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

Subtractive Immunization as a Method to Develop Respiratory Syncytial Virus (RSV)-Specific Monoclonal Antibodies

Respiratory Syncytial Virus (RSV) is a significant cause of lower respiratory tract infections in the young, the elderly, and in immunodeficient patients. As such, the virus represents an important cause of morbidity and mortality worldwide. Development of monoclonal antibodies against RSV has resulted in a commercial prophylaxis, palivizumab (Synagis®), and different antibodies that have improved our understanding of the structure of the viral proteins. In this study, a different immunization technique, subtractive immunization, was evaluated for its applicability to develop RSV-specific antibodies. One hybridoma which produced antibodies with the strongest staining of RSV infected cells, ATAC-0025, was selected for further characterization. This antibody belongs to the IgG1 class, has neutralizing capacity and recognizes the envelope F-protein. The antibody has a broad reactivity against a range of RSV reference strains and clinical isolates.

Antigenic and sequence variability of the human respiratory syncytial virus F glycoprotein compared to related viruses in a comprehensive dataset

A comprehensive analysis of sequence variation was carried out comparing the fusion (F) protein of human respiratory syncytial viruses (hRSV) from antigenic groups A and B with the prototype sequence of the A2 strain, also belonging to antigenic group A. The limited number of full bovine RSV F sequences available were included, as well as an extensive set of F sequences from the related human metapneumovirus (hMPV). The results were analysed in the context of the recently determined three dimensional F protein structures, with antigenic sites mapped to these. Although a high degree of sequence conservation in hRSV F exists, and sequence changes did not correlate with location of antigenic sites, preferential accumulation of amino acid changes in certain antigenic sites was noted. When the analysis was extended to hMPV F, a high number of changes was noticed, in agreement with the limited degree of sequence conservation. However, some conserved regions were noted, which may account for the limited number of cross-reactive monoclonal antibodies described between hRSV F and hMPV F. These results provide information about the degree of sequence and antigenic variation currently found in the F protein of circulating viruses. They highlight the importance of establishing a baseline dataset to monitor for future changes that might evolve should preventative immunological measures be made widely available.

Rapid Detection of Bovine Respiratory Syncytial Virus in Poland Using a Human Patient-Side Diagnostic Assay

Bovine respiratory syncytial virus (BRSV) plays a significant role in the etiopathogenesis of the respiratory syndrome in young cattle during their first year of life. Development of rapid and accurate BRSV diagnostic tools would aid in the appropriate control of this important pathogen. The objective of this study was to characterize infections induced by BRSV by means of rapid patient-side immunomigration assays used for diagnosis of human respiratory syncytial virus (hRSV) in humans. Nasal and tracheal swabs were obtained from healthy calves of various beef and dairy breeds - Holstein-Friesian, Simmental, Charolais, Belgian Blue and Limousin, between the ages of 5 and 12 months, from 26 farms. BRSV was identified using two rapid immunomigration assays, TruRSV® and Clearview® RSV, and compared with RT-PCR as a reference technique. BRSV was found in 73.1% of all the herds tested. High agreement with RT-PCR was obtained for TruRSV® (κ = 0.824), while in the case of the Clearview® RSV test, agreement with PCR was moderate (κ = 0.420). The results demonstrate that rapid patient-side immunomigration assays designed to detect hRSV can be used to accurately detect BRSV in field samples collected from cattle.

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 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 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.

High mortality rate associated with bovine respiratory syncytial virus (BRSV) infection in Belgian white blue calves previously vaccinated with an inactivated BRSV vaccine

In a group of 60 Belgian White Blue calves less than 8 months old still housed in barns, a bovine respiratory syncytial virus (BRSV) outbreak was revealed on the basis of a direct diagnosis (immunofluorescence and virus isolation) performed on the lungs of dead animals, and the kinetics of BRSV neutralizing antibodies. Clinical signs, macroscopical and microscopical pulmonary lesions were also compatible with a BRSV infection. This outbreak is peculiar because the 35 oldest calves (204 +/- 29 days old) had been vaccinated 3-4 months before with an inactivated BRSV vaccine and 30% of these animals had died of respiratory distress. While they experienced a mild respiratory symptomatology, no death was recorded among the 25 youngest calves (69 +/- 29 days old) which had been left unvaccinated. Another peculiarity was found at the histological level where a massive infiltration of eosinophils was demonstrated in the pulmonary tissues of the dead animals. Together these data parallel the dramatic story described 30 years ago in children previously vaccinated with a formalin-inactivated human RSV (HRSV) vaccine upon a natural HRSV challenge. This illustrates that an immunopathological phenomenon also takes place after BRSV vaccination in cattle.

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.

Cleavage of the respiratory syncytial virus fusion protein is required for its surface expression: role of furin

The fusion (F) glycoprotein of respiratory syncytial virus (RSV) is synthesized as a nonfusogenic precursor protein (F(0)), which during its migration to the cell surface is activated by cleavage into the disulfide-linked F(1) and F(2) subunits. In the present study, soluble secreted human furin produced by a recombinant baculovirus cleaved RSV F(0) into proteins the size of F(1) and F(2). Furthermore, cleavage of F(0) was partially inhibited in the furin defective LoVo cell line, in calcium depleted HEp-2 cells, and in HEp-2 cells treated with the furin inhibitor decanoyl-R-V-K-R-chloromethylketon. These findings strongly suggest an important role for furin in activation of the RSV F protein. The F(0) protein could not be detected on the surface of cells, in which F protein activation was inhibited, and RSV particles did not appear to be released from these cells. It thus seems that in contrast to the F proteins of most other paramyxoviruses, the RSV F(0) protein is very inefficient in reaching the cell surface or is unable to reach the cell surface and therefore cannot be incorporated into virus particles.

