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Single amino acid changes in the viral glycoprotein M affect induction of alpha interferon by the coronavirus transmissible gastroenteritis virus.

Transmissible gastroenteritis virus, an enteropathogenic coronavirus of swine, is a potent inducer of alpha interferon (IFN-alpha) both in vitro and in vivo. Previous studies have shown that virus-infected fixed cells or viral suspensions were able to induce an early and strong IFN-alpha synthesis by naive lymphocytes. Two monoclonal antibodies directed against the viral membrane glycoprotein M (29,000; formerly E1) were found to markedly inhibit virus-induced IFN production, thus assigning to M protein a potential effector role in this phenomenon (B. Charley and H. Laude, J. Virol. 62:8-11, 1988). The present report describes the selection and characterization of a collection of 125 mutant viruses which escaped complement-mediated neutralization by two IFN induction-blocking anti-M protein monoclonal antibodies. Two of these mutants, designated H92 and dm49-4, were found to exhibit a markedly reduced interferogenic activity. IFN synthesis by lymphocytes incubated with purified suspensions of these mutants was 30- to 300-fold lower than that of the parental virus. The transcription of IFN-alpha genes following induction by each mutant was decreased proportionally, as evidenced by Northern (RNA) blot analysis. The sequence of the M gene of 20 complement-mediated neutralization-resistant mutants, including the 2 defective mutants, was determined by direct sequencing of genome RNA. Thirteen distinct amino acid changes were predicted, all located at positions 6 to 22 from the N terminus of the mature M protein and within the putative ectodomain of the molecule. Two substitutions, Thr-17 to Ile and Ser-19 to Pro, were assumed to generate the defective phenotypes of mutants dm49-4 and H92, respectively. The alteration of an Asn-Ser-Thr sequence in dm49-4 virus led to the synthesis of an M protein devoid of a glycan side chain, which suggests a possible involvement of this structure in IFN induction. Overall, these data supported the view that an interferogenic determinant resides in the N-terminal, exposed part of the molecule and provided further evidence for the direct role of M protein in the induction of IFN-alpha by transmissible gastroenteritis virus. The acronym VIP (viral interferogenic protein) is proposed as a designation for this particular class of proteins.

Amino Acid Sequence↗

Is the sialic acid binding activity of the S protein involved in the enteropathogenicity of transmissible gastroenteritis virus?

Transmissible gastroenteritis virus (TGEV) is able to recognize sialic acid on sialo-glycoconjugates. Analysis of mutants indicated that single point mutations in the S protein (around amino acids 145-155) of TGEV may result both in the loss of the sialic acid binding activity and in a drastic reduction of the enteropathogenicity. From this observation we conclude that the sialic acid binding activity is involved in the enteropathogenicity of TGEV. On the basis of our recent results we propose that binding of sialylated macromolecules to the virions surface may increase virus stability. This in turn would explain how TGEV as an enveloped virus can survive the gastrointestinal passage and cause intestinal infections.

Animals↗

Hemagglutination with transmissible gastroenteritis virus.

Transmissible gastroenteritis virus grown in primary swine kidney cell cultures agglutinated erythrocytes from chicken, guinea pig and cattle but not erythrocytes from mouse and goose. The optimal incubation temperature was at 4 degrees C. The hemagglutination (HA) reaction was inhibited by specific antiserum. Some factors involved in the HA and HA-inhibition (HI) were investigated and standard HA and HI tests were established. HI antibody titers of individual pig sera showed a significant positive correlation with their neutralizing antibody titers.

Animals↗

Genomic organisation of a virulent Taiwanese strain of transmissible gastroenteritis virus.

Transmissible gastroenteritis (TGE) infection causes 65% of infectious piglet diarrhoea in Taiwan. A virulent Taiwanese strain, TFI, of transmissible gastroenteritis virus (TGEV) from a field outbreak was isolated in cell culture and plaque purified. Phenotypic differences were observed in the ability of TFI to infect certain cell lines. TGEV strains TLM-83 (PRCV Belgium), TO-163 (TGEV Japan) and Purdue-115 (TGEV USA) infected both ST (swine testis) and RPTG (pig kidney) cell lines whereas TFI infected ST but not RPTG cells. To investigate this phenotypic variation cDNA was generated from TFI genomic and amplified by PCR with oligonucleotides derived from published TGEV sequence data. An 8.4kb cDNA derived from the 3'-end of the TFI genome was sequenced. Eight ORFs, corresponding to the three structural protein genes, four potential genes and the 3'-end of an incomplete ORF whose amino acid sequence corresponded to the carboxyl end of the 1b subunit of the polymerase gene, were identified on the TFI sequence. The overall sequence similarity of TFI with the other TGEV strains was over 97%. However, several deletions, insertions and point mutations were found on the TFI sequence when compared with other TGEV strains. The TFI S protein was found to contain 1449 amino acids, as also identified for the FS772/70 and Miller TGEV strains, but two amino acids longer than the Purdue S protein. The TFI ORF-3a gene encodes 72 amino acids, however, a 37 nucleotide deletion was found 16 nucleotides downstream of the TFI ORF-3a stop codon.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

