At least five DH genes of human immunoglobulin heavy chains are encoded in 9-kilobase DNA fragments

Characterization of the human Ig heavy chain antigen binding complementarity determining region 3 using a newly developed software algorithm, JOINSOLVER

We analyzed 77 nonproductive and 574 productive human V(H)DJ(H) rearrangements with a newly developed program, JOINSOLVER. In the productive repertoire, the H chain complementarity determining region 3 (CDR3(H)) was significantly shorter (46.7 +/- 0.5 nucleotides) than in the nonproductive repertoire (53.8 +/- 1.9 nucleotides) because of the tendency to select rearrangements with less TdT activity and shorter D segments. Using criteria established by Monte Carlo simulations, D segments could be identified in 71.4% of nonproductive and 64.4% of productive rearrangements, with a mean of 17.6 +/- 0.7 and 14.6 +/- 0.2 retained germline nucleotides, respectively. Eight of 27 D segments were used more frequently than expected in the nonproductive repertoire, whereas 3 D segments were positively selected and 3 were negatively selected, indicating that both molecular mechanisms and selection biased the D segment usage. There was no bias for D segment reading frame (RF) use in the nonproductive repertoire, whereas negative selection of the RFs encoding stop codons and positive selection of RF2 that frequently encodes hydrophilic amino acids were noted in the productive repertoire. Except for serine, there was no consistent selection or expression of hydrophilic amino acids. A bias toward the pairing of 5' D segments with 3' J(H) segments was observed in the nonproductive but not the productive repertoire, whereas V(H) usage was random. Rearrangements using inverted D segments, DIR family segments, chromosome 15 D segments and multiple D segments were found infrequently. Analysis of the human CDR3(H) with JOINSOLVER has provided comprehensive information on the influences that shape this important Ag binding region of V(H) chains.

The influence of CD40-CD154 interactions on the expressed human V(H) repertoire: analysis of V(H) genes expressed by individual B cells of a patient with X-linked hyper-IgM syndrome

Analysis of the V(H)DJ(H) repertoire of peripheral blood IgM(+) B cells from a patient with X-linked hyper-IgM syndrome (X-HIgM) was undertaken to determine whether the distribution of V(H) families in the productive repertoire might be regulated by in vivo CD40-CD154 interactions. The distribution of V(H) genes in the non-productive repertoire of IgM(+) B cells was comparable in X-HIgM and normals. Unlike the normal productive V(H) repertoire, however, in the X-HIgM patient the V(H)4 family was found at almost the same frequency as the V(H)3 family. This reflected a diminution in the positive selection of the V(H)3 family observed in normals and the imposition of positive selection of the V(H)4 family in the X-HIgM patient. Unique among the V(H)3 genes, V(H)3-23/DP-47 was positively selected in both normals and the X-HIgM patient. No major differences in the usage of J(H) or D segments or the complementarity-determining region (CDR) 3 were noted, although the foreshortening of the CDR3 noted in the mutated V(H) rearrangements of normals was absent in the X-HIgM patient. Finally, a minor degree of somatic hypermutation was noted in the X-HIgM patient. These results have suggested that specific influences on the composition of the V(H) repertoire in normals require CD40-CD154 interactions.

Ig Heavy Chain Third Complementarity Determining Regions (H CDR3s) After Stem Cell Transplantation Do Not Resemble the Developing Human Fetal H CDR3s in Size Distribution and Ig Gene Utilization

Previous studies have suggested that the B-cell repertoire after stem cell transplantation resembles the developing repertoire in the fetus. Fetal and adult repertoires differ strikingly at the molecular level in Ig heavy chain third complementarity determining region (H CDR3) size distribution and Ig gene utilization. Previously, the posttransplant repertoire has not been studied fully in this regard. In this study, we analyzed H CDR3s posttransplant using CDR3 fingerprinting, single-strand conformation polymorphism (SSCP), and random sequencing. Eleven adult patients who received either autologous (n = 6) or allogeneic adult sibling (n = 5) hematopoietic stem cell transplants were studied. IgM H CDR3 repertoires demonstrated limited clonal diversity within the first 6 to 10 weeks posttransplant. By 3 to 4 months, the IgM H CDR3 repertoires were as diverse as those in healthy adults. Reconstitution of the IgM diversity correlated with the expansion of the multimember VH3 family. By contrast, the contribution of the single-member VH6 family was limited in most patients up to 6 to 9 months. No evidence was seen for greater contribution of VH6 posttransplant. IgG repertoires remained clonally restricted at all times. In all patients, H CDR3 sizes fell within adult limits. Direct nucleotide sequencing of H CDR3s showed adult-type N-nucleotide insertions and Ig gene utilization. These results indicate that the emerging repertoire posttransplant does not resemble the developing fetal repertoire at the molecular level.

© 1998 by The American Society of Hematology.

