Structure and physical map of 64 variable segments in the 3'0.8-megabase region of the human immunoglobulin heavy-chain locus

A subgroup of human VH3 germline genes that encode a high-avidity synovial rheumatoid factor

We have previously derived and identified a highly avid monoclonal IgM rheumatoid factor (mRF), C6, from unstimulated rheumatoid synovial cells (RSC). At the time, the closet VH germline gene, VH26, demonstrated only 88% homology with C6. To identify the germline counterpart of C6, genomic DNA from the same rheumatoid arthritis (RA) patient from whom C6 was derived was used in the polymerase chain reaction (PCR). Four of the six closely related germline genes that we sequenced had exonic regions that were identical with the VH region of C6 cDNA. These six germline sequences differed in their intronic regions, suggesting that they were distinct, but closely related genomic sequences. To further evaluate the extent of these related genes we identified nine additional germline genes having VH-encoding exons that were 86-97% identical to the C6 cDNA sequence. Furthermore, we examined the polymorphic nature of the C6 VH gene using single strand conformation polymorphism (SSCP), and identified two peaks, confirming the existence of highly homologous genes. The sequence and polymorphism data suggest that: (1) the VH region of the high avidity mRF C6 was derived from an unmutated germline gene; (2) C6 was encoded by a VH gene belonging to a set of homologous genes within the larger VH3 family; and (3) in addition to somatic rearrangements of B-cell genes and antigen-driven somatic mutation, gene duplication and conversion events of germline genes could be important in generating diversity and polyclonality among high-affinity pathogenic autoantibodies.

Combinatorial libraries: new insights into human organ-specific autoantibodies

The recent application of immunoglobulin (Ig) gene combinatorial library technology has led to a logarithmic increase in information concerning human, disease-associated, organ-specific autoantibodies of the IgG class. As reviewed here by Basil Rapoport, Stefano Portolano and Sandra McLachlan, the molecular cloning, analysis and expression of the genes for increasing numbers of these human, monoclonal autoantibodies is providing new insight into the genetic background and epitopic repertoires of such molecules.

Immunoglobulin gene expression in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by inflammation of synovium, in which immunoglobulin-secreting plasma cells are generally present. The forces driving immunoglobulin expression in RA synovium are unknown. Sequences of VH and VK transcripts from an RA synovial cDNA library demonstrate patterns of somatic mutation typical of an antigen-driven response. Moreover, 5% of the kappa repertoire appears to derive from the same B cell progenitor, suggesting an oligoclonal response. Immunoglobulin expression in this synovium thus appears to result from antigen stimulation. In addition, this patient's synovium is enriched for unusually long VK-JK joins (CDR3s), suggesting abnormal selection or regulation of the B cell response in RA.

Human antibodies from transgenic mice

We have used homologous recombination in ES cells to engineer B cell-deficient mice that are incapable of expressing endogenous immunoglobulin heavy and kappa light chain genes. We find that B cell development in these mutant mice can be rescued by the introduction of human germline-configuration heavy- and kappa light-chain minilocus transgenes. The transgenes rearrange during B cell differentiation, and subsequently undergo class switching and somatic mutation in response to antigen stimulation; thus recapitulating both stages of the humoral immune response using human, rather than mouse, sequences. The mice can be immunized; and human sequence, antigen specific, monoclonal antibodies can be obtained using conventional rodent hybridoma technology. These animals are also of interest for studying the normal processes of immunoglobulin gene expression. We discuss the example of heavy chain class switching, which has not been previously observed within an autonomous transgene.

The molecular structure of human antibodies specific for the human immunodeficiency virus

The molecular structure of human antibodies that are specific for human immunodeficiency virus-1 (HIV-1) are of increasing interest as AIDS research progresses toward passive immunotherapeutics in the maintenance and prevention of infection. In recent years a number of human, HIV-specific hybridomas and EBV-transformed B cell lines, as well as a combinatorial library, have been developed and characterized at the molecular level. These sources have provided valuable information on the immunoglobulin heavy- and light-chain variable-region gene usage and the extent and appearance of somatic mutation in a disease where the immune system is under constant stimulation over a long period of time. In this article we review the current data available on the molecular structure of these antibodies.

