Molecular and structural analysis of nuclear localizing anti-DNA lupus antibodies

Pin1-Catalyzed Conformation Changes Regulate Protein Ubiquitination and Degradation

The unique prolyl isomerase Pin1 binds to and catalyzes cis-trans conformational changes of specific Ser/Thr-Pro motifs after phosphorylation, thereby playing a pivotal role in regulating the structure and function of its protein substrates. In particular, Pin1 activity regulates the affinity of a substrate for E3 ubiquitin ligases, thereby modulating the turnover of a subset of proteins and coordinating their activities after phosphorylation in both physiological and disease states. In this review, we highlight recent advancements in Pin1-regulated ubiquitination in the context of cancer and neurodegenerative disease. Specifically, Pin1 promotes cancer progression by increasing the stabilities of numerous oncoproteins and decreasing the stabilities of many tumor suppressors. Meanwhile, Pin1 plays a critical role in different neurodegenerative disorders via the regulation of protein turnover. Finally, we propose a novel therapeutic approach wherein the ubiquitin-proteasome system can be leveraged for therapy by targeting pathogenic intracellular targets for TRIM21-dependent degradation using stereospecific antibodies.

Autoantibodies from SLE patients induce programmed cell death in murine fibroblast cells through interaction with TNFR1 receptor

Various pathological processes are known to be associated with the production of IgG autoantibodies, which have high affinity for self-antigens and often cause tissue injury and the development of autoimmune diseases. However, the mechanism of their cytotoxic activity is not clearly understood yet. Here, we have shown that the action of these autoantibodies on cells expressing TNFR1 (the cell surface receptor for TNFα) can cause both caspase-dependent apoptosis and necroptosis of these cells, with suppression of apoptosis resulting in switching to RIP1-dependent necroptosis. Analysis of necroptotic mechanisms has shown that a critical point of necroptosis is phosphorylation of RIP1 and RIP3 kinases, which is followed by the involvement of lysosomes and mitochondria in this process. The induction of cytotoxicity is initiated by the interaction of autoantibodies with TNFR1, and autoantibodies can therefore be regarded as a new functional ligand for this receptor. The innate immunity protein Tag7 (PGLYRP1) described in our recent studies is also a ligand for TNFR1 and competes with autoantibodies for binding with it. Supposedly, the cytotoxic effect of autoantibodies is one of the factors responsible for autoimmune diseases that lead to tissue injury.

Single-Molecule Interactions of a Monoclonal Anti-DNA Antibody with DNA

Interactions of DNA with proteins are essential for key biological processes and have both a fundamental and practical significance. In particular, DNA binding to anti-DNA antibodies is a pathogenic mechanism in autoimmune pathology, such as systemic lupus erythematosus. Here we measured at the single-molecule level binding and forced unbinding of surface-attached DNA and a monoclonal anti-DNA antibody MRL4 from a lupus erythematosus mouse. In optical trap-based force spectroscopy, a microscopic antibodycoated latex bead is trapped by a focused laser beam and repeatedly brought into contact with a DNA-coated surface. After careful discrimination of non-specific interactions, we showed that the DNA-antibody rupture force spectra had two regimes, reflecting formation of weaker (20-40 pN) and stronger (>40 pN) immune complexes that implies the existence of at least two bound states with different mechanical stability. The two-dimensional force-free off-rate for the DNA-antibody complexes was ~2.2 × 10^-3 s^-1, the transition state distance was ~0.94 nm, the apparent on-rate was ~5.26 s^-1, and the stiffness of the DNA-antibody complex was characterized by a spring constant of 0.0021 pN/nm, suggesting that the DNA-antibody complex is a relatively stable, but soft and deformable macromolecular structure. The stretching elasticity of the DNA molecules was characteristic of single-stranded DNA, suggesting preferential binding of the MRL4 antibody to one strand of DNA. Collectively, the results provide fundamental characteristics of formation and forced dissociation of DNA-antibody complexes that help to understand principles of DNA-protein interactions and shed light on the molecular basis of autoimmune diseases accompanied by formation of anti-DNA antibodies.

