Human immunoglobulin heavy-chain variable region genes: organization, polymorphism, and expression

Rheumatoid factors from the peripheral blood of two patients with rheumatoid arthritis are genetically heterogeneous and somatically mutated

We report the DNA sequences of the heavy and light chain immunoglobulin genes of 11 monoclonal rheumatoid factor (RF)-secreting lines derived from the peripheral blood of two patients with rheumatoid arthritis (RA). It is evident from immunogenetic analysis of these lines that RA-associated RF activity can arise from a wide variety of heavy and light chain genes and gene combinations. Although the RF response from our two patients shows a bias in gene usage toward those genes used to encode monoclonal RF, particularly VkIII, relatively few of these RFs are reactive with the monoclonal antiidiotypes 6B6.6 and 17.109 that define VkIII germline-encoded light chains and the loss of this idiotypic reactivity is clearly related to somatic mutation. Finally, RFs derived from peripheral blood of RA patients show a similar heterogeneity of epitope binding to Fc as that seen for synovium-derived RF and some are clearly different in binding specificity from the restricted RF population found in patients with B cell malignancies. Somatic mutations as well as different VH/VL combinations contribute to the heterogeneity in the binding patterns of these RA-derived RF.

Primary amyloidosis associated with a novel heavy-chain fragment (AH amyloidosis)

Primary or AL amyloidosis occurs in patients with monoclonal plasma cell-related disorders and is typically associated with the systemic deposition as amyloid fibrils of the light-chain portion of the immunoglobulin molecule. Recently, the discovery that heavy chains could be involved in amyloid formation led to the designation of this type of disease process as AH amyloidosis. We have now identified a second example of heavy chain-associated amyloidosis in a patient (MAD) who had a serum IgG monoclonal gammopathy and Bence Jones proteinuria. In this case, the renal and splenic amyloid deposits consisted solely of the VH-D-encoded portion of the heavy polypeptide chain, in contrast to the first case, where the amyloid contained an immunoglobulin component composed of the entire heavy-chain variable and third constant domains. In this respect, the chemical composition of the amyloid protein MAD differed not only from that of the first reported case of AH amyloidosis but from all other structurally abnormal components found in patients with heavy chain-associated disease. The discovery that certain forms of heavy chains, as well as light chains, can form amyloid provides further information on the chemical basis of amyloidogenicity and the diverse nature of this disease.

Clonotypic dominance and variable gene elements of pathogenic anti-DNA autoantibodies from a single patient with lupus

This study explores the usage and diversity of the variable gene elements expressed by human lupus antibodies to DNA bearing the 0-81 idiotype, a marker of pathogenic anti-DNA autoantibodies. Rather than studying DNA-specific clonotypes from different patients, a panel of idiotype positive anti-DNA autoantibody-secreting clones from a single individual were analysed. By cloning and nucleotide-sequencing the heavy-chain variable gene segments, evidence was found for dominance of clonotypic patterns. Also noted was a high rate of diversification among the variable (VH), diversity (DH) and junctional (JH) gene segments utilized, with a pattern of mutations indicative of antigenic selection. These features suggest that the clones secreting the lupus pathogenic autoantibodies have been selected over multiple generations through an affinity-maturation process that is reminiscent of antigen-driven immune responses.

Somatic diversification in the heavy chain variable region genes expressed by human autoantibodies bearing a lupus-associated nephritogenic anti-DNA idiotype

Monoclonal anti-DNA antibodies bearing a lupus nephritis-associated idiotype were derived from five patients with systemic lupus erythematosus (SLE). Genes encoding their heavy (H)-chain variable (VH) regions were cloned and sequenced. When compared with their closest VH germ-line gene relatives, these sequences exhibit a number of silent (S) and replacement (R) substitutions. The ratios of R/S mutations were much higher in the complementarity-determining regions (CDRs) of the antibodies than in the framework regions. Molecular amplification of genomic VH genes and Southern hybridization with somatic CDR2-specific oligonucleotide probes showed that the configuration of the VH genes corresponding to VH sequences in the nephritogenic antibodies is not present in the patient's own germ-line DNA, implying that the B-cell clones underwent somatic mutation in vivo. These findings, together with the characteristics of the diversity and junctional gene elements utilized to form the antibody, indicate that these autoantibodies have been driven through somatic selection processes reminiscent of those that govern antibody responses triggered by exogenous stimuli.

Generating the antibody repertoire in rabbit

We describe a model for B cell development and generation of the antibody repertoire in rabbits. In this model, B cells develop early in ontogeny, migrate to GALT, and undergo the first round of diversification by a somatic gene conversion-like process and by somatic mutation. We designate the repertoire developed by this mechanism as the primary antibody repertoire and it is this repertoire that makes the rabbit immunocompetent. We invoke GALT as the site for development of the primary repertoire because (1) surgical removal of GALT from neonatal rabbits results in highly immunocompromised animals, (2) in germfree rabbits essentially no lymphoid development occurs in GALT and the rabbits are immunoincompetent, and (3) the follicular development of rabbit GALT is highly similar to that of the chicken bursa, the site in which the primary antibody repertoire develops by somatic gene conversion in chicken. We suggest that once the primary antibody repertoire is formed, it is maintained by self-renewing CD5+ B cells and is expanded to a secondary antibody repertoire after the B cells encounter antigen.

Heavy-chain directed B-cell maturation: continuous clonal selection beginning at the pre-B cell stage

A number of laboratories have demonstrated a biased representation of certain V-region segments in the primary B-cell repertoire. This may reflect clonal selection at the pre-B cell stage of differentiation. Here, Robert Schwartz and David Stollar suggest that pre-B cells undergo positive selection directed by the presence of surface heavy chain with low affinity to autoantigen. This mechanism would account for the anti-self property of the pre-immune B-cell repertoire.

