Coronaviruses
Coronaviruses are a large family of viruses that can infect a range of hosts. They are known to cause diseases including the common cold, Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) in humans.
In January 2020, China saw an outbreak of a new coronavirus strain now named SARS-CoV-2. Although the animal reservoir for the SARS and MERS viruses are known, this has yet to have been confirmed for SARS-CoV-2. All three strains are transmissible between humans.
To allow the widest possible distribution of relevant research, the Microbiology Society has brought together articles from across our portfolio and made this content freely available.
Image credit: "MERS-CoV" by NIAID is licensed under CC BY 2.0, this image has been modified.
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261 - 280 of 298 results
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Monoclonal Antibodies to the S1 Spike and Membrane Proteins of Avian Infectious Bronchitis Coronavirus Strain Massachusetts M41
More LessSUMMARYWe have established four murine hybridoma cell lines which secrete specific antibody to avian infectious bronchitis virus (IBV) strain Massachusetts M41. Two monoclonal antibodies reacted with the spike protein and two reacted with the membrane protein. The specificity of the monoclonal antibodies for the external structural proteins was detected by immunoprecipitations using radiolabelled virus. The reactions of the monoclonal antibodies showed that one (S1) of the two glycopolypeptides associated with the spike protein has a strain-specific region involved in neutralization and haemagglutination, and the membrane protein has antigenic determinants which are present on the three strains of IBV tested (M41, Beaudette and D41).
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Hybridoma Antibodies to the Murine Coronavirus JHM: Characterization of Epitopes on the Peplomer Protein (E2)
More LessSUMMARYA panel of hybridoma antibodies that react with the surface peplomer glycoprotein (E2) of the murine coronavirus JHM were produced to characterize major antigenic domains associated with functions related to virulence. Three groups of hybridoma antibodies were differentiated by immunoprecipitation of lysates from JHM-infected cells. One group precipitated the virion structural proteins gp170 and gp98 together with the intracellular form of E2, gp150. A second group reacted with gp98 and gp150, and a third group precipitated gp150 only. Competition assays with biotinylated hybridoma antibodies allowed the definition of at least six different epitope groups. Only those antibodies which immunoprecipitated both gp170 and gp98 neutralized infectivity, inhibited cell fusion and protected infected rats against acute disease. Another class of antibodies binding to gp170 and gp98 also neutralized JHM virus, but did not inhibit fusion and did not protect against disease. Antibodies that immunoprecipitated gp150 and gp98 revealed only weak neutralization and did not inhibit cell fusion or protect animals. Four epitopes were defined by antibodies that immunoprecipitated gp150, but revealed no biological activity. These data indicate that the site responsible for cell fusion is associated with an epitope group carried by gp170 and gp98. Neutralizing antibodies bind to this and another epitope. Furthermore, protection of JHM-infected rats against acute disease requires both inhibition of cell fusion and neutralization of virus.
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Adaptation of Coronavirus JHM to Persistent Infection of Murine Sac(-) Cells
More LessSUMMARYCoronaviruses can establish persistent infections in the central nervous system of rodents, and these are associated with demyelinating encephalomyelitis. The effects of persistence on the virus are difficult to study in vivo but may have a crucial influence on the course of infection. We therefore produced a persistent infection in vitro using the neurotropic coronavirus JHM, in order to investigate the events underlying the establishment of such an infection and the adaptation of the virus to persistence. The persistent infection was maintained for over 115 passages and continued to release high levels of infectious virus. During the 18 months of culture the number of cells expressing virus antigen detected by indirect immune fluorescence decreased to 40%. Analysis showed that the carried virus contained a significant proportion of heterogeneous temperature-sensitive mutants. All virus clones isolated possessed the capacity to induce a more productive growth cycle, a less pronounced cytopathic effect and showed a much reduced neurovirulence when inoculated into newborn and weanling rats. Evidence for structural changes involving the surface peplomer protein (E2) was obtained using hybridoma antibodies, which neutralized the parental JHM virus but not the JHM-Pi virus. Defective interfering particles and interferon activities have been excluded as possible agents instrumental in the establishment and maintenance of the chronic infection, and we suggest that the emergence of virus variants of lowered virulence is central to these processes.
