Radio-adaptive Response Induced by Low-dose Ionizing Radiation in Innate Immunity for Radiotherapy

Radio-adaptive response (RAR) is a mechanism by which low doses of ionizing radiation (IR) protect cells from subsequent high doses. This study aimed to compare the immuno-radiological effects of 0.25, 0.5, and 5 Gy to 0.25 or 0.5 Gy as priming and 5 Gy as challenging doses. Thirty-five rats were irradiated whole-body with 0.25 and 0.5 Gy followed by 5 Gy, and the same single IR doses with non-irradiated animals serving as controls. Serum interferon-gamma (INF-γ), interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), nitric oxide (NO), and malondialdehyde (MDA) levels were measured 4 d post both priming and challenge doses. A 0.25-Gy priming dose significantly (P < 0.05) reduced serum TNF-α, MDA, and NO levels compared to all single-irradiated groups. Surprisingly, there was no difference in IFN-γ serum levels between the RAR-induced and non-irradiated groups (P ≥ 0.05). Compared to the same low priming dose (0.25 and 0.5 Gy), the effect of the challenging dose (5 Gy) remains unchanged or decreases. Serum IFN-γ, MDA, and NO concentrations, on the other hand, were significantly (P < 0.05) lower in the 0.5 Gy pre-challenging dose, whereas IL1β had no effect (P ≥ 0.05) compared to 5 Gy alone. The post-RAR group had significantly (P < 0.05) lower oxidative stress indicators than the other irradiation groups. The findings suggested that priming with low IR could help mitigate the negative effects on the hematopoietic system. Finally, RAR has significantly impacted endogenous cytokines, oxidative stress biomarkers, and lipid peroxidation parameters. RAR can improve patients' radiological safety profiles by mitigating adverse radiotherapy effects.