Cerebral malaria (CM) can be a fatal manifestation of Plasmodium falciparum infection. Using murine models of malaria, we found much greater up-regulation of a number of chemokine mRNAs, including those for CXCR3 and its ligands, in the brain during fatal murine CM (FMCM) than in a model of non-CM. Expression of CXCL9 and CXCL10 RNA was localized predominantly to the cerebral microvessels and in adjacent glial cells, while expression of CCL5 was restricted mainly to infiltrating lymphocytes. The majority of mice deficient in CXCR3 were found to be protected from FMCM, and this protection was associated with a reduction in the number of CD8+ T cells in brain vessels as well as reduced expression of perforin and FasL mRNA. Adoptive transfer of CD8+ cells from C57BL/6 mice with FMCM abrogated this protection in CXCR3−/− mice. Moreover, there were decreased mRNA levels for the proinflammatory cytokines IFN-γ and lymphotoxin-α in the brains of mice protected from FMCM. These data suggest a role for CXCR3 in the pathogenesis of FMCM through the recruitment and activation of pathogenic CD8+ T cells.

The chemokine receptor CXCR3 promotes the trafficking of activated T and NK cells in response to three ligands, CXCL9, CXCL10, and CXCL11. Although these chemokines are produced in the CNS in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), their role in the pathogenesis of CNS autoimmunity is unresolved. We examined the function of CXCR3 signaling in EAE using mice that were deficient for CXCR3 (CXCR3−/−). The time to onset and peak disease severity were similar for CXCR3−/− and wild-type (WT) animals; however, CXCR3−/− mice had more severe chronic disease with increased demyelination and axonal damage. The inflammatory lesions in WT mice consisted of well-demarcated perivascular mononuclear cell infiltrates, mainly in the spinal cord and cerebellum. In CXCR3−/− mice, these lesions were more widespread throughout the CNS and were diffused and poorly organized, with T cells and highly activated microglia/macrophages scattered throughout the white matter. Although the number of CD4+ and CD8+ T cells infiltrating the CNS were similar in CXCR3−/− and WT mice, Foxp3+ regulatory T cells were significantly reduced in number and dispersed in CXCR3−/− mice. The expression of various chemokine and cytokine genes in the CNS was similar in CXCR3−/− and WT mice. The genes for the CXCR3 ligands were expressed predominantly in and/or immediately surrounding the mononuclear cell infiltrates. We conclude that in EAE, CXCR3 signaling constrains T cells to the perivascular space in the CNS and augments regulatory T cell recruitment and effector T cell interaction, thus limiting autoimmune-mediated tissue damage.

The chemokines CXCL9 and CXCL10 bind to the common receptor CXCR3 and are implicated in the pathogenesis of T-cell-mediated immunity in the central nervous system (CNS). Here we examined the temporal and spatial regulation of the Cxcl9 and Cxcl10 genes in the CNS of mice with myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) and by glial cells in vitro. During peak disease the levels of CXCL9 and CXCL10 mRNA and protein were increased significantly in the cerebellum and spinal cord but were reduced during the recovery phase. Expression of these genes in the CNS was abolished in IFN-gamma-receptor deficient mice with MOG-EAE. In wild-type mice, CXCL9 RNA was localized mainly to infiltrating mononuclear cells including lesion and perilesional microglia, while CXCL10 RNA was seen primarily in more distal astrocytes that surrounded the inflammatory lesions. Examination of cultured glia following treatment with IFN-gamma revealed that while both CXCL9 and CXCL10 mRNA transcripts were induced in microglia, only CXCL10 mRNA was induced in astrocytes. Thus, although IFN-gamma is the pivotal mediator of both Cxcl10 and Cxcl9 gene expression in EAE, this cytokine differentially regulates the expression of these genes by astrocytes and microglia. The differential glial localization of these chemokines in EAE suggests CXCL9 and CXCL10 have specialized functions.

Intracranial infection of mice with lymphocytic choriomeningitis virus (LCMV) results in a lethal neurological disease termed lymphocytic choriomeningitis (LCM) that is mediated by antiviral CD8 ϩ T cells. Previous studies have implicated the chemokine receptor CXCR3 and its ligand CXCL10 in CD8 ϩ T cell trafficking in the brain and in the lethal disease following intracranial infection of mice with the LCMV-Traub strain. Here we investigated the role of CXCR3 in LCM following intracranial infection of mice with the LCMV-Armstrong strain. Significant induction of both CXCL9 and CXCL10 RNA and protein was seen in the central nervous system (CNS) in LCM. Cellular localization of the CXCL9 and CXCL10 RNA transcripts was identified predominantly in infiltrating mononuclear cells, as well as in subpial and paraventricular microglia (CXCL9) and astrocytes (CXCL10). Despite a primary role of interferon (IFN)-␥ in inducing the expression of the CXCL9 gene, and to a lesser extent the CXCL10 gene in LCM, the absence of the IFN-␥ receptor did not influence the disease outcome. This finding suggested that these chemokines may not play a major role in the pathogenesis of LCM. To evaluate this possibility further the development of LCM was examined in mice that were deficient for CXCR3. Surprisingly, in the absence of CXCR3 there was no alteration in mortality, cytokine expression, or T cell infiltration in the CNS, demonstrating that in contrast to LCMV-Traub, CXCR3 is not involved in the pathogenesis of LCMV-Armstrong-induced neurological disease in mice. Our findings indicate that despite similar immunopathogenetic mechanisms involving antiviral CD8 ϩ T cells, whether or not CXCR3 signaling has a role in LCM is dependent upon the infecting strain of LCMV. 425

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