TRIM21 and the Function of Antibodies inside Cells

Therapeutic antibodies targeting disease-associated antigens are key tools in the treatment of cancer and autoimmunity. So far, therapeutic antibodies have targeted antigens that are, or are presumed to be, extracellular. A largely overlooked property of antibodies is their functional activity inside cells. The diverse literature dealing with intracellular antibodies emerged historically from studies of the properties of some autoantibodies. The identification of tripartite motif (TRIM) 21 as an intracellular Fc receptor linking cytosolic antibody recognition to the ubiquitin proteasome system brings this research into sharper focus. We review critically the research related to intracellular antibodies, link this to the TRIM21 effector mechanism, and highlight how this work is exposing the previously restricted intracellular space to the potential of therapeutic antibodies.

Impacts of Anti-dsDNA Antibody on In Vitro Fertilization-Embryo Transfer and Frozen-Thawed Embryo Transfer

Our purpose is to explore whether anti-dsDNA antibody, which was demonstrated to enter living cells and induced apoptosis, could adversely affect reproductive outcomes. A total of 259 women receiving the in vitro fertilization-embryo transfer (IVF) cycle were enrolled in this study, including 52 women with positive ANA and anti-dsDNA (ANA+/anti-dsDNA+ group), 86 women with positive ANA and negative anti-dsDNA (ANA+/anti-dsDNA− group), and 121 women with negative ANA and anti-dsDNA (ANA−/anti-dsDNA− group). 136 nonpregnant women among 259 patients in the IVF-ET cycle were enrolled in the hormone replacement therapy frozen-thawed embryo transfer (HRT-TET) cycle. We compared basic characters and IVF outcomes among three groups in fresh embryo transfer and frozen-thawed embryo transfer cycle, respectively. The number of retrieved oocytes, available embryos, and high-quality embryos in the ANA+/anti-dsDNA+ group was lower than those in the other two groups in the fresh embryo transfer cycle. The rates of fertilization, implantation, and clinical pregnancy in the ANA+/anti-dsDNA+ group were the lowest, while the early miscarriage rate was the highest in the ANA+/anti-dsDNA+ group both in the fresh embryo transfer cycle and in the frozen-thawed embryo transfer cycle. Our data suggested that anti-dsDNA antibody may be the essential marker for defective oocytes or embryos in infertile women with any type of ANA.

Identification of novel antigens contributing to autoimmunity in cardiovascular diseases

In myocarditis and dilated cardiomyopathy (DCM) patients the immune system may play an important role in disease progression. In this study, we aimed to identify new antigens as a target for autoimmune response that might play a crucial role in these diseases. Therefore, a peptide-array was used to investigate antibody binding profiles in patients with autoimmune myocarditis or DCM compared to healthy controls and thus to identify disease relevant antigens. To analyze the pathogenicity of the identified antigens, an experimental autoimmune myocarditis (EAM) model was used. Hereby, 3 peptide sequences, derived from myosin-binding-protein-C (MYBPC) fast-type, RNA-binding-protein 20 (RBM20), and dystrophin, showed pathogenic effects on the myocardium of mice. In summary, 3 potentially cardiopathogenic peptides (MYBPC fast-type, RBM20, dystrophin) were identified. Thus, this study could serve as a basis for future investigations aimed at determining further antigens leading to pathogenic effects on the myocardium of DCM as well as myocarditis patients.

