Nucleotide sequence analysis of the bovine respiratory syncytial virus fusion protein mRNA and expression from a recombinant vaccinia virus

Identification of a DRB3*011:01-restricted CD4+ T cell response against bovine respiratory syncytial virus fusion protein

Although Human Respiratory Syncytial Virus (HRSV) is a significant cause of severe respiratory disease with high morbidity and mortality in pediatric and elderly populations worldwide there is no licensed vaccine. Bovine Respiratory Syncytial Virus (BRSV) is a closely related orthopneumovirus with similar genome structure and high homology between structural and nonstructural proteins. Like HRSV in children, BRSV is highly prevalent in dairy and beef calves and known to be involved in the etiology of bovine respiratory disease, in addition to being considered an excellent model for HRSV. Commercial vaccines are currently available for BRSV, though improvements in efficacy are needed. The aims of this study were to identify CD4+ T cell epitopes present in the fusion glycoprotein of BRSV, an immunogenic surface glycoprotein that mediates membrane fusion and a major target of neutralizing antibodies. Overlapping peptides representing three regions of the BRSV F protein were used to stimulate autologous CD4+ T cells in ELISpot assays. T cell activation was observed only in cells from cattle with the DRB3*011:01 allele by peptides from AA249-296 of the BRSV F protein. Antigen presentation studies with C-terminal truncated peptides further defined the minimum peptide recognized by the DRB3*011:01 allele. Computationally predicted peptides presented by artificial antigen presenting cells further confirmed the amino acid sequence of a DRB3*011:01 restricted class II epitope on the BRSV F protein. These studies are the first to identify the minimum peptide length of a BoLA-DRB3 class II-restricted epitope in BRSV F protein.

Prevalence and Molecular Characteristics of Bovine Respiratory Syncytial Virus in Beef Cattle in China

Bovine respiratory syncytial virus (BRSV) is an important pathogen of the bovine respiratory disease complex (BRDC); however, its prevalence and molecular characteristics in China remain largely unknown. In this study, 788 nasal swabs from 51 beef cattle farms with BRDC outbreaks in 16 provinces and one municipality were collected from October 2020 to July 2022, and 18.65% (147/788) of samples from 23 farms across 11 provinces were detected as BRSV-positive by reverse transcription-insulated isothermal PCR (RT-iiPCR) assay. Further, 18 complete G gene sequences were classified into BRSV subgroup III, and 25 complete F gene sequences were obtained from 8 and 10 provinces. Compared to the known BRSV strains in GenBank, the G proteins and F proteins in this study shared several identical amino acid (aa) mutations. Moreover, five nearly complete genome sequences were obtained and clustered into a large branch with two America BRSV subgroup III strains (KU159366 and OM328114) rather than the sole Chinese strain (MT861050) but were located in an independent small branch. In conclusion, this study reveals that BRSV has a wide geographical distribution in China, and subgroup III strains, which have unique evolution characteristics, are the dominant strains. The results contribute to a better understanding of the prevalence and genetic evolution of BRSV.

Human respiratory syncytial virus infection in the pre-clinical calf model

Human respiratory syncytial virus (hRSV) is the most important respiratory pathogen in young children worldwide. Experimental modelling of hRSV disease by bovine RSV (bRSV) infection in calves provides an important tool for developing new strategies for prevention and treatment. Depending on the scientific hypothesis under investigation, this cognate host-virus model might have the disadvantage of using a highly related but not genetically identical virus. In this study, we aim to describe viral kinetics and (clinical) disease characteristics in calves inoculated with hRSV. Our results show that hRSV infects the upper and, to a lesser extent, the lower respiratory tract of calves. Infection causes upper airway clinical disease symptoms and neutrophilic infiltration of the lower airways. We conclude that a hRSV model in calves may aid future research involving distinct scientific questions related to hRSV disease in children.

Respiratory syncytial virus: current progress in vaccine development

Respiratory syncytial virus (RSV) is the etiological agent for a serious lower respiratory tract disease responsible for close to 200,000 annual deaths worldwide. The first infection is generally most severe, while re-infections usually associate with a milder disease. This observation and the finding that re-infection risks are inversely associated with neutralizing antibody titers suggest that immune responses generated toward a first RSV exposure can significantly reduce morbidity and mortality throughout life. For more than half a century, researchers have endeavored to design a vaccine for RSV that can mimic or improve upon natural protective immunity without adverse events. The virus is herein described together with the hurdles that must be overcome to develop a vaccine and some current vaccine development approaches.

