The influence of variable-region somatic mutations on the specificity and pathogenicity of murine monoclonal anti-DNA antibodies

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

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

Type 1 diabetes pathogenesis and the role of inhibitory receptors in islet tolerance

Type 1 diabetes (T1D) affects over a million Americans, and disease incidence is on the rise. Despite decades of research, there is still no cure for this disease. Exciting beta cell replacement strategies are being developed, but in order for such approaches to work, targeted immunotherapies must be designed. To selectively halt the autoimmune response, researchers must first understand how this response is regulated and which tolerance checkpoints fail during T1D development. Herein, we discuss the current understanding of T1D pathogenesis in humans, genetic and environmental risk factors, presumed roles of CD4+ and CD8+ T cells as well as B cells, and implicated autoantigens. We also highlight studies in non-obese diabetic mice that have demonstrated the requirement for CD4+ and CD8+ T cells and B cells in driving T1D pathology. We present an overview of central and peripheral tolerance mechanisms and comment on existing controversies in the field regarding central tolerance. Finally, we discuss T cell- and B cell-intrinsic tolerance mechanisms, with an emphasis on the roles of inhibitory receptors in maintaining islet tolerance in humans and in diabetes-prone mice, and strategies employed to date to harness inhibitory receptor signaling to prevent or reverse T1D.

Chance, genetics, and the heterogeneity of disease and pathogenesis in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a remarkably complex and heterogeneous systemic autoimmune disease. Disease complexity within individuals and heterogeneity among individuals, even genetically identical individuals, is driven by stochastic execution of a complex inherited program. Genome-wide association studies (GWAS) have progressively improved understanding of which genes are most critical to the potential for SLE and provided illuminating insight about the immune mechanisms that are engaged in SLE. What initiates expression of the genetic program to cause SLE within an individual and how that program is initiated remains poorly understood. If we extrapolate from all of the different experimental mouse models for SLE, we can begin to appreciate why SLE is so heterogeneous and consequently why prediction of disease outcome is so difficult. In this review, we critically evaluate extrinsic versus intrinsic cellular functions in the clearance and elimination of cellular debris and how dysfunction in that system may promote autoimmunity to nuclear antigens. We also examine several mouse models genetically prone to SLE either because of natural inheritance or inheritance of induced mutations to illustrate how different immune mechanisms may initiate autoimmunity and affect disease pathogenesis. Finally, we describe the heterogeneity of disease manifestations in SLE and discuss the mechanisms of disease pathogenesis with emphasis on glomerulonephritis. Particular attention is given to discussion of how anti-DNA autoantibody initiates experimental lupus nephritis (LN) in mice.

Anti-DNA autoantibodies initiate experimental lupus nephritis by binding directly to the glomerular basement membrane in mice

The strongest serological correlate for lupus nephritis is antibody to double-stranded DNA although the mechanism by which anti-DNA antibodies initiate lupus nephritis is unresolved. Most recent reports indicate that anti-DNA must bind chromatin in the glomerular basement membrane or mesangial matrix to form glomerular deposits. Here we determined whether direct binding of anti-DNA antibody to glomerular basement membrane is critical to initiate glomerular binding of anti-DNA in experimental lupus nephritis. Mice were co-injected with IgG monoclonal antibodies or hybridomas with similar specificity for DNA and chromatin but different IgG subclass and different relative affinity for basement membrane. Only anti-DNA antibodies that bound basement membrane bound to glomeruli, activated complement, and induced proteinuria whether injected alone or co-injected with a non-basement membrane-binding anti-DNA antibody. Basement membrane-binding anti-DNA antibodies co-localized with heparan sulfate proteoglycan in glomerular basement membrane and mesangial matrix but not with chromatin. Thus, direct binding of anti-DNA antibody to antigens in the glomerular basement membrane or mesangial matrix may be critical to initiate glomerular inflammation. This may accelerate and exacerbate glomerular immune complex formation in human and murine lupus nephritis.

Autoantibodies: Focus on anti-DNA antibodies

Ever since the days of Ehrlich and the birth of humoral immunity, self-reactivity or 'horror autotoxicus' as referred to by Paul Ehrlich, has been of great concern. For instance, in patients with the autoimmune disease systemic lupus erythematosus (SLE), anti-nuclear and anti-DNA antibodies have been recognized for many years. Despite this, the exact mechanism as to how the immune system fails to protect the individual and allows these autoantibodies to develop in this and other systemic autoimmune diseases remains uncertain. So how can we explain their presence? Evidence suggests that B cells expressing autoreactive antibodies do not normally arise but rather undergo negative selection as they develop. In light of this, it might seem contradictory that not all autoreactive B cell clones are eliminated, although this may not even be the intention since autoantibodies are also found in healthy individuals and may even protect from autoimmunity. Here, we will discuss autoantibodies, in particular those recognizing DNA, with regard to their reactivity and their potentially pathogenic or protective properties.

