TCR gamma delta intraepithelial lymphocytes are required for self-tolerance

Neonatal thymectomy (NTX) impairs T cell regulation and leads to organ-specific autoimmune disease in susceptible mouse strains. In the NOD mouse model of spontaneous type 1 diabetes, we observed that NTX dramatically accelerated autoimmune pancreatic beta cell destruction and diabetes. NTX had only a minor effect in NOD mice protected from diabetes by transgenic expression of the beta cell autoantigen proinsulin in APCs, inferring that accelerated diabetes after NTX is largely due to failure to regulate proinsulin-specific T cells. NTX markedly impaired the development of intraepithelial lymphocytes (IEL), the number of which was already reduced in euthymic NOD mice compared with control strains. IEL purified from euthymic NOD mice, specifically CD8alphaalpha TCRgammadelta IEL, when transferred into NTX-NOD mice, trafficked to the small intestinal epithelium and prevented diabetes. Transfer of prototypic CD4+CD25+ regulatory T cells also prevented diabetes in NTX-NOD mice; however, the induction of these cells by oral insulin in euthymic mice depended on the integrity of TCRgammadelta IEL. We conclude that TCRgammadelta IEL at the mucosal interface between self and nonself play a key role in maintaining peripheral tolerance both physiologically and during oral tolerance induction.     

NK-like cytotoxicity of allospecific gamma delta TCR+ T cell clones]

We recently generated a series of human alloantigen-specific, CD3+, gamma delta- TCR+ clones by stimulating CD3+, CD4-, CD8- T cells from normal individuals with allogeneic lymphoblastoid cell lines (LCL). These clones display cytotoxic activity against their specific stimulators but not against irrelevant LCL. Most but not all of these clones express the NK cell associated marker, CD57, and kill NK-sensitive targets such as the K562 and Molt 4 lines, but not NK-resistant line, Raji. Gamma delta clones which lacked expression of CD57 had no detectable NK activity. The allospecific cytotoxicity of CD57+ and CD57- clones was inhibited by mAb to CD3 or the TCR delta- chain. In contrast, the NK-like activity of the CD57+ clones was enhanced by these antibodies over a wide range of antibody concentration. An HLA class I framework-specific mAb had no effect on NK-like cytolysis but did inhibit allospecific killing, suggesting that the target structures on the surface of allospecific and NK-sensitive cells are distinct. The receptors utilized by the gamma delta- TCR+ clones to recognize NK-sensitive and allospecific targets are also distinct, since killing of NK-sensitive targets was blocked by the presence of cold (unlabeled) NK-sensitive cells but not by cold allospecific targets, whereas allospecific cytolysis was inhibited by cold allospecific targets but not by NK-sensitive cells. We conclude that some CD3+, TCR- gamma delta+ clones exhibit NK-like as well as allospecific killing and that these two activities are mediated by distinct receptor-ligand interactions.     

An autoreactive gamma delta TCR derived from a polymyositis lesion

To investigate the role of gammadelta T cells in human autoimmune disease we expressed and characterized a gammadelta TCR from an autoimmune tissue lesion. The TCR was first identified in a rare form of polymyositis characterized by a monoclonal infiltrate of gammadelta T cells which invaded and destroyed skeletal muscle fibers. The Vgamma1.3-Jgamma1-Cgamma1/Vdelta2-Jdelta3 TCR cDNA of the original muscle invasive gammadelta T cell clone was reconstructed from unrelated cDNA and transfected into the mouse hybridoma BW58alpha(-)beta(-). Appropriate anti-human gammadelta TCR Abs stimulated the TCR transfectants to produce IL-2, thus demonstrating that the human gammadelta TCR functionally interacted with murine signaling components. The transfected Vgamma1.3/Vdelta2 TCR recognized a cytosolic protein expressed in cultured human myoblasts and TE671 rhabdomyosarcoma cells. The Ag was recognized in the absence of presenting cells. Using a panel of control gammadelta TCR transfectants with defined exchanges in different positions of both TCR chains, we showed that the gammadelta TCR recognized its Ag in a TCR complementarity-determining region 3-dependent way. To our knowledge, this is the first example of a molecularly defined gammadelta TCR directly derived from an autoimmune tissue lesion. The strategy used in this study may be applicable to other autoimmune diseases.     

