Restricted diversity of the variable region nucleotide sequences of the heavy and light chains of a human rheumatoid factor

Production and characterization of an Fv-clasp of rheumatoid factor, a low-affinity human autoantibody

Rheumatoid factor (RF) is an autoantibody against IgG that affects autoimmune diseases and inhibits the effectiveness of pharmaceuticals and diagnostic agents. Although RFs derived from various germline genes have been identified, little is known about their molecular recognition mechanisms. In this study, the Fv-clasp format was used to prepare YES8c, an RF. We developed an Escherichia coli secretion expression system capable of producing milligram-scale of YES8c Fv-clasp per 1 L of culture. Although YES8c is an autoantibody with very low affinity, the produced Fv-clasp maintained specific binding to IgG. Interestingly, the molecules prepared by E. coli secretion had a higher affinity than those prepared by refolding. In the structure of the YES8c-Fc complex, the N-terminus of the light chain is close to Fc; therefore, it is suggested that the addition of the N-terminal methionine may cause collisions with Fc, resulting in reduced affinity. Our findings suggest that the Fv-clasp, which provides sufficient stability and a high bacterial yield, is a useful format for studying RFs with very low affinity. Furthermore, the Fv-clasp produced from a secretion expression system, which can properly process the N-terminus, would be suitable for analysis of RFs in which the N-terminus may be involved in interactions.

Structure-function analyses of a stereotypic rheumatoid factor unravel the structural basis for germline-encoded antibody autoreactivity

Rheumatoid factors (RFs) are autoantibodies against the fragment-crystallizable (Fc) region of IgG. In individuals with hematological diseases such as cryoglobulinemia and certain B cell lymphoma forms, the RFs derived from specific heavy- and light-chain germline pairs, so-called "stereotypic RFs," are frequently produced in copious amounts and form immune complexes with IgG in serum. Of note, many structural details of the antigen recognition mechanisms in RFs are unclear. Here we report the crystal structure of the RF YES8c derived from the IGHV1-69/IGKV3-20 germline pair, the most common of the stereotypic RFs, in complex with human IgG1-Fc at 2.8 Å resolution. We observed that YES8c binds to the CH2-CH3 elbow in the canonical antigen-binding manner involving a large antigen-antibody interface. On the basis of this observation, combined with mutational analyses, we propose a recognition mechanism common to IGHV1-69/IGKV3-20 RFs: (1) the interaction of the Leu⁴³²-His⁴³⁵ region of Fc enables the highly variable complementarity-determining region (CDR)-H3 to participate in the binding, (2) the hydrophobic tip in the CDR-H2 typical of IGHV1-69 antibodies recognizes the hydrophobic patch on Fc, and (3) the interaction of the highly conserved RF light chain with Fc is important for RF activity. These features may determine the putative epitope common to the IGHV1-69/IGKV3-20 RFs. We also showed that some mutations in the binding site of RF increase the affinity to Fc, which may aggravate hematological diseases. Our findings unravel the structural basis for germline-encoded antibody autoreactivity.

Rheumatoid factors: host resistance or autoimmunity?

Rheumatoid factors (RFs), autoantibodies that bind to the Fc portion of IgG, are important in the immune response. RF-committed B-cells exist in the circulating lymphocyte pool in a high frequency (approximately 1-2 %) in normal individuals and in patients with pathological conditions associated with the sustained levels of circulating RF, such as rheumatoid arthritis (RA), Sjogren's syndrome (SS), and mixed cryoglobulinemia, associated with hepatitis C virus infection. RFs are induced by many infectious entities (viruses, bacteria, parasites) as a consequence of a secondary immune response to the pathogen, but usually the response is transient. It is likely that RFs play an important role in the host's defense against infection, both at the cellular level, where the RF B-cell can be an antigen presenting cell which can promote the antipathogen response, and at the humoral level, where RFs can contribute to the mopping up of the IgG antipathogen antibodies by contributing to immune complex formation and clearance. There has been much research on RFs in chronic pathological conditions, and the literature pertaining to their origin, structure, binding specificities, and possible roles in disease are discussed. The importance of the host defense, sometimes at the expense of an autoimmune response, is a balance that needs to be considered in light of a possible outcome of health or disease.

