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Bystander cell proliferation is modulated by the number of adjacent cells that were exposed to ionizing radiation
Author(s) -
Gerashchenko Bogdan I.,
Howell Roger W.
Publication year - 2005
Publication title -
cytometry part a
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.316
H-Index - 90
eISSN - 1552-4930
pISSN - 1552-4922
DOI - 10.1002/cyto.a.20150
Subject(s) - bystander effect , flow cytometry , cell , cell culture , cell growth , population , microbiology and biotechnology , ionizing radiation , thymidine , cell counting , cell division , biology , intracellular , chemistry , irradiation , in vitro , cell cycle , immunology , biochemistry , medicine , genetics , physics , environmental health , nuclear physics
Background Direct cell‐to‐cell contact appears to be a prerequisite for the proliferative response of bystander WB‐F344 cells co‐cultured with irradiated cells; however, neither gap junctional intercellular communication nor long‐range factors released into the medium appear to be involved (Cytometry 2003;56A:71–80). The present work investigated whether the proliferative bystander response depends on the number of irradiated cells (cells exposed to external γ‐rays or cells exposed to short‐range β‐particles emitted by DNA‐incorporated 3 H‐thymidine) that are adjacent to unirradiated bystander cells. Methods Subconfluent monolayers of rat liver epithelial cells (WB‐F344) were incubated in the presence of (methyl‐ 3 H)thymidine at a concentration of 5.8 kBq/ml for 18 h. Radiolabeled cells containing 0.7 × 10 −3 Bq/cell (absorbed dose: 0.14 Gy) were plated together with unlabeled cells in proportions of 6% and 94%, 12% and 88%, 25% and 75%, 50% and 50%, and 75% and 25%, respectively, keeping constant the total number of plated cells. In a parallel experiment, cells acutely exposed to 5 Gy of 137 Cs γ‐rays were plated with unirradiated cells in the same proportions. In both experiments, cells were co‐cultured for 24 h followed by a flow cytometric study of their proliferation. The two cell populations in the co‐cultures were distinguished by staining one population with carboxyfluorescein diacetate, succinimidyl ester, which metabolizes intracellularly. Results Increasing the fraction of irradiated cells relative to unirradiated bystander cells led to an increase in proliferation of bystander cells. Specifically, in co‐cultures in which irradiated cells were initially mixed with unirradiated cells in proportions of 50% and 50% and of 75% and 25%, respectively, bystander cells showed a statistically significant increase of their proliferation compared with the controls. Conclusions The proliferative response of WB‐F344 bystander cells is modulated by the number of adjacent cells that are exposed to ionizing radiation from external γ‐rays or intracellularly emitted 3 H β‐particles. © 2005 Wiley‐Liss, Inc.