Development of the primary antibody repertoire

In vitro cell cultures as a model of the basal forebrain

The basal forebrain has attracted considerable attention because of its putative role in complex functions such as learning, memory and behavioral state control as well as its vulnerability in neurological disorders such as Alzheimer's Disease (AD). The finding that nerve growth factor provides trophic support for the cholinergic basal forebrain neurons has stimulated further interest in understanding trophic interactions of basal forebrain neurons as well as in possible trophic factor therapeutic strategies for disease states. Our laboratory has utilized primary cell cultures and developed immortalized central nervous system cell lines to study the trophic interactions that establish and maintain the septohippocampal pathway, a basal forebrain component which plays an essential role in cognitive function and is prominently affected in AD. The results of our primary cell culture studies have demonstrated the importance of trophic signals elaborated by the hippocampus in mediating the development of septal cholinergic neurons. Nerve growth factor plays an important role in this process, but it cannot account for all of the trophic signals elaborated by authentic hippocampal target cells. The development by this laboratory of clonal cell lines of septal and hippocampal lineage offers the prospect of investigating both the response to and elaboration of neural trophic signals at a more precise level of resolution than can be achieved with primary cultures. The technology and information that is generated from the engineering of such cell lines will also serve as a strategy to study trophic interactions in other brain circuits in future years, and to investigate possible changes or dysfunctions that occur neurological diseases.

Identification and functional analysis of the transcriptional enhancer of the human T cell receptor beta gene

The productive rearrangement and transcription of T cell receptor (TcR) beta genes is confined to T lymphocytes and is subject to both tissue-specific and developmental regulation. In addition to their function in transcriptional control, cis-acting elements are likely to play a role in the regulation of the rearrangement process. In this report we describe the location of a strong and inducible transcriptional enhancer 3' to the human TcR C beta 2 gene segment. The core enhancer, defined by deletion analysis using a transient transfection assay, resided within 362 bp of DNA. This enhancer core was able to activate transcription from a heterologous promoter and functioned well in T and B lymphocytes, but only minimally in HeLa cells. In contrast, a longer fragment containing the enhancer core showed marked T cell specificity. The enhancer was highly inducible by phorbol esters, the molecular basis for the inducibility residing within a 118-bp region of the enhancer core. This inducibility may be important in modulation of TcR beta gene expression during T cell differentiation and/or activation.

Disruption of the human SCL locus by "illegitimate" V-(D)-J recombinase activity

A fusion complementary DNA in the T cell line HSB-2 elucidates a provocative mechanism for the disruption of the putative hematopoietic transcription factor SCL. The fusion cDNA results from an interstitial deletion between a previously unknown locus, SIL (SCL interrupting locus), and the 5' untranslated region of SCL. Similar to 1;14 translocations, this deletion disrupts the SCL 5' regulatory region. This event is probably mediated by V-(D)-J recombinase activity, although neither locus is an immunoglobulin or a T cell receptor. Two other T cell lines, CEM and RPMI 8402, have essentially identical deletions. Thus, in lymphocytes, growth-affecting genes other than immune receptors risk rearrangements.

Rapid, nonradioactive detection of clonal T-cell receptor gene rearrangements in lymphoid neoplasms

Southern blot hybridization analysis of clonal antigen receptor gene rearrangements has proved to be a valuable adjunct to conventional methods for diagnosing lymphoid neoplasia. However, Southern blot analysis suffers from a number of technical disadvantages, including the time necessary to obtain results, the use of radioactivity, and the susceptibility of the method to various artifacts. We have investigated an alternative approach for assessing the clonality of antigen receptor gene rearrangements in lymphoid tissue biopsy specimens. This approach involves the amplification of rearranged gamma T-cell receptor genes by the polymerase chain reaction and analysis of the polymerase chain reaction products by denaturing gradient gel electrophoresis. By use of this approach, clonal rearrangements from neoplastic lymphocytes constituting as little as 0.1-1% of the total cells in the tissue are detected as discrete bands in the denaturing gel after the gel is stained with ethidium bromide and viewed under ultraviolet light. In contrast, polyclonal rearrangements from reactive lymphocytes appear as a diffuse smear along the length of the gel. Our findings suggest that polymerase chain reaction combined with denaturing gradient gel electrophoresis may offer a rapid, nonradioactive, and sensitive alternative to Southern blot analysis for the diagnostic evaluation of lymphoid tissue biopsy specimens.

Functional analysis of the murine T-cell receptor beta enhancer and characteristics of its DNA-binding proteins

The minimal T-cell receptor (TCR) beta-chain (TCR beta) enhancer has been identified by transfection into lymphoid cells. The minimal enhancer was active in T cells and in some B-lineage cells. When a larger fragment containing the minimal enhancer was used, its activity was apparent only in T cells. Studies with phytohemagglutinin and 4 beta-phorbol-12,13-dibutyrate revealed that the enhancer activity was increased by these agents. By a combination of DNase I footprinting, gel mobility shift assay, and methylation interference analysis, seven different motifs were identified within the minimal enhancer. Furthermore, competition experiments showed that some of these elements bound identical or similar factors that are known to bind to the TCR V beta promoter decamer or to the immunoglobulin enhancer kappa E2 or muEBP-E motif. These shared motifs may be important in the differential gene activity among the different lymphoid subsets.

