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Biomedical subjects

A Wakeham

Publications and source records attributed to A Wakeham.

49 records · Page 3Linked to original sources
PubMed1996

Impaired negative selection of T cells in Hodgkin's disease antigen CD30-deficient mice.

CD30 is found on Reed-Sternberg cells of Hodgkin's disease and on a variety of non-Hodgkin's lymphoma cells and is up-regulated on cells after Epstein-Barr virus, human T cell leukemia virus, and HIV infections. We report here that the thymus in CD30-deficient mice contains elevated numbers of thymocytes. Activation-induced death of thymocytes after CD3 cross-linking is impaired both in vitro and in vivo. Breeding the CD30 mutation separately into alpha beta TCR-or gamma delta TCR-transgenic mice revealed a gross defect in negative but not positive selection. Thus, like TNF-receptors and Fas/Apo-1, the CD30 receptor is involved in cell death signaling. It is also an important coreceptor that participates in thymic deletion.

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PubMed1995

Lymphoproliferative disorders with early lethality in mice deficient in Ctla-4.

The role of the cell-surface molecule CTLA-4 in the regulation of T cell activation has been controversial. Here, lymph nodes and spleens of CTLA-4-deficient mice accumulated T cell blasts with up-regulated activation markers. These blast cells also infiltrated liver, heart, lung, and pancreas tissue, and amounts of serum immunoglobulin were elevated. The mice invariably became moribund by 3 to 4 weeks of age. Although CTLA-4-deficient T cells proliferated spontaneously and strongly when stimulated through the T cell receptor, they were sensitive to cell death induced by cross-linking of the Fas receptor and by gamma irradiation. Thus, CTLA-4 acts as a negative regulator of T cell activation and is vital for the control of lymphocyte homeostasis.

Abatacept↗
PubMed1995

Deregulated T cell activation and autoimmunity in mice lacking interleukin-2 receptor beta.

In mice lacking the interleukin-2 receptor beta chain (IL-2R beta), T cells were shown to be spontaneously activated, resulting in exhaustive differentiation of B cells into plasma cells and the appearance of high serum concentrations of immunoglobulins G1 and E as well as autoantibodies that cause hemolytic anemia. Marked infiltrative granulocytopoiesis was also apparent, and the animals died after about 12 weeks. Depletion of CD4+ T cells in mutant mice rescued B cells without reversion of granulocyte abnormalities. T cells did not proliferate in response to polyclonal activators, nor could antigen-specific immune responses be elicited. Thus, IL-2R beta is required to keep the activation programs of T cells under control, to maintain homeostasis, and to prevent autoimmunity.

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PubMed1995

MSH2 deficient mice are viable and susceptible to lymphoid tumours.

Alterations of the human MSH2 gene, a homologue of the bacterial MutS mismatch repair gene, co-segregate with the majority of hereditary non-polyposis colon cancer (HNPCC) cases. We have generated homozygous MSH2-/- mice. Surprisingly, these mice were found to be viable, produced offspring in a mendelian ratio and bred through at least two generations. Starting at two months of age homozygous-/- mice began, with high frequency, to develop lymphoid tumours that contained microsatellite instabilities. These data establish a direct link between MSH2 deficiency and the pathogenesis of cancer. These mutant mice should be good models to study the progression of tumours and also to screen carcinogenic and anti-cancer agents.

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PubMed1995

Disruption of the mouse RBP-J kappa gene results in early embryonic death.

The RBP-J kappa protein is a transcription factor that recognizes the sequence C(T)GTGGGGA. The RBP-J kappa gene is highly conserved in a wide variety of species and the Drosophila homologue has been shown to be identical to Suppressor of Hairless [Su(H)] which plays important roles in the development of the peripheral nervous system. To explore the function of the RBP-J kappa gene in mouse embryogenesis, a mutation was introduced into the functional RBP-J kappa gene in embryonic stem (ES) cells by homologous recombination. Null mutant ES cells survived but null mutant mice showed embryonic lethality before 10.5 days of gestation. The mutant mice showed severe growth retardation as early as 8.5 days of gestation. Developmental abnormalities, including incomplete turning of the body axis, microencephaly, abnormal placental development, anterior neuropore opening and defective somitogenesis, were observed in the mutant mice at 9.5 days of gestation. RBP-J kappa mutant embryos expressed a posterior mesodermal marker FGFR1. Their irregularly shaped somites expressed a somite marker gene Mox 1 but failed to express myogenin. The RBP-J kappa gene was revealed to be essential for postimplantation development of mice.

