Further evidence for a gamma/delta T cell receptor-mediated TCT.1/CD48 recognition.

We have demonstrated recently that a molecule, termed TCT.1 (Blast-1/CD48), is recognized on the surface of target cells by a series of alloreactive gamma/delta T cell clones generated from PBL of one healthy individual (designated E). Southern blot analyses suggested that these clones express a TCR associating a V3-JP2-C2 gamma-chain and V1-D-J1-C delta-chain. In the present study, we have developed from PBL of a second normal donor (designated G) a novel series of gamma/delta cloned T cell lines with similar functional activity (i.e., specific recognition of TCT.1 protein). The TCR gamma- and delta-chain nucleotide sequences of both the E and G clones were determined. Results show that 1) sequences from all the clones are identical in each individual donor, 2) the delta-chains expressed by the E and the G clones are encoded by distinct gene rearrangements including V1-D-J delta 1 and V1-D-J delta 2, respectively, 3) the gamma-chains expressed by the E and the G clones are encoded by the same genomic variable elements, namely V gamma 3 and JP2, whereas the junctional regions are distinct. Because the latter rearrangement is very infrequent in human peripheral blood, these data support the view that TCT.1/CD48 recognition is likely to be TCR dependent.     

Distribution of T cells bearing different forms of the T cell receptor gamma/delta in normal and pathological human tissues

Frozen sections from normal and pathologic human tissues were immunostained by the APAAP technique with three mAb directed against different epitopes of the TCR gamma delta; TCR delta 1 which binds to all cells bearing the TCR gamma delta; BB3 and delta TCS1 which, by immunoprecipitation studies, appear to react respectively with the disulfide-linked and nondisulfide-linked form of the TCR gamma delta. In normal thymus, TCR delta 1+ cells accounted for approximately 2% of the CD3+ thymocytes and were about three times more numerous in the medulla than in the cortex. TCR delta 1+ cells were mostly constituted by the delta TCS1 reactive subset (average ratio delta TCS1/BB3: 3.7). In the tonsil, the TCR delta 1+ cells (about 3% of CD3+ elements) were mainly located in the interfollicular area, where they frequently tended to arrange around high endothelium venules. In most samples, TCR delta 1+ cells were distributed beneath to the tonsil epithelium. Unlike thymus, the majority of TCR delta 1+ cells were usually constituted by the BB3-reactive subset (average BB3/delta TCS1 ratio: 2.0). A similar predominance of BB3+ over delta TCS1+ cells was also observed in normal peripheral blood. The spleen was the organ with the highest concentration of TCR delta 1+ cells that, like in the thymus, were mostly represented by delta TCS1+ elements. Noteworthy, the TCR delta 1+ cells were preferentially located in the splenic sinusoids while TCR alpha beta-bearing lymphocytes mostly occupied the periarteriolar sheaths of penicilliary arteries. The majority of neoplastic T cell proliferations studied lacked to express the TCR gamma delta. Two cases of beta F1-(TCR alpha beta-) T lymphoblastic lymphoma, however, were TCR gamma delta+ (delta TCS1+/BB3-). Both of them showed a stage II cortical phenotype, e.g., CD1+/CD3+/CD4+/CD8+/TCR delta 1+. Among inflammatory conditions, an increase of BB3+ cells was observed in close association with necrotic areas in cases of Kikuchi's and tuberculous lymphadenitis. The significance of this finding is under study.     

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.     

Immunohistochemical characterization,distribution and ultrastructure of lymphocytes bearing the gamma/delta T-cell receptor in the human gut

The phenotypic characterization and distribution of lymphocytes bearing the gamma/delta T-cell receptor (TCR) in the human gut were investigated by an immunohistochemical technique. A mirror section technique and double staining method were used for the phenotypic analysis. Intraepithelial delta-positive cells were almost all CD8-positive and rarely negative for both CD4 and CD8. On the other hand, lymphocytes bearing TCR gamma/delta in the lamina propria were largely negative for both CD4 and CD8. The ratio of delta-positive to CD3-positive cells amongst intraepithelial lymphocytes was larger in the lower intestine. Delta-positive cells were also observed in paracortical areas of lymphoid follicles. Immunoelectron microscopic observation revealed granular structures in these delta-positive cells, which are also present in large granular lymphocytes. The role of lymphocytes bearing TCR gamma/delta in mucosal immune responses in the human gut are discussed.     

