Parallel sets of autoantibodies in MRL-lpr/lpr mice. An anti-DNA, anti-SmRNP, anti-gp70 network

Serological and clinical associations of autoantibodies in Chinese patients with new-onset systemic lupus erythematosus

To study the clinical significance of autoantibodies in Chinese patients with new-onset systemic lupus erythematosus (SLE), we enrolled 526 new-onset patients who met the 1997 Updated American College of Rheumatology SLE Classification Criteria for a retrospective cohort study. Chi-square test and Wilcoxon rank-sum test were used to detect the relationship of autoantibodies with clinical manifestations and serological results respectively. Our results demonstrated that the positive rate of anti-ribosomal P protein (anti-P) antibody in female patients was higher than that in male patients (41.2% vs. 22%, P = 0.008). Patients with anti-SSB (43.95 ± 73.12 vs. 40.92 ± 75.75, P = 0.004; 63.93 ± 103.56 vs. 55.06 ± 120.84, P = 0.008 respectively) antibodies had higher levels of alanine aminotransferase (ALT) and aspartate transaminase (AST), whereas those with anti-P antibody (28.90 ± 25.70 vs. 50.08 ± 93.00, P = 0.014; 38.51 ± 48.19 vs. 69.95 ± 142.67, P = 0.047, respectively) had lower levels of them. Anti-dsDNA antibody (P = 0.021) was associated with pulmonary arterial hypertension (PAH). The patients with anti-Ro60 (P = 0.044), anti-P (P = 0.012) and anti-dsDNA (P = 0.013) antibodies were less likely to develop Interstitial lung disease. Anti-SmRNP antibody was correlated to lower prevalence of neuropsychiatric symptoms (P = 0.037), and patients with anti-centromere antibody (ACA) were more likely to develop serositis (P = 0.016).We identified five clusters of SLE-related autoantibodies, confirmed previously reported associations of autoantibodies, and discovered new associations.

Immune Response Regulation by Antigen Receptors' Clone-Specific Nonself Parts

Antigen determinants (epitopes) are recognized by the combining sites (paratopes) of B and T cell antigen receptors (BCR/TCR), which again express clone-specific epitopes (idiotopes) that can be recognized by BCR/TCR not only of genetically different donors but also within the autologous immune system. While xenogeneic and allogeneic anti-idiotypic BCR/TCR are broadly cross-reactive, only autologous anti-idiotypes are truly specific and of functional regulatory relevance within a particular immune system. Autologous BCR/TCR idiotopes are (a) somatically created at the third complementarity-determining regions, (b) through mutations introduced into BCRs during adaptive immune responses, and (c) through the conformational impact of both. As these idiotypic characters have no genomic counterparts they have to be regarded as antigen receptor-intrinsic nonself-portions. Although foreign, however, they are per se non-immunogenic, but in conjunction with immunogenicity- and adjuvanticity-providing antigen-induced immune responses, they induce abating regulatory idiotypic chain reactions. The dualistic nature of antigen receptors of seeing antigens (self and nonself alike) and being nonself at the same time has far reaching consequences for an understanding of the regulation of adaptive immune responses.

The role of positive feedback loops involving anti-dsDNA and anti-anti-dsDNA antibodies in autoimmune glomerulonephritis

Autoimmune glomerulonephritis (GN) is a potentially life-threatening renal inflammation occurring in a significant percentage of systemic lupus erythematosus (SLE) patients. It has been suggested that GN develops and persists due to a positive feedback loop, in which inflammation is promoted by the deposition in the kidney of immune complexes (IC) containing double-stranded DNA (dsDNA) and autoantibodies specific to it, leading to cellular death, additional release to circulation of dsDNA, continuous activation of dsDNA-specific autoreactive B cells and further formation of IC. We have recently presented a generic model exploring the dynamics of IC-mediated autoimmune inflammatory diseases, applicable also to GN. Here we extend this model by incorporating into it a specific B cell response targeting anti-dsDNA antibodies-a phenomenon whose occurrence in SLE patients is well-supported empirically. We show that this model retains the main results found for the original model studied, particularly with regard to the sensitivity of the steady state properties to changes in parameter values, while capturing some disease-specific observations found in GN patients which are unaccountable using our previous model. In particular, the extended model explains the findings that this inflammation can be ameliorated by treatment without lowering the level of anti-dsDNA antibodies. Moreover, it can account for the inverse oscillations of anti-dsDNA and anti-anti-dsDNA antibodies, previously reported in lupus patients. Finally, it can be used to suggest a possible explanation to the so-called regulatory role of TLR9, found in murine models of lupus; i.e., the fact that the knockdown of this DNA-sensing receptor leads, as expected, to a decrease in the level of anti-dsDNA antibodies, but at the same time results in a counter-intuitive amplification of the autoreactive immune response and an exacerbated inflammation. Several predictions can be derived from the analysis of the presented model, allowing its experimental verification.

