Time effect of adaptive response of apoptosis and cell cycle progression induced by low-dose ionizing radiation in EL-4 lymphoma cells in vitro

Objective: To study the time effect of adaptive response of apoptosis and cell cycle progression induced by low-dose ionizing radiation in EL-4 lymphoma cells in vitro to reveal the possible mechanism of biological effect and adaptive response induced by low-dose radiation. Methods: The experiment was divided into D2 (challenging dose) group, D1 (inductive dose) +D2 group and sham-irradiation group. EL-4 lymphoma cells were irradiated with D1 (75 mGy, 12.5 mGy·min-1) and D2 (1.5 Gy, 287 mGy·min-1), the interval time between D1 and D2 were 3-60 h. The cell percentages of apoptosis and each cell cycle phase were measured with flow cytometry. Results: When the time intervals between D1 and D2 were 3-24 h, the percentages of apoptotic cells in D1+D2 group were significantly lower than those in D2 group (P<0.05 or P<0.01); meantime, the percentages of G0/G1 phase cells decreased in varying degrees, and the percentage of S phase cells increased significantly (P<0.05). Conclusion: The adaptive response of apoptosis and cell cycle progression in EL-4 lymphoma cells in vitro could be induced by irradiation with 75 mGy (12.5 mGy·min-1) at 3-24 h before 1.5 Gy (287 mGy·min-1) exposure. (authors)