Exposure of chromatin and not high affinity for dsDNA determines the nephritogenic impact of anti-dsDNA antibodies in (NZBxNZW)F1 mice

Recent studies have demonstrated that the nephritogenicity of antibodies to dsDNA and nucleosomes confers to binding of glomerular membrane-associated nucleosomes, and not to cross-reacting glomerular antigens. There is no known parameter that determines antibody pathogenicity aside from specificity for dsDNA/nucleosomes, and systemic lupus erytheomatosus (SLE) patients may have high titer anti-dsDNA antibodies irrespective whether they have lupus nephritis or not. One parameter may be antibody affinity, as theoretically only high affinity antibodies may bind in vivo in a stable way. This was analyzed in (NZB x NZW)F1 mice with full-blown lupus nephritis. These mice had serum antibodies to dsDNA, and IgG autoantibodies bound in situ in glomerular membrane-associated electron dense structures as determined by immune electron microscopy (IEM). Intrinsic affinity of purified circulating and glomerular IgG anti-dsDNA antibodies was determined by surface plasmon resonance. The results demonstrate that affinity of glomerular-bound anti-dsDNA antibodies was higher than for those in circulation. However, affinity of glomerular in situ-bound antibodies from different mice varied considerably, from K(D) in the range from 10(- 8) to 10(- 13). These results indicate that antibody affinity is not a decisive pathogenic factor, but rather that availability of chromatin fragments may be the factor that determines whether an anti-dsDNA antibody binds in glomeruli or not.

Blunted Humoral Response to Influenza Vaccination in Patients Exposed to Zidovudine plus Trimethoprim-Sulfamethoxazole

STUDY OBJECTIVES

To determine as proof of principle the effect of combination exposure to zidovudine plus trimethoprim-sulfamethoxazole (TMP-SMX) on humoral immune responses to influenza vaccination in patients with human immunodeficiency virus (HIV).

DESIGN

Prospective, open-label trial.

SETTING

University-affiliated infectious diseases outpatient clinic.

PATIENTS

Twenty-three HIV-infected adults receiving antiretroviral therapy, with CD4+ cell counts greater than 350 cells/mm3 and undetectable viral loads.

INTERVENTION

Patients were assigned to one of four treatment groups: zidovudine (6 patients), TMP-SMX (7), zidovudine plus TMP-SMX (5), or neither drug (5); TMP-SMX was given as a 28-day course. Patients were subsequently immunized with the yearly influenza vaccine, and humoral responses were compared among groups 20-24 days after vaccination.

MEASUREMENTS AND MAIN RESULTS

Antibody responses to influenza A and B were measured, and total and activated T and B cell percentages in the peripheral blood were determined. Mean influenza B-specific serum immunoglobulin (Ig)G titers were significantly lower in patients receiving TMP-SMX alone (0.98 +/- 0.60 reference value, p=0.010) or the combination of zidovudine plus TMP-SMX (0.73 +/- 0.29 reference value, p=0.003) compared with those receiving neither drug (1.95 +/- 0.38 reference value). This corresponded to a significantly lower percentage of patients in the combination group that achieved immunoprotective titers to influenza B compared with the group who received neither drug (control group; 20% vs 100%, p=0.048). In addition, the relationship between serum IgG titer and CD4+ cell count was statistically significantly different for patients exposed to zidovudine plus TMP-SMX versus control patients for both influenza A and B (F statistics 8.72 and 11.70, respectively, compared with critical F value 7.26 for p<0.025). Likewise, the relationship between influenza B serum IgG and CD4+ cell count was different among patients who received TMP-SMX versus those who did not receive TMP-SMX (F statistic 5.95 compared with critical F value 4.56 for p<0.025). No significant differences were observed among T and B cell percentages in the blood.

CONCLUSION

Combination exposure to zidovudine plus TMP-SMX causes a clinically significant suppression of humoral immune responses to influenza vaccination in HIV-infected patients.

First clinical trials of a new heteropolymer technology agent in normal healthy volunteers and patients with systemic lupus erythematosus: safety and proof of principle of the antigen-heteropolymer ETI-104

BACKGROUND

The heteropolymer technology was developed to remove pathogens from the circulation.

