Characterization of monoclonal antibodies to bovine enteric coronavirus and antigenic variability among Quebec isolates

Antigenic variation among recent Japanese isolates of bovine coronaviruses belonging to phylogenetically distinct genetic groups

Bovine coronaviruses (BCoVs) isolated in Japan consist of four genetic groups, as determined by phylogenetic analysis using the polymorphic region (aa 456–592) of the S glycoprotein gene. Japanese field isolates of BCoV, reference Kakegawa strain, and vaccine strain 66/H were analyzed for their antigenic properties by indirect immunofluorescence and neutralization testing. There were no significant differences observed among these BCoVs in direct immunofluorescence tests. However, antigenic differences were observed between BCoVs in the neutralization tests, although there was no clear indication of a distinct serotype. A monoclonal antibody, 4H4, against the Kakegawa strain belonging to group 1 lacked significant neutralizing activity for viruses of groups 2, 3, and 4. Therefore, we speculate that the genetic differences between these groups may have altered their antigenicity. Analysis of mutant viruses resistant to neutralization by 4H4 revealed that the antigenic site of the Kakegawa strain maps to amino acid position 284 of the S glycoprotein. This site is not homologous to a known antigenic site (aa 528) of the Quebec strain belonging to group 1, and it is not located in the conformational domain comprising domain I (aa 351–403) and domain II (aa 517–621). This amino acid constitutes a neutralization epitope of BCoV, which is distinct from aa 528 of the Quebec strain. These results indicate antigenic evolution of BCoV between the genetic groups circulating in Japan.

Detection of a coronavirus from turkey poults in Europe genetically related to infectious bronchitis virus of chickens

Intestinal contents of 13-day-old turkey poults in Great Britain were analysed as the birds showed stunting, unevenness and lameness, with 4% mortality. At post mortem examination, the main gross features were fluid caecal and intestinal contents. Histological examination of tissues was largely unremarkable, apart from some sections that showed crypt dilation and flattened epithelia. Negative contrast electron microscopy of caecal contents revealed virus particles, which in size and morphology had the appearance of a coronavirus. RNA was extracted (turkey/UK/412/00) and used in a number of reverse transcription-polymerase chain reactions (RT-PCRs) with the oligonucleotides based on sequences derived from avian infectious bronchitis virus (IBV), a coronavirus of domestic fowl. The RT-PCRs confirmed that turkey/UK/412/00 was a coronavirus and, moreover, showed that it had the same partial gene order (S-E-M-5-N-3' untranslated region) as IBV. This gene order is unlike that of any known mammalian coronavirus, which does not have a gene analogous to the gene 5 of IBV.The gene 5 of the turkey virus had two open reading frames, 5a and 5b, as in IBV and the coronaviruses isolated from turkeys in North America. The turkey/UK/412/00 also resembled IBV, but not mammalian coronaviruses, in having three open reading frames in the gene encoding E protein (gene 3). The percentage differences between the nucleotide sequences of genes 3 and 5 and the 3' untranslated region of turkey/UK/412/00 when compared with those of IBVs were similar to the differences observed when different strains of IBV were compared with each other. No sequences unique to the turkey isolates were identified. These results demonstrate, for the first time, that a coronavirus was associated with disease in turkeys outside of North America and that it is a Group 3 coronavirus, like IBV.

Molecular analysis of Brazilian strains of bovine coronavirus (BCoV) reveals a deletion within the hypervariable region of the S1 subunit of the spike glycoprotein also found in human coronavirus OC43

Bovine coronavirus (BCoV) causes enteric and respiratory dis- orders in calves and dysentery in cows. In this study, 51 stool samples of calves from 10 Brazilian dairy farms were analysed by an RT-PCR that amplifies a 488-bp fragment of the hypervariable region of the spike glycoprotein gene. Maximum parsimony genealogy with a heuristic algorithm using sequences from 15 field strains studied here and 10 sequences from GenBank and bredavirus as an outgroup virus showed the existence of two major clusters (1 and 2) in this viral species, the Brazilian strains segregating in both of them. The mean nucleotide identity between the 15 Brazilian strains was 98.34%, with a mean amino acid similarity of 98%. Strains from cluster 2 showed a deletion of 6 amino acids inside domain II of the spike protein that was also found in human coronavirus strain OC43, supporting the recent proposal of a zoonotic spill- over of BCoV. These results contribute to the molecular characterization of BCoV, to the prediction of the efficiency of immunogens, and to the definition of molecular markers useful for epidemiologic surveys on coronavirus-caused diseases.

