The immune response of ruminant livestock to bluetongue virus: From type I interferon to antibody

Bluetongue virus seroprevalence and risk factor analysis in cattle and water buffalo in southern Italy (Campania region)

Bluetongue is an arthropod-borne viral infection that is notifiable in several countries and causes significant economic losses and major concerns for ruminant trade. In this study, we investigated bluetongue 1seroprevalence in the Campania region, southern Italy, in cattle and buffalo populations, and assessed which factors were correlated with a high risk of exposure. The infection was widespread, as evidenced by the high individual (43.6%) and herd prevalence (85.4%). The highest prevalence was found in adult animals. Among the climatic factors analyzed, average temperature played a prominent role, being capable of affecting the probability of being positive for this infection. Surprisingly, exposure to Schmallenberg virus did not predispose animals to be positive for bluetongue virus, even though these infections share the same vector (Culicoides). Our data, consistent with those in the literature, suggest the transversal spread of bluetongue virus in the Mediterranean area, and indicate a limited co-exposure rate between Bluetongue and Schmallenberg viruses.

Monitoring longitudinal immunological responses to bluetongue virus 17 in experimentally infected sheep

Bluetongue virus (BTV) is an economically important pathogen of ruminant species with worldwide prevalence. While many BTV infections are asymptomatic, animals with symptomatic presentation deteriorate quickly with the sickest succumbing to disease within one week. Animals that survive the infection often require months to recover. The immune response to BTV infection is thought to play a central role in controlling the disease. Key to understanding BTV disease is profiling vertebrate host immunological cellular and cytokine responses. Studies to characterize immune responses in ruminants have been limited by a lack of species-specific reagents and assay technology. Here we assess the longitudinal immunological response to experimental BTV-17-California (CA) infection in sheep using the most up to date assays. We infected a cohort of sheep with BTV-17-CA and longitudinally monitored each animal for clinical disease, viremia and specific immunological parameters (B cells, T cells, monocytes) by RT-qPCR, traditional flow cytometry and/or fluorescent based antibody arrays. BTV-inoculated sheep exhibited clinical signs characteristic of bluetongue virus disease. Circulating virus was demonstrated after 8 days post inoculation (DPI) and remained detectable for the remainder of the time course (24 DPI). A distinct lymphopenia was observed between 7 and 14 DPI that rebounded to mock-inoculated control levels at 17 DPI. In addition, we observed increased expression of pro-inflammatory cytokines after 8 DPI. Taken together, we have established a model of BTV infection in sheep and have successfully monitored the longitudinal vertebrate host immunological response and viral infection progression using a combination of traditional methods and cutting-edge technology.

Pathological features of African horse sickness virus infection in IFNAR-/- mice

African Horse Sickness (AHS) is a vector-borne viral disease of equids. The disease can be highly lethal with mortality rates of up to 90% in non-immune equine populations. The clinical presentation in the equine host varies, but the pathogenesis underlying this variation remains incompletely understood. Various small animal models of AHS have been developed over the years to overcome the financial, bio-safety and logistical constraints of studying the pathology of this disease in the target species. One of the most successful small animal models is based on the use of interferon-alpha gene knock-out (IFNAR^-/-) mice. In order to increase our understanding of African Horse Sickness virus (AHSV) pathogenesis, we characterised the pathology lesions of AHSV infection in IFNAR^-/- mice using a strain of AHSV serotype 4 (AHSV-4). We found AHSV-4 infection was correlated with lesions in various organs; necrosis in the spleen and lymphoid tissues, inflammatory infiltration in the liver and brain, and pneumonia. Significant viral antigen staining was only detected in the spleen and brain, however. Together these results confirm the value of the IFNAR^-/- mouse model for the study of the immuno-biology of AHSV infections in this particular in vivo system, and its usefulness for evaluating protective efficacy of candidate vaccines in preclinical studies.

