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

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.

Role of gamma-delta (γδ) T cells in autoimmunity

γδ T cells represent a small population of overall T lymphocytes (0.5-5%) and have variable tissue distribution in the body. γδ T cells can perform complex functions, such as immune surveillance, immunoregulation, and effector function, without undergoing clonal expansion. Heterogeneous distribution and anatomic localization of γδ T cells in the normal and inflamed tissues play an important role in alloimmunity, autoimmunity, or immunity. The cross-talk between γδ T cells and other immune cells and phenotypic and functional plasticity of γδ T cells have been given recent attention in the field of immunology. In this review, we discussed the cellular and molecular interaction of γδ T cells with other immune cells and its mechanism in the pathogenesis of various autoimmune diseases.

Evidence for the presence of murine primitive megakaryocytopoiesis in the early yolk sac

During mouse embryogenesis, primitive erythropoiesis occurs in blood islands of the yolk sac (YS) on the seventh day of gestation. This study demonstrated for the first time the presence of unique primitive megakaryocytic (Mk) progenitors in the early YS, which disappeared by 13.5 days postcoitum (dpc). When 7.5 dpc YS cells were incubated in the presence of stem cell factor (SCF), interleukin (IL)-3, IL-6, erythropoietin (EPO), thrombopoietin (TPO), and granulocyte colony-stimulating factor in methylcellulose clonal culture, not only erythroid bursts but also megakaryocyte colonies were observed. The megakaryocytes in the colonies matured to proplatelet stages and produced platelets as early as day 3 of culture, much earlier than those from adult bone marrow, although their ploidy class was lower. These megakaryocytes were stained with acetylcholine esterase, and expressed platelet glycoprotein (GP)Ib beta, GPIIIa, and platelet factor 4 by reverse transcription-polymerase chain reaction analysis. The analysis of hemoglobin types in erythrocytes obtained from hematopoietic multilineage colonies containing the megakaryocytes indicated that the Mk progenitors originated from primitive hematopoiesis. The primitive Mk progenitors formed colonies in the absence of any cytokines in fetal bovine serum (FBS)-containing culture, and SCF, IL-3, EPO, and TPO significantly enhanced the Mk colony formation. In FBS-free culture, however, no colony formation was induced without these cytokines. Because megakaryocytes were detected in 8.5-dpc YS, these unique primitive Mk progenitors may rapidly mature and give rise to platelets to prevent hemorrhage in the simultaneously developing blood vessels until definitive hematopoiesis begins to produce platelets. (Blood. 2001;97:2016-2022)

Immunological defense mechanisms in tuberculosis and MAC-infection

Protective immunity to mycobacterial infections develops in immunocompetent hosts after activation of alpha beta- and gamma delta-T cells in association with the generation of a protection-specific cytokine profile that stimulates the bactericidal potential of the macrophages. The maintenance of a delicate balance between Th1 and Th2 response is decisive for infection control and prevention of exacerbation of disease. Mycobacterial infection in the immunocompromised host is mainly due to the diminished cellular immune function. In addition, nontuberculous mycobacteria isolated from AIDS patients have special virulence factors that promote development of disease by further compromising the function of an already damaged cytokine network.

Tolerance and self-reactivity in V gamma 1.1C gamma 4 transgenic mice

Immunological tolerance is the process of inhibiting or eliminating lymphocytes that recognize self-derived antigens. By removing potentially harmful self-reactive clones, this mechanism allows for the random generation of a diverse repertoire of T-cells capable of responding to foreign pathogens. Although all self-reactive T-cells should be removed from the repertoire, it is quite clear from many recent studies that a significant fraction of T-cells bearing gamma delta T-cell receptors (TCR) recognize self-derived antigens in normal healthy mice. The presence of self-reactive T-cells in healthy animals presents a paradox which may be explained by understanding the transient expression of the antigens (e.g., MHC class Ib, Heat Shock Proteins) that have been identified for gamma delta T-cells thus far. Data from experiments with V gamma 1.1C gamma 4 transgenic mice demonstrating the presence of self-reactive gamma delta T-cells and their influence on lymphoid development and immune surveillance will be examined in this review.

A population of early fetal thymocytes expressing Fc gamma RII/III contains precursors of T lymphocytes and natural killer cells

We have identified a dominant fetal thymocyte population at day 14.5 of gestation in the mouse that lacks CD4 and CD8 but expresses Fc gamma RII/III several days prior to acquisition of the T cell receptor (TCR) in vivo. If maintained in a thymic microenvironment, this population of CD4-CD8-TCR-Fc gamma RII/III+ thymocytes differentiates first into CD4+CD8+TCRlowFc gamma RII/III- thymocytes and subsequently CD4+CD8-TCRhighFc gamma RII/III- and CD4-CD8+TCRhighFc gamma RII/III- mature Ti alpha-beta lineage T cells. However, if removed from the thymus, the CD4-CD8-TCR-Fc gamma RII/III+ thymocyte population selectively generates functional natural killer (NK) cells in vivo as well as in vitro. These findings show that a cellular pool of Fc gamma RII/III+ precursors gives rise to T and NK lineages in a microenvironment-dependent manner. Moreover, they suggest a hitherto unrecognized role for Fc receptors on primitive T cells.