Ig Heavy Chain Third Complementarity Determining Regions (H CDR3s) After Stem Cell Transplantation Do Not Resemble the Developing Human Fetal H CDR3s in Size Distribution and Ig Gene Utilization

Previous studies have suggested that the B-cell repertoire after stem cell transplantation resembles the developing repertoire in the fetus. Fetal and adult repertoires differ strikingly at the molecular level in Ig heavy chain third complementarity determining region (H CDR3) size distribution and Ig gene utilization. Previously, the posttransplant repertoire has not been studied fully in this regard. In this study, we analyzed H CDR3s posttransplant using CDR3 fingerprinting, single-strand conformation polymorphism (SSCP), and random sequencing. Eleven adult patients who received either autologous (n = 6) or allogeneic adult sibling (n = 5) hematopoietic stem cell transplants were studied. IgM H CDR3 repertoires demonstrated limited clonal diversity within the first 6 to 10 weeks posttransplant. By 3 to 4 months, the IgM H CDR3 repertoires were as diverse as those in healthy adults. Reconstitution of the IgM diversity correlated with the expansion of the multimember VH3 family. By contrast, the contribution of the single-member VH6 family was limited in most patients up to 6 to 9 months. No evidence was seen for greater contribution of VH6 posttransplant. IgG repertoires remained clonally restricted at all times. In all patients, H CDR3 sizes fell within adult limits. Direct nucleotide sequencing of H CDR3s showed adult-type N-nucleotide insertions and Ig gene utilization. These results indicate that the emerging repertoire posttransplant does not resemble the developing fetal repertoire at the molecular level.

© 1998 by The American Society of Hematology.

Characterization of the CDR3 region of rearranged alpha heavy chain genes in human fetal liver

The human fetal liver is an early site for B cell development. Pre B cells are first detectable in human fetal life at 8 weeks of gestation, when the rearrangement of the mu heavy chain genes starts. In this study we characterize the CDR3 region of rearranged alpha heavy chain transcripts from four human fetal livers ranging from 8 to 11 weeks of gestation. Each fetal liver showed a limited number of variations in CDR3 sequences compared with adult peripheral blood mononuclear cells (PBMC). Sequence analysis of 91 clones demonstrated that there was no preference for the usage of a certain JH gene segment, whereas a preference for usage of DH family genes, DXP and DLR, was seen in most cases during early fetal life. This is the first study where rearranged alpha heavy chain genes in fetal liver have been characterized. Our data suggest that the usage of JH genes is random, while there is a preference for DH family genes in human fetal liver.

Analysis of the human VH gene repertoire. Differential effects of selection and somatic hypermutation on human peripheral CD5(+)/IgM+ and CD5(-)/IgM+ B cells

To analyze the immunoglobulin repertoire of human IgM+ B cells and the CD5(+) and CD5(-) subsets, individual CD19(+)/ IgM+/CD5(+) or CD5(-) B cells were sorted and non-productive as well as productive VH gene rearrangements were amplified from genomic DNA and sequenced. In both subsets, the VH3 family was overrepresented largely as a result of preferential usage of a small number of specific individual family members. In the CD5(+) B cell subset, all other VH families were found at a frequency expected from random usage, whereas in the CD5(-) population, VH4 appeared to be overrepresented in the nonproductive repertoire, and also negatively selected since it was found significantly less often in the productive compared to the nonproductive repertoire; the VH1 family was significantly diminished in the productive rearrangements of CD5(-) B cells. 3-23/DP-47 was the most frequently used VH gene segment and was found significantly more often than expected from random usage in productive rearrangements of both CD5(+) and CD5(-) B cells. Evidence for selection based on the D segment and the JH gene usage was noted in CD5(+) B cells. No differences were found between the B cell subsets in CDR3 length, the number of N-nucleotides or evidence of exonuclease activity. Somatically hypermutated VHDJH rearrangements were significantly more frequent and extensive in CD5(-) compared to CD5(+) IgM+ B cells, indicating that IgM+ memory B cells were more frequent in the CD5(-) B cell population. Of note, the frequency of specific VH genes in the mutated population differed from that in the nonmutated population, suggesting that antigen stimulation imposed additional biases on the repertoire of IgM+ B cells. These results indicate that the expressed repertoire of IgM+ B cell subsets is shaped by recombinational bias, as well as selection before and after antigen exposure. Moreover, the influences on the repertoires of CD5(+) and CD5(-) B cells are significantly different, suggesting that human peripheral blood CD5(+) and CD5(-) B cells represent different B cell lineages, with similarities to murine B-1a and B-2 subsets, respectively.

