Genetic characterization of bovine respiratory syncytial viruses in Japan between 2017 and 2019

Bovine respiratory syncytial virus (BRSV) strains that were detected in Kagoshima prefecture and isolated in Hokkaido between 2017 and 2019, together with a BRSV vaccine strain, were subjected to full-genome sequencing. The BRSV strains identified in Japan were found to be genetically close to each other but distant from the vaccine strains. The deduced amino acids at positions 206 and 208 of the glycoprotein (G protein), which form one of the major epitopes of the recent Japanese BRSV strains, were different from those of the vaccine strains. Therefore, the recent Japanese BRSV strains might be antigenically different from the BRSV vaccine strains.

Limitations of bacterial culture, viral PCR, and tulathromycin susceptibility from upper respiratory tract samples in predicting clinical outcome of tulathromycin control or treatment of bovine respiratory disease in high-risk feeder heifers

A cross-sectional prospective cohort study including 1026 heifers administered tulathromycin due to high risk of clinical signs of bovine respiratory disease (BRD), measured poor association between BRD clinical outcomes and results of bacterial culture and tulathromycin susceptibility from BRD isolates of deep nasopharyngeal swabs (DNS) and adequate association with viral polymerase chain reaction (PCR) results from nasal swabs. Isolation rates from DNS collected on day-0 and at 1st BRD-treatment respectively were: Mannheimia haemolytica (10.9% & 34.1%); Pasteurella multocida (10.4% & 7.4%); Mycoplasma bovis (1.0% & 36.6%); and Histophilus somni (0.7% & 6.3%). Prevalence of BRD viral nucleic acid on nasal swabs collected exclusively at 1st BRD-treatment were: bovine parainfluenza virus type-3 (bPIV-3) 34.1%; bovine viral diarrhea virus (BVDV) 26.3%; bovine herpes virus type-1 (BHV-1) 10.8%; and bovine respiratory syncytial virus (BRSV) 54.1%. Increased relative risk, at 95% confidence intervals, of 1st BRD-treatment failure was associated with positive viral PCR results: BVDV 1.39 (1.17-1.66), bPIV-3 1.26 (1.06-1.51), BHV-1 1.52 (1.25-1.83), and BRSV 1.35 (1.11-1.63) from nasal swabs collected at 1st BRD-treatment and culture of M. haemolytica 1.23 (1.00-1.51) from DNS collected at day-0. However, in this population of high-risk feeder heifers, the predictive values of susceptible and resistant isolates had inadequate association with BRD clinical outcome. These results indicate, that using tulathromycin susceptibility testing of isolates of M. haemolytica or P. multocida from DNS collected on arrival or at 1st BRD-treatment to evaluate tulathromycin clinical efficacy, is unreliable.

Risk factors and genetic characterization of bovine respiratory syncytial virus in the inner Aegean Region, Turkey

Bovine respiratory syncytial virus (BRSV) is one of the causative viral agents of the bovine respiratory disease complex. This study was conducted to determine the seropositivity and risk factors associated with BRSV infection and to evaluate the phylogenetic relatedness of the BRSVs in the inner Aegean region of Turkey. In this cross-sectional study, serum samples (n = 557) and nasal swabs (n = 21) were collected from cattle herds (n = 43) between February 2018 and March 2019. A commercial indirect-ELISA kit was used for the detection of antibodies in the sera samples. Reverse-transcriptase PCR was used to detect viral RNA in nasal swabs. Nasal samples were also examined for the detection of bovine parainfluenza-3, bovine viral diarrhoea virus, and bovine herpesvirus 1 by molecular detection methods. Genetic characterization of the local BRSV field isolates was conducted by sequencing attachment glycoprotein (G) gene segment. Epidemiological data on potential risk factors were collected from each sampled herd during blood collection. All herds had at least one seropositive animal. After adjustment for assay sensitivity and specificity, the overall true seropositivity was 58.48% (95% CI: 53.32–63.47). BRSV RNA was detected in 2 of the 21 nasal swabs, whereas other infectious agents were not detected in the investigated samples. Phylogenetic analysis showed that the field isolates of BRSV obtained in this study belonged to subgroup III, but they were located on separate branch from previously characterised Turkish subgroup III isolates. BRSV field strains from this study displayed 3 new amino acid substitutions (P89S, D115G, and S165L) in the G protein chains compared to other main reference BRSV isolates, demonstrating that BRSV is still evolving. Generalised estimating equation model showed that there were positive associations between BRSV infection, age (OR = 2.36, p = 0.001), herd size (OR = 10.32, p < 0.001), herd type (OR = 8.97, p < 0.001), a past history of respiratory disease (OR = 4.06, p < 0.001). The results of this study revealed that BRSV infection is common among cattle herds in the inner Aegean region of Turkey. The obtained epidemiological and genetic data on BRSV infection from this study could be beneficial for designing effective biosecurity practices and vaccination strategies.

Analysis of lung transcriptome in calves infected with Bovine Respiratory Syncytial Virus and treated with antiviral and/or cyclooxygenase inhibitor

Bovine Respiratory Syncytial virus (BRSV) is one of the major infectious agents in the etiology of the bovine respiratory disease complex. BRSV causes a respiratory syndrome in calves, which is associated with severe bronchiolitis. In this study we describe the effect of treatment with antiviral fusion protein inhibitor (FPI) and ibuprofen, on gene expression in lung tissue of calves infected with BRSV. Calves infected with BRSV are an excellent model of human RSV in infants: we hypothesized that FPI in combination with ibuprofen would provide the best therapeutic intervention for both species. The following experimental treatment groups of BRSV infected calves were used: 1) ibuprofen day 3-10, 2) ibuprofen day 5-10, 3) placebo, 4) FPI day 5-10, 5) FPI and ibuprofen day 5-10, 6) FPI and ibuprofen day 3-10. All calves were infected with BRSV on day 0. Daily clinical evaluation with monitoring of virus shedding by qRT-PCR was conducted. On day10 lung tissue with lesions (LL) and non-lesional (LN) was collected at necropsy, total RNA extracted, and RNA sequencing performed. Differential gene expression analysis was conducted with Gene ontology (GO) and KEGG pathway enrichment analysis. The most significant differential gene expression in BRSV infected lung tissues was observed in the comparison of LL with LN; oxidative stress and cell damage was especially noticeable. Innate and adaptive immune functions were reduced in LL. As expected, combined treatment with FPI and Ibuprofen, when started early, made the most difference in gene expression patterns in comparison with placebo, especially in pathways related to the innate and adaptive immune response in both LL and LN. Ibuprofen, when used alone, negatively affected the antiviral response and caused higher virus loads as shown by increased viral shedding. In contrast, when used with FPI Ibuprofen enhanced the specific antiviral effect of FPI, due to its ability to reduce the damaging effect of prostanoids and oxidative stress.

Co-infection of epithelial cells established from the upper and lower bovine respiratory tract with bovine respiratory syncytial virus and bacteria

Bovine respiratory disease complex is a major disease affecting the global cattle industry. Multiple infections by viruses and bacteria increase disease severity. Previously, we reported that bovine respiratory syncytial virus (BRSV) infection increases adherence of Pasteurella multocida to human respiratory and bovine kidney epithelial cells. To examine the interaction between the virus and bacteria in bovine respiratory cells, we generated respiratory epithelial cell lines from bovine trachea (bTEC), bronchus (bBEC), and lung (bLEC). Although all established cell lines were infected by BRSV and P. multocida susceptibility differed according to site of origin. The cells derived from the lower respiratory tract (bBEC and bLEC) were significantly more susceptible to BRSV than those derived from the upper respiratory tract (bTEC). Pre-infection of bBEC and bLEC with BRSV increased adherence of P. multocida; this was not the case for bTEC. These results indicate that BRSV may reproduce better in the lower respiratory tract and encourage adherence of bacteria. Thus, we identify one possible mechanism underlying severe pneumonia.

