Primary structure of the membrane and nucleocapsid protein genes of feline infectious peritonitis virus and immunogenicity of recombinant vaccinia viruses in kittens

An adenovirus-vectored vaccine based on the N protein of feline coronavirus elicit robust protective immune responses

Feline coronavirus (FCoV) is an unsegmented, single-stranded RNA virus belonging to the Alphacoronavirus genus. It can cause fatal feline infectious peritonitis (FIP) in cats of any ages. Currently, there are no effective prevention and control measures to against FCoV. In this study, we developed a recombinant adenovirus vaccine, AD5-N, based on the nucleocapsid(N) protein of FCoV. The immunogenicity of AD5-N was evaluated through intramuscular immunization in 6-week-old Balb/c mice and 9-12 months old cats. Compared to the control group, AD5-N specifically induced a significant increase in IgG and SIgA levels in the vaccinated mice. Furthermore, AD5-N not only effectively promoted strong cellular immune responses in cats but also induced high levels of specific SIgA, effectively helping cats resist FCoV infection. Our findings suggest that adenovirus vector vaccines based on the N gene have the potential to become candidate vaccines for the prevention and control of FCoV infection.

Porcine Epidemic Diarrhea Virus: An Updated Overview of Virus Epidemiology, Virulence Variation Patterns and Virus-Host Interactions

The porcine epidemic diarrhea virus (PEDV) is a member of the coronavirus family, causing deadly watery diarrhea in newborn piglets. The global pandemic of PEDV, with significant morbidity and mortality, poses a huge threat to the swine industry. The currently developed vaccines and drugs are only effective against the classic GI strains that were prevalent before 2010, while there is no effective control against the GII variant strains that are currently a global pandemic. In this review, we summarize the latest progress in the biology of PEDV, including its transmission and origin, structure and function, evolution, and virus-host interaction, in an attempt to find the potential virulence factors influencing PEDV pathogenesis. We conclude with the mechanism by which PEDV components antagonize the immune responses of the virus, and the role of host factors in virus infection. Essentially, this review serves as a valuable reference for the development of attenuated virus vaccines and the potential of host factors as antiviral targets for the prevention and control of PEDV infection.

Predicted 3D model of the M protein of Porcine Epidemic Diarrhea Virus and analysis of its immunogenic potential

The membrane protein M of the Porcine Epidemic Diarrhea Virus (PEDV) is the most abundant component of the viral envelope. The M protein plays a central role in the morphogenesis and assembly of the virus through protein interactions of the M-M, M-Spike (S) and M-nucleocapsid (N) type. The M protein is known to induce protective antibodies in pigs and to participate in the antagonistic response of the cellular antiviral system coordinated by the type I and type III interferon pathways. The 3D structure of the PEDV M protein is still unknown. The present work exposes a predicted 3D model of the M protein generated using the Robetta protocol. The M protein model is organized into a transmembrane and a globular region. The obtained 3D model of the PEDV M protein was compared with 3D models of the SARS-CoV-2 M protein created using neural networks and with initial machine learning-based models created using trRosetta. The 3D model of the present study predicted four linear B-cell epitopes (RSVNASSGTG and KHGDYSAVSNPSALT peptides are noteworthy), six discontinuous B-cell epitopes, forty weak binding and fourteen strong binding T-cell epitopes in the CV777 M protein. A high degree of conservation of the epitopes predicted in the PEDV M protein was observed among different PEDV strains isolated in different countries. The data suggest that the M protein could be a potential candidate for the development of new treatments or strategies that activate protective cellular mechanisms against viral diseases.

A Comprehensive View on the Host Factors and Viral Proteins Associated With Porcine Epidemic Diarrhea Virus Infection

Porcine epidemic diarrhea virus (PEDV), a coronavirus pathogen of the pig intestinal tract, can cause fatal watery diarrhea in piglets, thereby causing huge economic losses to swine industries around the world. The pathogenesis of PEDV has intensively been studied; however, the viral proteins of PEDV and the host factors in target cells, as well as their interactions, which are the foundation of the molecular mechanisms of viral infection, remain to be summarized and updated. PEDV has multiple important structural and functional proteins, which play various roles in the process of virus infection. Among them, the S and N proteins play vital roles in biological processes related to PEDV survival via interacting with the host cell proteins. Meanwhile, a number of host factors including receptors are required for the infection of PEDV via interacting with the viral proteins, thereby affecting the reproduction of PEDV and contributing to its life cycle. In this review, we provide an updated understanding of viral proteins and host factors, as well as their interactions in terms of PEDV infection. Additionally, the effects of cellular factors, events, and signaling pathways on PEDV infection are also discussed. Thus, these comprehensive and profound insights should facilitate for the further investigations, control, and prevention of PEDV infection.

Evaluation of the immune response in conventionally weaned pigs infected with porcine deltacoronavirus

Although porcine deltacoronavirus (PDCoV) is a significant pandemic threat in the swine population and has caused significant economic losses, information regarding the immune response in conventionally weaned pigs infected with PDCoV is scarce. Hence, the immune response in conventionally weaned pigs infected with PDCoV was assessed after challenge and rechallenge. After the first challenge, obvious diarrhea and viral shedding developed successively in all pigs in the four inoculation dose groups from 3 to 14 days postinfection (dpi), and all pigs recovered (no clinical symptoms or viral shedding) by 21 dpi. All pigs in the four groups exhibited significantly increased PDCoV-specific IgG, IgA and virus-neutralizing (VN) antibody (Ab) titers and IFN-γ levels in the serum after the first challenge. All pigs were completely protected against rechallenge at 21 dpi. The serum levels of PDCoV-specific IgG, IgA, and VN Abs increased further after rechallenge. Notably, the IFN-γ level declined continuously after 7 dpi. In addition, the levels of PDCoV-specific IgG, IgA and VN Abs in saliva increased significantly after rechallenge and correlated well with the serum Ab titers. Furthermore, the appearance of clinical symptoms of PDCoV infection in conventionally weaned pigs was delayed with reduced inoculation doses. In summary, the data presented here offer important reference information for future PDCoV animal infection and vaccine-induced immunoprotection experiments.

Development and application of a recombinant M protein-based indirect ELISA for the detection of porcine deltacoronavirus IgG antibodies

Porcine deltacoronavirus (PDCoV) is a recently identified coronavirus in the genus Deltacoronavirus that can cause enteric disease including diarrhea, vomiting, dehydration and mortality in neonatal piglets. Serological assays to detect anti-PDCoV antibodies are presently limited to certain laboratories and geographic regions. In this study, a recombinant M protein-based indirect enzyme-linked immunosorbent assay (PDCoV-rM ELISA) was developed and utilized to determine the prevalence of anti-PDCoV IgG in Hebei province. The PDCoV-rM ELISA showed no cross-reaction with antisera against transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), porcine rotavirus (PRV), porcine circovirus 2 (PCV2), classical swine fever virus (CSFV) or porcine reproductive and respiratory syndrome virus (PRRSV). The diagnostic sensitivity was 90.6% and the diagnostic specificity was 93.3%. A total of 871 serum samples collected in Hebei from January 2015 to October 2016 were checked for presence of antibodies against PDCoV using the novel PDCoV-rM ELISA. Anti-PDCoV IgG antibodies were detected in 11% (96/871) of the samples and in 25% (10/40) of the investigated farms. The data suggest that PDCoV has a low seroprevalence in pig population in Hebei province, China.

