Nephritogenic lupus antibodies recognize glomerular basement membrane-associated chromatin fragments released from apoptotic intraglomerular cells

Association of Autoantibody Concentrations and Trajectories With Lupus Nephritis Histologic Features and Treatment Response

OBJECTIVE

Autoantibodies are a hallmark of lupus nephritis (LN), but their association with LN classes and treatment response are not adequately known. In this study, we quantified circulating autoantibodies in the Accelerating Medicines Partnership LN longitudinal cohort to identify serological biomarkers of LN histologic classification and treatment response and how these biomarkers change over time based on treatment response.

METHODS

Peripheral blood samples were collected from 279 patients with systemic lupus erythematosus undergoing diagnostic kidney biopsy based on proteinuria. Of these, 268 were diagnosed with LN. Thirteen autoantibody specificities were measured by bead-based assays (Bio-Rad Bioplex 2200) and anti-C1q by enzyme-linked immunosorbent assay at the time of biopsy (baseline) and at 3, 6, and 12 months after biopsy. Clinical response was determined at 12 months.

RESULTS

Proliferative LN (International Society of Nephrology/Renal Pathology Society class III/IV±V, n = 160) was associated with higher concentrations of anti-C1q, anti-chromatin, anti-double-stranded DNA (dsDNA), and anti-ribosomal P autoantibodies compared to nonproliferative LN (classes I/II/V/VI, n = 108). Anti-C1q and-dsDNA were independently associated with proliferative LN. In proliferative LN, higher baseline anti-C1q levels predicted complete response (area under the curve [AUC] 0.72; P = 0.002) better than baseline proteinuria (AUC 0.59; P = 0.21). Furthermore, all autoantibody levels except for anti-La/SSB decreased over 12 months in patients with proliferative, but not membranous, LN with a complete response.

CONCLUSION

Baseline levels of anti-C1q and anti-dsDNA may serve as noninvasive biomarkers of proliferative LN, and anti-C1q may predict complete response at the time of kidney biopsy. In addition, tracking autoantibodies over time may provide further insights into treatment response and pathogenic mechanisms in patients with proliferative LN.

Translational implications of newly characterized pathogenic pathways in systemic lupus erythematosus

Improved characterization of relevant pathogenic pathways in systemic lupus erythematosus (SLE) has been further delineated over the last decades. This led to the development of targeted treatments including belimumab and anifrolumab, which recently became available in clinics. Therapeutic targets in SLE encompass interferon (IFN) signaling, B-T costimulation including immune checkpoints, and increasing modalities of B lineage targeting, such as chimeric antigen receptor (CAR) T cells directed against CD19 or sequential anti-B cell targeting. Patient profiling based on characterization of underlying molecular abnormalities, often performed through comprehensive omics analyses, has recently been shown to better predict patients' treatment responses and also holds promise to unravel key molecular mechanisms driving SLE. SLE carries two key signatures, namely the IFN and B lineage/plasma cell signatures. Recent advances in SLE treatments clearly indicate that targeting innate and adaptive immunity is successful in such a complex autoimmune disease. Although those signatures may interact at the molecular level and provide the basis for the first selective treatments in SLE, it remains to be clarified whether these distinct treatments show different treatment responses among certain patient subsets. In fact, notwithstanding the remarkable amount of novel clues for innovative SLE treatment, harmonization of big data within tailored treatment strategies will be instrumental to better understand and treat this challenging autoimmune disorder. This review will provide an overview of recent improvements in SLE pathogenesis, related insights by analyses of big data and machine learning as well as technical improvements in conducting clinical trials with the ultimate goal that translational research results in improved patient outcomes.

Glomerulonephritis

Glomerulonephritis (GN) encompasses several disorders that cause glomerular inflammation and injury through an interplay of immune-mediated mechanisms, host characteristics, and environmental triggers, such as infections. GN can manifest solely in the kidney or in the setting of a systemic illness, and presentation can range from chronic and relatively asymptomatic hematuria to fulminant renal failure. Classic acute GN is characterized by hematuria, edema, and hypertension, the latter 2 of which are the consequence of sodium and water retention in the setting of renal impairment. Although presenting signs and symptoms and a compatible clinical history can suggest GN, serologic and urinary testing can further refine the differential diagnosis, and renal biopsy can be used for definitive diagnosis. Treatment of GN can include supportive care, renin-angiotensin-aldosterone system blockade, immunomodulatory therapy, and renal transplant. Prognosis is largely dependent on the underlying cause of GN and can vary from a self-limited course to chronic kidney disease. This review focuses on lupus nephritis, IgA nephropathy, IgA vasculitis, and postinfectious GN.

Patients with ACPA-positive and ACPA-negative rheumatoid arthritis show different serological autoantibody repertoires and autoantibody associations with disease activity

Patients with rheumatoid arthritis (RA) can test either positive or negative for circulating anti-citrullinated protein antibodies (ACPA) and are thereby categorized as ACPA-positive (ACPA+) or ACPA-negative (ACPA-), respectively. In this study, we aimed to elucidate a broader range of serological autoantibodies that could further explain immunological differences between patients with ACPA+ RA and ACPA- RA. On serum collected from adult patients with ACPA+ RA (n = 32), ACPA- RA (n = 30), and matched healthy controls (n = 30), we used a highly multiplex autoantibody profiling assay to screen for over 1600 IgG autoantibodies that target full-length, correctly folded, native human proteins. We identified differences in serum autoantibodies between patients with ACPA+ RA and ACPA- RA compared with healthy controls. Specifically, we found 22 and 19 autoantibodies with significantly higher abundances in ACPA+ RA patients and ACPA- RA patients, respectively. Among these two sets of autoantibodies, only one autoantibody (anti-GTF2A2) was common in both comparisons; this provides further evidence of immunological differences between these two RA subgroups despite sharing similar symptoms. On the other hand, we identified 30 and 25 autoantibodies with lower abundances in ACPA+ RA and ACPA- RA, respectively, of which 8 autoantibodies were common in both comparisons; we report for the first time that the depletion of certain autoantibodies may be linked to this autoimmune disease. Functional enrichment analysis of the protein antigens targeted by these autoantibodies showed an over-representation of a range of essential biological processes, including programmed cell death, metabolism, and signal transduction. Lastly, we found that autoantibodies correlate with Clinical Disease Activity Index, but associate differently depending on patients' ACPA status. In all, we present candidate autoantibody biomarker signatures associated with ACPA status and disease activity in RA, providing a promising avenue for patient stratification and diagnostics.

The Interaction of Anti-DNA Antibodies with DNA: Evidence for Unconventional Binding Mechanisms

Antibodies to DNA (anti-DNA) are the serological hallmark of systemic lupus erythematosus, a prototypic autoimmune disease. These antibodies bind to conserved sites on single-stranded and double-stranded DNA and display variable region somatic mutations consistent with antigen selection. Nevertheless, the interaction of anti-DNA with DNA has unconventional features. Anti-DNA antibodies bind by a mechanism called monogamous bivalency, in which stable interaction requires contact of both Fab sites with determinants on the same extended DNA molecule; the size of this DNA can be hundreds to thousands of bases, especially in solid phase assays. This binding also requires the presence of the Fc portion of IgG, a binding mechanism known as Fc-dependent monogamous bivalency. As shown by the effects of ionic strength in association and dissociation assays, anti-DNA binding is primarily electrostatic. Like anti-DNA autoantibodies, anti-DNA antibodies that bind specifically to non-conserved sites on bacterial DNA, a type of anti-DNA found in otherwise healthy individuals, also interact by monogamous bivalency. The unconventional features of anti-DNA antibodies may reflect the highly charged and polymeric nature of DNA and the need for molecular rearrangements to facilitate monogamous bivalency; the Fc portion contributes to binding in an as yet unknown way.