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.

The use of two-dimensional SDS-PAGE to analyze the glycan heterogeneity of the respiratory syncytial virus fusion protein

The respiratory syncytial virus (RSV) fusion (F) protein is synthesized as an inactive precursor (F0), which subsequently undergoes post-translational cleavage to give the disulphide bond-linked F1 and F2 subunits. The methodology detailing the use of two-dimensional electrophoresis, endoglycosidases, and alpha-mannosidase inhibitors, as applied to investigating F protein glycan maturation, is given. Examples are used to show how this methodology was used to provide evidence for glycan heterogeneity within the mature F protein.

Evidence that maturation of the N-linked glycans of the respiratory syncytial virus (RSV) glycoproteins is required for virus-mediated cell fusion: The effect of alpha-mannosidase inhibitors on RSV infectivity

Glycan heterogeneity of the respiratory syncytial virus (RSV) fusion (F) protein was demonstrated by proteomics. The effect of maturation of the virus glycoproteins-associated glycans on virus infectivity was therefore examined using the alpha-mannosidase inhibitors deoxymannojirimycin (DMJ) and swainsonine (SW). In the presence of SW the N-linked glycans on the F protein appeared in a partially mature form, whereas in the presence of DMJ no maturation of the glycans was observed. Neither inhibitor had a significant effect on G protein processing or on the formation of progeny virus. Although the level of infectious virus and syncytia formation was not significantly affected by SW-treatment, DMJ-treatment correlated with a one hundred-fold reduction in virus infectivity. Our data suggest that glycan maturation of the RSV glycoproteins, in particular those on the F protein, is an important step in virus maturation and is required for virus infectivity.

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.

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.

Recognition of bovine respiratory syncytial virus proteins by bovine CD8+ T lymphocytes

CD8+ T lymphocytes play a major role in the clearance of bovine respiratory syncytial virus (BRSV), an important respiratory pathogen of young calves that shares many of the epidemiological and pathological features of human respiratory syncytial virus (HRSV) in infants. Recombinant vaccinia virus (rVV) and recombinant fowlpox virus (rFPV), expressing individual BRSV proteins, were used to demonstrate that the F, N and M2 proteins were the major antigens recognized by bovine CD8+ T cells in major histocompatibility complex (MHC)-defined cattle. BRSV protein recognition by CD8+ T cells was analysed using cytotoxic T lymphocyte (CTL) assays or by the production of interferon-gamma (IFN-gamma) following restimulation with BRSV proteins. Strong recognition of the G protein by CD8+ T cells was observed in cattle that had been vaccinated with rVV expressing this protein and subsequently challenged with BRSV. Although there is variation in the number of expressed MHC genes in cattle with different class I haplotypes, this did not appear to influence BRSV protein recognition by CD8+ T cells. Knowledge of the antigenic specificity of BRSV-specific CD8+ T cells will facilitate the qualitative and quantitative analysis of BRSV-specific CD8+ T-cell memory in cattle and help to ensure that potential vaccines induce a qualitatively appropriate CD8+ T-cell response.

Identification of immunodominant epitopes derived from the respiratory syncytial virus fusion protein that are recognized by human CD4 T cells

Memory CD4 T-cell responses against respiratory syncytial virus (RSV) were evaluated in peripheral blood mononuclear cells of healthy blood donors with gamma interferon enzyme-linked immunospot (Elispot) assays. RSV-specific responses were detected in every donor at levels varying between 0.05 and 0.3% of CD4 T cells. For all donors tested, a considerable component of the CD4 T-cell response was directed against the fusion (F) protein of RSV. We characterized a set of 31 immunodominant antigenic peptides targeted by CD4 T cells in the context of the most prevalent HLA class II molecules within the Caucasian population. Most antigenic peptides were HLA-DR restricted, whereas two dominant DQ peptides were also identified. The antigenic peptides identified were located across the entire sequence of the F protein. Several peptides were presented by more than one major histocompatibility complex class II molecule. Furthermore, most donors recognized several F peptides. Detailed knowledge about immunodominant antigenic peptides will facilitate the ability to monitor CD4 T-cell responses in patients and the measurement of correlates of protection in vaccinated subjects.