Possible deletion of a developmentally regulated heavy-chain variable region gene in autoimmune diseases

Several autoantibody-associated variable region (V) genes are preferentially expressed during early ontogenic development, suggesting strongly that they are of developmental and physiological importance. As such, it is possible that polymorphisms in one or more of these genes may alter susceptibility to autoimmune disease. We have searched extensively for a probe related to a developmentally regulated V gene that has the power to differentiate among highly homologous V genes in human populations. Using such a probe (i.e., Humhv3005/P1) related to both anti-DNA and anti-IgG autoantibodies, we studied restriction fragment length polymorphisms in patients with rheumatoid arthritis and systemic lupus erythematosus and found an apparent heavy-chain V (VH) gene deletion that was nearly restricted to the autoimmune patients. These data suggest that deletions of physiologically important VH genes may increase the risk of autoimmunity through indirect effects on the development and homeostasis of the B-cell repertoire.

Functional analysis of the murine T-cell receptor beta enhancer and characteristics of its DNA-binding proteins

The minimal T-cell receptor (TCR) beta-chain (TCR beta) enhancer has been identified by transfection into lymphoid cells. The minimal enhancer was active in T cells and in some B-lineage cells. When a larger fragment containing the minimal enhancer was used, its activity was apparent only in T cells. Studies with phytohemagglutinin and 4 beta-phorbol-12,13-dibutyrate revealed that the enhancer activity was increased by these agents. By a combination of DNase I footprinting, gel mobility shift assay, and methylation interference analysis, seven different motifs were identified within the minimal enhancer. Furthermore, competition experiments showed that some of these elements bound identical or similar factors that are known to bind to the TCR V beta promoter decamer or to the immunoglobulin enhancer kappa E2 or muEBP-E motif. These shared motifs may be important in the differential gene activity among the different lymphoid subsets.

Regulation of the human T-cell receptor alpha gene enhancer: multiple ubiquitous and T-cell-specific nuclear proteins interact with four hypomethylated enhancer elements

Transcription of human T-cell receptor (TCR) alpha genes is regulated by a T-cell-specific transcriptional enhancer that is located 4.5 kilobases 3' of the C alpha gene segment. Previous studies have demonstrated that this enhancer contains at least five nuclear protein-binding sites called T alpha 1 to T alpha 5. In the studies described in this report, we have determined the molecular requirements for human TCR alpha enhancer function. In vitro mutagenesis and deletion analyses demonstrated that full enhancer activity is retained in a 116-base-pair fragment containing the T alpha 1 and T alpha 2 nuclear protein-binding sites and that both of these sites are required for full enhancer function. Functional enhancer activity requires that the T alpha 1 and T alpha 2 binding sites be separated by more than 15 and fewer than 85 base pairs. However, the sequence of this spacer region and the relative phase of the two binding sites on the DNA helix do not affect enhancer function. Deletion and mutation analyses demonstrated that the T alpha 3 and T alpha 4 nuclear protein-binding sites are not necessary or sufficient for TCR alpha enhancer activity. However, a fragment containing these two sites was able to compensate for T alpha 1 and T alpha 2 mutations that otherwise abolished enhancer activity. Electrophoretic mobility shift analyses of the TCR alpha enhancer binding proteins revealed that the T alpha 1, T alpha 3, and T alpha 4 binding proteins are expressed in a variety of T-cell and non-T-cell tumor cell lines. In contrast, one of the two T alpha 2 binding activities was detected only in T-cell nuclear extracts. The activity of the TCR alpha enhancer does not appear to be regulated solely at the level of DNA methylation on that the enhancer sequences were found to be identically hypomethylated in B and T cells as compared with fibroblasts. Taken together, these results suggest that TCR alpha enhancer activity is regulated by the interaction of multiple T-cell-specific and ubiquitous nuclear proteins with partially redundant cis-acting enhancer elements that are hypomethylated in cells of the lymphoid lineage.

Transcription stimulates homologous recombination in mammalian cells

Transcription stimulates homologous recombination in Saccharomyces cerevisiae and has been implicated in the control of recombinational events during the development of mammalian immune systems. Here, we describe a plasmid-based system in which an inducible promoter from the mouse mammary tumor virus is located upstream of heteroallelic neomycin genes carried on two plasmids. Pairs of plasmids are introduced into Chinese hamster ovary cells by electroporation, and recombination is monitored by scoring colonies resistant to the aminoglycoside G418. When transcription is induced with dexamethasone, a synthetic glucocorticoid hormone, and double-strand breaks are introduced at mutation sites, recombination is stimulated sixfold over noninduced levels. Inducing transcription in circular substrates or in substrates cleaved at sites distant from the mutations has no detectable effect on recombination between neomycin genes. Results are presented that are consistent with the observed stimulation of recombination occurring before plasmids integrate into the cellular DNA. Our results are discussed in relation to molecular models for extrachromosomal recombination in mammalian cells.

Regulation of the human T-cell receptor alpha gene enhancer: multiple ubiquitous and T-cell-specific nuclear proteins interact with four hypomethylated enhancer elements

Transcription of human T-cell receptor (TCR) alpha genes is regulated by a T-cell-specific transcriptional enhancer that is located 4.5 kilobases 3' of the C alpha gene segment. Previous studies have demonstrated that this enhancer contains at least five nuclear protein-binding sites called T alpha 1 to T alpha 5. In the studies described in this report, we have determined the molecular requirements for human TCR alpha enhancer function. In vitro mutagenesis and deletion analyses demonstrated that full enhancer activity is retained in a 116-base-pair fragment containing the T alpha 1 and T alpha 2 nuclear protein-binding sites and that both of these sites are required for full enhancer function. Functional enhancer activity requires that the T alpha 1 and T alpha 2 binding sites be separated by more than 15 and fewer than 85 base pairs. However, the sequence of this spacer region and the relative phase of the two binding sites on the DNA helix do not affect enhancer function. Deletion and mutation analyses demonstrated that the T alpha 3 and T alpha 4 nuclear protein-binding sites are not necessary or sufficient for TCR alpha enhancer activity. However, a fragment containing these two sites was able to compensate for T alpha 1 and T alpha 2 mutations that otherwise abolished enhancer activity. Electrophoretic mobility shift analyses of the TCR alpha enhancer binding proteins revealed that the T alpha 1, T alpha 3, and T alpha 4 binding proteins are expressed in a variety of T-cell and non-T-cell tumor cell lines. In contrast, one of the two T alpha 2 binding activities was detected only in T-cell nuclear extracts. The activity of the TCR alpha enhancer does not appear to be regulated solely at the level of DNA methylation on that the enhancer sequences were found to be identically hypomethylated in B and T cells as compared with fibroblasts. Taken together, these results suggest that TCR alpha enhancer activity is regulated by the interaction of multiple T-cell-specific and ubiquitous nuclear proteins with partially redundant cis-acting enhancer elements that are hypomethylated in cells of the lymphoid lineage.

