Characterisation of virus-specific peripheral blood cell cytokine responses following vaccination or infection with classical swine fever viruses
Introduction
Classical swine fever (CSF) is a devastating disease that poses one of the greatest risks to the swine industry worldwide. CSF is caused by the classical swine fever virus (CSFV), a highly contagious, small enveloped, single-stranded RNA virus that belongs to the family Flaviviridae. CSF has, since 1990, been controlled in the EU through a ‘stamping-out’ slaughter policy but the presence of a CSFV reservoir in European wild-boar populations, together with increasing public opposition against stamping-out policies, has now led to an increased likelihood that vaccination may be deployed as a last resort component of a control policy (Vandeputte and Chappuis, 1999, van Oirschot, 2003). Existing live attenuated CSFV vaccines, such as those based on lapinised or culture attenuated C-strain viruses, provide a rapid onset of complete protection but pose problems in discriminating infected amongst vaccinated animals whereas questions remain about the efficacy of available marker sub-unit vaccines for use under emergency outbreak conditions (van Oirschot, 2003).
The immunological mechanisms that underlie the rapid protection afforded by live attenuated C-strain vaccines are not well defined, however protection may precede the appearance of neutralising antibody but not IFN-γ secreting cells in peripheral blood (Suradhat et al., 2001, Suradhat and Damrongwatanapokin, 2003), suggesting that cellular immunity is responsible. A number of investigations have attempted to characterise these cellular mechanisms; both virus-specific CD4+ and CD8+ T cell IFN-γ responses occur following vaccination, with different studies suggesting prominent roles for either population (Suradhat et al., 2005). Following C-strain vaccination and challenge, CD6+CD8+ MHC class I restricted cytotoxic T lymphocyte responses, directed against the non-structural viral protein NS3, were evoked that could lyse virus-infected cells (Pauly et al., 1995). It was later demonstrated that the NS3 specific cytotoxic T lymphocytes also secrete IFN-γ (Rau et al., 2006). While IFN-γ appears to serve as a good marker for anti-CSFV cell-mediated responses, its role in the primary response to virulent CSFV is less well studied. Piriou et al. (2003) infected pigs with a sub-acute dose of CSFV that resulted in the induction of a strong IFN-γ response. Suradhat et al. (2001) reported a virus-specific IFN-γ response in pigs 8 days after a virulent CSFV infection and yet all animals died within 14 days.
Other cytokine responses induced by CSFV have been studied in vitro and in vivo but the mechanisms underlying these responses and their contribution to immunity/disease remain to be defined. In vitro infection of primary endothelial cells with virulent CSFV induces an up-regulation in the transcription of pro-inflammatory cytokines (Bensaude et al., 2004). Analyses of early cytokine responses following CSFV infection have shown that different dendritic cell types express different cytokine profiles. The dominant effect appeared to be highly elevated secretion of TNF-α and IFN-α, which could also be detected in sera, and may play a role in the disruption of immune responses (Jamin et al., 2008). In addition immunohistochemical studies have demonstrated macrophages expressing proinflammatory cytokines in both the spleen and liver of CSFV infected pigs (Sánchez-Cordón et al., 2005, Núñez et al., 2005).
With a view to providing additional information concerning the cytokine mediated mechanisms that may contribute to protection or pathology, and therefore aid the development of the next generation of CSFV vaccines, we explored the kinetics of the cytokine response from peripheral blood cells of pigs vaccinated with a highly efficacious attenuated C-strain vaccine and/or infected with a moderately virulent isolate from the UK CSF outbreak in 2000 (Sandvik et al., 2000, Everett et al., 2009).
Section snippets
Animals and viruses
‘High-health’ status Large White/Landrace cross male pigs, 8–10 weeks of age were purchased from a local commercial source. Lyophilized live attenuated Riemser C-strain CSFV (AC Reimser Schweinepestvakzine, Reimser Arzneimittel AG, Germany) was provided by the European Commission Vaccine Bank. For inoculation of pigs, the virus was reconstituted in vaccine diluent as described by the manufacturer. A UK CSFV isolate from the disease outbreak in 2000 (UK2000/7.1 Sandvik et al., 2000) was obtained
Outcome of vaccination and infection with CSFV viruses
Following infection with the CSFV isolate from a UK outbreak in 2000 (UK2000/7.1) (Experiment 1) or vaccination of pigs with the C-strain virus (Experiment 2), clinical signs were measured using a clinical score system (Fig. 1A). On infection with UK2000/7.1, pigs displayed signs of CSF from 7 to 14 days post-infection and progressed to reach clinical scores between 10 and 15 by 13–19 days post-infection. In contrast, no clinical signs were observed in any of the pigs vaccinated with the
Discussion
Experimental infection of pigs with UK2000/7.1 demonstrated this isolate to be of moderate virulence, causing high viraemia and clinical symptoms, and appears to be representative of CSFV strains causing recent outbreaks (Floegel-Niesmann et al., 2003, Everett et al., 2009). Vaccination of pigs with the C-strain virus induced no clinical signs and provided solid protection against the UK2000/7.1 virus after only 5 days. Thus, these viruses offered excellent model systems with which to analyse
Conflict of interest statement
The authors declare no conflict of interests.
Acknowledgments
We would like to thank Nicole Piontkowski, Reimser Arzneimittel AG, Germany and the European Commission for supplying the C-strain CSFV vaccine; Derek Clifford and colleagues at the Veterinary Laboratories Agency (VLA) Animal Services Unit for animal husbandry and provision of samples; Alex Nunez and Javier Salguero of the VLA Pathology Department for post-mortem dissection of lymphoid tissues; Joseph Newman and Falko Steinbach, VLA Virology Department, for statistical advice and critical
References (24)
- et al.
Validation of a real-time RT-PCR assay for sensitive and specific detection of classical swine fever
J. Virol. Methods
(2005) - et al.
Expression of proinflammatory cytokines by hepatic macrophages in acute classical swine fever
J. Comp. Pathol.
(2005) - et al.
Depletion of CD4(+) and CD8(high+) T-cells before the onset of viraemia during classical swine fever
Vet. Immunol. Immunopathol.
(2001) - et al.
The correlation of virus-specific interferon-gamma production and protection against classical swine fever virus infection
Vet. Immunol. Immunopathol.
(2001) - et al.
The influence of maternal immunity on the efficacy of a classical swine fever vaccine against classical swine fever virus, genogroup 2.2, infection
Vet. Microbiol.
(2003) - et al.
The kinetics of cytokine production and CD25 expression by porcine lymphocyte subpopulations following exposure to classical swine fever virus (CSFV)
Vet. Immunol. Immunopathol.
(2005) - et al.
Factors critical for successful vaccination against classical swine fever in endemic areas
Vet. Microbiol.
(2007) Experimental production of congenital persistent swine fever infections. I. Clinical, pathological and virological observations
Vet. Microbiol.
(1979)Vaccinology of classical swine fever: from lab to field
Vet. Microbiol.
(2003)- et al.
Classical swine fever virus induces proinflammatory cytokines and tissue factor expression and inhibits apoptosis and interferon synthesis during the establishment of long-term infection of porcine vascular endothelial cells
J. Gen. Virol.
(2004)
Induction and effector functions of T(H)17 cells
Nature
Interaction of classical swine fever virus with dendritic cells
J. Gen. Virol.
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Veterinary Medicine, Eleventh Edition
2016, Veterinary Medicine, Eleventh Edition