First record of antibodies to the bluetongue virus in ewe (Ovis aries) in the state of Amazonas, Brazil / Primeiro registro de anticorpos para o vírus da língua azul em ovino (Ovis aries) no estado do Amazonas, Brasil

The objective of this work was to describe the first record of antibodies to the Bluetongue Virus (BTV) in ewe, in the state of Amazonas. The ewe, which was in twin pregnancy, gave birth on May 9, 2015, but a lamb died hours after delivery. Veterinary service was then requested by the owner, where emaciation, loss of wool, pyrexia, apathy, dyspnea, mucoid nasal secretion, facial, lingual and submandibular edema were observed. There was a visit by the Agricultural Defense Agency of the State of Amazonas to the property and blood samples were collected from the animal. The whole blood and serum were sent to the National Agricultural Laboratory, where it was possible to detect the presence of specific antibodies to BTV, through the Agar Gel Double Immunodiffusion. The ewe was submitted to a new blood collection, following the same protocols and the samples were sent to the Biological Institute of São Paulo, confirmed diagnosis. The animal in a serious clinical condition, could not resist and died in July 2015. The occurrence of an allochthonous case, in an area where vector insects occur, can trigger an endemic process in the Amazon region. With this, the epidemiological control of these occurrences is necessary, in order to avoid the spread of the disease in the country.

O objetivo do trabalho foi descrever o primeiro registro de anticorpos para o Vírus da Língua Azul (VLA) em ovino, no estado do Amazonas. A ovelha, que se encontrava em gestação gemelar, pariu no dia 9 de maio de 2015, porém um cordeiro faleceu horas após o parto. Foi então solicitado serviço veterinário por parte do proprietário, onde foi observado emaciação, perda de lã, pirexia, apatia, dispneia, secreção nasal mucoide, edema facial, lingual e submandibular. Houve visita da Agência de Defesa Agropecuária do Estado do Amazonas na propriedade e coletadas amostras de sangue do animal. O sangue total e soro foram enviados ao Laboratório Nacional Agropecuário, no qual foi possível detectar a presença de anticorpos específicos para VLA, através do teste de Imunodifusão Dupla em Gel de Ágar. A ovelha foi submetida a uma nova coleta de sangue, seguindo os mesmos protocolos e as amostras foram enviadas ao Instituto Biológico de São Paulo, confirmando diagnóstico. O animal em estado clínico grave, não resistiu e veio a óbito em julho de 2015. A ocorrência de um caso alóctone, em uma área de ocorrência de insetos vetores, pode desencadear um processo de endemia na região amazônica. Com isso, o controle epidemiológico destas ocorrências, se fazem necessários, afim de se evitar a disseminação da doença no país.

The Combined Expression of the Nonstructural Protein NS1 and the N-Terminal Half of NS2 (NS21-180) by ChAdOx1 and MVA Confers Protection against Clinical Disease in Sheep upon Bluetongue Virus Challenge.

Bluetongue, caused by bluetongue virus (BTV), is a widespread arthropod-borne disease of ruminants that entails a recurrent threat to the primary sector of developed and developing countries. In this work, we report modified vaccinia virus Ankara (MVA) and ChAdOx1-vectored vaccines designed to simultaneously express the immunogenic NS1 protein and/or NS2-Nt, the N-terminal half of protein NS2 (NS21-180). A single dose of MVA or ChAdOx1 expressing NS1-NS2-Nt improved the protection conferred by NS1 alone in IFNAR(-/-) mice. Moreover, mice immunized with ChAdOx1/MVA-NS1, ChAdOx1/MVA-NS2-Nt, or ChAdOx1/MVA-NS1-NS2-Nt developed strong cytotoxic CD8+ T-cell responses against NS1, NS2-Nt, or both proteins and were fully protected against a lethal infection with BTV serotypes 1, 4, and 8. Furthermore, although a single immunization with ChAdOx1-NS1-NS2-Nt partially protected sheep against BTV-4, the administration of a booster dose of MVA-NS1-NS2-Nt promoted a faster viral clearance, reduction of the period and level of viremia and also protected from the pathology produced by BTV infection. IMPORTANCE Current BTV vaccines are effective but they do not allow to distinguish between vaccinated and infected animals (DIVA strategy) and are serotype specific. In this work we have develop a DIVA multiserotype vaccination strategy based on adenoviral (ChAdOx1) and MVA vaccine vectors, the most widely used in current phase I and II clinical trials, and the conserved nonstructural BTV proteins NS1 and NS2. This immunization strategy solves the major drawbacks of the current marketed vaccines.