Allelic exclusion at the TCR delta locus and commitment to gamma delta lineage: different modalities apply to distinct human gamma delta subsets

Expression of a beta-chain, as a pre-TCR, in T cell precursors prevents further rearrangements on the alternate beta allele through a strict allelic exclusion process and enables precursors to undergo differentiation. However, whether allelic exclusion applies to the TCR delta locus is unknown and the role of the gamma delta TCR in gamma delta lineage commitment is still unclear. Through the analysis of the rearrangement status of the TCR gamma, delta, and beta loci in human gamma delta T cell clones, expressing either the TCR V delta 1 or V delta 2 variable regions, we show that the rate of partial rearrangements at the delta locus is consistent with an allelic exclusion process. The overrepresentation of clones with two functional TCR gamma chains indicates that a gamma delta TCR selection process is required for the commitment of T cell precursors to the gamma delta lineage. Finally, while complete TCR beta rearrangements were observed in several V delta 2 T cell clones, these were seldom found in V delta 1 cells. This suggests a competitive alpha beta/gamma delta lineage commitment in the former subset and a precommitment to the gamma delta lineage in the latter. We propose that these distinct behaviors are related to the developmental stage at which rearrangements occur, as suggested by the patterns of accessibility to recombination sites that characterize the V delta 1 and V delta 2 subsets.     

Analysis of competition binding between soluble and membrane-bound ligands for cell surface receptors

Binding of the Fc portion of IgG coated on targets to Fcgamma receptors (e.g., CD16) expressed on leukocytes (i.e., 2D binding) is an initiating step for immune responses such as phagocytosis or antibody-dependent cellular cytotoxicity. In vivo, circulating leukocytes are exposed to plasma IgG. The competition from soluble IgG (i.e., 3D binding) may affect the 2D binding. Many cell surface receptors, CD16 included, have soluble counterparts. While their physiological significance is not clear, receptor-based competitive inhibition therapy, in which soluble receptors, ligands, and their analogs are employed to compete with surface-bound receptors and ligands to prevent unwanted adhesion, is widely used to treat various diseases. To provide a quantitative basis for design of these therapeutic approaches, we developed a mathematical model for 2D and 3D competition binding. The model relates cell-surface adhesion (in the presence and absence of dislodging forces) to the concentration of the soluble competitor, the densities of the surface-bound receptors and ligands, as well as the binding affinities of the 2D and 3D interactions. Binding of CD16-expressing cells to an IgG-coated surface in the presence of a soluble competitor (IgG or anti-CD16 antibody) was quantified by a centrifugation assay. The agreement between experiment and theory supports the validity of the model, which could be useful in predicting the efficacy of the competitor.     

Development of dendritic epidermal T cells with a skewed diversity of gamma delta TCRs in V delta 1-deficient mice

One of the most intriguing features of gammadelta T cells that reside in murine epithelia is the association of a specific Vgamma/Vdelta usage with each epithelial tissue. Dendritic epidermal T cells (DETCs) in the murine epidermis, are predominantly derived from the "first wave" Vgamma5+ fetal thymocytes and overwhelmingly express the canonical Vgamma5/Vdelta1-TCRs lacking junctional diversity. Targeted disruption of the Vdelta1 gene resulted in a markedly impaired development of Vgamma5+ fetal thymocytes as precursors of DETCs; however, gammadeltaTCR+ DETCs with a typical dendritic morphology were observed in Vdelta1-/- mice and their cell densities in the epidermis were slightly lower than those in Vdelta1+/- epidermis. Moreover, the Vdelta1-deficient DETCs were functionally competent in their ability to up-regulate cytokines and keratinocyte growth factor-expression in response to keratinocytes. Vgamma5+ DETCs were predominant in the Vdelta1-/- epidermis, though Vgamma5- gammadeltaTCR+ DETCs were also detected. The Vgamma5+ DETCs showed a typical dendritic shape, gammadeltaTCR(high), and age-associated expansion in epidermis as observed in conventional DETCs of normal mice, whereas the Vgamma5- gammadeltaTCR+ DETCs showed a less dendritic shape, gammadeltaTCR(low), and no expansion in the epidermis, consistent with their immaturity. These results suggest that optimal DETC development does not require a particular Vgamma/Vdelta-chain usage but requires expression of a limited diversity of gammadeltaTCRs, which allow DETC precursors to mature and expand within the epidermal microenvironment.     

