Circulating DNA and lupus nephritis

Glomerular immune deposits in murine lupus models may contain histones

Two types of lupus mice, NZB/NZW F1 female hybrids and mice with graft-versus-host disease (GVHD), were studied. Histones H3 and H2A were detected by immunofluorescence in glomeruli of 22/22 proteinuric GVHD and 8/12 proteinuric NZB/W F1 female mice; in non-proteinuric animals, 3/5 GVHD and 2/27 NZB/W F1 female were positive. Using antibodies to histone peptides it was shown that mainly the N-terminal regions of histones H3 and H2A were exposed in glomerular deposits. Western blot analysis revealed antibodies to histone subfractions in sera of 33/34 lupus mice that developed proteinuria. This study provides evidence that histones are involved in the pathogenesis of lupus nephritis.

Haemodialysis as a model for studying endogenous plasma DNA: oligonucleosome-like structure and clearance

The rate of clearance of extracellular plasma DNA in man has important implications for pathogenetic mechanisms in systemic lupus erythematosus (SLE), as well as for certain other clinical states. Present knowledge of this parameter is derived exclusively from studies of injected, naked DNA in animals. Recent information indicates that the physiologic form of plasma DNA in SLE is that of oligonucleosome-like molecules rather than of naked DNA and consists of multimeric complexes of DNA bound to histone, probably arising from an apoptotic process. In order to study the rate at which these oligonucleosome-like complexes are removed from plasma and to do so in man rather than experimental animals, we exploited the observation that during haemodialysis large amounts of DNA are released, apparently within the dialysis coil, into the patient's plasma. Since this release appears to cease promptly with termination of the procedure, it offered the potential for estimating the rate of removal of such DNA from human plasma. Moreover, if that DNA, as postulated, were shown to possess an oligonucleosome-like structure resembling that found endogenously in human SLE, the relevance of such information to the human disease state would be further enhanced. The present results support the conclusion that DNA released into plasma during haemodialysis possesses such an oligonucleosome-like structure. The plasma half-life of that DNA in man was found not to exceed 4 min. The highly dynamic state thus implied for extracellular endogenous plasma DNA in man has important implications for pathogenetic mechanisms dependent on dsDNA in SLE. Moreover, individuals undergoing chronic haemodialysis, who are thereby exposed to a very large cumulative amount of such DNA, might serve as models for studying its long-term sequelae.

The atherogenic effect of lupus sera: systemic lupus erythematosus-derived immune complexes stimulate the accumulation of cholesterol in cultured smooth muscle cells from human aorta

The influence of systemic lupus erythematosus (SLE) patients' sera on lipid accumulation in the cultured smooth muscle cells (SMC) from unaffected human aortic intima was examined. It was demonstrated that the cholesterol uptake in the SMC cultured in the presence of SLE sera is 1.5- to 6-fold higher than in the cells cultured with normal human sera (NHS) obtained from healthy donors. Incubation of the SMC with circulating immune complexes (CIC) isolated from lupus sera by precipitation with 2.5% polyethylene glycol 6000 (PEG) caused a 3- to 4-fold rise in the intracellular cholesterol level. The atherogenic effect of lupus sera, as well as isolated CIC, strongly correlated (r = 0.98) with the low density lipoprotein (LDL) content in the PEG-precipitated CIC. The cholesterol level in cultured SMC also increased 2- to 3-fold when growth medium was supplemented with LDL, DNA, and anti-DNA autoantibodies (IgG) affinity isolated from lupus sera. Using immunofluorescent staining, it was shown that the addition of a DNA-anti-DNA IgG mixture to the growth medium, together with NHS, stimulated LDL incorporation in the SMC. The results of double-label staining suggest the formation of LDL-DNA-IgG complexes which seem to be entrapped in cells more actively than free LDL. The composition of PEG-precipitated CIC was studied by electrophoresis and immunoblotting. Significant amounts of apolipoprotein B, as well as low molecular weight DNA and immunoglobulins, were found in SLE-derived CIC. The data obtained suggest that the atherogenic effect of human lupus sera in vitro is generally due to the appearance of LDL-containing immune complexes. Different mechanisms possibly involved in the lupus atherogenesis are discussed.