Histophilus somni Stimulates Expression of Antiviral Proteins and Inhibits BRSV Replication in Bovine Respiratory Epithelial Cells

Our previous studies showed that bovine respiratory syncytial virus (BRSV) followed by Histophilus somni causes more severe bovine respiratory disease and a more permeable alveolar barrier in vitro than either agent alone. However, microarray analysis revealed the treatment of bovine alveolar type 2 (BAT2) epithelial cells with H. somni concentrated culture supernatant (CCS) stimulated up-regulation of four antiviral protein genes as compared with BRSV infection or dual treatment. This suggested that inhibition of viral infection, rather than synergy, may occur if the bacterial infection occurred before the viral infection. Viperin (or radical S-adenosyl methionine domain containing 2—RSAD2) and ISG15 (IFN-stimulated gene 15—ubiquitin-like modifier) were most up-regulated. CCS dose and time course for up-regulation of viperin protein levels were determined in treated bovine turbinate (BT) upper respiratory cells and BAT2 lower respiratory cells by Western blotting. Treatment of BAT2 cells with H. somni culture supernatant before BRSV infection dramatically reduced viral replication as determined by qRT PCR, supporting the hypothesis that the bacterial infection may inhibit viral infection. Studies of the role of the two known H. somni cytotoxins showed that viperin protein expression was induced by endotoxin (lipooligosaccharide) but not by IbpA, which mediates alveolar permeability and H. somni invasion. A naturally occurring IbpA negative asymptomatic carrier strain of H. somni (129Pt) does not cause BAT2 cell retraction or permeability of alveolar cell monolayers, so lacks virulence in vitro. To investigate initial steps of pathogenesis, we showed that strain 129Pt attached to BT cells and induced a strong viperin response in vitro. Thus colonization of the bovine upper respiratory tract with an asymptomatic carrier strain lacking virulence may decrease viral infection and the subsequent enhancement of bacterial respiratory infection in vivo.

Vaccine safety and efficacy evaluation of a recombinant bovine respiratory syncytial virus (BRSV) with deletion of the SH gene and subunit vaccines based on recombinant human RSV proteins: N-nanorings, P and M2-1, in calves with maternal antibodies

The development of safe and effective vaccines against both bovine and human respiratory syncytial viruses (BRSV, HRSV) to be used in the presence of RSV-specific maternally-derived antibodies (MDA) remains a high priority in human and veterinary medicine. Herein, we present safety and efficacy results from a virulent BRSV challenge of calves with MDA, which were immunized with one of three vaccine candidates that allow serological differentiation of infected from vaccinated animals (DIVA): an SH gene-deleted recombinant BRSV (ΔSHrBRSV), and two subunit (SU) formulations based on HRSV-P, -M2-1, and -N recombinant proteins displaying BRSV-F and -G epitopes, adjuvanted by either oil emulsion (Montanide ISA71^VG, SUMont) or immunostimulating complex matrices (AbISCO-300, SUAbis). Whereas all control animals developed severe respiratory disease and shed high levels of virus following BRSV challenge, ΔSHrBRSV-immunized calves demonstrated almost complete clinical and virological protection five weeks after a single intranasal vaccination. Although mucosal vaccination with ΔSHrBRSV failed to induce a detectable immunological response, there was a rapid and strong anamnestic mucosal BRSV-specific IgA, virus neutralizing antibody and local T cell response following challenge with virulent BRSV. Calves immunized twice intramuscularly, three weeks apart with SUMont were also well protected two weeks after boost. The protection was not as pronounced as that in ΔSHrBRSV-immunized animals, but superior to those immunized twice subcutaneously three weeks apart with SUAbis. Antibody responses induced by the subunit vaccines were non-neutralizing and not directed against BRSV F or G proteins. When formulated as SUMont but not as SUAbis, the HRSV N, P and M2-1 proteins induced strong systemic cross-protective cell-mediated immune responses detectable already after priming. ΔSHrBRSV and SUMont are two promising DIVA-compatible vaccines, apparently inducing protection by different immune responses that were influenced by vaccine-composition, immunization route and regimen.

[Detection of bovine respiratory syncytial virus by RT-PCR]

The paper presents the results of studying the diagnostic efficiency of RT-PCR for the detection of respiratory syncytial virus in cattle of different ages. Glycoprotein F gene sequences were used as a target for amplification. The sensitivity of the reaction was 10 TCD50/ml and the virus detection rate in biomaterials averaged 19%. samples. That in RT-PCR correlated with the presence of clinical signs in sick animals.

Development of a real time reverse transcriptase polymerase chain reaction for the detection of bovine respiratory syncytial virus in clinical samples and its comparison with immunohistochemistry and immunofluorescence antibody testing

Bovine respiratory syncytial virus is an agent involved in calf pneumonia complex, a disease of significant economic importance. Accurate diagnosis of the agents involved on farm premises is important when formulating disease control measures, including vaccination. We have developed a real time reverse transcriptase polymerase chain reaction (rtRT-PCR) and compared it with the diagnostic tests currently available in the United Kingdom: immunohistochemistry (IHC) and immunofluorescence antibody test (IFAT). The rtRT-PCR had a detection limit of 10 gene copies and was 96% efficient. Recent UK isolates and clinical samples were tested; the rtRT-PCR was more sensitive than both conventional tests.

Development of a 1-step enzyme-linked immunosorbent assay for the rapid diagnosis of bovine respiratory syncytial virus in postmortem specimens

Bovine respiratory syncytial virus (BRSV) is associated with severe respiratory disease in cattle. BRSV infection frequently leads to the death of young infected animals. The presence of BRSV in postmortem specimens is routinely detected using indirect immunofluorescence (IIF). However, this technique requires special equipment and considerable expertise. The present paper describes the development of a 1-step ELISA for rapid (1.5 hours) detection of BRSV antigen in organ homogenates. The performance of the new 1-step ELISA was evaluated using bovine postmortem specimens (n = 108) in comparison with 3 other BRSV diagnostic techniques: indirect immunofluorescence, the Clearview respiratory syncytial virus (RSV) test, and real-time reverse transcriptase polymerase chain reaction (RT-PCR). The relative sensitivity, specificity, and the kappa coefficient of 1-step ELISA, the Clearview RSV electroimmunoassay (EIA), and IIF were calculated, using real-time RT-PCR as the reference test. The new 1-step ELISA was the most sensitive and specific of the 3 tests. Thus, the new 1-step ELISA is a reliable test for detecting BRSV antigen in organ homogenates.

DNA vaccination against pseudorabies virus and bovine respiratory syncytial virus infections of young animals in the face of maternally derived immunity

DNA vaccination represents a unique opportunity to overcome the limitations of conventional early life vaccine strategy which is restricted by the effects of maternally derived immunity. The pseudorabies virus (PRV) infection model in neonatal piglets was employed to demonstrate that a single DNA vaccination was able to prime memory humoral immune responses in the face of high concentrations of maternally derived antibodies. Immunity induced under these conditions protected against challenge with virulent PRV at the end of the fattening period, but long-term protective responses were not correlated with the kinetics of the initial serological responses. The bovine respiratory syncytial virus (BRSV) infection model in young calves was similarly studied, however the ability of DNA vaccination to prime memory humoral responses in the face of high concentrations of maternally derived antibodies was not confirmed, illustrating that the performance of DNA vaccination varies between species and/or infectious disease targets. However, in the BRSV model system it was evident that DNA vaccination could prime cell-mediated immunity in the face of high concentrations of maternally derived antibodies. Although not sufficient to ensure protection against clinical disease or viral excretion as a standalone vaccination strategy, priming by DNA vaccination was proven to establish cell-mediated immune responses for subsequent recall with an inactivated vaccine booster. Under these conditions, protection against challenge virus re-excretion was correlated with interferon (IFN) gamma-producing T-cell responses. The safety and the efficacy of DNA vaccine priming in very young animals in the face of high concentrations of maternally derived antibody provides a unique opportunity to design innovative and flexible vaccination programs to ensure uninterrupted protection under field conditions.

