Significance of anti-nuclear and anti-extracellular matrix autoantibodies for albuminuria in murine lupus nephritis; a longitudinal study on plasma and glomerular eluates in MRL/l mice

SLE: a cognitive step forward-a synthesis of rethinking theories, causality, and ignored DNA structures

Systemic lupus erythematosus (SLE) is classified by instinctual classification criteria. A valid proclamation is that these formally accepted SLE classification criteria legitimate the syndrome as being difficult to explain and therefore enigmatic. SLE involves scientific problems linked to etiological factors and criteria. Our insufficient understanding of the clinical condition uniformly denoted SLE depends on the still open question of whether SLE is, according to classification criteria, a well-defined one disease entity or represents a variety of overlapping indistinct syndromes. Without rational hypotheses, these problems harm clear definition(s) of the syndrome. Why SLE is not anchored in logic, consequent, downstream interdependent and interactive inflammatory networks may rely on ignored predictive causality principles. Authoritative classification criteria do not reflect consequent causality criteria and do not unify characterization principles such as diagnostic criteria. We need now to reconcile legendary scientific achievements to concretize the delimitation of what SLE really is. Not all classified SLE syndromes are "genuine SLE"; many are theoretically "SLE-like non-SLE" syndromes. In this study, progressive theories imply imperative challenges to reconsider the fundamental impact of "the causality principle". This may offer us logic classification and diagnostic criteria aimed at identifying concise SLE syndromes as research objects. Can a systems science approach solve this problem?

The dsDNA, Anti-dsDNA Antibody, and Lupus Nephritis: What We Agree on, What Must Be Done, and What the Best Strategy Forward Could Be

This study aims to understand what lupus nephritis is, its origin, clinical context, and its pathogenesis. Truly, we encounter many conceptual and immanent tribulations in our attempts to search for the pathogenesis of this disease—and how to explain its assumed link to SLE. Central in the present landscape stay a short history of the early studies that substantiated the structures of isolated or chromatin-assembled mammalian dsDNA, and its assumed, highly controversial role in induction of anti-dsDNA antibodies. Arguments discussed here may provoke the view that anti-dsDNA antibodies are not what we think they are, as they may be antibodies operational in quite different biological contexts, although they bind dsDNA by chance. This may not mean that these antibodies are not pathogenic but they do not inform how they are so. This theoretical study centers the content around the origin and impact of extra-cellular DNA, and if dsDNA has an effect on the adaptive immune system. The pathogenic potential of chromatin-anti-dsDNA antibody interactions is limited to incite lupus nephritis and dermatitis which may be linked in a common pathogenic process. These are major criteria in SLE classification systems but are not shared with other defined manifestations in SLE, which may mean that they are their own disease entities, and not integrated in SLE. Today, the models thought to explain lupus nephritis are divergent and inconsistent. We miss a comprehensive perspective to try the different models against each other. To do this, we need to take all elements of the syndrome SLE into account. This can only be achieved by concentrating on the interactions between autoimmunity, immunopathology, deviant cell death and necrotic chromatin in context of elements of system science. System science provides a framework where data generated by experts can be compared, and tested against each other. This approach open for consensus on central elements making up “lupus nephritis” to separate what we agree on and how to understand the basis for conflicting models. This has not been done yet in a systematic context.

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.

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.

Automated Evaluation of Crithidia luciliae Based Indirect Immunofluorescence Tests: A Novel Application of the EUROPattern-Suite Technology

Systemic lupus erythematosus (SLE) is a severe rheumatic autoimmune disease with various clinical manifestations. Anti-dsDNA antibodies are an important immunological hallmark of SLE and their occurrence represents a major criterion for the diagnosis. Among the commonly applied test systems for determination of anti-dsDNA antibodies, the indirect immunofluorescence test (IIFT) using the flagellated kinetoplastida Crithidia luciliae is considered to be highly disease specific at moderate sensitivity. Since IIFT, however, is claimed to be affected by subjective interpretation and a lack of standardization, there has been an increasing demand for automated pattern interpretation of immunofluorescence reactions in recent years. Corresponding platforms are already available for evaluation of anti-nuclear antibody (ANA) IIFT on HEp-2 cells, the recommended “gold standard” for ANA screening in the diagnosis of various systemic rheumatic autoimmune diseases. For one of these systems, the “EUROPattern-Suite” computer-aided immunofluorescence microscopy (CAIFM), automated interpretation of microscopic fluorescence patterns was extended to the Crithidia luciliae based anti-dsDNA IIFT.

The anti-DNA antibody: origin and impact, dogmas and controversies

The inclusion of 'the anti-DNA antibody' by the ACR and the Systemic Lupus International Collaborating Clinics (SLICC) as a criterion for systemic lupus erythematosus does not convey the diverse origins of these antibodies, whether their production is transient or persistent (which is heavily influenced by the nature of the inducing antigens), the specificities exerted by these antibodies or their clinical impact-or lack thereof. A substantial amount of data not considered in clinical medicine could be added from basic immunology evidence, which could change the paradigms linked to what 'the anti-DNA antibody' is, in a pathogenic, classification or diagnostic context.

