Reaction of systemic lupus erythematosus antinative DNA antibodies with native DNA fragments from 20 to 1,200 base pairs

Molecular Mechanisms of Neutrophil Extracellular Trap (NETs) Degradation

Although many studies have been exploring the mechanisms driving NETs formation, much less attention has been paid to the degradation and elimination of these structures. The NETs clearance and the effective removal of extracellular DNA, enzymatic proteins (neutrophil elastase, proteinase 3, myeloperoxidase) or histones are necessary to maintain tissue homeostasis, to prevent inflammation and to avoid the presentation of self-antigens. The persistence and overabundance of DNA fibers in the circulation and tissues may have dramatic consequences for a host leading to the development of various systemic and local damage. NETs are cleaved by a concerted action of extracellular and secreted deoxyribonucleases (DNases) followed by intracellular degradation by macrophages. NETs accumulation depends on the ability of DNase I and DNAse II to hydrolyze DNA. Furthermore, the macrophages actively engulf NETs and this event is facilitated by the preprocessing of NETs by DNase I. The purpose of this review is to present and discuss the current knowledge about the mechanisms of NETs degradation and its role in the pathogenesis of thrombosis, autoimmune diseases, cancer and severe infections, as well as to discuss the possibilities for potential therapeutic interventions. Several anti-NETs approaches had therapeutic effects in animal models of cancer and autoimmune diseases; nevertheless, the development of new drugs for patients needs further study for an effective development of clinical compounds that are able to target NETs.

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

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

Neutrophil Extracellular Traps-DNase Balance and Autoimmunity

Neutrophil extracellular traps (NETs) are macromolecular structures programmed to trap circulating bacteria and viruses. The accumulation of NETs in the circulation correlates with the formation of anti-double-stranded (ds) DNA antibodies and is considered a causative factor for systemic lupus erythematosus (SLE). The digestion of DNA by DNase1 and DNases1L3 is the rate- limiting factor for NET accumulation. Mutations occurring in one of these two DNase genes determine anti-DNA formation and are associated with severe Lupus-like syndromes and lupus nephritis (LN). A second mechanism that may lead to DNase functional impairment is the presence of circulating DNase inhibitors in patients with low DNase activity, or the generation of anti-DNase antibodies. This phenomenon has been described in a relevant number of patients with SLE and may represent an important mechanism determining autoimmunity flares. On the basis of the reviewed studies, it is tempting to suppose that the blockade or selective depletion of anti-DNase autoantibodies could represent a potential novel therapeutic approach to prevent or halt SLE and LN. In general, strategies aimed at reducing NET formation might have a similar impact on the progression of SLE and LN.

Autoantibody-mediated impairment of DNASE1L3 activity in sporadic systemic lupus erythematosus

Antibodies to double-stranded DNA (dsDNA) are prevalent in systemic lupus erythematosus (SLE), particularly in patients with lupus nephritis, yet the nature and regulation of antigenic cell-free DNA (cfDNA) are poorly understood. Null mutations in the secreted DNase DNASE1L3 cause human monogenic SLE with anti-dsDNA autoreactivity. We report that >50% of sporadic SLE patients with nephritis manifested reduced DNASE1L3 activity in circulation, which was associated with neutralizing autoantibodies to DNASE1L3. These patients had normal total plasma cfDNA levels but showed accumulation of cfDNA in circulating microparticles. Microparticle-associated cfDNA contained a higher fraction of longer polynucleosomal cfDNA fragments, which bound autoantibodies with higher affinity than mononucleosomal fragments. Autoantibodies to DNASE1L3-sensitive antigens on microparticles were prevalent in SLE nephritis patients and correlated with the accumulation of cfDNA in microparticles and with disease severity. DNASE1L3-sensitive antigens included DNA-associated proteins such as HMGB1. Our results reveal autoantibody-mediated impairment of DNASE1L3 activity as a common nongenetic mechanism facilitating anti-dsDNA autoreactivity in patients with severe sporadic SLE.

Evolving story of autoantibodies in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by antinuclear antibody (ANA) production. ANAs bind to DNA, RNA and complexes of proteins and nucleic acids and are important markers for diagnosis and activity. According to current models, ANAs originate from antigen-driven processes; nevertheless, antibody responses to both DNA and RNA binding proteins display features unexpected in terms of current paradigms for antigenicity. These differences may reflect disturbances in both B and T cells critical for autoreactivity. Clinically, ANA testing has new uses for determining classification as well as assessing eligibility for clinical trials. Studies of patients with established disease show frequent seronegativity. In this setting, seronegativity may indicate a stage of disease called post-autoimmunity in which the natural history of disease or effects of immunosuppressive therapies modifies responses. The new uses of ANA testing highlight the importance of understanding autoantigenicity and developing sensitive and informative assays for clinical assessments.

The role of monogamous bivalency and Fc interactions in the binding of anti-DNA antibodies to DNA antigen

Antibodies to DNA (anti-DNA) are the serological hallmark of systemic lupus erythematosus. These antibodies can bind DNA avidly by monogamous bivalency, a mechanism which requires the interaction of both Fab combining regions with antigenic determinants on the same polynucleotide. To explore further this mechanism, we tested Fab and F(ab')2 fragments prepared from IgG from patient plasmas in an ELISA with native DNA antigen, detecting antibody with a peroxidase conjugated anti-Fab reagent. These studies showed that Fab fragments, which can only bind monovalently, had negligible activity. Although bivalent F(ab')2 fragments would be predicted to bind DNA, these fragments also showed poor anti-DNA activity. Control studies showed that the fragments retained antibody activity to tetanus toxoid and an EBV antigen preparation. Together, these findings suggest that anti-DNA avidity depends on monogamous bivalency, with the antibody Fc portion also influencing DNA binding, in a mechanism which can be termed Fc-dependent monogamous bivalency.

