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A C Hayday

Publications and source records attributed to A C Hayday.

At least 55 records · Page 3Linked to original sources
PubMed1996

Raf regulates positive selection.

T cell development is regulated by extracellular signals that mediate cellular proliferation and differentiation via specific signal transduction pathways. To determine the importance of the mitogen-activated protein kinase (MAP kinase) pathway in thymocyte development, we analyzed transgenic mice expressing dominant negative Raf (DN Raf) and a constitutively active v-Raf under the control of the p56lck proximal promoter. DN Raf had a profound effect on T cell receptor (TCR)-mediated signaling events as assessed by the inhibition of mitogen-induced proliferation of thymocytes in vitro. Overall thymocyte numbers were decreased by at most twofold from nontransgenic littermates. Positive selection was inhibited in DN Raf transgenic mice, as evidenced by both reduced numbers of mature thymocytes and a decrease in CD8+ thymocytes in female mice doubly transgenic for DN-Raf and a class I-restricted H-Y TCR. In contrast, the differentiation of double-positive thymocytes to single-positive thymocytes was enhanced in H-YTCR transgenic mice expressing constitutively active Raf (v-Raf). Thus, Raf regulates positive selection in the thymus.

Animals↗
PubMed1995

Alpha beta and gamma delta T cells can share a late common precursor.

BACKGROUND: The subdivision of T cells into alpha beta and gamma delta subtypes is conserved throughout vertebrate development. The respective alpha beta and gamma delta T-cell receptors (TCRs) are encoded by somatically rearranged genes. There has been broad speculation as to whether an individual thymocyte can become either a gamma delta T cell or an alpha beta T cell as a result of stochastic gene rearrangement processes, or whether the two types of T cell are derived from separate lineages. Many of the experimental findings are apparently conflicting, however, and the issue--a basic one in immunology and development--remains unresolved. RESULTS: To address this issue, we have used the recently developed polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique, which allows us to examine quantitatively the status of TCR gamma and delta genes in postnatal alpha beta T cells and their progenitors. Interestingly, such cells are depleted of productively rearranged delta and gamma genes, which can encode delta and gamma TCR polypeptide chains. However, in mice that can rearrange TCR delta gene segments, but in which the TCR delta gene is non-functional in other respects, no such depletion of productive rearrangements is seen. CONCLUSION: The quantitative data that we have obtained fulfill the predictions of the stochastic hypothesis: that is, a progenitor T cell first attempts to become a gamma delta T cell and, if unsuccessful, then attempts to become an alpha beta T cell. Thus, alpha beta and gamma delta T cells can derive from a common precursor thymocyte. In the simplest case, therefore, lineage-determining factors are the successful rearrangement of both gamma and delta genes before TCR alpha gene rearrangements occur, which lead to deletion of the TCR delta locus and thereby preclude further gamma delta T-cell differentiation. In contrast, successful rearrangement of the TCR beta locus remains compatible with cells becoming either gamma delta or alpha beta T cells.

Animals↗
PubMed1995

Heavy-metal modulation of the human intercellular adhesion molecule (ICAM-1) gene expression.

The intercellular adhesion molecule 1 (ICAM-1) can be induced on many different cell types by a set of various modulators (IL1 beta, TNF, LPS, IFN-gamma), which are released during the inflammatory process. We have investigated the possibility that other factors, related to the stress and biophysical perturbations of the inflammatory response, may also modulate ICAM-1. Here, we report that heavy metals, in particular zinc, can enhance the expression of the ICAM-1 gene on cells actively involved at different levels during inflammation. Kinetic studies of ICAM-1 gene expression shows a maximum level of induction 4 h after treatment with metals, followed by a rapid decrease to basal levels within 12 h. The effect on enhanced gene expression is mostly due to a rapid increase of the transcriptional rate as shown by nuclear run-on experiments. In B lymphoblastoid cells, but not in fibroblasts, the increase in RNA expression seems significantly greater that the subsequent increase in protein expression, suggesting that a further point of post-transcriptional regulation of ICAM-1 occurs and may be linked to the cellular specificity. may be linked to the cellular specificity.

Cadmium↗
PubMed1995

T cell development and repertoire of mice expressing a single T cell receptor alpha chain.