Preparation of human-mouse heterohybridomas against an immunising antigen

The production of murine monoclonal antibodies against specific antigens by hybridomas is a well utilised technique. The production of hybridomas secreting specific human antibodies would have many advantages in therapeutic applications of monoclonal antibodies. The immortalised human lymphocytes themselves would also provide valuable tools in research on lymphocyte development. Preparation of human-human hybridomas has been limited by a lack of suitable fusion partners. This protocol paper describes the production of human-mouse heterohybridomas by two independent laboratories. The purpose of this protocol is to provide a basis for the development of heterohybridoma technology in laboratories with limited hybridoma experience.

Molecular analysis of rheumatoid factor (RF)-negative B cell hybridomas from rheumatoid synovial tissue: evidence for an antigen-induced stimulation with selection of high mutated IgVH and low mutated IgVL/lambda genes

The mutational pattern of IgVH and IgVL genes from synovial tissue B cell hybridomas (n = 8) of patients (n = 4) with rheumatoid arthritis (RA) was analysed, which had been produced by the electrofusion technique without prior in vitro stimulation. The molecular data were correlated with immunohistopathological data and parameters of local disease activity. The IgVH genes of the B cell hybridomas belonged to the VH3 family (DP42; DP47, n = 2; DP53), the VH1 family (DP75), the VH4 family (DP71) and the VH5 family (DP73); 7/7 IgVH genes showed somatic mutations, the R/S ratio (CDR) was > 3 in 4/7 IgVH genes and the mean R/S ratio of all IgVH genes was 9.3 (CDR) and 1.0 (FR), suggesting an antigen-dependent selection. The IgVL/lambda genes belonged to the Vlambda1 family (DPL2, DPL5, DPL8nf), the Vlambda2 family (DPL11, n = 2) and to the Vlambda6 family (IGLV6S1); 6/6 IgVL genes showed somatic mutations, the R/S ratio (CDR) was > 3 in 3/6 IgVL genes and the mean R/S ratio of all IgVL was 3.0 (CDR) and 2.3 (FR), suggesting an antigen-dependent selection. The synovial tissue exhibited germinal centres in the follicles (3/4), with the unique distribution of Ki-M4+ follicular dendritic cells and Ki-67+ proliferating cells and a dominance of IgA+ plasma cells (3/3). All patients were positive for RF in serum and exhibited severe local symptoms (swelling 4/4; warmth 4/4; effusion 2/4), whereas the hybridomas were negative for RF. Since B cell hybridomas showed hypermutation and affinity selection for IgVH and IgVL/lambda genes and the patients exhibited severe local symptoms with germinal centres in synovial tissue, this study indicates that an antigen-driven process is behind the B cell expansion in the synovial tissue of clinically affected joints. These mutated B hybridomas were negative for RF, thus suggesting that antigens different from RF are also involved in the local B cell expansion and in the chronic synovitis of RA.

V region gene analysis of human IgM hybridoma monoclonal anti-Sm antibodies

Anti-Sm antibodies although highly specific for systemic lupus erythematosus can only be found in 10-25% of lupus patients and lupus-prone MRL/lpr mice. Molecular studies of these autoantibodies from mice have suggested that the anti-Sm response is Ag driven, its expression is controlled by stochastic events and may originate from the same B cell precursors as anti-DNA antibodies. However, relatively little information regarding the molecular characteristics of anti-Sm antibodies in man has been reported. We studied the V region genes of three IgM hybridoma monoclonal antibodies (BUD 45.12.8, BUD 114.4.11 and BUD 94.91.8) which were selected for Sm reactivity and derived from B cells of a healthy child. Two of these antibodies BUD 45.12.8 and BUD 114.4.11 also-reacted with ssDNA, while the third (BUD 94.91.8) did not. Each of these anti-Sm/ RNP antibodies was encoded by different and predominantly unmutated Ig heavy chain germline genes (BUD 45.12.8 by VH3-23, DXP4 and JH4b; BUD 94.91.8 by VH3-33, D21-9 and JH6b; BUD 114.4.11 by VH1-2, DK1 or DM1 or unknown D and JH4b) and light chain genes (BUD 45.12.8 by Humkv325 and JK2; BUD 94.91.8 by hsiggll150 (lambda IIIb) and J lambda 2/3; BUD 114.4.11 by Humk18 and JK3). Many of these genes are also used by antibodies with other specificities including DNA. The two anti-Sm antibodies which also bound ssDNA shared an overall V region net positive charge, while the third antibody without ssDNA reactivity carried a negative V region net charge. These findings demonstrate that (1) normal individuals have the genetic potential to generate autoantibodies to Sm/RNP; (2) acquisition of Sm/RNP binding is not dependent on somatic mutations and (3) some human B cell clones exhibit specificity for Sm and ssDNA.

