Cross-reactions of anti-DNA antibodies and the central dogma of lupus nephritis

The greatest contribution to medical science is the transformation from studying symptoms to studying their causes-the unrelenting legacy of Robert Koch and Louis Pasteur-and a causality perspective to approach a definition of SLE

The basic initiative related to this study is derived from the fact that systemic lupus erythematosus (SLE) is a unique and fertile system science subject. We are, however, still far from understanding its nature. It may be fair to indicate that we are spending more time and resources on studying the complexity of classified SLE than studying the validity of classification criteria. This study represents a theoretical analysis of current instinctual SLE classification criteria based on "the causality principle." The discussion has its basis on the radical scientific traditions introduced by Robert Koch and Louis Pasteur. They announced significant changes in our thinking of disease etiology through the implementation of the modern version of "the causality principle." They influenced all aspects of today's medical concepts and research: the transformation of medical science from studies of symptoms to study their causes, relevant for monosymptomatic diseases as for syndromes. Their studies focused on bacteria as causes of infectious diseases and on how the immune system adapts to control and prevent contagious spreading. This is the most significant paradigm shift in the modern history of medicine and resulted in radical changes in our view of the immune system. They described acquired post-infection immunity and active immunization by antigen-specific vaccines. The paradigm "transformation" has a great theoretical impact also on current studies of autoimmune diseases like SLE: symptoms and their cause(s). In this study, the evolution of SLE classification and diagnostic criteria is discussed from "the causality principle" perspective, and if contemporary SLE classification criteria are as useful as believed today for SLE research. This skepticism is based on the fact that classification criteria are not selected based on cogent causal strategies. The SLE classification criteria do not harmonize with Koch's and Pasteur's causality principle paradigms and not with Witebsky's Koch-derived postulates for autoimmune and infectious diseases. It is not established whether the classification criteria can separate SLE as a "one disease entity" from "SLE-like non-SLE disorders"-the latter in terms of SLE imitations. This is discussed here in terms of weight, rank, and impact of the classification criteria: Do they all originate from "one basic causal etiology"? Probably not.

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.

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.

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.

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.

Assessment of trichloroethylene (TCE) exposure in murine strains genetically-prone and non-prone to develop autoimmune disease

There is increasing laboratory and epidemiologic evidence relating exposure to trichloroethylene (TCE) with autoimmune disease including scleroderma and lupus. New Zealand Black/New Zealand White (NZBWF1) and B6C3F1 mice were exposed to TCE (0, 1, 400 or 14,000 ppb) via drinking water for 27 or 30 weeks, respectively. NZBWF1 mice spontaneously develop autoimmune disease while B6C3F1 mice, a standard strain used in immunotoxicology testing, are not genetically prone to develop autoimmune disease. During the TCE exposure period, serum levels of total IgG, and autoantibodies (anti-ssDNA, -dsDNA, and -glomerular antigen [GA]) were monitored. At the termination of the study, renal pathology, natural killer (NK) cell activity, total IgG levels, autoantibody production, T-cell activation, and lymphocytic proliferative responses were evaluated. TCE did not alter NK cell activity, or T- and B-cell proliferation in either strain. Numbers of activated T-cells (CD4+/CD44+) were increased in the B6C3F1 mice but not in the NZBWF1 mice. Renal pathology, as indicated by renal score, was significantly increased in the B6C3F1, but not in the NZBWF1 mice. Serum levels of autoantibodies to dsDNA and ssDNA were increased at more time points in B6C3F1, as compared to the NZBWF1 mice. Anti-GA autoantibodies were increased by TCE treatment in early stages of the study in NZBWF1 mice, but by 23 weeks of age, control levels were comparable to those of TCE-exposed animals. Serum levels anti-GA autoantibodies in B6C3F1 were not affected by TCE exposure. Overall, these data suggest that TCE did not contribute to the progression of autoimmune disease in autoimmune-prone mice during the period of 11-36 weeks of age, but rather lead to increased expression of markers associated with autoimmune disease in a non-genetically prone mouse strain.

Glomerular binding of anti-dsDNA autoantibodies: the dispute resolved?

The binding of anti-double-stranded DNA (anti-dsDNA) autoantibodies to the glomerular basement membrane (GBM) in lupus nephritis can be explained by two mechanisms: (1) direct crossreactive binding to intrinsic glomerular antigens; (2) nucleosome-mediated binding to heparan sulfate in the GBM. Kalaaji et al. demonstrated using novel techniques that glomerular in vivo-bound antoantibodies bind to nucleosomes/dsDNA derived from apoptotic cells and not to intrinsic glomerular structures.

Association of alpha-actinin-binding anti-double-stranded DNA antibodies with lupus nephritis

OBJECTIVE

Anti-double-stranded DNA (anti-dsDNA) antibodies may contribute to the pathogenesis of glomerulonephritis (GN) by cross-reacting with alpha-actinin in murine models and in some patients with systemic lupus erythematosus (SLE). We therefore sought to determine possible disease associations with serologic and clinical features and to characterize this new autoantibody specificity.

METHODS

One hundred patients with SLE were recruited into this multicenter study, as well as 100 rheumatic disease controls and 2,100 healthy blood donors. Clinical disease was evaluated by the SLE Disease Activity Index (SLEDAI; excluding the anti-DNA component). Anti-dsDNA antibodies were detected by conventional enzyme-linked immunosorbent assay (ELISA) and by a commercial enzyme immunoassay (EIA). Anti-alpha-actinin antibodies were detected by ELISA, and their specificity was confirmed by Western blotting and by indirect immunofluorescence using rat kidney sections and mesangial cells as substrates. Highly positive sera were selected for absorption experiments and were affinity-purified for cross-reactivity studies and measurement of antibody avidity.

RESULTS

Sera from 62 of the SLE patients had anti-dsDNA antibodies; 21 of these sera also had anti-alpha-actinin antibodies, as compared with 1 of the 38 sera without anti-dsDNA antibodies. Of the 22 patients with anti-alpha-actinin antibodies, 10 had GN, as compared with 14 of the 78 without anti-alpha-actinin antibodies (P < 0.01). In patients with GN, anti-alpha-actinin, but not anti-dsDNA, antibodies correlated with the SLEDAI score (minus the anti-DNA component) and with treatment. The fraction of serum anti-dsDNA antibodies that cross-reacted with alpha-actinin exhibited high avidity for dsDNA, as determined using a commercial EIA for high-avidity anti-dsDNA antibodies and an in-house conventional ELISA.

