Cultivation of human rotaviruses in cell culture

Gene-edited vero cells as rotavirus vaccine substrates

Background

Rotavirus (RV) is a leading cause of severe gastroenteritis globally and can cause substantial morbidity associated with gastroenteritis in children <5 years of age. Orally administered live-attenuated RV vaccines offer protection against disease but vaccination efforts have been hampered by high manufacturing costs and the need to maintain a cold chain.

Methods

A subset of Vero cell host genes was identified by siRNA that when knocked down increased RV replication and these anti-viral host genes were individually deleted using CRISPR-Cas9.

Results

Fully-sequenced gene knockout Vero cell substrates were assessed for increased RV replication and RV vaccine antigen expression compared to wild type Vero cells. The results showed that RV replication and antigen production were logs higher in Vero cells having an EMX2 gene deletion compared to other Vero cell substrates tested.

Conclusions

We used siRNAs to screen for host genes that negatively affected RV replication, then CRISPR-Cas9 gene editing to delete select genes. The gene editing led to the development of enhanced RV vaccine substrates supporting a potential path forward for improving RV vaccine production.

Evaluation of BBL™ Sensi-Discs™ and FTA® cards as sampling devices for detection of rotavirus in stool samples

Rotavirus is the most important cause of severe childhood gastroenteritis worldwide. Rotavirus vaccines are available and rotavirus surveillance is carried out to assess vaccination impact. In surveillance studies, stool samples are stored typically at 4°C or frozen to maintain sample quality. Uninterrupted cold storage is a problem in developing countries because of power interruptions. Cold-chain transportation of samples from collection sites to testing laboratories is costly. In this study, we evaluated the use of BBL™ Sensi-Discs™ and FTA(®) cards for storage and transportation of samples for virus isolation, EIA, and RT-PCR testing. Infectious rotavirus was recovered after 30 days of storage on Sensi-Discs™ at room temperature. We were able to genotype 98-99% of samples stored on Sensi-Discs™ and FTA(®) cards at temperatures ranging from -80°C to 37°C up to 180 days. A field sampling test using samples prepared and shipped from Cameroon, showed that both matrices yielded 100% genotyping success compared with whole stool and Sensi-Discs™ demonstrated 95% concordance with whole stool in EIA testing. The utilization of BBL™ Sensi-Discs™ and FTA(®) cards for stool sample storage and shipment has the potential to have great impact on global public health by facilitating surveillance and epidemiological investigations of rotavirus strains worldwide at a reduced cost.

Characterization of in vivo anti-rotavirus activities of saponin extracts from Quillaja saponaria Molina

Rotavirus is the leading cause of severe diarrhea disease in newborns and young children worldwide with approximately 300,000 pre-adolescent deaths each year. Quillaja saponins are a natural aqueous extract obtained from the Chilean soapbark tree. The extract is approved for use in humans by the FDA for use in beverages as a food addictive. We have demonstrated that Quillaja extracts have strong antiviral activities in vitro against six different viruses. In this study, we evaluated the in vivo antiviral activity of these extracts against rhesus rotavirus (RRV) using a mouse model. We established that at a dosage of 0.015 mg/mouse of saponin extract, RRV induced diarrhea can be significantly reduced from 79% to 11% when mice are exposed to 500 plaque-forming-units (PFU) for each of five consecutive days. Additionally, while a reduction of RRV induced diarrhea depended both on the concentration of virus introduced and on the amount of Quillaja extract given to each mouse, the severity and interval of diarrhea under a variety of conditions tested, in all the treated mice were greatly reduced when compared to those that did not receive the Quillaja extracts. Mechanistically, there is strong evidence that the Quillaja extracts are able to "block" rotavirus infection by inhibiting virus-host attachment through disruption of cellular membrane proteins and/or virus receptors. We believe that Quillaja extracts have promise as antivirals to reduce rotavirus infection and the severity of the disease in humans.