The ovine respiratory syncytial virus F gene sequence and its diagnostic application

Ruminant respiratory syncytial viruses (RSVs) are classified into 2 subgroups, ovine RSV and bovine RSV. Although ovine RSV infects cattle, its contribution to bovine respiratory tract disease has not been established, which is an important issue for vaccine development in cattle. Diagnosis by virus isolation or serology has low or variable sensitivity and/or specificity and polymerase chain reaction (PCR) has been recommended as a rapid and sensitive technique for RSV detection. A simple procedure has been developed to detect and identify bovine and ovine RSVs. First, the nucleotide sequence of the ovine RSV fusion (F) gene was determined and compared with representative strains of bovine RSV and human RSV subgroups A and B. The ovine RSV F gene has 85 and 72-73% nucleotide identity with those of bovine RSV and human RSV, respectively. The predicted amino acid sequence of the ovine RSV F gene has 94 and 83-84% amino acid identity with those of bovine RSV and human RSV, respectively. Then PCR primers targeting a specific F gene fragment of bovine and ovine RSV were designed. The primers represented bases 85-103 and the complementary sequence to bases 510-493 of the ovine RSV F gene. A similar PCR product (426 bp) was obtained on agarose gel electrophoresis from bovine RSV and from ovine RSV. The products, however, were unique to the parent virus and could be distinguished by EcoRI or MspI restriction endonuclease cleavage. EcoRI cleaved the ovine product into 2 bands (285 and 141 bp) but failed to affect the bovine RSV PCR product. However, MspI cleaved the bovine product into 2 bands (229 and 197 bp) but had no effect on the ovine product. Also, this assay did not amplify any PCR product with human RSV. The reverse transcription-polymerase chain reaction (RT-PCR) followed by restriction enzyme digestion is a useful and practical approach for detection and differentiation of ruminant respiratory syncytial viruses.

Furin cleavage of the respiratory syncytial virus fusion protein is not a requirement for its transport to the surface of virus-infected cells

The intracellular cleavage of respiratory syncytial virus (RSV) fusion (F) protein by furin was examined. In RSV-infected LoVo cells, which express an inactive form of furin, and in RSV-infected Vero cells treated with the furin inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone (dec-RVKR-cmk), the F protein was expressed as a non-cleaved 73 kDa species. In both cases the F protein was initially expressed as an endoglycosidase H (Endo H)-sensitive precursor (F0(EHs)) which was modified approximately 40 min post-synthesis by the addition of complex carbohydrates to produce the Endo H-resistant form (F0(EHr)). The size and glycosylation state of F0(EHr) were identical to a transient intermediate form of non-cleaved F protein which was detected in RSV-infected Vero cells in the absence of inhibitor. Cell surface biotinylation and surface immunofluorescence staining showed that F0(EHr) was present on the surface of RSV-infected cells. RSV filaments have been shown to be the predominant form of the budding virus that is detected during virus replication. Analysis of the RSV-infected cells using scanning electron microscopy (SEM) showed that, in the presence of dec-RVKR-cmk, virus budding was impaired, producing fewer and much smaller viral filaments than in untreated cells. A comparison of immunofluorescence and SEM data showed that F0(EHr) was routed to the surface of virus-infected cells but not located in these smaller structures. Our findings suggest that activation of the F protein is required for the efficient formation of RSV filaments.

Identification of CD4+ T cell epitopes on the fusion (F) and attachment (G) proteins of bovine respiratory syncytial virus (BRSV)

To gain insight into the antigenic structure of the F and G proteins of BRSV, we have mapped CD4+ T cell epitopes on these proteins using synthetic peptides and lymphocytes from vaccinated, naturally infected or experimentally infected calves, in proliferation assays. Bovine CD4+ T cells recognised epitopes that were distributed predominantly within the F1 subunit of the F protein, some of which were adjacent to previously identified B cell epitopes. Bovine CD4+ T cell epitopes within the G protein were mainly located within the cytoplasmic tail. Several immunodominant bovine T cell epitopes within the F protein, that were recognised by calves with different haplotypes, are also recognised by human T cells. Thus, cattle and humans appear to recognise similar T cell epitopes on the F protein. Studies using antibodies to bovine MHC class II and BoLA DR-transfected CHO cells as antigen-presenting cells indicated that immunodominant regions of the F and G proteins contained both DR- and DQ-restricted epitopes. The finding that there was little recognition of the extracellular domain of the G protein by T cells has important implications for vaccine design based on the soluble form of this protein.