Multiplex reverse transcription-PCR for rapid differential detection of porcine epidemic diarrhea virus, transmissible gastroenteritis virus, and porcine group A rotavirus.

A novel multiplex reverse transcription polymerase chain reaction (multiplex RT-PCR) that can detect porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine group A rotavirus (GAR) was developed. The 3 viruses (PEDV, TGEV, and porcine GAR) are major agents in viral enteric diseases of piglets. As the clinical signs of these diseases are similar, including watery diarrhea, differential detection is required for etiologic diagnosis. A mixture of 3 pairs of published primers was used for amplification of viral nucleic acids, yielding 3 different amplicons with sizes of 859 bp, 651 bp, and 309 bp for TGEV, PEDV, and porcine GAR, respectively. A total of 157 specimens (78 fecal and 79 intestinal samples) from piglets with acute gastroenteritis were collected in Korea between January 2004 and May 2005. They were tested for the presence of 3 viruses by multiplex RT-PCR. Coinfections with PEDV and porcine GAR were identified in 16 farms (43.2%). PEDV, porcine GAR, and TGEV infection were 26.3%, 13.2%, and 2.7% respectively. The relative sensitivity and specificity of multiplex RT-PCR were evaluated, with results suggesting that this assay is equal in quality to conventional single-agent RT-PCR assays (sensitivity:100%, 92.9%, 100% for TGEV, PEDV, GARs; specificity: 100% for all 3 viruses). This multiplex RT-PCR is a simple assay and may be a potentially useful for rapid, sensitive, and cost-effective etiological diagnostic tool for acute viral gastroenteritis in piglets.

Animals↗

N-acetylneuraminic acid plays a critical role for the haemagglutinating activity of avian infectious bronchitis virus and porcine transmissible gastroenteritis virus.

Porcine transmissible gastroenteritis virus (TGEV) was found to resemble avian infectious bronchitis virus (IBV) in its interaction with erythrocytes. Inactivation of the receptors on erythrocytes by neuraminidase treatment and restoration of receptors by reattaching N-acetylneuraminic acid (Neu5Ac) to cell surface components indicated that alpha 2,3-linked Neu5Ac serves as a receptor determinant for TGEV as has been reported recently for IBV. Similar to IBV, the haemagglutinating activity of TGEV is evident only after pretreatment of virus with neuraminidase indicating that inhibitors on the virion surface have to be inactivated in order to induce the HA-activity of these viruses. A model is presented to explain why the HA-activity of untreated virus is masked and how neuraminidase treatment results in the unmasking of this activity.

Bacterial Proteins↗

Cellular immune responses of pigs after primary inoculation with porcine respiratory coronavirus or transmissible gastroenteritis virus and challenge with transmissible gastroenteritis virus.

