Molecular characterization of a somatically mutated anti-DNA antibody bearing two systemic lupus erythematosus-related idiotypes

The repertoire of human germline VH sequences reveals about fifty groups of VH segments with different hypervariable loops

We have used the polymerase chain reaction and VH family-based primers to clone and sequence 74 human germline VH segments from a single individual and built a directory to include all known germline sequences. The directory contains 122 VH segments with different nucleotide sequences, 83 of which have open reading frames. The directory indicates that the structural diversity of the germline repertoire for antigen binding is fixed by about 50 groups of VH segments: each group encodes identical hypervariable loops. The directory should help in mapping the VH locus, in estimating somatic mutation and VH segment usage and in designing and constructing synthetic antibody libraries.

Variable region cDNA sequences of three mouse monoclonal anti-idiotypic antibodies specific for anti-alpha(1----6)dextrans with groove- or cavity-type combining sites

The variables regions of three syngeneic anti-idiotypic antibodies (Ab2s) were cloned and sequenced. They are encoded by different VL genes, two are from different members of V kappa-Ox1 superfamily. The H chains are encoded by VH genes belonging to three different VH families, J558, Q52 and 7183. Together with a previous report from this laboratory, the nucleotide sequences of four Ab2s to anti-alpha(1----6)dextrans have been presented. They are derived from a number of unrelated germline genes, and differ from similar studies in anti-NP, anti-GAT and anti-Ars systems. Three of four Ab2s in the anti-alpha(1----6)dextran system appear to have D-D fusions, which has also been reported in several other Ab2s.

VH-gene representation in autoantibodies reflects the normal human B-cell repertoire

The recurrence in the V-gene repertoire of individual germline VH genes can now be extended from the restricted B-cell populations of the fetus, autoantibodies and B-cell malignancies to the expressed V-gene repertoire of normal adults. Why the human B cell preferentially utilizes these individual VH genes remains speculative. However, it is apparent that the population of VH genes used to encode autoantibodies reflects the normal expressed repertoire (Fig. 7). Even so, the overrepresentation of other V genes such as Dxp'1 in anti-DNA antibodies and the presence of somatic mutation in the pathogenic autoantibodies of autoimmune disease continues to suggest an antigenic influence on V-gene selection. We postulate that only a fraction of available germline V genes are utilized in the expressed repertoire, and that polyspecificity of naturally occurring antibodies and somatic mutation of CDR3 compensate for the loss of diversity entailed by the limited use of the potential repertoire. The mechanisms by which germline genes become pathogenic remains unclear but they presumably relate to mutation, loss of regulatory control or perhaps environmental factors (Isenberg et al. 1992). What then are the mechanisms which lead to escape of these VH genes from normal control? What antigenic drive if any produces anti-DNA specificity in SLE? Why indeed is the expressed repertoire using only a fraction of the available germline? To answer these questions, further study of the V-gene repertoire of selected populations of antigen-binding cells and of pathogenic IgG autoantibodies is necessary and is ongoing. The contribution of individual V genes to antigen binding and idiotype is also being dissected and promises to yield important information about the relative contribution of VH genes to autoimmunity.

Molecular analysis of the V kappa III-J kappa junctional diversity of polyclonal rheumatoid factors during rheumatoid arthritis frequently reveals N addition

Much interest was stirred in recent years by the evidence that rheumatoid factors (RF) variable regions are encoded by a restricted set of V genes, with little or no somatic mutations, that are often overexpressed in the fetal repertoire. This is reminiscent of what has been observed for natural autoantibodies. However, these data come from studies of monoclonal RF (mRF) isolated from patients with lymphoproliferative disorders who usually do not present autoimmune symptoms. The molecular characterization of RF during autoimmune diseases such as rheumatoid arthritis (RA) has been hampered for some time because of their polyclonality; recently using the polymerase chain reaction method, we have demonstrated that RF kappa variable regions from a patient with RA were encoded by V kappa III genes known to code for mRF but that these genes had undergone somatic mutations with a pattern suggesting an antigen-driven maturation. Because an important role of the light chain third complementarity-determining region (CDR3) in anti-IgG reactivity and idiotype expression has already been suspected for RF, we now report the molecular characterization of the junction regions of these rearranged V kappa gens. Surprisingly, our data show that in 55% of the cases there is addition of a proline and/or glycine amino acid residue at the recombination site between V kappa and J kappa. The sequence analysis of our patients' germ-line Vg and J kappa 4 genes segments and their flanking regions demonstrates that the additional codons are not readily explicable by recombination between germ-line sequences and probably result from an N addition process. Since we could not find such an additional codon in 15 previously published mRF kappa chains we suggest that "pathogenic" RF during RA and mRF derive from different, although overlapping, B cell subsets. Moreover, since additional codons at the recombination site of V kappa and J kappa seem exceptional in expressed human kappa chains and because the resulting amino acid residue is a proline in most cases, we think that RF kappa chain CDR3 is under a very strong selective pressure during RA.

