Identification of cross-reactive and serotype 2-specific neutralization epitopes on VP3 of human rotavirus

Generation and characterization of mouse monoclonal antibodies against the VP4 protein of group A human rotaviruses

Human rotaviruses (RVs) are the leading cause of severe diarrhea in infants and young children worldwide. Among the structural proteins, as a spike protein, rotavirus VP4 plays a key role in both viral attachment and penetration. Currently, studies on monoclonal antibodies (mAbs) against VP4 are limited. In this study, mice were immunized with truncated VP4* to produce murine mAbs. In total, 50 mAbs were produced and characterized. Twenty-four mAbs were genotype-specific and 20 mAbs recognized the common VP4 epitopes shared by P[8], P[4], and P[6] viruses. Thirty-five of the 50 mAbs were neutralizing mAbs, among which nine mAbs could neutralize all three P-genotype RVs, and 10 neutralizing mAbs exhibited conformational sensitivity. Ten mAbs recognized dominant neutralizing epitopes, including the broadly neutralizing mAb 9C4 recognized conformational epitope. Further investigation shows that S376 and S464 are key amino acids for 9C4 binding, however, the exact binding sites of 9C4 remain to be fully defined. Overall, this panel of mAbs has demonstrated utility as immunodiagnostic and research reagents, and could potentially serve as crucial tools for exploring the neutralizing mechanisms and quality control of VP4* protein-based RV subunit vaccines. Further evaluation of cross-neutralizing mAbs could not only improve the understanding of the heterotypic protection conferred by RV vaccines, but also facilitate the development of broadly protective RV vaccines.

Novel antigen panel for modern broad-spectrum recombinant rotavirus A vaccine

Purpose

Recombinant rotavirus A vaccines are being developed as an alternative to existing live oral attenuated vaccines. One of the main problems in the production of such vaccines is the genetic diversity of the strains that are in circulation. The goal of this study was to create an antigen panel for modern broad-spectrum recombinant rotavirus A vaccine.

Materials and Methods

The antigens of rotavirus were cloned and expressed in Escherichia coli. Antigenic specificity was investigated by Western blot analysis, which was performed using commercial polyclonal antisera to several RVA strains. Phylogenetic analysis was based on the amino acid sequences of the VP8^* protein fragment of human RVA isolates representing genotypes P[4], P[6], and P[8].

Results

A universal panel of antigens was established, including consensus and conserved sequences of structural proteins VP8^*, VP5^*, and VP7, which are the main targets of neutralizing antibodies. For the first time, a consensus approach was used in the design of extended antigens based on VP8^* (genotypes P[4], P[6], and P[8]) and VP5^* (genotype P[8]) proteins' fragments. In addition, a gene coding the protein (ep-875) containing several copies of conserved short neutralizing epitopes of VP8^*, VP7, and VP5^* was created. Western blot analysis demonstrated that three synthetic VP8^*-based antigens were not recognized by commercial antiserum against rotavirus strains isolated more than 35 years ago, but the specific activity of the VP5^* and ep-875 antigens was confirmed. The problems of serological mismatch of vaccine strains and antigens with currently circulating strains are discussed.

Conclusion

Five antigens representing sequences of structural proteins belonging to different genotypes can be used in various combinations (from mono- to pentavalent mixtures) for the development of an effective broad-spectrum rotavirus vaccine.

Rescue of Infectious Rotavirus Reassortants by a Reverse Genetics System Is Restricted by the Receptor-Binding Region of VP4

The rotavirus species A (RVA) capsid contains the spike protein VP4, which interacts with VP6 and VP7 and is involved in cellular receptor binding. The capsid encloses the genome consisting of eleven dsRNA segments. Reassortment events can result in novel strains with changed properties. Using a plasmid-based reverse genetics system based on simian RVA strain SA11, we previously showed that the rescue of viable reassortants containing a heterologous VP4-encoding genome segment was strain-dependent. In order to unravel the reasons for the reassortment restrictions, we designed here a series of plasmids encoding chimeric VP4s. Exchange of the VP4 domains interacting with VP6 and VP7 was not sufficient for rescue of viable viruses. In contrast, the exchange of fragments encoding the receptor-binding region of VP4 resulted in virus rescue. All parent strains and the rescued reassortants replicated efficiently in MA-104 cells used for virus propagation. In contrast, replication in BSR T7/5 cells used for plasmid transfection was only efficient for the SA11 strain, whereas the rescued reassortants replicated slowly, and the parent strains failing to produce reassortants did not replicate. While future research in this area is necessary, replication in BSR T7/5 cells may be one factor that affects the rescue of RVAs.

Development of Stable Rotavirus Reporter Expression Systems

Engineered recombinant viruses expressing reporter genes have been developed for real-time monitoring of replication and for mass screening of antiviral inhibitors. Recently, we reported using a reverse genetics system to develop the first recombinant reporter rotaviruses (RVs) that expressed NanoLuc (NLuc) luciferase. Here, we describe a strategy for developing stable reporter RVs expressing luciferase and green or red fluorescent proteins. The reporter genes were inserted into the open reading frame of NSP1 and expressed as a fusion with an NSP1 peptide consisting of amino acids 1 to 27. The stability of foreign genes within the reporter RV strains harboring a shorter chimeric NSP1-reporter gene was greater than that of those in the original reporter RV strain, independent of the transgene inserted. The improved reporter RV was used to screen for neutralizing monoclonal antibodies (MAbs). Sequence analysis of escape mutants from one MAb clone (clone 29) identified an amino acid substitution (arginine to glycine) at position 441 in the VP4 protein, which resides within neutralizing epitope 5-1 in the VP5* fragment. Furthermore, to express a native reporter protein lacking NSP1 amino acids 1 to 27, the 5'- and 3'-terminal region sequences were modified to restore the predicted secondary RNA structure of the NSP1-reporter chimeric gene. These data demonstrate the utility of reporter RVs for live monitoring of RV infections and also suggest further applications (e.g., RV vaccine vectors, which can induce mucosal immunity against intestinal pathogens).IMPORTANCE Development of reporter RVs has been hampered by the lack of comprehensive reverse genetics systems. Recently, we developed a plasmid-based reverse genetics system that enables generation of reporter RVs expressing NLuc luciferase. The prototype reporter RV had some disadvantages (i.e., the transgene was unstable and was expressed as a fusion protein with a partial NSP1 peptide); however, the improved reporter RV overcomes these problems through modification of the untranslated region of the reporter-NSP1 chimeric gene. This strategy for generating stable reporter RVs could be expanded to diverse transgenes and be used to develop RV transduction vectors. Also, the data improve our understanding of the importance of 5'- and 3'-terminal sequences in terms of genome replication, assembly, and packaging.