T cell differentiation model based on the expression of T cell receptor chains and genes--study in the human leukemia/lymphoma cell lines

A total of 33 human leukemia/lymphoma cell lines were classified into 4 groups with respect to the pattern of cell membrane (sm) expression of the CD3 and T cell receptor (TCR) molecules; (i) smCD3+TCR alpha beta (16 cell lines), (ii) smCD3+TCR beta delta (1 cell line), (iii) smCD3+TCR gamma delta (3 cell lines) amd (iv) smCD3-TCR- (13 cell lines), respectively. Using monoclonal antibodies (MoAbs) specific to CD3 (NU-T3), TCR alpha chain (alpha F1), TCR beta chain (beta F1), and TCR gamma chain (C gamma M1), respectively, cytoplasmic (cy) expression of these molecules was determined by immunofluorescence test. Expression of cyCD3 was present in all cell lines regardless of groups. In group (i), all 16 cell lines expressed both TCR alpha and beta chains. While only TCR beta chain was expressed in group (ii), TCR gamma chain was expressed in all 3 cell lines of group (iii). One (PEER) of the three in group (iii) expressed TCR beta chain as well. In group (iv), we found 8 cell lines with cyTCR alpha expression, 11 cell lines with cyTCR beta expression, and 10 cell lines with cyTCR gamma expression, respectively. For TCR genes, except 1 cell line all cell lines were found to present rearranged C beta gene and its mRNA, including all 3 TCR gamma/delta cell lines of group (iii). One of the TCR alpha beta cell lines exhibited rearranged C delta and J delta genes as well as its mRNA. Two cell lines of the 13 CD3-TCR- of group (iv) exhibited rearranged C delta and J delta and its mRNA. An NK-like activity and IL-2 production were induced in the TCR beta delta and gamma delta cell lines [group (ii) and (iii)] by treatment with PHA and PMA.     

Human T cell receptor-gamma and -delta chain pairing analyzed by transfection of a T cell receptor-delta negative mutant cell line

Specific TCR V gamma and V delta segments are found to be coordinately used on subpopulations of gamma delta T lymphocytes. The reasons for this phenomenon are unknown, but may include the inability of particular chains expressing unique V delta and V gamma segments to physically associate. V delta 2 is typically used together with V gamma 2 on human peripheral blood gamma delta T lymphocytes. To examine whether V delta 2 can be used in conjunction with distinct V gamma segments, a TCR- mutant of the human gamma delta T cell line MOLT-13, which expresses parental TCR gamma (V gamma 1.3) but not TCR-delta protein, was transfected with plasmids containing full-length TCR-delta cDNA using either V delta 2 or V delta 3. TCR reconstitution was successful in both transfectants and resulted in TCR protein and RNA levels similar to that of the parental MOLT-13 cell line. These cell lines could be activated through their receptors as assessed by increases in cytoplasmic free calcium. These studies imply that physical constraints cannot explain the observed chain pairing preferences. Other possible explanations are discussed.     

CD3.TCR1, a human CD3 epitope expressed on viable gamma/delta lymphocytes exclusively.

T lymphocytes express either the alpha/beta or the gamma/delta receptor (TCR) in a mutually exclusive fashion. Both structures are associated on the cell membrane with the CD3 proteins which are thought to transduce signals resulting from antigen recognition. The CD3 complex is present in both alpha/beta and gamma/delta cells and includes at least five proteins (designated gamma, delta, epsilon, zeta and eta). We have developed here a novel mAb, anti-CD3.TCR1, which immunoprecipitates the CD3 molecules from both alpha/beta and gamma/delta cells lysates following solubilization with Triton X-100. While the SDS-PAGE migration profile of the material recognized by either anti-CD3.TCR1 or anti-OKT3 are superimposable in both cell types, this mAb recognizes viable untreated gamma/delta T lymphocytes exclusively. These findings further support the view that molecular interactions within the TCR/CD3 protein complex are distinct in the two T lymphocyte populations.     