Immunoglobulin variable gene analysis of human autoantibodies reveals antigen-driven immune response to glutamate decarboxylase in type 1 diabetes mellitus

Insulin-dependent (type 1) diabetes mellitus is an organ-specific autoimmune disease frequently associated with an islet-specific humoral autoimmune response. The role of islet cell autoantibodies in the disease process is unclear; in particular, it is not known whether they are a non-specific side effect of islet cell destruction or play a role in the autoimmune network leading to type 1 diabetes. Here we report the immunoglobulin gene usage and somatic mutation rates of a panel of seven human monoclonal islet cell autoantibodies (MICA 1-7) directed towards the major islet cell autoantigen glutamate decarboxylase (GAD). These autoantibodies were produced from cells from two patients with newly diagnosed type 1 diabetes. VH1, VH4 and V lambda 2 gene segments were frequently used in the MICA, but no correlation between V gene usage and epitope recognition was found. The nonrandom ratio of replacement versus silent mutations in the variable gene region, an accumulation of replacement mutations in the complementarity determining regions, which confer antigen binding, and the high relative avidity for GAD observed for MICA 1, 3, 4, and 6, suggested that the immune response to GAD is driven by the antigen. In contrast, MICA 2, 5, and 7, revealing a lower affinity for antigen, have accumulated a large number of silent mutations. These latter antibodies may, therefore, be characteristic for later stages of the chronic autoimmune disease. Our results argue in favor of an antigen-driven autoantibody response to islets in human type 1 diabetes. They suggest that GAD is an important target of autoimmunity associated with type 1 diabetes.

Location and sequence of rearranged immunoglobulin genes in human thymus

Thymic B cells are a proliferating B cell population concentrated in normal thymic medulla. They are large cells, some with dendritic morphology, and are not associated with any organized follicular structure. Previous work in this laboratory has shown that most of these B cells are surrounded by tightly adherent thymocytes. The literature on human thymic B cells contains many inconsistencies. There is no consensus on whether they express CD5. Even the existence of thymic B cells has been questioned. In this study we have undertaken the first analysis of rearranged immunoglobulin (Ig) genes, looking in particular for evidence of affinity maturation. The Ig VH genes of human thymic B cells in this study are those of the fetal repertoire, though the resemblence to fetal Ig genes is limited in other respects. They are mostly unmutated, but the presence of mutated sequences suggests that this is not a uniform population, as has been previously indicated by phenotypic studies.

Immunoglobulin gene sequence analysis of anti-cardiolipin and anti-cardiolipin idiotype (H3) human monoclonal antibodies

Heavy and light chain variable region nucleotide sequences were derived from 6 human hybridoma antibodies which bear characteristics of antibodies associated with the phospholipid antibody syndrome. All antibodies originated from non-autoimmune individuals and were polyspecific. Four of these reacted with cardiolipin (and other antigens) and three carried the H3 idiotype which is expressed on a high percentage of disease-associated anti-cardiolipin antibodies. This idiotype was localized to the lambda light chain of the H3 monoclonal antibody and found on two other antibodies which like H3 expressed V lambda 4 or the related V lambda 3 subgroup light chains. The H3 idiotype however did not define these subgroups nor was it required or sufficient for anti-cardiolipin activity. Anti-cardiolipin binding was found in VH1, VH3 and VH4 heavy chain families and in a V kappa 1 light chain. The D region was diverse in both length and gene usage. Although all cardiolipin binding antibodies showed little deviation from germline variable (V) gene sequences, where mutations occurred they tended to be replacement mutations and clustered in complementarity determining regions (CDR) suggesting these B cells were derived from antigen-driven responses. These results from our panel of hybridomas and their comparison to other human antibodies provide extensive information on the diversity of genetic elements which can be used by cardiolipin-binding antibodies. We also show gene sequences which encode the disease-associated H3 idiotype and its location on lambda light chains, which imply that some labda light chains may be preferentially utilized in auto-reactive hybridomas.

Variable region gene analysis of B cell subsets derived from a 4-year-old child: somatically mutated memory B cells accumulate in the peripheral blood already at young age

Tonsillar germinal center and immunoglobulin M+ (IgM+)IgD+ B cells as well as peripheral blood (PB) CD5+ and CD5- (conventional) B cells from a 4-yr-old child were isolated and nucleotide sequences of expressed Ig heavy chain variable regions encoded by VH4 gene family members were determined from amplified cDNA. Whereas both tonsillar IgM+IgD+ cells and the majority of IgM-expressing CD5+ and CD5- PB B cells showed no or little somatic mutation, tonsillar germinal center (GC) B cells and IgG-expressing PB B cells carried a high load of somatic mutations in their V region genes. This suggests that somatically mutated memory B cells which have switched isotype accumulate in the PB already at young age. Their frequency seems to increase with age. On the other hand, the antibody repertoire of tonsillar IgM+IgD+ B cells and the majority of IgM-expressing PB B cells is determined by germline-encoded specificities and by generation of variability in the complementary determining region III through VH-DH-JH recombination. A fraction of IgM-bearing PB B cells carries somatically mutated V region genes and probably represents GC-derived B cells which have left the GC at an early stage of the GC reaction without undergoing isotype switching. 10 VH4 germline genes were found to be expressed. Three gene segments were overrepresented in the sequence collection (35 of 50 clones): VH4.21 (30%), V71-4 (20%), and 3D279D (20%). It appears that most potentially functional VH4 germline genes are expressed in peripheral B cells. Some members of this VH gene family are clearly overrepresented over others.

