Expression of the T-cell-specific gamma gene is unnecessary in T cells recognizing class II MHC determinants

Becoming aware of γδ T cells

The discovery that B cells and αβ T cells exist was predictable: These cells gave themselves away through their products and biological effects. In contrast, there was no reason to anticipate the existence of γδ T cells. Even the accidental discovery of a novel TCR-like gene (later named γ) that did not encode TCR α or β proteins did not immediately change this. TCR-like γ had no obvious function, and its early expression in the thymus encouraged speculation about a possible role in αβ T cell development. However, the identification of human PBL-derived cell-lines which expressed CD3 in complex with the TCR-like γ protein, but not the αβ TCR, first indicated that a second T cell-type might exist, and the TCR-like γ chain was observed to co-precipitate with another protein. Amid speculation about a possible second TCR, this potential dimeric partner was named δ. To determine if the δ protein was indeed TCR-like, we undertook to sequence it. Meanwhile, a fourth TCR-like gene was discovered and provisionally named x. TCR-like x had revealed itself through genomic rearrangements early in T cell development, and was an attractive candidate for the gene encoding δ. The observation that δ protein sequences matched the predicted amino acid sequences encoded by the x gene, as well as serological cross-reactivity, confirmed that the TCR-like x gene indeed encoded the δ protein. Thus, the γδ heterodimer was established as a second TCR, and the cells that express it (the γδ T cells) consequently represented a third lymphocyte-population with the potential of recognizing diverse antigens. Soon, it became clear that γδ T cells are widely distributed and conserved among the vertebrate species, implying biological importance. Consistently, early functional studies revealed their roles in host resistance to pathogens, tissue repair, immune regulation, metabolism, organ physiology and more. Albeit discovered late, γδ T cells have repeatedly proven to play a distinct and often critical immunological role, and now generate much interest.

Evolution and function of the TCR Vgamma9 chain repertoire: It's good to be public

Lymphocytes expressing a T cell receptor (TCR) composed of Vgamma9 and Vdelta2 chains represent a minor fraction of human thymocytes. Extrathymic selection throughout post-natal life causes the proportion of cells with a Vgamma9-JP rearrangement to increase and elevates the capacity for responding to non-peptidic phosphoantigens. Extrathymic selection is so powerful that phosphoantigen-reactive cells comprise about 1 in 40 circulating memory T cells in healthy adults and the subset expands rapidly upon infection or in response to malignancy. Skewing of the gamma delta TCR repertoire is accompanied by selection for public gamma chain sequences such that many unrelated individuals overlap extensive in their circulating repertoire. This type of selection implies the presence of a monomorphic antigen-presenting molecule that is an object of current research but remains incompletely defined. While selection on a monomorphic presenting molecule may seem unusual, similar mechanisms shape the alpha beta T cell repertoire including the extreme examples of NKT or mucosal-associated invariant T cells (MAIT) and the less dramatic amplification of public Vbeta chain rearrangements driven by individual MHC molecules and associated with resistance to viral pathogens. Selecting and amplifying public T cell receptors whether alpha beta or gamma delta, are important steps in developing an anticipatory TCR repertoire. Cell clones expressing public TCR can accelerate the kinetics of response to pathogens and impact host survival.

Identification of two distinct function gamma delta TCR complexes on the surface of a human T cell clone

In this study we describe the expression of two T cell receptor (TCR) gamma chains on the surface of a human T cell clone isolated from the peripheral blood. Each gamma chain was part of an independent and functional TCR. The dual receptor T cell clone (and all subclones derived from this clone) had stable expression of this phenotype. Immunoprecipitation studies revealed the expression of non-disulfide linked TCRs by this V gamma 4+V gamma 9+V delta 1+ T cell clone, which was in agreement with the finding that both V gamma gene transcripts were rearranged to C gamma 2-associated joining elements. Both gamma chains were derived from productive rearrangements of different (allelic) genes coding for a V gamma 4+ and a V gamma 9+ gamma-chain, and both were coupled to a V delta 1+ delta chain. Incubation of this V gamma 4+V gamma 9+V delta 1+ T cell clone with TCR gamma-chain-specific MoAbs rapidly induced an increase in intracellular Ca++, indicating that both gamma-chains are functional. Furthermore, this clone responded to stimulation with S. aureus derived superantigens. We suggest therefore that exogenous (super)antigens can trigger dual receptor T cells resulting in activation of these T cells.

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.

A molecular genetic linkage map of mouse chromosome 13 anchored by the beige (bg) and satin (sa) loci

A molecular genetic linkage map of mouse chromosome 13 was constructed using cloned DNA markers and interspecific backcross mice from two independent crosses. The map locations of Ctla-3, Dhfr, Fim-1, 4/12, Hexb, Hilda, Inhba, Lamb-1.13, Ral, Rrm2-ps3, and Tcrg were determined with respect to the beige (bg) and satin (sa) loci. The map locations of these genes confirm and extend regions of homology between mouse chromosome 13 and human chromosomes 5 and 7, and identify a region of homology between mouse chromosome 13 and human chromosome 6. The molecular genetic linkage map of chromosome 13 provides a framework for establishing linkage relationships between cloned DNA markers and known mouse mutations and for identifying homologous genes in mice and humans that may be involved in disease processes.

