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T W Mak

Publications and source records attributed to T W Mak.

At least 19 recordsLinked to original sources
PubMed1995

HIV-1 Tat directly interacts with the interferon-induced, double-stranded RNA-dependent kinase, PKR.

We present evidence that the HIV-1 Tat protein and the RNA-dependent cellular protein kinase, PKR, interact with each other both in vitro and in vivo. Using GST fusion chromatography, we demonstrate that PKR, interacts directly with the HIV-1 Tat protein. The region in Tat sufficient for binding PKR maps within amino acids 20 to 72. In in vitro assays, the two-exon form of Tat (Tat 86) was phosphorylated by PKR, while the one exon form of Tat (Tat 72) inhibited PKR autophosphorylation and substrate phosphorylation. The ability of Tat to interact with PKR was demonstrated in both yeast and mammalian cells. Expression of PKR in yeast results in a growth suppressor phenotype which was reversed by coexpression of a one exon form of Tat. Expression of Tat 72 in HeLa cells resulted in direct interaction with PKR as detected by coimmunprecipitation with a Tat antibody. Tat and PKR also form a coimmunoprecipitable complex in cell-free extracts prepared from productively infected T lymphocytes. The interaction of Tat with PKR provides a potential mechanism by which HIV could suppress the interferon system.

Cell Line↗
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

Effect of fluvastatin on lipoprotein profiles in treating renal transplant recipients with dyslipoproteinemia.

A single, blinded placebo-drug trial was conducted to study the efficacy and safety of fluvastatin, a new 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, in treating dyslipoproteinemia in 16 renal transplant recipients who had been on an immunosuppressive regimen that included cyclosporine (CsA). They were studied for 32 consecutive weeks, with 4 weeks of baseline treatment, 4 weeks of placebo, 12 weeks of treatment with fluvastatin 20 mg daily, and 12 weeks of fluvastatin 40 mg daily. Blood samples were obtained every 4 weeks for measurement of the lipoprotein profiles, which included total cholesterol (TC), triglyceride, low density lipoprotein (LDL)-, high density lipoprotein (HDL)-, HDL2-, HDL3- and very low density lipoprotein-cholesterol (C), apolipoprotein (Apo) A-1, Apo B, and lipoprotein(a). Fifteen patients completed the trial. After 12 weeks of treatment, fluvastatin 20 mg significantly reduced TC by 13.4% (from 6.7 +/- 0.5 [mean +/- SEM] to 5.8 +/- 0.2 mmol/L), LDL-C by 22% (from 4.1 +/- 0.3 to 3.2 +/- 0.2 mmol/L), and Apo B by 13.2% (from 159.6 +/- 8.8 to 138.6 +/- 9.2 mg/dl) (P < 0.005). The subsequent 12-week treatment of fluvastatin 40 mg significantly reduced TC by 16.4% to 5.6 +/- 0.3 mmol/L, LDL-C by 29.3% to 2.9 +/- 0.2 mmol/L, and Apo B by 18.2% to 130.6 +/- 5.5 mg/dl (P < 0.00005). There was no significant change in levels of other lipoproteins, including lipoprotein (a). There were no significant changes in the whole blood trough CsA concentrations, renal and liver function tests, and serum creatine phosphokinase level during treatment when compared with baseline and placebo. No patient complained of myalgia or failed to complete the study due to side effects of the drug. Fluvastatin appears to be safe and effective in treating dyslipoproteinemia in renal transplant recipients who are maintained on CsA.

Adult↗
PubMed1995

T cell development in CD8-/- mice. Thymic positive selection is biased toward the helper phenotype.

The CD4 and CD8 molecules are involved in T cell differentiation and activation. Nevertheless, efficient thymic maturation of helper T cells has been shown in the absence of the CD4 molecule. These CD4-deficient helper T cells expressed alpha beta-TCR and were able to control Leishmania infections and to mediate Ab class switch. Using mice deficient for the CD8 alpha-chain, we investigated whether a similar cytotoxic T cell population was generated in the absence of the CD8 coreceptor. A CD8-deficient cytotoxic T cell population corresponding to the described CD4-deficient helper T cell population was virtually absent both functionally and physically. These results support the idea that thymic maturation is asymmetrical and strongly biased toward the helper phenotype.

Animals↗
PubMed1995

Effect of gene-targeted mutation in TNF receptor (p55) on contact hypersensitivity and ultraviolet B-induced immunosuppression.

