Germline organization of the murine T cell receptor beta-chain genes

Expression of T-cell receptor genes during early T-cell development

Lymphoid cell development is an ordered process that begins in the embryo in specific sites and progresses through multiple differentiative steps to production of T- and B-cells. Lymphoid cell production is marked by the rearrangement process, which gives rise to mature cells expressing antigen-specific T-cell receptors (TCR) and immunoglobulins (Ig). While most transcripts arising from TCR or Ig loci reflect fully rearranged genes, germline transcripts have been identified, but these have always been thought to have no specific purpose. Germline transcription from either unrearranged TCR or unrearranged Ig loci was commonly associated with an open chromatin configuration during VDJ recombination. Since only early T and B cells undergo rearrangement, the association of germline transcription with the rearrangement process has served as an appropriate explanation for expression of these transcripts in early T- and B-cell progenitors. However, germline TCR-V beta 8.2 transcripts have now been identified in cells from RAG(-/-) mice, in the absence of the VDJ rearrangement event and recombinase activity. Recent data now suggest that germline TCR-V beta transcription is a developmentally regulated lymphoid cell phenomenon. Germline transcripts could also encode a protein that plays a functional role during lymphoid cell development. In the least, germline transcripts serve as markers of early lymphoid progenitors.

Distinct control of the frequency and allelic exclusion of the V beta gene rearrangement at the TCR beta locus

Ag receptor gene loci contain many V gene segments, each of which is recombined and expressed at a different frequency and is subject to allelic exclusion. To probe the parameters that mediate the different levels of regulation of V gene rearrangement, a Vbeta gene segment together with 3.6-kb 5' and 0.7-kb 3' flanking sequences was inserted 6.8 kb upstream of the Dbeta1 gene segment in the murine TCRbeta locus. Despite its proximity to the Dbeta gene segments and the Ebeta enhancer, the inserted Vbeta segment underwent VDJ recombination at the same frequency as the natural copy located 470 kb upstream. However, the inserted Vbeta segment was no longer under allelic exclusion control as it recombined at a similar frequency in the presence of a TCRbeta transgene. These results suggest that while the inserted fragment contains the necessary cis-regulatory elements for determining the frequency of Vbeta rearrangement, additional cis-regulatory elements are required for mediating Vbeta allelic exclusion. Interestingly, most of the inserted Vbeta rearrangements were not transcribed and expressed in the presence of a TCRbeta transgene, suggesting that TCRbeta allelic exclusion can also be achieved by blocking the transcription of the rearranged gene segments. These findings provide strong evidence for distinct control of the frequency and allelic exclusion of Vbeta gene rearrangement.

Oligoclonal T cell expansions in atherosclerotic lesions of apolipoprotein E-deficient mice

T cells are present in atherosclerotic lesions at all stages of development. They exhibit activation markers and are particularly prominent at sites of plaque rupture. This suggests that T-cell-mediated immune responses are involved in the pathogenesis of atherosclerosis. Antigen-specific T cells reactive with oxidized lipoproteins and heat shock proteins have been isolated from plaques, indicating that local activation and clonal expansion might occur. To analyze different stages of atherosclerosis, we have used a murine model. Targeted deletion of the apolipoprotein E gene results in severe hypercholesterolemia and spontaneous atherosclerosis, with lesions containing large numbers of T cells and macrophages. We have analyzed mRNA for T-cell antigen receptors (TCRs) from aortic fatty streaks, early fibrofatty plaques, and advanced fibrofatty plaques of such mice. Polymerase chain reaction amplification of complementarity-determining region 3 (CDR3 region) of TCRs was followed by spectratyping of fragment lengths. This analysis detected all types of variable (V) segments with a gaussian distribution of CDR3 in lymph nodes. In contrast, a restricted heterogeneity was found in atherosclerotic lesions, with expansion of a limited set of Vbeta and Valpha segments and a monotypic or oligotypic CDR3 spectrum in each lesion. Vbeta6 was expressed in all lesions; Vbeta5.2, Vbeta16, Valpha34s, and Valpha9, in the majority of lesions; and Vbeta6, Vbeta5.2, and Valpha34S, in lesions at all 3 stages of development. The strongly skewed pattern of the CDR3 region in the TCR is indicative of oligoclonal expansions of T cells and suggests the occurrence of antigen-driven T-cell proliferation in atherosclerosis.

