Development of the primary antibody repertoire

Dependence of Antibody Somatic Diversification on Gut-Associated Lymphoid Tissue in Rabbits

By ∼4 to 8 wk of age, the IgH VDJ genes of essentially all rabbit B lymphocytes have undergone somatic diversification. Some of this diversification occurs in the appendix, which is a gut-associated lymphoid tissue (GALT). To determine whether GALT is essential for somatic diversification, we surgically removed the appendix, sacculus rotundus, and Peyer’s patches from neonatal rabbits (designated GALT-less) and examined the extent to which VDJ genes were somatically diversified. We found that the IgM VDJ genes of peripheral B cells from 2- to 5-mo-old GALT-less rabbits had undergone considerably less somatic diversification than those of control rabbits. Further, the percentage of peripheral B cells in the GALT-less rabbits was generally less than that of controls. Our data suggest that, in rabbits, the primary Ab repertoire develops in GALT, and B cell expansion also occurs there. Hence, GALT may function as a mammalian bursal homologue.

Immune recognition of influenza hemagglutinin as a viral and a neo-self-antigen

To analyze mechanisms governing tolerance and autoimmunity to self-antigens, we have generated lineages of transgenic mice that express the influenza virus PR8 hemagglutinin (HA) as a neo-self-antigen. By comparing the HA-specific T and B cell responses that can be induced in HA Tg mice with those that are induced in non-Tg (BALB/c) mice, the specificity and genetic basis with which tolerance is induced to the HA has been examined. This article summarizes studies using lineages of HA Tg mice that express different forms and amounts of the HA under the control of the SV40 promoter/enhancer. Our studies have revealed that specific subsets of HA-specific T and B cells are negatively selected from the primary repertoires of HA Tg mice. However, substantial populations of HA-specific T and B cells evade negative selection and can be activated by virus immunization. Understanding the capacity of these autoreactive lymphocytes to differentiate and participate in antigen-specific immune responses will provide important insights into mechanisms by which autoimmunity might be induced by viruses bearing structural similarities with self-antigens.

Impaired immunoglobulin gene rearrangement in mice lacking the IL-7 receptor

To generate the full diversity of antibody heavy-chain genes, hundreds of dispersed germline V segments must undergo recombination following D-J segment joining. Here we report that this process is regulated by the alpha-chain of the receptor for interleukin-7, a cytokine that stimulates B-cell lymphopoiesis. D-J joining occurs normally in immature B lymphocytes from mice lacking the alpha-chain of the interleukin-7 receptor (IL-7Ralpha). But recombination of V segments is progressively impaired as their distance increases upstream of D/J, causing infrequent rearrangement of most V segments, which markedly reduces diversity. This is not simply due to defective cell proliferation or impaired recombinase expression. Rather, germline transcripts from distal, unrearranged V segments, a marker of chromatin changes that precede recombination, are specifically silenced. So too is expression of Pax-5, which binds to heavy-chain locus control elements and normally stimulates recombination, suggesting a mechanism for these effects. Thus ligands of the interleukin-7 receptor deliver an extrinsic signal that targets V segment recombination in the heavy-chain locus by altering the accessibility of DNA substrates to the recombinase. This mechanism augments the recombinational diversity of the primary antibody repertoire.

The antigen-binding characteristics of mAbs derived from in vivo priming of avian B cells

In most vertebrates, a primary antibody repertoire is created through the recombination of a diverse set of Ig variable (V), diversity (D), and joining (J) gene segments. In contrast, an avian immune repertoire is generated by gene conversion of rearranged Ig genes during B cell development within the bursa of Fabricius, a lymphoid organ unique to birds. To investigate the properties of antigen-specific Igs created through the process of gene conversion, we have developed a system for the production of avian-derived mAbs. This system was used to produce multiple antibodies after a single immunization with a conserved peptide from the human cystic fibrosis transmembrane conductance regulator gene. Each antibody isolated was found to have arisen independently through a distinct series of gene conversion events. These primary antibodies displayed evidence of diversity in all of the complementarity determining regions of both heavy and light chains, and both the heavy and the light chains contributed to antigen specificity. In the light chains, diversity could be attributed to gene conversion events. The measured affinity constants of two of the antibodies were between 10(8) and 10(9) M-1, and the antibodies were functional in quantitative ELISA as well as immunohistochemical studies of cystic fibrosis transmembrane conductance regulator expression. These data demonstrate that antigen-specific antibodies produced by Ig gene conversion display both high affinity and specificity. In addition, the methods developed here provide the description of a system for the production of mAbs derived from a nonmammalian species.

The Fas antigen and Fas-mediated apoptosis in B-cell differentiation

In the B-cell lineage, Fas, a type 1 membrane protein belonging to the tumor necrosis factor receptor (TNF) family, is expressed on B-cells at a restricted developmental stage and on activated B-cells, but not on naive mature B-cells. Apoptosis mediated by Fas-Fas ligand interactions may be involved in the peripheral elimination of autoreactive B-cells and in the regulation of the immune response through deletion of B-cells activated by foreign antigens, as for the T-cell lineage. Fas-mediated apoptosis associated with B-cell activation is affected by costimulation through other accessory signaling molecules like CD40, whose ligands are on T-cells.

Biochemical and Functional Analyses of Chromatin Changes at the TCR-β Gene Locus During CD4−CD8− to CD4+CD8+ Thymocyte Differentiation

Allelic exclusion is the process wherein lymphocytes express Ag receptors from only one of two possible alleles, and is effected through a feedback inhibition of further rearrangement of the second allele. The feedback signal is thought to cause chromatin changes that block accessibility of the second allele to the recombinase. To identify the putative chromatin changes associated with allelic exclusion, we assayed for DNase I hypersensitivity, DNA methylation, and transcription in 100 kb of the TCR-β locus. Contrary to current models, we identified chromatin changes indicative of an active and accessible locus associated with the occurrence of allelic exclusion. Of 11 DNase I hypersensitive sites identified, 3 were induced during CD4−CD8− to CD4+CD8+ thymocyte differentiation, and demethylation and increased germline transcription of the locus were evident. We further examined the role of the most prominently induced site near the TCR-β enhancer (Eβ) in allelic exclusion by targeted mutagenesis. Two other sites were also examined in New Zealand White (NZW) mice that have a natural deletion in the TCR-β locus. TCR-β gene recombination and allelic exclusion were normal in both mutant mice, negating dominant roles for the three hypersensitive sites in the control of allelic exclusion. The data suggest that alternative cis-regulatory elements, perhaps contained in the Eβ enhancer and/or in the upstream Vβ region, are involved in the control of TCR-β allelic exclusion.

