Assembly of productive T cell receptor delta variable region genes exhibits allelic inclusion

The generation of a productive "in-frame" T cell receptor beta (TCR beta), immunoglobulin (Ig) heavy (H) or Ig light (L) chain variable region gene can result in the cessation of rearrangement of the alternate allele, a process referred to as allelic exclusion. This process ensures that most alphabeta T cells express a single TCR beta chain and most B cells express single IgH and IgL chains. Assembly of TCR alpha and TCR gamma chain variable region genes exhibit allelic inclusion and alphabeta and gammadelta T cells can express two TCR alpha or TCR gamma chains, respectively. However, it was not known whether assembly of TCR delta variable regions genes is regulated in the context of allelic exclusion. To address this issue, we have analyzed TCR delta rearrangements in a panel of mouse splenic gammadelta T cell hybridomas. We find that, similar to TCR alpha and gamma variable region genes, assembly of TCR delta variable region genes exhibits properties of allelic inclusion. These findings are discussed in the context of gammadelta T cell development and regulation of rearrangement of TCR delta genes.     

A TCR alpha chain transgene induces maturation of CD4- CD8- alpha beta+ T cells from gamma delta T cell precursors

The proportion of CD4- CD8- double-negative (DN) alpha beta T cells is increased both in the thymus and in peripheral lymphoid organs of TCR alpha chain-transgenic mice. In this report we have characterized this T cell population to elucidate its relationship to alpha beta and gamma delta T cells. We show that the transgenic DN cells are phenotypically similar to gamma delta T cells but distinct from DN NK T cells. The precursors of DN cells have neither rearranged endogenous TCR alpha genes nor been negatively selected by the MIsa antigen, suggesting that they originate from a differentiation stage before the onset of TCR alpha chain rearrangements and CD4/CD8 gene expression. Neither in-frame V delta D delta J delta nor V gamma J gamma rearrangements are over-represented in this population. However, since peripheral gamma delta T cells with functional TCR beta gene rearrangements have been depleted in the transgenics, we propose that the transgenic DN population, at least partially, originates from the precursors of those cells. The present data lend support to the view that maturation signals to gamma delta lineage-committed precursors can be delivered via TCR alpha beta heterodimers.     

Recombinant soluble alphabeta T cell receptors protect T cells from immune suppression: requirement for aggregated multimeric, disulfide-linked alphabeta heterodimers

Recombinant soluble T cell receptors (sTCR) protected contact sensitivity (CS) effector T cells from down-regulation or immunosuppression. CS-protecting sTCR were released enzymatically from the surface of thymoma cells transfected with cDNAs encoding TCR-alpha and -beta extracellular domains that were expressed with a phosphatidylinositol linkage. sTCR affinity purified on anti-TCR-alpha and anti-TCR-beta mAb columns had identical CS-protective activity, as did sTCR from a CD4+ Th2 clone or from a CD8+ cytotoxic clone. Reduced sTCR alpha- and beta-chains had no CS-protective activity, but this was restored when the TCR chains were rejoined into disulfide-linked alphabeta heterodimers. sTCR CS protection was Ag nonspecific, MHC unrestricted, and not influenced by the relevant synthetic peptide specific for the TCR complexed with appropriate MHC. CS protection may have resided in the sTCR constant region. When heated at 62 degrees C for 30 min, sTCR formed a CS-protecting aggregate, with a molecular mass of 481 +/- 37 kDa, corresponding to an alphabeta TCR pentamer. HPLC gel filtration essentially confirmed the molecular mass at 516 kDa for the multimer, while the monomer, which was an alphabeta TCR heterodimer, had an expected molecular mass of approximately 104 kDa and no bioactivity. In summary, the pentameric sTCR may bind to and activate lymphoid cells, perhaps via constant domains, resulting in protection of CS effector T cells from down-regulation. The ability of sTCR to protect CS effector T cells from down-regulation/suppression, if generalized, could overcome immunosuppression accompanying infectious diseases, particularly AIDS, or in tumors.     