Caprine T-cell receptor variable beta-chain (TCRV beta) repertoire analysis and potential applications in cowdriosis immune response studies

Anchor polymerase chain reaction has been applied to the study of caprine TCR V beta-chain repertoire at the mRNA level in peripheral blood of a Saanen goat. Single stranded, g-tailed cDNA synthesized from total RNA was PCR-amplified using a sheep V beta constant region primer (3') and a poly(dC) anchor primer (5') at the variable region end of the TCR V beta-chain. The obtained amplicon was subsequently cloned into Bluescript plasmid vector. A total of 72 recombinant clones whereof 61 contained an insert of appropriate size were harvested. Up to now, the full length sequences of a total of 55 clones have been obtained. Nine clones were rearranged but not functional due to stop codons. Forty-five sequences were functionally rearranged and further analyzed. They were classified into 15 different V beta families on the basis of V-region sequence homology with their human counterpart. V beta families corresponding to the 9 published bovine families were represented in our library. This complexity enables us to develop V beta family-specific primers in order to study the TCR V beta repertoire of other goat breeds of interest, i.e., the Creole goat. There the TCR V beta repertoire analysis and kinetic study of the cowdriosis model will provide insight into the type of the immune response and the status of protection during the immunization process and challenge.

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.

A one step PCR procedure for analysis of tumor specific T lymphocyte responses

In an effort to develop optimal conditions for analysis of tumor specific T lymphocyte responses, we have studied the effect of changes in the concentration of oligonucleotide primers on the synthesis of TCR cDNAs in one step PCR procedure using Vbeta10 gene subfamily as a model. It was found that synthesis of the TCR cDNAs increases in a roughly linear fashion at primer concentrations between 0.005-0.05 muM. Evaluation of the use of low concentration (0.005 muM) of primers showed these conditions to be adequate for the analysis of TCR Vbeta subfamilies in the spleen of BALB/c mice, but not in the peritoneal exudate cells (PECs), the latter requiring ten-fold higher concentrations of the variable region primers to compensate for the overall low frequency of T lymphocytes in the PECs in comparison to the spleen. Use of these optimal conditions to detect L1210 tumor specific T lymphocyte responses showed that, in the immunized mice, L1210 specific T lymphocyte responses are detectable in the PECs, but not in the spleen cells from these mice. Thus, upon i.p. immunization of DBA/2 mice with irradiated L1210 lymphoma cells, followed by analysis of the PECs by RT/PCR, three TCR Vbeta subfamilies, including Vbeta8.2, Vbeta15 and Vbeta16 were found to contain specific major TCR cDNA bands. The approach described here is very efficient, as it uses a small amount of the 32P isotope (0.5 muCi) followed by direct analysis of the PCR products on a denaturing acrylamide/urea gel. Furthermore, data is also presented that shows that quantitative differences in the levels of individual TCR cDNAs in a particular Vbeta subfamily are preserved during PCR amplification.

Bacterial superantigen specificities of mouse T cell receptor V beta 20

The study of the mouse T cell receptor (TcR) beta chain repertoire in BALB/c thymocytes led to the identification of the V beta 20 gene segment. The expression of V beta 20 estimated at the transcriptional level differs among mouse strains, suggesting clonal deletion. In the present study, we reconstituted by transfection functional TcR using the V beta 20 segment with different V alpha segments and studied the action of superantigen toxins. The V beta 20-transfectant T cells are activated by staphylococcal enterotoxins A and E (SEA and SEE) but not by the other tested toxins. The activation is dependent on the presence of cells expressing major histocompatibility complex class II molecules. Different HLA DR alleles can present the bacterial toxins, establishing that they interact with TcRV beta 20 as superantigens. Moreover, the V alpha domain associated with the V beta 20 domain has an influence on the response to these toxins. The fact that V beta 20 is recognized by SEA and SEE, although both toxins are known to interact with different sets of V beta, suggests the presence of different TcR binding sites on the toxins.