Human immunoglobulin VH and VK repertoire revealed by in situ hybridization

We report in this paper the first analysis of the expression pattern of Ig VH and VK families in human adult normal peripheral B lymphocytes, by in situ hybridization using specific VH1 to VH6 and VK1 to VK4 probes, which cover the known human V gene families reported to date. The major families were VH3 and VK1, with the respective gradient VH3 greater than VH4 greater than VH1 greater than VH5 greater than VH6 greater than VH2, and VK1 greater than VK3 greater than VK4 greater than VK2. Using a large sampling of EBV clones, we found that the pattern of VH and VK family usage was similar. The expression level correlated fairly with the estimated gene number for the VH, but diverged noticeably for the K chains. Taken together with the fact that the level of light chain expression (K + lambda) was about two-fold that of heavy chains, these results suggest that the VH and the VK repertoires are not regulated by a similar selective process.

Heavy and light chain contributions to antigen binding in an anti-digoxin chain recombinant antibody produced by transfection of cloned anti-digoxin antibody genes

We used immunoglobulin gene transfection to study the effect that substituting an homologous light (L) chain for a parental L chain has on antigen fine specificity and affinity. High-affinity monoclonal anti-digoxin antibodies 26-10 and 40-100 were selected for study because their L chains are 92% homologous (although the H chains differ), and their binding with digoxin and digoxin analogs show very different properties. In order to generate a recombinant transfectoma, the genes encoding the 26-10 H and L chains were cloned. After the sequenced clones had been shown to contain the V gene and the transcriptional control elements, the H and L chain V region genes were subcloned into different expression vectors. Both constructs were transfected into myeloma J558L, a lambda 1 chain producer, to verify that the genetic constructs expressed correctly. The recombined 26-10 antibody was identical to parental 26-10 antibody in fine specificity and affinity. The 26-10 L chain construct was then transfected into a cell line, CR-101, that expresses the 40-100 H chain and a lambda 1 chain. The transfectoma 1E6, secreting 40-100 H chain and 26-10 L chain, was selected. Appropriate gene expression in 1E6 was proven by polymerase chain reaction cloning and sequencing. The fine specificity properties of the 1E6 recombinant derive from both the 40-100 and 26-10 antibodies; however, the affinity of 1E6 is 130 times less than that of the parental antibodies. We conclude that, in 1E6, the H and L chains are codominant in their influence on antigen specificity and that homologous pairing of H and L chains is required for optimal affinity.

Transcription stimulates homologous recombination in mammalian cells

Transcription stimulates homologous recombination in Saccharomyces cerevisiae and has been implicated in the control of recombinational events during the development of mammalian immune systems. Here, we describe a plasmid-based system in which an inducible promoter from the mouse mammary tumor virus is located upstream of heteroallelic neomycin genes carried on two plasmids. Pairs of plasmids are introduced into Chinese hamster ovary cells by electroporation, and recombination is monitored by scoring colonies resistant to the aminoglycoside G418. When transcription is induced with dexamethasone, a synthetic glucocorticoid hormone, and double-strand breaks are introduced at mutation sites, recombination is stimulated sixfold over noninduced levels. Inducing transcription in circular substrates or in substrates cleaved at sites distant from the mutations has no detectable effect on recombination between neomycin genes. Results are presented that are consistent with the observed stimulation of recombination occurring before plasmids integrate into the cellular DNA. Our results are discussed in relation to molecular models for extrachromosomal recombination in mammalian cells.

Isolation of coordinately regulated genes that are expressed in discrete stages of B-cell development

We have utilized subtractive hybridization to isolate 16 distinct cDNA sequences representing genes expressed in pre-B-cell lines but not myeloma cell or fibroblast lines. These sequences represent RNA transcripts that vary in abundance in pre-B-cell lines from 0.001% to 0.05%. Five of these sequences were not related to any known genes. One was related to but distinct from known myosin regulatory light chain genes and another encoded a protein with lectin domains. Three represented previously identified genes encoding carbonic anhydrase type II, thymosin, and CD2; these genes were not previously known to be specifically expressed in early stages of B-cell development. Other isolated genes corresponded to pre-B-cell-specific or pre-B-cell/B cell-specific genes recently described by others. The isolated cDNA sequences may be divided into two general categories--those representing genes expressed only in the pre-B-cell stage of B-cell development and those expressed in both the pre-B-cell and B-cell stages. The in vivo expression patterns of the identified genes suggest that some function specifically in lymphocytes while others may have roles in additional lineages.

Heavy-chain class switch does not terminate somatic mutation

We studied the H-chain class switch rearrangement in four groups of clonally related B cell hybridomas, to test the hypothesis that class switch terminates somatic mutation in a B cell. Using switch region-specific probes in Southern blot analysis individual mu-gamma switch rearrangement events can be distinguished. We show that clonally related IgG-producing hybridomas that differ by mutations often share a common switch rearrangement. This indicates that class switch in these cells did not terminate somatic mutation.