Tumor necrosis factor alpha (TNF-alpha) is a pleiotropic proinflammatory cytokine. TNF-alpha has been implicated in the pathogenesis of delayed-type hypersensitivity reactions such as allergic contact hypersensitivity and has been suggested as a mediator of ultraviolet B (UVB)-induced immunosuppression. Conflicting reports, however, exist concerning the effects of TNF-alpha on contact hypersensitivity (CHS). To determine the role of TNF-alpha in the generation and regulation of CHS, gene-targeted mutant mice lacking TNF-receptor (p55) gene (TNF-R1(-) mice) were treated with dinitrofluorobenzene (DNFB) to induce CHS. TNF-R1(-) mice showed significant hyperresponsiveness in CHS (152.8 +/- 20.9%, p < 0.025) compared with normal syngeneic mice (C57BL/6) assessed by ear swelling. To determine whether UVB can induce suppression in TNF-R1(-) mice, mice were irradiated on the shaved abdomen with 96 mj/cm2 UVB and 3 days later they were painted with 0.5% DNFB (sensitization dose), followed 5 days later with 0.2% DNFB to the left ear (challenge dose). Significant suppression of CHS was observed both locally (sensitization on irradiated site) and systemically (sensitization on unirradiated site) in UVB-irradiated TNF-R1(-) mice as well as in normal mice. To rule out possible signaling through p75 TNF-R, the mice were treated with anti-TNF-alpha Ab (V1q), which can neutralize any TNF effects through either receptor. V1q had no effect on these phenomena observed in TNF-R1(-) mice. These results suggest that TNF-alpha plays a regulatory role in CHS but is not required to induce UVB-mediated immunosuppression.

Animals↗
PubMed1995

Alloreactive gamma delta thymocytes utilize distinct costimulatory signals from peripheral T cells.

Interactions between CD28/CTLA-4 on T cells and CD80 (B7.1) and CD86 (B7.2) counter receptors provide crucial costimulatory signals for TCR-alpha beta+ lymphocytes. To test the role of CD28 in thymic development and activation of TCR-gamma delta+ T cells, we introduced the alloreactive V gamma 2V alpha 11.3 TCR into CD28-deficient mice (CD28-/-). We show that positive and negative selection of gamma delta Tg thymocytes proceeded normally in the absence of CD28. Although mature Tg gamma delta+ thymocytes required a second costimulatory signal for proliferation, gamma delta+ thymocytes from CD28-/- and CD28+/- littermates responded equally well to the alloantigen Tlab. Alloreactivity of CD28-/- and CD28+/- Tg gamma delta+ thymocytes could not be blocked with mAbs against CD80 and CD86 ligands. Thus gamma delta thymocytes utilize a costimulatory system during development and alloresponses that is independent of CD28/CD80 and CD28/CD86 interactions. By contrast to V gamma 2V alpha 11.3+ thymocytes, alloreactivity of V gamma 2V alpha 11.3+ lymph node T cells depended on CD28 costimulation and was severely impaired in CD28-/- mice. These data provide functional evidence that maturation and selection of gamma delta cells is independent of CD28. These results also indicate that distinct costimulatory pathways are operational in mature thymocytes and peripheral T cells.

Animals↗
PubMed1995

An IRF-1-dependent pathway of DNA damage-induced apoptosis in mitogen-activated T lymphocytes.

Lymphocytes are particularly susceptible to DNA damage-induced apoptosis, a response which may serve as a form of 'altruistic suicide' to counter their intrinsic high potential for mutation and clonal expansion. The tumour suppressor p53 has been shown to regulate this type of apoptosis in thymocytes, but an as yet unknown, p53-independent pathway(s) appears to mediate the same event in mitogen-activated mature T lymphocytes. Here we show DNA damage-induced apoptosis in these T lymphocytes is dependent on the antioncogenic transcription factor interferon regulatory factor (IRF)-1. Thus two different anti-onco-genic transcription factors, p53 and IRF-1, are required for distinct apoptotic pathways in T lymphocytes. We also show that mitogen induction of the interleukin-1 beta converting enzyme (ICE) gene, a mammalian homologue of the Caenorhabditis elegans cell death gene ced-3, is IRF-1-dependent. Ectopic overexpression of IRF-1 results in the activation of the endogenous gene for ICE and enhances the sensitivity of cells to radiation-induced apoptosis.

