Bovine respiratory syncytial virus (BRSV): a review

Animal pneumoviruses: molecular genetics and pathogenesis

Pneumoviruses are single-stranded, negative-sense, nonsegmented RNA viruses of the family Paramyxoviridae, subfamily Pneumovirinae, and include pathogens that infect humans (respiratory syncytial virus and human metapneumovirus), domestic mammals (bovine, ovine, and caprine respiratory syncytial viruses), rodents (pneumonia virus of mice), and birds (avian metapneumovirus). Among the topics considered in this review are recent studies focused on the roles of the individual virus-encoded components in promoting virus replication as well as in altering and evading innate antiviral host defenses. Advances in the molecular technology of pneumoviruses and the emergence of recombinant pneumoviruses that are leading to improved virus-based vaccine formulations are also discussed. Since pneumovirus infection in natural hosts is associated with a profound inflammatory response that persists despite adequate antiviral therapy, we also review the recent experimental treatment strategies that have focused on combined antiviral, anti-inflammatory, and immunomodulatory approaches.

Formalin-inactivated bovine RSV vaccine enhances a Th2 mediated immune response in infected cattle

Safe RSV vaccine development has challenged the medical community since a formalin-killed RSV vaccine caused disease exacerbation in the 1960s. Disease was replicated using the bovine RSV system in one of two studies. The studies differed in viral protein dose and length of time between vaccination and infection. Disease exacerbation occurred in study 2 (previously reported). We hypothesized that low protein concentration in study 2's vaccine stimulated a TH2/IgE response that enhanced disease. BRSV-specific IgG1, IgG2, and IgE were measured by ELISA/Western blot from vaccinated/infected, vaccinated/mock infected, mock vaccinated/infected calves in both studies. Results revealed that study 2 calves produced more IgE, particularly to the nucleoprotein (N); IgE among study 2 calves correlated with high clinical scores. In contrast, study 1 calves showed stronger IgG responses to viral proteins.

Priming of multiple T cell subsets by modified-live and inactivated bovine respiratory syncytial virus vaccines

T cell activity is a critical component of immunity to bovine respiratory syncytial virus (BRSV). We tested the effects of immunization by modified-live and inactivated BRSV vaccines on cell-mediated and humoral immunity in young calves. The two forms of vaccine stimulated similar serum neutralizing antibody production, although the early kinetics of those responses differed. CD4+, CD8+, and gammadelta T cells were analyzed before and after immunization for BRSV-specific in vitro recall responses, as evaluated by CD25 upregulation measured by flow cytometry. Modified-live virus (MLV) primed each of the three subsets for statistically significant in vitro responses to antigen. Inactivated vaccine also primed each T cell population for significant antigen-driven CD25 upregulation, including responses by CD4+ and gammadelta T cells that were stronger and longer-lasting than those primed by MLV. Monoclonal antibody was used in additional assays to block MHC class I during incubation of BRSV antigen with peripheral blood mononuclear cells from an animal in the inactivated vaccine group. The recall response by CD8+ T cells was more inhibited by this treatment than the other subsets, further suggesting that the inactivated vaccine had primed antigen-specific CD8+ T cells. In summary, the data indicate that balanced BRSV-specific T cell responses can be induced by inactivated, as well as modified-live, conventional vaccines, which may implicate an alternative pathway of MHC class I antigen presentation.

An experimental infection model for reproduction of calf pneumonia with bovine respiratory syncytial virus (BRSV) based on one combined exposure of calves

Bovine respiratory syncytial virus (BRSV) has been recognised as an important pathogen in calf pneumonia for 30 years, but surprisingly few effective infection models for studies of the immune response and the pathogenesis in the natural host have been established. We present a reproducible experimental infection model for BRSV in 2-5-month-old, conventionally reared Jersey calves. Thirty-four colostrum-fed calves were inoculated once by aerosol and intratracheal injection with BRSV. Respiratory disease was recorded in 91% of the BRSV-inoculated calves, 72% had an accompanying rise in rectal temperature and 83% exhibited >5% consolidation of the lung tissue. The disease closely resembled natural outbreaks of BRSV-related pneumonia, and detection of BRSV in nasal secretions and lung tissues confirmed the primary role of BRSV. Nine mock-inoculated control calves failed to develop respiratory disease. This model is a valuable tool for the study of the pathogenesis of BRSV and for vaccine efficacy studies.

Persistence of respiratory syncytial virus in macrophages alters phagocytosis and pro-inflammatory cytokine production

Functions of macrophage are known to be altered by acute infection with respiratory syncytial virus (RSV). However, it is unknown whether the persistent presence and expression of the RSV genome have any effect on the functions of these cells. We used a murine macrophage-like cell line (P388D1) persistently infected with RSV to determine: (i) phagocytic activity mediated by Fcgamma receptors, (ii) expression of Fcgamma receptors, and (iii) production of IL-1beta, IL-6 and TNF-alpha. Viral persistence was found to increase phagocytosis, expression of Fcgamma receptors and the production of IL-1beta and IL-6. In contrast the biological activity of secreted TNF-alpha decreased. In this study we give novel evidence that RSV persistence alters the biological activities of macrophages.