Immune system modulation by low-dose ionizing radiation-induced adaptive response.

Objective: Hormesis or low-dose ionizing radiation is known to induce various biological responses, a subcategory of which is the adaptive response, which has been reported to protect against higher radiation doses via multiple mechanisms. This study investigated the role of the cell-mediated immunological component of low-dose ionizing radiation-induced adaptive response.

Methods: Herein, male albino rats were exposed to whole-body gamma radiation, using a Cs¹³⁷ source with low-dose ionizing radiation doses of 0.25 and 0.5 Gray (Gy); 14 days later, another irradiation session at a dose level of 5 Gy was carried on. Four days post-irradiation at 5 Gy, rats were sacrificed. The low-dose ionizing radiation-induced immuno-radiological response has been assessed through the T-cell receptor (TCR) gene expression quantification. Also, the serum levels of each of interleukins-2 and -10 (IL-2, IL-10), transforming growth factor-beta (TGF-β), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were quantified.

Results: Results indicated that priming low irradiation doses resulted in significant decrements in TCR gene expression and the serum levels of IL-2, TGF-β, and 8-OHdG with an increment in IL-10 expression compared to the irradiated group, which did not receive low priming doses.

Conclusion: The observed low-dose ionizing radiation-induced radio-adaptive response significantly protected against high irradiation dose injuries, through immune suppression, representing a promising pre-clinical protocol that would be applied to minimize radiotherapy side effects on normal but not against the tumor cells.