The pathogenesis and diagnosis of systemic lupus erythematosus: still not resolved

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with various clinical manifestations affecting different tissues. A characteristic feature of SLE is the presence of autoantibodies against double-stranded (ds)DNA, histones and nucleosomes, and other chromatin components. SLE is a prototype type III hypersensitivity reaction. Local deposition of anti-nuclear antibodies in complex with released chromatin induces serious inflammatory conditions by activation of the complement system. The severe renal manifestation, lupus nephritis, is classified based on histological findings in renal biopsies. Apoptotic debris, including chromatin, is present in the extracellular matrix and circulation of patients with SLE. This may be due to an aberrant process of apoptosis and/or insufficient clearance of apoptotic cells/chromatin. The non-cleared apoptotic debris may lead to activation of both the innate and adaptive immune systems. In addition, an aberrant presentation of peptides by antigen-presenting cells, disturbed selection processes for lymphocytes, and deregulated lymphocyte responses may be involved in the development of autoimmunity. In the present review, we briefly will summarize current knowledge on the pathogenesis of SLE. We will also critically discuss and challenge central issues that need to be addressed in order to fully understand the pathogenic mechanisms involved in the development of SLE and in order to have an improved diagnosis for SLE. Disappointingly, in our opinion, there are still more questions than answers for the pathogenesis, diagnosis, and treatment of SLE.

Up-regulation of transcription factor Blimp1 in systemic lupus erythematosus

PURPOSE

B lymphocyte induced maturation protein 1 (Blimp1) is a transcription factor that is critical for differentiation and antibody production in plasma cells. In order to understand the mechanism of systemic lupus erythematosus (SLE), the role of Blimp1 expression was studied in patients with SLE and in healthy control subjects. And Blimp1 tissue distribution in MRL/lpr lupus mice was also investigated.

METHODS

The mRNA expression level of Blimp1 was analyzed by fluorescent real time PCR and compared between the 40 SLE patients and 30 control subjects. Expression of CD138, CD27 and CD19 in peripheral blood cells was analyzed by flow cytometry. Blimp1 mRNA and protein expression levels and tissue distribution in the kidneys, spleen and lymph nodes of MRL/lpr lupus and normal mice were analyzed.

RESULTS

Blimp1 mRNA expression level was 2.1 times greater in the SLE group as compared to the control group. The increased mRNA expression of Blimp1 seemed to be related to SLE disease activity and anti-nuclear antibody (ANA) titer. In SLE patients, the CD138+ plasma cells increased as the CD27+ cells decreased. Compared with normal mice, Blimp1 was strongly expressed in the kidneys, lymph nodes and spleen of MRL/lpr lupus mice. The expression level of Blimp1 mRNA in the kidneys, lymph nodes and spleen of MRL/lpr lupus mice was much higher than normal mice (1.76, 2.02, and 2.05 times greater, respectively, P<0.05). Similarly, protein levels in the above mentioned organs were also much higher (1.54, 1.99, and 2.21 times greater, respectively, P<0.05).

CONCLUSIONS

The elevated expression of Blimp1 in SLE patients and in the lupus mouse model is correlated with increases in plasma cells, autoantibodies and disease activity. It is closely related to differentiation of B-lymphocytes, antibody production and renal lesions. Blimp1 may play a role in SLE disease development.

Lupus nephritis: enigmas, conflicting models and an emerging concept

Autoantibodies to components of chromatin, which include double-stranded DNA (dsDNA), histones and nucleosomes, are central in the pathogenesis of lupus nephritis. How anti-chromatin autoantibodies exert their nephritogenic activity, however, is controversial. One model assumes that autoantibodies initiate inflammation when they cross-react with intrinsic glomerular structures such as components of membranes, matrices or exposed nonchromatin ligands released from cells. Another model suggests glomerular deposition of autoantibodies in complex with chromatin, thereby inducing classic immune complex-mediated tissue damage. Recent data suggest acquired error of renal chromatin degradation due to the loss of renal DNaseI enzyme activity is an important contributing factor to the development of lupus nephritis in lupus-prone (NZBxNZW)F1 mice and in patients with lupus nephritis. Down-regulation of DNaseI expression results in reduced chromatin fragmentation and in deposition of extracellular chromatin-IgG complexes in glomerular basement membranes in individuals who produce IgG anti-chromatin autoantibodies. The main focus of the present review is to discuss whether exposed chromatin fragments in glomeruli are targeted by potentially nephritogenic anti-dsDNA autoantibodies or if the nephritogenic activity of these autoantibodies is explained by cross-reaction with intrinsic glomerular constituents or if both models coexist in diseased kidneys. In addition, the role of silencing of the renal DNaseI gene and the biological consequences of reduced chromatin fragmentation in nephritic kidneys are discussed.

Lupus nephritis: role of antinucleosome autoantibodies

The discovery of autoantigen clustering in blebs at the surface of apoptotic cells boosted research on the role of apoptosis in systemic lupus erythematosus (SLE) and led to the discovery of autoantigen modification during apoptosis. Normally, apoptotic cells are cleared efficiently and swiftly. However, it became clear that in SLE insufficient removal of apoptotic material leads to the release of these modified autoantigens. This creates the danger that these modified autoantigens are recognized by the immune system. Indeed, dendritic cells, the professional antigen-presenting cells, phagocytose these modified autoantigens, which leads to maturation and induction of a proinflammatory state of these dendritic cells. As a consequence, they present these modified autoantigens to T cells in an immunogenic way, which become activated and stimulate autoreactive B cells to secrete autoantibodies. In this review the currently available evidence for the sequential steps in the pathogenesis of SLE is discussed. Furthermore, the mechanisms responsible for the nephritogenicity of antinucleosome antibodies are reviewed. This will reveal that nucleosomes are not only a major driving force in the formation of antinuclear antibodies, but also play a pivotal role in the development of tissue lesions by mediating binding of autoantibodies to basement membranes as exemplified for the kidney.