Multiple Introductions and Antigenic Mismatch with Vaccines May Contribute to Increased Predominance of G12P[8] Rotaviruses in the United States

Rotavirus is the leading global cause of diarrheal mortality for unvaccinated children under 5 years of age. The outer capsid of rotavirus virions consists of VP7 and VP4 proteins, which determine viral G and P types, respectively, and are primary targets of neutralizing antibodies. Successful vaccination depends upon generating broadly protective immune responses following exposure to rotaviruses presenting a limited number of G- and P-type antigens. Vaccine introduction resulted in decreased rotavirus disease burden but also coincided with the emergence of uncommon G and P genotypes, including G12. To gain insight into the recent predominance of G12P[8] rotaviruses in the United States, we evaluated 142 complete rotavirus genome sequences and metadata from 151 clinical specimens collected in Nashville, TN, from 2011 to 2013 through the New Vaccine Surveillance Network. Circulating G12P[8] strains were found to share many segments with other locally circulating strains but to have distinct constellations. Phylogenetic analyses of G12 sequences and their geographic sources provided evidence for multiple separate introductions of G12 segments into Nashville, TN. Antigenic epitopes of VP7 proteins of G12P[8] strains circulating in Nashville, TN, differ markedly from those of vaccine strains. Fully vaccinated children were found to be infected with G12P[8] strains more frequently than with other rotavirus genotypes. Multiple introductions and significant antigenic mismatch may in part explain the recent predominance of G12P[8] strains in the United States and emphasize the need for continued monitoring of rotavirus vaccine efficacy against emerging rotavirus genotypes.IMPORTANCE Rotavirus is an important cause of childhood diarrheal disease worldwide. Two immunodominant proteins of rotavirus, VP7 and VP4, determine G and P genotypes, respectively. Recently, G12P[8] rotaviruses have become increasingly predominant. By analyzing rotavirus genome sequences from stool specimens obtained in Nashville, TN, from 2011 to 2013 and globally circulating rotaviruses, we found evidence of multiple introductions of G12 genes into the area. Based on sequence polymorphisms, VP7 proteins of these viruses are predicted to present themselves to the immune system very differently than those of vaccine strains. Many of the sick children with G12P[8] rotavirus in their diarrheal stools also were fully vaccinated. Our findings emphasize the need for continued monitoring of circulating rotaviruses and the effectiveness of the vaccines against strains with emerging G and P genotypes.

VP4- and VP7-specific antibodies mediate heterotypic immunity to rotavirus in humans

Human rotaviruses (RVs) are the leading cause of severe diarrhea in young children worldwide. The molecular mechanisms underlying the rapid induction of heterotypic protective immunity to RV, which provides the basis for the efficacy of licensed monovalent RV vaccines, have remained unknown for more than 30 years. We used RV-specific single cell-sorted intestinal B cells from human adults, barcode-based deep sequencing of antibody repertoires, monoclonal antibody expression, and serologic and functional characterization to demonstrate that infection-induced heterotypic immunoglobulins (Igs) primarily directed to VP5*, the stalk region of the RV attachment protein, VP4, are able to mediate heterotypic protective immunity. Heterotypic protective Igs against VP7, the capsid glycoprotein, and VP8*, the cell-binding region of VP4, are also generated after infection; however, our data suggest that homotypic anti-VP7 and non-neutralizing VP8* responses occur more commonly in people. These results indicate that humans can circumvent the extensive serotypic diversity of circulating RV strains by generating frequent heterotypic neutralizing antibody responses to VP7, VP8*, and most often, to VP5* after natural infection. These findings further suggest that recombinant VP5* may represent a useful target for the development of an improved, third-generation, broadly effective RV vaccine and warrants more direct examination.

Pathogen evolution and the immunological niche

Host immunity is a major driver of pathogen evolution and thus a major determinant of pathogen diversity. Explanations for pathogen diversity traditionally assume simple interactions between pathogens and the immune system, a view encapsulated by the susceptible-infected-recovered (SIR) model. However, there is growing evidence that the complexity of many host-pathogen interactions is dynamically important. This revised perspective requires broadening the definition of a pathogen's immunological phenotype, or what can be thought of as its immunological niche. After reviewing evidence that interactions between pathogens and host immunity drive much of pathogen evolution, I introduce the concept of a pathogen's immunological phenotype. Models that depart from the SIR paradigm demonstrate the utility of this perspective and show that it is particularly useful in understanding vaccine-induced evolution. This paper highlights questions in immunology, evolution, and ecology that must be answered to advance theories of pathogen diversity.

A new rotavirus VP6-based foreign epitope presenting vector and immunoreactivity of VP4 epitope chimeric proteins

The VP6, the group antigenic rotavirus (RV), is highly conserved and the most abundant, constituting about 39% of the viral structure proteins by weight. The high degree of identity (>87%-99%) in the primary amino acid sequences suggests VP6-based vaccines could potentially provide heterotypic protection. Although some efforts have been made toward producing recombinant rotavirus VP6 vaccines, the native VP6 is still unsatisfactory as an optimal vaccine. The major neutralizing antigenic epitopes that exist on VP4 or VP7 are not on the native VP6, and as a vector the native VP6 lacks insertion sites that can be used for insertion of foreign epitopes. In this study, a new foreign epitope presenting system using VP6 as a vector (VP6F) was constructed on the outer surface of the vector six sites that could be used for insertion of the foreign epitopes created. Using this system, three VP6-based VP4 epitope chimeric proteins were constructed. Results showed that these chimeric proteins reacted with anti-VP6 and -VP4 antibodies, and elicited antibodies against VP6 and VP4 in guinea pigs. Antibodies against VP6F or antibodies against the chimeric proteins neutralized RV Wa and SA11 infection in vitro. It is optimistic that the limitation for using the native VP6 as a vaccine candidate or vector will be solved with our proposed approach. It is expected that this VP6-based epitope presenting system and the VP6-based VP4 epitope chimeric proteins will be valuable for and contribute to the development of novel RV vaccines and vaccine vectors.

[Reverse genetics system of rotaviruses: development and application for analysis of VP4 spike protein]

The rotavirus genome is composed of 11 gene segments of double-stranded (ds)RNA. Reverse genetics is the powerful and ideal methodology for the molecular analysis of virus biology, which enables the virus genome to be artificially manipulated. Although reverse genetics systems exist for nearly all major groups of RNA viruses, development of such a system for rotaviruses is more challenging owing in part to the technical complexity of manipulation of their multi-segmented genome. A breakthrough in the field of rotavirus reverse genetics came in 2006, when we established the first reverse genetics system for rotaviruses, which is a partially plasmid-based system that permits replacement of a viral gene segment with the aid of a helper virus. Although this helper virus-driven system is technically limited and gives low levels of recombinant viruses, it allows alteration of the rotavirus genome, thus contributing to our understanding of these medically important viruses. In this review, I describe the development and application of our rotavirus reverse genetics system, and its future perspectives.

Why does the world need another rotavirus vaccine?

A “Meeting on Upstream Rotavirus Vaccines and Emerging Vaccine Producers” was held at the World Health Organization in Geneva, Switzerland on March 28–30, 2006. The purpose was to discuss, evaluate, and weigh the importance of additional rotavirus vaccine candidates following the successful international licensure of rotavirus vaccines by two major pharmaceutical companies (GlaxoSmithKline and Merck) that had been in development for many years. Both licensed vaccines are composed of live rotaviruses that are delivered orally as have been all candidate rotavirus vaccines evaluated in humans. Each is built on the experience gained with previous candidates whose development had either been discontinued or, in the case of the previously licensed rhesus rotavirus reassortant vaccine (Rotashield), was withdrawn by its manufacturer after the discovery of a rare association with intussusception. Although which alternative candidate vaccines should be supported for development and where this should be done are controversial topics, there was general agreement expressed at the Geneva meeting that further development of alternative candidates is a high priority. This development will help insure that the most safe, effective and economic vaccines are available to children in Third World nations where the vast majority of the >600,000 deaths due to rotavirus occur each year. This review is intended to provide the history and present status of rotavirus vaccines as well as a perspective on the future development of candidate vaccines as a means of promulgating plans suggested at the Geneva meeting.