Serological Cross-Reactions between Expressed VP2 Proteins from Different Bluetongue Virus Serotypes.

Bluetongue (BT) is a severe and economically important disease of ruminants that is widely distributed around the world, caused by the bluetongue virus (BTV). More than 28 different BTV serotypes have been identified in serum neutralisation tests (SNT), which, along with geographic variants (topotypes) within each serotype, reflect differences in BTV outer-capsid protein VP2. VP2 is the primary target for neutralising antibodies, although the basis for cross-reactions and serological variations between and within BTV serotypes is poorly understood. Recombinant BTV VP2 proteins (rVP2) were expressed in Nicotiana benthamiana, based on sequence data for isolates of thirteen BTV serotypes (primarily from Europe), including three 'novel' serotypes (BTV-25, -26 and -27) and alternative topotypes of four serotypes. Cross-reactions within and between these viruses were explored using rabbit anti-rVP2 sera and post BTV-infection sheep reference-antisera, in I-ELISA (with rVP2 target antigens) and SNT (with reference strains of BTV-1 to -24, -26 and -27). Strong reactions were generally detected with homologous rVP2 proteins or virus strains/serotypes. The sheep antisera were largely serotype-specific in SNT, but more cross-reactive by ELISA. Rabbit antisera were more cross-reactive in SNT, and showed widespread, high titre cross-reactions against homologous and heterologous rVP2 proteins in ELISA. Results were analysed and visualised by antigenic cartography, showing closer relationships in some, but not all cases, between VP2 topotypes within the same serotype, and between serotypes belonging to the same 'VP2 nucleotype'.

Effects of an oral hydro-ethanolic purple coneflower extract on performance, clinical health and immune parameters in calves.

The objective of this randomized, placebo-controlled, double-blinded field trial was to investigate the effects of oral administration of purple coneflower (Echinacea purpurea L. (EP)) on performance, health and immune parameters in calves. Calves (n = 27) were enrolled to three groups (9 calves per group): 0.5 g EP/calf per day (ECL), 5 g EP/calf per day (ECH) or placebo. Calves were vaccinated with Bluetongue-Virus (BTV) serotype 4 vaccine to investigate EPs effects on seroconversion. Clinical and performance parameters, inter alia body weight, health and milk intake were recorded for 57 days. Blood samples were analyzed for BTV antibodies and IgG by ELISA, white and red blood cell counts by flow cytometry and mRNA abundance of various inflammatory markers in leukocytes (IL-1ß, IL-8, tumor necrosis factor α (TNFα), cyclooxygenase 2 (Cox-2) and prostaglandin E synthase) was studied. The findings demonstrated no differences between groups regarding performance parameters. In all groups, calves suffered from diarrhea for a minimum of 2 days, but EP reduced the number of diarrhea days by 44% in ECL and increased the body temperature. Interestingly, ECL resulted in an increased number of respiratory disease days during the follow-up period. EP did not change blood cell and IgG counts, whereas eosinophil granulocytes were reduced in ECL. Decreased levels of hemoglobin and hematocrit were found in ECH. Prostaglandin E synthase levels in leukocytes were higher in ECL and ECH, whereas no differences were obtained for IL-1ß, IL-8, TNFα and Cox-2. Due to the unexpected occurrence of BTV seropositive calves before the first vaccination, 13 calves were excluded from the evaluation on seroconversion and no statistical analyses could be performed regarding antibody production. BTV-4 antibodies were not produced in 4 placebo-calves, whereas 4 of 5 and 1 of 6 ECL- and ECH-calves produced antibodies. Further investigations are needed to draw final conclusions on mode of action and efficacy of EP in calves.