Mesangial cell-specific antibodies are central to the pathogenesis of lupus nephritis

Not only is nephritis a common complaint in systemic lupus erythematosus, but it is also the most life-threatening complication of the disease. Anti-double-stranded DNA antibodies (Abs), which are found in up to 80% of these patients, might be nephritogenic per se. That is, they may cross-react with mesangial cell (MC) surface proteins, such as alpha-actinin and annexin A2, they may cross-react with mesangial matrix protein such as laminine and fibronectin, or they may recognize chromatin material previously deposited in the glomeruli. The consequence of the binding of anti-MC Abs may be their internalization, which results in activation and proliferation of these MCs. In turn, these activated MCs are suspected of promoting immune complex formation by sequestering and thereby protecting chromatin from degradation. The present paper will explain the mechanisms through which such autoAbs may initiate nephritis.

Chromatin as a target antigen in human and murine lupus nephritis

The present review focuses on pathogenic molecular and transcriptional events in patients with lupus nephritis. These factors are renal DNaseI, exposed chromatin fragments and the corresponding chromatin-reactive autoantibodies. Lupus nephritis is the most serious complication in human systemic lupus erythematosus, and is characterised by deposition of chromatin fragment-IgG complexes in the mesangial matrix and glomerular basement membranes. The latter deposition defines end-stage disease. This event is stringently linked to a renal-restricted shutdown of expression of the DNaseI gene, as determined by loss of DNaseI mRNA level and DNaseI enzyme activity. The major aim of the present review is to generate new therapeutic strategies based on new insight into the disease pathogenesis.

Clinical significance of anti‐glomerular basement membrane antibodies in a cohort of Chinese patients with lupus nephritis

OBJECTIVES

To evaluate the clinical and laboratory features of patients with lupus nephritis (LN) in the presence and absence of anti-glomerular basement membrane antibodies (anti-GBM) and to establish whether the characteristics of the disease correlate with anti-GBM.

METHODS

We performed a retrospective study of 157 hospitalised patients with systemic lupus erythematosus (SLE), 91 of whom had LN. The test for anti-GBM used an enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory data were collected and assessed in LN patients with and without anti-GBM.

RESULTS

Anti-GBM was detected in 14 (8.9%) of 157 patients with SLE. All of the 14 patients developed LN; of these, 10 reached the criteria for crescentic glomerulonephritis (CGN) and five were diagnosed as Goodpasture's disease. Serum anti-GBM levels were correlated with the presence of both anti-double-stranded DNA antibodies (anti-dsDNA) and anti-nucleosome antibodies (anti-NuA). Significant differences in extrarenal clinical manifestations were found between anti-GBM-positive and -negative LN patients, with regard to pleuritis, pulmonary haemorrhage, sinusitis, and anaemia in particular.

CONCLUSIONS

LN with anti-GBM is not rare in Chinese patients. Anti-GBM, together with the additional nephritogenic potential of anti-dsDNA and anti-NuA, may play an essential role in the pathogenesis of the anti-GBM disease in LN. Therefore, in addition to routine anti-GBM assay, anti-dsDNA and anti-NuA measurements should be performed early to ensure a prompt diagnosis and immediate treatment in patients with anti-GBM-mediated disease.

Pathogenic anti-nucleosome antibodies

There is increasing evidence that in systemic lupus erythematosus, nucleosomes, the basic chromatin component, represent both a driving immunogen and a major in vivo target for antibodies. Either a disturbed apoptosis or a reduced clearance of apoptotic cells by phagocytes may lead to an increased exposure of apoptotic nucleosomes to the immune system. These nucleosomes, which have been cleaved and modified during the process of apoptosis, escape normal clearance and encompass epitopes that normally are not encountered by the immune system. This may then lead to tolerance breaking and autoimmunity by the activation of nucleosome-specific autoreactive T cells (that help B cells) and subsequently to the production of anti-nucleosome, anti-histone and anti-DNA autoantibodies. Some anti-nucleosome antibody subsets are pathogenic and are involved in the nephritogenic process in systemic lupus erythematosus. Accordingly, several studies reported: (i) increased plasma circulating nucleosomes that positively correlated with an active disease, (ii) nucleosomes in typical glomerular deposits as well as in the basement membrane of non-lesional skin of systemic lupus erythematosus patients and (iii) a close correlation between nephritis and the presence of anti-nucleosome antibodies. Recent studies reported anti-nucleosome antibodies also in primary anti-phospholipid syndrome and particularly in patients with associated lupus-like disease.

Relationship between antinuclear antibody and microalbuminuria in the general population: the Takahata study

BACKGROUND

Microalbuminuria, a marker of vascular damage, is associated with increased risk of progressive renal deterioration, cardiovascular disease and mortality. However, the relationship between antinuclear antibody (ANA) and microalbuminuria in the general population is unknown. Thus, we conducted a cross-sectional study to examine the relationship between ANA and microalbuminuria.

METHODS

The subjects of this community-based study were individuals over 40 years old in Takahata, Japan. The urine albumin-creatinine ratio (UACR) was calculated from a single-spot urine specimen collected in the morning. ANA was examined by enzyme immunoassay (EIA).

RESULTS

Among the 2,875 subjects (mean age 63 years; men 1,276; women 1,599), positive ANA (ANA index >or=20.0) was detected in 16.9% of the total population (men 12.9%, women 20.3%) and the prevalence of positive ANA increased with age. The prevalence of microalbuminuria (UACR 30-300 mg/g), but not macroalbuminuria (UACR > 300 mg/g), was significantly higher in the positive ANA group than the negative ANA group (24.1% vs. 16.0%, respectively, P < 0.001). Along with the increase of the ANA index, the prevalence of microalbuminuria and UACR levels were increased. Multivariate logistic regression analyses showed that ANA was significantly associated with microalbuminuria (odds ratio [OR] 1.63 and 95% confidence interval [95%CI] 1.27-2.10). These associations were significant in women, but not men, when examined separately.