Generation of immunoglobulin light chain gene diversity in Raja erinacea is not associated with somatic rearrangement, an exception to a central paradigm of B cell immunity

In all vertebrate species examined to date, rearrangement and somatic modification of gene segmental elements that encode portions of the antigen-combining sites of immunoglobulins are integral components of the generation of antibody diversity. In the phylogenetically primitive cartilaginous fishes, gene segments encoding immunoglobulin heavy and light chain loci are arranged in multiple clusters, in which segmental elements are separated by only 300-400 bp. In some cases, segmental elements are joined in the germline of nonlymphoid cells (joined genes). Both genomic library screening and direct amplification of genomic DNA have been used to characterize at least 89 different type I light chain gene clusters in the skate, Raja. Analyses of predicted nucleotide sequences and predicted peptide structures are consistent with the distribution of genes into different sequence groups. Predicted amino acid sequence differences are preferentially distributed in complementarity-determining versus framework regions, and replacement-type substitutions exceed neutral substitutions. When specific germline sequences are related to the sequences of individual cDNAs, it is apparent that the joined genes are expressed and are potentially somatically mutated. No evidence was found for the presence of any type I light chain gene in Raja that is not germline joined. The type I light chain gene clusters in Raja appear to represent a novel gene system in which combinatorial and junctional diversity are absent.

Rearrangement and diversity of T cell receptor beta chain genes in thymocytes: a critical role for the beta chain in development

Thymocytes from mice congenitally deficient for TCR alpha chain synthesis were examined for the status of their TCR beta chain genes, by DNA sequencing and by a novel technique that analyzes populations of gene rearrangements. TCR beta chain genes were predominantly productively rearranged, in contrast with the statistical prediction for a quasi-random rearrangement process. Therefore, productive TCR beta chain gene rearrangement appears to be a critical step in thymocyte maturation, independent of TCR alpha chain expression. Moreover, the beta chain gene rearrangements in TCR alpha-/-mice are typical of those found in the thymus and periphery of normal mice. Thus, the extent of junctional diversity is a property of TCR genes that is imposed prior to selection on the mature alpha beta TCR.

Antigen recognition properties of mutant V beta 3+ T cell receptors are consistent with an immunoglobulin-like structure for the receptor

We examined the effect of mutations in the V beta portion of a pigeon cytochrome c (cyto c)-specific V beta 3+/V alpha 11+ T cell receptor on its ability to recognize cyto c/IEk and various superantigens. The results were consistent with an immunoglobulin-like structure for the receptor V beta domain and with separate interaction sites on V beta for conventional antigen and superantigens. An amino acid predicted to lie in CDR1 was critical for cyto c/IEk but not superantigen recognition, while several amino acids predicted to lie in the hypervariable region 4 loop were critical for superantigen but not cyto c/IEk recognition.

T-cell receptor identification of an oligodendrocyte-specific autoreactive cytotoxic T-cell clone without self restriction

In addition to myelin basic protein (MBP) and proteolipid protein (PLP), oligodendrocyte (Od) membrane autoantigens, such as the glycoprotein M2/MOG, could participate in the pathogenesis of autoimmune demyelinating diseases of the central nervous system (CNS), such as experimental allergic encephalomyelitis (EAE) or multiple sclerosis (MS). We have described an Od-specific autoreactive and cytotoxic T-cell clone, named C2, which recognized M2/MOG without conventional MHC restriction. In order to analyse the Od/C2 interaction, we determined the alpha/beta T-cell receptor (TCR) variable region usages and structures of C2. Monoclonal antibody stainings of C2 and nucleotide sequences show that the alpha chain is composed of a V alpha 5 and a J alpha identical to J alpha 18BBM142 gene segments, and that the TCR beta chain is composed of V beta 17a, D beta 2.1 and J beta 2.2 gene segments indicating that C2 used a conventional alpha/beta TCR for M2/MOG recognition.

T cell receptor rearrangements in various S49 lymphoma sublines

The S49 cell lines are a unique series of tumor sublines isolated from a single BALB/c thymoma. Several different sublines were previously isolated from non-mutagenized cells using pharmacologic agents that would select for different stages of thymic development. In this report we show that all seven of the sublines studied express TL class I Ag confirming their derivation from immature thymocytes. This uniform TL expression is in contrast to the previously characterized locus-specific shut off of Kd,Dd, and/or LdAg by various S49 sublines. Furthermore, S49 sublines were found to display disparate CD4/CD8 expression. Whereas the unselected subline is a CD4+/CD8+ double positive, each of the selected sublines is singly positive for either CD4 or CD8. All seven sublines were found to be CD3+ and express alpha beta TCR heterodimers. To establish whether the S49 sublines have a monoclonal or polyclonal origin, their TCR rearrangements were compared. Based on the detection of identical but unusual TCR gamma rearrangements and similarity of the alpha and beta rearrangements, we propose that the S49 sublines probably had a monoclonal origin. However, significant differences between the TCR alpha and beta gene rearrangement were observed, suggesting that these sublines have undergone further differentiation at TCR loci in addition to CD4/CD8 and MHC loci. Evidence is presented that much of this phenotypic diversity preceded their in vitro selection.