Structure and expression of the T cell receptor gamma locus in pre-B and early hemopoietic cells

The genetic structure and expression of the T cell receptor (TcR) loci were examined in pre-B and early hemopoietic cells. Thirty-eight percent of Abelson murine leukemia virus-transformed pre-B cell lines were rearranged at TcR gamma. Moreover, many pre-B cell lines were rearranged at two distinct gamma loci, V gamma 1.2 and V gamma 2. The gamma rearrangements in the pre-B cell lines were similar to those observed previously in T cell lines. V + C-containing gamma mRNA was detected in two pre-B cell lines. In all other pre-B and interleukin (IL) 3-dependent lymphoid and myeloid lines examined, smaller C gamma-containing mRNA were detected. These C gamma transcripts were independent of the genetic configuration of the gamma locus. In contrast, the TcR alpha and beta loci were in the germ-line configuration in all non-T cell lines examined and mRNA encoding these loci were not detected. When IL3-dependent lymphoid and myeloid cell lines were transformed to growth factor independence by a non-autocrine mechanism, no mRNA transcripts encoding TcR C gamma were detected. However, TcR C gamma mRNA transcripts were detected in factor-independent cell lines that arose by an autocrine mechanism. The cell cycle expression of C gamma was compared with protooncogenes and other marker genes previously shown to be cell cycle specific. mRNA transcripts encoding C gamma were detected in the highest amounts 4-8 h after IL 3, but not phorbol myristate acetate, addition. A similar time period of expression was observed with ornithine decarboxylase which has been shown to be expressed in G1 phase. These observations indicate that TcR gamma is often rearranged in pre-B cell lines and may be directly regulated by IL3 in IL3-dependent cells.

Developmental biology of T cell receptors

T cell receptors are the antigen-recognizing elements found on the effector cells of the immune system. Two isotypes have been discovered, TCR-gamma delta and TCR-alpha beta, which appear in that order during ontogeny. The maturation of prothymocytes that colonize the thymic rudiment at defined gestational stages occurs principally within the thymus, although some evidence for extrathymic maturation also exists. The maturation process includes the rearrangement and expression of the T cell receptor genes. Determination of these mechanisms, the lineages of the cells, and the subsequent thymic selection that results in self-tolerance is the central problem in developmental immunology and is important for the understanding of autoimmune diseases.

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

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

T-cell receptor delta-chain diversity in peripheral lymphocytes

A small percentage (approximately 5%) of the cells in the adult thymus expresses a heterodimeric receptor, gamma delta, that exhibits extensive clonal diversity. The specificity and function of these cells are unclear. Furthermore, it is not known if their role in the immune system is primarily one that operates within the thymus during the selection of the T-cell repertoire or if they function primarily in an antigen-recognition capacity in the peripheral lymphoid system. To examine if gamma delta+ T cells in the periphery are as diverse as those in the thymus, we used the polymerase chain reaction to amplify delta-chain transcripts from polyclonal populations of thymic and splenic lymphocytes (the latter were derived from allogeneic mixed lymphocyte cultures). The nucleotide sequences of delta chains from the spleen, like those from the thymus, were all different. Most of the diversity was present in the region between the variable (V) and joining (J) gene segments and was generated through the use of the two known diversity (D) elements, D delta 1 and D delta 2, and by the addition or deletion of bases at the V delta D delta 1, D delta 1D delta 2, and D delta 2J delta junctions. The extensive gamma delta repertoire among peripheral cells suggests that they have the potential to recognize an array of ligands that could be as diverse as those recognized by alpha beta+ cells. The amplification strategy described here can be used to analyze rapidly the diversity exhibited by any of the members of the immunoglobulin-like gene families that undergo rearrangement.

Molecular analysis of T cell receptor gamma gene expression in allo-activated splenic T cells of adult mice

Northern analysis, hybridization in situ and cDNA sequence analysis have been used to demonstrate that the induction of T cell gamma-gene expression is a general occurrence when primary splenic T cells of adult mice are cultured in short-term mixed lymphocyte reactions (MLR). Splenic T cells from nine strains of mice examined in eleven different MLR all showed significant induction of gamma-RNA, even when the primary T cell response was to only a three amino acid mismatch in a major histocompatibility complex class I antigen. In MLR examined in detail, the expression is highly enriched for in CD3+ "double-negative" T cells (lacking both CD4 and CD8 expression). A cDNA sequence analysis, constituting the first such analysis of any size of gamma-gene transcripts from circulating, peripheral cells of adult mice, revealed transcription to be frequently of productively rearranged genes. These genes display extensive junctional diversity.

Rearrangement and expression of T cell receptor and immunoglobulin loci in immortalized CD4-CD8- T cell lines

Injection of newborn mice with mixtures of wild-type moloney murine leukemia (Mo-MuLV) virus and other recombinant retroviruses harboring the myc oncogene alone or in combination with the H-ras oncogene resulted in a 100% incidence of lymphatic leukemias from which permanent cell lines could be established in vitro. These cells are immunoglobulin (Ig)-, Thy-1+BP- and CD8-CD4- indicating that they are early thymocytes. Such transformed pre-T lines lack retroviral myc and ras genes but occasionally possess proviral insertion near to their endogenous myc and pim genes. We show that both Ig heavy chain (Igh) and T cell receptor (TcR) genes are rearranged in most of these lines. In some cases, a primary recombination was followed by a secondary rearrangement at the same locus. We show that VT gamma genes can rearrange outside of their known cluster suggesting that TcR gamma diversification in such pre-T cells may be different to that in more mature T cells. Ig D-JH recombinations may precede TcR gene recombination in these early T cell lines, and some but not all express sterile Cmu transcripts. Some of these lines express surface heterodimers that appear composed of alpha and beta chains that can be immunoprecipitated with a monoclonal anti-T3 antibody but not with the anti-V beta 8 monoclonal antibody F23.1. This established pre-T cell line represents novel biological material for the dissection of T cell development and function analogous to A-MuLV transformed pre-B cells.