DNA immunization with plasmids encoding fusion and nucleocapsid proteins of bovine respiratory syncytial virus induces a strong cell-mediated immunity and protects calves against challenge

Respiratory syncytial viruses (RSV) are one of the most important respiratory pathogens of humans and cattle, and there is currently no safe and effective vaccine prophylaxis. In this study, we designed two codon-optimized plasmids encoding the bovine RSV fusion (F) and nucleocapsid (N) proteins and assessed their immunogenicity in young calves. Two administrations of both plasmids elicited low antibody levels but primed a strong cell-mediated immunity characterized by lymphoproliferative response and gamma interferon production in vitro and in vivo. Interestingly, this strong cellular response drastically reduced viral replication, clinical signs, and pulmonary lesions after a highly virulent challenge. Moreover, calves that were further vaccinated with a killed-virus vaccine developed high levels of neutralizing antibody and were fully protected following challenge. These results indicate that DNA vaccination could be a promising alternative to the classical vaccines against RSV in cattle and could therefore open perspectives for vaccinating young infants.

In vivo evidence for quasispecies distributions in the bovine respiratory syncytial virus genome

We analysed the genetic evolution of bovine respiratory syncytial virus (BRSV) isolate W2-00131, from its isolation in bovine turbinate (BT) cells to its inoculation in calves. Results showed that the BRSV genomic region encoding the highly variable glycoprotein G remained genetically stable after virus isolation and over 10 serial infections in BT cells, as well as following experimental inoculation in calves. This remarkable genetic stability led us to examine the mutant spectrum of several populations derived from this field isolate. Sequence analysis of molecular clones revealed an important genetic heterogeneity in the G-coding region of each population, with mutation frequencies ranging from 6.8 to 10.1×10−4substitutions per nucleotide. The non-synonymous mutations of the mutant spectrum mapped preferentially within the two variable antigenic regions of the ectodomain or close to the highly conserved domain. These results suggest that BRSV populations may evolve as complex and dynamic mutant swarms, despite apparent genetic stability.

Bovine respiratory syncytial virus infection

Bovine respiratory syncytial virus (BRSV) belongs to the pneumovirus genus within the family Paramyxoviridae and is a major cause of respiratory disease in young calves. BRSV is enveloped and contains a negative sense, single-stranded RNA genome encoding 11 proteins. The virus replicates predominantly in ciliated respiratory epithelial cells but also in type II pneumocytes. It appears to cause little or no cytopathology in ciliated epithelial cell cultures in vitro, suggesting that much of the pathology is due to the host's response to virus infection. RSV infection induces an array of pro-inflammatory chemokines and cytokines that recruit neutrophils, macrophages and lymphocytes to the respiratory tract resulting in respiratory disease. Although the mechanisms responsible for induction of these chemokines and cytokines are unclear, studies on the closely related human (H)RSV suggest that activation of NF-kappaB via TLR4 and TLR3 signalling pathways is involved. An understanding of the mechanisms by which BRSV is able to establish infection and induce an inflammatory response has been facilitated by advances in reverse genetics, which have enabled manipulation of the virus genome. These studies have demonstrated an important role for the non-structural proteins in anti-interferon activity, a role for a virokinin, released during proteolytic cleavage of the fusion protein, in the inflammatory response and a role for the SH and the secreted form of the G protein in establishing pulmonary infection. Knowledge gained from these studies has also provided the opportunity to develop safe, stable, live attenuated virus vaccine candidates.

Bovine respiratory syncytial virus lacking the virokinin or with a mutation in furin cleavage site RA(R/K)R109 induces less pulmonary inflammation without impeding the induction of protective immunity in calves

The BRSV fusion (F) protein is cleaved at two furin consensus sequence sites, resulting in the generation of disulphide-linked F1 and F2 subunits and the release of an intervening peptide of 27 amino acids (pep27), which is converted into a biologically active tachykinin (virokinin). The role of the virokinin and the importance of one of the furin cleavage sites, FCS-2 [RA(R/K)R109], in the pathogenesis of BRSV infection and in the subsequent development of immunity was studied in gnotobiotic calves infected with a recombinant BRSV (rBRSV) lacking pep27 (rBRSVdelta p27) or with rBRSV108/109, which contains two amino acid substitutions in FCS-2 (RANN109). Although replication of the mutant viruses and the parental wild-type (WT) rBRSV in the lungs was similar, the extent of gross and microscopic lesions induced by the mutant viruses was less than that induced by WT rBRSV. Furthermore, the numbers of eosinophils in the lungs of calves infected with the mutant viruses were significantly less than that in calves infected with WT virus. These observations suggest a role for the virokinin in the pathogenesis of BRSV infection. Following mucosal immunization with rBRSVdelta p27, the levels of BRSV-specific serum antibodies were similar to those induced by WT virus. In contrast, the level of neutralizing antibodies induced by rBRSV108/109 was 10-fold lower than that induced by WT virus. Nevertheless, resistance to BRSV challenge induced by the mutant and WT viruses was similar, suggesting that neither pep27 nor FCS-2 plays a major role in the induction of protective immunity.

Live-cell characterization and analysis of a clinical isolate of bovine respiratory syncytial virus, using molecular beacons

Understanding viral pathogenesis is critical for prevention of outbreaks, development of antiviral drugs, and biodefense. Here, we utilize molecular beacons to directly detect the viral genome and characterize a clinical isolate of bovine respiratory syncytial virus (bRSV) in living cells. Molecular beacons are dual-labeled, hairpin oligonucleotide probes with a reporter fluorophore at one end and a quencher at the other; they are designed to fluoresce only when hybridizing to a complementary target. By imaging the fluorescence signal of molecular beacons, the spread of bRSV was monitored for 7 days with a signal-to-noise ratio of 50 to 200, and the measured time course of infection was quantified with a mathematical model for viral growth. We found that molecular beacon signal could be detected in single living cells infected with a viral titer of 2 x 10(3.6) 50% tissue culture infective doses/ml diluted 1,000 fold, demonstrating high detection sensitivity. Low background in uninfected cells and simultaneous staining of fixed cells with molecular beacons and antibodies showed high detection specificity. Furthermore, using confocal microscopy to image the viral genome in live, infected cells, we observed a connected, highly three-dimensional, amorphous inclusion body structure not seen in fixed cells. Taken together, the use of molecular beacons for active virus imaging provides a powerful tool for rapid viral infection detection, the characterization of RNA viruses, and the design of new antiviral drugs.

Phylogenetic relationships of Brazilian bovine respiratory syncytial virus isolates and molecular homology modeling of attachment glycoprotein

Bovine respiratory syncytial virus (BRSV) causes lower respiratory tract disease in young cattle. Recently, it was possible to determine the sequence of the G protein gene, which plays a role in the attachment of BRSV particles to the cells, from three distinct Brazilian isolates. The phylogenetic analysis conducted here using those sequences compared to other worldwide distributed isolates of BRSV allow us to allocate Brazilian strains within the subgroup B, which was no longer found in the world since the 1970s. One of the Brazilian strains has a major mutation between amino acid residues 173 and 178, within the central hydrophobic conserved region, exactly on the site of two of the four cysteine-noose forming cysteine residues. Homology modeling with the previously determined NMR structure of this protein domain was made to check whether these mutations altered the three-dimensional conformation of this immunodominant region. Possible consequences on the biological effects induced by such mutation on the G protein are discussed.