Gamma delta T cells of the murine vagina: T cell response in vivo in the absence of the expression of CD2 and CD28 molecules

While little is known about their activation requirements and function, the intraepithelial T cells of the murine vagina express TCR complexes in which the antigen recognition components and the signaling components have unusual features. These vaginal T cells express an invariant V gamma 4/V delta 1 TCR and appear to be the only intraepithelial gamma delta T cells that exclusively use FcR gamma chains in their TCR complex. To further characterize the vaginal gamma delta T cells we isolated them from normal mice and from mice injected systemically with an activation-inducing dose of anti-TCR mAb. The isolated gamma delta T cells were examined by flow cytometry for their surface expression of a panel of adhesion, proteins, activation antigens and cellular interaction molecules (CD44, CD62L, CD45RB, LFA-1, CD2 and CD28). The patterns of expression observed indicate that the vaginal gamma delta T cells of normal mice show the phenotype of effector T cells. The adhesion/co-stimulatory molecules CD28 and CD2 were not detected on vaginal gamma delta T cells, an interesting finding since the absence of CD2 from other T cells has been suggested to result in anergy. However, vaginal gamma delta T cells are responsive to TCR-mediated signals since injection of normal mice with pan-anti-TCR antibody or stimulating anti-gamma delta TCR antibody resulted in an increase in cell number and increased expression of transferrin and IL-2 receptors. These results indicate that vaginal gamma delta T cells might utilize other co-stimulatory molecules, if any, in connection with TCR-induced activation and differentiation. While the physiological function of vaginal gamma delta T cells remains unknown, the expression of an invariant V gamma 4/V delta 1 TCR, their exclusive use of gamma chain homodimers in their TCR, and the absence of CD2 and CD28 co-stimulatory molecules are a novel combination of properties that suggests specialized functional properties. Although vaginal gamma delta T cells share some features in common with gamma delta T cells that reside in other epithelial tissues, such as skin and intestine, the present studies provide additional evidence that vaginal gamma delta T cells are a highly specialized and distinct T cell population.     

Differential T cell receptor photoaffinity labeling among H-2Kd restricted cytotoxic T lymphocyte clones specific for a photoreactive peptide derivative. Labeling of the alpha-chain correlates with J alpha segment usage

Using a direct binding assay based on photoaffinity labeling, we studied the interaction of T cell receptor (TCR) with a Kd-bound photoreactive peptide derivative on living cells. The Kd-restricted Plasmodium berghei circumsporozoite (PbCS) peptide 253-260 (YIPSAEKI) was reacted NH2-terminally with biotin and at the TCR contact residue Lys259 with photoreactive iodo, 4-azido salicylic acid (IASA) to make biotin-YIPSAEK(IASA)I. Cytotoxic T lymphocyte (CTL) clones derived from mice immunized with this derivative recognized this conjugate, but not a related one lacking the IASA group nor the parental PbCS peptide. The clones were Kd restricted. Recognition experiments with variant conjugates, lacking substituents from IASA, revealed a diverse fine specificity pattern and indicated that this group interacted directly with the TCR. The TCR of four clones could be photoaffinity labeled by biotin-YIPSAEK(125IASA)I. This labeling was dependent on the conjugates binding to the Kd molecule and was selective for the TCR alpha (2 clones) or beta chain (1 clone), or was common for both chains (1 clone). TCR sequence analysis showed a preferential usage of J alpha TA28 containing alpha chains that were paired with V beta 1 expressing beta chains. The TCR that were photoaffinity labeled at the alpha chain expressed these J alpha and V beta segments. The tryptophan encoded by the J alpha TA28 segment is rarely found in other J alpha segments. Moreover, we show that the IASA group interacts preferentially with tryptophan in aqueous solution. We thus propose that for these CTL clones, labeling of the alpha chain occurs via the J alpha-encoded tryptophan residue.     

CD8 dimer usage on alpha beta and gama delta T lymphocytes from equine lymphoid tissues

Eight murine monoclonal antibodies (mAb) were used to identify the equine CD8 alpha or CD8 beta chains and to define the expression of these chains on lymphocytes from various lymphoid tissues. CD8 alpha was a 39 kDa protein and CD8 beta was a 32 kDa protein. Both chains were expressed on most of the CD8+ T lymphocytes in the peripheral blood, spleen, thymus, mesenteric lymph nodes and ileal intraepithelial lymphocytes (IEL), however, in each lymphoid compartment a percentage of lymphocytes expressed only the CD8 alpha chain. The largest percentage of CD8 alpha alpha expressing T lymphocytes was 37.7% of the IELs. Purified T lymphocytes from the ileum expressing CD8 alpha beta co-expressed the alpha beta T cell receptor (TCR). In contrast, purified CD8+ T lymphocytes from the PBMC co-expressed either the alpha beta or gamma delta TCR by RT-PCR. Use of pooled anti-CD8 alpha mAb of the murine IgG2a isotype and rabbit complement resulted in lysis of the entire CD8 expressing population in peripheral blood mononuclear cells (PBMC). These results indicated that CD8 dimer usage by equine T lymphocytes is similar to other species and that the mAb described can be further used to separate equine CD8+ T lymphocyte subsets from the lymphoid tissues to define their function in protection against viral and other infections.     

