Development of T cell receptor expression: studies using T cell hybridomas

Production of CD4⁺ and CD8⁺ T cell hybridomas

T cell hybridomas are very useful tools to investigate antigen presenting cell (APC) function. They were developed based on the fusion technology that led to monoclonal antibody section. Antigen-specific primary T cells are generated and fused to an immortal thymoma line. Unfused thymoma cells are eliminated by engineered metabolic selection. Antigen-specific hybridomas are identified and may be characterized in detail. Primary T cells are preferable for studies of the regulatory mechanisms intrinsic to T cells, but for study of antigen presentation T cell hybridomas have advantages over primary T cell clones, including their relative uniformity, stability over time, and ready availability in large numbers for extensive antigen presentation experiments.

T cell hybridomas to study MHC-II restricted B-cell receptor-mediated antigen presentation by human B cells

MHC-II antigen presentation by B cells is essential in order for B cells to receive optimal costimulation from helper CD4+ T cells. This process is facilitated and focused through the extremely efficient uptake, processing, and presentation of antigen recognized by an individual B cell's unique B-cell receptor (BCR). The investigation of human B-cell antigen presentation has been limited by the varied specificity of BCR found in the mixed populations of B cells in vivo. As a result, there is no readily available method to measure BCR-mediated antigen presentation in this heterogeneous population of B cells. We have overcome this limitation by developing HLA-DR-restricted T-cell lines capable of recognizing a specific antigen taken up via the BCR and presented by the mixed B-cell population through this physiologically relevant mechanism. BCR-mediated presentation was enhanced >4 logs compared to presentation by B cells taking up the antigen through nonspecific mechanisms. The studies presented here characterize T-cell hybridoma lines developed for HLA-DRB1*0101+ and HLA-DRB1*1501+ B cells, but clones could be generated for other HLA-DR types using the methods described. These hybridomas have potential applications including study of the mechanisms of BCR-mediated enhancement of presentation, determination of adjuvant effects on presentation, and optimization of vaccine antigen preparations. Therefore, these T-cell lines could significantly facilitate the study of BCR-mediated antigen presentation required by T helper cell-dependent vaccines in humans.

Preserved MHC class II antigen processing in monocytes from HIV-infected individuals

Background

MHC-II restricted CD4+ T cells are dependent on antigen presenting cells (APC) for their activation. APC dysfunction in HIV-infected individuals could accelerate or exacerbate CD4+ T cell dysfunction and may contribute to increased levels of immunodeficiency seen in some patients regardless of their CD4+ T cell numbers. Here we test the hypothesis that APC from HIV-infected individuals have diminished antigen processing and presentation capacity.

Methodology/Principal Findings

Monocytes (MN) were purified by immuno-magnetic bead isolation techniques from HLA-DR1.01+ or DR15.01+ HIV-infected and uninfected individuals. MN were analyzed for surface MHC-II expression and for antigen processing and presentation capacity after overnight incubation with soluble antigen or peptide and HLA-DR matched T cell hybridomas. Surface expression of HLA-DR was 20% reduced (p<0.03) on MN from HIV-infected individuals. In spite of this, there was no significant difference in antigen processing and presentation by MN from 14 HIV-infected donors (8 HLA-DR1.01+ and 6 HLA-DR15.01+) compared to 24 HIV-uninfected HLA-matched subjects.

Conclusions/Significance

We demonstrated that MHC class II antigen processing and presentation is preserved in MN from HIV-infected individuals. This further supports the concept that this aspect of APC function does not further contribute to CD4+ T cell dysfunction in HIV disease.

