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D B Lewis

Publications and source records attributed to D B Lewis.

At least 37 records · Page 2Linked to original sources
PubMed1995

The human gp39 promoter. Two distinct nuclear factors of activated T cell protein-binding elements contribute independently to transcriptional activation.

gp39, a cytokine expressed on the surface of activated T cells, is essential for T cell-dependent antibody responses in vivo. We cloned and sequenced 1.2 kilobases of the 5' flank region of the human gp39 gene promoter and determined its transcription start site. When used in reporter gene assays, this DNA segment conferred promoter activity in response to T cell activation. gp39 promoter function in transfectants was inhibited by cyclosporin A, as is expression of the endogenous gp39 gene in T-lineage cells. At least 0.5 kilobase of the 5' flank region was required for promoter activity. Two putative binding sites for the NF-AT family of transcriptional activator proteins were identified at -259 to -265 and -62 to -69 with respect to the transcription start site. Both sites contributed significantly and independently to promoter activity in response to T cell activation. Additionally, when incubated in vitro with nuclear protein purified from activated human CD4 T cells, both of these sites preferentially bound the NF-AT family member, NF-ATp. These results suggest that NF-ATp, via binding to at least two cis-elements, is essential for the induction of gp39 gene expression in response to T cell activation.

Base Sequence↗
PubMed1995

Hypomethylation of the interferon-gamma gene correlates with its expression by primary T-lineage cells.

To determine the potential role of methylation in the regulation of interferon-gamma (IFN-gamma) gene transcription by T cells, primary T-lineage cell populations were analyzed for the extent of methylation of three CpG sites within or near transcriptional activator elements in the 5' flank and first intron of the human IFN-gamma gene. A striking correlation was observed between the capacity of the IFN-gamma gene to be expressed and the degree of hypomethylation. The IFN-gamma gene was virtually completely methylated at all sites in thymocytes, neonatal T cells, and adult CD45RAhiCD45R0lo (antigenically naive) CD4 T cells, cell types that all have a low or undetectable capacity to express the IFN-gamma gene. In contrast, there was substantial hypomethylation in T-lineage cell types with relatively high capacities to express the IFN-gamma gene, including adult CD8 T cells and adult CD45RAloCD45R0hi (memory/effector) CD4 T cells. These results suggest that hypomethylation of the IFN-gamma genetic locus may be an important determinant of IFN-gamma gene expression in vivo by T-lineage cells.

Age Factors↗
PubMed1995

Diminished expression of CD40 ligand by activated neonatal T cells.

CD40 and CD40 ligand (gp39) mediate contact-dependent T-B cell interaction. We determined the expression of CD40 ligand by activated neonatal T cells and the response of neonatal B cells when activated through CD40. Although expression of CD40 ligand peaked simultaneously in both activated adult and neonatal cells, neonatal T cells expressed significantly less CD40 ligand surface protein and mRNA than adult T cells. Activated thymocytes also expressed far less CD40 ligand than adult T cells. Consistent with these results, activated neonatal T cells exhibited less helper function than activated adult T cells. Neonatal T cells primed and restimulated in vitro expressed CD40 ligand in amounts comparable with adult T cells and provided B cell help more effectively. This suggests that the poor expression of CD40 ligand reflects antigenic naiveté rather than an intrinsic defect of neonatal T cells. Neonatal B cells cultured with soluble CD40 ligand (sgp39) and IL-10 produced IgM in amounts comparable with adult cells, but much less IgG and IgA. Nevertheless, neonatal B cells were capable of proliferation and class switching, since sgp39 and IL-4 induced proliferation and IgE production comparable to adult B cells and production of modest amounts of IgG. Together, these results indicate that diminished CD40 ligand expression, along with decreased production of lymphokines, may be responsible, at least in part, for the transient immunodeficiency observed in human neonates.

Adult↗
PubMed1993

Osteoporosis induced in mice by overproduction of interleukin 4.

Osteoporosis is a common disease in which loss of bone mass results in skeletal fragility. The development of therapies for this disorder has been hampered by the lack of a convenient animal model. Here we describe a disorder in bone homeostasis in transgenic mice that inappropriately express the cytokine interleukin 4 (IL-4) under the direction of the lymphocyte-specific proximal promoter for the lck gene. Bone disease in lck-IL-4 mice appeared to result from markedly decreased bone formation by osteoblasts, features strikingly similar to those observed in cases of severe low-turnover human involutional osteoporosis. By 2 months of age, female and male lck-IL-4 mice invariably developed severe osteoporosis of both cortical and trabecular bone. Osteoporosis was observed in two independently derived founder animals, indicating that this phenotype was directly mediated by the IL-4 transgene.