OBJECTIVES

To evaluate the safety and tolerability of a single administration and to establish proof of principle for ETI-104 in normal healthy volunteers (NHV) and patients with systemic lupus erythematosus (SLE) METHODS: The drug was given intravenously to 11 NHV and six patients with SLE. Over 28 days, vital signs were noted, a haematological and chemical analysis of blood and urine was carried out, and adverse events were recorded. CR1 receptor numbers, the ability of antigen based heteropolymers to bind to red blood cells (RBCs), and the clearance of high avidity and total anti-dsDNA antibodies were measured by Farr assays and FACS analysis.

RESULTS

No safety measure differed significantly from normal in both groups; no drug related serious adverse events occurred. ETI-104 rapidly bound to RBCs in NHV and patients with SLE. Binding of the drug to RBCs of patients with SLE also caused a rapid reduction of circulating anti-dsDNA antibodies in the plasma 15 minutes after administration, with a maximum reduction of 55% (range 43-62). At 28 days statistically significant decreases were maintained in three patients, while in the other three the values had returned to baseline levels.

CONCLUSION

These clinical trials established the safety and the proof of principle of the new immunoconjugate ETI-104. This provides the basis for further development of this technology for numerous indications-for example, therapeutic options for autoimmune diseases or viral and bacterial infections.

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

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

Effect of genetic deficiency of terminal deoxynucleotidyl transferase on autoantibody production and renal disease in MRL/lpr mice

Terminal deoxynucleotidyl transferase (TdT) places non-template-coded nucleotides (N additions) in the VH CDR3 of T cell receptors and immunoglobulins. Amino acids coded for by N additions are important in autoantibody binding of dsDNA in lupus. We hypothesized that a genetic lack of TdT would modulate disease in lupus-prone mice. To test this hypothesis, we derived TdT-deficient MRL/lpr mice. Serum levels of anti-dsDNA antibodies and anti-dsDNA producing splenocytes were significantly lower in the TdT(-) versus TdT(+) littermates. Albuminuria, glomerular IgG deposition, and pathologic renal disease were significantly reduced in the TdT(-) mice. Sequence analysis of anti-dsDNA hybridomas derived from TdT(-) mice revealed a lack of N additions, short VH CDR3 segments, yet the presence of VH CDR3 arginines. Thus, the genetic absence of TdT reduces autoantibody production and clinical disease in MRL/lpr mice, confirming the importance of N additions in the autoimmune response in these mice.

Identification of an antigen-specific B cell population

The difficulty in characterizing antigen-specific B cells that arise in the native B cell repertoire has been a formidable obstacle to understanding both protective and pathogenic antibody responses. We have developed a tetramer-based technique for identifying antigen-specific B cells. Biotin-labeled antigen is made tetrameric by interaction with streptavidin. The enhanced avidity of this antigenic compound for the B cell membrane permits the visualization, characterization and isolation of antigen-specific B cells.

Molecular identification of pathogenetic IdLNF+1 autoantibody idiotypes derived from the NZBxSWR F1 model for systemic lupus erythematosus

The acceleration of nephritis in SNF(1) mice by CD4(+) T-cell clones reactive with a nephritogenic idiotype, Id(LN)F(1) [1], as well as the ability of anti-Id(LN)F(1) antisera to down-regulate the production of Id(LN)F(+)(1) immunoglobulin (Ig) in vivo and delay nephritis [2], suggests that dysregulation of this idiotype may contribute to the development of SNF(1) nephritis. Herein, we show that a monoclonal Id(LN)F(1)-expressing antibody, 540, significantly (P< or = 0.01) stimulated Id(LN)F(1)-reactive T-cell clones B6 and D2 to proliferate, while other Id(LN)F+1 antibodies did not. Further, injection of 540-producing hybridoma cells into nonautoimmune (SWRxBalb/c)F(1) mice resulted in the deposition of Id(LN)F(+)(1) Ig in the kidneys, in a pattern indicative of early nephritis. To identify the pathogenetic Id(LN)F(1) epitope(s) at the molecular level, we compared the deduced amino acid sequences of the heavy and light chain variable regions of pathogenetic and non-pathogenetic Id(LN)F(1)-expressing Igs 540, 317, and 533. Two overlapping peptides derived from the V(H) sequence of 540 (aa 54-66 and 62-73), which both contain the triple basic amino acid motif K(X)K(X)K, stimulated SNF(1) T cells and T-cell clones B6 and D2. These results further support the involvement of a subset of Id(LN)F(1)-expressing Ig in SNF(1) nephritis.