Serological and molecular prevalence study of bluetongue virus in small domestic ruminants in Morocco

Bluetongue is an arthropod-borne viral disease transmitted by Culicoides biting midges, affecting domestic and wild ruminants. The current study aims to assess the seroprevalence of the bluetongue virus (BTV) and confirm its active circulation among sheep and goats populations in Morocco, as well as study the risk factors associated with BTV infection. To this end, a total of 1651 samples were randomly collected from 1376 sheep and 275 goats in eight (out of 12) regions of the country between March 2018 and July 2021.These samples were primarily tested using competitive ELISA (c-ELISA). Subsequently, 65% of c-ELISA positives (n = 452) were analyzed by real-time reverse transcription-polymerase chain reaction (RT-qPCR). The results revealed an overall BTV seroprevalence in small ruminants in Morocco of 41.7%, including 42.6% in sheep and 37.5% in goats. The RT-qPCR results showed that the overall BTV viropositivity rate was 46.7%, including 48.1% in sheep and 41.8% in goats. These viro-serological rates varied significantly by age, sex, and breed of the tested animals, husbandry method, season, and geographic origin. This indicates that these parameters constitute risk factors for BTV transmission routes in Morocco. The findings also indicate that goats play a role as reservoirs in maintaining the BTV in Morocco. It appears from this study that bluetongue is endemic in Morocco. The environmental and climate conditions as well as the husbandry methods adopted in the country are particularly favorable for the virus transmission throughout the country.

An updated review on bluetongue virus: epidemiology, pathobiology, and advances in diagnosis and control with special reference to India

Bluetongue (BT) is an economically important, non-contagious viral disease of domestic and wild ruminants. BT is caused by BT virus (BTV) and it belongs to the genus Orbivirus and family Reoviridae. BTV is transmitted by Culicoides midges and causes clinical disease in sheep, white-tailed deer, pronghorn antelope, bighorn sheep, and subclinical manifestation in cattle, goats and camelids. BT is a World Organization for Animal Health (OIE) listed multispecies disease and causes great socio-economic losses. To date, 28 serotypes of BTV have been reported worldwide and 23 serotypes have been reported from India. Transplacental transmission (TPT) and fetal abnormalities in ruminants had been reported with cell culture adopted live-attenuated vaccine strains of BTV. However, emergence of BTV-8 in Europe during 2006, confirmed TPT of wild-type/field strains of BTV. Diagnosis of BT is more important for control of disease and to ensure BTV-free trade of animals and their products. Reverse transcription polymerase chain reaction, agar gel immunodiffusion assay and competitive enzyme-linked immunosorbent assay are found to be sensitive and OIE recommended tests for diagnosis of BTV for international trade. Control measures include mass vaccination (most effective method), serological and entomological surveillance, forming restriction zones and sentinel programs. Major hindrances with control of BT in India are the presence of multiple BTV serotypes, high density of ruminant and vector populations. A pentavalent inactivated, adjuvanted vaccine is administered currently in India to control BT. Recombinant vaccines with DIVA strategies are urgently needed to combat this disease. This review is the first to summarise the seroprevalence of BTV in India for 40 years, economic impact and pathobiology.

The Interplay between Bluetongue Virus Infections and Adaptive Immunity

Viral infections have long provided a platform to understand the workings of immunity. For instance, great strides towards defining basic immunology concepts, such as MHC restriction of antigen presentation or T-cell memory development and maintenance, have been achieved thanks to the study of lymphocytic choriomeningitis virus (LCMV) infections. These studies have also shaped our understanding of antiviral immunity, and in particular T-cell responses. In the present review, we discuss how bluetongue virus (BTV), an economically important arbovirus from the Reoviridae family that affects ruminants, affects adaptive immunity in the natural hosts. During the initial stages of infection, BTV triggers leucopenia in the hosts. The host then mounts an adaptive immune response that controls the disease. In this work, we discuss how BTV triggers CD8⁺ T-cell expansion and neutralizing antibody responses, yet in some individuals viremia remains detectable after these adaptive immune mechanisms are active. We present some unpublished data showing that BTV infection also affects other T cell populations such as CD4⁺ T-cells or γδ T-cells, as well as B-cell numbers in the periphery. This review also discusses how BTV evades these adaptive immune mechanisms so that it can be transmitted back to the arthropod host. Understanding the interaction of BTV with immunity could ultimately define the correlates of protection with immune mechanisms that would improve our knowledge of ruminant immunology.

