Rotavirus antigenicity is affected by the genetic context and glycosylation of VP7

Characterisation of a G2P[4] Rotavirus Outbreak in Western Australia, Predominantly Impacting Aboriginal Children

In May, 2017, an outbreak of rotavirus gastroenteritis was reported that predominantly impacted Aboriginal children ≤4 years of age in the Kimberley region of Western Australia. G2P[4] was identified as the dominant genotype circulating during this period and polyacrylamide gel electrophoresis revealed the majority of samples exhibited a conserved electropherotype. Full genome sequencing was performed on representative samples that exhibited the archetypal DS-1-like genome constellation: G2-P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2 and phylogenetic analysis revealed all genes of the outbreak samples were closely related to contemporary Japanese G2P[4] samples. The outbreak samples consistently fell within conserved sub-clades comprised of Hungarian and Australian G2P[4] samples from 2010. The 2017 outbreak variant was not closely related to G2P[4] variants associated with prior outbreaks in Aboriginal communities in the Northern Territory. When compared to the G2 component of the RotaTeq vaccine, the outbreak variant exhibited mutations in known antigenic regions; however, these mutations are frequently observed in contemporary G2P[4] strains. Despite the level of vaccine coverage achieved in Australia, outbreaks continue to occur in vaccinated populations, which pose challenges to regional areas and remote communities. Continued surveillance and characterisation of emerging variants are imperative to ensure the ongoing success of the rotavirus vaccination program in Australia.

Genetic Diversity of Human Rotavirus A Among Hospitalized Children Under-5 Years in Lebanon

Human rotavirus remains a major cause of gastroenteritis worldwide despite the availability of effective vaccines. In this study, we investigated the genetic diversity of rotaviruses circulating in Lebanon. We genetically characterized the VP4 and VP7 genes encoding the outer capsid proteins of 132 rotavirus-associated gastroenteritis specimens, previously identified in hospitalized children (<5 years) from 2011 to 2013 in Lebanon. These included 43 vaccine-breakthrough specimens and the remainder were from non-vaccinated subjects. Phylogenetic analysis of VP4 and VP7 genes revealed distinct clustering compared to the vaccine strains, and several substitutions were identified in the antigenic epitopes of Lebanese specimens. No unique changes were identified in the breakthrough specimens compared to non-breakthroughs that could explain the occurrence of infection in vaccinated children. Further, we report the emergence of a rare P[8] OP354-like strain with a G9 VP7 in Lebanon, possessing high genetic variability in their VP4 compared to vaccine strains. Therefore, human rotavirus strains circulating in Lebanon and globally have accumulated numerous substitutions in their antigenic sites compared to those currently used in the licensed vaccines. The successful spread and continued genetic drift of these strains over time might undermine the effectiveness of the vaccines. The effect of such changes in the antigenic sites on vaccine efficacy remains to be assessed.

Detection, molecular characterization and phylogenetic analysis of G3P[12] and G14P[12] equine rotavirus strains co-circulating in central Kentucky

Equine rotavirus A (ERVA) is the leading cause of diarrhea in neonatal foals and a major health problem to the equine breeding industry worldwide. The G3P[12] and G14P[12] ERVA genotypes are the most prevalent in foals with diarrhea. Control and prevention strategies include vaccination of pregnant mares with an inactivated vaccine containing a prototype ERVA G3P[12] strain with limited and controversial field efficacy. Here, we performed the molecular characterization of ERVA strains circulating in central Kentucky using fecal samples collected during the 2017 foaling season. The data indicated for the first time that the G14P[12] genotype is predominant in this region in contrast to a previous serotyping study where only G3 genotype strains were reported. Overall, analysis of antigenic sites in the VP7 protein demonstrated the presence of several amino acid substitutions in the epitopes exposed on the surface including a non-conserved N-linked glycosylation site (D123N) in G14P[12] strains, while changes in antigenic sites of VP8* were minor. Also, we report the successful isolation of three ERVA G14P[12] strains which presented a high identity with other G14 strains from around the world. These may constitute ideal reference strains to comparatively study the molecular biology of G3 and G14 strains and perform vaccine efficacy studies following heterologous challenge in the future.

Emergence of Human G2P[4] Rotaviruses in the Post-vaccination Era in South Korea: Footprints of Multiple Interspecies Re-assortment Events

After the introduction of two global rotavirus vaccines, RotaTeq in 2007 and Rotarix in 2008 in South Korea, G1[P8] rotavirus was the major rotavirus genotype in the country until 2012. However, in this study, an emergence of G2P[4] as the dominant genotype during the 2013 to 2015 season has been reported. Genetic analysis revealed that these viruses had typical DS-1-like genotype constellation and showed evidence of re-assortment in one or more genome segments, including the incorporation of NSP4 genes from strains B-47/2008 from a cow and R4/Haryana/2007 from a buffalo in India, and the VP1 and VP3 genes from strain GO34/1999 from a goat in Bangladesh. Compared to the G2 RotaTeq vaccine strain, 17–24 amino acid changes, specifically A87T, D96N, S213D, and S242N substitutions in G2 epitopes, were observed. These results suggest that multiple interspecies re-assortment events might have contributed to the emergence of G2P[4] rotaviruses in the post-vaccination era in South Korea.

Emergence of Double- and Triple-Gene Reassortant G1P[8] Rotaviruses Possessing a DS-1-Like Backbone after Rotavirus Vaccine Introduction in Malawi

To combat the high burden of rotavirus gastroenteritis, multiple African countries have introduced rotavirus vaccines into their childhood immunization programs. Malawi incorporated a G1P[8] rotavirus vaccine (Rotarix) into its immunization schedule in 2012. Utilizing a surveillance platform of hospitalized rotavirus gastroenteritis cases, we examined the phylodynamics of G1P[8] rotavirus strains that circulated in Malawi before (1998 to 2012) and after (2013 to 2014) vaccine introduction. Analysis of whole genomes obtained through next-generation sequencing revealed that all randomly selected prevaccine G1P[8] strains sequenced (n = 32) possessed a Wa-like genetic constellation, whereas postvaccine G1P[8] strains (n = 18) had a DS-1-like constellation. Phylodynamic analyses indicated that postvaccine G1P[8] strains emerged through reassortment events between human Wa- and DS-1-like rotaviruses that circulated in Malawi from the 1990s and hence were classified as atypical DS-1-like reassortants. The time to the most recent common ancestor for G1P[8] strains was from 1981 to 1994; their evolutionary rates ranged from 9.7 × 10⁻⁴ to 4.1 × 10⁻³ nucleotide substitutions/site/year. Three distinct G1P[8] lineages chronologically replaced each other between 1998 and 2014. Genetic drift was the likely driver for lineage turnover in 2005, whereas replacement in 2013 was due to reassortment. Amino acid substitution within the outer glycoprotein VP7 of G1P[8] strains had no impact on the structural conformation of the antigenic regions, suggesting that it is unlikely that they would affect recognition by vaccine-induced neutralizing antibodies. While the emergence of DS-1-like G1P[8] rotavirus reassortants in Malawi was therefore likely due to natural genotype variation, vaccine effectiveness against such strains needs careful evaluation.