Plant-produced Bluetongue chimaeric VLP vaccine candidates elicit serotype-specific immunity in sheep.

Bluetongue (BT) is a hemorrhagic non-contagious, biting midge-transmitted disease of wild and domestic ruminants that is caused by bluetongue virus (BTV). Annual vaccination plays a pivotal role in BT disease control in endemic regions. Due to safety concerns of the current BTV multivalent live attenuated vaccine (LAV), a safe efficacious new generation subunit vaccine such as a plant-produced BT virus-like particle (VLP) vaccine is imperative. Previously, homogenous BTV serotype 8 (BTV-8) VLPs were successfully produced in Nicotiana benthamiana plants and provided protective immunity in sheep. In this study, combinations of BTV capsid proteins from more than one serotype were expressed and assembled to form chimaeric BTV-3 and BTV-4 VLPs in N. benthamiana plants. The assembled homogenous BTV-8, as well as chimaeric BTV-3 and chimaeric BTV-4 VLP serotypes, were confirmed by SDS-PAGE, Transmission Electron microscopy (TEM) and protein confirmation using liquid chromatography-mass spectrometry (LC-MS/MS) based peptide sequencing. As VP2 is the major determinant eliciting protective immunity, the percentage coverage and number of unique VP2 peptides detected in assembled chimaeric BT VLPs were used as a guide to assemble the most appropriate chimaeric combinations. Both plant-produced chimaeric BTV-3 and BTV-4 VLPs were able to induce long-lasting serotype-specific neutralizing antibodies equivalent to the monovalent LAV controls. Antibody levels remained high to the end of the trial. Combinations of homogenous and chimaeric BT VLPs have great potential as a safe, effective multivalent vaccine with the ability to distinguish between vaccinated and infected individuals (DIVA) due to the absence of non-structural proteins.

Production of monoclonal antibodies binding to the VP7 protein of African horse sickness virus.

Monoclonal antibodies (MAbs) against AHSV were produced by immunising BALB/c mice with AHSV serotype 9 and six clones able to recognize specifically the VP7-AHSV with a strong reactivity were selected. The specificity of the MAbs was assessed in i-ELISA against a commercial VP7-AHSV and in immunoblot against a home-made VP7-AHSV, expressed by a Baculovirus expression system; potential cross-reactions with related orbiviruses (Bluetongue virus and Epizootic Haemorrhagic Disease virus) were investigated as well. One of the six MAbs selected, MAb 7F11E14, was tested in direct immunofluorescence and reacted with all nine AHSV serotypes, but didn't cross-react with BTV and EHDV. MAb 7F11E14 was also used to develop a competitive ELISA and was able to detect AHSV antibodies in the sera of AHS infected animals.

Evaluation of an IGM-specific ELISA for early detection of bluetongue virus infections in domestic ruminants sera.

