Expression of the E2 envelope glycoprotein of bovine viral diarrhoea virus (BVDV) elicits virus-type specific neutralising antibodies

Bovine Pestivirus Heterogeneity and Its Potential Impact on Vaccination and Diagnosis

Bovine Pestiviruses A and B, formerly known as bovine viral diarrhoea viruses (BVDV)-1 and 2, respectively, are important pathogens of cattle worldwide, responsible for significant economic losses. Bovine viral diarrhoea control programmes are in effect in several high-income countries but less so in low- and middle-income countries where bovine pestiviruses are not considered in disease control programmes. However, bovine pestiviruses are genetically and antigenically diverse, which affects the efficiency of the control programmes. The emergence of atypical ruminant pestiviruses (Pestivirus H or BVDV-3) from various parts of the world and the detection of Pestivirus D (border disease virus) in cattle highlights the challenge that pestiviruses continue to pose to control measures including the development of vaccines with improved cross-protective potential and enhanced diagnostics. This review examines the effect of bovine pestivirus diversity and emergence of atypical pestiviruses in disease control by vaccination and diagnosis.

Dendritic Cell Targeting of Bovine Viral Diarrhea Virus E2 Protein Expressed by Lactobacillus casei Effectively Induces Antigen-Specific Immune Responses via Oral Vaccination

Bovine viral diarrhea caused by bovine viral diarrhea virus (BVDV) is an important disease in cattle, resulting in significant economic losses to the cattle industry worldwide. In order to develop an effective vaccine against BVDV infection, we constructed a dendritic cell (DC)-targeting oral probiotic vaccine (pPG-E2-DCpep/LC W56) using Lactobacillus casei as antigen delivery carrier to express BVDV glycoprotein E2 fused with DC-targeting peptide, and the immunogenicity of orally administered probiotic vaccine was evaluated in mice model. Our results showed that after immunization with the probiotic vaccine, significantly levels of antigen-specific sera IgG and mucosal sIgA antibodies (p < 0.05) with BVDV-neutralizing activity were induced in vivo. Challenge experiment showed that pPG-E2-DCpep/LC W56 can provide effective immune protection against BVDV, and BVDV could be effectively cleared from the intestine of immunized mice post-challenge. Moreover, the pPG-E2-DCpep/LC W56 could efficiently activate DCs in the intestinal Peyer’s patches, and significantly levels of lymphoproliferative responses, Th1-associated IFN-γ, and Th2-associated IL-4 were observed in mice immunized with pPG-E2-DCpep/LC W56 (p < 0.01). Our results clearly demonstrate that the probiotic vaccine could efficiently induce anti-BVDV mucosal, humoral, and cellular immune responses via oral immunization, indicating a promising strategy for the development of oral vaccine against BVDV.

Genetic and Clinical Analyses of Bovine Viral Diarrhea Virus Isolates from Dairy Operations in the United States of America

To assess the prevalence of bovine viral diarrhea virus (BVDV) on the basis of the genotype and clinical signs, isolates from 16 dairy herds (bulk milk samples) and 37 BVDV-infected cattle were examined. Isolates for this study were selected from submissions that contained an adequate clinical history. A part of the E2 gene of BVDV from these isolates was amplified by reverse transcription-polymerase chain reaction. From the nucleotide sequence of the amplified products, phylogenetic analyses were performed and genotypes or subgenotypes were identified. Forty percent of the selected field isolates were BVDV-2, and 60% were BVDV-1. Eighty-one percent of BVDV-1 isolates were determined to be the BVDV-1b subgenotype. BVDV-1b and BVDV-2 formed more closely related clusters in each group than did the BVDV-1a isolates. There was no obvious association of any genotype or subgenotype with geographical localization or clinical manifestations. A higher prevalence of BVDV-2 infection was found in the United States than in other countries. BVDV-1a has been thought of as a prototype of BVDV; however, there were fewer isolations of BVDV-1a than of other subgenotypes of BVDV Phylogenetic analyses of BVDV isolates using the E2 region of the genome generated results similar to those of studies done in the United States using the 5' untranslated region.

Challenges in Veterinary Vaccine Development and Immunization

In approaching the development of a veterinary vaccine, researchers must choose from a bewildering array of options that can be combined to enhance benefit. The choice and combination of options is not just driven by efficacy, but also consideration of the cost, practicality, and challenges faced in licensing the product. In this review we set out the different choices faced by veterinary vaccine developers, highlight some issues, and propose some pressing needs to be addressed.