CONCLUSION

The alpha-actinin-binding antibodies are significantly associated with GN in SLE. Whether such autoantibodies may anticipate the development of this complication of SLE remains to be verified.

Electric charge and sugar chains of immunoglobulin G in systemic lupus erythematosus

BACKGROUND

The charge condition of anti-DNA antibody is thought to be closely related to the pathology of renal disorders in systemic lupus erythematosus (SLE).

METHODS

We examined the relationships among the electric charge of IgG, proteinuria, and DNA binding capacity in SLE patients. Abnormal sugar chains, which affect the IgG charge, were also studied.

RESULTS

IgG in SLE patients with proteinuria had a higher positive electric charge than that in SLE patients without proteinuria, healthy individuals, and patients with other collagen diseases. Anti-DNA antibody titers measured by enzyme-linked immunosorbent assay (ELISA) were high in the positive charge regions of the IgG fractions obtained by a cationic exchange column. The binding capacity of double-stranded (ds)DNA measured by the Farr assay tended to be present specifically in the positive charge region in SLE patients with proteinuria. In affinoblotting using lectins, the percentage of IgG deficient in negative-charged sugar chains was found to be high in patients with a preponderant positive charge on anti-DNA antibody.

CONCLUSIONS

Abnormal IgG-bound sugar chains result in a preponderantly positive charge and are involved in the etiology of SLE nephritis.

Treatment with a laminin-derived peptide suppresses lupus nephritis

The role of DNA as the target for pathogenic lupus autoantibodies in systemic lupus erythematosus is equivocal and renal damage may be due to cross-reactivity of lupus Abs with glomerular components. We have previously shown that lupus autoantibodies bind to the laminin component of the extracellular matrix. In the present work, we have analyzed the fine specificity of the interaction of pathogenic murine lupus autoantibodies with this molecule and the effect of inhibiting their binding to laminin during the course of the disease. We have found that pathogenic murine lupus autoantibodies react with a 21-mer peptide located in the globular part of the alpha-chain of laminin. Immunization of young lupus-prone mice with this peptide accelerated renal disease. Analysis of transgenic, congenic, and RAG-1(-/-) mice confirmed the importance of this epitope in the pathogenesis of lupus renal disease. We have synthesized a panel of peptides that cross-react with the anti-laminin Abs and have found that the binding of lupus autoantibodies to the extracellular matrix could be inhibited in vitro by some of these competitive peptides. Treatment of MRL/lpr/lpr mice with these peptides prevented Ab deposition in the kidneys, ameliorated renal disease, and prolonged survival of the peptide-treated mice. We suggest that laminin components can serve as the target for lupus Abs. The interaction with these Ags can explain both the tissue distribution and the immunopathological findings in lupus. Moreover, inhibition of autoantibody binding to the extracellular matrix can lead to suppression of disease.

Autoimmune Mouse Antibodies Recognize Multiple Antigens Proposed in Human Immune-Mediated Hearing Loss

HYPOTHESIS

Autoimmune diseased mice with hearing loss will have autoantibodies against the various cochlear antigens proposed in clinical autoimmune inner ear disease.

BACKGROUND

Serum antibodies of patients with hearing loss recognize several proteins that are proposed as possible antigenic targets in the ear. This often leads to a clinical diagnosis of autoimmune inner ear disease, although it is not clear how these antibodies cause inner ear disease. Therefore, to better understand the relationship of autoantibodies and ear disease, an examination was made of serum autoantibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse with hearing loss. Similar antibody patterns in the mouse would provide an animal model in which to investigate potential autoimmune mechanisms of this clinical ear disorder.

METHODS

Sera from MRL/MpJ-Fas(lpr) autoimmune mice and normal C3H mice were tested by the enzyme-linked immunosorbent assay technique for reactivity against various reported cochlear antigens: heat shock protein 70 (bovine, human, bacterial), laminin, heparan sulfate proteoglycan, cardiolipin, and collagen types II and IV.

RESULTS

The autoimmune mouse sera showed significantly greater antibody reactivity against all of the antigens when compared with normal mouse sera.

CONCLUSIONS

Serum antibodies from autoimmune mice recognized several putative autoantigens reported for patients with hearing loss, suggesting that comparable antigen-antibody mechanisms might be operating. However, the recognition of multiple antigens did not identify any one as being the specific target in autoimmune hearing loss. The correlation of antibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse and human studies indicates this animal model should aid further investigations into potential cochlear antigens in autoimmune hearing loss.

Lupus anti-DNA autoantibodies cross-react with a glomerular structural protein: a case for tissue injury by molecular mimicry

Anti-DNA autoantibodies are the hallmark of human and murine systemic lupus erythematosus (SLE), an autoimmune rheumatic disease of unknown etiology. Some of these antibodies are believed to be pathogenic for kidney tissue and to initiate immune glomerulonephritis. However, the mechanisms by which anti-DNA antibodies participate in tissue injury remain controversial. We have studied the in vivo pathogenicity of anti-DNA monoclonal antibodies in immune deficient mice, using a panel of murine B cell hybridomas. No consistent genetic or immunochemical differences were found between pathogenic and non-pathogenic anti-DNA antibodies. However, the two antibody populations differed in their cross-reaction with the acidic actin-binding protein, alpha-actinin, that is known to play a major role in the structural integrity of glomerular filtration components. These results suggest that kidney dysfunction in SLE may be facilitated by protein-nucleic acid antigenic mimicry.

Lupus nephritis: lessons from experimental animal models

Lupus nephritis is a frequent and severe complication of SLE. In the last decades, animal models for SLE have been studied widely to investigate the immunopathology of this autoimmune disease because abnormalities can be studied and manipulated before clinical signs of the disease become apparent. In this review an overview is given of our current knowledge on the development of lupus nephritis, as derived from animal models, and a hypothetical pathway for the development of lupus nephritis is postulated. The relevance of the studies in experimental models in relationship with our knowledge of human SLE is discussed.