Detection of porcine rotavirus from tissue and faecal specimens

Porcine small intestinal sub-mucosa is a cell-free collagen matrix that has demonstrated its ability as a scaffold material. Transplantation poses special hazards because grafted tissues and organs transmit pathogens efficiently, especially viruses. Rotavirus is thought to be confined to the intestine, causing acute diarrhoea. The purpose of this study was to evaluate the porcine intestinal tissue scaffold for Rotavirus and to study the incidence of this virus among pig herds. Only one isolate was successfully adapted to grow in cell line MA 104 from faecal samples. This isolate was further confirmed by reverse transcriptase polymerase chain reaction and sequence analysis.

G8 rotavirus strains isolated in the Democratic Republic of Congo belong to the DS-1-like genogroup

Several G8P[6] and G8P[8] rotavirus strains were isolated from hospitalized patients in the Democratic Republic of Congo in 2003. To investigate their overall genomic relatedness and to determine to which genogroup they belonged, the complete genomes of strains DRC88 (G8P[8]) and DRC86 (G8P[6]) were determined. Genomic comparison of these two African G8 strains revealed that 10 out of their 11 gene segments, except for VP4, were nearly identical (>98.9% identical at the nucleotide level), suggesting that this rare G8P[8] rotavirus strain originated recently from a reassortment between a common G8P[6] strain and a strain with a P[8] specificity. A very close evolutionary relationship between 9 out of the 11 gene segments of DRC88 and DRC86 and rotavirus strains belonging to the DS-1-like (G2P[4]) "genogroup" was found, and several possible reassortment events preceding the occurrence of G8P[8] and G8P[6] human rotaviruses were hypothesized. Since the genes of G2P[4] rotavirus strains are very well adapted to infect humans, the acquirement of a new VP7 (G8) gene, and especially the replacement of P[6] (believed to be of animal origin) by P[8] (most common in human rotaviruses), might make DRC88-like rotaviruses very well equipped to become a predominant human rotavirus strain and an important pathogen on the African continent and the rest of the world. These findings have important implications for rotavirus vaccine development and highlight that typing of new rotavirus strains by merely sequencing their VP7 and VP4 genes provides us with only the tip of the iceberg regarding rotavirus diversity.

Extended excretion of rotavirus after severe diarrhoea in young children

BACKGROUND

Rotaviruses are the major cause of severe childhood diarrhoea. Knowledge of the natural history of infection, including duration of intestinal virus shedding, is important in the understanding of transmission, sources of infection, and immune responses.

METHODS

We carried out a study of rotavirus excretion in 37 children admitted to hospital with severe rotavirus diarrhoea. Sequential faecal specimens were collected from each child during 100 days of surveillance, and screened for rotavirus by EIA and by amplification of genome double-stranded RNA by reverse-transcription PCR. IgA coproantibody was estimated by EIA.

FINDINGS

Duration of rotavirus excretion ranged from 4 to 57 days after onset of diarrhoea. Excretion ceased within 10 days in 16 (43%) children, and within 20 days in 26 (70%) children. Extended excretion was detected for 25-57 days in the remaining 11 (30%) children owing mainly to continued excretion of the primary infecting strain. Extended excretion was significantly associated with antirotavirus IgA coproantibody boosts during 100 days of surveillance (p=0.001, log-rank test), and with recurrence of mild diarrhoea symptoms during convalescence (p=0.006, Fisher's exact test).

INTERPRETATION

Severe rotavirus disease in young children may be followed by extended excretion of rotavirus. The risk of transmission to others may be greater than previously believed. Extended excretion could also explain some cases of the postgastroenteritis syndrome.

A rearranged genomic segment 11 is common to different human rotaviruses

Gene 11 of human rotaviruses with short electropherotype, independently obtained from infected children in Argentina, have an insertion of 148 nt in the 3' untranslated region. All viruses were highly homologous among them and with two others human strains, DS-1 and RV5.