IMPORTANCE The error-prone RNA-dependent RNA polymerase and the segmented RNA genome predispose rotaviruses to genetic mutation and genome reassortment, respectively. These evolutionary mechanisms generate novel strains and have the potential to lead to the emergence of vaccine escape mutants. While multiple African countries have introduced a rotavirus vaccine, there are few data describing the evolution of rotaviruses that circulated before and after vaccine introduction. We report the emergence of atypical DS-1-like G1P[8] strains during the postvaccine era in Malawi. Three distinct G1P[8] lineages circulated chronologically from 1998 to 2014; mutation and reassortment drove lineage turnover in 2005 and 2013, respectively. Amino acid substitutions within the outer capsid VP7 glycoprotein did not affect the structural conformation of mapped antigenic sites, suggesting a limited effect on the recognition of G1-specific vaccine-derived antibodies. The genes that constitute the remaining genetic backbone may play important roles in immune evasion, and vaccine effectiveness against such atypical strains needs careful evaluation.

Modeling of the rotavirus group C capsid predicts a surface topology distinct from other rotavirus species

Rotavirus C (RVC) causes sporadic gastroenteritis in adults and is an established enteric pathogen of swine. Because RVC strains grow poorly in cell culture, which hinders generation of virion-derived RVC triple-layered-particle (TLP) structures, we used the known Rotavirus A (RVA) capsid structure to model the human RVC (Bristol) capsid. Comparative analysis of RVA and RVC capsid proteins showed major differences at the VP7 layer, an important target region for vaccine development due to its antigenic properties. Our model predicted the presence of a surface extended loop in RVC, which could form a major antigenic site on the capsid. We analyzed variations in the glycosylation patterns among RV capsids and identified group specific conserved sites. In addition, our results showed a smaller RVC VP4 foot, which protrudes toward the intermediate VP6 layer, in comparison to that of RVA. Finally, our results showed major structural differences at the VP8* glycan recognition sites.

Emergence of a novel equine-like G3P[8] inter-genogroup reassortant rotavirus strain associated with gastroenteritis in Australian children

During 2013, a novel equine-like G3P[8] rotavirus emerged as the dominant strain in Australian children with severe rotavirus gastroenteritis. Full genome analysis demonstrated that the strain was an inter-genogroup reassortant, containing an equine-like G3 VP7, a P[8] VP4 and a genogroup 2 backbone I2-R2-C2-M2-A2-N2-T2-E2-H2. The genome constellation of the equine-like G3P[8] was distinct to Australian and global G3P[8] strains. Phylogenetic analysis demonstrated a genetic relationship to multiple gene segments of Japanese strains RVA/JPN/S13-30/2013/G3P[4] and RVA/Human-wt/JPN/HC12016/2012/G1P[8]. The Australian equine-like G3P[8] strain displayed a distinct VP7 antigenic profile when compared with the previously circulating Australian G3P[8] strains. Identification of similar genes in strains from several geographical regions suggested the equine-like G3P[8] strain was derived by multiple reassortment events between globally co-circulating strains from both human and animal sources. This study reinforces the dynamic nature of rotavirus strains and illustrates the potential for novel human/animal reassortant strains to emerge within the human population.

Characterization of G2P[4] rotavirus strains associated with increased detection in Australian states using the RotaTeq® vaccine during the 2010-2011 surveillance period

The introduction of rotavirus vaccines Rotarix® and RotaTeq® into the Australian National Immunisation Program in July 2007 has resulted in a dramatic decrease in the burden of rotavirus disease. G2P[4] strains became the dominant genotype Australia-wide during the 2010-2011 surveillance period and for the first time since vaccine introduction, a higher proportion were isolated in jurisdictions using RotaTeq® vaccine compared to locations using Rotarix®. Phylogenetic analysis of the VP7 gene of 32 G2P[4] strains identified six genetic clusters, these distinct clusters were also observed in the VP4 gene for a subset of 12 strains. The whole genome was determined for a representative strain of clusters; A (RVA/Human-wt/AUS/SA066/2010/G2P[4]), B (RVA/Human-wt/AUS/WAPC703/2010/G2P[4]), C (RVA/Human-wt/AUS/MON008/2010/G2P[4]) and E (RVA/Human-wt/AUS/RCH041/2010/G2P[4]). All of the strains possessed the archetypal DS-1 like genome constellation G2-P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2. Three of the strains, SA066, MON008 and WAPC703 clustered together and were distinct to RCH041 for all 11 genes. The VP7 genes of 31/32 of the strains characterized in this study possessed five conserved amino acid substitutions when compared to the G2 VP7 gene present in the RotaTeq® vaccine. Three of the substitutions were in the VP7 antigenic regions A and C, the substitutions A87T, D96N and S213D have been reported in the majority of G2P[4] strains circulating globally over the previous decade. These changes may have improved the ability of strains to circulate in settings of high vaccine use.

Group A rotavirus universal mass vaccination: how and to what extent will selective pressure influence prevalence of rotavirus genotypes?

Two human group A rotavirus (RVA) vaccines are available and highly effective in preventing severe gastroenteritis caused by all commonly circulating human RVA genotypes. The effect of universal mass vaccination on the RVA genotype distribution is discussed based on the knowledge of complete RVA genotype constellations, data from clinical efficacy trials and effectiveness studies, and genotype surveillance data from countries with universal mass vaccination programs. The theoretically predicted relative enrichment of RVA strains with the G2P[4] DS-1-like genotype constellation in regions with high coverage by Rotarix(®) (GlaxoSmithKline Biologicals, Rixensart, Belgium) seems to become apparent. A G3P[8] genotype increase, which was noted in several regions with a high coverage of RotaTeq(®) (Merck and Co., Inc., NJ, USA), is more difficult to explain based on the theoretical considerations.