A novel subset of adult gamma delta thymocytes that secretes a distinct pattern of cytokines and expresses a very restricted T cell receptor repertoire

We have characterized the function, phenotype, ontogenic development, and T cell receptor (TCR) repertoire of a subpopulation of gamma delta thymocytes, initially defined by expressing low levels of Thy-1, that represents around 5% and 30% of total gamma delta thymocytes in adult C57BL/6 and DBA/2 mice, respectively. Activation of FACS-sorted Thy-1dull gamma delta thymocytes from DBA/2 mice with anti-gamma delta monoclonal antibodies in the presence of interleukin-2 (IL-2) results in the secretion of high levels of several cytokines, including interferon-gamma (IFN-gamma), IL-4, IL-10, and IL-3. In contrast, only IFN-gamma was detected in parallel cultures of Thy-1bright gamma delta thymocytes. Virtually all Thy-1dull gamma delta thymocytes express high levels of CD44 and low levels of the heat-stable antigen and CD62 ligand, while around half of them express the NK1.1 marker. Thy-1dull gamma delta thymocytes are barely detectable in newborn animals, and their representation increases considerably during the first 2 weeks of postnatal life. The majority of Thy-1dull gamma delta thymocytes from DBA/2 mice express TCR encoded by the V gamma 1 gene and a novel V delta 6 gene named V delta 6.4. Sequence analysis of these functionally rearranged gamma and delta genes revealed highly restricted V delta-D delta-J delta junctions, and somewhat more diverse V gamma-J gamma junctions. We conclude that Thy-1dull gamma delta thymocytes exhibit properties that are equivalent to those of natural killer TCR alpha beta T cells. Both cell populations produce the same distinct pattern of cytokines upon activation, share a number of phenotypic markers originally defined for activated or memory T cells, display similar postnatal kinetics of appearance in the thymus and express a very restricted TCR repertoire.     

Close phenotypic and functional similarities between human and murine alphabeta T cells expressing invariant TCR alpha-chains

Several studies have demonstrated the existence of a murine NK1.1+ alphabeta T cell subset expressing V alpha14+ TCR alpha-chains with highly conserved invariant junctional sequences and able to secrete Th2 cytokines when exposed to CD1+ stimulator cells. In humans, alphabeta T cells carrying invariant V alpha24+ TCR alpha-chains highly homologous to those expressed by murine NK1.1 cells have been recently described. Here we show that these cells (referred to as V alpha24inv T cells) and murine NK1.1+ alphabeta T cells resemble each other in several ways. First, like their murine counterparts, T cells expressing high levels of V alpha24inv TCRs can be either CD4- CD8- double negative (DN) or CD4+, but they never express heterodimeric CD8 molecules. Second, most V alpha24inv T cells are brightly stained by NKRP1-specific mAb but not by mAb directed against other type II transmembrane proteins of the NK complex. Third, DN and particularly CD4+ V alpha24inv T cells are greatly enriched for IL-4 producers. The concomitant expression of highly conserved TCRs of a particular set of NK markers and of Th2 cytokines in human and murine alphabeta T cells suggests a coordinate acquisition of these phenotypic and functional properties. Furthermore, the relatively high frequency of human V alpha24inv T cells, which are presently shown to represent on average 1/500 PBL, and the high interindividual variations of the size of this cell subset under physiologic conditions go for a major role played by alphabeta T cells carrying invariant TCR in a large array of immune responses.     

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CD4-CD8- (double negative [DN]) alpha/beta T cells are a largely uncharacterized subpopulation of unknown function. To investigate whether these cells are selected to recognize particular antigens or antigen-presenting molecules, DN alpha/beta T cells were purified from the peripheral blood of five normal donors and their T cell receptor (TCR) alpha and beta chains were examined. Random cloning of TCR alpha chains by single-sided polymerase chain reaction (PCR) amplification identified an invariant rearrangement between V alpha 24 and J alpha Q, with no N region diversity, which was expressed preferentially by DN alpha/beta T cells from all donors. Random cloning also identified a precise V alpha 7.2-J alpha (IGRJa14) rearrangement, with two variable amino acids encoded in the V-J junction, which was enriched in the DN alpha/beta T cell preparations from some, but not all, donors. Analysis of TCR beta chains by quantitative PCR amplification demonstrated that the expression of four V beta gene families, V beta 2, 8, 11, and 13, was markedly increased in these DN alpha/beta T cell preparations. The expression of particular TCRs by DN alpha/beta T cells from multiple donors indicates that these cells, or at least a subpopulation of cells with this phenotype, recognize a limited spectrum of antigens and suggests that they may use nonpolymorphic antigen-presenting molecules.     

