Abstract: Abstract: Objective　To investigate the effects of shikonin on thymic stromal lymphopoietin (TSLP)/OX40 ligand (OX40L) pathway and balance of helper T cell 1 (Th1)/helper T cell 2 (Th2) in mice with atopic dermatitis (AD). Methods　AD mouse model was established by topical application of 2,4-dinitrofluorobenzene (DNFB).Model mice were randomly divided into model group, low shikonin group (10 mg/kg), medium shikonin group (20 mg/kg), high shikonin group (30 mg/kg), and the positive control group (prednisolone,10 mg/kg) by random number table method, with 15 mice in each group. Another 15 mice were used as the normal control group. The drug groups were given the corresponding drugs by gavage, with the volume of 10 mL/kg. The model group and the normal control group were given the same volume of solvent by gavage, once a day for 15 days. The scratch behavior of mice was observed on the 5th, 10th and 15th day after administration. The condition of skin lesions was evaluated on the 7th and 15th days after administration. At the end of the last administration, hematoxylin eosin (HE) staining was used to observe the histopathological changes of skin lesions. The ratio of Th1/Th2 cells in peripheral blood of mice was detected by flow cytometry. Levels of TSLP, tumor necrosis factor (TNF)-α, interleukin (IL)-4 and γ-interferon (IFN-γ) were detected by enzyme linked immunosorbent assay (ELISA). Western blot assay was used to detect the protein expression levels of TSLP and OX40L. Results　Compared with the normal control group, the scratching behavior increased and the skin inflammatory injury aggravated in model group. There were dense infiltration of inflammatory cells in the epidermis and dermis in the model group, and the epidermis was thickened. The blood levels of Th2 cells, TSLP, TNF-α and IL-4, and the protein expression levels of TSLP and OX40L in skin lesions were significantly higher (P＜0.05), and the levels of Th1 cells, IFN-γ and Th1/Th2 ratio were significantly lower (P＜0.05). Compared with the model group, the scratching behavior were decreased on the 5th, the 10th and the 15th day, and the skin inflammatory injury decreased on the 7th and the 15th day in turn in low, middle and high dose shikonin groups (P＜0.05). After the last administration, the inflammatory cell infiltration and epidermal thickening in the epidermis and dermis of mice decreased in turn in low, medium and high dose shikonin groups. The scratching behavior, the degree of skin inflammatory injury, the levels of Th2 cells, TSLP, TNF-α and IL-4, and the protein expression levels of TSLP and OX40L decreased in turn (P＜0.05), and the levels of Th1 cells, IFN-γ and Th1/Th2 ratio increased in turn (P＜0.05). Conclusion　Shikonin may maintain the balance of Th1/Th2 cells in peripheral blood and improve skin inflammatory injury of AD mice by inhibiting TSLP/OX40L pathway.

Key words: SHIKONIN, dermatitis, atopic, Th1-Th2 balance, OX40 ligand, thymic stromal lymphopoietin/OX40L pathway