Structure of the VH and VL segments of polyreactive and monoreactive human natural antibodies to HIV-1 and Escherichia coli beta-galactosidase

B lymphocytes committed to the production of antibodies binding to antigens on pathogenic bacteria and viruses (natural antibodies) are common components of the normal human B cell repertoire. A major proportion of natural antibodies is capable of binding multiple antigens (polyreactive antibodies). Using B cells from three HIV-1 seronegative healthy subjects, and purified HIV-1 and beta-galactosidase from Escherichia coli as selecting antigen, we generated three natural IgM mAb to HIV-1 and a natural IgM mAb to beta-galactosidase. The three HIV-1-selected antibodies (mAb102, mAb103, and mAb104) were polyreactive. They bound with different affinities (Kd = 10(-6) to 10(-8) M) to the HIV-1 envelope gp160, the p24 core protein, and the p66 reverse transcriptase, but not to the 120 glycosylated env protein. They also bound to beta-galactosidase (Kd approximately 10(-7) M), tetanus toxoid, and various various self antigens. In contrast, the natural mAb selected for binding to beta-galactosidase (mAb207.F1) was monoreactive, in that it bound with a high affinity (Kd < 10(-8) M) to this antigen, but to none of the other antigens tested, including HIV-1. Structural analysis of the VH and VL segments revealed that the natural mAb utilized three segments of the VHIV gene family and one of the VHIII family, in conjunction with VL segments of the V lambda I, V lambda II, V lambda III, or V kappa IV subgroups. In addition, the natural mAb VH and VL segments were in unmutated or virtually unmutated (germline) configuration, including those of the monoreactive mAb207.F1 to beta-galactosidase, and were identical or closely related to those utilized by specific autoantibodies or specific antibodies to viral and/or bacterial pathogens. Thus, the present data show that both polyreactive and monoreactive natural antibodies to foreign antigen can be isolated from the normal human B cell repertoire. They also suggest that the VH and VL segments of not only polyreactive but also monoreactive natural antibodies can be encoded in unmutated or minimally mutated genes, and possibly provide the templates for the specific high affinity antibodies elicited by self or foreign antigens.

Molecular characterization of human antibodies to bacterial antigens: utilization of the less frequently expressed VH2 and VH6 heavy chain variable region gene families

Structural analysis of the human immunoglobulin repertoire holds promise for determining the basis of variable region gene usage in response to a variety of auto and exogenous antigens. Here we report the nucleotide sequences of the heavy and light chain variable regions expressed by three human monoclonal antibodies specific for two clinically relevant bacterial pathogens, Bordetella pertussis and Haemophilus influenzae type b. The cell lines were derived by in vitro stimulation of lymphocytes from spleen or tonsillar tissue, respectively, and bind to different antigens from the two organisms. The single B. pertussis antibody is of the IgM lambda isotype and utilizes the single VH6 gene segment in combination with a V lambda 2 gene and demonstrates limited somatic mutation, yet is highly indicative of an antigen-driven immune response. One H. influenzae antibody is of the IgG2 lambda isotype and expresses a VH3 gene segment with a V lambda 1 gene, while the second cell line produces an IgG3 lambda antibody expressing a combination of VH2/V lambda 3. Both molecules show evidence of somatic mutation. The D gene segments of the heavy chains vary in length and display limited sequence homology with known germline D segments. As demonstrated previously, JH4 predominates (two JH4 and one JH3) and all three utilize the J lambda 3 gene segment. In addition, we have isolated and sequenced a number of germline VH2 gene segments in an attempt to better understand the nature of the VH2 germline repertoire. In addition to contributing to the understanding of the human antibody repertoire, such clinically relevant molecules may prove to be a source of passive immunotherapy for those at risk to developing disease.

Variable region genes of anti-HIV human monoclonal antibodies: non-restricted use of the V gene repertoire and extensive somatic mutation

The extent of the expressed human V gene repertoire for the most part has been derived from fetal cDNA libraries, autoantibodies, and myeloma proteins. In order to continue to explore the utilization of the VH and VL gene repertoire in response to exogenous viral antigens, the heavy and light chain cDNAs from four human anti-HIV monoclonal antibodies were PCR amplified from human-mouse heterohybridomas, cloned, and nucleotide sequence analysis performed. Of the monoclonals analyzed, three were directed against gp120 and one reacted with gp41. Three of the antibodies were of the IgG1 lambda isotype and one was an IgG1 kappa. Three of the four heavy chains were derived from VHI gene segments and one VHII was observed. D segments showed evidence of D-D joining and three JH4 and one JH5 gene were utilized. Two V lambda II lambda chains and one from the V lambda III gene family were observed and the single kappa chain sequenced was from the V kappa III family. DNA sequence comparison with known germline gene segments identified putative precursor V gene segments for one of the heavy chains and two light chains. Comparison of the expressed amino acid sequences with the predicted germline sequences indicated that changes were clustered in the CDRs and FR3 regions of the V gene segments. We reported previously the nucleotide sequences of five human monoclonal antibodies from HIV-infected individuals, three of which utilized VHIV, one VHV and one a VHI gene segment and also found extensive evidence of somatic mutation. Collectively, our results indicate that an antigen driven response is functioning following HIV infection and, surprisingly, to date we have not encountered a VHIII gene segment. Since VHIII is the largest human VH gene family, it may well be that this under-representation has both functional and clinical implications.

Complementarity-determining region 2 is implicated in the binding of staphylococcal protein A to human immunoglobulin VHIII variable regions

Staphylococcal protein A (SPA) has two distinct binding sites on human immunoglobulins. In addition to binding to the Fc region of most IgG molecules, an "alternative" binding site has been localized to the Fab region of human immunoglobulins encoded by heavy chain variable gene segments belonging to the VHIII family. Comparison of amino acid sequences of closely related SPA-binding and -non-binding proteins suggested that VHIII-specific residues in the second complementarity-determining region (CDR2) were likely responsible for SPA binding activity. Site-directed mutagenesis of a single amino acid residue in CDR2 converted an IgM rheumatoid factor which did not bind SPA to an SPA binder. These findings, therefore, locate a critical site involved in SPA binding to the CDR2 of human immunoglobulins encoded by VHIII family gene segments.