Cross-linking of rotavirus outer capsid protein VP7 by antibodies or disulfides inhibits viral entry

Antibodies that neutralize rotavirus infection target outer coat proteins VP4 and VP7 and inhibit viral entry. The structure of a VP7-Fab complex (S. T. Aoki, et al., Science 324:1444-1447, 2009) led us to reclassify epitopes into two binding regions at inter- and intrasubunit boundaries of the calcium-dependent trimer. It further led us to show that antibodies binding at the intersubunit boundary inhibit uncoating of the virion outer layer. We have now tested representative antibodies for each of the defined structural epitope regions and find that antibodies recognizing epitopes in either binding region neutralize by cross-linking VP7 trimers. Antibodies that bind at the intersubunit junction neutralize as monovalent Fabs, while those that bind at the intrasubunit region require divalency. The VP7 structure has also allowed us to design a disulfide cross-linked VP7 mutant which recoats double-layered particles (DLPs) as efficiently as does wild-type VP7 but which yields particles defective in cell entry as determined both by lack of infectivity and by loss of α-sarcin toxicity in the presence of recoated particles. We conclude that dissociation of the VP7 trimer is an essential step in viral penetration into cells.

Molecular identification of a novel G1 VP7 gene carried by a human rotavirus with a super-short RNA pattern

AU19 is a human rotavirus strain carrying a G1P2C[6] specificity and a super-short RNA pattern. Neutralization assay revealed an asymmetric cross neutralization between AU19 and Wa, a representative G1 rotavirus strain, and it is noteworthy that AU19 was neutralized poorly by anti-Wa hyper-immune serum. In the phylogenetic tree the VP7 gene of AU19 formed a lineage different from the established lineages of known human G1 rotaviruses. A signature code MFTKLLTAA was noted for AU19 lineage. These results provide evidences that the VP7 gene of AU19 represents a novel G1 lineage.

Sequence analysis of the VP7 gene of human rotavirus G1 isolated in Japan, China, Thailand, and Vietnam in the context of changing distribution of rotavirus G-types

Over the last decade, rotavirus G1 has represented the most common genotype worldwide. Since 2000, the prevalence of rotavirus G1 has decreased in some countries such as Japan and China. To monitor the trend of the VP7 encoding gene of rotavirus G1, we performed a sequence analysis of 74 G1 rotavirus strains isolated in Japan, China, Thailand, and Vietnam during the period from 2002 to 2005. The phylogenetic tree showed that all of the studied G1 strains from the four countries clustered into lineage III, the same as the majority of the G1 strains isolated in China and Japan in 1990 and 1991. Examination of the deduced amino acid sequences of the G1 strains from China and Japan revealed an amino acid substitution at position 91 (Asn instead of Thr) in antigenic region A when compared to the G1 strains isolated in China and Japan in 1990, 1991, and global reference strains. For the G1 strains from Thailand and Vietnam, there were three amino acid substitutions, not belonging to any antigenic regions. The study showed that there have been no considerable changes of human rotavirus G1 isolated in Japan, China, Thailand, and Vietnam. Further studies need to be carried out for a better understanding of why such changes in the prevalence of rotavirus G1 occur in these countries.

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.

Amino acid substitutions in the VP7 protein of human rotavirus G3 isolated in China, Russia, Thailand, and Vietnam during 2001–2004

The distribution of rotavirus G-types in the world appears to be changing, especially with the emergence of G3 and G9 in many countries. Sequence analysis of the VP7 gene was performed on the 27 human G3 rotavirus strains isolated in China, Russia, Thailand, and Vietnam during 2001-2004. All the strains studied were clustered into the same branch of the phylogenetic tree. The comparison of the G3 deduced amino acid sequences between the studied Chinese strains and the strains circulating in China during 1986-1992 showed a wide range of amino acid substitutions (up to 13 amino acids in the VP7 antigenic regions). The two considerable changes both from aspartic acid to asparagine were located at positions 96 in antigenic region A and 213 in antigenic region C. Those amino acid substitutions of the Chinese G3 strains might involve in the emergence of G3 rotavirus in China during 2001-2003.

Characterization of the capsid protein glycosylation of adeno-associated virus type 2 by high-resolution mass spectrometry

Adeno-associated virus type 2 (AAV-2) capsid proteins have eight sequence motifs that are potential sites for O- or N-linked glycosylation. Three are in prominent surface locations, close to the sites of cellular receptor attachment and to neutralizing epitopes on or near protrusions surrounding the three-fold axes, raising the possibility that AAV-2 might use glycosylation as a means of immune escape or for preventing reattachment on release of progeny virus. Peptide mapping and structural analysis by Fourier transform ion cyclotron resonance mass spectrometry demonstrates, however, no glycosylation of the capsid protein for virus prepared in cultured HeLa cells.

Rotaviruses interact with alpha4beta7 and alpha4beta1 integrins by binding the same integrin domains as natural ligands

Group A rotaviruses are major intestinal pathogens that express potential alpha4beta1 and alpha4beta7 integrin ligand sequences Leu-Asp-Val and Leu-Asp-Ile in their outer capsid protein VP7, and Ile-Asp-Ala in their spike protein VP4. Monkey rotavirus SA11 can use recombinant alpha4beta1 as a cellular receptor. In this study a new potential alpha4beta1, alpha4beta7 and alpha9beta1 integrin ligand sequence, Tyr-Gly-Leu, was identified in VP4. It was shown that several human and monkey rotaviruses bound alpha4beta1 and alpha4beta7, but not alpha9beta1. Binding to alpha4beta1 mediated the infectivity and growth of monkey rotaviruses, and binding to alpha4beta7 mediated their infectivity. A porcine rotavirus interacted with alpha4 integrins at a post-binding stage to facilitate infection. Activation of alpha4beta1 increased rotavirus infectivity. Cellular treatment with peptides containing the alpha4 integrin ligand sequences Tyr-Gly-Leu and Ile-Asp-Ala eliminated virus binding to alpha4 integrins and infectivity. In contrast, rotavirus recognition of alpha4 integrins was unaffected by a peptide containing the sequence Leu-Asp-Val or by a mutation in the VP7 Leu-Asp-Val sequence. VP4 involvement in rotavirus recognition of alpha4beta1 was demonstrated with rotavirus reassortants. Swapping and point mutagenesis of alpha4 surface loops showed that rotaviruses required the same alpha4 residues and domains for binding as the natural alpha4 integrin ligands: mucosal addressin cell adhesion molecule-1, fibronectin and vascular cell adhesion molecule-1. Several rotaviruses are able to use alpha4beta7 and alpha4beta1 for cell binding or entry, through the recognition of the same alpha4-subunit domains as natural alpha4 ligands.