Changes in the V(H) gene repertoire of developing precursor B lymphocytes in mouse bone marrow mediated by the pre-B cell receptor

The V(H) repertoire on both H chain alleles of normal and lambda5-deficient B lineage cells were analyzed by single-cell PCR. The mu H chains were tested for their capacity to form a pre-B cell receptor. In bone marrow, D-proximal V(H) genes were found preferentially expressed in lambda5-deficient pre-B cells and in a newly identified early c-kit+ cytoplasmic mu H chain+ pre-B cell population of normal mice. Only half of the mu H chains expressed in these cells have the capacity to form a pre-B cell receptor. Representation of the D-proximal V(H) genes was found suppressed on the productive but not on the nonproductive V(H)DJ(H) rearranged alleles of c-kit preB-II cells and splenic lambda5-deficient B cells. More than 95% of the mu H chains expressed in preB-II cells can form a pre-B cell receptor. These results demonstrate that the pre-B cell receptor in normal mice and the B cell receptor in lambda5-deficient mice mediate a shift in the V(H) repertoire.

Enhancer control of local accessibility to V(D)J recombinase

We have studied the role of transcriptional enhancers in providing recombination signal sequence (RSS) accessibility to V(D)J recombinase by examining mice carrying a transgenic human T-cell receptor (TCR) delta gene minilocus. This transgene is composed of unrearranged variable (Vdelta and Vdelta2), diversity (Ddelta3), joining (Jdelta1 and Jdelta3), and constant (Cdelta) gene segments. Previous data indicated that with the TCR delta enhancer (Edelta) present in the Jdelta3-Cdelta intron, V(D)J recombination proceeds stepwise, first V to D and then VD to J. With the enhancer deleted or mutated, V-to-D rearrangement is intact, but VD-to-J rearrangement is inhibited. We proposed that Edelta is necessary for J segment but not D segment accessibility and that J segment inaccessibility in the enhancerless minilocus resulted in the observed V(D)J recombination phenotype. In this study, we tested this notion by using ligation-mediated PCR to assess the formation of recombination-activating gene (RAG)-dependent double-strand breaks (DSBs) at RSSs 3' of Ddelta3 and 5' of Jdelta1. In five lines of mice carrying multicopy integrants of constructs that either lacked Edelta or carried an inactivated Edelta, the frequency of DSBs 5' of Jdelta1 was dramatically reduced relative to that in the wild type, whereas the frequency of DSBs 3' of Ddelta3 was unaffected. We interpret these results to indicate that Edelta is required for Jdelta1 but not Ddelta3 accessibility within the minilocus, and we conclude that enhancers regulate V(D)J recombination by providing local accessibility to the recombinase. cis-acting elements other than Edelta must maintain Ddelta3 in an accessible state in the absence of Edelta. The analysis of DSB formation in a single-copy minilocus integrant indicates that efficient DSB formation at the accessible RSS 3' of Ddelta3 requires an accessible partner RSS, arguing that RSS synapsis is required for DSB formation in chromosomal substrates in vivo.

Ig DH Gene Segment Transcription and Rearrangement Before Surface Expression of the Pan-B–Cell Marker CD19 in Normal Human Bone Marrow

The onset of IgH transcription and rearrangement is a defining characteristic of the progenitor population in which B-lineage commitment occurs. These features were used to better define the earliest stage of B-cell commitment in humans and to determine if these stages differ as a function of human ontogeny. Fetal and adult bone marrow mononuclear cells were sorted into B-lineage subpopulations on the basis of surface expression of the stem cell marker CD34, the pan-B–cell marker CD19, and IgM and analyzed for transcription and rearrangement of the IgH locus. The locus was found to be transcriptionally active before surface expression of CD19, as indicated by the presence of germline Iμ, Cμ, and DHQ52 transcripts in the CD34+ CD19− subpopulation. Transcripts from IgH alleles that had undergone DJCμ rearrangements were also detected in the CD34+ CD19− subpopulation. Within this subpopulation, low levels of DXP-containing DJCμ transcripts were detected in both fetal and adult cells. Although DHQ52 DJCμ transcripts were abundant in fetal CD34+ CD19− cells, they were not detected in cells of the same phenotype derived from adult bone marrow. In both fetus and adult, VH3-and VH6-containing VDJCμ transcripts were detected only in the CD19+ subpopulations. These data indicate that transcription of DHQ52-JH and DXP-JH rearrangements differs during fetal and adult B lymphopoiesis. Moreover, in both fetus and adult, transcription of unrearranged components of the IgH locus and DJ rearrangements can proceed before the surface expression of CD19.

Ig DH Gene Segment Transcription and Rearrangement Before Surface Expression of the Pan-B–Cell Marker CD19 in Normal Human Bone Marrow

The onset of IgH transcription and rearrangement is a defining characteristic of the progenitor population in which B-lineage commitment occurs. These features were used to better define the earliest stage of B-cell commitment in humans and to determine if these stages differ as a function of human ontogeny. Fetal and adult bone marrow mononuclear cells were sorted into B-lineage subpopulations on the basis of surface expression of the stem cell marker CD34, the pan-B–cell marker CD19, and IgM and analyzed for transcription and rearrangement of the IgH locus. The locus was found to be transcriptionally active before surface expression of CD19, as indicated by the presence of germline Iμ, Cμ, and DHQ52 transcripts in the CD34+ CD19− subpopulation. Transcripts from IgH alleles that had undergone DJCμ rearrangements were also detected in the CD34+ CD19− subpopulation. Within this subpopulation, low levels of DXP-containing DJCμ transcripts were detected in both fetal and adult cells. Although DHQ52 DJCμ transcripts were abundant in fetal CD34+ CD19− cells, they were not detected in cells of the same phenotype derived from adult bone marrow. In both fetus and adult, VH3-and VH6-containing VDJCμ transcripts were detected only in the CD19+ subpopulations. These data indicate that transcription of DHQ52-JH and DXP-JH rearrangements differs during fetal and adult B lymphopoiesis. Moreover, in both fetus and adult, transcription of unrearranged components of the IgH locus and DJ rearrangements can proceed before the surface expression of CD19.