α-enolase autoantibodies cross-reactive to viral proteins in a mouse model of biliary atresia

BACKGROUND & AIMS

Biliary atresia (BA) is a neonatal cholangiopathy of unknown etiology. The bile duct injury that occurs in patients with BA might result from a hepatobiliary viral infection followed by an autoimmune response against the bile duct epithelia. We aimed to identify autoantigens recognized by serum antibodies in the Rhesus rotavirus (RRV)-induced mouse model of BA; findings were correlated with BA in humans.

METHODS

Bile duct epithelial proteins were screened for their reactivity with serum antibodies from the mouse model of BA using immunoblot assays. Unique proteins that reacted with sera antibodies were identified by mass spectrometry and verified using enzyme-linked immunosorbent assay (ELISA) and immunoblot analyses. Candidate autoantibodies in BA patient sera were analyzed by ELISA.

RESULTS

A bile duct epithelial antigen that reacted strongly with serum immunoglobulin (Ig) G from the mouse model of BA was identified as α-enolase. α-Enolase autoantibody specificity was confirmed by ELISA and immunoblot analyses. Anti-RRV and anti-enolase antibodies cross-reacted with enolase and RRV proteins; we identified regions of sequence homology between RRV and enolase. Serum samples from patients with BA had increased levels of anti-enolase IgM and IgG.

CONCLUSIONS

We have identified autoantibodies against α-enolase in a mouse model of BA (infected with RRV) and in serum samples from patients, indicating a role of humoral autoimmunity in disease pathogenesis. The cross-reactivity between an anti-enolase antibody and RRV proteins indicates that molecular mimicry might activate humoral autoimmunity in BA patients; further studies are required.

[Present and future of reverse genetics of rotavirus]

Rotavirus is the leading pathogen for acute gastroenteritis in mammals and birds. Although the reverse genetics system has been utilized in many viruses, the system using a helper virus was developed for rotavirus in 2006. As a step for antigenic analysis of VP4 antigen of rotavirus, we prepared an infectious rotavirus with a spike protein VP4 having an antigenic mosaic by substituting one of the cross-reactive neutralization epitopes of a simian strain SA-11 with the corresponding one of a human strain DS-1. The future improvement and application of the rotavirus reverse genetics were discussed in this review.

Characterization of full-length VP4 genes of OP354-like P[8] human rotavirus strains detected in Bangladesh representing a novel P[8] subtype

The G1 and G9 rotavirus strains MMC71 and MMC38 (subgroup II, NSP4 genogroup B), respectively, isolated from children in Bangladesh, were analyzed genetically. Full-length VP4 genes of these strains had 98.9% identity to each other and showed 83.9-89.4% identity to those of the P[4] and P[8] rotaviruses. Phylogenetic analysis of VP4 nucleotide sequences revealed that strains MMC38 and MMC71 were located in a lineage of P[8] strains. However, the cluster was highly divergent from the previously established P[8] strains. The VP8* portions of strains MMC38 and MMC71 showed more than 93.9% nucleotide sequence identity to OP354-like P[8] strains, and these strains were clustered into the same lineage. These findings indicate that the VP4 of these strains should be classified into a subtype of the P[8] genotype (P[8]b) that is distinct from that of common P[8] rotaviruses (P[8]a).

Generation of recombinant rotavirus with an antigenic mosaic of cross-reactive neutralization epitopes on VP4

Recombinant rotavirus (RV) with cDNA-derived chimeric VP4 was generated using recently developed reverse genetics for RV. The rescued virus, KU//rVP4(SA11)-II(DS-1), contains SA11 (simian RV strain, G3P[2])-based VP4, in which a cross-reactive neutralization epitope (amino acids 381 to 401) on VP5* is replaced by the corresponding sequence of a different P-type DS-1 (human RV strain, G2P[4]). Serological analyses with a panel of anti-VP4- and -VP7-neutralizing monoclonal antibodies revealed that the rescued virus carries a novel antigenic mosaic of cross-reactive neutralization epitopes on its VP4 surface. This is the first report of the generation of a recombinant RV with artificial amino acid substitutions.

Rotavirus-neutralizing antibodies inhibit virus binding to integrins alpha 2 beta 1 and alpha 4 beta 1

Rotavirus outer capsid proteins VP5(*), VP8(*) and VP7 elicit neutralizing, protective antibodies. The alpha 2 beta 1 integrin is a cellular receptor for rotavirus that is bound by VP5(*). Some rotaviruses also recognize the alpha 4 beta 1 integrin. In this study, the effects of antibodies to rotavirus on virus binding to recombinant alpha 2 beta 1 and alpha 4 beta 1 expressed on K562 cells were determined. All neutralizing monoclonal antibodies to VP5(*) tested (YO-2C2, 2G4, 1A10) and two to VP7 (RV-3:2, RV-4:2) inhibited rotavirus binding to alpha 2 beta 1. Rotavirus binding to alpha 4 beta 1 was reduced by 2G4 and neutralizing antibody F45:2, directed to VP7. However, a neutralizing antibody to VP8(*) (RV-5:2) and one to VP7 (RV-3:1) did not affect rotavirus binding to these integrins. Virus-cell binding was unaffected by non-neutralizing antibody RVA to the rotavirus inner capsid protein VP6. The attachment of human rotavirus strain Wa to these integrins was inhibited by infection sera with neutralizing activity collected from two children hospitalised with severe rotavirus gastroenteritis. A negative reference serum did not affect rotavirus-cell attachment. As the binding of rotaviruses to alpha 2 beta 1 and alpha 4 beta 1 is inhibited by neutralizing antibodies to VP5(*) and VP7, and serum from children with rotavirus disease, rotavirus recognition of these integrins may be important for host infection.

Cloning, expression, and purification of recombinant bovine rotavirus hemagglutinin, VP8*, in Escherichia coli

Rotavirus VP8* subunit is the minor trypsin cleavage product of the spike protein VP4, which is the major determinant of the viral infectivity and neutralization. To study the structure-function relationship of this fragment and to obtain type-specific reagents, substantial amounts of this protein are needed. Thus, full-length VP8* cDNA, including the entire trypsin cleavage-encoding region in gene 4, was synthesized and amplified by RT-PCR from total RNA purified from bovine rotavirus strain C486 propagated in MA104 cell culture. The extended VP8* cDNA (VP8ext) was cloned into the pGEM-T Easy plasmid and subcloned into the Escherichia coli expression plasmid pET28a(+). The correspondent 30 kDa protein was overexpressed in E. coli BL21(DE3)pLysS cells under the control of the T7 promoter. The identity and the antigenicity of VP8ext were confirmed on Western blots using anti-His and anti-rotavirus antibodies. Immobilized Ni-ion affinity chromatography was used to purify the expressed protein resulting in a yield of 4 mg of VP8ext per liter of induced E. coli culture. Our results indicate that VP8ext maintained its native antigenicity and specificity, providing a good source of antigen for the production of P type-specific immune reagents. Detailed structural analysis of pure recombinant VP8 subunit should allow a better understanding of its role in cell attachment and rotavirus tropism. Application of similar procedure to distinct rotavirus P serotypes should provide valuable P serotype-specific immune reagents for rotavirus diagnostics and epidemiologic surveys.