Thyroglobulin monoclonal antibody cross-reacting with thyroperoxidase induces in syngeneic mice anti-idiotypic monoclonal antibodies with dual autoantigen binding properties. The intertope hypothesis

Autoimmune thyroid diseases are characterized by antibodies (Ab) directed to thyroglobulin (Tg) and thyroperoxidase (TPO). Some of them, TGPO Ab, are Tg Ab with an interspecies idiotype (Id) reacting with TPO. Taking advantage of a carefully studied TGPO monoclonal antibody (mAb), we examined the basis of the hypothesis that TPO Ab would ultimately derive from TGPO Ab through idiotypic induction. We repeatedly immunized naive, syngeneic mice with the TGPO mAb and we derived three novel mAb directed to both Tg and TPO. The most reactive of them, mAb 4F8, was further purified, radiolabeled and its binding properties studied by radioimmunoassay. mAb 4F8 bound to Tg, TPO, the immunogen Ab1 and even to itself, being thus considered as a self-binding Ab2. Competitive binding inhibition experiments demonstrated that Tg, TPO, Ab1 and Ab2 cross-reacted for Ab2 binding to Tg, TPO and Ab1. Fine specificity mapping using panels of specific mAb revealed that Ab1 and Ab2 were similar because they were directed against the same immunodominant regions on Tg and TPO. We propose that unique Id of TGPO Ab resemble dominant epitopes of Tg as well as paratopes of Ab directed against dominant TPO epitopes. This category of Id that we called intertopes may induce TPO-monospecific Ab from TGPO Ab by idiotypically driven somatic mutations.

Idiotype usage by polyclonally activated B cells in experimental autoimmunity and infection

Both in animal models and in human systemic lupus erythematosus (SLE) the occurrence of nephritogenic autoantibodies bearing dominant idiotypes has been described. In this study we investigate the relation between the induction pathway of polyclonal B cell activation and the production and glomerular deposition of nephritogenic antibodies with shared dominant idiotype(s). Polyclonal B cell activation was induced in several experimental models characterized by glomerular immune deposit formation. We monitored the occurrence of dominant idiotypes among immunoglobulins deposited in the glomeruli. In addition, we studied the species specificity of the dominant idiotypes, by monitoring their presence in kidney sections of patients with an immunologically mediated kidney disease. Anti-idiotype antisera against two monoclonal anti-DNA autoantibodies were used, derived from MRL-lpr/lpr mice, i. e. clone H241 and clone H130. Autoantibodies with the H241 idiotype were present in immune complex depositions in all experimental models but not in humans. We therefore conclude that the presence of this dominant idiotype is independent of the induction pathway of polyclonal B cell activation. However, autoantibodies bearing the H130 idiotype were only detected in kidney sections of mice with spontaneous lupus.

Chronic parvovirus B19 infection induces the production of anti-virus antibodies with autoantigen binding properties

Human parvovirus B19 infection in adults shows some clinical features similar to those found in autoimmune connective tissue diseases. To better clarify the relationship between viral infection and autoimmunity, we have evaluated the ability of anti-parvovirus antibodies to specifically recognize autoantigens in ten patients with chronic symmetric arthritis resembling rheumatoid arthritis or with recurrent episodes of arthritis and cutaneous manifestations and persistence of specific IgM antibodies against B19 parvovirus. We synthetized a 24-amino acid immunodominant peptide corresponding to a part of the virus protein 1 and virus protein 2 overlapping region. The peptide has been used to test patients' sera at different time points with an enzyme-linked immunosorbent assay (ELISA) and to purify anti-virus antibodies by affinity chromatography on a peptide-Sepharose column. Eluted immunoglobulins recognized the B19 peptide in both direct and competitive ELISA. Affinity-purified anti-parvovirus antibodies were then tested on a panel of autoantigens including human keratin, collagen type II, thyreoglobulin, single-strand (ss)DNA, cardiolipin and ribonucleoprotein antigen Sm. Eluted antibodies specifically recognized keratin, collagen type II, ssDNA and cardiolipin. Autoantibody activity was not detected in the immunoglobulin fraction after complete removal of anti-peptide antibodies and in antibodies eluted from normal donors. Epstein-Barr virus-transformed cell clones obtained from two subjects produced antibodies which simultaneously recognize the viral peptide and several autoantigens. To further confirm the role of the virus in inducing an autoantibody response, eight BALB/c mice were immunized with the viral peptide coupled to a carrier protein. Autoantibody activity against keratin, collagen II, cardiolipin and ssDNA was detected in six of the eight mice which developed a strong anti-virus response. Together, these data indicate that B19 parvovirus may be linked to the induction of an autoimmune response.