Clinical significance of renal biopsy in subacute lupus erythematosus

The renal biopsy plays an important role in the clinical evaluation of patients with lupus erythematosus. From numerous studies of renal biopsies in patients with lupus nephritis, it has become clear that although renal lesions are quite varied, the pattern of renal involvement correlates well with the clinical outcome. The broad spectrum of the lesions seen in lupus nephritis has been attributed to individual differences in the immune response in different patients or in the same patient during the course of illness. A classification of lupus nephritis authorized by the World Health Organization is presented. The classification combines all of the morphologic modalities of biopsy interpretation and semiquantitative assessment of activity and chronicity. The clinical correlation of this histologic classification is emphasized and demonstrates that the specific nature of the renal histopathology can predict both the acute and long term course of renal disease in lupus nephropathy and be useful in determining the management of individual patients.

Thromboxane receptor blockade reduces renal injury in murine lupus nephritis

To investigate the role of thromboxane A2 (TxA2) in murine lupus, we assessed the effects of the specific thromboxane receptor antagonist GR32191 on immune complex glomerulonephritis in MRL-lpr/lpr mice. Forty mg/kg/day GR32191 was given by twice daily subcutaneous injection for eight weeks beginning at 12 weeks of age. This dose completely blocked the renal vasoconstriction produced by the thromboxane agonist U46619. After eight weeks of treatment, both glomerular filtration rate (GFR) (8.9 +/- 0.6 vs. 6.8 +/- 1.1 ml/min/kg; P less than 0.05) and PAH clearance (CPAH) (37.4 +/- 2.5 vs. 29.9 +/- 3.3 ml/min/kg; P less than 0.05) were significantly higher in mice given GR32191 compared to vehicle treated animals. Administration of GR32191 also reduced proteinuria from 18.1 +/- 11.6 to 3.7 +/- 1.3 mg/24 hours (P less than 0.05). In GR32191 treated MRL-lpr/lpr mice, renal hemodynamic function and proteinuria were not significantly different from congenic MRL-+/+ controls. Thromboxane receptor blockade had striking affects on renal histomorphology reducing both hyaline thrombi in glomeruli (P = 0.022) and interstitial inflammation (P = 0.006). Glomerular crescents and severity of vasculitis also tended to be reduced in mice receiving the thromboxane receptor antagonist. The overall histopathologic score in mice given GR32191 was significantly lower than vehicle treated animals (4.7 +/- 0.5 vs. 8.4 +/- 1.5; P = 0.016). These effects of GR32191 were associated with decreased excretion of thromboxane B2 (TxB2) in urine (292 +/- 37 vs. 747 +/- 155 pg/24 hr; P less than 0.005) as well as a modest reduction in glomerular deposits of IgG (semiquantitative score 2.6 +/- 0.2 vs. 3.5 +/- 0.2; P less than 0.02). Thus, chronic thromboxane receptor blockade markedly altered the course of renal disease in MRL-lpr/lpr mice, suggesting that TxA2 is an important mediator of renal dysfunction and injury in this murine model of lupus nephritis.

Different mechanisms by which anti-DNA MoAbs bind to human endothelial cells and glomerular mesangial cells

The mechanisms by which anti-DNA MoAbs derived from MRL-lpr/lpr mice, bind to human umbilical vein endothelial cells (HUVEC) and glomerular mesangial cells were studied using a cellular ELISA. DNAse-treatment of either the MoAb or HUVEC followed by reconstitution with DNA and/or histones was performed to determine whether DNA and histones mediated such binding. It was found that MoAb410 bound to HUVEC and mesangial cells in the form of preformed DNA/anti-DNA immune complex, and such binding was facilitated by histones. In contrast, MoAb 152 bound directly to cell membrane-associated DNA, and adding DNA to MoAb 152 reduced its cellular binding. DNA binds endothelial cell surface and histones enhance the binding of both MoAb 410 and MoAb 152 to HUVEC by increasing cell membrane-associated DNA. Finally, the degree of MoAb binding to HUVEC is critically influenced by the relative concentrations of antibody, DNA, and histones.