Monoclonal antibodies raised against engineered soluble mouse T cell receptors and specific for V alpha 8-, V beta 2- or V beta 10-bearing T cells

We have characterized a panel of monoclonal antibodies (mAb) produced by immunizing rats with two distinct soluble mouse alpha/beta T cell receptor (TcR). Fifty mAb were found to react with the corresponding surface-bound TcR. Such observations suggest that the soluble TcR molecules used as immunogen are folded in a conformation similar to the native structure. Furthermore, the binding to T cells of four antibodies was found to correlate with the expression of the V alpha 8, V beta 2 or V beta 10 gene segments. Finally, staining of T lymphocytes from various mouse strains suggests that (a) the two anti-V alpha 8 antibodies recognize different epitopes, and each on only a fraction of V alpha 8+ cells; (b) the anti-V beta 10 mAb identifies a V beta 10 polymorphism among mouse strains, and (c) T cells expressing the V beta 2 or V beta 10 gene segments are not subject to major clonal deletion events induced by the major histocompatibility complex class II and Mls products which were tested.

Identification of a T cell receptor beta chain variable region, V beta 20, that is differentially expressed in various strains of mice

A cDNA library of TCR beta chain transcripts from BALB/c thymocytes was constructed using anchored polymerase chain reaction (PCR). Screening of this library led to the identification of a V beta gene segment, V beta 20, structurally related to V beta 3 and V beta 17. Genomic analysis of mice displaying deletions in their V beta loci, together with mapping of cosmid clones, situated V beta 20 2.5 kb beside V beta 17. The expression of V beta 20 was estimated by PCR in mice of different H-2 and Mls types. Peripheral T cells from H-2k and H-2d mice did not express V beta 20, whereas in I-E-negative mice (C57Bl/6 and SJL), V beta 20 transcripts were detected. The lack of V beta 20 transcripts in (C57Bl/6 x CBA/J)F1, (C57Bl/6 x BALB/c)F1, and in congenic B6.H-2k mice suggests that the differential use of V beta 20 is due to an I-E-mediated clonal deletion process. The involvement of the Mls super antigens was excluded by analysis of all Mls type combinations. The nature of the V beta 20-deleting element(s) is discussed in the context of the I-E/superantigen systems controlling the expression of V beta 11 and V beta 17.

Analysis of the immune system with transgenic mice: T cell development

Transgenic mice carrying functionally rearranged T cell receptor genes have contributed significantly to our knowledge of T cell development and thymic positive and negative selection processes. In addition, TCR-transgenic mice have been used to investigate mutations affecting thymocyte development, like scid and lpr. Gene targeting by homologous recombination will allow to analyze more specifically the molecular mechanisms underlying thymic selection and peripheral tolerance.

Genetic differences in the T cell receptor alleles of LEW rats and their encephalomyelitis-resistant derivative, LER, and their impact on the inheritance of EAE resistance

Experimental allergic encephalomyelitis (EAE) is an animal model for the human disease, multiple sclerosis. The LEW rat strain is very susceptible to induction of EAE, whereas the closely related, major histocompatibility complex (MHC)-identical, inbred strain LER is resistant. In this report, the two rat strains have been compared for differences at a number of immunologically relevant loci by restriction fragment length analysis and by nucleotide sequencing. A major difference between the two strains was discovered at the T cell receptor beta chain locus (TcR beta). Both variable (V beta 8) and constant (C beta 1) region elements of TcR beta showed allelic variation between LEW and LER. The known genetic influences in rat models of autoimmunity are currently limited to those encoded by the rat MHC, RT-1. In this study we report our characterization of the allelic differences in TcR beta chains between two rats which differ in their susceptibility to induced EAE, with the goal of understanding the role played by these allelic forms of TcR in the pathogenesis of EAE. The importance of the TcR beta allelic difference in resistance or susceptibility to EAE was assessed in a study of backcross rats scored for both EAE and for the novel LER TcR beta allele. We found that the TcR beta allele from the susceptible strain was present in three out of four susceptible rats, suggesting that it is an important, but not the only, genetic factor in EAE. Supporting this conclusion were the observations that 12 of 13 rats with homozygous LER-derived TCR beta alleles were resistant to EAE.