gamma delta T cells in the human intestine express surface markers of activation and are preferentially located in the epithelium

We have investigated the expression of the alpha beta and the gamma delta T cell receptor (TCR) in the human intestine. By immunohistology we found that 39% of CD3+ intraepithelial lymphocytes (IEL) expressed the gamma delta TCR compared to 3% of CD3+ lamina propria lymphocytes (LPL). Cytofluorometric analysis of isolated cells revealed a significantly higher proportion of gamma delta T cells among CD3+ IEL compared to LPL and peripheral blood lymphocytes. This was due to an increase in both CD8+ (low density) and CD4-CD8- gamma delta T cells in IEL. Most alpha beta IEL expressed high-density CD8. About 30% of both IEL and LPL expressed CD25 (alpha-chain of the IL-2 receptor). HML-1 expression was detected on nearly all IEL and on 27% of LPL. CD25 and HML-1 were preferentially expressed on intestinal alpha beta and gamma delta T cells, respectively. Thus, human gamma delta T cells are located preferentially in the gut epithelium and are phenotypically different from alpha beta T cells, which constitute the majority of both LPL and IEL.     

Characterization and expression of the human alpha beta T cell receptor by using a framework monoclonal antibody

A monoclonal antibody (mAb) with framework reactivity against the T cell receptor (TCR) alpha beta complex is characterized. The mAb, beta Framework 1 (beta F1) is capable of immunoprecipitating the TCR alpha beta complex from 125I-labeled human T cell tumors, immunocompetent T cell clones, and peripheral blood lymphocytes (PBL). beta F1 recognizes the separated TCR beta subunit in Western blotting. Because it does not bind to the surface of viable T cells but does react with the plasma membrane form of the TCR after treatment with membrane solubilizing agents, the beta F1 mAb reacts with a "hidden" determinant on the TCR beta subunit. After solubilization with 70% ethanol, the TCR alpha beta complex is shown to exist on greater than 92% of T3+ human PBL, whereas 2 to 8% of T3+ PBL do not react with the mAb. The beta F1 mAb demonstrates the existence of differently glycosylated surface 125I-labeled TCR alpha-chains (alpha, alpha', alpha") in association with a common TCR beta-chain on the HPB-MLT T cell leukemia. Reactivity of the beta F1 mAb on thymus tissue sections is similar to that of anti-Leu-4 (anti-T3). The beta F1 mAb should prove useful as a research tool for both the immunochemical characterization and isolation of virtually any alpha beta T cell receptor, whether from individual T cell clones or polyclonal populations of T lymphocytes. Recognition of T cell receptors in histologic tissue sections suggests that the beta F1 mAb may be useful in the clinical diagnosis of T cell lineage neoplasms. In failing to recognize all T3+ lymphocytes, it allows the identification of novel populations of T3+ lymphocytes that may express non-alpha, non-beta T cell receptors.     

人和猴T淋巴细胞表面TRBC受体和E受体的比例研究

In 1985, rosette formation of human and macaque pan-T lymphocytes with tree shrew red blood cells (TRBC) (TRBC rosette) was first found by Ben K et al, showing different physico-chemical properties from that of rosette formation with sheep red blood cells (E-rosette). In order to approach the correlation between TRBC receptor, E receptor (CD2) and other differentiation antigens (CDs) on T lymphocytes, rosette inhibition assay and antigenic modulation or co-modulation were performed with monoclonal antibodies (McAbs) to CDs, and the distribution of TRBC receptor in other peripheral immunocytes, cell lines was also examined. TRBC rosette appeared in 88.8% of E rosette positive peripheral blood lymphocytes (E(+)-PBL) and in 4.16% of E(-)-PBL. TRBC receptor was also found on all T cell lines tested (CEM, H33 HJ-JA 1, Jurkat, MLA-144, Molt-3, Molt-4, Molt-4 clone 8, PEER) and some myeloid lines (U 937 and HL 60), but not on human granulocytes, B cell lines (Daudi, Raji and Reh) and myeloid line K 562. The modulation or co-modulation of CD 3, TCR, CD 5, CD 6 and CD 7 with McAbs OKT 3, T 108 (F 1), T 136 (F 101-15), T 149 (M-T 604) and T 152 (7 G 5) did not affect TRBC rosette formation of PBL. TRBC rosette of human and rhesus monkey PBL was not inhibited by T 11.1 McAb OKT 11 (CD 2 McAb), in contrast human and rhesus monkey E rosette formations were obviously blocked at inhibition rates of 77.9% and 49.3%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Depletion of mouse alpha beta T cell antigen receptor bearing lymphocytes by neonatal monoclonal antibody treatment.

