Objective To investigate the expression of magnesiun transporter 1 protein(MagT1)in peripheral blood T lymphocytes of patients with systemic lupus erythematosus(SLE),and elucidate its clinical significance.Methods A total of 79 SLE patients admitted to the People's Hospital of Xishuangbanna Dai Autonomous Prefecture from January 2019 to June 2021 were selected as the study subjects,and SLE patients were divided into moderate to severe group(SLEDAI ≥ 10,n=32)and mild group(SLEDAI＜10,n=47),according to SLE disease activity index(SLEDAI)score.Another 40 healthy patients who underwent physical examinations during the same period were selected as control group.The levels of clinical biochemical and serum immune-related indexes were recorded.The expressions of MagT1 mRNA and protein in peripheral blood T lymphocytes were detected by quantitative real-time PCR(qRT-PCR)and Western Blot methods.The correlation between the expression of MagT1 protein in peripheral blood T lymphocytes and biochemical and immunity-related indexes was analyzed by Pearson correlation analysis.Receiver working characteristic(ROC)curve was drawn to analyze the diagnostic value of MagT1 protein expression of peripheral blood T lymphocytes in diagnosing SLE and its severity.Results Compared with the control group,the expression levels of MagT1 mRNA[0.65(0.36,0.99),0.23(0.07,0.36)vs 1.20(0.83,1.37)]and MagT1 protein[0.35(0.22,0.42),0.22(0.15,0.27)vs 0.53(0.40,0.63)]of peripheral blood T lymphocytes in the mild group and the moderate to severe group were reduced,with significant differences(Z=5.247,7.078;5.128,7.257,all P＜0.05).Compared with the mild group,the expression levels of MagT1 mRNA[0.65(0.36,0.99)vs 0.23(0.07,0.36)]and protein[0.35(0.22,0.42)vs 0.22(0.15,0.27)]of peripheral blood T lymphocytes in the moderate to severe group were reduced,with significant differences(Z=5.169,3.599,all P＜0.05).Pearson correlation results showed that MagT1 protein expression in peripheral blood T lymphocytes was positively correlated with serum hemoglobin(HGB),complement 3(C3)and C4 levels(r=0.496,0.637,0.588,all P＜0.05),but was negatively correlated with serum erythrocyte sedimentation rate(ESR),hypersensitive C-reactive protein(hs-CRP),IgG levels and SLEDAI(r=-0.598,-0.476,-0.646,-0.514,all P＜0.05).The results of the ROC curve showed that the area under the curve in diagnostic SLE for the expression level of peripheral blood T lymphocyte MagT1 protein was 0.893(95％CI:0.838～0.948),with a sensitivity and a specificity of 90.0％and 67.1％,respectively,and the area under the curve in diagnostic SLE severity was 0.739(95％CI:0.631～0.848),with a sensitivity and a specificity of 57.4％and 84.4％,respectively.Conclusion The expressions of peripheral blood T lymphocyte and MagT1 were down regulated in SLE patients,and they had a negative trend with the severity of SLE.They may have a certain diagnostic value for the diagnosis and severity of SLE.