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

[gamma][delta] cells: a right time and a right place for a conserved third way of protection

The tripartite subdivision of lymphocytes into B cells, alphabeta T cells, and gammadelta cells has been conserved seemingly since the emergence of jawed vertebrates, more than 450 million years ago. Yet, while we understand much about B cells and alphabeta T cells, we lack a compelling explanation for the evolutionary conservation of gammadelta cells. Such an explanation may soon be forthcoming as advances in unraveling the biochemistry of gammadelta cell interactions are reconciled with the abnormal phenotypes of gammadelta-deficient mice and with the striking differences in gammadelta cell activities in different strains and species. In this review, the properties of gammadelta cells form a basis for understanding gammadelta cell interactions with antigens and other cells that in turn form a basis for understanding immunoprotective and regulatory functions of gammadelta cells in vivo. We conclude by considering which gammadelta cell functions may be most critical.

Primary γδ Cell Clones Can Be Defined Phenotypically and Functionally as Th1/Th2 Cells and Illustrate the Association of CD4 with Th2 Differentiation

The division of CD4+ αβ T cells into Th1 and Th2 subsets has become an established and important paradigm. The respective activities of these subsets appear to have profound effects on the course of infectious and autoimmune diseases. It is believed that specific programs of differentiation induce the commitment of an uncommitted Th0 precursor cell to Th1 or Th2. A component of these programs is hypothesized to be the nature of MHC-peptide antigen presentation to the αβ T cell. It has heretofore remained uncertain whether a Th1/Th2 classification likewise defines, at the clonal level, γδ T cells. Such cells do not, as a general rule, express either CD4 or CD8αβ, and they do not commonly recognize peptide-MHC. In this report, γδ cell clones are described that conform strikingly to the Th1/Th2 classification, both by cytokine expression and by functional activities of the clones in vitro and in vivo. Provocatively, both the γδ cell clones and primary γδ cells in vivo showed a strong association of the Th2 phenotype with CD4 expression. These results are discussed with regard to the immunoregulatory role that is increasingly emerging for γδ cells.

Gamma delta T-cell help in responses to pathogens and in the development of systemic autoimmunity

Mice rendered deficient in alpha beta T-cells by single-gene knockout mutation show enhanced levels of autoantibody formation and even some symptoms of autoimmune disease. This is remarkable given that most experimental studies heretofore have indicated that the development of autoimmune disease is highly multigenic, requiring the complementary actions of multiple loci. The basis of the phenomenon in alpha beta T-cell-deficient mice appears to be the provision of help to B-cells by other cells, including gamma delta T-cells. Perhaps surprisingly, gamma delta T-cell help seems quite efficacious, particularly after infection, when it can culminate in the formation of germinal centers. Furthermore, two independent sets of studies reviewed here indicate that significant levels of self-reactive IgG can also be provoked by gamma delta T-cells independent of germinal center formation. The task ahead is to integrate this pathway into the physiologic immune responses to healthy individuals, immunocompromised individuals, and newborns.

Tissue distribution of human gamma delta T cells: no evidence for general epithelial tropism

In man and mice only a small proportion of T cells in the peripheral lymphoid compartment express the gamma delta T cell receptor (TCR). In mice, however, gamma delta T cells comprise the predominant population at particular epithelial sites--in epidermis and epithelia of intestine, reproductive organs, and tongue. The distribution of gamma delta T cells in normal human tissues was investigated, paying particular attention to epithelial layers. In all lymphatic organs and in epithelia of a wide variety of non-lymphatic organs, including the respiratory tract, male and female reproductive organs and tongue, gamma delta T cells constituted less than 5% of total T cells, with the remainder expressing TCR alpha beta. The only exception was the intestine, where gamma delta T cells were preferentially situated in the columnar epithelium of the crypts, rather than in the lamina propria. It is concluded, therefore, that human gamma delta T cells do not display a general epithelial tropism and are, in terms of relative numbers, no more able than alpha beta T cells to carry out continuous surveillance of the immune system against infection or transformation in epithelia. gamma delta T cells may, however, have a specialised function in the epithelium of the intestinal tract.

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.