Variable regions of two murine antibodies that bind the SLE associated 16/6 idiotype

Experimental systemic lupus erythematosus can be induced in naive mice of different strains using a human monoclonal antibody bearing the 16/6 idiotype and a murine anti-16/6 Id monoclonal antibody designated 1A3-2. Herein we report the isolation of a second anti-16/6 Id antibody, 3F7-8, from BALB/c mice afflicted with experimental SLE. In contrast to the previously reported (1A3-2) anti-16/6 Id monoclonal antibody, mAb 3F7-8 does not induce experimental SLE upon immunization. The variable heavy and light chains of both antibodies were cloned and their sequences were determined. The VH of mAb 1A3-2 was found to express a germ line gene from the Q52 family, with a high homology to an anti-lysozyme antibody. The VH of monoclonal antibody 3F7-8 was found to express a 7183 germ line gene, showing over 95% homology with the VH of 12 anti-Sm antibodies isolated from MRL-lpr mice. Based on sequence homology to other known antibodies, we further demonstrated that monoclonal antibodies 1A3-2 and 3F7-8 bind lysozyme and the Sm ribonucleoproteins, respectively, in addition to their binding to the 16/6 Id.

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.

IL-1 beta gene expression in B cells derived from the murine MRL/lpr model of lupus

The MRL/lpr model of SLE resembles human lupus in its various immunopathologic characteristics including the presence of high-level IgG and anti-DNA antibody production and multisystem organ involvement (nephritis, arthritis, and vasculitis). Our previous studies have shown that IL-1 overactivity in B cells plays a potentially important role in driving IgG and autoantibody production. However, the underlying mechanisms determining IL-1 overactivity are poorly understood. We studied IL-1 beta gene expression and transcriptional rates in B cells derived from old and young MRL/lpr, MRL/+ +, and non-autoimmune control mice using semi-quantitative RT-PCR and the nuclear run-on assay. RT-PCR demonstrated increased steady-state IL-1 beta gene expression in B cells derived from old MRL/lpr mice as compared to either young MRL/lpr or control mice. Furthermore, IL-1 beta gene expression in B cells was associated with the presence of the lpr mutation because heightened IL-1 beta message was observed in RNA obtained from MRL/lpr but not MRL/+ + B cells. IL-1 beta transcriptional rates measured by the nuclear run-on assay were very similar in B cells from old and young MRL/lpr and control mice. These observations suggest that IL-1 overactivity in B cells obtained from old diseased MRL/lpr results from heightened IL-1 beta message, is associated with the presence of the lpr mutation, and is likely to reflect post-transcriptional stabilization of IL-1 beta mRNA.

Anti-collagen antibodies in systemic sclerosis and in primary Raynaud's phenomenon

The frequency and specificity of antibodies to native and denatured collagens were evaluated in systemic sclerosis (SSc) and in primary Raynaud's phenomenon (PRP) by direct and competitive ELISA. Antibodies reactive with denatured collagen type I (CI) were found in 43% of the SSc sera, and anti-CIV and anti-CV in 31%. In PRP, anti-CI, anti-CIV and anti-CV antibodies were detected in 8% of patient sera. Anti-CI, anti-CIV and anti-CV antibodies reacted with determinants expressed on the native as well as on the denatured molecule. Anti-CI and anti-CIV were cross-reactive; a reactivity with CII and a lower one with CV were detected. Anti-CV antibodies also reacted with CI and CII and, in a smaller proportion of cases, with CIV. Anti-collagen antibodies, affinity-purified from blotted collagen IV and V and cyanogen bromide (CBr)-digested CI, displayed the cross-reactivities shown by inhibition studies on sera. Moreover, antibodies eluted from a CBr fragment of CI reacted with the other CBr fragments as well. These data show that one-third of SSc sera contain antibodies that react with epitopes expressed on native as well as on heat-denatured CI, CII, CIV and CV, and therefore have the potential to bind collagens in vivo.

Anti-DNA antibodies bind to DNase I

Polyspecificity is a well-known property of the anti-DNA antibodies produced by autoimmune animals. In our search for antigen targets of anti-DNA antibodies within tissue extracts, we identified a 32-kD polypeptide that was recognized by a large panel of anti-DNA antibodies. Direct sequencing of this protein disclosed its identity with DNase I. 22 monoclonal anti-DNA antibodies bound to DNase I in direct and competitive immunoassays; out of 15 autoantibodies that did not bind DNA, none had the ability to bind DNase I. The ability of anti-DNA antibodies to interfere with DNase I enzymatic activity was evaluated in an assay based on the enzyme digestion of phage double strand DNA. Six monoclonal anti-single strand DNA antibodies that did not bind double strand DNA were tested in this assay. Three out of six inhibited DNase I-mediated digestion of phage DNA. The interaction of anti-DNA antibodies with DNase I was further investigated by testing their ability to bind a synthetic peptide that corresponds to the catalytic site of the molecule. 4 out of 22 anti-DNA antibodies bound the active site peptide; two of these had been shown to inhibit DNase I enzymatic activity. This report show that anti-DNA antibodies recognize both DNA and its natural ligand DNase I. Some anti-DNA antibodies inhibit DNase I enzymatic activity, thus displaying the potential to modulate DNA catabolism. The dual specificity of anti-DNA antibodies offers a clue for understanding the mechanisms that lead to anti-DNA antibody production in autoimmune animals.

