Expression, self-assembly, and antigenicity of a snow mountain agent-like calicivirus capsid protein

Expression and self-assembly of recombinant capsid protein from the antigenically distinct Hawaii human calicivirus

The Norwalk and Hawaii viruses are antigenically distinct members of the family Caliciviridae and are considered to be important etiologic agents of epidemic gastroenteritis, with most studies focusing on the role of Norwalk virus. To further investigate the importance of Hawaii virus, Hawaii virus-like particles (VLPs) were produced by expression of its capsid protein in the baculovirus system and these VLPs were used as the antigen in an enzyme-linked immunosorbent assay that was efficient in the detection of a serologic response to Hawaii virus. The ready availability of Hawaii VLPs should enable larger-scale epidemiological studies to further elucidate the importance of this agent.

Incidence of human calicivirus and rotavirus infection in patients with gastroenteritis in South Africa

Human caliciviruses (HuCVs) are reportedly responsible for 2.5-4% of nonbacterial sporadic gastroenteritis. The incidence of HuCV infection in South Africa is unknown. Stool specimens from 1,296 South African patients with sporadic gastroenteritis were screened for the presence of HuCVs using electron microscopy, recombinant enzyme immunoassays for Norwalk (NV) and Mexican (MX) viruses, and the reverse transcriptase-polymerase chain reaction (RT-PCR). RT-PCR products were sequenced to ascertain which HuCV genogroups were present. HuCVs were detected in 43/1,296 (3.3%) specimens examined, with RT-PCR proving to be the most sensitive detection method. Genetic analysis of the isolates indicated that 81% were Snow Mountain Agent, or MX-like; 8% were NV-like; and 11% were HuCV/Sapporo-like. This study indicates that a combination of assays is needed for the accurate detection of HuCVs. Comparative data on hospitalised patients showed that the incidence of rotavirus infection was approximately ten times greater than that of HuCV infection.

A one-tube method of reverse transcription-PCR to efficiently amplify a 3-kilobase region from the RNA polymerase gene to the poly(A) tail of small round-structured viruses (Norwalk-like viruses)

Amplification of a 3-kb genome region from the RNA polymerase gene to the 3' poly(A) tail of small round-structured virus (SRSV) by reverse transcription-PCR (RT-PCR) has been difficult to achieve because of a stable secondary structure in a region between the RNA polymerase gene and the 5' end of the second open reading frame. We have developed a one-tube RT-PCR method to efficiently amplify this region. The method comprises three procedures: purification of poly(A)+ RNA from a starting RNA solution by oligo(dT)30 covalently linked to latex particles, buffer exchange, and continuous RT and PCR in a single tube containing all reaction components. The key elements of this method are (i) first-strand cDNA synthesis with the Superscript II version of RNase H- Moloney murine leukemia virus reverse transcriptase at 50 degrees C for 10 min by using the RNA-oligo(dT)30 hybrid on the latex particles as the template and primer, and (ii) PCR by Taq and Pwo DNA polymerases mixed together with a mixture of 12 phased oligo(dT)25 antisense primers. The detection threshold of the one-tube RT-PCR method was as little as 0.2 ng of the crude RNA used as the source of the template. Using this method, we obtained 3-kb products from 24 SRSV strains previously characterized into four genetic groups. These included 5 P1-A, 4 P1-B, 5 P2-A, and 10 P2-B strains. Because SRSVs have not yet been cultivated in vitro, this novel method should facilitate molecular characterization of SRSVs to provide a firm scientific foundation for improvements and refinements of SRSV diagnostics.

Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part II. The epidemiological perspective

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Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part I. The clinical and diagnostic perspective

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Attachment and entry of recombinant Norwalk virus capsids to cultured human and animal cell lines

Norwalk virus (NV) is the prototype strain of a group of noncultivable human caliciviruses responsible for epidemic outbreaks of acute gastroenteritis. While these viruses do not grow in tissue culture cells or animal models, expression of the capsid protein in insect cells results in the self-assembly of recombinant Norwalk virus-like particles (rNV VLPs) that are morphologically and antigenically similar to native NV. We have used these rNV VLPs to examine virus-cell interactions. Binding and internalization of VLPs to cultured human and animal cell lines were studied in an attempt to identify potentially susceptible cell lines for virus propagation in vitro and to determine if early events in the replication cycle were responsible for the narrow host range and restriction of virus growth in cell culture. Radiolabeled VLPs specifically bound to a saturable number of binding molecules on the cell surface of 13 cell lines from different origins, including human intestine (differentiated and undifferentiated Caco-2) and insect (Spodoptera frugiperda 9) ovary. Differentiated Caco-2 cells bound significantly more rNV VLPs than the other cell lines. Variations in the amount of bound VLPs among the different cell lines did not correlate with the tissue or species of origin. VLP binding was specific, as determined by competition experiments with unlabeled rNV VLPs; however, only 1.4 to 6.8% of the specifically prebound radiolabeled VLPs became internalized into cells. Blocking experiments using polygonal and monoclonal anti-rNV sera and specific antipeptide sera were performed to map the domains on rNV VLPs involved in binding to cells. One monoclonal antibody (NV8812) blocked binding of rNV VLPs to human and animal cell lines. The binding site of monoclonal antibody NV8812 was localized to the C-terminal 300 to 384 residues of the capsid protein by immunoprecipitation with truncated and cleaved forms of the capsid protein. These data suggest that the C-terminal region of the capsid protein is involved in specific binding of rNV VLPs to cells.

Characterization of Toronto virus capsid protein expressed in baculovirus

Toronto virus (TV), previously called "minireovirus", a human calicivirus classified as genogroup 2 and phylogenetic type P2-A, was originally described in association with diarrhea in children. The second open reading frame, encoding the capsid protein of TV24, was expressed in a baculovirus recombinant. The recombinant baculovirus produced a protein (rTV) with an apparent molecular mass of 58 kDa that self-assembled into virus-like particles approximately 30 nm in diameter with a density of 1.29 g/ml. Antigenic and immunogenic characteristics of these particles were determined by protein immunoblot, immunoprecipitation, and enzyme immunoassay. Seroconversion to the rTV protein was detected in 6 of 8 (75%) patients from a recent outbreak of gastroenteritis associated with a virus of similar phylogenetic type. These results confirm and extend the previous reports of the expression of the Norwalk and Mexico virus capsid proteins.

Study on occurrence of human calicivirus (Mexico strain) as cause of sporadic cases and outbreaks of calicivirus-associated diarrhoea in the United Kingdom, 1983-1995

The use of a recently developed EIA using antisera raised against purified baculovirus expressed recombinant Mexico virus (rMx) capsid protein is described for screening for human calicivirus in stools. The results show that MX-like viruses have been circulating in the UK periodically since 1983 and were an occasional cause of sporadic cases of diarrhoea in infants and outbreaks of infection among elderly patients in hospitals and old people's homes. Further evidence is presented that some strains of caliciviruses with characteristic surface morphology (HuCVs) and some with an indistinct appearance, small round structured viruses (SRSVs) are antigenically related to MxV. Tests on SRSVs from four unrelated outbreaks typed as UK3 failed to react in the Mx EIA or recombinant Norwalk virus (rNV) EIA. A 2-month survey of 206 children treated in two London hospitals for diarrhoea showed that only one was positive for MxV, a child known to be infected with HIV-1. None of the samples reacted in the rNV EIA.

Evaluation of an antigen capture ELISA based on recombinant mexico virus capsid protein

BACKGROUND

The diagnosis of gastrointestinal infections caused by small round structured viruses (SRSV) has relied upon electron microscopy and antigen/antibody assays based on Norwalk virus. We investigated cases of gastroenteritis associated with SRSVs employing a new sandwich enzyme-linked immunosorbent assay (ELISA) using hyperimmune animal anti-sera against recombinant Mexico virus capsid protein (rMXV).

STUDY DESIGN

One hundred and thirty-five specimens from 86 episodes of gastroenteritis associated with SRSVs, collected in the UK between October 1993 and September 1994, were tested in the rMXV assay.

