Macrophage responses are regulated by multiple secreted factors as well as by cell surface receptors, including the inhibitory signals resulting from ligation of myeloid CD200 receptors (CD200R) by the widely distributed CD200. In the absence of CD200, animals display increased susceptibility to autoimmunity and earlier onset aggressive autoimmune disease. In these current experiments, an agonist monoclonal rat antimouse CD200R (DX109) antibody delivered a negative signal to bone marrow-derived macrophages, which suppressed interferon (IFN)␥-mediated nitric oxide (NO) and interleukin-6 production. Experimental autoimmune uveoretinitis (EAU) was used as a model of organ-specific autoimmunity in the eye, a tissue with extensive neuronal and endothelial CD200 expression. In mice lacking CD200 (CD200 ؊/؊ ), increased numbers of retina-infiltrating macrophages displaying heightened NO responses were observed during EAU. In addition, we aimed to suppress disease by maintaining tonic suppression of macrophage activation via CD200R. Systemically administered DX109 monoclonal antibody suppressed EAU despite maintained T-cell proliferation and IFN␥ production. Furthermore, locally administered DX109 monoclonal antibody resulted in an earlier resolution of disease. These experiments demonstrate that promoting CD200R-mediated signaling can successfully prevent full expression of IFN␥-mediated macrophage activation and protect against tissue damage during autoimmune responses. (Am J

EtxB preimmunization protects mice from EAU induction by inhibiting Th1 responses, but the resultant reduction in IFN-gamma responses by EtxB does not effect infiltration or structural damage in established EAU, where Th17 responses predominate. These data highlight the critical importance of the dynamics of T-cell phenotype and infiltration during EAU when considering immunomodulatory therapy.

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Previously, we reported that NR4A2, an orphan nuclear receptor, is upregulated by peripheral blood cells during the human autoimmune disease multiple sclerosis (MS), as well as by peripheral blood cells and leukocytes infiltrating the central nervous system (CNS) during experimental autoimmune encecephalomyelitis (EAE). The pathology of MS and EAE is mediated by infiltration of both Th1 and Th17 cells into the CNS, but we reveal that upregulation of NR4A2 observed in CNS-infiltrating leukocytes and peripheral blood cells is most apparent amongst IL-17-secreting CD4+ T cells. Therefore, we examined the role of NR4A2 in the differentiation of these Th17 cells: transfection of naïve T cells with NR4A2 siRNA precludes IL-17 secretion when cultured under Th17 polarising conditions. However, such cells do proliferate and upregulate RORγt to the same extent as fully functional Th17 cells. IL-23 stimulation is critical in licensing IL-17 production by Th17 cells and that this depends on the upregulation of IL-23R by Th17 cells subsequent to autocrine IL-21 signalling. NR4A2 siRNA knock-down in CD4+ T cells prevents IL-21 production under Th17 polarising conditions and consequently such cells do not upregulate IL-23R. Addition of exogenous IL-21 circumvented NR4A2 knock-down, leading to IL-23R upregulation and IL-17 production. Furthermore, NR4A2 appears to be critical in generating Th17-mediated autoimmunity as systemic administration of NR4A2 siRNA prevented EAE induction.