Oligonucleotide-Based Drug Development: Considerations for Clinical Pharmacology and Immunogenicity

The field of oligonucleotide (OGN)-based therapeutics has been growing dramatically in the past decade, providing innovative platforms to develop agents for the treatment of a wide variety of clinical conditions. OGN agents have unique physicochemical properties and pharmacokinetic/pharmacodynamic characteristics. This review considers findings from the literature and information on new molecular entities submitted to the US Food and Drug Administration as OGN-based therapeutics. In addition, the article discusses several challenging issues from the perspective of clinical pharmacology, emphasizing the potential of immunogenicity, the effect of renal impairment on OGN exposure, drug-drug interactions, and the utility of pharmacokinetic/pharmacodynamic modeling. The field of OGN-based therapeutics is in evolution and will benefit from further studies as well as clinical experience to formulate guidelines and promote the development of this class of agents.

Anti-DNA antibodies--quintessential biomarkers of SLE

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

The inhibition of anti-DNA binding to DNA by nucleic acid binding polymers

Antibodies to DNA (anti-DNA) are the serological hallmark of systemic lupus erythematosus (SLE) and can mediate disease pathogenesis by the formation of immune complexes. Since blocking immune complex formation can attenuate disease manifestations, the effects of nucleic acid binding polymers (NABPs) on anti-DNA binding in vitro were investigated. The compounds tested included polyamidoamine dendrimer, 1,4-diaminobutane core, generation 3.0 (PAMAM-G3), hexadimethrine bromide, and a β-cylodextrin-containing polycation. As shown with plasma from patients with SLE, NABPs can inhibit anti-DNA antibody binding in ELISA assays. The inhibition was specific since the NABPs did not affect binding to tetanus toxoid or the Sm protein, another lupus autoantigen. Furthermore, the polymers could displace antibody from preformed complexes. Together, these results indicate that NABPs can inhibit the formation of immune complexes and may represent a new approach to treatment.

Preparation and characterization of an anti-DNA monoclonal antibody showing size selectivity toward DNA fragments

Anti-DNA monoclonal antibodies were prepared using an in vitro immunization method. Balb/c mouse splenocytes were immunized with HeLa cell nuclear extract in the presence of N-acetylmuramyl-L-alanyl-D-isoglutamine and fused with P3U1 myeloma cells using PEG 4000. After HAT selection and ELISA using fragmented HeLa genomic DNA, an anti-DNA monoclonal antibody was obtained. The monoclonal antibody D-1-1, whose isotype was IgM, interacted with a variety of double-stranded DNA. The antibody reacted only with DNA fragments longer than 0.8 kbp, and its apparent dissociation constant for a 1.0-kbp DNA fragment was 34 nM. This antibody will be a helpful tool for the detection of DNA structures.

Inhibition of adenovirus DNA synthesis in vitro by sera from patients with systemic lupus erythematosus

Sera containing antinuclear antibodies from patients with systemic lupus erythematosus (SLE) and related disorders were tested for their effect on the synthesis of adenovirus (Ad) DNA in an in vitro replication system. After being heated at 60 degrees C for 1 h, some sera from patients with SLE inhibited Ad DNA synthesis by 60 to 100%. Antibodies to double-stranded DNA were present in 15 of the 16 inhibitory sera, and inhibitory activity copurified with anti-double-stranded DNA in the immunoglobulin G fraction. These SLE sera did not inhibit the DNA polymerases alpha, beta, gamma and had no antibody to the 72,000-dalton DNA-binding protein necessary for Ad DNA synthesis. The presence of antibodies to single-stranded DNA and a variety of saline-extractable antigens (Sm, Ha, nRNP, and rRNP) did not correlate with SLE serum inhibitory activity. Methods previously developed for studying the individual steps in Ad DNA replication were used to determine the site of inhibition by the SLE sera that contained antibody to double-stranded DNA. Concentrations of the SLE inhibitor that decreased the elongation of Ad DNA by greater than 85% had no effect on either the initiation of Ad DNA synthesis or the polymerization of the first 26 deoxyribonucleotides.

A bispecific dsDNAxmonoclonal antibody construct for clearance of anti-dsDNA IgG in systemic lupus erythematosus

High avidity anti-dsDNA IgG antibodies are believed to play an important role in the pathogenesis of the autoimmune disease systemic lupus erythematosus (SLE) and therefore attempts have been made to reduce the concentration of these antibodies in the bloodstream of SLE patients. Previously we reported the development of an antigen based heteropolymer (AHP), a bispecific complex prepared by using the avidin-biotin system to crosslink dsDNA to a mAb specific for the human erythrocyte (E) complement receptor. Our studies indicated that this AHP could bind anti-dsDNA antibodies to E and facilitate clearance of these autoantibodies from the circulation of a monkey without E destruction. Here we report an improved covalent crosslinking procedure and purification scheme in which the AHP construct is isolated by precipitation in 50% saturated ammonium sulfate. We used a dsDNA binding dye, PicoGreen, to demonstrate specificity of binding of dsDNA to E via the AHP. The efficacy of the AHP in binding IgG anti-dsDNA antibodies to E was demonstrated in a sensitive and quantitative assay, based on the time resolved fluorescence properties of europium-labeled anti-human IgG mAbs used to probe the E. We also used this assay to screen SLE patient and normal plasmas for levels of anti-dsDNA IgG. The results of this assay correlate very well with the Farr assay, and therefore this approach may be useful in the development of informative and specific assays for a variety of autoantibodies. Treatment of SLE plasmas with E-AHP under conditions close to physiological led to substantial reductions (> or = 90%) in anti-dsDNA titers. It should be possible to test these new AHP for their ability to target and safely remove IgG anti-dsDNA antibodies from the circulation in animal models.