Development of an enzyme-linked immunosorbent assay for the monitoring and surveillance of antibodies to porcine epidemic diarrhea virus based on a recombinant membrane protein

•

Expressed membrane protein of porcine epidemic diarrhea virus in Escherichia coli.

•

An indirect ELISA was developed using purified recombinant M protein as detection antigen.

•

Assessing fit for immunologic surveillance and sero-diagnosis of PEDV.

•

The developed iELISA is specific, sensitive and does not require PEDV cultivation.

•

This iELISA could be used for large-scale serological testing.

The recent dramatic increase in reported cases of porcine epidemic diarrhea (PED) in pig farms is a potential threat to the global swine industry. Therefore, the accurate diagnosis, serological monitoring, and surveillance of specific antibodies in pigs resulting from porcine epidemic diarrhea virus (PEDV) infection or vaccination would be essential in helping to control the spread of PED. We developed and validated an indirect enzyme-linked immunosorbent assay (ELISA) based on the recombinant membrane (M) protein of PEDV. To detect PEDV antibodies in eight herds, 382 serum samples were collected from sows that had been immunized with a PED vaccine, and screened using the developed ELISA in parallel with a serum neutralization (SN) assay. Of the tested samples, 276 were positive for the presence of PEDV antibodies according to both assays, while 98 were negative. An excellent agreement between the ELISA and the SN assay was observed (kappa = 0.947; 95% confidence interval = 0.910–0.984; McNemar's test, P = 0.727). No cross-reaction was detected for the developed ELISA with other coronaviruses or other common pig pathogens. The developed ELISA could be used for serological evaluation and indirect diagnosis of PED infection.

M gene analysis of canine coronavirus strains detected in Korea

The purpose of this study was to investigate the genetic features of canine coronavirus (CCV) strains detected in Korea. M gene sequences obtained for isolates from 22 dogs with enteritis over a 5-year period were evaluated. Sequence comparison revealed that the 22 Korean CCV strains had an 87.2 to 100% nucleotide homology. Comparing to the typical reference CCV strains (type II), the nucleotide sequence of Korean strains had homology ranged from 86.3% to 98.3% (89.1% to 99.2% for the amino acid sequence) and 87.7% to 97.8% (92.4% to 100% for the amino acid sequence) when compared to FCoV-like CCV strains (type I). Three amino acid variations in the M gene were characteristic for the Korean CCV strains. Phylogenetic analysis demonstrated that the 22 Korean CCV strains belonged to four typical CCV clusters (i.e., a unique Korean CCV cluster, a type II and transmissible gastroenteritis virus cluster, an intermediate cluster between type I and II, and a type I cluster). This study was the first to identify genetic differences of the M gene from Korean CCV strains and provided a platform for molecular identification of different Korean CCV strains.

Identification and genotyping of feline infectious peritonitis-associated single nucleotide polymorphisms in the feline interferon-γ gene

Feline infectious peritonitis (FIP) is an immune-mediated, highly lethal disease caused by feline coronavirus (FCoV) infection. Currently, no protective vaccine or effective treatment for the disease is available. Studies have found that some cats survive the challenge of virulent FCoV isolates. Since cellular immunity is thought to be critical in preventing FIP and because diseased cats often show a significant decrease in interferon-γ (IFN-γ) production, we investigated whether single nucleotide polymorphisms (SNP) in the feline IFN-γ gene (fIFNG) are associated with the outcome of infection. A total of 82 asymptomatic and 63 FIP cats were analyzed, and 16 SNP were identified in intron 1 of fIFNG. Among these SNP, the fFING + 428 T allele was shown to be a FIP-resistant allele (p = 0.03), and the heterozygous genotypes 01C/T and +408C/T were found to be FIP-susceptible factors (p = 0.004). Furthermore, an fIFNG + 428 resistant allele also showed a clear correlation with the plasma level of IFN-γ in FIP cats. For the identification of these three FIP-related SNP, genotyping methods were established using amplification refractory mutation system PCR (ARMS-PCR) and restriction fragment length polymorphisms (RFLP), and the different genotypes could easily be identified without sequencing. The identification of additional FIP-related SNP will allow the selection of resistant cats and decrease the morbidity of the cat population to FIP.

Phylogeny and expression of the nucleocapsid gene of porcine epidemic diarrhoea virus

Porcine epidemic diarrhoea virus (PEDV) is one of the important pathogens that may cause severe diarrhoea in piglets. In this study, the nucleocapsid (N) gene of a Chinese PEDV isolate designated HLJBY was cloned. The phylogeny of PEDV strains was investigated by constructing a phylogenetic tree based on the N protein sequences. The results indicate that there are two major groups of Chinese PEDVs, a Japanese PEDV group and a Korean PEDV group. High-level expression of the N protein was achieved in Escherichia coli. The immunoreactivity between PEDV particles or the bacterially expressed N protein and rabbit anti-PEDV serum was confirmed by immunofluorescence assays and Western blot. Both PEDV N protein and the polyclonal antibody generated in this study are valuable diagnostic reagents for PEDV surveillance.

Identification of a conserved linear B-cell epitope in the M protein of porcine epidemic diarrhea virus

Background

The major structural protein of coronaviruses, the membrane (M) protein, can elicit the formation of protective antibodies, but little information is available about the M protein of porcine epidemic diarrhea virus (PEDV). Identification of epitopes on the PEDV M protein will be helpful in the elucidation of the antigenic properties of this protein.

Results

One hybridoma cell line secreting anti-M protein monoclonal antibody (McAb) was generated and designated 4D4. To map the epitopes on the PEDV M protein, a total of 17 partially overlapping fragments covering the C-terminus of M protein were expressed as fusion proteins with a 6×His tag or a GST tag. A linear motif, ¹⁹³TGWAFYVR²⁰⁰, was identified by enzyme-linked immunosorbent assay (ELISA) and western blot (WB) analysis using McAb 4D4. The motif ¹⁹⁵WAFYVR²⁰⁰ was the minimal requirement for reactivity, as demonstrated by removing amino acids individually from both ends of the motif ¹⁹³TGWAFYVR²⁰⁰. The result of WB analysis showed that the 4D4-defined epitope could be recognized by PEDV-positive serum, but not transmissible gastroenteritis virus (TGEV)-positive serum. Furthermore, this epitope was highly conserved among different PEDV strains, as shown by alignment and comparison of sequences.