Animals↗
PubMed1995

Effects of fluvastatin on lipid profile and apolipoproteins in Chinese patients with hypercholesterolemia.

The effects of fluvastatin treatment on lipid profile and apolipoproteins were assessed in a group of 31 Chinese patients with hypercholesterolemia, maintained on a constant low-fat diet. Some patients had the additional cardiovascular risk factors of hypertension and non-insulin-dependent diabetes mellitus, and 6 patients had familial hypercholesterolemia. Baseline lipid levels were measured after a 4-week placebo period, and these were repeated after 4 weeks of treatment with fluvastatin 20 mg daily, and after 4 weeks of treatment with fluvastatin 40 mg daily. Total cholesterol, low density lipoprotein cholesterol, and apolipoprotein (apo) B were each reduced to the same extent with the 2 doses of fluvastatin (-20%, -26%, and -20%, respectively). Triglycerides and very low density lipoprotein cholesterol were also reduced by about 12% with the 2 doses of fluvastatin. Apo A-I was increased by 7% and high density lipoprotein cholesterol (HDL-C) was increased by 10% with the 40 mg dose. The increase in HDL-C was due to increases in both HDL2-C (18%) and HDL3-C (7%). Lipoprotein(a) levels did not show any significant change with the 2 doses of fluvastatin in this short-term study. One patient developed reversible asymptomatic elevation of liver enzymes with the higher dose of fluvastatin; otherwise the drug was well tolerated and no patients had to be withdrawn from the study.

Adult↗
PubMed1995

Molecular cloning of LSIRF, a lymphoid-specific member of the interferon regulatory factor family that binds the interferon-stimulated response element (ISRE).

Interferon regulatory factor (IRF) genes encode a family of DNA-binding proteins that are involved in the transcriptional regulation of type-I interferon and/or interferon-inducible genes. We report here the characterization of LSIRF, a new member of the IRF gene family cloned from mouse spleen by the polymerase chain reaction using degenerate primers. LSIRF was found to encode a 51 kDa protein that shares a high degree of amino acid sequence homology in the DNA-binding domain with other IRF family members. LSIRF expression was detectable only in lymphoid cells. In contrast to other IRF genes, LSIRF expression was not induced by interferons, but rather by antigen-receptor mediated stimuli such as plant lectins, CD3 or IgM crosslinking. In in vitro DNA binding studies, LSIRF was able to bind to the interferon-stimulated response element (ISRE) of the MHC class I promoter. The expression pattern and DNA binding activities suggest that LSIRF plays a role in ISRE-targeted signal transduction mechanisms specific to lymphoid cells.

Amino Acid Sequence↗
PubMed1995

CD28 signals through acidic sphingomyelinase.

T cell receptor recognition of antigen can lead either to T lymphocyte differentiation and proliferation or to a state of unresponsiveness, which is dependent on whether appropriate costimulatory signals are provided to the mature T cell. We have investigated a novel intracellular signaling pathway provided by the costimulatory molecule CD28. CD28 engagement triggers the activation of an acidic sphingomyelinase (A-SMase), which results in the generation of ceramide, an important lipid messenger intermediate. A-SMase activation by CD28 occurred in resting as well as in activated primary T cells or leukemic Jurkat cells. In contrast, ligation of either CD3 or CD2 did not result in A-SMase activation. Overexpression of recombinant A-SMase in Jurkat T cells substituted for CD28 with regard to nuclear factor-kB activation. These data suggest that CD28 provides an important costimulatory signal by activation of an acidic sphingomyelinase pathway.

Animals↗
PubMed1995

Generation of T cells with differential responses to alloantigens in CD45 exon 6-deficient mice.