Anti-DNA autoantibodies and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that affects most of the organs and tissues of the body, causing glomerulonephritis, arthritis, and cerebritis. SLE can be fatal with nephritis, in particular, predicting a poor outcome for patients. In this review, we highlight what has been learned about SLE from the study of mouse models, and pay particular attention to anti-DNA autoantibodies, both as pathological agents of lupus nephritis and as DNA-binding proteins. We summarize the current approaches used to treat SLE and discuss the targeting of anti-DNA autoantibodies as a new treatment for lupus nephritis.

The influence of DNA size on the binding of antibodies to DNA in the sera of normal human subjects and patients with systemic lupus erythematosus (SLE)

To elucidate antibody recognition of DNA in normal and aberrant immunity, the binding of sera of normal human subjects (NHS) and patients with SLE was tested with mammalian and bacterial DNA varying in size. Klebsiella pneumoniae (KP) and calf thymus (CT) single-stranded DNA (ssDNA) were investigated as model antigens using the restriction enzyme HinfI to generate fragments with the size range of 800-5000 base pairs. The influence of size on activity was assessed by ELISA by both titration of serum as well as coating antigen concentration. In both assay formats, SLE sera bound equivalently to intact CT and KP DNA, but had dramatically reduced reactivity to fragments of both antigens. In contrast, NHS bound similarly to intact KP DNA and its fragments but had low reactivity to CT DNA. These results suggest that SLE and NHS anti-DNA react with different antigenic determinants on DNA, as shown by cross-reactivity as well as size dependency in solid-phase assays.

Thermodynamic analysis of monoclonal antibody binding to duplex DNA

A technique based on fluorescence polarization (anisotropy) was used to measure the binding of antibodies to DNA under a variety of conditions. Fluorescein-labeled duplexes of 20 bp in length were employed as the standard because they are stable even at low ionic strength yet sufficiently short so that both arms of an IgG cannot bind to the same duplex. IgG Jel 274 binds duplexes in preference to single-stranded DNA; in 80 mM NaCl Kobs for (dG)20.(dC)20 is 4.1x10(7) M-1 compared with 6.4x10(5) M-1 for d(A5C10A5). There is little sequence specificity, but the interaction is very dependent on ionic strength. From plots of log Kobs against log[Na+] it was deduced that five or six ion pairs are involved in complex formation. At low ionic strength,Kobs is independent of temperature and complex formation is entropy driven with DeltaH degrees obs and DeltaC degrees p,obs both zero. In contrast, in 80 mM NaCl DeltaC degrees p,obs is -630 and -580 cal mol-1K-1 for [d(TG)]10.[d(CA)]10 and (dG)20.(dC)20 respectively. IgG Jel 241 also binds more tightly to duplexes than single-stranded DNA, but sequence preferences were apparent. The values for Kobs to [d(AT)]20 and [d(GC)]20 are 2.7x10(8) and 1.3x10(8) M-1 respectively compared with 5.7x10(6) M-1 for both (dA)20. (dT)20 and (dG)20.(dC)20. As with Jel 274, the binding of Jel 241 is very dependent on ionic strength and four or five ionic bonds are involved in complex formation with all the duplex DNAs which were tested. DeltaC degrees p,obs for Jel 241 binding to [d(AT)]20 was negative (-87 cal mol-1K-1) in 80 mM NaCl but was zero at high ionic strength (130 mM NaCl). Therefore, for duplex-specific DNA binding antibodies DeltaC degrees p,obs is dependent on [Na+] and a large negative value does not correlate with sequence-specific interactions.

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.

Glomerular uptake of nucleosomes: evidence for receptor-mediated mesangial cell binding

DNA-containing immune complexes (IC) are believed to have a central causal role in the glomerulonephritis of systemic lupus erythematosus. Extracellular DNA which provides the antigenic source for these ICs circulates as oligonucleosomes (ON). The in vivo glomerular uptake of radiolabeled ON in rats, as well as its binding by cultured rat mesangial cells, was examined. The data show that the binding of ON to kidney, and specifically glomeruli, was almost fourfold greater than that of purified DNA. Uptake appeared dose-dependent and saturable, while there were no differences in hepatic or splenic uptake. Most of the nucleosomal DNA recovered from glomeruli was TCA-precipitable, and on gel electrophoresis was about 100 to 300 bp, a size sufficient to allow formation of large ICs. In vitro studies demonstrated that ON are bound by cultured mesangial cells in a dose-dependent and saturable manner, with a dissociation constant of 1.25 x 10(-10) M/liter and 750 binding sites per cell. Autoradiography of cell cultures incubated with radiolabeled ON showed deposition along the plasma membrane which was inhibited by excess unlabeled ON. The data show that binding of ON to glomeruli exceeds that of purified DNA and may be mediated by histones. ON bind to mesangial cells in a receptor-mediated fashion. The data support the hypothesis of in situ formation of DNA-containing ICs and suggest a role for the mesangial cell in lupus glomerulonephritis.