Conclusion

A McAb, 4D4, directed against the M protein of PEDV, was obtained, and the 4D4-defined minimal epitope sequence was ¹⁹⁵WAFYVR²⁰⁰. The McAb could serve as a candidate for development of a McAb-based antigen capture ELISA for detection of PEDV. The epitope identified provides a basis for the development of epitope-based differential diagnostic techniques and may be useful in the design of epitope-based vaccines.

Molecular targets for diagnostics and therapeutics of severe acute respiratory syndrome (SARS-CoV)

PURPOSE

The large number of deaths in a short period of time due to the spread of severe acute respiratory syndrome (SARS) infection led to the unparalleled collaborative efforts world wide to determine and characterize the new coronavirus (SARS-CoV). The full genome sequence was determined within weeks of the first outbreak by the Canadian group with international collaboration. As per the World Health Organization (WHO), the continual lack of a rapid laboratory test to aid the early diagnosis of suspected cases of SARS makes this area a priority for future research. To prevent deaths in the future, early diagnosis and therapy of this infectious disease is of paramount importance.

METHODS

This review describes the specific molecular targets for diagnostics and therapeutics of viral infection.

RESULTS

The three major diagnostic methods available for SARS includes viral RNA detection by reverse transcription polymerase chain reaction (RT-PCR), virus induced antibodies by immunofluorescence assay (IFA) or by enzyme linked immunosorbant assay (ELISA) of nucleocapsid protein (NP). The spike glycoprotein of SARS-CoV is the major inducer of neutralizing antibodies. The receptor binding domain (RBD) in the S1 region of the spike glycoprotein contains multiple conformational epitopes that induces highly potent neutralizing antibodies. The genetically engineered attenuated form of the virus or viral vector vaccine encoding for the SARS-CoV spike glycoprotein has been shown to elicit protective immunity in vaccinated animals.

CONCLUSION

NP is the preferred target for routine detection of SARS-CoV infection by ELISA which is an economical method compared to other methods. The RBD of the spike glycoprotein is both a functional domain for cell receptor binding and also a major neutralizing determinant of SARS-CoV. The progress in evaluating a therapeutic or vaccine would depend on the avail ability of clinically relevant animal model.

The carbohydrate-binding plant lectins and the non-peptidic antibiotic pradimicin A target the glycans of the coronavirus envelope glycoproteins

Objectives

Many enveloped viruses carry carbohydrate-containing proteins on their surface. These glycoproteins are key to the infection process as they are mediators of the receptor binding and membrane fusion of the virion with the host cell. Therefore, they are attractive therapeutic targets for the development of novel antiviral therapies. Recently, carbohydrate-binding agents (CBA) were shown to possess antiviral activity towards coronaviruses. The current study further elucidates the inhibitory mode of action of CBA.

Methods

Different strains of two coronaviruses, mouse hepatitis virus and feline infectious peritonitis virus, were exposed to CBA: the plant lectins Galanthus nivalis agglutinin, Hippeastrum hybrid agglutinin and Urtica dioica agglutinin (UDA) and the non-peptidic mannose-binding antibiotic pradimicin A.

Results and conclusions

Our results indicate that CBA target the two glycosylated envelope glycoproteins, the spike (S) and membrane (M) protein, of mouse hepatitis virus and feline infectious peritonitis virus. Furthermore, CBA did not inhibit virus–cell attachment, but rather affected virus entry at a post-binding stage. The sensitivity of coronaviruses towards CBA was shown to be dependent on the processing of the N-linked carbohydrates. Inhibition of mannosidases in host cells rendered the progeny viruses more sensitive to the mannose-binding agents and even to the N-acetylglucosamine-binding UDA. In addition, inhibition of coronaviruses was shown to be dependent on the cell-type used to grow the virus stocks. All together, these results show that CBA exhibit promising capabilities to inhibit coronavirus infections.

Modulation of the immune response to the severe acute respiratory syndrome spike glycoprotein by gene-based and inactivated virus immunization

Although the initial isolates of the severe acute respiratory syndrome (SARS) coronavirus (CoV) are sensitive to neutralization by antibodies through their spike (S) glycoprotein, variants of S have since been identified that are resistant to such inhibition. Optimal vaccine strategies would therefore make use of additional determinants of immune recognition, either through cellular or expanded, cross-reactive humoral immunity. Here, the cellular and humoral immune responses elicited by different combinations of gene-based and inactivated viral particles with various adjuvants have been assessed. The T-cell response was altered by different prime-boost immunizations, with the optimal CD8 immunity induced by DNA priming and replication-defective adenoviral vector boosting. The humoral immune response was enhanced most effectively through the use of inactivated virus with adjuvants, either MF59 or alum, and was associated with stimulation of the CD4 but not the CD8 response. The use of inactivated SARS virus with MF59 enhanced the CD4 and antibody response even after gene-based vaccination. Because both cellular and humoral immune responses are generated by gene-based vaccination and inactivated viral boosting, this strategy may prove useful in the generation of SARS-CoV vaccines.

Isolation of feline herpesvirus-1 and feline calicivirus from healthy cats in Swedish breeding catteries

Feline calicivirus (FCV) could be isolated from four cats (2.6%) and feline herpesvirus-1 (FHV) from none of 152 clinically healthy cats from 22 Swedish breeding catteries. These cats had all previously shown signs of respiratory tract disease or conjunctivitis, although several years ago. The results suggest that carriers of FCV and FHV were uncommon in Swedish breeding catteries studied. Prevalence rates in other European countries and North America are usually higher, especially of FCV. The lower prevalence rates in our study might be explained by test group selection, differences in factors such as management, environment, or genetic constitution of the cats, or by sample handling. It was concluded that the presence of an FCV shedder in the cattery does not mean that all cats in the group are infected, but special measures are recommended to avoid infection of susceptible cats.

Péritonite infectieuse féline

La péritonite infectieuse féline (PIF) est une maladie mortelle des félidés due à un coronavirus, qui touche surtout les jeunes animaux entre 6 mois et 2 ans. Cette maladie se traduit cliniquement par des symptômes divers dont le plus caractéristique est l'accumulation de liquide d'épanchement dans la cavité abdominale ou pleurale. Il existe en fait deux biotypes de coronavirus félins, l'un pathogène responsable de la PIF (FIPV) et l'autre non pathogène (FeCV), plus répandu dans la population féline. La forte homologie génétique entre les souches FeCV et FIPV suggère que les virus responsables de la PIF dérivent d'une mutation génétique des coronavirus non pathogènes FeCV. Cette parenté entre les deux biotypes pose un problème dans l'interprétation du diagnostic viral, car aucun test à l'heure actuelle ne permet de les distinguer. Cet article s'intéresse tout particulièrement aux aspects cliniques, diagnostiques, épidémiologiques et prophylactiques de la PIF.

Clinicopathological findings associated with feline infectious peritonitis in Sydney, Australia: 42 cases (1990-2002)

OBJECTIVES

To review the clinicopathological findings in naturally-occurring, histopathologically confirmed cases of feline infectious peritonitis in client-owned cats in Sydney, Australia, with the purpose of identifying factors assisting in the diagnosis of this complex disease syndrome and to characterise the disease as it occurs in this region.