We characterized the CD45+ population in the CD45 exon 6-deficient mice and addressed a question as to whether the T cells keep responsive properties to alloantigens. The peripheral CD45+ T cells from the untreated knockout mice showed a decreased expression level of CD45 but increased expression levels of LFA-1 alpha and CD44, indicating that the T cells are possibly in an activation state. The CD45 exon 6-deficient mice could readily reject fully allogeneic skin grafts but not non-MHC-disparate skin grafts. The skin allograft-rejected CD45 exon 6-deficient mice showed an increased number of peripheral CD8+ T cells expressing an isoform of CD45RB (CD45 zeta). In vitro assays including mixed lymphocyte reaction, CTL, and cytokine productions were consistent to the in vivo results. Furthermore, the effector cells shown in these assays were CD45+CD8+ T cells expressing a CD45RB isoform, CD45 zeta. Moreover, the CD45+ T cells had an abnormal regulation of CD45 expression level, as they could not increase their CD45 expression level after in vitro allogeneic stimulation. These results indicate that abnormal mature T cells in the periphery of CD45 exon 6-deficient mice cannot respond to nominal Ags presented by MHC but can react to allo-MHC. The reason that such functionally impaired T cells can be generated in the mice is still unknown but these results imply that there is differential requirement of CD45 function for alloreactive T cells in a thymic selection(s) and in effector functions.

Animals↗
PubMed1995

Spontaneous resistance to acute T-cell leukaemias in TCRV gamma 1.1J gamma 4C gamma 4 transgenic mice.

The concept of tumour surveillance implies that specific and non-specific components of the immune system eliminate tumours in the early phase of malignancy. The immunological mechanisms that control growth of preneoplastic cells are, however, not known. T cells expressing gamma delta T-cell receptors (TCR) were first described as lymphocytes with reactivity against various tumour cells, which suggests that gamma delta T cells could mediate tumour surveillance. Here we show that TCRV gamma 1.1J gamma 4C gamma 4 transgenic mice are spontaneously resistant to acute T-cell leukaemias but cannot reject non-haematopoietic tumours. TCRV gamma 1.1J gamma 4C gamma 4+ hybridomas isolated from these mice react in vitro against almost all haematopoietic tumour cell lines tested. Recognition of tumour cells depends on the gamma delta TCR but is independent of major histocompatibility complex (MHC) class I, MHC class II, or TAP-2 peptide transporter expression. Ligand recognition is influenced by the murine Nromp gene, which confers resistance or susceptibility to tuberculosis, lepra and leishmaniasis. These data indicate that TCRV gamma 1.1+ T cells confer spontaneous immunity against haematopoietic tumours in vivo and link innate resistance to bacterial infections with tissue-specific tumour surveillance by gamma delta+ T cells.

3T3 Cells↗
PubMed1995

Impaired development of V gamma 3 dendritic epidermal T cells in p56lck protein tyrosine kinase-deficient and CD45 protein tyrosine phosphatase-deficient mice.

To determine whether p56lck protein tyrosine kinase and CD45 protein tyrosine phosphatase are involved in the signal transduction during intrathymic differentiation of gamma/delta T cells, we have examined the development of T cells expressing V gamma 3 T cell receptor (TCR) in mice deficient for either protein. The skin from both mice contained significantly reduced numbers of dendritic epidermal T cells expressing decreased levels of V gamma 3 TCR at the cell surface. Analysis of the fetal thymus from these mice suggested that maturation of V gamma 3 thymocytes was blocked at the immature stage that was characterized by the low level of V gamma 3 TCR and the high level of heat stable antigen. These results imply that both p56lck and CD45 are involved in the signal transduction during maturation of V gamma 3 T cells in the fetal thymus.

Animals↗
PubMed1995

T cell repertoire and clonal deletion of Mtv superantigen-reactive T cells in mice lacking CD4 and CD8 molecules.

CD4-CD8- double-negative T cells constitute a lymphocyte subpopulation within the thymus and peripheral lymphatic organs that express a unique T cell receptor (TCR) repertoire and do not undergo negative selection. To test whether these cells develop as a distinct lineage or due to altered selection in the absence of CD4 and CD8 expression, we analyzed the TCR repertoire in mice lacking both CD4 and CD8 accessory molecules after homologous recombination (CD40/0CD80/0). We show that mature T cells of CD40/0CD80/0 mice express an unbiased diverse TCR V beta repertoire comparable to wild type mice. In addition, clonal deletion of mouse mammary tumor virus superantigen-reactive T cells did occur in CD40/0CD80/0 mice. These data show that the intrinsic lack of CD4 and CD8 expression has no effect on the mature TCR repertoire and that clonal deletion of superantigen-reactive cells is independent of CD4 and CD8 co-receptors.

Animals↗
PubMed1995

Murine lupus in MRL/lpr mice lacking CD4 or CD8 T cells.