Application of the gel shift assay to study the affinity and specificity of anti-DNA autoantibodies

We have demonstrated that the gel shift assay, a powerful method to study protein.DNA interactions under equilibrium conditions, is both an accurate and precise method to measure the affinity of anti-DNA.DNA immune complexes. One difficulty in performing gel shift assays is disruption of protein.DNA equilibria during the time needed for complexes to enter the gel matrix. However, we have found that highly cross-linked polyacrylamide gels which are known to form non-restrictive matrices, do not perturb anti-DNA.DNA complexes. Using anti-ssDNA BV04-01 as a model antibody, we find good agreement between the dissociation constants (Kd) measured in the gel shift assay using a 5.4% polyacrylamide gel cross-linked with 0.6% (bis)acrylamide, and those obtained previously by fluorescence quenching. Because gel shift assays require only nanogram quantities of analyte and can be performed in several hours, it is well suited for a range of anti-DNA binding studies.

Conjugates or dsDNA linked to human gammaglobulin inhibit anti-dsDNA antibodies in vitro

Previous studies have shown that both nucleosides and oligonucleotides linked to isologous gammaglobulin suppress anti-nucleic acid antibody production both in vivo and in vitro. The aim of this study was to determine whether one can make a DNA-human gammaglobulin (HGG) conjugate which can inhibit anti-double stranded DNA (dsDNA) antibodies obtained from a heterogeneous population of systemic lupus erythematosus (SLE) sera. To do so, we constructed conjugates of sonicated dsDNA fragments of 100-400 base pairs covalently linked to HGG with varying degrees of substitution of DNA:HGG. An ELISA inhibition assay was used to determine which conjugate best inhibits the binding of anti-dsDNA antibodies. Conjugate 2, prepared with monomeric HGG (150 kD) with a high degree of substitution (3.72 DNA:HGG) inhibited the binding of anti-dsDNA antibodies from 27 of 31 SLE sera. In addition, this conjugate inhibited the spontaneous formation of anti-dsDNA in vitro by cultured lymphoid cells from selected SLE patients. Together, this data suggests that a 'generic' tolerogen may provide an antigen specific therapy for SLE.

Genesis and evolution of antichromatin autoantibodies in murine lupus implicates T-dependent immunization with self antigen

Autoantibodies reacting with chromatin and its components, histones and DNA, are characteristic of the human autoimmune disease SLE and drug-induced lupus, but the mechanisms of their induction remain unknown. Serial serum samples collected over short intervals from lupus-prone MRL/MP-lpr/lpr and BXSB mice were tested by ELISA on chromatin and its substructures to characterize the initial autoimmune response to these antigens. Direct binding studies demonstrated that the early autoantibodies recognized discontinuous epitopes on native chromatin and the (H2A-H2B)-DNA subnucleosome. As the immune response progressed, native DNA and other chromatin constituents generally became antigenic. Based on adsorption studies and IgG subclass restriction, antibodies to native DNA were more related to chromatin than to denatured DNA. The kinetics of autoantibody appearance and the Ig class distribution were similar to the kinetics and distribution seen in antibodies induced by immunization with an exogenous T-dependent antigen. These results are most consistent with the view that autoantibodies reacting with chromatin are generated by autoimmunization with chromatin, and antibodies to native DNA are a subset of the wide spectrum of antichromatin autoantibodies.

Immunogenicity of Z-DNA depends on the size of polynucleotide presented in complexes with methylated BSA

The importance of polynucleotide size for immunogenicity was tested with size-fractionated Z-DNA. High molecular weight Z-DNA, larger than 1000 bp, was fragmented by digestion with micrococcal nuclease. Fractions corresponding to less than 60, 60-120, 100-200, 200-400 and 400-900 bp were isolated by gel filtration on Sepharose 4B. These fractions and the greater than 1000 bp Z-DNA were mixed with methylated BSA and the complexes were injected into C57BL/6 mice with RIBI adjuvant. Only one of four mice responded to the less than 60 bp immunogen. All the fractions larger than 60 bp induced specific anti-Z-DNA antibodies, mostly of IgG isotype, in all animals injected. Fractions larger than 200 bp induced antisera of higher titer than did 60-120 or 100-200 bp fractions. All positive sera reacted with Z-DNA but not with B-DNA and only very weakly with denatured DNA. In competitive assays, similar concentrations of fragments larger than 60 bp inhibited binding to immobilized Z-DNA. A higher concentration of less than 60 bp fragments was required for competitive binding. Even for a highly immunogenic nucleic acid that differs from the B-DNA conformation, a polynucleotide larger than 100 bp is much more immunogenic than smaller fragments.

Antinuclear autoantibodies in healthy nonpregnant and pregnant women and their offspring

Antinuclear autoantibodies have previously been detected in sera of healthy women although less frequently than in sera of women with autoimmune disorders. The effect of pregnancy on antinuclear autoantibody production in healthy women is as yet debatable. We present four studies in which, by employing the ELISA method, we evaluated the presence of six antinuclear autoantibodies (anti-ds DNA, anti-ss DNA, anti-poly(I), anti-cardiolipin, anti-Sm, and anti-RNP) in the sera of more than 1,000 healthy pregnant and nonpregnant women, including 196 pairs of matched maternal and cord blood sera. In all four studies healthy pregnant women did not demonstrate significantly higher prevalence rates of various serum antinuclear autoantibodies as compared to healthy non-pregnant women. All detected autoantibodies were of the IgM isotype. In only one infant (born to a healthy seronegative mother) was an autoantibody (IgM anti-ss DNA) detected. This may indicate that in certain circumstances the fetus is capable of self-production of autoantibodies.

