were analyzed by Western blotting and immunoprecipitation. Newborn mice responded with diarrhea after inoculation with each of the recombinant NSP4 proteins.

Evidence for genetic linkage between the gene segments encoding NSP4 and VP6 proteins in common and reassortant human rotavirus strains

NSP4-encoding genes of 78 human rotavirus strains of common or reassortant genotypes were characterized by reverse transcription-PCR followed by sequencing and phylogenetic analysis. It was found that all the human strains characterized clustered into only two of the five known NSP4 genotypes. Linkage between NSP4 genotypes and VP6 subgroups was 100%, NSP4 genotype A being linked to VP6 of subgroup I (SGI) and NSP4 of genotype B being linked to VP6 of SGII. The diversity among the NSP4- and VP6-encoding genes was significantly less than that among the VP7 and VP4 genes in cocirculating human rotavirus strains. Whereas G and P types appear to be shared among different animal species and humans, the NSP4- and VP6-encoding genes appear to segregate according to their host of origin, suggesting that these two proteins may be host restriction determinants. The NSP4-VP6 association may be structurally determined during rotavirus replication (morphogenesis).

Assembly of cholera toxin B subunit full-length rotavirus NSP4 fusion protein oligomers in transgenic potato

A CTB-NSP4(175) fusion gene encoding the entire 175-aa murine rotavirus NSP4 enterotoxin protein was transferred into Solanum tuberosum cells by Agrobacterium tumefaciens-mediated transformation. The CTB-NSP4(175) enterotoxin fusion gene was detected in the genomic DNA of transformed leaves by PCR DNA amplification. Synthesis and assembly of the full-length CTB-NSP4(175) fusion protein into oligomeric structures of pentamer size was detected in transformed tuber extracts by immunoblot analysis. The binding of CTB-NSP4(175 )fusion protein pentamers to intestinal epithelial cell membrane receptors was quantified by G(M1)-ganglioside enzyme-linked immunosorbent assay (G(M1)-ELISA). The ELISA results showed that CTB-NSP4(175) fusion protein was 0.006-0.026% of the total soluble tuber protein. The synthesis of CTB-NSP4(175) monomers and their assembly into biologically active oligomers in transformed potato tubers demonstrates the feasibility of using edible plants for the synthesis of enterocyte-targeted full-length rotavirus enterotoxin antigens that retain all of their pathogenic epitopes for initiation of a maximum mucosal immune response.

Viruses causing gastroenteritis

Acute gastroenteritis is one of the most common diseases in humans worldwide. Viruses are recognized as important causes of this disease, particularly in children. Since the Norwalk virus was identified as a cause of gastroenteritis, the number of viral agents associated with diarrheal disease in humans has steadily increased. Rotavirus is the most common cause of severe diarrhea in children under 5 years of age. Astrovirus, calicivirus and enteric adenovirus are also important etiologic agents of acute gastroenteritis. Other viruses, such as toroviruses, coronaviruses, picobirnaviruses and pestiviruses, are increasingly being identified as causative agents of diarrhea. In recent years, the availability of diagnostic tests, mainly immunoassays or molecular biology techniques, has increased our understanding of this group of viruses. The future development of a safe and highly effective vaccine against rotavirus could prevent, at least, cases of severe diarrhea and reduce mortality from this disease.

Rotavirus vaccines--an update

Rotavirus vaccines offer the best hope to reduce the toll of acute rotaviral gastroenteritis in both developed and developing countries. An association with intussusception (IS) led to the withdrawal of the first licensed rotavirus vaccine in the USA in 1999, forcing a re-evaluation of the safety profile of potentially lifesaving vaccines. Development of new rotavirus vaccine candidates has continued, with a bovine-human reassortant vaccine and an attenuated human monovalent vaccine commencing Phase III trials. Several other candidates are in early Phase I and II clinical trials. The creation of innovative funding strategies to support vaccine development and production, specifically in developing countries, aim to make vaccines available where rotavirus causes the greatest impact.