The role of C5 and T-cell receptor Vb genes in susceptibility to collagen-induced arthritis

Collagen-induced arthritis (CIA) is a rodent arthritis model in which immunization with heterologous type II collagen induces an inflammatory polyarthritis. Susceptibility to the disease is mediated by major histocompatibility complex (MHC) genes as well as genes at other loci. Previous studies of the SWR/J mouse strain, which is resistant to CIA despite bearing the susceptible H-2q haplotype, have suggested that this resistance is the result of a deletion of T-cell receptor (Tcr) Vb gene segments which is carried by this strain. Other studies have implicated a deficiency in complement component C5 as the cause for the resistance. In order to assess the relative importance of these two genes in susceptibility to CIA, and to provide an estimate of the number of independent genes involved in the disease, we analyzed 196 F2 progeny of a (DBA/1 x SWR/J) cross for arthritis susceptibility, and expression of both C5 and Tcr genes. Thirty of the F2 progeny developed arthritis. All of the arthritic mice had at least one copy of the wild-type C5 allele, while the Tcr-Vb haplotypes were distributed in Mendelian fashion. These results demonstrate that C5 sufficiency is an absolute requirement for CIA, but that Tcr-Vb genes located within the SWR deletion have little influence. Genetic analysis of the incidence rate suggests that there is polygenic control of susceptibility to CIA and that in addition to H-2, 5-6 other independent loci (including C5) may be involved.

A rapid method for genotyping mice for T cell receptor V beta a and V beta b haplotypes by PCR analysis of whole blood

Strains of laboratory mice bearing a germline deletion of some T cell receptor V beta genes have proven useful in a variety of studies of T cell receptor function. Analysis of genetic crosses between deleted and wild type strains can provide information about the relevance of genes located within the deletion to specific T cell responses. Existing techniques for genotyping offspring of such crosses usually involve flow cytometric analysis which may not be available to all laboratories. Recent nucleotide sequence data indicate the presence of two restriction enzyme site polymorphisms in the closely linked V beta 1 gene which discriminate between deleted and wild-type strains. Amplification of a DNA segment containing the diagnostic sites by polymerase chain reaction followed by restriction enzyme digestion of the product offers a simple and rapid method for genotyping animals.

T-cell receptor and autoimmune disease

Since the genes encoding the TCR have been cloned, their structure, organization, pattern of rearrangement, diversification and expression in ontogeny have been classified. However, there are still many important questions to be addressed, such as the nature of thymic education, tolerance, the mechanism of MHC-restricted antigen recognition and the relation between TCR repertoire and autoimmunity. In the future, new approaches to study these issues, such as transgenic mice, X-ray crystallography, and severe combined immune deficiency mice reconstituted with human hematopoietic cells will lead to a more profound understanding of these questions. This will hopefully allow us to manipulate the immune response in different and more effective ways than are currently available.

Identification and characterization of new murine T cell receptor beta chain variable region (V beta) genes

By screening previously isolated genomic clones spanning the mouse TCR V beta locus with V beta-specific oligonucleotides, we have isolated one new functional V beta gene and six V beta pseudogenes. Because this method of identifying new genes does not depend on expression levels, we conclude that most, if not all, V beta genes in the mouse have been identified. The newly identified pseudogenes increase the frequency of mouse TCR V beta pseudogenes to 28%, a frequency similar to that estimated for mouse Ig VH pseudogenes (24). Three of the newly discovered pseudogenes are clustered in a region around another pseudogene (V beta 17b). The extensive DNA diversity, as reflected in both the nucleotide sequence and the RFLP, indicates that this genomic region is a possible hotspot of recombination. The new functional gene, V beta 19a, is expressed at very low levels, which explains why it has not been isolated earlier. V beta 19 shows expression patterns that correlate with the previously described Va beta and Vb beta haplotypes.