CONCLUSIONS

These results indicate that the presence of ANA is associated with microalbuminuria in the general population, especially women.

Lupus nephritis: the central role of nucleosomes revealed

Systemic lupus erythematosus (SLE) is an autoimmune syndrome characterized by autoantibodies to nuclear constituents. Some of these antibodies are diagnostically important, whereas others act as disease-modifying factors. One clinically important factor is autoantibodies against dsDNA and nucleosomes, which have overlapping diagnostic and nephritogenic impact in SLE. Although a scientific focus for 5 decades, the molecular and cellular origin of these antibodies, and why they are associated with lupus nephritis, is still not fully understood. A consensus has, however, evolved that antibodies to dsDNA and nucleosomes are central pathogenic factors in the development of lupus nephritis. In contrast, no agreement has been reached as to which glomerular structures are bound by nephritogenic anti-nucleosome antibodies in vivo. Mutually contradictory paradigms and models have evolved simply because we still lack precise and conclusive data to provide definitive insight into how autoantibodies induce lupus nephritis and which specificity is critical in the nephritic process(es). In this review, data demonstrating the central role of nucleosomes in inducing and binding potentially nephritogenic antibodies to DNA and nucleosomes are presented and discussed. These autoimmune-inducing processes are discussed in the context of Matzinger's danger model (Matzinger P: Friendly and dangerous signals: is the tissue in control? Nat Immunol 2007, 8:11-13; Matzinger P: The danger model: a renewed sense of self. Science 2002, 296:301-305; Matzinger P: Tolerance, danger, and the extended family. Annu Rev Immunol 1994, 12:991-1045) and Medzhitov's and Janeway's (Medzhitov R, Janeway CA Jr: Decoding the patterns of self and nonself by the innate immune system. Science 2002, 296:298-300; Medzhitov R, Janeway CA Jr: How does the immune system distinguish self from nonself? Semin Immunol 2000, 12:185-188; Janeway CA Jr, Medzhitov R: Innate immune recognition. Annu Rev Immunol 2002, 20:197-216) distinction of noninfectious self (NIS) and infectious nonself (INS). The mechanisms leading to production of potentially nephritogenic anti-nucleosome antibodies and to overt lupus nephritis are interpreted in the context of these paradigms.

Glomerular apoptotic nucleosomes are central target structures for nephritogenic antibodies in human SLE nephritis

Antibodies to double-stranded (dsDNA) are associated with systemic lupus erythematosus (SLE) and directly involved in human lupus nephritis. Information about their glomerular target antigens is inconsistent, and whether availability of target antigens, antibody specificity or avidity are nephritogenic parameters, is not determined. In this study, we analyzed renal tissue from anti-dsDNA antibody-positive lupus patients with nephritis by morphological and immunological assays, including immune electron microscopy (IEM) and colocalization IEM, an EM-based confocal microscopy assay. IEM demonstrated that antibody deposits were confined to electron dense structures (EDS) in glomerular membranes. These autoantibodies colocalized with nucleosome-binding anti-dsDNA/-histone/-transcription factor antibodies. To confirm the colocalization IEM-data, we developed a colocalization terminal deoxynucleotidyl-transferase (TdT) biotin-dUTP nicked end-labeled (TUNEL) IEM assay where extracellular DNA was traced by TdT-mediated introduction of biotinylated nucleotides and autoantibodies by IEM. Results consistently demonstrated that DNA colocalized with autoantibodies in glomerular membrane-associated EDS. The colocalization IEM and colocalization TUNEL IEM assays thus demonstrate that intra-glomerular membrane-associated nucleosomes are targeted by anti-dsDNA autoantibodies in human lupus nephritis. The data provide a new approach to understand basic molecular and immunological processes accounting for antibody-mediated nephritis in human SLE.

Alpha-actinin-binding antibodies in relation to systemic lupus erythematosus and lupus nephritis

This study investigated the overall clinical impact of anti-α-actinin antibodies in patients with pre-selected autoimmune diseases and in a random group of anti-nuclear antibody (ANA)-positive individuals. The relation of anti-α-actinin antibodies with lupus nephritis and anti-double-stranded DNA (anti-dsDNA) antibodies represented a particular focus for the study. Using a cross-sectional design, the presence of antibodies to α-actinin was studied in selected groups, classified according to the relevant American College of Rheumatology classification criteria for systemic lupus erythematosus (SLE) (n = 99), rheumatoid arthritis (RA) (n = 68), Wegener's granulomatosis (WG) (n = 85), and fibromyalgia (FM) (n = 29), and in a random group of ANA-positive individuals (n = 142). Renal disease was defined as (increased) proteinuria with haematuria or presence of cellular casts. Sera from SLE, RA, and Sjøgren's syndrome (SS) patients had significantly higher levels of anti-α-actinin antibodies than the other patient groups. Using the geometric mean (± 2 standard deviations) in FM patients as the upper cutoff, 20% of SLE patients, 12% of RA patients, 4% of SS patients, and none of the WG patients were positive for anti-α-actinin antibodies. Within the SLE cohort, anti-α-actinin antibody levels were higher in patients with renal flares (p = 0.02) and correlated independently with anti-dsDNA antibody levels by enzyme-linked immunosorbent assay (p < 0.007) but not with other disease features. In the random ANA group, 14 individuals had anti-α-actinin antibodies. Of these, 36% had SLE, while 64% suffered from other, mostly autoimmune, disorders. Antibodies binding to α-actinin were detected in 20% of SLE patients but were not specific for SLE. They correlate with anti-dsDNA antibody levels, implying in vitro cross-reactivity of anti-dsDNA antibodies, which may explain the observed association with renal disease in SLE.