Structural rearrangements in the membrane penetration protein of a non-enveloped virus

Non-enveloped virus particles (those that lack a lipid-bilayer membrane) must breach the membrane of a target host cell to gain access to its cytoplasm. So far, the molecular mechanism of this membrane penetration step has resisted structural analysis. The spike protein VP4 is a principal component in the entry apparatus of rotavirus, a non-enveloped virus that causes gastroenteritis and kills 440,000 children each year. Trypsin cleavage of VP4 primes the virus for entry by triggering a rearrangement that rigidifies the VP4 spikes. We have determined the crystal structure, at 3.2 A resolution, of the main part of VP4 that projects from the virion. The crystal structure reveals a coiled-coil stabilized trimer. Comparison of this structure with the two-fold clustered VP4 spikes in a approximately 12 A resolution image reconstruction from electron cryomicroscopy of trypsin-primed virions shows that VP4 also undergoes a second rearrangement, in which the oligomer reorganizes and each subunit folds back on itself, translocating a potential membrane-interaction peptide from one end of the spike to the other. This rearrangement resembles the conformational transitions of membrane fusion proteins of enveloped viruses.

Isolation of human monoclonal antibodies that neutralize human rotavirus

A human antibody library constructed by utilizing a phage display system was used for the isolation of human antibodies with neutralizing activity specific for human rotavirus. In the library, the Fab form of an antibody fused to truncated cp3 is expressed on the phage surface. Purified virions of strain KU (G1 serotype and P[8] genotype) were used as antigen. Twelve different clones were isolated. Based on their amino acid sequences, they were classified into three groups. Three representative clones-1-2H, 2-3E, and 2-11G-were characterized. Enzyme-linked immunosorbent assay with virus-like particles (VLP-VP2/6 and VLP-VP2/6/7) and recombinant VP4 protein produced from baculovirus recombinants indicated that 1-2H and 2-3E bind to VP4 and that 2-11G binds to VP7. The neutralization epitope recognized by each of the three human antibodies might be human specific, since all of the antigenic mutants resistant to mouse monoclonal neutralizing antibodies previously prepared were neutralized by the human antibodies obtained here. After conversion from the Fab form of an antibody into immunoglobulin G1, the neutralizing activities of these three clones toward various human rotavirus strains were examined. The 1-2H antibody exhibited neutralizing activity toward human rotaviruses with either the P[4] or P[8] genotype. Similarly, the 2-3E antibody showed cross-reactivity against HRVs with the P[6], as well as the P[8] genotype. In contrast, the 2-11G antibody neutralized only human rotaviruses with the G1 serotype. The concentration of antibodies required for 50% neutralization ranged from 0.8 to 20 micro g/ml.

The rhesus rotavirus VP4 sialic acid binding domain has a galectin fold with a novel carbohydrate binding site

Cell attachment and membrane penetration are functions of the rotavirus outer capsid spike protein, VP4. An activating tryptic cleavage of VP4 produces the N-terminal fragment, VP8*, which is the viral hemagglutinin and an important target of neutralizing antibodies. We have determined, by X-ray crystallography, the atomic structure of the VP8* core bound to sialic acid and, by NMR spectroscopy, the structure of the unliganded VP8* core. The domain has the beta-sandwich fold of the galectins, a family of sugar binding proteins. The surface corresponding to the galectin carbohydrate binding site is blocked, and rotavirus VP8* instead binds sialic acid in a shallow groove between its two beta-sheets. There appears to be a small induced fit on binding. The residues that contact sialic acid are conserved in sialic acid-dependent rotavirus strains. Neutralization escape mutations are widely distributed over the VP8* surface and cluster in four epitopes. From the fit of the VP8* core into the virion spikes, we propose that VP4 arose from the insertion of a host carbohydrate binding domain into a viral membrane interaction protein.

Proteolysis of monomeric recombinant rotavirus VP4 yields an oligomeric VP5* core

Rotavirus particles are activated for cell entry by trypsin cleavage of the outer capsid spike protein, VP4, into a hemagglutinin, VP8*, and a membrane penetration protein, VP5*. We have purified rhesus rotavirus VP4, expressed in baculovirus-infected insect cells. Purified VP4 is a soluble, elongated monomer, as determined by analytical ultracentrifugation. Trypsin cleaves purified VP4 at a number of sites that are protected on the virion and yields a heterogeneous group of protease-resistant cores of VP5*. The most abundant tryptic VP5* core is trimmed past the N terminus associated with activation for virus entry into cells. Sequential digestion of purified VP4 with chymotrypsin and trypsin generates homogeneous VP8* and VP5* cores (VP8CT and VP5CT, respectively), which have the authentic trypsin cleavages in the activation region. VP8CT is a soluble monomer composed primarily of beta-sheets. VP5CT forms sodium dodecyl sulfate-resistant dimers. These results suggest that trypsinization of rotavirus particles triggers a rearrangement in the VP5* region of VP4 to yield the dimeric spikes observed in icosahedral image reconstructions from electron cryomicroscopy of trypsinized rotavirus virions. The solubility of VP5CT and of trypsinized rotavirus particles suggests that the trypsin-triggered conformational change primes VP4 for a subsequent rearrangement that accomplishes membrane penetration. The domains of VP4 defined by protease analysis contain all mapped neutralizing epitopes, sialic acid binding residues, the heptad repeat region, and the membrane permeabilization region. This biochemical analysis of VP4 provides sequence-specific structural information that complements electron cryomicroscopy data and defines targets and strategies for atomic-resolution structural studies.

Rotavirus strain diversity in Blantyre, Malawi, from 1997 to 1999

In a 2-year study of viral gastroenteritis in children in Blantyre, Malawi, the diversity of rotavirus strains was investigated by using electropherotyping, reverse transcription-PCR amplification of the VP7 and VP4 genes (G and P genotyping), and nucleotide sequencing. Of 414 rotavirus strains characterized, the following strain types were identified: P[8], G1 (n = 111; 26.8%); P[6], G8 (n = 110; 26.6%); P[8], G3 (n = 93; 22.5%); P[4], G8 (n = 31; 7.5%); P[8], G4 (n = 21; 5.1%); P[6], G3 (n = 12; 2.9%); P[6], G1 (n = 7; 1.7%); P[6], G9 (n = 3; 0.7%); P[6], G4 (n = 3; 0.7%); P[4], G3 (n = 1; 0.2%); and mixed (n = 15; 3.6%). While all strains could be assigned a G type, seven strains (1.7%) remained P nontypeable. The majority of serotype G8 strains and all serotype G9 strains had short electropherotype profiles. All remaining typeable strains had long electropherotypes. Divergent serotype G1 rotaviruses, which contained multiple base substitutions in the 9T-1 primer binding site, were commonly identified in the second year of surveillance. Serotype G2 was not identified. Overall, G8 was the most frequently identified VP7 serotype (n = 144; 34.8%) and P[8] was the most frequently detected VP4 genotype (n = 227; 54.8%). Partial sequence analysis of the VP4 gene of genotype P[8] rotaviruses identified three distinct clusters, which predominantly (but not exclusively) comprised strains belonging to a distinct VP7 serotype (G1, G3, or G4). As a result of mutations in the 1T-1 primer binding site, strains belonging to each cluster required a separate primer for efficient typing. One cluster, represented by P[8], G4 strain OP354, was highly divergent from the established Wa and F45 VP4 P[8] lineages. As is the case for some other countries, the diversity of rotaviruses in Malawi implies that rotavirus vaccines in development will need to protect against a wider panel of serotypes than originally envisioned.

