96 Urinary biomarker related with tubular inflammation in lupus nephritis

Background and aims Severe tubulointerstitial damage represents a poor prognosis of lupus nephritis (LN). Immunoglobulin binding protein 1 (IGBP1) was known as a phosphoprotein associated with the immunoglobulin receptor in B cells. Our study determined urinary IGBP1 levels in LN patients and addressed correlations between urinary IGBP1 levels and clinical variables. Methods The levels of IGBP1 were measured in urine of SLE patients with or without nephritis, and healthy subjects. Correlation analyses between urinary IGBP1 levels and the disease-related variables including C3/4, anti-dsDNA, and SLE Disease Activity Index (SLEDAI) were examined. We performed correlation analyses of urinary IGBP1 levels with activity index score or chronicity index score in renal tissues. To define IGBP1 expression in renal pathologies, immunohistochemical staining were performed. In addition, to identify genetic relationship with IGBP1, microarray was performed in HK2 tubular cells treated with IGBP1-siRNA. Results Urinary levels of IGBP1 were significantly higher in LN patients than in SLE patients without nephritis and healthy individuals. Among the disease-related variables, SLEDAI scores, anti-dsDNA, and C3 were correlated with the levels of urinary IGBP1. Further, urinary IGBP1 levels represented a positive association with activity index score in renal pathology. IGBP1 was stained mainly in tubules, especially in class III, IV and V. In microarray analysis, IL-7 receptor was closely related with IGBP1 down-regulation. Conclusions This study demonstrates that the levels of urinary IGBP1 were higher in LN patients and correlated with disease activity and activity index score of renal pathology. Therefore, urinary IGBP1 might be a valuable marker for determining the activity of LN.