Objective:The aim of this study was to investigate the expression of Tim-3 in pathogenesis of IgA nephropathy(IgAN)and its clinical significance. Methods:Real time qPCR was performed to detect Tim-3 mRNA in peripheral blood mononuclear cells(PBMCs)from 41 IgAN patients and 21 normal subjects. The proportion of Tim-3+ cells was assayed by flow cytometry. Results:24-hour proteinuria,serum creatinine,routine urine test,urine sediment examination and red blood cell count at high magnification were recorded before renal biopsy. Results:Tim-3 mRNA expression was increased significantly in IgAN patients compared with that in healthy controls(0.64 ± 0.27 vs. 0.18 ± 0.09,P < 0.01),and there was a nearly positive correlation between pathological grade and expression degree of Tim-3 mRNA. Levels of Tim-3 mRNA expression in patients with grade Ⅲ,Ⅳ and Ⅴ were higher than those in patients with grade Ⅰ and Ⅱ(P < 0.05). Also,we found that the proportion of Tim-3+ cells in PBMCs from IgAN patients was higher than that from normal controls[(1.94 ± 0.77)% vs. (0.59 ± 0.24)%,P < 0.01]. The proportion of Tim-3+ cells in patients with grade Ⅳ and Ⅴ was higher than that in patients with grade Ⅰ,Ⅱ and Ⅲ(P < 0.05). Moreover,the expression of Tim-3 mRNA and the proportion of Tim-3+ cells were significantly positively related to 24-hour proteinuria and serum creatinine. Conclusion:Up-regulation of Tim-3 in IgAN patients was positively correlated with some clinical indexes including 24-hour proteinuria and serum creatinine. Tim-3 may be involved in the pathogenesis of IgAN,and can be a reliable biomarker for evaluating disease severity and prognosis of IgAN.