ZO-1 mRNA and protein expression during tight junction assembly in Caco-2 cells

We previously identified and characterized ZO-1 as a peripheral membrane protein specifically associated with the cytoplasmic surface of tight junctions. Here we describe the identification of partial cDNA sequences encoding rat and human ZO-1 and their use to study the assembly of tight junctions in the Caco-2 human intestinal epithelial cell line. A rat cDNA was isolated from a lambda-gtll expression library by screening with mAbs. Polyclonal antibodies were raised to cDNA-encoded fusion protein; several properties of these antibodies support this cDNA as encoding ZO-1. Expression of ZO-1 mRNA occurs in the rat and Caco-2 cells with a major transcript of approximately 7.5 kb. To disrupt tight junctions and study the subsequent process of assembly, Caco-2 cells were grown in suspension for 48 h in Ca++/Mg++-free spinner medium during which time they lose cell-cell contacts, become round, and by immunofluorescence microscopy show diffuse and speckled localization of ZO-1. Within hours of replating at confluent density in Ca++/Mg++-containing media, attached cells show discrete localization of ZO-1 at cell-cell contacts. Within 2 d, fully confluent monolayers form, and ZO-1 localizes in a continuous gasket-like fashion circumscribing all cells. ZO-1 mRNA levels are highest in cells in spinner culture, and upon replating rapidly fall and plateau at approximately 10% of initial levels after 2-3 wk in culture. ZO-1 protein levels are lowest in contact-free cells and rise five- to eightfold over the same period. In contrast, mRNA levels for sucrase-isomaltase, an apical membrane hydrolase, increase only after a confluent monolayer forms. Thus, in this model of contact-dependent assembly of the tight junction, there is both a rapid assembly beginning upon cell-cell contact, as well as a long-term modulation involving changes in expression of ZO-1 mRNA and protein levels.

Structure and specificity of a class II MHC alloreactive gamma delta T cell receptor heterodimer

Two distinct CD3-associated T cell receptors (TCR alpha beta and TCR gamma delta) are expressed in a mutually exclusive fashion on separate subsets of T lymphocytes. While the specificity of the TCR alpha beta repertoire for major histocompatibility complex (MHC) antigens is well established, the diversity of expressed gamma delta receptors and the ligands they recognize are less well understood. An alloreactive CD3+CD4-CD8- T cell line specific for murine class II MHC (Ia) antigens encoded in the I-E subregion of the H-2 gene complex was identified, and the primary structure of its gamma delta receptor heterodimer was characterized. In contrast to a TCR alpha beta-expressing alloreactive T cell line selected for similar specificity, the TCR gamma delta line displayed broad cross-reactivity for multiple distinct I-E-encoded allogeneic Ia molecules.

Diversity in T-cell receptor gamma gene usage in intestinal epithelium

The intraepithelial cells of the murine small intestine include a significant number of CD3+ T cells that use T-cell receptor gamma genes rather than T-cell receptor beta genes. As with other sites of T-cell receptor gamma expression, combinatorial diversity is limited, but there is junctional diversity, and this, together with the specific variable region gamma gene segments used, distinguishes gamma gene expression in the gut epithelium from that in cells derived from the dermal epithelium. The restriction of productive gamma gene expression largely to one V-J-C (V, variable; J, joining; C, constant) gene combination may result from nonproductive joining of other V-J combinations and from productively rearranged genes rendered nonfunctional by incorrect splicing.

Developmental control of lymphokine gene expression in fetal thymocytes during T-cell ontogeny

We have used the technique of in situ hybridization to investigate the expression of lymphokine genes by immature thymocytes during intrathymic development. In 13-day fetal thymocytes a population of cells constitutively produces low levels of interleukin 2 (IL-2) and interleukin 4 (IL-4) mRNAs. A second phase of lymphokine gene expression occurs in the majority of 15-day thymocytes, and a population of cells constitutively produces both IL-2 and IL-4 mRNAs. Thymocytes at 14 days of gestation and after 16 days up until birth do not express detectable lymphokine mRNA. By contrast, the population of IL-2 receptor mRNA-producing thymocytes increases progressively up to 15 days of gestation, and expression thereafter decreases up to birth. In addition, thymocytes expressing interferon gamma mRNA were not present until just prior to birth. Our findings indicate developmental control of lymphokine and lymphokine receptor gene expression in fetal thymocytes during ontogeny.