Virulent African horse sickness virus serotype 4 interferes with the innate immune response in horse peripheral blood mononuclear cells in vitro

African horse sickness (AHS) is caused by African horse sickness virus (AHSV), a double stranded RNA (dsRNA) virus of the genus Orbivirus, family Reoviridae. For the development of new generation AHS vaccines or antiviral treatments, it is crucial to understand the host immune response against the virus and the immune evasion strategies the virus employs. To achieve this, the current study used transcriptome analysis of RNA sequences to characterize and compare the innate immune responses activated during the attenuated AHSV serotype 4 (attAHSV4) (in vivo) and the virulent AHSV4 (virAHSV4) (in vitro) primary and secondary immune responses in horse peripheral blood mononuclear cells (PBMC) after 24 h. The pro-inflammatory cytokine and chemokine responses were negatively regulated by anti-inflammatory cytokines, whereas the parallel type I and type III IFN responses were maintained downstream of nucleic acid sensing pattern recognition receptor (PRR) signalling pathways during the attAHSV4 primary and secondary immune responses. It appeared that after translation, virAHSV4 proteins were able to interfere with the C-terminal IRF association domain (IAD)-type 1 (IAD1) containing IRFs, which inhibited the expression of type I and type III IFNs downstream of PRR signalling during the virAHSV4 primary and secondary immune responses. Viral interference resulted in an impaired innate immune response that was not able to eliminate virAHSV4-infected PBMC and gave rise to prolonged expression of pro-inflammatory cytokines and chemokines during the virAHSV4 induced primary immune response. Indicating that virAHSV4 interference with the innate immune response may give rise to an excessive inflammatory response that causes immunopathology, which could be a major contributing factor to the pathogenesis of AHS in a naïve horse. Viral interference was overcome by the fast kinetics and increased effector responses of innate immune cells due to trained innate immunity and memory T cells and B cells during the virAHSV4 secondary immune response.

The Tip Region on VP2 Protein of Bluetongue Virus Contains Potential IL-4-Inducing Amino Acid Peptide Segments

Bluetongue is an infectious viral hemorrhagic disease of domestic and wild ruminants that has a considerable economic impact on domestic ruminants. There are currently at least 29 serotypes of bluetongue virus (BTV) in the world. Noteworthily, the pathogenesis among BTV serotypes is different, even in the same animal species. In this study, BTV2/KM/2003 and BTV12/PT/2003 were used to investigate the differential immunological effects on bovine peripheral blood mononuclear cells (PBMCs). The BTV viral load and the expression of cytokine messenger RNA (mRNA) in PBMCs were measured by fluorescence-based real-time reverse-transcription PCR (qRT-PCR). The immunofluorescence assay (IFA) was applied to detect BTV signals in monocyte-derived macrophages (MDMs). The SWISS-MODEL and IL-4pred prediction tools were used to predict the interleukin 4 (IL-4)-inducing peptides in BTV-coat protein VP2. Synthetic peptides of VP2 were used to stimulate PBMCs for IL-4-inducing capability. This study demonstrated that the cytokine profiles of BTV-induced PBMCs were significantly different between BTV2/KM/2003 and BTV12/PT/2003. BTV2 preferentially activated the T helper 2 (Th2) pathway, represented by the early induction of IL-4, and likely fed back to inhibit the innate immunity. In contrast, BTV12 preferentially activated the innate immunity, represented by the induction of tumor necrosis factor -α (TNF-α) and interleukin 1 (IL-1), with only minimal subsequent IL-4. The BTV nonstructural protein 3 antibody (anti-BTV-NS3) fluorescent signals demonstrated that monocytes in PBMCs and MDMs were the preferred targets of BTV replication. Bioinformatics analysis revealed that the capability to induce IL-4 was attributed to the tip region of the VP2 protein, wherein a higher number of predicted peptide segments on BTVs were positively correlated with the allergic reaction reported in cattle. Synthetic peptides of BTV2-VP2 induced significant IL-4 within 12-24 h post-infection (hpi) in PBMCs, whereas those of BTV12 did not, consistent with the bioinformatics prediction. Bovine PBMCs and synthetic peptides together seem to serve as a good model for pursuing the BTV-induced IL-4 activity that precedes the development of an allergic reaction, although further optimization of the protocol is warranted.