The contribution of cell-mediated immunity to protective immunity against virulent transmissible gastroenteritis virus (TGEV) infection conferred by primary porcine respiratory coronavirus (PRCV) or TGEV exposure was assessed in pigs that were challenged with TGEV 24 days after a primary oronasal inoculation with PRCV or TGEV when 11 days old. PRCV exposure induced partial protection against TGEV challenge in suckling pigs based upon a decreased number of diarrhea cases (42% vs. 90% in age-matched control pigs), limited virus shedding in feces, and increases in virus-neutralizing serum antibody titers; in contrast, all 11-day-old pigs inoculated with TGEV were completely protected after challenge. Weaned pigs were also studied to eliminate any possibility that lactogenic immunity from contact PRCV-exposed sows contributed to protection against TGEV. Once weaned, none of the PRCV-exposed or age-matched control pigs had diarrhea after TGEV challenge; moreover, both groups exhibited less rectal virus shedding than suckling pigs. Vigorous lymphocyte proliferative responses (> 96,000 counts per minute (cpm)) were detected in mononuclear cells prepared from mesenteric (MLN) and bronchial (BLN) lymph nodes of TGEV-primed pigs. Analyses of these responses indicate that virus-specific cell-mediated immune responses correlated with protection against rectal and nasal virus shedding after TGEV challenge. Primary inoculation of 11-day-old pigs with PRCV induced moderate, transient virus-specific lymphocyte proliferation (> 47,000 cpm) in MLN from both suckling and weaned pigs after TGEV challenge. Substantial BLN proliferative responses (> 80,000 cpm) correlated with failure to detect TGEV in nasal secretions from these pigs. Virus-specific lymphocyte proliferation in spleens was delayed in onset and of lower magnitude than that observed in MLN and BLN. Virulent TGEV exposure resulted in increased percentages of T cell subsets, especially in the lamina propria and MLN, mucosa-associated lymphoid tissues in proximity to the primary replication site of TGEV in the small intestine. Our results confirm that PRCV infection primes anti-viral immune responses and, thus, contributes to partial immunity against virulent TGEV challenge.

Animals↗

Analysis of the sialic acid-binding activity of the transmissible gastroenteritis virus.

Porcine transmissible gastroenteritis virus (TGEV) has been shown to agglutinate erythrocytes using alpha 2,3-linked sialic acid on the cell surface as binding site. The hemagglutinating activity requires the pretreatment of virus with neuraminidase. We obtained evidence that TGEV recognizes not only N-acetylneuraminic acid but also N-glycoloylneuraminic acid, a sialic acid present on many porcine cells.

Animals↗

Physicochemical properties of transmissible gastroenteritis virus hemagglutinin.

Transmissible gastroenteritis virus was readily adsorbed onto chicken erythrocytes at 4 degrees C. The hemagglutinin thus adsorbed could be eluted from the erythrocytes by incubating in phosphate buffered saline at 37 degrees C. The receptor on chicken erythrocytes for the hemagglutinin was inactivated by neuraminidase and potassium periodate, but not by trypsin, 2-mercaptoethanol and formalin. The hemagglutinin was inactivated by trypsin, papain, pepsin, alpha-amylase, phospholipase C, neuraminidase, formalin, 2-mercaptoethanol, potassium periodate, ethyl ether, chloroform, Tween-80 and beta-propiolactone, but not by sodium deoxycholate and trichlorotrifluoroethane, suggesting that the active component of the hemagglutinin involved glycoproteins. The hemagglutinin was stable at 37 degrees C or lower temperatures but not at 60 degrees C or higher temperatures. The hemagglutinin activity was resistant to ultraviolet irradiation, while the infectivity was very susceptible. The hemagglutinin and the infectivity were readily sedimented by ultracentrifugation at 45,000 x g for 60 minutes. In rate zonal centrifugation of the hemagglutinin preparation on a sucrose density gradient, the hemagglutinin activity showed a sharp peak at 1.19 g/ml coinciding with the peak of infectivity. The activity in the peak fraction seemed to be structurally associated with virus particles.

Chemical Phenomena↗

Differentiation between porcine epidemic diarrhea virus and transmissible gastroenteritis virus in formalin-fixed paraffin-embedded tissues by multiplex RT-nested PCR and comparison with in situ hybridization.

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) were detected and differentiated in formalin-fixed, paraffin-embedded tissues from experimentally and naturally infected pigs by multiplex reverse transcription-nested polymerase chain reaction (RT-nPCR). The results of this new method were compared with in situ hybridization. A method based on xylene deparaffinization followed by proteinase K digestion yielded RNA of a suitable quality for reliable and consistent multiplex RT-nPCR analyses. PEDV and TGEV cDNAs were detected in jejunal tissues from experimentally and naturally infected pigs by multiplex RT-nPCR. Distinct positive signals for PEDV and TGEV were also detected in the same jejunal tissues by in situ hybridization. The rate of conformity between multiplex RT-nPCR and in situ hybridization was 100% for the detection of PEDV and TGEV in formalin-fixed paraffin-embedded jejunal tissues.

Animals↗

Effect of temperature on the detection of porcine epidemic diarrhea virus and transmissible gastroenteritis virus in fecal samples by reverse transcription-polymerase chain reaction.

