Title: The Radiation-induced Bystander Response: Different Protocols, Similar Effects.

Authors: C.R. Geard, A. Balajee, R. Baskar, G. Jenkins-Baker, A. Bigelow, S. Marino and B. Ponnaiya.

Normal Human Fibroblasts (multiple origins) were exposed as hit cells and bystander cells -either in contact (Site-specific Microbeam delivered α-particles) or separated (Track segment α-particles and media transfer after low LET γ-irradiation). For each protocol there were dose dependent increases in micronuclei (multiple assay points in situ) but non-dose dependent increases in bystander cells (~2 fold). p21/WAF1/cip1protein levels in individual cells was a sentinel marker of response in bystander cells. There were indications that all non-hit cells could respond to bystander signals. All single cell assays (for both mRNA and protein) demonstrated substantial inter-cell variability. These results support similar mechanisms for initiation of bystander responses under different experimental protocols.

This work was supported by the U.S. DOE’s Low Dose Radiation Research Program under Contract No. DE-FG 0298ER62687 and Department of Health and Human Services P41, RR-11623 (RARAF).