Positive selection of CD4+ T cells mediated by MHC class II-bearing stromal cell in the thymic cortex

T lymphocytes differentiate in the thymus, where functionally immature, CD4+CD8+ (double positive) thymocytes develop into functionally mature CD4+ helper cells and CD8+ cytotoxic (single positive) T cells. The thymus is the site where self-reactive T cells are negatively selected (clonally deleted) and where T cells with the capacity to recognize foreign antigens in association with self-proteins encoded by the major histocompatibility complex (MHC) are positively selected. The net result of these developmental pathways is a T-cell repertoire that is both self-tolerant and self-restricted. One unresolved issue is the identity of the thymic stromal cells that mediate the negative and positive selection of the T-cell repertoire. Previous work has pointed to a bone-marrow-derived macrophage or dendritic cell as the inducer of tolerance, whereas a radiation-resistant, deoxyguanosine-resistant thymic cell seems to mediate the positive selection of self-MHC restricted T cells. Thymic stromal cells in the cortex interact with the T-cell antigen receptor on thymocytes. Using several strains of transgenic mice that express the class II MHC molecule I-E in specific regions of the thymus, we show directly that the positive selection of T cells is mediated by an I-E-bearing cell in the thymic cortex.

Different large deletions of T cell receptor V beta genes in natural populations of mice

A panel of geographically separate Mus m. domesticus and Swiss mice from several sources was screened for deletions in the T cell receptor variable (V) beta locus. Four out of forty-three strains tested show a deletion identical to or larger than the deletion previously described in SJL mice. To our knowledge, this is the first time that such important V beta deletions are described in inbred or partially inbred wild-derived strains of mice. On the other hand there seems to be very little polymorphism between the remaining V beta genes. Expression of V beta genes in peripheral and intra-thymic T cells was tested using antibodies specific for different V beta polypeptide chains. Flow cytometry analysis revealed a high expression of V beta 6 and V beta 17 genes in the Copacabana Swiss-derived strain and an absence of V beta 17 expression in the WLA wild-derived strain. The three Mus m. domesticus strains (WLA, DDO and WBG) having deleted two to three additional V beta subfamilies compared to SJL present no apparent immune deficiencies or autoimmune disorders. We conclude that relatively few V beta genes may suffice for unimpaired survival of wild mice and that there is a selective pressure for the structural conservation of the remaining V beta genes.

RIII S/J (H-2r). An inbred mouse strain with a massive deletion of T cell receptor V beta genes

We have identified an inbred strain of mouse, RIII S/J (H-2r), that has the largest known deletion of the TCR V beta genes by screening with mAb and TCR V beta specific probes. Upon screening of PBL with mAb F23.1, which is specific for V beta 8 TCR, RIII S/J was found to be negative. On further screening with mAb KJ 23a, which is specific for V beta 17a TCR, RIII S/J was completely negative. We next tested RIII S/J with mAb 44-22-1, which is specific for V beta 6 TCR, and found it also to be negative. The (B10 X RIII)F1 mice showed a 50% expression of V beta 6 gene, indicating a genomic rather than a clonal deletion. mAb KJ25, detecting V beta 3, was positive in RIII S/J, denoting the downstream boundary for the deletion. Southern blot analysis of liver DNA using TCR V beta-specific probes confirmed the deletion of V beta 8 gene subfamily and V beta 5 gene subfamily, along with V beta 9, V beta 11, V beta 12, and V beta 13 genes similar to the known TCR V beta deletion mutants (SWR, SJL, C57L, and C57Br). In addition, RIII S/J is missing V beta 6, V beta 15, and V beta 17 genes. Our mapping of the deletion indicates that RIII S/J has lost approximately 130 kb of V beta chromosome and with it 13 V beta genes out of the known 21 V beta genes of the TCR. The deletion is marked by the presence of V beta 10 gene upstream and V beta 3 gene downstream.

Analysis of V beta 17a expression in new mouse strains bearing the V beta a haplotype

A set of new mouse strains were produced that carry the V beta a haplotype of the TCR-alpha/beta and any of a number of different H-2 haplotypes on backgrounds derived from related C57BL, C57L, and C57BR mice. Study of V beta 17a expression in these mice confirms the association between the presence of IE and the deletion of V beta 17a+ T cells. A second H-2 gene causing deletion of V beta 17a+ T cells was mapped in these mice to the K end of H-2k, and H-2 influences on the level of selection of CD4+ V beta 17a+ T cells were indicated.