Intra- and inter-season genetic variability in the VP7 gene of serotype 1 (monotype 1 a) rotavirus clinical isolates

Nucleotide sequence variation was detected in the VP7 gene of serotype 1 (monotype 1 a) rotavirus isolates collected from children admitted to hospital in Melbourne with acute diarrhoea in 1990 and 1991. Two co-circulating electropherotypes were detected during the 1991 winter epidemic. Using chemical cleavage of mismatches in heteroduplexes, the genes encoding VP7 were found to be genetically stable within each electropherotype during the study period, although differences between the two types were apparent. Direct nucleotide sequencing confirmed this finding. The two electropherotypes exhibited four nucleotide differences in the VP7 gene, only one of which resulted in a substitution in the deduced amino acid sequence. The degree of variation was more pronounced between the 1991 isolates and those from the previous winter, with approximately 3% nucleotide sequence diversity between isolates from both winters. The regions encoding the neutralization epitopes of VP7 were conserved among all isolates. Comparison to the local prototype monotype 1 a strain, RV 4 (isolated from a child admitted to hospital in Melbourne in 1981), implies that the 1990 and 1991 isolates have diverged independently. This suggests that genetically distinct strains emerge from a pool of related viruses to predominate in any given year.

Analysis of homotypic and heterotypic serum immune responses to rotavirus proteins following primary rotavirus infection by using the radioimmunoprecipitation technique

Three sequential serum samples collected from each of 20 young children with a naturally acquired primary rotavirus infection were assayed by the radioimmunoprecipitation technique for immunoglobulin G antibodies to rotavirus structural and nonstructural proteins of the four major human rotavirus serotypes G1, P1A; G2, P1B; G3, P2; and G4, P2. Fourteen children were infected with a serotype G1 rotavirus strain and six children were infected with a serotype G4 rotavirus strain. Sera were collected from each child in the acute and convalescent periods postinfection and also approximately 4 months later. Serum immune responses to rotavirus core antigens VP2 and VP3, to the major inner capsid antigen VP6, to nonstructural proteins NS35, NS28, and NS26, and to the outer capsid neutralization antigen VP4 of all test strains were detected in the majority of patients. These responses do not appear to be influenced by the G type or P type of the rotavirus strain used in the reactions. Homologous responses to the main neutralization antigen VP7 were detected in 93% of patients with serotype G1 infections and 50% of patients with serotype G4 infections. Heterologous VP7 responses were less frequently detected and were restricted to G1, G3, and G4 serotype rotavirus strains. No responses to VP7 of the serotype G2 rotavirus strain were detected in any patients. Heterotypic immune responses to the neutralization antigens, at least following serotype G1 and G4 infections, therefore appear to consist primarily of responses to VP4 rather than to VP7.

HT-29 cells: a new substrate for rotavirus growth

Susceptibilities of a continuous rhesus monkey kidney cell line (MA-104) and that of a human colon carcinoma cell line (HT-29) to infection by different human and animal rotavirus strains were compared. HT-29 cells appeared to be more sensitive to human rotavirus infection than MA-104 cells, whereas the latter cell line was more susceptible to animal rotavirus replication. The greater sensitivity to human rotavirus infection of HT-29 cells was confirmed by the successful, direct isolation of these viruses from faecal specimens. Human rotavirus infection of HT-29 cells was also followed by transmission electron microscopy. In ultra-thin sections, unenveloped particles of rotaviruses, representing infectious mature virions, were observed in large number. Moreover, many "double-shelled" particles were detected in negative-stained supernatants from infected cultures. Scanning electron microscopy of uninfected HT-29 cells showed that in the presence of Ca++, required for rotavirus growth, they are able to express some of the features of mature intestinal cells. In view of these results, HT-29 cells appear to be a useful in vitro model for the study of rotavirus infection.

Homotypic serum antibody responses to rotavirus proteins following primary infection of young children with serotype 1 rotavirus