TCR-gamma delta cells in CD3 zeta-deficient mice contain Fc epsilon RI gamma in the receptor complex but are specifically unresponsive to antigen

Unlike TCR-alpha beta cells, TCR-gamma delta cells express a distinct member of the zeta family, the gamma-chain of Fc epsilon RI (Fc epsilon RI gamma) within the TCR complex. To study the role of the Fc epsilon RI gamma-chain in TCR-gamma delta cells, a TCR-gamma delta transgenic mouse (G8) has been crossed with CD3 zeta-chain-deficient mice (G8.zeta-/-). Thy-1+ spleen and lymph node cells of these animals expressed low levels of CD3/TCR. These results suggested that the zeta-chain is required for effective TCR transport to the cell surface. In contrast, intraepithelial TCR-gamma delta cells of G8.zeta-/- mice expressed high levels of TCR. Immunoprecipitation with anti-CD3 showed that Fc epsilon RI gamma-chains were associated with the TCR complex in T cells isolated from zeta-deficient mice. Although the Fc epsilon RI gamma-expressing T cells proliferated in response to stimulation by TCR-specific Abs including anti-CD3 epsilon, anti-pan gamma delta, and anti-V gamma 2 mAb, the G8.zeta-/- T cells did not respond to the G8-specific Ag (T10b), anti-Thy-1 mAb, or Con A. The unresponsiveness to the Ag was not due to the reduced TCR expression, because intraepithelial TCR-gamma delta cells from the zeta-deficient mice did not respond to Ag. The inability of the G8.zeta-/- T cells to respond to Ag could not be overcome by providing an anti-CD28 costimulatory signal or by adding exogenous rIL-2. Taken together, our data suggest that the Fc epsilon RI gamma-chain associates with the TCR-gamma delta complex in the absence of the zeta-chain, but it is not able to substitute for the zeta-chain for effective transport of TCR to the cell surface or functional responses to Ag.     

Rearrangement of T-cell receptor delta/gamma genes: application to the study of clonality in childhood B-lineage acute lymphoblastic leukaemia

DNA-based PCR with various sets of primers for T-cell receptor gamma/delta (TCR gamma/delta) chain genes was used to study clonality in childhood B-lineage acute lymphoblastic leukaemia. TCR delta genes rearrangements were the most common and were observed in 77 patients (64.2%). The typical pattern of rearrangements was defined as an incomplete V delta 2 to D delta 3 or to D delta 2 recombination product. Rearrangements of TCR gamma genes were observed in 61 cases (50.8%). Predominantly, TCR gamma genes rearrangements were detected in null-ALL and the early B-ALL (55.2% and 60%, respectively) and were rather rare in other groups. From all eight V segments of V gamma l group rearrangements concerned mostly regions V gamma 2, V gamma 4 and V gamma 7. We have confirmed that TCR gamma and delta genes amplification provides a rapid, sensitive method for assessing clonality in ALL almost in 100%.     

Diminution of the number of gamma delta T lymphocytes in hepatocellular carcinoma patients treated with transcatheter arterial embolization

gamma delta T lymphocytes, which are CD3+ lymphocytes that express gamma delta chains of the T-cell antigen receptor (TCR) on their surface, are functionally distinct from alpha beta T lymphocytes, which express alpha beta chains of the TCR. gamma delta T lymphocytes are thought to differentiate in mouse hepatic sinusoids, to play a role in antitumor action, and to act as natural killer cells. The purpose of this study was to examine whether gamma delta T lymphocytes in the peripheral blood are suppressed when hepatic sinusoids are damaged during transcatheter arterial embolization (TAE). The numbers of alpha beta T lymphocytes and gamma delta T lymphocytes in the peripheral blood were examined with monoclonal antibodies and flow cytometry before and after TAE in 32 patients (from 46 to 78 years of age) with liver cirrhosis and hepatocellular carcinoma. The number of alpha beta T lymphocytes before and after TAE was unchanged. However, the number of gamma delta T lymphocytes and the ratio of gamma delta T lymphocytes to CD3+ lymphocytes were significantly decreased for 3 weeks after TAE treatment. This decrease suggests that TAE suppresses the supply of gamma delta T lymphocytes to the peripheral blood. In addition, TAE may weaken a patient's antitumor immunity, because gamma delta T lymphocytes that have antitumor activity decrease after TAE.     