The Anti-DNA Antibodies: Their Specificities for Unique DNA Structures and Their Unresolved Clinical Impact-A System Criticism and a Hypothesis

Systemic lupus erythematosus (SLE) is diagnosed and classified by criteria, or by experience, intuition and traditions, and not by scientifically well-defined etiology(ies) or pathogenicity(ies). One central criterion and diagnostic factor is founded on theoretical and analytical approaches based on our imperfect definition of the term “The anti-dsDNA antibody”. “The anti-dsDNA antibody” holds an archaic position in SLE as a unique classification criterium and pathogenic factor. In a wider sense, antibodies to unique transcriptionally active or silent DNA structures and chromatin components may have individual and profound nephritogenic impact although not considered yet – not in theoretical nor in descriptive or experimental contexts. This hypothesis is contemplated here. In this analysis, our state-of-the-art conception of these antibodies is probed and found too deficient with respect to their origin, structural DNA specificities and clinical/pathogenic impact. Discoveries of DNA structures and functions started with Miescher’s Nuclein (1871), via Chargaff, Franklin, Watson and Crick, and continues today. The discoveries have left us with a DNA helix that presents distinct structures expressing unique operations of DNA. All structures are proven immunogenic! Unique autoimmune antibodies are described against e.g. ssDNA, elongated B DNA, bent B DNA, Z DNA, cruciform DNA, or individual components of chromatin. In light of the massive scientific interest in anti-DNA antibodies over decades, it is an unexpected observation that the spectrum of DNA structures has been known for decades without being implemented in clinical immunology. This leads consequently to a critical analysis of historical and contemporary evidence-based data and of ignored and one-dimensional contexts and hypotheses: i.e. “one antibody - one disease”. In this study radical viewpoints on the impact of DNA and chromatin immunity/autoimmunity are considered and discussed in context of the pathogenesis of lupus nephritis.

Transforming mutations in the development of pathogenic B cell clones and autoantibodies

Autoimmune diseases are characterized by serum autoantibodies, some of which are pathogenic, causing severe manifestations and organ injury. However, autoantibodies of the same antigenic reactivity are also present in the serum of asymptomatic people years before they develop any clinical signs of autoimmunity. Autoantibodies can arise during multiple stages of B cell development, and various genetic and environmental factors drive their production. However, what drives the development of pathogenic autoantibodies is poorly understood. Advances in single-cell technology have enabled the deep analysis of rare B cell clones producing pathogenic autoantibodies responsible for vasculitis in patients with primary Sjögren's syndrome complicated by mixed cryoglobulinaemia. These findings demonstrated a cascade of genetic events involving stereotypic immunoglobulin V(D)J recombination and transforming somatic mutations in lymphoma genes and V(D)J regions that disrupted antibody quality control mechanisms and decreased autoantibody solubility. Most studies consider V(D)J mutations that enhance autoantibody affinity to drive pathology; however, V(D)J mutations that increase autoantibody propensity to form insoluble complexes could be a major contributor to autoantibody pathogenicity. Defining the molecular characteristics of pathogenic autoantibodies and failed tolerance checkpoints driving their formation will improve prognostication, enabling early treatment to prevent escalating organ damage and B cell malignancy.

Interferon Lambda Regulates Cellular and Humoral Immunity in Pristane-Induced Lupus

A pivotal role of type I interferons in systemic lupus erythematosus (SLE) is widely accepted. Type III interferons (IFN-λ) however, the most recently discovered cytokines grouped within the interferon family, have not been extensively studied in lupus disease models yet. Growing evidence suggests a role for IFN-λ in regulating both innate and adaptive immune responses, and increased serum concentrations have been described in multiple autoimmune diseases including SLE. Using the pristane-induced lupus model, we found that mice with defective IFN-λ receptors (Ifnlr1^−/−) showed increased survival rates, decreased lipogranuloma formation and reduced anti-dsDNA autoantibody titers in the early phase of autoimmunity development compared to pristane-treated wild-type mice. Moreover, Ifnlr1^−/− mice treated with pristane had reduced numbers of inflammatory mononuclear phagocytes and cNK cells in their kidneys, resembling untreated control mice. Systemically, circulating B cells and monocytes (CD115⁺Ly6C⁺) were reduced in pristane-treated Ifnlr1^−/− mice. The present study supports a significant role for type III interferons in the pathogenesis of pristane-induced murine autoimmunity as well as in systemic and renal inflammation. Although the absence of type III interferon receptors does not completely prevent the development of autoantibodies, type III interferon signaling accelerates the development of autoimmunity and promotes a pro-inflammatory environment in autoimmune-prone hosts.

Serum IgG2 antibody multicomposition in systemic lupus erythematosus and lupus nephritis (Part 1): cross-sectional analysis

OBJECTIVES

Serum anti-dsDNA and anti-nucleosome IgGs have been proposed as signatures for SLE and LN in limited numbers of patients. We sought to show higher sensitivity and specificity of the same antibodies with the IgG2 isotype and included IgG2 antibodies vs specific intracellular antigens in the analysis.

METHODS

A total of 1052 SLE patients with (n = 479) and without (n = 573) LN, recruited at different times from the beginning of symptoms, were included in the study. Patients with primary APS (PAPS, n = 24), RA (RA, n = 24) and UCTD (UCTD, n = 96) were analysed for comparison. Anti-nucleosome (dsDNA, Histone2A, Histone3), anti-intracellular antigens (ENO1), anti-annexin A1 and anti-C1q IgG2 were determined by non-commercial techniques.

RESULTS

The presence in the serum of the IgG2 panel was highly discriminatory for SLE/LN vs healthy subjects. Serum levels of anti-dsDNA and anti-C1q IgG2 were more sensitive than those of IgGs (Farr radioimmunoassay/commercial assays) in identifying SLE patients at low-medium increments. Of more importance, serum positivity for anti-ENO1 and anti-H2A IgG2 discriminated between LN and SLE (ROC T0-12 months), and high levels at T0-1 month were detected in 63% and 67%, respectively, of LN, vs 3% and 3%, respectively, of SLE patients; serum positivity for each of these was correlated with high SLEDAI values. Minor differences existed between LN/SLE and the other rheumatologic conditions.

CONCLUSION

Nephritogenic IgG2 antibodies represent a specific signature of SLE/LN, with a few overlaps with other rheumatologic conditions. High levels of anti-ENO1 and anti-H2A IgG2 correlated with SLE activity indexes and were discriminatory between SLE patients limited to the renal complication and other SLE patients.

TRIAL REGISTRATION

The Zeus study was registered at https://clinicaltrials.gov, NCT02403115.

Serum IgG2 antibody multi-composition in systemic lupus erythematosus and in lupus nephritis (Part 2): prospective study

OBJECTIVES

Circulating anti-ENO1 and anti-H2A IgG2 have been identified as specific signatures of LN in a cross-over approach. We sought to show whether the same antibodies identify selected population of patients with LN with potentially different clinical outcomes.

METHODS

Here we report the prospective analysis over 36 months of circulating IgG2 levels in patients with newly diagnosed LN (n=91) and SLE (n=31) and in other patients with SLE recruited within 2 years from diagnosis (n=99). Anti-podocyte (ENO1), anti-nucleosome (DNA, histone 2 A, histone 3) and anti-circulating proteins (C1q, AnnexinA1-ANXA1) IgG2 antibodies were determined by home-made techniques.

RESULTS

LN patients were the main focus of the study. Anti-ENO1, anti-H2A and anti-ANXA1 IgG2 decreased in parallel to proteinuria and normalized within 12 months in the majority of patients while anti-dsDNA IgG2 remained high over the 36 months. Anti-ENO1 and anti-H2A had the highest association with proteinuria (Heat Map) and identified the highest number of patients with high proteinuria (68% and 71% respectively) and/or with reduced estimated glomerula filtration rate (eGFR) (58% for both antibodies) compared with 23% and 17% of anti-dsDNA (agreement analysis). Anti-ENO1 positive LN patients had higher proteinuria than negative patients at T0 and presented the maximal decrement within 12 months.

CONCLUSIONS

Anti-ENO1, anti-H2A and anti-ANXA1 antibodies were associated with high proteinuria in LN patients and Anti-ENO1 also presented the maximal reduction within 12 months that paralleled the decrease of proteinuria. Anti-dsDNA were not associated with renal outcome parameters. New IgG2 antibody signatures should be utilized as tracers of personalized therapies in LN.

TRIAL REGISTRATION

The Zeus study was registered at https://clinicaltrials.gov (study number: NCT02403115).