T lymphocyte development in horses. I. Characterization of monoclonal antibodies identifying three stages of T lymphocyte differentiation

Six monoclonal antibodies reacting with equine T lymphocytes at different stages of maturation were selected from antibodies produced against lymphoid cell preparations. EqT12 and EqT13 antibodies identified subsets of cortical thymocytes with high terminal deoxynucleotidyltransferase (TdT) activity and no phytolectin responsiveness. EqT12+ thymocytes were scattered throughout the cortex while EqT13+ thymocytes were located in the subcapsular cortex. EqT12 bound to small numbers of bone marrow cells, splenocytes, and circulating lymphoid cells, but not to mature T lymphocytes. EqT13 bound to very small numbers of bone marrow cells but not to more mature lymphocytes. EqT6 and EqT7 reacted with a large population of cortical thymocytes with high TdT activity and no phytolectin responsiveness. EqT2 and EqT3 bound primarily to medullary thymocytes with low TdT activity. Eq2+ thymocytes responded to phytolectin stimulation while EqT3+ thymocytes did not. EqT2 and EqT3 bound to 33% and 91% of circulating T lymphocytes, respectively. The T lymphocytes bound by both antibodies included cells capable of suppressing a mixed lymphocyte reaction. Thus, EqT12 and EqT13 identify cells with the functional characteristics of prothymocytes. EqT6 and EqT7 identify resident cortical thymocytes, and EqT2 and EqT3 identify a subpopulation of mature T lymphocytes and all mature T lymphocytes, respectively.

Diversity of the mouse T cell receptor C gamma 1 gene: structural analysis in C57BL/Ka

We have isolated an unusual T cell receptor gamma chain cDNA clone (gamma 7.1) from a library made from RNA derived from adult thymus of C57BL/Ka mice. This cDNA clone corresponds to the appropriately processed C gamma 1 constant region exons preceded by 1.5 kb of J-C gamma 1 intron. The gamma 7.1 coding region is extremely homologous to the C gamma 1 gene of BALB/c mice, differing at the protein level by a single deletion (alanine 139) and a single substitution. This latter change eliminates the sole N-linked sugar attachment site, providing a basis for strain-specific glycosylation patterns. The J-C gamma 1 intronic region contains two DNA segments (termed psi J gamma 1 and psi J gamma 2) that are highly reminiscent of joining (J) segments; both have potentially functional recombination and donor splice sequences flanking an open reading frame. Northern analysis suggests that gamma 7.1 may be derived from a large, variable region-containing precursor.

Two types of gamma T cell receptors expressed by T cell acute lymphoblastic leukemias

CD3+ cells, isolated from peripheral blood of two patients with T cell acute lymphoblastic leukemia (T-ALL), did not react with the monoclonal antibody WT31, which is thought to recognize a framework determinant on the conventional T cell receptor (TcR), consisting of disulfide-linked alpha and beta chains. The T-ALL cells of neither patient synthesized TcR alpha mRNA; the cells of patient DD contained only truncated (D-J) TcR beta mRNA, while the cells of patient HZ contained truncated as well as mature (V-D-J) TcR beta mRNA. The leukemic cells of both patients made TcR gamma mRNA. At the cell surface, the T-ALL cells of patient DD expressed a CD3-associated disulfide-linked dimer, which contained the TcR gamma protein. On the leukemic cells of patient HZ the TcR gamma protein was present as a 41-44-kDa CD3-associated subunit in a noncovalently linked form. The TcR gamma genes in the T-ALL cells of patient DD were rearranged exclusively to the C gamma 1 locus, while in the T-ALL cells of patient HZ both C gamma 1 alleles were deleted and rearrangement to the C gamma 2 locus had occurred. The C gamma 1 gene segment, just like the TcR alpha and TcR beta gene segments, contains a cysteine codon in its second exon. This cysteine residue is involved in the formation of the interchain disulfide bond. The human C gamma 2 gene segment, however, does not contain a cysteine codon in its second exon. The absence of the cysteine residue in C gamma 2 encoded TcR gamma chains explains the lack of an interchain disulfide bond in the TcR on the T-ALL cells of patient HZ. The TcR gene configuration, as well as the expression of model for T cell differentiation in which the TcR gamma gene rearranges first to the C gamma 1 locus prior to or coinciding with D-J joining of the TcR beta gene, followed by rearrangement to the C gamma 2 locus and V-D-J joining of the TcR beta gene.

