Upregulation of chemokine receptor gene expression in brains of Borna disease virus (BDV)-infected rats in the absence and presence of inflammation

Infection of adult rats with Borna disease virus (BDV) causes CD8 T cell-mediated meningoencephalitis. Previously, we described a complex pattern of chemokine gene expression in the central nervous system (CNS) of such rats, We now found that expression of chemokine receptor genes CXCR3, CCR5, CX(3)CR1, and CXCR4 was also upregulated, which is in agreement with the predominance in brains of adult infected rats of T cells and monocytes/macrophages that express these receptors. In contrast to these rats, neonatally infected rats (designated PTI-NB) develop a persistent CNS infection associated with neurodegenerative processes in the absence of inflammation. In brains of PTI-NB rats, sustained expression of chemokines also takes place. We therefore analyzed mRNA expression of selected chemokine receptor genes, as well as of the chemokine fractalkine in brains of PTI-NB rats. We observed a marked increase of CCR5 and CX(3)CR1 transcripts in brains of these rats. CX(3)CR1 expressing cells were predominantly microglia, and upregulation Of CX(3)CR1 was mainly due to an increase in the number of CX(3)CR1 expressing microglia. Fractalkine gene expression was found to be reduced to similar extents in brains of adult and newborn infected rats. These findings might be of relevance with respect to the selective neuronal cell loss observed in brains of PTI-NB rats.