DESIGN

Retrospective clinical study: the clinical records of all cats with histopathologically confirmed feline infectious peritonitis at the University Veterinary Centre Sydney and a private cat hospital in Sydney between 1990 and 2002 were reviewed for signalment, history, physical findings, diagnostic test results and the distribution of histological lesions throughout the body at necropsy.

RESULTS

Forty-two cats met the inclusion criteria. Significant features of this study that unique to the contemporary literature are i) the over-representation of certain breeds (Burmese, Australian Mist, British Shorthaired, and Cornish Rex) and the under-representation of other breeds (Domestic Shorthaired, Persian); ii) the overrepresentation of males; iii) the tendency for effusive disease in Australian Mist cats and non-effusive disease in Burmese; iv) the even age distribution of disease seen in cats older than 2 years-of-age; and v) the presence of fulminant immune-mediated haemolytic anaemia in two cats in this study.

CONCLUSION

The study highlights the diverse range of clinical manifestations and the complexities experienced by clinicians in diagnosing this fatal disease. Some aspects of the epidemiology and clinical manifestations of feline infectious peritonitis appear different to the disease encountered in Europe and North America, most notably the over-representation of specific breeds and the presence of immune-mediated haemolytic anaemia.

Identification of immunodominant epitopes on the membrane protein of the severe acute respiratory syndrome-associated coronavirus

Similar to other coronaviruses, the membrane (M) protein of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) is a major transmembrane glycoprotein with multiple biological functions. To date, limited information is available about its antigenic properties. In this study, we identified two major immunodominant epitopes on the M protein located in the extreme N-terminal region (residues 1 to 31) and the interior C-terminal region (residues 132 to 161), respectively, by Pepscan analyses against convalescent-phase sera from SARS patients and antisera from virus-immunized mice and rabbits. Synthetic peptides M1-31 derived from the N-terminal epitope and M132-161 derived from the C-terminal epitope were highly reactive with all of the convalescent-phase sera from 40 SARS patients but not with 30 control serum samples from healthy blood donors, suggesting their potential application for serologic diagnosis of SARS. We showed that both peptides (M1-31 and M132-161) were able to induce high titers of antibody responses in the immunized rabbits, highlighting their antigenicity and immunogenicity. These findings provide important information for developing SARS diagnostics and vaccines.

Natural history of a recurrent feline coronavirus infection and the role of cellular immunity in survival and disease

We describe the natural history, viral dynamics, and immunobiology of feline infectious peritonitis (FIP), a highly lethal coronavirus infection. A severe recurrent infection developed, typified by viral persistence and acute lymphopenia, with waves of enhanced viral replication coinciding with fever, weight loss, and depletion of CD4+ and CD8+ T cells. Our combined observations suggest a model for FIP pathogenesis in which virus-induced T-cell depletion and the antiviral T-cell response are opposing forces and in which the efficacy of early T-cell responses critically determines the outcome of the infection. Rising amounts of viral RNA in the blood, consistently seen in animals with end-stage FIP, indicate that progression to fatal disease is the direct consequence of a loss of immune control, resulting in unchecked viral replication. The pathogenic phenomena described here likely bear relevance to other severe coronavirus infections, in particular severe acute respiratory syndrome, for which multiphasic disease progression and acute T-cell lymphopenia have also been reported. Experimental FIP presents a relevant, safe, and well-defined model to study coronavirus-mediated immunosuppression and should provide an attractive and convenient system for in vivo testing of anticoronaviral drugs.

Contributions of the structural proteins of severe acute respiratory syndrome coronavirus to protective immunity

We investigated the contributions of the structural proteins of severe acute respiratory syndrome (SARS) coronavirus (CoV) to protective immunity by expressing them individually and in combinations from a recombinant parainfluenza virus (PIV) type 3 vector called BHPIV3. This vector provided direct immunization of the respiratory tract, the major site of SARS transmission, replication, and disease. The BHPIV3/SARS recombinants were evaluated for immunogenicity and protective efficacy in hamsters, which support a high level of pulmonary SARS-CoV replication. A single intranasal administration of BHPIV3 expressing the SARS-CoV spike protein (S) induced a high titer of SARS-CoV-neutralizing serum antibodies, only 2-fold less than that induced by SARS-CoV infection. The expression of S with the two other putative virion envelope proteins, the matrix M and small envelope E proteins, did not augment the neutralizing antibody response. In absence of S, expression of M and E or the nucleocapsid protein N did not induce a detectable serum SARS-CoV-neutralizing antibody response. Immunization with BHPIV3 expressing S provided complete protection against SARS-CoV challenge in the lower respiratory tract and partial protection in the upper respiratory tract. This was augmented slightly by coexpression with M and E. Expression of M, E, or N in the absence of S did not confer detectable protection. These results identify S among the structural proteins as the only significant SARS-CoV neutralization antigen and protective antigen and show that a single mucosal immunization is highly protective in an experimental animal that supports efficient replication of SARS-CoV.

Live, attenuated coronavirus vaccines through the directed deletion of group-specific genes provide protection against feline infectious peritonitis

Feline infectious peritonitis (FIP) is a fatal immunity-mediated disease caused by mutants of a ubiquitous coronavirus. Since previous attempts to protect cats under laboratory and field conditions have been largely unsuccessful, we used our recently developed system of reverse genetics (B. J. Haijema, H. Volders, and P. J. M. Rottier, J. Virol. 77:4528-4538, 2003) for the development of a modified live FIP vaccine. With this objective, we deleted the group-specific gene cluster open reading frame 3abc or 7ab and obtained deletion mutant viruses that not only multiplied well in cell culture but also showed an attenuated phenotype in the cat. At doses at which the wild-type virus would be fatal, the mutants with gene deletions did not cause any clinical symptoms. They still induced an immune response, however, as judged from the high levels of virus-neutralizing antibodies. The FIP virus (FIPV) mutant lacking the 3abc cluster and, to a lesser extent, the mutant missing the 7ab cluster, protected cats against a lethal homologous challenge; no protection was obtained with the mutant devoid of both gene clusters. Our studies show that the deletion of group-specific genes from the coronavirus genome results in live attenuated candidate vaccines against FIPV. More generally, our approach may allow the development of vaccines against infections with other pathogenic coronaviruses, including that causing severe acute respiratory syndrome in humans.

