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Borna disease virus (BDV) infection in horses either occurs as persistent infection without any clinical symptoms, or is associated with various clinical entities. Recent discoveries to diagnose BDV-infections intra vitam indicate blood mononuclear cells (PBMCs) to play a key-role in pathogenesis of disease symptoms of horses and man.
PBMCs from diseased and clinically healthy horses as well as from human origin were used in flow cytometry, RT-PCR and in some cases tested by ELISAs. Cells were infected with BDV strain V, kept in culture to monitor the presence of antigens and nucleic acid. After infection, monocytes were differentiated towards macrophages or dendritic cells by IFN? or GM-CSF and IL-4, or treated with other cytokines to modulate infection. As a prerequisite, equine IFN?, GM-CSF and IL-4 were cloned and expressed.
In acutely diseased horses, traces of markers for a BDV-infection could be detected. PCR analysis revealed a number of infected, but clinically healthy horses. Monocytes could be infected and over a weeks´ period (five to eight days), cells remained PCR-positive, indicating a persistent infection. The detection of live virus and mRNA (PCR or in situ hybridization) strongly indicates virus replication in monocytes. This replication could be modulated by the use of cytokines. Our results demonstrate that monocytes are possible target cells for Bornavirus, thus extending the in vivo studies. Additionally, studies to evaluate a role of dendritic cells in the BDV-infection process are in progress.