CD5+ B cells and the immune system

The CD5+ B-cell population is prominent in early life and may play a key role in the ontogeny of the immune system. Transplantation studies in mice are in support of CD5+ B cells as a separate lineage from CD5- B cells. In both mice and men there is evidence in favour of CD5 being an activation antigen rather than a lineage marker, but the jury is still out! The frequency of CD5+ B cells appears to be under genetic influence. CD5+ B cells are receptive to many cytokines including IL-2 and IL-5 and themselves produce a number of cytokines especially IL-10. The function of the CD5 molecule on B cells is presently unknown but it might be involved in interaction with CD72 on other B cells. CD5+ B cells generally utilise minimally mutated germ-line genes and produce low avidity auto- and polyreactive antibodies (natural antibodies) generally of the IgM class.

The genetic basis of human VH4 gene family-associated cross-reactive idiotype expression in CD5+ and CD5- cord blood B-lymphocyte clones

In a recent study we have observed a high frequency expression of cross-reactive idiotypes encoded by genes from the relatively small VH4 family of immunoglobulin heavy chain genes in cord blood B-lymphocyte lines. Furthermore, we have demonstrated a selective pattern of expression of two VH4-associated cross-reactive idiotype (CRI) in B-lymphocyte lines established from CD5+ and CD5- cord blood B-lymphocytes. There was a restricted expression of one CRI marker recognized by the 9G4 monoclonal antibody in lines established from CD5+ B-lymphocytes but not in those established from the CD5- population. In the current study we examine the molecular basis for the selective pattern of CRI expression. Nucleotide-sequence analysis of functional immunoglobulin heavy chain (IgH) gene rearrangements in three CD5+ lines expressing the CRI recognised by 9G4 reveal that all use a single gene from the VH4 family, the V4.21 gene. However, all three lines have distinct third complementarity determining regions (CDR3) implying different clonal origins. In contrast, four cord blood cell lines (two established from CD5+ B-lymphocytes) expressing the CRI recognized by MoAb Lc1 have functional IgH gene rearrangements involving two different genes from the VH4 family, the V71-4, and V2-1 genes. Antigen specificity analysis reveals that all three 9G4-reactive lines produce antibodies that react with the I and/or i red blood cell carbohydrate antigens. These data suggest that the distinction in VH4 gene use in CD5+ B-lymphocytes in cord blood results from a selection process in vivo that shapes the repertoire of CD5+ B-lymphocytes. This study extends recent observations that the monoclonal anti-CRI antibodies 9G4 and Lc1 are markers of two distinct subgroups of proteins encoded by two subsets of genes within the VH4 family. Furthermore, it appears that amino acid residues in framework region one and complementarity determining region two are critical for the expression of the cross reactive idiotypes and the serological distinction between the two subgroups of proteins.

Diversification, not use, of the immunoglobulin VH gene repertoire is restricted in DiGeorge syndrome

Immunoglobulin (Ig) genes were isolated from unamplified conventional as well as polymerase chain reaction-generated cDNA libraries constructed from the peripheral blood cells of a patient with complete DiGeorge syndrome. Comparison of the sequences of 36 heavy chain clones to the recently expanded database of human VH genes permitted identification of the germline VH genes that are expressed in this patient as well as placement of 19 of these genes in a partially resolved 0.8-mb region of the human VH locus. The pattern of VH gene use does not resemble the fetal (early) repertoire. However, as in the fetal repertoire, there are a number of cDNAs derived from germline genes that previously have been identified as autoantibodies. Two D mu sequences also were identified, as was another sequence resulting from a unique recombination event linking JH to an unidentified sequence containing a recombination signal sequence-like heptamer. All of the DiGeorge cDNAs are closely related to germline VH genes, showing little or no evidence of somatic mutation. In contrast, comparably selected IgM VH sequences derived from normal adult and age-matched human libraries, and from a second DiGeorge syndrome patient in whom the degree of thymic dysfunction is much less severe, exhibit considerable evidence of somatic mutation. The absence of somatic mutation is consistent with the atypical development of functional antibody responses associated with complete DiGeorge syndrome and implicates a role for T cells in the generation of diversity within the B cell repertoire.

Diversity of expressed V and J regions of immunoglobulin light chains in Xenopus laevis

In Xenopus laevis, two immunoglobulin light chain isotypes, designated L1 or rho and L2 or sigma, have been identified. The genomic organization of the L1 locus has been described previously: a constant (C) gene segment is preceded by a joining (J) gene segment; in addition, there are many cross-hybridizing variable (V) gene segments. To evaluate the extent of sequence diversity of L1 V regions, we screened three cDNA libraries, constructed from mitogen-stimulated Xenopus splenocytes, with probes for the C or the J gene segment. Eighteen cDNA clones that contain complete or truncated V regions were chosen for sequence analysis. The C regions of all clones are identical or nearly identical to the genomic C gene segment; the V regions are greater than 80% identical in nucleotide sequence and are presumably derived from a single family of V gene segments. Although framework regions are nearly identical, complementarity-determining regions are quite diverse. The expressed J segments fall into distinct groups, suggesting the presence of more than one germ-line J segment. Therefore, a genomic library was screened with a J region probe. A clone overlapping with the previously identified J-C clone, and containing four additional J gene segments, was isolated. All five J gene segments are very similar and three are identical in nucleotide sequence. Each of the three distinct germ-line J sequences is represented in the set of cDNA clones, suggesting that combinatorial diversification occurs; imprecision of V-J joining also appears to contribute to variability. Overall, these results suggest that the immunoglobulin repertoire in this species is not significantly restricted by a limitation in the diversity of light chain V regions.