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Replication of Transmissible Gastroenteritis Coronavirus (TGEV) in Swine Alveolar Macrophages
H. Laude, B. Charley and J. GelfiSUMMARYSeveral strains of the enteropathogenic coronavirus transmissible gastroenteritis virus (TGEV) have been shown to replicate in alveolar macrophages maintained in vitro. A distinct cytopathic effect was observed at a multiplicity of infection ≥0.1. Infected cells released infectious virus. The extent of both virus production and cell destruction was highly dependent upon the virus input. At low input, cell viability was affected only slightly, and a delayed and persistent virus production could be observed. TGEV infection of macrophages also led to a marked synthesis of type I interferon. Thus, the possibility that alveolar macrophages act as an extra-intestinal target for TGEV must be considered.
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Coronavirus IBV: Structural Characterization of the Spike Protein
More LessSUMMARYThe spike protein (S; surface projection) of avian infectious bronchitis virus (IBV) strain M41 comprises two glycopolypeptides, S1 (mol. wt. 90 × 103) and S2 (mol. wt. 84 × 103), in equimolar proportions. The apparent mol. wt. of S was calculated as 354 (±17) × 103 following co-sedimentation with catalase in sucrose gradients. Incubation of radiolabelled IBV with urea resulted in the removal of most S1, but none of S2, from the virus particle. A similar result was obtained using low concentrations of SDS, although some nucleocapsid, but not matrix, protein was also released. 2% SDS alone was as effective as 2% SDS plus 2% 2-mercaptoethanol for the separation of S1 and S2 prior to SDS–polyacrylamide gel electrophoresis. Dithiothreitol did not remove S from virions but did decrease the buoyant density of the virus from 1.18 g/ml to 1.16 g/ml, and changed the configuration of S. It is concluded that IBV S protein is an oligomer comprising two copies of each of S1 and S2, although the possibility that there are three copies of each glycopolypeptide cannot be discounted. S is attached to the membrane by S2, while S1 has little or no contact with the membrane and may form the major part of the bulbous end of S. Interpeptide disulphide bonds do not occur in S, and the association of S1 and S2 is weak.
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Expression of Feline Infectious Peritonitis Coronavirus Antigens on the Surface of Feline Macrophage-like Cells
More LessSUMMARYGrowth of feline infectious peritonitis virus in a continuous feline cell line is described and evidence for the macrophage-like character of these cells is presented. Under one-step growth conditions, cytopathic changes and giant cell formation were observed 12 h after infection; more than 99% of the virus remained cell-associated 15 h after infection. Viral proteins at the surface of infected cells were detected by immunofluorescence. The exposed antigens were localized on four proteins with molecular weights of 225.5K, 175K, 138K and 25K using radioiodination followed by immunoprecipitation. Another viral polypeptide of 44K (the nucleocapsid protein) was only labelled when the cell membranes had been disrupted. Expression of viral antigens on the cell surface may be a significant factor in the immune pathogenesis of feline infectious peritonitis.
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Coronavirus IBV: Further Evidence that the Surface Projections are Associated with Two Glycopolypeptides
More LessSUMMARYThe surface projections (peplomers) of avian infectious bronchitis virus (IBV) strain M41 have been separated from the nucleocapsid (N) and matrix (M) proteins by sedimentation in a sucrose gradient after virus disruption by the non-ionic detergent Nonidet P40. The peplomers comprised two glycopolypeptides of mol. wt. 90 × 103 (90K; S1) and 84K (S2), shown by analysis of differentially radiolabelled virus to be present in equimolar proportions. Polypeptides of 75K and 110K, which were detected by Coomassie Brilliant Blue staining in similar amounts to S1 and S2 in some unlabelled virus preparations, were absent from peplomer preparations and are probably host cell polypeptides. The S1:S2:N:M polypeptide molar ratio for IBV-M41 was approximately 1:1:6:15.