Competitive-ELISA (c-ELISA) is the most widely used serological test for the detection of Bluetongue virus (BTV) viral protein 7 (VP7) antibodies (Ab). However, these BTV c-ELISAs cannot to distinguish between IgG and IgM. IgM Ab are generated shortly after the primary immune response against an infectious agent, indicating a recent infection or exposure to antigens, such as after vaccination. Because the BTV genome or anti-VP7 Ab can be detected in ruminant blood months after infection, BTV diagnostic tools cannot discriminate between recent and old infections. In this study, we evaluated an IgM-capture ELISA prototype to detect ruminant anti-BTV VP7 IgM on 1,650 serum samples from cattle, sheep, or goats. Animals were BTV-naive, infected, or/and vaccinated with BTV-1, -2, -4, -8, -9, -16, or -27, and we also included 30 sera from cattle infected with the Epizootic haemorrhagic disease virus (EHDV) serotype 6. Results demonstrated that this ELISA kit is specific and can detect the presence of IgM with satisfactory diagnostic specificity and sensitivity from 1 to 5 weeks after BTV infection in domestic ruminants (for goats and cattle; for sheep, at least up to 24 days). The peak of anti-VP7 IgM was reached when the level of infectious viruses and BTV RNA in blood were the highest. The possibility of detecting BTV-RNA in IgM-positive sera allows the amplification and sequencing of the partial RNA segment 2 (encoding the serotype specific to VP2) to determine the causative BTV serotype/strain. Therefore, BTV IgM ELISA can detect the introduction of BTV (or EHDV) in an area with BTV-seropositive domestic animals regardless of their serological BTV status. This approach may also be of particular interest for retrospective epidemiological studies on frozen serum samples.

Multiple bluetongue virus serotypes causing death in Brazilian dwarf brocket deer (Mazama nana) in Brazil, 2015-2016.

Bela Vista Biological Sanctuary (RBV) is a protected area of Itaipu Binacional, a hydroelectric power company located on the border of Brazil and Paraguay. A captive population of Brazilian dwarf brocket deer (Mazama nana, Cervidae, Artiodactyla) is maintained for conservation purposes. Despite the reproductive success of the animals, outbreaks of a fatal hemorrhagic disease have been registered over the years, compromising conservation efforts. In order to identify the etiological agents of these hemorrhagic diseases, 32 captive Brazilian dwarf brockets were sampled to investigate bluetongue virus (BTV), epizootic hemorrhagic disease (EHD), and adenovirus hemorrhagic disease (AHD), in 2015. Only one deer (1/32; 3.12%) was seropositive for BTV. After this survey, five animals died in the early autumn of 2015 and 2016, again presenting clinical signs of hemorrhagic disease. Using RT-qPCR, RT-PCR and DNA sequencing, five BTV serotypes (3, 14, 18, 19, and 22) were identified in blood and tissues collected during necropsies. These BTV serotypes had not been previously described or isolated in Brazil, either in wild or domestic ruminants. Additionally, differential diagnosis was performed for EHD and AHD, but all samples were negative for both diseases. The multiple distinct BTV serotypes identified in these outbreaks resulted in a high lethality (100%) of Brazilian dwarf brockets and indicated that various BTV serotypes are circulating in the area.

Seroprevalence of Bluetongue Virus in small ruminants in Balochistan province, Pakistan.

Bluetongue (BT), caused by bluetongue virus (BTV), is a vector-borne disease of small ruminants that has the potential to spread across international borders. Despite large populations of susceptible animals and borders with BTV endemic countries, little is known of the disease burden and prevalent serotypes in the province of Balochistan in Pakistan. We conducted a cross-sectional study to determine seroconversion and prevalent serotypes in selected districts of the province using a competitive enzyme-linked immunosorbent assay (cELISA) and real-time polymerase chain reaction (RT-PCR). Sera (n = 876) were collected from clinically healthy sheep and goats originating from the districts of Quetta (n = 300), Mastung (n = 201), Killa Saifullah (n = 75) and Kech (n = 300). None of the study herds (n = 97) were seronegative for BTV, and at the individual level, the overall prevalence of BTV seroconversion was 47.26% (n = 414/876, 95% CI = 43.92%-50.63%). A higher percentage of goats (50.87%, 95% CI = 45.99%-55.73%) were seropositive for anti-VP7 immunoglobulins (IgG) than sheep (44.21%, 95% CI = 39.81%-48.70%). Odds ratios of seroconversion for goats were associated with breed type (χ2  = 16.84, p = .01), parity (χ2  = 23.66, p = .00) and presence of vector (χ2  = 2.63, p = .10), whereas for sheep, it was associated with breed type (χ2  = 13.80, p = .01) and parity (χ2  = 53.40, p = .00). Serotype 8 was the most prevalent (26.82%, 95% CI = 14.75%-43.21%) followed by an equal prevalence of serotypes 2 and 9 (7.31%, 95% CI = 1.91%-21.01%). To the best of our knowledge, this is the first study conducted in Balochistan province and the results indicate that there is a necessity to initiate intervention strategies to control BT disease burden not only in this region of Pakistan but also in adjacent areas of the neighbouring countries, Iran and Afghanistan.

