ObjectiveTo study the therapeutic effect of CpG-ODN, an agonist of Toll-like receptor 9 (TLR9), on irradiation injury of bone marrow hematopoietic system in mice. MethodsMice were treated with intraperitoneal injection of CpG-ODN (50 μg each) at 30 min, 24 h and 48 h after irradiation. The survival rates of animals were observed after irradiation with different doses, the numbers of white blood cell (WBC) and bone marrow nucleated cells within a certain period of time were observed, the bone marrow was pathologically studied, and the number of endogenous colony forming unit-spleen (endoCFU-S) was counted. ResultsOur results showed that intraperitoneal injection of CpG-ODN significantly improved the survival rate of mice and increased the numbers of peripheral WBC and bone marrow nucleated cells (P<0.01); moreover, it also ameliorated the pathological injury of the bone marrow and reduced the death of bone marrow stem cells.ConclusionIntraperitoneal CpG-ODN injection can ameliorate the irradiation injury of bone marrow hematopoietic system in mice.