Human alpha beta and gamma delta thymocyte development: TCR gene rearrangements, intracellular TCR beta expression, and gamma delta developmental potential--differences between men and mice

To evaluate the role of the TCR in the alphabeta/gammadelta lineage choice during human thymocyte development, molecular analyses of the TCRbeta locus in gammadelta cells and the TCRgamma and delta loci in alphabeta cells were undertaken. TCRbeta variable gene segments remained largely in germline configuration in gammadelta cells, indicating that commitment to the gammadelta lineage occurred before complete TCRbeta rearrangements in most cases. The few TCRbeta rearrangements detected were primarily out-of-frame, suggesting that productive TCRbeta rearrangements diverted cells away from the gammadelta lineage. In contrast, in alphabeta cells, the TCRgamma locus was almost completely rearranged with a random productivity profile; the TCRdelta locus contained primarily nonproductive rearrangements. Productive gamma rearrangements were, however, depleted compared with preselected cells. Productive TCRgamma and delta rearrangements rarely occurred in the same cell, suggesting that alphabeta cells developed from cells unable to produce a functional gammadelta TCR. Intracellular TCRbeta expression correlated with the up-regulation of CD4 and concomitant down-regulation of CD34, and plateaued at the early double positive stage. Surprisingly, however, some early double positive thymocytes retained gammadelta potential in culture. We present a model for human thymopoiesis which includes gammadelta development as a default pathway, an instructional role for the TCR in the alphabeta/gammadelta lineage choice, and a prolonged developmental window for beta selection and gammadelta lineage commitment. Aspects that differ from the mouse are the status of TCR gene rearrangements at the nonexpressed loci, the timing of beta selection, and maintenance of gammadelta potential through the early double positive stage of development.     

T cell receptor (TCR) beta chain homodimers on the surface of immature but not mature alpha, gamma, delta chain deficient T cell lines.

Transfected T cell receptor (TCR) beta chain genes are expressed as homodimers on the surface of immature (Sci/ET27F) but not on mature (58 alpha-beta-) T cell lines which lack TCR alpha, gamma and delta chains. The homodimer on Sci/ET27F cells is tightly bound to CD3 delta and CD3 epsilon while the association with CD3 gamma and CD3 zeta proteins is rather weak. Crosslinking of the TCR beta homodimers resulted in a strong and rapid calcium flux. In 58 alpha-beta- T cells the beta TCR chain could be easily visualized intracellularly but was not transported to the cell surface. The Scid cell lines considerably facilitate the molecular analysis of early differentiation events in the thymus which are likely to be regulated by the beta TCR homodimer.     

A keratinocyte-responsive gamma delta TCR is necessary for dendritic epidermal T cell activation by damaged keratinocytes and maintenance in the epidermis

A unique population of T lymphocytes, designated dendritic epidermal T cells (DETC), homes to the murine epidermis during fetal development. DETC express a canonical gammadelta TCR, Vgamma3/Vdelta1, which recognizes Ag expressed on damaged, stressed, or transformed keratinocytes. Recently, DETC were shown to play a key role in the complex process of wound repair. To examine the role of the DETC TCR in DETC localization to the epidermis, maintenance in the skin, and activation in vivo, we analyzed DETC in the TCRdelta(-/-) mouse. Unlike previous reports in which the TCRdelta(-/-) skin was found to be devoid of any DETC, we discovered that TCRdelta(-/-) mice have alphabeta TCR-expressing DETC with a polyclonal Vbeta chain repertoire. The alphabeta DETC are not retained over the life of the animal, suggesting that the gammadelta TCR is critical for the maintenance of DETC in the skin. Although the alphabeta DETC can be activated in response to direct stimulation, they do not respond to keratinocyte damage. Our results suggest that a keratinocyte-responsive TCR is necessary for DETC activation in response to keratinocyte damage and for DETC maintenance in the epidermis.     

Functional and morphologic characterization of human T lymphocytes expressing the TCR gamma /delta

A minor subset of T lymphocytes express a TCR composed of gamma and delta chains. This subset differs from conventional T cells for a number of phenotypic and functional characteristics. TCR gamma/delta+ cells simultaneously lack both CD4 and CD8 antigens. Cloning of CD4-8- peripheral blood lymphocytes, under limiting dilution conditions, revealed that they are homogeneously composed of cytolytic cells which efficiently lyse tumor target cells. Formal proofs have been provided that TCR gamma/delta+ cells are able to recognize antigens. For example, they proliferated in response to allogeneic mixed lymphocyte culture (MLC); in addition, MLC-derived TCR gamma/delta+ cells specifically lysed PHA-induced blast cells bearing the stimulating alloantigens. The selection of monoclonal antibodies specific for TCR gamma/delta molecules allowed to identify two distinct subsets of TCR gamma/delta+ cells. Both of these mABs, termed BB3 and delta TCS-1 respectively, induced specific activation of cloned cells expressing the corresponding antigenic determinants (as assessed by measurements of intracellular Ca++ and/or lymphokine production or cytolytic activity). Analysis of the distribution of subsets expressing different forms of TCR gamma/delta, showed that the BB3-reactive form is prevalent in the peripheral blood. In contrast, delta-TCS-1-reactive cells are relatively unfrequent in peripheral blood but represent the majority of TCR gamma/delta+ cells in tissues.     

