Abstract: 【Abstract】 Objective To evaluate the therapeutic effect of baicalin on lupus nephritis in a lupus-prone mouse model, and to investigate its regulatory role in the differentiation of follicular helper T （Tfh） cells. Methods Eight 12-week-old female MRL/lpr lupus-prone mice were randomly and equally divided into two groups by a random number table i.e., baicalin group and control group intraperitoneally injected with 200 mg/kg baicalin sodium and chloride physiological solution, respectively, once every day for 4 weeks. After the end of treatment, Coomassie brilliant blue staining was performed to detect the level of 24-hour urine protein. Then, the mice were sacrificed, and the spleens were resected and weighed. Mononuclear cells were isolated from these spleens, and flow cytometry was conducted to determine the proportion of Tfh cells. Additionally, the kidneys were resected and subjected to hematoxylin and eosin （HE） staining for the evaluation of kidney impairment. Moreover, some other mononuclear cells were isolated from the spleens of the lupus-prone mice in the control group, and magnetic activated cell sorting （MACS） was performed to isolate naive CD4+ T cells, which were divided into 3 groups: blank control group receiving no treatment, induction group treated with 10 μg/L anti-interleukin （IL）-21 and anti-IL-6 antibodies and 3 μg/L anti-CD3 and anti-CD28 antibodies for 5 days, and intervention group additionally treated with 40 μmol/L baicalin for 5 days besides the above treatment. Then, 50 μg/L phorbol ester, 750 μg/L ionomycin and 20 mg/L brefeldin A were used to stimulate some cultured naive CD4+ T cells in the above groups. Flow cytometry was conducted to determine the proportion of CD4+CXCR5+PD-1+ cells and CD4+IL-21+ cells. Statistical analysis was carried out with SPSS20.0 software by using one-way analysis of variance （ANOVA） and student t test for the comparison of quantitative data between groups. Results The baicalin treatment could effectively improve the kidney impairment in the lupus-prone mice. Compared with the control group, the baicalin group showed significantly decreased 24-hour urine protein level （［1 416 ± 171］ vs. ［2 623 ± 278］ μg/24 h, P = 0.022）, and significantly decreased proportion of Tfh cells in the spleen （12.6% ± 2.3% vs. 40.2% ± 1.1%, P = 0.005）. In vitro baicalin could further inhibit the differentiation of Tfh cells. Compared with the induction group, the intervention group showed significantly decreased proportion of CD4+CXCR5+PD-1+ Tfh cells （13.3% ± 0.8% vs. 17.6% ± 0.9%, P = 0.04） and CD4+IL-21+ cells （1.0% ± 0.4% vs. 2.7% ± 0.2%, P < 0.01）. Conclusion Baicalin can effectively ameliorate lupus nephritis, which may be associated with the inhibition of Tfh cell differentiation.

Key words: Lupus erythematosus, systemic, Lupus nephritis, Baicalin, Disease models, animal, Follicular helper T cells, Interleukin-21