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BACKGROUND: In the initial stage of multiple sclerosis, central immune cells activate and release a large number of inflammatory factors, causing white matter demyelination and even involving gray matter neurons. The equilibrium of differentiation between different subsets of CD4+ T cells plays an important role in the progression of experimental autoimmune encephalomyelitis. The previous results of the research group showed that the active ingredient astragalus glycoprotein in astragalus can regulate the immune response in experimental autoimmune encephalomyelitis mice, and whether it has a regulatory effect on the differentiation of T cell subsets has not been determined. OBJECTIVE: To explore the therapeutic effects and immune regulatory mechanisms of astragaloside IV on experimental autoimmune encephalomyelitis mice. METHODS: Female C57BL/6 mice were divided into the normal control group, experimental autoimmune encephalomyelitis disease model group, and astragaloside IV treatment group (n=8 per group). Myelin oligodendrocyte glycoprotein peptides 35-55 were used for experimental autoimmune encephalomyelitis model induction in the last two groups. On day 10 to 28 after immunization, the astragaloside IV treatment group was treated with 40 mg/kg per day astragaloside IV intragastrically. Body weight and clinical scores of mice in each group were recorded from the immunization day to the 28th day. On the 28th day after immunization, the mouse spinal cord was taken and made into frozen sections for hematoxylin-eosin staining and Lux fast blue staining to observe pathological changes in the spinal cord. Percentage of splenic T cell subsets was detected using flow cytometry. Western blot assay was used to determine the protein expression of interferon-γ, interleukin-17 and interleukin-6 in the spinal cord. Levels of interferon-γ, interleukin-17, interleukin-6 and interleukin-4 in supernatants of cultured splenocytes were determined by ELISA. RESULTS AND CONCLUSION: (1) Compared with the experimental autoimmune encephalomyelitis disease model group, astragaloside IV could reduce the degree of weight loss in experimental autoimmune encephalomyelitis mice (P < 0.05), ameliorate clinical symptoms (P < 0.05), inhibit the infiltration of inflammatory cells and alleviate myelin loss (P < 0.01, P < 0.05). (2) Compared with the experimental autoimmune encephalomyelitis disease model group, astragaloside IV could inhibit the proportion of CD4+ T cell subsets expressing interferon-γ (P < 0.001) and interleukin-17 (P < 0.001), but increase percentages of CD4+ interleukin-10+ (P < 0.001) and CD4+ transforming growth factor-β+ (P < 0.01) T cell subsets. (3) Astragaloside IV could inhibit the expression of interferon-γ (P < 0.05, P < 0.01), interleukin-17 (P < 0.05, P < 0.05), and interleukin-6 (P < 0.05, P < 0.05) in the spinal cord and spleen, and up-regulate the expression of interleukin-4 (P < 0.01) in spleen. (4) These findings confirm that astragaloside IV alleviates clinical symptoms in experimental autoimmune encephalomyelitis mice, which may be related to regulating the splenic T cell subsets, therefore, inhibiting the infiltration of inflammatory cells into the center and reducing the demyelination. [ABSTRACT FROM AUTHOR]