Molecular characterization of a major outer capsid protein encoded by the Threadfin aquareovirus (TFV) gene segment 10 (S10)

Genome segment 10 (S10) of Threadfin aquareovirus (TFV) was cloned, sequenced, analyzed and found to be 987 bp long encoding a protein of 298 aa with a predicted molecular mass of 32.0 kDa. The TFV S10 gene possesses terminal motifs, (5' GTTTTA and ATTCATC 3') which are also conserved in the S6 and S11 TFV gene segments. Sequence comparison revealed that the TFV S10 gene was similar to the Striped bass reovirus (SBR) VP7 outer capsid protein (OCP). A conserved putative zinc-finger motif, CCHC, present in the mammalian reovirus (MRV) delta3 protein, was identified in TFV and other aquareovirus VP7 protein. Phylogenetic analysis of the TFV VP7 protein indicated that TFV is closely related to SBR and Chum salmon reovirus (CSV) and possibly belong to the same species Aquareovirus A as SBR and CSV. The TFV VP7 protein was expressed in E. coli, purified and injected into mice. Serum specific antibodies were generated, however, the serum showed weak neutralizing activity. In contrast, co-incubation of this serum with another serum obtained from mice immunized with another OCP encoded by the TFV S6 gene segment resulted in a highly elevated antibody neutralization titer.

Sequence analysis of the VP7 and VP4 genes identifies a novel VP7 gene allele of porcine rotaviruses, sharing a common evolutionary origin with human G2 rotaviruses

During an epidemiological survey encompassing several porcine herds in Saragoza, Spain, the VP7 and VP4 of a rotavirus-positive sample, 34461-4, could not be predicted by using multiple sets of G- and P-type-specific primers. Sequence analysis of the VP7 gene revealed a low amino acid (aa) identity with those of well-established G serotypes, ranging between 58.33% and 88.88%, with the highest identity being to human G2 rotaviruses. Analysis of the VP4 gene revealed a P[23] VP4 specificity, as its VP8* aa sequence was 95.9% identical to that of the P14[23],G5 porcine strain A34, while analysis of the VP6 indicated a genogroup I, that is predictive of subgroup I specificity. Analysis of the 10th and 11th RNA segments revealed close identity to strains of porcine and human origin, respectively. The relatively low overall aa sequence conservation (<89% aa) to G2 human rotaviruses, the lack of N-glycosylation sites that are usually highly conserved in G2 rotaviruses, and the presence of several amino acid substitutions in the major antigenic hypervariable regions hampered an unambiguous classification of the porcine strain 34461-4 as G2 serotype on the basis of sequence analysis alone. The identification of a borderline, G2-like, VP7 gene allele in pigs, while reinforcing the hypotheses of a tight relationship in the evolution of human and animal rotaviruses, provides additional evidence for the wide genetic/antigenic diversity of group A rotaviruses.

Phylogenetic analyses of human rotavirus in central Taiwan in 1996, 2001 and 2002

BACKGROUND

Rotavirus epidemiology information is required for gastroenteritis disease control and prevention. Information gathered about the serotype distribution of rotaviruses isolated in Taiwan is of crucial significance, before a licensed rotavirus vaccine is introduced.

OBJECTIVES

The purpose of the present study is to investigate the epidemiological diversity of rotaviruses in Taiwan.

STUDY DESIGN

A total of 51 stool samples taken from cases of acute gastroenteritis were collected from three teaching hospitals in central Taiwan in 1996, 2001 and 2002. The samples were subjected to RT-PCR tests of VP7 gene of the human rotavirus group A, B, C.

RESULTS

A total of 16 stool samples were detected positive by RT-PCR and 10 were sequence analyzed and classified into G1, G3, and G9 types. Compared with other HRV strains: the sequences of CS96-40 of G1 are similar to MVD9816 (identity rate 97.15% and 96.09%, respectively, from Uruguay); the sequences of CS02-01 of G3 are similar to 98-B31 (identity rate 98.93% and 98.72%, respectively, from Japan); the sequences of CS01-05, CS01-06, CS01-07, CS01-09, CS01-13, CS02-02, CS02-03, CS02-04 are very similar to other established G9 rotaviruses sequences (identity rate 96.85-99.88%), especially between CS02-04 and SP2737 (from Japan) with an identity rate of 99.88% and 100% nucleotide and amino acid, respectively. Except for CS01-06 strain, it is VR3, but not VR5, VR7 or VR8, that found to be the most frequent mutated amino acid regions of VP7 in these strains.

CONCLUSIONS

Our findings are the first to document the high prevalence of G9 HRV strains in Taiwan, and suggest the re-emergence of G3 strains in central Taiwan since 1991. Epidemiological surveys carried out in this study suggest genotype shifts from type G1 before 1996, to G9 in 2001 and 2002 and the re-emergence of G3 type in 2002.

Rotavirus serotype G9P[8] and acute gastroenteritis outbreak in children, Northern Australia

Amino acid substitutions on the VP7 and NSP4 proteins were identified in regions known to influence function and may have contributed to the emergence and increased dominance of the outbreak strains.

During 2001, an outbreak of severe acute gastroenteritis swept through Central and northern Australia and caused serious disruption to health services. We tracked and characterized the rotavirus strain implicated in the outbreak. Comparison of the electropherotypes of outbreak samples suggested that one G9P[8] strain was likely responsible for the outbreak. Samples were obtained from geographically distinct regions of Australia where the epidemic had occurred. The outbreak strains showed identical nucleotide sequences in genes encoding three rotavirus proteins, VP7, VP8, and NSP4, but they were distinct from G9P[8] strains isolated in previous years. Several of the amino acid substitutions on the VP7 and NSP4 proteins were identified in regions known to influence function and may have contributed to the emergence and increased dominance of the outbreak strains. Rotavirus serotype surveillance should continue with methods capable of identifying new and emerging types.