Alpha, beta and gamma T-cell receptor genes: rearrangements correlate with haematological phenotype in T cell leukaemias

We have studied the arrangement of the alpha, beta and gamma T cell receptor (TCR) genes in 27 patients with T cell lymphoproliferative disorders. Nine patients had acute lymphoblastic leukaemia (T-ALL), nine patients had prolymphocytic leukaemia (PLL), six patients presented with a T-CLL/T-lymphocytosis syndrome, two patients had Sezary syndrome (SS) and one patient had HTLV-I positive T-cell leukaemia/lymphoma (ATLL). alpha TCR gene rearrangement could be demonstrated by the use of three available probes in only one case. By contrast, both beta and gamma TCR gene rearrangement could be demonstrated by Southern blot analysis of DNA samples digested with appropriate restriction enzymes in the majority of cases. In general, when rearrangements were present they involved both alleles. The proportion of rearranged chromosomes was lower in T-ALL than in other forms of T-cell leukaemia and it was lower in cases with the CD4-/CD8+ phenotype than in those with a CD4+/CD8- phenotype. In three out of 34 cases of B-cell leukaemia the TCR beta-gene but not the TCR gamma-gene was rearranged, just as in two out of 26 cases of T-cell leukaemia the immunoglobulin (Ig) heavy chain but not the light chain genes were rearranged. These data suggest that development of the machinery required for gene rearrangement may precede commitment to B or T cell lineage. The use of this technique is especially useful for the classification of cases of ALL in which the cells are negative with respect to most current phenotypic markers and in cases of T cell lymphocytosis in which the finding of a gene rearrangement identifies a monoclonal cell population.

T-cell gamma gene is allelically but not isotypically excluded and is not required in known functional T-cell subsets

The T-cell gamma genes, structurally related to immunoglobulin genes and the T-cell antigen-receptor alpha- and beta-chain genes, undergo somatic rearrangement in T-lineage cells. However, the role of the T-cell gamma genes has not yet been determined. To determine the potential for gamma gene expression in a set of well-characterized, cloned T-cell lines, we cloned all of the rearranged gamma genes from each cell line. The genes were sequenced to determine if the junction of the variable and joining regions maintained the proper translational reading frame. We then attempted to correlate the presence of an in-frame gamma gene with a T-cell subset. We were unable to establish such a correlation. We found evidence, however, that allelic exclusion influences the rearrangement of the gamma gene. This is consistent with the idea that the gamma gene product participates in establishing a clonally diverse population of T cells recognizing a polymorphic ligand. Isotypic exclusion does not apply to the gamma gene, however, suggesting different roles for the different gamma gene isotypes.

Expression of the T-cell receptor gamma-chain gene products on the surface of peripheral T cells and T-cell blasts generated by allogeneic mixed lymphocyte reaction

The gamma-chain genes of the T-cell receptors form a family of related genes that are specifically expressed and somatically rearranged in T cells. Using poly- and monoclonal anti-gamma antibodies, we studied the cell-surface expression of the gamma-chain gene products in mouse peripheral T cells as well as in the T-cell blasts generated by allogeneic mixed lymphocyte reactions. The gamma chains are expressed in the Lyt2-,L3T4- subsets of these T-cell populations as disulfide-linked heterodimers. Whereas the electrophoretic mobility and the N-glycosylation of the spleen and lymph-node gamma chains are indistinguishable from those of the reported thymocyte gamma chain, a minor fraction of the T blasts generated by allogeneic stimulation of B10 lymph-node T cells with B10.BR spleen cells seems to express gamma chains with distinct properties. This suggests that the mixed lymphocyte culture conditions exert a selective effect on the expression of gamma chains among peripheral T-cell populations.

T-cell receptor genes in autoimmune mice: T-cell subsets have unexpected T-cell receptor gene programs

Two unique cell subsets have been identified in the autoimmune-prone MRL/MP lpr/lpr and C3H/HeJ gld/gld murine strains that have the Lyt-2-,L3T4-,Thy-1+, and Lyt-2-,L3T4-,Ia-,Thy-1- phenotypes, respectively. We have now found that these cells express T-cell receptor proteins on their surface. Our observations further indicate that the expression of the Thy-1 antigen does not correlate with the expression of alpha-chain and beta-chain T-cell receptor polypeptides. Interestingly, T-cell receptor gamma-chain RNA expression may be influenced or correlate with Thy-1 molecular expression. These studies indicate unusual relationships of different cell-surface structures that may reflect unexpected developmental programs.

Resistance of cytotoxic T lymphocytes to lysis by a clone of cytotoxic T lymphocytes

To investigate how cytotoxic T lymphocytes (CTL) avoid killing themselves when they destroy target cells, we compared 20 different cell lines as target cells, including several CTL cell lines, for their susceptibility to lysis by CTL. Variations in recognition of this diverse set of target cells was circumvented by attaching to all of them a monoclonal antibody to the antigen-specific receptor of a cloned CTL cell line (clone 2C) and using the 2C cell line as the standard aggressor or effector cell. All of the nine tumor cell lines and the four noncytolytic T-helper cell lines tested as targets were highly susceptible to lysis by the aggressor CTL, but seven cytotoxic T-cell lines (six CTL and one T-helper cell line with cytotoxic activity) were largely resistant. These results, and the use of the lectin Con A as an alternative means for triggering CTL activity, point clearly to a level of resistance that could enable CTL to avoid their own destruction when they lyse target cells. The resistance of the cytolytic T cells did not appear to be accompanied by a similar resistance to complement-mediated lysis, indicating that mechanisms of CTL-mediated and complement-mediated lysis are not identical.