IL-2-dependent murine T-cell lines and clones expressing gamma/delta T-cell antigen receptors. I. Functional and biochemical characterization

We have developed two stable IL-2-dependent T-cell lines designated AKV-I and AKV-N from the enlarged spleens, respectively, of an AKV1 and an NFS mouse. Immunofluorescence staining with the appropriate monoclonal antibodies revealed that cells of the AKV-I cell line were alpha beta TCR-CD3+CD4-CD5-CD8+CD25+, whereas cells of the AKV-N cell line were alpha beta TCR-CD3+CD4-CD5+CD8-CD25+. A number of T-cell clones were developed from the AKV-I or AKV-N T-cell lines by limiting dilution and analysed by immunofluorescence. All clones tested were alpha beta TCR-CD3+CD4-CD25+. Certain T-cell clones expressed the CD5 antigen, whereas others expressed the CD8 antigen. The AKV-I cell line responded by proliferation to rIL2, rIL4, phorbol myristate acetate (PMA), PMA plus IL-4 and PMA plus PHA or Con A. In contrast, the AKV-N cell line did not respond to rIL-4 or rIL-4 plus PMA and exhibited only a modest proliferative response to PMA alone. Both AKV-I and AKV-N T-cell lines as well as a large number of T-cell clones examined were able to lyse cells of the PU5-IR murine cell line in the presence of the anti-CD3 (clone 145-2C11) MoAb, demonstrating their ability to mediate cytotoxicity in this system. Biochemical analysis of both AKV lines and a number of clones by immunoprecipitation with the anti-CD3 MoAb, followed by one-dimensional (either non-reducing or reducing) or two-dimensional (non-reducing/reducing) SDS-PAGE, revealed that the AKV lines and clones expressed a disulphide-linked dimer. Under non-reducing conditions, a band in the range of 75-85 kDa was observed and upon reduction it was resolved into two discrete polypeptide chains of 43-44 kDa and 48 kDa in certain AKV-I cells or 38 kDa and 42 kDa in certain AKV-N cells. In other T-cell clones or lines a broad band of 42-47 kDa was observed in AKV-I cells or 38-45 kDa in AKV-N cells. These results suggest the presence of different forms of disulphide-linked dimers on these cells. Northern blotting analysis using probes specific for the constant regions of the alpha-, beta-, gamma- and delta-chains of the T-cell antigen receptor revealed that all the AKV cell lines or clones tested expressed full-length alpha-, gamma- and delta-chain mRNA, whereas beta-chain mRNA was absent.(ABSTRACT TRUNCATED AT 250 WORDS)

Recognition of a single hsp-60 epitope by an entire subset of gamma delta T lymphocytes

We can conclude that a large subset of gamma delta cells, present in both murine newborn thymus and in adult spleen, respond to the stress protein, hsp60. hsp60 seems to be stimulatory whether it is derived from a foreign pathogen such as mycobacteria, or whether it originates from the mouse's own cells. The gamma delta cells that respond to this antigen bear very similar receptors, all expressing V gamma 1 and most expressing V delta 6, although their junctional variations indicate that not all members of the subset stem from clonal expansion of only one or a few cells. The hsp60-reactive subset has not at this time been shown to "home" to an epithelial location, in contrast to other known gamma delta cell subsets, and may rather carry out its functions while in circulation. Whether the hsp60 antigen requires a "presenting" molecule remains at this point unclear, but because the gamma delta cells all respond to a synthetic peptide representing an epitope of hsp60, presentation is implied. Human gamma delta cells that respond to PPD from mycobacteria, as do the mouse hsp60-reactive gamma delta cells, have also been described, many as members of a major subset in peripheral blood, although only rarely have these been reported to respond to mycobacterial hsp60. The antigenic source in PPD for these cells has not yet been determined, but as for the mouse, a low molecular weight peptide appears to be sufficient for stimulation (P. Brennan and R. Modlin, personal communication). The PPD-reactive gamma delta cells, when their receptors have been characterized, have been found to express a V gamma 9+ chain. Some evidence indicates that these cells can also recognize self hsp60; hence, in several ways, this human subset has characteristics similar to the mouse hsp60-reactive subset. Perhaps gamma delta cells that respond to hsp60 play an important role, in both mice and humans, in the detection of transformed self cells or cells containing intracellular pathogens, that escape detection by alpha beta T cells.

Recognition of MHC TL gene products by gamma delta T cells

We have studied the ligand specificity of a gamma delta T-cell receptor (TCR) derived from a mouse T-cell hybridoma (KN6). KN6 cells reacted with syngeneic (C57BL/6) cells from various origins (splenocytes, thymocytes, peritoneal exudate cells, etc.) and cells from many different mouse strains. KN6 reactivity against cells from a panel of congenic and recombinant mouse strains demonstrated that the ligand recognized by KN6 is controlled by an MHC-linked gene that most probably maps in the TL region. We cloned this gene and formally proved that it does map in the TL region. This gene turned out to be a novel class I gene (designated T22b) belonging to a hitherto unidentified cluster of TL region genes in strain C57BL/6. This gene was expressed in many different tissues and cell types. We also examined the tissue expression of several other TL genes. One of these, the structural gene (T3b) encoding the thymus leukemia (TL) antigen from C57BL/6 mice, was specifically expressed in the epithelium of the small intestine. Since the intestinal epithelium of the mouse is known to be the homing site for a subset of gamma delta T cells (i-IEL) bearing diverse TCR with V7 rearranged gamma chains, we propose that the T3b gene product is part of the ligand recognized by some of the i-IEL. Our data support the idea that gamma delta T cells might be specific for non-classical class I or class I-like molecules and suggest that gamma delta TCR and non-classical MHC co-evolved for the recognition of a conserved set of endogenous or foreign peptides.

Natural killer (NK) activity of cultured S100 beta-positive T-leukemia cells

In order to clarify the function of human S100 beta-positive T-cells, S100 beta-positive T-leukemia cells (S100 beta TLC) were examined in vitro. S100 beta TLC were obtained from the peripheral blood of a patient with S100 beta-positive T-cell leukemia and enriched by an E-rosetting method. Two dimensional flow cytometric analysis indicated that the vast majority of the E-positive fraction were S100 beta TLC expressing CD3 and CD8 antigens. Although S100 beta TLC expressed CD3 antigen, they were negative for the alpha/beta and gamma/delta T-cell antigen receptor (TCR) defined by monoclonal antibodies (mabs) WT-31 and delta TCS-1, respectively. It was speculated that S100 beta TLC initially expressed alpha/beta TCR but lost it during malignant transformation. When S100 beta TLC were cultured for 24 h, they acquired cytotoxic activity towards various NK-sensitive cell lines including K-562, Molt-3 and CEM-CCLF, but did not exhibit lysing activity towards NK-resistant cell lines including Raji, Daudi and MT-1. Despite the NK-activity of cultured S100 beta TLC, they lacked the morphological features of large granular lymphocytes (LGL). S100 beta TLC did not exhibit lymphokine-activated killer (LAK) activity. When S100 beta TLC were cocultivated with NK-sensitive cells or NK-resistant cells, they selectively bound to NK-sensitive cells, indicating that they lysed target cells by cell-to-cell contact. The finding that S100 beta TLC lacked TCR molecules and their NK activity was not inhibited by mabs reactive with the CD3-TCR complex indicated that the CD3-TCR complex was not involved in their target recognition.(ABSTRACT TRUNCATED AT 250 WORDS)