Genetic variation in the VP7 gene of human rotavirus isolated in Montevideo-Uruguay from 1996-1999

The gene encoding the protein VP7 that induces the major neutralizing response has been sequenced from 34 human rotaviruses isolated from children with acute diarrhea in Montevideo (Uruguay) over a 4-year period (1996-1999). These sequences were analyzed and compared to representative corresponding sequences available on databases. In most years, serotype G1 was present as the single serotype, except in 1999 when serotypes G1 and G4 were present simultaneously. Two G1 VP7 lineages were identified. Serotype G2 was present in 1997. The G4 isolates are grouped with Argentine strains and emerged during 1998 in a recently defined sublineage. Neither serotype G3 nor the emerging serotype G9 were isolated during the study. Antigenic domains of isolates and of representative reference strains of each serotype were compared. Sequences of strains isolated during the same year, showed a high degree of homology among strains belonging to the same serotype.

Monkey rotavirus binding to alpha2beta1 integrin requires the alpha2 I domain and is facilitated by the homologous beta1 subunit

Rotaviruses utilize integrins during virus-cell interactions that lead to infection. Cell binding and infection by simian rotavirus SA11 were inhibited by antibodies (Abs) to the inserted (I) domain of the alpha2 integrin subunit. To determine directly which integrins or other proteins bind rotaviruses, cell surface proteins precipitated by rotaviruses were compared with those precipitated by anti-alpha2beta1 Abs. Two proteins precipitated by SA11 and rhesus rotavirus RRV from MA104 and Caco-2 cells migrated indistinguishably from alpha2beta1 integrin, and SA11 precipitated beta1 from alpha2beta1-transfected CHO cells. These viruses specifically precipitated two MA104 cell proteins only, but an additional 160- to 165-kDa protein was precipitated by SA11 from Caco-2 cells. The role of the alpha2 I domain in rotavirus binding, infection, and growth was examined using CHO cell lines expressing wild-type or mutated human alpha2 or alpha2beta1. Infectious SA11 and RRV, but not human rotavirus Wa, specifically bound CHO cell-expressed human alpha2beta1 and, to a lesser extent, human alpha2 combined with hamster beta1. Binding was inhibited by anti-alpha2 I domain monoclonal Abs (MAbs), but not by non-I domain MAbs to alpha2, and required the presence of the alpha2 I domain. Amino acid residues 151, 221, and 254 in the metal ion-dependent adhesion site of the alpha2 I domain that are necessary for type I collagen binding to alpha2beta1 were not essential for rotavirus binding. Rotavirus-alpha2beta1 binding led to increased virus infection and RRV growth. SA11 and RRV require the alpha2 I domain for binding to alpha2beta1, and their binding to this integrin is distinguishable from that of collagen.

Integrin-using rotaviruses bind alpha2beta1 integrin alpha2 I domain via VP4 DGE sequence and recognize alphaXbeta2 and alphaVbeta3 by using VP7 during cell entry

Integrins alpha2beta1, alphaXbeta2, and alphaVbeta3 have been implicated in rotavirus cell attachment and entry. The virus spike protein VP4 contains the alpha2beta1 ligand sequence DGE at amino acid positions 308 to 310, and the outer capsid protein VP7 contains the alphaXbeta2 ligand sequence GPR. To determine the viral proteins and sequences involved and to define the roles of alpha2beta1, alphaXbeta2, and alphaVbeta3, we analyzed the ability of rotaviruses and their reassortants to use these integrins for cell binding and infection and the effect of peptides DGEA and GPRP on these events. Many laboratory-adapted human, monkey, and bovine viruses used integrins, whereas all porcine viruses were integrin independent. The integrin-using rotavirus strains each interacted with all three integrins. Integrin usage related to VP4 serotype independently of sialic acid usage. Analysis of rotavirus reassortants and assays of virus binding and infectivity in integrin-transfected cells showed that VP4 bound alpha2beta1, and VP7 interacted with alphaXbeta2 and alphaVbeta3 at a postbinding stage. DGEA inhibited rotavirus binding to alpha2beta1 and infectivity, whereas GPRP binding to alphaXbeta2 inhibited infectivity but not binding. The truncated VP5* subunit of VP4, expressed as a glutathione S-transferase fusion protein, bound the expressed alpha2 I domain. Alanine mutagenesis of D308 and G309 in VP5* eliminated VP5* binding to the alpha2 I domain. In a novel process, integrin-using viruses bind the alpha2 I domain of alpha2beta1 via DGE in VP4 and interact with alphaXbeta2 (via GPR) and alphaVbeta3 by using VP7 to facilitate cell entry and infection.

Distribution of rotavirus VP7 genotypes among children suffering from watery diarrhea in Kolkata, India

A combined reverse transcriptase-polymerase chain reaction (RT/PCR) was used to produce cDNA of the VP7 gene of rotavirus present in the stool samples. A total of 150 rotavirus positive stool samples were used in this study. Multiplex PCR, using the type specific primers, revealed the presence of G1 (49/150, 32.7%), G2 (27/150, 18%) and G4 (30/150, 20%) genotypes among the samples collected during 1999-2000 from children suffering from acute watery diarrhea. Eighteen samples (12%) were of mixed genotype and the remaining 16 samples (10.6%) could not be typed. Comparative analysis of the full length genes of the representative strains with corresponding genotypes incorporated in the human-rhesus rotavirus tetravalent vaccine (RRV-TV) formulation demonstrates variations of the circulating G1, G2 and G4 strains with the corresponding G genotypes present in the vaccine strain.

Amino acid substitution within the VP7 protein of G2 rotavirus strains associated with failure to serotype

Rotavirus strains collected in the United Kingdom during the 1995-1996 season and genotyped as G2 by reverse transcription-PCR failed to serotype in enzyme-linked immunosorbent assays using three different G2-specific monoclonal antibodies. The deduced amino acid sequences of the antigenic regions A (amino acids 87 to 101), B (amino acids 142 to 152), and C (amino acids 208 to 221) of VP7 revealed that a substitution at position 96 (Asp-->Asn) correlated with the change in ability to serotype these G2 strains.