Binding of glycoprotein 120 and peptides from the HIV-1 envelope by autoantibodies in mice with experimentally induced systemic lupus erythematosus and in patients with the disease

Systemic lupus erythematosus (SLE) and infection with the human immunodeficiency virus type 1 (HIV) are diseases that are characterized by immune dysregulation and autoantibody production. In this article we identify and characterize IgG antibodies from mice with SLE and SLE patients that bind HIV gp120 and HIV envelope-derived peptides. SLE can be induced in susceptible mouse strains by immunization with a human monoclonal anti-DNA antibody that bears a common idiotype designated 16/6 Id. We tested sera from various strains of mice in which experimental SLE was induced by this method, as well as from 93 patients with SLE and 31 controls (17 healthy controls, 14 patients with other autoimmune diseases) for the presence of antibodies reactive to gp120 by an ELISA. Antibodies reactive with gp120 were produced by BALB/c, C3H.SW, AKR, and DBA/2 mice, all of which were 16/6 Id immunized and had experimental SLE. C57BL/6 mice, which are resistant to induction of SLE by this method, did not produce antibodies reactive with gp120 despite 16/6 immunization. Forty-three percent of SLE patients made antibodies that bound to gp120 at titers greater than 1:40, whereas 12% of healthy control sera (p < or = 0.02) and 14% of patients with other autoimmune diseases contained such antibodies (p < or = 0.05). We delineated the specificity of this antibody activity by testing for reactivity to six HIV envelope peptides. In both mice and SLE patients, sera reactive with gp120 recognized the same three envelope peptides. Removal of the anti-DNA antibodies from the sera by DNA-agarose affinity purification did not change anti-gp120 specificity.

(SWR x SJL)F1 mice: a new model of lupus-like disease

During the study of autoimmune models we found that (SWR x SJL)F1 mice (both parental strains with the V beta a phenotype) spontaneously produced immunoglobulin G (IgG) antibodies directed against Sm/U1 small nuclear ribonucleoproteins (snRNPs). In some of these females, the presence of these autoantibodies was found as early as 10 wk of age. Their frequency increased with age i.e., 70% at 40 wk. At that time, only 10% of males developed anti-Sm/U1snRNP antibodies. Anti-Sm/U1snRNP antibodies from positive mice generally recognized the peptides BB', D, 70 kD, and A from RNPs. These polypeptides are known to bear the autoantigenic epitopes that are recognized by human sera containing anti-Sm and anti-U1snRNP antibodies. Reactivity of IgG antibodies with the octapeptide sequence PPPGMRPP was also found in 30% of anti-Sm/U1snRNP positive (SWR x SJL)F1 mice that precipitated BB' peptides. This octapeptide has been described as the most immunoreactive linear epitope in systemic lupus erythematosus (SLE) patients with anti-Sm and anti-U1snRNP antibodies. Approximately 30% of anti-Sn/U1snRNP positive females, later produced anti-dsDNA antibodies. This fact was accompanied by the development of proteinuria due to glomerulonephritis mediated by immunocomplexes. In addition to the specific autoimmune response, (SWR x SJL)F1 females also showed other immunologic abnormalities such as hypergammaglobulinemia, and an approximately twofold increase in spleen cell number compared with control mice. These results indicate that (SWR x SJL)F1 females develop clinical and serological abnormalities similar to those observed in human SLE and constitute a novel model for the study of the genetic mechanisms that result in autoimmunity.

Induction of an anti-Fab, anti-DNA and anti-RNA polymerase I autoantibody response network in rabbits immunized with SLE anti-DNA antibody

Systemic lupus erythematosus (SLE)-like anti-IgG Fab autoantibodies (autoAb) were induced in rabbits by immunization with either human, mouse or rabbit anti-DNA Ab. In direct-binding radioimmunoassay (RIA), affinity-purified anti-normal rabbit (NR) Fab autoAb cross-reacted with normal mouse (NM) Fab, ssDNA (but not dsDNA), poly(dA,dT), and RNA polymerase I (RPI). Affinity-purified anti-NM IgG Ab isolated from the same antisera cross-reacted with NR Fab, ssDNA and RPI. In inhibition RIA, soluble NR Fab inhibited anti-NR Fab binding to NR Fab and ssDNA, but enhanced binding to RPI. In contrast, ssDNA or RPI inhibitors had no effect upon autoAb binding to NR Fab. Anti-DNA, anti-RPI and anti-RPI 190 kD subunit autoAb, induced by immunization with lupus mouse anti-DNA Ab, also reacted with NM Fab, but were idiotypically specific for lupus mouse anti-DNA Fab. Further, rabbit anti-DNA and anti-RPI IgG autoAb, induced by immunization with rabbit anti-DNA IgG, were each idiotypically specific for homologous and autologous rabbit anti-ssDNA Fab. Together, these data provide evidence that anti-DNA, anti-RPI and anti-Fab autoAb are linked in a complex, multiple-specific and perhaps regulatory, immune response idiotype network in SLE.