Complete sequence of the RNA genome of pneumonia virus of mice (PVM)

Pneumonia virus of mice (PVM) is an enveloped RNA-containing virus of Family Paramyxoviridae. Sequences had been determined previously for a number of PVM genes, although these represented cloned cDNAs rather than consensus sequences. Sequences were not available for the 3' -leader and 5' -trailer regions that constitute the genome termini or for the large polymerase L gene that accounts for 43% of the genome. Also, the available sequences were from an attenuated variant of strain 15, whereas the present study analyzed the version of strain 15 that is available from the American Type Culture Collection (ATCC) and is highly virulent in mice. Analysis of unclosed RT-PCR products yielded a complete consensus sequence of 14,886 nt (GenBank accession number AY729016). Of the regions for which sequences had been previously reported for the non-pathogenic strain, there were 13 nucleotide differences and 10 amino acid differences compared to the present consensus sequence for the virulent isolate. The various genes of PVM shared 29-62% nucleotide sequence identity and 10-60% amino acid sequence identity with human or bovine respiratory syncytial virus (HRSV and BRSV), its closest relatives.

Real Time RT-PCR for the detection and quantitation of bovine respiratory syncytial virus

A quantitative Real Time RT-PCR assay was developed to detect and quantify bovine respiratory syncytial virus (BRSV) in the respiratory tract of infected animals. A pair of primers and a TaqMan probe targeting conserved regions of the nucleoprotein gene of BRSV were designed. The detection limit of the assay was shown to be 10(3) RNA copies and standard curve demonstrated a linear range from 10(3) to 10(8) copies as well as an excellent reproducibility. The efficiency of the BRSV Real Time RT-PCR was then assessed by detecting BRSV in lungs, tracheas and bronchoalveaolar fluids (BAL) samples of experimentally infected calves. The assay was shown to be 100 times more sensitive than conventional RT-PCR and was more efficient for BRSV diagnosis. Finally, the Real Time RT-PCR was used to quantify BRSV load in BAL fluids of four experimentally infected calves for 14 days. The high sensitivity, rapidity and reproducibility of the BRSV Real Time RT-PCR make this method suitable for diagnostic and for the evaluation of the efficiency of new vaccines.

DNA vaccination against respiratory syncytial virus in young calves

A DNA vaccine encoding the fusion (F) gene (DNA-F) of bovine respiratory syncytial virus (BRSV) induced significant protection against BRSV infection in young calves. However, serum antibody to RSV developed more slowly in animals vaccinated with DNA-F when compared with those previously infected with BRSV. Furthermore, protection against BRSV infection was not as great as that induced by prior BRSV infection. Although there was little difference in the level of protection induced in calves vaccinated with DNA-F by either the intramuscular (i.m.) or intradermal (i.d.) routes, only the i.m. route primed for a rapid BRSV-specific IgA response after BRSV challenge. These results indicate that a DNA vaccination may be effective against RSV infection even in very young infants and calves.

Evaluation of a single-tube fluorogenic RT-PCR assay for detection of bovine respiratory syncytial virus in clinical samples

Bovine respiratory syncytial virus (BRSV) causes severe disease in naïve cattle of all ages and is a common pathogen in the respiratory disease complex of calves. Simplified methods for rapid BRSV diagnosis would encourage sampling during outbreaks and would consequently lead to an extended understanding of the virus. In this study, a BRSV fluorogenic reverse transcription PCR (fRT-PCR) assay, based on TaqMan principle, was developed and evaluated on a large number of clinical samples, representing various cases of natural and experimental BRSV infections. By using a single-step closed-tube format, the turn-around time was shortened drastically and results were obtained with minimal risk for cross-contamination. According to comparative analyses, the detection limit of the fRT-PCR was on the same level as that of a nested PCR and the sensitivity relatively higher than that of a conventional PCR, antigen ELISA (Ag-ELISA) and virus isolation (VI). Interspersed negative control samples, samples from healthy animals and eight symptomatically or genetically related viruses were all negative, confirming a high specificity of the assay. Taken together, the data indicated that the fRT-PCR assay can be applied to routine virus detection in clinical specimens and provides a rapid and valuable tool in BRSV research.

Restriction enzyme analysis of RT-PCR amplicons as a rapid method for detection of genetic diversity among bovine respiratory syncytial virus isolates

Our current knowledge of antigenic variability of the bovine respiratory syncytial virus (BRSV) is quite limited and is mainly dependent on the use of monoclonal antibodies (mAb). In this study, we present not only analysis of the antigenic, but also of the genetic variability of BRSV. Using a panel of BRSV-specific mAb we distinguished five main reactivity patterns, three of which corresponded to the previously established subgroups A, B and AB. A single viral strain yielded the fourth pattern, while four viral strains did not react with any of the used mAbs forming the fifth pattern. To investigate the genetic basis for the antigenic heterogeneity of the BRS virus G protein, DNA of 11 BRSV isolates was directly sequenced. The comparison of the obtained nucleotide or amino acid sequences to those BRSV strains present in the GenBank revealed 88.1-99.4% and 77.7-98.4% similarity, respectively. These results supported the previously stated suggestion to type BRSV isolates according to their genetic relationship. In order to introduce a rapid and simple method to study the genetic variability of BRSV, we utilized the restriction enzyme analysis of RT-PCR products derived from mRNAs corresponding to the most variable region of the BRSV glycoprotein G ectodomain. Using this restriction enzyme analysis we were able to identify genetic variability among BRSV isolates. The detected non-synonymous mutations led frequently to a change in digestion pattern and were predominantly located in two mucin-like regions of the G protein gene. A correlation has been found between grouping of isolates in the phylogenetic tree and their restriction patterns clustering together isolates with the same restriction profiles. However, viruses placed distant in the tree sharing the same restriction patterns were detected supposing that phylogenetic analysis should be necessary for BRSV typing. Thus, we propose to use DNA restriction polymorphism for a rapid detection of genetic variants among BRSV isolates circulating in cattle population and as a preliminary tool for their typing.

Detection and quantitation of bovine respiratory syncytial virus using real-time quantitative RT-PCR and quantitative competitive RT-PCR assays

A single tube, fluorogenic probe-based, real-time quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) assay was developed for detection and quantitation of bovine respiratory syncytial virus (BRSV) using BioRad's iCycler iQ. Real-time Q-RT-PCR was compared with quantitative competitive RT-PCR (QC-RT-PCR) and viral titers. Viral mRNA levels were measured in BRSV-infected bovine turbinate cell lysate harvested at eight time points (1.5, 6, 12, 24, 36, 48, 60, 72 h) post-infection. A homologous BRSV cRNA standard was used for quantitation of the mRNA by plotting a standard curve of cycle threshold (Ct) values versus standard 10-fold dilutions of cRNA of known concentrations. Detection as low as 171 copies/microl of standard BRSV cRNA was possible. For QC-RT-PCR, a competitor RNA molecule having a deletion was designed and used for quantitation of the BRSV viral mRNA. The results of real-time Q-RT-PCR and QC-RT-PCR assays showed a positive correlation. Real-time Q-RT-PCR was a sensitive, specific, rapid, and efficient method that eliminates the post-PCR processing steps when compared to QC-RT-PCR. Quantitation of BRSV using real-time Q-RT-PCR will have application in studies aimed at understanding the pathogenesis of BRSV.

Genetic and Antigenic Analyses of Bovine Respiratory Syncytial Virus Detected in Japan

Genetic and antigenic analyses of bovine respiratory syncytial virus were conducted on 12 field strains from Tohoku and Hokuriku districts in Japan during from 2002 to 2004. On the phylogenetic tree of the nucleotide sequences of the glycoprotein region, the examined strains fell in the same cluster as the strain isolated in Nebraska and were classified as the subgroup III. The examined strains were subdivided into 2 lineages (A, B). Isoleucine 200 of the epitope domain was replaced by threonine as a feature of the lineage B strains. The examined strains showed the nucleotide sequence homologies of 88.3-93.3% with the known Japanese strains classified as the subgroup II and of 86.1-96.6% with those in the subgroup III. No significant difference was found on the neutralization index between the examined strain and the 52-163-13 phylogenetically similar to the Japanese vaccine one. The results suggest that the subgroup III strains have existed in Japan and that epidemics of the strains could be protected due to the present vaccination.