EBF and E47 collaborate to induce expression of the endogenous immunoglobulin surrogate light chain genes

Early B cell factor (EBF) and E47 participate in the transcriptional control of early B lymphocyte differentiation. With the aim of identifying genetic targets for these transcription factors, we stably transfected cDNAs encoding EBF or a covalent homodimer of E47, individually or together, into immature hematopoietic Ba/F3 cells, which lack both factors. In combination, EBF and E47 induce efficient expression of the endogenous immunoglobulin surrogate light chain genes, lambda5 and VpreB, whereas other pre-B cell-specific genes remain silent. Multiple functionally important EBF and E47 binding sites were identified in the lambda5 promoter/enhancer region, indicating that lambda5 is a direct genetic target for these transcription factors. Taken together, these data suggest that EBF and E47 synergize to activate expression of a subset of genes that define an early stage of the B cell lineage.

Age-related impaired affinity maturation and differential D-JH gene usage in human VH6-expressing B lymphocytes from healthy individuals

To elucidate the basic molecular events underlying humoral immunity during ontogeny and senescence, we analyzed a panel of 179 polymerase chain reaction-derived VH6-D-JH rearrangements from cord blood, peripheral blood, and spleen. Nucleotide sequence analysis of the CDR3 region shows that there is a difference in D and JH gene usage in functional rearrangements between lymphocytes from peripheral blood and spleen. Analysis of the VH6 gene shows that the mutational frequencies rise from 0.81% in cord blood to 1.96% in peripheral blood lymphocytes derived from young adults, and decrease to 0.80% in samples from individuals older than 50 years. The number of rearrangements carrying mutations follows a similar pattern: 22% in cord blood, 73% in the age group 20-49 years, and 57% in the age group over 50 years. The mutational frequencies among the mutated genes are, however, similar for cord blood and young adults, 2.76% and 2.51%, respectively, and 1.3% in older adults. These data show an age-related impaired affinity maturation which might relate to the decrease in immunological responsiveness among the elderly.

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.

Regulation of T cell receptor delta gene rearrangement by CBF/PEBP2

We have analyzed transgenic mice carrying versions of a human T cell receptor (TCR)-delta gene minilocus to study the developmental control of VDJ (variable/diversity/joining) recombination. Previous data indicated that a 1.4-kb DNA fragment carrying the TCR-delta enhancer (E(delta)) efficiently activates minilocus VDJ recombination in vivo. We tested whether the transcription factor CBF/PEBP2 plays an important role in the ability of E(delta) to activate VDJ recombination by analyzing VDJ recombination in mice carrying a minilocus in which the deltaE3 element of E(delta) includes a mutated CBF/PEBP2 binding site. The enhancer-dependent VD to J step of minilocus rearrangement was dramatically inhibited in three of four transgenic lines, arguing that the binding of CBF/PEBP2 plays a role in modulating local accessibility to the VDJ recombinase in vivo. Because mutation of the deltaE3 binding site for the transcription factor c-Myb had previously established a similar role for c-Myb, and because a 60-bp fragment of E(delta) carrying deltaE3 and deltaE4 binding sites for CBF/PEBP2, c-Myb, and GATA-3 displays significant enhancer activity in transient transfection experiments, we tested whether this fragment of E(delta) is sufficient to activate VDJ recombination in vivo. This fragment failed to efficiently activate the enhancer-dependent VD to J step of minilocus rearrangement in all three transgenic lines examined, indicating that the binding of CBF/PEBP2 and c-Myb to their cognate sites within E(delta), although necessary, is not sufficient for the activation of VDJ recombination by E(delta). These results imply that CBF/PEBP2 and c-Myb collaborate with additional factors that bind elsewhere within E(delta) to modulate local accessibility to the VDJ recombinase in vivo.

Generation of antibody diversity in rabbits

Most rabbit B lymphocytes use the same VH gene in V(D)J gene rearrangements and undergo somatic diversification by gene conversion and hypermutation. Recent experiments have shown that V(D)J genes in essentially all rabbit B cells diversify shortly after birth and that this diversification occurs in the gut-associated lymphoid tissue. Still to be determined is whether this diversification is developmentally programmed or is driven by exogenous microbial antigens.

Changes in locus-specific V(D)J recombinase activity induced by immunoglobulin gene products during B cell development

The process of V(D)J recombination is crucial for regulating the development of B cells and for determining their eventual antigen specificity. Here we assess the developmental regulation of the V(D)J recombinase directly, by monitoring the double-stranded DNA breaks produced in the process of V(D)J recombination. This analysis provides a measure of recombinase activity at immunoglobulin heavy and light chain loci across defined developmental stages spanning the process of B cell development. We find that expression of a complete immunoglobulin heavy chain protein is accompanied by a drastic change in the targeting of V(D)J recombinase activity, from being predominantly active at the heavy chain locus in pro-B cells to being exclusively restricted to the light chain loci in pre-B cells. This switch in locus-specific recombinase activity results in allelic exclusion at the immunoglobulin heavy chain locus. Allelic exclusion is maintained by a different mechanism at the light chain locus. We find that immature, but not mature, B cells that already express a functional light chain protein can undergo continued light chain gene rearrangement, by replacement of the original rearrangement on the same allele. Finally, we find that the developmentally regulated targeting of V(D)J recombination is unaffected by enforced rapid transit through the cell cycle induced by an E mu-myc transgene.

Cloning and characterization of HUPF1, a human homolog of the Saccharomyces cerevisiae nonsense mRNA-reducing UPF1 protein

Levels of most nonsense mRNAs are normally reduced in prokaryotes and eukaryotes when compared with that of corresponding functional mRNAs. Genes encoding polypeptides that selectively reduce levels of nonsense mRNA have so far only been identified in simple eukaryotes. We have now cloned a human cDNA whose deduced amino acid sequence shows the highest degree of homology to that of UPF1, a bona fide Saccharomyces cerevisiae group I RNA helicase required for accelerated degradation of nonsense mRNA. Based on the total sequence of the shorter yeast UPF1 protein, the overall identity between the human protein and UPF1 is 51%. Besides NTPase and other RNA helicase consensus motifs, UPF1 and its human homolog also share similar putative zinc finger motifs that are absent in other group I RNA helicases. Northern blot analysis with the human cDNA probe revealed two transcripts in several human cell lines. Further, antibodies raised against a synthetic peptide of the human polypeptide detected a single 130 kDa polypeptide on Western blots from human and mouse cells. Finally, immunofluorescence and Western blot analyses revealed that the human and mouse polypeptides, like yeast UPF1, are expressed in the cytoplasm, but not in the nucleus. We have thus identified the first mammalian homolog of yeast UPF1, a protein that regulates levels of nonsense mRNA, and we tentatively name this protein human HUPF1 (for human homolog of UPF1).