Production of mouse T cell hybridomas

T cell hybridomas can be obtained by fusing activated T cells with tumor cells. A heterogeneous population of hybridomas can be cloned by limiting dilution to obtain hybridomas that express specificity to one T cell receptor (TCR). This unit describes cell fusion and selection of T cell hybridomas. A protocol is provided for screening of T cell hybridomas for expression of the CD3-TCR complex by flow cytometry analysis. Those hybridomas expressing a CD3-TCR complex are then further tested for expression of antigen specificity by screening for specific antigen-induced lymphokine production. The procedures for establishment of stable hybridoma lines and cloning of stable lines by limiting dilution are identical to those described for B cell hybridomas and can be found in UNIT 2.5. Protocols for freezing and thawing T cell hybridomas are identical to those described for B cell hybridomas and other cell lines.

T-cell hybridomas from HLA-transgenic mice as tools for analysis of human antigen processing

The study of antigen processing and presentation by human antigen presenting cells (APC) has been limited by difficulties of producing and maintaining human T-cell clones. Murine T-cell hybridomas have advantages for detecting specific peptide-MHC complexes on APC. Human antigen-specific immortalized T-cell lines have not been successfully produced. We report and validate the use of transgenic mice with human MHC genes for HLA-A2, DR1 and DR4 to produce murine T-cell hybridomas that are restricted to human HLA alleles and respond to human macrophages, dendritic cells (DC), and B-cell lines. Hybridomas restricted by human MHC-I and -II specific for influenza matrix protein, tetanus toxoid, diphtheria antigen CRM(197), and various M. tuberculosis antigens were produced. Epitope specificity was determined for several hybridomas. T hybridomas recognized peptide-MHC complexes on fixed APC for analysis of kinetics or susceptibility to inhibitors of antigen processing. T hybridomas restricted by human MHC represent convenient and powerful tools for the study of antigen processing by human APC.

Complex carbohydrates are not removed during processing of glycoproteins by dendritic cells: processing of tumor antigen MUC1 glycopeptides for presentation to major histocompatibility complex class II-restricted T cells

In contrast to protein antigens, processing of glycoproteins by dendritic cells (DCs) for presentation to T cells has not been well studied. We developed mouse T cell hybridomas to study processing and presentation of the tumor antigen MUC1 as a model glycoprotein. MUC1 is expressed on the surface as well as secreted by human adenocarcinomas. Circulating soluble MUC1 is available for uptake, processing, and presentation by DCs in vivo and better understanding of how that process functions in the case of glycosylated antigens may shed light on antitumor immune responses that could be initiated against this glycoprotein. We show that DCs endocytose MUC1 glycopeptides, transport them to acidic compartments, process them into smaller peptides, and present them on major histocompatability complex (MHC) class II molecules without removing the carbohydrates. Glycopeptides that are presented on DCs are recognized by T cells. This suggests that a much broader repertoire of T cells could be elicited against MUC1 and other glycoproteins than expected based only on their peptide sequences.

Presence of a novel subset of NKT cells bearing an invariant V(alpha)19.1-J(alpha)26 TCR alpha chain

CD1d-deficient (CD1d-/-) mouse lymphocytes were analyzed to classify the natural killer T (NKT) cells without reactivity to CD1d. The cells bearing a V(alpha)19.1-J(alpha)26 (AV19-AJ33) invariant TCR alpha chain, originally found in the peripheral blood lymphocytes, were demonstrated to be abundant in the NK1.1+ but not NK1.1- T cell population isolated from CD1d-/- mice. Moreover, more than half (11/21) of the hybrid cell lines established from CD1d-/- NKT cells expressed the V(alpha)19.1-J(alpha)26 invariant TCR alpha chain. The expression of the invariant V(alpha)19.1-J(alpha)26 mRNA was absent in beta2-microglobulin-deficient mice. Collectively, the present findings suggest the presence of a second NKT cell repertoire characterized by an invariant TCR alpha chain (V(alpha)19.1-J(alpha)26) that is selected by an MHC class I-like molecule other than CD1d.