Analysis of the molecular basis of synovial rheumatoid factors in rheumatoid arthritis

The objective of this study was to better understand the molecular basis of IgM rheumatoid factor in rheumatoid arthritis (RA). We recently generated 10 different monoclonal IgM RF (mRF) molecules isolated from the synovium of a single patient with RA. The heavy (H) and light chain (L) variable region (V) genes of these 10 mRFs were cloned and sequenced. Six mRFs used kappa light chains and 4 mRFs used lambda light chains. Of particular interest, 8 of 10 heavy chains used the JH4 joining region gene, and all five VH4 heavy chains used the DK4 diversity region gene with the JH4. Four of the VH4 clones used the same germline gene, likely representing a novel but closely related germline gene to VH4.18, and may be clonally related because of the extensive homology in their heavy chain sequence. Two VH4 clones shared the same light chain gene, VkappaIIIb kv325 (99% homology) and the same JK4 joining region gene, while three VH4 clones used two different light chain genes, an uncommon Vkappa4 and a Vlambda4 gene, respectively. In this RA patient, there was recurrent utilization of VH4-DK4-21/10-JH4 genes and a recurring association with gene elements Vkappa3 and Vlambda4. Recurring usage of Vkappa3 (kv325) and Vlambda4 (lv418) gene elements may result from a light chain editing process whereby immature autoreactive B cells encountering self-antigen attempt, and often succeed, in altering their specificities through secondary Ig light chain gene rearrangement. Moreover, the oligoclonality of these RFs suggest clonal relatedness secondary to an antigen-driven response.

Rheumatoid factor autoantibodies in health and disease

Recent advances in molecular biological and human cell hybridization technology have significantly advanced the knowledge of mechanisms that underlie human rheumatoid factor (RF) production. These advances have provided insight into the etiopathogenesis of synovial inflammation and lymphocyte recruitment in rheumatoid arthritis (RA) joints. We have examined the mechanisms that lead to RF production in RA patients and those that regulate RF production in normals. The studies revealed structural features that distinguish RF produced in normals from those produced in RA synovial tissue. There are significant differences in the use of VL and VH genes between the two RF populations. Furthermore, IgV genes encoding synovial RF in RA have extensive evidence for nucleotide changes, leading to amino acid replacement in the complementarity determining regions (CDRs). In addition, RF produced in RA synovia show evidence for affinity maturation, isotype switch to IgG RF, and repertoire shift indicative of a continued recruitment of B cells. Together with computer modeling and crystallographic studies, our data suggest that the mechanisms that operate on RF selection in RA synovia are similar to immune responses to exogenous antigens. In contrast, RF established from human immunized donors (HID) are characterized by a very low ratio of replacement to silent (R:S) nucleotide changes in the CDR1+2. In addition, there is little increase in affinity with increasing numbers of mutations. There is thus evidence for regulatory mechanisms that limit affinity maturation of RF in normals.

Differences in mutational patterns between rheumatoid factors in health and disease are related to variable heavy chain family and germ-line gene usage

