Flow cytometry as a strategy to study radiation-induced bystander effects in co-culture systems

Background: There is growing interest in the role of bystander effects in the biological response of mammalian Cells to ionizing radiation. Qualitative and quantitative assessment of bystander effects requires quick and reliable methodologies. The present work uses a flow cytometric approach to study proliferation of bystander cells co-cultured with irradiated cells. Methods: Confluent monolayers; of rat liver epithelial cells (WB-F344) were irradiated with Cs-137 gamma-rays at dose ranges 0.5, 1, 5, 10, and 20 Gy. Irradiated cells were mixed with unirradiated cells (i.e., bystander cells) at a ratio of 1:1 and Cultured together for 24 h followed by a flow cytometry (FCM) study of their proliferation. In order to discriminate the two populations of co-cultured cells, one of the cell populations (unirradiated cells) was stained with the lipophilic fluorescent dye DiI. Results: Unirradiated cells, in the presence of cells irradiated at doses above 0.5 Gy, showed an enhanced cell growth by approximately 14-17%. Conclusions: Cells irradiated with gamma rays can induce increased proliferation in neighboring unirradiated bystander cells. FCM provides an excellent basis for characterization of these and other bystander effects in coculture systems. (C) 2003 Wiley-Liss, Inc.