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 irradiation 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. (authors)