Autoimmunity and inflammation are controlled in part by regulatory B (Breg) cells, including the recently identified IL-10-competent B10 cell subset that represents 1%-3% of mouse spleen B cells. In this study, the influence of irradiation on Breg/B10 cell generation and IL-10 production mediated by TLR9 signaling pathways was investigated. Spleen and peritoneal cavity Breg/B10 cell frequencies were significantly expanded three weeks after sub-total body irradiation (sub-TBI, 5Gy or 10Gy) in adult male wild type (WT) C57BL/6(B6) mice but not in TLR9(-/-) mice. TLR9 agonist ODN1826 stimulation in vitro for 5h induced more B10 cells to express cytoplasmic IL-10 in sub-TBI WT mice than in TLR9(-/-) mice. Prolonged ODN1826 stimulation (48h) induced additional spleen CD19(hi)CD5(+)CD1d(hi) B cells to express IL-10. TLR9-dependent signaling molecules, MyD88, TRAF6 and IRF8 are involved in sub-TBI induced Breg/B10 cells development and expansion. Furthermore, using a mouse model for multiple sclerosis, we show here that sub-TBI induced Breg/B10 cells dramatically inhibit disease onset and severity when transferred into mice with established experimental autoimmune encephalomyelitis (EAE). Adoptively transferred sub-TBI induced Breg cells significantly suppress inflammatory T cell responses of TH17 and TH1 types in EAE mice. In conclusion, sub-TBI can drive Breg/B10 cell development and expansion, which could be used as a novel tool for suppressing undesirable immunity. The ex vivo expansion and reinfusion of autologous Breg/B10 cells may provide a novel and effective in vivo treatment for severe autoimmune diseases that are resistant to current therapies.