Polyreactivity is a property of natural and disease-associated human autoantibodies

Polyreactivity was earlier recognized as a feature of naturally expressed autoantibodies in serum. In the present study, we have compared the reactivity on a panel of self antigens of affinity-purified anti-DNA and anti-thyroglobulin (TG) IgG autoantibodies from the serum of patients with systemic lupus erythematosus (SLE) and autoimmune thyroiditis with their affinity-purified counterparts isolated from the serum of healthy individuals. Anti-DNA autoantibodies exhibited a similar degree of polyreactivity whether originating from patients or from healthy adults. Natural anti-TG autoantibodies were also found to be polyreactive. Anti-TG autoantibodies from patients with Hashimoto's thyroiditis showed little or no polyreactivity. Natural anti-TG autoantibodies were equally polyreactive whether or not they belonged to a fraction of normal IgG that is connected through V regions with other IgG molecules from the same source. These results indicate that polyreactivity of autoantibodies is a feature that does not allow one to distinguish between natural and disease-associated autoantibodies as well as between V-region-connected and unconnected autoantibodies.

Human organ-specific autoimmune disease. Molecular cloning and expression of an autoantibody gene repertoire for a major autoantigen reveals an antigenic immunodominant region and restricted immunoglobulin gene usage in the target organ

The most common organ-specific autoimmune disease in humans involves the thyroid. Autoantibodies against thyroid peroxidase (TPO) are present in the sera of virtually all patients with active disease. We report the molecular cloning of the genes for 30 high-affinity, IgG-class human autoantibodies to TPO from thyroid-infiltrating B cells. Analysis of the putative germline genes used for the TPO human autoantibodies suggests the use of only five different H and L chain combinations involving four H chains and three L chains. In addition, the same combination of H and L chains was found in multiple patients. The F(ab) proteins expressed by these genes define two major, closely associated domains (A and B) in an immunodominant region on TPO. These A and B domains contain the binding sites of approximately 80% of IgG-class TPO autoantibodies in the sera of patients with autoimmune thyroid disease. The present information permits analysis, not previously possible, of the relationship between autoantibody H and L chain genes and the antigenic domains on an autoantigen. Our data, obtained using target organ-derived autoantibodies, indicate that there is restriction in H and L chain usage in relation to the interaction with specific antigenic domains in human, organ-specific autoimmune disease.

The structural basis of germline-encoded VH3 immunoglobulin binding to staphylococcal protein A

The ability of human VH3 immunoglobulins (Ig) to bind to staphylococcal protein A (SPA) via their Fab region is analogous to the binding of bacterial superantigens to T cell receptors. The present report establishes the structural basis for the interaction of SPA and VH3 Ig. We have studied a panel of 27 human monoclonal IgM that were derived from fetal B lymphocytes. As such, these IgM were expected to be encoded by unmutated germline genes. Binding to SPA in ELISA occurred with 15 of 15 VH3 IgM, but none of 12 IgM from the VH1, VH4, VH5, or VH6 families. The VH sequences of the 27 IgM were derived from 20 distinct VH elements, including 11 from the VH3 family. Use of D, JH, and CL genes was similar among VH3 and non-VH3 IgM. A comparison of the corresponding VH protein sequences, and those of previously studied IgM, identified a probable site for SPA binding that includes VH3 residues in framework region 3 (FR3), and perhaps FR1 and 3' complementary determining region 2. The results thus demonstrate that among human IgM, specificity for SPA is encoded by at least 11 different VH3 germline genes. Furthermore, like the T cell superantigens, SPA likely binds to residues in the VH framework region, outside the classical antigen-binding site of the hypervariable loops.

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.

Genetic analysis of the variable region genes encoding a monospecific human natural anti-DNA antibody

Recent evidence suggests that natural autoantibodies may play an integral role in the development of the normal immune repertoire. To explore the genetic origins of these antibodies, we have isolated and sequenced the variable (V) region genes encoding both the heavy (H) and light (L) chains of a natural anti-DNA antibody, Kim11.4. The genes appear to be derived from the VH4.18 (subgroup VHIV), JH5, Hum1L1 (subgroup V lambda I) and J lambda 3 germline genes. The origin of the H chain diversity gene is more obscure, being potentially derived from one or more of several germline genes, arranged in either the forward or reverse orientations. Both the Kim11.4 VH and VL genes share significant degrees of similarity with those utilized in other autoantibodies, indicating that at least some degree of V restriction may exist in human autoreactive B cells. The pattern of nucleotide differences between the Kim11.4 VH and VL genes and their putative germline counterparts suggests that the Kim11.4 genes may have undergone somatic mutation and arisen as a result of antigen selection.

Immunoglobulin VH4 gene usage in B lymphoid leukaemias

VH4 gene rearrangements occur in a similar proportion of cases of B lineage acute lymphoblastic leukaemia (ALL) and B chronic lymphocytic leukaemia (B CLL). However, there may be differences in the pattern of VH4 gene usage between these disorders as is the case for VH1 gene rearrangements. To examine this, we analysed the sequences of 24 PCR-amplified clonal VH4 gene rearrangements from a series of 15 cases of ALL and nine cases of CLL. Five distinct groups of genes were rearranged, three of which (represented by V2-1, V71-2/V71-4, V4.21) have been described in rearranged form in normal B lymphoid tissues. The most frequently rearranged gene was V4.21 which is strongly associated with autoimmune reactivity. V71-2, V71-4 and V2-1 were more frequently rearranged in CLL than ALL. The remaining two groups (represented by V4.33, V4.35) have not previously been described in rearranged form. One of these, V4.35, was seen only in ALL rearrangements. Both V4.35 and a VH1 gene, 20P3, which is also preferentially rearranged in ALL, are located at the 3' end of the VH locus. The location of these genes suggests that their rearrangement may be developmentally regulated in ALL. The findings in this study confirm restricted repertoires of IgH gene rearrangement in ALL and CLL. Characterization of IgH repertoires provides a means of correlating these transformed B cell populations with normal B cell developmental compartments. Moreover, the distinctive repertoires in ALL and CLL may reflect important differences in the ontogenic timing and microenvironmental milieu of tumourigenesis in these disorders.