Development, characterization, and diagnostic applications of monoclonal antibodies against bovine rotavirus

Hybridomas secreting monoclonal antibodies (MAbs) against the Nebraska calf diarrhea strain of bovine rotavirus (BRV) were characterized. Indirect fluorescent-antibody assay, immunodot assay, and immunoprecipitation were used to select hybridomas that produced anti-BRV MAbs. Seven of the MAbs were shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot assay to be reactive with the BRV outer capsid protein, VP7, which has a molecular mass of 37.5 kDa. None of the seven MAbs were reactive with canine rotavirus, bovine coronavirus, or uninfected Madin-Darby bovine kidney cells. Two clones, 8B4 (immunoglobulin G2a [IgG2a]) and 2B11 (IgG1), were found suitable for use in an antigen capture enzyme-linked immunosorbent assay for detecting BRV in bovine fecal samples. Both were subtype A specific (G6 subtype) but did not react with all isolates of BRV group A.

Immune response to rotavirus VP4 expressed in an attenuated strain of Shigella flexneri

An attenuated strain of Shigella flexneri was utilised to express viral protein (VP) 4 of rotavirus and the immunogenicity of the recombinant constructs was studied in BALB/c mice. VP4 was expressed as a fusion with maltose binding protein (MBP) in both the cytoplasm and periplasm, with a much higher level of expression occurring in the former. While all constructs induced a Shigella-specific response in mice, only the construct expressing MBP-VP4 in the cytoplasm of Shigella stimulated an immune response specific to rotavirus. This study demonstrates that Shigella can be used to deliver rotavirus antigens and induces an immune response directed towards both rotavirus and Shigella.

Genetic and antigenic characterization of a serotype P[6]G9 human rotavirus strain isolated in the United States

During an epidemiologic survey of rotavirus infections established to monitor the prevalent G serotypes circulating in the United States, human P[6]G9, subgroup I rotavirus strains causing symptomatic infections were identified as the fourth most common serotype. In this report we describe the molecular and antigenic characterization of one of these P[6]G9 isolates (US1205). Neutralization and sequencing studies have demonstrated that both outer capsid proteins, VP7 and VP4, of US1205 are closely related to but genetically and antigenically distinguishable from those of standard G9 strains (e.g., F45, WI61) and standard P2A[6] strains (e. g., ST3, M37). Thus the complete antigenic type of US1205 is P2A[6]G9, subgroup I. Sequence analysis of the VP6 and NSP4 genes of US1205 indicates that strain US1205 possessed VP6 subgroup I and NSP4A genotype specificities. Finally, Northern hybridization studies suggest that the P[6]G9 strains are closely related to members of the DS-1 genogroup except for their P[6] VP4 gene, which has been commonly identified in strains of both major human genogroups, and their G9 VP7 gene, which may have been derived by reassortment with a Wa genogroup strain. Examination of historic collections and prospective surveillance of strains will be needed to determine whether this strain has been present for some time or if it is emerging to compete with the other common serotypes of rotavirus.

Serotype specificity of the neutralizing-antibody response induced by the individual surface proteins of rotavirus in natural infections of young children

The relative contribution of the rotavirus surface proteins, VP4 and VP7, to the induction of homotypic as well as heterotypic neutralizing antibodies (NtAbs) in natural infections was studied. The NtAb titers of paired sera from 70 infants with serologically defined primary rotavirus infections were determined with a panel of rotavirus reassortants having one surface protein from a human rotavirus (serotypes G1 to G4 for VP7 and P1A and P1B for VP4) and the other surface protein from a heterologous animal rotavirus strain. A subset of 37 children were evaluated for epitope-specific antibodies to the two proteins by an epitope-blocking assay. The infants were found to seroconvert more frequently to VP4 than to VP7 by both methods, although the titers of the seroconverters were higher to VP7 than to VP4. Both proteins induced homotypic as well as heterotypic NtAbs. G1 VP7 frequently induced a response to both G1 and G3 VP7s, while G3 VP7 and P1A VP4 induced mostly homotypic responses.

A neutralizing monoclonal antibody to bovine rotavirus VP8 neutralizes rotavirus infection without inhibiting virus attachment to MA-104 cells

VP8*, the N-terminal cleavage product of rotavirus VP4, contains the virus neutralizing epitopes in the hemagglutination domain. To map the neutralizing epitope, we developed monoclonal antibodies specific for VP4 of bovine rotavirus C486 (BRV). A neutralizing escape mutant was generated by one of these monoclonal antibodies (2E8) and a point mutation (Glu-->Asp) was found at aa 116 of VP8*. To investigate the effect of this mutation on the cellular binding and hemagglutination activities, the VP8* genes of the escape mutant and wild type (WT) virus were expressed in E. coli and their functional activities were compared. Both the escape mutant and WT virus VP8* showed hemagglutination and MA-104 cell binding activities. However, hemagglutination activity of the WT virus VP8* was inhibited by 2E8, but that of the escape mutant VP8* was not. These data indicate that the neutralizing epitope is located in the HA domain but is not critical for rotavirus attachment to MA-104 cells. To understand virus neutralization, radiolabelled BRV was incubated with 2E8 and the distribution of radioactivity in a CsCI density gradient was analysed as was the morphology of the virions in peak fractions. Interaction of 2E8 with rotavirus led to virus morphological changes with a concomitant shift in buoyant density. These data suggest that aa 116 influences the binding of 2E8 which in turn may alter virus integrity.

Comparison of enzyme immunoassay, PCR, and type-specific cDNA probe techniques for identification of group A rotavirus gene 4 types (P types)

This study was designed to evaluate three techniques most commonly used to identify the VP4 (P) types of human group A fecal rotaviruses. The techniques included PCR with nested primers and hybridization with PCR-generated probes (to determine the P genotypes). The results obtained by these genetic techniques were evaluated against those obtained by an enzyme immunoassay (EIA) incorporating neutralizing monoclonal antibodies (N-MAbs) reacting with three major human P serotypes (serotypes P1A, P1B, and P2A). The P types of the rotaviruses present in 102 fecal specimens were determined under code by each of the three assays. The specificity of each assay was evaluated against a "gold standard" putative P type (P serotype and genotype) deduced from knowledge of the VP7 (G) type and the origin of the fecal specimen. Overall comparison of the results showed respective sensitivities and specificities of 92 and 92% for reverse transcription-PCR, 80 and 99% for hybridization, and 73 and 91% for EIA with N-MAbs. The hybridization assay retained high sensitivity with specimens stored for > or = 10 years. Hybridization assays with nonradioactive probes are relatively inexpensive and are suited for use in developing countries. In summary, both genetic assays showed high sensitivities and specificities in assigning a P type to human fecal rotavirus strains. Further evaluation of the EIA with N-MAbs is required, together with incorporation of new N-MAbs for the detection of the additional P types detected in developing countries.