An anti-DNA antibody prefers damaged dsDNA over native

DNA-protein interactions, including DNA-antibody complexes, have both fundamental and practical significance. In particular, antibodies against double-stranded DNA play an important role in the pathogenesis of autoimmune diseases. Elucidation of structural mechanisms of an antigen recognition and interaction of anti-DNA antibodies provides a basis for understanding the role of DNA-containing immune complexes in human pathologies and for new treatments. Here we used Molecular Dynamic simulations of bimolecular complexes of a segment of dsDNA with a monoclonal anti-DNA antibody's Fab-fragment to obtain detailed structural and physical characteristics of the dynamic intermolecular interactions. Using a computationally modified crystal structure of a Fab-DNA complex (PDB: 3VW3), we studied in silico equilibrium Molecular Dynamics of the Fab-fragment associated with two homologous dsDNA fragments, containing or not containing dimerized thymine, a product of DNA photodamage. The Fab-fragment interactions with the thymine dimer-containing DNA was thermodynamically more stable than with the native DNA. The amino acid residues constituting a paratope and the complementary nucleotide epitopes for both Fab-DNA constructs were identified. Stacking and electrostatic interactions were shown to play the main role in the antibody-dsDNA contacts, while hydrogen bonds were less significant. The aggregate of data show that the chemically modified dsDNA (containing a covalent thymine dimer) has a higher affinity toward the antibody and forms a stronger immune complex. These findings provide a mechanistic insight into formation and properties of the pathogenic anti-DNA antibodies in autoimmune diseases, such as systemic lupus erythematosus, associated with skin photosensibilization and DNA photodamage.

A nucleic-acid hydrolyzing single chain antibody confers resistance to DNA virus infection in hela cells and C57BL/6 mice

Viral protein neutralizing antibodies have been developed but they are limited only to the targeted virus and are often susceptible to antigenic drift. Here, we present an alternative strategy for creating virus-resistant cells and animals by ectopic expression of a nucleic acid hydrolyzing catalytic 3D8 single chain variable fragment (scFv), which has both DNase and RNase activities. HeLa cells (SCH7072) expressing 3D8 scFv acquired significant resistance to DNA viruses. Virus challenging with Herpes simplex virus (HSV) in 3D8 scFv transgenic cells and fluorescence resonance energy transfer (FRET) assay based on direct DNA cleavage analysis revealed that the induced resistance in HeLa cells was acquired by the nucleic acid hydrolyzing catalytic activity of 3D8 scFv. In addition, pseudorabies virus (PRV) infection in WT C57BL/6 mice was lethal, whereas transgenic mice (STG90) that expressed high levels of 3D8 scFv mRNA in liver, muscle, and brain showed a 56% survival rate 5 days after PRV intramuscular infection. The antiviral effects against DNA viruses conferred by 3D8 scFv expression in HeLa cells as well as an in vivo mouse system can be attributed to the nuclease activity that inhibits viral genome DNA replication in the nucleus and/or viral mRNA translation in the cytoplasm. Our results demonstrate that the nucleic-acid hydrolyzing activity of 3D8 scFv confers viral resistance to DNA viruses in vitro in HeLa cells and in an in vivo mouse system.

Most strategies for developing virus-resistant transgenic cells and animals are based on the concept of virus-derived resistance, in which dysfunctional virus-derived products are expressed to interfere with the pathogenic process of the virus in transgenic cells or animals. However, these viral protein targeting approaches are limited because they only target specific viruses and are susceptible to viral mutations. We describe a novel strategy that targets the viral genome itself, rather than viral gene products, to generate virus-resistant transgenic cells and animals. We functionally expressed 3D8 scFv which has both DNase and RNase activities, in HeLa cells and transgenic mice. We found that the transgenic cells and mice acquired complete resistance to two DNA viruses (HSV and PRV) without accumulating the virus, and showed delayed onset of disease symptoms. The antiviral effects against DNA viruses demonstrated in this study were caused by (1) DNase activity of 3D8 scFv in the nucleus, which inhibited DNA replication or RNA transcription and (2) 3D8 scFv RNase activity in the cytoplasm, which blocked protein translation. This strategy may facilitate control of a broad spectrum of viruses, including viruses uncharacterized at the molecular level, regardless of their genome type or variations in gene products.