Noncognate binding to histones of IgG from patients with idiopathic systemic lupus erythematosus

The mechanism of attachment of circulating immune complexes (CIC) to glomerular basement membranes (GBM) has not yet been elucidated. Since it has been proposed that histone may be the ligand between GBM and DNA/anti-DNA CIC, we explored by ELISA and Western blots the nature of the interaction of IgG with histone on solid phase. Cognate binding of IgG anti-histone antibody was characteristically dependent on in its F(ab')(2) fragment and was inhibited by free histone. On the other hand, heat-aggregated IgG, a model for CIC, and IgG from most patients with idiopathic SLE had a characteristic noncognate binding behavior to histone: it was dependent on Fcgamma rather than on the F(ab')(2) fragment and was not effectively inhibited by free histones. Also, binding to histone of in vitro generated DNA/anti-DNA immune complexes was not dependent on DNA as a histone ligand, but on Fcgamma. Finally, there was good agreement between the binding of this IgG to histone and to C1q. We concluded that: (1) altered IgG and/or CIC bind to solid-phase-attached histone primarily through their Fcgamma and (2) CIC may mimic IgG antihistone antibodies in solid-phase immunoassays.

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.

Down-regulation of surface antigens recognized by systemic lupus erythematosus antibodies on embryonal cells following differentiation and exposure to corticosteroids

We have previously suggested that anti-DNA antibodies present in systemic lupus erythematosus patients can bind directly to tissues as a result of cross-reactivity with embryonal tissue-based antigens. Here we have analyzed the interaction between polyclonal and monoclonal mouse and human lupus autoantibodies and an embryonal cell line. We report that a murine embryonal stem cell line (ES) expresses a surface antigen which is recognized by mouse and human lupus autoantibodies. This surface antigen is down-regulated following maturation of the cells or incubation with corticosteroids. Adhesion molecules may serve as the target membrane antigen in ES cells since preincubation with these antibodies decreases the ability of ES cells to adhere to the plate.

Molecular cloning of metaphase chromosome protein 1 (MCP1), a novel human autoantigen that associates with condensed chromosomes during mitosis

Systemic lupus erythematosus autoantibodies were used to identify and to characterize new human chromosome-associated proteins. Previous immunolocalization studies in human and murine tissue culture cells showed that some of these monoclonal antibodies recognize nuclear antigens that associate with condensed chromosomes during mitosis. One antibody was selected for screening a human HeLa S3 cDNA expression library, and cDNAs that code for an antigen of 31-33 kDa were isolated. Immunological, biochemical and cell fractionation data indicate that the 31- to 33-kDa antigen corresponds to the chromosome-associated protein recognized by the original monoclonal antibody. Sequence analysis shows that we isolated a novel human gene. Immunolocalization to human tissue culture cells shows that during interphase the antigen is dispersed in the nucleus and that during mitosis it associates exclusively with condensed chromosomes. A similar pattern of localization was also observed in mouse fibroblasts, suggesting that the antigen is conserved among different species. Finally, we show that part of the antigen remains bound to the scaffold/matrix component, even after high salt extraction.

Nephritogenic autoantibodies in lupus: current concepts and continuing controversies

In summary, we suggest that the following statements regarding lupus nephritis are best supported by the existing data. 1) Lupus nephritis is an immunologically complex disorder. Autoantibodies directed against multiple epitopes on chromatin, including but not limited to dsDNA, may contribute to nephritis. 2) The presence of charged residues within autoantibody heavy chain CDR regions, particularly CDR3, may be essential to the property of nephritogenicity. 3) Chromatin/antichromatin immune complexes (formed either in the circulation or in situ in the GBM) are likely the proximal cause of lupus nephritis. Cross-reactive autoantibodies or antibodies reacting directly to glomerular antigens are less likely to play a major pathogenic role. 4) The induction of lupus nephritis may relate to the propensity of chromatin or its components to bind to the GBM by virtue of the interactions of histones with type IV collagen and heparan-sulfated glycosaminoglycans. Nonetheless, as indicated above, there are numerous issues that remain to be addressed and clarified with respect to lupus nephritis. Insight into these issues is not only of theoretical interest, but may lead to new approaches to diagnostic testing and more specific therapies to replace currently use nonspecific immunosuppressive drugs, which have substantial toxicities.

Ligand recognition by anti-DNA autoantibodies. Affinity, specificity, and mode of binding

Understanding the molecular basis of DNA recognition by anti-DNA autoantibodies is a key element in defining the role of antibody.DNA complexes in the pathogenesis of the autoimmune disorder systemic lupus erythematosus. As part of our efforts to relate anti-DNA affinity and specificity to antibody structure, and ultimately to disease pathogenesis, we have generated a panel of eight anti-DNA mAbs from an autoimmune MRL MpJ-lpr/lpr mouse and have assessed the binding properties of these antibodies. We find that none of our anti-DNA mAbs bind to RNA and only one low-affinity mAb cross-reacts with non-DNA antigens, albeit weakly. None of the mAbs in our panel bind double-stranded DNA exclusively. Antibodies that recognize single-stranded DNA can be categorized into two groups based on their affinity and apparent mode of binding. One group possesses relatively high affinity for oligo(dT) and may recognize single-stranded DNA ligands by accommodating thymine bases in hydrophobic pockets on the antigen binding site. The second group binds more weakly, apparently recognizes single-stranded DNA nonspecifically, and in some cases also binds double-stranded DNA. Although different mechanisms are used for binding single- and double-stranded ligands, the mode of DNA recognition appears conserved within groups of antibodies.