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.

In situ hybridization detection of bovine respiratory syncytial virus in the lung of experimentally infected lambs

We studied the distribution of bovine respiratory syncytial virus (BRSV) RNA in lungs of experimentally inoculated lambs by in situ hybridization at different times postinoculation. The probe used for in situ hybridization was prepared by reverse transcription of BRSV RNA, followed by polymerase chain reaction (PCR) amplification of the cDNA. Twenty-five Merino lambs of both sexes with a live weight of 17 +/- 3 kg received an intratracheal inoculation of 20 ml saline solution containing 1.26 X 10(6) TCID50 BRSV (strain NMK7)/ml. Lambs were slaughtered 1, 3, 7, 11, and 15 days postinoculation (PID). Bronchial and bronchiolar epithelial cells were positive for BRSV nucleic acid by ISH at 1, 3, 7, and 11 PID. However, alveolar epithelial cells contained positive cells at 1, 3, and 7 PID. Cells containing viral RNA were detected from 1 to 11 PID in exudate within bronchial and bronchiolar lumina and from 3 to 7 PID in alveolar exudates. Positive hybridization signals were identified in interstitial mononuclear cells and in bronchi-associated lymphoid tissue from 3 to 11 PID. Mononuclear cells were located in peribronchiolar tissue and interalveolar septa. The highest signal intensity in positive cells was observed at 3 and 7 PID, coinciding with the most important histopathological findings.

Bovine respiratory syncytial virus (BRSV): a review

Bovine respiratory syncytial virus (BRSV) infection is the major cause of respiratory disease in calves during the first year of life. The study of the virus has been difficult because of its lability and very poor growth in cell culture. However, during the last decade, the introduction of new immunological and biotechnological techniques has facilitated a more extensive study of BRSV as illustrated by the increasing number of papers published. Despite this growing focus, many aspects of the pathogenesis, epidemiology, immunology etc. remain obscure. The course and outcome of the infection is very complex and unpredictable which makes the diagnosis and subsequent therapy very difficult. BRSV is closely related to human respiratory syncytial virus (HRSV) which is an important cause of respiratory disease in young children. In contrast to BRSV, the recent knowledge of HRSV is regularly extensively reviewed in several books and journals. The present paper contains an updated review on BRSV covering most aspects of the structure, molecular biology, pathogenesis, pathology, clinical features, epidemiology, diagnosis and immunology based on approximately 140 references from international research journals.

Diagnosis of enzootic pneumonia in Danish cattle: reverse transcription-polymerase chain reaction assay for detection of bovine respiratory syncytial virus in naturally and experimentally infected cattle

A reverse transcription-polymerase chain reaction (RT-PCR) assay was developed for detection of bovine respiratory syncytial virus (BRSV) in lung tissue of naturally and experimentally infected cattle. Primers were selected from the gene coding the F fusion protein, which is relatively conserved among BRSV isolates. The RT-PCR assay was highly specific, it yielded positive reactions only when performed on BRSV-infected cell cultures or tissues. The detection limit of the RT-PCR assay was assessed as 5 TCID50. BRSV was detected in tissues of the respiratory tract and in the tracheobroncheal lymph node of calves euthanized 2-8 days after experimental infection with BRSV, whereas samples of other tissues and samples from mock-infected animals were negative at all time points. Examination of lung samples from 8 different regions of the lungs revealed that although the virus was most often found in the cranioventral lobules, it was frequently present in all lung lobules. Microbiologic examinations of all acute fatal cases of pneumonia (135 animals) in cattle submitted for diagnostic purposes during 1 year revealed that Actinomyces pyogenes (11%), Haemophilus somnus (10%), Pasteurella sp. (7%), and Pasteurella haemolytica (7%) were the most common bacterial agents found in the lungs. BRSV was identified using a conventional antigen enzyme-linked immunosorbent assay (ELISA) in 23 (17%) animals. The established BRSV-specific RT-PCR assay yielded positive results for the same 23 animals. In addition, 10 animals that were negative with the ELISA were positive with the RT-PCR assay. These results indicates that the RT-PCR assay can be a sensitive, reliable alternative to conventional diagnostic procedures.

