radio-adaptive response of peripheral blood lymphocytes following bystander effects induced by preirradiated cho-k1 cells using the micronucleus assay

Background: radio-adaptive response and bystander effects are known phenomena occurring in cells following exposure to ionizing radiation (ir). in this study we examined possible radio-adaptation of lymphocytes following bystander effects induced by cho-k1 cells. materials and methods: whole blood and cho-k1 cells were cultured in rpmi-1640 complete medium. cells were separately irradiated with various doses of gamma rays. a co-culture was set to examine the bystander effects induced by cho-k1 cells on lymphocytes exposed later to a challenge dose of 4 gy. treated cells were exposed to cytochalasin-b to arrest cells in cytokinesis stage. micronucleus (mn) as end point was scored in binucleate cells after staining in giemsa. results: the frequency of mn increased significantly with increasing dose of radiation both in lymphocytes and cho-k1 cells (p<0.001). although, no significant difference was observed between control non-irradiated cells and those exposed to 0.2 gy (p>0.05). co-culture of the non-irradiated lymphocytes with pre-irradiated cho-k1 cells significantly reduced the mean frequency of mn in lymphocytes irradiated with a dose of 4gy (p<0.001). conclusion: results showed that bystander effects induced by gamma-irradiated cho-k1 cells led to induction of radio-adaptive response in lymphocytes. the mechanism by which radio-adaptive response is induced following bystander effect is not clearly known, however cellular signaling and genome instability induced in cells indirectly might be considered as possible triggering events for radio-adaptive response.