Objective:To investigate the effect of Xuebijing injection against blood-brain barrier(BBB)damage in the mice with anti-N-methyl-D-aspartate receptor(NMDAR)encephalitis,and to elucidate its regulatory effect on the imbalance of helper T cells 17(Th17)/regulatory T cells(Treg).Methods:The active immunization models of anti-NMDAR encephalitis in the mice were established using glutamate receptor N1 subunit(GluN1)356-385 antigen peptide,and the serum anti-NMDAR immunoglobulin G(IgG)antibody levels were detected by enzyme-linked immunosorbent assay(ELISA).The healthy mice without modeling were served as control group,and the mice with successful modeling were randomly divided into model group,low dose of Xuebijing injection(XBJ-L)group,and high dose of Xuebijing injection(XBJ-H)group,with 10 mice in each group.After modeling,the mice in XBJ-L and XBJ-H groups were intraperitoneally injected with 5 and 10 mL·kg-1 Xuebijing injection,respectively.The Longa score was used to assess the neurological impairment of the mice in various groups;evans blue(EB)staining was used to determine the BBB permeability;immunofluorescence staining was used to detect the expressions of zonula occludens 1(ZO-1)and Occludin in cerebral cortex of the mice in various groups;Western blotting method was used to determine the expression levels of ZO-1,Occludin,Claudin-5,and neuron-specific nuclear protein(NeuN)in cerebral cortex of the mice in various groups;ELISA method was used to determine the levels of Th17-and Treg-related cytokines including interleukin(IL)-17,IL-22,and IL-10 in serum of the mice;flow cytometry was used to determine the percentages of Th17 and Treg cells in peripheral blood of the mice in various groups,and the Th17/Treg ratio was calculated.Results:The serum of the mice induced with the GluN1 356-385 antigen peptide was positive for NMDAR IgG antibodies,indicating that the models were successfully established.Compared with control group,the neurological impairment score of the mice in model group was significantly increased(P＜0.05),and the EB level in brain tissue was significantly increased(P＜0.05);the fluorescence staining intensities of ZO-1 and Occludin in the cerebral cortex were decreased,and the expression levels of ZO-1,Occludin,Claudin-5,and NeuN proteins in the cerebral cortex were significantly decreased(P＜0.05);the serum levels of IL-17 and IL-22 were significantly increased(P＜0.05),while the IL-10 level was significantly decreased(P＜0.05);the percentage of Th17 cells in peripheral blood was significantly increased(P＜0.05),while the percentage of Treg cells was significantly decreased(P＜0.05),and the Th17/Treg ratio was significantly increased(P＜0.05).Compared with model group,the neurological impairment scores of the mice in XBJ-L and XBJ-H groups were significantly decreased(P＜0.05),the EB levels in brain tissue were significantly decreased(P＜0.05),the fluorescence staining intensities of ZO-1 and Occludin in cerebral cortex were increased,and the expression levels of ZO-1,Occludin,Claudin-5,and NeuN proteins were significantly increased(P＜0.05);the levels of IL-17 and IL-22 in serum were significantly decreased(P＜0.05),and the level of IL-10 was significantly increased(P＜0.05);the percentages of Th17 cells in peripheral blood were significantly decreased(P＜0.05),the percentages of Treg cells were significantly increased(P＜0.05),and the Th17/Treg ratios were significantly decreased(P＜0.05).Compared with XBJ-L group,the neurological function injury score of the mice in XBJ-H group was significantly decreased(P＜0.05),the EB level in brain tissue was significantly decreased(P＜0.05);the fluorescence staining intensities of ZO-1 and Occludin in the cerebral cortex were increased,and the expression levels of ZO-1,Occludin,Claudin-5,and NeuN proteins were significantly increased(P＜0.05);the serum levels of IL-17 and IL-22 were significantly decreased(P＜0.05),and the level of IL-10 was significantly increased(P＜0.05);the percentage of Th17 cells in peripheral blood was significantly decreased(P＜0.05),the percentage of Treg cells was significantly increased(P＜0.05),and the Th17/Treg ratio was significantly decreased(P＜0.05).Conclusion:Xuebijing injection can improve BBB injury,regulate Th17/Treg balance,and thereby alleviate the neurological functional damage in anti-NMDAR encephalitis.