Objective:To explore effects and mechanisms of medium and low doses X-ray irradiation on polarization type changes of tumor associated macrophages(TAMs).Methods:Mouse RAW264.7 macrophage line was cultured with supernatant of 4T1 tumor cell culture(4T1-TCS)of mouse breast cancer,and induced to M2 TAMs.On this basis,medium and low doses X-ray irra-diation was conducted,and NO was detected by Griess method,CD86 and CD206 were detected by flow cytometry.ELISA was use to detect cytokines IL-10 and IL-12p70,immunofluorescence was use to detect iNOS and Arg-1.Western blot was used to detect polariza-tion related pathway proteins,and whether medium and low doses of radiation could alter polarization type of TAMs was observed.Results:4T1-TCS induced TAM had decreasing NO secretion and increasing CD206 and Arg-1 expressions,iNOS expression was decreased;with low doses irradiation(0.075 Gy,0.5 Gy,1 Gy)of TCS-TAM,compared with non irradiation group,NO secretion,expressions of CD86,CD206,Arg-1 and iNOS showed no significant changes;medium doses(2 Gy,4 Gy,6 Gy)of irradiation on TCS-TAM resulted in increased secretion of NO,and flow cytometry results showed increased expressions of CD86,decreased CD206 expression;immunofluorescence results showed an increase in iNOS expression and a decrease in Arg-1 expression in cells;ELISA results showed an increase in secretion of IL-12p70 by cells and a decrease in secretion of IL-10.Western blot results showed that NOX2,ATMS1981*,IRF5 proteins expressions were increased.Conclusion:4T1-TCS can successfully induce macrophage RAW264.7 polarize into M2 phenotype,while low dose irradiation has no significant effect on polarization phenotype of TCS-TAM.Medium dose irradiation can induce TCS-TAM polarization into M1 phenotype that inhibits tumor growth,and reversal mechanism of polarization may be related to IRF5 pathway.