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

Antibodies to dsDNA represent a classification criterion for systemic lupus erythematosus. Subpopulations of these antibodies are involved in lupus nephritis. No known marker separates nephritogenic from non-nephritogenic anti-dsDNA antibodies. It is not clear whether specificity for glomerular target antigens or intrinsic antibody-affinity for dsDNA or nucleosomes is a critical parameter. Furthermore, it is still controversial whether glomerular target antigen(s) is constituted by nucleosomes or by non-nucleosomal glomerular structures. Previously, we have demonstrated that antibodies eluted from murine nephritic kidneys recognize nucleosomes, but not other glomerular antigens. In this study, we determined the structures that bind nephritogenic autoantibodies in vivo by transmission electron microscopy, immune electron microscopy, and colocalization immune electron microscopy using experimental antibodies to dsDNA, to histones and transcription factors, or to laminin. The data obtained are consistent and point at glomerular basement membrane-associated nucleosomes as target structures for the nephritogenic autoantibodies. Terminal deoxynucleotidyl-transferase-mediated dUTP nick end-labeling or caspase-3 assays demonstrate that lupus nephritis is linked to intraglomerular cell apoptosis. The data suggest that nucleosomes are released by apoptosis and associate with glomerulus basement membranes, which may then be targeted by pathogenic anti-nucleosome antibodies. Thus, apoptotic nucleosomes may represent both inducer and target structures for nephritogenic autoantibodies in systemic lupus erythematosus.

Critical comparative analyses of anti-alpha-actinin and glomerulus-bound antibodies in human and murine lupus nephritis

OBJECTIVE

Although anti-double-stranded DNA (anti-dsDNA) antibodies are important in lupus nephritis, the question regarding which glomerular structures (alpha-actinin, nucleosomes, or others) are recognized by nephritogenic anti-dsDNA antibodies is still controversial. In this study, we determined which glomerular structures are recognized by monoclonal and in vivo-bound nephritogenic antibodies.

METHODS

Western blotting was used to analyze the ability of nephritogenic anti-dsDNA antibodies to recognize glomerular and nucleosomal structures. Sera from patients with lupus nephritis, sera from random antinuclear antibody-positive patients, and paired antibodies from sera and kidney eluates from nephritic (NZB x NZW)F(1) mice were analyzed for activity against proteins identified by monoclonal nephritogenic antibodies, and against alpha-actinin, dsDNA, nucleosomes, histone H1, heparan sulfate, DNase I, and type IV collagen. Immunoelectron microscopy was used to determine the glomerular localization of alpha-actinin and in vivo-bound autoantibodies in nephritic (NZB x NZW)F1 mouse kidneys.

RESULTS

Anti-alpha-actinin antibodies were observed in human and murine lupus nephritis sera and in sera from patients without systemic lupus erythematosus and were not detected in kidney eluates from nephritic mice. Antibodies to dsDNA and histone H1 were detected in all eluates. Western blot analyses revealed that nephritogenic anti-dsDNA antibodies recognized a 32-kd band, identified as histone H1. Competitive enzyme-linked immunosorbent assay demonstrated that nephritogenic monoclonal antibodies, and dominant antibodies eluted from nephritic kidneys, cross-reacted with dsDNA and H1. This cross-reactive anti-H1 specificity was largely absent in sera from those mice. Immunoelectron microscopic analysis of nephritic (NZB x NZW)F1 mouse kidneys revealed that antibodies eluted from kidneys, but not anti-alpha-actinin antibodies, bound to distinct nephritis-associated electron-dense structures linked to glomerular basement membranes.

CONCLUSION

Cross-reactive anti-dsDNA/anti-histone H1 antibodies, but not anti-alpha-actinin antibodies, are central among those deposited in nephritic glomeruli.

Nucleosome autoantibodies

The nucleosome is a large protein-nucleic acid complex involved in DNA packing and in controlling genetic information. Under circumstances described below, this component, normally sequestered in the cell nucleus, is released into the extracellular milieu and then is easily accessible to cells of the immune system. For still not completely understood reasons, nucleosomes become immunogenic under particular conditions. Thus, anti-nucleosome autoantibodies (autoAb) have been described in connective tissue diseases and especially in systemic lupus erythematosus (SLE). This review describes the mechanisms leading to nucleosome production and anti-nucleosome autoimmunity, as well as the pathogenesis associated with nucleosomes.

Clinical significance of antinucleosome antibodies in Tunisian systemic lupus erythematosus patients

The aim of this study was to investigate the clinical significance of antinucleosome antibodies in Tunisian systemic lupus erythematosus (SLE) patients. IgG antinucleosome antibodies were detected by a qualitative enzyme immunoassay (immunodot) in the sera of SLE patients at onset of disease. The patients were divided into two groups according to the result of the antinucleosome antibodies test: positive (group A) and negative (group B). The two groups were also evaluated for clinical and biological parameters. Of 84 patients with SLE, 66 (78.6%) had antinucleosome antibodies. Among 21 patients negative for anti-double-stranded DNA (anti-dsDNA), 5 (23.8%) were antinucleosome positive. The most common initial features were haematological disorders (80.1%) and arthritis or arthralgias (79.8%). Renal disorders, observed in 59.5% of SLE patients, were more common in group A compared to group B (65 vs 38%) (p=0.04). The European Consensus Lupus Activity Measurement (ECLAM) mean score was higher in group A (6.42) than in group B (4.44) (p=0.002). Antinucleosome antibodies were positive in nearly one-fourth of SLE patients negative for anti-dsDNA. We found a correlation between antinucleosome antibodies, nephritis and SLE disease activity. Therefore, the determination of circulating antinucleosome antibodies could be a useful parameter for early diagnosis and follow-up of SLE patients.

