Chemokine receptor expression and function in experimental autoimmune neuroinflammation

Abstract

Neuroinflammatory lesions in the central nervous system (CNS) are characterized by the presence of leukocytes, mainly monocytes/macrophages, derived from the systemic compartment. We believe CC inflammatory chemokine receptors (CkRs), CCR1, CCR2 and CCR5 are prerequisite for controlling the migration of monocytes/macrophages into inflammatory foci. The role of fractalkine (CX3CL1) and its receptor CX3CR1 in the CNS is more unclear, but their expression pattern suggests a role in neuron-microglia interaction.

Chronic rat model for Multiple Sclerosis (MS), myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE), was employed here to determine the role of these CkRs during neuroinflammation. In situ hybridization histochemistry combined with immunohistochemistry (ISH/IHC) demonstrated high-level of CCR1/CCR5, and moderate-level of CCR2 mRNA expression on mononuclear phagocytes (ED1+ GSA/B4+) correlated with active demyelination. Expression of CCR1, CCR2 and CCR5 was substantially reduced during clinical remission. CX3CR1 displayed a low constitutive expression on microglia on the basis of their cellular morphology and positive lectin staining. There was a notably increased density of CX3CR1 mRNA expressing cells within the inflammatory areas, especially during the acute and relapse phase of the perivascular and submeningeal lesions. CCR1 and CX3CR1 were also found to be differentially expressed at the protein level on monocyte/ microglia populations by flow cytometric analysis of leukocytes extracted from the inflamed CNS tissue, confirming non-overlapping expression. CkR Ls ligands, MIP-1 ¿ (CCL3) and RANTES (CCL5), were found abundantly expressed in neuroinflammatory lesions, but not in the healthy CNS. There was a neuronal expression of CX3CL1 throughout the CNS at all time points examined (constitutive expression), with induced expression on astrocytes within inflammatory lesions.

A low-molecular weight CCR1 selective antagonist was able to potently abrogate both clinical and histopathological signs of the disease during the effector stage of EAE without any signs of peripheral immune compromise. The antagonist also reduced the severity of ongoing disease when given after clinical onset of disease.

In conclusion, the thesis shed light on some of CkRs and provide new information about mechanisms controlling their mRNA expression during neuroinflammation. Because this research carries potential medical implications, detailed knowledge of the roles of specific CkRs and ligands in the CNS in health and in disease and identifying their cellular phenotypes could be of use in the identification of disease mechanisms, and enabling more specific future therapeutic interventions