Factors that determine the severity of experimental myasthenia gravis

Based on our current information, the robust differences in responses of B6 and bm12 mice after immunization with AChR are as follows: (1) The AChR-specific T cell repertoires are strikingly different. The epitope specificities, as well as the rearranged TCR alpha and beta chains and their CDR3 domains, are virtually nonoverlapping in the two strains of mice. (2) The AChR antibody responses are quantitatively different, both to Torpedo AChR and to the autoantigen--mouse AChR. (3) The isotype distribution of AChR antibodies favors IgG2b in B6 mice, but not in bm12 mice. (4) The clinical manifestations of EAMG are qualitatively and quantitatively different in the two strains. These considerations have led to the following scheme, illustrated diagrammatically in FIGURE 2, to explain the differences in EAMG in B6 and bm12 mice: (1) The MHC Class II of B6 mice binds the alpha 146-162 peptide of Torpedo AChR with high affinity, while the genetically altered MHC Class II of bm12 mice does not, as previously suggested (see FIGURE 2). (2) The alpha 146-162/MHC Class II complex occurs only in B6 mice and interacts with T cells having appropriate TCRs, resulting in their stimulation and expansion. Although T cells of appropriate specificity are also available in the bm12 strain, the relevant peptide/MHC Class II complex is not present. Therefore, very few T cells with specificity for alpha 146-162 are stimulated, and those that are stimulated have different TCRs. T cells with specificity for other AChR peptides are also present and expanded in both strains of mice, but they have less influence on the outcome of the immune response. (3) The alpha 146-162-specific T cells of B6 mice, in turn, interact strongly with AChR-specific B cells of B6 mice. These B cells present the same epitope/MHC Class II complex as the APCs and therefore interact well with the alpha 146-162-specific T cells (FIGURE 2). Thus, T cells of this specificity appear to provide more efficient help for AChR antibody production than T cells with specificity for other Torpedo AChR epitopes. This results in production of greater amounts of AChR antibodies, including a critical subset that cross-reacts with autologous mouse AChR. The higher autoantibody levels contribute to the greater susceptibility to EAMG and to the greater severity of manifestations in the B6 strain compared with the bm12 strain. (4) There is a bias in B6 mice toward the production of AChR antibodies of IgG2b isotype. We suggest that T cells specific for alpha 146-162 may contribute to this isotype bias. The IgG2b antibodies appear to have particularly potent "myasthenogenic" effects in rats and mice. (5) Finally, it should be emphasized that these differences in immunological and clinical aspects of EAMG in B6 and bm12 mice are relative rather than absolute. T cells that respond to AChR epitopes other than alpha 146-162 can also provide help for AChR antibody production, albeit less potent. In a sense, this model represents a special case of molecular mimicry. In this case, the source of the foreign antigenic molecule is injection rather than the more usual route of infection. The antigen (Torpedo AChR) is one that these mice would never naturally encounter, and the critical amino acid (lysine 155) of the key epitope (alpha 146-162) is present only in the AChR of electric organs of electric fish and not in the AChR of mice, chickens, cows, or humans. The important point is that a detail of the structure of the foreign antigen--that is, a particular peptide of Torpedo AChR--can determine the severity of an antibody-mediated autoimmune disease, depending on how it interacts with a detail of the structure of the MHC Class II molecule and, in turn, on how the peptide/MHC Class II complex interacts with the available T cell repertoire. (ABSTRACT TRUNCATED)

How subtle differences in MHC class II affect the severity of experimental myasthenia gravis

Myasthenia gravis is an autoimmune disorder characterized by muscle weakness, due to an antibody-mediated deficit of acetylcholine receptors (AChRs) at neuromuscular junctions. We analyzed the factors that determine the severity of experimental myasthenia gravis (EAMG) induced by immunization with Torpedo AChR, in two congenic strains of mice--B6 mice, which are highly susceptible to EAMG; and bm12 mice, which are relatively resistant, and differ only in a change of three amino acids in MHC Class II. We prepared large numbers of AChR-specific T cell hybridomas from each strain and characterized their epitope specificities and T cell receptor (TCR) gene usage: Half the B6 hybridomas responded to a single AChR peptide (alpha 146-162), and their TCR genes encoded restricted V alpha and V beta chains and CDR3 motifs. bm12 hybridomas had different epitope specificities and different, less restricted TCR genes. APCs were able to present AChR or AChR-derived peptides virtually exclusively to hybridomas of their own strain. Levels of antibodies to Torpedo and autoantibodies to mouse AChR were higher in B6 mice, and were biased toward the IgG2b isotype. We conclude that the "better fit" of MHC II, peptide, and TCR in the B6 mice enhanced cognate interactions of APCs with T cells, and T cells with B cells, resulting in a more abundant and pathogenic AChR antibody response, and thus more severe EAMG.