Quantitative assessment by flow cytometry of T-lymphocytes producing antigen-specific gamma-interferon in Brucella immune cattle

Peripheral blood mononuclear cells (PBMC) isolated from cattle infected with Brucella secreted gamma-interferon (IFN-gamma) after antigen-specific stimulation with Brucellergene, which is a mixture of cytoplasmic proteins of rough Brucella melitensis B115. Following the depletion of the monocyte-macrophages from the PBMC, the enriched lymphocyte populations stimulated with Brucellergene did not produce IFN-gamma. Two-colour immunofluorescence staining of intracellular IFN-gamma and bovine cell surface molecules identified the cells producing IFN-gamma among the PBMC stimulated with Brucellergene. Moreover, this method could be used to estimate the number of T-cells specifically producing IFN-gamma. For a given animal, there is a significant correlation (p < 0.05) between the production of IFN measured by an ELISA of the supernatant of whole blood stimulated with Brucellergene and the number of T-cells producing IFN-gamma after in vitro stimulation with Brucellergene. The development of the immunofluorescence staining technique provides a new tool for analysing and for measuring the T-cell immune response in cattle.

Immunological response of mice to the bovine respiratory syncytial virus fusion glycoprotein expressed in recombinant baculovirus infected insect cells

Bovine respiratory syncytial virus (BRSV) is a major cause of respiratory disease in calves. The BRSV genome encodes two major glycoproteins, G and F, which are the major targets for the host antibody response. We have expressed the F glycoprotein in insect cells (Sf9) using a recombinant baculovirus vector. A comparison of the F protein expressed in mammalian and insect cells by SDS-PAGE showed that only part of the baculovirus-produced protein was soluble and processed like the native protein. The antigenicity of the soluble form of the F protein expressed in insect cells was identical to that of the F protein expressed in mammalian cells. Immunization with the F protein expressed in insect cells induced neutralizing antibodies in mice. This antigenic preparation adjuvanted with Quil-A produced an increased neutralizing antibody titer and induced protection.

Analysis of the bovine respiratory syncytial virus fusion protein (F) using monoclonal antibodies

Seven monoclonal antibodies (MAbs) directed against bovine respiratory syncytial virus (BRSV) fusion (F) protein were produced and characterized by radioimmunoprecipitation and immunofluorescence assays. These seven MAbs together with the previously described MAbs (Beeler and Van Wyke Coelingh, 1989) to the F protein of human respiratory syncytial virus (HRSV) were used to study the antigenic variation of 12 strains of ungulate RSV. All except one MAbs specific for the HRSV-F protein reacted with ungulate RSV strains less efficiently, indicating that some epitopes are conserved, and others are not conserved on the F proteins of HRSV and BRSV strains. Three MAbs specific to the BRSV-F protein neutralized virus infectivity and reacted with all the ungulate RSV strains, suggesting that these epitopes are well conserved. Based on the reactivity of three other MAbs specific to the BRSV-F protein, ungulate RSVs could be grouped into two subgroups. The results indicated that there are antigenic variations in the F protein among ungulate RSV strains.

Antigenic differentiation of turkey rhinotracheitis virus strains using monoclonal antibodies and polyclonal antisera

Monoclonal antibodies (mAbs) were prepared against the 8597/CV94 strain of turkey rhinotracheitis virus (TRTV). These mAbs were used to investigate antigenic relationships among three strains (8597/CV94, 1162/92 and CVL14/1 strain) of TRTV, together with polyclonal chicken and rabbit antisera to 8597/CV94 strain, and guinea pig antisera to each of the three strains. Thirty mAbs to the glycoprotein (G:3 clones), fusion (F1:6 clones), phosphorylated (P:6 clones), nucleocapsid (N:12 clones), and matrix (M:3 clones) proteins of viral antigen were obtained by cell fusion. Among these, two mAbs to F1 protein showed virus neutralizing activity. The results of ELISA test indicated that some mAbs only reacted to the 8597/CV94 strain, some reacted to 8597/CV94 and 1162/92 strains, and others reacted to all three viral strains. In neutralization tests with the three virus strains, polyclonal chicken and rabbit antisera against the 8597/ CV94 strain showed the same antibody titers. Results with four neutralizing mAbs including two previously reported mAbs [Ref. 21] indicated the titers of two mAbs (Pn2-2E and Pn3-2F) to 8597/CV94 were much higher than those to the other two viral strains. No differences were observed in the titers of the other two mAbs (Pn01-8E and Pn06-4D) against any viral strains. In cross-neutralization tests with polyclonal guinea pig antisera, there was some variations among viral strains. This work demonstrated that the Japanese isolate 8597/CV94 of TRTV is somewhat different in antigenicity from two British isolates from chickens and turkeys.