Immunoglobulin allotypes (GM and KM) and their interactions with HLA antigens in autoimmune diseases: a review

GM and KM immunoglobulin (Ig) allotypes and their interactions with HLA antigens have been analyzed in various autoimmune diseases: multiple sclerosis, rheumatoid arthritis, insulin-dependent diabetes mellitus (IDDM), systemic lupus erythematosus, coeliac disease, Crohn's disease, Graves' disease, atrophic thyroiditis, Hashimoto's thyroiditis, myasthenia gravis, chronic active hepatitis, alopecia areata, uveitis, vitiligo, Turner's syndrome, glomerular nephritis, Berger's disease and idiopathic dilated cardiomyopathy. This review reports published results about associations or linkages, as well as the origins of the populations, the numbers of patients and controls tested. The possible role of Ig polymorphisms in the physiopathology of autoimmune diseases is discussed. Ig allotypes and statistical methods used to analyse the HLA and Ig data are also described.

Anti-B cell autoantibodies encoded by VH 4-21 genes in human fetal spleen do not require in vivo somatic selection

We isolated immunoglobulin (Ig) VH4 genes that were rearranged in the genomic DNA of 160 day human fetal spleen. Productively rearranged VH 4-21 genes were cloned into pRTM1, a human IgM expression vector. This allowed us to generate IgM kappa-expressing transfectomas by co-transfecting each of these constructs with pSVG-V kappa 3, an Ig kappa light-chain expression vector that has a variable region encoded Humkv325, a conserved V kappa gene that is frequently expressed early B cell ontogeny. We find that all transfectomas expressing IgM kappa encoded by VH 4-21 make IgM autoantibodies reactive with i, a linear poly-N-acetyllactosamine determinant present on neonatal red blood cells and a B cell-restricted isoform of the CD45 surface molecule. In contrast, a transfectoma expressing pSVG-V kappa 3 and pRTM1 containing a rearranged VH4-59 (V71-4) gene isolated from a chronic lymphocytic leukemia B cell population, designated WIL, produced IgM kappa antibodies that had no detectable anti-i binding activity. However, transfectomas expressing VH 4-21 fused onto the Ig heavy-chain third complementarity determining region (CDR3) of WIL are found to make anti-B cell autoantibodies with anti-i activity. These studies indicate that VH 4-21 genes rearranged in human fetal B cell ontogeny can encode anti-B cell autoantibodies with a binding specificity that does not require in vivo somatic selection.

Structural conservation of hypervariable regions in immunoglobulins evolution

Analysis of human and mouse immunoglobulins has shown that five of six hypervariable regions that form the antigen binding site have a small repertoire of main chain conformations (canonical structures). Cartilaginous fishes are the most distantly related species to humans known to have an immune system, their evolutionary lines having diverged 450 million years ago. An analysis of VH and V kappa sequences from these fishes shows that all the main chain structures in their L1, L2, H1 and H2 hypervariable regions, and one of those in the L3 region, are the same as those most commonly found in human and mouse. This implies that the canonical structures occurring most commonly in hypervariable regions arose very early in the stages of the evolution of the immune system.

The immunoglobulin heavy chain and disease association: application to pemphigus vulgaris

Genes involved in the immune response are generally encoded from a complex cluster of gene segments. Studies of the association of diseases with such genes require well-defined genetic markers throughout the selected region. A set of 15 polymorphic loci that span 1500 kb of the immunoglobulin heavy chain (IGH) complex, 8 in the variable (VH) region and 7 in the constant (CH) region, were selected for the study of disease association. We present a protocol for the use of multiple immunoglobulin heavy chain (IGH) polymorphisms for general application in disease association studies. No microsatellite repeat markers are available for this region. To demonstrate the applicability of this approach, we have examined these IGH polymorphisms in families with individuals affected with pemphigus vulgaris (PV), an autoimmune dermatologic disease. Allele frequencies in 12 patients with PV were compared with those found in their spouses, and with those in a white Canadian control population. A significant difference was found between PV patients and both control groups for the presence of the VH gene VH3f-R4, and possibly for the absence of VH3f-R3, suggesting the possibility of susceptibility factors in these regions. Examination of the frequencies of the IGH region C gamma-haplotypes of PV patients indicated that, while the patients did not differ significantly from their spouses (chi 2 = 1.79), both groups were found to differ significantly from the white Canadian control group (chi 2 = 10.10), emphasizing the importance of matching the ethnic background of controls with that of the patient test group in disease association studies. Unexpectedly, two patients had large deletions of genes in the IGH constant region, which could play a role in the development of PV and require further investigation.

