Dominance of Autoantibodies to Nuclear Antigens and Extracellular Matrix Proteins in Lupus Nephritis Urine

Background: Improved non-invasive biomarkers are needed for the diagnosis and monitoring of lupus nephritis (LN). The goal of this study is to identify novel biomarkers in LN urine using mass spectrometry. Since multiple immunoglobulin species were detected, we also explored the autoantigen specificity of these antibodies in LN urine. Methods: Urine samples from patients with active LN, inactive LN, and healthy controls (N=24) were analyzed using mass spectrometry, followed by autoantibody array screens against 128 autoantigens. Results: Mass spectrometry analysis of LN urine revealed not only previously known LN associated proteins, but also elevated levels of antibodies. Thus, the top 35 most significantly elevated proteins in LN urine (p-value < 0.01, Fold Change > 2) included multiple immunoglobulins. When applied to 128-plex autoantigen arrays, LN urine exhibited increased IgG antibodies to Histone H2B (38X; p< 0.00001), dsDNA, and SmD1, canonical targets in LN (Fig. 1, Left). Additionally, IgKappa autoantibodies in LN urine showed elevated reactivity to Collagens I, II, III, IV, Complement C9 and Histone H1, among others, alluding to the presence of other heavy chain isotypes (Fig. 1, Right). Conclusion: This study reveals a novel spectrum of urinary biomarkers in LN, including autoantibodies, complementing previous biomarker studies using ligand-based proteomics. The high prevalence of autoantibodies to collagen and complement proteins, not common in LN serum, suggests that these may be products from intra-renal immune hotspots. Studies are in progress to assess the origins of these autoantibodies and their diagnostic significance. Funding: NIDDK Support, Private Foundation SupportSpecificities of autoantibodies increased in Lupus Nephritis Urine