Objective： To observe the effect of norcantharidin（NCTD） on collagen-induced arthritis（CIA） rats. Methods： Sixty Sprague-Dawley（SD） rats were randomly divided into 6 groups（n=10）： normal group, CIA model group（model group）, NCTD low-dose group [1.35 mg/（kg·d）], NCTD middle-dose group [2.7 mg/（kg·d）], NCTD high-dose group [5.4 mg/（kg·d）] and methotrexate（MTX） group [1.8 mg/（kg/w）]. Anesthetized rats were sacrificed by luxation of cervical vertebra after 4 weeks of administration. The arthritis scores were evaluated twice a week. The pathological changes in the ankle joints of rats were observed by hematoxylin-eosin（H＆E） staining. The serum levels of interleukin（IL） 1β, IL-6, tumor necrosis factor（TNF）-α, vascular endothelial growth factor（VEGF）, IL-17 and transform growth factor（TGF） β were detected by enzyme linked immunosorbent assay（ELISA）. The mRNA expression of retinoid-related orphan nuclear receptor γ t（ROR γ t） and forkhead box P3（Foxp3） in peripheral blood lymphocytes were confirmed by real-time polymerase chain reaction. Results： MTX and high-dose NCTD not only decreased the arthritis scores but also alleviated the pathological changes in CIA rats＇ ankle joints compared with the model group（P〈0.05 or P〈0.01）. All doses of NCTD significantly inhibited the serum levels of IL-6, IL-17 and TNF-α in CIA rats（P〈0.05）. Only middle-and high-dose of NCTD prominently decreased serum IL-1β and TGF-β levels of CIA rats（P〈0.05）. However, NCTD has no effect on vascular endothelial growth factor（VEGF） level in CIA rats. The Foxp3 mRNA expression in all NCTD groups were increased significantly than in the model group（P〈0.05）. The mRNA expression of RORγt in NCTD high-dose group was decreased apparently in comparison with the model group（P〈0.05）. Conclusion： NCTD showed therapeutic effect on CIA rats by inhibition of cytokines and regulation of Th17/Treg cells.