The effect of storage temperature was determined for the detection of porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) in fecal samples from experimentally and naturally infected pigs by multiplex reverse transcription-polymerase chain reaction (RT-PCR). To examine the effect of storage temperature on the ability to detect PEDV and TGEV RNA by multiplex RT-PCR, fecal samples were stored for different temperatures (4, 21, 36, and 45 C) before extracting viral RNA. The PEDV and TGEV nucleic acids in fecal samples were stable up to 3 days at 4 C. The PEDV and TGEV nucleic acids were consistently detected in fecal samples up to 60 hours at 21 C and 24 hours only at 36 and 45 C. Thereafter, the number of positive signals declined. Positive signals were detected in fecal samples stored at 4 C by 240 hours. The PEDV and TGEV nucleic acids were consistently detected in fecal samples up to 60 hours at 21 C and 24 hours only at 36 and 45 C. The results of this study suggested that storage temperature has significant effect on the detection of PEDV and TGEV nucleic acids from fecal samples by multiplex RT-PCR.

Animals↗

Detection and differentiation of porcine epidemic diarrhoea virus and transmissible gastroenteritis virus in clinical samples by multiplex RT-PCR.

A multiplex reverse-transcriptase-PCR (RT-PCR) procedure was developed for the simultaneous detection of porcine epidemic diarrhoea virus (PEDV) and transmissible gastroenteritis virus (TGEV) in preweaning pigs with diarrhoea. The membrane gene of PEDV and the nucleocapsid gene of TGEV were chosen as targets. The PCR products of PEDV and TGEV had molecular sizes of 412 and 612 base pairs, respectively. Primers from PEDV did not react with any TGEV tested and vice versa. In addition, the primers did not react with other pig viruses. The multiplex RT-PCR was able to detect 10 tissue culture-infective doses 50 per cent (TCID50)/ml of PEDV or TGEV with each of the primer sets for PEDV and TGEV, respectively. The RNAS of PEDV and TGEV were detected directly in intestinal and faecal samples from pigs infected experimentally with either virus. The results of the assay correlated well with the results of virus isolation. None of the five control specimens was positive. PEDV was detected in 10 intestinal and nine faecal samples, and among the nine positive faecal samples two were culture-negative. TGEV was also detected in 10 intestinal and nine faecal samples, and among the nine positive faecal samples, three were culture-negative.

Animals↗

RT-PCR-based dot blot hybridization for the detection and differentiation between porcine epidemic diarrhea virus and transmissible gastroenteritis virus in fecal samples using a non-radioactive digoxigenin cDNA probe.

Multiplex reverse transcription-polymerase chain reaction (RT-PCR)-based dot blot hybridization was developed to increase the sensitivity for the detection and differentiation between porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) in fecal samples. Fecal samples found positive by RT-PCR-based agarose gel electrophoresis were always found positive by RT-PCR-based dot blot hybridization. In addition, 5 out of 10 fecal samples which were negative for PEDV by RT-PCR-based agarose gel electrophoresis were positive for PEDV by RT-PCR-based dot blot hybridization. This RT-PCR-based dot blot hybridization increased 1000-fold in sensitivity for PEDV and 100-fold for TGEV; weakly positive bands in the agarose gel electrophoresis gave a clear positive result with dot blot hybridization.

Animals↗

Laboratory evaluation of selected disinfectants as virucidal agents against porcine parvovirus, pseudorabies virus, and transmissible gastroenteritis virus.

Of a variety of disinfectants evaluated, only sodium hypochlorite and sodium hydroxide inactivated porcine parvovirus (PPV) after a 5-minute incubation period. After the same incubation time, pseudorabies and transmissible gastroenteritis viruses were inactivated by all of the disinfectants tested. When the incubation time was increased to 20 minutes, 2% glutaraldehyde and a double-strength concentration of a commercial formaldehyde preparation also inactivated PPV. Formaldehyde vapor and ultraviolet radiations inactivated PPV also, but relatively long exposure times were required.

Animals↗

Interspecies aminopeptidase-N chimeras reveal species-specific receptor recognition by canine coronavirus, feline infectious peritonitis virus, and transmissible gastroenteritis virus.

We report that cells refractory to canine coronavirus (CCV) and feline infectious peritonitis virus (FIPV) became susceptible when transfected with a chimeric aminopeptidase-N (APN) cDNA containing a canine domain between residues 643 and 841. This finding shows that APN recognition by these viruses is species related and associated with this C-terminal domain. The human/canine APN chimera was also able to confer susceptibility to the porcine transmissible gastroenteritis virus (TGEV), whereas its human/porcine homolog failed to confer susceptibility to CCV and FIPV. A good correlation was observed between the capacity of CCV, FIPV, and TGEV to recognize the different interspecies APN chimeras and their ability to infect cells derived from the relevant species. As an exception, TGEV was found to use a human/bovine APN chimera as a receptor although itself unable to replicate in bovine cells.

