Abstract: AIM: To study the protective effects of platelet factor 4(PF4) on the bone marrow cellsof the ra-diation injury mice and to do some preliminary studies for its mechanism.METHODS: BALB/c male mice were randomly divided into three groups:exposure group, pro-tection group with PF4 and control group.The mice of protection group were injected PF4 (40 μg·kg^-1) into abdominal cavity twice at 26 h and 20 h before irradiation of 4 Gy⁶⁰Co-γray.The cell cycle of bone marrow cells was determinedwith flow cytometry on d 1、2、4、8 after ir-radiation.The expression level of p21 in BMSCswere de-tected with immunohistochemistry.RESULTS: The cells on G₀ +G₁ phase of exposure group on d 1、2 and of pro-tection group on d 1 were significantly higher than that of control group, the difference between exposure group and protection group is notable at every time point (P<0.05), while the difference between protection group on d 2、8 and exposure group on the same day was not signifi-cant(P >0.05).On d 2、4 after irradiation, the expres-sion of p21 in BMSCs of protection group was up-regulat-ed compared with that of exposure group.On d8 the result was opposite.CONCLUSION: PF4 has obvious protec-tive effects on the bone marrow of the radiation injury mice by controlling cell cycle and recovering its hemato-poietic function as early as possible.The high expression of p21maybe has a certain effect on the protective mecha-nism.

Key words: platelet factor 4, radiation injury, P21