Characterization of autoantibody activities in sera anti-DNA antibody and circulating immune complexes from 12 systemic lupus erythematosus patients

To examine autoantibodies present in patients with active systemic lupus erythematosus (SLE), sera, circulating immune complexes (CIC), and antibodies purified on DNA-immunoadsorbent were tested by enzyme immunoassay. A panel of self-antigens, including DNA, histones (HIS), glomerular basal membrane (GBM), thymus cell extract (TCE), actin (ACT), myosin (MS), and tubulin (TUB), was used to define their specificities. IgM antibodies against all antigens of the panel were detected in sera, CIC, and in antibodies eluted from the DNA-immunoadsorbent and demonstrated a large polyreactivity. IgG antibodies showed restricted activities against DNA, HIS, GBM, and TCE in sera and a large polyreactivity in CIC. Inhibition experiments were performed to assess their mono- or polyreactivities. Among the IgG autoantibody population recognizing DNA, two populations of IgG antibodies were detected in the sera and in the affinity purified anti-DNA: one recognizes DNA, HIS, and GBM, and the other binds to DNA and to cytoskeletal proteins. These autoantibody populations were found in CIC, which also often contained high amounts of IgG antibodies recognizing ACT and MS. A third population of IgG antibody that recognizes only TCE and could not be inhibited by DNA or other antigens was found in serum and CIC. Our data demonstrate the existence of several populations of autoantibody in serum and CIC of SLE patients: (1) IgM polyreactive autoantibodies, (2) IgG polyreactive autoantibodies recognizing DNA and cytoskeletal proteins, (3) IgG specific to DNA, which cross react with HIS and GBM, and (4) IgG specific to TCE antigens.

Increased release of von Willebrand factor antigen from endothelial cells by anti-DNA autoantibodies

OBJECTIVE

To determine whether antibodies to double stranded DNA (anti-dsDNA) have a pathogenic role in systemic lupus erythematosus (SLE).

METHODS

IgG was purified from 17 patients with SLE (median anti-dsDNA titre 1212 IU/ml) and nine healthy controls (median titre 40 IU/ml). Anti-dsDNA depleted polyclonal IgG (median anti-dsDNA titre 17 IU/ml) was also prepared from sera of the 17 patients by affinity chromatography on a DNA cellulose column. Binding to antiendothelial cell antibodies (AECA) and expression of von Willebrand factor (VWF) antigen by cultured human umbilical vein endothelial cells (HUVECs) were studied by flow cytometry.

RESULTS

The percentage of HUVECs binding to AECA or expressing VWF was greater for cells incubated with IgG from patients with SLE than for cells incubated with control IgG, though values did not reach statistical significance; nevertheless, HUVECs incubated with IgG from patients expressed a greater mean fluorescence intensity with AECA (p = 0.0001) and greater VWF expression (p = 0.019). Both the fluorescence intensity and percentage of HUVECs binding to AECA or expressing VWF were significantly greater in HUVEC incubated with IgG containing anti-dsDNA than in those incubated with anti-dsDNA depleted IgG. The concentration of VWF in the supernatant was significantly increased in HUVECs incubated with IgG containing anti-dsDNA compared with control IgG or anti-dsDNA depleted IgG. Pretreatment of HUVECs with native DNA before incubation with IgG from lupus patients did not increase binding to AECA, or expression or release of VWF.

CONCLUSIONS

Our study provides in vitro evidence that antibodies to DNA have a pathogenic role in the induction of inflammatory injury of the vascular endothelium in SLE.

No evidence for an independent role of anti-heparan sulphate reactivity apart from anti-DNA in lupus nephritis

The presence of anti-heparan sulphate (HS) reactivity in serum is closely related to the occurrence of nephritis in patients with systemic lupus erythematosus (SLE). Since patients with lupus nephritis in general also have high titres of anti-DNA antibodies, we wanted to clarify the relationship between anti-HS and anti-DNA reactivity in serum. Therefore, we studied longitudinally six patients with lupus nephritis who experienced 12 exacerbations of their disease, and five SLE patients without nephritis experiencing 10 periods of non-renal disease exacerbations. In addition, we tested single serum samples of another 24 patients obtained during a renal disease exacerbation and 22 sera of patients without nephritis. The sera of all patients were tested for anti-DNA (Farr assay) and anti-HS reactivity (ELISA). We confirmed that SLE patients during renal exacerbations have a significantly higher anti-HS reactivity than patients without nephritis (P < 0.003). In addition, patients with nephritis also had higher titres of anti-DNA antibodies during renal exacerbations than during non-renal exacerbations (P < 0.01). A correlation between anti-DNA and anti-HS reactivity was observed (r = 0.40, P < 0.02), which in itself explains the correlation between nephritis and anti-HS reactivity. Comparing sera from nephritis and non-nephritis patients matched for anti-DNA titre, we found no difference in anti-HS reactivity, and therefore must conclude that the anti-HS reactivity is a direct reflection of anti-DNA reactivity.

Structure-function correlates of autoantibodies to nucleic acids. Lessons from immunochemical, genetic and structural studies

Nucleic acid binding autoantibodies are the hallmark of the human autoimmune disease, systemic lupus erythematosus (SLE) and are also prevalent in mouse models of this disease. The immunologic stimuli for the production of these antibodies as well as their pathogenic mechanisms are not well understood. However, extensive immunochemical and genetic studies, together with initial crystallographic analysis and computer modeling, have suggested several structure-function correlates which will form the basis for future research. The anti-DNA and anti-RNA autoantibodies comprise a continuous spectrum of specificities in which a delicate balance exists between the binding to the sugar-phosphate backbone and the interactions with the heterocyclic bases of the nucleic acid. Prominent in these interactions are the products of specific V-region immunoglobulin genes, some of which appear to be uniquely suitable for nucleic acid binding. Other structural elements encoded by D minigenes, N sequences and somatic mutations, help to increase the affinity of the binding interaction, and may also increase the repertoire of nucleic acid binding antibodies by combining with a relatively large number of additional V-gene products. Initial crystallographic analyses of anti-DNA antibodies indicate some fundamental differences in the structure and shape of ssDNA and dsDNA antibody combining sites. However, they also suggest a considerable degree of flexibility of both antibody and antigen, which is induced by their binding interaction.