Relative V beta transcript levels in thymus and peripheral lymphoid tissues from various mouse strains. Inverse correlation of I-E and Mls expression with relative abundance of several V beta transcripts in peripheral lymphoid tissues

We have measured the relative levels of transcripts for 15 of the 22 known V beta gene segments. The level of transcripts for the highest and lowest expressed V beta gene segment differed by greater than 20-fold in the thymus and an even larger difference was observed in the periphery. The levels of expressions were unrelated to the order of the V beta genes on the chromosome. For most of the V beta gene segments, the relative transcript levels were the same in the thymus and periphery, suggesting that thymic selection in general does not act solely upon the V beta gene segment. One V beta gene segment in the BALB and B10 mice strains was an exception to this rule. V beta 5.2 expression in the periphery of BALB and B10 mice inversely correlated with the expression of the MHC class II molecule I-E. Five V beta gene segments had reduced transcript levels in the periphery of Mls-1a mice compared with their thymic levels or to the levels found in Mls-1b mice. The peripheral level of V beta 3 transcripts vary with MHC and Mls-2 haplotypes. The observation that certain V beta transcript levels are reduced in the periphery when compared with the thymus favors the hypothesis that self tolerance at the T cell level results in the elimination of self-reactive T cells, rather than paralysis by a block at some post-transcriptional step. Finally, the wide variability of V beta gene segment expression in the thymus suggests mechanisms exist to import an early bias to the repertoire. Whether this bias results from differential V beta segment rearrangement rates, differential V beta expression rates, or events occurring after TCR-alpha/beta expression on immature/nonmature thymocyte cell surfaces is yet to be determined.

Isolation and restriction map of the V-J interval of the human T cell receptor gamma chain locus

The human T cell receptor gamma chain locus encodes the immunoglobulin-like gamma chain polypeptide and spans a distance of approximately 150 kb. Previous studies have not precisely characterized the interval separating variable regions from joining--constant regions which is excised during gamma gene rearrangement. We report a series of overlapping cosmids which includes the portion of the gamma chain locus beginning with V2 and extends to the second exon of C2. Sixteen kilobases separate the most 3' variable region gene, V4, from the most 5' joining segment, J1.1.

Restriction fragment length polymorphisms of the mouse T-cell receptor gene families

We have studied the restriction fragment length polymorphisms (RFLPs) found in the germline T-cell receptor genes of 25 inbred Mus musculus strains and 8 wild Mus species. Included in the inbred mice tested were several strains which spontaneously develop systemic autoimmune disease. Extensive polymorphism was evident for the variable (V) gene segments of the alpha gene family for both the inbred strains and wild mouse species. Changes in the total number of bands hybridizing with probes for V alpha gene segments suggest that members of a V alpha gene segment subfamily are not closely linked, but are interspersed with members of other subfamilies; that expansion and contraction of the multimembered subfamilies may be an important diversifying factor. Our data obtained with beta gene probes revealed genomic diversity that is much more limited than that seen for the alpha locus. Analysis of inbred mice with probes for the gamma gene locus revealed some RFLPs, but little evidence of expansion or contraction in the numbers of gene segments. Among the autoimmune mice, NZW, NZB, and BXSB/MpJ all display distinctive differences with alpha gene probes. NZW mice have a large deletion of the beta gene family, which has been reported previously. We found no differences to distinguish the MRL/MpJ lpr/lpr mice from non-autoimmune strains.

Identification of T-cell receptor V beta deletion mutant mouse strain AU/ssJ (H-2q) which is resistant to collagen-induced arthritis

Our laboratory is involved in investigating the role of T-cell receptor (Tcr) in collagen-induced arthritis (CIA). During these studies we found AU/ssJ (H-2q) mice to be resistant to CIA like SWR (H-2q), as compared with other H-2q strains with wild-type Tcr like DBA/1 and B10.Q. Upon screening with monoclonal antibodies F23.1 and KJ23a, AU/ssJ was found to be F23.1 negative (V beta 8 Tcr negative) and KJ23a positive (V beta 17a Tcr positive). Southern blot analysis on liver DNA using specific Tcr-V beta probes confirmed the deletion of V beta 8 gene family and also showed that AU/ssJ mice have deletions of V beta 9, V beta 13, V beta 12, and V beta 11 genes of Tcr. Further, these mice show a restriction fragment length polymorphism pattern with V beta 10, V beta 6, and V beta 17 probes similar to SWR mice as compared with B10 mice. Since SWR and AU/ssJ are from different backgrounds, these studies indicate that specific variable region beta chain genes of Tcr are crucial for susceptibility to CIA in mice. Furthermore, these studies identify an additional inbred strain which has also deleted 50% of its Tcr-V beta genes.

