Serum anti-lipocalin 2 IgG is a novel biomarker in the diagnosis of systemic lupus erythematosus

Background: Previous work suggests that lipocalin 2 is involved in the pathogenesis of systemic lupus erythematosus (SLE) and that this novel antigen could serve as a high-quality renal biomarker of acute kidney injury in SLE. However, serum lipocalin 2 antibody levels remain unclear. We have therefore undertaken this study to assess the level of serum IgG antibody against lipocalin 2 in different disease states and to evaluate the diagnostic value of this potential biomarker in SLE. Methods: Serum levels of anti-lipocalin IgG antibodies were measured by ELISA in 103 SLE patients, 93 rheumatoid arthritis (RA) patients, 29 primary Sjö gren's syndrome (pSS) patients, 13 systemic sclerosis (SSc) patients, and 91 healthy controls. Diagnostic properties of anti-lipocalin IgG were determined by receiver-operating characteristic (ROC) curve analysis. Results: The level of serum anti-lipocalin IgG in patients with SLE was significantly higher than in patients with RA, pSS, SSc, or healthy controls (p<0.05), effectively distinguishing SLE from other conditions with high sensitivity and specificity (49.5% and 90.7%, respectively). In ROC curve analysis, the area under the curve (AUC) is 0.783, with a 95% confidence interval (CI) extending from 0.729 to 0.839. Antilipocalin antibodies were present in 48.1% of anti-Sm-negative SLE patients, and also occurred in SLE patients lacking anti-dsDNA (52%) or anti-nucleosome antibodies (46.3%) antibodies. Finally, SLE patients with positive anti-lipocalin IgG possessed higher levels of IgA and CRP than the negative group (p<0.05), clearly demonstrating a positive correlation between anti-lipocalin IgG and these laboratory parameters. Conclusions: Antilipocalin 2 IgG is a promising biomarker for the diagnosis of SLE, particularly when obtained in conjunction with anti-Sm, anti-dsDNA, and anti-nucleosome antibody levels.