Human coronavirus OC43 infection induces chronic encephalitis leading to disabilities in BALB/C mice

The notion that an infectious respiratory pathogen can damage the central nervous system (CNS) and lead to neurological disease was tested using a human respiratory coronavirus, the OC43 strain of human coronavirus (HCoV-OC43). First, primary cell cultures were used to determine the susceptibility of each type of neural cells to virus infection. Neurons were the target cells, undergoing degeneration during infection, in part due to apoptosis. Second, neuropathogenicity was investigated in susceptible mice. Intracerebral inoculation of HCoV-OC43 into BALB/c mice led to an acute encephalitis with neuronal cell death by necrosis and apoptosis. Infectious virus was apparently cleared from surviving animals, whereas viral RNA persisted for several months. Some of the animals surviving to acute encephalitis presented an abnormal limb clasping reflex and a decrease in motor activity starting several months post-infection. These results suggest that viral persistence could be associated with an increased neuronal degeneration leading to neuropathology and motor deficits in susceptible individuals.

Sequence of the 3'-terminal end (8.1 kb) of the genome of porcine haemagglutinating encephalomyelitis virus: comparison with other haemagglutinating coronaviruses

A cytopathogenic coronavirus, serologically identified as porcine haemagglutinating encephalomyelitis virus (HEV), has recently been associated with acute outbreaks of wasting and encephalitis in nursing piglets from pig farms in southern Québec and Ontario, Canada. The 3'-terminal end of the genome of the prototype HEV-67N strain and that of the recent Québec IAF-404 field isolate, both propagated in HRT-18 cells, were sequenced. Overall, sequencing data indicated that HEV has remained antigenically and genetically stable since its first isolation in North America in 1962. Compared with the prototype strain of bovine enteropathogenic coronavirus (BCoV), HEV, as well as the human respiratory coronavirus (HCoV-OC43) showed a major deletion in their ORF4 gene. Deduced amino acid sequences for both HEV strains revealed 89/88, 80, 93/92 and 95/94% identities with the structural proteins HE, S, M and N of BCoV and HCoV-OC43, respectively. Major variations were observed in the S1 portion of the S gene of both HEV strains, with only 73/71% amino acid identities compared with those of the two other haemagglutinating coronaviruses.

Antigenic relationship of turkey coronavirus isolates from different geographic locations in the United States

The purpose of the present study was to examine the antigenicity of turkey coronavirus (TCV) isolates from various geographic areas with antibodies to different viruses. Seventeen isolates of TCV were recovered from intestinal samples submitted to Animal Disease Diagnostic Laboratory, Purdue University, from turkey farms located in different geographic areas. The prototype TCV Minnesota isolate (TCV-ATCC) was obtained from the American Type Culture Collection. Intestinal sections were prepared from turkey embryos infected with different TCV isolates and reacted with polyclonal or monoclonal antibodies to TCV, infectious bronchitis virus (IBV), bovine coronavirus (BCV), transmissible gastroenteritis virus (TGEV), reovirus, rotavirus, adenovirus, or enterovirus in immunofluorescent antibody staining. All 18 TCV isolates have the same antigenic reactivity pattern with the same panel of antibodies. Positive reactivity was seen with polyclonal antibodies to the TCV Indiana isolate, the TCV Virginia isolate, TCV-ATCC, and the IBV Massachusetts strain as well as monoclonal antibodies to the TCV North Carolina isolate or the membrane protein of IBV. Antibodies to BCV or TGEV were not reactive with any of the TCV isolates. Reactivity of antibodies to unrelated virus, rotavirus, reovirus, adenovirus, or enterovirus with different TCV isolates was all negative, except positive response was seen between enterovirus antibody and a TCV western North Carolina isolate, suggesting coinfection of turkeys with TCV and enterovirus in that particular case. The results indicated that the TCV isolates from these geographic locations in the U.S. shared close antigenicity and were antigenically related to IBV.