Neonatal treatment with a monoclonal antibody specific for the alpha beta TCR results in mice with a long term, severe depletion in the number of alpha beta T cells in the periphery. Significant numbers of T cells reappear in the periphery about age 65 days, but these cells tend to lack expression of CD4 or CD8. Splenocytes of antibody-treated mice are less sensitive to mitogen stimulation or stimulation with MHC allogeneic cells. The level of serum IgG but not IgM was decreased by the treatment. Anti-alpha beta TCR antibody treatment decreased single-positive T lymphocytes that express high levels of the CD3/alpha beta TCR complex from the thymus, suggesting that the treatment could act in part by affecting negative selection of alpha beta TCR+ thymocytes. This treatment does not, however, detectably affect either the homing or the numbers of gamma delta T cells which are abundant in the intestinal epithelium, but which remain a minor population in the spleen and lymph nodes. This supports the hypothesis that gamma delta T cells are developmentally autonomous from alpha beta T cells. These mice provide an excellent model system for assessing the developmental and functional role of gamma delta T lymphocytes in vivo.     

Assembly, intracellular processing, and expression at the cell surface of the human alpha beta T cell receptor/CD3 complex. Function of the CD3-zeta chain

The TCR/CD3 complex is a multimeric protein complex composed of a minimum of seven transmembrane chains (TCR alpha beta-CD3 gamma delta epsilon zeta 2). Whereas earlier studies have demonstrated that both the TCR-alpha and -beta chains are required for the cell surface expression of the TCR/CD3 complex, the role of the CD3 chains for the TCR/CD3 expression have not been experimentally addressed in human T cells. In this study the function of the CD3-zeta chain for the assembly, intracellular processing, and expression of the TCR/CD3 complex in the human leukemic T cell line Jurkat was investigated. The results indicate that: 1) CD3-zeta is required for the cell surface expression of the TCR/CD3 complex; 2) the pentameric form (TCR alpha beta-CD3 gamma delta epsilon) of the TCR/CD3 complex and single TCR chains associated with CD3 (TCR alpha-CD3 gamma delta epsilon and TCR beta-CD3 gamma delta epsilon) are produced in the endoplasmic reticulum in the absence of CD3-zeta; 3) the CD3-zeta does not associate with TCR alpha-CD3 gamma delta epsilon or TCR beta-CD3 gamma delta epsilon complexes; 4) CD3-zeta associate with the pentameric form of the TCR/CD3 complex in the endoplasmic reticulum to form the heptameric complex (TCR alpha beta-CD3 gamma delta epsilon----TCR alpha beta-CD3 gamma delta epsilon 2); and 5) CD3-zeta is required for the export of the TCR/CD3 complex from the endoplasmic reticulum to the Golgi apparatus for subsequent processing.     

A predominance of the T cell receptor V gamma 2/V delta 2 subset in human mycobacteria-responsive T cells suggests germline gene encoded recognition.

Little is known about the nature of Ag recognition by the TCR-gamma delta. The recent observation that gamma delta T cells preferentially recognize mycobacterial Ag provides a model to examine the molecular basis of gamma delta-TCR recognition. Here, examination of the Mycobacteria-stimulated peripheral blood T cells with TCR-specific mAb revealed a predominance of T cells bearing V gamma 2/V delta 2 gene products. PCR cloning and sequence analysis of the TCR chains demonstrated extensive junctional diversity indicating that the response was polyclonal. The marked in vitro gamma delta T cell response to Mycobacteria was also detected in newborns before encounters with foreign Ag and exclusively involved the same V-gene usage observed in adults. Together, these results suggest that a major mechanism of gamma delta T cell reactivity involves recognition mediated by germline-encoded segments of the TCR.     

