Time-effect of adaptive response of mouse thymocyte apoptosis and cell cycle progression induced by low dose radiation

? Objective: In the present study we observed the general pattern of the adaptive response of thymocyte apoptosis and cell cycle progression induced by low dose radiation (LDR). Methods: Kunming male mice were irradiated with the inductive dose (D_1, 75 mGy) and the challenging dose (D_2, 1.5 Gy). The intervals between D_1 and D_2 were 3, 6, 12, 24 and 60 hours. The changes of thymocyte apoptotic bodies (TAB) and cell cycle progression were measured with flow cytometry with the thymocytes cultured for 4, 20 and 44 hours, respectively, 18 hours after irradiation with D_2. Results: When the intervals between D_1 and D_2 were 3, 6 and 12 hours, the percentages of TAB in the D_1 + D_2 groups in the thymocytes cultured for 4 and 20 hours were significantly lower than those in the D_2 groups (P0.05) and the percentages of G_0/G_1 and G_2 + M phase cells decreased in varying degrees, while the percentages of S phase cells increased significantly (P0.05 or P0.01). Conclusion: The results mentioned above indicate that when the mice were irradiated with 75 mGy (D_1, 12.5 mGy/min ) 3~12 hours before 1.5 Gy (D_2, 0.285 Gy/min) exposure, the adaptive response of apoptosis and cell cycle progression may be induced with the thymocytes cultured for 4 and 20 hours after whole-body irradiation with D_2. 〔