A murine thymocyte clone expressing gamma delta T cell receptor mediates natural killer-like cytolytic function and TH1-like lymphokine production

The murine CD4- CD8- (double negative, DN) thymocyte cell line and clones expressing T cell receptor gamma delta chains in association with CD3 complex have been established and characterized. This line and a representative clone (DN7.12.11) which appear to derive from the minor population of CD3+ DN thymocytes can be stimulated to proliferate and to produce lymphokines by anti-CD3 or anti-Thy-1 antibodies or calcium ionophore plus phorbol ester. Autocrine proliferation is dependent on binding of interleukin (IL)2 to functional IL2 receptor. Upon stimulation, these cells produce IL2 and IFN-gamma but not IL4, resembling conventional CD4+ TH1 cells in this regard. The cloned line also mediates spontaneous cytolysis against a variety of tumor targets without regard for the presence of conventional major histocompatibility complex molecules on the target cell surface. Blocking and modulation experiments suggest that target recognition by the gamma delta/CD3 complex is not involved in the spontaneous lysis, resembling natural killer (NK) cells. The results suggest that gamma delta +DN T cells are able to have mature functions such as NK-like cytotoxicity and lymphokine secretion as peripheral gamma delta +T cells. They also provide a possible role of gamma delta + DN thymocytes in establishing a intrathymic environment for differentiation and selection of alpha beta-expressing T cells.

Developmentally regulated fetal thymic and extrathymic T-cell receptor gamma delta gene expression

The gamma delta T-cell receptor (TCR) is the first TCR to be expressed in ontogeny in all vertebrates in which it has been examined thoroughly. Murine gamma delta cell-surface protein is detected by the fourteenth day of gestation. In this work, the activation of gamma delta RNA has been studied. Data indicate that the first TCR protein to appear in the thymus is encoded by gamma genes that are activated after cells colonize the thymus. However, the sequential appearance of different gamma delta TCR proteins during thymic ontogeny cannot be readily explained by differential temporal activation of V gamma genes in the thymus. There are distinct patterns of gamma and delta gene expression during fetal liver development and in the fetal gut (or tissue associated with it). Cells apparent in the liver of mice at birth express gamma delta cell-surface protein, but they disappear from the liver very soon afterward. One V gamma gene is rearranged and expressed prethymically. In addition, gamma gene expression is detectable in the livers of newborn athymic mice. Together, these observations indicate a thymic-independent pathway of activation of TCR genes.

Characterization of gamma/delta T cell clones isolated from human fetal liver and thymus

The origin and development of T cells bearing gamma/delta T cells receptors (TcR) has been extensively studied in the mouse. By contrast, little is known about development patterns and diversity of the human gamma/delta T cell lineage. To study the repertoire of human gamma/delta+ T cells during T cell ontogeny, we have isolated clonal populations of gamma/delta+ T cells from 14-week fetal thymus and liver and characterized the molecular composition of their TcR. The technique of in situ hybridization was used to identify cells expressing TcR genes in fetal liver and thymus. A panel of clones representative of developing T cell populations found in vivo was subsequently isolated from both tissues and clones expressing cell surface gamma/delta receptors were identified. Although both the liver-derived gamma/delta+ T cell clone, L2, and the thymus-derived gamma/delta+ T cell clone, T6, had similar cell surface phenotypes, namely CD3+, CD7+, CD45+ and CD8-, their reactivity with anti-CD2 and -CD4 antibodies was different. L2 was CD2high, CD4- whereas T6 was CD2low, CD4low. Both clones possessed effector functions similar to those of adult T cells as demonstrated by the synthesis and secretion of cytokines in response to stimulation through the CD3/TcR complex. Analysis of the TcR composition of the fetal clones showed both clones to possess similar or identical gamma chain components, C gamma 1, J gamma 1/2, V gamma 8, and both utilize V delta gene segments other than V delta 1. This TcR genotype has not been previously reported in the analysis of adult gamma/delta+ T cells. Our studies have identified a unique population of human gamma/delta+ T cells that may be derived extrathymically and appear to be preferentially and perhaps transiently expressed during fetal life.

The role of gamma delta T cells in the normal and disordered immune system

A small population of T cells does not express the conventional T cell receptor characterized by the alpha and beta polypeptide chains (TCR alpha beta) but instead, two polypeptides termed gamma and delta (TCR gamma delta). This alternative receptor is able to recognize antigen. It appears early in T cell ontogeny, but its role in the thymus prior to the availability of TCR alpha beta remains unclear. In selected sites such as skin or gut TCR gamma delta predominates in mice which might suggest a role of gamma delta T cells in the first line of defense against infection. gamma delta T cells secrete lymphokines and display cytotoxic activity. However, their activation requirements may differ from what is known for alpha beta T cells since MHC-nonrestricted and also CD4 and CD8 negative gamma delta T cells have been described. Preferential activation by mycobacterial antigens possibly indicates a special repertoire of the gamma delta T cells. In various diseases slightly increased numbers of gamma delta T cells were found, but these preliminary studies have not yet provided evidence for a major pathogenetic role of gamma delta T cells.