Expression of human T cell receptor-gamma delta structural forms

The human TCR-gamma delta occurs in three biochemically distinct forms (forms 1, 2bc, and 2abc). A 40-kDa TCR gamma-chain is disulfide-linked to the TCR delta-chain in form 1, whereas 40-kDa or 55-kDa TCR-gamma polypeptides are noncovalently associated with the TCR delta-chain in forms 2bc and 2abc, respectively. Sequence analysis of TCR-gamma cDNA clones indicates that form 1 utilizes the C gamma 1 gene segment, whereas forms 2bc and 2abc appear to use allelic C gamma 2 gene segments containing either two copies (b and c) or three copies (a, b, and c) of the CII exon, respectively. We transfected TCR-gamma cDNA encoding form 1 or form 2abc into the MOLT-13 cell line that expresses form 2bc. The transfected TCR gamma-chains associate with the resident MOLT-13 TCR-delta, normally part of form 2bc, to yield CD3-associated TCR-gamma delta heterodimers identical to those seen on the donor cell lines (form 1 or 2abc). These transfection experiments show directly that, 1) when a single TCR-delta subunit is available, the presence or absence of disulfide linkage between TCR gamma- and TCR delta-chains is controlled by the TCR gamma-chain, and 2) the difference in the amount of N-linked carbohydrate attached to the transfected TCR-gamma proteins of form 2bc vs form 2abc is influenced by the presence or absence of CII exon copy "a" which appears to alter the secondary and/or tertiary structure of these TCR gamma-chain constant regions, thereby affecting the attachment of N-linked glycans. In contrast to the similar structure and usage of C beta 1 and C beta 2, TCR-gamma delta forms show striking differences in structure and are not equally represented in peripheral blood. Although the role of each form is unknown, it is possible that variable or joining-gene segment selection events or functional differences account for their unequal usage.     

The CD3-gamma and CD3-delta subunits of the T cell antigen receptor can be expressed within distinct functional TCR/CD3 complexes.

The T cell receptor for antigen (TCR) consists of two glycoproteins containing variable regions (TCR-alpha/beta or TCR-gamma/delta) which are expressed on the cell surface in association with at least four invariant proteins (CD3-gamma, -delta, -epsilon and -zeta). CD3-gamma and CD3-delta chains are highly homologous, especially in the cytoplasmic domain. The similarity observed in their genomic organization and their proximity in the chromosome indicate that both genes arose from duplication of a single gene. Here, we provide several lines of evidence which indicate that in human and murine T cells which expressed both the CD3-gamma and CD3-delta chains on their surface, the TCR/CD3 complex consisted of a mixture of alpha beta gamma epsilon zeta and alpha beta delta epsilon zeta complexes rather than a single alpha beta gamma delta epsilon zeta complex. First, a CD3-gamma specific antibody failed to co-immunoprecipitate CD3-delta and conversely, several CD3-delta specific antibodies did not coprecipitate CD3-gamma. Secondly, analysis of a panel of human and murine T cell lines demonstrated that CD3-gamma and CD3-delta were expressed at highly variable ratios on their surface. This suggested that these chains were not expressed as a single complex. Thirdly, CD3-gamma and CD3-delta competed for binding to CD3-epsilon in transfected COS cells, suggesting that CD3-gamma and CD3-delta formed mutually exclusive complexes. The existence of these two forms of TCR/CD3 complexes could have important implications in the understanding of T cell receptor function and its role in T cell development.     

A delta T-cell receptor deleting element transgenic reporter construct is rearranged in alpha beta but not gamma delta T-cell lineages.