T-cell receptor and immunoglobulin genes are rearranged together in Abelson virus-transformed pre-B and pre-T cells

We have assessed the state of rearrangement and expression of B- and T-cell antigen receptor genes in cells of Abelson murine leukemia virus-transformed thymomas and other tumors. We found that unrearranged TcR gamma genes are expressed, as are unrearranged C mu genes, in pre-T, pre-B, and myeloid cells. We also found TcR gamma genes rearranged and expressed in putative pre-T cells and in cells apparently committed to the B-cell lineage. This is in contrast to the data from more mature T- and B-cell tumors. We conclude that in immature lymphoid cells both immunoglobulin and TcR gamma genes are accessible for rearrangement. We discuss the implications of these observations for an understanding of the B-T lymphoid differentiation event.

A T-cell receptor gamma/CD3 complex found on cloned functional lymphocytes

Cloned blood lymphocytes that do not express the alpha- and beta-chains of the T-cell receptor show MHC-unrestricted cytotoxicity. These cells carry the gamma-protein, disulphide-linked either to another molecule or to itself, and associated with the CD3 complex. These observations may help to solve the mystery posed by the discovery of the gamma gene.

T gamma protein is expressed on murine fetal thymocytes as a disulphide-linked heterodimer

During the search for genes coding for the mouse alpha and beta subunits of the antigen-specific receptor of mouse T cells we encountered a third gene, subsequently designated gamma. This gene has many properties in common with the alpha and beta genes, somatic assembly from gene segments that resemble the gene segments for immunoglobulin variable (V), joining (J) and constant (C) regions; rearrangement and expression in T cells and not in B cells; low but distinct sequence homology to immunoglobulin V, J and C regions; other sequences that are reminiscent of the transmembrane and intracytoplasmic regions of integral membrane proteins; and a cysteine residue at the position expected for a disulphide bond linking two subunits of a dimeric membrane protein. Despite these similarities the gamma gene also shows some interesting unique features. These include a relatively limited repertoire of the germ-line gene segments, more pronounced expression at the RNA level in immature T cells such as fetal thymocytes and an apparent absence of in-frame RNA in some functional, alpha beta heterodimer-bearing T cells or cultured T clones and hybridomas. To understand the function of the putative gamma protein it is essential to define the cell population that expresses this protein. To this end we produced a fusion protein composed of Escherichia coli beta-galactosidase and the gamma-chain (hereafter referred to a beta-gal-gamma) using the phage expression vector lambda gt11 and raised rabbit antisera against the gamma determinants. Using the purified anti-gamma antibody we detected a polypeptide chain of relative molecular mass 35,000 (Mr 35K) on the surface of 16-day old fetal thymocytes. The gamma-chain is linked by a disulphide bridge to another component of 45K. No such heterodimer was detected on the surface of a cytotoxic T lymphocyte (CTL) clone 2C from which an in-phase gamma cDNA clone was originally isolated.

AKXD recombinant inbred strains: models for studying the molecular genetic basis of murine lymphomas

We analyzed the lymphoma susceptibility of 13 AKXD recombinant inbred mouse strains derived from AKR/J, a highly lymphomatous strain, and DBA/2J, a weakly lymphomatous strain. Of the 13 strains used, 12 showed a high incidence of lymphoma development. However, the average age at onset of lymphoma varied considerably among the different AKXD strains, suggesting that they have segregated several loci that affect lymphoma susceptibility. A relatively unambiguous classification of lymphomas was made possible by using histopathology in addition to detailed molecular characterization of rearrangements in immunoglobulin heavy and kappa light genes and in T-cell receptor beta-chain genes. Among the 12 highly lymphomatous strains, only 2 were identified that, like the parental AKR/J strain, died primarily of T-cell lymphomas. Three strains died primarily of B-cell lymphomas, and one strain primarily of myeloid lymphomas. Six strains were susceptible to both T-cell and B-cell lymphomas. Thus, these strains have segregated genes that affect both lymphoma susceptibility and lymphoma type and should prove to be useful models for studying the molecular genetic basis of murine lymphomas.

T-cell antigen receptors with identical variable regions but different diversity and joining region gene segments have distinct specificities but cross-reactive idiotypes

The T-cell antigen receptor alpha-chain genes of an alloreactive, H-2Db-specific cytotoxic T-cell clone (3F9) are described. This study and our work on the 3F9 beta-chain genes reveal that the variable region gene segments for the alpha and beta chains expressed in 3F9 are identical to the ones used by a chicken erythrocyte-specific, I-Ab-restricted helper T-cell clone (LB2). These two clones differ, however, in the diversity and joining portions of the alpha and beta chains of their T-cell receptor molecules. The analysis of 3F9 and LB2 with monoclonal antibodies specific for the 3F9 T-cell receptor shows that these two T-cell clones share the same idiotype; however, 3F9 and LB2 do not exhibit any antigen and/or major histocompatibility complex cross-reactivity. This suggests that the diversity and joining regions of the T-cell receptor may play a key role in antigen and/or major histocompatibility complex recognition.