Bovine coronaviruses associated with enteric and respiratory diseases in Canadian dairy cattle display different reactivities to anti-HE monoclonal antibodies and distinct amino acid changes in their HE, S and ns4.9 protein

Bovine coronavirus isolates associated with recent outbreaks of respiratory disease in Ontario and Quebec dairy farms were compared to reference strains known to be responsible for neonatal calf diarrhea (NCD) or winter dysentery (WD) of adult cattle. In respect to their hemagglutinating properties and their higher RDE activities with rat erythrocytes, WDBCoV strains differed from NCDBCoV strains and respiratory bovine coronaviruses RBCoV strains. Serologically, three MAbs directed to the HE glycoprotein of the WDBCoV strain BCQ.2590 recognized two serogroups amongst NCDBCoV strains by hemagglutination inhibition, whereas only one of the MAbs failed to react toward three of the four RBCoV isolates tested. Sequencing analysis of the S (S1 portion), HE, ORF4 and ORF5 genes of BCoV isolates associated with different clinical syndromes indicated that neither insertions or deletions could explain their distinct tropism. For the HE glycoprotein, a total of 15 amino acids (aa) substitutions were identified by comparing field isolates to the prototype Mebus strain. Two specific proline substitutions were identified for virulent strains being located in the signal peptides (aa 5) and aa position 367; one specific aa change was revealed at position 66 for RBCoV field isolates. Analysis of the S1 portion of the S glycoprotein revealed a total of eight aa changes specific to enteropathogenic (EBCoV) strains and eight aa changes specific to RBCoV strains. For all BCoV isolates studied, the region located between the S and M genes (ORF4) apparently encodes for two non-structural (ns) proteins of 4.9 and 4.8 kDa. A specific non-sense mutation was identified for the nucleotide at position 88 of the putative 4.9 kDa protein gene of RBCoV isolates resulting in 29 rather that 43 aa residues. The ORF5, which encodes a 12.7 ns protein and the 9.5 kDa E protein, was highly conserved amongst the BCoV field isolates.

Characterization of bovine coronavirus isolates/from eight different states in the USA

Bovine coronavirus isolates from eight different states of the USA were compared for their antigenic properties and susceptibility to hygromycin B. Antigenic differences were observed among the isolates in a one-way hemagglutination-inhibition (HI) test using a polyclonal antiserum against the Mebus bovine coronavirus isolate. Differences were observed on isoelectric focusing among viral proteins with isoelectric points between 4.45-4.65. Most of the BCV isolates were susceptible to hygromycin B (0.5 mM) whereas a few hygromycin B resistant isolates were also found.

Characterization of monoclonal antibodies to the hemagglutinin-esterase glycoprotein of a bovine coronavirus associated with winter dysentery and cross-reactivity to field isolates

Seven hybridoma cell lines producing monoclonal antibodies (MAbs) to the hemagglutinin-esterase (HE) glycoprotein of bovine coronavirus (BCV) were obtained from BALB/c mice that were immunized with an enriched peplomeric fraction of the winter dysentery (WD)-associated strain BCQ.2590. The specificities of these MAbs to either the dimeric (140-kDa) or the monomeric (65-kDa) form of the HE glycoprotein were determined by Western immunoblotting experiments with purified virus and immunoprecipitation tests with [35S]methionine-labelled infected cell extracts. Four of these anti-HE MAbs inhibited the hemagglutinating activity of the virus and three weakly neutralized its infectivity in vitro. In addition, competition binding assays allowed for the definition of two independent antigenic domains (domains A and D) and two overlapping antigenic domains (domains B and C) for the HE glycoprotein of the WD-associated strain; epitopes located within antigenic domain A were not associated with hemagglutination inhibition (HAI) and virus neutralization activities. In HAI tests, the four anti-HA MAbs defined two distinct antigenic subgroups among 24 BCV field isolates that have been associated with either typical outbreaks of WD or neonatal calf diarrhea (NCD) in Quebec dairy herds from 1986 to 1996. The Quebec WD-associated strains of BCV, as well as some of the NCD-associated strains isolated since 1991, fell within a subgroup distinct from that of the prototype Mebus strain.