Anti-DNA antibody subpopulations and lupus nephritis

As a consequence of increased insight into the cellular and molecular mechanisms responsible for induction of B cell and T cell autoimmunity to DNA and nucleosomes, there is an obvious need to reconsider the dogma stating that anti-dsDNA antibodies serve as marker antibodies for SLE and also that anti-dsDNA antibodies per se are responsible for the initiation of lupus nephritis. Given that the potential to produce anti-dsDNA antibodies is an inherent property of the normal immune system and that few anti-DNA antibodies have nephritogenic potential, we must try to solve the problem whether it is avidity for DNA, specificity for unique DNA structures or cross-reactivity with non-DNA molecules, that make such antibodies pathogenic and thus potential markers for SLE and lupus nephritis. In this review, we will summarize contemporary problems related to these questions; (1) try to focus on phenotypic differences with respect to the ability to produce anti-dsDNA antibodies between individuals suffering from SLE and those not belonging to this diagnostic group, and (2) to describe differences between pathogenic and non-pathogenic anti-dsDNA antibodies.

Pathogenic profiles and molecular signatures of antinuclear autoantibodies rescued from NZM2410 lupus mice

Two outstanding questions concerning antinuclear antibodies (ANAs) in lupus involve their pathogenic potential and their molecular signatures. To address these questions, a panel of 56 antinuclear and 47 nonnuclear binding monoclonal antibodies was rescued from four seropositive NZM2410 lupus mice. The monoclonals varied in their reactivity to nucleosomes, ssDNA, dsDNA, and glomerular substrate. A large fraction of the antibodies demonstrated apparent polyreactivity (to DNA, histones, and glomerular antigens) due to bound, DNase-1 sensitive nuclear antigenic bridges. Although nephrophilic immunoglobulin (Ig) M and IgG antibodies were the most pathogenic, the dsDNA-binding antibodies were modestly so; in contrast, antinucleosome antibodies were clearly not pathogenic. Compared with the nonnuclear antigen-binding monoclonal antibodies rescued from the same mice, ANAs exhibited increased utilization of VH5/7183 genes and highly cationic heavy chain (HC) CDR3 regions. Most intriguingly, the CDR3 regions of the ANAs exhibited alternating arginine/lysine peaks at H96, H98, and H100, with neutral troughs at H95, H97, and H99. To summarize, glomerular-binding anti-dsDNA antibodies appear to be the most pathogenic variety of lupus autoantibodies. The presence of an alternating charge pattern in their HC CDR3 regions appears to be a prominent hallmark of ANAs.

Use of a novel elution regimen reveals the dominance of polyreactive antinuclear autoantibodies in lupus kidneys

OBJECTIVE

The autoantibody specificities that dominate the deposits in lupus kidneys remain unclear. Reasoning that previously utilized elution buffers such as acidic glycine and ammonium thiocyanate may not have been maximally effective in eluting all Ig deposits from the kidneys, this study was conducted to experiment with a stronger dissociating agent, urea-glycine.

METHODS

Seven antinuclear antibody-positive, nephritic female (SWR x NZB)F(1) (SNF1) lupus mice were selected for the elution study. Deposited Ig was eluted from their kidneys using 3 different elution buffers: 0.15M glycine-HCl buffer, 1.3M ammonia thiocyanate/0.15M glycine-HCl buffer, and 5M urea/0.15M glycine-HCl buffer. All eluates were tested for specificity against a variety of nuclear and glomerular antigens.

RESULTS

Compared with conventional elution buffers, the urea-based regimen eluted severalfold more IgG and IgM antinuclear antibodies from the kidneys of nephritic SNF1 lupus mice. IgG anti-double-stranded DNA (anti-dsDNA) antibodies were not only the most prevalent species in these renal deposits, they were also heavily enriched in the kidneys, relative to the corresponding serum levels. A substantial fraction of the anti-single-stranded DNA and antihistone/DNA (but not antihistone) reactivity in these eluates was due to cross-reactive anti-dsDNA antibodies. No reactivity with SSA, SSB, Sm, RNP, Jo-1, Scl-70, or ribosomal P antigens could be demonstrated in these eluates. Importantly, the urea-glycine eluates differed from the conventional eluates in having significantly greater reactivity to glomerular substrate and laminin.

CONCLUSION

This novel urea-based elution provides further support for the dominance of antibodies in lupus kidneys, with strong polyreactivity to DNA and glomerular substrate.

CD4+ T cells from (New Zealand Black x New Zealand White)F1 lupus mice and normal mice immunized against apoptotic nucleosomes recognize similar Th cell epitopes in the C terminus of histone H3

