Objective  To detect the expressions of X-box binding protein 1 unspliced （xbp1u） and X-box binding protein 1 spliced （xbp1s） mRNA in peripheral blood CD19⁺B cells of patients with lupus nephritis （LN） and healthy subjects and explore the clinical significance of XBP1 in LN patients.

Methods  The expression levels of xbp1u and xbp1s in peripheral blood CD19⁺B cells of 65 LN patients and 30 healthy controls were detected by real-time polymerase chain reaction （RT-PCR）. And the ratio of CD19⁻CD138⁺plasma cells/CD19⁺B cells in peripheral blood was detected by flow cytometry.

Results  The expression level of xbp1u mRNA in CD19⁺B cells of active LN group （0.078±0.034） was higher than that in control group（0.035±0.011）（P＜0.05） and in stable group（0.049±0.016）（P＜0.05）. The expression level of xbp1s mRNA in CD19⁺B cells of active LN group（0.076±0.037）was higher than that in control group（0.022±0.010）（P＜0.05） and stable group（0.043±0.017）（P＜0.05）. The ratio of CD19⁻CD138⁺ plasma cells /CD19⁺B cells in LN group（0.059±0.024）was significantly higher than that in control group （P＜0.01） and stable group （0.073±0.036）（P＜0.05）; XBP1 expression in LN patients was correlated positively with the ratio of CD19⁻CD138⁺ plasma cells/CD19⁺B cells （r value = 0.138 & 0.036）, positively with anti-ds-DNA antibody and systemic lupus erythematosus disease activity index（SLEDAI）score （r value = 0.417 & 0.058） and negatively with hemoglobin and complement C3 （r value = −0.559 & −0.219）.

Conclusion  The expressions of xbp1u and xbp1s mRNA in peripheral blood mononuclear cells of LN patients in active group are higher than those in healthy group. Both are correlated positively with SLEDAI score and anti-DS DNA antibody. The expression of XBP1 is up-regulated in B cells of LN patients and it is significantly correlated with plasma cells. It implies that XBP1 may participate in the pathogenesis of LN through promoting the differentiation of B cells.