Expression of inactive stage anti-dsDNA idiotypes on anti-ssDNA antibodies in a lupus patient during active stage of lupus cerebritis

The possibility that idiotypes (Ids) defined on anti-double stranded DNA (dsDNA) antibodies during active and inactive stages of lupus (1/84 Id and 4/90 Id, respectively) were expressed on anti-DNA antibodies during a subsequent active period (9/90) of the disease was investigated in a lupus patient with lupus cerebritis. Using rabbit (R)-anti-Ids specific to 1/84 Id and 4/90 Id in inhibition assays, the 4/90 Id was shown to be expressed on the framework regions of anti-single stranded DNA (ssDNA) but poorly on co-existing anti-dsDNA antibodies of active (9/90) stage. The 1/84 Id was poorly expressed on both types of 9/90 anti-DNA antibodies. While the 9/90 anti-ssDNA significantly bound to immobilized ssDNA and several single-stranded polynucleotides, only ssDNA inhibited the binding of the anti-ssDNA to ssDNA, suggesting its monospecificity toward ssDNA. Western blot analysis following isoelectric focusing showed that a spectrotype pattern of 4/90 Id-positive 9/90 anti-ssDNA IgG was similar to that of the 4/90 anti-dsDNA, suggesting that they are of related clonal origin. The present study suggests the idiotypic heterogeneity of anti-DNA antibodies and the shift of antigen specificity within an idiotypically related anti-DNA population during exacerbation of the disease.

Clonal frequency analysis of B cells producing pathogenic anti-DNA antibody-associated idiotypes in systemic lupus erythematosus

In order to identify the mechanism responsible for autoantibody production in systemic lupus erythematosus (SLE), B cell repertoires associated with anti-DNA idiotypes were explored by a limiting dilution analysis using Epstein-Barr virus (EBV) transformation methods and ELISA spot assays. The frequencies of B cell clones producing antibodies to DNA and to conventional antigens, tetanus toxoid, dinitrophenyl, or keyhole limpet hemocyanin were higher in active SLE compared to those in inactive SLE and in normal subjects. In addition, there was a disproportionate increase in anti-DNA antibody- and anti-DNA idiotype (Id)-producing clones at the precursor cell levels as well as at the mature cell level. On the other hand, numbers of anti-Id clones against anti-DNA-Id, termed 0-81 Id, were markedly increased at inactive stages of the disease but not at active stages. These were confirmed by serial studies in some patients with SLE. These results support a two-step mechanism for autoantibody production, in which initial polyclonal activation is followed by an antigen-driven process, and indicate an alteration of the precursor B cell repertoire in SLE, which may also associate with a preferential expansion of anti-DNA clones.

Complete amino acid sequence of the variable regions of two highly related heavy and light chains of human IgG (SFL) and IgM (RIV) rheumatoid factors

The complete amino acid structure of the variable regions of two monoclonal human rheumatoid factors (RF), antibodies that bind to the Fc portion of IgG, is presented. Although these RFs are of different isotypes, IgG (SFL) and IgM (RIV), they are highly related. They probably derive from the same KIII light chain variable region used, but the heavy chains are derived from genes of the VHIII family that are probably evolutionarily related. An analysis of the level of somatic mutation reveals that antigen selection was probably involved in the maturation of these clones. These antibodies, although highly related, are not merely IgM to IgG switch variants which occurred independently in different individuals. Little is currently known about the structure of IgG RFs and this study indicates that the level of somatic mutation of SFL is similar to other autoantibodies or antiviral antibodies of the IgG isotype.