Modified vaccinia virus Ankara as a vaccine against feline coronavirus: immunogenicity and efficacy

Feline infectious peritonitis virus (FIPV) is a coronavirus that induces a fatal systemic disease mediated by an inappropriate immune response. Most previous vaccination attempts against FIPV were unsuccessful because IgG antibodies against the surface protein enhance the infection. However, two studies have shown that poxvirus vectors (vaccinia WR and canarypox) expressing only the FIPV membrane (M) protein can elicit a partially protective immunity which is supposed to be cell-mediated (Virology 181 (1991) 327; International patent WO 97/20054 (1997)). In our study, we report the construction of another poxvirus, the modified vaccinia virus Ankara (MVA), as an expression vector for the FIPV M protein. In this vector, the M gene has been inserted downstream a strong early/late promoter, whereas the two previously described poxviruses expressed the M protein during their early stage only. The immunogenicity of the recombinant MVA-M was evaluated in the murine model which revealed an effect of the vector on the Th1/Th2 balance. The vaccine was then tested in cats to evaluate its efficacy in an FIPV 79-1146 challenge. Vaccinated kittens developed FIPV-specific antibodies after immunization, however, none of them was protected against FIPV. Our results suggest a crucial role for the type of poxviral promoter that must be used to induce an effective immune response against FIPV.

Two genotypes of canine coronavirus simultaneously detected in the fecal samples of dogs with diarrhea

Sixty-nine fecal samples from diarrheic puppies were examined by reverse transcription-PCR assays for the M and the S genes of canine coronaviruses (CCoVs). The isolates in 10 samples were recognized as CCoV type I, and the isolates in 6 samples were recognized as CCoV type II, while isolates of both genotypes were simultaneously detected in 53 samples.

Vaccine efficacy of a cell lysate with recombinant baculovirus-expressed feline infectious peritonitis (FIP) virus nucleocapsid protein against progression of FIP

The Type II feline infectious peritonitis virus (FIPV) infection of feline macrophages is enhanced by a monoclonal antibody (MAb) to the S protein of FIPV. This antibody-dependent enhancement (ADE) activity increased with the MAb that showed a neutralizing activity with feline kidney cells, suggesting that there was a distinct correlation between ADE activity and the neutralizing activity. The close association between enhancing and neutralizing epitopes is an obstacle to developing a vaccine containing only neutralizing epitopes without enhancing epitopes. In this study, we immunized cats with cell lysate with recombinant baculovirus-expressed N protein of the Type I FIPV strain KU-2 with an adjuvant and investigated its preventive effect on the progression of FIP. Cats immunized with this vaccine produced antibodies against FIPV virion-derived N protein but did not produce virus-neutralizing antibodies. A delayed type hypersensitivity skin response to N protein was observed in these vaccinated cats, showing that cell mediated immunity against the FIPV antigen was induced. When these vaccinated cats were challenged with a high dose of heterologous FIPV, the survival rate was 75% (6/8), while the survival rate in the control group immunized with SF-9 cell-derived antigen was 12.5% (1/8). This study showed that immunization with the cell lysate with baculovirus-expressed N protein was effective in preventing the progression of FIP without inducing ADE of FIPV infection in cats.

Dengue hemorrhagic fever in infants: research opportunities ignored

The age distribution of cases of dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) in infants under the age of 1 year are reported from Bangkok, Thailand, and for the first time for Ho Chi Minh City, Vietnam; Yangon, Myanmar; and Surabaya, Indonesia. The four dengue viruses were isolated from Thai infants, all of whom were having a primary dengue infection. Progress studying the immunologically distinct infant DHF/DSS has been limited; most contemporary research has centered on DHF/DSS accompanying secondary dengue infections. In designing research results obtained in studies on a congruent animal model, feline infectious peritonitis virus (FIPV) infections of kittens born to FIPV-immune queens should be considered. Research challenges presented by infant DHF/DSS are discussed.

Adverse effects of feline IL-12 during DNA vaccination against feline infectious peritonitis virus

Cell-mediated immunity is thought to play a decisive role in protecting cats against feline infectious peritonitis (FIP), a progressive and lethal coronavirus disease. In view of the potential of DNA vaccines to induce cell-mediated responses, their efficacy to induce protective immunity in cats was evaluated. The membrane (M) and nucleocapsid (N) proteins were chosen as antigens, because antibodies to the spike (S) protein of FIP virus (FIPV) are known to precipitate pathogenesis. However, vaccination by repeated injections of plasmids encoding these proteins did not protect kittens against challenge infection with FIPV. Also, a prime-boost protocol failed to afford protection, with priming using plasmid DNA and boosting using recombinant vaccinia viruses expressing the same coronavirus proteins. Because of the role of IL-12 in initiating cell-mediated immunity, the effects of co-delivery of plasmids encoding the feline cytokine were studied. Again, IL-12 did not meet expectations - on the contrary, it enhanced susceptibility to FIPV challenge. This study shows that DNA vaccination failed to protect cats against FIP and that IL-12 may yield adverse effects when used as a cytokine adjuvant.

Preliminary studies on feline coronavirus distribution in naturally and experimentally infected cats

The shedding, tissue distribution and quasispecies composition of feline coronaviruses were studied in naturally and experimentally infected cats. The infection remained subclinical, but the majority of the animals shed the virus via faeces throughout the experiment. Sequences corresponding to the viral nucleocapsid region were amplified by reverse-transcription polymerase chain reaction from the cortex, dura mater, pancreas, lungs, third eyelid, and the heart muscle in four cases. Interestingly, the ORF7b viral region - a supposed virulence factor - was detected in fewer organs, raising the possibility that this region can be affected by deletions during virus replication in vivo. It is demonstrated that the composition of the viral quasispecies differs between organs, and that genomic regions with different functions undergo distinct processes of selection, which should be considered during the evolution of feline coronaviruses.

Observations on the quasispecies composition of three animal pathogenic RNA viruses

The quasispecies nature of three animal pathogenic RNA viruses of field origin was examined by testing variants of classical swine fever virus (CSFV) originating from geographically different areas, feline coronavirus (FCoV) detected from the same animal by successive sampling, and rabbit haemorrhagic disease virus (RHDV) originating from successive outbreaks in the same geographic area. Clinical samples were investigated using reverse transcriptase polymerase chain reaction (RT-PCR) and ensuing single strand conformational polymorphism (SSCP) assay. By the combination of these methods even subtle differences could be detected among the amplified fragments of the same virus species of different origin. FCoV proved to comprise the most and CSFV the less heterogeneous virus quasispecies. The results show that the combination of RT-PCR and SSCP provides novel and highly sensitive means for the characterisation of RNA viruses, with special regard to genome composition, evolution, features of pathogenicity and molecular epizootiology.

Prevalence and genetic pattern of feline coronaviruses in urban cat populations

The prevalence and phylogeny of feline coronaviruses were studied in urban cat populations by sampling of 113 clinically healthy cats. Rectal swab samples were subjected to a nested reverse-transcription polymerase chain reaction, specific for the conservative nucleocapsid region of the virus genome. More than 30% of the sampled animals proved positive for the presence of feline coronaviruses. The nucleotide sequences of amplified 440 bp products were determined, aligned and the phylogenetic analysis revealed noticeable genetic clusters among the prevalent feline coronaviruses in the surveyed geographic area. These findings will hopefully contribute to the elucidation of the epidemiology of feline infectious peritonitis.

