title: The role of target and bystander cells in dose-response relationship of radiation-induced bystander effects in two cell lines.
abstract: OBJECTIVE
  Radiation effect induced in nonirradiated cells which are adjacent or far from irradiated cells is termed radiation-induced bystander effect (RIBE). Published data on dose-response relationship of RIBE is controversial. In the present study the role of targeted and bystander cells in RIBE dose-response relationship of two cell lines have been investigated.
  
  
  METHODS
  Two cell lines (QU-DB and MRC5) which had previously exhibited different dose-response relationship were selected. In the previous study the two cell lines received medium from autologous irradiated cells and the results showed that the magnitude of damages induced in QU-DB cells was dependent on dose unlike MRC5 cells. In the present study, the same cells irradiated with 0.5, 2 and 4 Gy gamma rays and their conditioned media were transferred to nonautologous bystander cells; such that the bystander effects due to cross-interaction between them were studied. Micronucleus assay was performed to measure the magnitude of damages induced in bystander cells (RIBE level).
  
  
  RESULTS
  QU-DB cells exhibited a dose-dependent response. RIBE level in MRC5 cells which received medium from 0.5 and 2 Gy QU-DB irradiated cells was not statistically different, but surprisingly when they received medium from 4Gy irradiated QU-DB cells, RIBE was abrogated.
  
  
  CONCLUSIONS
  RESULTS pertaining to QU-DB and MRC5 cells indicated that both target and bystander cells determined the outcome. Triggering the bystander effect depended on the radiation dose and the target cell-type, but when RIBE was triggered, dose-response relationship was predominantly determined by the bystander cell type.
authors.affiliation: Medical Physics Resaerch Center, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran ; Department of Medical Physics, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Shokouhozaman
authors.initials: S
authors.lastname: Soleymanifard
authors.forename: Mohammad Taghi
authors.initials: MT
authors.lastname: Bahreyni Toossi
authors.forename: Ameneh
authors.initials: A
authors.lastname: Sazgarnia
authors.forename: Shokoufe
authors.initials: S
authors.lastname: Mohebbi
keywords: Dose-response relationship; MRC5; Micronucleus assay; QU-DB; Radiation-induced bystander effect