Molecular Monitoring of Minimal Residual Disease in Follicular and Mantle Cell Non-Hodgkin's Lymphomas Treated With High-Dose Chemotherapy and Peripheral Blood Progenitor Cell Autografting

Minimal residual disease (MRD) was evaluated in 30 patients with follicular or mantle cell non-Hodgkin's lymphoma (NHL) undergoing an intensive treatment with high-dose sequential (HDS) chemotherapy and peripheral blood progenitor cell (PBPC) autografting. To minimize the potential tumor cell contamination, PBPC harvests were scheduled at the end of HDS pretransplant phase. All patients had advanced-stage disease and most of them presented with bone marrow (BM) involvement. A tumor marker could be generated in 90% of patients using bcl-2 or Ig heavy-chain genes. MRD was analyzed on PBPC, BM harvests, and after autografting by polymerase chain reaction (PCR). All evaluable follicular and 6 of 9 mantle cell patients achieved clinical complete remission. PCR negativity of PBPC and/or BM harvests was documented in 68% of follicular and 12% of mantle cell lymphomas. Molecular remission of PBPC and/or BM harvests was achieved in 9 of 15 patients with overt marrow involvement and in all patients with only molecular marrow infiltration at onset. Molecular follow-up was conducted on 14 patients: all 7 evaluable patients who received at least one PCR-negative graft maintained the negative status at a median follow-up of 24 months and none of them relapsed so far. Thus, the results show that (1) a molecular marker to monitor MRD can be obtained in most follicular and mantle cell NHL patients, (2) the HDS regimen may provide PCR-negative PBPC and/or BM harvests even from patients with BM disease, and (3) autograft with at least one PCR-negative harvest is associated with a durable clinical and molecular remission.

Structure and function of the pre-T cell receptor

The pre-T cell receptor (pre-TCR) that minimally consists of the TCR beta chain and the disulfide-linked pre-T cell receptor alpha (pT alpha) chain in association with signal-transducing CD3 molecules rescues from programmed cell death cells with productive TCR beta rearrangements. The pre-TCR induces expansion and differentiation of these cells such that they become TCR alpha beta bearing CD4+8+ thymocytes, which express only a single TCR beta chain and then either die of neglect or--upon TCR-ligand interaction--undergo either positive or negative selection. The newly discovered pT alpha gene encodes a transmembrane protein that belongs to the Ig superfamily and contains a cytoplasmic tail that, however, has no essential function in signal transduction, which is mediated by CD3 molecules and most likely p56lck. Experiments in pT alpha gene-deficient mice show that the pre-TCR has a crucial role in maturation as well as allelic exclusion of alpha beta T cells but is not required for the development of gamma delta-expressing cells. The function of the pre-TCR cannot be fully assumed by an alpha beta TCR that is expressed abnormally early in T cell development.

V lambda-light chain genes reconstitute immune responses to defined carbohydrate antigens or haptens by utilizing different VH genes

The contribution of the lambda-light chain to the development of peripheral B cell repertoire and generation of specific antibodies to haptens and polysaccharide antigens was studied in genetically manipulated kappa-deficient and lambda 2-transgenic mice. The results clearly demonstrate a non-stoichiometric VH gene family expression in the absence of k-light chain and suggest a non-stochastic pairing between VH and V lambda genes, expressed in the peripheral B cell repertoire. A shift in VH gene utilization in the case of VI lambda + antibodies was evident in response to beta 2-6 fructosan and TNP hapten. These observations demonstrate the availability of compensatory mechanisms in the absence of VK genes and are consistent with the hypothesis that VH gene family expression is controlled by genetic factors from inside the VH locus. Furthermore, genetic factors from outside the VH locus, namely restricted available light chain diversity, may lead to a shift in VH gene utilization in the peripheral B cell repertoire.

Rabbit DQ52 and DH gene expression in early B-cell development

Rabbits predominantly rearrange the most 3'VH gene (VH1); thus combinatorial diversity is very limited. In man and mouse, the most 3'DH gene, DQ52, is preferentially rearranged early in B-cell development. To test whether this preference for rearranging a DH gene segment based on 3' end proximity exists in rabbit, we cloned and sequenced the rabbit DQ52 gene. The 11 base pair coding region sequence is identical to a published mouse DQ52, and 81.8% similar to the human sequence. It is localized approximately 805 bp upstream of the JH1 gene. However, the 3' recombination signal sequence has an atypical nonamer. We prepared mRNA from 15- to 28-day fetal rabbits and amplified expressed VDJ sequences of mu mRNA by RT-PCR. The PCR products with VDJ rearrangements were cloned and sequenced. As expected, 44 of 45 VDJ sequences reflected use of the 3' VH1a2 gene, but the DQ52 gene was utilized very infrequently, if at all. We found only one VDJ sequence from 28-day fetal liver B-cells with 8 bp that matched the germline DQ52 sequence. Instead of expressing DQ52, another DH gene, Df was frequently expressed. We cloned the genomic Df gene and localized it about 32 kb upstream of the JH region. Thus, in contrast to man and mouse, rabbits preferentially express a DH gene located in the middle of the DH region early in B cell ontogeny. This may correlate with more frequent initial rearrangement of VH to DH in rabbit B cells.

Identification and functional characterization of a highly conserved sequence in the intron of the kappa light chain gene

A highly conserved 225 bp sequence was identified within the J-C intron of the murine kappa light-chain immunoglobulin gene and its nuclear protein-binding and regulatory function were examined. The binding of nuclear proteins to this fragment was found to reflect the differentiation state of the cell used to prepare the nuclear extracts and three different complexes are seen with this fragment: CI, CII and CIII. CIII is present in all cell types. CI is present in fibroblasts, T cells and early B cells, but not mature B cells. Moreover, nuclear extracts prepared from the early pre-B cell line, 70Z/3, that was treated with agents which activate kappa gene transcription have a reduced ability to form CI. Therefore, the presence of CI correlates with the absence of kappa gene transcription. CII is present in all stages of B cell development, however its composition changes with B cell maturation. Contained within the 225 bp element is the ets family-binding motif GGAA and the B-cell-and-macrophage-specific family member, PU.1 binds this sequence and participates in CII formation. The 225 bp fragment showed modest augmentation of expression in CAT reporter constructs containing the heavy chain enhancer (HCE) and a light chain promoter in the plasmacytoma, S194, and uninduced 70Z/3 cells and mediated a small but reproducible response to IFN-gamma in 70Z/3 cells. Thus, the 225 bp sequence contained within the J-C intron may function as a regulatory element for kappa light chain gene expression.