Transformation of murine bone marrow cells with combined v-raf-v-myc oncogenes yields clonally related mature B cells and macrophages

Murine bone marrow cells infected with replication-defective retroviruses containing v-raf alone or v-myc alone yielded transformed pre-B cell lines, while a retroviral construct containing both v-raf and v-myc oncogenes produced clonally related populations of mature B cells and mature macrophages. The genealogy of these transformants demonstrates that mature myeloid cells were derived from cells with apparent B-lineage commitment and functional immunoglobulin rearrangements. This system should facilitate studies of developmental relationships in hematopoietic differentiation and analysis of lineage determination.

Sequence homologies, N sequence insertion and JH gene utilization in VHDJH joining: implications for the joining mechanism and the ontogenetic timing of Ly1 B cell and B-CLL progenitor generation

Sequence analysis of rearranged VHDJH genes of B lineage cells from various stages of ontogeny indicates that short sequence homologies at the breakpoints of recombination contribute to V region gene assembly. Such homologies are regularly seen at DJH junctions of neonatal pre-B cells, most of which do not contain N sequences. In the same cells, but not at later developmental stages, preferential usage of the JH1 element is observed. After birth, N sequence insertion increases with time and is always more prominent at the VHD border than the DJH border. In pre-B cells from adult animals and in mature B cells, in cases where N sequences were not detectable, sequence homologies at the DJH border were found in only half of the instances. This lower incidence could be due to N sequence addition to one of the recombining DNA ends and/or cellular selection. Inspection of VHDJH junctions for N sequence insertion, sequence homologies at the DJH border and JH1 usage allows the estimation of the timepoint in ontogeny at which particular B cell subsets are seeded into the immune system. Specifically, the present data show that the cells of the Ly1 B cell subset are generated not only neonatally but also beyond the first weeks of life. However, the DJH junctions of the progenitors of chronic B cell leukemias which originate from the same B cell subset resemble those of neonatal pre-B cells, suggesting that these cells have already undergone a transforming event at this early developmental stage.

Transformation of murine bone marrow cells with combined v-raf-v-myc oncogenes yields clonally related mature B cells and macrophages

Murine bone marrow cells infected with replication-defective retroviruses containing v-raf alone or v-myc alone yielded transformed pre-B cell lines, while a retroviral construct containing both v-raf and v-myc oncogenes produced clonally related populations of mature B cells and mature macrophages. The genealogy of these transformants demonstrates that mature myeloid cells were derived from cells with apparent B-lineage commitment and functional immunoglobulin rearrangements. This system should facilitate studies of developmental relationships in hematopoietic differentiation and analysis of lineage determination.

Review of the molecular characteristics of gene mutations of the germline and somatic cells of the human

Molecular analyses of the limited number of de novo germinal mutations identified in humans indicate that an array of alterations in gene structure can be generated. Similar conclusions are derived from the large data set obtained from molecular analyses of alleles that segregate in the human population and cause genetic diseases. The molecular alterations include nucleotide substitutions as well as insertions, deletions and other rearrangements of the DNA. The lesions may be located in the coding or the noncoding regions of genes or may involve the flanking sequences. The insertions and deletions involve fragments ranging from single nucleotides to many kilobases, and involve both unique sequences and repetitive elements. The nature of the lesions observed to date as either de novo mutations or segregating variants suggests there are locus-specific characteristics of the alterations in DNA structure that are recovered as genetic diseases. Differences in mutation spectra among genetic loci appear to reflect both the structure of the target sequences and the relationship between gene structure and gene function. No induced germinal mutations have been identified, thus no data are available that reveal the relationships between mutagenic exposures and the molecular fingerprints of the lesion induced in the human germ cell and transmitted to the subsequent generations. In contrast, the prospects for analyzing the roles of genetic target, exposure history and individual responsiveness to exposure in creating particular molecular lesions in somatic cells are excellent, both for alterations of single nucleotides and for major alterations of gene structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Stochastic pairing of heavy-chain and kappa light-chain variable gene families occurs in polyclonally activated B cells

Frequencies of 25 immunoglobulin heavy-chain and kappa light-chain variable (VH + V kappa) gene-family pairings expressed in splenic B-cell populations were determined by hybridization of VH- and V kappa-family-specific DNA probes to mitogen-induced B-cell colonies from C57BL/6 mice or hybridomas derived from BALB/c and NZB mice. Both analyses support the conclusion that VH and V kappa gene families pair without bias; as would be expected for random association, the frequencies of specific VH + V kappa pairs may be estimated by the product of the independent VH and V kappa frequencies. Based upon the frequencies at which 9 VH and 12 V kappa gene families are expressed, we calculated the expected usage for approximately 100 VH + V kappa family pairings in neonatal and adult C57BL/6 mice. Variability in the expression of such VH + V kappa pairings is considerable; pairs representing greater than 10% to less than 0.01% of the splenic B-cell population occur. This variability is most pronounced in the neonate, where 6 VH + V kappa family pairs account for nearly 40% of all mitogen-reactive B cells. As the neonate matures, the distribution of frequencies for VH + V kappa pairings becomes more nearly uniform. This process may underlie the patterned acquisition of humoral immune responsiveness.

