Abstract

BackgroundThe CC chemokine receptors CCR1, CCR2 and CCR5 are critical for the recruitment of mononuclear phagocytes to the central nervous system (CNS) in multiple sclerosis (MS) and other neuroinflammatory diseases. Mononuclear phagocytes are effector cells capable of phagocytosing myelin and damaging axons. In this study, we characterize the regional, temporal and cellular expression of CCR1, CCR2 and CCR5 mRNA in the spinal cord of rats with myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE). While resembling human MS, this animal model allows unique access to CNS-tissue from various time-points of relapsing neuroinflammation and from various lesional stages: early active, late active, and inactive completely demyelinated lesions.MethodsThe expression of CCR1, CCR2 and CCR5 mRNA was studied with in situ hybridization using radio labelled cRNA probes in combination with immunohistochemical staining for phenotypic cell markers. Spinal cord sections from healthy rats and rats with MOG-EAE (acute phase, remission phase, relapse phase) were analysed. In defined lesion stages, the number of cells expressing CCR1, CCR2 and CCR5 mRNA was determined. Data were statistically analysed by the nonparametric Mann-Whitney U test.ResultsIn MOG-EAE rats, extensive up-regulation of CCR1 and CCR5 mRNA, and moderate up-regulation of CCR2 mRNA, was found in the spinal cord during episodes of active inflammation and demyelination. Double staining with phenotypic cell markers identified the chemokine receptor mRNA-expressing cells as macrophages/microglia. Expression of all three receptors was substantially reduced during clinical remission, coinciding with diminished inflammation and demyelination in the spinal cord. Healthy control rats did not show any detectable expression of CCR1, CCR2 or CCR5 mRNA in the spinal cord.ConclusionOur results demonstrate that the acute and chronic-relapsing phases of MOG-EAE are associated with distinct expression of CCR1, CCR2, and CCR5 mRNA by cells of the macrophage/microglia lineage within the CNS lesions. These data support the notion that CCR1, CCR2 and CCR5 mediate recruitment of both infiltrating macrophages and resident microglia to sites of CNS inflammation. Detailed knowledge of expression patterns is crucial for the understanding of therapeutic modulation and the validation of CCR1, CCR2 and CCR5 as feasible targets for therapeutic intervention in MS.

Highlights

  • The CC chemokine receptors CCR1, CCR2 and CCR5 are critical for the recruitment of mononuclear phagocytes to the central nervous system (CNS) in multiple sclerosis (MS) and other neuroinflammatory diseases

  • Our results demonstrate a prominent accumulation of monocytes and macrophages expressing CCR1, CCR2 or CCR5 mRNA within and around inflammatory foci in the spinal cord of rats with EAE, identifying potential determinants for trafficking of these cells to the CNS

  • Since infiltration of leukocytes including monocyte-derived macrophages into the CNS is a key step in the pathogenesis of MS [38], we designed this study to identify chemokine receptors that may control infiltration of monocyte-derived macrophages into inflammatory CNS lesions of rats with myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE)

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Summary

Introduction

The CC chemokine receptors CCR1, CCR2 and CCR5 are critical for the recruitment of mononuclear phagocytes to the central nervous system (CNS) in multiple sclerosis (MS) and other neuroinflammatory diseases. Multiple sclerosis (MS) is the most common non-traumatic cause of neurological disability in young adults in the Western world It is a chronic inflammatory disease, characterized by the appearance of focal demyelinated plaques within the central nervous system (CNS) [1]. The pathogenetic mechanisms leading to demyelination and tissue injury are not fully understood, activated macrophages and microglia seem to play a central role in the destructive process both in MS and in EAE [6,7] In accordance with this assumption, elimination of macrophages or microglia has been shown to suppress clinical and histopathological manifestations in rodent models for MS [8,9]

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