Actins↗
PubMed1993

Lymphokine regulation and the role of abnormal regulation in immunodeficiency.

T cell-derived lymphokines mediate or modulate various aspects of the immune response and immunodeficiency states related to abnormalities in lymphokine production or regulation are now being recognized. One example of this is seen in the fetus and neonate, in whom a physiologic immunodeficiency appears to reflect in part deficient production of certain lymphokines, including interferon-gamma, IL-4, and IL-5. The deficiency in production of these lymphokines appears to reflect to a large extent the paucity of memory T cells during these periods of life. Diminished lymphokine production has also recently been implicated as the cause for three cases of primary severe combined immunodeficiency. In disorders associated with excess IgE production, including allergy, hyper IgE syndrome, and Omenn's syndrome, excess IL-4 production relative to the production of interferon-gamma may play a contributory role. Regulation of the production of these and other T cell-derived lymphokines appears to be affected predominantly by control of lymphokine gene transcription, the basis for which is just now becoming understood at a molecular level. The elucidation of these regulatory mechanisms offers the promise for understanding the basis for disordered lymphokine production in immunodeficiency states.

Humans↗
PubMed1992

Clinical and microbiologic characteristics of cutaneous infection with Yersinia enterocolitica.

The clinical and microbiologic features of primary cutaneous infections by Yersinia enterocolitica are described in three children. Vesiculobullous lesions developed in two patients, and an intense granulation response followed incision and drainage. In the third child, cellulitis and abscess formation developed at the site of minor skin trauma. Y. enterocolitica isolates from the patients were extensively serologically, biochemically, and molecularly analyzed and compared with virulent Y. enterocolitica strains. The ability of the isolates to adhere to and invade eukaryotic cells was determined using in vitro assays; virulence was assessed by inoculation of suckling mice. The resulting data suggest that primary cutaneous infections by Y. enterocolitica involve strains that are as virulent as pathogenic gastrointestinal isolates.

Animals↗
PubMed1992

Decreased granulocyte-macrophage colony-stimulating factor production by human neonatal blood mononuclear cells and T cells.

Impaired production and delivery of neutrophils to the site of infection have been implicated in the increased susceptibility of the neonate to infection. Because granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) play critical roles in the production of neutrophils from marrow precursors, we assessed the ability of leukocytes from neonates and adults to produce GM-CSF, G-CSF, and, for comparison, macrophage colony-stimulating factor (M-CSF) after stimulation with concanavalin A +/- phorbol myristate acetate [blood mononuclear cells (MC) and T lymphocytes] or lipopolysaccharide (monocytes). MC and monocytes from adult and neonatal subjects produced mRNA for GM-CSF, G-CSF, and M-CSF, whereas T cells produced only GM-CSF mRNA. Neonatal MC and T cells accumulated only approximately 30% as much GM-CSF mRNA as did adult MC and T cells. In contrast, the accumulation of GM-CSF mRNA by neonatal and adult monocytes was similar. Neonatal MC also accumulated similar amounts of G-CSF mRNA and somewhat more M-CSF mRNA than did adult MC; results with monocytes were similar to those with MC. Results of colony-stimulating activity bioassays on supernatants from neonatal and adult MC stimulated with concanavalin A paralleled the mRNA results.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Developmental regulation of lck gene expression in T lymphocytes.

In the mouse and human, mRNA transcripts encoding the lymphocyte-specific protein tyrosine kinase p56lck are derived from two separate promoters resulting in heterogeneity in the 5' untranslated region sequence. The proximal promoter lies just 5' to the coding region for the gene and is active only in thymocytes. In contrast, the distal promoter lies 34 kilobases (kb) 5' in the human, and is active both in thymocytes and mature peripheral T cells. As previously reported, transgenic mice bearing functional proximal promoter sequence juxtaposed with the SV40 large T antigen gene invariably develop lymphoid tumors confined to the thymus. In the current work, transgenic mice bearing a 2.6-kb fragment of the human distal promoter fused to the SV40 large T antigen gene express large T antigen in thymocytes and in peripheral lymphoid cells, and develop tumors of both the thymus and the peripheral lymphoid organs. The ability of the human distal promoter to function appropriately in transgenic mice is consistent with the strong similarity observed between the mouse and human distal promoter sequences. With the exception of a single short interval that serves as a target for binding of nuclear factors, significant sequence similarity is not seen when the distal and proximal promoter sequences are compared. Hence, developmentally regulated, lineage-specific transcription of the lck gene is mediated by distinct promoter sequences that appear to be capable of functioning independently.