Harnessing Tolerogenic Histone Peptide Epitopes From Nucleosomes for Selective Down-Regulation of Pathogenic Autoimmune Response in Lupus (Past, Present, and Future)

Autoantigen-directed tolerance can be induced by certain nucleosomal histone peptide epitope/s in nanomolar dosage leading to sustained remission of disease in mice with spontaneous SLE. By contrast, lupus is accelerated by administration of intact (whole) histones, or whole nucleosomes in microparticles from apoptotic cells, or by post-translationally acetylated histone-peptides. Low-dose therapy with the histone-peptide epitopes simultaneously induces TGFβ and inhibits IL-6 production by DC in vivo, especially pDC, which then induce CD4+CD25+ Treg and CD8+ Treg cells that suppress pathogenic autoimmune response. Both types of induced Treg cells are FoxP3+ and act by producing TGFβ at close cell-to-cell range. No anaphylactic adverse reactions, or generalized immunosuppression have been detected in mice injected with the peptides, because the epitopes are derived from evolutionarily conserved histones in the chromatin; and the peptides are expressed in the thymus during ontogeny, and their native sequences have not been altered. The peptide-induced Treg cells can block severe lupus on adoptive transfer reducing inflammatory cell reaction and infiltration in the kidney. In Humans, similar potent Treg cells are generated by the histone peptide epitopes in vitro in lupus patients’ PBMC, inhibiting anti-dsDNA autoantibody and interferon production. Furthermore, the same types of Treg cells are generated in lupus patients who are in very long-term remission (2-8 years) after undergoing autologous hematopoietic stem cell transplantation. These Treg cells are not found in lupus patients treated conventionally into clinical remission (SLEDAI of 0); and consequently they still harbor pathogenic autoimmune cells, causing subclinical damage. Although antigen-specific therapy with pinpoint accuracy is suitable for straight-forward organ-specific autoimmune diseases, Systemic Lupus is much more complex. The histone peptide epitopes have unique tolerogenic properties for inhibiting Innate immune cells (DC), T cells and B cell populations that are both antigen-specifically and cross-reactively involved in the pathogenic autoimmune response in lupus. The histone peptide tolerance is a natural and non-toxic therapy suitable for treating early lupus, and also maintaining lupus patients after toxic drug therapy. The experimental steps, challenges and possible solutions for successful therapy with these peptide epitopes are discussed in this highly focused review on Systemic Lupus.

Patients with Proliferative Lupus Nephritis Have Autoantibodies That React to Moesin and Demonstrate Increased Glomerular Moesin Expression

Kidney involvement in systemic lupus erythematosus (SLE)—termed lupus nephritis (LN)—is a severe manifestation of SLE that can lead to end-stage kidney disease (ESKD). LN is characterized by immune complex deposition and inflammation in the glomerulus. We tested the hypothesis that autoantibodies targeting podocyte and glomerular cell proteins contribute to the development of immune complex formation in LN. We used Western blotting with SLE sera from patients with and without LN to identify target antigens in human glomerular and cultured human-derived podocyte membrane proteins. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identified the proteins in the gel regions corresponding to reactive bands observed with sera from LN patients. We identified 102 proteins that were present in both the podocyte and glomerular samples. We identified 10 high-probability candidates, including moesin, using bioinformatic analysis. Confirmation of moesin as a target antigen was conducted using immunohistochemical analysis (IHC) of kidney biopsy tissue and enzyme-linked immunosorbent assay (ELISA) to detect circulating antibodies. By IHC, biopsies from patients with proliferative lupus nephritis (PLN, class III/IV) demonstrated significantly increased glomerular expression of moesin (p < 0.01). By ELISA, patients with proliferative LN demonstrated significantly increased antibodies against moesin (p < 0.01). This suggests that moesin is a target glomerular antigen in lupus nephritis.

Antibodies to an Epstein Barr Virus protein that cross-react with dsDNA have pathogenic potential

Pathogens such as the Epstein Barr virus (EBV) have long been implicated in the etiology of systemic lupus erythematosus (SLE). The Epstein Barr virus nuclear antigen I (EBNA-1) has been shown to play a role in the development of anti-nuclear antibodies characteristic of SLE. One mechanism by which EBV may play a role in SLE is molecular mimicry. We previously generated two monoclonal antibodies (mAbs) to EBNA-1 and demonstrated that they cross-react with double-stranded DNA (dsDNA). In the present study, we demonstrate that these mAbs have pathogenic potential. We show that they can bind to isolated rat glomeruli and that binding can be greatly diminished by pretreatment of glomeruli with DNase I, suggesting that these mAbs bind dsDNA in the kidney. We also demonstrate that these antibodies can deposit in the kidney when injected into mice and can induce proteinuria and elicit histopathological alterations consistent with glomerulonephritis. Finally, we show that these antibodies can cross-react with laminin and collagen IV in the extracellular matrix suggesting that direct binding to the glomerular basement membrane or mesangial matrix may also contribute to the antibody deposition in the kidney. In summary, our results indicate that EBNA-1 can elicit antibodies that cross-react with dsDNA, that can deposit in the kidney, and induce kidney damage. These results are significant because they support the role of a viral protein in SLE and lupus nephritis.

Autoimmunity and SLE: Factual and Semantic Evidence-Based Critical Analyses of Definitions, Etiology, and Pathogenesis

One cannot discuss anti-dsDNA antibodies and lupus nephritis without discussing the nature of Systemic lupus erythematosus (SLE). SLE is insistently described as a prototype autoimmune syndrome, with anti-dsDNA antibodies as a central biomarker and a pathogenic factor. The two entities, "SLE" and "The Anti-dsDNA Antibody," have been linked in previous and contemporary studies although serious criticism to this mutual linkage have been raised: Anti-dsDNA antibodies were first described in bacterial infections and not in SLE; later in SLE, viral and parasitic infections and in malignancies. An increasing number of studies on classification criteria for SLE have been published in the aftermath of the canonical 1982 American College of Rheumatology SLE classification sets of criteria. Considering these studies, it is surprising to observe a nearby complete absence of fundamental critical/theoretical discussions aimed to explain how and why the classification criteria are linked in context of etiology, pathogenicity, or biology. This study is an attempt to prioritize critical comments on the contemporary definition and classification of SLE and of anti-dsDNA antibodies in context of lupus nephritis. Epidemiology, etiology, pathogenesis, and measures of therapy efficacy are implemented as problems in the present discussion. In order to understand whether or not disparate clinical SLE phenotypes are useful to determine its basic biological processes accounting for the syndrome is problematic. A central problem is discussed on whether the clinical role of anti-dsDNA antibodies from principal reasons can be accepted as a biomarker for SLE without clarifying what we define as an anti-dsDNA antibody, and in which biologic contexts the antibodies appear. In sum, this study is an attempt to bring to the forum critical comments on the contemporary definition and classification of SLE, lupus nephritis and anti-dsDNA antibodies. Four concise hypotheses are suggested for future science at the end of this analytical study.

Complement Deficiencies Result in Surrogate Pathways of Complement Activation in Novel Polygenic Lupus-like Models of Kidney Injury

Lupus nephritis (LN) is a major contributor to morbidity and mortality in lupus patients, but the mechanisms of kidney damage remain unclear. In this study, we introduce, to our knowledge, novel models of LN designed to resemble the polygenic nature of human lupus by embodying three key genetic alterations: the Sle1 interval leading to anti-chromatin autoantibodies; Mfge8-/- , leading to defective clearance of apoptotic cells; and either C1q-/- or C3-/- , leading to low complement levels. We report that proliferative glomerulonephritis arose only in the presence of all three abnormalities (i.e., in Sle1.Mfge8 -/- C1q -/- and Sle1.Mfge8 -/- C3 -/- triple-mutant [TM] strains [C1q -/-TM and C3-/- TM, respectively]), with structural kidney changes resembling those in LN patients. Unexpectedly, both TM strains had significant increases in autoantibody titers, Ag spread, and IgG deposition in the kidneys. Despite the early complement component deficiencies, we observed assembly of the pathogenic terminal complement membrane attack complex in both TM strains. In C1q-/- TM mice, colocalization of MASP-2 and C3 in both the glomeruli and tubules indicated that the lectin pathway likely contributed to complement activation and tissue injury in this strain. Interestingly, enhanced thrombin activation in C3-/- TM mice and reduction of kidney injury following attenuation of thrombin generation by argatroban in a serum-transfer nephrotoxic model identified thrombin as a surrogate pathway for complement activation in C3-deficient mice. These novel mouse models of human lupus inform the requirements for nephritis and provide targets for intervention.