A programmed site-specific DNA rearrangement in Tetrahymena thermophila requires flanking polypurine tracts

During macronuclear development in ciliates, precise deletion events eliminate thousands of specific DNA segments. Each segment is bounded by a unique pair of short direct repeats, but no other common feature has been reported. To determine the critical cis-acting sequences, we developed an in vivo system for analyzing this process in Tetrahymena. We show that sequences essential for recognition and excision of one such region are located within the 70 bp of DNA flanking either side of it. Three authentic splice sites and one cryptic site are each adjacent to an unusual polypurine tract (5'-A5G5) situated 40-50 bp distal to each terminal repeat. Removal of this tract or substitution of 3 bp within it abolishes splicing to the adjacent site. The normal chromosomal environment and the integrity of the eliminated sequence are not required for its removal. We believe the polypurine tract is a signal essential for excision of this sequence.

The need for central and peripheral tolerance in the B cell repertoire

The immune system normally avoids producing antibodies that react with autologous ("self") antigens by censoring self-reactive T and B cells. Unlike the T cell repertoire, antibody diversity is generated within the B cell repertoire in two phases; the first occurs by gene rearrangement in primary lymphoid organs, and the second phase involves antigen-driven hypermutation in peripheral lymphoid organs. The possibility that distinct cellular mechanisms may impose self tolerance at these two different phases of B cell diversification may explain recent findings in transgenic mouse models, in which self-reactive B cells appear to be silenced both by functional inactivation and by physical elimination.

A physical map and analysis of the murine C kappa-RS region show the presence of a conserved element

Lambda-producing B lymphocytes have frequently deleted one or, more often, both Ig kappa loci. This deletion is mediated by the rearrangement of an element which lies 3' of C kappa and which is called RS (recombining sequence) in the mouse and Kde (kappa-deleting element) in the human. The tight correlation between V lambda to J lambda rearrangements and an RS-mediated deletion may indicate that sequences in the C kappa-RS region are controlling the activation of the Ig lambda locus. We have linked the C kappa exon and the RS element by phage cloning and compared the C kappa-RS region to the previously cloned human C kappa-Kde region. The distance between C kappa and RS is 25 kb and is thus similar to the distance of 24 kb separating the human C kappa exon and Kde element. Both mouse and man carry a conserved sequence of 470 bp (Rx) which lies 9 kb 3' of the mouse C kappa and 12 kb 3' of the human C kappa exon. The conserved mouse Rx sequence contains part of the kappa 3' enhancer.

The early expression of some human autoantibody-associated heavy chain variable region genes is controlled by specific regulatory elements

Recent molecular cloning studies have revealed that some autoantibodies may be encoded directly by germline Ig variable (V) genes without any somatic mutation, suggesting strongly that such autoantibodies are physiologically important. Independent analyses of Ig gene expression in a human fetal liver showed that only nine heavy chain V (Vh) genes were used, out of a potential germline Vh gene repertoire of 100-200. We have observed that four of these nine Vh genes encode sequences identical or almost identical to human autoantibody heavy chains. This unexpected overlap implies that some autoantibodies are expressed preferentially during early development. Recent structural analyses of two Vh3 genes expressed in fetal liver revealed many more enhancer-like sequences in the flanking regions than expected for a typical Vh gene. It is hypothesized that these autoantibody-related Vh genes may contain various combinations of cis regulatory elements which influence their specific expression during early ontogenic development. Furthermore, these observations are consistent with network hypotheses, which suggest that early B-cell development is driven by reactivity with self. The cis regulatory elements in the autoantibody genes may act in concert with the positional effects that have been shown to facilitate Vh gene engagement.

Initiation and processing of two kappa immunoglobulin germ line transcripts in mouse B cells

The splicing patterns and sequences of two processed kappa immunoglobulin germ line mRNAs are presented. A 1.1-kilobase (kb) mRNA appeared to be derived from splicing of the previously characterized 8.4-kb germ line transcript, while a 0.8-kb mRNA was the splice product of a second 4.7-kb germ line transcript that initiated 50 base pairs upstream of J kappa 1. The interaction of the two kappa germ line promoters with nuclear binding factors is also examined. The potential role of these germ line transcripts in establishing the rearrangement potential of the locus is discussed.

Initiation and processing of two kappa immunoglobulin germ line transcripts in mouse B cells

The splicing patterns and sequences of two processed kappa immunoglobulin germ line mRNAs are presented. A 1.1-kilobase (kb) mRNA appeared to be derived from splicing of the previously characterized 8.4-kb germ line transcript, while a 0.8-kb mRNA was the splice product of a second 4.7-kb germ line transcript that initiated 50 base pairs upstream of J kappa 1. The interaction of the two kappa germ line promoters with nuclear binding factors is also examined. The potential role of these germ line transcripts in establishing the rearrangement potential of the locus is discussed.

T-cell receptor gamma delta and gamma transgenic mice suggest a role of a gamma gene silencer in the generation of alpha beta T cells

A T lymphocyte expresses on its surface one of two types of antigen receptor, T-cell receptor alpha beta or T-cell receptor gamma delta, encoded by a pair of somatically rearranged alpha and beta or gamma and delta genes. It has been suggested that alpha beta T cells are generated only from precursor T cells that failed to rearrange gamma and delta genes in a functional form. However, we found that transgenic mice constructed with functionally rearranged gamma and delta genes produce a normal number of alpha beta T cells. The transgene gamma present in these alpha beta T cells is repressed apparently through an associated cis DNA element (silencer). We propose that some T-cell precursors are committed to generate alpha beta T cells independent of the rearrangement status of their gamma gene and that this commitment involves activation of a factor(s) that interacts with the gamma gene-associated silencer.

A T cell-specific transcriptional enhancer within the human T cell receptor delta locus

The T cell antigen receptor (TCR) delta gene is located within the TCR alpha locus. A T cell-specific transcriptional enhancer, distinct from the TCR alpha enhancer, has been identified within the J delta 3-C delta intron of the human T cell receptor delta gene. This enhancer activates transcription from the V delta 1 and V delta 3 promoters as well as from heterologous promoters. Enhancer activity has been localized to a 250-bp region that contains multiple binding sites for nuclear proteins. Thus, transcriptional control of the TCR delta and TCR alpha genes is mediated by distinct regulatory elements.