Somatic variation precedes extensive diversification of germline sequences and combinatorial joining in the evolution of immunoglobulin heavy chain diversity

In Heterodontus, a phylogenetically primitive shark species, the variable (VH), diversity (DH), joining (JH) segments, and constant (CH) exons are organized in individual approximately 18-20-kb "clusters." A single large VH family with > 90% nucleic acid homology and a monotypic second gene family are identified by extensive screening of a genomic DNA library. Little variation in the nucleotide sequences of DH segments from different germline gene clusters is evident, suggesting that the early role for DH was in promoting junctional diversity rather than contributing unique coding specificities. A gene-specific oligodeoxynucleotide screening method was used to relate specific transcription products (cDNAs) to individual gene clusters and showed that gene rearrangements are intra- rather than intercluster. This provides further evidence for restricted diversity in the immunoglobulin heavy chain of Heterodontus, from which it is inferred that combinatorial diversity is a more recently acquired means for generating diversity. The observed differences between cDNA sequences selected and the sequences of segmental elements derived from conventional genomic libraries as well as from VH segment-specific libraries generated by direct PCR amplification of genomic DNA indicate that the VH repertoire is diversified by both junctional diversity and somatic mutation. Taken together, these findings suggest a heretofore unrecognized contribution of somatic variation that preceded both extensive diversification of the germline repertoire and the combinatorial joining process in the evolution of humoral immunity.

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.

Germline variable region gene segment derivation of human monoclonal anti-Rh(D) antibodies. Evidence for affinity maturation by somatic hypermutation and repertoire shift

To date, there has been no systematic study of the process of affinity maturation of human antibodies. We therefore sequenced the variable region genes (V genes) of 14 human monoclonal antibodies specific for the erythrocyte Rh(D) alloantigen and determined the germline gene segments of origin and extent of somatic hypermutation. These data were correlated with determinations of antibody affinity. The four IgM antibodies (low affinity) appear to be derived from two germline heavy chain variable region gene segments and one or two germline light chain variable region gene segments and were not extensively mutated. The 10 IgG antibodies (higher affinity) appear to be derived from somatic hypermutation of these V gene segments and by use of new V gene segments or V gene segment combinations (repertoire shift). Affinity generally increased with increasing somatic hypermutation; on average, there were 8.9 point mutations in the V gene segments of the four IgM antibodies (Ka = 1-4 x 10(7)/M-1) compared with 19 point mutations in the V gene segments of the 10 IgG antibodies. The four highest affinity antibodies (Ka = 0.9-3 x 10(9)/M-1) averaged 25.5 point mutations. The use of repertoire shift and somatic hypermutation in affinity maturation of human alloantibodies is similar to data obtained in inbred mice immunized with haptens.

Rapid cloning of rearranged immunoglobulin heavy chain genes from human B-cell lines using anchored polymerase chain reaction

A general method to obtain the variable region DNA sequence of the immunoglobulin heavy chain using anchored polymerase chain reaction is described. Based on this DNA sequence, clone-specific oligonucleotides were designed to anneal to the complementarity determining regions. These were used to identify the original B-cell clone in serial dilutions of polyclonal lymph node DNA with high specificity and sensitivity. This method should be useful for studying minimal residual disease in B-cell neoplasia.

The human cord blood antibody repertoire. Frequent usage of the VH7 gene family

We have previously demonstrated a consistent preferential usage of a small set of VH, DH and JH gene segments in second-trimester fetal liver. To examine the extent of heavy chain repertoire diversification in newborns, we generated an unrestricted cDNA library from cord blood mononuclear cells and sequenced the variable domains of randomly isolated Cmu+ transcripts. We found this set of transcripts to be enriched for JH4, 5 and 6, whereas previously reported fetal transcripts preferentially expressed JH3 and 4. The cord blood transcripts used a number of different DH gene segments, whereas fetal transcripts were enriched for DHQ52. Of the thirteen cord blood sequenced, three were members of the newly described VH7 family which to date has not been detected in fetal liver. Indeed, only one of the isolated VH gene segments had been previously observed in fetal transcripts. As a result of enhanced N-region addition and use of longer DH and JH gene segments, both the sequence diversity and range of potential antigen-binding structures of cord blood complementarity-determining region 3 domains was vastly expanded. Thus, the repertoire bias evident in fetal liver was no longer apparent in this more mature population of cord blood B cells.

Restricted utilization of germ-line VH3 genes and short diverse third complementarity-determining regions (CDR3) in human fetal B lymphocyte immunoglobulin heavy chain rearrangements

Twenty-one independent immunoglobulin heavy chain VH3DJH rearrangements were cloned and sequenced from livers of human fetuses at 7, 13 and 18 weeks of gestation. The VH elements expressed were not somatically mutated. Eight out of the estimated 30 VH3 elements were utilized with a preference for five of them. One of these VH3 sequences, designated FL13-28, represented a thus-far unknown VH3 gene segment. From the six functional JH elements the JH3 and JH4 segments were utilized preferentially and from the estimated 30 D segments the DQ52 element and the Dxp family were found to rearrange frequently. D elements were utilized both in normal and inverted orientation, as single copies or in D to D fusions. Addition of N nucleotides, removal of nucleotides from the coding sequences and utilization of DIR elements (D genes with irregular recombination signals) further expanded the third complementarity-determining region (CDR3) diversity. One fourth of the fetal CDR3 regions lacked N regions. Due to utilization of DQ52, the relative absence of N regions and extensive exonuclease activity operating on the D elements, the fetal CDR3 regions were significantly shorter than those found in adult B lymphocytes.