Serum Deoxyribonuclease 1-like 3 is a potential biomarker for diagnosis of ankylosing spondylitis

BACKGROUND

Ankylosing spondylitis (AS) is an autoimmune disease with high disability rate, and it is sometimes difficult to distinguish from generalized osteoarthritis (GOA). Deoxyribonuclease 1-like 3 (DNASE1L3) was associated with a variety of autoimmune diseases. However, the serum DNASE1L3 level in AS and GOA remain unreported. Herein, this study was designed to gauge serum DNASE1L3 level in patients with AS and GOA, and to discern the utility of serum DNASE1L3 as a biomarker for assessing the severity of patients with AS.

METHODS

The study population consisted of 60 patients with AS, 60 patients with GOA and 60 control subjects. Serum DNASE1L3 levels were measured using enzyme-linked immunosorbent assay (ELISA) assay. Disease activity were assessed with Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) in AS patients.

RESULTS

Our data showed that serum DNASE1L3 levels were significantly higher in patients with AS than that of the healthy controls and patients with GOA. Serum DNASE1L3 levels in patients with AS were positively correlated with BASDAI scores, C3 and C-reactive protein (CRP). Furthermore, serum DNASE1L3 showed higher discriminatory accuracy in the diagnosis of AS from GOA (AUC = 0.851, sensitivity = 78.33% and specificity = 81.67%).

CONCLUSIONS

Elevated Serum DNASE1L3 levels in patients with AS were significantly associated with the clinic features and disease activity. DNASE1L3 could be a serum biomarker with a positive diagnostic value in patients with AS, and which could be used as a differential diagnostic indicator for GOA and AS.

An Update on Antibodies to Necleosome Components as Biomarkers of Sistemic Lupus Erythematosus and of Lupus Flares

Systemic lupus erythematosus (SLE) is an autoimmune disease with variable clinical expression. It is a potentially devastating condition affecting mostly women and leading to clinically unpredictable outcomes. Remission and flares may, in fact, alternate over time and a mild involvement limited to few articular sites may be followed by severe and widespread organ damage. SLE is the prototype of any autoimmune condition and has, for this reason, attracted the interest of basic immunologists. Therapies have evolved over time and clinical prognosis has, in parallel, been improved. What clinicians still lack is the possibility to use biomarkers of the disease as predictors of outcome and, in this area, several studies are trying to find solutions. Circulating autoantibodies are clearly a milestone of clinical research and the concrete possibility is to integrate, in the future, classical markers of activation (like C3) with target organ autoantibodies. Anti-dsDNA antibodies represent a basic point in any predictive attempt in SLE and should be considered the benchmark for any innovative proposal in the wide field of target organ pathologies related to SLE. DNA is part of the nucleosome that is the basic unit of chromatin. It consists of DNA wrapped around a histone octamer made of 2 copies each of Histone 2A, 2B, 3, and 4. The nucleosome has a plastic organization that varies over time and has the potential to stimulate the formation of antibodies directed to the whole structure (anti-nucleosome) or its parts (anti-dsDNA and anti-Histones). Here, we present an updated review of the literature on antibodies directed to the nucleosome and the nucleosome constituents, i.e., DNA and Histones. Wetriedto merge the data first published more than twenty years ago with more recent results to create a balanced bridge between old dogma and more recent research that could serve as a stimulus to reconsider mechanisms for SLE. The formation of large networks would provide the chance of studying large cohorts of patients and confirm what already presented in small sample size during the last years.

Podocyte Injury in Lupus Nephritis

Systemic lupus erythematosus (SLE) is characterized by a broad spectrum of renal lesions. In lupus glomerulonephritis, histological classifications are based on immune-complex (IC) deposits and hypercellularity lesions (mesangial and/or endocapillary) in the glomeruli. However, there is compelling evidence to suggest that glomerular epithelial cells, and podocytes in particular, are also involved in glomerular injury in patients with SLE. Podocytes now appear to be not only subject to collateral damage due to glomerular capillary lesions secondary to IC and inflammatory processes, but they are also a potential direct target in lupus nephritis. Improvements in our understanding of podocyte injury could improve the classification of lupus glomerulonephritis. Indeed, podocyte injury may be prominent in two major presentations: lupus podocytopathy and glomerular crescent formation, in which glomerular parietal epithelial cells play also a key role. We review here the contribution of podocyte impairment to different presentations of lupus nephritis, focusing on the podocyte signaling pathways involved in these lesions.

Cell Death in the Kidney

Apoptotic cell death is usually a response to the cell's microenvironment. In the kidney, apoptosis contributes to parenchymal cell loss in the course of acute and chronic renal injury, but does not trigger an inflammatory response. What distinguishes necrosis from apoptosis is the rupture of the plasma membrane, so necrotic cell death is accompanied by the release of unprocessed intracellular content, including cellular organelles, which are highly immunogenic proteins. The relative contribution of apoptosis and necrosis to injury varies, depending on the severity of the insult. Regulated cell death may result from immunologically silent apoptosis or from immunogenic necrosis. Recent advances have enhanced the most revolutionary concept of regulated necrosis. Several modalities of regulated necrosis have been described, such as necroptosis, ferroptosis, pyroptosis, and mitochondrial permeability transition-dependent regulated necrosis. We review the different modalities of apoptosis, necrosis, and regulated necrosis in kidney injury, focusing particularly on evidence implicating cell death in ectopic renal calcification. We also review the evidence for the role of cell death in kidney injury, which may pave the way for new therapeutic opportunities.

Parvovirus B19V Nonstructural Protein NS1 Induces Double-Stranded Deoxyribonucleic Acid Autoantibodies and End-Organ Damage in Nonautoimmune Mice

BACKGROUND

Viral infection is implicated in development of autoimmunity. Parvovirus B19 (B19V) nonstructural protein, NS1, a helicase, covalently modifies self double-stranded deoxyribonucleic acid (dsDNA) and induces apoptosis. This study tested whether resulting apoptotic bodies (ApoBods) containing virally modified dsDNA could induce autoimmunity in an animal model.

METHODS

BALB/c mice were inoculated with (1) pristane-induced, (2) B19V NS1-induced, or (3) staurosporine-induced ApoBods. Serum was tested for dsDNA autoantibodies by Crithidia luciliae staining and enzyme-linked immunosorbent assay. Brain, heart, liver, and kidney pathology was examined. Deposition of self-antigens in glomeruli was examined by staining with antibodies to dsDNA, histones H1 and H4, and TATA-binding protein.

RESULTS

The B19V NS1-induced ApoBod inoculation induced dsDNA autoantibodies in a dose-dependent fashion. Histopathological features of immune-mediated organ damage were evident in pristane-induced and NS1-induced ApoBod groups; severity scores were higher in these groups than in staurosporine-treated groups. Tissue damage was dependent on NS1-induced ApoBod dose. Nucleosomal antigens were deposited in target tissue from pristane-induced and NS1-induced ApoBod inoculated groups, but not in the staurosporine-induced ApoBod inoculated group.

CONCLUSIONS

This study demonstrated proof of principle in an animal model that virally modified dsDNA in apoptotic bodies could break tolerance to self dsDNA and induce dsDNA autoantibodies and end-organ damage.

Circulating S100 proteins effectively discriminate SLE patients from healthy controls: a cross-sectional study

S100 proteins are currently being investigated as potential diagnostic and prognostic biomarkers of several cancers and inflammatory diseases. The aims of this study were to analyse the plasma levels of S100A4, S100A8/9 and S100A12 in patients with incomplete systemic lupus erythematosus (iSLE), in patients with established SLE and in healthy controls (HCs) and to investigate the potential utility of the S100 proteins as diagnostic or activity-specific biomarkers in SLE. Plasma levels were measured by ELISA in a cross-sectional cohort study of 44 patients with SLE, 8 patients with iSLE and 43 HCs. Disease activity was assessed using the SLEDAI-2K. The mean levels of all S100 proteins were significantly higher in SLE patients compared to HCs. In iSLE patients, the levels of S100A4 and S100A12 but not S100A8/9 were also significantly higher compared to HCs. There were no significant differences in S100 levels between the iSLE and SLE patients. Plasma S100 proteins levels effectively discriminated between SLE patients and HCs. The area under the curve (AUC) for S100A4, S100A8/9 and S100A12 plasma levels was 0.989 (95% CI 0.976-1.000), 0.678 (95% CI 0.563-0.792) and 0.807 (95% CI 0.715-0.899), respectively. S100 levels did not differentiate between patients with high and low disease activity. Only the S100A12 levels were significantly associated with SLEDAI-2K and with cSLEDAI-2K. S100 proteins were significantly higher in SLE patients compared HCs and particularly S100A4 could be proposed as a potential diagnostic biomarker for SLE.