The class-specific antibody responses to serotype 1 rotavirus structural proteins were examined by immunoblotting with sera obtained from young children hospitalized with acute rotavirus diarrhea caused by serotype 1. All were believed to be primary infections. Three consecutive samples were obtained from 16 patients during the acute and convalescent phases of the disease and then approximately 4 months later. Immunoglobulin G (IgG)-class antibody responses to two inner capsid proteins (VP2 and VP6) and to the major homologous outer capsid protein (VP7) were detected in all patients. Antibody responses to VP6 were rapid, increased in intensity during 20 to 40 days after the onset of symptoms, and persisted for more than 4 months. Responses to VP2 and VP7 were more delayed, were maximal in convalescent-phase sera, and decreased markedly in intensity 4 months after the onset of symptoms in the majority of children. Two patients with evidence of mixed infection showed persisting high levels of antibody to VP7. Responses to the outer capsid protein VP4 were detected in 67% of patients, peaked at 20 to 40 days after the onset of symptoms, and were no longer detected at 4 months in the majority of patients. It is likely that the immunoblotting technique underestimated responses to VP4. Acute- and convalescent-phase sera (known to contain antirotavirus IgM or IgA measured by enzyme immunoassay) were also examined by immunoblotting. IgM- and IgA-class antibody responses to viral proteins VP2, VP4, and VP7 appeared to be qualitatively identical to those observed for IgG in the same serum samples.

Comparison of rotavirus immunoglobulin A coproconversion with other indices of rotavirus infection in a longitudinal study in childhood

In order to determine the sensitivity and reliability of antirotaviral fecal immunoglobulin A (IgA) as an indicator of rotavirus reinfection, the antibody responses to rotavirus of 44 infants with severe rotavirus gastroenteritis recruited on admission to a hospital were studied. Feces were collected daily during hospitalization and weekly thereafter, and sera were obtained every 4 months, for 6 to 32 months (median, 17 months). Antirotaviral IgG, IgA, and IgM were measured by enzyme immunoassay in all samples. Rotavirus antigen, rotavirus-neutralizing antibody, and total IgA were measured in feces. The results showed that use of an IgA index (ratio of specific IgA to total IgA) was unnecessary to identify copro-IgA conversion to rotavirus. The other markers of rotavirus infection tested showed a high level of predictive accuracy of coproconversion in rotavirus-neutralizing antibody. Copro-IgM, serum IgM, and virus in feces were insensitive measures of neutralizing antibody coproconversion. Seroconversion in IgG or IgA was detected in 46% of neutralizing coproconversions. The most sensitive marker, present in 92% of neutralizing coproconversions, was antirotaviral fecal IgA conversion. This correlation of fecal IgA with fecal neutralizing antibody suggests that coproconversions in IgA represent true elevations in antirotaviral IgA with neutralizing capacity. A coproconversion in IgA appears to indicate genuine rotavirus infection. Copro-IgA conversions in feces collected weekly are likely to be more sensitive markers of rotavirus reinfection than are seroconversion and virus detection combined in epidemiological studies of acute diarrhea in children and in rotavirus vaccine trials.

Passive immunisation of children with bovine colostrum containing antibodies to human rotavirus

The efficacy of a 10-day course of bovine colostrum with high antibody titre against the four known human rotavirus serotypes in protecting children against rotavirus infection was examined in patients admitted to hospital. Children aged 3 to 15 months were blocked in pairs according to ward accommodation (ie, isolation or open area). Each block contained 1 treated and 1 control child. The allocation to treatment or control (an artificial infant formula) was randomised. 9 of 65 control children but none of 55 treated children acquired rotavirus infection during the treatment period (p less than 0.001). The importance of protecting against rotavirus infection was highlighted by the fact that parents of symptomatic rotavirus-positive children sought medical attention seven times more often than did parents of symptomatic rotavirus-negative children (p less than 0.05).

Efficiency of isolation of human rotavirus in primary African green monkey kidney cells

Out of 212 human rotavirus (HRV) containing fecal specimens, 173 (81.6%) yielded virus on first passage in primary African Green monkey kidney cells (AGMK), while additional 34 specimens, did not yield virus on first passage. However, following blind passages, 18 of the 34 yielded virus in passage levels 2-8, thus raising the overall isolation rate to 90.1%. The isolation rate of HRV strains obtained in embryonic Rhesus monkey kidney cell line (MA-104), was only 41.4%. ELISA tests performed on fluids from infected cell cultures proved to be an efficient tool to measure virus replication. No differences were encountered in the isolation rates between subgroup I and II strains, while viruses lacking the antigenic determinants of both subgroups did not grow at all. However, one of those unusual group A strains was isolated and grew well in AGMK cells. Primary AGMK and MA-104 cells supported the growth of tissue culture adapted virus most efficiently when compared with six human and primate cell types.