Lack of directed V alpha 14-J alpha 281 rearrangements in NK1+ T cells

NK1.1+ T cells are an unusual subset of TCR alpha beta cells distinguished by their highly restricted V beta repertoire and predominant usage of an invariant V alpha 14-J alpha 281 chain. To assess whether a directed rearrangement mechanism could be responsible for this invariant alpha chain, we have analyzed V alpha 14 rearrangements by polymerase chain reaction and Southern blot in a panel of cloned T-T hybrids derived from thymic NK1.1+ T cells. As expected a high proportion (17/20) of the hybrids had rearranged V alpha 14 to J alpha 281. However, V alpha 14-J alpha 281 rearrangements always occurred on only one chromosome and were accompanied by other V alpha-J alpha rearrangements (not involving V alpha 14) on the homologous chromosome. These data argue that rigorous ligand selection rather than directed rearrangement is responsible for the high frequency of V alpha 14-J alpha 281 rearrangements in NK1.1+ T cells.

Fc gamma receptor II dependency of enhanced presentation of major histocompatibility complex class II peptides by a B cell lymphoma

Here we show that the B cell lymphoma A20.292 is capable of enhanced antigen presentation to CD4+ T cells in the presence of specific antibodies. This enhancement was inhibited by anti-Fc gamma receptor (R) antibodies, suggesting that it might be due to preferential uptake of the antigen/antibody complex through the Fc gamma RII receptor. However, immunoprecipitation studies revealed that the FcR of A20.292 cells was of the B cell type, Fc gamma RIIb1, which is not thought to be able to internalize antigen/antibody complexes via clathrin-coated pits. It was considered unlikely that A20.292 had an altered form of the B cell Fc gamma R (RIIb1) receptor that enabled internalization, since similar enhancing effects were also observed using an Fc gamma RII cell line that had been transfected with Fc gamma RIIb1. To reconcile these findings with the expression of Fc gamma RIIb1, it is postulated that immune complexes are concentrated on the cell surface by the Fc gamma RIIb1 and are thus available for preferential uptake by random fluid-phase endocytosis. This results in more efficient generation of the epitopes recognized by these T cell hybridomas.

T cell receptor alpha gene rearrangement and transcription in adult thymic gamma delta cells

T cells belong to two separate lineages based on surface expression of alpha beta or gamma delta T cell receptors (TCR). Since during thymus development TCR beta, gamma, and delta genes rearrange before alpha genes, and gamma delta cells appear earlier than alpha beta cells, it has been assumed that gamma delta cells are devoid of TCR alpha rearrangements. We show here that this is not the case, since mature adult, but not fetal, thymic gamma delta cells undergo VJ alpha rearrangements more frequently than immature alpha beta lineage thymic precursors. Sequence analysis shows VJ alpha rearrangements in gamma delta cells to be mostly (70%) nonproductive. Furthermore, VJ alpha rearrangements in gamma delta cells are transcribed normally and, as shown by analysis of TCR beta-/- mice, occur independently of productive VDJ beta rearrangements. These data are interpreted in the context of a model in which precursors of alpha beta and gamma delta cells differ in their ability to express a functional pre-TCR complex.

