Abstract: Objective To observe N-acetyl-cysteine's protective effect on irradiation-induced bone marrow mononuclear cells(BMMNCs) injury, and explore the possible mechanism. Methods There were 3 groups in the research: control group,irradiation group(doses of irradiation were 1Gy and 4Gy) and irradiation with NAC group(The NAC was cocultured with BMMNCs half hour before irradiation).We added 2×106/mL BMMNCs and the RPMI-1640 medium or 2×10-5 mol/L NAC into the 2mL EP tubes according to the different requirement of groups,then all the tubes were cultured in 37 ℃ CO2 incubator for 30 mins and irradiated 1Gy and 4Gy. Mouse BMMNCs 'cell viability was measured by bioluminescence, the level of cell reactive oxygen species was measured by DCFH-DA, and the ability of colony-forming units was reflected by CFU-GM. Results After 4Gy irradiation exposure,the BMMNCs 'cell viability was (284 296.7±16 541.2) Relative Light Units,which was lower than the control group(848 586.7±61 404.4) Relative Light Units. And After 1Gy irradiation exposure , the level of cell reactive oxygen species was （6 750.0±103.5）, which was higher than control group(5 710.7±56.2)Fluorescence Value; The number of colony-forming units per 105 cells after irradiation exposure was (626.7±51.3),significantly lower than the control group (986.7±100.7).Compared to the irradiation group, when administrate NAC half hour before irradiation, the BMMNCs 'cell viability increased to (352 770.0±23 466.1) Relative Light Units , the level of cell reactive oxygen species decreased to (5 430.0±61.0) Fluorescence Value , the number of colony-forming units per 105 cells increased to(773.3±49.3),and the result has significantly difference. Conclusion NAC has protective effect on irradiation-induced BMMNCs injury，it can play the role of positive control for the following work.

Key words: acetylcysteine, monocytes, bone marrow, radiation injuries, radiation dosage, radiation protection, mice, 近交C57BL/6