We have previously reported that peptide 88-99 of histone H4 represents a minimal T cell epitope recognized by Th cells from nonautoimmune BALB/c (H-2(d/d)) mice immunized with nucleosomes. In this study, we tested a panel of overlapping peptides spanning the whole sequences of H4 and H3 for recognition by CD4(+) T cells from unprimed (New Zealand Black (NZB) x New Zealand White (NZW))F(1) lupus mice (H-2(d/z)). None of the 11 H4 peptides was recognized by CD4(+) T cells from (NZB x NZW)F(1) mice. In contrast, these cells proliferated and secreted IL-2, IL-10, and IFN-gamma upon ex vivo stimulation with H3 peptides representing sequences 53-70, 64-78, and 68-85. Peptides 56-73 and 61-78 induced the production of IFN-gamma and IL-10, respectively, without detectable proliferation, suggesting that they may act as partial agonist of the TCR. Th cells from unprimed BALB/c mice and other lupus-prone mice such as SNF(1) (H-2(d/q)) and MRL/lpr (H-2(k/k)) mice did not recognize any peptides present within the H3 region 53-85. We further demonstrated that immunization of normal BALB/c mice with syngeneic liver nucleosomes and spleen apoptotic cells, but not with nonapoptotic syngeneic cells, induced Th cell responses against several peptides of the H3 region 53-85. Moreover, we found that this conserved region of H3, which is accessible at the surface of nucleosomes, is targeted by Abs from (NZB x NZW)F(1) mice and lupus patients, and contains motifs recognized by several distinct HLA-DR molecules. It might thus be important in the self-tolerance breakdown in lupus.

Deposition of nucleosomal antigens (histones and DNA) in the epidermal basement membrane in human lupus nephritis

OBJECTIVE

Antinuclear autoantibodies complexed to nucleosomes can bind to heparan sulfate (HS) in the glomerular basement membrane. This binding is due to the binding of the positively charged histones to the strongly anionic HS. Nucleosomes and histones have been identified in glomerular deposits in human lupus nephritis. We investigated whether nucleosomes are present in the basement membrane of nonlesional skin of lupus patients.

METHODS

Skin biopsy samples from patients with systemic lupus erythematosus (SLE) (30 with active lupus nephritis and 15 with inactive disease) and controls (with parapemphigus or diabetes) were stained for IgG, histones, DNA, and nucleosomes.

RESULTS

IgG deposits were found in 87% of the patients with lupus nephritis, in 33% of the patients with inactive disease, and in 71% of the parapemphigus patients. Using polyclonal antihistone antibodies, histones were detected in 87% of lupus nephritis patients, but in none of the other SLE patients or the diabetes controls (P < 0.0001). Among the parapemphigus controls, 14% of samples stained positive in one of the polyclonal antihistone stainings (P < 0.0001). Using monoclonal antibodies, histones and DNA were identified in 21% of the lupus nephritis patients. Although none of the other groups showed positive staining for nucleosomes, 7% of the lupus nephritis biopsy samples were positive using antinucleosome monoclonal antibodies. Colocalization of nucleosomal antigens and IgG was confirmed using confocal laser microscopy.

CONCLUSION

These findings suggest that nucleosome-mediated binding of autoantibodies to basement membranes may also occur at sites in the body other than in the glomerulus.

Increased expression of heparanase in puromycin aminonucleoside nephrosis

BACKGROUND

The beta-D-endoglycosidase heparanase has been proposed as an important contributor to loss of glomerular charge in proteinuria. Expression of heparanase was, therefore, determined in acute puromycin aminonucleoside (PAN) nephrosis.

METHODS

A rabbit polyclonal antibody was produced against a 17-amino acid peptide derived from the predicted amino acid sequence of heparanase. The antibody was validated by Western blot. Immunohistochemical staining and Western blotting were used to localize heparanase protein in normal kidneys and kidneys from rats with PAN nephrosis. Northern blot analysis was used to determine mRNA expression.

RESULTS

Immunohistochemical staining showed that heparanase protein was localized to tubular cells in the distal convoluted tubules, thick ascending limb of the loop of Henle, and transitional cell epithelium in normal kidney. Minimal expression was noted in normal glomeruli. Western blot analysis of protein from isolated normal glomeruli showed minimal expression of the 65 kD proheparanase protein. A marked increase in the staining for heparanase was found at day 5 of the PAN nephrosis model, at approximately the time of onset of proteinuria, and at day 14. Expression was predominantly seen in podocytes. At day 5, only the 65 kD proheparanase species was identified, but at day 14, mature 58 kD heparanase also was present. Northern blot analysis of sieved glomeruli at day 14 confirmed an increase in heparanase mRNA. The human podocyte cell line 56/10A1 also produced both proheparanase and mature heparanase, suggesting that podocytes can activate heparanase without other cell types.

CONCLUSION

The previously mentioned data confirm that the novel beta-D-endoglycosidase heparanase is up-regulated and activated in glomeruli from rats with proteinuria. Heparanase may be involved, therefore, in the loss of glomerular charge seen in proteinuria. Moreover, the presence of heparanase in normal tubules suggests that it may also be involved in cell migration or turnover.

Plasma levels of nucleosomes and nucleosome-autoantibody complexes in murine lupus: effects of disease progression and lipopolyssacharide administration

OBJECTIVE

To evaluate the effect of disease progression and lipopolysaccharide (LPS) administration on the presence of nucleosomes, antinucleosome reactivity, and nucleosome-Ig complexes in the circulation of MRL and control mice.

METHODS

Plasma samples from lupus-prone (MRL/lpr and MRL/+) and control (CBA, Swiss, and BALB/c) mice were tested in enzyme-linked immunosorbent assays for the presence of nucleosomes, antinucleosome antibodies, and nucleosome-Ig complexes. Nucleosome kinetics, apoptosis induction, and phagocytosis of apoptotic cells were also analyzed in MRL/lpr, MRL/+, and CBA control mice after a single injection of LPS or phosphate buffered saline.