Fra-2 is a novel candidate drug target expressed in the podocytes of lupus nephritis

Lupus nephritis (LN) is a common and devastating complication caused by systemic lupus erythematosus. In this study, we evaluated the expression and mechanism of Fos-related antigen 2 (Fra-2) in LN. The results showed that Fra-2 was significantly increased in kidney biopsies of LN patients compared with healthy controls and other kidney disease in glomerular podocytes. The MRL/lpr mouse strain is a murine model of lupus, and it was used to study the mechanisms of Fra-2 in LN. The results showed that Fra-2 was expressed in the glomerular podocytes. We investigated the effects of inflammatory stimuli on Fra-2 protein expression in the glomerular podocytes, and found that interferon gamma was most effective at increasing Fra-2 protein expression. Knockdown of Fra-2 using siRNA enhanced the protein expression of nephrin. Therefore, Fra-2 may be a specific drug target for podocyte injury in LN.

Protective effects of quercetin treatment in a pristane-induced mouse model of lupus nephritis

INTRODUCTION

Lupus nephritis (LN) is one of the most severe complications of systemic lupus erythematosus. As murine models of LN are valuable tools to better understand its pathophysiology and to search for new effective treatments, we investigated the effects of the bioflavonoid quercetin on pristane-induced LN mice through histomorphological analyses.

METHODS

Immunofluorescence and biochemical assays were used to evaluate the expression of markers of inflammation (interleukin-6, IL-6; tumour necrosis factor-α, TNF-α), oxidative stress (catalase, CAT; superoxide dismutase 1, SOD1; thiobarbituric acid reactive substances, TBARS), apoptosis (Bax), and fibrosis (transforming growth factor-β1, TGF-β1). Glomerular and tubular ultrastructure was analysed, and tissue messenger RNA of podocin, podoplanin and α3β1-integrin were quantified using the real-time polymerase chain reaction.

RESULTS

Pristane-induced LN mice showed severe kidney injury, characterized by increased proteinuria, glomerular mesangial expansion and inflammation, high expression of the pro-fibrotic, apoptotic and prooxidant markers and reduction of antioxidants. In the kidney ultrastructure, foot process (FP) effacement, apoptotic mesangial cells and abnormal mitochondria with disrupted cristae were observed, along with suppressed tissue mRNA of podocin, podoplanin and α3β1-integrin. Treatment with quercetin in the pristane-induced LN mice model was nephroprotective, decreasing proteinuria levels and significantly lowering tissue expression of IL-6, TNF-α, TGF-β1, Bax and TBARS. Simultaneously, quercetin significantly increased CAT and SOD1 expressions in these mice. In addition, it was observed improvement of the kidney ultrastructure, and tissue mRNA of podocin, but not podoplanin and α3β1-integrin, was restored to the levels found in the control mice.

CONCLUSION

In conclusion, these findings provide experimental evidence of the renoprotective effects of quercetin in the pristane-induced LN mice model. We suggest that quercetin effectively ameliorates the kidney damage caused by pristane, a bioflavonoid to be further evaluated as a new therapeutic strategy in this disease.

IL-1β Promotes a New Function of DNase I as a Transcription Factor for the Fas Receptor Gene

Recently we described that endonuclease inactive DNase I translocated into the nucleus in response to increased endogenous IL-1β expression. Here, we demonstrate impact and function of translocated DNase I in tubular cells. Effect of cytokines on expression level and nuclear localisation of DNase I and corresponding levels of Fas receptor (FasR) and IL-1β were determined by confocal microscopy, qPCR and western blot analyses, in presence or absence of siRNA against IL-1β and DNase I mRNA. Nuclear DNase I bound to the FAS promotor region as determined by chromatin immuno-precipitation analysis. Data demonstrate that; (i) translocation of DNase I depended on endogenous de novo-expressed IL-1β, (ii) nuclear DNase I bound FAS DNA, (iii) FasR expression increased after translocation of DNase I, (iv) interaction of exogenous Fas ligand (FasL) with upregulated FasR induced apoptosis in human tubular cells stimulated with TNFα. Thus, translocated DNase I most probably binds the promoter region of the FAS gene and function as a transcription factor for FasR. In conclusion, DNase I not only executes chromatin degradation during apoptosis and necrosis, but also primes the cells for apoptosis by enhancing FasR expression.

Extensively re-organized systemic lymph nodes provide a feasible environment for self-reactivity in lupus-prone NZB × NZW F1 mice

Lymphadenopathy is a frequently observed symptom in systemic lupus erythematosus, although the immunological role of lymph nodes (LNs) in systemic autoimmunity remains largely unknown. Here, we performed comprehensive and systematic analyses of LNs in lupus-prone NZB × NZW F1 (BWF1) mice, demonstrating extensive tissue re-organization of the systemic LNs with follicular expansion, hyper germinal center (GC) formation, atrophy of the paracortical T-cell area and expansion of the medulla in aged BWF1 mice bearing glomerulonephritis. The proportion of B cells was significantly increased in these reactive LNs but not in the spleen, and lymphocyte subsets involved in antibody production, i.e. GC B cells, follicular helper T cells and plasma cells, were elevated. Draining LNs of the affected organs, such as the renal and cervical nodes, showed enhanced tissue re-organization and accumulation of effector lymphocytes, suggesting the presence of a positive feedback loop of regional responses. LN cells isolated from disease-bearing animals produced anti-DNA antibody, indicating activation of autoreactive lymphocytes in situ. The substantial development of disease and LN alterations in mice that received a splenectomy at a young age points to the importance of other secondary lymphoid organs, most likely LNs, for the progression of autoimmune responses independent of the spleen. Taken together, our findings highlight the value of taking LN alterations and activities into consideration for understanding the pathogenesis of systemic autoimmunity.

Lupus nephritis progression in FcγRIIB-/-yaa mice is associated with early development of glomerular electron dense deposits and loss of renal DNase I in severe disease

FcγRIIB^-/-yaa mice develop severe lupus glomerulonephritis due to lack of an inhibitory immune cell receptor combined with a Y-chromosome linked autoimmune accelerator mutation. In the present study, we have investigated nephritis development and progression in FcγRIIB^-/-yaa mice to find shared features with NZB/NZW F1 lupus prone mice and human disease. We sacrificed 25 male FcγRIIB^-/-yaa mice at various disease stages, and grouped them according to activity and chronicity indices for lupus nephritis. Glomerular morphology and localization of electron dense deposits containing IgG were further determined by immune electron microscopy. Renal DNase I and pro-inflammatory cytokine mRNA levels were measured by real-time quantitative PCR. DNase I protein levels was assessed by immunohistochemistry and zymography. Our results demonstrate early development of electron dense deposits containing IgG in FcγRIIB^-/-yaa mice, before detectable levels of serum anti-dsDNA antibodies. Similar to NZB/NZW F1, electron dense deposits in FcγRIIB^-/-yaa progressed from being confined to the mesangium in the early stage of lupus nephritis to be present also in capillary glomerular basement membranes. In the advanced stage of lupus nephritis, renal DNase I was lost on both transcriptional and protein levels, which has previously been shown in NZB/NZW F1 mice and in human disease. Although lupus nephritis appears on different genetic backgrounds, our findings suggest similar processes when comparing different murine models and human lupus nephritis.

B cell epitope of human cytomegalovirus phosphoprotein 65 (HCMV pp65) induced anti-dsDNA antibody in BALB/c mice

Background

HCMV phosphoprotein 65 (HCMVpp65) is a putative immunogen that acts as an accelerator, inducing autoantibody and exacerbating autoimmune response in susceptible animals. The immunity to pp65_336-439 instigates autoimmunity, suggesting that pp65_336-439 contains crucial B cell epitope(s) for the development of nephritis. This study narrowed down the target epitope to pp65_422-439 for immunization of BALB/c mice and mapping of B cell epitope.