Complete sequence of the genes encoding the VH and VL regions of low- and high-affinity monoclonal IgM and IgA1 rheumatoid factors produced by CD5+ B cells from a rheumatoid arthritis patient

We have characterized the VH and VL genes of three low-affinity polyreactive and two high-affinity monoreactive IgM and IgA1 rheumatoid factor (RF) mAb generated using circulating CD5+ B cells from a single rheumatoid arthritis patient. We found that four and one RF mAb utilized genes of the VHIV and VHIII families, respectively. The VHIV gene usage by these RF mAb differs from the preferential VHIII, VHI, and, to a lesser extent, VHII gene usage by the IgM with RF activity found in patients with mixed cryoglobulinemia, Waldenstrom's macroglobulinemia, and other monoclonal gammopathies. In addition, in contrast to the preponderant kappa L chain usage by the RF in these patients, a lambda L chain was utilized by all RF mAb from our rheumatoid arthritis patient. Two RF mAbs utilized V lambda I, two V lambda IV, and one V lambda III L chains. The VH genes of the two low-affinity polyreactive IgM RF mAb were in germline configuration. When compared with the deduced amino acid sequence of the putatively corresponding genomic segment, the VH gene of the high-affinity monoreactive IgM RF mAb displayed five amino acid differences, all of which are in the complementarity determining regions (CDR), possibly the result of a process of somatic point mutation and clonal selection driven by Ag. The unavailability of the corresponding genomic VH segment sequences made it impossible to infer whether the VH genes utilized by the two IgA1 RF were in a germline or somatically mutated configuration. Sequencing of the genes encoding the H chain CDR3 (D segments) revealed that all three low-affinity polyreactive RF mAb displayed a much longer D segment (36-45 bases) than their high-affinity monoreactive counterparts (15-24 bases), raising the possibility that a long D segment may be one of the factors involved in antibody polyreactivity.

A deletion map of the human immunoglobulin heavy chain variable region

Analysis of VH gene segments deleted in the process of immunoglobulin heavy chain (IGH) variable region assembly in three series of monoclonal B cell lines has been used to determine the human VH region organization. A deletion map of the relative positions of 21 different VH gene segments has been determined. The characterization of B cell lines from three unrelated adults of two racial groups yielded the same relative VH gene segment order, suggesting that the overall order of VH genes in the normal population is constant. This VH gene segment order was consistent with what we had previously generated from physical mapping techniques. DH segments from the second DH cluster, distinct from the major DH locus 3' of the VH region, were not observed to be used in 32 different rearrangements. Approximately 77% of the VH-(D)JH rearrangements involved VH gene segments within 500 kb of the JH region, indicating that human B cell lines preferentially rearrange JH-proximal VH gene segments. The switch, observed in mice, from the fetal use of JH-proximal VH gene segments to an adult VH use dependent upon VH family size may therefore not occur in humans. This detailed map of the VH gene segments is a necessary prerequisite for understanding VH usage in development and disease.

Relationship of the CD5 B cell to human tonsillar lymphocytes that express autoantibody-associated cross-reactive idiotypes

We examined human tonsillar B cells for expression of autoantibody heavy-chain or kappa light-chain cross-reactive idiotypes (CRIs), respectively defined by murine MAbs G6 or 17.109. We find 17.109 or G6 each specifically binds a subpopulation of B cells, respectively reacting with 3.8 +/- 3% (mean +/- SD) or 2.0 +/- 1.2% of all tonsillar lymphocytes. Cells reactive with both 17.109 and G6 comprise only 0.4 +/- 0.3% of tonsillar lymphocytes. Although each tested specimen had 17.109-positive cells, 2 of 19 tonsils (11%) did not have any G6-reactive cells. We find that CRI-positive cells and CD5 B cells both co-express slgD but fail to bind peanut agglutinin or MAbs specific for CD10, indicating that both cell types reside in the mantle zones of secondary B cell follicles. However, less than half of the B cells bearing one or both of these CRIs express detectable levels of CD5. Nevertheless, we find that G6-reactive lymphocytes constitute a multiclonal population of cells that express homologous heavy chain variable region genes, each rearranged to one of several distinct and apparently nonmutated D and JH gene segments. Collectively, these studies indicate that expression of nondiversified autoantibody-encoding variable region genes may not be an exclusive property of B cells that bear detectable levels of the CD5 surface antigen.