A Novel Method for Real-Time, Continuous, Fluorescence-Based Analysis of Anti-DNA Abzyme Activity in Systemic Lupus

Systemic Lupus Erythematosus (SLE) is an autoimmune disease characterized by the production of antibodies against a variety of self-antigens including nucleic acids. These antibodies are cytotoxic, catalytic (hydrolyzing DNA, RNA, and protein), and nephritogenic. Current methods for investigating catalytic activities of natural abzymes produced by individuals suffering from autoimmunity are mostly discontinuous and often employ hazardous reagents. Here we demonstrate the utility of dual-labeled, fluorogenic DNA hydrolysis probes in highly specific, sensitive, continuous, fluorescence-based measurement of DNA hydrolytic activity of anti-ssDNA abzymes purified from the serum of patients suffering from SLE. An assay for the presence and levels of antibodies exhibiting hydrolytic activity could facilitate disease diagnosis, prediction of flares, monitoring of disease state, and response to therapy. The assay may allow indirect identification of additional targets of anti-DNA antibodies and the discovery of molecules that inhibit their activity. Combined, these approaches may provide new insights into molecular mechanisms of lupus pathogenesis.

Catalytic antibodies: balancing between Dr. Jekyll and Mr. Hyde

The immunoglobulin molecule is a perfect template for the de novo generation of biocatalytic functions. Catalytic antibodies, or abzymes, obtained by the structural mimicking of enzyme active sites have been shown to catalyze numerous chemical reactions. Natural enzyme analogs for some of these reactions have not yet been found or possibly do not exist at all. Nowadays, the dramatic breakthrough in antibody engineering and expression technologies has promoted a considerable expansion of immunoglobulin's medical applications and is offering abzymes a unique chance to become a promising source of high-precision "catalytic vaccines." At the same time, the discovery of natural abzymes on the background of autoimmune disease revealed their beneficial and pathogenic roles in the disease progression. Thus, the conflicting Dr. Jekyll and Mr. Hyde protective and destructive essences of catalytic antibodies should be carefully considered in the development of therapeutic abzyme applications.

Cell-penetrating autoantibody induces caspase-mediated apoptosis through catalytic hydrolysis of DNA

In the present study, we investigated the substrate specificity of catalytic activity of a cytotoxic anti-DNA monoclonal autoantibody, G1-5, which was obtained from an MRL-lpr/lpr mouse by hybridoma technology. The antibody catalyzed hydrolysis of single- and double-stranded DNA with a higher substrate specificity for thymine than adenine by either beta-glycosidic or phosphodiester bond cleavage. The hydrolysis rate (kcat) showed maximum at acidic pH conditions, suggesting that the catalytic site of the antibody contains essential carboxylic group(s). Treatment of cells with the antibody promoted cell death and induced the activation of caspases. The cell death induced by the antibody was inhibited by the pan-caspase inhibitor. Furthermore, the antibody binds to cell membrane and penetrates into the cells. Our results suggest that the cell death is initiated by antibodies penetrating to cells and nucleus, hydrolyzing considerable amount of DNA, and mediating the caspase-dependent apoptotic pathway.

Nuclear localizing anti-DNA antibodies enter cells via caveoli and modulate expression of caveolin and p53

After administration to normal mice, a subset of monoclonal (m) anti-DNA antibodies (Ab) derived from MRL-lpr/lpr mice was identified that enter cells, in vivo. In the kidneys, this was associated with glomerular hypercellularity and proteinuria. In cultured cells, the same mAb bound to myosin 1 on the cell surface, prior to internalization, nuclear localization and inhibition of apoptosis. The present study focuses on the mechanisms underlying the observed functional effects. Subcellular localization studies revealed that following internalization, a prototypic, nuclear localizing, m antibody (Ab; termed H7) co-localized with myosin 1, shortly after internalization, within caveolae, near the cell membrane. Cell fractionation studies confirmed the presence of both H7 and myosin within the caveolar fraction. Since variations in caveolin protein expression have been associated with apoptotic events in cancer cells, through p53 dependent and independent pathways, modulation of caveolin by intracellular H7 was evaluated. Cellular entry of the anti-DNA Ab resulted in an increase in caveolin protein expression. Furthermore, after exposure of cells to dexamethasone to induce apoptosis, the usual increase in p53 was inhibited in the presence of intracellular H7. Taken together, the results suggest that upregulation of caveolin and inhibition of p53 induction are involved in H7-induced, inhibition of apoptosis. Furthermore, they suggest that this inhibition contributes to the glomerular hypercellularity observed in normal mice with intranuclear H7. The results also raise the possibility that inhibition of apoptotic pathways during inflammation or/and autoimmunity could influence subsequent disease events. The novel mechanism of cellular perturbation is indirect and dependent on apoptotic stimuli, and it may account for the presence of intranuclear antibodies in inflammatory and normal tissues of individuals with lupus.