CAG expansions in a novel gene for Machado-Joseph disease at chromosome 14q32.1

We have identified a novel gene containing CAG repeats and mapped it to chromosome 14q32.1, the genetic locus for Machado-Joseph disease (MJD). In normal individuals the gene contains between 13 and 36 CAG repeats, whereas most of the clinically diagnosed patients and all of the affected members of a family with the clinical and pathological diagnosis of MJD show expansion of the repeat-number (from 68-79). Southern blot analyses and genomic cloning demonstrates the existence of related genes. These results raise the possibility that similar abnormalities in related genes may give rise to diseases similar to MJD.

Molecular detection of clonally rearranged cells in peripheral blood progenitor cell harvests from multiple myeloma patients

Peripheral blood progenitor cells (PBPC) are increasingly used for autologous reconstitution following high-dose chemotherapy in multiple myeloma but it is unclear whether these cells are less likely to be contaminated with malignant cells than bone marrow (BM). We have investigated this using immunoglobulin heavy-chain (IgH) gene fingerprinting, a polymerase chain reaction based technique with a sensitivity of 0.1-0.01% (10(-3)-10(-4)). We have looked for patient-specific IgH rearrangements in leukapheresis samples from eight myeloma patients undergoing PBPC harvest. Seven were in first remission (six partial, one complete) and one in second complete remission. Mobilization of PBPC was accomplished using cyclophosphamide (4 or 7 mg/m2) and rhG- or GM-CSF. Between two and five leukaphereses were performed in each patient. Patient-specific IgH rearrangements were identified in diagnostic BM in all patients and bands of identical size were found in one or more leukaphereses from 6/8 patients. Overall, 14/32 leukaphereses were shown to be contaminated. Two patients who showed contamination of at least one PBPC harvest had BM harvests in which contaminating cells were not detectable, suggesting that PBPC are not necessarily less likely to be contaminated than marrow stem cells. These results indicate that PBPC harvests from the majority of myeloma patients are likely to contain contaminating cells. Further studies are needed to determine whether these cells are clonogenic and whether they contribute to relapse.

Variable region sequences of a protective human monoclonal antibody specific for the Haemophilus influenzae type b capsular polysaccharide

A hybridoma secreting a human immunoglobulin G2 kappa monoclonal antibody (MAb) specific for the capsular polysaccharide of Haemophilus influenzae type b (Hib) was isolated. This MAb, designated CA4, was bactericidal to Hib in vitro and protected infant rats from Hib bacteremia. Nucleotide sequence analysis of CA4 variable (V) region cDNA showed that the heavy (H)-chain V region was of subgroup III and was 96% identical to the VH germ line gene segment DP77 (V3-21). The light (L)-chain V region was of the kappa subgroup III and was 94% identical to the A27 (Humkv325) germ line gene, which is commonly used by rheumatoid factors and other autoantibodies. MAb CA4 did not have rheumatoid factor activity and did not react with histones, DNA, or chromatin. These findings identify an additional VHIII gene segment which can contribute to the anti-Hib capsular polysaccharide repertoire and demonstrate that a VL gene commonly encoding autoantibodies can be utilized for protective immunity.

The immunoglobulin repertoire of the rainbow trout (Oncorhynchus mykiss): definition of nine Igh-V families

An Igh-V library was constructed from the head kidney cytoplasmic RNA of an 8.5-month-old non-immunized rainbow trout, Oncorhynchus mykiss, using the 5' RACE polymerase chain reaction. Six new Igh-V segments were identified, bringing to nine the number of Igh-V families actually defined in that species. A phylogenetic analysis shows that these nine Igh-V families can be classified into three major groups. The first includes the Igh-V1, Igh-V3, Igh-V4, and Igh-V7 families, and is homologous to the human and mouse Group III Igh-V families. The second includes the Igh-V5, Igh-V8, and Igh-V9 families and is more closely related to the Group I and Group II human and mouse Igh-V families. The third group includes the Igh-V2 and Igh-V6 families, which are not closely related to any other vertebrate Igh-V gene. Six Igh-J segments were characterized. They can recombine with Igh-V segments belonging to different families and there is a high level of junctional diversity between the Igh-V and Igh-J segments.