Shift of private and not of cross-reactive anti-DNA idiotypes in systemic lupus erythematosus

The shift of private idiotype (Id) and cross-reactive Id (CRI) on anti-DNA antibodies in a lupus patient KE was investigated during a 7-year period. Anti-private Id and anti-CRI activities were separated by affinity chromatography from rabbit (R)-anti-Ids raised against KE anti-DNA antibodies during active (1/84) and inactive (4/90) stages of the disease. Anti-CRI isolated from the 84 R-anti-Id appeared to recognize binding site-related Ids that are shared with KE non-anti-DNA antibodies, unrelated lupus patients' sera, and certain normal sera. Id expression on serial serum samples of KE using these fractionated R-anti-Ids as probes showed that the 1/84 private Id expression declined while the 4/90 private Id expression gradually increased. Expression of the CRI showed a relatively stable pattern. These results suggest that anti-DNA populations detected by anti-private Id can shift, while populations expressing CRI may stay stable.

CD5 negative IGM rheumatoid factor B cells in B-chronic lymphocytic leukemia and benign mixed cryoglobulinemia

IgM-RF B cell precursors are abnormally overrepresented in "well differentiated" lymphoid monoclonal proliferations while data on less mature lymphoid malignancies are still awaited. This nevertheless suggests that RF activity plays a role in the transforming process perhaps by inducing constant stimulation of the precursor B cells. Despite the preferential use of similar VH and VL genes with little or no somatic hypermutations in both malignant B-cell CLL and nonmalignant mixed cryoglobulinemia, these proliferations do differ in CD5 membrane expression and in their clinical evolution. One possibility could be that CD5 glycoprotein is lost during maturation of the lymphocyte into a secreting cell as suggested by data on Waldenström's disease and the LES-CLL and by in vitro studies. Alternatively, CD5 expression could play an additional direct role in malignant transformation as suggested by recent data on the CD5 receptor ligand. Further data on the proliferating cells in both situations as well as on the genetic control of CD5 expression in B cells and its physiology should shed additional light on the mechanisms of B-cell malignancy.

Conserved natural humoral immunity to thyroglobulin in patients with multiple myeloma

We studied humoral immunity to human thyroglobulin (hTg) during the course of multiple myeloma (MM). In this report, we describe the anti-hTg antibody activity in the sera of patients with MM. Among 63 sera tested, 28 (44%) had IgG anti-hTg autoantibodies (aAb), 16 (25%) exhibited IgM aAb, and six (9%) had IgA anti-hTg aAb. For the majority of sera the anti-hTg autoantibody activity was associated with more than one immunoglobulin class. IgG anti-hTg antibodies were observed in 9/11 patients with IgA MM and in 19/40 patients with IgG MM. The IgM anti-hTG antibody activity was found in the sera of 11 patients with IgG MM. These results show that the anti-hTg activity in these patients is associated with residual polyclonal immunoglobulins. However, in the serum of one patient presenting a double monoclonal gammopathy (IgG and IgA lambda MM), the anti-hTg activity was carried by both the IgG lambda and the IgA lambda molecules, suggesting that in this case the activity was due to the monoclonal immunoglobulin itself. We also studied the epitopic specificity pattern of all these anti-hTg aAb. Only three sera recognized one antigenic region on hTg, suggesting that the majority of the anti-hTg aAb in MM patients were directed against antigenic regions other than those recognized by our panel of murine mAb. In conclusion, our results demonstrated that humoral immunity to hTg is maintained in MM patients. These data contrast with the well-documented suppression of immunity to foreign, especially bacterial, antigens described in MM.

Antitopoisomerase I monoclonal autoantibodies from scleroderma patients and tight skin mouse interact with similar epitopes

We have generated for the first time monoclonal antibodies (mAbs) specific for topoisomerase I (topo I) from scleroderma patients, and tight skin mice which develop a scleroderma-like syndrome. The epitope specificity of these antibodies has been determined using a series of fusion proteins containing contiguous portions of topo I polypeptide. Western blot analysis demonstrated that both human and mouse mAbs bound strongly to fusion protein C encompassing the NH2-terminal portion of the enzyme, and weakly to fusion proteins F and G containing regions close to the COOH-terminal end of the molecule. This crossreactivity is related to a tripeptide sequence homology in F, G, and C fusion proteins. It is interesting that a pentapeptide sequence homologous to that in fusion protein C was identified in the UL70 protein of cytomegalovirus, suggesting that activation of autoreactive B cell clones by molecular mimicry is possible. Both human and mouse mAbs exhibiting the same antigen specificity, also share an interspecies cross-reactive idiotope. These data suggest that B cell clones producing antitopo autoantibodies present in human and mouse repertoire are conserved during phylogeny, and are activated during the development of scleroderma disease.