Antigenically distinct G glycoproteins of BRSV strains share a high degree of genetic homogeneity

Bovine respiratory syncytial (BRS) virus can be divided into antigenic subgroups based on the reactivity of monoclonal antibodies (mAbs) to the attachment glycoprotein, G. Further, the polyclonal antibody response of calves vaccinated with recombinant vaccinia viruses expressing the G protein of a particular subgroup is also subgroup-specific. To investigate the genetic basis for the antigenic heterogeneity of the BRS virus G protein, the genes for the G protein from 6 BRS virus strains representative of the antigenic subgroups were cloned, sequenced, and compared with the prototype subgroup A strain, 391-2. There was only 10% nucleic acid difference and 15% amino acid difference between strains from different subgroups. These findings are in sharp contrast to the situation with human RS virus, where there is a 45% difference in amino acid identity between subgroups. In fact, the extent of amino acid difference between BRS virus subgroups is similar to the level of heterogeneity observed within human subgroups. Analysis of the reactivity of mAbs with peptides from the cysteine-rich region (174-188) of the G protein representing each antigenic subgroup indicated that amino acids at positions 180, 183, and possibly 184 are important in subgroup distinction. Taken together, these data suggest that although the genetic variation responsible for the antigenic differences determining subgroups among BRS viruses is more limited than that observed among human RS virus subgroups, the amino acid differences that exist have a profound effect upon antibody recognition.

Expression in Escherichia coli and purification of soluble forms of the F protein of bovine respiratory syncytial virus

Six fragments of the F gene from bovine respiratory syncytial virus (BRSV) were engineered into the pMAL-c2 Escherichia coli expression vector and expressed as C-terminal maltose-binding protein (MBP) fusion products. The resulting polypeptides were partially soluble and single-step purified by affinity chromatography. These fusion proteins were recognized in Western blots by several MAbs directed against human respiratory syncytial virus F protein. In addition, rabbit polyclonal antisera raised against two purified MBP-derived proteins reacted with the BRSV-F protein.

Antigenic analysis of the F protein of the bovine respiratory syncytial virus: identification of two distinct antigenic sites involved in fusion inhibition

From two independent fusions, fifteen MAbs directed to the F protein of the bovine respiratory syncytial virus (BRSV) were characterized by radio-immunoprecipitation assays. Competition binding assays among these MAbs identified two distinct antigenic sites (A and B) and one overlapping site (AB). All of the MAbs specific to epitopes belonging to site A neutralized the infectivity of the virus in vitro and recognized human and bovine RSV strains. Only two out of the five MAbs directed to epitopes of site B were neutralizing and three reacted with all of the RSV strains tested, suggesting that the epitopes constituting this domain present heterogeneous characteristics. In each of sites A and B, one of the neutralizing MAbs also inhibited cell fusion. The biological relevance of these domains was established by competing representative MAbs and sera from BRSV-infected calves.

Variation in the fusion glycoprotein gene of human respiratory syncytial virus subgroup A

Six different genotypes (designated lineages SHL1-6) of human respiratory syncytial (RS) virus have been defined by partial nucleotide sequence analysis of the variable SH and the hypervariable G membrane protein genes, and by restriction fragment analysis of the conserved N protein gene of viruses isolated in south Birmingham. Viruses of very similar genotype appear to be present worldwide at the present time. We have determined the nucleotide sequences of the fusion protein genes of five viruses isolated in south Birmingham in the same year, but belonging to different lineages, and have compared them with the sequences of four subgroup A viruses isolated at earlier times from diverse localities. The sequence diversity of the F genes of these five viruses, as measured by nucleotide (94.5-98.5%) and inferred amino acid (97.0-99.3%) identifies, is comparable with that of the nine subgroup A viruses considered as a whole. No sequence changes occur in any of the sites of known epitopes. Comparison of the nine subgroup A sequences with the published sequences of a subgroup B strain and three bovine RS viruses confirms that the F protein sequences are most divergent in the F2 region.