Effects of Kampo medicines on the clearance of circulating immune complexes in mice

Toki-Shakuyaku-san (TSS), a Japanese (Kampo) formulation which consists of six herbs, was administered orally to MRL Mp-lpr/lpr mice for 6 weeks. Clearance was measured by in vivo enzymatic immune complex clearance (EIC) assay. Glucose oxidase-anti-glucose-oxidase complexes (GAG), as a model of immune complexes (ICs), was injected into mouse tail veins and at intervals thereafter the enzyme activity of the GAG remaining in the circulation were estimated. The half life (T1/2) of GAG from the circulation was significantly shortened in the TSS-treated group. Furthermore, the amount of circulating immune complexes, measured by anti-mouse C3 ELISA, tended to decrease in the TSS-treated group. We also evaluated three other Kampo formulas, but no significant effect was observed for these formulations. We then examined the activity of the individual herbs in TSS and in formulations excluding one component herb. No significant changes were observed with individual herbs. On the other hand, the activity observed in the TSS-treated group disappeared in the TSS minus Angelicae Radix formulation and the TSS minus Atractylodis Lanceae Rhizoma formulation. These observations indicate that TSS is a potent formula and its enhancing activity on ICs clearance is strengthened by both Angelicae Radix and Atractylodis Lanceae Rhizoma.

CD5-positive and CD5-negative plaque-forming cells against poly-L-lysine-treated sheep erythrocytes in patients with systemic lupus erythematosus

While attempting to evaluate CD5+ and CD5- anti-DNA-secreting plaque-forming cells (PFC) in patients with systemic lupus erythematosus (SLE), significant numbers of PFC against control sheep erythrocytes (ShE) treated with poly-L-lysine (PLL) but not further conjugated with single-stranded (ss) or double-stranded (ds) DNA were noted. Numbers of PFC obtained using PLL-ShE, ssDNA-ShE and dsDNA-ShE were not significantly different, all reactivity to DNA apparently being accounted for by binding of antibodies to PLL-treated ShE. Nevertheless, anti-PLL-PFC could be inhibited by soluble dsDNA included in the plaque assay. These findings might be explained by cationic anti-DNA antibodies binding non-specifically to anionic PLL. Control healthy subjects gave few PFC against PLL-ShE, ssDNA-ShE or dsDNA-ShE. Anti-PLL-PFC appeared to be related to disease activity, with higher numbers of both CD5+ and CD5- PFC in patients with clinically active SLE.

Preferential adsorption of cationic anti-DNA antibodies with immobilized polyanionic compounds, dextran sulfate

It has been shown that cationic anti-DNA antibodies have nephritogenic potential in murine models of lupus nephritis. More recently, we have reported that there is a close relationship between the presence of circulating cationic anti-DNA antibodies and the development of lupus nephritis in humans, and that the cationic anti-DNA antibodies bind to heparan sulfate, a major glycosaminoglycan in glomerular basement membrane, much better than neutral anti-DNA antibodies. This suggests that cationic anti-DNA antibodies of the IgG class may be responsible for development of nephritis in vivo in patients with systemic lupus erythematosus. In this study, we first studied reactivity of anti-DNA antibodies with a panel of glycosaminoglycans in vitro using ELISA methods, and found that anti-DNA antibodies cross-react with dextran sulfate, hyaluronic acid and chrondroitin sulfate. The reactivity and selectivity of dextran sulfate with anti-DNA antibodies was confirmed by in vitro immunoadsorption of the patient's sera with dextran sulfate-fixed column; incubation of auto-antibody-positive sera with dextran sulfate cellulose column removed anti-DNA, but not anti-RNP, anti-Sm, anti-SSA and anti-SSB antibodies from the sera in vitro. Of note is that dextran sulfate cellulose column absorbed exclusively, if not all, cationic anti-DNA antibodies in their sera. Nonspecific binding of total immunoglobulins as well as total proteins to the column was marginal. It has been suggested that cationic anti-DNA antibodies in sera of patients with refractory lupus nephritis could be efficiently removed by apheresis using dextran sulfate column.

Evidence for direct anti-heparin-sulphate reactivity in sera of SLE patients

Recently it has been suggested that anti-ds-DNA antibodies (Abs) promote tissue damage in systemic lupus erythematosus (SLE) by cross-reactivity with highly negatively charged tissue components such as heparan sulphate (HS), the major glycosaminoglycan of the glomerular basement membrane (GBM). Other authors, however, support the theory of DNA-anti-dsDNA immune complex deposition in situ. To further elucidate the possible role of HS antibodies, we developed a new ELISA system with heparan sulphate bound to solid phase. SLE patients (n = 40) showed a higher reactivity against HS (mean = 28.4, SD = 34.3) as compared to normal donors (n = 28, mean = 15.2, SD = 6.3) and patients with rheumatoid arthritis (n = 35, mean = 14.3, SD = 6.4). The addition of native dsDNA or HS to SLE sera was followed by a dose-dependent reduction in anti-HS reactivity. In contrast, in an anti-dsDNA ELISA, no reduction was observed when HS was added to SLE sera. An increase in reactivity was observed when SLE sera with and without a prior incubation with dsDNA were digested with DNAse I or II. After the purification of serum samples by protein A sepharose under dissociative conditions, seven out of eight SLE patients showed an increase in anti-HS reactivity. No correlation of the anti-HS Abs was found with organ involvement or other serological parameters. We concluded, that there is evidence for a direct anti-HS Ab reactivity in SLE sera. A part of these antibodies seems to show low avidity anti-dsDNA cross-reactivity.

Higher anti-heparan sulphate reactivity during systemic lupus erythematosus (SLE) disease exacerbations with renal manifestations; a long term prospective analysis

Cross-reactive antibodies against heparan sulphate (HS) have been suggested to play a role in initiating renal disease in SLE. Recently, we found that HS-reactivity is mediated by anti-DNA antibodies complexed with DNA and histones. To evaluate the clinical significance of anti-HS reactivity, we studied prospectively a cohort of 72 consecutive SLE patients, of whom 22 experienced 40 exacerbations. In 20 of these exacerbations renal symptoms were present. In these 20 exacerbations significantly higher anti-DNA (median 1:160) and anti-HS (median 1:30) titres were detected compared with exacerbations without renal manifestations (median 1:60 for anti-DNA and negative for anti-HS). There were no correlations with other symptoms of SLE. Anti-HS titres showed a significant correlation with anti-DNA antibody titres (rs = 0.57, P < 0.05). Anti-HS without anti-DNA reactivity was never detected. Some SLE patients showed a high anti-DNA titre without anti-HS reactivity, suggesting that not all anti-DNA antibodies are able to bind to histone/DNA complexes and thus to exhibit anti-HS reactivity. Our findings indicate that anti-HS reactivity is correlated with renal disease in SLE.