Immunocompetent truncated E2 glycoprotein of bovine viral diarrhea virus (BVDV) expressed in Nicotiana tabacum plants: a candidate antigen for new generation of veterinary vaccines

The bovine viral diarrhea virus (BVDV) is the etiological agent responsible for a wide spectrum of clinical diseases in cattle. The glycoprotein E2 is the major envelope protein of this virus and the strongest inductor of the immune response. There are several available commercial vaccines against bovine viral diarrhea (BVD), which show irregular performances. Here, we report the use of tobacco plants as an alternative productive platform for the expression of the truncated version of E2 glycoprotein (tE2) from the BVDV. The tE2 sequence, lacking the transmembrane domain, was cloned into the pK7WG2 Agrobacterium binary vector. The construct also carried the 2S2 Arabidopsis thaliana signal for directing the protein into the plant secretory pathway, the Kozak sequence, an hexa-histidine tag to facilitate protein purification and the KDEL endoplasmic reticulum retention signal. The resulting plasmid (pK-2S2-tE2-His-KDEL) was introduced into Agrobacterium tumefaciens strain EHA101 by electroporation. The transformed A. tumefaciens was then used to express tE2 in leaves of Nicotiana tabacum plants. Western blot and ELISA using specific monoclonal antibodies confirmed the presence of the recombinant tE2 protein in plant extracts. An estimated amount of 20 μg of tE2 per gram of fresh leaves was regularly obtained with this plant system. Injection of guinea pigs with plant extracts containing 20 μg of rtE2 induced the production of BVDV specific antibodies at equal or higher levels than those induced by whole virus vaccines. This is the first report of the production of an immunocompetent tE2 in N. tabacum plants, having the advantage to be free of any eventual animal contaminant.

Transdominant inhibition of bovine viral diarrhea virus entry

Bovine viral diarrhea virus (BVDV) is a positive-strand RNA virus and a member of the genus Pestivirus in the family Flaviviridae. To identify and characterize essential factors required for BVDV replication, a library expressing random fragments of the BVDV genome was screened for sequences that act as transdominant inhibitors of viral replication by conferring resistance to cytopathic BVDV-induced cell death. We isolated a BVDV-nonpermissive MDBK cell clone that harbored a 1.2-kb insertion spanning the carboxy terminus of the envelope glycoprotein 1 (E1), the envelope glycoprotein E2, and the amino terminus of p7. Confirming the resistance phenotype conferred by this library clone, naïve MDBK cells expressing this fragment were found to be 100- to 1,000-fold less permissive to both cytopathic and noncytopathic BVDV infection compared to parental MDBK cells, although these cells remained fully permissive to vesicular stomatitis virus. This restriction could be overcome by electroporation of BVDV RNA, indicating a block at one or more steps in viral entry prior to translation of the viral RNA. We determined that the E2 ectodomain was responsible for the inhibition to BVDV entry and that this block occurred downstream from BVDV interaction with the cellular receptor CD46 and virus binding, suggesting interference with a yet-unidentified BVDV entry factor.

Selection of mimotopes of Bovine Viral Diarrhoea Virus using a solid-phase peptide library

Bovine Viral Diarrhoea Virus (BVDV) is an important pathogen of cattle, causing important economical losses world-wide. In this study, an 8-mer solid-phase peptide library was screened with a neutralising monoclonal antibody 157 to generate mimotopes mimicking a conformational neutralising epitope of BVDV E2 protein. Two sequences selected 157A1 LFEQYYYF and 157A2 LYRFGEFD that did not show a high structural or sequence similarity with BVDV E2 glycoprotein reacted specifically with monoclonal antibody 157 when presented as solid-phase peptides in a SPOT scan assay. These results indicate that combinatorial peptide libraries can be used to identify potential mimotopes of conformational epitopes.