Isolation and Cultivation of a New Isolate of BTV-25 and Presumptive Evidence for a Potential Persistent Infection in Healthy Goats

Recently, several so-called “atypical” Bluetongue virus (BTV) serotypes were discovered, including BTV-25 (Toggenburg virus), in Switzerland. Most “atypical” BTV were identified in small ruminants without clinical signs. In 2018, two goats from a holding in Germany tested positive for BTV-25 genome by RT-qPCR prior to export. After experimental inoculation of the two goats with the BTV-25 positive field blood samples for generation of reference materials, viremia could be observed in one animal. For the first time, the BTV-25-related virus was isolated in cell culture from EDTA-blood and the full genome of isolate “BTV-25-GER2018” could be generated. BTV-25-GER2018 was only incompletely neutralized by ELISA-positive sera. We could monitor the BTV-25 occurrence in the respective affected goat flock of approximately 120 goats over several years. EDTA blood samples were screened with RT-qPCR using a newly developed BTV-25 specific assay. For serological surveillance, serum samples were screened using a commercial cELISA. BTV-25-GER2018 was detected over 4.5 years in the goat flock with intermittent PCR-positivity in some animals, and with or without concomitantly detected antibodies since 2015. We could demonstrate the viral persistence of BTV-25-GER2018 in goats for up to 4.5 years, and the first BTV-25 isolate is now available for further characterization.

Ovine viperin inhibits bluetongue virus replication

Viral infections can lead to interferon production, which achieves its antiviral function primarily by activating the JAK/STAT pathway and inducing multiple interferon-stimulated genes (ISGs). Although considerable ISGs have been identified in antiviral researches, little is known about ISGs in bluetongue virus (BTV) infection. Viperin is the most highly induced ISG following BTV infection, which suggests that it may play a critical role in the anti-BTV immune response. The aim of this study was to characterize ovine Viperin (oViperin) and explore whether it can inhibit BTV replication. We cloned the coding sequences (CDS) of sheep Viperin, and the sequence analysis showed that oViperin displayed a high similarity with other species. oViperin has a leucine zipper in the N-terminal, a CxxxCxxC motif in the SAM domain, and a conservative C-terminus. We found that oViperin mRNA expression was significantly up-regulated in a time- and multiplicity of infection (MOI)-dependent manner following BTV infection. oViperin overexpression resulted in a significant inhibition in BTV replication, whereas an oViperin knockdown in MDOK cells increased BTV replication. This study shows for the first time, that oViperin has antiviral activity towards BTV infection and provides important information to research the interaction between BTV and oViperin.

Ecological Dynamics Impacting Bluetongue Virus Transmission in North America

Bluetongue virus (BTV) is an arbovirus transmitted to domestic and wild ruminants by certain species of Culicoides midges. The disease resulting from infection with BTV is economically important and can influence international trade and movement of livestock, the economics of livestock production, and animal welfare. Recent changes in the epidemiology of Culicoides-transmitted viruses, notably the emergence of exotic BTV genotypes in Europe, have demonstrated the devastating economic consequences of BTV epizootics and the complex nature of transmission across host-vector landscapes. Incursions of novel BTV serotypes into historically enzootic countries or regions, including the southeastern United States (US), Israel, Australia, and South America, have also occurred, suggesting diverse pathways for the transmission of these viruses. The abundance of BTV strains and multiple reassortant viruses circulating in Europe and the US in recent years demonstrates considerable genetic diversity of BTV strains and implies a history of reassortment events within the respective regions. While a great deal of emphasis is rightly placed on understanding the epidemiology and emergence of BTV beyond its natural ecosystem, the ecological contexts in which BTV maintains an enzootic cycle may also be of great significance. This review focuses on describing our current knowledge of ecological factors driving BTV transmission in North America. Information presented in this review can help inform future studies that may elucidate factors that are relevant to longstanding and emerging challenges associated with prevention of this disease.