A second B cell-specific enhancer 3' of the immunoglobulin heavy-chain locus

The expression of immunoglobulin heavy-chain (IgH) genes is generally thought to be regulated by the combination of the VH promoter with the enhancer element which is located in the JH-CH intron. This is probably an oversimplification: there are cell lines that transcribe IgH genes despite the deletion of the intron-enhancer. These findings could imply that other enhancer element(s) exist in the IgH locus. Here we show that a strong B-cell-specific enhancer is indeed located at the 3'-end of the rat IgH locus, 25 kilobases downstream of C alpha. This enhancer should be retained downstream of all rearranged IgH genes, regardless of the VH or CH segment used. Taken together with analogous findings for the mouse kappa locus, the results prompt a re-evaluation of the mechanism of regulation of immunoglobulin gene transcription. Furthermore, unlike the intron-enhancer, the IgH 3' enhancer would become linked to a c-myc that rearranges into an IgH switch region. The IgH 3' enhancer could therefore play a part in the activation of the translocated c-myc genes in rat immunocytomas, mouse plasmacytomas and Burkitt lymphomas.

Specific deletion of the J-C delta locus in murine alpha/beta T cell clones and studies using transgenic mice

A deletion event in the T cell receptor (TcR) delta locus has been characterized in a panel of mouse alpha/beta cytotoxic T lymphocyte (CTL) clones. Data presented here shows that J delta 1, J delta 2 and C delta are absent from functional CTL clones while a germ-line D delta 1 fragment is retained, thus suggesting a specific deletion of this region. We have investigated the possible significance of the J-C delta deletion by generating T cell lines from TcR alpha/beta transgenic mice. Unlike control T cell lines which included a T cell line derived from a beta transgenic mouse, the lines expressing the transgenic alpha/beta heterodimer have not deleted the C delta region. This strongly suggests that the J-C delta deletion event is not responsible for directing T cells to the alpha/beta lineage, but rather is involved in the rearrangement or transcriptional activity of the alpha locus. In addition, to ensure that the alpha/beta transgene does not have any inhibitory affects on the rearrangement of the delta loci in general, the gamma/delta expressing dendritic epithelial T cell (DETC) population was examined in TcR alpha/beta transgenic mice and alterations in this T cell subset were not found. This finding that normal gamma/delta DETC cells are present in alpha/beta transgenic mice, together with the data showing that the D delta 1 region remains in an unrearranged germ-line configuration in functional alpha/beta CTL, suggests that commitment to the alpha/beta or gamma/delta lineage is predetermined at a particular stage in early T cell ontogeny.

In rat B lymphocyte genesis sixty percent is lost from the bone marrow at the transition of nondividing pre-B cell to sIgM+ B lymphocyte, the stage of Ig light chain gene expression

The cycling B precursor cells in rat bone marrow (BM) that carry the B220 antigen and no surface Ig daily produce 780 million new cells. The pool of recirculating B lymphocytes in the rat, however, renew at a rate of only about 40 million cells/day. To analyze at which stages in B lymphocyte genesis the cell loss occurs, we identified post-mitotic cells in the rat BM B lineage, and determined their renewal rates. We used 5-bromo-deoxyuridine (BrdUrd) to label DNA-synthesizing cells, identifying incorporated BrdUrd with the mouse monoclonal antibody BU-1. B lineage cell subsets were identified by the markers HIS24 antigen (rat B220), terminal deoxynucleotidyl transferase (TdT), Ig mu heavy chain, and complete Ig. By use of double and triple immunocytology, we determined the extent of BrdUrd incorporation in the various B lineage compartments [HIS24+TdT-Ig-, TdT+, cytoplasmic mu chain (c mu)+ surface (s) IgM- pre-B, sIgM+ B]. Both sIgM+ B lymphocytes and all B precursors with cell diameters less than 11-12 microns were virtually devoid of DNA synthesis, as indicated by S-phase indices below 2%. In contrast, S-phase indices of large B precursors ranged between 43%-66%. We established the renewal rates of nondividing BM B lineage cells by placing osmotic minipumps containing BrdUrd subcutaneously in the flank of rats. The nondividing BM B lineage cells all renewed rapidly at rates between 2.4% and 5.6%/h, representing average half-lives of 29 to 12 h. In absolute numbers, the renewal/day/whole body BM was 165 X 10(6) for sIgM+ B lymphocytes, 422 X 10(6) for small c mu+ sIgM- pre-B cells, 89 X 10(6) for small TdT+ cells and 35 X 10(6) for small HIS24+TdT-Ig- cells. Assuming that recirculating B lymphocytes in the periphery are the descendants of BM sIgM+ B lymphocytes, which in their turn are the progeny of small pre-B cells, the renewal data indicate the following. Of the 165 million potentially available BM B lymphocytes, only 40 million cells become incorporated in the pool of recirculating B lymphocytes, representing a loss of 75%. BM B lymphocytes, in turn, use only (165/422 X 100% = ) 40% of the potential output from their immediate precursors. The 60% loss that occurs here may reflect the extent of aberrant Ig light chain gene rearrangement in normal B lymphocyte genesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Phorbol ester regulation of terminal deoxynucleotidyl transferase, proliferation, and TcR alpha in a pre-T cell line