Antibodies to viral and mammalian native DNA in response to BK virus inoculation and subsequent immunization with calf thymus DNA

Recent studies have demonstrated that anti-DNA antibodies share important genetical features with antibodies to exogenous antigens, suggesting that anti-DNA antibody responses may be (auto-) antigen driven. We have earlier defined three out of five rabbits as anti-dsDNA antibody responders based on reactivity with calf thymus (CT) dsDNA after inoculation with the human dsDNA virus BK. In the present study we demonstrate that all five animals that received BK virus inoculations produced antibodies to BK virus dsDNA. These antibodies did not cross-react with CT dsDNA, as shown by inhibition experiments. The anti-BK dsDNA antibodies persisted over time, in contrast to the anti-CT dsDNA antibodies that decreased shortly after a peak following the first boost of BK virus. While the anti-CT dsDNA antibodies decreased, the anti-BK dsDNA antibodies remained elevated, thus supporting the results of the inhibition experiments which showed that two independent antibody populations are produced after BK virus inoculations. In the three animals producing anti-mammalian dsDNA antibodies, antibodies recognizing CT dsDNA reappeared after intravenous administration of a complex of CT dsDNA and methylated bovine serum albumin (MBSA) without adjuvant. The latter anti-CT dsDNA antibodies did not cross-react with BK dsDNA. In contrast to earlier studies we conclude that mammalian dsDNA may be immunogenic, and that discrete molecular differences in DNA antigens from different sources may induce anti-dsDNA antibodies specific for dsDNA molecules of different origin.

Anti-DNA antibodies induced by BK virus inoculations. Demonstration of the specificities for eukaryotic dsDNA and synthetic polynucleotides

The ability of BK virus to induce anti-DNA antibodies in rabbits, and the ability of these antibodies to bind natural eukaryotic DNA and synthetic polynucleotides have been analysed. The specificity of the binding was assayed by inhibition of anti-dsDNA and -ssDNA ELISA tests with dsDNA, ssDNA, and synthetic single-stranded as well as double-stranded polynucleotides. The anti-dsDNA activity of two rabbit antisera was effectively inhibited by dsDNA and ssDNA and poly(dAdT)-poly(dAdT). The other nucleotide antigens produced relatively less inhibition. The anti-ssDNA binding was most efficiently inhibited by the homologous antigen, whereas inhibition by dsDNA only reached approximately 70% of the maximum as defined by ssDNA as inhibitor. This indicates the existence of a selective anti-ssDNA antibody population and a population recognizing both ssDNA and dsDNA within the sera. Cross-reaction of the induced anti-DNA antibodies with phospholipid antigens, such as cardiolipin, phosphatidylic acid, and bacterial cell surface, could not be demonstrated. We conclude that antibodies resulting from inoculation with BK virus specifically bind to dsDNA and ssDNA and possess a high affinity for the synthetic duplex poly(dAdT). In this way, they have some similarities with anti-DNA antibodies encountered in SLE (systemic lupus erythematosus) in both man and mouse.

BK virus terminates tolerance to dsDNA and histone antigens in vivo

In order to characterize the immune response to BK virus, a human polyomavirus containing dsDNA and host cell histones, we followed the appearance of antibodies in five outbred rabbits after intravenous inoculation with purified infectious BK virus without any adjuvant. The animals were followed for 15 weeks after the first inoculation and booster doses were given after four and eight weeks. Antibodies were studied by ELISA techniques with the BK virus particle, dsDNA, ssDNA or the individual histones as test antigens. Antibodies to BK virus structural proteins were detected in all rabbits. Two out of five rabbits produced antibodies to dsDNA, ssDNA, nucleosomes and histones H1 and H3. Even a weak reactivity to H2B was detected in one serum. The autoantibody response was transient as it declined after a few weeks, but it reappeared after a second boost in one of the rabbits. The other animals did not respond in the same manner. The specificity of the antibodies against dsDNA was ascertained by inhibition studies employing S1 nuclease treated DNA as inhibitor. Furthermore, the dsDNA used as coating antigen was not recognized by a human reference serum with known specificity for ssDNA. The rabbit antisera did not show any reactivity to a panel of other (in this context irrelevant) autoantigens. This suggests that the anti-DNA and -histone antibodies are not a result of non-specific polyclonal B cell activation. Thus, inoculation of dsDNA viruses may represent a new model that allows us to investigate mechanisms responsible for circumvention of tolerance to self molecules.

Binding properties of human anti-DNA antibodies to cloned human DNA fragments

The DNA-anti-DNA antibody immune complexes were isolated from plasma of systemic lupus erythematosus (SLE) patients and DNA fragments separated from immune complexes were subjected to molecular cloning. The resulting recombinant DNA clones showed a molecular size of 37-79 base pairs, a high guanine and cytosine content, high frequencies of CpG dinucleotides, and palindromic sequences, and also clusters of G + C- and A + T-rich segments. These clones hybridized randomly to total human DNA. The reactivity of dsDNA antibodies, both monoclonal and polyclonal, from SLE was examined with a cloned SLE antigen DNA. A competitive inhibition assay showed that human monoclonal antibodies had at least one magnitude higher affinity to the cloned DNA than to the native DNA fragments. In order to characterize the factors that were recognized by antibodies, human G + C-rich and also A + T-rich 100 bp DNA fragments were cloned, and their base sequences determined. The antibody showed a higher affinity to the G + C-rich DNA fragment (71% G + C) than to the A + T-rich DNA fragment (46% G + C). When cytosines in CpG doublets in G + C-rich fragments were methylated (mCpG), the reactivity increased up to 100-fold. The native anti-DNA antibodies from SLE patients also showed preferential binding to G + C-rich fragments. These observations suggested that human anti-dsDNA antibodies may recognize some unique structures around the G + C regions or G + C clusters of DNA.