Molecular heterogeneity of auto-anti-idiotypic antibodies in MLR-lpr/lpr mice

The VH and V kappa gene families expressed by 20 monoclonal auto-anti-idiotypes (Ab2) derived from unmanipulated MLR-lpr/lpr mice were determined by Northern blotting. Complete variable region sequences of six Ab2, along with three additional V kappa-JH Ab2 sequences, were obtained. These auto-anti-idiotypes arose spontaneously in the animals, and they bound specifically to an idiotypic determinant (Id/r) on mAb 28/12, a monoclonal IgG2b MLR-lpr/lpr anti-small nuclear ribonucleoprotein antibody. The 16 Ab2 heavy chains belonged to 7 different VH gene families, and the 10 Ab2 light chains were derived from 8 V kappa families. The light chains of two Ab2 were approximately 99% identical; the remaining variable region sequences were highly heterogeneous. There was no correlation between primary amino acid sequence of either heavy or light chain and idiotypic properties of the auto-anti-idiotypes. Six Ab2 used VH or V kappa genes that are identical to known germ-line genes. A high proportion of the spontaneous auto-anti-idiotypes was shown to have autoantibody activity (anti-DNA, anti-ribonucleoprotein), or specific binding reactions with lipopolysaccharide of Salmonella RE, or both properties. The structural diversity of spontaneous MLR-lpr/lpr auto-anti-idiotypes differs sharply from the structural homogeneity reported for Ab2 induced in normal animals against syngeneic Ab1. Our results suggest that auto-anti-idiotypes might arise independently of an immunogenic stimulus from an Ab1.

Idiotype specific T-cell lines inducing experimental systemic lupus erythematosus in mice

Immunization of mice with either antibodies bearing the 16/6 idiotype (16/6 Id) or anti-idiotypic antibodies against the 16/6 Id induces experimental systemic lupus erythematosus (SLE). We report here the establishment and characterization of 16/6 Id-specific T-cell lines from C3H.SW (H-2b) and BALB/c (H-2d) mice. Both lines proliferate specifically in response to the 16/6 Id in an H-2-restricted manner. The injection of 16/6 Id-specific T cells into syngeneic mice led to the development of experimental SLE. Furthermore, inoculation of the 16/6 Id-specific T-cell line derived from C3H.SW mice into the H-2 compatible C57BL/6 mice, which are non-responders to the 16/6 Id, induced experimental SLE. This report provides direct evidence for the role of idiotype-specific T cells in the induction of experimental SLE.

Analysis of a positive feedback mechanism in the anti-Sm autoantibody response of MRL/MPJ-lpr/lpr mice

The mechanism of induction of anti-Sm antibodies by passive transfer of anti-Sm mAb in MRL/lpr mice was investigated. No idiotypic relationship was detected between the inducing monoclonal antibody KSm2 and either the induced circulating anti-Sm antibodies or the products of anti-Sm-producing hybridomas derived from spleen cell fusion of treated mice. Treatment of mice with ribonucleoprotein Sm antigen, alone or as an immune complex, induced anti-Sm and anti-ribonucleoprotein antibodies similarly to treatment with KSm2. This suggests that autoantigen contributes to the development of the anti-Sm response in MRL mice.

An immunoglobulin light chain from a lupus-prone mouse induces autoantibodies in normal mice

Autoantibodies against the 70-kD U1 RNP nucleoprotein autoantigen and DNA were elicited in normal BALB/c mice with a purified Ig light chain. This light chain, derived from a lupus-prone MRL-lpr/lpr mouse, has two distinctive properties: it contains an idiotypic marker recognized by a monoclonal MRL-lpr/lpr anti-snRNP autoantibody, and the amino acid sequence of its third hypervariable region (CDR3) is homologous to a sequence in an antigenic region of the 70-kD U1 RNP polypeptide. The results demonstrate that an Ig idiotype that mimics an autoantigen can induce autoimmunization.

Cross-reactivity of murine monoclonal anti-DNA antibodies with human and murine skin: a possible pathogenetic role in skin lesions of lupus erythematosus

Anti-DNA autoantibodies are known to cross-react with a wide variety of substances including cell-surface molecules. Thus, we examined cross-reactivities of 20 murine monoclonal anti-DNA antibodies with normal human and mouse skin tissues. Hybridomas producing these monoclonal antibodies were established from non-immunized spleen cells from autoimmune MRL-lpr/lpr mice, a strain characterized by spontaneous development of SLE-like disorders including skin changes. They were selected based on their reactivity to DNA in a typical enzyme-linked immunosorbent assay, in which nine monoclonal antibodies were reactive with both double-stranded DNA and single-stranded DNA, whereas nine monoclonals were reactive only with single-stranded DNA. Even though only seven of them were observed to stain nuclei, most of the monoclonal antibodies revealed strong and distinct cross-reactivities to various components of the skin tissues including the epidermal basement membrane, keratinocytes at different locations of the epidermis, melanocytes, Langerhans cells, Thy-1+ dendritic cells in the case of murine skin, and mast cells. Our results suggest a possible role of so-called anti-DNA antibodies with high or low affinities to DNA in the pathogenesis of cutaneous lesions of lupus erythematosus.