We examined T cell development and T cell repertoire in transgenic mice expressing a single T cell receptor (TCR) alpha chain derived from the H-2Db-lymphocytic choriomeningitis virus (LCMV)-specific cytolytic T lymphocyte (CTL) clone P14. To generate these alpha P14 mice, mice transgenic for the P14 TCR alpha chain were backcrossed to TCR alpha-deficient mice. Thymi from alpha P14 mice exhibited a marked decrease of mature CD4+8- and CD8+4- single-positive thymocytes comparable to thymi from TCR alpha-deficient mice. Correspondingly, the number of peripheral T cells was reduced in the CD4 (tenfold) and in the CD8 (twofold) subsets when compared to normal mice. T cells from alpha P14 mice generated a primary anti-LCMV CTL response when stimulated in vitro with LCMV in contrast to normal mice which require priming in vivo; elimination of LCMV in vivo was, however, not improved. Flow cytometric analysis of T cells with V beta-specific antibodies showed a diverse endogenous TCR V beta repertoire. Functional analysis of the T cell repertoire, however, revealed a strongly reduced (30-fold) allogeneic and the absence of a vesicular stomatitis virus-specific CTL response and an impaired ability to provide T cell help for antibody isotype switching. Thus, T cell selection in the thymus was impaired and the T cell repertoire was limited in mice expressing only one type of TCR alpha chain.

Animals↗
PubMed1995

Transcriptional modulation of the human intercellular adhesion molecule gene I (ICAM-1) by retinoic acid in melanoma cells.

Retinoids play an important role as differentiating agents in a variety of normal and neoplastic cells and have been reported to induce ICAM-1 levels in melanomas, a phenomenon that we confirm in this paper. The effects of retinoids on gene expression usually involve the binding of specific retinoic acid receptor trans-acting factors (RARs) with their ligands, which then interact with specific target sites, the retinoic acid responsive elements (RAREs) present in the promoters of responsive genes. In the case of ICAM-1, we have cloned and analyzed the proximal regulatory region of the human gene. We show that the ICAM-1 promoter is RA-inducible, that it contains a putative consensus RARE (GGGTCATCGCCCTGCC), which binds in vitro RAR alpha complemented with RXRs, and that mutation of the RARE abrogates promoter responsiveness to RA. These studies allow ICAM-1 to be added to the list of genes transcriptionally activated by RA acting through an RARE element.

Base Sequence↗
PubMed1995

Expansion of gamma delta+ T cells in BALB/c mice infected with Leishmania major is dependent upon Th2-type CD4+ T cells.

T cells belong to either the alpha beta+ or gamma delta+ lineage as defined by their antigen receptor. Although both T-cell subsets have been shown to be involved in the immune response to the parasite Leishmania major, very little is known about possible interactions between these two populations. In this study, using a mouse model of infection with L. major, we showed that expansion of a subset of gamma delta+ T cells in vivo is dependent upon the presence of alpha beta+ CD4+ T cells. Moreover, this effect appears to be mediated via the secretion of lymphokines by CD4+ cells with a T-helper 2 (Th2) functional phenotype. Results showing that activation of Th2-type cells in mice treated with anti-immunoglobulin D antibodies or infected with Nippostrongylus brasiliensis also results in gamma delta+ T-cell expansion suggest that this effect of the Th2-type CD4+ cells is a general phenomenon not restricted to infection with L. major.

Animals↗
PubMed1995

Immune responsiveness in mutant mice lacking T-cell receptor alpha beta+ cells.

Immune responses of mice with T-cell receptor (TCR)gamma delta+ T cells but lacking TCR alpha beta+ cells because of a disruption in the TCR alpha gene, were analysed against alloantigens, soluble protein antigen, killed Mycobacterium tuberculosis and exogenous superantigen. Rejection of skin allografts mismatched for classical major histocompatibility complex (MHC) plus multiple minor H antigens was virtually abrogated but the presence of mismatched Qa-1 non-classical MHC antigens on donor tissue resulted in a significant proportion of TCR alpha-/- mice rejecting such grafts. In view of the proposed role for gamma delta T cells in mycobacterial responses, and particularly against self- or mycobacterial heat-shock protein HSP 65, we examined these responses in TCR alpha-/- mice. Local responses after immunization were low in lymph nodes and no component of these was directed against mycobacterial HSP 65. However, splenic T cells from mutant mice responded strongly to either purified protein derivative (PPD) or M. tuberculosis. Our findings indicate that TCR alpha-/- mice are selectively compromised: while responses to (undefined) mycobacterial antigens were substantial, responses to some other target antigens such as MHC alloantigens and HSP 65, believed to be preferentially recognized by gamma delta receptors, were poor or absent. However, the fact that the mutant mice more readily rejected allografts that are mismatched for the non-classical MHC antigen Qa-1 in addition to classical MHC and minor-H incompatibility, indicates that in some mice the residual immune response, presumed to be by gamma delta cells, is sufficient to cause skin graft rejection and that recognition of non-classical MHC antigens may play an important part in the response.

Animals↗
PubMed1994

Lymphocyte proliferation in mice congenitally deficient in T-cell receptor alpha beta + cells.