Terminal deoxynucleotidyl transferase (TdT) is a template-independent DNA polymerase that is transiently expressed during the normal development of T and B lymphocytes. Phorbol 12-myristate 13-acetate (PMA) has been reported to induce maturation-like changes, including the loss of TdT, in many leukemic cell lines. We investigated the mechanism of TdT repression by PMA in an early thymocyte-like cell line, RPMI 8402. At a concentration of 8 nM, PMA caused both repression of TdT synthesis and arrest of proliferation. At greater concentrations of PMA, these same changes initially occurred, but then cell proliferation resumed, and TdT was reexpressed. At both 8 and 160 nM PMA, TdT biosynthesis and TdT mRNA became undetectable within 8 hours, while cell proliferation and DNA synthesis were not significantly reduced until 16 hours. Growth arrest induced by serum starvation did not result in a similar reduction of TdT RNA even after 48 hours. With 160 nM PMA, TdT mRNA could be detected again by 24 hours, and proliferation resumed. Transcription run-off assays indicated that TdT RNA synthesis ceased within 1 hour after exposure to both 8 and 160 nM PMA. T cell receptor alpha (TcR alpha) RNA was induced when TdT RNA was repressed. TcR beta RNA levels were unchanged, and TcR gamma RNA was up-regulated. TdT gene repression and modulation of cell proliferation as well as induction of TcR gene expression are normal events during intrathymic T cell maturation. This cell model provides a system for analyzing the molecular regulation of these significant developmental events.

The peritoneal Ly-1 (CD5) B cell repertoire is unique among murine B cell repertoires

Ly-1 (CD5) B cells and conventional B cells represent two distinct lineages of murine B cells which are distinguishable by expression of surface molecules, organ location, ontogeny and development and antibody production in vivo. In order to assess whether the different developmental pathways of Ly-1 B cells and conventional B cells result in different antibody repertoires, we have used limiting dilution analyses to determine frequencies of B cells making antibodies capable of binding to a range of antigens including haptens, proteins, bacterial polysaccharides and bromelain-treated mouse red blood cells. Starting populations of B cells were purified from spleen, peritoneum and bone marrow of adult BALB/c mice or from spleens of newborn mice by use of the fluorescence-activated cell sorter. The peritoneal Ly-1 B cell repertoire was found to be different from that of conventional B cells, with between 5- and 100-fold higher frequencies of clones producing IgM antibodies capable of binding to the antigens tested. However, when tested, the majority of Ly-1 B cell anti-haptenic antibodies did not show the high affinity binding or fine specificity characteristics of specific antibodies elicited in immune responses in vivo. The high frequencies of antigen-reactive antibodies within the Ly-1 B repertoire are most likely explained by the presence of clones secreting low-affinity or multireactive antibodies. The Ly-1 B cell repertoire is not mirrored in repertoires from either newborn B cells or virgin B cells in adult bone marrow. Therefore, either Ly-1 B cells develop from distinct precursors with intrinsically different mechanisms of V gene usage and recombination, or newly formed Ly-1 B are heavily selected on specificity for entry into this peritoneal lineage. If the second alternative is true, bacterial antigens in the gut are not required for selection of this unique repertoire, as Ly-1 B cells in germ-free mice also show the multireactive repertoire characteristic of this B cell lineage in normal mice.

Structural analyses of human developmentally regulated Vh3 genes

In mice, a restricted set of the Jh-proximal Vh genes are preferentially expressed during early ontogeny. Recently, analyses of human Ig cDNA from a fetal liver revealed a restricted set of Vh genes which belong to the Vh1, 3, 4, and 6 families. Although the Vh6 and some Vh5 genes are proximal to the Jh region, no Vh5 gene was found in the fetal liver, suggesting that the distance between the Jh genes and some early-expressed Vh genes may not be the only factor responsible for Vh gene expression during early development. As an initial step in searching for other underlying mechanisms, we characterized two human germline Vh3 genes which belong to the developmentally restricted Vh repertoire, and found that they contain many enhancer-like sequences which are identical, or highly homologous to, various transcriptional enhancer motifs. Hence, it is conceivable that, in addition to the established positional effects, cis regulatory elements may be important in the programmed expression of some Vh genes during early B-lymphocyte development.

Corrective recombination of mouse immunoglobulin kappa alleles in Abelson murine leukemia virus-transformed pre-B cells

Previous characterization of mouse immunoglobulin kappa gene rearrangement products cloned from murine plasmacytomas has indicated that two recombination events can take place on a single kappa allele (R. M. Feddersen and B. G. Van Ness, Proc. Natl. Acad. Sci. USA 82:4792-4797, 1985; M. A. Shapiro and M. Weigert, J. Immunol. 139:3834-3839, 1987). To determine whether multiple recombinations on a single kappa allele can contribute to the formation of productive V-J genes through corrective recombinations, we have examined several Abelson murine leukemia virus-transformed pre-B-cell clones which rearrange the kappa locus during cell culture. Clonal cell lines which had rearranged one kappa allele nonproductively while maintaining the other allele in the germ line configuration were grown, and secondary subclones, which subsequently expressed kappa protein, were isolated and examined for further kappa rearrangement. A full spectrum of rearrangement patterns was observed in this sequential cloning, including productive and nonproductive recombinations of the germ line allele and secondary recombinations of the nonproductive allele. The results show that corrective V-J recombinations, with displacement of the nonproductive kappa gene, occur with a significant frequency (6 of 17 kappa-producing subclones). Both deletion and maintenance of the primary (nonfunctional) V-J join, as a reciprocal product, were observed.