Characterization of cross-reactive anti-DNA autoantibodies in murine lupus

The role of crossreactive anti-DNA autoantibodies in the pathogenesis of Systemic Lupus Erythematosus (SLE) and its counterpart in the mouse (murine lupus) remains undefined. Five murine monoclonal anti-DNA autoantibodies tested in ELISA and immunofluorescence assays were found to cross-react with a variety of both nucleic acid and non-nucleic acid antigens. These included double stranded DNA (dsDNA), single stranded DNA (ssDNA), transfer RNA (tRNA), and the murine thymoma cell lines WEHI-22, WEHI-7, and EL-4. The majority of the autoantibodies reacted with all antigens tested; none of the autoantibodies reacted with only one antigen. To determine if the multiple reactivities demonstrated by these hybridoma-derived monoclonal anti-DNA autoantibodies accurately reflects the in vivo, autoimmune environment, the same assays were used to measure the reactivities of autoantibodies secreted directly from unfused autoimmune spleen cells cultured in vitro. These spleen cell-derived autoantibodies were found to display reactivities very similar to those demonstrated by the monoclonal anti-DNA autoantibodies indicating that the hybridoma process itself does not appear to select and amplify reactivities which are not present in vivo. Initial molecular characterization of F11, a monoclonal anti-DNA autoantibody crossreactive with both dsDNA and ssDNA, revealed that it utilizes the same VH gene segment as an anti-DNA autoantibody specific for ssDNA. F11 was also found to utilize similar VH, D, and JH gene segments as an antibody directed against the hapten polymer (Glutamic acid60, Alanine30, Tyrosine10)n (GAT). Thus, the same Ig gene segments used to encode crossreactive anti-DNA autoantibodies can also be utilized by anti-DNA autoantibodies displaying strict antigen specificity as well as by antibodies directed against exogenous antigens.

Detection of glomerular-binding immune elements in murine lupus using a tissue-based ELISA

The glomerulonephritis in systemic lupus erythematosus (SLE) is presumably triggered by the binding of circulating immune elements (autoantibodies and immune complexes) to the glomerulus; however, the nature of these elements is unclear. In order to detect and characterize such elements, we developed an ELISA using whole intact glomeruli as the substrate. With this assay, glomerular binding activity (GBA) was detected in the serum of MRL lpr, NZB x W, and B x SB mice, but not in non-autoimmune BALB/c mice. Less activity was present in the serum of C3H lpr, C57Bl/6J lpr and AKR lpr animals which develop signs of autoimmunity but only modest renal disease. The GBA in MRL lpr mice contained IgG (subclasses 1, 2a and 2b), but not IgG3, IgM, IgA, or C3. GBA was not significantly decreased by preadsorption of MRL lpr serum by DNA-agarose (although anti-DNA antibodies were). Binding activity in serum, however, was diminished by DNAase treatment. Fractionation of MRL lpr serum over a molecular sizing column showed that GBA eluted in a broad peak. GBA bound to the glomerulus ex vivo in a tissue-specific fashion and was enriched in renal eluates relative to serum in vivo. In sum, the binding activity detected by this assay appeared to be a heterogeneous entity (possibly in part immune complexes containing DNA) which bound specifically to the glomerulus and which appeared to parallel the presence of renal disease. This novel assay system may help elucidate the pathogenesis of SLE nephritis and have utility as a disease marker.

Cross-reactions of anti-DNA autoantibodies with cell surface proteins

Anti-DNA autoantibodies are thought to play a major role in the pathogenesis of systemic lupus erythematosus. However, the mechanism(s) by which they participate in tissue and organ damage is not well understood. It has been suggested that these antibodies combine with DNA or DNA-histone complexes to produce circulating immune complexes which may deposit in various tissues. Alternatively, anti-DNA autoantibodies could interact directly with tissue components by way of immunological cross-reaction. In this study we have used a panel of mouse monoclonal autoantibodies with anti-nuclear specificity and measured their binding to membrane proteins of several tissues and cell lines. We show that the anti-DNA antibodies, but not anti-RNA or anti-histone antibodies bind to membrane proteins of molecular weights 102, 80, 42, 35 and 31 kDa, which are expressed in different combinations on several cell types. The binding of anti-DNA antibodies to these cell surface proteins was not affected by DNase treatment of the target cells, was increased by DNase treatment of the antibody preparations and was completely inhibited by DNA, indicating a true cross-reaction and not an indirect interaction of antibody and membrane proteins through a DNA bridge. Our results suggest that direct binding of anti-DNA autoantibodies to cell surface membrane proteins may play an important role in the induction of the pleomorphic tissue damage in systemic lupus erythematosus.

Specific increases in urinary excretion of anti-DNA antibodies in lupus mice induced by lysozyme administration: further evidence for DNA-anti-DNA immune complexes in the pathogenesis of nephritis

We previously reported that lysozyme electrostatically inhibits the fibronectin-mediated DNA binding to the glomerular basement membrane (GBM) and reduces in situ DNA-anti-DNA complex formation in the GBM in NZB/W F1 mice [1]. In this study, we further noticed significant increases in urinary excretion of anti-DNA antibodies and immune complexes (IC) in lysozyme-treated NZB/W F1 mice. Their clearance ratios of IgG anti-DNA antibody to whole IgG were markedly high compared with those of saline-treated animals. A large number of IgG and C3 positive granules were observed in the tubular cells of NZB/W F1 mice treated with lysozyme. On the contrary, nil or only small amounts of anti-DNA antibodies were detected in the urine of NZB/W F1 mice without lysozyme administration despite a large amount of proteinuria, suggesting entrapment of the antibodies in lupus glomeruli. Lysozyme neither inhibited the binding of anti-DNA antibodies to DNA or heparan sulphate nor did it displace anti-DNA antibodies and IC from the kidney homogenates of lupus mice. It thus appears that the inhibition of DNA binding to the GBM due to lysozyme reduced the entrapment of anti-DNA antibodies in the GBM, resulting in urinary excretion of the antibodies.