Human polyclonal and monoclonal IgG and IgM complement 3 nephritic factors: evidence for idiotypic commonality

Complement 3 nephritic factors (C3NeF) were isolated from the sera of patients with membranoproliferative glomerulonephritis (MPGN) and the supernatants of pokeweed mitogen-stimulated mononuclear cells from patients with MPGN. Three human monoclonal C3NeF antibodies (two IgGs, CK and PH, and one IgM, K3C4) were established. Using an exhaustive series of affinity columns, we isolated anti-C3NeF idiotypic antibodies (anti-IdNeF) (three from normal and two from patient sera). Anti-IdNeF preparations bound to F(ab')2-NeF and prevented its ability to stabilize C3bBb convertase. We have used the above reagents to address questions on the genesis and the diversity of C3NeF antibodies. The following results were obtained: All anti-IdNeF preparations bound to C3NeF isolated from patient sera, cell culture supernatants, and IgG and IgM monoclonal C3NeF. None of the monoclonal C3NeF bound to an extensive battery of common antigens, including Fc portion of IgG, TNP, beta-galactosidase, DNA, and bacterial products. These data indicate that C3NeF express one common idiotype and that these antibodies are not raised in response to an obvious antigen.

Activation of clones producing self-reactive antibodies by foreign antigen and antiidiotype antibody carrying the internal image of the antigen

Because we found in previous work that a high fraction of antibodies exhibiting various specificities bound to glutamic acid 50-tyrosine50 homopolymer (GT) and expressed pGAT cross-reactive idiotype (IdX), we studied the activation of clones producing multireactive antibodies in 1-mo-old MRL/lpr and C3H/HeJ mice bearing VHJ haplotype. The activation of such clones was studied after mice were immunized with GT in CFA, HP20 (an anti-Id MAb carrying the internal image of GT in the D region), and a synthetic peptide corresponding to the D segment of HP20. Our results indicate that immunized mice produced both GT- and self-reactive antibodies. Study of the immunochemical properties of MAb showed that they exhibit multispecific properties and bind with similar-affinity constants to GT or self-antigens such as DNA, Smith antigen (Sm), and IgG2a. An important fraction of antibodies obtained from MRL/lpr mice immunized with HP20 expressed pGAT IdX and some of these antibodies share IdX expressed on anti-DNA, Sm, and rheumatoid factor (RFs) antibodies. The hybridomas producing multispecific autoantibodies use heavy-chain- (VH) and light-chain-variable region (VK) genes from various V gene families, suggesting that they do not derive from the pool of GAT precursors. Sequencing of VH and VK genes of two antibodies show that they can use closely related VHJ558, unmutated VK1, or different VK genes than those used by anti-GT antibodies. Our data demonstrate that clones producing antibodies binding to GT and self-antigens with similar-affinity constants can be activated by foreign or anti-Id antibodies carrying the internal image of the antigen or even by a synthetic peptide corresponding to the D segment of anti-Id antibodies.

Revised immune network concepts

The idiotype network concept needs to be revised in order to be in agreement with current data on protein/protein interactions, with the phenomenon of T and B cell recognition of idiotopes, and with the failure of certain anti-idiotypes to stimulate a given immune response. It is proposed that the distinction among Ab2 alpha, beta, and gamma is abandoned, as well as the concept of an internal image idiotope which mimics the three-dimensional shape of nominal antigen. In place of these definitions, the concept of "network antigen" is introduced. Network antigens are potentially the entire repertoire of anti-idiotypes. However, their biological effectiveness is controlled and established by two factors: (i) the affinity to the idiotype Ig receptor; and (ii) the preexisting regulatory network segment that controls the outcome of immune stimulation or suppression. Screening for effective idiotype therapeutic agents has to be done with panels of anti-idiotype and idiotype antibodies in order to establish correlations between idiotope expression and disease progression. Recognizing the importance of network segments will be the first step in the direction toward a rational design of idiotype-based therapies.

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.

Anti-DNA antibodies, autoimmunity and the immunoglobulin repertoire

The advent of hybridoma and recombinant DNA technology about a decade ago has allowed a detailed analysis the structure, properties and molecular genetics of antibodies. These techniques, combined with studies of idiotypes and of Abelson-transformed and other cell lines, have resulted in major findings which are of particular importance to both the normal immune system and to autoimmunity. The rearrangement and expression of antibody genes in the normal immune system are discussed first, as a background for an appreciation of the significance of the molecular genetics of autoantibodies. We then turn to autoantibody genes, with an emphasis on anti-DNA antibodies and their role in the autoimmune disease, systemic lupus erythematosus. A model for the genetics of lupus which includes a possible role for Ig genes is considered.