T cell receptor delta gene rearrangement and T early alpha (TEA) expression in immature alpha beta lineage thymocytes: implications for alpha beta/gamma delta lineage commitment

Mature T cells comprise two mutually exclusive lineages expressing heterodimeric alpha beta or gamma delta antigen receptors. During development, beta, gamma, and delta genes rearrange before alpha, and mature gamma delta cells arise in the thymus prior to alpha beta cells. The mechanism underlying commitment of immature T cells to the alpha beta or gamma delta lineage is controversial. Since the delta locus is located within the alpha locus, rearrangement of alpha genes leads to deletion of delta. We have examined the rearrangement status of the delta locus immediately prior to alpha rearrangement. We find that many thymic precursors of alpha beta cells undergo VDJ delta rearrangements. Furthermore, the same cells frequently coexpress sterile T early alpha (TEA) transcripts originating 3' of C delta and 5' of the most upstream J alpha, thus implying that individual alpha beta lineage cells undergo sequential VDJ delta and VJ alpha rearrangements. Finally, VDJ delta rearrangements in immature alpha beta cells appear to be random, supporting models in which alpha beta lineage commitment is determined independently of the rearrangement status at the TCR delta locus.

Molecular analysis of a pro-T cell clone transformed by Abelson-murine leukemia virus, displaying progressive gamma delta T cell receptor gene rearrangement and surface expression

We present a molecular analysis of T cell differentiation in a set of clones derived from in vitro Abelson murine leukemia virus (A-MuLV) infection of fetal liver cells. The parental clone had partial rearrangement of the beta and gamma loci and spontaneously displayed progressive rearrangement of V gamma genes during in vitro culture. Further differentiation of these clones leading to delta gene rearrangement and CD4 expression, then CD8, CD3 and T cell receptor gamma delta chain surface expression was obtained after intrathymic transfer followed by in vitro co-culture with thymic tissue. These A-MuLV clones, therefore, appear to represent a powerful model system for studying the early molecular events of T cell development at the clonal level.

Co-expression of T-cell receptor beta and delta mRNA detected at high frequency in hybridomas derived from adult thymus

Two different hybridoma collections from adult C3H/HeJ thymus were generated in order to analyse T-cell receptor (TcR) rearrangements, surface expression of T-cell receptors and differentiation markers as well as lymphokine production. Large, low density thymocytes were either directly fused to the thymoma BW 5147 alpha-beta- variant, or fused after stimulation with Concanavalin A in the presence of interleukin-2 for 48 h. The hybrids obtained from Concanavalin A-stimulated cells represented rather mature thymocytes, with regard to TcR rearrangements and surface T-cell receptor expression. The collection of hybrids derived from freshly isolated large thymocytes contained cells in various stages of T-cell development. An unexpectedly large number of hybrids (46 out of 84) from this group expressed full-length C beta together with full-length, or shorter, C delta mRNA. This finding suggests that a considerable proportion of alpha beta T cells proceeds through a stage in development where delta genes are being rearranged and transcribed.

Mouse autoreactive gamma/delta T cells. I. Functional properties of autoreactive T cell hybridomas

A minor population of dendritic epidermal T cells (DETC) express the V gamma 1.1C gamma 4V delta 6 T cell receptor and T cell clones and hybridomas derived from this subset constitutively secrete cytokines in culture secondary to recognition of an autoantigen. Activation of these autoreactive cells requires the use of the vitronection receptor (VNR) as an accessory molecule which interacts with the Arg-Gly-Asp-Ser (RGDS) sequence of extracellular matrix (ECM) proteins. We have compared the functional properties of C gamma 4+ hybridomas derived from newborn thymocytes and from adult spleen with the DETC hybridomas/lines in terms of their ability to secrete cytokines spontaneously and for the use of the VNR as an accessory molecule. Almost all the C gamma 4+ thymocyte hybridomas secreted cytokines spontaneously and in the majority of lines the most prominent cytokine secreted was granulocyte-monocyte colony-stimulating factor. In contrast, none of the four splenic C gamma 4+ hybridomas secreted cytokines spontaneously although all were capable of cytokine production following activation via the T cell receptor. Although the thymocyte hybridomas did not grow as adherent cell lines in culture, constitutive cytokine production required engagement of the VNR by its ligand in ECM proteins. In all cases, cytokine production could be inhibited by an anti-VNR monoclonal antibody as well as by soluble RGDS. The strong correlation of functional and molecular properties between thymocyte C gamma 4+ hybridomas and C gamma 4+ DETC suggests that the C gamma 4+ DETC may be of thymic origin and that cells with potential for autoreactivity residing in the thymus at birth may populate other peripheral locations in the mouse. The data also support the concept that the VNR, and possibly other integrins, play a role as accessory elements for autoreactive cells and may be essential for the regulation of such activity.