Immunization with plasmid DNA encoding a truncated, secreted form of the bovine viral diarrhea virus E2 protein elicits strong humoral and cellular immune responses

The major protective antigen of bovine viral diarrhea virus (BVDV), the E2 protein, is cell-associated and not expressed on the cell surface. In this study we evaluated a DNA vaccine encoding various secreted versions of E2. In vitro analysis demonstrated that deletion of the transmembrane anchor and addition of the signal sequence of bovine herpesvirus-1 (BHV-1) (gDsDeltaE2) resulted in efficient secretion of E2 into the culture medium. In contrast, full-length E2, either without or with gDs (gDsE2), as well as truncated E2 without gDs (DeltaE2), remained entirely cell-associated. Mice immunized with plasmid encoding gDsDeltaE2 developed significantly higher IgG and virus neutralizing antibody titres compared to animals vaccinated with plasmid encoding E2, DeltaE2 or gDsE2. To optimize secretion of E2, the efficiency of gDs was compared with that of the tissue plasminogen activator signal (tPAs) sequence. In addition, the effect of the plasmid backbone was assessed by comparing two vectors. Four plasmids, pMASIA-gDsDeltaE2, pMASIA-tPAsDeltaE2, pSLKIA-gDsDeltaE2 and pSLKIA-tPAsDeltaE2, were constructed and administered intradermally to mice. The mice immunized with pMASIA-tPAsDeltaE2 developed the strongest and most balanced immune responses. Vaccination of cattle confirmed that pMASIA-tPAsDeltaE2 elicited both strong humoral and cellular immune responses and thus could be a candidate DNA vaccine against BVDV.

Dual mechanisms of pestiviral superinfection exclusion at entry and RNA replication

For many viruses, primary infection has been shown to prevent superinfection by a homologous second virus. In this study, we investigated superinfection exclusion of bovine viral diarrhea virus (BVDV), a positive-sense RNA pestivirus. Cells acutely infected with BVDV were protected from superinfection by homologous BVDV but not with heterologous vesicular stomatitis virus. Superinfection exclusion was established within 30 to 60 min but was lost upon passaging of persistently infected cells. Superinfecting BVDV failed to deliver a translatable genome into acutely infected cells, indicating a block in viral entry. Deletion of structural protein E2 from primary infecting BVDV abolished this exclusion. Bypassing the entry block by RNA transfection revealed a second block at the level of replication but not translation. This exclusion did not require structural protein expression and was inversely correlated with the level of primary BVDV RNA replication. These findings suggest dual mechanisms of pestivirus superinfection exclusion, one at the level of viral entry that requires viral glycoprotein E2 and a second at the level of viral RNA replication.

Origination and consequences of bovine viral diarrhea virus diversity

The potential consequences of BVDV genetic and antigenic diversity are far ranging. The complexity of clinical presentations associated with BVDV likely arises from factors encoded by the virus genome. More importantly,prevention and control of BVDV may be complicated by diagnostic and immunization failure resulting from virus diversity. Evolutionary pressures will continue to drive further diversity, making control of BVDV challenging. Current and the potential for future BVDV strain diversity should be considered when designing BVDV control programs both at the individual farm and national herd level.

The immune response to bovine viral diarrhea virus: a constantlychanging picture

Bovine viral diarrhea virus (BVDV) is one of the major immuno-suppressive viruses of cattle. The effect on the innate and acquired immune system is unique and results in dramatic immune dysfunction. BVDV infection also has the ability to cause persistent infection (PI) in the developing fetus. This Pl syndrome creates a requirement for high levels of BVDV immunity from vaccines to prevent these infections. BVDV vaccines and their future development continue to be an enigma in the control of BVDV.

Genetic typing of ruminant pestivirus strains from Northern Ireland and the Republic of Ireland

A study was performed to investigate the genotypes and sub-groups of pestiviruses present in ruminants in Ireland. These comprised one ovine and eighteen bovine pestiviruses from Northern Ireland and six bovine pestiviruses from the Republic of Ireland. A 288 base pair (bp) portion of the 5'-non coding region (5'-NCR) from each of 25 pestiviruses collected over a period of 31 years was amplified by reverse-transcription-polymerase chain reaction (RT-PCR) and the product directly sequenced. From each pestivirus, nucleotide sequences corresponding to bases 130 to 374 of the 5'-NCR of NADL were aligned and compared with each other and with the corresponding sequences of a number of reference, field or vaccinal strains of BVDV types I and II, border disease virus and classical swine fever virus. All of the 25 sequenced pestiviruses were found to be BVDV type Ia. These were closely related to the constituent viruses of the 2 inactivated vaccines currently licensed for use in Northern Ireland and to recent bovine isolates from England.