A large fraction of human peripheral blood gamma/delta + T cells is activated by Mycobacterium tuberculosis but not by its 65-kD heat shock protein

We report that M. tuberculosis organisms, but neither PHA nor allogeneic stimulator cells, preferentially activate gamma/delta+ cells within E rosette-purified peripheral blood T cells. gamma/delta+ T cells from purified protein derivative (PPD)-nonimmune healthy donors were enriched by depletion of CD4+ and CD8+ cells; double-negative (DN) cells contained 65-92% gamma/delta+ T cells. Limiting dilution (LD) analyses revealed that 1 of 2-19 purified DN cells proliferated in response to mycobacteria, while frequencies of DN cells proliferating in response to a recombinant 65-kD heat shock protein (hsp 65) of M. tuberculosis/M. bovis were 10-20-fold lower. Established clones of mycobacteria-reactive gamma/delta+ T cells specifically recognized mycobacteria, but neither PPD nor hsp 65. Restimulation of these clones required the presence of PBMC feeder cells; EBV-transformed lymphoblastoid cell lines could not substitute for PBMC. Mycobacteria-reactive gamma/delta+ clones proliferated equally well in the presence of autologous or allogeneic (HLA-DR-different) PBMC feeder cells and thus were not MHC class II restricted. Taken together, these results demonstrate that mycobacteria-reactive gamma/delta+ T cells are present in high frequency in the peripheral blood of healthy individuals, and suggest that hsp 65 of mycobacteria is not a major antigen for gamma/delta+ T cells of normal PPD-nonimmune blood donors.

Alpha beta lineage-specific expression of the alpha T cell receptor gene by nearby silencers

T cells expressing either the alpha beta or gamma delta antigen receptor (TCR) are distinct cell lineages. The single locus encoding the TCR alpha and delta genes requires special regulation to avoid alpha gene expression in gamma delta T cells. We show here that the minimal alpha enhancer is active in the gamma delta T cell lineage but gains alpha beta lineage specificity through negative cis-acting elements 3' of the C alpha gene that silence the enhancer in gamma delta T cells. The negative elements at the C alpha locus consist of several silencers that work in an orientation- and distance-independent fashion. These silencers also act on a retroviral enhancer that is normally ubiquitously expressed, restricting its activity to alpha beta cells. The alpha silencers are active in non-T cell lines, suggesting that the decision of a cell to differentiate into the alpha beta T cell lineage may involve specific relief from these silencers. Silencers are likely to be as important as enhancers in establishing lineage-specific gene expression in many systems.

Intraepithelial lymphocytes. Anatomical site, not T cell receptor form, dictates phenotype and function

The function and structure of the TCR proteins of intraepithelial lymphocytes (IEL) were examined using a panel of mAbs specific for TCR-gamma/delta. Three subsets of TCR-gamma/delta+ IEL could be detected with five mAbs, termed GL1-GL5. The mAbs were able to trigger lysis via crosslinking of the IEL TCR and all of the subsets were constitutively cytolytic. Immunoprecipitation of IEL TCR proteins revealed that the GL2 mAb reacted only with gamma, delta heterodimers containing high Mr delta chains, while the other mAbs precipitated all of the observed gamma and delta proteins. Two-color fluorescence analysis showed that the GL2+ subset was contained within the larger GL1+ subset. The GL3 and GL4 mAbs appear to be specific for all TCR-gamma/delta while GL2 was V delta 4 specific. Analysis of IEL for TCR-alpha/beta expression demonstrated that approximately 20% of B6 IEL were TCR-alpha/beta+. Interestingly, this population of IEL contained Thy-1- and CT1+ cells, indicating that the unique phenotype of IEL was not restricted to TCR-gamma/delta+ cells. Moreover, the TCR-alpha/beta+ IEL were also constitutively cytolytic, suggesting that the intestinal milieu was controlling the functional programming of IEL regardless of TCR type. The mAbs reported here as well as the ability to exploit the distinct phenotype of IEL should prove useful in determining the function of IEL and the TCR-gamma/delta.

Recognition of a self major histocompatibility complex TL region product by gamma delta T-cell receptors

Ligand specificity of a murine gammadelta T-cell receptor-expressing hybridoma (KN6) derived from adult thymocytes has been analyzed in detail. The molecule recognized by the KN6 gammadelta T-cell receptor is expressed on syngeneic cells of various sources (peritoneal macrophages, thymocytes, spleen cells, and Abelson murine leukemia virus-transformed cell lines) and on transformed cells arrested at an early stage of development (e.g., PCC3 embryonal carcinoma cells). Linkage of the gene coding for the KN6 ligand to the major histocompatibility complex genes could be demonstrated by testing KN6 hybridoma reactivity to cells from congenic strains that differ only at H-2. In addition, analysis of recombinant strains indicates that the gene controlling the KN6 ligand is located in or distal to the TL region. Involvement of the KN6 gammadelta T-cell receptor in this recognition process could be directly demonstrated by transferring the KN6 TL specificity after introduction of the productively rearranged KN6 gamma and delta genes into an alphabeta T-cell clone or into the germ line in transgenic mice. These observations raise the possibility that at least some gammadelta cells regulate hemopoietic cell maturation and activation.

Analysis of T cell receptor gamma chains from adult CD4- CD8- thymocytes

The role of T cell receptor (TcR) gamma genes in T cell development has not been determined. To extend our understanding of the repertoire of TcR gamma expression, we prepared a cDNA library from CD4-CD8- adult BALB/c thymocytes and cloned and sequenced 15 TcR gamma genes from this cDNA library. We found that two clones were transcripts of the unrearranged C gamma 2 gene and that three clones terminated in the J gamma 2 region. Nine of the remaining clones were V gamma 1.2 J gamma 2 C gamma 2 genes and five of these were in frame. Only one clone corresponded to C gamma 1 and resulted from an in-frame V gamma 2 J gamma 1 C gamma 1 join. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the gamma chain proteins from the surface of both BALB/c and C57BL/6 adult CD4-CD8- thymocytes did not detect the 32-kDa V gamma 1.2 C gamma 2 protein, but did detect the 35-kDa V gamma C gamma 1 protein. These results suggest that despite the abundance of full-length functional V gamma 1.2 C gamma 2 transcripts in the thymocyte subset, the protein product is not expressed on the cell surface as the predicted 32-kDa gamma protein. Finally, our analysis of the V-J joining of the gamma genes reveals both flexibility at the V-J junction and extensive N-region nucleotide addition that lead to diversity of the predicted protein sequence.