Mapping of the coronavirus membrane protein domains involved in interaction with the spike protein

The coronavirus membrane (M) protein is the key player in virion assembly. One of its functions is to mediate the incorporation of the spikes into the viral envelope. Heterotypic interactions between M and the spike (S) protein can be demonstrated by coimmunoprecipitation and by immunofluorescence colocalization, after coexpression of their genes in eukaryotic cells. Using these assays in a mutagenetic approach, we have mapped the domains in the M protein that are involved in complex formation between M and S. It appeared that the 25-residue luminally exposed amino-terminal domain of the M protein is not important for M-S interaction. A 15-residue deletion, the insertion of a His tag, and replacement of the ectodomain by that of another coronavirus M protein did not affect the ability of the M protein to associate with the S protein. However, complex formation was sensitive to changes in the transmembrane domains of this triple-spanning protein. Deletion of either the first two or the last two transmembrane domains, known not to affect the topology of the protein, led to a considerable decrease in complex formation, but association was not completely abrogated. Various effects of changes in the part of the M protein that is located at the cytoplasmic face of the membrane were observed. Deletions of the extreme carboxy-terminal tail appeared not to interfere with M-S complex formation. However, deletions in the amphipathic domain severely affected M-S interaction. Interestingly, changes in the amino-terminal and extreme carboxy-terminal domains of M, which did not disrupt the interaction with S, are known to be fatal to the ability of the protein to engage in virus particle formation (C. A. M. de Haan, L. Kuo, P. S. Masters, H. Vennema, and P. J. M. Rottier, J. Virol. 72:6838-6850, 1998). Apparently, the structural requirements of the M protein for virus particle assembly differ from the requirements for the formation of M-S complexes.

Clearance of infection in cats naturally infected with feline coronaviruses is associated with an anti-S glycoprotein antibody response

We have investigated by Western blotting the antibody responses against the three major structural proteins in cats naturally infected with feline coronaviruses that cleared virus infection (group I), established chronic asymptomatic infection (group II) or were sick (group III). The cats of group I developed an anti-S glycoprotein response that was, relative to the anti-M glycoprotein response, at least 30-fold higher than that of chronically infected cats from groups II and III. These results suggest that the anti-S glycoprotein response against antigenic domains revealed by Western blot is associated with clearance of the virus after natural infection, and is not a risk factor for the establishment of a chronic infection.

Sequence analysis of the matrix/nucleocapsid gene region of turkey coronavirus

A reverse transcriptase, polymerase chain reaction (RT-PCR) procedure was used to amplify a segment of the genome of turkey coronavirus (TCV) spanning portions of the matrix and nucleocapsid (MN) protein genes (approximately 1.1 kb). The MN gene region of three epidemiologically distinct TCV strains (Minnesota, NC95, Indiana) was amplified, cloned into pUC19, and sequenced. TCV MN gene sequences were compared with published sequences of other avian and mammalian coronaviruses. A high degree of similarity (>90%) was observed between the nucleotide, matrix protein, and nucleocapsid protein sequences of TCV strains and published sequences of infectious bronchitis virus (IBV). The matrix and nucleocapsid protein sequences of TCV had limited homology (<30%) with MN sequences of mammalian coronaviruses. These results demonstrate a close genetic relationship between the avian coronaviruses, IBV and TCV.

Feline coronavirus type II strains 79-1683 and 79-1146 originate from a double recombination between feline coronavirus type I and canine coronavirus

Recent evidence suggests that the type II feline coronavirus (FCoV) strains 79-1146 and 79-1683 have arisen from a homologous RNA recombination event between FCoV type I and canine coronavirus (CCV). In both cases, the template switch apparently took place between the S and M genes, giving rise to recombinant viruses which encode a CCV-like S protein and the M, N, 7a, and 7b proteins of FCoV type I (K. Motowaka, T. Hohdatsu, H. Hashimoto, and H. Koyama, Microbiol. Immunol. 40:425-433, 1996; H. Vennema, A. Poland, K. Floyd Hawkins, and N. C. Pedersen, Feline Pract. 23:40-44, 1995). In the present study, we have looked for additional FCoV-CCV recombination sites. Four regions in the pol gene were selected for comparative sequence analysis of the type II FCoV strains 79-1683 and 79-1146, the type I FCoV strains TN406 and UCD1, the CCV strain K378, and the TGEV strain Purdue. Our data show that the type II FCoVs have arisen from double recombination events: additional crossover sites were mapped in the ORF1ab frameshifting region of strain 79-1683 and in the 5' half of ORF1b of strain 79-1146.

Feline infectious peritonitis viruses arise by mutation from endemic feline enteric coronaviruses

Feline infectious peritonitis virus (FIPV) strains from six cats and three different geographic areas were compared genetically with feline enteric coronavirus (FECV) isolates obtained from cats inhabiting the same environments. Sequence comparisons were made from 1.2- to 8.9-kb segments on the 3' end of the genome. FECV/FIPV pairs from the same catteries or shelters were 97.3-99.5% related but were genetically distinct from FIPV and FECV strains obtained from cats living in geographically distinct environments. The high genetic similarity between FECVs and FIPVs from the same environment strongly suggested a common ancestry. Based on the presence of deletion mutations in the FIPVs and not in the FECVs, it was concluded that FIPVs evolved as mutants of FECVs. The mutations are deletions in the FIPVs and not insertions in the FECVs since similar sequences are present in other strains that have segregated earlier from a common ancestor. Therefore, the order of descent is form FECV to FIPV. Mutations unique to FIPVs were found in open reading frames (ORFs) 3c in 4 of 6 isolates and/or 7b in 3 of 6 isolates. When the study was extended to include 7 additional FIPV isolates, 11/13 of the FIPVs sequenced were found to have mutated 3c ORFs.

The molecular biology of coronaviruses

This chapter discusses the manipulation of clones of coronavirus and of complementary DNAs (cDNAs) of defective-interfering (DI) RNAs to study coronavirus RNA replication, transcription, recombination, processing and transport of proteins, virion assembly, identification of cell receptors for coronaviruses, and processing of the polymerase. The nature of the coronavirus genome is nonsegmented, single-stranded, and positive-sense RNA. Its size ranges from 27 to 32 kb, which is significantly larger when compared with other RNA viruses. The gene encoding the large surface glycoprotein is up to 4.4 kb, encoding an imposing trimeric, highly glycosylated protein. This soars some 20 nm above the virion envelope, giving the virus the appearance-with a little imagination-of a crown or coronet. Coronavirus research has contributed to the understanding of many aspects of molecular biology in general, such as the mechanism of RNA synthesis, translational control, and protein transport and processing. It remains a treasure capable of generating unexpected insights.

The molecular biology of coronaviruses

This chapter discusses the manipulation of clones of coronavirus and of complementary DNAs (cDNAs) of defective-interfering (DI) RNAs to study coronavirus RNA replication, transcription, recombination, processing and transport of proteins, virion assembly, identification of cell receptors for coronaviruses, and processing of the polymerase. The nature of the coronavirus genome is nonsegmented, single-stranded, and positive-sense RNA. Its size ranges from 27 to 32 kb, which is significantly larger when compared with other RNA viruses. The gene encoding the large surface glycoprotein is up to 4.4 kb, encoding an imposing trimeric, highly glycosylated protein. This soars some 20 nm above the virion envelope, giving the virus the appearance-with a little imagination-of a crown or coronet. Coronavirus research has contributed to the understanding of many aspects of molecular biology in general, such as the mechanism of RNA synthesis, translational control, and protein transport and processing. It remains a treasure capable of generating unexpected insights.

