Analysis was performed using Mann-Whitney values 0.05 were considered significant. Results Wlds Mice Experience an Attenuated Course of EAE with Delayed Onset of Disease mice and WT C57BL/6 mice were immunized with MOGp35-55 (Figure 1). and was associated with increased CNS inflammation and neurodegeneration. neuronal cultures were protected from microglial-induced neurotoxicity compared with control cultures, but protection was abrogated by anti-CD200 antibody. The CD200-CD200R pathway plays a critical role in attenuating EAE and reducing inflammation-mediated damage in the CNS. Strategies that up-regulate the expression of CD200 in the CNS or molecules that ligate the CD200R may be CD109 relevant as neuroprotective strategies in multiple sclerosis. Multiple sclerosis (MS) is an immune-mediated demyelinating and degenerative disease of the central nervous system (CNS). Axonal damage and demyelination are present in both MS and its animal model, experimental autoimmune encephalomyelitis (EAE), and are implicated as the primary determinants of irreversible neurological deficits.1,2 Axonal damage is a consequence of both immune-mediated damage as well as activation of degenerative pathways; however, the underlying mechanisms are not well understood. The mouse is a spontaneously occurring mutant with the unique phenotype of protection against several forms of axonal injury. Degeneration of the distal portion of the axon or Wallerian degeneration has been shown to be delayed in the mouse after both peripheral3,4 and CNS nerve transections.5 In addition, axons have been shown to remain viable after apoptosis of the neuronal cell body.6 The gene has also been shown to be protective in models of vincristine- and paclitaxel-induced neuropathy, suggesting that it has multifaceted neuroprotective effects.7,8 Several studies have demonstrated reduced microglial responses after axonal transection in the model.9,10,11,12,13 Experiments using bone marrow chimaeras have proven that this is a property that affects cell populations intrinsic to the nerve and is not attributable to an anomaly in circulating monocytes.14 We have recently shown that compared with wild-type (WT) mice, mice, Razaxaban when immunized to induce chronic EAE, developed a delayed onset and an attenuated disease course,15 which was associated with a reduction in both axonal Razaxaban loss and demyelination in spinal cord sections. Axonal protection in mice was associated with increased nicotinamide adenine dinucleotide (NAD) levels; however, the molecular mechanisms mediating axon protection in mice have not been elucidated. In this study, we explored molecular mediators of neuroprotection in the EAE model with the goal of identifying potential therapeutic targets for MS. Although there was no difference in T-cell infiltrates in the CNS,15 we found that microglia and macrophage accumulation and activation in the CNS were diminished in mice compared with WT mice. Microglia and macrophages have been associated with axonal damage within MS lesions,16 as well as in diffuse axonal damage in the normal appearing white matter.17 Because of these observations, we explored the differential expression of molecules Razaxaban associated with microglial regulation. We found that disease protection in mice as well as in neuronal cultures was associated with enhanced neuronal and glial expression of CD200, a nonsignaling molecule that has previously been described on neurons18,19,20 and belongs to the immunoglobulin superfamily of glycoproteins. Interaction of CD200 with its ligand, CD200R, has been shown to initiate tyrosine phosphorylation.21 Thus, the effects of CD200 are mediated through cells expressing the CD200 receptor (CD200R), including microglia/macrophages.21,22,23 Macrophage/microglial responses to nerve trauma and EAE were accelerated in mice deficient for CD200.24 These and other studies25 suggest that ligation of CD200R delivers a negative signal for microglia/macrophage activation. CD200R has been found to also be expressed on dendritic cells, mast cells, granulocytes, and to a limited extent on CD8+ T cells, natural killer (NK) cells, NKT cells, and CD4+ cells of the Th2 phenotype.23 Four isoforms of CD200R have been described, and at least in one study, all four have been shown to bind CD200.26 More recently CD200R agonists have been shown to inhibit proinflammatory cytokine secretion by macrophage cell lines, including interleukin (IL)-17-induced IL-6 production.27 CD200R ligation on mast cells inhibits degranulation and cytokine production.28 CD200R ligation induces regulatory dendritic cell populations capable of secreting indolamine dioxygenase.29 Moreover, in animal models, CD200R agonists have been shown to ameliorate collagen-induced arthritis30 and prolong graft survival.31 Using the model, we studied the effects of neuronal CD200 overexpression in models of inflammation-induced neurotoxicity. We show that increased expression of CD200 is capable of protecting neurons and axons from microglia-induced damage and and wild-type C57BL/6O1aHSD (WT) from Harlan UK Limited (Bicester, Oxon, UK) were obtained for EAE studies. C57BL/6O1aHSD-mice are homozygous mutants. Mice were 6 to 10 weeks old at the time of immunization. Induction of EAE, Scoring, and Analysis of Clinical Disease Myelin oligodendrocyte glycoprotein peptide 35-55 (MOG 35-55) (MEVGWYRSPFSRVVHLYRNGK) corresponding to mouse sequence was synthesized by QCB.