Monocytes and Monocyte-derived Antigen-presenting Cells have Distinct Gene Signatures in Experimental Model of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease mediated by a complex interaction between the autoreactive lymphocytes and the effector myeloid cells within the central nervous system (CNS). In a murine model of MS, experimental autoimmune encephalomyelitis (EAE), Ly6Chi monocytes migrate into the CNS and further differentiate into antigen-presenting cells (APCs) during disease progression. Currently, there is no information about gene signatures that can distinguish between monocytes and the monocyte-derived APCs. We developed a surface marker-based strategy to distinguish between these two cell types during the stage of EAE when the clinical symptoms were most severe, and performed transcriptome analysis to compare their gene expression. We report here that the inflammatory CNS environment substantially alters gene expression of monocytes, compared to the monocyte differentiation process within CNS. Monocytes in the CNS express genes that encode proinflammatory cytokines and chemokines, and their expression is mostly maintained when the cells differentiate. Moreover, monocyte-derived APCs express surface markers associated with both dendritic cells and macrophages, and have a significant up-regulation of genes that are critical for antigen presentation. Furthermore, we identified Ccl17, Ccl22, and Ccr7 as signature genes for monocyte-derived APCs but not the Ly6Chi monocytes. These findings may shed light on identifying molecular signals that control monocyte differentiation and functions during EAE. Overall design: Experimental autoimmune encephalomyelitis (EAE) was induced in mice on a C57BL/6J background by subcutaneously injection of myelin oligodendrocyte glycoprotein peptide emulsified in complete Freund's adjuvant. Pertussis toxin (250 ng) was injected intraperitoneally at 2- and 24-hours following the injection of emulsion. At days 14-15 following EAE induction, bone marrow monocytes (CD45+ CD11b+ Ly6Chi Ly6G- CD11c-), spinal cord monocytes (CD45+ CD11b+ CD64+ Ly6Chi Ly6G-), and spinal cord monocyte-derived APCs (CD45+ CD11b+ CD64+ Ly6Clow/- Ly6G-) were isolated. RNA were purified from the cells. Gene expression was analyzed by RNA-Sequencing.