Comparative sequence analysis of VP7 genes from five Australian porcine rotaviruses

The genes coding for the rotavirus major neutralizing protein, VP7, from 5 Australian porcine rotaviruses representing glycoprotein (i.e. VP7 or G) serotypes 3, 4, and 5, were sequenced. The genes were each 1,062 nucleotides long with two long open reading frames for proteins of either 326 or 297 amino acids and containing only one potential glycosylation site at amino acid position 69. When compared to the corresponding genes of human viruses, the porcine genes showed very high nucleotide and deduced amino acid homology. Sequence comparison also revealed that Australian porcine rotaviruses of G serotype 4 and 5 were similar to the corresponding porcine strains found in the U.S.A. and U.K., while G serotype 3 and 4 porcine rotaviruses were closely related to human G serotype 3 strain, RV-3 and serotype 4 strain, ST-3, respectively. These Australian rotavirus VP7 sequences were found to correlate with serological data we reported previously.

Sequences of VP9 genes from short and supershort rotavirus strains

Segment 10 genes from a short (RV-5, serotype G2) and a supershort (B37, a new G serotype) strain were cloned and their sequences compared to the (corresponding) segment 11 sequences of Wa, SA11, and UK rotaviruses. The determined nucleotide sequences were 817 (RV-5) and 947 (B37) bases in length and showed extensively conserved 5' noncoding and protein coding regions. The major open reading frame codes for a protein of 200 (RV-5) or 198 (B37) amino acids, and the newly proposed second open reading frame can code for a protein of 92 amino acids. Compared to long strain gene segments, the base sequences of the short and supershort strains were found to contain extended, AT-rich 3' noncoding regions which were not significantly homologous to each other, to other parts of the VP9 gene, or to other rotavirus genes that have been sequenced. The function(s) of these 3' regions is not apparent.

The VP7 gene of a new G serotype of human rotavirus (B37) is similar to G3 proteins in the antigenic c region

The human rotavirus isolate B37 has a characteristic "super-short" RNA electropherotype and has been shown to represent a new VP7 serotype (M. J. Albert, L. E. Unicomb, and R. F. Bishop, 1987, J. Clin. Microbiol. 25, 183-185). The VP7 gene was cloned, and its nucleotide and predicted amino acid sequences were compared to other published VP7 gene sequences. Consistent with the serological evidence, two major antigenic regions of the B37 VP7 (i.e., regions A and B) differ in sequence from those of other G serotypes. Unexpectedly, the C antigenic region shows close similarity to G3 rotaviruses, but we were unable to detect a serological relationship using serotype 3 monoclonal antibodies.

Experience with an enzyme immunoassay for serotyping human group A rotaviruses

An enzyme immunoassay utilizing neutralizing monoclonal antibodies to VP7 of four human group A rotavirus serotypes successfully typed rotaviruses in 71.4% (568 of 796) of fecal specimens. Sensitivity was enhanced by using homologous capture and detector antibodies. Serotyping was most successful with specimens stored for less than 3 years and containing 10(4) or more particles per ml.

Nucleotide sequence of UK bovine rotavirus segment 4: possible host restriction of VP3 genes

The bovine UK and simian SA11 rotaviruses are commonly used VP7-type reference strains. Since the surface protein VP3 is a significant neutralization antigen, it is important to fully characterize the VP3 types associated with current reference strains. Here we present the complete nucleotide and predicted amino acid sequence of VP3 from UK rotavirus (VP7 type 6) and compare it to the published sequences of SA114fm and RV-5. We also compare the deduced amino acid sequence covering the trypsin cleavage region of UK VP3 to 25 other available sequences. The UK protein is clearly different from that of bovine NCDV (another commonly used VP7 type 6 strain) and represents a second VP3 type associated with bovine rotaviruses. Our SA11 sequence differs from that determined by Lopez et al. [1985, Virology 144, 11-19; later referred to as SA114fM by Lopez et al. (1986, Virology 154, 224-227], their sequence being very similar to the published sequence of NCDV VP3. The significance of these results with regard to virus serotypes is discussed. Finally, in analyzing the nucleotide sequence surrounding the initiation codon, a potential hairpin-loop structure was identified which may be involved in translational regulation.