Chemokine expression by intraepithelial gamma delta T cells. Implications for the recruitment of inflammatory cells to damaged epithelia

T cells expressing gamma delta TCR may have evolved to recognize Ag in a different manner as well as perform a broader set of functions than T cells with alpha beta TCR. In this study, we tested the hypothesis that dendritic epidermal T cells (DETC) bearing the invariant V gamma 3V delta 1 TCR may be able to signal the migration of peripheral alpha beta T cells to the epidermis by secreting specific chemokines. Expression of macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta, RANTES, and lymphotactin was inducible in DETC 7-17 cells, whereas mRNA for monocyte chemoattractant protein (MCP)-1 could not be detected. Strikingly, lymphotactin was the most abundant chemokine produced by activated DETC 7-17 cells. Activated primary DETC cultures also produced copious amounts of lymphotactin mRNA. Similarly, freshly isolated and activated intestinal intraepithelial T cells (i-IEL) with gamma delta TCR expressed high levels of lymphotactin mRNA. In contrast, lymphotactin mRNA was present in activated spleen gamma delta T cells at low basal levels. Migration of CD8+ T cells induced by culture supernatants from stimulated DETC 7-17 cells was strongly reduced in the presence of a neutralizing anti-lymphotactin antiserum and to a lesser extent by neutralizing anti-MIP-1 alpha, anti-MIP-1 beta, or anti-RANTES antiserum. The presence of lymphotactin in supernatants from activated DETC 7-17 cultures was directly demonstrated by Western blot analysis. These observations are consistent with a model in which gamma delta IEL play an active multi-faceted role in the maintenance of epithelia homeostasis.     

Preferential but not exclusive T cell receptor V beta chain utilization of myelin basic protein and peptide-specific T cell clones in mice

The repertoire of T cell receptor (TCR) V beta chain utilization was investigated in PL/J, CXJ-1, SJL/J and B10.S-->SJL/J chimeric mice in response to either myelin basic protein (MBP) or the strain-specific encephalitogenic peptide. Our analysis showed that there was an overlapping predominance in the TCR V beta gene utilization in the MBP-specific responses, which were independent of the major histocompatibility complex (MHC) class II haplotype present, and the immunodominant peptide region recognized in these different strains. In those mice having the TCR V beta b haplotype (PL/J, CXJ-1, and the B10.S-->SJL chimera) either the TCR V beta 4, 8, and 13 or the TCR V beta 4, 6, and 13 predominated. In contrast, in mice with TCR V beta a haplotype (SJL/J) V beta 4, 6, and 17a were found. However, the quantitative distribution of these preferentially utilized TCR V beta chains in each strain was defined by the MHC class II haplotype and the immunodominant peptide recognized. The expression of the V beta 8 gene product in the peripheral TCR repertoire did not always correlate with predominant V beta 8 utilization in the MBP-specific response.     

Isolation and characterization of a carbonic anhydrase homologue from the zebrafish (Danio rerio)