Antinuclear antibodies as molecular and diagnostic probes

Much progress has been made in the past decade in defining the specificities of antinuclear antibodies (ANA) that are present in the blood of patients with multi-system autoimmune rheumatic diseases, and ANA now have an important place in diagnostic immunology. Disease-specific ANA have been defined and the intracellular autoantigens against which they react have been characterized. ANA have also established an important place in cell biology. Their use as probes has enabled molecular biologists to isolate, purify and assay the function of the highly conserved molecules with which they react, revealing new insights into the role these molecules play in gene transcription and translation. Cloning of the genes encoding these molecules in addition to providing information on primary structure has also provided human recombinant proteins for use as pure substrates for the development of simple and highly sensitive diagnostic assays in rheumatology. Studies on the epitopes with binding sites for ANA should provide new knowledge on how the immune response to these molecules evolves, how it is maintained and what role ANA play in the pathogenesis of disease.

Binding specificity of antiidiotypic autoantibodies to anti-DNA antibodies in humans

Human antiidiotypic antibodies to anti-DNA antibodies can be separated into at least two categories based on their binding to anti-DNA, antiidiotypic antibodies, and antigens. One type was found mainly in inactive stage of SLE. The antiidiotypic antibodies appear to be directed towards idiotype (Id) determinants in the antigen-binding sites of anti-DNA antibodies. Antibody from patient T.K. acted like a mirror image of anti-single-stranded DNA antibodies, O-81, as determined by a competitive inhibition RIA. Antibodies from patient S.U. also seemed to be Ab 2 beta and Ab 2 gamma to anti-double-stranded(ds) DNA antibodies, NE-1. Most of normal subjects, on the other hand, had antibodies that bound to the human monoclonal anti-ds DNA antibodies, NE-1, NE-13, 7F4, and O-81. The Id-anti-Id interaction was not inhibited by the addition of DNA. Thus, normal subjects had Ab2 alpha activity that recognizes Id determinants in the framework region common among anti-DNA antibodies, whereas antiidiotypic antibodies in most SLE sera appear to show Ab 2 beta and Ab 2 gamma activity. The results provide evidence that the Id network system regulates immunological tolerance to DNA in humans.

Anti-Klebsiella K30 phospholipid antibodies in systemic lupus erythematosus: antigen cross-reactions and idiotypic sharing with antibodies to DNA and Klebsiella K30 polysaccharide

Patients with systemic lupus erythematosus were examined for the presence of serum antibodies reactive with phospholipids (PL) extracted from the membranes of Klebsiella K30 (K30PL). Affinity-purified anti-K30PL antibodies were tested for their ability to cross-react with other PL antigens or DNA and for the presence of idiotypic markers known to be associated with anti-DNA antibodies or antibodies to Klebsiella K30 polysaccharide (K30p). Affinity-purified antibodies to K30PL, phosphatidylserine (PS), or phosphatidylinositol (PL) uniformly cross-reacted with each other. Analysis of the PL preparations by thin-layer chromatography and reversed-phase high-performance liquid chromatography (HPLC) showed the presence of several components. Lupus sera reacted with one component mainly in the HPLC-fractionated K30PL preparation, although this component appeared to be present in the other PL preparations. Direct-binding and inhibition studies showed that affinity-purified antibodies to the K30PL extract, PS, or PI reacted poorly with DNA. However, the anti-K30PL antibodies possessed a prominent anti-DNA idiotypic marker (AM Id) in 61% of the patients and an anti-K30p idiotypic marker (SP Id) in 94% of the patients. The results thus show that anti-K30PL antibodies are idiotypically related to anti-DNA and anti-K30p antibody subpopulations, although they do not share the same antigen-binding characteristics.

A monoclonal DNA-binding autoantibody causes a deterioration in renal function in MRL mice with lupus disease

Two DNA-binding monoclonal antibodies (MoAb) derived from lupus mice were examined for their effects on kidney function. Antibody IV-228, reactive with single-stranded DNA (ssDNA) but not double-stranded DNA (dsDNA) significantly altered kidney function in some MRL/Mp-lpr/lpr (MRL/lpr) mice with lupus glomerulonephritis. Antibody II-410, preferentially reactive with dsDNA, did not modify kidney function in MRL/lpr mice. Neither antibody affected normal healthy MRL/Mp- +/+ (MRL/n) mice. Not all MRL/lpr mice were equally affected by IV-228 and in some animals with clinical disease it was without effect even when high circulating antibody levels were maintained by five sequential daily injections. Its affects upon kidney function appeared to be related to its ability to localize in vivo in glomeruli. It is assumed that epitopes on trapped immune complexes are immunologically available to circulating antibodies, and in those animals where injected antibody is not captured this is because the antigen epitope is either absent or is masked by the animals' own auto-antibodies. We conclude that antibodies which bind to ssDNA contribute to lupus nephritis; that individual mice make DNA-binding antibodies of different fine specificity; and that kidney disease is not always due to the same balance of antibodies in members of a genetically homogeneous stock.

