Chemokine receptor expression by inflammatory T cells in EAE

Chemokines direct cellular infiltration to tissues, and their receptors and signaling pathways represent targets for therapy in diseases such as multiple sclerosis (MS). The chemokine CCL20 is expressed in choroid plexus, a site of entry of T cells to the central nervous system (CNS). The CCL20 receptor CCR6 has been reported to be selectively expressed by CD4(+) T cells that produce the cytokine IL-17 (Th17 cells). Th17 cells and interferon-gamma (IFNγ)-producing Th1 cells are implicated in induction of MS and its animal model experimental autoimmune encephalomyelitis (EAE). We have assessed whether CCR6 identifies specific inflammatory T cell subsets in EAE. Our approach was to induce EAE, and then examine chemokine receptor expression by cytokine-producing T cells sorted from CNS at peak disease. About 7% of CNS-infiltrating CD4(+) T cells produced IFNγ in flow cytometric cytokine assays, whereas less than 1% produced IL-17. About 1% of CD4(+) T cells produced both cytokines. CCR6 was expressed by Th1, Th1+17 and by Th17 cells, but not by CD8(+) T cells. CD8(+) T cells expressed CXCR3, which was also expressed by CD4(+) T cells, with no correlation to cytokine profile. Messenger RNA for IFNγ, IL-17A, and the Th1 and Th17-associated transcription factors T-bet and RORγt was detected in both CCR6(+) and CXCR3(+) CD4(+) T cells. IFNγ, but not IL-17A mRNA expression was detected in CD8(+) T cells in CNS. CCR6 and CD4 were co-localized in spinal cord infiltrates by double immunofluorescence. Consistent with flow cytometry data some but not all CD4(+) T cells expressed CCR6 within infiltrates. CD4-negative CCR6(+) cells included macrophage/microglial cells. Thus we have for the first time directly studied CD4(+) and CD8(+) T cells in the CNS of mice with peak EAE, and determined IFNγ and IL17 expression by cells expressing CCR6 and CXCR3. We show that neither CCR6 or CXCR3 align with CD4 T cell subsets, and Th1 or mixed Th1+17 predominate in EAE

Interferon regulatory factor-7 modulates experimental autoimmune encephalomyelitis in mice

<p>Abstract</p> <p>Background</p> <p>Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) with unknown etiology. Interferon-β (IFN-β), a member of the type I IFN family, is used as a therapeutic for MS and the IFN signaling pathway is implicated in MS susceptibility. Interferon regulatory factor 7 (IRF7) is critical for the induction and positive feedback regulation of type I IFN. To establish whether and how endogenous type I IFN signaling contributes to disease modulation and to better understand the underlying mechanism, we examined the role of IRF7 in the development of MS-like disease in mice.</p> <p>Methods</p> <p>The role of IRF7 in development of EAE was studied by immunizing IRF7-KO and C57BL/6 (WT) mice with myelin oligodendrocyte glycoprotein using a standard protocol for the induction of EAE. We measured leukocyte infiltration and localization in the CNS using flow cytometric analysis and immunohistochemical procedures. We determined levels of CD3 and selected chemokine and cytokine gene expression by quantitative real-time PCR.</p> <p>Results</p> <p>IRF7 gene expression increased in the CNS as disease progressed. IRF7 message was localized to microglia and infiltrating leukocytes. Furthermore, IRF7-deficient mice developed more severe disease. Flow cytometric analysis showed that the extent of leukocyte infiltration into the CNS was higher in IRF7-deficient mice with significantly higher number of infiltrating macrophages and T cells, and the distribution of infiltrates within the spinal cord was altered. Analysis of cytokine and chemokine gene expression by quantitative real-time PCR showed significantly greater increases in CCL2, CXCL10, IL-1β and IL17 gene expression in IRF7-deficient mice compared with WT mice.</p> <p>Conclusion</p> <p>Together, our findings suggest that IRF7 signaling is critical for regulation of inflammatory responses in the CNS.</p

Blood-brain barrier disruption in CCL2 transgenic mice during pertussis toxin-induced brain inflammation