New Zealand white rabbits immunized with RNA-complexed total histones develop an autoimmune-like response

The antibody response of rabbits immunized with a total histone mixture containing randomly coiled H1/H5, H2A, H2B, H3 and H4 devoid of DNA was investigated in direct and competitive ELISA. The antisera were tested with isolated histones and chromatin and with a series of overlapping synthetic peptides covering the entire sequences of the four core histones and two peptides of H1. It was found that the New Zealand (NZ) white rabbits immunized with the total histone (TH) mixture complexed with RNA produced IgG antibodies reacting with histones and with a number of histone peptides but not with chromatin. The antisera also contained IgG antibodies which bound components that correspond to common target antigens in autoimmune diseases such as native dsDNA, peptides of Sm-D antigen, ubiquitin, branched peptides of ubiquitinated H2A and poly(ADP-ribose). By competition experiments, it was shown that these antibodies corresponded to non-crossreacting antibody populations. New Zealand rabbits immunized with TH in the absence of RNA or random outbred rabbits immunized with the RNA-complexed histone fraction produced antibodies reacting with histone, chromatin and very few histone peptides, while no activity with non-related antigens was observed. The pattern of reactivity of antisera raised in NZ rabbits with RNA-complexed TH was found to be very similar to that observed in sera of patients with systemic lupus erythematosus while, in contrast, the antibody response was very different in NZ or outbred rabbits immunized with various native nuclear particles and with individual histones. Altered nucleosome particles rather than native nucleosomes may represent the antigenic stimulus giving rise to autoantibodies.

Relation between serological data at the time of biopsy and renal histology in lupus nephritis

As autoantibodies are thought to participate in the pathogenesis of renal inflammation in systemic lupus erythematosis (SLE) we investigated associations between serological markers of disease activity in SLE and the activity of renal histopathological lesions in thirty-five patients with lupus nephritis (LN). We found the following prevalence of serum auto-antibodies in LN: IgG antinuclear antibodies (ANA) 100%, IgM ANA 69%, IgA ANA 60%, IgG anti-dsDNA 60%, IgM anti-dsDNA 71%, IgA anti-dsDNA 60%, anti-RNP 20%, anti-Sm 14%, anti-SSA 31%, anti-SSB 14%, anti-histone 37%, anti-cardiolipin 80% and antibody to ribosomal protein (anti-P) 6%. No correlation was found between serological parameters and the WHO-classification of biopsies. The activity-index of histological lesion, assessed according to the NIH-renal histology scoring system, correlated with IgM ANA and IgM anti-dsDNA titers. Of all the specific features of histological renal inflammation, glomerular proliferation showed the best overall correlation with serological parameters of disease activity. Anticardiolipin antibodies were correlated with overall disease activity, but not with renal histological activity. Thus, serological markers of disease activity did not adequately reflect the amount of renal inflammation in LN and cannot replace renal biopsy as a diagnostic tool.

The beta-blocker acebutolol down modulates the spontaneous polyclonal activation of lymphocytes in NZB X NZW lupus mice

Acebutolol is a beta blocking agent that induces in C57Bl/6 mice a polyclonal activation of lymphocytes (PAL). In this study, its effect on cellular parameters of spontaneous PAL and lupus disease in NZB x NZW female mice is investigated. A significant reduction of PAL is found in 10-week-old mice after only five injections of 50 mg/kg/day of acebutolol. This effect is also observed in 7- and 9-month-old mice after 12 weeks of treatment. In these chronically treated mice, a significant decrease in incidence and levels of proteinuria as compared with untreated mice is found. No statistically significant increase in survival is observed. In conclusion, acebutolol down modulates the spontaneous PAL which characterizes the NZB x NZW mouse lupus disease and might prevent to some extent the development of nephritis.

Anti-heparan sulphate reactivity in sera from patients with systemic lupus erythematosus with renal or non-renal manifestations