Polymorphism of human immunoglobulin VH4 germ-line genes

The human immunoglobulin VH4 gene family is thought to contain approximately 10 germ-line genes and to exhibit little polymorphism. We report here an analysis of VH4 germ-line genes that were amplified from DNA of two unrelated individuals. Ten unique (non-repetitive) sequences were obtained from individual A and 11 from individual B. Nine of these sequences represent new germ-line genes, and 8/9 exhibit only 89%-96% similarity to genes identified previously. Subsets of VH4 genes displayed distinctive nucleotide motifs that account for most of the differences between them. This observation suggests that diversity in the VH4 gene family arose from the acquisition of blocks of nucleotides, rather than by accumulation of point mutations. These nucleotide blocks could have been acquired by gene conversion or by homologous recombination. All of the VH4 genes have a potential N-linked glycosylation site at Asn 60, and some genes encode a second site at Asn 52. The VH4 gene family is larger and more polymorphic than appreciated previously. Immunoglobulin gene polymorphism may make a significant contribution to hereditary variations in the immune response and to the genetic predisposition to autoimmune diseases.

A systematic approach to defining the germline gene counterparts of a mutated autoantibody from a patient with rheumatoid arthritis

OBJECTIVE

To define the germline counterparts of potentially highly mutated autoantibodies in disease states.

METHODS

We developed a systematic approach by first characterizing a rearranged Ig gene and its upstream flank, and then designing suitable primers to amplify specifically the putative germline counterpart.

RESULTS

We identified and characterized the germline counterpart of a rheumatoid factor heavy chain variable region.

CONCLUSION

We showed unequivocally that the heavy chain of a rheumatoid factor, derived from synovial tissue, has 4 replacement mutations from the corresponding germline gene. The technique allows quick assessment of the degree of somatic mutation in many autoantibodies, and thus can help to elucidate the underlying mechanisms for the induction and sustained production of such antibodies in patients.

Isotypic and allotypic analysis with monoclonal antibodies and jacalin of 309 serum monoclonal IgA from French and Japanese myeloma patients

The subclass and allotype distribution of serum monoclonal IgA from myeloma patients was determined by ELISA with monoclonal antibodies in two French and one Japanese laboratory. In addition, the French sera were tested for their reactivity with the lectin jacalin. No significant difference in the isotypic distribution between French and Japanese series could be demonstrated: kappa/lambda ratios were 0.99 and 1.17, and the IgA1 subclass accounted for 93.9% and 91% of cases in the French and Japanese studies, respectively. Five out of 7 myeloma IgA2 from Japan and only one of the 12 IgA2 from France belonged to the A2m(2) allotype (P less than 0.01). All 219 IgA1 tested reacted with jacalin by immunoelectrophoresis (IEP), although with variable intensities. Among IgA2 proteins, only one (of the A2m(1) allotype) yielded a precipitating line with jacalin by IEP. Molecular analysis demonstrated that this protein was an IgA1-IgA2 hybrid bearing most of the A2m(1) epitopes.

The human VH repertoire: a restricted set of VH genes may be the target of immune regulation

During the development of the immune system, a restricted set of VH gene segments provides the bulk of the immunoglobulin heavy chain repertoire. Most of these VH genes have been found later in life encoding autospecificities either in normals or in patients with autoimmune diseases. Additionally, there is considerable evidence that the fetal/neonatal B-cell repertoire is autoreactive and idiotypically connected. In the course of sequencing the heavy chain of a panel of human autoantibodies mainly derived from patients with autoimmune diseases, we found that one of the VH families, and more specifically one single VH gene contributes to a large extent to the adult autoimmune repertoire in restricted as well as unrestricted responses. This VH gene segment is not particularly overexpressed in the fetus. Since the only common element to these autoreactive responses is the region encoded by the VH gene itself, these observations may provide an important insight into B-cell regulation.