Monoclonal antibodies specific to native murine T-cell receptor gamma delta: analysis of gamma delta T cells during thymic ontogeny and in peripheral lymphoid organs

Three hamster monoclonal antibodies (mAbs), all recognizing different epitopes present on the native form of the murine T-cell antigen receptor (TCR) gamma delta subunits, have been generated. mAb 3A10 is specific to a pan-murine TCR gamma delta, recognizing a C delta constant region determinant. mAb 8D6 is specific to a subset of T cells expressing V gamma 4- and V delta 5-encoded gamma delta TCR, and mAb 5C10 is clonotypic. Using these and other mAbs directed against a variety of T-cell surface markers, we quantitated and characterized gamma delta T cells present in developing thymuses as well as in the conventional lymphatic organs by flow cytometry. These studies revealed that (i) many gamma delta thymocytes and peripheral T cells bear CD4 and/or CD8 molecules, (ii) T cells bearing both alpha beta and gamma delta TCRs are scarce, and (iii) thymocyte subsets bearing TCR gamma delta encoded by different combinations of V gamma and V delta gene segments appear in waves during ontogeny.

Diversity of gamma delta T-cell receptors on murine intestinal intra-epithelial lymphocytes

The search for the genes encoding the T-cell receptor (TCR) alpha- and beta-subunits revealed a third gene gamma which shares with the alpha- and beta-genes several properties including somatic rearrangement. This gene, together with a fourth rearranging gene delta, encodes a second type of T-cell receptor, TCR gamma delta. Although TCR gamma delta-bearing T cells constitute a relatively minor subpopulation in the thymus and in peripheral lymphoid organs, they are the major lymphocytes of epidermis (dendritic epidermal cells or DEC) and of intestinal epithelium (intestinal intraepithelial lymphocytes or IEL) in mice, suggesting that at least some gamma delta T cells are important in the surveillance of a variety of epithelia. It was recently reported, however, that the TCR gamma delta on DEC has essentially no structural diversity, implying that the putative ligand is monomorphic. As this finding, if generally applicable, poses severe restrictions on the origin of the ligand, we investigated the diversity of the TCR on the second major epithelium-associated gamma delta T cells, namely IEL from mice. We report here that by contrast with the DEC gamma delta, the IEL gamma delta TCR are structurally diverse.

Murine anti-CD3 monoclonal antibody induces potent cytolytic activity in both T and NK cell populations

Antibodies specific for the CD3 complex have the capacity to both stimulate and inhibit a variety of T cell functions. We show here that a monoclonal antibody to the epsilon chain of CD3 can induce efficient non-MHC-restricted cytolytic activity in murine lymphocytes with peak activity occurring after 48 hr of incubation. In a panel of targets, the anti-CD3-activated effectors lysed tumor cells but not normal lymphoblasts. Cytolysis was not dependent on the presence of the antibody in the cytolytic assay. Moderate to high cytolytic activity was elicited from lymph nodes, spleen, and thymus by anti-CD3 treatment in vitro, whereas only low activity was apparent in bone marrow. The precursors of anti-CD3-activated cells consisted largely of mature T cells, although a smaller component of immature T cells was also involved. Thus, separation of thymocytes based on adhesion to peanut agglutinin revealed that both positive (immature) and negative (mature) fractions could be activated, while cytotoxic pretreatment of spleen cells with an antibody (J11d) to immature T cells before anti-CD3 activation significantly decreased the resulting cytotoxicity. The majority of precursors in spleen were Thy 1+ and CD8+ and/or AGM1+. Antibody depletion studies showed that the effector cells have both a T and a NK component consisting of Thy 1+, CD5+, CD8+, CD4-, and AGM1- cells and Thy 1-, CD5-, CD8-, CD4-, and AGM1+ cells, respectively. The production of significant amounts of IL-2 and TNF in culture following anti-CD3 treatment, along with the synergistic effect of exogenously added IL-2, suggests that one or both of the effector cell types could be induced by lymphokines. The intraperitoneal administration of the anti-CD3 antibody induces cytolytic activity in vivo. Therefore, the direct activation of cytolysis by anti-CD3 antibody and the additional effects, both direct and synergistic, of lymphokines produced by the activated lymphocytes could conceivably provide a potent anti-tumor therapy.

Development of a monoclonal antibody specific for the gamma chain of the T-cell antigen receptor using an open reading frame expression vector

To develop an anti-framework monoclonal antibody (mab) specific for the gamma (gamma)-chain of the T-cell antigen receptor (TCR), we expressed a part of the constant region of the gamma-chain (C gamma 2 gene segment) in E. coli using the pWR590 vector. This plasmid contains the E. coli lac promoter, operator, a truncated beta-galactosidase (beta-gal) gene (coding for the first 590 of the 1,007 amino acids of the beta-gal) and a polylinker region (at the 3' end of the beta-gal) containing nine restriction sites. These can be cleaved by any one of eight common restriction enzymes, permitting the introduction of the DNA fragment of interest. We employed the pT gamma 1 gamma-chain cDNA probe, which like the vast majority of the gamma-chain specific probes is aberrant and contains an in-frame stop codon at the junction of V and J regions. Computer analysis of the pT gamma 1 sequence revealed several MaeIII restriction sites that could result in a number of fragments. One of these fragments consisted of 245 base pairs (nucleotides 404-648) and contained most of the CI exon of the C gamma 2. Successful insertion of this fragment to the pWR590 vector was confirmed using restriction enzyme analysis. The C gamma insert was 12% of the construct. Expression of the pWR590-HpT gamma 1 recombinant plasmid in E. coli followed by SDS-PAGE analysis revealed a hybrid protein with a molecular weight of 85 kd which constituted at least 25% of the total E. coli insoluble protein. In contrast, cells transformed with the control pWR590 vector without insert expressed a 78 kd polypeptide chain. We developed several mabs against the pWR590-HpT gamma 1 hybrid protein by fusing spleen lymphocytes from BALB/c mice immunized with the pWR590-HpT gamma 1 protein, with cells of the NS1 mouse myeloma cell line. Screening of the mabs was carried out by ELISA against the pWR590-HpT gamma 1 hybrid protein and the control pWR590 beta-gal protein (beta-gal 590), derived by expressing in E. coli the pWR590 vector without gamma-chain insert. Two groups of mabs were obtained, those reacting with the pWR590-HpT gamma 1 hybrid protein only and those reacting with both the hybrid and the control beta-gal 590 proteins. The specificity of these mabs was further studied by Western blotting with similar results.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of gamma delta T cells in the primary immune response to Mycobacterium tuberculosis