Development of nested PCR assays for detection of bovine respiratory syncytial virus in clinical samples

Two nested PCR assays were developed for the detection of bovine respiratory syncytial virus (BRSV). Primers were selected from the gene encoding the F fusion protein (PCR-F) and the gene encoding the G attachment protein (PCR-G). Biotinylated oligonucleotide probes, termed F and G, were selected for the hybridization of the respective PCR products. The sensitivities of the PCR-F and PCR-G assays were similar, both detecting 0.1 tissue culture infective dose of the virus. The PCR-F assay amplified all bovine strains and one human strain (RS32) tested. No cross-reactions were observed with nine heterologous respiratory viruses. PCR-F products of bovine and human RSV strains were discriminated by using endonuclease restriction enzyme ScaI, which specifically cleaved, products of BRSV. Oligonucleotide probe F was also specific for products of BRSV. The PCR-G assay detected all bovine strains and none of the human strains tested. A faint electrophoretic band was also observed with products of Sendai virus. However, probe G did not hybridize with this product, only with products of BRSV. Nasal swabs collected from cattle with no symptoms and cattle in the acute stage of respiratory disease were analyzed for BRSV by the immunofluorescence (IF) method and by the PCR-F and PCR-G assays. The virus was detected by the PCR assays in 31 of 35 (89%) samples tested. Only 23 samples (66%) were positive by the IF method, and these samples were also positive by both the PCR-F and PCR-G assays. The 31 samples detected as positive by PCR originated from cattle presenting clinical signs of acute respiratory disease; the four PCR-negative samples originated from clinically asymptomatic neighboring cattle. All sampled animals subsequently seroconverted and became reactive to BRSV. Thus, the detection of BRSV by PCR correlated with clinical observations and was considerably more sensitive (66 versus 89%) than IF. These results indicate that both nested PCR assays provide rapid and sensitive means for the detection of BRSV infection in cattle. Considering its higher specificity, the PCR-F assay can be recommended as the method of choice in the analysis of clinical specimens of BRSV.

An update on approaches to the development of respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) vaccines

RSV and PIV3 are responsible for about 30% of severe viral respiratory tract disease leading to hospitalization of infants and children. For this reason, there is a need to develop vaccines effective against these viruses. Since these viruses cause severe disease in early infancy, vaccines must be effective in the presence of maternal antibody. Currently, several strategies for immunization against these viruses are being explored including peptide vaccines, subunit vaccines, vectored vaccines (e.g., vaccinia-RSV or adenovirus-RSV recombinants), and live attenuated virus vaccines. The current status of these approaches is reviewed. In addition, the immunologic basis for the disease potentiation seen in vaccinees immunized with formalin-inactivated RSV during subsequent RSV infection is reviewed. The efficacy of immunization in the presence of maternal antibody is discussed. Much progress for a RSV and PIV3 vaccine has been made and successful immunization against each of these pathogens should be achieved within this decade.

Structural difference in the fusion protein among strains of bovine respiratory syncytial virus

The polypeptides of different strains of bovine respiratory syncytial virus (RSV) were compared. Altered electrophoretic migrations were observed in the G, F, P, M and 22 kDa polypeptides. The molecular weight of the F2 fragment in human RSV (Long strain) and bovine RSV (A51908 and Md-X strains) was approximately 20 kDa whereas it was approximately 15.5 kDa in caprine RSV and bovine RSV (FS-1 and VC-464 strains). The size difference of the F2 subunit was due to difference in the extent of glycosylation.

Structure and sequence comparison of bovine respiratory syncytial virus fusion protein

The fusion (F) proteins of 10 strains of bovine respiratory syncytial virus (BRSV) were compared by radioimmunoprecipitation with fractionation on SDS-polyacrylamide gels. Two different molecular weights (15 kDa and 20 kDa) of the F2 proteins were demonstrated among the BRSV strains tested. To delineate the molecular basis for differences in the molecular weights of F2 subunits among the BRSV strains, the nucleotide sequences of the F genes of FS1 and VC464 strains were determined from cDNA clones. The deduced amino acid sequences were then compared to those of BRSV strains RB94, 391-2 and A51908. The F gene was highly conserved (> 95%) among BRSV strains. Comparison of the deduced F2 amino acid sequences showed that the strain with F2 subunits of 20 kDa had three N-linked glycosylation sites, whereas the strains with F2 subunits of 15 kDa had two N-linked glycosylation sites. Analysis of F2 subunits in their deglycosylated forms indicated that the difference in the molecular weights of the F2 subunits was due to the difference in the extent of glycosylation.