Antigenic and biological comparisons of bovine coronaviruses derived from neonatal calf diarrhea and winter dysentery of adult cattle

The antigenic and biological properties of 6 strains of bovine coronavirus (BCV) derived from neonatal calf diarrhea (CD) and 8 strains of BCV from winter dysentery (WD) of adult cattle, propagated in HRT-18 cells, were compared to determine if CD and WD strains belong to distinct serotypes or subtypes of BCV. All strains hemagglutinated both mouse and chicken erythrocytes at 4 degrees C, but the ratios of hemagglutination titers with mouse erythrocytes compared to chicken erythrocytes showed diversity for both CD and WD strains. Some CD and WD strains did not hemagglutinate chicken erythrocytes at 37 degrees C and showed receptor-destroying enzyme activity against chicken erythrocytes. Hyperimmune antisera were produced in guinea pigs against 3 and 7 strains of BCV from CD and WD, respectively. No significant differences in antibody titers against these strains were observed by indirect immunofluorescence tests. However, in virus neutralization tests, antisera to 1 CD and 2 WD strains had 16-fold or lower antibody titers against 3 WD and 1 CD strains than against the homologous strains, and this variation reflected low antigenic relatedness values (R = 13-25%), suggesting the presence of different subtypes among BCV. In hemagglutination inhibition tests, some one-way antigenic variations among strains were also observed. These results suggest that some antigenic and biological diversity exists among BCV strains, but these variations were unrelated to the clinical source of the strains; i.e. CD or WD.

Biological and molecular differentiation between coronaviruses associated with neonatal calf diarrhoea and winter dysentery in adult cattle

Cytopathic coronaviruses were isolated in HRT-18 cells from bloody faecal samples collected from cows in Québec dairy herds with classical winter dysentery (WD). The formation of polykaryons in the infected cell cultures was found to be dependent on the presence of trypsin in the medium. Virus identification was confirmed by indirect immunofluorescence and indirect protein A-gold immunoelectron microscopy using rabbit hyperimmune serum, as well as monoclonal antibodies directed against the spike (S) and hemagglutinin-esterase (HE) glycoproteins of the prototype Mebus strain of bovine coronavirus (BCV-Meb). Four WD isolates differed from BCV-Meb by their ability to agglutinate rat erythrocytes at 4 and 37 degrees C, their higher receptor destroying enzyme activity, but lower acetylesterase activity. The WD isolates were serologically indistinguishable from the reference BCV-Meb strain by virus neutralization and Western immunoblotting, but could be differentiated by hemagglutination-inhibition. Sequence analysis of the PCR-amplified HE gene of a plaque-purified WD isolate (BCQ-2590) revealed sufficient number of nucleotide and amino acid substitutions which may explain this antigenic variability.

Comparative sequence analysis of a polymorphic region of the spike glycoprotein S1 subunit of enteric bovine coronavirus isolates

Complementary oligonucleotide primers which flank a 1146-nucleotide gene fragment (S1B: nt 1185 to 2333) encompassing a polymorphic region (nt 1368 to 1776) of the S1 subunit of bovine coronavirus spike glycoprotein were used for enzymatic amplification by PCR. We chose four clinical isolates, recovered from cases of epidemic diarrhea in neonatal calves in Québec dairy herds between 1987-1990, to specifically amplify and analyze their sequences in the selected genomic area. Nucleotide sequence analysis of the four clinical isolates indicated that their S1B gene fragments were highly conserved. We also compared the S1B gene sequences of the Québec BCV isolates to the published corresponding sequences from BCV-L9 [37], BCV-MEB [1], and BCV-F15 [3] reference strains. A high degree of similarity was demonstrated for all viruses, no deletions or insertions were observed, and the only variations that were identified consisted of nucleotide substitutions. The differing nucleotides and amino acids (aa) were not distributed randomly over the entire sequence but rather were clustered in the polymorphic region. Of these, four sporadic aa changes were located in antigenic domain II (aa residues 517 to 720) of S1. This correlates with varied antigenicity observed among the BCV Québec isolates when reacting with MAbs directed against the S glycoprotein of the Mebus strain. The other mutations seem to be fixed in all Québec isolates.