Chemokine receptor expression and function in experimental autoimmune neuroinflammation

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 glycoproteininduced 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 nonoverlapping expression. CkR s ligands, MIP-1α (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. LIST OF PUBLICATIONS This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I. Dan Sunnemark, Sana Eltayeb, Erik Wallstrom, Lena Appelsved, Asa Malmberg, Hans Lassmann, Anders Ericsson-Dahlstrand, Fredrik Piehl, Tomas Olsson. Differential Expression of the Chemokine Receptors CX3CR1 and CCR1 by Microglia and Macrophages in Myelin Oligodendrocyte Glycoprotein Induced Experimental Autoimmune Encephalomyelitis. Brain Pathol. 2003, 13:617-29. II. Dan Sunnemark*, Sana Eltayeb*, Maria Nilsson, Erik Wallstrom, Hans Lassmann, Tomas Olsson, Anna-Lena Berg and Anders Ericsson-Dahlstrand. CX3CL1 (fractalkine) and CX3CR1 expression in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis: kinetics and cellular origin. J Neuroinflammation. 2005, 2:17. III. Sana Eltayeb, Anna-Lena Berg, Hans Lassmann, Maria Nilsson, Erik Wallstrom, Tomas Olsson, Anders Ericsson-Dahlstrand and Dan Sunnemark. Temporal expression and cellular origin of CC chemokine receptors CCR1, CCR2 and CCR5 in the central nervous system: insight into mechanisms of MOG-induced EAE. J Neuroinflammation. 2007, 4:14. IV. Sana Eltayeb*, Dan Sunnemark*, Anna-Lena Berg, Gunnar Nordvall, Asa Malmberg, Hans Lassmann, Erik Wallstrom, Tomas Olsson, Anders Ericsson-Dahlstrand. Effector stage CC chemokine receptor-1 selective antagonism reduces multiple sclerosis-like rat disease. J Neuroimmunol. 2003, 142:75-85. *Contributed equally to the work. Copyright holders are acknowledged for permission to reproduce the published articles in this thesis