The affinity of allergen specific IgE and the competition between IgE and IgG for the allergen in Amb a V sensitive individuals

We have calibrated a solid state RAST assay with affinity purified allergen-specific IgE. We then utilized the calibrated assay to measure the average affinity of individual IgE-containing sera in terms of the average association constant < K > for purified allergen Amb a V. The binding data yielded linear reciprocal plots indicating that the range of affinities of the responding clones was narrow. The range of the average association constant for the IgE-Amb a V complex was 0.9-26 x 10(10) M-1. The average affinity of the corresponding IgG response in the same individual, estimated by inhibition studies of IgE binding, was 10(7) M-1 in one case and lower than 10(6) M-1 in all the other cases.

Potential role of DNA polymerase beta in gene therapy against cancer: a case for colorectal cancer

Genetic instability characterized by the accumulation of mutations of tumor suppressor genes and oncogenes appears to be associated with carcinogenesis in colorectal and other cancers. Mutations of DNA polymerase beta (pol beta) and related chromosomal alterations appear to be consistent with the causal role of a "mutator phenotype' in carcinogenesis. However, homozygous knockout pol beta mutations appear to interfere with embryogenesis. Increased pol beta activity (i.e. relative to pol alpha activity) has been associated with cell cycle arrest. The related aphidicolin-resistant DNA replication has been observed primarily in differentiating cells, including the mammalian blastocyst, adrenal cortex, thyroid, anterior pituitary, and the mechanism of endoreduplication (amitotic over-replication of DNA) can be traced to lower eukaryotes. This increased activity in relation to terminal commitment is inconsistent with a simple "DNA repair' view of pol beta. It is therefore proposed that pol beta may play a more fundamental role in cellular differentiation through involvement in a putative subgenomic DNA replication-based model of terminal gene expression. Thus genetic instability, loss of differentiation, and carcinogenesis may result from aberration(s) or "derailment' of such replication-based mechanism of terminal gene expression. It is suggested to examine the relationship of DNA pol beta to genomic instability and carcinogenesis using genetic analyses and antisense technology with possible applications for gene therapy against colorectal cancer.

Clonal selection and learning in the antibody system

Each antibody-producing B cell makes antibodies of unique specificity, reflecting a series of ordered gene rearrangements which must be successfully performed if the cell is to survive. A second selection process occurs during immune responses in which a new antibody repertoire is generated through somatic hypermutation. Here only mutants binding antigen with high affinity survive to become memory cells. Cells expressing autoreactive receptors are counter-selected at both stages. This stringent positive and negative selection allows the generation and diversification of cells while rigorously controlling their specificity.

Cell type-specific chromatin structure determines the targeting of V(D)J recombinase activity in vitro

A common V(D)J recombinase that recognizes a conserved recombination signal sequence (RSS) mediates the assembly of immunoglobulin (Ig) and T cell receptor (TCR) genes in B and T cell precursors. The rearrangement of particular Ig and TCR gene segments, however, is tightly regulated with respect to cell lineage and developmental stage. Using an in vitro system, we analyzed recombinase cleavage of RSSs flanking Ig and TCR gene segments in nuclei. We found that both the lineage-specificity and temporal ordering of gene rearrangement is reflected in the accessibility of RSSs within chromatin to in vitro cleavage.

A developmentally modulated chromatin structure at the mouse immunoglobulin kappa 3' enhancer

Transcription of the mouse immunoglobulin kappa gene is controlled by two enhancers: the intronic enhancer (Ei) that occurs between the joining (J kappa) and constant (C kappa) exons and the 3' enhancer (E3') located 8.5 kb downstream of the gene. To understand the role of E3' in the activation of the mouse immunoglobulin kappa gene, we studied its chromatin structure in cultured B-cell lines arrested at various stages of differentiation. We found that 120 bp of the enhancer's transcriptional core becomes DNase I hypersensitive early in B-cell development. Genomic footprinting of pro-B and pre-B cells localized this chromatin alteration to B-cell-specific protections at the region including the direct repeat (DR) and the sequence downstream of the DR (DS), the PU.1-NFEM-5 site, and the core's E-box motif, identifying bound transcription factors prior to kappa gene rearrangement. Early footprints were, however, not detected at downstream sites proposed to play a negative role in transcription. The early chromatin structure persisted through the mature B-cell stage but underwent a dramatic shift in plasma cells, correlating with the loss of guanosine protection within the DR-DS junction and the appearance of novel footprints at a GC-rich motif upstream and the NF-E1 (YY1/delta)-binding site downstream. Gel shift analysis demonstrated that the DR-DS junction is bound by a factor with properties similar to those of BSAP (B-cell-specific activator protein). These results reveal developmental-stage-specific changes in the composition of nuclear factors bound to E3', clarify the role of factors that bind constitutively in vitro, and point to the differentiation of mature B cells to plasma cells as an important transitional point in the function of this enhancer. The observed changes in nuclear factor composition were accompanied by the rearrangement of positioned nucleosomes that flank the core region, suggesting a role for both nuclear factors and chromatin structure in modulating kappa E3' function during B-cell development. The functional implications of the observed chromatin alterations are discussed in the context of recent studies on kappa E3' and the factors that bind to it.

Hydrolytic antibodies: variations on a theme

Comparison of four independently-derived hydrolytic antibodies reveals striking similarities in their active sites. A common structural motif appears to be induced when the immune system is challenged with antigens containing aryl phosphonate and phosphonamidate groups, and key variations on this 'theme' must account for the observed differences in catalytic efficacy and mechanism. The limited structural repertoire accessed through standard immunization procedures suggests that new approaches may be needed to produce antibody catalysis with enzyme-like efficiencies.