Microspheres-prime/rMVA-boost vaccination enhances humoral and cellular immune response in IFNAR(-/-) mice conferring protection against serotypes 1 and 4 of bluetongue virus.

Bluetongue virus (BTV) is the causative agent of bluetongue disease (BT), which affects domestic and wild ruminants. At the present, 27 different serotypes have been documented. Vaccination has been demonstrated as one of the most effective methods to avoid viral dissemination. To overcome the drawbacks associated with the use of inactivated and attenuated vaccines we engineered a new recombinant BTV vaccine candidate based on proteins VP2, VP7, and NS1 of BTV-4 that were incorporated into avian reovirus muNS-Mi microspheres (MS-VP2/VP7/NS1) and recombinant modified vaccinia virus Ankara (rMVA). The combination of these two antigen delivery systems in a heterologous prime-boost vaccination strategy generated significant levels of neutralizing antibodies in IFNAR(-/-) mice. Furthermore, this immunization strategy increased the ratio of IgG2a/IgG1 in sera, indicating an induction of a Th1 response, and elicited a CD8 T cell response. Immunized mice were protected against lethal challenges with the homologous serotype 4 and the heterologous serotype 1 of BTV. All these results support the strategy based on microspheres in combination with rMVAs as a promising multiserotype vaccine candidate against BTV.

Analysis of the three-dimensional structure of the African horse sickness virus VP7 trimer by homology modelling.

VP7 is the major core protein of orbiviruses and is essential for virion assembly. African horse sickness virus (AHSV) VP7 self-assembles into highly insoluble crystalline particles - an attribute that may be related to the role of AHSV VP7 in virus assembly but also prevents crystallization. Given that this inherent insolubility is unique to AHSV VP7, we use amino acid sequence conservation analysis between AHSV VP7 and other orbiviruses to identify putative key residues that drive AHSV VP7 self-assembly. A homology model of the AHSV VP7 trimer was generated to analyze surface properties of the trimer and to identify surface residues as candidates for the AHSV VP7 trimer-trimer interactions that drive AHSV VP7 self-assembly. Nine regions were identified as candidate residues for future site-directed mutagenesis experiments that will likely result in a soluble AHSV VP7 protein. Additionally, we identified putative residues that function in the intermolecular interactions within the AHSV VP7 trimer as well as several epitopes. Given the many previous efforts of solubilizing AHSV VP7, we propose a useful strategy that will yield a soluble AHSV VP7 that can be used to study AHSV assembly and increase yield of recombinant vaccine preparations.

A competitive ELISA for detection of group specific antibody to bluetongue virus using anti-core antibody.

Bluetongue virus (BTV) is transmitted by biting midges, which infects domestic and wild ruminants. In present study, a competitive enzyme-linked immunosorbent assay (C-ELISA) for the detection of serogroup-specific antibodies against VP7 protein of BTV has been developed. The assay measures the competition between a group specific antibody against core protein of BTV and a test serum to an optimized concentration of BTV recombinant-VP7 (r-VP7) antigen. Serum samples (n = 895) collected from small and large ruminants were used to optimize the C-ELISA. Percent inhibition (PI) values were used for estimation of the cut-off value for the C-ELISA. On receiver operator characteristic (ROC) analysis, different cut-off values along with their diagnostic sensitivity (DSn) and diagnostic specificity (DSp) were obtained. Among these, >50% PI value was accepted as cut-off at which DSn and Dsp was achieved as 97.6% and 98.0% respectively, at >95% confidence interval. Results show the present C-ELISA assay described to be sensitive, specific and reliable and could be adopted for serological investigation of small and large ruminants.