Methods

The target epitope pp65_422-439 reactivity and B cell epitope mapping was examined in serum from pp65_422-439-immunized mice and patients with systemic lupus erythematosus (SLE). Kidney tissue from immunized mice was examined for signs of immune complex nephritis.

Results

Anti-pp65_422-439 antibody in serum either from patients with SLE or from pp65_422-439-immunized mice exhibited cross-reactivity to several nuclear components such as double-stranded DNA (dsDNA). Moreover, the pp65_422-439-immunized mice developed initial signs of glomerulonephritis such as deposition of immunoglobulin G/M (IgG/IgM) and third complement component (C3). With B cell epitope mapping by pp65_422-439-derived decapeptides, one dominant epitope, pp65_428-437, was identified in serum from pp65_422-439-immunized mice and patients with SLE with anti-pp65_422-439 antibody. Epitope spreading from pp65_428-437 to pp65_430-439 was found in pp65_422-439-immunized mice in which we generated monoclonal antibodies to pp65_425-434 and pp65_430-439. However, dsDNA positive reactivity was exclusively observed in Crithidia luciliae stains with pp65_430-439-reactive monoclonal antibody. Additionally, we observed the amelioration of autoimmunity following the elevation of IgM targeting pp65_428-437.

Conclusions

Our data suggest that pp65_428-437 may be an autoimmune or lupus-prone B cell epitope and may catalyze further epitope spreading for inducing autoantibodies in lupus-susceptible individuals.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1268-2) contains supplementary material, which is available to authorized users.

Molecular and Immunological Basis of Tubulo-Interstitial Injury in Lupus Nephritis: a Comprehensive Review

Lupus nephritis is an important cause of kidney failure in patients of Asian, African, or Hispanic descent. Its etiology and pathogenesis are multifactorial and remain to be elucidated. Accumulating evidence suggests that anti-double-stranded DNA (dsDNA) antibodies play a critical role in the pathogenesis, through its direct binding to cross-reactive antigens on resident renal cells or indirect binding through chromatin material to extracellular matrix components, resulting in complement activation, cell activation and proliferation, and induction of inflammatory and fibrotic processes. While tubulo-interstitial damage portends poor long-term renal prognosis, the mechanisms leading to tubulo-interstitial injury in lupus nephritis has received relatively less attention to date. Immune deposition along the tubular basement membrane is often observed in lupus nephritis and correlates with tubulo-interstitial infiltration of immune cells and interstitial fibrosis. Anti-dsDNA antibodies bind to resident renal cells, including proximal renal tubular epithelial cells, and contribute to renal inflammation and fibrosis. There is emerging evidence that epigenetic influence such as DNA methylation, histone modification, and microRNAs (miRs) also contribute to kidney fibrosis. Overexpression of miR-150 is observed in renal biopsies from patients with lupus nephritis and correlates with kidney fibrosis and chronicity score. Mycophenolate mofetil (MMF) is an established and effective standard-of-care therapy for patients with lupus nephritis. Accumulating data suggest that in addition to its immunosuppressive actions on lymphocyte proliferation, mycophenolic acid (MPA), the active metabolite of MMF, can exert a direct effect on nonimmune cells. Mediators of inflammation and fibrosis induced by anti-dsDNA antibodies in cultured proximal renal tubular epithelial cells are ameliorated by the addition of MPA, suggesting that in addition to its immunosuppressive actions, MPA may also have a beneficial effect in improving tubulo-interstitial inflammation and fibrosis through its direct action on proximal renal tubular epithelial cells.

Dysregulation of miRNA-146a contributes to the development of lupus nephritis via targeting of TRAF6

Aim: The objective of this study was to identify the association between genotypes of miR-146a rs2910164 and expression of TRAF6 as well as the risk of lupus nephritis (LN). Results: A total of 567 systemic lupus erythematosus patients both with and without LN were included in the study. The luciferase activity of cells that carried miR-146a mimics was much lower than control and the miR-146a mRNA expression with the GG SNP was significantly overexpressed compared with that in GC and CC groups. Expressions of TRAF6 mRNA and protein with GG were markedly lower than those in GC and CC groups. Mesangial cells treated with miR-146a inhibitors displayed higher expression of TRAF6 mRNA and protein compared with scramble control, miR-146a mimics and TRAF6 siRNA groups. Conclusion: Rs2910164 is associated with the risk of LN and could function as a therapeutic target of the disease.

BAFF Induces Tertiary Lymphoid Structures and Positions T Cells within the Glomeruli during Lupus Nephritis

Tissue-specific immune responses play an important role in the pathology of autoimmune diseases. In systemic lupus erythematosus, deposits of IgG-immune complexes and the activation of complement in the kidney have long been thought to promote inflammation and lupus nephritis. However, the events that localize cells in non-lymphoid tertiary organs and sustain tissue-specific immune responses remain undefined. In this manuscript, we show that BAFF promotes events leading to lupus nephritis. Using an inducible model of systemic lupus erythematosus, we found that passive transfer of antinucleosome IgG into AID^-/-MRL/lpr mice elevated autoantibody levels and promoted lupus nephritis by inducing BAFF production in the kidneys, and the formation of renal tertiary lymphoid structures (TLSs). Reducing BAFF in vivo prevented the formation of TLSs and lupus nephritis; however, it did not reduce immune cell infiltrates, or the deposits of IgG and complement in the kidney. Mechanistically, lowering BAFF levels also diminished the number of T cells positioned inside the glomeruli and reduced inflammation. Thus, BAFF plays a previously unappreciated role in lupus nephritis by inducing renal TLSs and regulating the position of T cells within the glomeruli.

Annexin II-binding immunoglobulins in patients with lupus nephritis and their correlation with disease manifestations

Annexin II on mesangial cell surface mediates the binding of anti-dsDNA antibodies and consequent downstream inflammatory and fibrotic processes. We investigated the clinical relevance of circulating annexin II-binding immunoglobulins (Igs) in patients with severe proliferative lupus nephritis, and renal annexin II expression in relation to progression of nephritis in New Zealand Black and White F1 mice (NZBWF1/J) mice. Annexin II-binding Igs in serum were measured by ELISA. Ultrastructural localization of annexin II was determined by electron microscopy. Seropositivity rates for annexin II-binding IgG and IgM in patients with active lupus nephritis were significantly higher compared with controls (8.9%, 1.3% and 0.9% for annexin II-binding IgG and 11.1%, 4.0% and 1.9% for annexin II-binding IgM for patients with active lupus nephritis, patients with non-lupus renal disease and healthy subjects respectively). In lupus patients, annexin II-binding IgM level was higher at disease flare compared with remission. Annexin II-binding IgG and IgM levels were associated with that of anti-dsDNA and disease activity. Annexin II-binding IgG and IgM levels correlated with histological activity index in lupus nephritis biopsy samples. In NZBWF1/J mice, serum annexin II-binding IgG and IgM levels and glomerular annexin II and p11 expression increased with progression of active nephritis. Annexin II expression was present on mesangial cell surface and in the mesangial matrix, and co-localized with electron-dense deposits along the glomerular basement membrane. Our results show that circulating annexin II-binding IgG and IgM levels are associated with clinical and histological disease activity in proliferative lupus nephritis. The co-localization of annexin II and p11 expression with immune deposition in the kidney suggests pathogenic relevance.

The contribution of the programmed cell death machinery in innate immune cells to lupus nephritis

Systemic lupus erythematosus (SLE) is a chronic multi-factorial autoimmune disease initiated by genetic and environmental factors, which in combination trigger disease onset in susceptible individuals. Damage to the kidney as a consequence of lupus nephritis (LN) is one of the most prevalent and severe outcomes, as LN affects up to 60% of SLE patients and accounts for much of SLE-associated morbidity and mortality. As remarkable strides have been made in unlocking new inflammatory mechanisms associated with signaling molecules of programmed cell death pathways, this review explores the available evidence implicating the action of these pathways specifically within dendritic cells and macrophages in the control of kidney disease. Although advancements into the underlying mechanisms responsible for inducing cell death inflammatory pathways have been made, there still exist areas of unmet need. By understanding the molecular mechanisms by which dendritic cells and macrophages contribute to LN pathogenesis, we can improve their viability as potential therapeutic targets to promote remission.