Transendothelial migratory pathways of V delta 1+TCR gamma delta+ and V delta 2+TCR gamma delta+ T lymphocytes from healthy donors and multiple sclerosis patients: involvement of phosphatidylinositol 3 kinase and calcium calmodulin-dependent kinase II

We have previously reported that the Vdelta2(+)TCRgammadelta(+) T lymphocyte subset, expressing the NK receptor protein 1a (NKRP1a; CD161), is expanded in patients with relapsing-remitting multiple sclerosis and uses this molecule to migrate through endothelium. In this work, we show that Vdelta1(+) and Vdelta2(+) gammadelta T lymphocytes use distinct signal transduction pathways to accomplish this function. Indeed, we have found that Vdelta1(+) cells lack NKRP1a and selectively express the platelet endothelial cell adhesion molecule 1 (PECAM1; CD31), which drives transendothelial migration of this cell subset, at variance with Vdelta2(+) T cells, which are PECAM1 negative and use NKRP1a for transmigration. Interestingly, when Vdelta2(+) T cells were pretreated with two specific inhibitors of the calcium calmodulin-dependent kinase II KN62 and KN93, but not with the inactive compound KN92, the number of migrating cells and the rate of transmigration were significantly decreased. In turn, the phosphatidylinositol 3 kinase blockers wortmannin and LY294002 exerted a dose-dependent inhibition of Vdelta1(+) cell migration. Finally, NKRP1a and PECAM1 engagement led to activation of different signal transduction pathways: indeed, oligomerization of NKRP1a on Vdelta2(+) T cells activates calcium calmodulin-dependent kinase II, while occupancy of PECAM1 on Vdelta1(+) cells triggers the phosphatidylinositol 3 kinase-dependent Akt/protein kinase Balpha activation. These findings suggest that subsets of gammadelta T lymphocytes may migrate to the site of lesion in multiple sclerosis using two different signaling pathways to extravasate.     

A novel gamma delta T cell receptor for antigen adds limited diversity to the gamma delta repertoire in adult thymus

The surface expression of CD3-associated TCR chains on hybridoma cell lines derived from adult gamma delta thymocytes was analyzed. These cell lines were unusual, in that a) they expressed a surface heterodimer consisting of a 40- and a 42-kDa chain, i.e., comprised of chains different from any previously reported gamma delta-TCR all of which express C gamma 1- or C gamma 2-encoded gamma-chains; b) their CD3-associated TCR could not be categorized as alpha beta-TCR dimers, despite the similarities in m.w. of the TCR chains, because full size 1.3-kb beta-chain mRNA capable of encoding a functional beta-chain could not be detected in these cells; c) neither of the receptor chains could be precipitated with anti-C gamma 1C gamma 2-peptide antisera. Biochemical analysis demonstrated that the 42-kDa delta-chain is a novel chain, which differs from any reported delta-chains in size, charge and number of glycosylation sites. Collectively, the data on analysis of the 40-kDa chain strongly suggest that it represents a gamma-chain encoded for by the C gamma 4 locus, protein products of which have not yet been reported in the thymus. This gamma-chain was also unique, in that its isoelectric point was much lower than that of other gamma-chains. The gamma- and delta-chains on these C gamma 4-expressing hybridomas were indistinguishable from one another in size and charge (as determined by nonequivalent pH gradient electrophoresis/SDS-PAGE analysis and analysis after endoglycosidase treatment). Because the cell lines were randomly chosen from large panels of hybridomas, these results may well imply strikingly nonrandom pairing of thymocyte-derived C gamma 4 chains and the delta-chains reported here. Thus, only limited additional gamma delta repertoire diversity may be generated by availability of this gamma delta-TCR in the thymus.     