New approaches to the renal pathogenicity of anti-DNA antibodies in systemic lupus erythematosus

Autoantibodies against double stranded (ds) DNA are not only a helpful serological marker for diagnosis of systemic lupus erythematosus (SLE), but have also been shown to be crucial in the pathogenesis of lupus nephritis. However, the question of how anti-dsDNA antibodies contribute to renal damage is unresolved. Many authorities believe that indirect binding (mediated by nuclear antigens) or direct cross-reactivity of anti-dsDNA antibodies with kidney antigens are important determinants of anti-dsDNA nephritogenicity. An alternative hypothesis for the renal pathogenicity of anti-dsDNA antibodies was proposed more than 20 years ago, namely that certain autoantibodies could penetrate into living cells and thus induce damage. Work from several laboratories has recently provided firm support for this iconoclastic theory, which contradicted prevailing immunologic dogma that cell interiors are inaccessible to antibodies. Here, we review the evidence that anti-dsDNA antibodies may penetrate into living cells, and discuss which intracellular events may follow from binding of anti-dsDNA antibodies to the cell surface and subsequent intracellular penetration. Determining the mechanism by which anti-dsDNA antibodies induce renal injury is important for understanding a major disease manifestation of lupus, and may lead to the development of novel approaches to the treatment of lupus renal disease.

Antigenic triggers and molecular targets for anti-double-stranded DNA antibodies

While anti-double-stranded (ds)DNA antibodies are a characteristic serologic hallmark for SLE, the triggering antigen is unknown. Using phage display libraries, we identified DWEYSVWLSN as a peptide mimic of DNA for a pathogenic anti-dsDNA antibody. Peptide immunization of non-autoimmune mice induced anti-dsDNA as well as other lupus-associated antibodies. Molecular analysis of the induced anti-dsDNA antibodies revealed several similarities with anti-dsDNA antibodies that appear spontaneously in lupus mice. Furthermore, lupus-prone mice immunized with this peptide DNA mimic had higher autoantibody titers as well as more severe nephritis. Anti-DNA antibodies may contribute to lupus nephritis via cross-reactivity with renal antigen. Using western blotting of lysates of mesangial cells from a lupus mouse, we found that a pathogenic anti-DNA antibody binds to alpha-actinin. High titers of anti-alpha-actinin antibodies were present in the sera and kidney eluates of lupus mice with active disease. Binding to alpha-actinin was diminished in mesangial cells derived from BALB/c mice, suggesting that target antigen expression may play a role in determining autoantibody binding to the kidney. We conclude that a pathogenic, lupus-like autoantibody response can be induced by a peptide antigen, and that alpha-actinin is a cross-reactive renal target for the pathogenic anti-dsDNA autoantibody response in lupus mice.

Some Bence-Jones proteins enter cultured renal tubular cells, reach nuclei and induce cell death

Eighteen monoclonal Bence-Jones proteins (BJPs) were examined for their effects on cultured LLC-PK1 (porcine kidney proximal tubule) cells as well as for their amidase and DNase activities. Five proteins were found to enter the cell and to gain access to the nucleus without degradation of epitopes. Intranuclear BJPs ultimately induced DNA fragmentation and cell death. BJPs with relatively high amidase activity were cytotoxic. On the other hand, three of four BJPs with DNase activity had a cytocidal effect on cultured cells; the remaining BJP, which had a relatively high DNase activity but a very low amidase activity, failed to enter the cell and was not cytotoxic in vitro. These results suggest that catalytic and cytotoxic activities of some BJPs may make a significant contribution, in a substantial proportion of myeloma patients, to the development and/or deterioration of the disease.