BACKGROUND: The chemokine CCL2 has an important role in the recruitment of inflammatory cells into the central nervous system (CNS). A transgenic mouse model that overexpresses CCL2 in the CNS shows an accumulation of leukocytes within the perivascular space surrounding vessels, and which infiltrate into the brain parenchyma following the administration of pertussis toxin (PTx). METHODS: This study used contrast-enhanced magnetic resonance imaging (MRI) to quantify the extent of blood–brain barrier (BBB) disruption in this model pre- and post-PTx administration compared to wild-type mice. Contrast-enhanced MR images were obtained before and 1, 3, and 5 days after PTx injection in each animal. After the final imaging session fluorescent dextran tracers were administered intravenously to each mouse and brains were examined histologically for cellular infiltrates, BBB leakage and tight junction protein. RESULTS: BBB breakdown, defined as a disruption of both the endothelium and glia limitans, was found only in CCL2 transgenic mice following PTx administration and seen on MR images as focal areas of contrast enhancement and histologically as dextrans leaking from blood vessels. No evidence of disruption in endothelial tight junctions was observed. CONCLUSION: Genetic and environmental stimuli were needed to disrupt the integrity of the BBB in this model of neuroinflammation

Type I interferon-activated microglia are critical for neuromyelitis optica pathology

Neuromyelitis optica (NMO) is an inflammatory disease of the central nervous system (CNS) most frequently mediated by serum autoantibodies against the water channel aquaporin 4, expressed on CNS astrocytes, resulting in primary astrocytopathy. There is no cure for NMO, and treatment with Type I interferon (IFNI)-IFN beta is ineffective or even detrimental. We have previously shown that both NMO lesions and associated microglial activation were reduced in mice lacking the receptor for IFN beta. However, the role of microglia in NMO is not well understood. In this study, we clarify the pathomechanism for IFNI dependence of and the role of microglia in experimental NMO. Transcriptome analysis showed a strong IFNI footprint in affected CNS tissue as well as in microglial subpopulations. Treatment with IFN beta led to exacerbated pathology and further microglial activation as evidenced by expansion of a CD11c(+) subset of microglia. Importantly, depletion of microglia led to suppression of pathology and decrease of IFNI signature genes. Our data show a pro-pathologic role for IFNI-activated microglia in NMO and open new perspectives for microglia-targeted therapies

A novel microglial subset plays a key role in myelinogenesis in developing brain

Microglia are resident macrophages of the central nervous system that contribute to homeostasis and neuroinflammation. Although known to play an important role in brain development, their exact function has not been fully described. Here, we show that in contrast to healthy adult and inflammation-activated cells, neonatal microglia show a unique myelinogenic and neurogenic phenotype. A CD11c(+) microglial subset that predominates in primary myelinating areas of the developing brain expresses genes for neuronal and glial survival, migration, and differentiation. These cells are the major source of insulin-like growth factor 1, and its selective depletion from CD11c(+) microglia leads to impairment of primary myelination. CD11c-targeted toxin regimens induced a selective transcriptional response in neonates, distinct from adult microglia. CD11c(+) microglia are also found in clusters of repopulating microglia after experimental ablation and in neuroinflammation in adult mice, but despite some similarities, they do not recapitulate neonatal microglial characteristics. We therefore identify a unique phenotype of neonatal microglia that deliver signals necessary for myelination and neurogenesis

Influence of type I IFN signaling on anti-MOG antibody-mediated demyelination

Abstract Background Antibodies with specificity for myelin oligodendrocyte glycoprotein (MOG) are implicated in multiple sclerosis and related diseases. The pathogenic importance of anti-MOG antibody in primary demyelinating pathology remains poorly characterized. Objective The objective of this study is to investigate whether administration of anti-MOG antibody would be sufficient for demyelination and to determine if type I interferon (IFN) signaling plays a similar role in anti-MOG antibody-mediated pathology, as has been shown for neuromyelitis optica-like pathology. Methods Purified IgG2a monoclonal anti-MOG antibody and mouse complement were stereotactically injected into the corpus callosum of wild-type and type I IFN receptor deficient mice (IFNAR1-KO) with and without pre-established experimental autoimmune encephalomyelitis (EAE). Results Anti-MOG induced complement-dependent demyelination in the corpus callosum of wild-type mice and did not occur in mice that received control IgG2a. Deposition of activated complement coincided with demyelination, and this was significantly reduced in IFNAR1-KO mice. Co-injection of anti-MOG and complement at onset of symptoms of EAE induced similar levels of callosal demyelination in wild-type and IFNAR1-KO mice. Conclusions Anti-MOG antibody and complement was sufficient to induce callosal demyelination, and pathology was dependent on type I IFN. Induction of EAE in IFNAR1-KO mice overcame the dependence on type I IFN for anti-MOG and complement-mediated demyelination