Comparison of the amino acid sequence and phylogenetic analysis of the peplomer, integral membrane and nucleocapsid proteins of feline, canine and porcine coronaviruses

Complete nucleotide sequences were determined by cDNA cloning of peplomer (S), integral membrane (M) and nucleocapsid (N) genes of feline infectious peritonitis virus (FIPV) type I strain KU-2, UCD1 and Black, and feline enteric coronavirus (FECV) type II strain 79-1683. Only M and N genes were analyzed in strain KU-2 and strain 79-1683 which still had unknown nucleotide sequences. Deduced amino acid sequences of S, M and N proteins were compared in a total of 7 strains of coronaviruses, which included FIPV type II strain 79-1146, canine coronavirus (CCV) strain Insavc-1 and transmissible gastroenteritis virus of swine (TGEV) strain Purdue. Comparison of deduced amino acid sequences of M and N proteins revealed that both M and N proteins had an identity of at least 90% between FIPV type I and type II. The phylogenetic tree of the M and N protein-deduced amino acid sequences showed that FIPV type I and type II form a group with FECV type II, and that these viruses were evolutionarily distant from CCV and TGEV. On the other hand, when the S protein-deduced amino acid sequences was compared, identity of only about 45% was found between FIPV type I and type II. The phylogenetic tree of the S protein-deduced amino acid sequences indicated that three strains of FIPV type I form a group, and that it is a very long distance from the FIPV type II, FECV type II, CCV and TGEV groups.

Localization of antigenic sites of the S glycoprotein of feline infectious peritonitis virus involved in neutralization and antibody-dependent enhancement

The S glycoprotein of feline infectious peritonitis virus (FIPV) has been shown to contain the antigenic sites responsible for eliciting both neutralization and antibody-dependent enhancement. To determine the region of S responsible, overlapping DNA fragments spanning the entire S gene were cloned and expressed as fusion proteins by in vitro transcription and translation. Fusion proteins containing relevant epitopes were identified by radioimmunoprecipitation with neutralizing and enhancing FIPV-specific monoclonal antibodies (MAbs). A region spanning residues 509 to 673 reacted with most MAbs tested. Translation in the presence of microsomal membranes did not enhance reactivity, suggesting that glycosylation is not essential for recognition by the MAbs. To localize the antigenic sites further, several MAb-resistant (mar) mutants of FIPV were cloned and sequenced. Amino acid residues that contribute to the neutralizing and enhancing epitopes were localized to two regions, designated A1 and A2, which show partial overlap with the homologous antigenic site A of transmissible gastroenteritis virus. Site A1 contains residues 568 and 591 and is homologous with part of subsite Aa of transmissible gastroenteritis virus. Site A2 contains residues 643, 649, and 656. Double mutations in sites A1 and A2 were found in mar mutants derived from neutralizing and enhancing MAbs 23F4.5 and 18A7.4, while a single mutation in site A2 was found in a mar mutant derived from MAb 24H5.4, which is neutralizing but not enhancing. The data suggest that site A2, which includes residues 643 to 656, is a dominant neutralizing site of FIPV and that sites A1 and A2 may act in concert to induce antibody-dependent enhancement.

Predominance of MHC class II-restricted CD4+ cytotoxic T cells against mouse hepatitis virus A59

Coronavirus-induced acute hepatitis is a complex event and the role of different components of the immune system with regard to defined viral proteins and the course of the infection is not yet clear. We have analysed the cytotoxic T-lymphocyte (CTL) response in mouse hepatitis virus (MHV-A59) infection. Surprisingly, we detected only a very clear virus-specific major histocompatibility complex (MHC) class II-restricted cytotoxicity in mice infected with MHV-A59. We found no evidence of activation of the classical CD8+ MHC class I-restricted CTL. The virus-specific CD4+ CTL derived from two different mouse strains having different MHC haplotypes recognized the same immunodominant epitope. This epitope, comprising the amino acid residues 329-343 of the viral S-glycoprotein, was recognized both at the polyclonal level and by virus-specific CTL clones. Transfer studies using a MHV-A59-specific CD4+ CTL clone showed significant protection against a lethal challenge with MHV-A59, implicating that these CD4+ CTL play a pivotal role in the protection against MHV-A59 infections.

Mouse hepatitis virus-specific cytotoxic T lymphocytes protect from lethal infection without eliminating virus from the central nervous system

Acute infection of the central nervous system by the neurotropic JHM strain of mouse hepatitis virus (JHMV) induces nucleocapsid protein specific cytotoxic T lymphocytes (CTL) not found in the periphery (S. Stohlman, S. Kyuwa, J. Polo, D. Brady, M. Lai, and C. Bergmann, J. Virol. 67:7050-7059, 1993). Peripheral induction of CTL specific for the nucleocapsid protein of JHMV by vaccination with recombinant vaccinia viruses was unable to provide significant protection to a subsequent lethal virus challenge. By contrast, the transfer of nucleoprotein-specific CTL protected mice from a subsequent lethal challenge by reducing virus replication within the central nervous system, demonstrating the importance of the CTL response to this epitope in JHMV infection. Transfer of these CTL directly into the central nervous system was at least 10-fold more effective than peripheral transfer. Histological analysis indicated that the CTL reduced virus replication in ependymal cells, astrocytes, and microglia. Although the CTL were relatively ineffective at reducing virus replication in oligodendroglia, survivors showed minimal evidence of virus persistence within the central nervous system and no evidence of chronic ongoing demyelination.

Enhancement of feline infectious peritonitis virus type I infection in cell cultures using low-speed centrifugation

The effects of centrifugation on the ability of feline infectious peritonitis virus (FIPV) to infect cells in culture was investigated. The infectivity titer was the highest when the plates were centrifuged at 400 x g (1500 rpm) for 2 h. All five strains classified as FIPV Type I showed infectivity titers enhanced 10-100-fold by centrifugation at 400 x g for 2 h. The centrifugal enhancement of infection was obtained only by centrifugation immediately after inoculation of the virus, suggesting that the enhancement occurs during attachment or adsorption of viruses to the cells. This method may be useful for the culture of FIPV Type I strains.

