Objective This study aimed to analyze the expression of the high mobility group box-1 (HMGB1) protein in neutrophil extracellular traps (NETs) of patients with lupus nephritis (LN) and its association with clinical and histopathological features of the disease. Methods Twenty-three patients with biopsy-confirmed LN and 14 systemic lupus erythematosus (SLE) patients with active disease (SLE Disease Activity Index (SLEDAI) score ≥ 6) and no evidence of LN were included. Clinical and laboratory features were recorded. NETs and the expression of HMGB1 were assessed by confocal microscopy, and serum HMGB1 levels were measured by ELISA. Results In comparison to patients without kidney disease, patients with LN had a higher expression of HMGB1 in spontaneous (57 vs. 30.4; p = 0.027) and lipopolysaccharide (LPS)-induced (55.8 vs. 24.9; p = 0.005) NETs. We found a positive correlation between serum HMGB1 and the expression of HMGB1 in LPS-induced NETs ( r = 0.447, p = 0.017). The expression of HMGB1 in spontaneous NETs correlated with SLEDAI score ( r = 0.514, p = 0.001), anti-dsDNA antibodies ( r = 0.467, p = 0.004), the rate of glomerular filtration descent ( r = 0.543, p = 0.001), and diverse histopathological components of active nephritis in the kidney biopsy, such as the activity index ( r = 0.581, p = 0.004), fibrinoid necrosis ( r = 0.603, p = 0.002), and cellular crescents ( r = 0.486, p = 0.019). Conclusions In patients with SLE, NETs are a source of extracellular HMGB1. The expression of HMGB1 in NETs is higher among patients with LN, which correlates with clinical and histopathological features of active nephritis and suggest a possible role of this alarmin in the pathophysiology of kidney damage in SLE.

Lupus nephritis (LN) is one of the most common manifestations of systemic lupus erythematosus (SLE), characterized by abnormal B cell activation and differentiation to memory or plasma effector cells. However, the role of these cells in the pathogenesis of LN is not fully understood, as well as the effect of induction therapy on B cell subsets, possibly associated with this manifestation, like aged-associated B cells (ABCs). Consequently, we analyzed the molecules defining the ABCs subpopulation (CD11c, T-bet, and CD21) through flow cytometry of blood samples from patients with lupus presenting or not LN, following up a small sub-cohort after six months of induction therapy. The frequency of ABCs resulted higher in LN patients compared to healthy subjects. Unexpectedly, we identified a robust reduction of a CD21hi subset that was almost specific to LN patients. Moreover, several clinical and laboratory lupus features showed strong and significant correlations with this undefined B cell subpopulation. Finally, it was observed that the induction therapy affected not only the frequencies of ABCs and CD21hi subsets but also the phenotype of the CD21hi subset that expressed a higher density of CXCR5. Collectively, our results suggest that ABCs, and more importantly the CD21hi subset, may work to assess therapeutic response since the reduced frequency of CD21hi cells could be associated with the onset of LN.

Background Lupus nephritis (LN) is one of the most common severe organ manifestations of systemic lupus erythematosus (SLE). LN is associated with significant morbidity and mortality in SLE patients, as up to 20% of patients progress to end-stage renal disease (ESRD). The clinical manifestations of LN are variable, ranging from asymptomatic proteinuria to a myriad of manifestations associated with nephritic and nephrotic syndromes and ESRD. It is therefore important to screen all SLE patients for LN. Content Urinalysis is a useful screening test in LN. Quantification of proteinuria can be performed with either a urine protein-to-creatinine ratio or 24-h urine sample collection for protein. Renal biopsy remains the gold standard for diagnosis of LN. Traditional serum biomarkers used to monitor SLE and LN disease activity and flares include anti–double-stranded DNA antibodies and complement components 3 and 4. Other nonconventional biomarkers found to correlate with LN include anti-C1q and surrogate markers of type 1 interferon regulatory genes (INF gene signature). Potential urinary biomarkers for LN include monocyte chemoattractant protein 1, neutrophil gelatinase-associated lipocalin, tumor necrosis factor-like inducer of apoptosis, and vascular cell adhesion molecule 1. Summary Although studies have shown promising results for the use of alternative biomarkers, these require validation in prospective studies to support their use. Renal remission rates in patients receiving standard of care therapy for induction and maintenance treatment of LN remain low. This has prompted further research in newer therapeutic targets in LN ,which have shown promising results.

1117 Figure 1 Comparison of NET complex levels (Elastase-DNA and HMGB1-DNA) between (a) active SLE (n=49), inactive SLE (n=23) and HC (n=20); (b) ALN (n=18) and active non LN (ANLN, n=31); (c) Proliferative ( n=7) and non-Proliferative LN (n=6). All graphs represent the media with IQR. Kruskal-Wallis Test was used to assess the differences in NET complex levels between Active SLE, Inactive SLE and HC and Mann-Whitney test to assess the differences between ALN and ANLN and between Proliferative and non-Proliferative LN. Units for all graphs are in UI/ml.