Detection of Brazilian bovine respiratory syncytial virus strain by a reverse transcriptase-nested-polymerase chain reaction in experimentally infected calves

A reverse transcriptase (RT)-nested-polymerase chain reaction (PCR) was standardised to detect bovine respiratory syncytial virus (BRSV), using a Brazilian isolate, in three experimentally infected calves. This followed initial tests in infected chicken embryo related (CER) cells. One animal had lesions, characterized by interstitial multifocal pneumonia, severe interstitial and subpleural emphysema, and lung consolidated areas. Lung and tracheal tissues collected 6 days after infection were analysed by RT-nested-PCR. Primers, specific for the BRSV G and F glycoproteins genes, yielded amplification fragments of 371 and 481 bp, respectively, from the RNA of the cell-propagated virus. Using RNA extracted from organs of infected calves, RT-nested-PCR amplified the fragment of the G gene in all tracheal samples, but in only two of three lung samples analysed. These results suggest that RT-nested-PCR could be a promising assay for diagnosis and epidemiological analysis of BRSV in Brazil.

A novel protein expression strategy using recombinant bovine respiratory syncytial virus (BRSV): modifications of the peptide sequence between the two furin cleavage sites of the BRSV fusion protein yield secreted proteins, but affect processing and function of the BRSV fusion protein

The bovine respiratory syncytial virus (BRSV) fusion (F) protein is cleaved at two furin cleavage sites, which results in generation of the disulfide-linked F(1) and F(2) subunits and release of an intervening peptide of 27 aa (pep27). A series of mutated open reading frames encoding F proteins that lacked the entire pep27, that contained an arbitrarily chosen 23 aa sequence instead of pep27 or in which pep27 was replaced by the amino acid sequences for the bovine cytokines interleukin 2 (boIL2), interleukin 4 (boIL4) or gamma interferon (boIFN-gamma) was constructed. Transient expression experiments revealed that the sequence of the intervening peptide influenced intracellular transport, maturation of the F protein and F-mediated syncytium formation. Expression of boIL2, boIL4 or boIFN-gamma in place of pep27 resulted in secretion of the cytokines into the culture medium. All mutated F proteins except the boIFN-gamma-containing variant could be expressed by and were functional for recombinant BRSV. Characterization of the cell culture properties of the recombinants demonstrated that the amino acid sequence between the two furin cleavage sites affected entry into target cells, direct spreading of virions from cell to cell and virus growth. Secretion of boIL2 and boIL4 into the medium of cells infected with the respective recombinants demonstrated that the F protein can be used to express secreted heterologous bioactive peptides or (glyco)proteins, which might be of interest for the development of novel RSV vaccines.

Detection of bovine respiratory syncytial virus in experimentally infected balb/c mice

The present study used an RT-nested-PCR and an immunohistochemistry assay to detect bovine respiratory syncytial virus in tissues from experimentally infected balb/c mice. As a first step, Chicken Embryo Related (CER) cell monolayers infected with the BRSV-25-BR strain isolated in Brazil were used for antigen production. Then, the infected lung and tracheal tissues of female balb/c mice were collected on 3, 5, 7 and 10 days post-infection and submitted to both techniques. Primers specific to F and G genes that amplify fragments of 481 bp and 371 bp, respectively, were used. The BRSV detection was not successful in all of the animals tested. The genomic fragment of the G gene from the organs of some infected mice on all analyzed post-infection days was amplified. However, in the RT-nested-PCR corresponding to the F gene, it was not possible to observe any amplified fragment. This was probably due to the higher sensitivity of the developed technique to amplify the fragment corresponding to the G gene compared to the F gene. Moreover, only three of the lungs collected five days post-infection were positive by immunohistochemistry. To the author's knowledge, this is the first study reporting bovine respiratory syncytial virus detection in balb/c mice after experimental inoculation.

T Cells from a High Proportion of Apparently Naive Cattle Can Be Activated by Modified Vaccinia Virus Ankara (MVA)

Modified vaccinia virus Ankara (MVA) was used as a vector to express genes from bovine respiratory syncytial virus (BRSV). Using these recombinant viruses as recall antigens for cells from BRSV-immuned cattle proved to be problematic because non-recombinant MVA itself frequently stimulated high levels of T lymphocyte activation. This phenomenon was observed in a high percentage of cattle from multiple herds. Gamma delta TCR(+) T cells were more sensitive to activation by MVA than other classes of T cells. A serological assay for MVA neutralization detected low, fluctuating titers of serum virus neutralizing (SVN) activity toward MVA in some cattle, but these were lower titers than those observed in cattle that underwent MVA vaccination. T cell reactivity in non-vaccinated cattle did not correlate significantly (p > 0.05) with SVN activity, undermining the notion that any adaptive immune response was responsible for the observed T cell sensitivity. More probable explanations are that MVA has mitogenic or superantigenic properties, or that the virus induces gammadelta TCR(+) T cell activation through interactions with innate pattern recognition receptors.

Cytotoxic T lymphocyte activity and cytokine expression in calves vaccinated with formalin-inactivated bovine respiratory syncytial virus prior to challenge

The development of effective, safe vaccines for human and bovine respiratory syncytial virus (RSV) has been problematic. Inactivated RSV vaccines are of variable efficacy; poor efficacy may be related to induction of ineffective cell-mediated immunity (CMI). To characterize CMI in calves vaccinated with formalin inactivated (FI) BRSV, 11 calves were vaccinated twice with FI-BRSV (n=5) or mock vaccine (n=6) at a 2 week interval and challenged 1 month later. Prior to challenge a cannula was placed in the efferent lymphatic of the caudal mediastinal lymph node of each calf; lymph derived lymphocytes (LDL) were collected for analysis of CMI. Cytotoxic T lymphocyte (CTL) activity by LDL and/or peripheral blood mononuclear cells (PBMC) was measured by 51Cr release on days 5, 7, 9, and 10 post-challenge. Messenger RNA for interferon gamma (IFN-gamma), interleukin 2 (IL-2) and IL-4 was measured on days 0-10 by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) of RNA of LDL. BRSV-specific IFN-gamma production by PBMC was measured on days 0 and 10 by ELISA. Clinical signs and postmortem changes following challenge were evaluated. There was no difference between groups in clinical signs, postmortem changes, CTL activity, cytokine message expression, or IFN-gamma production. For both groups, percentage lysis by CTL peaked on days 7-10 and ranged from 11 to 25%. Failure of vaccination to prevent disease following challenge was likely associated with failure to prime for improved CMI responses.

Bovine respiratory syncytial virus strains currently circulating in the Czech Republic are most closely related to Danish strains from 1995

In this study we showed a high degree of genetic homogeneity among recently (2002-2003) circulating Bovine respiratory syncytial virus (BRSV) strains in cattle population in the Czech Republic. These strains are in a phylogenetic tree more closely related to the Danish strains from 1995 than to the Czech strain VS97 from 1997 that shares the highest similarity with the French strain F1 and the Belgian strain P10. From the sequence analysis we deduce that the revealed high diversity between BRSV strains from 2002-2003 and those from 1997, at both nucleotide (0-11.4%) and amino acid (0-21%) level, is more likely due to distinct sources of the virus strains than to the sequence evolution.