T-cell receptor and immunoglobulin genes are rearranged together in Abelson virus-transformed pre-B and pre-T cells

We have assessed the state of rearrangement and expression of B- and T-cell antigen receptor genes in cells of Abelson murine leukemia virus-transformed thymomas and other tumors. We found that unrearranged TcR gamma genes are expressed, as are unrearranged C mu genes, in pre-T, pre-B, and myeloid cells. We also found TcR gamma genes rearranged and expressed in putative pre-T cells and in cells apparently committed to the B-cell lineage. This is in contrast to the data from more mature T- and B-cell tumors. We conclude that in immature lymphoid cells both immunoglobulin and TcR gamma genes are accessible for rearrangement. We discuss the implications of these observations for an understanding of the B-T lymphoid differentiation event.

AKXD recombinant inbred strains: models for studying the molecular genetic basis of murine lymphomas

We analyzed the lymphoma susceptibility of 13 AKXD recombinant inbred mouse strains derived from AKR/J, a highly lymphomatous strain, and DBA/2J, a weakly lymphomatous strain. Of the 13 strains used, 12 showed a high incidence of lymphoma development. However, the average age at onset of lymphoma varied considerably among the different AKXD strains, suggesting that they have segregated several loci that affect lymphoma susceptibility. A relatively unambiguous classification of lymphomas was made possible by using histopathology in addition to detailed molecular characterization of rearrangements in immunoglobulin heavy and kappa light genes and in T-cell receptor beta-chain genes. Among the 12 highly lymphomatous strains, only 2 were identified that, like the parental AKR/J strain, died primarily of T-cell lymphomas. Three strains died primarily of B-cell lymphomas, and one strain primarily of myeloid lymphomas. Six strains were susceptible to both T-cell and B-cell lymphomas. Thus, these strains have segregated genes that affect both lymphoma susceptibility and lymphoma type and should prove to be useful models for studying the molecular genetic basis of murine lymphomas.

Genetic polymorphism and exon changes of the constant regions of the human T-cell rearranging gene gamma

The genomic nucleotide sequences of the constant-region (C) genes of the human T-cell rearranging gene gamma are given. These sequences show considerable allelic and nonallelic variation. Allelic variants exist at both C gamma 1 and C gamma 2 loci in coding regions (as well as in restriction enzyme sites). Both C gamma genes are in the same transcriptional orientation. Moreover, the organization of the nonallelic C gamma genes reveals some interesting features: the C gamma 1 gene, like the mouse C gamma gene, has three exons, whereas the C gamma 2 gene has four exons, including a duplicated second exon that would create a putative protein with an enlarged constant region. However, these two duplicated exons in C gamma 2 have lost the cysteine residue that is thought to be involved in the interchain disulfide bridge.

Effect of an inhibitor of DNA methylation on T cells. II. 5-Azacytidine induces self-reactivity in antigen-specific T4+ cells

During T-cell maturation, thymocytes interact with thymic stromal major histocompatibility complex (MHC) determinants and thymic hormones, and proliferate, apparently in response to MHC gene products, in the absence of antigen. The maturing thymocytes also express a series of cell surface molecules, at one stage coexpressing T4, T6, and T8. Mature T cells express either T4 or T8, lack T6, bear the T3-Ti receptor complex on the cell surface, and require antigen in addition to MHC determinants to proliferate. To study whether DNA methylation may be involved in regulating phenotypic and functional changes observed during thymocyte maturation, cloned, T4+ Interleukin-2 dependent, antigen-specific T cells were treated with an inhibitor of DNA methylation, 5-azacytidine (5-azaC). The 5-azaC treated cells lost the requirement for antigen and could be activated by autologous macrophages alone. Anti-class II and anti-T3, but not anti-class I monoclonal antibodies, inhibited activation of 5-azaC treated T4+ cells by macrophages, implying that the T3-Ti receptor complex may be recognizing class II MHC molecules without antigen. No changes in T3 and T4 expression were noted, and neither T8 nor T6 was induced.

The context of T-cell receptor gamma chain genes among wild mouse species

We have examined the context of mouse T-cell receptor gamma (Tcr gamma) chain variable (V gamma) and constant (C gamma) genes among a panel of geographically isolated species of mice. Our Southern hybridization survey with C gamma reveals that essentially three C gamma genes are found among mouse species extending phylogenetically from inbred mice through the feral species Mus pahari. However, a V gamma DNA probe detects three to nine V gamma restriction fragment bands among the same group of mice. These results suggest that certain feral mice such as M. pahari, M. platythrix, and M. shortridgei have amplified numbers of V gamma genes. Studies of individual mice from these particular species indicate the highly amplified V gamma content is not the result of a catastrophic gene duplication or deletion event. We conclude that certain species of mice maintain increased content of V gamma presumably for increased diversity in a T-cell response.

What is a T-cell clone? Effect of rIFN on T-cell clone function and T-cell receptor gene rearrangement

A T4+ proliferative, noncytotoxic cloned line acquires specific lytic function by treatment with recombinant interferon alpha or gamma. Simultaneous with the acquisition of this new cell function, a rearrangement of the T-cell receptor alpha gene occurs. These changes necessitate a revised concept of a T-cell clone regarding its T-cell receptor gene configuration and cell function.