Although the immunologic role of T cells bearing the conventional alpha beta T cell receptor (TCR) has been well characterized, little is known about the function of the population of T cells bearing the gamma delta TCR. Therefore, the role of gamma delta T cells in the immune response to Mycobacterium tuberculosis (MT) was investigated. The number of TCR gamma delta cells in the draining lymph nodes of mice immunized with MT was greatly increased in comparison with the number of TCR alpha beta cells. Three biochemically distinct gamma delta TCRs were detected. Analyses of cell cycle, of interleukin-2 receptor expression, and of interleukin-2 responsiveness showed that a large proportion of the gamma delta T cells were activated in vivo. TCR gamma delta cells responded to solubilized MT antigens in vitro but, in contrast to MT-specific alpha beta T cells, the response of gamma delta T cells to MT did not require major histocompatability complex class II recognition. These results provide an example of antigen-specific activation of gamma delta T cells in vivo and indicate that gamma delta T cells may have a distinct role in generating a primary immune response to certain microorganisms.

Dendritic epidermal T cells: activation requirements and phenotypic characterization of proliferating cells

Dendritic epidermal T cells (DETC) are CD45+, Thy-1+, CD5-, CD8-, CD4- murine lymphocytes that express surface-bound CD3 antigens associated with T cell receptor gamma/delta heterodimers. Using epidermal cells greatly enriched for DETC and depleted of Langerhans cells, we found that DETC have growth requirements quite different from those of accessory cell-depleted lymph node and splenic T cells. Although the latter cells strongly proliferate in response to phorbol myristate acetate (PMA) + ionomycin, DETC, when exposed to interleukin-1 (IL-1), interleukin-3 (IL-3), concanavalin A (ConA), PMA, and ionomycin used either alone or in combination, do not exhibit significant mitotic activity. Recombinant interleukin 2 (rIL-2), albeit ineffective by itself, leads to vigorous proliferation of DETC when used with either ConA or PMA + ionomycin + IL-1. In contrast, the combination of PMA and recombinant interleukin-4 (rIL-4), which triggers growth of lymph node T cells, does not induce proliferation of DETC. Although a portion of proliferating DETC expressed CD8 antigens, essentially none bore detectable amounts of surface-bound CD4 or CD5 antigens, or both. Continuing stimulation of primary DETC cultures with lectin/lymphokine-rich media results in the propagation of cells with the essential phenotypic features of resident DETC.

Strain differences in the early development of the thymus-dependent cells: precocity of T lineage cells in AKR mice as compared to those in C3H mice

Early development of T lineage cells were compared between AKR and C3H mice by using two experimental strategies--neonatal thymectomy (NTx) and bone marrow transplantation (BMT)--between these two strains of mice. After NTx, AKR mice developed less wasting disease and showed better maintenance of several T cell functions. In addition, the response of neonatal spleen cells to PHA and ConA was much greater in AKR mice than in C3H mice. Further, when AKR mice were used as recipients of BMT, cell numbers recovered from thymuses between 2 and 7 weeks after reconstitution were consistently much greater (about 10 times greater) than those from chimeras where C3H mice were used as recipients, regardless of the donor strains of bone marrow cells. However, 4 weeks after BMT the proliferative responses to ConA were consistently higher in the donor-derived thymocytes from chimeras where AKR mice were used as bone marrow donors than in those from chimeras in which C3H were donors. The present findings suggest that these differences may be attributed to characteristics of recipient microenvironment (e.g., thymic stroma) which maintain developing thymocytes and supply them to the peripheral lymphoid tissue. Alternatively the differences may to some degree also be attributable to characteristics of the thymic progenitors themselves, which may determine the rates of maturation of thymocyte functions.

Characterization of T-cell-receptor gamma (TRG) gene rearrangements in alloreactive T-cell clones

Rearrangements of the T-cell Rearranging Gene (TRG) or T-cell-receptor gamma-chain genes were analyzed in 24 in vivo-sensitized alloreactive T-cell clones. This analysis represents the first complete assignment of TRG gene rearrangements to given variable and joining gene segments in nonleukemic T cells and provides some evidence for the hypothesis of sequential gamma genes rearrangements during T-lymphocyte differentiation. TRG gene rearrangements in our T-cell panel involved the known "active" V gamma genes, with a preferential use of V2 and V4 genes. In most clones, rearrangements occurred on both chromosomes and involved the J2 segment, but only 2 and 4 out of the 49 described rearrangements involved the additional J gamma segments JP1 and JP2, respectively. Two peculiar rearrangements were found. The first one was probably due to the creation of a new restriction enzyme site in the N-region at the V-J junction; the second can be explained by an aberrant rearrangement of a V gene to a sequence located between exons 2 and 3 of the TRGC1 gene.

Different gamma delta T-cell receptors are expressed on thymocytes at different stages of development

We have analyzed the structural diversity of the murine gamma delta T-cell receptor (TCR) heterodimer expressed on CD4- CD8- thymocyte populations and on TCR gamma delta-expressing hybridomas derived from thymocytes of fetal, newborn, and adult mice. We found that CD4- CD8- thymocytes derived from mice of different pre- and postnatal age preferentially express a gamma delta TCR encoded by different subsets of gamma and delta gene segments. This age-dependent differential expression of gamma delta TCR on thymocytes seems to be accomplished in part by a specific control of rearranged gamma genes operating at the level of transcription and/or RNA stability. We discuss the implications of these findings with respect to the recognition roles of the gamma delta TCR.