Previously, we have shown that anti-DNA can bind to heparan sulphate (HS), a constituent of the glomerular basement membrane (GBM). We hypothesized that binding of anti-DNA to HS in the GBM plays a role in the onset of systemic lupus erythematosus (SLE) nephritis. To test this hypothesis we measured the anti-HS reactivity in cross-sectional and longitudinal studies of SLE patients with or without nephritis. In the transverse serum study single serum samples from 26 SLE patients were studied. We found no correlation between anti-HS reactivity and previously development of nephritis (anti-HS positive: seven out of 16 with history of nephritis, two out of 10 without nephritis). However, six of the seven anti-HS positive sera in the nephritis group were obtained within 1 month of the onset of nephritis, suggesting a temporal relationship between anti-HS reactivity and onset of nephritis. In the longitudinal serum study between six and 16 serum samples were studied from each of 10 SLE-patients. In five out of five episodes of nephritis we found anti-HS reactivity before the onset or exacerbation of the nephritis. In four non-renal manifestations anti-HS reactivity was found in only one episode; in none of the three patients who remained clinically stable did serum samples show anti-HS reactivity. Anti-HS reactivity was only found in sera positive for anti-DNA by Farr assay but the anti-HS titre was not a mere reflection of the reactivity measured in the Farr assay. This indicates that only a subpopulation of anti-DNA can bind to HS. We found a high correlation (r = 0.99) between anti-HS reactivities in plasma and serum and we conclude that anti-HS reactivity in serum samples from SLE patients is not due to in vitro complex formation during clotting. Although further prospective analysis is necessary, our data suggest that measurement of anti-HS reactivity in SLE patients might identify patients at risk for the development of nephritis.

Cross-reactivity of monoclonal anti-DNA antibodies with heparan sulfate is mediated via bound DNA/histone complexes

To study in more detail the cross-reactive binding of anti-DNA antibodies to heparan sulfate (HS) and heparan sulfate proteoglycan (HSPG) purified from glomerular basement membranes (GBM), the binding pattern of 31 murine IgG anti-DNA MoAbs, derived from MRL/lpr, NZB/W and graft-versus-host diseased mice, was analysed. In ELISA we found binding of 10 anti-DNA MoAbs to HS. Seven of the 10 anti-HS positive clones bound to HSPG but not to the HSPG core protein in ELISA and/or on Western blots. However, DNase-I treatment partly reduced this binding, whereas after purification of MoAb by protein-A sepharose chromatography under dissociative conditions, all clones completely lost their binding capacity to HS and HSPG. Culturing of hybridoma cells in the presence of 3H-thymidine revealed DNA bound to the MoAb. Although the binding to HS and HSPG could be reconstituted by the addition of the protein-A column effluent, this was not possible by the addition of DNA alone. Therefore, we performed immunoprecipitation of the effluent with purified MoAb and subsequent SDS-PAGE which showed that the complex also contained histones. However, histones alone were also not able to reconstitute the binding to HS and HSPG. It is concluded that binding of anti-DNA MoAb to HS and GMB-HSPG is mediated via bound complexes containing both DNA and histones. A comparable reaction with polyclonal anti-DNA Ab might play a role in the pathogenesis of SLE nephritis, since histones have a very high affinity for HS, the major glycosaminoglycan of the GBM.

Endogenous circulating DNA in systemic lupus erythematosus. Occurrence as multimeric complexes bound to histone

Little is known about endogenous systemic lupus erythematosus (SLE) plasma DNA even though it is the presumed precursor of DNA-containing immune complexes, thought to play a central role in lupus glomerulonephritis. DNA purified from SLE plasma formed discrete bands, corresponding to sizes of about 150-200, 400, 600, and 800 bp, closely resembling the characteristic 200 bp "ladder" found with oligonucleosomal (ON) DNA. By radiolabeling DNA while in whole plasma, the very small amounts present could be further characterized. All of 24 such specimens formed two or more discrete bands on 6% PAGE. Detergent treatment of plasma resulted in a DNA migration pattern similar to that of purified DNA, suggesting disruption of DNA-protein complexes. DNA purified from authentic ON and detergent-treated ON behaved similarly. A significant portion of DNA, labeled in SLE plasma could be specifically immunoprecipitated with monoclonal antihistone antibody as was the case with ON. These immunoprecipitates, when redissolved, exhibited the expected size distribution upon PAGE. It is concluded that DNA in SLE plasma occurs as a series of multimeric complexes, at least a portion of which is noncovalently bound to histone. These results are consistent with an ON-like structure for SLE plasma DNA as had been suggested by theoretical considerations and may have important implications for its immunologic behavior in SLE and perhaps other disorders.

Anti-DNA antibodies and lupus nephritis: the complexity of crossreactivity

It has been suggested that crossreactivity of anti-DNA antibodies plays a central role in the development of lupus nephritis. Experiments with monoclonal anti-DNA antibodies initially seemed to sustain this intriguing hypothesis but such studies may easily lead to incorrect conclusions. In this short article, Kees Brinkman and colleagues discuss the validity of these studies and challenge the role of crossreactivity in the pathogenesis of lupus nephritis.