The sequences of the heavy chain variable (V(H)) segment and dissociation constants (Kd) of 14 IgM rheumatoid factors (RF) derived from 11 different germline gene segments from five healthy immunized donors (HID) are described. We extend a previous analysis of two clones from one donor using only the germline segment DP-10. In the present study, the mutation patterns of these new RF and the two earlier reported HID RF clones are analyzed in relation to V(H) family, germ-line origin, and Kd. The panel of HID RF is further compared with 33 previously described IgM RF from patients with rheumatoid arthritis (RA). There is a high rate of mutation in the panel of HID RF (mean of ten mutations/V(H)). RF originating in RA patients have a comparable mutation rate (mean of 11 mutations/V(H)), suggesting that hypermutation of IgM RF is not disease related. The HID RF have, however, a significantly lower affinity for IgG than the RA RF. We found that the structural basis of the differences between HID and RA RF is related to V(H) family usage. RF of the V(H)1 family use very similar germ-line genes in HID and RA patients. HID RF of the V(H)1 family have, however, a low ratio of replacement-to-silent (R:S) mutations of only 0.41 in the heavy chain complementarity region (CDR(H))1 and 2. This is statistically significantly lower than the corresponding ratio of 3.14 in the V(H)1 RA RF. In contrast, RF of the V(H)3 family from HID and RA patients have very similar R:S ratios of 1.75 and 1.71 in CDR(H)1 and 2, respectively. The V(H)3 RA RF are, however, predominantly encoded by genes not encoding any HID RF. Thus, both repertoire differences and hypermutation resulting in significantly lower R:S ratios can be observed in RF from HID compared with RA RF.

V-gene repertoire and hypermutation of rheumatoid factors produced in rheumatoid synovial inflammation and immunized healthy donors

We have compared RF from normal, immunized donors and RF derived from the synovial tissues of RA patients. We have found a difference in the preferential use of VL and VH gene families. In both conditions, RFs were found to have accumulated somatic mutations. However, there was a striking difference in the patterns of mutation. RFs from normals were characterized by a very low R:S ratio in the CDR1+2, considerably lower than seen among the RARFs. In addition, there was little increase in affinity with increasing numbers of mutations in a group of clonally related RFs from an immunized normal. This contrasts with RF from RA, where there is evidence of both affinity maturation and class switching. Together these data suggest that in healthy persons there is a controlling mechanism to limit the affinity of RF autoantibodies, and that this is lost in RA. The higher affinity of the RA-derived RF may be of significance in the pathology of the disease.

Somatic mutation and CDR3 lengths of immunoglobulin kappa light chains expressed in patients with rheumatoid arthritis and in normal individuals

Immunoglobulin secretion by plasma cells infiltrating synovial membranes is a prominent feature of RA. Previous analyses of a cDNA library generated from synovium of RA patient BC revealed immunoglobulin kappa light chain transcripts with extensive somatic mutation, frequent N region addition, and unexpected variation in the lengths of CDR3 regions which form the center of the antigen binding site. To determine if these characteristics are present in other individuals, we performed reverse transcription-polymerase chain reaction amplification and sequenced > or = 10 V kappa-containing amplicons from nine tissue samples: synovia of three individuals with long-standing RA (including patient BC), PBLs of two of these individuals, and PBLs or splenocytes of four normal individuals. Increased levels of somatic mutation in PBLs appeared to correlate with increased age, which may reflect accumulation of circulating memory cells and/or decreased bone marrow production of naive B lymphocytes. Two of three RA synovial samples and both RA PBL samples exhibited increased proportions of clones with unusual CDR3 lengths. Enrichment for these antibody binding sites could be due to abnormal regulation of the emerging repertoire or to selection for B lymphocytes bearing antibodies of unusual specificity, and may play a role in the pathogenesis of RA.

Control of autoantibody affinity by selection against amino acid replacements in the complementarity-determining regions

Rheumatoid factor (RF) autoantibodies can be produced in healthy individuals after infections or immunizations and thus escape normal tolerization mechanisms. It has not been clear whether such autoantibodies can undergo somatic hypermutation and affinity maturation similar to antibodies to exogenous antigens. We have investigated how these autoantibodies are regulated in normal individuals by analyzing the sequences of monoclonal IgM RFs obtained as hybridomas from donors after immunization. The variable regions undergo extensive hypermutation, but in contrast to antibodies against exogenous antigens, there is a strong selection against mutations that result in replacement of amino acids in the hypervariable, or complementarity-determining, regions. Furthermore, we found no increase in affinity of these RFs with the accumulation of mutations. This suggests that high-affinity variants are tolerized during the hypermutation process and there is a peripheral mechanism operating on certain autoreactive B cells that, while not deleting or anergizing all autoreactive cells, prevents the generation of high-affinity autoantibodies. Comparison of RFs by using the VH1 DP-10 heavy chain variable region segment from both normal individuals and rheumatoid arthritis (RA) patients suggests that RF from RA patients may not be subject to such a controlling mechanism.