Lymphomas with T-cell phenotype represent a heterogeneous group of diseases differing in histopathology, tumour site, and cell origin. They include peripheral T-cell lymphomas (PTCLs) derived from alpha beta cells, but also some recently recognized entities such as gamma delta, hepatosplenic lymphomas and natural killer (NK) cell lymphomas. Only a few studies have investigated the possibility that at least some PTCLs could be derived from lymphocytes with cytotoxic potential. In order to investigate this possibility, 60 cases of PTCL, including 27 cases expressing the alpha beta T-cell receptor (TCR alpha beta), 15 TCR gamma delta cases and 18 cases expressing neither TCR (TCR silent), as well as 14 cases of NK-cell lymphomas, were studied by immunohistochemistry for the expression of TIA-1, perforin, and granzyme B proteins. Expression of TIA-1 is characteristic of cytotoxic cells regardless of their activation status, whereas expression of perforin and granzymes is highly increased in activated cytotoxic cells and correlates with the induction of cytolytic activity. All NK-cell lymphomas (11 sinonasal, three systemic cases) expressed TIA-1, perforin, and granzyme B in most tumour cells. All gamma delta PTCLs (15 cases) expressed TIA-1 protein in most tumour cells, with a different cytotoxic antigen profile in hepatosplenic gamma delta PTCL (TIA-1+, perforin-, granzyme B-) and in non-hepatosplenic gamma delta PTCLs (three nasal, one skin, one lung), the latter expressing the three cytotoxic proteins. Of the 45 cases of alpha beta and TCR silent PTCL, 15 (33 per cent) were considered to be derived from cytotoxic lymphocytes with expression of at least one cytotoxic protein (TIA-1, 15/45; perforin, 10/41; granzyme B, 14/38) in tumour cells. This cytotoxic protein expression appeared to be related to the site of localization, since 7/13 (54 per cent) extranodal and only 8/32 (25 per cent) nodal alpha beta and TCR silent PTCLs expressed TIA-1, and to histology, since this pattern was observed in a proportion of anaplastic (6/8, 75 per cent) and pleomorphic (8/17, 47 per cent) lymphomas, but not in AILD-type NHL (0/16). Taken together, our data suggest that NK-cell lymphomas and non-hepatosplenic gamma delta PTCLs represent tumours of activated cytotoxic NK cells and gamma delta T cells, respectively; that hepatosplenic gamma delta PTCLs represent tumours of non-activated cytotoxic gamma delta T cells; and that a small proportion of alpha beta and TCR silent PTCLs, mostly extranodal cases, or nodal anaplastic lymphomas, represent tumours of cytotoxic T cells.     

Control of self-reactive cytotoxic T lymphocytes expressing gamma delta T cell receptors by natural killer inhibitory receptors

The majority of peripheral blood gamma delta T cells in human adults expresses T cell receptors (TCR) with identical V regions (V gamma 9 and V delta 2). These V gamma 9 V delta 2 T cells recognize the major histocompatibility complex (MHC) class I-deficient B cell line Daudi and broadly distributed nonpeptidic antigens present in bacteria and parasites. Here we show that unlike alpha beta or V gamma 9- gamma delta T cells, the majority of V gamma 9V delta 2 T cells harbor natural killer inhibitory receptors (KIR) (mainly CD94/NKG2A heterodimers), which are known to deliver inhibitory signals upon interaction with MHC class I molecules. Within V gamma 9V delta 2 T cells, KIR were mainly expressed by clones exhibiting a strong lytic activity against Daudi cells. In stark contrast, almost all V gamma 9V delta 2 T cell clones devoid of killing activity were KIR-, thus suggesting a coordinate acquisition of KIR and cytotoxic activity within V gamma 9V delta 2 T cells. In functional terms, KIR inhibited lysis of MHC class I-positive tumor B cell lines by V gamma 9V delta 2 cytotoxic T lymphocytes (CTL) and raised their threshold of activation by microbial antigens presented by MHC class I-positive cells. Furthermore, masking KIR or MHC class I molecules revealed a TCR-dependent recognition by V gamma 9V delta 2 CTL of ligands expressed by activated T lymphocytes, including the effector cells themselves. Taken together, these results suggest a general implication of V gamma 9V delta 2 T cells in immune response regulation and a central role of KIR in the control of self-reactive gamma delta CTL.     

Reactions of anti-immunoglobulin sera with synthetic T cell receptor peptides: implications for the three-dimensional structure and function of the TCR beta chain

The derived amino acid sequence of the human TCR beta chain shows considerable homology to lg lambda light chains in its variable (V) and constant (C) domains, and in its joining segment (J). We assessed the cross-reactivity between TCR beta chains and lg light chains by synthesizing a set of nested, overlapping 16-mer peptides that duplicated the sequence that corresponds to the continuous VDJC sequence of TCR beta chain and determining the capacity of rabbit antisera to human or murine lgs to react with these peptides. The reactivities we observed were consistent with homologies to lambda and kappa light chains. The strongest reactivity in ELISA binding and competitive inhibition was with a peptide that corresponds to the 'switch peptide' of light chains. The sequence is encoded by the C-terminal region of the J segment (Fr4) and the N-terminus of the C region. Other regions reactive with anti-light chain sera corresponded respectively to CDR1 and Fr3 segments of the V region, and a segment of the constant region predicted to loop out of the tight globular structure. The peptide immunochemical results, coupled with the identification of specific regions of sequence correspondence between TCR beta and the characterized lambda light chain Mcg, allowed us to develop a three-dimensional model of the beta chain consistent with its role in antigen recognition and response to superantigens.