Nucleotide sequence of the human autoantibody 2E7 specific for the platelet integrin IIb heavy chain

The platelet glycoprotein (GP) IIb-IIIa complex figures prominently as an immunogen in autoimmune (idiopathic) thrombocytopenic purpura (ITP). 2E7 is a human monoclonal IgM autoantibody, derived from splenocytes of a patient with ITP, that recognizes a specific octapeptide amino acid sequence, Phe-Asp-Gly-Tyr-Trp-Gly-Tyr-Ser, on the heavy chain of GPIIb. This represents the first precise identification of an epitope on GPIIb-IIIa recognized by a human antibody. In this study, we have isolated total mRNA from 2E7, synthesized the corresponding cDNA using reverse transcriptase, and amplified the immunoglobulin mu and kappa chain cDNA by the Taq 1 polymerase chain reaction (PCR) using specific primers. The 2E7 mu chain variable region is encoded by a VH3 gene segment that is 98% homologous to the germline gene VH1.9III, a D-gene that is not homologous to any of the germline D-genes reported to date, and a JH6 gene segment that is essentially germline. The heavy-chain sequence, save for the unique D-gene, is similar to that of a number of human autoantibodies. The 2E7 kappa variable region is encoded by a Vk1 gene segment linked to a Jk1 gene segment. The Vk1 sequence of 2E7, with the exception of one nucleotide, is identical to that of autoantibody HF2-1/17, a prototype of SLE-associated anti-DNA autoantibodies bearing the 16/6 idiotype. The single base substitution results in a relatively conservative exchange of Asp for Glu at position 70 of the protein sequence. Despite this near identity in sequence, 2E7 does not bind to either single-stranded or double-stranded DNA. From these results, we conclude that specificity of 2E7 is likely to reside in either or both the D-JH region (CDR3) of the mu chain and the Jk region (CDR3) of the kappa chain. In addition to the identification of a novel D-gene, we also provide evidence that the 2E7 VHIII gene is probably a prototype of a VHIII subfamily, that the germline Vk1 gene shared by 2E7 and autoantibodies of the 16/6 idiotype probably represents a separate Vk family, and that this Vk gene cannot itself attribute specificity for DNA.

Analysis of the structural diversity of monoclonal antibodies to cyclosporine

The immunosuppressive cyclic undecapeptide cyclosporine (Cs) represents a useful model for studying the molecular basis of antibody-antigen interactions. The three-dimensional structure of the Cs molecule is known and a large panel of monoclonal antibodies (mAbs) to Cs has been well characterized by cross-reactivity studies with numerous Cs analogs. In the present study, the sequences of the variable regions of seven mAbs to Cs were determined and a striking relationship was found between the expressed variable region genes and the Cs recognition pattern. An analysis of the length and hydrophobic content of the hypervariable regions and sequence similarities suggested that the heavy chain plays a major role in Cs recognition. Different fine specificities were observed for mAbs exhibiting identical light chains, while two antibodies differed by only a single amino acid located in the heavy chain. The presence of a duplication of 12 nucleotides within the heavy chain third hypervariable region of two antibodies suggests the existence of an additional mechanism for creating antibody diversity.

Immunoglobulin heavy-chain-associated amyloidosis

Immunoglobulin- or multiple myeloma-associated amyloidosis has been distinguished by the tissue deposition of Congophilic, fibrillar protein consisting of light chains or light-chain fragments (AL amyloidosis). We now report the isolation and characterization of another form of immunoglobulin-associated amyloid obtained from a patient who had extensive systemic amyloidosis and in whom the amyloid deposits consisted not of light chains but rather of an unusual form of heavy chain. This component, isolated from splenic amyloid extracts, represented an internally deleted IgG1 heavy chain as evidenced by immunochemical, electrophoretic, and amino acid sequence analyses. A comparable immunoglobulin-related monoclonal protein, consisting only of IgG heavy chains, was present in the patient's urine. Based on serologic reactivity with a battery of anti-immunoglobulin antisera, these two immunoglobulin-related components were antigenically identical; however, when compared to normal IgG, both were deficient in Fc-associated gamma-chain determinants. The structural abnormality of the amyloid gamma-chain protein was further evidenced by SDS/PAGE and immuno-blotting analyses: An unusually low molecular mass of approximately 22 kDa was found for this material vs. the expected value of approximately 55 kDa for a normal gamma heavy chain. Despite the lack of certain Fc determinants, the amyloid and urinary heavy-chain proteins expressed the IgG1 subclass allotype marker G1m(a) located on the third constant region (CH3) domain of the internally deleted IgG1 heavy chains. That the amyloid protein contained an intact CH3 domain was established through amino acid sequence analyses of cyanogen bromide fragments and peptides generated by a lysine-specific protease. These studies also revealed that the gamma-chain amyloid protein contained the complete heavy-chain variable (VH) domain [including the diversity (DH) and joining (JH) segments] that was contiguous with the CH3 domain. The low molecular mass of the protein resulted from the total absence of the first (CH1), hinge, and second (CH2) heavy-chain constant regions. Such extensive CH deletions and the presence of a complete VH distinguish this amyloid-associated heavy chain from all other heretofore characterized gamma-heavy-chain disease proteins. This heavy-chain-related form of immunoglobulin-associated amyloidosis is tentatively designated AH amyloidosis.