Development of a Double-Antigen Microsphere Immunoassay for Simultaneous Group and Serotype Detection of Bluetongue Virus Antibodies.

Bluetongue viruses (BTV) are arboviruses responsible for infections in ruminants. The confirmation of BTV infections is based on rapid serological tests such as enzyme-linked immunosorbent assays (ELISAs) using the BTV viral protein 7 (VP7) as antigen. The determination of the BTV serotype by serological analyses could be only performed by neutralization tests (VNT) which are time-consuming and require BSL3 facilities. VP2 protein is considered the major serotype-defining protein of BTV. To improve the serological characterization of BTV infections, the recombinant VP7 and BTV serotype 8 (BTV-8) VP2 were synthesized using insect cells expression system. The purified antigens were covalently bound to fluorescent beads and then assayed with 822 characterized ruminant sera from BTV vaccinations or infections in a duplex microsphere immunoassay (MIA). The revelation step of this serological duplex assay was performed with biotinylated antigens instead of antispecies conjugates to use it on different ruminant species. The results demonstrated that MIA detected the anti-VP7 antibodies with a high specificity as well as a competitive ELISA approved for BTV diagnosis, with a better efficiency for the early detection of the anti-VP7 antibodies. The VP2 MIA results showed that this technology is also an alternative to VNT for BTV diagnosis. Comparisons between the VP2 MIA and VNT results showed that VNT detects the anti-VP2 antibodies in an early stage and that the VP2 MIA is as specific as VNT. This novel immunoassay provides a platform for developing multiplex assays, in which the presence of antibodies against multiple BTV serotypes can be detected simultaneously.

Follicular dendritic cell disruption as a novel mechanism of virus-induced immunosuppression.

Arboviruses cause acute diseases that increasingly affect global health. We used bluetongue virus (BTV) and its natural sheep host to reveal a previously uncharacterized mechanism used by an arbovirus to manipulate host immunity. Our study shows that BTV, similarly to other antigens delivered through the skin, is transported rapidly via the lymph to the peripheral lymph nodes. Here, BTV infects and disrupts follicular dendritic cells, hindering B-cell division in germinal centers, which results in a delayed production of high affinity and virus neutralizing antibodies. Moreover, the humoral immune response to a second antigen is also hampered in BTV-infected animals. Thus, an arbovirus can evade the host antiviral response by inducing an acute immunosuppression. Although transient, this immunosuppression occurs at the critical early stages of infection when a delayed host humoral immune response likely affects virus systemic dissemination and the clinical outcome of disease.

Immunogenicity and protective efficacy of recombinant major envelope protein (rH3L) of buffalopox virus in animal models.

Buffalopox virus, a zoonotic Indian vaccinia-like virus, is responsible for contagious disease affecting mainly buffaloes, cattle and humans. H3L gene, encoding for an immunodominant major envelope protein of intracellular mature virion of orthopoxviruses, is highly conserved and found to elicit neutralizing antibodies. Therefore in the present study, the immunogenicity and protective efficacy of the recombinant H3L protein of buffalopox virus in laboratory animal models has been evaluated. A partial H3L gene encoding for the C-terminal truncated ectodomain of H3L protein (1M to I280) of BPXV-Vij/96 strain was cloned, over-expressed and purified as histidine-tagged fusion protein (50 kDa) from Escherichia coli using Ni-NTA affinity chromatography. The purified rH3L protein was further used for active immunization of guinea pig (250 µg/dose) and adult mice (10 µg and 50 µg/dose) with or without adjuvants (alum, Freund's Complete Adjuvant and CpG). Subsequently, a gradual increase in antigen specific serum IgG as well as neutralizing antibody titres measured by using indirect-ELISA and serum neutralization test respectively, was noted in both guinea pigs and mouse models. Suckling mice immunized passively with anti-H3L serum showed 80% pre-exposure prophylaxis upon challenge with virulent buffalopox virus strain. An indirect-ELISA based on rH3L protein showed no cross-reactivity with hyperimmune sera against sheeppox virus (SPPV), goatpox virus (GTPV), orf virus (ORFV), foot- and- mouth disease virus (FMDV), peste des petits ruminants virus (PPRV) and bluetongue virus (BTV) during the course of study. The study highlights the potential utility of rH3L protein as a safer prophylactic and diagnostic reagent for buffalopox.