Synchronized rearrangement of T-cell gamma and beta chain genes in fetal thymocyte development

Kinetics of mouse T-cell gamma gene rearrangements in ontogeny were determined as an approach to understanding the possible role of these genes in the development of fetal thymocytes. Two of these genes (C gamma 1 and C gamma 2) rearranged rapidly during days 14 to 17 of the gestational period in BALB/c mice. Moreover, these rearrangements seemed to be tightly synchronized with rearrangements of T-cell receptor beta chain genes in the same cells. It is suggested that the early transcriptional activity of gamma genes, which precedes that of beta chain genes, may not reflect the functional activation of these genes. Nevertheless, productive and therefore potentially functional gamma gene rearrangements precede surface expression of T-cell receptors in the thymus by 2 to 3 days, which is compatible with a role for gamma gene products in thymocyte development prior to antigen-specific stages.

Transcripts of functionally rearranged gamma genes in primary T cells of adult immunocompetent mice

The T-cell specific, rearranging gamma-chain genes bear striking resemblance to T-cell receptor and immunoglobulin genes, but the role of gamma remains unknown. A central problem is to understand the conditions under which gamma RNA is expressed in cells. The transcription of gamma is abundant in T cells of fetal thymi, but is negligible in peripheral T cells of adults, suggesting that gamma is involved in development of the T-cell repertoire. However, gamma RNA was originally cloned from established lines of cytotoxic T cells (CTLs) derived from adult mice and this expression has been ascribed to non-physiological cell growth. Possibly consistent with this, most of the gamma RNA derives from genes rearranged abortively at the V gamma-J gamma junction of immunoglobulin genes, where V is the variable segment and J the joint segment. Here, we report the detailed analysis of gamma transcription in T cells of adult mice, and find that transcription may occur in T cells with a broad range of surface phenotypes; that it is predominantly of a single V gamma-C gamma unit (where C is the constant region); and that in cells freshly explanted from animals it can be of productively rearranged genes.

A phosphorylated, disulfide-linked membrane protein in murine cytotoxic T lymphocytes

The previously determined sequence of the murine T-cell gamma gene and its transcription in cloned T lymphocytes suggests that the polypeptide encoded by this gene is generally present in cytotoxic T cells as a 33-kDa monomer in a disulfide-bonded dimer. The gamma chain is also expected to be phosphorylated because a sequence in its cytoplasmic domain is homologous to an active site for serine phosphorylation in the regulatory subunit of cAMP-dependent protein kinase. We describe here a cytotoxic-T-cell-associated phosphorylated protein, many of whose properties suggest that it may be the product of the T-cell gamma gene. Its phosphorylation is greatly enhanced by interleukin 2 stimulation.

Diversity of murine gamma genes and expression in fetal and adult T lymphocytes

The search for the genes encoding the T-cell receptor alpha and chains revealed a third gene, T gamma (ref. 1), which shares with t T alpha (refs 2-7) and T beta (refs 8-15) genes a number of structure features, including somatic rearrangement during T-cell development. T gamma gene expression appears to be unnecessary in son mature T cells and is at its greatest in fetal thymocytes encouraging speculation that T gamma has a role in T-cell development and may be involved in the recognition of polymorphic major histocompatibility complex (MHC) products during thymic education. One argument against the participation of T gamma in such a process has been its apparently limited diversity, due to the small number of gene segments available for rearrangement. We here describe the identification of additional T gamma V-gene segments and demonstrate that they can be rearranged to previously identified J- and C-gene segments and are expressed in fetal thymocytes. In addition we describe a variety of patterns of T gamma mRNA processing which may be significant for T gamma gene regulation.

Human T-cell gamma genes contain N segments and have marked junctional variability

The gamma-chain genes are encoded by immunoglobulin-like gene segments in germline DNA which rearrange during the somatic development of T cells to form an active gene. The protein produced by these genes has not been identified and the diversity of the proteins that the genes can express has not been determined. We expect that the diversity of expressed gamma-chains is produced by the same three mechanisms that produce diversity of other immunoglobulin-like genes: (1) germline variable (V) and joining (J) region repertoires; (2) somatic mutation; and (3) junctional diversity. To define the contribution of each of these mechanisms to the generation of gamma-chain diversity, several gamma-chain complementary clones and rearranged gamma-chain genes have been characterized. Most of these clones seem to encode a defective gamma-chain, the variable- and constant-region portions being joined such that they would not be translated in the same reading frame. Here we report that the germline J-region diversity of the human T-cell gamma-chain is very limited and that somatic mutation does not contribute to the diversity of the gamma-chains encoded by the cloned segments. However, the junctional diversity of these gamma-chain genes is extensive. We suggest that N sequences (template-independent sequences) have been inserted enzymatically into all of the gamma-chain genes characterized.

Normal T cell development is possible without 'functional' gamma chain genes

The T cell-specific gamma gene family is organized into four V, J and C gene segments containing clusters (gamma 1, gamma 2, gamma 3, gamma 4) in germline DNA. We found that the V, J and C elements of gamma 2 are physically linked on a stretch of 6 kb of DNA while those of gamma 3 are found within a 15-kb region. Rearrangements take place only within the clusters, explaining the rigid rearrangement patterns seen in T lymphocytes. New V gamma, J gamma and C gamma gene segments were discovered and characterized allowing the better understanding of the potential germline diversity of the gamma gene family. No correlation with T cell function, i.e. cytolytic or helper, and the type of the productive gamma rearrangement could be established. In contrast we found that functional T cell clones have been able to mature without any functional gamma chain genes.