Restricted immunoglobulin VH usage and VDJ combinations in the human response to Haemophilus influenzae type b capsular polysaccharide. Nucleotide sequences of monospecific anti-Haemophilus antibodies and polyspecific antibodies cross-reacting with self antigens

To examine the human antibody repertoire generated against a biologically significant antigen we have obtained sequences of heavy chain variable region genes (IgVH) from 15 monoclonal antibodies specific for the capsular polysaccharide of Haemophilus influenzae type b (Hib PS). All VH segments are members of the VH3 family and 9 of 15 are members of the smaller VH3b subfamily. Restriction is evident by the shared use of certain VDJ joints in independent hybridomas from different subjects. Two hybridomas generated from the same subject demonstrate identical heavy chain variable region gene sequences but differ in isotype and rearrange alternative light chain variable region genes (IgVL), suggesting that in a normal immune response, a single pre-B cell clone may use different light chain rearrangements and give rise to progeny capable of reacting with antigen. Using a polymerase chain reaction assay optimized to detect base pair differences among VH genes we demonstrate that at least a portion of expressed anti-Hib PS VH genes have undergone somatic mutation. Anti-Hib PS heavy chain genes are homologous to VH segments encoding autoantibodies and two hybridomas secrete anti-Hib PS antibody that cross-reacts with self antigens (double-stranded DNA and single-stranded DNA). Comparison of VH regions of self-reactive and monospecific anti-Hib PS Ab demonstrates no consistent structural feature correlating with fine antigen specificity. These data demonstrate significant restriction in VH usage and VDJ recombination in the anti-Hib PS response and confirm that autoantibodies may be elicited during normal immune responses.

Human immunoglobulin heavy-chain minilocus recombination in transgenic mice: gene-segment use in mu and gamma transcripts

We (N.L. and L.D.T.) have introduced a human heavy-chain minilocus into mice transgenically. Constructs contain 2 heavy-chain variable (VH; psi VH3-105 and VH5-251), 10 diversity (D), 6 heavy-chain joining (JH), and either constant (C)mu or C mu and C gamma gene segments. Several founder lines were established and studied before immunization. Seventy heavy-chain transcripts were cloned and sequenced from murine splenic B lymphocytes, and gene-segment use was assessed before and after class-switching. In general, the repertoire was "fetal" in appearance with little evidence of somatic mutation in any gene segment. The two VH gene segments were found rearranged to mu- and gamma-chain C segments, with a preference of VH5-251. We observed a preponderance of the most-J-proximal D gene (DHQ52) segments among the mu transcripts (44%). The JH gene-segment use mimics most patterns seen in human antibodies. Diversification in CDR3 was extensive and included clear examples of D inversions and D-D fusions. These data suggest that a human immunoglobulin minilocus can undergo recombinatorial processes in a manner analogous to that seen in the human fetal/preimmune repertoire. This model, in addition to providing a potential source of human monoclonal antibodies, is ideal for the study of further questions concerning immunoglobulin gene-segment recombination.

Isolation of germinal centerlike events from human spleen RNA. Somatic hypermutation of a clonally related VH6DJH rearrangement expressed with IgM, IgG, and IgA

12 rearranged human VH6 immunoglobulin heavy chain genes arising from the same rearrangement were isolated without preselection from the RNA of a fragment of human spleen. The 12 clones were isolated from a pool of 31 unique VH6 clones arising from 18 unique rearrangements. 2 of the 12 related clones were expressed with IgM, 2 with IgG, and 8 with IgA1. All the clones, including those expressing IgM, showed extensive somatic mutation of germline bases (5.6%), which was consistent with antigen-driven activation of these VH6-expressing clones with recruitment into the immune repertoire. On the basis of significant sharing of somatic mutations between the IgM clones and clones expressing the other isotypes (six mutations shared with IgG clones and eight mutations shared with IgA clones), it was apparent that the IgM-expressing precursor in this diversified family had undergone extensive antigen-driven somatic mutation prior to isotype switching. This family of related clones suggests that a germinal centerlike event had been sampled. The highly mutated IgM clones suggest that there may exist memory B cells capable of further somatic mutation and differential isotype-switching depending on the specific antigenic stimulus.

Bone marrow cells in X-linked agammaglobulinemia express pre-B-specific genes (lambda-like and V pre-B) and present immunoglobulin V-D-J gene usage strongly biased to a fetal-like repertoire

Expression of Ig and Ig-related genes has been studied in bone marrow cells from two patients with severe form of X-linked agammaglobulinemia (XLA). Phenotypic analysis revealed the presence of pre-B cells, in the absence of mature B cell markers. The pre-B-specific genes, lambda-like and V pre-B, were normally transcribed. Sequence analysis of 48 distinct V-D-J cDNA clones directly derived from XLA bone marrow cells indicated that they had characteristics of an early fetal pre-B repertoire. All VH families were identified, with a strong bias in the gene usage: a few VH genes were largely overexpressed, either germline or slightly mutated; most genes had been located 3' of the VH locus and were also used in fetal liver (8-13 wk of gestation). Short D regions, (resulting from D-D fusion, making usage of all D genes in both orientations with utilization of the three reading frames), restricted N diversity, and a fetal JH usage pattern were also observed. Taken together, our data suggest that the XLA defect does not alter V-D-J rearrangements nor the expression of mu, lambda-like, and V pre-B transcripts and most likely results in a poor efficiency of some critical steps of the B cell maturation.

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.

Restriction fragment length polymorphisms and single germline coding region sequence in VH18/2, a duplicated gene encoding autoantibody

In this study, we analyze the restriction fragment length polymorphisms of VH18/2, a gene encoding the heavy chain of an anti-DNA antibody, and correlate that with the germline sequence of the gene's coding region. Oligonucleotides probes complementary to the CDR1 and to both the 5' and 3' halves of the CDR2 gene segments were hybridized under stringent conditions to genomic DNA digested with XbaI, and yielded polymorphic bands of 26, 24 and 18 kb with all three probes. Individuals had either one, two, or three bands in common in their genomic DNA, indicating duplication of VH18/2 genes at two sites within the IgH locus. While it is difficult to say which of the three polymorphic gene segments constitute an allelic pair, the 26 and 24 kb fragments were the most commonly seen (97% of individuals had one or both). VH18/2 is known to be over-represented in the expressed repertoire with very little nucleotide divergence from the germline sequence. In order to determine whether the observed RFLPs are due to sequence polymorphism of the VH18/2 coding region, and whether differences in the expressed genes arise from somatic mutation, size-selected genomic DNA containing the gene was cloned and sequenced. A single coding region sequence was found in the germline. The results of this study suggest that overexpression of VH18/2 may in part be due to its duplication. Like other genes encoding autoantibody, which are well conserved, nonpolymorphic and expressed early in programmed immunologic development, VH18/2 may be instrumental in the establishment or regulation of the immune repertoire.