Comparative sensitivities of solid-phase immune electron microscopy and enzyme-linked immunosorbent assay for serotyping of human rotavirus strains with neutralizing monoclonal antibodies

Suspensions of 24 rotavirus strains, 6 for each known human rotavirus serotype, were serially diluted and titrated by (i) enzyme-linked immunosorbent assay (ELISA) for rotavirus detection, using monoclonal antibodies (MAbs) specific for group-specific sites of the VP6 inner capsid protein; (ii) ELISA for subgrouping, using MAbs reactive with subgroup-specific determinants of rotavirus VP6; (iii) ELISA for serotyping, using MAbs directed to serotype-specific sites of the VP7 outer capsid glycoprotein; and (iv) solid-phase immune electron microscopy (SPIEM) for serotyping, using VP7-specific MAbs. In addition, in each preparation the proportion of double-shelled rotavirus particles were determined by direct electron microscopy. Results showed that SPIEM was 2- to 16-fold more sensitive than ELISA for serotyping of rotavirus. The titers in VP7-specific tests correlated well with the proportion of double-shelled virus particles in each of the samples. Titers obtained by ELISA for serotyping of suspensions containing 20% or fewer complete particles were up to 4,096-fold lower than those obtained by ELISA for detection. ELISA serotyping titers of samples containing 20 to 80% double-shelled rotavirus particles were up to 128-fold lower than ELISA detection titers, whereas preparations with nearly 100% complete particles had ELISA titers that were less different from each other. ELISA subgrouping titers were four- to eightfold lower than corresponding rotavirus detection titers. It was concluded that, although SPIEM appears to be more sensitive than ELISA, the amount of complete virus particles in the specimens is of critical importance for successful serotyping of human rotavirus strains. Samples rich in single-shelled particles but containing low amounts of VP7 outer capsid glycoprotein might even be strongly reactive in assays for rotavirus detection and subgrouping but virtually unreactive in tests for serotyping.

New porcine rotavirus serotype antigenically related to human rotavirus serotype 3

Serotyping of porcine rotaviruses isolated in MA104 cells from Australian piglets with diarrhea showed that two strains belonged to serotype 3 and one strain was antigenically similar to the OSU strain of porcine rotavirus (serotype 5). In addition, neutralizing antibodies to human rotavirus serotype 4 (ST-3 strain) were detected in serum samples from sows in one area, and so it seems probable that porcine rotaviruses of at least three serotypes occur in Australia.

Non-neutralizing monoclonal antibodies to a trypsin-sensitive site on the major glycoprotein of rotavirus which discriminate between virus serotypes

Monoclonal antibodies were derived to a human rotavirus purified from stools. Three of the antibodies immunoprecipitated the rotavirus outer capsid glycoprotein gp 34 and were non-neutralizing. These antibodies reacted by enzyme immunoassay with cultivable rotaviruses showing the "long" RNA electropherotype but were inefficient as detectors of "long" RNA pattern rotaviruses in stools. Treatment of SA 11 rotavirus with 7.5 micrograms/ml porcine trypsin for 30 minutes at 37 degrees C irreversibly reduced binding of the antibodies to SA 11 rotavirus in enzyme immunoassays by 50 per cent. Binding was abolished in the presence of rotavirus-negative faecal extracts. These results indicate that non-neutralizing sites on gp 34 of rotaviruses can vary with RNA electropherotype and serotype, and that levels of trypsin currently in use to assist growth of rotaviruses in cell culture may alter the serological profile of the viruses.

Production and characterization of neutralizing monoclonal antibody to a human rotavirus strain with a "super-short" RNA pattern

A neutralizing monoclonal antibody, B37:1, against a human rotavirus (B37) with a "super-short" RNA pattern was derived. The antibody gave serotype-specific reactions with a panel of standard rotaviruses and was reactive in an enzyme immunoassay. Epidemiological studies of this new human serotype should now be possible.