No functional gamma-chain transcripts detected in an alloreactive cytotoxic T-cell clone

Three groups of genes that undergo rearrangements during T-cell maturation have been isolated from T cells. Two of them encode the alpha- and beta-subunits of the T-cell antigen receptor and are shared between antigen-specific, major histocompatibility (MHC) class I-restricted cytotoxic T cells and antigen-specific, MHC class II-restricted helper T cells. The third group of genes, called gamma, is preferentially transcribed in cytotoxic T cells. This led to the hypothesis that the unidentified gamma-gene products could be part of a putative T-cell receptor responsible for MHC class I recognition. We report here on the isolation of three different types of gamma-gene transcripts of an alloreactive cytotoxic T-cell clone (3F9). Two are derived from two rearrangements that have occurred at the same locus (V gamma 10.8A to J gamma 10.5 and transcribed with C gamma 10.5), while the third involves a new V gamma-gene segment that is joined to J gamma 13.4 and transcribed with C gamma 13.4. All these rearrangements are abortive and lead to the formation of non-functional gamma-chain genes because the proper translational reading frame is not maintained. Because the second copy of the C gamma 13.4 gene segment is deleted and as C gamma 7.5 is considered to be a pseudogene and has not undergone any rearrangements in 3F9, we conclude that the alloreactive cytotoxic T-cell clone 3F9 does not contain a functional transcript of a known gamma-chain gene.

A functional gamma gene formed from known gamma-gene segments is not necessary for antigen-specific responses of murine cytotoxic T lymphocytes

Structural similarities between surface immunoglobulins (s Ig) on B cells and antigen-specific receptors on T cells suggest that a T cell, like a B cell, should express only two immunoglobulin-like genes, one for each subunit of the disulphide-linked, heterodimeric, antigen-specific (alpha beta) T-cell receptor. However, cytotoxic T lymphocytes (Tc cells) and immature thymocytes also contain RNA transcripts of a third immunoglobulin-like gene, called gamma (refs 1-4). A polypeptide corresponding to the gamma gene has not yet been identified and the function of this gene remains an enigma. Judging from its nucleotide sequence, the rearranged gamma gene is expected to encode an integral membrane polypeptide chain, and gamma complementary DNAs from two cloned Tc cell lines have previously been found to have different sequences around the V-J (variable region-joining region) junction, suggesting that, in these cells, the gamma-gene product is a clonally diverse surface structure that may form part of an as yet unidentified, antigen-specific receptor. To analyse further the extent of diversity of the gamma-gene product, we have determined the partial sequences of 11 gamma cDNA clones from three other cloned Tc cell lines, and report here that the sequences are indeed clonally diverse, but in all instances they are out-of-phase in the region of the V-J junction. This finding and the pattern of gamma-gene rearrangements in these cell lines indicate that a polypeptide product of the previously reported gamma gene, V2J2-C2, is not expressed in them and is, therefore, not necessary for the antigen-specific cytotoxic and proliferative responses of these mature T cells.

Diversity, rearrangement, and expression of murine T cell gamma genes

Although the T cell gamma genes are similar in many respects to T cell receptor alpha and beta genes, earlier studies suggested that only a single gamma variable (V gamma) gene is expressed in mature T cells. We report the isolation and characterization of three new rearranged V gamma genes from murine fetal thymocytes. Although each of the new V gamma gene rearrangements is present in fetal thymocytes, two of them are undetectable in mature T cells. The levels of mRNA corresponding to each type of V gamma gene rearrangement in mature T cells are dramatically diminished compared with those in fetal thymocytes, although the abundance of two of the rearranged genes is increased in mature T cells. Our results demonstrate that there is significant expressed variability of gamma genes in immature T cells. Furthermore, the dynamics of gamma gene rearrangement and expression support the idea that gamma genes function in immature T cells.

Exon/intron organization of the genes coding for the delta chains of the human and murine T-cell receptor/T3 complex

Genomic DNA clones containing the gene coding for the 20-kDa T3 glycoprotein of the T-cell receptor/T3 complex (T3-delta chain) of human and mouse were isolated and characterized. The human T3-delta gene is approximately equal to 4 kilobases (kb) long and contains five exons: a 151-base-pair (bp) exon containing the 5' untranslated and the coding sequences of the signal peptide, one exon of 219 bp, which contains most of the extracellular segment of the T3-delta chain, one 130-bp-long exon coding mainly for the transmembrane portion of the molecule, and two exons of 44 bp and 156 bp encoding the cytoplasmic domain and 3' untranslated region of the T3-delta chain, respectively. The murine T3-delta gene, which has a similar organization, contains 5 kb, because the first intron is approximately equal to 1 kb larger than in the human gene. Two major mRNA initiation sites within a small area approximately equal to 100 nucleotides 5' of the AUG codon were determined by S1 nuclease analysis and primer-extension studies. The remarkably high level of conservation of nucleotide sequences in this region suggests that this segment may be important for the regulation of T-cell-specific transcription of the T3-delta gene. The T3-delta gene does not contain the "TATA box" found in many eukaryotic promoters.