Quantitation of blood plasma DNA as an index of in vivo cytotoxicity

Cell death triggers the release into extracellular spaces of products of chromatin catabolism, particularly of DNA. A sensitive DNA assay has been used to investigate in the mouse whether the quantitation of plasma DNA may be used as an index of in vivo cytotoxicity. It has been found that toxic doses of bacterial lipopolysaccharide, HgCl2, CCl4, cyclophosphamide and hydroxyurea, are responsible for the release of extracellular DNA in plasma, in a dose dependent relationship. In conclusion, quantitation of extracellular DNA may be used for investigating in vivo cell death phenomena induced by toxic agents and drugs. Such a method could be applied to toxicological studies in animals and man.

The role of germline gene expression and somatic mutation in the generation of autoantibodies to DNA

Several distinctive features of anti-DNA autoantibodies have been identified by a detailed analysis of the available heavy and light chain sequences. They include unique VH gene segments that are not normally expressed in antibodies to external antigens, somatic mutations which may serve to change the antigenic specificity as well as to increase affinity, a less stringent choice of light chains, and a unique basic peptide in the heavy chain CDR3. It is proposed that in the majority of cases, the regulatory mechanism of self-tolerance in the healthy animal operates via VH gene expression to prevent the synthesis of potentially high affinity anti-DNA autoantibodies.

Pathogenic anti-DNA antibodies in SLE: idiotypic families and genetic origins

We have adopted an idiotypic approach to study the double stranded DNA (dsDNA) binding antibodies of systemic lupus erythematosus (SLE). Three anti-idiotypic reagents, 8.12, 3I, and F4, identify cross reactive idiotypes that are each expressed on anti-dsDNA antibodies in the sera of many patients with SLE. These idiotypic antibodies are implicated in the pathogenesis of SLE as they are present in immune complex deposits in the kidneys of patients with SLE glomerulonephritis. The autoantibody associated idiotypes are also expressed on antibodies that do not bind DNA. We are investigating the origin of the pathogenic anti-dsDNA antibodies of SLE by comparing the autoantibodies, the antibodies to foreign antigens, and the myeloma proteins that express each SLE associated idiotype. In conjunction with serological analysis of these idiotypic systems, molecular genetic studies indicate that both the 8.12 and the 3I autoantibody associated idiotypes may be germline encoded, while the F4 idiotype is generated by somatic mutation. The data further suggest that the antigenic specificity of the pathogenic anti-DNA antibodies of SLE is acquired through somatic mutation of germline immunoglobulin genes. By studying the regulation of genes capable of encoding pathogenic autoantibodies, in both SLE patients and non-autoimmune individuals, we may be able to elucidate the pathogenesis of autoimmune disease and begin to design more effective therapeutic interventions.

Histones have high affinity for the glomerular basement membrane. Relevance for immune complex formation in lupus nephritis

An effort has been made to integrate insights on charge-based interactions in immune complex glomerulonephritis with nuclear antigen involvement in lupus nephritis. Attention was focussed on the histones, a group of highly cationic nuclear constituents, which could be expected to bind to fixed anionic sites present in the glomerular basement membrane (GBM). We demonstrated that all histone subfractions, prepared according to Johns (4), have a high affinity for GBM and the basement membrane of peritubular capillaries. Tissue uptake of 125I-labeled histones was measured by injecting 200 micrograms of each fraction into the left kidney via the aorta and measuring organ uptake after 15 min. In glomeruli isolated from the left kidneys, the following quantities of histones were found: f1, 13 micrograms; f2a (f2al + f2a2), 17 micrograms; f2b, 17 micrograms; and f3, 32 micrograms. Kinetic studies of glomerular binding showed that f1 disappeared much more rapidly than f2a. The high affinity of histones (pI between 10.5 and 11.0; mol wt 10,000-22,000) for the GBM correlates well with their ability to form aggregates (mol wt greater than 100,000) for comparison lysozyme (pI 11, mol wt 14,000), which does not aggregate spontaneously bound poorly (0.4 micrograms in isolated glomeruli). The quantity of histones and lysozyme found in the isolated glomeruli paralleled their in vitro affinity for a Heparin-Sepharose column (gradient elution studies). This gel matrix contains the sulfated, highly anionic polysaccharide heparin, which is similar to the negatively charged heparan sulfate present in the GBM. Lysozyme eluted with 0.15 M NaCl, f1 with 1 M NaCl, and f2a, f2b, and f3 could not be fully desorbed even with 2 M NaCl; 6 M guanidine-HCl was necessary. Two further findings of great relevance for the concept of induction of immune complex glomerulonephritis by histones were: (a) glomerular-bound histone was accessible for specific antibody given intravenously; and (b) prior binding of histones promoted glomerular deposition of anionic antigens, as could be shown with ssDNA fragments. These data justify the proposal that glomerular deposition of histones can induce immune complex formation, start an inflammatory process, and produce tissue damage.