Rotavirus contains integrin ligand sequences and a disintegrin-like domain that are implicated in virus entry into cells

Rotavirus contains two outer capsid viral proteins, the spike protein VP4 and major capsid component VP7, both of which are implicated in cell entry. We show that VP4 and VP7 contain tripeptide sequences previously shown to act as recognition sites for integrins in extracellular matrix proteins. VP4 contains the alpha2beta1 integrin ligand site DGE. In VP7, the alphaxbeta2 integrin ligand site GPR and the alpha4beta1 integrin ligand site LDV are embedded in a novel disintegrin-like domain that also shows sequence similarity to fibronectin and the tie receptor tyrosine kinase. Microorganism sequence homology to these ligand motifs and to disintegrins has not been reported previously. In our experiments, peptides including these rotaviral tripeptides and mAbs directed to these integrins specifically blocked rotavirus infection of cells shown to express alpha2beta1 and beta2 integrins. Rotavirus VP4-mediated cell entry may involve the alpha2beta1 integrin, whereas VP7 appears to interact with alphaxbeta2 and alpha4beta1 integrins.

Human rotavirus VP4 contains strain-specific, serotype-specific and cross-reactive neutralization sites

The neutralization epitopes of human rotavirus VP4 were studied by using a panel of neutralization monoclonal antibodies previously shown to be strain-specific (RV-3:3), serotype-specific (RV-5:2, ST-3:3) or cross-reactive (F45:4). Antigenic variants of human rotaviruses RV-3, ST-3, RV-5 and F45 resistant to neutralization by the appropriate of VP4 specific monoclonal antibodies (RV-3:3, ST-3:3, RV-5:2 and F45:4 respectively) were selected. By nucleotide sequence analysis and single strand conformational polymorphism analysis of these variants, three sites of neutralization on VP5* and one site on VP8* were identified. At or near to the putative fusion region on VP5*, a strain-specific site (aa383), a serotype P1A-P2 cross-reactive site (aa392) and a serotype P2-specific site (aa397) were found. On VP8*, a serotype P1B-specific site at aa148 was detected. These results confirmed the importance of the putative fusion region in neutralization and have identified a new neutralization site in the hypervariable region of VP8* which is specific for serotype P1B human rotaviruses.

Nucleotide sequence and expression in E. coli of the complete P4 type VP4 from a G2 serotype human rotavirus

The complete sequence of a P4 type VP4 gene from a G2 serotype human rotavirus, IS2, isolated in India has been determined. Although the IS2 VP4 is highly homologous to the other P4 type alleles, it contained acidic amino acid substitutions at several positions that make it acidic among the P4 type alleles that are basic. Moreover, comparative sequence analysis revealed unusual polymorphism in members of the P4 type at amino acid position 393 which is highly conserved in members of other VP4 types. To date, expression of complete VP4 in E. colic has not been achieved. In this study we present successful expression in E. coli of the complete VP4 as well as VP8* and VP5* cleavage subunits in soluble form as fusion proteins of the maltose-binding protein (MBP) and their purification by single-step affinity chromatography. The hemagglutinating activity exhibited by the recombinant protein was specifically inhibited by the antiserum raised against it. Availability of pure VP4 proteins should facilitate development of polyclonal and monoclonal antibodies (MAbs) for P serotyping of rotaviruses.

VP4 and VP7 typing using monoclonal antibodies

Both rotavirus outer capsid proteins, VP4 and VP7, elicit neutralizing antibodies. Neutralizing mouse monoclonal antibodies (N-MAbs) to VP7 are easily derived and have been used widely and successfully to serotype both stool-derived and culture-adapted rotaviruses by enzyme immunoassay (EIA). Generally, approximately 70% of rotaviruses in stool samples are typable by VP7 EIA, an inexpensive and practical method. Variations in antigenic regions between strains within human rotavirus serotypes 1, 2, 4, and 9 have been recorded. These have been termed monotypes because they are detected with N-MAbs. The molecular basis for monotypes has been determined by mapping mutations selected in N-MAb-resistant antigenic variants, and by sequence analysis of the gene encoding VP7 in newly recognized monotypes. Antigenic regions A, B and C in VP7 are involved. In order to detect all members of a particular VP7 serotype, it is necessary to type with a panel of N-MAbs specific for that serotype. N-MAbs to VP4 of human rotavirus are difficult to raise and few have proven suitable for VP4 serotyping by EIA. The specificity of the assay for each P type is highest when the VP7 serotype specificity of the capture antiserum is matched to the G type of the rotavirus in the test sample. The VP4 EIA gives similar typing rates to the VP7 typing EIA. N-MAbs directed to VP8, the smaller subunit of VP4 generated by proteolytic cleavage, are more likely to show serotype specificity. Some N-MAbs that select mutations in the putative fusion region of VP5, the larger subunit of VP4, show cross-reactivity with extracts of normal, uninfected MA 104 cells and with fetal bovine serum. These N-MAbs also give elevated EIA OD readings with rotavirus-positive, but previously non-reactive fecal samples which have been frozen and thawed repeatedly. Overall, VP8-reactive N-MAbs appear most suitable for VP4 typing by EIA.

Characterization of recombinant polioviruses expressing regions of rotavirus VP4, hepatitis B surface antigen, and herpes simplex virus type 2 glycoprotein D

Recombinant polioviruses expressing antigens from rotavirus, herpes simplex virus type 2, and hepatitis B virus were generated. Fusion of the heterologous polypeptides to the amino terminus of the poliovirus polyprotein did not prevent myristylation of VP0, suggesting a novel mechanism of myristylation for these recombinant viruses. The effects of the parental genetic background, different foreign sequences, and different insert sizes on growth characteristics were compared. Both the size and the nature of the heterologous sequence appeared to be factors influencing the growth and stability of recombinant polioviruses. All of the recombinants showed a temperature-sensitive phenotype, regardless of the genetic background (attenuated or wild type) from which they were derived. Preliminary studies with transgenic mice carrying the poliovirus receptor gene are discussed.

Geographic distribution of human rotavirus VP4 genotypes and VP7 serotypes in five South African regions

The rotavirus outer capsid proteins elicit the production of neutralizing antibodies and are known to play a role in inducing resistance to disease. In this study, cDNA probes directed at the six most common human rotavirus VP7 serotypes (G1 to G4, G8, and G9) and five human rotavirus VP4 genotypes (P4, P6, P8, P9, and P10) were utilized. Hybridization analysis of 572 human rotavirus strains collected from five regions in South Africa was performed to determine the distribution of the VP7 serotypes and VP4 genotypes in nature. VP7 serotype G1 was identified most frequently, occurring in 51% of the rotavirus strains tested. VP7 serotypes G2 and G4 occurred in similar numbers, although their distribution varied regionally. Few serotype G3 strains and no G8 or G9 strains were identified. The P8 VP4 genotype occurred most frequently overall (66%), and the P4 genotype was detected next most frequently. The P6 genotype was identified in 28 symptomatically infected neonates and in 8 symptomatic infants. Few P9 strains were identified. The potential for reassortment events was demonstrated by dual infections with different viruses.