Distinct requirements for IL-7 in development of TCR gamma delta cells during fetal and adult life

TCRgammadelta-transgenic IL-7(-/-) mice were generated to determine whether T cells containing productively rearranged TCRgammadelta genes have additional requirements for IL-7 within the thymus or peripheral lymphoid tissues. Differences in developmental requirements for IL-7 by TCRgammadelta cells were noted and were linked to derivation from fetal- vs adult-type precursors in the thymus. Although TCRgammadelta cells are absent from IL-7(-/-) mice, TCRgammadelta cells were restored to the thymus and periphery by expression of TCRgammadelta transgenes. Endogenous TCRgamma chains were expressed by IL-7(+/-) but not IL-7(-/-) TCRgammadelta-transgenic mice, providing direct support for findings that IL-7 is necessary for rearrangement and expression of TCRgamma genes. The number of TCRgammadelta thymocytes was 10-fold reduced in TCRgammadelta-transgenic IL-7(-/-) embryos; however, adult TCRgammadelta-transgenic IL-7(-/-) or IL-7(+/-) mice had similar numbers of fetal thymus-derived TCRgammadelta cells in their skin. Thus, fetal TCRgammadelta cells required IL-7 for TCR rearrangement, but not for proliferation or survival in the periphery. In contrast, the numbers of TCRgammadelta cells in other tissues of TCRgammadelta-transgenic IL-7(-/-) mice were not completely restored. Moreover, coincident with the transition from the first to second wave of T cell precursors maturing in neonatal thymus, thymus cellularity of TCRgammadelta-transgenic IL-7(-/-) mice dropped significantly. These data indicated that in addition to TCRVgamma gene rearrangement, TCRgammadelta cells differentiating from late fetal liver or adult bone marrow precursors have additional requirements for IL-7. BrdU incorporation studies indicated that although IL-7 was not required for TCRgammadelta cell proliferation, it was required to prolong the life span of mature TCRgammadelta cells.     

Transcriptional profiling of gamma delta T cells identifies a role for vitamin D in the immunoregulation of the V gamma 9V delta 2 response to phosphate-containing ligands

Vitamin D is a steroid hormone that, in addition to its well-characterized role in calcium/phosphate metabolism, has been found to have regulatory properties for immune system function. The nuclear vitamin D receptor is widely expressed in tissues, but has also been shown to be regulated by hormones, growth factors, and cytokines. In this study we show that activation of human Vdelta2Vgamma9 T cells by nonpeptidic monoalkyl phosphates such as isopentenyl pyrophosphate leads to the up-regulation of the vitamin D receptor via a pathway that involves the classical isoforms of protein kinase C. We further show that this receptor is active by demonstrating that the ligand 1alpha,25-dihydroxyvitamin D3 (vitD3) significantly inhibits in a dose-dependent fashion phospholigand-induced gammadelta T cell expansion, IFN-gamma production, and CD25 expression. We also show that vitD3 negatively regulates signaling via Akt and ERK and, at high concentrations, potentiates Ag-induced cell death. As such, these data provide further support for the immunoregulatory properties of vitamin D, and suggest that the ability of vitD3 to negatively regulate the proinflammatory activity of gammadelta T cells may contribute to the protection this vitamin affords against inflammatory and autoimmune disorders dependent upon Th1-type responses.     

Extrathymic selection of TCR gamma delta + T cells by class II major histocompatibility complex molecules

The influence of MHC antigens on TCR gamma delta usage in CD8+ intraepithelial lymphocytes (IELs) was examined using a pan-reactive and V delta 4 region-specific MAb. While an average of 30% of IELs from the majority of mice of various MHC haplotypes were V delta 4+, a 2-fold or greater percentage of IELs from H-2k mice were V delta 4+. Analysis of IELs from F1 mice indicated that the increase in TCRs using V delta 4 was likely to be the result of positive selection. The V delta 4 usage patterns of IELs from recombinant inbred strains and from mice recombinant within H-2 revealed that the increase in V delta 4 usage mapped to H-2 and required I-E expression. Moreover, selection of TCRs using V delta 4 occurred in chimeric mice in the absence of a thymus. The results demonstrate an extrathymic selective mechanism for gamma delta TCRs of CD8+ IELs and suggest that these cells may exhibit MHC class II-restricted antigen recognition.     