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Coronavirus IBV Glycopolypeptides: Size of Their Polypeptide Moieties and Nature of Their Oligosaccharides
More LessSUMMARYAnalysis of differentially radiolabelled avian infectious bronchitis virus (IBV) indicated that the matrix (M) polypeptides of mol. wt. 23 × 103 (23K), 26K, 28K, 30K and 34K (M23 to M34) which have been shown to give the same peptide maps, differed in their degree of glycosylation; M23 was not glycosylated while glycosylation increased with increasing mol. wt. from M26 to M34. Both glucosamine and mannose were components of M26 to M34 but [3H]fucose appeared to be associated mainly with M34. Endo-β-N-acetylglucosaminidase H removed oligosaccharides from M28 and M30 but not M26 and M34, to give a polypeptide of 23K. The surface projection glycopolypeptides S1 (90K) and S2 (84K) incorporated 3H-labelled glucosamine and mannose but not fucose and had oligosaccharides removed by endoglycosidase H. The mol. wt. of the resultant polypeptides varied among experiments; the lowest mol. wt. observed were 64K and 61K. These results indicate (i) that the polypeptide moieties of the S polypeptides are approximately 64K and 61K, and 23K for the M polypeptide, (ii) that the oligosaccharides of the S and M polypeptides are of the high-mannose type and are linked to the polypeptides by N-glycosidic linkages, and (iii) that the M glycoprotein of IBV differs from that of murine coronaviruses and bovine coronavirus L9 which have O-linked oligosaccharides.
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The Biology of Coronaviruses
More LessIntroductionThe Coronaviridae is a monogeneric family comprising 11 viruses which infect vertebrates. Members of the group are responsible for diseases of clinical and economic importance, in particular respiratory and gastrointestinal disorders (Table 1). The group was originally recognized on the basis of a characteristic virion morphology (Tyrrell et al., 1968), but can now be defined by biological and molecular criteria. Various aspects of coronavirus biology have been dealt with in recent reviews (Robb & Bond, 1979; Siddell et al., 1982; Wege et al., 1982).
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Characterization of Murine Coronavirus RNA by Hybridization with Virus-specific cDNA Probes
More LessSUMMARYGenome RNA of mouse hepatitis virus (MHV) strain A59 has been used as a template to synthesize two virus-specific probes: cDNArep, representing the majority of sequences of the genome RNA and cDNA3′, representing the 3′ end of the genome RNA. Molecular hybridization with these cDNAs was used to characterize both genome RNA and intracellular virus-specific RNAs. Hybridization of genome RNAs of MHV strains A59, JHM, and MHV-3 with A59 cDNArep showed that, although these three strains exhibit different pathogenicities, they contain closely related nucleotide sequences. Hybridization of intracellular RNA from MHV-infected cells with virus-specific cDNA shows that (i) the majority of virus-specific RNA is polyadenylated, (ii) virus-specific intracellular RNA contains six subgenomic species of the same polarity as genome RNA and (iii) all subgenomic RNAs contain the same 3′ sequences as the genome RNA and thus form a nested set of RNAs.
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Coronavirus JHM: Coding Assignments of Subgenomic mRNAs
More LessSUMMARYProtein synthesis in the murine hepatitis virus JHM-infected cells was temporarily inhibited by hypertonic shock. When the cells were returned to isotonic medium the synthesis of six virus-specific polypeptides, 150K, 65K, 60K, 30K, 23K and 14K was reinitiated simultaneously. Polyadenylated RNA isolated from the cytoplasm or polysomes of infected cells was translated in vitro and the products included polypeptides with molecular weights (mol. wt.) of 120000, 60000, 30000, 23000 and 14000. Immunoprecipitation and fingerprinting of [35S]methionine-containing tryptic peptides showed that the 60000 and 23000 mol. wt. products were identical to the 60K and 23K polypeptides found in infected cells; the 120000 mol. wt. product showed identity with the 150K intracellular polypeptide and a virus-specific 120K polypeptide synthesized in tunicamycin-treated cells. Two-dimensional polyacrylamide gel electrophoresis strongly suggested that the 30000 and 14000 mol. wt. products are equivalent to virus-specific 30K and 14K intracellular polypeptides. [3H]Uridine-labelled polyadenylated virus RNA was isolated from infected cells and sedimented in sucrose gradients containing formamide. The distribution in the gradient of each of the previously identified virus RNAs was determined by gel electrophoresis and gradient fractions enriched for each RNA were translated in vitro. The 120000, 60000, 30000, 23000 and 14000 mol. wt. polypeptides were found to be encoded by mRNAs 3, 7, 2, 6, and 4 or 5 respectively. These results demonstrate that the virus-specific polypeptides in JHM-infected cells are encoded in separate subgenomic mRNAs and are translated independently. The assignment of coding functions and the known sequence relationships of JHM RNAs permitted a gene order to be deduced.