Epstein-Barr virus-transformed B cells bearing idiotypes of anti-DNA autoantibodies

Epstein-Barr virus (EBV)-transformed B cells obtained from healthy subjects had the same idiotypes of anti-DNA autoantibodies on their surface as those obtained from patients suffering from systemic lupus erythematosus. These clones secreted anti-single-stranded or anti-double-stranded DNA antibodies. Among them, some produced anti-DNA idiotype-positive antibodies but failed to bind DNA. This was confirmed by a competitive inhibition radioimmunoassay. It was then considered whether or not the expression of anti-DNA idiotype on B-cell clones related to the anti-DNA antibody activity in vivo. The amounts of anti-DNA antibodies were not associated with the incidence of idiotype-positive B cells in the EBV-transformed cell lines from normals. The results indicate that the clones committed to the synthesis of anti-DNA idiotype-positive antibodies commonly exist at a resting state in the circulation of healthy subjects, probably through the self-tolerance regulatory system.

Relationship of age and sex to autoantibody expression in MRL-+/+ and MRL-lpr/lpr mice: demonstration of an association between the expression of antibodies to histones, denatured DNA and Sm in MRL-+/+ mice

Despite the protean nature of the clinical characteristics of systemic lupus erythematosus (SLE), autoantibodies represent an almost constant feature. Furthermore they are common to both human SLE and murine lupus. Nonetheless, the mechanism by which they arise has not been established. Amongst the several processes that have been proposed, evidence has emerged supporting specific antigen drive as a significant mechanism. We have documented the age- and sex-related differences in the prevalence of antibodies to both chromatin-related (histone and DNA) and non-chromatin-related (Sm) antigens in MRL mice. Our finding of an association between antihistone antibodies and anti-denatured DNA antibodies is consistent with chromatin being the putative antigen. Additionally, antibodies to the individual histones H1 and H2B, the most exposed histones in chromatin, were more prevalent than antibodies to the remaining histones (H2A, H3, H4). This, again, supports specific antigen drive as a mechanism for autoantibody production. However, associations were also found between antibodies to histone and DNA and antibodies to Sm. As Sm is a non-chromatin protein antigen, the associations between antibodies to Sm and those to histone and DNA suggest that mechanisms in addition to specific antigen drive are important in autoantibody production.

Specific antigen/antibody complexes induce the in vivo production of a parallel set of nonantigen-binding idiotype-positive antibodies

Immune complexes prepared with the polysaccharide antigen (PnC) extracted from Streptococcus pneumoniae R36a and two different PnC-specific antibodies were found to differ in their regulatory properties depending on the isotype of the antibody. Thus, complexes formed in antibody excess with TEPC15 (IgA) were suppressive whereas complexes formed with 96-G (IgG3) antibodies enhanced the IgM response to PnC. During the course of these studies, we found that little or no PnC-specific IgG antibody was induced during the response to PnC coupled to sheep red blood cells (PnC-SRBC). Interestingly, however, immunization with 96-G/PnC complexes either alone or with PnC-SRBC resulted in the induction of IgG3 antibodies that express the T15 idiotype (Id) but which do not bind PnC. This unique IgG3 response occurred after injection of 96-G/PnC complexes formed in antibody excess but not when complexes were formed in antigen excess. The Id+ nonspecific IgG3 response peaked on day 5 and could be activated with 96-G/PnC complexes but not with free PnC antigen. The Id+ nonspecific response was not due to polyclonal activation of IgG3 production since there was no difference in IgG3 levels in mice injected with 96-G/PnC complexes with those injected with PnC-SRBC. Finally, mice that had been suppressed for expression of the T15 Id by neonatal injection of anti-Id antibody were able to produce Id+-unspecific IgG3 antibody after immunization with 96-G/PnC complexes, further suggesting that Id+ IgG3 was produced by different clones than those that usually comprise the antibody response to PnC. The results suggest that the formation of IgG immune complexes during an immune response may result in stimulation of idiotypically related clones thus resulting in degeneracy of the immune response.

Autoantibodies of various specificities encoded by genes from the VH J558 family bind to foreign antigens and share idiotopes of antibodies specific for self and foreign antigens

We examined the binding to foreign antigens and the expression of crossreactive idiotypes by a panel of 20 murine monoclonal autoantibodies encoded by V genes from the VH J558 family. 9 of 20 antibodies bound to foreign antigens such as bacterial polysaccharides, poly(Glu50, Tyr50), poly(Glu54,Lys37,Phe9), arsonate, and lysozyme, known to interact with antibodies encoded by genes from the VH J558 family. A high proportion of our panel of autoantibodies expressed crossreactive idiotypes originally borne by monoclonal rheumatoid factors, anti-Sm, and anti-DNA antibodies, all encoded by V genes from the VH J558 family. Some of these VH J558+ autoantibodies shared crossreactive idiotypes with VH J558+ antibodies directed against foreign antigens such as influenza virus hemagglutinin, poly(Glu60,Ala30,Tyr10), arsonate, and dextran. The implications of these findings are discussed with respect to the process of activation of self-reactive clones.