Amino Acid Sequence↗

Molecular mimicry between Fc receptor and S peplomer protein of mouse hepatitis virus, bovine corona virus, and transmissible gastroenteritis virus.

We have previously demonstrated molecular mimicry between the S peplomer protein of mouse hepatitis virus (MHV) and Fc gamma R (Fc gamma R). A monoclonal antibody (MAb) to mouse Fc gamma R (2.4G2 anti-Fc gamma R MAb), purified rabbit immunoglobulin, but not their F(ab')2 fragments, as well as mouse and rat IgG, immunoprecipitated (1) recombinant S peplomer protein expressed by a vaccinia virus recombinant in human, rabbit, and mouse cells, and (2) natural S peplomer protein from cells infected with several strains of MHV and MHV escaped mutants. We report here results of studies documenting molecular mimicry between Fc gamma R and S peplomer protein of viruses representing three distinct antigenic subgroups of the Coronaviridae. We have shown a molecular mimicry between the S peplomer protein of bovine corona virus (BCV) and Fc gamma R. The 2.4G2 anti-Fc gamma R MAb, rabbit IgG, but not its F(ab')2 fragments, as well as homologous bovine serum, free of anti-BCV antibodies, immunoprecipitated S peplomer protein of BCV (Mebus strain). In contrast, we did not find molecular mimicry between S peplomer protein of human corona virus (HCV-OC43) and Fc gamma R. Although the OC43 virus belongs to the same antigenic group as MHV and BCV, MAb specific for human Fc gamma RI or Fc gamma RII and purified human IgG1, IgG2, and IgG3 myeloma proteins did not immunoprecipitate the S peplomer protein from HCV-OC43-infected RD cells. In addition, we did demonstrate molecular mimicry between the S peplomer protein of porcine transmissible gastroenteritis virus (TGEV) and Fc gamma R. TGEV belongs to the second antigenic subgroup of coronaviridae.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Polymeric display of immunogenic epitopes from herpes simplex virus and transmissible gastroenteritis virus surface proteins on an enteroadherent fimbria.

The strong immunogenicity of bacterial fimbriae results from their polymeric and proteinaceous nature, and the protective role of these immunogens in experimental or commercial vaccines is associated with their capacity to induce antiadhesive antibodies. Fimbria-mediated intestinal colonization by enteropathogens typically leads to similar antibody responses. The possibility of taking advantage of these properties was investigated by determining whether enteroadhesive fimbriae, like the 987P fimbriae of enterotoxigenic Escherichia coli, can serve as carriers for foreign antigens without losing their adhesive characteristics. Random linker insertion mutagenesis of the fasA gene encoding the major 987P subunit identified five different mutants expressing wild-type levels of fimbriation. The linker insertion sites of these mutants were used to introduce three continuous segments of viral surface glycoproteins known to be accessible to antibodies. These segments encode residues 11 to 19 or 272 to 279 of herpes simplex virus type 1 (HSV-1) glycoprotein D [gD(11-19) and gD(272-279), respectively] or residues 379 to 388 of the transmissible gastroenteritis virus (TGEV) spike protein [S(379-388)]. Studies of bacteria expressing fimbriae incorporating mutated FasA subunits alone or together with wild-type FasA subunits (hybrid fimbriae) indicated that foreign epitopes were best exported and displayed on assembled fimbriae when they were inserted near the amino terminus of FasA. Fimbriated bacteria expressing FasA subunits carrying the HSV gD(11-19) or the TGEV S(379-388) epitope inserted between the second and third residues of mature FasA elicited high levels of foreign epitope antibodies in all rabbits immunized parenterally. Antibodies against the HSV epitope were also shown to recognize the epitope in the context of the whole gD protein. Because the 987P adhesive subunit FasG was shown to be present on mutated fimbriae and to mediate bacterial attachment to porcine intestinal receptors, polymeric display of foreign epitopes on 987P offers new opportunities to test the potential beneficial effect of enteroadhesion for mucosal immunization and protection against various enteric pathogens.

Adhesins, Escherichia coli↗