Reproductive failure because of autoantibodies: unexplained infertility and pregnancy wastage

Abnormal polyclonal B cell activation has been demonstrated in patients with endometriosis. To determine whether the noted B cell abnormalities were primarily a feature of the disease endometriosis or its manifestations of infertility and pregnancy wastage, we investigated antibody profiles in 26 female patients with unexplained infertility (group A) and 24 patients with unexplained pregnancy wastage (group B) but without documented endometriosis. Group A and B patients exhibited an unusual incidence of gammopathies (10 of 26 patients in group A and 11 of 24 in group B), with a majority representing immunoglobulin M gammopathies. Mean immunoglobulin M values were significantly elevated in both groups (p less than 0.03 and p less than 0.05, respectively, Student t test), whereas immunoglobulin G was significantly increased only among group B patients (p less than 0.05, Student t test). Lupus anticoagulant by tissue thromboblastin inhibition test was abnormally elevated in 2 of 26 group A and 2 of 24 group B patients. Activated partial thromboplastin time values were abnormal in only 3 of 26 group A and 2 of 24 group B women. Immunoglobulin G, immunoglobulin M, and immunoglobulin A autoantibodies to two phospholipid antigens, five histones, and four polynucleotide autoantibodies were detected in 23 of 26 (88%) group A patients and 17 of 24 (70.8%) group B patients. We conclude that some patients with unexplained infertility and pregnancy wastage suffer from polyclonal B cell activation. It is therefore tempting to speculate that autoantibody abnormalities may be causally related to infertility and pregnancy loss.

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.

Antibody binding of macromolecular DNA and RNA in the plasma of SLE patients

Plasmapheresis fluids from 20 patients with clinically active SLE, from three patients with Waldenstrom's disease, from three patients with rheumatoid arthritis, two patients with myasthenia gravis and other diseases including active systemic disorders were precipitated using polyethylene glycol 6000 (PEG). By applying ethidium bromide staining, plasma nucleic acids (PNA) could be demonstrated in PEG-precipitates of SLE patients exclusively. Purified immunoglobulins of SLE plasma precipitates were shown to form antigen-antibody complexes with PNA as demonstrated by electronmicroscopy. Further characterization of PNA by agarose gel electrophoresis revealed a molecular weight up to 20 kbp. Cesium chloride buoyant density gradients showed non-homogeneous molecules, excluding pure microbial origin. In spite of RNase digestion, the PNA contained RNA with 30-70% riboguanosine as shown by nucleoside analysis. The high amount of guanosine-rich RNA was further supported by similarities between PNA and polyriboguanylic acid in hyperchrome shifting due to thermic denaturation. HPLC analysis showed a molecular weight of ribonucleic acids of more than 60 b thus excluding mere oligonucleotides. In contrast to B-type dsDNA, PNA from SLE patients were immunogenic. Antibodies against PNA could be induced in rabbits by subcutaneous injection. The antisera thus obtained showed crossreactivity with polyriboguanylic acid and dsDNA preparations.

Immune complex assays: diagnostic and clinical application

The presence of circulating immune complexes have been described in many different human disease states but the significance of their presence has always been a subject for debate. Improvements in the methods of detecting immune complexes have demonstrated a wide degree of heterogeneity, which accounts for the difficulty in obtaining accurate and reproducible measurements, even in the same individual. Techniques for isolating individual complexes, characterizing their pathophysiological properties, and biochemically analyzing the nature of the complexed antigen are now being used to provide data that is helping to clarify the role of immune complexes in the pathogenesis of disease. In addition, such studies are also providing data which is proving that immune complexes have a potential role in immune regulation.

Immunochemistry of DNA

Since the first reports of anti-DNA antibodies in sera of patients with systemic lupus erythematosus (SLE) in 1957, studies of nucleic acid immunochemistry have grown in two directions. One has been the analysis of the specificity, the nature and the origins of these autoantibodies. The second has been exploration of anti-nucleic acid antibodies that can be induced experimentally, their specificities, and their application as biochemical reagents. Although the properties of autoantibodies and experimentally induced antibodies differ in certain respects, these two lines of research are complementary and provide important information for each other. For example, the production of autoantibodies by adjuvant-stimulated B cells yields a background that has to be considered in evaluating the specificity of weak responses to experimental nucleic acid immunogens: in turn, the possibilities and limitations of experimental immunization should be considered in evaluating possible stimuli for autoantibody production. Several aspects of nucleic acid immunochemistry have been described and evaluated in previous reviews. Following some general statements of historical perspective, this review will emphasize questions addressed and findings of about the last five years.