RESULTS

Forty-seven (35%) specimens from 35 of 86 (41%) episodes were positive in the rMXV ELISA and these could further be divided into high and low reactors. Sequencing of a 266-base region of the RNA polymerase gene revealed that strains highly reactive in the rMXV assay demonstrated a high degree of similarity to MXV (97-99% at the nucleotide level), whereas low-reactive strains consist of Mexico-like strains and a heterogeneous group of viruses exhibiting 70-75% similarity to MXV.

CONCLUSION

Our results indicate that the rMXV ELISA is predominantly a type specific assay, although some cross reactivity with other genogroup 2 SRSVs was observed. MXV was responsible for 26% of SRSV-associated gastrointestinal infections investigated in the UK during one year's surveillance.

Genetic and antigenic diversity of human caliciviruses (HuCVs) using RT-PCR and new EIAs

RT-PCR using primers from conserved regions of calicivirus genomes, followed by sequencing, permits characterization of genetic variation within the family. EIAs based on baculovirus-expressed viral capsid proteins and hyperimmune antisera against the capsid proteins were developed to detect HuCV antigens and antibodies. Serologic surveys using recombinant Norwalk virus (rNV) and recombinant Mexico virus (rMX, a SMA-like virus) EIAs showed that infections by HuCVs are common and that children acquire antibodies to HuCVs at an early age in both developed and developing countries. Three HuCV genogroups have been described that are represented by Norwalk virus (NV), Snow Mountain agent (SMA), and Sapporo virus, although recently accumulated sequences of HuCV strains indicate these genogroups can be further divided. These genogroups also correspond to distinct antigenic groups based on the results of the recombinant EIAs. The three genogroups co-circulate and have a worldwide distribution, although the SMA genogroup seems to be predominant currently. Application of these new assays for further characterization of the genetic and antigenic properties of HuCVs remains an important task for HuCV research.

Historical background and classification of caliciviruses and astroviruses

Infections caused by caliciviruses, i.e., vesicular exanthema virus of swine were recognised as a major cause of economic loss in the 1930s. However, it was not until the application of electronmicroscopy in the 1970s that caliciviruses and astroviruses were recognised and proven to be a cause of diarrhoea and vomiting. The following review briefly describes the steps which have led to the development of diagnostic tests and enabled the characterization of several members of the Caliciviridae and Astroviridae. In the past five years this has culminated in the sequencing of their genomes and the expression of viral proteins. This in turn has led to the development of improved diagnostic tests e.g., RT-PCR and enzyme immunoassays, and may pave the way towards producing effective vaccines in the future.

Enzyme immunoassay using baculovirus-expressed human calicivirus (Mexico) for the measurement of IgG responses and determining its seroprevalence in London, UK

The use of an enzyme immunoassay (EIA) employing a baculovirus-expressed recombinant human calicivirus (Mexico virus, MxV) for the detection of IgG-specific antibodies is described. MxV appeared to be related antigenically to a strain of small round structured virus, SRSV/UK4/Leeds/91, which had previously been shown by solid phase immune electron microscopy (SPIEM) to be related to Snow Mountain agent (SMA). One other outbreak which occurred in San Anita, USA in 1980 and was due to consumption of contaminated water was caused by a virus antigenically related to MxV. Volunteers and patients who developed significant IgG responses to rMxV showed anamnestic IgG responses (2 to 4-fold) in the recombinant Norwalk virus (rNV) IgG assay. Patients and volunteers who were known to have been infected with several other strains of calicivirus/small round spherical viruses (SRSV) including NV and SRSV UK3 showed no significant antibody response to rMxV in the EIA. A seroepidemiological survey of sera from 338 children in London showed that infection with MxV occurred earlier in life than NV. Primary infections with MxV were common after the age of 6 months. Over 70% of children had evidence of infection by the ages of 2 years, whereas only 12% of these children had been infected with NV. High concentrations of maternal antibody were present during the first month of life which was detected in 96% of the neonates. The results suggest that the high sensitivity of the EIA may be detecting maternal antibody throughout the first 8 months of life.