Future Perspectives on Pathogenesis of Lupus Nephritis: Facts, Problems, and Potential Causal Therapy Modalities

Divergent incommensurable models have been developed to explain the pathogenesis of lupus nephritis. Most contemporary models favor a central role for anti-chromatin antibodies. How they exert their pathogenic effect has, however, endorsed conflicts that at least for now preclude insight into definitive pathogenic pathways. The following paradigms are contemporarily in conflict with each other: i) the impact of anti-double-stranded DNA (dsDNA) antibodies that cross-react with inherent renal antigens, ii) the impact of anti-dsDNA antibodies targeting exposed chromatin in glomeruli, and iii) the impact of relative antibody avidity for dsDNA, chromatin fragments, or cross-reacting antigens. Aside from these three themes, the pathogenic role of T cells in lupus nephritis is not clear. These different models should be tested through a collaboration between scientists belonging to the different paradigms. If it turns out that there are different pathogenic pathways in lupus nephritis, the emerging pathogenic mechanism(s) may be encountered with new individual causal therapy modalities. Today, therapy is still unspecific and far from interfering with the cause(s) of the disorder. This review attempts to describe what we know about processes that may cause lupus nephritis and how such basic processes may be affected if we can specifically interrupt them. Secondary inflammatory mechanisms, cytokine signatures, activation of complement, and other contributors to inflammation will not be discussed herein; rather, the events that trigger these factors will be discussed.

Anti-dsDNA antibodies and resident renal cells - Their putative roles in pathogenesis of renal lesions in lupus nephritis

Lupus nephritis affects up to 70% of patients with systemic lupus erythematosus and is an important treatable cause of kidney failure. Cardinal features of lupus nephritis include loss of self-tolerance, production of autoantibodies, immune complex deposition and immune-mediated injury to the kidney, resulting in increased cell proliferation, apoptosis, and induction of inflammatory and fibrotic processes that destroy normal nephrons. The production anti-dsDNA antibodies is a cardinal feature in lupus and their level correlates with disease activity. In addition to the formation of immune complexes thereby triggering complement activation, how anti-dsDNA antibodies home to the kidney and induce pathological processes in the renal parenchyma remain to be fully elucidated. Data from our laboratory and other investigators show that the properties of anti-dsDNA antibodies vary between patients and change over time, and that anti-dsDNA antibodies could bind directly to integral cell surface molecules such as annexin II or α-actinin, or indirectly through chromatin material deposited on the cell surface. The binding of anti-dsDNA antibodies to mesangial cells and proximal renal tubular epithelial cells triggers downstream inflammatory and fibrotic pathways, which include the activation of the PKC and MAPK signaling pathways, increased secretion of pro-inflammatory cytokines and matrix protein deposition that contribute to pathological processes in the renal parenchyma.

Murine and Human Lupus Nephritis: Pathogenic Mechanisms and Theoretical Strategies for Therapy

Lupus nephritis is one of the most serious manifestations of systemic lupus erythematosus, and represents one of the criteria implemented to classify systemic lupus erythematosus. Although studied for decades, no consensus has been reached related to the basic cellular, molecular, and immunologic mechanism(s) responsible for lupus nephritis. No causal treatments have been developed; therapy is approached mainly with nonspecific immunosuppressive medications. More detailed insight into disease mechanisms therefore is indispensable to develop new therapeutic strategies. In this review, contemporary knowledge on the pathogenic mechanisms of lupus nephritis is discussed based on recent data in murine and human lupus nephritis. Specific focus is given to the effect of anti-double-stranded DNA/antinucleosome antibodies in the kidneys and whether they bind exposed chromatin fragments in glomeruli or whether they bind inherent glomerular structures by cross-recognition. Overall, the data presented here favor the exposed chromatin model because we did not find any indication to substantiate the anti-double-stranded DNA antibody cross-reacting model. At the end of this review we present data on why chromatin fragments are expressed in the glomeruli of patients with lupus nephritis, and discuss how this knowledge can be used to direct the development of future therapies.

The Role of Anti-DNA Antibodies in the Development of Lupus Nephritis: A Complementary, or Alternative, Viewpoint?

Kidney disease, or lupus nephritis, is the organ involvement that is most closely associated with specific autoantibodies in patients with SLE. The concept of anti-DNA antibodies being instrumental in the pathogenesis of lupus nephritis emerged ~50 years ago, and has been a topic of debate ever since. This article focuses on the description of the renal sub-cellular targets of nephritogenic autoantibodies and offers a counter-point opinion to the article by Pedersen et al. In addition, we provide an overview of some of the mechanisms by which anti-DNA antibodies bind to their renal targets and the pathogenic relevance to clinical nephritis.

Cell death in the pathogenesis of systemic lupus erythematosus and lupus nephritis

Nephritis is one of the most severe complications of systemic lupus erythematosus (SLE). One key characteristic of lupus nephritis (LN) is the deposition of immune complexes containing nucleic acids and/or proteins binding to nucleic acids and autoantibodies recognizing these molecules. A variety of cell death processes are implicated in the generation and externalization of modified nuclear autoantigens and in the development of LN. Among these processes, apoptosis, primary and secondary necrosis, NETosis, necroptosis, pyroptosis, and autophagy have been proposed to play roles in tissue damage and immune dysregulation. Cell death occurs in healthy individuals during conditions of homeostasis yet autoimmunity does not develop, at least in part, because of rapid clearance of dying cells. In SLE, accelerated cell death combined with a clearance deficiency may lead to the accumulation and externalization of nuclear autoantigens and to autoantibody production. In addition, specific types of cell death may modify autoantigens and alter their immunogenicity. These modified molecules may then become novel targets of the immune system and promote autoimmune responses in predisposed hosts. In this review, we examine various cell death pathways and discuss how enhanced cell death, impaired clearance, and post-translational modifications of proteins could contribute to the development of lupus nephritis.

Complement-Mediated Glomerular Diseases: A Tale of 3 Pathways

A renewed interest in the role of complement in the pathogenesis of glomerular diseases has improved our understanding of their basic, underlying physiology. All 3 complement pathways—classical, lectin, and alternative—have been implicated in glomerular lesions both rare (e.g., dense deposit disease) and common (e.g., IgA nephropathy). Here we review the basic function of these pathways and highlight, with a disease-specific focus, how activation can lead to glomerular injury. We end by exploring the promise of complement-targeted therapies as disease-specific interventions for glomerular diseases.

"Kill" the messenger: Targeting of cell-derived microparticles in lupus nephritis

Immune complex (IC) deposition in the glomerular basement membrane (GBM) is a key early pathogenic event in lupus nephritis (LN). The clarification of the mechanisms behind IC deposition will enable targeted therapy in the future. Circulating cell-derived microparticles (MPs) have been proposed as major sources of extracellular autoantigens and ICs and triggers of autoimmunity in LN. The overabundance of galectin-3-binding protein (G3BP) along with immunoglobulins and a few other proteins specifically distinguish circulating MPs in patients with systemic lupus erythematosus (SLE), and this is most pronounced in patients with active LN. G3BP co-localizes with deposited ICs in renal biopsies from LN patients supporting a significant presence of MPs in the IC deposits. G3BP binds strongly to glomerular basement membrane proteins and integrins. Accordingly, MP surface proteins, especially G3BP, may be essential for the deposition of ICs in kidneys and thus for the ensuing formation of MP-derived electron dense structures in the GBM, and immune activation in LN. This review focuses on the notion of targeting surface molecules on MPs as an entirely novel treatment strategy in LN. By targeting MPs, a double hit may be achieved by attenuating both the autoantigenic fueling of immune complexes and the triggering of the adaptive immune system. Thereby, early pathogenic events may be blocked in contrast to current treatment strategies that primarily target and modulate later events in the cellular and humoral immune response.