Defining the genetic origins of three rheumatoid synovium-derived IgG rheumatoid factors

A major diagnostic marker in most rheumatoid arthritis (RA) patients is the rheumatoid factor (RF), an autoantibody that binds to the Fc region of IgG. To delineate the Ig genes and the underlying mechanism for RF production in RA patients, we applied a systematic approach to define the genetic origins of three IgG RFs derived from the synovial fluid of two RA patients. The results show that two of three IgG RF have substantial numbers of somatic mutations in their variable (V) regions, ranging from 13 to 23 mutations over a stretch of 291-313 nucleotides, resulting in a frequency of 4.4-7.8%. However, one IgG RF has only one mutation in each V region. This result indicates that an IgG RF may arise from a germline gene by very few mutations. The mutations occur mainly in the complementarity-determining regions (CDRs), and the mutations in the CDRs often lead to amino acid substitutions. Five of the six corresponding germline V genes have been found to encode either natural autoantibodies or autoantibodies in other autoimmune disorders; and three of the six V genes have been found in fetal liver. Taken together with other results, the data show that (a) several potentially pathogenic RFs in RA patients arise from natural autoantibodies, and (b) only a few mutations are required to convert the natural autoantibodies to IgG RFs.

Preferential utilization of a novel V lambda 3 gene in monoclonal rheumatoid factors derived from the synovial cells of rheumatoid arthritis patients

OBJECTIVE

To further our understanding about the molecular genetics of rheumatoid factor (RF) in rheumatoid arthritis (RA).

METHODS

The heavy and light chain variable region (V) genes of 5 new human monoclonal IgM RFs were cloned and sequenced using the polymerase chain reaction and the dideoxynucleotide termination method.

RESULTS

The results reveal the recurrent usage in two RA patients of a novel V lambda 3 germline gene, designated Humlv3c93. Specifically, in 2 of 3 RFs (C93 and D53) from one patient, the light chains in the V lambda gene-encoded region were identical to each other and to the light chain of an RF (H4) from another patient. Serologically, the light chains of these 3 RFs were classified as members of the V lambda 3b sub-subgroup. Each of the RFs was encoded by a different VH gene. Both C93 and D53 bound specifically with human and rabbit IgG, whereas H4 was monospecific for rabbit IgG.

CONCLUSION

Since the lv3c93 gene is not homologous to any reported V lambda sequence from natural autoantibodies, it is possible that lv3c93 may represent a disease-specific RF-related V lambda gene. Moreover, the amino acid sequence CSGGSCY in the third complementarity-determining regions of 2 of the RF heavy chains is encoded by the DLR2 gene segment and has been found previously in 2 other RA-derived RFs, and thus may play a significant role in antigen binding.

Monospecific but not polyreactive human hybridoma rheumatoid factors exhibit preferential binding specificities for IgG3 and IgG4

Among 38 human hybridoma-derived monoclonal rheumatoid factors (RFs) generated from patients with either rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE), two groups of RFs can be identified. Monospecific RFs were derived primarily from patients with RA and are characterized by a binding specificity for IgG3 and/or IgG4. Polyreactive RFs were derived largely from patients with SLE and show a broader pattern of reactivity to all four isotypes of IgG. Neither population of RFs was exclusive to either disease. The binding specificities identified appear to be different from the RFs isolated from patients with mixed cryoglobulinemia and may reflect a different antigen selection mechanism.

Generation and molecular analyses of two rheumatoid synovial fluid-derived IgG rheumatoid factors

OBJECTIVE

To study the Ig genes that encode IgG rheumatoid factor (IgG-RF) from rheumatoid synovial fluid.

METHODS

We used rheumatoid synovial fluid B cells to generate IgG-RF-secreting hybridomas. We then characterized their binding properties and determined their nucleotide sequences.

RESULTS

Two monospecific IgG-RFs were obtained. Sequence analysis of the RFs revealed a new V lambda gene family (designated V lambda 9) and extensive somatic diversification, including a duplication-insertion of 18 nucleotides (6 amino acid residues) into a hypervariable region.

CONCLUSION

The data provide further support for an antigen-driven response in the sustained production of potentially pathogenic IgG-RFs in rheumatoid synovium.