Antinuclear autoantibodies in sera of healthy pregnant women and their offspring

The presence of autoantibodies in the fetus has previously been investigated in the offspring of mothers with autoimmune diseases, but not in the offspring of healthy pregnant women. Employing the ELISA method, we examine four SLE-associated auto-antibodies (anti-dsDNA, anti-ssDNA, anti-poly(I), and anti-cardiolipin) in sera obtained from 196 healthy pregnant women and their offspring. All detected autoantibodies in maternal and blood cord sera were of the IgM isotype. Thirty-four maternal sera (17.3%) were positive for one or more tested autoantibodies: 16 (8.1%) for one autoantibody alone, 17 (8.6%) for two autoantibodies, and one (0.5%) for three autoantibodies; 1.5%, 5.6%, 9.6%, and 10.2% of the maternal sera were positive for autoantibodies against dsDNA, ssDNA, poly(I), and cardiolipin, respectively. In only one blood cord serum sample was an autoantibody (IgM anti-ssDNA) detected. This infant was born to a healthy seronegative mother. The finding that all offspring of IgM seropositive mothers are IgM seronegative is not surprising since maternal IgM autoantibodies do not cross the placenta. The finding of an IgM seropositive infant born to an IgM seronegative mother may indicate that the fetus is capable of self-production of autoantibodies.

Oligonucleotide linked to human gammaglobulin specifically diminishes anti-DNA antibody formation in cultured lymphoid cells from patients with systemic lupus erythematosus

In vitro studies were undertaken to determine whether the level of anti-DNA antibody can be modulated in humans with systemic lupus erythematosus (SLE). DNA fragments of different sizes, i.e., oligonucleotide (N20-30) or oligonucleotide (N10-100), were covalently linked either to human gammaglobulin (HGG) and used as tolerogens or to keyhole limpet hemocyanin and used as immunogens. Experiments were done to determine whether such tolerogens specifically diminish antibodies to denatured DNA, native DNA, or both. PBL were obtained from 87 patients with SLE, 55 of whom spontaneously produced anti-DNA antibodies in vitro. Furthermore, of these 55 test subjects 23 made anti-DNA antibodies in response to antigen challenge in vitro. Exposure of PBL to tolerogenic oligonucleotide-HGG reduced spontaneous antibody formation in 34 of the 55 patients' PBL and abrogated the in vitro-induced response in all instances. The suppression was tolerogen specific. In some SLE patients lymphoid cells were suppressed by both (N10-100)-HGG and (N20-30)-HGG, while in others lymphoid cells were suppressed by only one. Longitudinal studies of spontaneous antibody production showed that the same tolerogens consistently reduced anti-DNA antibody formation in lymphoid cells of 12 patients on several occasions over a 2-yr interval, but in 8 others the results were either variable or inconsistent. In contrast, tolerogens consistently abrogated the antigen-induced response in all 23 patients' PBL. These results obtained in humans in vitro suggest that the principle of carrier-determined tolerance could be applied as a specific therapy for SLE in vivo.

A haemolytic plaque forming assay for identifying cells producing anti-DNA antibodies

A murine hybridoma cell line (aDNA35I9) secreting anti-DNA antibodies was used as a model for haemolytic plaque forming cells in an assay where DNA-conjugated sheep red blood cells (DNA-SRBC) were used as target cells. DEAE-dextran, employed to abolish the anti-complementary activity of agar gel, completely inhibited anti-DNA plaques. This problem was solved by using agarose instead of agar. Since the occurrence of small plaques may make reading of the test difficult, it was established that plaque size could be increased by decreasing the antigen density on the target cells. Free DNA in the gel inhibited plaque formation, indicating the specificity of the assay. Spleen cells from mice of the strains MRL/MP and NZB/W which are known to develop a stage of autoimmunity, produced plaques in numbers which were correlated to the age of the mice and to the anti-DNA antibody level in serum.

Glomerular localization of circulating single-stranded DNA in mice. Dependence on the molecular weight of DNA

Although it has been observed that DNA has a high binding affinity for the glomerular basement membrane (GBM) in vitro, glomerular localization of DNA has not been demonstrated in vivo. To evaluate this possibility, after injection of 125I ssDNA of varying molecular weight (mol. wt.) to normal mice, we measured glomerular levels of DNA in vivo. Following administration of 2 mg of 125I high mol. wt. purified single stranded(ss) DNA (2-6 kilobases; 0.7-2.0 x 10(6)D) to normal mice, DNA was not detected in glomeruli, despite measurable blood levels of DNA for 72 h. In contrast, after injection of 280 micrograms of low mol. wt. 125ssDNA (160-200 bases; mol. wt. = 5.3-6.6 x 10(4)D) to normal mice, glomerular localization was observed throughout the 24-h study period despite relatively low 125IssDNA blood levels. The results of these studies indicate that free circulating DNA can bind to sites within glomeruli in vivo, and that the size of DNA is crucial for this interaction. Since low mol. wt. DNA is present in the plasma of patients with active lupus, these findings raise the possibility that DNA may bind to glomeruli and serve as a planted antigen for in situ immune complex formation with circulating anti-DNA antibodies.