Evidence of reduced viremia, pathogenicity and vector competence in a re-emerging European strain of bluetongue virus serotype 8 in sheep

The outbreak of bluetongue virus (BTV) serotype 8 (BTV-8) during 2006-2009 in Europe was the most costly epidemic of the virus in recorded history. In 2015, a BTV-8 strain re-emerged in France which has continued to circulate since then. To examine anecdotal reports of reduced pathogenicity and transmission efficiency, we investigated the infection kinetics of a 2007 UK BTV-8 strain alongside the re-emerging BTV-8 strain isolated from France in 2017. Two groups of eight BTV-naïve British mule sheep were inoculated with 5.75 log₁₀ TCID₅₀ /ml of either BTV-8 strain. BTV RNA was detected by 2 dpi in both groups with peak viraemia occurring between 5-9 dpi. A significantly greater amount of BTV RNA was detected in sheep infected with the 2007 strain (6.0-8.8 log₁₀ genome copies/ml) than the re-emerging BTV-8 strain (2.9-7.9 log₁₀ genome copies/ml). All infected sheep developed BTV-specific antibodies by 9 dpi. BTV was isolated from 2 dpi to 12 dpi for 2007 BTV-8-inoculated sheep and from 5 to 10 dpi for sheep inoculated with the remerging BTV-8. In Culicoides sonorensis feeding on the sheep over the period 7-12 dpi, vector competence was significantly higher for the 2007 strain than the re-emerging strain. Both the proportion of animals showing moderate (as opposed to mild or no) clinical disease (6/8 vs. 1/8) and the overall clinical scores (median 5.25 vs. 3) were significantly higher in sheep infected with the 2007 strain, compared to those infected with the re-emerging strain. However, one sheep infected with the re-emerging strain was euthanized at 16 dpi having developed severe lameness. This highlights the potential of the re-emerging BTV-8 to still cause illness in naïve ruminants with concurrent costs to the livestock industry.

Acute Phase Protein Levels as An Auxiliary Tool in Diagnosing Viral Diseases in Ruminants-A Review

We examined acute phase protein (APP) concentrations in viral infections of dairy ruminants and assessed the potential role of characteristic patterns of APP changes in auxiliary diagnosing viral diseases. All viruses reviewed are common causes of farm animal diseases. APPs are among the first agents of immunity, and their concentrations could be diagnostically relevant. In the most common ruminant viral diseases, elevated serum amyloid A (SAA) and haptoglobin (Hp) levels in blood serum have been observed. However, since these proteins are the main APPs in many viral infections, it is impossible to use their levels for diagnosing particular infections. Decreased Cp and albumin expression could help differentiate the bluetongue virus infection from other diseases. Lastly, analysis of SAA levels in blood serum and milk could be helpful in diagnosing small ruminant lentivirus infection. While promising, APP levels can only be considered as an auxiliary tool in diagnosing viral diseases in ruminants.

A review of potential bluetongue virus vaccine strategies

Bluetongue (BT) is an economically important, non-zoonotic arboviral disease of certain wild and domestic species of cloven-hooved ungulates. Bluetongue virus (BTV) is the causative agent and the occurrence of BTV infection is distinctly seasonal in temperate regions of the world, and dependent on the presence of vector biting midges (e.g. Culicoides sonorensis in much of North America). In recent years, severe outbreaks have occurred throughout Europe and BTV is endemic in most tropical and temperate regions of the world. Several vaccines have been licensed for commercial use, including modified live (live-attenuated) and inactivated products, and this review summarizes recent strategies developed for BTV vaccines with emphasis on technologies suitable for differentiating naturally infected from vaccinated animals. The goal of this review is to evaluate realistic vaccine strategies that might be utilized to control or prevent future outbreaks of BT.

Transcriptome analysis reveals common differential and global gene expression profiles in bluetongue virus serotype 16 (BTV-16) infected peripheral blood mononuclear cells (PBMCs) in sheep and goats

Bluetongue is an economically important infectious, arthropod borne viral disease of domestic and wild ruminants, caused by Bluetongue virus (BTV). Sheep are considered the most susceptible hosts, while cattle, buffalo and goats serve as reservoirs. The viral pathogenesis of BTV resulting in presence or absence of clinical disease among different hosts is not clearly understood. In the present study, transcriptome of sheep and goats peripheral blood mononuclear cells infected with BTV-16 was explored. The differentially expressed genes (DEGs) identified were found to be significantly enriched for immune system processes - NFκB signaling, MAPK signaling, Ras signaling, NOD signaling, RIG signaling, TNF signaling, TLR signaling, JAK-STAT signaling and VEGF signaling pathways. Greater numbers of DEGs were found to be involved in immune system processes in goats than in sheep. Interestingly, the DEHC (differentially expressed highly connected) gene network was found to be dense in goats than in sheep. Majority of the DEHC genes in the network were upregulated in goats but down-regulated in sheep. The network of differentially expressed immune genes with the other genes further confirmed these findings. Interferon stimulated genes - IFIT1 (ISG56), IFIT2 (ISG54) and IFIT3 (ISG60) responsible for antiviral state in the host were found to be upregulated in both the species. STAT2 was the TF commonly identified to co-regulate the DEGs, with its network showing genes that are downregulated in sheep but upregulated in goats. The genes dysregulated and the networks perturbed in the present study indicate host variability with a positive shift in immune response to BTV in goats than in sheep.