Cultivation and characterization of rotavirus strains infecting newborn babies in Melbourne, Australia, from 1975 to 1979

Twenty-three rotavirus strains obtained from the stools of 71 newborn babies were adapted to growth in MA-104 cells. Babies were housed in newborn nurseries of eight different obstetric hospitals in Melbourne between 1975 and 1979. All strains belonged to serotype 3 when reacted with serotype-specific neutralizing monoclonal antibodies in an enzyme immunoassay. Genome RNA of these 23 strains and of one stool virus not adapted to cell culture were compared by coelectrophoresis of mixtures of RNA. When strains were compared by coelectrophoresis of RNA for 4 h at 40 mA current, the majority appeared to be identical. Coelectrophoresis at 4 degrees C for 17 h at 10 mA current with 0.75-mm-thick polyacrylamide gels resulted in increased resolution of segments, revealing more genetic diversity than previously observed. Seventeen different electropherotypes showing slight variations in migration of one to seven segments were identified. Segments 5 and 7, 8, 9, 10, and 11 varied more frequently than segments 1, 2, 3, 4, and 6. Strains endemic in one hospital from 1975 to 1983 showed increased numbers of segmental changes over time. Differing patterns of reaction with two neutralizing monoclonal antibodies reacting with VP3 and VP7 were observed. Comparison of electropherotypes of three neonatal strains with a serotype 3 community strain showed marked differences in segment migration. The serotypic similarity, electropherotypic dissimilarity from community strains, and asymptomatic nature of most infections are additional evidence that these viruses infecting newborn babies form a unique group of rotaviruses.

Simple and specific enzyme immunoassay using monoclonal antibodies for serotyping human rotaviruses

An enzyme immunoassay for serotyping human rotaviruses in stools and in cell culture was developed. Hyperimmune rabbit antisera to rotaviruses were used as capture antibodies, and rotavirus-neutralizing mouse monoclonal antibodies specific for serotypes 1, 2, 3, and 4 were used as detection reagents. Partial purification of monoclonal antibodies and inclusion of skim milk powder in antibody diluents contributed to assay specificity. The sensitivity of this assay was greater than that of a direct enzyme immunoassay in which rotaviruses of the appropriate serotype were adsorbed directly to the solid phase. When fecal extracts were concentrated threefold, this serotyping enzyme immunoassay was of equal specificity and approached the sensitivity of electron microscopy for rotavirus detection. This assay is simple and rapid and is suitable for serotyping the large numbers of isolates obtained from epidemiological studies and vaccine trials.

Marked sequence variation between segment 4 genes of human RV-5 and simian SA 11 rotaviruses

The complete nucleotide sequence of dsRNA gene segment 4 of a human serotype 2 rotavirus, RV-5, was determined by sequencing overlapping cloned DNA copies of the gene. Segment 4 is 2359 base pairs in length and contains a single long open reading frame of 2325 bases capable of coding for a protein of 775 amino acids, with 5' and 3' non coding regions of 9 and 25 nucleotides respectively. Comparison with SA 11 segment 4 sequence reveals a moderately conserved trypsin cut site and an overall amino acid homology of 69.8 percent. One localized region of 126 amino acids is only 37.8 percent homologous. Localized frame shifts account for some of this variation, but at the nucleotide level the segment 4 sequences show more variability than other rotavirus genes that have been studied so far.

Isolation and serotyping of animal rotaviruses and antigenic comparison with human rotaviruses. Brief report

Rotaviruses were isolated from Australian farm animals (calf, pig and foal) with diarrhoea. Reciprocal cross neutralisation studies showed antigenic similarities with overseas animal strains and with human strains including a newly defined fifth human serotype.

Cultivation and characterization of human rotaviruses with "super short" RNA patterns

Two group A, subgroup I, rotavirus strains possessing "super short" RNA patterns were adapted to growth in MA-104 cells. Both produced marked cytopathic effect in primary culture. Reciprocal cross-neutralization titers, polypeptide analysis, and the serum neutralizing antibody response of an infected child suggested that super short viruses are serotypically distinct from the four recognized human serotypes.

