Background/Purpose: Systemic lupus erythematous (SLE) is a multisystem autoimmune inflammatory disease. Lupus nephritis (LN) is one of the most serious complications in patients with SLE. Immunoglobulin binding protein 1 (IGBP1) originally was discovered as a phosphoprotein associated with the immunoglobulin receptor in B cells. This protein interacts with the catalytic subunit of protein phosphatase PP2A (PP2A), highly conserved serine/threonine phosphatase, and regulates differentiation, proliferation, and apoptosis of B cells. It has been reported that expression and activity of its catalytic subunit (PP2Ac) is increased in T cells from patients with SLE. However, the study of IGBP1 in patients with SLE has not been examined. The objective of the present study was to determine IGBP1 levels in SLE patients and identify any correlations between IGBP1 levels with other clinical variables and especially, renal pathology in patients with LN.

Methods: The levels of IGBP1 were measured in plasma and urine of SLE patients with (n=40) or without (n=30) LN, and healthy subjects (n=18). Correlation analyses between IGBP1 levels and the diseases-related variables including c-reactive protein (CRP), erythrocyte sedimentation rate (ESR), anti-double-stranded DNA antibody (anti-dsDNA), and SLE Disease Activity Index (SLEDAI) were examined. In addition, to evaluate if IGBP1 can differentiate LN disease severity, we performed IGBP1 levels regarding classes of kidney biopsy samples and correlation analyses of plasma IGBP1 levels with activity index score or chronicity index score in renal biopsy samples.

Results: Plasma levels of IGBP1 in SLE patients were significantly higher in SLE patients with (8.48 ng/ml) or without (9.69 ng/ml) LN than in healthy individuals (4.90 ng/ml). Among the diseases-related variables, SLEDAI scores were significantly correlated with the levels of IGBP1 in plasma (p= 0.0429) and urine (p= 0.0011). Interestingly, LN patients with Class III and IV had higher IGBP1 levels compared to those of II and V groups. Further, plasma IGBP1 levels had a significant positive association with chronicity index score (p= 0.0072).

Conclusion: This study demonstrates that the levels of plasma and urinary IGBP1 were significantly higher in SLE patients and were correlated with disease activity and chronicity index score of renal pathology. Therefore, IGBP1 might be a valuable tool for determining high disease activity in SLE patients and more severe kidney damage in LN patients.