Human Mesenchymal Stem Cells Upregulate CD1d^highCD5⁺ Regulatory B Cells in Experimental Autoimmune Encephalomyelitis

<b><i>Background/Aims:</i></b> Multiple sclerosis (MS) causes significant neurological disability. Experimental autoimmune encephalomyelitis (EAE) is an animal model of MS. Human bone marrow mesenchymal stem cells (hMSCs) possess anti-inflammatory and immunosuppressive effects. We studied whether hMSCs affect CD1d^highCD5⁺ regulatory B-cell activity in EAE. <b><i>Methods:</i></b> EAE was induced in C57BL/6N mice by immunization with MOG_35-55 peptide. hMSCs were injected intravenously into EAE mice on day 3 and day 12 after first immunization. Mice were sacrificed on day 26. Immunohistochemistry of the spinal cord, serum cytokines levels, production of cytokines by cultured splenic cells, and flow cytometry for splenic Th17 and CD1d^highCD5⁺ regulatory B cells were studied. <b><i>Results:</i></b> EAE mice with hMSC treatment on day 3 and day 12 had reduced EAE scores from day 14 to day 26 compared to EAE mice without hMSC treatment, and reduced infiltration of inflammatory cells and demyelination in the spinal cord. EAE mice with hMSC treatment on day 3 and day 12 had: (1) lower serum levels of IL-6, TNF-α (p < 0.0005), and IL-17 (p < 0.005 for day 3, p < 0.0005 for day 12); (2) reduced splenic cell production and secretion of IL-6, TNF-α (p < 0.05), and IL-17 (p < 0.05), and increased splenic production of IL-10; (3) reduced splenic Th17 cells (p < 0.05 for day 3, p < 0.005 for day 12), and (4) increased CD1d^highCD5⁺ regulatory B cells (p < 0.005) compared to EAE mice without hMSC treatment. <b><i>Conclusion:</i></b> hMSC treatment on day 3 and day 12 suppresses EAE severity. The underlying mechanisms involve downregulation of Th17 cells and upregulation of CD1d^highCD5⁺ regulatory B-cell activity.