EXPLORING THE BYSTANDER EFFECT FOLLOWING VERY LOW DOSE RADIATION

Abstract

Bystander effects are defined as the phenomenon in which unirradiated cells respond biologically when their neighbors are irradiated. The exact mechanisms of these cellular responses are still not known, especially in the region considered to be very low dose radiation (<20cGy). Many studies have shown cytokine levels are altered following exposure to radiation and may play a significant role in bringing about bystander responses. A non-tumorigenic (MCF10A) and tumorigenic (A375) cell line were used to determine if chemical factors released from irradiated MCF10A cells will bring about bystander- induced proliferation on naïve (unirradiated) A375 or MCF10A cells using the Irradiated Conditioned Medium (ICM) model. A transfer of conditioned medium 5 hours post- irradiation appeared to bring about a marked bystander response in the naïve A375 cultures which were observed to be maximal between 2 and 6 cGy. This response was not observed at the 1 hour transfer of conditioned medium. Additionally, the data suggest that there is no temporal correlation between the proliferative bystander effects elicited and the levels of IL-6 within the conditioned medium. The data indicate that the MCF10A ICM IL-8 levels were statistically significant only at the 6 cGy dose at 1 hour. Although a significant proliferative bystander effect was observed in A375 cells when exposed to 5 hour MCF10A ICM, the data suggest that both IL-6 and IL-8 do not contribute significantly to this proliferative response.