Lupus anti-DNA antibodies bearing the 8.12 idiotype appear to be somatically mutated

Anti-DNA antibodies in systemic lupus erythematosus (SLE) sera were analyzed using an antiidiotype designated 8.12 which recognizes a determinant on lambda light chains highly expressed in SLE sera. Eight of ten normal individuals had peripheral blood lymphocytes which produced high-titered 8.12-positive antibodies, following transformation with Epstein Barr virus, implying that the 8.12-reactive sequence originates in the germline gene (GLG). Of 58 SLE sera, 32 contained elevated titers of 8.12-reactive antibodies. Twenty-three of these sera had 8.12-reactive anti-DNA antibodies, suggesting a strong correlation between 8.12 idiotype and DNA binding. Moreover, 20 of 26 8.12-reactive IgG antibodies and only 4 of 10 8.12-reactive IgM antibodies bound DNA (P less than 0.05). These observations strengthen our previous findings in myeloma sera that DNA binding is associated with IgG isotype in the 8.12 idiotype system and suggest that the acquisition of anti-DNA reactivity in antibodies bearing the GLG idiotype 8.12 is achieved by somatic mutation, a feature of an antigen-driven response.

Idiotypic and immunochemical differences of anti-DNA antibodies of a lupus patient during active and inactive disease

IgG anti-DNA antibodies of a lupus patient during active and inactive stages of her disease were studied. There were no significant differences in the amounts, in double-stranded DNA-binding activity, or in complement-fixing ability between purified IgG anti-DNA antibodies of both stages. However, their idiotype (Id) expressions were different as revealed by binding to rabbit anti-Ids raised against each of the anti-DNA antibodies. Moreover, the active stage anti-DNA antibodies had higher activity and less cross-reactivity with polynucleotides. Dominant anti-DNA populations during the active and inactive stages of systemic lupus erythematosus are clonally and qualitatively different.

Molecular characteristics of antibodies bearing an anti-DNA-associated idiotype

Anti-double-stranded DNA antibodies are the hallmark of the disease systemic lupus erythematosus and are believed to contribute to pathogenesis. While a large number of anti-DNA antibodies from mice with lupus-like syndromes have been characterized and their variable region genes sequenced, few human anti-DNA antibodies have been reported. We describe here the variable region gene sequences of eight antibodies produced by Epstein-Barr virus (EBV)-transformed B cells that bear the 3I idiotype, an idiotype expressed on anti-DNA antibodies and present in high titer in patients with systemic lupus. The comparison of these antibodies to the light chains of 3I+ myeloma proteins and serum antibodies reveals that EBV transformation yields B cells producing antibodies representative of the expressed antibody repertoire. The analysis of nucleotide and amino acid sequences of these antibodies suggests the first complementarity determining region of the light chain may be important in DNA binding and that paradigms previously generated to account for DNA binding require modification. The understanding of the molecular genetics of the anti-DNA response requires a more complete description of the immunoglobulin germ line repertoire, but data reported here suggest that somatic diversification is a characteristic of the anti-DNA response.

Sequence analysis and idiotypic relationships of BEG-2, a human fetal antibody reactive with DNA

Monoclonal antibody (mAb) BEG-2 is a dsDNA binding IgM lambda derived from a 12-week human fetus. Two binding site idiotypes (BEG-2 Id alpha and BEG-2 Id beta) have been defined with the use of polyclonal rabbit anti-idiotypic anti-serum. BEG-2 Id alpha is located on the lambda light chain and has been described previously. The BEG-2 Id beta is present on the mu heavy chain. By means of a direct binding ELISA, BEG-2 Id beta has been identified on EBV-derived mAbs from human fetal liver or spleen (5%), human cord blood (2.7%) and adult peripheral blood (1%). In addition, the Id is present on 8.5% of adult spleen-derived hybridoma antibodies and 6% of RA synovium-derived hybridoma antibodies. In all populations the presence of the Id is strongly associated with binding to DNA and other polyanions. Competition assays indicated that the Id was located at or near the antigen-binding site on these molecules. To explore the structural basis of this binding, a major part of the BEG-2 heavy chain was sequenced and found to be encoded by a member of the VH4 family joined to a variant of JH5 by a very short Diversity or N region. Of the BEG-2 Id beta positive mAbs for which the VH family has been determined, five are encoded by VH4 and two are encoded by VH6, but none is encoded by other families. Thus, the BEG-2 Id beta identifies a set of polyreactive antibodies that are common in fetal life, persist into adulthood and are encoded by VH6 and, a subset of VH4 genes.