The Salmonella ompC gene: structure and use as a carrier for heterologous sequences

The Salmonella typhi (St) ompC gene codes for a major outer membrane protein (OMP) that is highly expressed in both low and high osmolarity. By hybridization studies with the entire gene or with segments thereof, ompC was found to be highly conserved within 11 different Salmonella serotypes, with the exception of S. arizonae. The study included several St isolates from Mexico and Indonesia. Variation was only detected in two (e and f) of the seven regions previously found to vary between St and E. coli ompC. Chimeric OmpC proteins, carrying a rotavirus VP4 capsid protein epitope, are well recognized by a specific monoclonal antibody (mAb) against this epitope, either in OMP preparations (by enzyme-linked immunosorbent assay; ELISA) or intact cells (by ELISA and immunogold-labelling), indicating that regions c and f are oriented towards the cell surface and are probably exposed. As has been shown before for other regulated OMP, this experimental approach could be useful for the presentation of heterologous epitopes in order to gain knowledge about porin topology, for testing the effect of altered porin surface epitopes on bacterial physiology, or else, in the development of multivalent vaccines.

Mapping the hemagglutination domain of rotaviruses

Most strains of animal rotaviruses are able to agglutinate erythrocytes, and the surface protein VP4 is the virus hemagglutinin. To map the hemagglutination domain on VP4 while preserving the conformation of the protein, we constructed full-length chimeras between the VP4 genes of hemagglutinating (YM) and nonhemagglutinating (KU) rotavirus strains. The parental and chimeric genes were expressed in insect cells, and the recombinant VP4 proteins were evaluated for their capacity to agglutinate human type O erythrocytes. Three chimeric genes, encoding amino acids 1 to 208 (QKU), 93 to 208 (QC), and 93 to 776 (QYM) of the YM VP4 protein in a KU VP4 background, were constructed. YM VP4 and chimeras QKU and QC were shown to specifically hemagglutinate, indicating that the region between amino acids 93 and 208 of YM VP4 is sufficient to determine the hemagglutination activity of the protein.

Identification of two independent neutralization domains on the VP4 trypsin cleavage products VP5* and VP8* of human rotavirus ST3

The antigenic structure of the VP4 protein of human rotavirus (HRV) strains Wa and ST3 was studied by using a panel of Wa- and ST3-derived VP4-specific neutralizing monoclonal antibodies (NMAbs) and NMAb-resistant variants. The VP4-coding genes from three Wa and three ST3 variants were sequenced. For Wa VP4, one homotypic and one heterotypic neutralization site, at amino acids 458 and 392, respectively, were identified. For ST3 VP4, three neutralization sites were found at amino acids 72, 217, and 385 that are either homotypic or associated with limited cross-reactivity. Cross-neutralization assays using several pairs of NMAbs and resistant variants showed that Wa VP4 has at least one large neutralization domain on its larger trypsin cleavage product, VP5*, consisting of several operationally related epitopes. VP4 of ST3 has at least two neutralization domains, one located on VP5* that is operationally related to the large neutralization domains on VP5* from HRVs Wa and KU, as well as an independent neutralization domain on VP8*, the smaller trypsin cleavage product of VP4.

Localization of rotavirus VP4 neutralization epitopes involved in antibody-induced conformational changes of virus structure

We previously characterized three neutralization-positive epitopes (NP1 [1a and 1b], NP2, and NP3) and three neutralization-negative epitopes on the simian rotavirus SA11 VP4 with 13 monoclonal antibodies (MAbs). Conformational changes occurred as a result of the binding of NP1 MAbs to the SA11 spike VP4, and enhanced binding of all neutralization-negative MAbs was observed when NP1 MAbs bound VP4 in a competitive MAb capture enzyme-linked immunosorbent assay. To further understand the structure and function of VP4, we have continued studies with these MAbs. Electron microscopic and sucrose gradient analyses of SA11-MAb complexes showed that triple-layered viral particles disassembled following treatment with NP1b MAbs 10G6 and 7G6 but not following treatment with NP1a MAb 9F6, NP2 MAb 2G4, and NP3 MAb 23. Virus infectivity was reduced approximately 3 to 5 logs by the NP1b MAbs. These results suggest that NP1b MAb neutralization occurs by a novel mechanism. We selected four neutralization escape mutants of SA11 with these VP4 MAbs and characterized them by using plaque reduction neutralization assays, hemagglutination inhibition assays, and an antigen capture enzyme-linked immunosorbent assay. These analyses support the previous assignment of the NP1a, NP1b, NP2, and NP3 MAbs into separate epitopes and confirmed that the viruses were truly neutralization escape mutants. Nucleotide sequence analyses found 1 amino acid (aa) substitution in VP8* of VP4 at (i) aa 136 for NP1a MAb mutant 9F6R, (ii) aa 180 and 183 for NP1b MAb mutants 7G6R and 10G6R, respectively, and (iii) aa 194 for NP3 MAb mutant 23R. The NP1b MAb mutants showed an unexpected enhanced binding with heterologous nonneutralization MAb to VP7 compared with parental SA11 and the other mutants. Taken together, these results suggest that the NP1b epitope is a critical site for VP4 and VP7 interactions and for virus stability.

Survey on the distribution of the gene 4 alleles of human rotaviruses by polymerase chain reaction

The presence of six gene 4 alleles (or VP4 genotypes) in human rotaviruses has been recognized. Using 16 representative cultivable human rotavirus strains, we confirmed the specificity of VP4 genotyping by polymerase chain reaction (PCR) using the nested oligonucleotides specific to each of the four representative gene 4 alleles. Using the PCR, we surveyed the gene 4 alleles of 199 human rotaviruses in stools collected in Japan and Thailand. Strains with the gene 4 allele, corresponding to P1A serotype, were shown to be the most prevalent, but two strains with P2 gene 4 allele and one strain with P3 gene 4 allele were detected in Thailand and in Japan, respectively.

Rotaviruses: immunological determinants of protection against infection and disease

Although studies of rotavirus immunity in experimental animals and humans have often yielded conflicting data, a preponderance of evidence supports the following answers to the questions initially posed. 1. What is the importance of virus serotype in formulating an optimal vaccine? Both vp4 and vp7 induce virus-neutralizing antibodies after either natural infection or immunization; the capacity of vp4 to induce rotavirus-specific neutralizing antibodies is probably greater than that of vp7. However, protection against disease after immunization of infants and young children is induced by strains heterotypic to the challenge virus (e.g., immunization with WC3 induces protection against disease induced by serotypically distinct human G1 strains). In addition, oral inoculation of infants with primate or bovine reassortant rotaviruses containing genes that encode human vp7 has not consistently induced a higher level of protection against challenge than that induced by parent animal rotaviruses (see Table I). Therefore, although vp4 or vp7 or both are probably important in inducing protection against challenge, it has not been clearly demonstrated that inclusion of the epidemiologically important human (as distinct from animal) P or G type is important in protection against human disease. 2. Which immunological effector arm most likely protects against rotavirus disease? No immunological effector arm clearly explains protection against heterotypic challenge. Protection against disease is not predicted by rotavirus-specific neutralizing antibodies in serum. Rotavirus-specific, binding sIgA in feces [detected by enzyme-linked immunosorbent assay (ELISA)] induced after natural infection does correlate with protection against disease induced by subsequent infection. However, protection after immunization with WC3 may occur in the absence of a detectable fecal sIgA response. The relationship between rotavirus-binding sIgA and sIgA-mediated neutralizing activity directed against the challenge virus remains to be determined. Binding rotavirus-specific sIgA in feces detected by ELISA may only be a correlate of other events occurring at the intestinal mucosal surface. The presence of broadly cross-reactive, rotavirus-specific CTLs at the intestinal mucosal surface of mice acutely after infection is intriguing. It would be of interest to determine the degree to which the presence of cross-reactive, rotavirus-specific CTLs in the circulation is predictive of the presence of virus-specific CTLs among intestinal lymphocytes and protection against challenge. Unfortunately, studies of virus-specific CTLs are difficult to perform in children. 3. By what means is virus antigen best presented to the host to elicit a protective immune response? Oral inoculation may not be necessary to induce a protective, virus-specific immune response at the intestinal mucosal surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Rotavirus vaccines and vaccination potential