MRL/lpr mice develop a systemic autoimmune disease similar to systemic lupus erythematosus in humans. The mice show progressive lymphadenopathy due to the accumulation of an unusual population of CD4-8-(DN) B220+ alpha beta+ T cells. We bred MRL/lpr mice with mice lacking CD4+ or CD8+ T cells by gene targeting via homologous recombination in embryonal stem cells to determine the roles of these cells in the autoimmune disease. No difference in survival or autoantibody levels was noted between CD8-/-lpr and littermate controls. Interestingly, these CD8-/- lpr mice have a reduced level of B220+ DN T cells despite the fact that the degree of lymphadenopathy was unaltered. CD4-/- lpr mice had a diminished autoimmune disease with a reduction in autoantibody production and skin vasculitits, and increased survival compared to littermate controls. However, CD4-/- lpr mice had an enhanced splenomegaly that developed massively by 16-20 weeks of age (5 to 8 greater than lpr control mice) due to the accumulation of DN B220+ T cells. In addition, there were no differences in peripheral lymph node enlargement, although the proportion of DN B220+ T cells was about twofold higher in the CD4-/- lpr mice. These cells were phenotypically identical to the DN population in control lpr mice, indicating that the accumulating DN T cells can be dissociated from the autoimmune disease in these mice. Collectively, our results reveal that the autoimmune disease is dependent on CD4+, but not CD8+ T cells, and that many of the B220+ DN T cells traverse a CD8 developmental pathway.

Animals↗
PubMed1995

Allo-skin graft rejection, tumor rejection and natural killer activity in mice lacking p56lck.

Mice lacking the p56lck molecule (lck -/-) have a profound block in the maturation of thymocytes and a greatly reduced number of peripheral mature T cells. To analyze further the functions of the T cells developed in lck -/- mice in vivo, we evaluated the ability of lck -/- mice to reject allo-skin grafts and methylcholanthrene (MCA)-induced syngeneic fibrosarcoma, and also examined the biological activity of lck -/- natural killer (NK) cells. Mice lacking p56lck failed to reject skin grafts from either MHC-disparate or minor-histocompatibility-different donors, even after they had been primed with donor spleen cells. They also failed to reject the MCA-induced immunogenic syngeneic fibrosarcoma, MC57X. NK activity in mice lacking p56lck was normal, and there were no differences in the NK cell activation induced by poly(I).poly(C) stimulation or interleukin-2 stimulation (lymphokine-activated killer induction) between mice lacking p56lck and their immunocompetent heterozygous littermates. NK cells lacking p56lck mediated a normal antibody-dependent cell-mediated cytotoxicity (ADCC) response. The results of this study indicate that the loss of p56lck severely impairs the effectors of the immune system which mediate the rejection of allo-skin grafts and syngeneic tumors. The normal NK activity in lck -/- mice suggests that p56lck is not required for the development and activation of NK cells.

Animals↗
PubMed1995

Intestinal T cells in CD8 alpha knockout mice and T cell receptor transgenic mice.

Intraepithelial lymphocytes (IEL) refer to the T cells located at the epithelium of the intestines. Unlike the T cells in other peripheral lymphoid organs, the majority of IEL express the CD8 cell surface protein. To study the role of CD8 in the ontogeny and the function of IEL, phenotypic analysis of IEL from CD8 alpha knockout mice and normal mice was performed. The CD8 alpha gene in CD8 alpha knockout mice was disrupted by homologous recombination. These mice are defective in thymic maturation of cytotoxic T cells. In normal mice, alpha beta T cells that were CD8 alpha alpha+ or CD4+ CD8 alpha alpha+, and gamma delta T cells that were CD8 alpha alpha+, were the distinct populations found only in IEL. In CD8 alpha knockout mice, the population size of IEL remained normal, but the majority of IEL were CD4- CD8- T cells expressing alpha beta or gamma delta T cell receptors. IEL from the H-Y transgenic mice2, which express the male H-Y antigen specific T cell receptor in a normal and in a CD8 alpha-null background, were also studied. In contrast to thymic derived T cells, CD8 alpha alpha+ IEL with the autoreactive transgenic T cell receptor were not deleted, but clonally expanded in the male transgenic mice. Interestingly, no pathological symptoms were observed in the intestines of these mice. In the absence of CD8 alpha expression, the H-Y specific autoreactive IEL did not accumulate in the intestines. The results suggest that CD8 alpha alpha+ IEL are derived extra-thymically and their responses towards antigens require the CD8 accessory molecule.

Animals↗