High-frequency representation of a single VH gene in the expressed human B cell repertoire

Idiotype (Id) 16/6 marks a variable (V) region structure that occurs frequently in the human immunoglobulin repertoire. The basis of the Id has been traced to a germline heavy chain gene segment, VH18/2 (VH26). To pursue the molecular basis for the frequency of Id 16/6, we have analyzed polymerase chain reaction-generated C mu, C gamma, and VH3 family V gene libraries derived from the circulating and tonsillar B cells of four normal individuals and from the B cells of two patients with active systemic lupus erythematosus (SLE). The frequency of VH18/2 in these libraries was compared with three control VH genes, VH56P1, VH21/28, and VHA57. Plaque lifts from C mu and C gamma VH cDNA libraries were screened with gene-specific oligonucleotide probes. The frequency of VH18/2 ranged from 4 to 10% of JH+ plaques (two of five times that of control VH genes). In four VH3 family-specific libraries derived from rearranged DNA, VH18/2 represented 19-33% of VH3+ plaques. Hybridizing VH18/2 plaques were 98-100% homologous to the germline VH gene; mutations when present were often in framework 3. Extensive variation was seen in the complementarity determining region 3 sequences of these rearranged V genes. The high frequency of VH18/2 expression in the B cell repertoire was confirmed by sequencing randomly picked JH+ plaques. In two patients with active SLE the frequency of use of VH18/2 was not greater than that observed in normal subjects. These results show that VH18/2 is overrepresented in the B cell repertoire of normal subjects and suggest that the immune repertoire may be dominated by relatively few V genes.

Human Tcrb-V6.10 is a pseudogene with Alu repetitive sequences in the promoter region

Tcrb-V6.10 represents an abnormal human V gene with an Alu insertion in the promoter, a point mutation of a conserved Cys at position 23, and a missing nonamer within the usually conserved recombinase signal sequence. Here it is shown that b-V6.10 is found in the genome of most individuals, is normally located in the Tcrb-V locus on chromosome 7, but is not rearranged or transcribed. Thus, it is likely that the abnormal signal sequence precludes recombination and that the Alu insertion results in a disabled promoter, indicating the functional importance of the affected regions. Tcrb-V6.10 probably evolved by duplication of an ancestral Tcrb V13-V6-V5 cassette, like other members of the large b-V6 subfamily, and more recently became inactivated into a pseudogene.

Production and characterisation of a human monoclonal thyroid peroxidase autoantibody

A human-mouse hybridoma has been produced by fusion of Hashimoto thyroid lymphocytes with the mouse myeloma line X63-Ag8.653. The cloned hybridoma secreted 2.5 micrograms per 10(6) cells per day of an IgG kappa thyroid peroxidase (TPO) autoantibody (2G4) with high affinity (2.5 x 10(9) molar-1) and specificity for human TPO. 2G4 did not react with lactoperoxidase, horseradish peroxidase or human myeloperoxidase or with porcine TPO or with human thyroglobulin. Plastic tubes coated with 2G4 bound about 50% of 125I-labelled human TPO added and the binding was inhibited by IgGs prepared from 18/18 TPO autoantibody-positive sera. This indicated that all 18 sera contained autoantibodies which recognised the same (or closely related) epitope as 2G4. Plastic tubes coated with IgGs from different TPO autoantibody-positive patient sera also bound 125I-labelled TPO but inhibition by 2G4 in this system was not complete. This suggested that the sera contained at least 2 types of TPO autoantibodies, with only one type of autoantibody reactive with the same epitope as 2G4.

Human anti-acetylcholine receptor antibodies use variable gene segments analogous to those used in autoantibodies of various specificities

The production of autoantibodies to the nicotinic acetylcholine receptor are responsible for many of the neurological symptoms observed in myasthenia gravis. An understanding of the structural organization of the anti-receptor antibodies may help to define the role of these antibodies in the pathogenesis of this disease. The nucleotide sequences of the heavy and light chains of three human monoclonal anti-receptor antibodies isolated from peripheral blood lymphocytes from two patients with myasthenia gravis were analyzed. In addition, the structure of an anti-idiotypic antibody was studied. The VH and VL gene segments used in the anti-receptor antibodies appear to be derived from the same repertoire as gene segments that have been found in other autoantibodies isolated from patients with various autoimmune diseases. The IgM anti-receptor antibodies are direct copies of germline gene segments, while the structures of the IgG anti-receptor antibody and the anti-idiotypic antibody appear to be mutated suggesting that they have undergone antigenic selection.

Predominance of fetal type DJH joining in young children with B precursor lymphoblastic leukemia as evidence for an in utero transforming event

The presence of N sequences in the complementarity determining region 3 (CDR3) of the rearranged immunoglobulin H chain is developmentally regulated: N regions are generally present in the DJH joinings of adult B cells but are often absent in fetal B cells. Analysis of the CDR3 in 61 B precursor acute lymphoblastic leukemias indicated that 87.5% of the leukemias obtained from children < or = 3 yr old lacked N regions at the DJH junction. In contrast, in children > 3 yr old, only 11.1% of the leukemias lacked N regions at this junction, a frequency similar to what we have observed in B cells from children and adults. These findings suggest that the majority of leukemias presenting within the first 3 yr of age arise from an in utero transforming event.

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.