In mice and humans, T cells are characterized on the basis of T-cell receptor (TcR) expression and divided into the major TcR alpha beta + and minor TcR gamma delta + populations. TcR alpha beta + cells are considered to be the primary regulators of the immune response, whereas the function of TcR gamma delta + cells is unclear. Mice congenitally deficient in TcR alpha beta-expressing cells provide an ideal model for analyzing the independent in vivo function of TcR gamma delta + cells in the absence of TcR alpha beta + cells. Here we report that lymphoid organs in TcR alpha mutant mice undergo substantial enlargement after being challenged by environmental antigens. This organ expansion can be attributed in part to increases in the relative proportions and absolute numbers of TcR gamma delta + cells, but an expansion of the recently described TcR beta + alpha - population also has a role. The expansion of the TcR gamma delta + population is polyclonal, as evidenced by the usage of multiple gamma and delta variable chain segments. Furthermore, a substantial proportion of the cells appears to be activated and these activated cells express surface activation markers. The results clearly demonstrate that TcR gamma delta + cells proliferate independently in response to a broad spectrum of challenges. Moreover, since the expansion of the lymphoid tissues and the TcR gamma delta + cell population is excessive relative to that seen in wild-type animals, one role of TcR alpha beta + cells is directly or indirectly to limit the responses of the other lymphoid components.

Animals↗
PubMed1994

Immunoglobulin synthesis and generalized autoimmunity in mice congenitally deficient in alpha beta(+) T cells.

Through cognate B-cell-T-cell interactions and provision of cytokines, CD4+ T-cell antigen receptor (TCR) alpha beta+ T cells regulate immunoglobulin isotype synthesis. Murine IgG1 and IgE secretion is therefore substantially T-cell-dependent, whereas IgM and IgG3 secretion is not. Here we report that in the absence of alpha beta T cells, B cells expand, differentiate and secrete copious amounts of antibodies of 'T-dependent' isotypes. Moreover, the antibodies are reactive towards self-antigens, as in patients with systemic lupus erythematosus, so autoantibodies of 'T-dependent' type can develop without the help of CD4+ alpha beta T cells. This phenotype is not evident in mice or humans that are congenitally deficient in specific alpha beta T-cell functions, but bears comparison with B-cell hyperactivity and autoimmunity in transplant rejection and in immunodeficiencies such as AIDS.

Animals↗
PubMed1994

T cell receptor beta chain gene rearrangement and selection during thymocyte development in adult mice.

The identification is made in normal mice of the stages in T cell development at which the rearranged beta chain of the T cell receptor (TCR) is utilized to promote T cell maturation, independent of the TCR alpha chain. In addition, evidence is provided that utilization of beta chains in T cell progenitors does not preclude differentiation to TCR gamma delta + T cells. This is consistent with the view that an initial consequence of beta chain expression by early thymocytes is clonal expansion, increasing the size of the pool of useful precursors. This allows the proposal to be made that allelic exclusion may be a byproduct of cell cycle regulation during early thymocyte differentiation, which may in turn explain why the efficiency of allelic exclusion varies at different TCR or immunoglobulin loci.

Animals↗
PubMed1993

A novel disulfide-linked heterodimer on pre-T cells consists of the T cell receptor beta chain and a 33 kd glycoprotein.

We describe a novel signal-transducing protein complex, which consists of the T cell receptor (TCR) beta chain that is disulfide linked to a 33 kd glycoprotein and noncovalently associated with proteins of the CD3 complex on the surface of the pre-T cell line SCB.29. This 33 kd glycoprotein, provisionally designated gp33, represents neither of the known TCR chains and has escaped previous detection because it labels poorly by surface iodination. This glycoprotein is absent from the surface of mature T cell lines. A TCR beta complex with identical molecular masses before and after reduction can be immunoprecipitated from surface-iodinated large thymocytes of TCR alpha-deficient mice. The novel gp33-TCR beta complex may be entirely or partly responsible for control of early T cell development exerted by the TCR beta protein.

Animals↗
PubMed1993

Rearrangement and diversity of T cell receptor beta chain genes in thymocytes: a critical role for the beta chain in development.

Thymocytes from mice congenitally deficient for TCR alpha chain synthesis were examined for the status of their TCR beta chain genes, by DNA sequencing and by a novel technique that analyzes populations of gene rearrangements. TCR beta chain genes were predominantly productively rearranged, in contrast with the statistical prediction for a quasi-random rearrangement process. Therefore, productive TCR beta chain gene rearrangement appears to be a critical step in thymocyte maturation, independent of TCR alpha chain expression. Moreover, the beta chain gene rearrangements in TCR alpha-/-mice are typical of those found in the thymus and periphery of normal mice. Thus, the extent of junctional diversity is a property of TCR genes that is imposed prior to selection on the mature alpha beta TCR.

