Expression of interferon gamma in the brain of cats with natural Borna disease virus infection.

Borna disease virus (BDV) is a neurotropic, negative-stranded RNA virus, which causes a non-suppurative meningoencephalomyelitis in a wide range of animals. In cats, BDV infection leads to staggering disease. In spite of a vigorous immune response the virus persists in the central nervous system (CNS) in both experimentally and naturally infected animals. Since the CNS is vulnerable to cytotoxic effects mediated via NK-cells and cytotoxic T-cells, other non-cytolytic mechanisms such as the interferon (IFN) system is favourable for viral clearance. In this study, IFN-γ expression in the brain of cats with clinical signs of staggering disease (N=12) was compared to the expression in cats with no signs of this disease (N=7) by quantitative RT-PCR. The IFN-γ expression was normalised against the expression of three reference genes (HPRT, RPS7, YWHAZ). Cats with staggering disease had significantly higher expression of IFN-γ compared to the control cats (p-value ≤ 0.001). There was no significant difference of the IFN-γ expression in BDV-positive (N=7) and -negative (N=5) cats having clinical signs of staggering disease. However, as BDV-RNA still could be detected, despite an intense IFN-γ expression, BDV needs to have mechanisms to evade this antiviral immune response of the host, to be able to persist.