Discovery of antibodies

Passive immunisation has been used in clinical practice since the end of last century, mainly for prophylaxis. Success of early treatments was marred by anaphylactic reactions and serum sickness because antibodies or antitoxins were not raised in humans. Recombination of gene segments during antibody synthesis means that specific antibodies for numerous antigens can be produced from a limited gene pool. Killer lymphocytes, phagocytes, and complement then bind to the constant region of the antibody facilitating elimination of the pathogen. Development of a method of obtaining large quantities of antibodies against a specific antigen (monoclonal antibodies) offers the possibility of initiating host defence mechanisms against any unwanted antigen, though some problems still remain in preventing the body from attacking the monoclonal antibody.

“Primatization” of Recombinant Antibodies for Immunotherapy of Human Diseases: A Macaque/Human Chimeric Antibody Against Human CD4

Immunoglobulin variable region genes from non-human primates, cynomolgus macaques, were shown to have 85%-98% homology with human immunoglobulin sequences and yet macaques are phylogenetically distant enough to respond against conserved human antigens. Immunoglobulin genes were isolated from monkeys immunized with human CD4 antigen and a human/monkey chimeric anti-CD4 antibody with 91-92% homology to human immunoglobulin framework regions was cloned and expressed. The antibody has an apparent affinity of 3.2 x 10(-11) M and exhibits potent immunosuppressive properties in vitro.

Idiotypic heterogeneity of VKIII autoantibodies to red blood cell antigens

VKIII light (L) chains are commonly expressed by human autoantibodies with diverse binding specificities, including red blood cell antigens. To better understand the physiologic and pathologic expression of these L chain variable region genes, we have created a panel of murine monoclonal anti-idiotypic antibodies by immunization with a human lymphoblastoid B cell line that secretes an IgM VKIII autoantibody specific for the I red blood cell carbohydrate determinant. The binding specificities of these nine murine monoclonal antibodies, termed IV.1-IV.9, were evaluated against a large panel of monoclonal Ig proteins and compared to two previously well-characterized monoclonal anti-idiotypes, 6B6.6 and 17.109; these two anti-idiotypes have been shown to primarily identify VKIII rheumatoid factors derived from the kv328 (VKIIIa) and kv325 (VKIIIb) genes, respectively. In contrast, our anti-idiotypic antibodies identified (public) cross-reactive idiotypes present on many VKIII proteins that included both anti-erythrocyte and rheumatoid factor autoantibodies. Certain anti-idiotypic antibodies (IV.2 and IV.6) were restricted to VKIIIa L chains but differed from the 6B6.6 anti-idiotype by binding to a larger subset of VKIIIa proteins representing the products of at least two VKIIIa genes. One antibody of our panel (IV.5) recognized a private idiotope expressed only by the immunizing antibody. Using the panel of anti-idiotypic antibodies to evaluate erythrocyte autoantibodies with different serologic specificities, we found striking heterogeneity of L chain idiotype expression, even among known VKIII anti-i/I autoantibodies. These findings differ from the recently described structural and idiotypic conservation associated with the H chain of anti-i/I autoantibodies. From correlations of idiotypic reactivity with L chains of known sequence, it is postulated that the observed heterogeneity of L chain idiotype expression is due to differences in the genetic origin and/or somatic diversification of L chain variable region genes. Furthermore, subtle variability of L chain structure may contribute in part to the differences in fine binding specificity among anti-I and anti-i autoantibodies.

Autoantibody activity and V gene usage by B-cell malignancies

Autoreactive B cells account for a substantial part of the B-cell repertoire. They frequently secrete polyspecific natural autoantibodies, which probably bind with low affinity to the different antigens they recognize and which express germinal genes. The role of this pre-immune repertoire still remains to be defined but it has been suggested that it participates in the elimination of cell breakdown products, serves as a first barrier of defense or acts as a template upon which antigen driven selection and somatic recombinations could induce the emergence of high affinity induced antibodies. The present study, reviews the evidence favouring the idea that this autoreactive B-cell repertoire, which expresses a restricted set of V genes, frequently undergoes malignant transformation. This evidence arises from the study of the autoantibody activity and V gene usage in three different models of B-cell malignancies namely monoclonal immunoglobulins; chronic lymphocytic leukemia; and follicular non-Hodgkin's lymphomas.

MONOMORPHIC ORGANIZATION OF HUMAN DIVERSITY (DH) HEAVY CHAIN VARIABLE GENES

While recent evidence indicates that human immunoglobulin heavy chain variable (VH) genes exhibit a high degree of heterogeneity, little is known concerning the polymorphism of the diversity (DH) gene complex. This locus comprises two clusters, major and minor, which are physically linked with the VH locus. In assessing the variability of the human major and minor DH clusters, we found no evidence for a substantial restriction site polymorphism. We also noted that, in contrast to what was found in the Japanese population, the DH1 gene is not deleted in an appreciable proportion of the European population. We propose that, because DH genes impart the critical functions associated with the third complementarity-determining region, the genomic organization of the human DH locus has been evolutionarily conserved through selection pressure mechanisms.

Self tolerance to human A and B histo-blood group antigens exists at the B cell level and cannot be broken by potent polyclonal B cell activation in vitro

It is generally considered that tolerance to self antigens is less complete in B than in T lymphocytes. However, B cell tolerance through either functional inactivation (anergy) or clonal deletion has been demonstrated in transgenic mice. In the present study, we investigated whether B cells specific for self A/B histo-blood group antigens can be detected in normal humans. It is a key feature of the ABO system that all normal individuals make natural antibodies against those A or B carbohydrates which are not present in their organism. To detect B cells by the limiting dilution approach we used a specific enzyme-linked immunosorbent assay for the quantitation of anti-A/B antibodies, and a culture system in which polyclonal B cell activation occurs through cell contact with EL4 thymoma cells. As was reported for other B cell studies, we frequently detected "polyreactive" immunoglobulin (Ig)M (but not IgG) with apparent autoreactivity but of uncertain significance regarding physiologic conditions. However, A- or B-specific B cell responses occurred with selective patterns in agreement with classical blood group serology in 14 individuals with A, B, AB or 0 blood group phenotypes: 1/11,600 B cells made anti-allo A/B IgM and 1/26,500 B cells such as IgG, while only 1/104,000 B cells apparently made anti-self A/B IgM and 1/350,000 B cells such as IgG. This shows self tolerance at the B cell level. Since anergy of B cells can frequently be broken by polyclonal B cell activation in vitro, and EL4 cells are potent B cell stimulators, the present results argue for either a highly resistant anergic state or for clonal deletion of self-A/B histo-blood group-specific human B cells.