Molecular analysis in the diagnosis of pediatric lymphomas

Thirty-five pediatric lymphomas were categorized as either Burkitt's lymphoma (BL), lymphoblastic lymphoma (LL), or large cell anaplastic lymphoma (LCAL) by histological and immunophenotypic methods. They were further characterized by molecular analysis of their antigen receptor genes. Southern blot (SB) and polymerase chain reaction (PCR) techniques were compared in the detection of immunogloblin heavy chain gene (IgH) rearrangement. T cell receptor beta (TCR beta) rearrangements were analyzed by SB and TCR gamma gene rearrangements by PCR. The PCR method of IgH and TCR gamma gene analysis was preferred to the SB methods, because there were fewer equivocal results in IgH gene analysis, TCR gamma rearrangement was more frequently detected than TCR beta in both lymphoblastic and large cell anaplastic lymphomas, and the PCR technique was more rapid, required less DNA, and could be used with archival material. In addition, analysis of IgH gene rearrangement by PCR was more specific for assessing B cell lineage. Although most of the molecular data were easily interpreted, occasional ambiguous results were seen due to genetic events other than antigen receptor gene rearrangement affecting the genetic analysis. Thus, it is imperative to interpret these genetic data in the context of adequate morphological and immunophenotypic analysis.

Fetal lambs are depleted of IgM+ cells following a single injection of an anti-IgM antibody early in gestation

B-cell depleted fetal sheep were created following a single injection of an anti-IgM monoclonal antibody early in gestation. Six sheep fetuses were given a single intraperitoneal injection of a monoclonal antibody directed against IgM at 63 days of gestation (gestation in sheep = 150 days). The fetuses were killed at 138-142 days of gestation and lymphoid tissues were collected for subsequent light microscopy and immunohistochemical examination. The ileal and jejunal Peyer's patch (PP) follicles in four of the six injected fetuses were markedly reduced in size. Cells in the rudimentary follicles of the ileal PP of these animals showed no reactivity for IgM and most were negative for CD45. The dome regions contained many T cells, which were predominantly CD8+ cells and included gamma delta T cells. The interfollicular areas of the PP of the markedly affected fetuses contained large populations of T cells. The spleen and lymph nodes were also markedly depleted of IgM+ cells and these tissues contained only a small, scattered population of weakly IgM+ cells. Follicular accumulations of IgM+ cells were absent. Large populations of T cells were present in the white pulp of the spleen and cortex of the lymph nodes. The liver did not contain IgM+ cells and the medulla of the thymus was depleted of IgM+ cells. The results of this study suggest that a surface IgM+ B-cell population is present in the sheep fetus at 63 days of gestation, which is essential for the colonization of the ileal PP and subsequent B-cell development.

Information processing in mammalian olfactory system

In recent years, considerable progress has been made in understanding how the olfactory system uses neural space to encode sensory information. In this review, we focus on recent studies aimed at understanding the organizational strategies used by the mammalian olfactory system to encode information. The odorant receptor gene family is discussed in the context of its genomic organization as well as the specificity of olfactory sensory neurons. These data have important consequences for the mechanisms of odorant receptor gene choice by a given sensory neuron. Division of the olfactory epithelium into zones that express different sets of odorant receptors is the first level of input organization. The topographical relationship between periphery and olfactory bulb represents a further level of processing of information and results in the formation of a highly organized spatial map of information in the olfactory bulb. There, local circuitry refines the sensory input through various lateral interactions. Finally, the factors that may drive the development of such a spatial map are discussed. The onset of expression and the establishment of the zonal organization of odorant receptor genes in the epithelium are not dependent upon the presence of the olfactory bulb, suggesting that the functional identity of olfactory sensory neurons is determined independently of target selection.

Regulation of an early developmental checkpoint in the B cell pathway by Ig beta

Many of the cell fate decisions in precursor B cells and more mature B cells are controlled by membrane immunoglobulin (Ig)M heavy chain (mu) and the Ig alpha-Ig beta signal transducers. The role of Ig beta in regulating early B cell development was examined in mice that lack Ig beta (Ig beta-/-). These mice had a complete block in B cell development at the immature CD43+B220+ stage. Immunoglobulin heavy chain diversity (DH) and joining (JH) segments rearranged, but variable (VH) to DJH recombination and immunoglobulin messenger RNA expression were compromised. These experiments define an unexpected, early requirement for Ig(beta) to produce B cells that can complete VDJH recombination.

Involvement of the Saccharomyces cerevisiae HDF1 gene in DNA double-strand break repair and recombination

The HDF1 protein of Saccharomyces cerevisiae shares biochemical properties and structural homology with the 70-kDa subunit of the human autoantigen Ku. The Ku protein, a heterodimer composed of a 70-kDa subunit and an 80-kDa subunit, has been identified as the regulatory subunit of the DNA-dependent protein kinase. This enzyme has recently been shown to be involved in DNA repair and recombination processes in mammalian cells. Here we show that hdf1-disrupted S. cerevisiae strains are strongly sensitive toward the radiomimetic antibiotic bleomycin. In addition, mating-type switching and rates of spontaneous mitotic recombination are strongly reduced. This phenotype is similar to that of mammalian cells lacking components of the DNA-dependent protein kinase holoenzyme, suggesting that HDF1 participates in and exerts equivalent functions in S. cerevisiae.

Rearrangement-enhancing element upstream of the mouse immunoglobulin kappa chain J cluster

Transcriptional regulatory elements have been shown to be necessary but not sufficient for the developmental regulation of immunoglobulin gene rearrangement in mouse precursor B cells. In the chicken lambda light chain locus, additional elements in the V-J intervening sequence are involved in negative and positive regulation of rearrangement. Here, mutation of the mouse homolog of a chicken element, located in the V(K)-J(K) intervening sequence upstream of the J(K) cluster, was shown to significantly decrease rearrangement. This cis-acting recombination-enhancing element affects the rearrangement process without being involved in regulating transcription.

Frequent aberrant immunoglobulin gene rearrangements in pro-B cells revealed by a bcl-xL transgene

During B lymphocyte development, pro-B cells that fail to rearrange an immunoglobulin heavy (IgH) chain allele productively are thought to undergo developmental arrest and death, but because these cells are short-lived in vivo they are not well characterized. Transgenic mice expressing the apoptosis regulatory gene bcl-xL in the B lineage developed large expansions of pro-B cells in bone marrow. V(D)J rearrangements in the expanded populations were nearly all nonproductive, and DJH rearrangements were enriched for joints in DH reading frame 2 and for aberrant joints with extensive DH or JH deletions. Thus, the death of pro-B cells with failed immunoglobulin rearrangements occurs by apoptosis, and bcl-xL can deliver a strong survival signal at the pro-B stage. This analysis also demonstrated that immunoglobulin gene rearrangement is less precise than previously appreciated.