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PubMed1993

Targeted disruption of IRF-1 or IRF-2 results in abnormal type I IFN gene induction and aberrant lymphocyte development.

Interferon regulatory factor 1 (IRF-1), a transcriptional activator, and its antagonistic repressor, IRF-2, were originally identified as regulators of the type I interferon (IFN) system. We have generated mice deficient in either IRF-1 or IRF-2 by gene targeting in embryonic stem cells. IRF-1-deficient fibroblasts lacked the normally observed type I IFN induction by poly(I):poly(C), while they induced type I IFN to similar levels as the wild type following Newcastle disease virus (NDV) infection. In contrast, IRF-2-deficient fibroblasts showed up-regulated type I IFN induction by NDV infection. A profound reduction of TCR alpha beta+CD4-CD8+ T cells in IRF-1-deficient mice, with a thymocyte developmental defect, reveals a critical role for IRF-1 in T cell development. IRF-2-deficient mice exhibited bone marrow suppression of hematopoiesis and B lymphopoiesis and mortality following lymphocytic choriomeningitis virus infection.

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PubMed1993

Differential T cell costimulatory requirements in CD28-deficient mice.

T cell receptor stimulation without costimulation is insufficient for the induction of an optimal immune response. It is thought that engagement of the CD28 molecule with its ligand B7 provides an essential costimulatory signal without which full activation of T cells cannot occur. A mouse strain with a defective CD28 gene was established. Development of T and B cells in the CD28-deficient mice appeared normal. However, T lymphocytes derived from CD28-/- mutant mice had impaired responses to lectins. Lectin stimulation did not trigger interleukin-2 (IL-2) production, IL-2 receptor alpha expression was significantly decreased, and exogenous IL-2 only partially rescued the CD28 defect. Basal immunoglobulin (Ig) concentrations in CD28-deficient mice were about one-fifth of those found in wild-type controls, with low titers of IgG1 and IgG2b but an increase in IgG2a. In addition, activity of T helper cells in CD28-/- mice was reduced and immunoglobulin class switching was diminished after infection with vesicular stomatitis virus. However, cytotoxic T cells could still be induced and the mice showed delayed-type hypersensitivity after infection with lymphocytic choriomeningitis virus. Thus, CD28 is not required for all T cell responses in vivo, suggesting that alternative costimulatory pathways may exist.

Animals↗
PubMed1993

Normal B lymphocyte development but impaired T cell maturation in CD45-exon6 protein tyrosine phosphatase-deficient mice.

The transmembrane tyrosine phosphatase CD45 is expressed in multiple isoforms on all nucleated hematopoietic cells, resulting from alternative splicing of variable exons. We generated mice with a mutation in the variable CD45 exon 6, using homologous recombination. In mice homozygous for the CD45-exon6 mutation, B cells and most T cells did not express CD45. Development of B cells appeared normal, although Ig mu-induced proliferation was completely abrogated. Thymocyte maturation was blocked at the transitional stage from immature CD4+CD8+ to mature CD4+ or CD8+ cells, and only a few T cells could be detected in peripheral lymphoid organs. Clonal deletion of superantigen-reactive T cells still occurred. Cytotoxic T cell responses to lymphocytic choriomeningitis virus were absent in CD45-exon6-/- mice. These data imply that CD45 is differentially required for the development and function of B and T lymphocytes.

Animals↗
PubMed1993

Mice deficient for the 55 kd tumor necrosis factor receptor are resistant to endotoxic shock, yet succumb to L. monocytogenes infection.

The multiple biological activities of tumor necrosis factor (TNF) are mediated by two distinct cell surface receptors of 55 kd (TNFRp55) and 75 kd (TNFRp75). Using gene targeting, we generated a TNFRp55-deficient mouse strain. Cells from TNFRp55-/-mutant mice lack expression of TNFRp55 but display normal numbers of high affinity TNFRp75 molecules. Thymocyte development and lymphocyte populations are unaltered, and clonal deletion of potentially self-reactive T cells is not impaired. However, TNF signaling is largely abolished, as judged by the failure of TNF to induce NF-kappa B in T lymphocytes from TNFRp55-deficient mice. The loss of TNFRp55 function renders mice resistant to lethal dosages of either lipopolysaccharides or S. aureus enterotoxin B. In contrast, TNFRp55-deficient mice are severely impaired to clear L. monocytogenes and readily succumb to infection. Thus, the 55 kd TNFR plays a decisive role in the host's defense against microorganisms and their pathogenic factors.