Evidence for quantitative and qualitative differences in functional activation of Mls-reactive T cell clones and hybridomas by antigen or TcR/CD3 antibodies

In this study, we demonstrated that some V beta 6+, CD4+, Mls-1a-specific T cell clones had cytolytic activity when stimulated with anti-T cell receptor(TcR)/CD3 monoclonal antibodies (mAb), but not with targets expressing Mls-1a, although they produced lymphokines (interleukin 2 and interferon-gamma) in response to both types of stimuli. To examine the possibility that lack of cytolysis resulted from expression of the Mls-1a antigen on merely a fraction of splenic B blasts, we (a) used the B cell lymphoma LBB.3.4.16 and (b) measured esterase secretion which is generally concurrent with cytotoxic T lymphocyte (CTL) activity. The B cell lymphoma maximally stimulated the T cell clone for interferon-gamma production when responding and stimulating cells were incubated at a 1:1 ratio, but it was never killed by the Mls-1a-specific T cell clone unless TcR/CD3-specific mAb were added. Furthermore, a fivefold excess of the Mls-1a B cell lymphoma did not induce any secretion of esterase, which was observed only in the presence of the TcR/CD3-specific mAb. Comparison of the reactivity of two Mls-1a-specific T cell hybridomas expressing the same TcR at similar surface density, revealed both quantitative and qualitative differences between CD3-specific mAb and Mls stimulation of the hybridomas. A small quantitative difference in the sensitivity of hybridoma FJ22.5 to stimulation with V beta 6 or CD3-specific mAb resulted in a marked decrease in efficiency of stimulation by Mls-1a for interleukin 2 production and to inability to detect growth inhibition by Mls-expressing cells. A qualitative difference was observed when analyses of inositol phosphate production were performed under optimal conditions of stimulation of the highly responsive T cell hybridoma (FJ8.1): only stimulation with CD3-specific mAb, but not Mls-expressing cells, could induce detectable inositol phosphate production. Lack of cytolysis of Mls-1a class II-expressing B cells may have evolutionary significance in view of the recent mapping of Mls to mouse mammary tumor virus genes.

Screening cDNA expression libraries in lambda gt11 with a T cell hybridoma

A T cell hybridoma specific for a protein of Plasmodium chabaudi chabaudi has been used to test a system for direct T cell screening of a cDNA library of P. chabaudi in the phage lambda gt11. The technique is based upon the rapid separation of the recombinant beta-galactosidase fusion protein from the bacterial mixtures using polystyrene beads coated with anti-beta-galactosidase antibodies. These coated beads are cultured with antigen-presenting cells and the T cell hybridoma. The technique is sufficiently sensitive to pick up the products of one recombinant phage in a pool of 1000-10,000 other phages. Individual plaques or clones of recombinant phage can be selected after testing of sequential dilutions of pools containing positive recombinant phages. This technique will be generally applicable and should be useful for the identification of important T cell peptides in infectious diseases.

Identification of the region of T cell receptor beta chain that interacts with the self-superantigen MIs-1a

Superantigen-MHC complexes are known to stimulate T cells primarily via the V beta element of the T cell receptor. In this paper we identify a number of amino acid residues that define the region of a particular V beta element interacting with one of the self-superantigens, MIs-1a. These residues are predicted to lie on a beta-pleated sheet of the T cell receptor, away from the complementarity determining regions of the receptor, which are thought to interact with complexes of conventional peptide antigens and MHC. In support of this prediction, mutations affecting MIs-1a activity have no effect on the response to conventional antigen and MHC.