Systemic and intestinal antibody responses to NSP4 enterotoxin of Wa human rotavirus in a gnotobiotic pig model of human rotavirus disease

Antibody responses to the Wa human rotavirus (HRV) nonstructural protein NSP4, a viral enterotoxin, were evaluated in neonatal gnotobiotic (Gn) pigs. Gn pigs were inoculated orally with one dose of 10(5) fluorescent focus units (FFU) of virulent Wa HRV (HRV-V), to mimic natural infection, or with three doses of 5 x 10(7) FFU attenuated Wa HRV (HRV-A) at 10-day intervals, to mimic oral attenuated rotavirus vaccines, or they were mock inoculated (mock). Subsets of pigs were challenged with 10(6) FFU of virulent Wa HRV at post-inoculation day 28 (PID 28). Post-challenge, the HRV-V pigs were completely protected against diarrhea and virus shedding, whereas the HRV-A pigs had a 50% protection rate against diarrhea and a 67% protection rate against virus shedding. All mock-inoculated pigs shed virus and had diarrhea post-challenge. Isotype antibody titers to NSP4 were compared in serum and intestinal contents, at post-inoculation day (PID) 28 and at post-challenge day 7 (PCD 7/PID 35) by indirect ELISA, using purified recombinant NH2-6xHis-tagged NSP4 of virulent Wa HRV. Pre-challenge, both the HRV-V and HRV-A-inoculated pigs had similar moderate titers of serum IgG antibodies to NSP4. However, only the HRV-V-inoculated pigs developed detectable serum and intestinal IgA antibody titers to NSP4 pre-challenge, compared with the HRV-A-inoculated pigs. The mock-inoculated pigs had no IgM, IgA, or IgG antibodies to NSP4 pre-challenge. All Wa HRV-inoculated pigs developed low to moderate titers of serum IgM, IgG, and IgA antibodies to NSP4 post-challenge, but the mock-inoculated pigs had only IgM antibodies post-challenge. Both Wa HRV-inoculated groups developed low titers of IgA antibody to NSP4 in the small intestinal contents post-challenge, but titers were 5.8-fold higher in the HRV-V pigs. Our results concur with findings that both rotavirus vaccinated and naturally infected children seroconvert with modest IgG antibodies to NSP4 [Johansen et al. (1999) J Med Virol 59:369-367]. These data suggest that Gn pigs could be a useful model to evaluate serum and intestinal IgA antibodies to NSP4 and their role in protection against HRV infection. Further experiments may clarify whether (1) the NSP4 antibodies detected pre-challenge in the HRV-V pigs contribute to the higher protection rates observed, or (2) the reduced or delayed NSP4 antibody responses of the HRV-A pigs are associated with the lower protection rates in these pigs.

Antibody-secreting cell responses to rotavirus proteins in gnotobiotic pigs inoculated with attenuated or virulent human rotavirus

Because of their similarities to infants in mucosal immune responses and their susceptibility to human rotavirus (HRV) diarrhea, gnotobiotic pigs provide a useful model for rotaviral disease. In this study, we performed quantitative enzyme-linked immunospot (ELISPOT) assays to measure local and systemic isotype-specific antibody-secreting cell (ASC) responses to individual structural (VP4, VP6, and VP7) and nonstructural (NSP3 and NSP4) proteins of Wa HRV. The Spodoptera frugiperda cells expressing each recombinant baculovirus HRV protein were formalin fixed and used as antigen for ELISPOT assays. Neonatal gnotobiotic pigs were orally inoculated once with virulent Wa (WaV) or three times with attenuated Wa (WaA) HRV or mock inoculated (Mock) and then were challenged with virulent Wa (WaV/PC) 28 days after the first inoculation. The ASCs from intestinal and systemic lymphoid tissues of pigs from each group were quantitated by ELISPOT assay at the day of challenge, at postinoculation day 28 (WaV, WaA, and Mock) or at postchallenge day (PCD) 7 (WaV+WaV/PC, WaA+WaV/PC, and Mock+WaV/PC). In all virus-inoculated pigs, regardless of the inoculum, lymphoid tissue, or isotype, VP6 induced the highest numbers of ASCs, followed by VP4; ASCs specific for VP7, NSP3, and NSP4 were less numerous. At challenge, total HRV- and HRV protein-specific immunoglobulin A (IgA) and IgG ASCs in intestinal lymphoid tissues were significantly greater in WaV- than in WaA-inoculated pigs, and WaV pigs were fully protected against diarrhea postchallenge, whereas the WaA pigs were partially protected. At PCD 7, there were no significant differences in ASC numbers for any HRV proteins between the WaV+WaV/PC and WaA+WaV/PC groups.

