Flow cytometry as a quantitative and sensitive method to evaluate low dose radiation induced apoptosis in vitro in human peripheral blood lymphocytes.

Human peripheral blood lymphocytes, irradiated in vitro, die by an apoptotic process. The number of apoptotic cells after in vitro gamma-irradiation (0, 0.1, 0.2, 1, 2 and 5 Gy) was measured by flow cytometry using Annexin V and DiOC6 (a cationic dye) after 24 and 48 h incubation. The mean dose-response curves for apoptosis of six healthy volunteers obtained with both methods were steep below 1 Gy and flatter at higher doses. A slightly higher number of apoptotic cells was observed with DiOC6, compared to Annexin V. This can be assigned to a minor DiOC6-int/PI- population. Forty-eight hour cultures contained higher numbers of apoptotic cells compared with 24 h cultures. For both culture times, DiOC6 and Annexin V detected a statistically significant difference between a control sample and a 0.1 Gy irradiated one, illustrating the high sensitivity of the methods.