Characterization of two highly homologous autoantibody-related VH1 genes in humans

Previously, we showed that the Humha 1lr rearranged gene was almost identical to the consensus amino acid sequence of several G6 idiotype-positive rheumatoid factor (RF) heavy chains, and to the VH gene-encoded region of the fetally expressed 51P1 cDNA. The finding led us to suggest that the ha 1lr-corresponding germline gene encodes the heavy chains of many human IgM RFs. We now report the isolation of the proposed germline gene, designated Humhv1051; it is identical to the consensus sequence of the G6 heavy chain V regions. During this experiment, we also isolated unexpectedly an additional VH1 gene, termed Humhv1051K; it differs from hv1051 by one amino acid residue. Importantly, hv1051K is identical to Humha113, the rearranged VH1 gene of a natural anti-cardiolipin antibody.

Molecular analysis of rheumatoid factors derived from rheumatoid synovium suggests an antigen-driven response in inflamed joints

OBJECTIVE

Understanding the molecular genetic basis for rheumatoid factor (RF) production is necessary to a better understanding of the etiology and pathogenesis of rheumatoid arthritis (RA). We sought to define the genetic basis of RF in RA.

METHODS

The heavy and light chain variable region genes encoding 4 human monoclonal RF were cloned and sequenced using the polymerase chain reaction and the dideoxynucleotide chain-termination method.

RESULTS

The heavy and light chains of the C6 RF and the light chain of the G9 RF were encoded by 3 new RF-related Ig V-region genes. The heavy and light chains of D5 and G4 RFs were identical; most of their mutations caused amino acid substitutions.

CONCLUSIONS

The RF-related Ig V-region gene repertoire is large and is still expanding. The data from D5 and G4 strongly suggest that these 2 RFs arise in an antigen-driven response in rheumatoid synovium. The presumed germline V genes for C6 may represent disease-specific RF-related V genes.

Restricted immunoglobulin variable region gene usage by hybridoma rheumatoid factors from patients with systemic lupus erythematosus and rheumatoid arthritis

Rheumatoid factors (RFs) are autoantibodies that are produced by approximately 75% of patients with rheumatoid arthritis (RA). Their role in pathogenesis is not well understood. In this study of 81 human hybridoma IgM antibodies derived from unstimulated peripheral blood B-cells of patients with RA and systemic lupus erythematosus (SLE), we have demonstrated that idiotypes associated with RFs derived from patients with mixed cryoglobulinemia were expressed by approximately 60% of RFs and 6% of IgM antibodies lacking RF activity. The specificity of the RFs for the Fc portion of IgG only (monospecificity) or for Fc and additional self antigens (polyreactivity) was found to correlate with the expression of specific heavy chain associated idiotypes. The VH3 associated RF idiotypes, D12 and B6, were expressed by 0/16 (0%) of monospecific RFs compared with 6/22 (27%) of polyreactive RFs. The predominant use of VH3 was verified by analysis of the expressed Ig with VH family specific anti-peptide antibodies. The light chains expressed by both populations of IgM RFs were found to be predominantly VKIII, both by detection of specific epitopes/idiotypes and V family analysis. This non-random gene usage of both the heavy and light chains suggests that there is a selective expression of V regions in the RF producing B-cells in patients with RA and SLE. We suggest that different antigen-driven, clonal selection events may occur which result in either monospecific RFs or polyreactive RFs.

Sequence analyses of three immunoglobulin G anti-virus antibodies reveal their utilization of autoantibody-related immunoglobulin Vh genes, but not V lambda genes

Accumulated sequence analyses of the antibody repertoire have revealed that most autoantibodies and developmentally regulated antibodies share a small set of germline Ig-variable region (V) genes. The findings have prompted speculation that certain autoantibodies are of developmental importance and may be instrumental in maintaining homeostasis of the adult antibody repertoire. In order to evaluate this hypothesis critically, it is first necessary to determine the V gene usage in human antibodies against foreign substances. Unfortunately, only a few such antibodies have had their heavy and light chains characterized. To rectify the situation, we adapted the anchored polymerase chain reaction to clone and analyze rapidly the expressed V genes for three anti-virus IgG antibodies. The results show that all three heavy chain V (Vh) genes are highly homologous to the known autoantibody-related Vh genes. In contrast, two light chain V (VL) genes of the V lambda 1 subgroup are similar to a non-autoantibody-related germline V lambda 1 gene. Taken together with the reported Vh and VL sequences of several antibodies against viruses and bacteria, the data show that many antipathogen antibodies may use the same small set of Vh genes that encode autoantibodies, but diverse VL genes that are distinct from autoantibody-related VL genes. Thus, only a small portion of the potentially functional germline Vh genes are used recurrently to generate most antibodies in a normal antibody repertoire, regardless of their reactivities with either self or non-self.