Mercury-induced anti-nucleolar autoantibodies can transgress the membrane of living cells in vivo and in vitro

Treatment with HgCl2 induces a systemic autoimmune disease in certain mice and rats. The major characteristic of this disease in mice with H-2s genotype is the production of anti-nucleolar autoantibodies (ANoIA). The exact mechanism(s) for the production and the functional role of mercury-induced ANoIA are not known. We have studied the ability of mercury-induced ANoIA to enter the living cells in vivo and in vitro. We found that in highly susceptible mice, treatment with mercury induced ANoIA capable of localizing in the nucleoli of kidney and liver cells in vivo. No detectable nucleoli localization of ANoIA were found in the cells of the heart, stomach, intestine and spleen. Consistent with the in vivo studies, mercury-induced ANoIA were also able to enter and translocate in the nucleoli of certain cells in vitro. The highest degree of antibody penetration was found in A-498 cells (a human kidney cell line) followed by 3T3 cells (a mouse fibroblast cell line), whereas the cells of lymphoid origin exhibited a very low degree of antibody penetration. Penetrated ANoIA could be recovered from the nucleoli of live 3T3 cells previously treated with ANoIA. The in vitro nucleolar translocation by ANoIA did not affect the DNA synthesis, but was found to be an active process dependent on time and temperature. Furthermore, pre-treatment of living cells with trypsin markedly inhibited both cell entry and nucleolar accumulation of ANoIA. Thus, mercury-induced ANoIA have a unique ability to transgress the membrane of certain living cells in vivo and in vitro, and to localize in the nucleoli.

Early anti-nucleosome autoantibodies from a single MRL+/+ mouse: fine specificity, V gene structure and pathogenicity

In systemic lupus erythematosus, the nucleosome assumes a central role in the autoimmune response to self antigens. To gain insight into the etiology and pathogenesis of anti-nucleosome antibodies (Ab), we analyzed a panel of six IgG-secreting hybridomas derived from a single young MRL +/+ mouse at the onset of the autoimmune response. All monoclonal antibodies (mAb) bound exclusively the native nucleosome, and represented five different clonotypes that recognized diverse nucleosomal epitopes, typical of a polyclonal response. The VH-complementarity-determining region (CDR)3 regions exhibited unique stretches of charged amino acids with different polarity that may be important for the interaction with the nucleosome. These early anti-nucleosome mAb displayed striking structural differences with not only anti-DNA, but also with anti-nucleosome Ab, that appear later in disease. Two of the mAb deposited in kidney glomeruli after in vivo administration to RAG-1-deficient mice, suggesting that diverse B cell clones, possibly selected by the nucleosome itself, may play a role in the initiation of kidney damage.

Antibodies to DNA--towards an understanding of their origin and pathophysiological impact in systemic lupus erythematosus

In 1997, the discovery of autoantibodies reactive with DNA celebrates its fortieth anniversary. Over these 4 decades, hardly any other single spontaneously produced antibody population has been subjected to such a wide scientific interest both from a basic immunological as well as from a clinical point of view. From the time of their first description, myths and enigmas regarding their biological origin have dominated the scene. Only during the last few years results have been obtained that have justified new conceptual frameworks for the understanding of the molecular bases for their production, as well as for their pathophysiological potential in systemic lupus erythematosus (SLE). Central, newly obtained experimental and clinical results that have profoundly improved our understanding of the origin and biology of anti-DNA antibodies will be presented and discussed below.

Receptor-mediated cellular entry of nuclear localizing anti-DNA antibodies via myosin 1

A unique subset of anti-DNA antibodies enters living cells, interacts with DNase 1, and inhibits endonuclease activity, before their nuclear localization and subsequent attenuation of apoptosis. We now report that endocytosis of these immunoglobulins is mediated by cell surface binding to brush border myosin (myosin 1). Cellular entry and internalization via this unique receptor provides initial contact for entry and sorting these immunoglobulins to translocate to the nuclear pore and enter the nucleus, interact with DNase 1 within the cytoplasm, or recycle back to the cell surface. This internalization pathway provides clues to the translocation of large proteins across cell membranes and the functional effects of intracellular antibodies on cytopathology. This is the first demonstration that brush border myosin functions as a specific cell surface receptor for internalization of large proteins.