Plasma DNA in systemic lupus erythematosus. Characterization of cloned base sequences

Little is known about plasma DNA in patients with systemic lupus erythematosus (SLE). Previous studies have suggested that it may, in fact, not be derived from the random nucleolysis that might be expected to accompany cell death, which might have been the simplest explanation of its origin. To extend the results of other studies, plasma DNA, obtained from a subgroup of SLE patients who had large amounts of immunoprecipitable plasma DNA, was cloned into a plasmid vector, and the nucleotide base sequences were studied by nucleic acid hybridization. One possible explanation for the anomalous renaturation kinetics of plasma DNA in SLE--namely, that it contained non-human genomic base sequences--was rendered untenable by the fact that 51 consecutive DNA clones from 2 SLE patients were each shown to contain human genomic DNA sequences. Plasma DNA from SLE patients also differed from human genomic control DNA in that those sequences derived from the highly repetitive fraction of human DNA were specifically enriched in one such sequence, Alu, which constituted 55% of the repeat sequences in the plasma DNA clones as compared with 13% in control DNA clones. There was a decrease in the frequency of non-Alu repeat sequences (9% for plasma DNA compared with 23% in control DNA). These differences were statistically significant, and they indicate that SLE plasma DNA contains a nonrandom selection of human genomic base sequences. Several explanations for these findings are considered.

Binding of double-stranded DNA to glomeruli of rats in vivo

In vivo binding of double-stranded DNA (dsDNA) to renal glomeruli of rats was examined. 125I-dsDNA (600 basepairs) was perfused with 131I-IgG as a blood marker into the right renal artery of normal rats, and blood flow was restored. After 10 minutes, isolated glomeruli showed a specific uptake of DNA, which increased in a saturable fashion with increasing doses of administered DNA. To exclude the possibility that 125I in the glomeruli represented only DNA breakdown products, we extracted the DNA from the glomeruli for analysis by polyacrylamide gel electrophoresis. The extracted DNA was 120-200 bp in size, which is large enough to bind antibodies to DNA. In contrast, the radioactivity of DNA taken up by the liver or renal tissues other than glomeruli was predominantly trichloroacetic acid soluble, i.e., less than 15 bp. Immunofluorescence studies showed that antibodies to DNA, administered after DNA, were present in glomeruli. Our data indicate that dsDNA binds to glomeruli in vivo in a saturable manner, and remains large enough to be antigenic. Therefore, the binding of DNA to glomeruli, followed by interaction with antibodies to dsDNA may be a mechanism for DNA-anti-DNA complex formation in glomeruli in patients with systemic lupus erythematosus.

Immunogenetics of SLE and primary Sjögren's syndrome

SLE is a syndrome defined by clinical criteria and by the presence of autoantibodies reactive with nucleic acids and proteins concerned with transcription and translation. Breeding experiments in mice have illustrated the enormous genetic heterogeneity of this syndrome, of which the final common pathway is a widespread immune complex disease. The causes of SLE in humans are likely to be equally multifactorial. Family studies have demonstrated that genetic factors exist, but each factor appears to be a relatively weak disease-susceptibility gene. The major exceptions to this are the very rare complete deficiencies of classical pathway complement components, which are almost invariably accompanied by the development of SLE. Observations of these patients have led to the formulation of hypotheses relating complement and its receptor, CR1, to the defective removal of immune complexes from the circulation.