Quantification of cross-reactive idiotype-positive rheumatoid factor produced in autoimmune rheumatic diseases. An indicator of clonality and B cell proliferative mechanisms

The aetiology of sustained autoantibody production in human autoimmune diseases is unknown. Evidence for structural similarities and common clonal origin among autoantibodies have been demonstrated through the expression of cross-reactive idiotype (CRI). In the present study we use four monoclonal antibodies (MoAbs) with specificity for non-overlapping CRI on human rheumatoid factor (RF) autoantibodies to define the structural features of polyclonal RF characteristic of patients with autoimmune rheumatic diseases. The pattern of CRI expression in the serum of 12 patients with rheumatoid arthritis (RA), eight with systemic lupus erythematosus (SLE) and 20 with primary Sjögren's syndrome and 34 normal individuals were determined in parallel with the level of IgM RF, IgA RF and autoantibodies to the cellular antigens SS-A, SS-B, Sm, nRNP and dsDNA and cryoglobulins. The results demonstrate significant elevation in the level of IgM and IgA expressing VHI (G6 and G8) and VHIII (B6 and D12) associated CRI in the serum of patients with autoimmune rheumatic diseases compared with normal individuals. These increases paralleled, but did not equal the increase in the level of immunoglobulins and RF. However, when expressed as proportion of immunoglobulin, only the VHI-associated CRI were significantly elevated in patients compared with normal individuals. The proportion of IgM RF expressing the VHI-associated CRI was higher in patients with Sjögren's syndrome compared with SLE and RA. Furthermore, the proportion of IgA RF expressing the G6 CRI was higher than G6+ IgM RF. These findings imply that different mechanisms contribute to RF production in autoimmune diseases. It is suggested that polyconal B cell activation is likely to be a contributing mechanism. However, such polyclonal activation is unlikely to be random since a selective elevation in the level of specific autoantibodies and VHI-associated CRI is observed. Furthermore, the data demonstrate that a proportion of autoantibodies in autoimmune diseases are immunoglobulin germline gene encoded. This is more evident in some patients with primary Sjögren's syndrome, where RF is likely to be oligoclonal or monoclonal in individuals with lymphoproliferation.

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

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

Generation and analysis of clonal IgM- and IgG-producing human B cell lines expressing an anti-DNA-associated idiotype

This study describes a methodology for generating stable, cloned, EBV-transformed IgG- and IgM-producing human B cell lines. Using these lines we have characterized immunoglobulin V gene utilization in an anti-DNA-associated idiotypic system. The 31 anti-DNA-associated idiotype is encoded preferentially by the VK1 gene family, and, in all probability, reflects a germ line gene-encoded framework determinant. Analysis of these lines indicates that the DNA-binding antibodies produced by B cell lines from SLE patients may differ from DNA binding myeloma proteins and from natural autoantibodies.

Molecular analysis of V kappa III variable regions of polyclonal rheumatoid factors during rheumatoid arthritis

We report the first molecular characterization of V kappa regions of the main human autoantibodies occurring during rheumatoid arthritis, the polyclonal rheumatoid factors. Using two sets of polymerase chain reactions in order to amplify the cDNA derived from both peripheral blood and synovial fluid rheumatoid factor-secreting cells, nucleotide analysis of the V kappa III family usage shows the following: (a) at least three different V kappa III genes are used to encode polyclonal rheumatoid factors in a single patient, (b) each one of these genes seems more or less somatically mutated (from 1 to 14 mutations), (c) the mutation process preferentially affects the complementarity determining regions suggesting a selective pressure of antigen and (d) there is no clear difference between the mutation rates affecting the synovial fluid and peripheral blood rheumatoid factor-secreting cells. These results are able to explain some of the known idiotypic differences between monoclonal and polyclonal rheumatoid factors in humans. They also provide evidence that polyclonal autoantibodies arising during an autoimmune disease can be the products of multiple somatically mutated genes and suggest that this process is antigen driven, whether this antigen is the Fc piece of IgG or another unknown antigen.