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PubMed1992

Profound block in thymocyte development in mice lacking p56lck.

The protein Lck (p56lck) has a relative molecular mass of 56,000 and belongs to the Src family of tyrosine kinases. It is expressed exclusively in lymphoid cells, predominantly in thymocytes and peripheral T cells. Lck associates specifically with the cytoplasmic domains of both CD4 and CD8 T-cell surface glycoproteins and interacts with the beta-chain of the interleukin-2 receptor, which implicates Lck activity in signal transduction during thymocyte ontogeny and activation of mature T cells. Here we generate an lck null mutation by homologous recombination in embryonic stem cells to evaluate the role of p56lck in T-cell development and activation. Lck-deficient mice show a pronounced thymic atrophy, with a dramatic reduction in the double-positive (CD4+CD8+) thymocyte population. Mature, single-positive thymocytes are not detectable in these mice and there are only very few peripheral T cells. These results illustrate the crucial role of this T-cell-specific tyrosine kinase in the thymocyte development.

Animals↗
PubMed1991

Normal development and function of CD8+ cells but markedly decreased helper cell activity in mice lacking CD4.

T cells express T-cell antigen receptors (TCR) for the recognition of antigen in conjunction with the products of the major histocompatibility complex. They also express two key surface coreceptors, CD4 and CD8, which are involved in the interaction with their ligands. As CD4 is expressed on the early haemopoietic progenitor as well as the early thymic precursor cells, a role for CD4 in haemopoiesis and T-cell development is implicated. Thymocytes undergo a series of differentiation and selection steps to become mature CD4+8- or CD4-8+ (single positive) T cells. Studies of the role of CD4+ T cells in vivo have been based on adoptive transfer of selected or depleted lymphocytes, or in vivo treatment of thymectomized mice with monoclonal antibodies causing depletion of CD4+ T cells. In order to study the role of the CD4 molecule in the development and function of lymphocytes, we have disrupted the CD4 gene in embryonic stem cells by homologous recombination. Germ-line transmission of the mutation produces mutant mouse strains that do not express CD4 on the cell surface. In these mice, the development of CD8+ T cells and myeloid components is unaltered, indicating that expression of CD4 on progenitor cells and CD4+ CD8+ (double positive) thymocytes is not obligatory. Here we report that these mice have markedly decreased helper cell activity for antibody responses, although cytotoxic T-cell activity against viruses is in the normal range. This differential requirement for CD4+ helper T cells is important to our understanding of immune disorders including AIDS, in which CD4+ cells are reduced or absent.

Animals↗
PubMed1991

Effects of hydrogen peroxide-induced oxidative damage on outflow facility and washout in pig eyes.

Previous studies show that hydrogen peroxide (H2O2) is present in the aqueous humor of many species and is capable of affecting outflow facility in animal model experiments. To study the hypothesis that oxidative damage to the outflow pathway may play a role in the pathogenesis of primary open-angle glaucoma, 3 mM H2O2 with 20 mM 3-aminotriazole and 1 mM carmustine (BCNU) in Dulbecco's phosphate-buffered saline (DPBS) was perfused into enucleated pig eyes at constant pressure. Baseline and experimental perfusions were done at two different pressures (7.5 and 30 mm Hg) to study the effect of pressure on the response to oxidative damage. Outflow facility in the baseline experiments (with DPBS only) was observed to increase nonlinearly with time during the perfusions, but could be linearized if plotted as a function of the volume perfused. Thus, a term "volumetric washout" (W) was introduced and defined as the fractional rate of change of outflow facility with respect to the volume perfused. This quantity was found to be independent of pressure in the baseline studies. Perfusion of H2O2 and inhibitors increased W at 7.5 mm Hg but decreased W at 30 mm Hg. These results indicate that oxidative damage increases outflow facility at normal pressure but decreases it at elevated pressure, suggesting that elevated pressure may increase the susceptibility of the outflow pathway to this form of insult.

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