Bovine gamma delta T cell subsets express distinct patterns of chemokine responsiveness and adhesion molecules: a mechanism for tissue-specific gamma delta T cell subset accumulation

Subsets of gammadelta T cells localize to distinct tissue sites in the absence of exogenous Ag stimulation or development of effector/memory cells. Selective lymphocyte homing from the blood into tissues is controlled by a multistep process involving vascular and lymphocyte adhesion molecules, and G protein-linked chemokine receptors. The role of these mechanisms in the tissue tropism of gammadelta T cells is still poorly understood. In this study, we demonstrate that a subset of gammadelta T cells, most of which express an antigenically distinct TCR and are characterized by coexpression of CD8, selectively accumulated in tissues that expressed high levels of the mucosal vascular addressin, mucosal addressin cell adhesion molecule 1. These cells expressed higher levels of alpha(4)beta(7) integrins than other gammadelta T cell subsets and selectively migrated to the CCR7 ligand secondary lymphoid-tissue chemokine (CCL21). Integrin activation by CCL21 selectively increased CD8(+)gammadelta T cell binding to recombinant mucosal addressin cell adhesion molecule 1. These results suggest that the tropism of circulating CD8(+)gammadelta T cells for mucosal tissues is due, at least in part, to selective developmental expression of adhesion molecules and chemokine receptors.     

The specificity of a weak gamma delta TCR interaction can be modulated by the glycosylation of the ligand.

The gamma delta T cell clone LBK5 recognizes the MHC molecule IEk. Here, we demonstrate that the affinity of this interaction is weaker than those typically reported for alpha beta TCRs that recognize peptide/MHC complexes. Consistent with our previous finding that peptide bound to the IE molecule does not confer specificity, we show that the entire epitope for LBK5 is contained within the polypeptide chains of the molecule, centered around the polymorphic residues 67 and 70 of the IE beta-chain. However, LBK5 recognition is profoundly influenced by the N-linked glycosylation at residue 82 of the IE alpha-chain. Since infected, stressed, or transformed cells often change the posttranslational modifications of their surface glycoproteins, this finding suggests a new way in which gamma delta T cell Ag recognition can be regulated.     

Identification of distinct T cell receptor (TCR)-gamma delta heterodimers using an anti-TCR-gamma variable region serum

T cell hybridomas were generated from CD3+, CD4-, CD8- splenocytes and fetal thymocytes. V gamma 1-expressing proteins present on these murine TCR-gamma delta hybridomas were identified by using an anti-TCR V gamma 1 peptide serum. This antiserum specifically immunoprecipitated 41-kDa TCR V gamma-C gamma 4 chains and 31-kDa TCR V gamma-C gamma 1/2 chains from distinct heterodimers expressed on the TCR-gamma delta T cell hybridomas. The RNA from a hybridoma with a 31-kDa TCR-gamma chain hybridized with a V gamma 1 probe but failed to hybridize with a V gamma 2 probe. In contrast, the RNA from a hybridoma with a 32-kDa TCR-gamma chain hybridized with a V gamma 2 probe. This 32-kDa TCR-gamma chain was not immunoprecipitated by the anti-V gamma 1 serum. These data were consistent with the conclusion that the 31-kDa protein was the product of a V gamma 1 to C gamma 2 rearrangement, whereas the 32-kDa protein was the product of a V gamma 2 to C gamma 1 rearrangement. Furthermore, Southern analyses confirmed that the 32-kDa protein was the product of a V gamma 1.2-J gamma 2 rearrangement, and all three of the 41-kDa TCR-gamma chains were the results of V gamma 1.1-J gamma 4 rearrangements. This was the first demonstration at the clonal level of TCR-gamma proteins which use members of the V gamma 1 gene family, as well as the C gamma 2 constant region. Additional biochemical analyses of the TCR-gamma and -delta proteins from three independently derived C gamma 4-bearing T cell hybridomas suggested that most of the molecular mass diversity observed in the bulk subpopulation of peripheral C gamma 4-containing heterodimers may be contributed by the TCR-delta chains.     

Junctional sequences of T cell receptor gamma delta genes: implications for gamma delta T cell lineages and for a novel intermediate of V-(D)-J joining

Nucleotide sequences of a large number of V-(D)-J junctions of T cell receptor (TCR) gamma and delta genes show that most fetal thymocytes express on their surface one of just two gamma delta TCRs known to be expressed by epidermal gamma delta T cells (s-IEL) or intraepithelial gamma delta T cells associated with female reproductive organs (r-IEL). In contrast, gamma delta TCRs expressed on adult thymocytes are highly diverse as a result of multiple combinations of gene segments as well as junctional deletions and insertions, indicating that developmental time-and cell lineage-dependent mechanisms exist that control the extent of gamma delta TCR diversity. In addition, this study revealed a new type of junctional insertion (P nucleotides), which led to a new model of V-(D)-J joining generally applicable to immunoglobulin and TCR genes.