Generation of Recombinant Modified Vaccinia Virus Ankara Encoding VP2, NS1, and VP7 Proteins of Bluetongue Virus.

Modified Vaccinia Virus Ankara (MVA) is employed widely as an experimental vaccine vector for its lack of replication in mammalian cells and high expression level of foreign/heterologous genes. Recombinant MVAs (rMVAs) are used as platforms for protein production as well as vectors to generate vaccines against a high number of infectious diseases and other pathologies. The portrait of the virus combines desirable elements such as high-level biological safety, the ability to activate appropriate innate immune mediators upon vaccination, and the capacity to deliver substantial amounts of heterologous antigens. Recombinant MVAs encoding proteins of bluetongue virus (BTV), an Orbivirus that infects domestic and wild ruminants transmitted by biting midges of the Culicoides species, are excellent vaccine candidates against this virus. In this chapter we describe the methods for the generation of rMVAs encoding VP2, NS1, and VP7 proteins of bluetongue virus as a model example for orbiviruses. The protocols included cover the cloning of VP2, NS1, and VP7 BTV-4 genes in a transfer plasmid, the construction of recombinant MVAs, the titration of virus working stocks and the protein expression analysis by immunofluorescence and radiolabeling of rMVA infected cells as well as virus purification.

Preparation and Characterization of a Monoclonal Antibody Against the Core Protein VP7 of the 25th Serotype of Bluetongue Virus.

Bluetongue virus (BTV) is a member of the genus Orbivirus, within the family Reoviridae. The VP7 protein of BTV is used for developing group-specific serological assays. To prepare monoclonal antibody (MAb) against VP7 of the 25th serotype BTV, the RNA S7 encoding VP7 was cloned into prokaryotic expression vectors pET-28a (+) and pGEX-6P-1 to generate recombinant plasmids. The recombinant protein VP7 was expressed in Escherichia coli BL21 (DE3), respectively. The results of SDS-PAGE revealed that the VP7 was expressed and the molecular mass of recombinant fusion protein pET-28a (+)/VP7 and pGEX-6P-1/VP7 was approximately 44 kDa and 64 kDa, respectively. The Western blot analysis indicated that the recombinant VP7 possessed good immunoreactivity. After purification, pET-28a (+)/VP7 was used to immunize BALB/c mice, while pGEX-6P-1/VP7 was used to screen for well-to-well MAb-secreting hybridomas. The hybridoma cell line 3H7 against recombinant VP7 that secreted MAbs was obtained. The isotype of 3H7 was identified as IgG1. The purification of recombinant VP7 protein and the monoclonal antibody will have potential applications on competitive ELISA format for BT-specific serum detection method.

Comparative analysis of cellular immune responses and cytokine levels in sheep experimentally infected with bluetongue virus serotype 1 and 8.