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.

A somatically mutated V kappa IV gene encoding a human rheumatoid factor light chain

The light chain of an IgA kappa rheumatoid factor (RF) produced by a hybridoma derived from a patient with rheumatoid arthritis (RA) has been shown to belong to the V kappa IV family. This RF light chain has 31 nucleotide differences compared with the single V kappa IV germline gene reported for the human genome. The patient's V kappa IV germline gene was sequenced, using the polymerase chain reaction (PCR), and shown to be identical to that previously reported. This demonstrates that the RF light chain is the product of a somatically mutated gene. A comparison with other known V kappa IV sequences shows that the RF light chain has more replacement mutations than most of the known V kappa IV light chains.

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.

Antibody multispecificity in immunoassay interference

Recent findings indicate that many endogenous antibodies exhibit multispecificity. These antibodies exhibit a potential for interference with immunoassays. Antibodies that interfere with immunoassays have been called heterophile or heterophilic antibodies. The purpose of this review is: (1) to identify the nature of heterophile antibodies; (2) to delineate the processes that produce them; (3) to examine the mechanisms by which these antibodies cause interference; and (4) to explore how this information can be used to reduce immunoassay interference. In addition to producing specific antibodies, the process of antibody production gives rise to rudimentary antibodies that are polyspecific; e.g., the antigen-combining site has an affinity for antigens of different chemical composition. This process also generates idiotypic antibodies containing cross-reactive idiotopes. These antibodies along with rheumatoid factors, which are themselves polyspecific and rich in cross-reactive idiotopes, are inherent parts of the process of antibody production, and exhibit multispecificity. Mechanisms by which these antibodies cause immunoassay interference are outlined. These properties of antibodies may have substantial consequence in directing future assays toward greater clinical predictive value.

Genetic analysis of self-associating immunoglobulin G rheumatoid factors from two rheumatoid synovia implicates an antigen-driven response

Although much has been learned about the molecular basis of immunoglobulin M (IgM) rheumatoid factors (RFs) in healthy individuals and in patients with mixed cryoglobulinemia and rheumatoid arthritis, little is known about the genetic origins of the potentially pathogenic IgG RFs in the inflamed rheumatoid synovia of patients. Recently, we generated from unmanipulated synovium B cells several hybridomas that secreted self-associating IgG RFs. To delineate the genetic origins of such potentially pathogenic RFs, we adapted the anchored polymerase chain reaction to rapidly clone and characterize the expressed Ig V genes for the L1 and the D1 IgG RFs. Then, we identified the germline counterparts of the expressed L1 IgG RF V genes. The results showed that the L1 heavy chain was encoded by a Vh gene that is expressed preferentially during early ontogenic development, and that is probably located within 240 kb upstream of the Jh locus. The overlap between this RF Vh gene and the restricted fetal antibody repertoire is reminiscent of the natural antibody-associated Vh genes, and suggests that at least part of the "potential pathogenic" IgG RFs in rheumatoid synovium may derive from the "physiological" natural antibody repertoire in a normal immune system. Indeed, the corresponding germline Vh gene for L1 encodes the heavy chain of an IgM RF found in a 19-wk-old fetal spleen. Furthermore, the comparisons of the expressed RF V genes and their germline counterparts reveal that the L1 heavy and light chain variable regions had, respectively, 16 and 7 somatic mutations, which resulted in eight and four amino acid changes. Strikingly, all eight mutations in the complementarity determining regions of the V gene-encoded regions were replacement changes, while only 6 of 11 mutations in the framework regions caused amino acid changes. Combined with L1's high binding affinity toward the Fc fragment, these results suggest strongly that the L1 IgG RF must have been driven by the Fc antigen.

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.