The organization of the mouse Igh-V locus. Dispersion, interspersion, and the evolution of VH gene family clusters

We have constructed a panel of Abelson murine leukemia virus-transformed pre-B cells to study the organization of the mouse VH gene families. Based on the analyses of VH gene deletions on 51 chromosomes with VH gene rearrangements, we have inferred a map order of the Igh locus that holds for both the Igha and Ighb haplotypes. We show that members of each VH gene family are generally clustered, although three family clusters (VHS107, VH36-60, VGAM3.8) are dispersed in two or three subregions of the locus. Members of two VH gene families, VHQ52 and VH7183, are extensively interspersed and map within the same subregion. An examination of the distribution of VH group members (VH II, I, and III) within the locus suggests that two major duplications may, in part, explain the dispersed pattern of VH family clusters. The relationship of VH organization and functional expression is discussed in terms of position-dependent and complexity-driven models.

Selective expression of an antigen receptor on CD8-bearing T lymphocytes in transgenic mice

The major problem in the study of T-cell development is that of tracking thymocytes of a given specificity. Recent studies have exploited natural correlations between the expression of a particular V beta gene segment and T-cell receptor (TCR) specificity. We and others (refs 5, 6 and M. Davis, personal communication) have taken an alternative approach. We have generated transgenic mice expressing the alpha beta antigen receptor from the cytotoxic T-lymphocyte clone 2C (ref. 7). In transgenic mice of the same haplotype as the 2C clone, the 2C TCR was expressed on 20-95% of peripheral T cells. Very few of these T cells carried the CD4 antigen; the vast majority were CD4-CD8+ and were able to lyse targets with the same specificity as the original 2C clone. These results indicate that the alpha beta heterodimer transfers specificity to recipient cells as expected from earlier studies, and that receptor specificity in T-cell repertoire selection is determined by both alpha beta heterodimer and CD4 or CD8 accessory molecules.

T-cell antigen receptor genes and T-cell recognition

The four distinct T-cell antigen receptor polypeptides (alpha, beta, gamma, delta) form two different heterodimers (alpha:beta and gamma:delta) that are very similar to immunoglobulins in primary sequence, gene organization and modes of rearrangement. Whereas antibodies have both soluble and membrane forms that can bind to antigens alone, T-cell receptors exist only on cell surfaces and recognize antigen fragments only when they are embedded in major histocompatibility complex (MHC) molecules. Patterns of diversity in T-cell receptor genes together with structural features of immunoglobulin and MHC molecules suggest a model for how this recognition might occur. This view of T-cell recognition has implications for how the receptors might be selected in the thymus and how they (and immunoglobulins) may have arisen during evolution.

The V beta 8 gene family is preferentially used by 'naturally' activated T cells

Receptors encoded by the V beta 8 gene family detected by the monoclonal antibody F23.1 are expressed among 'naturally' activated T cells in normal spleen at frequencies significantly higher than in the total CD4+ and CD8+ cell populations. The positive selection of these clones into 'natural' T-cell activity could be the reason for the high frequencies of cells expressing V beta 8 genes. This phenotype is strain-dependent.

Conserved organization of the human and murine T-cell receptor beta-gene families

Generation of an immune response depends on the interaction of haematopoietic cell types, among which T cells and their receptors are of central importance. The T-cell receptor is a heterodimer consisting of disulphide-linked alpha and beta-chains, each chain divided into variable (V) and constant (C) regions. The beta-chain is encoded by the rearrangement of separate variable (V beta), diversity (D beta) and joining (J beta) gene segments during T-cell differentiation. To examine the mechanisms of somatic DNA rearrangement and evolution of the beta-gene segments, we have constructed a physical map of the human T-cell receptor beta-chain family containing 40 V beta gene segments as well as both C beta gene clusters. A comparison of the published nucleotide sequences of human and murine V beta gene segments reveals 12 examples of gene segments sharing 65% or more interspecies homology. The relative order of these human and murine V beta gene segment homologues is also conserved along the chromosome, apart from more extensive human gene duplication, presumably as a consequence of constraints imposed on evolutionary mechanisms operating to diversify these gene families or of selective pressures operating to maintain order.