Heterologous protection against rotavirus-induced disease in gnotobiotic piglets

Administration per os of 2 X 10(6) fluorescent cell-forming units of a human serotype 3 rotavirus (RV-3) protected all of nine gnotobiotic piglets against severe diarrheal disease when they were challenged 10 to 14 days later with 8 X 10(3) fluorescent cell-forming units of virulent wild-type porcine rotavirus (AT/76). The porcine virus was similar antigenically to porcine prototype strain OSU, previously described as antigenically distinct from all four recognized human serotypes. Administration of RV-3 was associated with the development of serum-neutralizing antibody to both RV-3 and AT/76 in piglets that excreted RV-3. Neutralizing antibody levels to RV-3 and AT/76 increased rapidly postchallenge. Vaccinated piglets were not immune to infection with AT/76 but showed no or minimal gastrointestinal symptoms after challenge. Control nonvaccinated piglets that were fed AT/76 developed severe dehydrating diarrhea and low levels of neutralizing antibody to AT/76 alone. The apparent heterologous clinical protection observed in this study could have been predicted from results of in vitro assays. Neutralization tests with reduction of fluorescence focus indicated a one-way cross-reaction between RV-3 and AT/76 such that hyperimmune antiserum to RV-3 neutralized porcine virus to moderate titer, but not vice versa. The results emphasize the importance of neutralizing antibody in protection against disease and the need to determine reciprocal cross-neutralization titers, rather than serotype alone, in order to predict the ability of rotavirus strains to cross protect.

Derivation of neutralizing monoclonal antibodies to human rotaviruses and evidence that an immunodominant neutralization site is shared between serotypes 1 and 3

Neutralizing monoclonal antibodies were derived to human rotaviruses RV-4 (serotype 1), RV-5 (serotype 2), and ST-3 (serotype 4). By enzyme immunoassay and fluorescent focus neutralization, eight of the antibodies appeared to be specific for the immunizing serotype, and so have potential as reagents for rotavirus serotyping by enzyme immunoassay. Seven of these were shown by Western blotting, enzyme immunoassay for antibody additivity, and reaction with rotavirus reassortants, to be directed against the major outer capsid glycoprotein. The remaining serotype-specific antibody immunoprecipitated the 84-kD outer capsid protein. One antibody reacted with all serotype 1 and 3 rotaviruses but not with serotypes 2 or 4. When tested with virus mutants, this antibody recognized an immunodominant determinant of neutralization shared between serotypes 1 and 3 on the major outer shell glycoprotein. Our results suggest that two outer capsid proteins possess determinants of neutralization, and that viruses of different serotypes may share immunodominant neutralization sites.

Neutralizing monoclonal antibodies to human rotavirus and indications of antigenic drift among strains from neonates

Cells producing neutralizing monoclonal antibodies to a serotype 3 human neonatal rotavirus strain RV-3 were derived by fusion of hyperimmunized mouse spleen cells with mouse myeloma cells. As ascites fluid, three rotavirus-neutralizing monoclonal antibodies were characterized by hemagglutination inhibition and reacted with 17 cultivable mammalian rotaviruses representing five virus serotypes, by fluorescent focus neutralization and enzyme immunoassay. Two antibodies, Mab RV-3:1 and Mab RV-3:2, reacted with the seven serotype 3 rotaviruses only. Mab RV-3:1 was shown to bind to the outer capsid glycoprotein gp34 of rotavirus when variants of SA 11 rotavirus were used, and it therefore appears to react with the major neutralization epitope of serotype 3 rotaviruses. The antibody Mab RV-3:3 was specific for an epitope of RV-3 rotavirus not present on any other rotavirus of any serotype tested, including another neonatal isolate of identical RNA electropherotype isolated from the same ward of the same hospital as RV-3 3 months earlier. These two viruses were also distinguishable by fluorescent focus neutralization, using antiserum to RV-3 virus. Western blot analysis showed binding of Mab RV-3:3 to the trypsin cleavage product of the outer capsid protein p86 of RV-3. This suggests that antigenic drift may have occurred among neonatal rotaviruses in Melbourne. These monoclonal antibodies will be useful in serotyping assays of rotaviruses directly in stool samples, and in further analysis of antigenic variation within the serotype.