Anti-DNA antibodies can bind to the glomerulus via two distinct mechanisms

It is generally assumed that antibodies to double stranded DNA (anti-DNA) play a pivotal role in the pathogenesis of SLE nephritis. Recently, we reported that anti-DNA antibodies can bind to heparan sulphate proteoglycan (HSPG), a constituent of the glomerular basement membrane (GBM), via histones and DNA. We postulated that these histone/DNA/anti-DNA complexes can bind via their histone part to the glomerulus in vivo. To test this hypothesis we performed in vitro binding studies with isolated GBM loops and renal perfusion studies in the rat using histones, DNA and an anti-DNA monoclonal antibody (mAb) with high avidity for dsDNA. A strong granular binding of anti-DNA mAb to isolated GBM loops occurred via histones and DNA and a moderate granular binding was found via DNA alone. Anti-DNA mAb alone did not bind to the GBM loops. After perfusion of histones, DNA and immediately thereafter anti-DNA, we found with immunoelectron microscopy (IEM) a strong binding to endothelial cells in the glomerulus and to a lesser extent in the GBM. When the anti-DNA mAb was injected i.v. one hour after perfusion of histones and DNA, we observed a strong fine granular binding to the capillary wall by immunofluorescence (IF) in a membranous pattern along with some minor mesangial deposits. After perfusion of DNA alone followed by anti-DNA mAb, binding in the glomerulus was less than with histones and DNA, and was more restricted to the mesangium. No direct binding to the glomerulus was observed after perfusion with anti-DNA mAb alone, histones and anti-DNA mAb, or histones, DNA and a control mAb.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of anti-DNA IgG and IgE antibodies in BALB/c mice

Immunization of BALB/c mice with denatured DNA (dnDNA)-methylated bovine serum albumin (MBSA) complex along with aluminium hydroxide gel as adjuvant, resulted in the induction of anti-DNA antibodies of both IgG and IgE isotypes demonstrable by avidin-biotin micro enzyme-linked immunosorbent assay (ELISA) and solid phase radioimmunoassay (SPRIA), respectively. In contrast to the high levels of IgG2a and IgG2b anti-DNA antibodies observed in SLE-prone autoimmune mice, more than 90% of the anti-DNA antibodies of IgG isotype were found to be of IgG1 subclass. Specificity of both IgG and IgE antibodies which recognized activated DNA, dnDNA and double-stranded DNA but not RNA was established by competitive ELISA and SPRIA inhibition assays. These antibodies cross-reacted with cibacron blue and chondroitin sulfate but not with various other proteoglycans, nucleosides and nucleotides. Passive cutaneous anaphylaxis reaction in rats showed that these antibodies are capable of inducing in vivo degranulation of mast cells in a dose-dependent manner. These studies lend support to the concept that IgE antibodies directed against DNA may mediate mast cell degranulation and thus contribute to immediate-type hypersensitivity phenomena including hives seen in patients with systemic lupus erythematosus and to the localization of IgE-nucleic acid complexes.

Probing molecular changes induced in DNA by reactive oxygen species with monoclonal antibodies

Antibodies reactive with native double stranded DNA are characteristic of the chronic inflammatory disease systemic lupus erythematosus. Native DNA is however, a poor immunogen and the mechanism of anti-DNA antibody production is incompletely understood. Modification of DNA can increase its immunogenicity and in inflammatory disease states reactive oxygen species produced from phagocytic cells have been shown to thus modify DNA. In this study, monoclonal antibodies produced spontaneously by two mice strains with lupus-like disease were used in a competition ELISA to monitor changes to DNA induced by reactive oxygen species. Different procedures for reactive oxygen species generation were found to cause distinct and characteristic changes to DNA involving modifications of base residues, the sugar-phosphate backbone and the gross conformational structure of double-stranded DNA. In view of this, it may be possible to use these antibodies further to probe DNA and infer the source and nature of the reactive oxygen species it has been exposed to, particularly in vivo.

Hidden high-avidity anti-DNA antibodies occur in normal human gammaglobulin preparations

An ability to detect hidden high-avidity DNA-binding protein in human gammaglobulin samples was investigated. Using ion exchange chromatography on QAE-Sephadex A-50 a highly positive Farr assay DNA-binding fraction was reproducibly isolated from several commercial normal human gammaglobulin preparations. The estimated dissociation constant had a value of 1.04 x 10(-11) M thus confirming high avidity protein-DNA complex formation. Anti-DNA antibodies (Ab) ELISA data revealed that immunoglobulin (Ig) G, IgM and IgA participated in the protein-DNA interaction. Inhibitory experiments involving a number of polynucleotides, synthetic and natural polyanions demonstrated that both double-stranded DNA (dsDNA) and heat-denatured DNA but not RNA inhibited the protein-3H-DNA binding. Generally, the inhibiting effect was more pronounced when purine base-containing polynucleotides and polydeoxy- rather than polyribonucleotides were used. Synthetic polyanions and normal human sera (NHS) also markedly reduced the binding. The presence of hidden high-avidity DNA-binding antibodies in normal gammaglobulin preparations was suggested.

Anti-histone reactivity in systemic lupus erythematosus sera: a disease activity index linked to the presence of DNA:anti-DNA immune complexes

This study shows that purified murine monoclonal anti-DNA antibodies and human polyclonal anti-DNA antibodies (from systemic lupus erythematosus--SLE--patients), preincubated with DNA, acquire anti-histone reactivity. Conversely, DNAse I treatment of SLE patients' antibodies with anti-histone activity abolishes such activity. It has previously been demonstrated that anti-DNA antibodies bind to the cell membrane and recognize cell-surface polypeptides that have been identified with histones by partial sequencing. In a series of 33 sera from patients with clinically active disease and 29 sera from patients in clinical remission, positivity of an immunoblot analysis detecting antibodies against these polypeptides was associated with clinical activity of SLE (sensitivity, 0.88; specificity, 0.90). Anti-histone reactivity detected by ELISA appeared to be also a good marker of SLE activity (sensitivity, 0.64; specificity, 0.54). As expected, anti-native DNA antibody positivity and lowered complement dosage were also associated with clinical activity (sensitivity, 0.79 and 0.63, respectively; specificity, 0.48 and 0.93, respectively). Since anti-histone reactivity reflects, at least partly, the presence of anti-DNA antibodies complexed to DNA, which could bind to cell-membrane determinants, and is associated with disease clinical activity, it is suggested that this mechanism can contribute to explain the pathogenicity of anti-DNA antibodies.