The chromosomal distribution of mouse odorant receptor genes

Odorant receptors (ORs) on nasal olfactory sensory neurons are encoded by a large multigene family. Each member of the family is expressed in a small percentage of neurons that are confined to one of several spatial zones in the nose but are randomly distributed throughout that zone. This pattern of expression suggests that when the sensory neuron selects which OR gene to express it may be confined to a particular zonal gene set of several hundred OR genes but select from among the members of that set via a stochastic mechanism. Both locus-dependent and locus-independent models of OR gene choice have been proposed. To investigate the feasibility of these models, we determined the chromosomal locations of 21 OR genes expressed in four different spatial zones. We found that OR genes are clustered within multiple loci that are broadly distributed in the genome. These loci lie within paralogous chromosomal regions that appear to have arisen by duplications of large chromosomal domains followed by extensive gene duplication and divergence. Our studies show that OR genes expressed in the same zone map to numerous loci; moreover, a single locus can contain genes expressed in different zones. These findings raise the possibility that OR gene choice may be locus-independent or involve consecutive stochastic choices.

Rapid cloning of any rearranged mouse immunoglobulin variable genes

Immunoglobulins (Ig) have been the focus of extensive study for several decades and have become an important research area for immunologists and molecular biologists. The use of polymerase chain reaction (PCR) technology has accelerated the cloning, sequencing, and characterization of genes of the immune system. However, cloning and sequencing the Ig variable (V) genes using the PCR technology has been a challenging task, primarily due to the very diverse nature of Ig V region genes. We have developed a simple, rapid, and reproducible PCR-based technique to clone any rearranged mouse Ig heavy or light chain genes. A close examination of all Ig heavy and light chain V gene families has resulted in the design of 5' and 3' universal primers from regions that are highly conserved across all heavy or light chain V gene families, and the joining or constant regions, respectively. We present our strategy for designing universal primers for Ig V gene families. These primers were able to rapidly amplify the rearranged Ig V genes, belonging to diverse Ig V gene families from very different cell lines, i.e., J558, MOPC-21, 36-60, and a chicken ovalbumin specific B-cell hybridoma. In addition, the present study provides the complete alignment of nucleotide sequences of all heavy and light chain variable gene families. This powerful method of cloning Ig V genes, therefore, allows rapid and precise analysis of B-cell hybridomas, B-cell repertoire, and B-cell ontogeny.

Activation and negative selection of functionally distinct subsets of antibody-secreting cells by influenza hemagglutinin as a viral and a neo-self antigen

We have compared transgenic mice that express the influenza virus PR8 hemagglutinin (PR8 HA) as a membrane-bound neo-self antigen (HA104 mice) with nontransgenic (non-Tg) mice for their ability to generate HA-specific B cell responses after primary immunization with PR8 virus. HA-specific, IgM-secreting B cells were induced with similar frequencies in HA104 and non-Tg mice. In addition, a B cell clonotype (C4) that is characteristic of anti-HA immune responses of BALB/c mice was identified among HA-specific IgM hybridomas from HA104 mice. A subset of HA-specific, IgG-secreting B cells that arises rapidly after primary virus immunization in non-Tg mice, however, was substantially reduced in HA104 mice. Likewise, a B cell clonotype (C12) that dominates HA-specific IgG hybridomas generated after primary immunization of non-Tg mice was present at greatly reduced frequencies among hybridomas from HA104 mice. Because HA-specific, IgG-secreting B cells were generated by HA104 mice in response to a mutant HA containing an amino acid interchange in a B cell antigenic site, we conclude that these PR8 HA-specific, IgG-secreting B cells are negatively selected in HA104 mice as a result of their specificity for the neo-self PR8 HA. The findings demonstrate that HA-specific B cells that display distinct phenotypic potentials in non-Tg mice also differ in their susceptibility to negative selection from the primary B cell repertoire of HA104 mice: a subset of B cells that undergo rapid differentiation to become HA-specific IgG antibody-secreting cells (ASC) after activation in non-Tg mice is negatively selected in HA104 mice. By contrast, a subset that gives rise to HA-specific, IgM-secreting ASC persists in the primary repertoire of HA104 mice and can be activated by virus immunization.

The primary antibody repertoire of normal, immunodeficient and autoimmune mice is characterized by differences in V gene expression

During the last decade, the structure and organization of the immunoglobulin heavy and light chain locis have been defined in mice and humans. Studies on VH gene expression at different stages of development, in different organs and disease states have provided useful insight into the construction of a primary antibody repertoire in mice. Clearly, 3'VH genes 7183, Q52 and Vh11, which are conserved during evolution, are preferentially expressed during early development of the B-lymphocyte repertoire. A preferential use for the V kappa 4 gene family is evident during early B-cell development. The initial development of the primary antibody repertoire is therefore influenced by a restricted set of VH and V kappa gene elements. The restricted B-cell repertoire is subsequently normalized in the periphery, as revealed by stochastic VH gene expression, as a result of exposure to environmental antigens. Obviously, the peripheral B-cell pool characterized by stochastic VH gene expression is selectively replenished by newly generated B cells in bone marrow that preferentially expresses 3'VH genes. The V kappa genes are, however, expressed in a non-random manner in the neonatal and adult B-lymphocyte repertoire that is probably related to VH and V kappa association dynamics and/or positive or negative selection. Interestingly, these characteristics of neonatal and adult primary repertoire are noted in both B1 and B2 lymphocytes. No remarkable age-related differences are evident for VH and V kappa gene expression. In healthy mice, both the mitogen responsive (available) and unstimulated (expressed) B-cell repertoire show similar VH gene expression. Interestingly, VH gene expression varies in different organs which may reflect, or occur as a result of, the specialized function of each organ. For example, J558 gene expression is higher in the peripheral LN where B cells continuously encounter exogenous antigens. The skewed VH and V kappa gene expression noted in immunodeficient and autoimmune lupus-prone mice reflects the impairment of the primary antibody repertoire associated with immunodeficiency and autoimmune disorders.