Identifying bovine respiratory syncytial virus by reverse transcription-polymerase chain reaction and oligonucleotide hybridizations

An assay to identify tissue culture cells infected with bovine respiratory syncytial virus (BRSV) that utilizes reverse transcription (RT), the polymerase chain reaction (PCR), and a synthetic oligonucleotide hybridization probe has been developed. The RT-PCR assay uses a BRSV-specific negative-sense oligonucleotide primer to synthesize cDNA from a BRSV fusion protein mRNA template and another BRSV-specific oligonucleotide primer (positive sense) upstream from the negative-sense primer for PCR amplification. In the presence of mRNA templates of BRSV isolates originating from locations throughout the United States, the BRSV RT-PCR assay resulted in amplified products (381 bp) that were specific to BRSV, as demonstrated in hybridizations with a positive-sense oligonucleotide probe complementary to internal sequences and in sequence comparisons with the F protein of BRSV 391-2. In analysis of the BRSV RT-PCR assay with prototype strains of human RSV subgroups A and B, amplification of a similar 381-bp RT-PCR product was not evident, and no RT-PCR product hybridized with the internal probe. We conclude that the specific ability to amplify DNA sequences of BRSV F protein mRNA by RT-PCR and then to demonstrate the presence of the amplified product with a BRSV-specific oligonucleotide probe will greatly add to the speed, sensitivity, and specificity of BRSV diagnostics.

Polylactosaminoglycan modification of the respiratory syncytial virus small hydrophobic (SH) protein: a conserved feature among human and bovine respiratory syncytial viruses

We investigated the nature of the oligosaccharide modification of the glycosylated forms of the small hydrophobic integral membrane protein, SH (previously designated 1A), of respiratory syncytial (RS) virus. Analysis of SH protein expressed in cells infected with RS virus or with a recombinant vaccinia virus revealed two glycosylated SH protein species, SHg and SHp, which contained N-linked carbohydrate residues. SHp migrated diffusely on polyacrylamide gels, which suggested modification by polylactosaminoglycan oligosaccharides. Polylactosaminoglycan modification of SHp was established from three lines of investigation: (1) the synthesis of SHp in a cell line (IdID) conditionally defective in the ability to add specific carbohydrate residues to N- or O-linked oligosaccharide chains required the addition of galactose, which is a component of the N-acetyllactosamine repeating unit; (2) SHp was sensitive to digestion with endo-beta-galactosidase, which cleaves the beta 1-4 linkage between galactose and N-acetylglucosamine of the repeated N-acetyllactosamine subunit; and (3) SHp was selected by Datura stramonium lectin (Dsl), which has specificity for polylactosaminoglycans. The presence of SHp as a component of purified human subgroups A and B and bovine RS virus particles was demonstrated by Dsl affinity selection. In addition to SHp, nonglycosylated SHo was selected by Dsl affinity, indicating that SHp and SHo may associate to form complexes within infected cells and virus particles. To identify conserved amino acid residues among the human and bovine SH glycoproteins that may function as signals for polylactosaminoglycan modification, the nucleotide sequences of the SH protein genes of a human subgroup B virus (8/60) and a bovine virus (391-2) were determined and compared to those of a human subgroup A virus (A2), a subgroup B virus (18537), and a bovine virus (A51908). A comparison of the deduced amino acid sequences of the human and bovine RS virus SH proteins indicated that a central hydrophobic region and the presence of potential N-linked glycosylation sites on either side of the central hydrophobic region were conserved features that may be required for the polylactosaminoglycan modification of SH.

Gene junction sequences of bovine respiratory syncytial virus

The nucleotide sequences of seven gene junctions (N-P, P-M, M-SH, SH-G, G-F, F-M2 and M2-L) of bovine respiratory syncytial virus (BRSV) strain A51908 were determined by dideoxynucleotide sequencing of cDNAs from polytranscript mRNAs and from genomic RNA. By comparison with the consensus sequences derived from human respiratory syncytial virus (HRSV) mRNAs, gene-start and gene-end sequences were found in all BRSV mRNAs. There was a perfect match between the BRSV and HRSV in all gene-start sequences, except for the sequence of the SH gene which contained one nucleotide difference compared to HRSV A2; and the gene-start sequence of the L gene, which was one nucleotide shorter than the corresponding sequence of HRSV. Analysis of the intergenic regions showed a high degree of divergence in the nucleotide sequence between BRSV and HRSV. However, the length of the nucleotides in the intergenic sequences was similar for a given gene junction. As in the case of HRSV, the M2 and L genes of BRSV overlap by 68 nucleotides, suggesting a similar transcription attenuation mechanism. The sequences of the overlap, corresponding to the 3' end of the L gene, were almost identical between BRSV and HRSV.