Effect of ionizing radiation on the cytokines of mouse thymus Th17 cells

Objective To study the cytokine releases in the thymus Th17 cells of irradiated mice, and to explore the function of Th17 cells in different immune responses to radiation of different doses. Methods According to the random number table method, ICR mice were divided into three groups i. e., healthy control group, low-dose group (0.05, 0.075 Gy) and high-dose group (0.5, 1.0, 2.0, 4.0 Gy) to explore the dose-effect relationship. In the dose-effect group, the ICR mice exposed to different dosages of whole body X-ray irradition were decapitated at 24 h after irradiation. Meanwhile, ICR mice were divided into three groups i. e., healthy control group, low-dose group (0.075 Gy) and high-dose group (2.0 Gy) to explore the time-effect relationship. The mice were decapitated after 12, 24, and 48 h of 0.075 and 2 Gy of whole body X-ray irradiation, then prepared for the thymus tissue homogenization. The expressions of IL-17a and IL-21 in the thymus tissue homogenization were detected by ELISA. Results For the time-effect, following a low dose irradiation of 0.075 Gy, the levels of IL-17a and IL-21 in the thymocytes continuously decreased along with the time post-irradiation and reached its lowest value at 48 h after radiation but it was still higher than that in the control group (t=3.85, 4.73, P<0.05); the expressions of these cytokines dramatically increased along with the time post-irradiation and reached to its highest level at 48 h after irradiation of 2.0 Gy (t=-6.74, -6.19, P<0.05). For the dose-effect group, at 24 h after irradiation, the expressions of IL-17a and IL-21 in mouse thymocytes were lower than controls for low dose groups and had the lowest level at 0.05 Gy(t=8.39, 16.45, P<0.05), while they increased in the high dose groups and had the highest level at 4.0 Gy(t=-15.60, -18.62, P<0.05). Conclusions After irradiation, the secretions of IL-17a and IL-21 in mouse thymocytes are inhibited by low dose irradiation but triggered by higher doses, which indicates that Th17-related cytokines play an important role in immune suppression induced by a high dose radiation, while the immune function enhancement is induced by low dose radiation. Key words: Ionizing Radiation; Th17 cells; Cytokines; Immune function