Demonstration of bovine respiratory syncytial virus RNA in peripheral blood leukocytes of naturally infected cattle

RNA of Bovine respiratory syncytial virus (BRSV) was found in peripheral leukocytes and nasal mucosa of infected cows by nested reverse transcription-polymerase chain reaction (nRT-PCR). We suppose that this finding obtained in the convalescent phase of infection indicates possible persistence of the virus in cells of the immune system.

Role of alpha/beta interferons in the attenuation and immunogenicity of recombinant bovine respiratory syncytial viruses lacking NS proteins

Alpha/beta interferons (IFN-alpha/beta) are not only a powerful first line of defense against pathogens but also have potent immunomodulatory activities. Many viruses have developed mechanisms of subverting the IFN system to enhance their virulence. Previous studies have demonstrated that the nonstructural (NS) genes of bovine respiratory syncytial virus (BRSV) counteract the antiviral effects of IFN-alpha/beta. Here we demonstrate that, in contrast to wild-type BRSVs, recombinant BRSVs (rBRSVs) lacking the NS proteins, and those lacking NS2 in particular, are strong inducers of IFN-alpha/beta in bovine nasal fibroblasts and bronchoalveolar macrophages. Furthermore, whereas the NS deletion mutants replicated to wild-type rBRSV levels in cells lacking a functional IFN-alpha/beta system, their replication was severely attenuated in IFN-competent cells and in young calves. These results suggest that the NS proteins block the induction of IFN-alpha/beta gene expression and thereby increase the virulence of BRSV. Despite their poor replication in the respiratory tract of young calves, prior infection with virus lacking either the NS1 or the NS2 protein induced serum antibodies and protection against challenge with virulent BRSV. The greater level of protection induced by the NS2, than by the NS1, deletion mutant, was associated with higher BRSV-specific antibody titers and greater priming of BRSV-specific, IFN-gamma-producing CD4(+) T cells. Since there were no detectable differences in the ability of these mutants to replicate in the bovine respiratory tract, the greater immunogenicity of the NS2 deletion mutant may be associated with the greater ability of this virus to induce IFN-alpha/beta.

Recent isolates of bovine respiratory syncytial virus from Britain are more closely related to isolates from USA than to earlier British and current mainland European isolates

Eight isolates of Bovine respiratory syncytial virus (BRSV) were made from calves with severe respiratory disease on seven farms in one region of Britain. Genetic analysis of the viruses showed that seven, which were isolated between 1997 and 1999 were almost identical and were distinguishable from an earlier 1991 isolate. When compared with the available sequences of BRSVs from other countries, the recent British isolates were more closely related to US isolates than to earlier British and current mainland European isolates.

Respiratory syncytial virus (RSV) fusion protein subunit F2, not attachment protein G, determines the specificity of RSV infection

Human respiratory syncytial virus (HRSV) and bovine RSV (BRSV) infect human beings and cattle in a species-specific manner. We have here analyzed the contribution of RSV envelope proteins to species-specific entry into cells. In contrast to permanent cell lines, primary cells of human or bovine origin, including differentiated respiratory epithelia, peripheral blood lymphocytes, and macrophages, showed a pronounced species-specific permissiveness for HRSV and BRSV infection, respectively. Recombinant BRSV deletion mutants lacking either the small hydrophobic (SH) protein gene or both SH and the attachment glycoprotein (G) gene retained their specificity for bovine cells, whereas corresponding mutants carrying the HRSV F gene specifically infected human cells. To further narrow the responsible region of F, two reciprocal chimeric F constructs were assembled from BRSV and HRSV F1 and F2 subunits. The specificity of recombinant RSV carrying only the chimeric F proteins strictly correlated with the origin of the membrane-distal F2 domain. A contribution of G to the specificity of entry could be excluded after reintroduction of BRSV or HRSV G. Virus with F1 and G from BRSV and with only F2 from HRSV specifically infected human cells, whereas virus expressing F1 and G from HRSV and F2 from BRSV specifically infected bovine cells. The introduction of G enhanced the infectiousness of both chimeric viruses to equal degrees. Thus, the role of the nominal attachment protein G is confined to facilitating infection in a non-species-specific manner, most probably by binding to cell surface glycosaminoglycans. The identification of the F2 subunit as the determinant of RSV host cell specificity facilitates identification of virus receptors and should allow for development of reagents specifically interfering with RSV entry.

Mucosal immunization with live recombinant bovine respiratory syncytial virus (BRSV) and recombinant BRSV lacking the envelope glycoprotein G protects against challenge with wild-type BRSV

Recombinant bovine respiratory syncytial virus (rBRSV) and an rBRSV deletion mutant lacking the G gene (rBRSVDeltaG) were characterized in calves with respect to replication competence, attenuation, and protective efficacy as live-attenuated BRSV vaccines. Both recombinant viruses were safe and induced protection against a BRSV challenge infection. rBRSV replicated efficiently in the upper respiratory tract. Intranasal immunization with rBRSVDeltaG led to infection but not to mucosal virus replication. Neutralizing antibodies were induced by rBRSV and rBRSVDeltaG. Thus, the BRSV attachment glycoprotein G seems to be dispensable in vaccinating calves against BRSV.

Cleavage at the furin consensus sequence RAR/KR(109) and presence of the intervening peptide of the respiratory syncytial virus fusion protein are dispensable for virus replication in cell culture

Proteolytic processing of the respiratory syncytial virus F (fusion) protein results in the generation of the disulfide-linked subunits F1 and F2 and in the release of pep27, a glycopeptide originally located between the two furin cleavage sites FCS-1 (RKRR(136)) and FCS-2 (RAR/KR(109)). We made use of reverse genetics to study the importance of FCS-2 and of pep27 for BRSV replication in cell culture. Replacement of FCS-2 in the F protein of recombinant viruses by either of the sequences NANR(109), RANN(109) or SANN(109), respectively, abolished proteolytic processing at this position, whereas the cleavage of FCS-1 was not affected. All mutants replicated in calf kidney and Vero cells in the absence of exogenous trypsin, although somewhat higher titers of BRSV containing the NANR(109) or the RANN(109) motif were achieved in the presence of trypsin. The virus mutants showed a reduced cytopathic effect which was lowest in the case of the SANN(109) mutant. These findings demonstrate that cleavage at FCS-2 is dispensable for replication of respiratory syncytial virus in cell culture. A deletion mutant containing FCS-1 but lacking FCS-2 and most of pep27 replicated in cell culture as efficiently as the parental virus, indicating that this domain of the F protein is not essential for virus maturation and infectivity.

Respiratory syncytial virus (RSV) nonstructural (NS) proteins as host range determinants: a chimeric bovine RSV with NS genes from human RSV is attenuated in interferon-competent bovine cells

Bovine respiratory syncytial virus (BRSV) escapes from cellular responses to alpha/beta interferon (IFN-alpha/beta) by a concerted action of the two viral nonstructural proteins, NS1 and NS2. Here we show that the NS proteins of human RSV (HRSV) are also able to counteract IFN responses and that they have the capacity to protect replication of an unrelated rhabdovirus. Even combinations of BRSV and HRSV NS proteins showed a protective activity, suggesting common mechanisms and cellular targets of HRSV and BRSV NS proteins. Although able to cooperate, NS proteins from BRSV and HRSV showed differential protection capacity in cells from different hosts. A chimeric BRSV with HRSV NS genes (BRSV h1/2) was severely attenuated in bovine IFN competent MDBK and Klu cells, whereas it replicated like BRSV in IFN-incompetent Vero cells or in IFN-competent human HEp-2 cells. After challenge with exogenous IFN-alpha, BRSV h1/2 was better protected than wild-type BRSV in human HEp-2 cells. In contrast, in cells of bovine origin, BRSV h1/2 was much less resistant to exogenous IFN than wild-type BRSV. These data demonstrate that RSV NS1 and NS2 proteins are major determinants of host range. The differential IFN escape capacity of RSV NS proteins in cells from different hosts provides a basis for rational development of attenuated live RSV vaccines.