Animals↗
PubMed1993

Dynamic response of murine gut intraepithelial T cells after infection by the coccidian parasite Eimeria.

The response of murine intraepithelial lymphocyte (IEL) populations to challenge by Eimeria vermiformis, a naturally occurring protozoan parasite of the gut epithelium, has been studied. The number of recoverable IEL increased within 3 days post infection, was depleted by day 7 post infection, but was significantly increased again by about day 14 post infection. Special attention was paid to gamma delta+ IEL T cells, because they are of unknown functions. These cells showed changes in numbers similar to the total IEL population. Moreover, by day 3, increased expression was detected among gamma delta+ IEL T cells, of T cell receptor genes not constitutively associated with the intestine. These results demonstrate that the IEL repertoire, and within that, the gamma delta+ T cell repertoire, can be extremely dynamic post infection with a naturally occurring epithelial-tropic pathogen. In considering the potential benefits of such IEL changes, we hypothesize that they may be relevant to the transient protection of the host's epithelium, both from parasitic re-infection, and from potentially damaging inflammation.

Animals↗
PubMed1993

Expression of the alpha beta T-cell receptor is necessary for the generation of the thymic medulla.

The architecture of the thymus of mice that congenitally fail to express the alpha beta T-cell receptor (TCR alpha beta) has been examined by immunohistology. In these mice, a defined mutation was introduced into the TCR alpha gene by homologous recombination. By using antibodies specific for cortical or medullary epithelium and for major histocompatibility complex antigens, the network of cortical epithelium in these mice was shown to be essentially unaltered in comparison with that of normal mice. In contrast, the thymic medulla was considerably reduced in size. This analysis shows that expression of the alpha beta TCR but not the gamma delta TCR is obligatory for establishing the thymic medulla and suggests that the growth of medullary epithelial cells may require contact with TCR alpha beta-expressing cells.

Animals↗
PubMed1993

Gamma delta T-cell lines isolated from intestinal epithelium respond to a B-cell lymphoma.

gamma delta T-cell hybrid clones were obtained from intestinal intraepithelial lymphocytes (i-IEL) by fusion with the BW5147 thymoma line. Four clones which expressed different V gamma/V delta genes were selected for further study. All of the gamma delta clones secreted interleukin-2 (IL-2) in the presence of the BALB/c-derived B-lymphoma line, A20. No alpha beta T-cell hybrid clones derived from spleen or i-IEL responded to A20. We obtained several pieces of evidence which strongly suggest that these responses are mediated by the gamma delta T-cell receptor (TcR). Class II major histocompatibility complex (MHC), FcR and surface Ig expressed on A20 are not involved in the response. Native i-IEL derived from BALB/c selectively survive in culture in the presence of A20 cells. The ligand may be a superantigen-like molecule because all our gamma delta T-cell clones responded to A20 in spite of their different combinations of V gamma/V delta gene segments.

Animals↗
PubMed1992

Lymphoid development in mice congenitally lacking T cell receptor alpha beta-expressing cells.

Vertebrate T cells express either an alpha beta or gamma delta T cell receptor (TCR). The developmental relatedness of the two cell types is unresolved. alpha beta + T cells respond to specific pathogens by collaborating with immunoglobulin-producing B cells in distinct lymphoid organs such as the spleen and Peyer's patches. The precise influence of alpha beta + T cells on B cell development is poorly understood. To investigate the developmental effects of alpha beta + T cells on B cells and gamma delta + T cells, mice homozygous for a disrupted TCR alpha gene were generated. The homozygotes showed elimination of alpha beta + T cells and the loss of thymic medullae. Despite this, gamma delta + T cells developed in normal numbers, and there was an increase in splenic B cells.

Animals↗
PubMed1991

Regulated expression and structure of T cell receptor gamma/delta transcripts in human thymic ontogeny.

Gamma delta (gamma delta) T cells have been found in all vertebrates examined, yet their function in vivo remains unknown. Because gamma delta T cell receptors are related to immunoglobulin, and because they are encoded by rearranging, multi-gene families, the receptors are thought to be antigen recognition molecules. However, a capacity to recognize naturally diverse antigens has not yet been shown. In this work, the expression and structure of human gamma delta transcripts have been examined in the fetal and early post-natal thymus. The data indicate that many gamma and delta genes are rearranged and expressed throughout ontogeny, but that as ontogeny proceeds, quite dramatic changes occur in the patterns of gene expression and rearrangement. In particular, receptors encoded by early to mid-gestation fetal thymic transcripts would be of quite restricted diversity. Only later in ontogeny can receptors of substantial diversity be generated. These properties are very similar to the patterns of gamma delta gene activation in the mouse, and they serve to reiterate similarities both in gene rearrangement and in gamma delta across vertebrate species.

Base Sequence↗