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Bovine Enteric Coronavirus Structure as Studied by a Freeze-drying Technique
More LessSUMMARYA strain of bovine coronavirus (FI5) was studied by electron microscopy using a freeze-drying technique. Purified coronavirus preparations show three different categories of image : (i) ‘blackberry-like’ virions, (ii) virions with a smooth depression at their surface, and (iii) apparently broken particles showing very clearly the areas of spike insertion in the virus membrane. Virus projections resemble ‘mushrooms’ with the ‘stalk’ inserted at the virus membrane. A model of the virion structure is proposed.
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Coronavirus JHM: Tryptic Peptide Fingerprinting of Virion Proteins and Intracellular Polypeptides
More LessSUMMARYThe virion proteins and intracellular polypeptides of the murine coronavirus MHV-JHM have been analysed by two-dimensional fingerprinting of their [35S]methionine-containing tryptic peptides. The analysis shows that the virion proteins gp98, gp65, pp60 and p23 are distinct. Virion protein gp25 has the same polypeptide component as p23, and virion protein gp170 has a polypeptide component related to gp98. The six virus polypeptides synthesized in infected cells, 150K, 65K, 60K, 30K, 23K and 14K are also distinct. The 170K and 98K species, which are produced by processing, are related to 150K. The 25K species is a processed form of 23K. The identity of corresponding species in the cell and in the virion has been shown and a model describing the genesis of coronavirus JHM proteins can now be proposed.
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Reactivity of Human Coronavirus OC43 and Neonatal Calf Diarrhoea Coronavirus Membrane-associated Antigens
More LessSUMMARYHuman embryonic lung fibroblast cultures and Vero cell cultures infected with cell culture-adapted strains of human coronavirus (HCV) OC43 or neonatal calf diarrhoea coronavirus (NCDCV) were shown to possess highly cross-reactive membrane-associated antigens (MAA) by the indirect fluorescent antibody technique (IFAMA). MAA appeared 3 h post-infection, concurrently with the appearance of cytoplasmic antigens. Electron microscopic observations of cell cultures infected with either coronavirus strain and labelled with the immunoperoxidase antibody (IPA) technique for MAA detection showed that MAA consisted mainly of a strongly labelled, discontinuous, brush-like layer of amorphous material, strictly associated with the infected cell membrane. By light microscopy, reactivity of MAA with homologous and heterologous immune serum was similar to that of antigens detected by IPA in ethanol-fixed infected cells. IPA and IFAMA, but not haemagglutination-inhibiting (HI) and neutralizing (Nt) antibody, were strongly decreased by absorption of immune sera with trypsin-treated glutaraldehyde-fixed cell cultures infected with homologous virus. MAA IgG antibodies were detected by IFAMA in both human and animal sera. Sera from infants showing an HI and Nt, but not an IPA, antibody response to HCV OC43 were also free of detectable IFAMA antibody to HCV OC43.
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Replication of Human Respiratory Coronavirus Strain 229E in Human Macrophages
More LessSUMMARYEvidence for the replication of human coronavirus strain 229E (HCV 229E) in macrophages is presented. Virus antigen was detected in macrophages by an immunofluorescent technique 24 h after infection and virus particles were observed in the cisternae of the endoplasmic reticulum by electron microscopy. Giant cells were observed by light and scanning electron microscopy, and large multinucleate cells were seen by thin-section electron microscopy, suggesting that HCV 229E can induce syncytial formation in cultured human macrophages. Furthermore, the production of infectious virus by macrophages was demonstrated by an infectious centre assay.