Selection of rotavirus VP4 cell receptor binding domains for MA104 cells using a phage display library

Rotavirus infection of host cells, like other viruses, is a complex process that has not been fully elucidated, and much attention has been focused on the regions of the viral attachment protein, VP4, that are involved in binding to the cellular receptor. In this study, phage display technology was employed to generate a g3p VP4 gene-targeted phage display peptide library using the porcine rotavirus strain CRW8, and a method was optimised for panning this library on adherent MA104 cells to identify receptor binding domains. Recombinant phage that displayed expressed peptides from both the rotavirus VP4 trypsin cleavage products VP8* and VP5* were selected, and while some of the phage clones contained insert sequences from regions of VP4 implicated previously in cell binding and infection, new domains were also identified. In all, four regions within VP8* and six regions of VP5* were selected by panning. To our knowledge, this paper is the first description of using a gene-targeted phage display library to identify receptor binding domains on viral proteins.

Rotavirus infection of MA104 cells is inhibited by Ricinus lectin and separately expressed single binding domains

Various lectins were tested for blocking rotavirus infection of MA104 cells and it was observed that galactose-specific lectins were the most inhibitory. Of these Ricinus agglutinin was able to inhibit infection (by human and animal strains) at concentrations as low as 10(-9) M. In addition, in a virus overlay protein blot assay Ricinus agglutinin competed with simian rotavirus SA11 for binding to solubilized MA104 proteins. Amino acid sequence comparisons revealed similarity between the ricin toxin B subunit (which contains two separate carbohydrate-binding motifs: single binding domains (SBD) 1 and 2) and rotavirus spike protein VP4. A filamentous phage display system was used to independently express the two binding domains and while SBD1 inhibited infection of MA104 cells by CRW8, NCDV, and to a lesser extent Wa, SBD2 blocked only CRW8 and NCDV infection. Furthermore inhibition of CRW8 infection was a direct result of phage inhibiting virus attachment to cells. When amino acid 248 within SBD2 was mutated from the ricin toxin to the Ricinus agglutinin sequence this phage clone showed reduced binding to galactose and was no longer able to inhibit virus infection. Thus, rotavirus recognizes galactose as an important component of the receptor on MA104 cells.

Rotavirus VP7 epitope mapping using fragments of VP7 displayed on phages

cDNA copies of the complete porcine rotavirus CRW-8 VP7 gene were randomly digested to fragments of about 30-60 or 30-500 base pairs by DNase1 in the presence of Mn(2+). The fragments were cloned and expressed in a filamentous phage fd-tet-derived vector to create specific-gene-related peptide libraries. Polyclonal antibodies were then used to pan the SGRP libraries for antibody-binding phages. Analysis of the phage isolates revealed that the majority (86%) of them only had a single insert. However, phages displaying composite inserts containing the VP7 antigenic regions A, B, and C, originally defined by neutralising monoclonal antibody escape mutants, were also isolated. Inserts containing A or C region peptide were found to contain extra sequences from the C region, while the B region epitope was linear and had additional sequence from either upstream or downstream. In addition a dominant and possibly non-neutralising VP7 epitope was identified around amino acids 263-270. One of the recreated antigenic epitopes has also been fused to the outer membrane protein A (OmpA) of Escherichia coli and shown to maintain its antigenicity. The results in this study may have significant implication for recreation of conformational epitopes and vaccine development.

Sequence comparison of the VP7 of serotype G2 rotaviruses from diverse geographical locations

The sequences of the genes encoding the outer capsid glycoprotein, VP7, of twelve serotype G2 rotavirus isolates from Australia were determined. The deduced amino acid sequences were compared by phylogenetic analysis to published sequences from strains collected from various geographical locations worldwide between 1976 an 1993. This analysis showed that geographical clustering of strains was apparent and that most strains were distantly related to strain DS1 whose VP7 is included in the rhesus rotavirus tetravalent vaccine formulation. Comparisons of the neutralization epitope regions of VP7 also indicated that most strains might exhibit antigenic differences to DS1. These results have implications for the development of future vaccine strategies.

Comparison of enzyme immunoassay and reverse transcriptase PCR for identification of serotype G9 rotaviruses

While only four globally important rotavirus G serotypes (1 to 4) have been documented, many studies suggest that serotype G9 viruses may be widely distributed and more important than previously recognized. We have evaluated 10 serotype G9 rotavirus-neutralizing monoclonal antibodies (MAbs) directed to VP7, which bound by direct enzyme immunoassay (EIA) to P1A[8], G9 rotaviruses F45, WI61, and AU32, for their ability to recognize the New Delhi G9 rotavirus 116E. Only one MAb (MAb F45:1) bound to P[11], G9 virus 116E to a high titer by EIA. This MAb was incorporated into an indirect EIA for G serotyping, which was validated with prototype cultivable human rotaviruses of G types 1 to 4 and 9. The EIA was compared with genotyping by reverse transcriptase PCR (RT-PCR) under code for the determination of the G types of rotaviruses obtained from neonates in New Delhi, India. The sensitivities of RT-PCR and EIA (after two additional freeze-thaw cycles) for the typing of G9 rotaviruses were 91 and 86%, respectively, for 24 culture-adapted rotavirus strains. The untypeable culture-adapted rotavirus samples also were unreactive with VP7 group antigen-reactive MAb 60. After two additional freeze-thaw cycles, only 26 of 42 (62%) of stools containing rotavirus typed as G9 by RT-PCR were positive for G9 rotavirus by EIA. Stools containing rotavirus untypeable by EIA contained significantly less MAb 60-reactive VP7 antigen (P = 0. 0001) than the stools containing typeable rotavirus. Thus, RT-PCR genotyping was the more sensitive method for determination of G9 type, but a serotype was readily determined in rotavirus samples containing MAb 60-reactive VP7 antigen by an EIA that incorporates MAb F45:1.