Animals↗
PubMed1991

Interleukin 4 expressed in situ selectively alters thymocyte development.

Using a transgenic mouse model we show that increased intrathymic expression of interleukin 4 (IL-4) significantly perturbs the development of thymocytes. Transgenic double-positive (CD4+CD8+) thymocytes, which are present in dramatically reduced numbers, exhibit increased T cell receptor (TCR) expression and increased mobilization of calcium mediated by these receptors. In contrast, transgenic single-positive (CD4+CD8- and CD4-CD8+) thymocytes and peripheral T cells exhibit decreased TCR-mediated calcium mobilization. The development of CD4-CD8+ thymocytes is significantly perturbed by IL-4 expressed in vivo; only peripheral CD4+ T cells are found in significant numbers in transgenic mice, while CD4-CD8+ thymocytes are present in increased numbers, apparently because of their failure to emigrate to the periphery. In contrast to these selective effects on T cell development, no significant differences in the numbers of B cells or mast cells, or in the plasma levels of IgE and IgG1 are observed between transgenic and control mice. These observations suggest that IL-4 in vivo exerts its major effects locally rather than systemically, even when its expression is constitutively increased.

Animals↗
PubMed1991

Cellular and molecular mechanisms for reduced interleukin 4 and interferon-gamma production by neonatal T cells.

The mechanisms by which T lymphocytes acquire the capacity to produce interleukin 4 (IL-4) and other lymphokines during intrathymic and extrathymic development are poorly understood. To gain insight into this process, we determined the capacity of human neonatal and adult T lineage cell populations to produce IL-4 after polyclonal activation. IL-2 and interferon-gamma (IFN-gamma) production were studied in parallel, since their production by neonatal T cells is known to be similar or diminished, respectively, compared to adult T cells. Production of IL-4 by neonatal CD4+ T cells and IFN-gamma by neonatal CD4+ and CD8+ T cells was markedly lower compared with analogous adult cell populations, whereas IL-2 production was similar. Transcription of IL-4, as determined by nuclear run-on assays, and IL-4 mRNA-containing cells, as determined by in situ hybridization, were undetectable in neonatal T cells, whereas both were detectable in adult T cells. IFN-gamma transcription and IFN-gamma mRNA-containing cells were reduced in neonatal T cells compared with adult T cells. Reduced lymphokine production by neonatal T cells correlated with their lack of a CD45R- (putative memory T cell) population; cells with this surface phenotype comprised 30-40% of the adult CD4+ T cells and were highly enriched for IL-4 and IFN-gamma, but not IL-2 production. IL-4, IFN-gamma, and IL-2 mRNA expression by neonatal CD4+CD8- thymocytes was similar to that found in circulating neonatal CD4+ T cells. Taken together, these findings suggest that the extrathymic generation of memory T cells during postnatal life may result in an increased capacity for IL-4 and IFN-gamma gene expression. In addition, IFN-gamma and IL-2 mRNA were significantly more abundant than IL-4 mRNA in activated neonatal CD4+CD8- thymocytes and CD4+ T cells, as well as adult CD4+ CD45R- T cells. Therefore, the capacity of T lineage cells to express the IL-4 gene may be more restricted compared to other lymphokine genes beginning in intrathymic development. This restricted capacity appears to persist during postnatal extrathymic maturation of T cells.

Adult↗
PubMed1990

Regulation of immunoglobulin (Ig)E synthesis in the hyper-IgE syndrome.

The hyper-IgE (HIE) syndrome is characterized by high IgE serum levels, chronic dermatitis, and recurrent infections. The mechanisms responsible for hyperproduction of IgE in HIE patients are presently unknown. We investigated whether spontaneous in vitro IgE synthesis by PBMC from seven HIE patients was sensitive to signals (cell adhesion, T/B cell cognate interaction and lymphokines: IL-4, IL-6, and IFN-gamma) known to regulate IgE induction in normals. Our results show that, unlike IL-4 dependent IgE synthesis induced in normals, spontaneous IgE production by PBMC from HIE patients was not blocked by monoclonal antibodies to CD2, CD4, CD3, and MHC class II antigens. Furthermore, antibodies to IL-4 and IL-6 did not significantly suppress IgE production. IFN-gamma had no significant effects on spontaneous in vitro IgE synthesis. To test whether an imbalance in lymphokine production might underlie hyperproduction of IgE in HIE patients, mitogen-induced secretion of IL-4 and IFN-gamma by PBMC was assessed. No significant difference was detected between HIE patients and normal controls. Thus, ongoing IgE synthesis in the HIE syndrome is largely independent of cell-cell interactions and endogenous lymphokines, and is due to a terminally differentiated B cell population, no longer sensitive to regulatory signals.