A map of the human immunoglobulin VH locus completed by analysis of the telomeric region of chromosome 14q

Analysis of the telomeric region of chromosome 14q has enabled us to complete a map of the immunoglobulin VH locus which accounts for almost all VH segments known to rearrange in B-lymphocytes. The human germline VH repertoire consists of approximately 50 functional VH segments--the exact number depending on the haplotype--spanning 1,100 kilobases upstream of the JH segments. A yeast artificial chromosome used to map these segments was isolated by its ability to provide telomere activity in yeast, suggesting that the VH locus may be located within a few kilobases of the 14q telomere. The limited structural diversity encoded by the functional VH segments demonstrates the importance of combinatorial diversity produced by VDJ joining and the association of heavy and light chains in producing the human antibody repertoire.

The pathogenesis of chronic lymphocytic leukemia: analysis of the antibody repertoire

CD5+ B cells predominate early in ontogeny and have been associated with autoantibody production. In chronic lymphocytic leukemia (CLL), B lymphocytes express CD5 and frequently produce autoantibodies using developmentally regulated variable (V)-gene segments. Does the self-reactivity observed in CLL reflect transformation of a 'fetal' lineage of cells, or could overexpansion of these B cells occur as a consequence of antigen stimulation? Harry Schroeder and Guillermo Dighiero have reviewed the literature describing antibody sequences in CLL and have compared them with the 'fetal' repertoire. This analysis indicates that CLL cells use a repertoire characteristic of mature cells, and suggests that antigen may play a role in the pathogenesis of this disease.

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

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

From esoteric theory to therapeutic antibodies

Theoretical analyses of amino acid and nucleotide sequences of immunoglobulins have provided a unique approach to the understanding of structure and function of antibodies. Variability plots unambiguously identified that the antibody-combining site is formed by six short complementarity determining regions (CDRs), three each from light and heavy chains. Since three-dimensional (3-D) foldings of framework regions (FRs) are similar among different antibodies, the 3-D configurations of CDRs from a specific antibody can be predicted based on their amino acid sequences. The resulting structure forms a compact surface that fits the antigen molecule tightly. The third CDR of the heavy chain (CDRH3), which is coded by the D-minigene together with the N- and/or P-segments, appears to play a unique role in fine fitting between antibody and antigen molecules. In order to maintain biological activities, the grafting of mouse CDRs onto human FRs should closely match the human FR amino acid sequences with the original mouse antibody. Similarities between human and mouse FR sequences that have been preserved for over 20 million years of evolution can be a useful tool in humanizing mouse antibodies.

Antigen-specific human monoclonal antibodies from mice engineered with human Ig heavy and light chain YACs

We describe a strategy for producing human monoclonal antibodies in mice by introducing large segments of the human heavy and kappa light chain loci contained on yeast artificial chromosomes into the mouse germline. Such mice produce a diverse repertoire of human heavy and light chains, and upon immunization with tetanus toxin have been used to derive antigen-specific, fully human monoclonal antibodies. Breeding such animals with mice engineered by gene targeting to be deficient in mouse immunoglobulin (Ig) production has led to a mouse strain in which high levels of antibodies are produced, mostly comprised of both human heavy and light chains. These strains should provide insight into the adoptive human antibody response and permit the development of fully human monoclonal antibodies with therapeutic potential.

Bidirectional transcription from the human immunoglobulin VH6 gene promoter

The human immunoglobulin (Ig) heavy chain VH6 gene promoter contains an imperfect octamer (AgGCAAAT) and is not dependent on the Ig heavy chain enhancer for activity; reporter constructs containing this promoter are very active in non-B cells. In experiments designed to characterize regions upstream of the transcriptional start site that are important for promoter function, we produced a series of deletion constructs, including one containing sequences between -74 and -146. Surprisingly, this fragment had promoter activity in both orientations. Inspection of the VH6 promoter sequence indicated that there was a possible TATA box in the proper orientation upstream of the imperfect octamer. The -74 to -146 fragment functioned as a promoter in the reverse orientation in three B cell lines and in non-B (HeLa) cells, with a much higher level of activity seen in the HeLa cells. To determine if the promoter could work in both directions simultaneously, reporter genes were positioned up- and downstream of a VH6 promoter fragment. Reporter gene activity was found for both genes in B cells and HeLa cells. Using a reverse transcriptase-polymerase chain reaction procedure (RT-PCR), we found a transcript corresponding to sequences upstream of the VH6 promoter in RNA from both the lymphoblastoid cell line ML-1, which actively transcribes the VH6 promoter, and the REH cell line, which does not. No transcripts were found in the KB epithelial cell line. Two or three mRNA 5' ends were found that mapped between -137 to -143 from the authentic VH6 transcription site, 31-37 nucleotides upstream of the putative TATA box. Inspection of the sequence upstream of the VH6 promoter demonstrated the presence of an open reading frame capable of coding for 96 amino acids. The VH6 promoter represents the second Ig promoter with bidirectional activity.