The development of a successful rotavirus vaccine is a complex problem. Our review of rotavirus vaccine development shows that many challenges remain, and priorities for future studies need to be established. For example, the evaluation of administration of a vaccine with OPV or breast milk might receive less emphasis until a vaccine is made that shows clear efficacy against all virus serotypes. Samples remaining from previous trials should be analyzed to determine epitope-specific serum and coproantibody responses to clarify why only some trials were successful. Detailed evaluation of the antigenic properties of the viruses circulating and causing illness in vaccinated children also should be performed for comparisons with the vaccine strains. In future trials, sample collection should include monitoring for asymptomatic infections and cellular immune responses should be analyzed. The diversity of rotavirus serotype distribution must be monitored before, during, and after a trial in the study population and placebo recipients must be matched carefully to vaccine recipients. Epidemiologic and molecular studies should be expanded to document, or disprove, the possibility of animal to human rotavirus transmission, because, if this occurs, vaccine protection may be more difficult in those areas of the world where cohabitation with animals occurs. We also need to have an accurate assessment of the rate of protection that follows natural infections. Is it realistic to try to achieve 90% protective efficacy with a vaccine if natural infections with these enteric pathogens only provide 60% or 70% protection? Subunit vaccines should be considered to be part of vaccine strategies, especially if maternal antibody interferes with the take of live vaccines. The constraints on development of new vaccines are not likely to come from molecular biology. The challenge remains whether the biology and immunology of rotavirus infections can be understood and exploited to permit effective vaccination. Recent advances in developing small animal models for evaluation of vaccine efficacy should facilitate future vaccine development and understanding of the protective immune response(s) (Ward et al. 1990b; Conner et al. 1993).

Immunological characterization of a rotavirus-neutralizing epitope fused to the cholera toxin B subunit

A highly conserved neutralizing epitope from the surface protein VP4 (amino acids 296-313) of human rotaviruses was genetically fused to the B subunit of cholera toxin (CTB). Synthetic oligodeoxyribonucleotides encoding the VP4 peptide were inserted between the 3' end of the DNA that codes for the leader peptide, and the 5' end of the gene encoding mature CTB. The hybrid protein synthesized in Escherichia coli was found to maintain the ability of CTB to pentamerize, and to adhere to its cell receptor, the GM1 ganglioside. The chimera was efficiently recognized by a monoclonal antibody (mAb) directed at CTB and by a virus-neutralizing mAb against the VP4 peptide. The hybrid polypeptide was shown to induce high titers of serum antibodies (Ab) against CTB and the synthetic VP4 peptide following subcutaneous immunization; paradoxically, however, the Ab obtained did not recognize the virus by an enzyme-linked immunosorbent assay method, nor had detectable neutralizing activity. Potential implications of these results for future design and evaluation of fusion proteins as immunogens are discussed.

Determination of human rotavirus VP4 using serotype-specific cDNA probes

The VP4 genetic groups of 151 field strains of human rotaviruses obtained from infants and young children with diarrhea from four locations in Malaysia were analyzed. The strains were adapted to growth in tissue culture and studied further by molecular hybridization of northern blotted RNA to PCR-generated cDNA probes representing amino acids 84-180 of the KU strain VP4, 83-181 of the DS-1 strain VP4, and 83-180 of either the 1076 or K8 strain VP4, representing VP4 genetic groups 1-4 (P1A, P1B, P2, and P3), respectively. The majority (79% of the field strains hybridized with the KU VP4 genetic group 1 probe and were associated with G1, G3, G4, untypable, or mixed G serotypes. VP4 genetic group 1 (P1A) strains were the most common in all locations in Malaysia between 1978-1988. Three strains which exhibited G3 and subgroup I specificity hybridized with the K8 VP4 genetic group 4 probe. These three VP4 genetic group 4 (P3) strains were detected in two different years and locations, extending the initial detection of this VP4 genetic group (the K8 strain) in Japan to a larger geographical area of Asia.

Binding to sialic acids is not an essential step for the entry of animal rotaviruses to epithelial cells in culture

The infection of target cells by animal rotaviruses requires the presence of sialic acids on the cell surface. Treatment of the cells with neuraminidases or incubation of the viruses with some sialoglycoproteins, such as glycophorin A, greatly reduces virus binding, with the consequent reduction of viral infectivity. In this work, we report the isolation of animal rotavirus variants whose infectivity is no longer dependent on the presence of sialic acids on the cell surface. In addition, although these variants bind to glycophorin A as efficiently as the wild-type virus, this interaction no longer inhibit viral infectivity. These observations indicate that the initial interaction of the mutants with the cell occurs at a site different from the sialic acid-binding site located on VP8, the smaller trypsin cleavage product of VP4. Reassortant analysis showed that the mutant phenotype segregates with the VP4 gene. Neutralizing monoclonal antibodies directed to VP4 and VP7 were tested for their ability to neutralize the variants. Antibodies to VP7 and VP5, the larger trypsin cleavage product of VP4, neutralized the mutants as efficiently as the wild-type virus. In contrast, although antibodies to VP8 were able to bind to the mutants, they showed little or no neutralizing activity. The implications of these findings in rotavirus attachment to and penetration of epithelial cells in culture are discussed.

Sequence conservation within neutralization epitope regions of VP7 and VP4 proteins of human serotype G4 rotavirus isolates

Serotype G4 rotavirus isolates causing four separate epidemics of severe diarrhoea in young children in Melbourne, Australia (from 1974-1990) were investigated for sequence variation in genes encoding the outer capsid proteins, VP4 and VP7. Complementary DNA of the gene encoding the major outer capsid neutralization antigen, VP7, of eighteen isolates was synthesized and amplified by coupled reverse transcription and polymerase chain reaction. Direct sequencing methods were used to derive the deduced amino acid sequences of the immunodominant A, B, and C neutralization epitope regions of the protein. Limited variation was observed among all isolates. A threonine to asparagine change in region A, at amino acid 96, was associated with altered binding of serotype G4-specific neutralizing monoclonal antibodies. The VP8* region of the outer capsid protein VP4 (containing the proposed serotype-specific neutralization epitopes) was investigated in eight isolates. This region was found to highly conserved both within Melbourne isolates and in relation to the standard strains Wa, P, and VA70. The characteristic periodicity of occurrence of serotype G4 isolates causing severe diarrhoea in Melbourne children is unlikely to be due to changes in neutralization epitopes located on the outer capsid proteins, VP7 or VP4.