Cellular and molecular analysis of lymphoid development using Rag-deficient mice

The establishment of a functional immune system with diverse antigen receptors is dependent on the V(D)J recombination activating gene products Rag-1 and Rag-2. These two proteins constitute the key lymphoid components required for the activation of antigen receptor rearrangement. Both Rag-1 and Rag-2 are required for the catalysis of the initial stages of V(D)J recombination. Thus, functional disruption of either the Rag-1 or Rag-2 genes by homologous recombination, leads to immunodeficiency due to lymphoid arrest at a stage prior to the recombination of the antigen receptor loci. In Rag-deficient mice, both B- and T-cell differentiation is eliminated due to the absence of antigen receptors. Lymphoid development can be restored by the introduction of rearranged antigen receptor transgenes that give rise to monoclonal populations of fully mature B- or T-cells. The absence of the major conventional populations of B- and T-cells from the Rag-deficient mice provided an excellent background for studying the molecular and cellular mechanisms of lymphoid differentiation. The Rag-deficient background has been used as a system for: the functional analysis of Rag-1 and Rag-2; studying the developmental functions of antigen receptors and other molecules of the immune system; the molecular analysis of the early stages of the B- and T-cell lineages; the co-development of lymphocytes with stroma cells; the identification of minor subpopulations of the developing immune system; the involvement of lymphoid populations in the onset of pathogenesis. In addition, the development of the "blastocyst complementation assay" methodology, based on the phenotype of the Rag-/- mice, allowed the functional analysis of numerous lymphoid specific components.

Localization, interaction, and RNA binding properties of the V(D)J recombination-activating proteins RAG1 and RAG2

The RAG1 and RAG2 gene products are indispensable for activating somatic rearrangement of antigen receptor gene segments. The two proteins form a stable complex in primary thymocytes as well as when expressed in adherent cells. In both cell types, most cells localize RAG proteins at the periphery of the nucleus. However, when overexpressed in fibroblast cells, RAG1 is found largely in the nucleolus. Nucleolar localization of RAG1 is mediated by several domains containing stretches of basic amino acids, indicating that RAG1 has affinity for RNA or ssDNA. The RAG1 interacting proteins SRP1 and Rch1 directly bind to the nuclear localization signals of RAG1, which mediate the nuclear and nucleolar translocation of the protein. RAG1 appears to have a binary structure, each half containing multiple regions that can act as NLSs, binding sites for the SRP1/Rch1 family, and RNA binding domains.

A human follicular lymphoma B cell line hypermutates its functional immunoglobulin genes in vitro

The functional immunoglobulin (Ig) genes of B lymphocytes undergo somatic mutations during immune responses. These mutations modify the antigen binding site of the immunoglobulins, thereby enhancing the average affinity of the antibodies produced. The molecular mechanism underlying these B cell hypermutations remains unresolved, partly because it is difficult to grow normal B cells in long-term cell cultures and because there is no suitable transformed or malignant B cell line which generates mutations in its immunoglobulin genes in vitro. Here, we show that the recently established follicular lymphoma line HF-1.3.4 generates somatic hypermutations in vitro at a high frequency of 0.7 x 10(-6) mutations per base pair per generation in standard cell cultures (RPMI 1640 + 5% fetal calf serum). This shows for the first time that B cell hypermutation can occur without T cells or T cell factors. The mutation frequency increased approximately tenfold to 1 x 10(-5) mutations/base pair/generation with B cell-specific growth factors (interleukins-2 and -4 and three antibodies stimulatory to HF-1.3.4 cells). This HF-1.3.4 lymphoma line may help to elucidate the molecular mechanism of Ig gene hypermutation.

Analysis of immunoglobulin VH gene repertoire by an anchored PCR-ELISA

We developed a novel technique to analyze the relative concentration of the expressed immunoglobulin (Ig) VH genes using an enzyme-linked immunosorbent assay (ELISA). Expressed Ig cDNA are amplified via anchored PCR and then subjected to a "nested PCR" reaction that attaches biotin to the 5' end of the antisense strand. This allows us to tether the antisense strand of PCR products onto avidin-coated ELISA plates. Digoxigenin-labeled oligonucleotides specific for the leader sequence sense strand of each major Ig VH gene subgroup are used to probe the plate-tethered, alkaline-denatured, and single-stranded antisense cDNA. Bound probes then are detected with alkaline-phosphatase-conjugated anti-digoxigenin antibodies. Using this method, we assessed the distribution of Ig VH genes used by IgM-expressing blood B cells of normal adults. We found the predominant subgroup is VH3, representing approximately half (range 41-59%) of the expressed IgM repertoire. The next largest subgroups used are VH4 (19-23%), VH1 (15-17%), and VH5 (7-11%). The VH2, VH6, and VH7 subgroups each constitute less than 3% of the expressed IgM repertoire. These results agree with those obtained using traditional and more laborious methods that analyze the distribution of Ig clones in cDNA libraries. In addition, we find that this method compares favorably in sensitivity and specificity to more conventional techniques for assessing the clonality of blood or tissue B-cell populations. This rapid and nonradioactive method should have utility for assessing the Ig repertoires expressed by normal, autoimmune, or neoplastic B-cell populations.

Various V-J rearrangement efficiencies shape the mouse lambda B cell repertoire

The diversity of the B cell repertoire of C kappa knockout mice is limited by the expression of four lambda light chain types. Among the spleen B cells, lambda 1 is expressed by the majority (58%) of cells, and lambda 3 by the minority (8%), while lambda 2 (V2) and lambda 2 (Vx) are expressed in intermediate quantities (18% and 16%, respectively). To assess the influence of mechanistic pressures on the lambda subtype distribution, the proportions of the different lambda rearrangements were determined in various B cell subpopulations divided on the basis of the lambda subtype expressed, and the V lambda J lambda junction sequences were studied at different steps of B cell differentiation (pre-B, immature and mature B cells). The data show that (1) the ratio of productive/non-productive VJ junctions is determined by the nature of the lambda segments that are rearranged as can be observed in the pre-B cells, (2) V1-J1 non-productive rearrangements are often found in the lambda 1-negative B cells in the periphery, and (3) V1J3 junctions are often non-productive regardless of the nature of the cells analyzed. Our results, therefore, suggest that a strong probability of initiating a V1-J1 rearrangement and a weak probability of giving a productive V1J3 junction are responsible for the lambda 1 dominance and the lambda 3 under-expression, respectively. The intermediate proportion of lambda 2(V2) subtype is most likely due to a probability of obtaining a productive joint that is better than that for V1J3 and a probability of initiating a rearrangement that is lower than that for V1J1. However, the lambda 2(Vx) cell proportion cannot be determined only by these parameters.