Sequence analysis and fine specificity of two human monoclonal antibodies to histone H1

Two human IgM lambda monoclonal antibodies (MAb) derived from the splenic lymphocytes of patients with idiopathic thrombocytopenia (Ben) and systemic lupus erythematosus (Wri) were studied. BEN-27 and WRI-170 hybridoma supernatants were screened for binding to ssDNA, dsDNA, poly (ADP-ribose), cardiolipin, histone subclasses and Klebsiella K30 cell wall antigen. Of this panel of antigens, BEN-27 and WRI-170 antibodies reacted only with histone H1. Their fine specificity was defined by direct and inhibition ELISA with synthetic peptides of the major human H1b variant. Antibody WRI-170 was shown to bind to both the N- and C-terminal peptides encompassing residues 1-16 and 204-218 of H1b whereas BEN-27 reacted only with peptide 204-218. To analyse the genetic origin of these autoantibodies, we determined the nucleotide sequence of the heavy (H) and light (L) chain variable regions of these two hybridomas. BEN-27 and WRI-170 MAbs were found to use VH1-DN1-JH4/V lambda 3-J lambda 2 and VH3-DIR2-D21/9-JH1/V lambda 2-J lambda 2 gene segment combinations respectively. Between 70 and 95% homology was demonstrated when the mRNA sequences for BEN-27 and WRI-170 were compared with published VH and V lambda germline sequences. This finding suggests that BEN-27 heavy and light chains and WRI-170 light chain use unidentified VH and V lambda germline gene segments whereas WRI-170 heavy chain derives from a VH gene segment recently identified. It is noteworthy that the CDRs of the two MAbs contain several negatively charged amino acids which are assumed to be of critical importance in antigen binding. Moreover, striking similarities are observed between BEN-27 heavy chain CDR2 and a previously described murine anti-H1 Ab heavy chain CDR2.

Somatic hypermutations in the immunoglobulin genes of two new human lymphoma lines of lymphatic follicle origin

Variable immunoglobulin heavy-chain regions (VDJ) of two newly established human lymphoma cell lines (HF-1 and HF-4) were sequenced. The most homologous germline VH gene found for both the HF-1 and HF-4 sequences was VH26 of the VH3a (V gene) family (82% and 91% homologies, respectively). The JH region of the HF-4 heavy-chain sequence contained two nucleotide differences compared to the published germline JH3 gene. The DHJH region of the HF-1 gene had a record high number (20%) of somatic mutations. The numerous hypermutations found in the HF-1 cell line support the hypothesis that in some human follicular lymphomas, mutations continue to accumulate in immunoglobulin genes during the malignant growth. Follicular lymphoma cell lines, which have an active mutational machinery, in future may help to solve the molecular events behind the somatic hypermutations modifying immunoglobulin genes of B lymphocytes.

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.

Utilization of a potentially universal downstream primer in the rapid identification and characterization of V lambda genes from two new human V lambda gene families

Polymerase chain reaction (PCR) has increased dramatically the speed of cloning and characterizing numerous genes. However, its application to identifying and analysing new germline Ig-variable (V) gene families has been hampered by the lack of sequence information in the downstream flanking regions of the concerned V genes, which are deleted during V(D)J rearrangements. To circumvent this problem, the possibility was explored that a degenerate downstream primer may be used in conjunction with a specific upstream primer, to clone members of new V lambda gene families, as much less is known about V lambda genes than Vh and Vk genes in humans. Firstly the feasibility and the specificity of a degenerate primer was examined by comparing it with an established downstream primer in amplifying known V lambda 1 genes. The results were positive. Thus, the degenerate primer was used to clone and characterize germline V lambda genes of the recently defined V lambda 8 and V lambda 9 gene families. This current strategy may help speed up the identification and characterization of all human V lambda genes. Moreover, a similar strategy can be applied to identify and characterize rapidly new V genes of either known or unknown Ig and T-cell receptor V gene families.