Protective immunity in sheep with bluetongue virus (BTV) infection as well as the role of BTV-induced cytokines during immune response remains unclear. Understanding the basis immunological mechanisms in sheep experimentally infected with serotypes 1 and 8 (BTV-1 and -8) was the aim of this study. A time-course study was carried out in order to evaluate cell-mediated immune response and serum concentrations of cytokines (IL-1ß, TNFα, IL-12, IFNγ, IL-4 and IL-10) with inflammatory and immunological functions. Depletion of T cell subsets (mainly CD4(+), γδ and CD25(+)) together with the absence of cytokines (IFNγ and IL-12) involved in the regulation of cell-mediated antiviral immunity at the first stage of the disease suggested that both BTV-1 and BTV-8 might impair host's capability against primary infections which would favor viral replication and spreading. However, cellular immune response and cytokines elicited an immune response in sheep that efficiently reduced viremia in the final stage of the experiment. Recovery of T cell subsets (CD4(+) and CD25(+)) together with a significant increase of CD8(+) T lymphocytes in both infected groups were observed in parallel with the decrease of viremia. Additionally, the recovery of CD4(+) T lymphocytes together with the significant increase of IL-4 serum levels at the final stage of the experiment might contribute to humoral immune response activation and neutralizing antibodies production against BTV previously described in the course of this experiment. These results suggested that both cellular and humoral immune response may contribute to protective immunity against BTV-1 and BTV-8 in sheep. The possible role played by IL-10 and CD25(+) cells in controlling inflammatory and immune response in the final stage of the experiment has also been suggested.

Isolation of a Bluetongue virus group-specific monoclonal antibody and application to a diagnostic competitive ELISA.

The Bluetongue virus (BTV) VP7 protein represents an important group-specific antigen that can serve as a basis for diagnostic tests. Here, we report the generation of a novel BTV group-specific monoclonal antibody (Mab; herein named 4H7) that recognizes a conformational epitope in the VP7 protein. We used a phage-displayed peptide screen and site-directed mutagenesis to define the VP7 amino acid residues that most strongly contribute to the conformational epitope recognized by Mab 4H7. Amino acid residues at positions 175, 185, 186, and 278 of the BTV VP7 protein strongly contributed to Mab 4H7 binding. These key amino acid residues are conserved among all BTV serotypes, whereas related Orbiviruses possess at least one amino acid substitution at these positions. We developed a competitive enzyme-linked immunosorbent assay (c-ELISA) using Mab 4H7 and recombinant BTV VP7 protein to detect serum antibodies against this BTV group-specific VP7 epitope. The c-ELISA was used to screen 833 clinical samples collected from animals in three provinces of China. BTV seroprevalence in the three provinces ranged from 25.42 to 47.45 %. This work provides the foundation for a new diagnostic c-ELISA that can be further applied to BTV surveillance activities and informs our understanding of the structure of the BTV VP7 protein.

Expression of VP7, a Bluetongue virus group specific antigen by viral vectors: analysis of the induced immune responses and evaluation of protective potential in sheep.

Bluetongue virus (BTV) is an economically important Orbivirus transmitted by biting midges to domestic and wild ruminants. The need for new vaccines has been highlighted by the occurrence of repeated outbreaks caused by different BTV serotypes since 1998. The major group-reactive antigen of BTV, VP7, is conserved in the 26 serotypes described so far, and its role in the induction of protective immunity has been proposed. Viral-based vectors as antigen delivery systems display considerable promise as veterinary vaccine candidates. In this paper we have evaluated the capacity of the BTV-2 serotype VP7 core protein expressed by either a non-replicative canine adenovirus type 2 (Cav-VP7 R0) or a leporipoxvirus (SG33-VP7), to induce immune responses in sheep. Humoral responses were elicited against VP7 in almost all animals that received the recombinant vectors. Both Cav-VP7 R0 and SG33-VP7 stimulated an antigen-specific CD4+ response and Cav-VP7 R0 stimulated substantial proliferation of antigen-specific CD8+ lymphocytes. Encouraged by the results obtained with the Cav-VP7 R0 vaccine vector, immunized animals were challenged with either the homologous BTV-2 or the heterologous BTV-8 serotype and viral burden in plasma was followed by real-time RT-PCR. The immune responses triggered by Cav-VP7 R0 were insufficient to afford protective immunity against BTV infection, despite partial protection obtained against homologous challenge. This work underscores the need to further characterize the role of BTV proteins in cross-protective immunity.