Transcription from a murine T-cell receptor V beta promoter depends on a conserved decamer motif similar to the cyclic AMP response element

We identified a regulatory region of the murine V beta promoter by both in vivo and in vitro analyses. The results of transient transfection assays indicated that the dominant transcription-activating element within the V beta 8.3 promoter is the palindromic motif identified previously as the conserved V beta decamer. Elimination of this element, by linear deletion or specific mutation, reduced transcriptional activity from this promoter by 10-fold. DNase I footprinting, gel mobility shift, and methylation interference assays confirmed that the palindrome acts as the binding site of a specific nuclear factor. In particular, the V beta promoter motif functioned in vitro as a high-affinity site for a previously characterized transcription activator, ATF. A consensus cyclic AMP response element (CRE) but not a consensus AP-1 site, can substitute for the decamer in vivo. These data suggest that cyclic AMP response element-binding protein (ATF/CREB) or related proteins activate V beta transcription.

Corrective recombination of mouse immunoglobulin kappa alleles in Abelson murine leukemia virus-transformed pre-B cells

Previous characterization of mouse immunoglobulin kappa gene rearrangement products cloned from murine plasmacytomas has indicated that two recombination events can take place on a single kappa allele (R. M. Feddersen and B. G. Van Ness, Proc. Natl. Acad. Sci. USA 82:4792-4797, 1985; M. A. Shapiro and M. Weigert, J. Immunol. 139:3834-3839, 1987). To determine whether multiple recombinations on a single kappa allele can contribute to the formation of productive V-J genes through corrective recombinations, we have examined several Abelson murine leukemia virus-transformed pre-B-cell clones which rearrange the kappa locus during cell culture. Clonal cell lines which had rearranged one kappa allele nonproductively while maintaining the other allele in the germ line configuration were grown, and secondary subclones, which subsequently expressed kappa protein, were isolated and examined for further kappa rearrangement. A full spectrum of rearrangement patterns was observed in this sequential cloning, including productive and nonproductive recombinations of the germ line allele and secondary recombinations of the nonproductive allele. The results show that corrective V-J recombinations, with displacement of the nonproductive kappa gene, occur with a significant frequency (6 of 17 kappa-producing subclones). Both deletion and maintenance of the primary (nonfunctional) V-J join, as a reciprocal product, were observed.

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

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

Uniform high frequency expression of autoantibody-associated crossreactive idiotypes in the primary B cell follicles of human fetal spleen

At 23 wk of gestation, the fetal spleen contains follicles of lymphocytes that coexpress B cell differentiation antigens, surface Ig, and the 67-kD pan-T lymphocyte antigen, CD5 (Leu-1). Such cells are thought to represent the normal equivalent cells of B chronic lymphocytic leukemia (CLL). This B cell leukemia is distinctive in that high proportions of patients have leukemic cells that express sIg bearing one or more crossreactive idiotypes (CRIs) that commonly are found on IgM autoantibodies. We performed immunohistochemical studies on fetal spleen at 23 wk of gestation using a panel of mAbs specific for autoantibody-associated CRIs. We find that high proportions (5-17%) of the lymphocytes within each follicle react with any one of the anti-CRI mAbs. Furthermore, there is little variation between primary follicles in the proportions of cells that express a particular CRI. Using a cocktail of four anti-CRI mAbs, we detect autoantibody-associated CRIs on approximately one-third of the lymphocytes within each of the primary B cell follicles. These data indicate that the many of the Igs produced during early B cell development may be structurally related to IgM autoantibodies and to Ig expressed in CLL and related CD5 B cell malignancies. Furthermore, these studies suggest that the repertoire of Ig V genes expressed in each primary B cell follicle may be representative of the total restricted Ig V gene repertoire expressed during early B cell ontogeny.

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

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

Identification of a germ line transcript from the unrearranged kappa gene in human B cells

A novel kappa immunoglobulin-hybridizing mRNA in cell lines derived from human B cells arrested at several stages of development has been identified. Hybridization studies demonstrate that this 1.5-kilobase mRNA species is the spliced product of a precursor germ line transcript initiating upstream of the unrearranged JKappa locus.

Blockage of alpha beta T-cell development by TCR gamma delta transgenes

T lymphocytes recognize antigens by means of T-cell receptors (TCR) composed of alpha beta or gamma delta heterodimers. The mechanism governing the development of alpha beta- and gamma delta-bearing T cells from a common precursor T cell is so far unknown. It has been proposed that T-cell precursors rearrange their gamma- and delta-chain genes first, and alpha beta T cells are generated only from those cells that fail to rearrange productively both gamma- and delta-chain genes. Our recent study on gamma delta-transgenic mice contradicted this hypothesis, however, and indicated that repression of gamma-chain gene expression mediated by a transcriptional silencer element has a critical role in the generation of alpha beta T cells. Here we report that the generation of alpha beta T cells is severely blocked in transgenic mice carrying gamma- and delta-chain transgenes without the associated silencer, thereby strengthening the validity of the silencer model of T-cell development.

No preferential use of the VH(V) family in human multiple myeloma

A recently described immunoglobulin VH family (the VH(V) family) close to the DH and JH genes is preferentially rearranged in immature B-cell tumours. The question of the emergence of multiple myeloma (MM) from a tumorous pre-B cell is not yet resolved. To draw a comparison with chronic lymphocytic leukaemia (CLL), we studied the VH(V) rearrangements in 28 MM patients. A rearranged Hind III-Bam HI fragment of 9.5 kb was detected in only one patient instead of the rearranged fragment of 8.5 kb described in CLL. Rearrangements of a member of the VH(V) family in a 9.5 kb fragment were also observed in two out of 20 lymphoblastoid cell lines obtained from peripheral blood of MM patients. We report here that the VH(V) family is not preferentially involved in this pathology and that the size of the only rearrangement obtained is larger than the 8.5 kb fragment observed in CLL. These results do not favour the hypothesis of a pre-B cell involvement in MM.