Normal B lymphocyte differentiation

Normal differentiation of B lineage cells has been the subject of intensive investigation over the past three decades. Current models of this process in humans are melded from the results of studies in a variety of organisms, including humans, mice and birds. Several recent developments have significantly reshaped and refined these models. The technique of homologous recombination in embryonic stem cells has allowed the production of mice with selectively disrupted genes that are important for B cell development in mice. At the same time, functional studies of human B cell differentiation, together with analysis of naturally occurring mutations that disrupt this process, have progressed rapidly. This has provided insight into the pathogenesis of lymphoproliferative and immunodeficiency diseases as well as a clearer view of normal developmental events. In this chapter we have reviewed human B cell differentiation with particular emphasis on newly emerging concepts. We also discussed CD5, a pan-T cell antigen that is expressed in low levels on a subpopulation of B cells implicated in the pathogenesis of chronic lymphocytic leukaemia (CLL). Finally, we discussed the issue of restricted variable region gene usage during B cell ontogeny and in CLL.

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.

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.

HAPPY mapping of a YAC reveals alternative haplotypes in the human immunoglobulin VH locus

We have identified and sequenced 14 human immunoglobulin VH segments cloned in a yeast artificial chromosome, and have used a rapid PCR-based technique (HAPPY mapping, 12) to derive the order and approximate distances between them. The sequences mapped comprise thirteen germline VH segments and one rearranged VH3 gene. Comparison of our map with other data suggests the existence of at least two distinct haplotypes, differing in the presence or absence of the consecutive genes DP-78, DP-46 and DP-64, and in the duplication of segments DP-49 and DP-65. Screening of ten individuals confirms the existence of both haplotypes, and indicates that both are common amongst the population.

Cloning of a human immunoglobulin gene fragment containing both VH-D and D-JH rearrangements: implication for VH-D as an intermediate to VH-D-JH formation

In an Epstein-Barr virus-transformed human B cell line we found an unusual immunoglobulin heavy chain gene rearrangement. Restriction mapping and sequencing analysis led us to conclude that VH-D and D-JH recombination took place in a single allele. Both VH-D and D-JH complexes still had their recombination signal sequences adjacent and the DNA sandwiched by these two complexes retained a germ-line configuration, suggesting the potential for a secondary rearrangement resulting in a VH-D(-D)-JH formation. With this finding, we propose a novel pathway, in which the VH-D complex is an intermediate in the formation of a functional VH exon.

A fetally expressed immunoglobulin VH1 gene belongs to a complex set of alleles

The immunoglobulin VH gene 51p1, a member of the large VH1 gene family, is preferentially expressed by B cells in the fetus and in chronic lymphocytic leukemia (CLL) and appears to be the source for many cryoglobulin rheumatoid factors. Polymorphism of 51p1 may therefore be functionally important. We have studied the germline representation of 51p1 and closely related VH elements to establish their prevalence and allelic relationship. A panel of oligonucleotide probes directed to the complementarity determining regions (CDR1 and CDR2) of 51p1 and a similar gene, hv1263, was used in restriction fragment polymorphism analysis of 48 unrelated individuals and six families. 13 VH alleles to the 51p1 locus were identified, each distinguished by its restriction fragment size, hybridization profile, or both. On some haplotypes the locus was duplicated. Null alleles were not seen. The 13 alleles were cloned, yielding nine distinct nucleotide sequences that were > 98.2% identical and included 51p1 and hv1263. These germline variations could influence specificity for antigen, because the corresponding protein sequences differed by up to five amino acids, including three nonconservative changes in the CDR. Two of the most prevalent variants contained 51p1. These findings expand the spectrum of polymorphism seen among human VH genes and elucidate the germline origin of VH1 sequences frequently expressed in autoantibodies and CLL. We conclude that the 51p1 locus is polymorphic, and that the 51p1 element is the predominant member of a complex set of alleles.

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.