A Review of Knowledge Gaps and Tools for Orbivirus Research

Although recognized as causing emerging and re-emerging disease outbreaks worldwide since the late 1800 s, there has been growing interest in the United States and Europe in recent years in orbiviruses, their insect vectors, and the diseases they cause in domestic livestock and wildlife. This is due, in part, to the emergence of bluetongue (BT) in northern Europe in 2006-2007 resulting in a devastating outbreak, as well as severe BT outbreaks in sheep and epizootic hemorrhagic disease (EHD) outbreaks in deer and cattle in the United States. Of notable concern is the isolation of as many as 10 new BT virus (BTV) serotypes in the United States since 1999 and their associated unknowns, such as route of introduction, virulence to mammals, and indigenous competent vectors. This review, based on a gap analysis workshop composed of international experts on orbiviruses conducted in 2013, gives a global perspective of current basic virological understanding of orbiviruses, with particular attention to BTV and the closely related epizootic hemorrhagic disease virus (EHDV), and identifies a multitude of basic virology research gaps, critical for predicting and preventing outbreaks.

Proteomic analysis of sheep primary testicular cells infected with bluetongue virus

Bluetongue virus (BTV) causes a non‐contagious, arthropod‐transmitted disease in wild and domestic ruminants, such as sheep. In this study, we used iTRAQ labeling coupled with LC‐MS/MS for quantitative identification of differentially expressed proteins in BTV‐infected sheep testicular (ST) cells. Relative quantitative data were obtained for 4455 proteins in BTV‐ and mock‐infected ST cells, among which 101 and 479 proteins were differentially expressed at 24 and 48 h post‐infection, respectively, indicating further proteomic changes during the later stages of infection. Ten corresponding genes of differentially expressed proteins were validated via real‐time RT‐PCR. Expression levels of three representative proteins, eIF4a1, STAT1 and HSP27, were further confirmed via western blot analysis. Bioinformatics analysis disclosed that the differentially expressed proteins are primarily involved in biological processes related to innate immune response, signal transduction, nucleocytoplasmic transport, transcription and apoptosis. Several upregulated proteins were associated with the RIG‐I‐like receptor signaling pathway and endocytosis. To our knowledge, this study represents the first attempt to investigate proteome‐wide dysregulation in BTV‐infected cells with the aid of quantitative proteomics. Our collective results not only enhance understanding of the host response to BTV infection but also highlight multiple potential targets for the development of antiviral agents.

Protective Efficacy in Sheep of Adenovirus-Vectored Vaccines against Bluetongue Virus Is Associated with Specific T Cell Responses

Bluetongue virus (BTV) is an economically important Orbivirus of the Reoviridae family that causes a hemorrhagic disease in ruminants. Its control has been achieved by inactivated-vaccines that have proven to protect against homologous BTV challenge although unable to induce long-term immunity. Therefore, a more efficient control strategy needs to be developed. Recombinant adenovirus vectors are lead vaccine candidates for protection of several diseases, mainly because of their potency to induce potent T cell immunity. Here we report the induction of humoral and T-cell mediated responses able to protect animals against BTV challenge by recombinant replication-defective human adenovirus serotype 5 (Ad5) expressing either VP7, VP2 or NS3 BTV proteins. First we used the IFNAR(-/-) mouse model system to establish a proof of principle, and afterwards we assayed the protective efficacy in sheep, the natural host of BTV. Mice were completely protected against BTV challenge, developing humoral and BTV-specific CD8+- and CD4+-T cell responses by vaccination with the different rAd5. Sheep vaccinated with Ad5-BTV-VP2 and Ad5-BTV-VP7 or only with Ad5-BTV-VP7 and challenged with BTV showed mild disease symptoms and reduced viremia. This partial protection was achieved in the absence of neutralizing antibodies but strong BTV-specific CD8+ T cell responses in those sheep vaccinated with Ad5-BTV-VP7. These data indicate that rAd5 is a suitable vaccine vector to induce T cell immunity during BTV vaccination and provide new data regarding the relevance of T cell responses in protection during BTV infection.

