OBJECTIVE:To investigate the protective effects of Jiayan Kangtai (JYKT) granules,consisting of 9 Chinese herbs,in a rat model of autoimmune thyroiditis (AIT),and the possible underlying mechanism.METHODS:Female Lewis rats (6-8 weeks) were randomly apportioned to 5 groups of 10,including a normal control.AIT was induced in the untreated AIT-model group,and rats treated subsequently with daily low,medium,or high dose JYKT granules.After 12 weeks,plasma levels of thyroid autoantibodies and morphological changes in the thyroid were detected by enzyme-linked immunosorbent assay and histological examination,respectively.The presence of interleukin (IL)-6,IL23p19,and IL-2 in thyroid tissue was assessed by immunohistochemical staining.The percentages of T helper (Th)17 cells and regulatory T cells (Tregs) in the peripheral blood were analyzed by flow cytometry.Relevant levels of cytokines and proteins were examined via bead-based multiplex flow cytometry and ELISA,respectively.Expressions of genes and proteins regulated by Th17 cells and Tregs were shown by real-time PCR and West blot.RESULTS:Compared to the control,AIT-model rats had higher plasma concentrations of thyroid autoantibodies.The high-dose JYKT rats showed significantly lower levels of thyroid autoantibodies compared with the AIT model group.Rats in the AIT-JYKT groups also had fewer thyroid lesions and less lymphocytic infiltration,a lower percentage of Th17 cells,and a higher percentage of Tregs,compared with the AIT-model.Rats given high-dose JYKT had a significantly lower Th1 7/Treg ratio compared with the AIT model.Differences in plasma cytokine concentrations and relevant gene and protein expressions in the spleens of JYKT-treated rats and the AIT group suggested an association between JYKT treatment and lower Th17 cell percentage and higherTreg activity.CONCLUSION:JYKT treatment appeared to be protective against AIT in rats,possibly via the regulation of the Th1 7 cell/Treg imbalance in AIT.