High frequency of somatically mutated IgM molecules in the human adult blood B cell repertoire

Nucleotide sequence analysis of cDNA encoded by the single member of the human immunoglobulin VH6 gene family show that blood B cells in adults, but not in neonates, frequently express somatically mutated IgM molecules. The number of mutations in VH6-encoded cDNA from adult blood ranged from 2 to 19 mutations/VH gene (average 10.1/VH gene). The distribution of silent and replacement mutations suggests that at least some of the VH6 genes were derived from B cells that were activated and selected by antigen. We conclude that the blood B cell repertoire in adult humans, in contrast to its much-studied murine splenic counterpart, is a rich source of highly mutated IgM molecules.

CD5 and immunoglobulin VH gene expression in B-cell lines from patients with autoimmune diseases

We studied the CD5 mRNA expression and VH gene family usage in Epstein-Barr virus (EBV)-immortalized B-cell lines derived from the blood of patients with type 1 diabetes (IDDM) of recent onset and of patients with polyneuritis cranialis multiplex (cranial neuritis; CN). After immortalization with EBV, at least 10 cell lines from each subject were tested for surface CD5 and CD20. mRNA expression was studied using cDNA probes for the six VH families as well as for CD5. The EBV lines from the IDDM patients used the VHIV family more frequently and VHI and VHII families less frequently than lines from controls. EBV lines from CN patients expressed the VHI and VHII families more often than those of the controls. When the IDDM and CN lines were compared, the lines derived from IDDM patients were found to use VH families I and II less frequently and VH families IV and V more frequently than lines from CN patients. There were no significant differences in the mean numbers of CD5+ B cells in the cell lines tested. More than half of the lines from each patient expressed CD5 at the mRNA level. No correlation was seen between the expression of surface CD5 and the level of CD5 mRNA expression. There was, however, a positive correlation between the usage of VH families III, V and VI, and the CD5 mRNA expression. In conclusion, the usage of VH families I to VI seemed to differ in patients with IDDM and CN. No differences were seen in the surface CD5 expression, but the lines expressing CD5 mRNA preferentially used the VH families III, V and VI.

Recognition by recombinant autoimmune thyroid disease-derived Fab fragments of a dominant conformational epitope on human thyroid peroxidase

To characterize the nature of thyroid peroxidase (TPO) autoantibodies present in the sera of patients with autoimmune thyroid disease, we cloned three IgG1/kappa Fab fragments which bind 125I-TPO. This was accomplished by the molecular cloning and expression in bacteria of IgG gene fragments from B cells infiltrating the thyroid of a patient with Graves' disease. The three Fab fragments (SP2, SP4, and SP5) are coded for by a common heavy chain (VH1, D, JH3) and three related, but different, light chains (VK1, JK2). The SP Fab fragments bind specifically to TPO with high affinities (6 x 10(-11)-2 x 10(-10) M) comparable to those of serum TPO autoantibodies. TPO autoantibodies represented by the SP Fab fragments are present in all 11 patients studied, constitute a high proportion (36-72%) of serum TPO autoantibodies in individual patients and interact with a conformational epitope on TPO.

Immunoglobulin heavy chain variable region gene utilization by B cell hybridomas derived from rheumatoid synovial tissue

Rheumatoid arthritis (RA) is a chronic inflammatory disease that primarily affects synovial joints. Activated B lymphocytes and plasma cells are present in the synovial tissue and are thought to contribute to the immunopathology of the rheumatoid joint. To investigate rheumatoid synovial B lymphocytes, we have generated B cell hybridomas from synovial tissue of an RA patient. Here we describe the immunoglobulin VH gene repertoire of eight IgM- and 10 IgG-secreting synovial-derived hybridomas. The VH4 gene family is highly represented (38.5%) in this panel of hybridomas compared with the frequency of VH4 gene expression in circulating B lymphocytes reported previously (19-22%) and with the VH4 gene frequency we observed in a panel of hybridomas derived in the same manner from the spleen and tonsil of normal individuals (19%). The increased frequency of VH4 gene expression was not due to the expansion of a single B cell clone in vivo as none of these hybridomas was clonally related. Two synovial-derived hybridomas secreted autoantibodies; one (VH3+) secreted an IgM-rheumatoid factor (RF) and the other (VH4+) secreted IgM with polyreactive binding to cytoskeletal proteins and cardiolipin. The antibodies secreted by the remaining synovial-derived hybridomas were not reactive with the autoantigens tested. The VH gene usage in a proportion (5/17) of synovial-derived hybridomas that expressed CD5 antigen provided preliminary evidence that CD5+ B cells in RA synovium have a similar increase of VH4 gene expression reported for CD5+ B cells from normal individuals and patients with chronic lymphocytic leukaemia.

Molecular approaches to the study of human B-cell and (auto)antibody repertoire generation and selection

We have shown that the restricted repertoire of VH genes expressed in second trimester human fetal liver is not solely determined by JH proximity. Furthermore, by following the fate of two VH gene segments in different B-cell repertoires, we have provided evidence that multiple factors contribute to the frequency with which individual VH genes are utilized. We found that the repertoire of adult blood IgM-bearing B cells contains a high proportion of B lymphocytes that express extensively mutated VH genes. Finally, we show that somatically-mutated variants of particular VH and VL genes that, in germline configuration, are frequently found in the early B-cell repertoire and in natural autoantibodies, encode pathogenic IgG autoantibodies characteristic of human SLE. These VH and VL genes harbor all the characteristics of an antigen-driven B-cell activation and selection process.

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.