Defective B-cell tolerance in New Zealand black mice. Fc receptor-independence of resistance to low-epitope-density tolerogens

Trinitrophenyl (TNP) human gamma-globulin with low-epitope-density tolerizes B cells from normal BDF1 mice in a Fc gamma receptor-dependent manner but does not tolerize B cells from preautoimmune NZB mice. In order to investigate the relationships between tolerance induction and epitope density independently of Fc gamma receptor function in these two strains, TNP conjugates of two additional thymic-independent tolerogenic carriers, D-glutamic acid-D-lysine (D-GL) and carboxymethyl cellulose (CMC), were tested. A brief pulse with low-epitope-density conjugates such as TNP4.4-D-GL rendered unfractionated or T-cell-depleted spleen cells from BDF1 but not NZB mice tolerant in a hapten-specific manner. Spleen cells from NZB mice, however, were susceptible to tolerization with TNP13.5-D-GL. NZB mice were also resistant to tolerance induction in vivo with TNP5.5-D-GL, TNP3-CMC, and TNP6-CMC, all of which tolerize BDF1 mice in vivo. Both strains were tolerized with TNP13.5-D-GL and TNP13-CMC in vivo. NZB mice were also significantly less susceptible to tolerance induction with TNP3-CMC when TNP-Ficoll was substituted for TNP Brucella abortus as the challenge antigen. These findings militate against the possibility that an Fc gamma receptor defect is the principal mechanism of resistance of NZB B cells to tolerance induction with-low-epitope density conjugates.

Immune hemolytic assay for identification of human anti-dsDNA antibodies with DNA-coated red blood cells as target cells

A hemolytic assay was developed with the primary aim of being able to identify human lymphocytes producing anti-dsDNA antibodies found in patients with systemic lupus erythematosus (SLE). The coating of sheep red-blood cells with DNA was performed after precoating the cells with poly-L-lysine. The DNA-SRBC were lysed by anti-DNA antibodies from SLE sera, and the percent hemolysis was found to correlate with the anti-DNA activity demonstrated by the Farr assay (r = 0.87). Single-stranded DNA at the surface of the coated cells could be removed after digestion with nuclease S1. The effect of the digestion was verified by SLE serum specific for single-stranded DNA. With slight modifications, the target cells may be used to determine not only the titer of anti-DNA antibodies but also the complement-consumption and immunoglobulin classes of the anti-DNA antibodies.

Murine lupus

In mice with lupus nephritis qualitative changes in anti-DNA antibodies occur, such as IgG switch and increased cationic charge, to render these antibodies pathogenic. Pathogenic anti-DNA idiotypes can be encoded by genes of a normal mouse strain such as SWR, where they remain dormant. When the normal mice are crossed with an autoimmune strain like NZB, the F1 hybrids express these idiotypes owing to defects in immunoregulation, resulting in the development of lethal glomerulonephritis.

A common anti-DNA idiotype and other autoantibodies in sera of offspring of mothers with systemic lupus erythematosus

Since the immune response in fetuses of mothers with systemic lupus erythematosus (SLE) is unknown, we investigated sera from six mothers and their paired offspring by enzyme-linked immunosorbent assay (ELISA) for the presence of a common anti-DNA idiotype (16/6 Id) and, as control, for the presence of an unrelated public idiotype of antibody to hepatitis B surface antigen (HBsAg). In addition, maternal as well as fetal sera were evaluated for the presence of antibodies to ssDNA, dsDNA, poly(I), poly (dT), RNA, cardiolipin, total histones and the presence of lupus anticoagulant. Clinically active SLE mothers showed in general increased IgG and, to a lesser extent, IgM autoantibody activity. Circulating lupus anticoagulant was detectable in clinically active mothers only. All offspring of clinically active SLE mothers showed increased IgG autoantibodies to a variety of antigens, while IgM antibodies were detected in only one fetus. In contrast, fetuses of clinically inactive mothers showed only minor IgG activity. Common anti-DNA-idiotype (16/6 Id) activity also correlated with disease activity in both maternal and fetal compartments. One clinically active mother was 16/6-negative; her offspring was, however, positive, indicating de novo production of the idiotype by the fetus. In contrast, a control anti-HBsAg idiotype was not detected in either maternal or fetal sera. It therefore appears that offspring of clinically active SLE mothers serologically reflect maternal disease activity. Furthermore, autoantibodies and common idiotype of autoantibodies can be found within the fetal compartment even in the absence of such antibodies in the maternal serum. Discrepancies between mothers and offspring in IgM-autoantibody levels and the presence of new idiotypes in fetuses are indicative of fetal de novo autoantibody production.

Studies of gut and hepatic metabolism in conscious rabbits

The present study was designed to develop the techniques for chronic catheterization of the hepatic and portal venous circulation in conscious rabbits and to apply these techniques to a study of hepatic metabolism in this species. Experiments were made after an 18-h fast and for 4 h after the initial feeding. Measurements of arteriovenous differences of substrates were combined with measurements of hepatic and gastrointestinal blood flow. Hepatic glucose production was suppressed by 60% at 1 h and had returned to control levels by 4 h. The hepatic uptake of lactate declined slightly at 1 h and had returned to control level 2 h after the meal. There was a marked and rapid fall in hepatic ketone body output after refeeding. Although amino acid concentrations displayed a transient increase 1 h after the meal, only the arterial concentration of branched-chain amino acids remained significantly elevated for 4 h. The total hepatic uptake of the gluconeogenic amino acids (alanine, serine, threonine) remained constant. Refeeding resulted in a doubling of arterial insulin concentrations at 1 h followed by a progressive decline over the next 3 h. It is concluded that in rabbits fed a mixed meal partial suppression of hepatic glucose output is mainly due to a decline in glycogenolysis rather than a decrease in gluconeogenesis, shortly after refeeding the liver is able to virtually shut off its ketone body production, the major gluconeogenic precursors (lactate, alanine, glycine, serine, and threonine) may contribute to approximately 40% of the glucose release.(ABSTRACT TRUNCATED AT 250 WORDS)