Rotavirus and calicivirus infections of the gastrointestinal tract

Virus infections of the gastrointestinal tract, leading to gastroenteritis, are a common problem in both developed and developing countries. Rotavirus and Norwalk-like viruses are the most common agents responsible for clinically severe disease in humans, and this paper focuses on new information about the mechanisms of pathogenesis and epidemiology of these two pathogens. Rotavirus-induced disease involves a viral enterotoxin and activation of the enteric nervous system, as well as malabsorption, suggesting that common mechanisms of pathogenesis may exist between viral and bacterial pathogens. Each gastrointestinal virus possesses unique molecular properties that can be exploited to discover new information about responses of cells of the gastrointestinal tract. Work continues toward making vaccines for rotavirus and Norwalk-like viruses.

Why should a clinician care about the molecular biology of transport?

This review outlines the progress made over the last few years in three chosen areas of intestinal ion transport. In the field of intestinal secretion, research on the secretion of bicarbonate by pancreatic ducts and duodenal epithelia in cystic fibrosis revealed the crucial role of chloride channel (CFTR) in the control of activity of other transporters involved in bicarbonate secretion. In the area of intestinal absorption, studies on the regulation and physiologic roles of epithelial Na(+)/H(+) exchangers confirmed the suspected involvement of recycling in the acute regulation of NHE3 activity and resulted in formulation of new concepts for the roles of NHE3 and NHE2 in the gastrointestinal tract. Finally, the recent discovery of the first known viral enterotoxin revolutionized our understanding of pathomechanisms of secretory diarrhea during viral infections in humans. All of these findings are discussed in the context of their utility to the practicing gastroenterologist.

Intranasal administration of 2/6-rotavirus-like particles with mutant Escherichia coli heat-labile toxin (LT-R192G) induces antibody-secreting cell responses but not protective immunity in gnotobiotic pigs

We investigated the immunogenicity of recombinant double-layered rotavirus-like particle (2/6-VLPs) vaccines derived from simian SA11 or human (VP6) Wa and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were administered to gnotobiotic pigs intranasally (i.n.) with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT), as mucosal adjuvant. Pigs were challenged with virulent Wa (P1A[8],G1) human rotavirus at postinoculation day (PID) 21 (two-dose VLP regimen) or 28 (three-dose VLP regimen). In vivo antigen-activated antibody-secreting cells (ASC) (effector B cells) and in vitro antigen-reactivated ASC (derived from memory B cells) from intestinal and systemic lymphoid tissues (duodenum, ileum, mesenteric lymph nodes [MLN], spleen, peripheral blood lymphocytes [PBL], and bone marrow lymphocytes) collected at selected times were quantitated by enzyme-linked immunospot assays. Rotavirus-specific immunoglobulin M (IgM), IgA, and IgG ASC and memory B-cell responses were detected by PID 21 or 28 in intestinal and systemic lymphoid tissues after i.n. inoculation with two or three doses of 2/6-VLPs with or without mLT. Greater mean numbers of virus-specific ASC and memory B cells in all tissues prechallenge were induced in pigs inoculated with two doses of SA11 2/6-VLPs plus mLT compared to SA11 2/6-VLPs without mLT. After challenge, anamnestic IgA and IgG ASC and memory B-cell responses were detected in intestinal lymphoid tissues of all VLP-inoculated groups, but serum virus-neutralizing antibody titers were not significantly enhanced compared to the challenged controls. Pigs inoculated with Wa-RF 2/6-VLPs (with or without mLT) developed higher anamnestic IgA and IgG ASC responses in ileum after challenge compared to pigs inoculated with SA11 2/6-VLPs (with or without mLT). Three doses of SA 11 2/6-VLP plus mLT induced the highest mean numbers of IgG memory B cells in MLN, spleen, and PBL among all groups postchallenge. However, no significant protection against diarrhea or virus shedding was evident in any of the 2/6-VLP (with or without mLT)-inoculated pigs after challenge with virulent Wa human rotavirus. These results indicate that 2/6-VLP vaccines are immunogenic in gnotobiotic pigs when inoculated i.n. and that the adjuvant mLT enhanced their immunogenicity. However, i.n. inoculation of gnotobiotic pigs with 2/6-VLPs did not confer protection against human rotavirus challenge.