Rescue of bovine respiratory syncytial virus from cloned cDNA: entire genome sequence of BRSV strain A51908

Infectious bovine respiratory syncytial virus (BRSV) was produced by intracellular co-expression of five plasmid borne cDNAs, each under the control of a T7 RNA polymerase promoter. These separately encoded a full-length, genetically-marked copy of BRSV antigenome along with either BRSV or human respiratory syncytial virus (HRSV) support plasmids, which express N, P, L and M2-1 proteins. HEp2 cells were used in transfection and recombinant vaccinia virus (MVA-T7) provided T7 RNA polymerase to drive the transcription. The recovery of recombinant BRSV (rBRSV) was confirmed by immunological staining of plaques, restriction enzyme digestion and nucleotide sequencing of PCR fragments carrying the genetic markers from the rescued virus. The rBRSV was indistinguishable from its parental wild-type virus in its growth characteristics in cell culture. The present work has completed the entire genome sequence of BRSV strain A51908 (15,140 nt) and has also identified changes in sequence and growth characteristics in cell culture from the original BRSV strain A51908 laboratory isolate.

Persistent infection of B lymphocytes by bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) is a major cause of respiratory disease in young cattle. Here we demonstrate BRSV persistence at low levels in tracheobronchial and mediastinal lymph nodes up to 71 days after the experimental infection of calves. Positive results were obtained on viral genomic RNA and messenger RNA coding for the nucleoprotein, glycoprotein (G), and fusion protein (F). G and F proteins were also detected in the pulmonary lymph nodes by immunohistochemistry. Double-staining experiments revealed that viral antigen was present in B-lymphocytes. Coculture experiments with the lymph node cells showed that the virus was still able to infect permissive target cells, even though no cytopathic effect was recorded. In vitro studies indicate that BRSV was still able to replicate in bovine B-lymphocyte cell lines 6 months after infection. These results may also be relevant to the understanding not only of the epidemiology and the peculiarities of the immune response of BRSV infections but also of human respiratory syncytial virus infections.

Bovine respiratory syncytial virus can induce apoptosis in MDBK cultured cells

Bovine respiratory syncytial virus (BRSV) is a major cause of respiratory disease in calves. BRSV infection is associated with epithelial cell death and inflammation. Over the past few years, a growing number of viruses have been found to induce apoptosis. In order to determine the ability of BRSV to induce apoptosis, we studied the effect of BRSV infection in cultured MDBK cells. We used ligation-mediated PCR assay to detect specific blunt-end cellular DNA fragments produced by cellular endonucleases cleaving the genomic DNA between the nucleosomes during apoptosis. We found that BRSV infection resulted in apoptosis in MDBK cells. This data demonstrates for the first time that BRSV can induce apoptosis. This data also may contribute to delineate the mechanisms that regulate tissue injury and potential lung repair following BRSV infection.

Chimeric bovine respiratory syncytial virus with attachment and fusion glycoproteins replaced by bovine parainfluenza virus type 3 hemagglutinin-neuraminidase and fusion proteins

Chimeric bovine respiratory syncytial viruses (BRSV) expressing glycoproteins of bovine parainfluenza virus type 3 (BPIV-3) instead of BRSV glycoproteins were generated from cDNA. In the BRSV antigenome cDNA, the open reading frames of the major BRSV glycoproteins, attachment protein G and fusion protein F, were replaced individually or together by those of the BPIV-3 hemagglutinin-neuraminidase (HN) and/or fusion (F) glycoproteins. Recombinant virus could not be recovered from cDNA when the BRSV F open reading frame was replaced by the BPIV-3 F open reading frame. However, cDNA recovery of the chimeric virus rBRSV-HNF, with both glycoproteins replaced simultaneously, and of the chimeric virus rBRSV-HN, with the BRSV G protein replaced by BPIV-3 HN, was successful. The replication rates of both chimeras were similar to that of standard rBRSV. Moreover, rBRSV-HNF was neutralized by antibodies specific for BPIV-3, but not by antibodies specific to BRSV, demonstrating that the BRSV glycoproteins can be functionally replaced by BPIV-3 glycoproteins. In contrast, rBRSV-HN was neutralized by BRSV-specific antisera, but not by BPIV-3 specific sera, showing that infection of rBRSV-HN is mediated by BRSV F. Hemadsorption of cells infected with rBRSV-HNF and rBRSV-HN proved that BPIV-3 HN protein expressed by rBRSV is functional. Colocalization of the BPIV-3 glycoproteins with BRSV M protein was demonstrated by confocal laser scan microscopy. Moreover, protein analysis revealed that the BPIV-3 glycoproteins were present in chimeric virions. Taken together, these data indicate that the heterologous glycoproteins were not only expressed but were incorporated into the envelope of recombinant BRSV. Thus, the envelope glycoproteins derived from a member of the Respirovirus genus can together functionally replace their homologs in a Pneumovirus background.

Deletion and substitution analysis defines regions and residues within the phosphoprotein of bovine respiratory syncytial virus that affect transcription, RNA replication, and interaction with the nucleoprotein

The phosphoprotein (P) of bovine respiratory syncytial virus (BRSV) is a multifunctional protein that plays a central role in transcription and replication of the viral genomic RNA. To investigate the domains and specific residues involved in different activities of the P protein, we generated a total of 22 deletion and 17 point mutants of the P protein. These mutants were characterized using an intracellular BRSV-CAT minigenome replication system for the ability to (1) direct minigenome transcription, (2) direct minigenome replication, and (3) form complexes with nucleocapsid protein (N) and large polymerase protein (L). These studies revealed that all the regions of P protein except amino acids 41-80 are essential for minigenome transcription and replication. Interestingly, amino acids 41-60 appeared to contain sequences that negatively regulate transcription and replication. Analysis of the N- or C-terminal ends indicated that deletion of up to 3 amino acids from the N- or C-terminus completely ablated the replication, while leaving substantial residual transcription. Single amino acid substitutions within the N-terminal 4 or C-terminal 13 amino acids showed that substitution at position 2, 4, 234, 236, 238, 240, or 241 was highly inhibitory to both transcription and replication, whereas substitution at position 3 was highly inhibitory to replication while leaving substantial residual transcription. Substitution of serine residues at the C-terminus indicated that loss of phosphorylation sites did not appear to have any effect on transcription and replication. Coimmunoprecipitation of P-N and P-L complexes with P-specific antiserum revealed that substitution mutations at the N- or C-terminus did not affect binding to N and L proteins, except that substitution mutation at C-terminus position 234, 236, 238, 240, or 241 affected binding to N protein by 10-fold.

Mapping the domains on the phosphoprotein of bovine respiratory syncytial virus required for N-P and P-L interactions using a minigenome system

The interaction of bovine respiratory syncytial virus (BRSV) phosphoprotein (P) with nucleocapsid (N) and large polymerase (L) proteins was investigated using an intracellular BRSV-CAT minigenome replication system. Coimmunoprecipitation assays using P-specific antiserum revealed that the P protein can form complexes with N and L proteins. Deletion mutant analysis of the P protein was performed to identify the regions of P protein that interact with N and L proteins. The results indicate that two independent N-binding sites exist on the P protein: an internal region of 161-180 amino acids and a C-terminal region of 221-241 amino acids. The L-binding site was mapped to a region of P protein encompassing amino acids 121-160. The data suggest that N and L protein binding domains on the P protein do not overlap.