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-1β, 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.

VP2, VP7, and NS1 proteins of bluetongue virus targeted in avian reovirus muNS-Mi microspheres elicit a protective immune response in IFNAR(-/-) mice

Vaccination is critical for controlling the spread of bluetongue virus (BTV). The inactivated BTV vaccines that are now being used in Europe are effective in preventing outbreaks of BTV but secondary effects associated to repetitive inoculation of aluminum-containing adjuvants and the need to develop safer, cross-reactive, and more efficacious vaccines with differential diagnostic capability have re-stimulated the interest in developing improved vaccination strategies against BTV. We have engineered a subunit BTV vaccine candidate based on proteins VP2, VP7, and NS1 of BTV-4 incorporated into avian reovirus (ARV) muNS-Mi microspheres (MS-VP2/MS-VP7/MS-NS1). IFNAR(-/-) mice immunized with MS-VP2/MS-VP7/MS-NS1 without adjuvant generated significant levels of neutralizing antibodies specific to BTV-4. In addition, vaccination stimulated specific T cell responses, predominantly CD4+, against the virus. Immunized mice were fully protected against a homologous challenge with a lethal dose of BTV-4 and partially cross-protected against a heterologous challenge with a lethal dose of BTV-1. These results support MS-VP2/MS-VP7/MS-NS1 as a promising subunit vaccine candidate against multiple serotypes of BTV as well as the use of microspheres as an alternative delivery method with potent intrinsic adjuvant activity.

Dual modulation of type I interferon response by bluetongue virus

Bluetongue virus (BTV) is a double-stranded RNA (dsRNA) virus that causes an economically important disease in ruminants. BTV infection is a strong inducer of type I interferon (IFN-I) in multiple cell types. It has been shown recently that BTV and, more specifically, the nonstructural protein NS3 of BTV are able to modulate the IFN-I synthesis pathway. However, nothing is known about the ability of BTV to counteract IFN-I signaling. Here, we investigated the effect of BTV on the IFN-I response pathway and, more particularly, the Janus tyrosine kinase (JAK)/signal transducer and activator of transcription protein (STAT) signaling pathway. We found that BTV infection triggered the expression of IFN-stimulated genes (ISGs) in A549 cells. However, when BTV-infected cells were stimulated with external IFN-I, we showed that activation of the IFN-stimulated response element (ISRE) promoter and expression of ISGs were inhibited. We found that this inhibition involved two different mechanisms that were dependent on the time of infection. After overnight infection, BTV blocked specifically the phosphorylation and nuclear translocation of STAT1. This inhibition correlated with the redistribution of STAT1 in regions adjacent to the nucleus. At a later time point of infection, BTV was found to interfere with the activation of other key components of the JAK/STAT pathway and to induce the downregulation of JAK1 and TYK2 protein expression. Overall, our study indicates for the first time that BTV is able to interfere with the JAK/STAT pathway to modulate the IFN-I response.

IMPORTANCE

Bluetongue virus (BTV) causes a severe disease in ruminants and has an important impact on the livestock economy in areas of endemicity such as Africa. The emergence of strains, such as serotype 8 in Europe in 2006, can lead to important economic losses due to commercial restrictions and prophylactic measures. It has been known for many years that BTV is a strong inducer of type I interferon (IFN-I) in vitro and in vivo in multiple cell types. However, the ability of BTV to interact with the IFN-I system remains unclear. Here, we report that BTV is able to modulate the IFN-I response by interfering with the Janus tyrosine kinase (JAK)/signal transducer and activator of transcription protein (STAT) signaling pathway. These findings contribute to knowledge of how BTV infection interferes with the host's innate immune response and becomes pathogenic. This will also be important for the design of efficacious vaccine candidates.