T cells can be divided into two groups on the basis of the expression of either alpha beta or gamma delta T-cell receptors (TCRs). Because the TCR delta chain locus lies within the larger TCR alpha chain locus, control of the utilization of these two receptors is important in T-cell development, specifically for determination of T-cell type: rearrangement of the alpha locus results in deletion of the delta coding segments and commitment to the alpha beta lineage. In the developing thymus, a relative site-specific recombination occurs by which the TCR delta chain gene segments are deleted. This deletion removes all D delta, J delta, and C delta genes and occurs on both alleles. This delta deletional mechanism is evolutionarily conserved between mice and humans. Transgenic mice which contain the human delta deleting elements and as much internal TCR delta chain coding sequence as possible without allowing the formation of a complete delta chain gene were developed. Several transgenic lines showing recombinations between deleting elements within the transgene were developed. These lines demonstrate that utilization of the delta deleting elements occurs in alpha beta T cells of the spleen and thymus. These recombinations are rare in the gamma delta population, indicating that the machinery for utilization of delta deleting elements is functional in alpha beta T cells but absent in gamma delta T cells. Furthermore, a discrete population of early thymocytes containing delta deleting element recombinations but not V alpha-to-J alpha rearrangements has been identified. These data are consistent with a model in which delta deletion contributes to the implementation of a signal by which the TCR alpha chain locus is rearranged and expressed and thus becomes an alpha beta T cell.     

In vitro and in vivo activation of murine gamma/delta T cells induces the expression of IgA, IgM, and IgG Fc receptors.

The present studies examined resting and activated murine gamma/delta T lymphocytes, in vitro and in vivo, for surface expression of FcR. Polyclonal gamma/delta TCR+ lymphocytes selectively grown from the spleen and intestine of normal mice did not express FcR when the cells were in a resting state, but when cells were activated with anti-CD3 antibody virtually all of the splenic gamma/delta lymphocytes and a large subpopulation of the intestinal gamma/delta lymphocytes expressed IgA and IgM FcR. This was confirmed by using transgenic mice. Resting gamma/delta TCR+ lymphocytes from the spleen, thymus, lymph node, and blood of gamma/delta TCR transgenic mice did not express FcR for any of the five major classes of Ig H chains. Activation of the gamma/delta TCR+ cells via the CD3/TCR complex induced high levels of IgM and IgA FcR and low levels of IgG FcR. Finally, in hepatic granulomas of schistosome-infected mice, activated gamma/delta TCR+ cells are present and express high levels of IgA and IgM FcR and low levels of IgG FcR. These investigations establish that transition of gamma/delta TCR+ lymphocytes from a resting to an activated state (triggered via the T3Ti TCR complex) is accompanied by the induction of surface membrane receptors specific for Ig H chain isotypes. The activation-linked expression of FcR on gamma/delta TCR+ lymphocytes provides potential mechanisms for coupling the functional activities of gamma/delta T lymphocytes with immune mechanisms that involve Ig molecules, such as antibody-dependent cellular cytotoxicity.     

Introduction of T cell receptor (TCR)-alpha cDNA has differential effects on TCR-gamma delta/CD3 expression by PEER and Lyon-1 cells

A TCR heterodimer composed of a TCR gamma-chain and a TCR delta-chain was found to be expressed in association with CD3 by a small population of human peripheral blood T cells, thymocytes, and certain leukemic T cell lines. The leukemic T cell lines PEER and Lyon-1 express such a TCR-gamma delta/CD3 complex at the cell surface. In addition, PEER and Lyon-1 cells transcribe a productively rearranged TCR-beta gene. Introduction of TCR alpha-chain cDNA of human or murine origin resulted in cell surface expression of a TCR-alpha beta/CD3 complex on PEER and Lyon-1 cells. The expression of the TCR-gamma delta/CD3 complex on PEER cells was not affected by introduction of TCR-alpha cDNA. In contrast, introduction of a TCR-alpha cDNA and expression of the TCR-alpha beta/CD3 complex in Lyon-1 cells resulted in the disappearance of the TCR-gamma delta/CD3 complex. These data were confirmed by indirect immunofluorescence, at the protein level and by gene expression analysis. Triggering of the TCR-alpha beta/CD3 complexes by anti-CD3 mAb or anti-TCR mAb resulted in increased internal Ca2+ levels, indicating that these receptors were functional in signal transduction. These results indicate that, besides TCR gene rearrangements, membrane expression of TCR-alpha beta heterodimers may be important in regulating TCR-gamma delta cell surface expression.