Using a mouse model of systemic lupus erythematosus (SLE), we recently demonstrated that the two major manifestations of SLE are mechanistically independent because the type I IFN pathway leads to the autoantibody production whereas the NF-κB activation is sufficient for the development of glomerulonephritis. To further advance our understandings on the molecular pathways regulating the development of SLE, we studied the role of IRF8 because it controls both type I IFN and NF-κB pathways and saw that IRF8-deficient mice failed to develop either glomerulonephritis or the autoantibody production. Furthermore, these genetically engineered mice prompted us to realize the important role of Ly6Chigh inflammatory monocytes in the development of SLE. These monocytes migrate to the peritoneal cavity in WT and IRF7-deficient mice but not in IRF8-deficient mice, and there they produce both type I IFN and proinflammatory cytokines in WT mice, while in IRF7-deficient mice they only produce proinflammatory cytokines. Upon migration to the spleen, Ly6Chigh inflammatory monocytes differentiate into dendritic cells (DCs) which are capable of producing proinflammatory cytokines in response to dsDNA autoantigen. Collectively, type I IFN produced from inflammatory monocytes/monocyte-derived DCs might be essential for autoantibody production whereas proinflammatory cytokines produced from them might mediate tissue damages in this model. Our study reveals a specialized role for monocyte-derived antigen presenting cells in autoimmunity. Plasticity of monocyte might play an important role not only in the pathogenesis of the disease but also in flare-ups of the disease.
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