Genetic dissection of lupus pathogenesis: a recipe for nephrophilic autoantibodies

Sle1 and Sle3 are 2 loci that confer susceptibility to lupus nephritis in the NZM2410 strain of mice. Our previous work has shown that B6.NZMc1 mice, congenic for Sle1, exhibit loss of tolerance to chromatin but do not develop any pathogenic autoantibodies or disease. B6.NZMc7 mice, congenic for Sle3, exhibit low-grade polyclonal B- and T-cell activation, elevated CD4/CD8 ratios, and mildly penetrant glomerulonephritis. In contrast to these monocongenics, the present study reveals that B6.NZMc1|c7 mice, bicongenic for Sle1 and Sle3, exhibit splenomegaly, significantly expanded populations of activated B and CD4(+) T cells, and a robust, variegated IgG autoantibody response targeting multiple components of chromatin (including double-stranded DNA), intact glomeruli, and basement membrane matrix antigens. As one might predict, these mice, particularly the females, exhibit highly penetrant glomerulonephritis. These findings lend strong support to a two-step epistatic model for the formation of pathogenic, nephrophilic autoantibodies in lupus. Whereas loci such as Sle1 may serve to breach tolerance to chromatin, full-blown pathogenic maturation of the autoantibody response appears to require additional input from other loci (such as Sle3) and gender-based factors.

Maternal Ig Mediates Neonatal Tolerance in Rheumatoid Factor Transgenic Mice but Tolerance Breaks Down in Adult Mice

We have recently demonstrated that B cell deletion occurs in the bone marrow of IgHa high affinity anti-IgG2aa (RF) transgenic mice. Here we demonstrate via genetic crosses that the source of IgG2a is the mother, thus establishing a transplacental mechanism that ensures tolerance to developmentally expressed Ags. Since maternal IgG can mediate tolerance in young mice, whether tolerance is maintained or, instead, autoimmunity ensues after weaning was investigated. We find that deletion remits abruptly in these RF transgenic mice beginning at 2 to 3 wk postweaning, and some degree of autoreactivity can be observed thereafter for weeks to months. The mechanism of sustained expression of autoreactive RF B cells in normal mice is unclear as yet, but a plausible mechanism is that once self-reactive cells are present, the antibody they secrete markedly reduces the autoantigen levels, presumably allowing further development, rather than deletion, of newly arising B lineage cells. The phenotype of these RF transgenic mice suggests a positive feedback mechanism that tends to perpetuate autoimmunity once it has been established. If such a mechanism were to exist in autoimmune animals, it could have important implications for the establishment and maintenance of B and T cell tolerance in chronic autoimmune diseases.

Identification and characterization of a cell membrane nucleic acid channel

We have identified a 45-kDa protein purified from rat renal brush border membrane that binds short single-stranded nucleic acid sequences. This activity was purified, reconstituted in proteoliposomes, and then fused with model planar lipid bilayers. In voltage-clamp experiments, the reconstituted 45-kDa protein functioned as a gated channel that allows the passage of nucleic acids. Channel activity was observed immediately after addition of oligonucleotide. Channel activity was not observed in the absence of purified protein or of oligonucleotide or when protein was heat-inactivated prior to forming proteoliposomes. In the presence of symmetrical buffered solution and oligonucleotide, current passed linearly over the range of holding potentials tested. Conductance was 10.4 +/- 0.4 picosiemens (pS) and reversal potential was 0.2 +/- 1.7 mV. There was no difference in channel conductance or reversal potential between phosphodiester and phosphorothioate oligonucleotides. Ion-substitution experiments documented a shift in reversal potential only when a concentration gradient for oligonucleotide was established, indicating that movement of oligonucleotide alone was responsible for current. Movement of oligonucleotide across the bilayer was confirmed by using 32P-labeled oligonucleotides. Channel open probability decreased significantly in the presence of heparan sulfate. These studies provide evidence for a cell surface channel that conducts nucleic acids.

Lupus-like nephrotropic autoantibodies in non-autoimmune mice harboring an anti-basement membrane/anti-DNA Ig heavy chain transgene

Autoantibodies target a diverse group of tissue antigens in human and experimental autoimmune nephritis. The proximal events that generate and regulate these various pathogenic Ab remain obscure. To examine the origins and fate in normal mice of autoantibodies reactive with renal basement membrane antigen, we established mice transgenic for an IgM H chain encoding an unmutated nephrotropic V region, termed LamH, derived from an MRL/lpr mouse and directed against basement membrane laminin. We previously demonstrated that in vitro transfectants combining LamH-Cmu with unmutated L chains generate distinct nephrotropic autoantibodies. Herein we report in vivo reconstruction of diverse pathogenic autoreactivity by association of LamH-Cmu with endogenous L chains. Progeny of one founder, termed M7, express a distinct phenotype characterized by minimal B cell mIgM and spontaneous production of LamH-Cmu autoreactivity. Similar Ab were not recovered from two phenotypically distinct transgenic lines expressing abundant transgene mIgM. The results suggest that lupus-like autoantibodies are readily generated in the normal genetic background by random recombinatorial events in the absence of mutation and that these Ab may contribute to disease if normal regulation is disturbed.