Carbohydrates facilitate correct disulfide bond formation and folding of rotavirus VP7

It is well established that glycosylation is essential for assembly of enveloped viruses, but no information is yet available as to the function of carbohydrates on the nonenveloped but glycosylated rotavirus. We show that tunicamycin and, more pronouncedly, a combination of tunicamycin and brefeldin A treatment caused misfolding of the luminal VP7 protein, leading to interdisulfide bond aggregation. While formation of VP7 aggregates could be prevented under reducing conditions, they reoccurred in less than 30 min after a shift to an oxidizing milieu. Furthermore, while glycosylated VP7 interacted during maturation with protein disulfide isomerase, nonglycosylated VP7 did not, suggesting that glycosylation is a prerequisite for protein disulfide isomerase interaction. While native NSP4, which does not possess S-S bonds, was not dependent on N-linked glycosylation or on protein disulfide isomerase assistance for maturation, nonglycosylated NSP4 was surprisingly found to interact with protein disulfide isomerase, further suggesting that protein disulfide isomerase can act both as an enzyme and as a chaperone. In conclusion, our data suggest that the major function of carbohydrates on VP7 is to facilitate correct disulfide bond formation and protein folding.

Preferential selection of heterologous G3-VP7 gene in the genetic background of simian rotavirus SA11 detected by using a homotypic single-VP7 gene-substitution reassortant

Introduction of segmented genomes into virion is an important process in viral replication of rotavirus. We previously studied the assortment of the VP7 gene segment (encoding outer capsid protein VP7) in the genetic background of simian rotavirus SA11 (G serotype 3, G3) and found the preferential selection of homologous G3 VP7 gene over VP7 gene of heterologous G serotype (G1, G2 or G4). In the present study, in order to clarify whether or not VP7 gene derived from different G3 rotavirus (heterologous G3-VP7 gene) is also preferentially selected in the SA11 background, a single-VP7 gene-substitution reassortant was prepared from SA11 through multiple steps of coinfection with rotaviruses in vitro. The isolated reassortant, SNR1, possessed VP7 gene derived from canine G3 rotavirus K9 and all other gene segments of SA11 origin, and showed an identical growth characteristic to that of SA11. Amino acid sequence of K9 VP7 gene showed a high degree of identity (93.6%) to SA11 VP7 gene. In analysis by mixed infection and multiple passages of SNR1 and a single VP7 gene (with G1, G2 or G4 specificity) reassortant in the SA11 background, the G3-VP7 gene became predominant at early passage numbers. However, in mixed infection with SA11 and SNR1, homologous G3-VP7 gene (SA11-VP7 gene) was preferentially selected into progenies over heterologous one (K9-VP7 gene). These results together with our previous findings suggested that G3-VP7 gene, irrespective of origin of species, was functionally adapted to the genetic background of SA11, although the homologous gene had a better fit with other SA11 genes than did heterologous one, providing suggestions for efficaciousness of multivalent reassortant rotavirus vaccine.

Single point mutations may affect the serotype reactivity of serotype G11 porcine rotavirus strains: a widening spectrum?

A panel of single and double neutralization-resistant escape mutants of serotype G11 porcine rotavirus strains A253 and YM, selected with G11 monotype- and serotype-specific neutralizing monoclonal antibodies (MAbs) to VP7, was tested in neutralization assays with hyperimmune sera raised against rotavirus strains of different serotypes. Escape mutants with an amino acid substitution in antigenic region A (amino acids [aa] 87 to 101) resulting in a residue identical or chemically similar to those present at the same positions in serotype G3 strains, at positions 87 for strain A253 and 96 for strain YM, were significantly more sensitive than the parental strains to neutralization with sera against some serotype G3 strains. Also, one YM antigenic variant (YM-5E6.1) acquired reactivity by enzyme-linked immunosorbent assay with MAbs 159, 57/8, and YO-1E2, which react with G3 strains, but not with the serotype G11 parental strain YM. Cross-adsorption studies suggested that the observed cross-neutralization by the G3-specific sera was due to the sera containing antibodies reactive with the parental strain plus antibodies reactive with the epitope(s) on the antigenic variant that mimick the serotype G3 specific one(s). Moreover, antibodies reactive with antigenic region F (aa 235 to 242) of VP7 might also be involved since cross-reactivity to serotype G3 was decreased in double mutants carrying an additional mutation, which creates a potential glycosylation site at position 238. Thus, single point mutations can affect the serotype reactivity of G11 porcine rotavirus strains with both monoclonal and polyclonal antibodies and may explain the origin of rotavirus strains with dual serotype specificity based on sequence divergence of VP7.

Genetics of the rotaviruses

Genetic analyses have contributed significantly to our understanding of the biology of the rotaviruses. The distinguishing feature of the virus is a genome consisting of 11 segments of double-stranded RNA. The segmented nature of the genome allows reassortment of genome segments during mixed infections, which is the major distinguishing feature of rotavirus genetics. Reassortment has been a powerful tool for mapping viral mutations and other determinants of biological phenotypes to specific genome segments. However, more detailed genetic analysis of rotaviruses is currently limited by the inability to perform reverse genetics. Development of a reverse genetic system will facilitate analysis of the molecular mechanisms involved in various genetic, biochemical, and biological phenomena of the virus.

Production of reassortant viruses containing human rotavirus VP4 and SA11 VP7 for measuring neutralizing antibody following natural infection

The outer capsid proteins VP4 and VP7 of group A rotaviruses are both targets of neutralizing antibody produced following natural infection in humans. Of interest is the relative importance and immunodominance of each protein in the generation of a protective immune response. In order to measure neutralizing antibody responses to VP4 and VP7 separately, reassortants bearing VP4 of each of the major human rotavirus P types with VP7 of SA11 origin were successfully produced by neutralizing monoclonal antibody selection. The resulting reassortants, together with reassortants representing each of the major VP7 types, were antigenically characterized with serotype-specific neutralizing monoclonal antibodies and hyperimmune sera. The neutralization proteins of human rotavirus origin were found to be unaffected antigenically by reassortment. The abilities of these reassortants to discriminate between VP4 and VP7 immune responses were evaluated with postinfection sera collected from three patients infected with either a P1A[8],G1, a P1B[4],G2, or a P1A[8],G4 rotavirus strain. The reassortants were shown to be capable of separating the neutralizing antibody responses to VP4 and VP7, with each patient showing a different immune response with respect to VP4 or VP7 immunodominance. These reassortants can now be applied to analyses of individual immune responses to VP4 and VP7 proteins after primary rotavirus infections and reinfections in humans.

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.

