Coxsackieviruses are significant human pathogens, and the neonatal central nervous system (CNS) is a major target for infection. Despite the extreme susceptibility of newborn infants to coxsackievirus infection and viral tropism for the CNS, few studies have been aimed at determining the long-term consequences of infection on the developing CNS. We previously described a neonatal mouse model of coxsackievirus B3 (CVB3) infection and determined that proliferating stem cells in the CNS were preferentially targeted. Here, we describe later stages of infection, the ensuing inflammatory response, and subsequent lesions which remain in the adult CNS of surviving animals. High levels of type I interferons and chemokines (in particular MCP-5, IP10, and RANTES) were upregulated following infection and remained at high levels up to day 10 postinfection (p.i). Chronic inflammation and lesions were observed in the hippocampus and cortex of surviving mice for up to 9 months p.i. CVB3 RNA was detected in the CNS up to 3 months p.i at high abundance (ϳ10 6 genomes/mouse brain), and viral genomic material remained detectable in culture after two rounds of in vitro passage. These data suggest that CVB3 may persist in the CNS as a low-level, noncytolytic infection, causing ongoing inflammatory lesions. Thus, the effects of a relatively common infection during the neonatal period may be long lasting, and the prognosis for newborn infants recovering from acute infection should be reexplored.

An imbalance in the matrix metalloproteinase (MMP) : tissue inhibitor of MMP (TIMP) ratio may be associated with tissue injury. Here, we studied the regulation of TIMP and MMP gene expression in primary glial cultures to ascertain the factors involved in the regulation of these genes in conditions of inflammatory neuropathology. Astrocytes were found to basally express TIMP-1 and TIMP-3 mRNA while microglia expressed only TIMP-2 mRNA. TIMP-4 mRNA was not detectable in either cell type. Treatment with interferon-a (IFN-a), IFN-c, interleukin-3 (IL-3), IL-6 or tumor necrosis factor-a (TNF-a) did not alter expression of the TIMP genes. However, in astrocytes, but not in microglia, serum, IL-1b or lipopolysaccharide (LPS) evoked a dose-and time-dependent increase in TIMP-1 mRNA and a coincident down-regulation of the TIMP-3 gene. Astrocytes were found to express mRNA constitutively for MMPs -3, -11 and -14. In contrast, microglia expressed only MMP-12 mRNA under basal conditions. IL-1b enhanced MMP-3 mRNA levels while LPS increased the MMP-3, -9, -12, -13 and -14 mRNAs. Our findings reveal that regulatory control of TIMP and MMP gene expression by glial cells is agonist-and cell-type specific, and suggest that innate immune signals govern the temporal and spatial expression patterns of TIMP and MMP genes in neuroinflammatory conditions of the CNS.

The CXC chemokine ligand (CXCL)10 is induced locally in the CNS in diverse pathologic states. The impact of CXCL10 production in the CNS was examined in transgenic mice with astrocyte-directed production of this chemokine. These glial fibrillary acidic protein (GF)-CXCL10 transgenic mice spontaneously developed transgene dose- and age-related leukocyte infiltrates in perivascular, meningeal, and ventricular regions of the brain that were composed of, surprisingly, mainly neutrophils and, to a lesser extent, T cells. No other overt pathologic or physical changes were evident. In addition, the cerebral expression of a number of inflammation-related genes (e.g., cytokines) was not significantly altered in the transgenic mice. The extent of leukocyte recruitment to the brain could be enhanced markedly by peripheral immunization of GF-CXCL10 mice with CFA and pertussis toxin. This was paralleled by a modest, transient increase in the expression of some cytokine and chemokine genes. Analysis of the expression of the CXCL10 receptor, CXCR3, by the brain-infiltrating leukocytes from immunized GF-CXCL10 transgenic mice revealed a significant enrichment for CXCR3-positive cells in the CNS compared with spleen. The majority of cells positive for CXCR3 coexpressed CD3, whereas Gr1-positive granulocytes were negative for CXCR3 expression. Thus, while astrocyte production of CXCL10 can promote spontaneous and potentiate immune-induced recruitment of leukocytes to the CNS, this is not associated with activation of a degenerative immune pathology. Finally, the accumulation of neutrophils in the brain of GF-CXCL10 transgenic mice is apparently independent of CXCR3 and involves an unknown mechanism.

The type I IFNs (IFN-α and IFN-β), which are crucial in antiviral defense and immune regulation, signal via the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway with activation of STAT1 and STAT2. Here, the function of STAT2 was studied in transgenic mice (termed GIFN/STAT2 -/-) with CNS production of IFN-α. Surprisingly, GIFN/STAT2 -/-, but not GIFN/STAT1-null, transgenic mice, with CNS production of IFN-α, died prematurely with medulloblastoma. An immune response also induced in the brain of the GIFN/STAT2 -/-mice was associated with IFN-γ gene expression by CD3 + T cells and the activation of the STAT1, STAT3, STAT4, and STAT5 molecules. Expression of the Sonic hedgehog (Shh) and the downstream transcriptional factor Gli-1 genes, implicated in the pathogenesis of medulloblastoma, was found to be significantly increased and cotranscribed in cerebellar granule neurons of the GIFN/STAT2 -/-mice. IFN-γ, but not IFN-α, induced STAT1-dependent expression of the Shh gene in cultured cerebellar granule neurons. Thus, there is an unexpected and extraordinarily adverse biological potency of IFN-α in the CNS when the primary signal transduction molecule STAT2 is absent. Moreover, a hitherto unknown role is indicated for the immune system in the pathogenesis of developmental disorders and tumorigenesis of the CNS via dysregulated Shh signaling mediated by IFN-γ.

Targeted expression of biologically active interleukin-12 (IL-12) in astrocytes of the central nervous system (CNS) results in spontaneous neuroimmunological disease of aged mice. Borna disease virus (BDV) can readily multiply in the mouse CNS but does not trigger disease in most strains. Here we show that a large percentage of IL-12 transgenic mice developed severe ataxia within 5 to 10 weeks after infection with BDV. By contrast, no disease developed in mock-infected IL-12 transgenic and wild-type mice until 4 months of age. Neurological symptoms were rare in infected wild-type animals, and if they occurred, these were milder and appeared later. Histological analyses showed that the cerebellum of infected IL-12 transgenic mice, which is the brain region with strongest transgene expression, contained large numbers of CD4 ؉ and CD8 ؉ T cells as well as lower numbers of B cells, whereas other parts of the CNS showed only mild infiltration by lymphocytes. The cerebellum of diseased mice further showed severe astrogliosis, calcifications and signs of neurodegeneration. BDV antigen and nucleic acids were present in lower amounts in the inflamed cerebellum of infected transgenic mice than in the noninflamed cerebellum of infected wild-type littermates, suggesting that IL-12 or IL-12-induced cytokines exhibited antiviral activity. We propose that BDV infection accelerates the frequency by which immune cells such as lymphocytes and NK cells enter the CNS and then respond to IL-12 present in the local milieu causing disease. Our results illustrate that infection of the CNS with a virus that is benign in certain hosts can be harmful in such normally disease-resistant hosts if the tissue is unfavorably preconditioned by proinflammatory cytokines.