Inhibiting effect of charged polymers on interaction of human lupus autoantibodies with certain intracellular proteins

The influence of charged polymers on the reaction of immunoglobulins from human lupus sera with cellular proteins was investigated in this study. Through immunoblotting it was shown that polyanions (dextran sulfate, heparin, polyinosinic acid) and polylysine inhibited autoantibody binding to several polypeptides of different molecular mass. Using immunofluorescent staining with affinity isolated monospecific autoantibodies it was demonstrated that the immunoreactivity of two nuclear antigens (p30 and p85) and one cytoplasmic antigen (p40) was sensitive to the presence of charged polymers. The inhibiting effect correlated with the concentration of the polymers. The data obtained suggested the competitive mechanism of inhibition of autoantibody-protein reaction by the charged polymers.

Circulating anti-DNA immune complexes in active lupus nephritis

PURPOSE

The role that circulating anti-DNA immune complexes play in autoimmunity has not yet been elucidated in humans. The aim of this study was to relate circulating anti-DNA immune complexes to a variety of renal histologic features and to immunoglobulin deposits in active lupus nephritis.

PATIENTS AND METHODS

The study population consisted of 47 patients with active lupus nephritis, 28 with active systemic lupus erythematosus (SLE) in the absence of renal lesions, and 40 with other categories of the disease. All patients were examined for anti-DNA circulating immune complexes (CIC) and their anti-DNA idiotype expression by an isoelectrofocusing analysis. Patients with renal lesions were also examined for renal histologic and immunofluorescent findings in renal biopsy specimens.

RESULTS

Anti-DNA CIC expressing an anti-DNA idiotype termed 0-81 Id occurred in patients with active lupus nephritis but not in acute episodes lacking renal involvement or in remission. Positive test results for anti-DNA CIC were associated with the incidence of diffuse proliferative glomerulonephritis (DPGN). Patients with anti-DNA CIC were also found to have a statistically significant increase in the prevalence of immunoglobulin immune deposits in the subendothelial area of the renal glomeruli.

CONCLUSION

The findings suggest that anti-DNA CIC preferentially occurred in lupus patients with DPGN. Examination for anti-DNA CIC may be a useful predictor of renal lesions, and therefore may contribute to the management of SLE. The results also indicate that anti-DNA CIC may be associated with immunoglobulin deposition in the subendothelial area of the renal glomeruli.

Anti-dsDNA: choice of assay in relation to clinical value

Antibodies to DNA are quite specific for systemic lupus erythematosus (SLE) and occur in the majority of SLE patients. Therefore, their detection is an important diagnostic aid to the clinician. Detection of anti-dsDNA may precede the diagnosis of SLE by more than a year. Fluctuations in the level of anti-dsDNA in an individual patient may give important information on the clinical status of the patient. Four of the most important methods developed for the measurement of anti-dsDNA antibodies will be discussed in this paper: the Farr assay, the PEG assay, the indirect immunofluorescence test on Crithidia luciliae and the ELISA. They will also be compared with one commercially available (Farr) assay, the Amersham anti-dsDNA kit. Each method, detects a part of the spectrum of anti-dsDNA antibodies produced by a patient. The Farr assay is the most specific for SLE; however, milder forms of the disease in which patients have only low avidity anti-dsDNA may easily be missed by this technique. Clinically, high avidity anti-dsDNA is related more frequently to the occurrence of nephritis, whereas low avidity anti-dsDNA antibodies are found more often in patients with central nervous system involvement. Traditionally, SLE is considered an immune-complex disease, in which inflammatory processes are initiated by local deposition of DNA/anti-dsDNA complexes. More recently, a major role was thought to be played by crossreactions of anti-dsDNA with tissue constituents. Our current view, however, is that such a crossreactivity plays only a minor role; we postulate that binding to glomerular constituents is caused by anti-dsDNA antibodies complexed with DNA and histones.

Heterogeneity of immune complex-derived anti-DNA antibodies associated with lupus nephritis

The mechanisms responsible for the tissue injuries associated with lupus nephritis have not yet been well explained. We have investigated the characteristics of anti-DNA antibodies in circulating immune complexes (CIC) and in the deposits of renal glomeruli in patients with active lupus nephritis. The CIC-derived antibodies expressed anti-DNA idiotypes (Id) designated as 0-81 Id and NE-1 Id, and bound mainly to single-stranded DNA but never to glomerular basement membrane (GBM) antigens. On the other hand, the immunoglobulins (Ig) eluted from renal glomeruli of lupus patients reacted not only with DNA but also with GBM, proteoglycan, and heparan sulfate. The binding of glomeruli-deposited Ig was markedly low when GBM antigens were used after treatment with heparitinase, suggesting that some anti-DNA antibodies may bind directly to GBM antigens associated with heparan sulfate, and form in situ IC in renal glomeruli. It was also revealed that the renal eluates obtained after passing through GBM antigen-coupled Sepharose lost the binding ability with GBM but still retained DNA-binding and 0-81 Id activity, showing the participation of circulating IC-derived anti-DNA antibodies in the glomerular deposits. Theoretically there may be two mechanisms in the pathogenesis of lupus nephritis through the deposition of circulating IC and through in situ formation of anti-DNA IC in renal glomeruli. The diversity of histological features in lupus kidneys may be attributed to the heterogeneity of the mechanisms.

LDL-mediated interaction of DNA and DNA-anti-DNA immune complexes with cell surface

The effect of low-density lipoprotein (LDL) on the binding of DNA and DNA-anti-DNA immune complexes to cultured human skin fibroblasts was examined. Using radioisotope analysis, ELISA and indirect immunofluorescent staining, a correlation between plasma membrane-bound DNA or DNA-anti-DNA immune complexes and cell-associated LDL was established. It was demonstrated that cytotoxicity and internalization of DNA-anti-DNA immune complexes may be LDL mediated. The data obtained suggest that the binding of the major part of DNA and immune complexes bound to surface of normal skin fibroblasts is due to the formation of a DNA-LDL-LDL receptor linkage. A possible role of LDL-containing immune complexes in the pathogenesis of systemic lupus erythematosus is discussed.