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

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

Surprisingly uneven distribution of the T cell receptor V beta repertoire in wild mice

We have examined TCR V beta expression in a collection of wild mice. Many of the mice were homozygous for a large deletion at the V beta locus, and many animals also suppressed expression of several V betas using self superantigens. Expression of V beta 8.2 was unexpectedly suppressed by a self superantigen in some wild mice, which was due to the presence in these animals of a variant V beta 8.2 gene. The amino acid changes in this gene product suggest contact sites between V beta and the superantigen. Although all V betas are expressed within each wild mouse population, individual mice have a limited and variable V beta repertoire. The independent origin of multiple V beta deletions and the presence of polymorphic self superantigens suggest that this variation may be maintained by balancing selection.

Derivation of a T cell hybridoma variant deprived of functional T cell receptor alpha and beta chain transcripts reveals a nonfunctional alpha-mRNA of BW5147 origin

We have isolated a variant of the DO-11.10.7 mouse T cell hybridoma which does not express functional T cell receptor alpha/beta chains. This variant, denoted 58 alpha-beta-, can be used as a recipient for T cell receptor alpha/beta gene transfer experiments to obtain cell lines which express only the products of the transfected alpha/beta genes at their surfaces. In the process of characterizing the defects affecting the 58 alpha-beta-T cell receptor genes, we have found that the parental BW5147 thymoma has undergone a previously unnoticed V alpha-J alpha rearrangement. This alpha rearrangement involves a V alpha pseudogene segment and accounts for the high level of alpha-mRNA transcripts present in the BW5147 alpha-beta- variant. Knowledge of the existence of this second, albeit nonfunctional, alpha-mRNA in BW5147 is of importance, since it could be, and actually already has been, mistakenly identified (due to partial nucleotide sequencing) in T hybrids as a functionally significant message donated by the normal T cell parent.

Stimulation of a major subset of lymphocytes expressing T cell receptor gamma delta by an antigen derived from Mycobacterium tuberculosis

To investigate the possible function(s) of T cell receptor (TcR) gamma delta expressing lymphocytes, we generated a series of gamma delta TcR surface positive hybridomas. Spontaneous producers of IL-2 were quite common among these hybridomas, particularly those expressing a certain V delta gene or gene family (V delta M23). Several other experiments indicated that IL-2 production in these hybridomas is triggered via TcR gamma delta. Surprisingly, every spontaneously reactive gamma delta+ hybridoma was further stimulated by purified protein derivative (PPD) of Mycobacterium tuberculosis, perhaps due to crossreaction with a bacterial antigen homologous to certain eukaryotic heat shock proteins. The finding of an antigen recognized by a gamma delta TcR could aid in understanding the functional role of the gamma delta TcR+ lymphocytes.

Presentation of antigen, foreign major histocompatibility complex proteins and self by thymus cortical epithelium

In mouse and man most peripheral T cells bear clonally variable receptors made up of alpha- and beta-chains which bind ligands on target cells consisting of peptide fragments of foreign antigens, complexed with cell surface proteins encoded by the major histocompatibility complex (MHC) of the individual. In the thymus, developing T cells are selected to mature only if their receptors will be able to participate in self-MHC plus antigen recognition in the periphery. This positive selection occurs in the presence of self-MHC, but in the apparent absence of antigen, leading to the paradoxical conclusion that developing thymocytes must be positively selected by engagement of their receptors and self-MHC alone, although thymocytes that react too well with self-MHC are eliminated. To account for this, it has been suggested that MHC molecules in the thymus are not identical to those found elsewhere. To test this and other hypotheses, we have examined the ability of the presumed selecting cells, those of the thymus cortical epithelium, to present various MHC complexes to T cells. Our results indicate that MHC molecules on thymus epithelium are not always the same as those found elsewhere.