Heterogeneity and clinical significance of glomerular-binding antibodies in systemic lupus erythematosus

We used an ELISA employing extracts of human glomerular basement membrane (GBM) to detect, characterize, and evaluate the clinical significance of glomerular-binding IgG in patients with SLE nephritis. Most patients with SLE nephritis exhibited GBM-binding IgG, although many patients with active nonrenal SLE or symptomatic, drug-induced lupus had similar reactivity, albeit at lower levels. IgG binding to GBM in SLE nephritis patients was decreased by DNase pretreatment of GBM, restored after DNase with nuclear antigens (most notably with nucleosomes), inhibited by exogenous nuclear antigens (particularly nucleosomes), but unaffected by exposure of serum to DNase/high ionic strength. The characteristics of IgG binding to GBM largely paralleled the patients' underlying autoimmune response, which was dominated either by antibodies to DNA/nucleosomes or to nucleosomes alone. Binding of lupus sera to nonrenal extracellular matrix (even with nucleosomes) was not equivalent to GBM. Collagenase pretreatment of GBM variably decreased IgG binding, depending on the level and type of binding. SLE nephritis patients with high levels of GBM-binding IgG exhibited more severe disease clinically, but the same renal histopathology, as patients with lower levels. The level of GBM-binding IgG at presentation did not predict the therapeutic response, but decreased in responders to therapy. In sum, glomerular-binding IgG in lupus nephritis binds to epitopes on chromatin, which adheres to GBM in part via collagen. These autoantibodies appear necessary, but not sufficient, for the development of nephritis, and correlate with clinical rather than histopathologic parameters of disease activity.

Differences in V kappa gene utilization and VH CDR3 sequence among anti-DNA from C3H-lpr mice and lupus mice with nephritis

To investigate the molecular properties of anti-DNA from lpr mice that express high levels of anti-DNA without immune-mediated nephritis, the sequences of VH and V kappa genes encoding 11 monoclonal anti-DNA antibodies derived from C3H-lpr/lpr (C3H-lpr) mice were studied. All of the C3H-lpr monoclonal anti-DNA bound single-stranded DNA while five also bound double-stranded DNA. Two of the hybridomas were clonally related as determined by Southern analysis and sequencing. Sequence analysis of C3H-lpr anti-DNA revealed the use of VH genes that encode anti-DNA from the MRL-lpr/lpr and (NZB X NZW) F1 mouse models of lupus, although differences occurred in the VH CDR3 amino acid content. In contrast, the V kappa genes from C3H-lpr mice lacked significant identity with previously reported V kappa genes for anti-DNA from lupus models. These results indicate that anti-DNA from C3H-lpr mice differ from anti-DNA from lupus mice with nephritis in patterns of V gene expression and suggest a molecular basis for the lack of pathogenicity of anti-DNA in these mice.

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 murine anti-DNA autoantibodies. II. Genetic analysis and pathogenicity

Although anti-DNA autoantibodies are an important hallmark of lupus, the relationships among anti-DNA structure, reactivity, and pathogenicity have not been fully elucidated. To further investigate these relationships, we compare the variable genes and primary structure of eight anti-DNA mAbs previously obtained from an MRL/MpJ-lpr/lpr mouse along with the ability of three representative mAbs to induce nephritis in nonautoimmune mice using established adoptive transfer protocols. One monospecific anti-single-stranded (ss) DNA (11F8) induces severe diffuse proliferative glomerulonephritis in nonautoimmune mice whereas another anti-ssDNA with apparently similar in vitro binding properties (9F11) and an anti-double-stranded DNA (4B2) are essentially benign. These results establish a murine model of anti-DNA-induced glomerular injury resembling the severe nephritis seen in lupus patients and provide direct evidence that anti-ssDNA can be more pathogenic than anti-double-stranded DNA. In vitro binding experiments using both protein-DNA complexes and naive kidney tissue indicate that glomerular localization of 11F8 may occur by recognition of a planted antigen in vivo. Binding to this antigen is DNase sensitive which suggests that DNA or a DNA-containing molecule is being recognized.