Adult↗
PubMed1989

Lymphocyte activation provokes modification of a lymphocyte-specific protein tyrosine kinase (p56lck).

The protein tyrosine kinase p56lck is implicated in the control of lymphocyte growth by virtue of its overexpression in some lymphoid malignancies and its transforming activity in heterologous systems. Previous studies have demonstrated that levels of lck mRNA and of p56lck decline rapidly after T cell activation. The disappearance of p56lck results primarily from post-translational conversion of p56lck to more slowly migrating forms with apparent sizes of approximately 60 kDa. This modification can be provoked by treatment of lymphocytes with PMA, and has been associated with increased serine phosphorylation of the p56lck molecule. Here we demonstrate that conversion of p56lck to p60lck is a feature of the physiologic activation of T lymphocytes by antigen-presenting cells. In addition, we show that the PMA-induced modification of p56lck proceeds via a mechanism distinct from conventional protein kinase C activation. The rapid conversion of p56lck to p60lck after antigenic stimulation is consistent with the view that this membrane-associated protein tyrosine kinase regulates some aspects of the lymphocyte activation sequence.

Adult↗
PubMed1988

Structure and expression of lck transcripts in human lymphoid cells.

The murine lck gene encodes a membrane-associated protein tyrosine kinase that has been implicated in lymphocyte oncogenesis. Here we report the structure of normal human lck transcripts and the pattern of expression of these transcripts in developing thymus and in peripheral T cell subsets. The human lck gene encodes a 509 amino acid polypeptide that is closely related to the murine lck-encoded protein throughout its length. Analysis of the deduced amino acid sequence of human p56lck demonstrates that an amino-terminal domain, widely divergent among the seven known src family members, has been conserved between murine and human p56lck, and thus probably includes sequences crucial to the lymphocyte-specific function of this molecule. Human lck transcripts were detected in CD4+ and CD8+ T cells, in partially purified B cells, and in Epstein-Barr virus-immortalized B cell lines, but not in monocytes, granulocytes, or in nonhematopoetic cell types. Human lck transcripts are readily detectable in fetal thymocytes at 70 days of gestation, but not at 57 days of gestation, indicating that lck expression appears coordinately with the appearance of lymphoid cells in the developing thymus. Thus lck gene expression is a marker for cells of the lymphocyte lineage in man. We conclude that the lck gene probably participates in a signal transduction pathway uniquely present in lymphoid cells.

Base Sequence↗
PubMed1988

Restricted production of interleukin 4 by activated human T cells.

Interleukin 4 (IL-4) is secreted by activated T cells and pleiotropically modulates both B- and T-lymphocyte function. In murine helper (CD4+) T-cell clones IL-4 production appears to be regulated independently of interferon gamma and interleukin 2. To determine whether production of these lymphokines is also differentially regulated in uncloned human T cells, we studied lymphokine production by normal human peripheral T cells and T-cell subsets after in vitro polyclonal activation. After maximal induction of lymphokine expression, IL-4 mRNA was detectable in less than 5% of CD4+ and 1-2% of unfractionated T cells, whereas approximately 33% and 60% of CD4+ cells expressed detectable mRNA for interferon gamma and interleukin 2, respectively. This finding correlated with dramatically lower production of IL-4 mRNA and protein than of interferon gamma and interleukin 2 by peripheral blood and tonsillar T cells. The helper-inducer (CD4+ CD45R-) T-cell subset, which significantly enhances in vitro immunoglobulin production, accounted for the preponderance of IL-4 mRNA accumulation and protein production by CD4+ T cells; nevertheless, cells with detectable IL-4 mRNA constituted less than 10% of the CD4+ CD45R- subset. Limitation of IL-4 production to a comparatively small population of normal human T cells could selectively regulate the effects of this lymphokine in T-cell-mediated immune responses; such selective regulation may be a fundamental mechanism for restricting the potentially pleiotropic effects of certain lymphokines to appropriate responder cells.

Antigens, Differentiation, T-Lymphocyte↗