Cytokine adjuvancy of BVDV DNA vaccine enhances both humoral and cellular immune responses in mice

The effect of cytokine adjuvancy on a bovine viral diarrhoea virus (BVDV) DNA vaccine expressing the major glycoprotein E2 was investigated in mice. Murine interleukin-2 (IL-2) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were chosen for their potential ability to enhance the humoral and cellular immune responses involved in protection against BVDV. Both cytokines, co-administered as separate plasmid constructs, had a marked effect on ELISA and neutralising antibody titres, improving the spectrum of neutralisation induced by the E2 DNA vaccine, as demonstrated in heterologous neutralisation assays. The predominance of IgG2a isotypes, in sera from all DNA injected groups, indicated a Th1 biased immune response. Antigen specific proliferation of murine splenocytes from immunised mice was enhanced by cytokine co-administration, with the highest stimulation indexes observed in the group co-injected with the GM-CSF construct. These results obtained in the mouse (Balb/c; H2-kd) animal model demonstrate the value of the two cytokines as adjuvants for the E2 DNA vaccine. The need for an adjuvant in this system was emphasised by the MHC restriction observed when C57BL/6 mice (H2-kb) were immunised with the E2 DNA construct. Antibody levels were dramatically lower in this mouse strain.

Co-administration of IL-2 enhances antigen-specific immune responses following vaccination with DNA encoding the glycoprotein E2 of bovine viral diarrhoea virus

Induction of effective immunity requires the delivery of a protective antigen with appropriate co-stimulatory signals. For bovine viral diarrhoea virus (BVDV) this antigen is the major viral glycoprotein E2. Neutralising antibodies are directed towards the E2 protein and passive transfer of antibodies in serum or colostrum can completely protect against viral infection. DNA vaccination of mice with a construct encoding the E2 glycoprotein induced neutralising antibody levels that were potentially sufficient to prevent virus replication in a challenge system. The co-delivery of interleukin-2 (IL-2) further enhanced the levels of antibody raised. The strong IgG2a component of the antigen-specific antibody suggests a Th1 bias to the immune response induced following vaccination.

Presence of bovine viral diarrhea virus (BVDV) E2 glycoprotein in VSV recombinant particles and induction of neutralizing BVDV antibodies in mice

We generated a recombinant vesicular stomatitis virus (VSV-E2) encoding the bovine viral diarrhea virus (BVDV) E2 glycoprotein with the VSV-G protein signal peptide. Infection of BHK21 cells with VSV-E2 induced the synthesis of a recombinant E2 (rE2) that comigrated with authentic BVDV-E2 in PAGE-SDS gels. Non-reducing immunoblots showed that rE2 is a disulfide bond-linked homodimer with at least 10-fold higher avidity for conformation-dependent anti-BVDV-E2 antibodies than its reduced monomeric counterpart. Immunofluorescence microscopy also showed that rE2 was transported to the plasma membrane of infected cells and analysis of purified particles demonstrated that dimeric rE2 was incorporated into VSV-E2 virions in approximately 1:10 ratio with respect to the G glycoprotein. BALB/c mice inoculated intranasally with VSV-E2 doses of up to 10(7) plaque forming units (pfu) showed no symptoms of viral-induced disease and developed a specific BVDV neutralizing response that lasted for at least 180 days post inoculation.

Genetic diversity of pestiviruses: identification of novel groups and implications for classification

The complete Npro coding sequences were determined for 16 pestiviruses isolated from cattle, pig, and several wild ruminant species including reindeer, bison, deer, and bongo. Phylogenetic analysis enabled the segregation of pestiviruses into the established species bovine viral diarrhea virus-1 (BVDV-1), BVDV-2, border disease virus (BDV), and classical swine fever virus (CSFV). For BVDV-1 five distinct subgroups were identified, while BVDV-2, BDV, and CSFV were each subdivided into two subgroups. The virus isolates from bongo and deer as well as one porcine virus isolate belong to BVDV-1. Interestingly, the isolates from reindeer and bison are distinct from the established pestivirus species. The Npro sequences from these two viruses are more similar to BDV than to the other pestivirus species. Calculation of the pairwise evolutionary distances allowed a clear separation of the categories species, subgroup, and isolate only when the reindeer/bison viruses were considered as members of an additional pestivirus species. Furthermore, the entire E2 coding sequences of a representative set of virus isolates covering all recognized species and subgroups were studied. Segregation of pestiviruses based on the E2 region was identical with that obtained with the N(pro) sequences.