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.

Intestinal intraepithelial lymphocytes are a distinct set of gamma delta T cells

Lymphocytes are most reliably subdivided on the basis of their receptors for antigen at the cell surface. Three subtypes of lymphocytes are well defined: B cells that bear surface immunoglobulin and make antibody, CD4+T cells with CD3 alpha beta receptors specific for antigen associated with class II major histocompatibility complex molecules, and CD8+T cells with CD3 alpha beta receptors specific for antigen associated with class I MHC molecules. These T cells are responsible for known forms of cell-mediated immunity. The discovery of a third rearranging T-cell specific gene called gamma (refs 1 and 2) has revealed the presence of a new class of T cells bearing a new receptor type, CD3 gamma delta (refs 3-7). To date, neither the function nor the specificity of cells bearing this receptor has been determined. Because gamma delta T cells are the main lymphocyte of epidermis, it was proposed that such cells could be important in surveillance of all epithelia. We have isolated intraepithelial lymphocytes from murine small intestine, and shown that they predominantly or exclusively express CD3 gamma delta receptors. Unlike the epidermal lymphocytes, these cells also express CD8, and they use a different V lambda gene to form their receptor. This strongly suggests that gamma delta T cells home in a very specific manner to epithelia, where they presumably mediate their function.

Structure and specificity of T cell receptor gamma/delta on major histocompatibility complex antigen-specific CD3+, CD4-, CD8- T lymphocytes

Analyses of TCR-bearing murine and human T cells have defined a unique subpopulation of T cells that express the TCR-gamma/delta proteins. The specificity of TCR-gamma/delta T cells and their role in the immune response have not yet been elucidated. Here we examine alloreactive TCR-gamma/delta T cell lines and clones that recognize MHC-encoded antigens. A BALB/c nu/nu (H-2d)-derived H-2k specific T cell line and derived clones were both cytolytic and released lymphokines after recognition of a non-classical H-2 antigen encoded in the TL region of the MHC. These cells expressed the V gamma 2/C gamma 1 protein in association with a TCR-delta gene product encoded by a Va gene segment rearranged to two D delta and one J delta variable elements. A second MHC-specific B10 nu/nu (H-2b) TCR-gamma/delta T cell line appeared to recognize a classical H-2D-encoded MHC molecule and expressed a distinct V gamma/C gamma 4-encoded protein. These data suggest that many TCR-gamma/delta-expressing T cells may recognize MHC-linked antigens encoded within distinct subregions of the MHC. The role of MHC-specific TCR-gamma/delta cells in immune responses and their immunological significance are discussed.

Age-associated increase in the expression of T cell antigen receptor gamma chain genes in mice

T cell function generally declines with age. To determine the underlying cause of the age-related decline, we compared the expression levels of T cell antigen receptor genes encoding gamma, beta and alpha chains in the lymphoid tissues of young (8 wk old) vs. aged (40 wk old) mice. An age-associated increase in gamma chain gene transcripts was evident in the thymocytes, spleen cells and mesenteric lymph node cells. Aged mice had a relatively high proportion of CD3+CD4-CD8- cells but a reduced level of CD3+CD4-CD8+ cells in the lymphoid tissues, as compared with young counterparts. The allo-reactivity in the lymphoid cells, as assessed by mixed lymphocyte reaction (MLR) responses, decreased with advancing age. On the contrary, increased levels of syngeneic MLR and spontaneous cytolytic activity were noted in the lymphoid cells of aged mice, as compared with findings in their young counterparts. A remarkable increase in the number of CD3+CD4-CD8- cells and level of the gamma chain gene messages was also detected in the responder cells of day 4 syngeneic MLR culture from aged mice. An increase in the number of T cells bearing gamma chain may be related to the alterations in immunological functions in aged mice.

In situ localization of T cell receptor beta chain in the murine thymus: changes in the intrathymic distribution of thymocytes expressing beta chain during fetal development

The expression of T cell receptor beta chain in the developing thymus was examined at the light and electron microscopic levels using the monoclonal antibody F23.1. Cells expressing cytoplasmic forms of beta chain were first observed at Day 16 of gestation, while thymocytes expressing cell surface beta chain were detected about a day later. Clustering of cortical F23.1+ cells was more pronounced in fetal thymus when compared to adult. The density of F23.1+ cells in the subcapsular areas of the thymus was initially lower than that in the rest of the cortex or the medulla. Within the subcapsular and cortical areas of the thymus there was an inverse relationship between the density of F23.1+ cells and cells labeled with the lectin from Dolichos bifloris, which binds to terminal alpha-linked N-acetylgalactosamine residues preferentially expressed by L3T4-/Lyt2- thymocytes. Although this pattern was less pronounced with increasing gestational age, it was still apparent at birth.

Predominant variable region gene usage by gamma/delta T cell receptor-bearing cells in the adult thymus

Previous studies have indicated that the diversity of gamma genes expressed by gamma/delta-bearing murine T cells is limited, but comparable information concerning the expressed diversity of delta genes is lacking. In this study, we have investigated the rearrangement and expression of delta and gamma genes in T cell hybridomas that express gamma/delta T cell receptors. Three productive delta chain cDNA clones were isolated (delta 7.3, delta 7.1, and delta 2.3) that encode new variable region sequences. Two of the delta cDNAs differ significantly from those observed in the V alpha repertoire. In addition, one cDNA expressed a new J delta region (J delta 2), which was localized between J delta 1 and C delta genes. Using these and other delta gene probes and gamma gene probes, we found that five independent hybridomas expressed four different V delta s and three different V gamma s. However, analysis of an enriched population of gamma/delta-expressing cells from the adult thymus suggests that only a few V delta genes and one V gamma gene are used by the majority of the cells. These results suggest that important components of receptor chain that contribute to specificity (i.e., the germline V gene sequences) are relatively nondiverse in the thymic gamma/delta population.