Reactivity in ELISA with DNA-loaded nucleosomes in patients with proliferative lupus nephritis

Autoantibodies against nucleosomes are considered a hallmark of systemic lupus erythematosus (SLE). We compared in patients with proliferative lupus nephritis the diagnostic usefulness of a dsDNA-loaded nucleosome ELISA (anti-dsDNA-NcX) with ELISAs in which dsDNA or nucleosomes alone were coated. First, we analysed whether DNA loading on nucleosomes led to masking of epitopes by using defined monoclonal anti-DNA, anti-histone and nucleosome-specific autoantibodies to evaluate the accessibility of nucleosomal epitopes in the anti-dsDNA-NcX ELISA. Second, autoantibody levels were measured in these 3 ELISAs in 100 patients with proliferative lupus nephritis (LN) before immunosuppressive treatment and in 128 non-SLE disease controls. In patients with LN inter-assay comparisons and associations with clinical and serological parameters were analysed. The panel of monoclonal antibodies revealed that all epitopes were equally accessible in the anti-dsDNA-NcX ELISA as in the two other ELISAs. Patients with proliferative lupus nephritis were positive with dsDNA-loaded nucleosomes in 86%, with DNA in 66% and with nucleosomes in 85%. In the non-lupus disease control group these frequencies were 1.6% (2 out of 128) for both the anti-dsDNA-NcX and the anti-dsDNA ELISA and 0% in the anti-nucleosome ELISA. The levels in the anti-dsDNA-NcX ELISA were high in a group of patients with LN that showed absent reactivity in the anti-DNA or low levels in the anti-nucleosome ELISA. Anti-dsDNA-NcX positivity was associated with higher SLEDAI scores within this group. Within nucleosome-based ELISAs, we propose the anti-dsDNA-NcX ELISA as the preferred test system.

Autoantibodies in SLE: Specificities, Isotypes and Receptors

Systemic Lupus Erythematosus (SLE) is characterized by a wide spectrum of auto-antibodies which recognize several cellular components. The production of these self-reactive antibodies fluctuates during the course of the disease and the involvement of different antibody-secreting cell populations are considered highly relevant for the disease pathogenesis. These cells are developed and stimulated through different ways leading to the secretion of a variety of isotypes, affinities and idiotypes. Each of them has a particular mechanism of action binding to a specific antigen and recognized by distinct receptors. The effector responses triggered lead to a chronic tissue inflammation. DsDNA autoantibodies are the most studied as well as the first in being characterized for its pathogenic role in Lupus nephritis. However, others are of growing interest since they have been associated with other organ-specific damage, such as anti-NMDAR antibodies in neuropsychiatric clinical manifestations or anti-β2GP1 antibodies in vascular symptomatology. In this review, we describe the different auto-antibodies reported to be involved in SLE. How autoantibody isotypes and affinity-binding to their antigen might result in different pathogenic responses is also discussed.

Anti-DNA antibodies--quintessential biomarkers of SLE

Antibodies that recognize and bind to DNA (anti-DNA antibodies) are serological hallmarks of systemic lupus erythematosus (SLE) and key markers for diagnosis and disease activity. In addition to common use in the clinic, anti-DNA antibody testing now also determines eligibility for clinical trials, raising important questions about the nature of the antibody-antigen interaction. At present, no 'gold standard' for serological assessment exists, and anti-DNA antibody binding can be measured with a variety of assay formats, which differ in the nature of the DNA substrates and in the conditions for binding and detection of antibodies. A mechanism called monogamous bivalency--in which high avidity results from simultaneous interaction of IgG Fab sites with a single polynucleotide chain--determines anti-DNA antibody binding; this mechanism might affect antibody detection in different assay formats. Although anti-DNA antibodies can promote pathogenesis by depositing in the kidney or driving cytokine production, they are not all alike, pathologically, and anti-DNA antibody expression does not necessarily correlate with active disease. Levels of anti-DNA antibodies in patients with SLE can vary over time, distinguishing anti-DNA antibodies from other pathogenic antinuclear antibodies. Elucidation of the binding specificities and the pathogenic roles of anti-DNA antibodies in SLE should enable improvements in the design of informative assays for both clinical and research purposes.

Mechanisms of Kidney Injury in Lupus Nephritis - the Role of Anti-dsDNA Antibodies

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by a breakdown of self-tolerance, production of auto-antibodies and immune-mediated injury, resulting in damage accrual in multiple organs. Kidney involvement, termed lupus nephritis, is a major cause of morbidity and mortality that affects over half of the SLE population during the course of disease. The etiology of lupus nephritis is multifactorial and remains to be fully elucidated. Accumulating evidence suggests that in addition to forming immune complexes and triggering complement activation, anti-dsDNA antibodies contribute to the pathogenesis of lupus nephritis through binding, either directly or indirectly, to cross-reactive antigens or chromatin materials, respectively, to resident renal cells and/or extracellular matrix components, thereby triggering downstream cellular activation and proliferation as well as inflammatory and fibrotic processes. Several cross-reactive antigens that mediate anti-dsDNA antibody binding have been identified, such as annexin II and alpha-actinin. This review discusses the mechanisms through which anti-dsDNA antibodies contribute to immunopathogenesis in lupus nephritis. Corticosteroids combined with either mycophenolic acid (MPA) or cyclophosphamide is the current standard of care immunosuppressive therapy for severe lupus nephritis. This review also discusses recent data showing distinct effects of MPA and cyclophosphamide on inflammatory and fibrotic processes in resident renal cells.

Novel Autoantigens Associated with Lupus Nephritis

Systemic lupus erythematosus (SLE) is characterized by production of a variety of autoantibodies. Although anti-double-stranded DNA (anti-dsDNA) antibodies contribute to the pathogenesis of lupus nephritis (LN), they are not sufficient for diagnosis and evaluation of disease activity. To obtain other autoantibodies associated with LN, we screened autoantigens reacting with the sera of LN patients by using an N-terminal biotinylated protein library created from a wheat cell-free protein production system. We screened 17 proteins that showed higher positive signals in the active phase than in the inactive phase of SLE, and higher positive signals in the serum of SLE patient with nephritis than in that of patient without nephritis. Of these, two LN-associated autoantigens, ribosomal RNA-processing protein 8 (RRP8) and spermatid nuclear transition protein 1 (TNP1) were identified by immunoprecipitation and immunofluorescence of renal tissues. Circulating anti-RRP8 and anti-TNP1 autoantibodies were recognized and deposited as an immune complex (IC) in glomeruli. IC was deposited preferentially in glomeruli rather than in other organs in C57BL/6 mice injected with RRP8 or TNP1. ELISA analysis of sera from patients with various rheumatic diseases demonstrated reactivity for RRP8 and TNP1 in 20% and 14.7% of SLE patients, respectively, whereas there was little or no reactivity in patients with other rheumatic diseases. Among SLE patients, 63.6% and 45.5% of those with LN were positive for anti-RRP8 and anti-TNP1 antibodies, compared with 12.5% and 9.4% of SLE patients without nephritis, respectively. Both proteins are cationic, and their respective antibodies did not cross-react with dsDNA. These proteins released from apoptotic cells form ICs with each autoantibody, and their ICs may become trapped at anionic sites in the glomerular basement membrane, leading to deposition in glomeruli. These autoantibodies may be useful for prediction of LN in subsets of SLE patients who are negative for anti-dsDNA antibodies.

Autoantibodies targeting glomerular annexin A2 identify patients with proliferative lupus nephritis

PURPOSE

Patients with systemic lupus erythematosus (SLE) frequently develop lupus nephritis (LN), a complication frequently leading to end stage kidney disease. Immune complex deposition in the glomerulus is central to the development of LN. Using a targeted proteomic approach, we tested the hypothesis that autoantibodies targeting glomerular antigens contribute to the development of LN.

EXPERIMENTAL DESIGN

Human podocyte and glomerular proteins were separated by SDS-PAGE and immunoblotted with sera from SLE patients with and without LN. The regions of those gels corresponding to reactive bands observed with sera from LN patients were analyzed using LC-MS/MS.

RESULTS

LN reactive bands were seen at approximately 50 kDa in podocyte extracts and between 36 and 50 kDa in glomerular extracts. Those bands were analyzed by LC-MS/MS and 102 overlapping proteins were identified. Bioinformatic analysis determined that 36 of those proteins were membrane associated, including a protein previously suggested to contribute to glomerulonephritis and LN, annexin A2. By ELISA, patients with proliferative LN demonstrated significantly increased antibodies against annexin A2.

CONCLUSION AND CLINICAL RELEVANCE

Proteomic approaches identified multiple candidate antigens for autoantibodies in patients with LN. Serum antibodies against annexin A2 were significantly elevated in subjects with proliferative LN, validating those antibodies as potential biomarkers.