Two proline residues are essential in the calcium-binding activity of rotavirus VP7 outer capsid protein

Rotavirus maturation and stability of the outer capsid are calcium-dependent processes. It has been shown previously that the concentration of Ca2+-solubilizing outer capsid proteins from rotavirus particles is dependent on the virus strain. This property of viral particles has been associated with the gene coding for VP7 (gene 9). In this study the correlation between VP7 and resistance to low [Ca2+] was confirmed by analyzing the origin of gene 9 from reassortant viruses prepared under the selective pressure of low [Ca2+]. After chemical mutagenesis, we selected mutant viruses of the bovine strain RF that are more resistant to low [Ca2+]. The genes coding for the VP7 proteins of these independent mutants have been sequenced. Sequence analysis confirmed that these mutants are independent and revealed that all mutant VP7 proteins have proline 75 changed to leucine and have an outer capsid that solubilized at low [Ca2+]. The mutation of proline 279 to serine is found in all but two mutants. The phenotype of mutants having a single proline change can be distinguished from the phenotype of mutants having two proline changes. Sequence analysis showed that position 75 is in a region (amino acids 65 to 78) of great variability and that proline 75 is present in most of the bovine strains. In contrast, proline 279 is in a conserved region and is conserved in all the VP7 sequences in data banks. This region is rich in oxygenated residues that are correctly allocated in the metal-coordinating positions of the Ca2+-binding EF-hand structure pattern, suggesting that this region is important in the Ca2+ binding of VP7.

G3P2 rotaviruses causing diarrhoeal disease in neonates differ in VP4, VP7 and NSP4 sequence from G3P2 strains causing asymptomatic neonatal infection

During longitudinal epidemiological studies of rotavirus infections in children in Melbourne, Australia human G3P2 rotavirus strains causing asymptomatic or symptomatic infections have been identified. Eleven strains (AS strains) associated with asymptomatic infection of newborn babies from 1974-1984, and five strains (S strains) associated with symptomatic infection of newborn babies (4) or a 22 week old infant (1) during 1980-1986 were studied. The entire nucleotide sequences of genes coding for VP4, VP7, NSP4 and VP6 were derived for representative AS and S strains. The nucleotide sequences of neutralization epitope regions present on the outer capsid proteins VP4 and VP7 (regions C and F) showed extensive conservation of nucleotide and deduced amino acid sequence in all strains. Minor variations were observed over the 12 year period in VP7 epitope regions A and B in some strains. Specific conserved amino acids differences between the asymptomatic and symptomatic strains were observed in the genes encoding VP4 at aa133 and 303 (asparagine or threonine) and 380 (serine or isoleucine), VP7 at aa27 (threonine or isoleucine), aa29 (isoleucine or threonine), aa42 (valine or alanine) and aa238 (asparagine or aspartic acid/serine) and NSP4 at aa135 (isoleucine or valine). No amino acid changes were identified in gene 6. The observed amino acid differences occurred in proteins that have been implicated in virulence, and correlate with differences in clinical symptoms of infants infected with these strains. These results permit speculation about the genetic basis for virulence of human strains.

Effects of the route of infection on immunoglobulin G subclasses and specificity of the reovirus-specific humoral immune response

Reovirus serotype 1, strain Lang (T1/L), a well characterized enteric virus, elicits humoral and cellular immune responses in mice. Although orally and intradermally induced infections generate comparable reovirus-specific serum antibody titers, little is known about the effects of the route of infection on the systemic immunoglobulin G (IgG) response. To assess whether the route of exposure affects virus-specific humoral immunity, we infected various strains of mice with reovirus T1/L by the oral or intradermal routes. At day 10 following infection, virus-specific serum antibody titers and IgG subclasses were determined by enzyme-linked immunosorbent assay. Serum IgG2a and IgG2b antibodies were detected in all mouse strains independent of the route of infection. Mice of the H-2d haplotype that received an intradermal infection also had high levels of reovirus-specific serum IgG1. This dichotomy of responses was not associated with differences in the types of cytokine produced by draining peripheral lymph nodes. However, peripheral lymph node lymphocytes from C3H mice produced significantly higher levels of gamma interferon than did BALB/c, C57BL/6, and B10.D2 mice. Additionally, peripheral lymph node lymphocytes from all strains of mice produced only low levels of interleukin-5, with no detectable level of interleukin-4 or interleukin-6. Analysis of specific antibody at inductive sites of the immune response showed that orally infected Peyer's patches produced predominantly IgA and intradermally infected peripheral lymph nodes produced predominantly IgG2a. Western blot (immunoblot) analysis showed that virus-specific IgA, IgG1, and IgG2a reacted with reovirus structural proteins. These data suggest that the route of infection affects the isotype and IgG subclasses, but not the antigen specificity, of the local antibody response. In addition, virus-specific IgG1 generated following an intradermally induced infection is linked to the H-2d major histocompatibility complex haplotype.

Selection of rotavirus VP7 gene in the genetic background of simian rotavirus SA11: implications for rotavirus reassortant vaccine development

We previously reported that the VP7 gene from simian rotavirus SA11 with G-serotype 3(G3-VP7 gene) was preferentially selected in the genetic background of SA11 compared with the G1- or G2-VP7 gene. In the present study, selection of the G4-VP7 gene in competition with G1-, G2- or G3-VP7 gene in the SA11 background was analyzed through mixed infection experiments using SA11 and SA11-human rotavirus single-VP7 gene-substitution reassortants with G-serotypes 1, 2, and 4 (G1-, G2- and G4-reassortant). In virus clones from coinfection of SA11 and G4-reassortant, the frequency of G4 virus decreased to 7% at the 3rd passage and the G4 virus disappeared at the 10th passage, whereas the majority of the clones possessed G3 specificity. However, the predominance of either of the viruses coinfected was not observed in the mixed infection with G4-reassortant and G1- or G2-reassortant. Although growth kinetics of SA11 and G4-reassortant was similar, G4-reassortant showed significantly smaller plaque size than SA11, G1- and G2-reassortant did. These results indicated that the G3-VP7 gene from SA11 might be preferentially selected in the SA11 genetic background compared with the G4-VP7 gene, and suggested that the introduction of a single G4-VP7 gene may affect growth characteristics of recipient virus SA11. These results together with our previous findings suggested the significance of genetic compatibility between recipient viral genes and foreign VP7 gene in the development of multivalent reassortant rotavirus vaccines.