RESULTS

Nucleosomes were found in the circulation of MRL/lpr and MRL/+ mice from week 4 onward. Nucleosomes were also detected in young control mice, but with increasing age, the nucleosomes disappeared. Antinucleosome antibodies, nucleosome-Ig complexes, and albuminuria were found only in the MRL/lpr mice. LPS administration led to a significant increase in circulating nucleosomes (3-8-fold) in all strains tested. In only the MRL/lpr mice was this increase followed by a significant decrease in antinucleosome titers and an increase in nucleosome-Ig complexes. The number of apoptotic cells in the thymus after LPS was significantly higher in the MRL/lpr mice than in the MRL/+ and CBA control mice. LPS caused a profound reduction (50-70%) of the phagocytosis of apoptotic cells by peritoneal macrophages, which was comparable for all strains.

CONCLUSION

In MRL lupus-prone mice, nucleosomes are persistently present in the circulation, whereas in control mice, nucleosomes are present only at a young age. The formation of antinucleosome antibodies and nucleosome-Ig complexes is a characteristic feature of MRL/lpr mice. LPS administration increases systemic nucleosome release due to an enhancement of apoptosis and a decrease in the clearance of apoptotic cells.

Glomerular heparan sulfate alterations: mechanisms and relevance for proteinuria

Heparan sulfate (HS) is the anionic polysaccharide side chain of HS proteoglycans (HSPGs) present in basement membranes, in extracellular matrix, and on cell surfaces. Recently, agrin was identified as a major HSPG present in the glomerular basement membrane (GBM). An increased permeability of the GBM for proteins after digestion of HS by heparitinase or after antibody binding to HS demonstrated the importance of HS for the permselective properties of the GBM. With recently developed antibodies directed against the GBM HSPG (agrin) core protein and the HS side chain, we demonstrated a decrease in HS staining in the GBM in different human proteinuric glomerulopathies, such as systemic lupus erythematosus (SLE), minimal change disease, membranous glomerulonephritis, and diabetic nephropathy, whereas the staining of the agrin core protein remained unaltered. This suggested changes in the HS side chains of HSPG in proteinuric glomerular diseases. To gain more insight into the mechanisms responsible for this observation, we studied GBM HS(PG) expression in experimental models of proteinuria. Similar HS changes were found in murine lupus nephritis, adriamycin nephropathy, and active Heymann nephritis. In these models, an inverse correlation was found between HS staining in the GBM and proteinuria. From these investigations, four new and different mechanisms have emerged. First, in lupus nephritis, HS was found to be masked by nucleosomes complexed to antinuclear autoantibodies. This masking was due to the binding of cationic moieties on the N-terminal parts of the core histones to anionic determinants in HS. Second, in adriamycin nephropathy, glomerular HS was depolymerized by reactive oxygen species (ROS), mainly hydroxyl radicals, which could be prevented by scavengers both in vitro (exposure of HS to ROS) and in vivo. Third, in vivo renal perfusion of purified elastase led to a decrease of HS in the GBM caused by proteolytic cleavage of the agrin core protein near the attachment sites of HS by the HS-bound enzyme. Fourth, in streptozotocin-induced diabetic nephropathy and during culture of glomerular cells under high glucose conditions, evidence was obtained that hyperglycemia led to a down-regulation of HS synthesis, accompanied by a reduction in the degree of HS sulfation.

Isolation of anti-nucleosome antibodies from the plasma of lupus nephritis patients

Anti-nucleosome antibodies, which recognise conformational epitopes consisting of histone and DNA in chromatin, have been described in autoimmune diseases. In this study, an attempt was made to isolate anti-nucleosome antibodies from the anti-DNA-depleted plasma IgG of two lupus patients either with or without nephritis by nucleohistone affinity chromatography. The purified nucleohistone-binding antibodies bound to nucleohistone in a specific manner and contained enriched anti-histone antibodies. However, adsorption of the purified antibodies with histone revealed that the nephritis patient-derived antibodies contained nucleohistone-specific antibodies. Although such purified antibodies may not recognise native structures of nucleosomes, this chromatography may provide a method to isolate and determine the fine specificity of anti-nucleosome antibodies in various autoimmune diseases.

Antigen specificity of anti-nuclear antibodies complexed to nucleosomes determines glomerular basement membrane binding in vivo

Monoclonal anti-nuclear antibodies which are complexed to nucleosomes are able to bind to the glomerular basement membrane (GBM) in vivo, whereas purified antibodies do not bind. The positively charged histone moieties in the nucleosome are-responsible for the binding to anionic determinants in the GBM. We tested the hypothesis that the specificity of the autoantibodies complexed to the nucleosome influences the glomerular binding of the antibody-nucleosome complex. We induced the formation of these immune complexes in vivo, by intraperitoneal inoculation of hybridomas producing monoclonal anti-nuclear antibodies (four anti-histone, three anti-double stranded (ds)DNA and three anti-nucleosome antibodies) into nude BALB/c mice. In ascites and plasma from the mice inoculated with these hybridomas, nucleosome/autoantibody complexes were detected in comparable amounts. Immunofluorescence of kidney sections revealed that about 60% of the mice inoculated with anti-nucleosome or anti-dsDNA hybridomas had immunoglobulin deposits in the GBM, whereas only 15% of the mice with anti-histone hybridomas showed these deposits (p < or = 0.04). In the Matrigel-ELISA (used as a GBM surrogate) ascites from anti-nucleosome or anti-DNA hybridomas displayed significantly higher titers (p < or = 0.002) than ascites from anti-histone hybridomas. In conclusion, nucleosome/immunoglobulin complexes comprising anti-nucleosome or anti-dsDNA auto-antibodies do bind more frequently to the GBM in vivo than nucleosome/immunoglobulin complexes containing anti-histone antibodies. It therefore appears that the specificity of the antibody bound to the nucleosome is a critical determinant for the nephritogenic potential of the nucleosome-autoantibody complex.