Abstract: Objective To investigate the protective effect of theaflavins on thymus injury caused by total body irradiation (TBI). Methods Twenty- five C57BL/6 mice were randomly divided into 5 groups: control group, 4 Gy TBI group, 4 Gy TBI + 25 mg/kg theaflavins group, 4 Gy TBI + 50 mg/kg theaflavins group and 4 Gy TBI + 100 mg/kg theaflavins group. Thymus index and total number of thymocytes were detected at the 14th d post-irradiation to determine the optimal dose of theaflavins. According to this optimal dose, 32 C57BL/6 mice were randomly divided into 4 groups: control group,theaflavins group, 4 Gy TBI group and 4 Gy TBI + theaflavins group. Thymus histomorphology, CD4CD8 T cell subsets, and reactive oxygen species (ROS) in thymocytes were examined at the 14th d post-irradiation. Results The irradiated thymus exhibited decreased thymus index and total number of thymocytes (P＜0.05), aberrant histomorphology and T cell subsets (P＜0.05), and increased ROS level in thymocytes (P＜0.05). Compared with 4 Gy TBI group, the thymus index and total number of thymocytes were significantly increased in 4 Gy TBI + 50 mg/kg theaflavins group (P＜0.05). The total number of thymocytes was significantly higher in 4 Gy TBI + 50 mg/kg theaflavins group than that in 4 Gy TBI + 25 mg/kg theaflavins group (P＜0.05). Therefore, 50 mg/kg theaflavins was chosen as the optimal dose for subsequent experiments. Moreover, the aberrant histomorphology of irradiated thymus was alleviated by theaflavins. A decline in the percentage of CD4-CD8- T cellsand an elevation of CD4+CD8- and CD4+CD8+ T cells were found in irradiated mice administered with theaflavins (P＜0.05).Compared with 4 Gy TBI group, the ROS level was significantly decreased in 4 Gy TBI + theaflavins group (P＜0.05).Conclusion Theaflavins exhibits a protective effect on radiation-induced thymus injury.

Key words: thymus gland, radiation injuries, reactive oxygen species, mice, inbred C57BL, theaflavins, immune function