Preferential utilization of conserved immunoglobulin heavy chain variable gene segments during human fetal life

The ability to respond to specific antigens develops in a programmed fashion. Although the antibody repertoire in adults is presumably generated by stochastic combinatorial joining of rearranged heavy variable, diversity, and joining (VH-DH-JH) and light (VL-JL) chains, experimental evidence in the mouse has shown nonrandom utilization of variable gene segments during ontogeny and in response to specific antigens. In this study, we have performed sequence analysis of 104-day human fetal liver-derived, randomly isolated constant region C+ mu transcripts and demonstrate a consistent preference during fetal life for a small subset of three highly conserved VH3 family gene segments. In addition, the data show that this preferential gene segment utilization extends to the DHQ52 and the JH3 and JH4 loci. Sequence analysis of two "sterile" DH-JH transcripts suggests that transcriptional activation of the JH-proximal DHQ52 element may precede initiation of DH-JH rearrangement and influence fetal DH utilization. Sequence comparisons reveal striking nucleotide polymorphism in allelic gene segments which is poorly reflected in the peptide sequence, implying considerable evolutionary selection pressure. Although vertebrate species utilize a variety of strategies to generate their antibody repertoire, preferential utilization of VH3 elements is consistently found during early development. These data support the hypothesis that VH3 gene segments play an essential role in the development of the immune response.

Nucleotide sequences and three-dimensional modelling of the VH and VL domains of two human monoclonal antibodies specific for the D antigen of the human Rh-blood-group system

The nucleotide sequences were determined for the VH and VL domains of two human IgG1 antibodies, Pag-1 and Fog-B, specific for the D antigen of the Rh-blood-group system. The VH-region genes of the two antibodies were derived from separate germ-line genes within the VH-IV gene family, but both antibodies used the same JH6 gene. The D-region genes differed from each other, and no similarity was found to known D regions. The light chain of Fog-B belongs to the V lambda-I subgroup and that of Pag-1 probably belongs to the V lambda-V subgroup; both light chains used the J2/3 gene. Three-dimensional models of the variable domains were made, based on those of known crystallographic structure. The surface contours at the combining sites are clearly different, consistent with the evidence that the antibodies recognize different but overlapping epitopes. Some details of the molecular modelling of hypervariable regions have been deposited as Supplementary Publication SUP 50155 (6 pages) at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1990) 265, 5.

Autoantibodies and the fetal antibody repertoire

Developing fetal B cells preferentially rearrange a restricted subset of the encoded antibody gene segments. There are striking structural similarities between elements expressed early in man and in mouse, most evident on comparison of murine VH elements from the VH7183 family to human VH elements of the VH3 family. The similarity is pronounced in two framework regions which together encode a possible binding site that is distinct from the classical antigen-combining site. By comparing all known human and murine VH gene sequences, we have demonstrated that these regions have been conserved in a family-specific manner throughout the mammalian radiation. The "non-conserved" spacer of the recombinase recognition signal is also highly conserved in a family-specific manner, suggesting a mechanism by which the expression of family-dependent features may be regulated. The evidence that such features contribute to the high incidence of self- and poly-specificity in the fetal antibody repertoire is reviewed.

Heavy chain variable region gene utilization in human antibodies

We have sequenced by the polymerase chain reaction the heavy chain variable regions of over thirty human antibodies of defined specificity. The distribution of VH families in this group of antibodies is disproportionately skewed toward the recently discovered VH gene families. Within a family, there is also a disproportional use of individual gene segments. Numerous explanations for these imbalances are discussed.

Human heavy chain variable region gene diversity, organization, and expression

Elucidation of the cellular and molecular mechanisms which determine the expressed antibody repertoire remains a major challenge in immunology. Knowledge of V gene diversity, organization, and expression is important to an understanding of the formation of the antibody repertoire in normal as well as diseased states. In the last few years, great advances have been made in our understanding of the human heavy chain variable region (VH) gene locus. In this review we present the current knowledge of VH gene diversity, organization, and utilization in normal individuals followed by a discussion of the possible relevance of these findings to autoimmunity.

A human anti-cardiolipin autoantibody is encoded by developementally restricted heavy and light chain variable region genes

Based on recent structural analyses of monoclonal autoantibodies, it appears that a number of these antibodies express germ-line immunoglobulin variable region (V) genes with little or no somatic mutation. In addition, our group and others have noted the identity or near identity of some autoantibody-associated V genes to V genes apparently expressed preferentially in the fetal pre-B cell repertoire. To extend these data, we now report that the heavy and light chain V genes of an anti-cardiolipin antibody derived from a healthy individual display 99% nucleotide sequence homology with V genes expressed in early B cell ontogeny. Sequence comparisons indicate the likely use of fetal-restricted V genes by this autoantibody. Taken together with other data on autoantibody V gene usage, these findings provide further evidence for overlap between the autoantibody-associated and early ontogeny expressed V gene repertoires and suggest that natural autoreactivity may be instrumental in the development and maintenance of the normal immune repertoire.