Predominant expression of circulating CD3+ lymphocytes bearing gamma T cell receptor in a prolonged immunodeficiency after allogeneic bone marrow transplantation

The cell surface expression of alpha:beta heterodimer was studied using WT31 monoclonal antibody, in peripheral blood lymphocytes (PBL) from a patient who developed a prolonged immunodeficiency after allogeneic bone marrow transplantation. This patient, grafted for chronic myelogenous leukemia, received T cell depleted bone marrow from her HLA, A, B, D matched sibling. The late occurrence of opportunistic infection, led us to analyze the phenotype of patient PBL. 70% of PBL were CD3+ and 29% WT31+, indicating that the majority of CD3+ PBL did not express the alpha:beta heterodimer. Transcription of the genes encoding the alpha, beta, and gamma chains was assessed in cell lines derived from PBL, by Northern blot analysis. We showed that the CD3+ WT31- subset expressed a truncated, beta mRNA (1.0 kb) and also truncated alpha transcript (1.4 kb). To determine the CD3-associated structure on CD3+ WT31- cell line, immunoprecipitation assays were performed using monoclonal anti-CD3 and an hetero antiserum against gamma peptides. These CD3+ WT31- cells expressed a disulfide linked dimer, composed of products of gamma gene (37 kD, 40 kD) and of undefined delta chain (45 kD). Functional analyses were performed in PBL before and after sorting with WT31 and anti-CD3 antibody. These circulating CD3+ WT31- cells were unable to proliferate when triggered with anti-T3 beads and they seemed to mediate a suppressor activity on CD3+ WT31+ cells.

Age-associated increase in the expression of T-cell antigen receptor gamma-chain gene in conventional and germfree mice

To determine whether environmental antigens such as intestinal microflora contribute to expansion of the T-cell repertoire, age-related changes in the expression level of T-cell antigen receptor genes encoding gamma, beta, and alpha chains were compared in the lymphoid tissues of conventional versus germfree mice. Irrespective of the conditions of maintenance, an age-associated increase in the expression of the gamma-chain gene was evident in the thymus and spleen. Both conventional and germfree old mice (age, 40 weeks) had a relatively high proportion of Thy1+ L3T4- Lyt2- cells but a reduced level of Thy1+ L3T4- Lyt2+ cells in the thymus compared with their counterparts (age 8 weeks). The thymic dysfunction but not the stimulation by intestinal microflora may contribute to this age-related increase in gamma-gene transcripts in these tissues. On the other hand, an age-associated increase in the expression of gamma RNA was not evident in the mesenteric lymph nodes of germfree mice, although a remarkable increase in the gamma-chain gene messages was detected in the lymph nodes of the aged conventional mice. These results suggest that the expression of gamma RNA in cells of gut-associated lymphoid tissue is partly influenced by intestinal microflora.

Functional T cell receptor delta chain gene messages in athymic nude mice

The rearrangement and expression of T cell antigen receptor (TcR) delta chain genes were investigated in congenitally athymic nude mice. The lymphoid cells derived from nude mice showed evidence of rearranged delta chain genes and a relatively high level of delta chain gene messages. Nucleotide sequence analysis revealed that nude mice contained an in-frame delta chain transcript, composed of V delta 5-D delta 1-D delta 2-J delta 1-C delta genes in the spleen. We have previously described functionally rearranged TcR gamma chain genes in the spleen of nude mice. Taken together, T cell precursors appear to proliferate and differentiate along the extrathymic pathway into TcR gamma/delta-bearing T cells in nude mice.

Phenotypic heterogeneity and cytotoxic activity of Con A and IL-2-stimulated cultures of mouse Thy-1+ epidermal cells

Short-term and long-term cultures of mouse Thy-1+ epidermal cells (EC) were established in order to characterize their phenotypic and functional properties. Concanavalin A (Con A) and Interleukin 2 (IL-2) stimulated Thy-1+ EC mediated non-MHC directed cytotoxicity preferentially against the NK-sensitive target, YAC-1 vs the NK-resistant target, P815; these cells also mediated antibody-dependent cell-mediated cytotoxicity (ADCC), indicating the presence of IgG-FcR on at least some of them. Freshly isolated Thy-1+ EC failed to lyse YAC-1 targets; however, this activity was observed after 9 d of culture with Con A and IL-2. While dendritic Thy-1+ EC, in vivo, do not express the T-cell markers, L3T4 and Lyt-2, short-term cultured cells displayed phenotypic heterogeneity with small but significant percentages of Lyt-2+ and L3T4+ cells appearing transiently. The phenotype of the effector cell(s), which mediates cytotoxic activity, was determined by utilizing flow cytometry to sort short-term cultured EC into positively and negatively stained populations. Cells which express L3T4, or which lack asialo GM1, did not lyse YAC-1 targets; maximum cytotoxic activity was found within populations of cells which are asialo GM1+, Lyt-2-, and asialo GM1+, Lyt-2+. These studies indicate that Thy-1+ cells derived from mouse epidermis when cultured in the presence of Con A and IL-2 have the capacity to generate a phenotypically heterogeneous population, some cells of which are capable of mediating cytotoxic activities.

Extensive junctional diversity of rearranged human T cell receptor delta genes

The human T cell receptor delta (TCR delta) gene encodes one component of the TCR gamma delta-CD3 complex found on subsets of peripheral blood and thymic T cells. Human TCR delta diversity was estimated by characterizing rearrangements in TCR gamma delta cell lines and determining the structures of complementary DNA clones representing functional and nonfunctional transcripts in these cell lines. One V delta segment and one J delta segment were identified in all functional transcripts, although a distinct J delta segment was identified in a truncated transcript. Further, one D delta element was identified, and evidence for the use of an additional D delta element was obtained. Thus human TCR delta genes appear to use a limited number of germline elements. However, the apparent use of two D delta elements in tandem coupled with imprecise joining and extensive incorporation of N nucleotides generates unprecedented variability in the junctional region.