The penetrating potential of autoantibodies into live cells in vitro coincides with the in vivo staining of epidermal nuclei

We have previously demonstrated that IgG autoantibodies derived from SLE patients are capable of penetrating into nuclei of living COLO-16 cells, in vitro. To address the possible correlation in Lupus Erythematosus (LE) between the in vivo ANA binding to nuclei of epidermal cells and the presence of intranuclear penetrating antibodies in sera of those patients, 25 consecutive patients were studied. Out of 25 skin biopsies, 11 specimens (8 of SLE and 3 of DLE) showed by immunofluorescent microscopy extensive in vivo presence of IgG in epidermal nuclei, whereas all sera of these patients stained nuclei of living COLO-16 cells, in vitro. Such penetration was also observed in additional 6/25 sera of patients, but with in vivo negative biopsies. This in vitro nuclear binding, which was unrelated to clinical symptoms of patients or their serological autoantibody profile and titer, was reproduced following cross-linking of intracellular protein by PLP fixation. Likewise, western blotting (immunoblotting) analysis, demonstrated the intranuclear presence of IgG in all in vitro intranuclear IgG staining sera. Furthermore, this in vitro presence, which neither affects cell viability nor DNA synthesis, is time-dependent and of a transient nature: nuclear staining disappears within 48 h following removal of the penetrating sera from medium. In conclusion, since the COLO-16 in vitro assay mirrors exactly the in vivo situation, and because of its higher sensitivity, it provides an excellent tool for the study of non-degraded autoantibody penetration into the nuclei of living cells.

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.

Structural properties and mutation patterns of anti-nucleosome monoclonal antibodies are similar to those of anti-DNA antibodies

Four monoclonal antibodies (mAb) derived from an (NZB x NZW)F1 mouse bound to nucleosomes, total histones and to the H2A-H2B dimers but not to individual histones or DNA. Sequencing of their heavy (H)- and light (L)-chain variable region genes showed that they derived by somatic mutations from the same B cell precursor. The distribution of negatively and positively charged amino acids in the H-chain complementarity-determining regions was very similar to that observed not only in anti-H2A-H2B mAb derived from different lupus-prone mouse strains but also in anti-DNA mAb. Combined analysis of the mAb structures and their interactions with immobilized H2A-H2B dimer or total histones by plasmon resonance allowed us to assign the H-chain mutations a major role in the binding profiles of these anti-nucleosome mAb. Interestingly, four of the five H-chain mutations that distinguished mAb 3F6 from 2E1 generated negatively or positively charged amino acid residues, and two of them occurred at positions 56 and 76, which are frequently involved in the maturation process of anti-DNA antibodies. A modeling study of the 3F6 variable fragment (Fv) predicted that acidic residues occupy the cleft of the Ab combining site and have the potential to participate in electrostatic interactions. Thus, the demonstration that (NZB x NZW)F1-derived anti-H2A-H2B antibodies share certain structural features and mutation patterns with anti-DNA mAb suggest that common selection and maturation processes account for the production of these lupus-related autoantibodies.

Structural properties of a subset of nephritogenic anti-DNA antibodies

Structural analysis of lupus autoantibodies is beginning to provide clues to the molecular basis for antigenic specificity and pathogenicity. The present analysis indicates that multiple light and heavy chains contain residues which can facilitate DNA binding, reaffirming the notion that there are multiple ways that different amino acids combine to form an antigen-binding pocket with affinity for dsDNA and ssDNA. Furthermore, this analysis suggests that these conformations and contact residues are intrinsic to germline sequences, although amino acid changes at critical locations (somatically introduced) modulate antigen binding, and appear to influence the capacity of individual immunoglobulin to form immune deposits. Analysis of additional individual immunoglobulins with closely related V-region sequences and differing pathogenic properties will be required to resolve the contribution of specific motifs to pathogenecity.