Recombinant bovine respiratory syncytial virus with deletions of the G or SH genes: G and F proteins bind heparin

Bovine respiratory syncytial virus (BRSV) encodes three transmembrane envelope glycoproteins, namely the small hydrophobic (SH) protein, the attachment glycoprotein (G) and the fusion glycoprotein (F). The BRSV reverse genetics system has been used to generate viable recombinant BRSV lacking either the G gene or the SH gene or both genes. The deletion mutants were fully competent for multicycle growth in cell culture, proving that, of the BRSV glycoprotein genes, the SH and G genes are non-essential. Virus morphogenesis was not impaired by either of the deletions. The deletion mutants were used to study the role of the F glycoprotein and the contributions of SH and G with respect to virus attachment. Attachment mediated by the F protein alone could be blocked by soluble heparin, but not by chondroitin sulphate. Heparin affinity chromatography revealed that both the BRSV G and F glycoproteins have heparin-binding activity, with the affinity of the F glycoprotein being significantly lower than that of G. Therefore, the roles of the BRSV glycoproteins in virus attachment and receptor binding have to be reconsidered.

Evolution of bovine respiratory syncytial virus

Until now, the analysis of the genetic diversity of bovine respiratory syncytial virus (BRSV) has been based on small numbers of field isolates. In this report, we determined the nucleotide and deduced amino acid sequences of regions of the nucleoprotein (N protein), fusion protein (F protein), and glycoprotein (G protein) of 54 European and North American isolates and compared them with the sequences of 33 isolates of BRSV obtained from the databases, together with those of 2 human respiratory syncytial viruses and 1 ovine respiratory syncytial virus. A clustering of BRSV sequences according to geographical origin was observed. We also set out to show that a continuous evolution of the sequences of the N, G, and F proteins of BRSV has been occurring in isolates since 1967 in countries where vaccination was widely used. The exertion of a strong positive selective pressure on the mucin-like region of the G protein and on particular sites of the N and F proteins is also demonstrated. Furthermore, mutations which are located in the conserved central hydrophobic part of the ectodomain of the G protein and which result in the loss of four Cys residues and in the suppression of two disulfide bridges and an alpha helix critical to the three-dimensional structure of the G protein have been detected in some recent French BRSV isolates. This conserved central region, which is immunodominant in BRSV G protein, thus has been modified in recent isolates. This work demonstrates that the evolution of BRSV should be taken into account in the rational development of future vaccines.

Extensive sequence divergence among bovine respiratory syncytial viruses isolated during recurrent outbreaks in closed herds

The nucleotides coding for the extracellular part of the G glycoprotein and the full SH protein of bovine respiratory syncytial virus (BRSV) were sequenced from viruses isolated from numerous outbreaks of BRSV infection. The isolates included viruses isolated from the same herd (closed dairy farms and veal calf production units) in different years and from all confirmed outbreaks in Denmark within a short period. The results showed that identical viruses were isolated within a herd during outbreaks and that viruses from recurrent infections varied by up to 11% in sequence even in closed herds. It is possible that a quasispecies variant swarm of BRSV persisted in some of the calves in each herd and that a new and different highly fit virus type (master and consensus sequence) became dominant and spread from a single animal in connection with each new outbreak. Based on the high level of diversity, however, the most likely explanation was that BRSV was (re)introduced into the herd prior to each new outbreak. These findings are highly relevant for the understanding of the transmission patterns of BRSV among calves and human respiratory syncytial virus among humans.

Mutational analysis of the bovine respiratory syncytial virus nucleocapsid protein using a minigenome system: mutations that affect encapsidation, RNA synthesis, and interaction with the phosphoprotein

The nucleocapsid (N) protein of bovine respiratory syncytial virus (BRSV) is a multifunctional protein that plays a central role in transcription and replication of viral genomic RNA. To investigate the domains and specific residues involved in different N activities, we generated a total of 27 deletion and 12 point mutants of the N protein. These mutants were characterized using an intracellular BRSV-CAT minigenome replication system for the ability to (1) direct minigenome RNA synthesis, (2) direct minigenome encapsidation, and (3) form a complex with the phosphoprotein (P). The mutations tested were defective in synthesis of RNA from the BRSV-CAT minigenome template with the exception of the following: a deletion involving the first N-terminal amino acid and mutations involving conservative substitution at the second amino acid and at certain internal cysteine residues. Micrococcal nuclease enzyme protection assays showed that mutations involving amino acids 1-364 of the 391-amino-acid N protein prevented minigenome encapsidation. Thus the BRSV N protein has a C-terminal, 27-amino-acid tail that is not required for encapsidation. Interestingly, two of the mutations that ablated encapsidation did not greatly affect RNA synthesis; the mutant involving deletion of the N-terminal amino acid and the mutant involving a substitution at position 2. This finding indicates that the formation of a nucleocapsid sufficient to protect the RNA from nuclease is not required for template function. Coimmunoprecipitation of N and P using N- or P-specific antiserum revealed two regions of the N protein that are important for association with the P protein: a central portion of 244-290 amino acids and a C-terminal portion of 338-364 amino acids.

Fusion of the green fluorescent protein to amino acids 1 to 71 of bovine respiratory syncytial virus glycoprotein G directs the hybrid polypeptide as a class II membrane protein into the envelope of recombinant bovine herpesvirus-1

It was recently shown that the class II membrane glycoprotein G of bovine respiratory syncytial virus (BRSV) is integrated into the envelope of recombinant bovine herpesvirus-1 (BHV-1) virions in the correct orientation. To verify the hypothesis that the membrane anchor of BRSV G might be suitable to target heterologous polypeptides into the membrane of recombinant BHV-1 particles, an open reading frame encoding a fusion protein between amino acids 1 to 71 of the BRSV G glycoprotein and the green fluorescent protein (TMIIGFP) was recombined into the genome of BHV-1. The resulting recombinant BHV-1/eTMIIGFP had growth properties similar to those of wild-type BHV-1. Live-cell analysis of cells infected with BHV-1/eTMIIGFP indicated that the fusion protein localized to the cell surface. Immunoprecipitations and virus neutralization assays using a GFP-specific antiserum proved that TMIIGFP was incorporated as a class II membrane protein into virions.

Bovine respiratory syncytial virus-specific IgE is associated with interleukin-2 and -4, and interferon-gamma expression in pulmonary lymph of experimentally infected calves

OBJECTIVE

To study the local immune response of calves to bovine respiratory syncytial virus (BRSV) infection with emphasis on IgE production and cytokine gene expression in pulmonary lymph.

ANIMALS

Twelve 6- to 8-week-old Holstein bull calves. Six similar control calves were mock infected to obtain control data.

PROCEDURE

Lymphatic cannulation surgery was performed on 12 calves to create a long-term thoracic lymph fistula draining to the exterior. Cannulated calves were exposed to virulent BRSV by aerosol. Lymph fluid collected daily was assayed for BRSV and isotype-specific IgE antibody, total IgG, IgA, IgM, and protein concentrations. Interleukin-4 (IL-4), interleukin-2 (IL-2), and interferon-gamma were semi-quantitated by reverse transcription-polymerase chain reaction (RT-PCR). Cell counts and fluorescence-activated cell scanner (FACSCAN) analysis of T-cell subsets were performed on lymph cells.

RESULTS

Calves had clinical signs of respiratory tract disease during days 5 to 10 after infection and shed virus. Bovine respiratory syncytial virus-specific IgE in infected calves was significantly increased over baseline on day 9 after infection. Mean virus-specific IgE concentrations strongly correlated with increases in severity of clinical disease (r = 0.903). Expression of IL-2, IL-4, and interferon-gamma was variably present in infected and control calves, with IL-4 expression most consistent during early infection.

CONCLUSIONS AND CLINICAL RELEVANCE

Infection with BRSV was associated with production of BRSV-specific IgE, and IL-4 message was commonly found in lymph cells of infected calves. This finding supports the concept that BRSV-induced pathophysiology involves a T helper cell type-2 response. Effective therapeutic and prophylactic strategies could, therefore, be developed using immunomodulation to shift the immune response more toward a T helper cell type-1 response.