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The Ultrastructure of Feline Infectious Peritonitis Virus in Feline Embryonic Lung Cells
More LessSUMMARYThe ultrastructure of feline infectious peritonitis virus in cultured feline embryonic lung cells is reported. Feline embryonic lung cells were infected with feline infectious peritonitis virus and studied by transmission electron microscopy. The virus was not apparent in the cultured cells until 24 h after infection when it occurred in the endoplasmic reticulum, perinuclear space, Golgi apparatus, free in the cytoplasm, in large vacuoles in the cytoplasm and outside the cell membrane. The virus possessed typical coronavirus morphology and was produced by budding into the endoplasmic reticulum. There was no evidence to indicate that this virus budded through the cell membrane. Multinucleate giant cells were formed by infection of the cultured cells with the virus. The host cells were destroyed by the virus and phagocytosed by apparently healthy cells.
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Serological Relationships of the Subcomponents of Human Coronavirus Strain 229E and Mouse Hepatitis Virus Strain 3
More LessSUMMARYAntibodies were raised in rabbits against the structural components of human coronavirus strain 229E and mouse hepatitis virus strain 3, prepared from disrupted virus particles. Hyperimmune sera to the subcomponents showed cross-reactions by enzyme-linked immunosorbent assay between ribonucleoprotein antigens of these viruses, indicating the presence of a common antigen(s). None of the other virus structural components showed any cross-reactivity.
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Plaque Assay for Titration of Bovine Enteric Coronavirus
More LessSUMMARYThe plaquing ability of two isolates of bovine enteric coronavirus (BECV) was studied in HRT18 (human rectal adenocarcinoma) cell monolayers. Both isolates were able to induce plaque formation within 2 to 3 days; plaques appeared as round opalescent areas which remained colourless after neutral red or crystal violet staining. A good correlation was found between the titres as determined either by counting the plaques that were visible to the naked eye before and after neutral red staining, or by enumerating fluorescence or haemadsorption foci.
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Antigenic and Biological Relationships between Human Coronavirus OC43 and Neonatal Calf Diarrhoea Coronavirus
More LessSUMMARYMonospecific antisera were prepared in mice to human coronavirus OC43 and neonatal calf diarrhoea coronavirus (NCDCV) which had been previously adapted to growth in suckling mouse brain. Brain suspension from infected suckling mice was used as immunogen. The antigenic relationship between OC43 and NCDCV was studied by the indirect immunoperoxidase antibody technique, by the haemagglutination-inhibition (HI) test and a new infectious centre-reduction neutralization test. In mouse immune sera, a two-way cross-reaction between OC43 and NCDCV was detected. However, the antigenic relationship appeared to be closer for internal (as shown by immunoperoxidase staining) as compared to surface antigens (as shown by HI and neutralization). In primary infections of natural hosts there was a high degree of cross-reactivity between the two coronavirus strains for both surface and internal antigens, and homologous and heterologous titres were consistently within an eightfold dilution difference by all tests. Most human adults and calves had antibody to both OC43 and NCDCV and geometric mean titres of homologous antibody were higher than titres of heterologous antibody. Although OC43 and NCDCV share antigenic determinants, they possessed several different biological properties, including plaque morphology by the infectious centre assay, agglutination of 1-day-old chick erythrocytes and resistance of haemagglutinin to physical and chemical treatments.
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Coronavirus JHM: Characterization of Intracellular Viral RNA
More LessSUMMARYAfter infection of Sac(-) cells with the murine coronavirus JHM the synthesis of seven major and two minor RNA species was induced. These RNAs were polyadenylated and single-stranded. Their mol. wt. were estimated by electrophoresis in agarose gels containing methylmercury hydroxide. The values for the major species were 6.67 × 106 for RNA of genome size (RNA 1), 3.42 × 106 for RNA 2, 2.76 × 106 for RNA 3, 1.35 × 106 for RNA 4, 1.19 × 106 for RNA 5, 0.93 × 106 for RNA 6 and 0.62 × 106 for RNA 7. The minor species have a size of 4.7 × 106 (RNA a) and 1.5 × 106 (RNA b). The same number of species were found by electrophoresis after denaturation with glyoxal-dimethyl sulphoxide. No gross difference in number of RNAs and the amount of each species was found between total cytoplasmic RNA, polyadenylated cytoplasmic RNA and RNA extracted from pelleted polysomes.
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