Developmentally restricted immunoglobulin heavy chain variable region gene expressed at high frequency in chronic lymphocytic leukemia

During fetal development, murine and human B-lineage cells rearrange and express a highly restricted set of immunoglobulin heavy chain variable region genes (VH genes). We noted that a VH gene of the restricted human fetal repertoire, designated 51p1, potentially could encode the VH region of two human IgM rheumatoid factor proteins. These rheumatoid factors share a cross-reactive idiotype (CRI) defined by reactivity with G6, a murine monoclonal antibody that recognizes an antibody heavy chain determinant present on many human IgM autoantibodies, particularly rheumatoid factors. Recently, we found that the G6 CRI also is expressed frequently by neoplastic CD5 (Leu1) B cells from patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma. However, neoplastic CD5-negative B cells from patients with lymphomas of follicular center cell origin rarely express this CRI. Here, we report that G6-reactive leukemic cells from two unrelated CLL patients express a VH gene that shares greater than 99% homology with a rearranged VH gene previously isolated from the leukemic cell DNA of another CLL patient and that is identical to VH 51p1. Using the polymerase chain reaction, we find that this VH gene is rearranged, and presumably expressed, in the genomic DNA of all examined cases of G6-reactive CLL or small lymphocytic lymphoma. Thus these data indicate that the autoantibody-associated G6 CRI is a serologic marker for a conserved and developmentally restricted VH1 gene that is expressed at high frequency in CD5 B-cell malignancies and early B-cell ontogeny.

Relationship of variable region genes expressed by a human B cell lymphoma secreting pathologic anti-Pr2 erythrocyte autoantibodies

To study the biology of cold agglutinin disease we previously established EBV-transformed B cell clones isolated from a patient with splenic lymphoma of an early plasmacytic cell type and immune hemolysis due to an anti-Pr2 cold agglutinin. These clones had an aberrant chromosomal marker identical to the patient's B cell lymphoma and each secreted IgMk anti-Pr2 similar to the pathologic autoantibody in the serum of the patient. In this study, we have further investigated the Pr2-specific autoimmune response through nucleotide sequencing of VH and VL region genes. We have shown that the seven clones share the same VDJ/VJ gene segments and junctional elements confirming their clonal origin. The VH sequences were 88% homologous to a VHI germline gene while the VL sequences were 97% homologous to a VkIII germline gene. Only 4 somatic mutations (3 silent and 1 conservative) were found in greater than 5,000 bp sequenced, suggesting that a low mutation rate existed. Based on a tumor mass of 10(12) cells and a minimum of 40 divisions, we estimated the somatic mutation rate to be 4.45 x 10(-5) m/bp/d. This somatic mutation rate is similar to those estimated for acute lymphocytic leukemia (pre-B cell) and chronic lymphocytic leukemia (intermediate B cell), but significantly lower than the mutation frequency in follicular lymphomas (activated B cell). We propose that the difference in somatic mutation frequency of a B cell tumor may be related to the stage of B cell differentiation. In addition, the low mutation frequency observed in the Pr2-specific B cell tumor may also reflect, in part, selection by autoantigen to conserve sIg structure and specificity.

Early human IgH gene assembly in Epstein-Barr virus-transformed fetal B cell lines. Preferential utilization of the most JH-proximal D segment (DQ52) and two unusual VH-related rearrangements

We have analyzed the phenotypic characteristics and IgH gene rearrangements in a panel of EBV-transformed B lineage cell lines from human fetal liver and bone marrow. Some lines contained only populations of immature, Ig- Be cells, while others contained mixed populations of mature and immature B cells. The majority of identifiable IgH rearrangements involved joining of the most JH-proximal D segment, DQ52, to various JH segments, implying that DQ52 is a preferred target for initial DJH rearrangements. Three other rearrangements involving VH-related sequences were also characterized. Two involved VHDJH joining using VH3 genes, although one of these had a very unusual DJH structure. The third consisted of inverted 3' signal sequences and flanking regions of a VH4 gene appended to a JH. The mechanisms by which the later rearrangement could have occurred and its potential physiological significance are discussed.

Isolation of an IgH gene circular DNA clone from human bone marrow

Circular DNA was obtained from human bone marrow. Then a phage library was prepared and screened by use of two probes of the IgH gene; 5'-DHQ52, containing the 5' flanking region of DHQ52, and JH4.3, containing the sequence from JH3 to the 3' flanking region of JH6. One clone, HBMC-1, that was DHQ52+JH4.3- was obtained. HBMC-1 had the germline IgH region upstream of JH1 and the 3' flanking region of DXP1. A recombination signal sequence flanking the 5' side of the JH1 segment was attached to the recombination signal sequence flanking the 3' side of DXP1 forming a head-to-head structure of two 7mers with 10 nucleotides in-between. HBMC-1 is thus considered to be a circular DNA deleted as a consequence of DXP1-JH1 joining of the IgH gene.