Cloning and expression of FECV spike gene in vaccinia virus. Immunization with FECV S causes early death after FIPV challenge

The spike gene of the feline enteric coronavirus (FECV), strain FECV-1683, was PCR amplified from total RNA extracted from FECV-infected cells and its sequence determined. A primary translation product of 1454 amino acids is predicted from the nucleotide sequence, containing a N-terminal signal sequence, a C-terminal transmembrane region and 33 potential N-glycosylation sites. The sequence shares 92% homology with the previously published feline infectious peritonitis virus, strain WSU-1146; however, several regions were identified that distinguished FECV from Feline Infectious Peritonitis virus, FIPV. The full length FECV S gene was cloned and expressed in vaccinia virus. Recombinants produced a 200 kD protein which was recognized by sera from cats infected with FIPV. When kittens were immunized with the vaccinia/FECV S recombinant, neutralizing antibodies to FIPV were induced. After challenge with a lethal dose of FIPV, the recombinant vaccinated animals died earlier than control animals immunized with vaccinia virus alone.

Molecular cloning and sequence determination of the peplomer protein gene of feline infectious peritonitis virus type I

cDNA clones spanning the entire region of the peplomer (S) gene of feline infectious peritonitis virus (FIPV) type I strain KU-2 were obtained and their complete nucleotide sequences were determined. A long open reading frame (ORF) encoding 1464 amino acid residues was found in the gene, which was 12 residues longer than the ORF of the FIPV type II strain 79-1146. The sequences of FIPV type I and mainly -tPV type II were compared. The homologies at the N- (amino acid residues 1-693) and C- (residues 694-1464) terminal halves were 29.8 and 60.7%, respectively. This was much lower than that between FIPV type II and other antigenically related coronaviruses, such as transmissible gastroenteritis virus of swine and canine coronavirus. This supported the serological relatedness of the viruses and confirmed that the peplomer protein of FIPV type I has distinct structural features that differ from those of antigenically related viruses.

Protection of cats from infectious peritonitis by vaccination with a recombinant raccoon poxvirus expressing the nucleocapsid gene of feline infectious peritonitis virus

Feline Infectious Peritonitis Virus (FIPV) is a coronavirus that induces an often fatal, systemic infection in cats. Various vaccines designed to prevent FIPV infection have been shown to exacerbate the disease, probably due to immune enhancement mediated by virus-specific immunoglobulins against the outer envelope (S) protein. An effective vaccine would be one that induces cell-mediated immunity without disease enhancing antibodies. In this report, we describe the use of a recombinant raccoon poxvirus that expresses the gene encoding the nucleocapsid protein of FIPV (rRCNV-FIPV N) as an effective vaccine against FIPV-induced disease. Cats were parenterally or orally vaccinated twice, three weeks apart. Cats were then orally challenged with Feline Enteric Coronavirus (FECV), which induces a subclinical infection that can cause enhancement of subsequent FIPV infection. Three weeks later, cats were orally challenged with FIPV. The FIPV challenge induced a fatal infection in 4/5 (80%) of the controls. On the other hand, all five cats vaccinated subcutaneously with rRCNV-FIPV N showed no signs of disease after challenge with FIPV. Four of the five subcutaneous vaccinates survived an additional FIPV challenge. Vaccination with rRCNV-FIPV N induced serum IgG antibody responses to FIPV nucleocapsid protein, but few, if any, FIPV neutralizing antibodies. In contrast to the controls, protected vaccinates maintained low FIPV serum neutralizing antibody titers after FIPV challenge. This suggests that the protective immune response involves a mechanism other than humoral immunity consisting of FIPV neutralizing antibodies.

Identification of the membrane protein of porcine epidemic diarrhea virus

Sequence information on the genome of porcine epidemic diarrhea virus(PEDV) has only recently been determined. In contrast, very little is known about the viral proteins. In the present report we have identified the membrane glycoprotein (M) of PEDV by use of rabbit anti-peptide sera and transient expression of the cloned M gene in Vero cells and by expression in the baculovirus system. The native M protein of PEDV is incorporated into virions, is N-glycosylated, and migrates with a relative mobility (Mr) of 27 k in polyacrylamide gels. In contrast, the M protein synthesized by recombinant baculoviruses migrates with a Mr of 23 k, that is, with identical mobility as the deglycosylated product of PEDV. Thus, it appears that M protein specified by the recombinant baculovirus is poorly, if at all, glycosylated. Using monoclonal antibodies and rabbit and rabbit antipeptide sera specific for the N and C termini of the M protein, we were able to show that a 19 k band detected in PEDV-infected cells but not in virions represented a fragment of M from which the C terminus had been cleaved off. Finally, by electron microscopy and immunogold labelling, the relative orientation of M within the virion envelope was determined as NexoCcyt. In conclusion, all of these data strongly support the hypothesis that PEDV should be classified with the group I coronaviruses.

The S1 glycoprotein but not the N or M proteins of avian infectious bronchitis virus induces protection in vaccinated chickens

The S1, N and M proteins, obtained from the nephropathogenic N1/62 strain of infectious bronchitis virus (IBV) by immunoaffinity purification with monoclonal antibodies, were used for immunization of chickens. For all three antigens multiple immunizations were necessary for induction of an antibody response. Protection of chickens vaccinated with the S1 glycoprotein against virulent challenge was demonstrated by the complete absence of virus in tracheas and kidneys of vaccinated chickens. Following four immunizations with the S1 glycoprotein 71% and 86% of chickens were protected at the level of tracheas and kidneys, respectively. Three immunizations with the S1 glycoprotein protected 70% and 10% of chickens at the level of kidney and trachea, respectively. Neither the N nor the M antigen induced protection to a virulent challenge with the nephropathogenic N1/62 strain of IBV after four immunizations. Virus neutralizing, haemagglutination inhibiting and ELISA antibodies were detected in chickens immunized with the S1 glycoprotein and inactivated N1/62 virus, however there was no correlation between the presence of any of these antibodies and protection.

Optimization of targeted RNA recombination and mapping of a novel nucleocapsid gene mutation in the coronavirus mouse hepatitis virus

We have recently described a method of introducing site-specific mutations into the genome of the coronavirus mouse hepatitis virus (MHV) by RNA recombination between cotransfected genomic RNA and a synthetic subgenomic mRNA (C. A. Koetzner, M. M. Parker, C. S. Ricard, L. S. Sturman, and P. S. Masters, J. Virol. 66:1841-1848, 1992). By using a thermolabile N protein mutant of MHV (Alb4) as the recipient virus and synthetic RNA7 (the mRNA for the nucleocapsid protein N) as the donor, we selected engineered recombinant viruses as heat-stable progeny resulting from cotransfection. We have now been able to greatly increase the efficiency of targeted recombination in this process by using a synthetic defective interfering (DI) RNA in place of RNA7. The frequency of recombination is sufficiently high that, with Alb4 as the recipient, recombinants can be directly identified without using thermal selection. The synthetic DI RNA has been used to demonstrate that the lesion in another temperature-sensitive and thermolabile MHV mutant, Alb1, maps to the N gene. Sequencing of the Alb1 N gene revealed two closely linked point mutations that fall in a region of the N molecule previously noted as being the most highly conserved region among all of the coronavirus N proteins. Analysis of revertants of the Alb1 mutant revealed that one of the two mutations is critical for the temperature-sensitive phenotype; the second mutation is phenotypically silent.