Morphogenesis of callosal arbors in the parietal cortex of hamsters.
(1/1925)
The morphogenesis of callosal axons originating in the parietal cortex was studied by anterograde labeling with Phaseolus lectin or biocytin injected in postnatal (P) hamsters aged 7-25 days. Some labeled fibers were serially reconstructed. At P7, some callosal fibers extended as far as the contralateral rhinal fissure, with simple arbors located in the homotopic region of the opposite cortical gray matter, and two or three unbranched sprouts along their trajectory. From P7 to P13, the homotopic arbors became more complex, with branches focused predominantly, but not exclusively, in the supra- and infragranular layers of the homotopic region. Simultaneously, the lateral extension of the trunk axon in the white matter became shorter, finally disappearing by P25. Arbors in the gray matter were either bilaminar (layers 2/3 and 5) or supragranular. A heterotopic projection to the lateral cortex was consistently seen at all ages; the heterotopic arbors follow a similar sequence of events to that seen in homotopic regions. These observations document that callosal axons undergo regressive tangential remodeling during the first postnatal month, as the lateral extension of the trunk fiber gets eliminated. Radially, however, significant arborization occurs in layer-specific locations. The protracted period of morphogenesis suggests a correspondingly long plastic period for this system of cortical fibers. (+info)
Potent immunoregulatory effects of Salmonella typhi flagella on antigenic stimulation of human peripheral blood mononuclear cells.
(2/1925)
A key function of monocytes/macrophages (Mphi) is to present antigens to T cells. However, upon interaction with bacteria, Mphi lose their ability to effectively present soluble antigens. This functional loss was associated with alterations in the expression of adhesion molecules and CD14 and a reduction in the uptake of soluble antigen. Recently, we have demonstrated that Salmonella typhi flagella (STF) markedly decrease CD14 expression and are potent inducers of proinflammatory cytokine production by human peripheral blood mononuclear cells (hPBMC). In order to determine whether S. typhi and soluble STF also alter the ability of Mphi to activate T cells to proliferate to antigens and mitogens, hPBMC were cultured in the presence of tetanus toxoid (TT) or phytohemagglutinin (PHA) and either killed whole-cell S. typhi or purified STF protein. Both whole-cell S. typhi and STF suppressed proliferation to PHA and TT. This decreased proliferation was not a result of increased Mphi production of nitric oxide, prostaglandin E2, or oxygen radicals or the release of interleukin-1beta, tumor necrosis factor alpha, interleukin-6, or interleukin-10 following exposure to STF. However, the ability to take up soluble antigen, as determined by fluorescein isothiocyanate-labeled dextran uptake, was reduced in cells cultured with STF. Moreover, there was a dramatic reduction in the expression of CD54 on Mphi after exposure to STF. These results indicate that whole-cell S. typhi and STF have the ability to alter in vitro proliferation to soluble antigens and mitogens by affecting Mphi function. (+info)
Membrane dielectric responses of human T-lymphocytes following mitogenic stimulation.
(3/1925)
Human peripheral blood T-lymphocytes, normally resting at the G0 phase, were stimulated with phytohemagglutinin (PHA) and interleukin-2 (IL-2) to induce the cell division cycle. The cells were examined at 24-h intervals for up to 96 h by flow cytometry to determine cell cycle distributions and by electrorotation to determine dielectric properties. The average membrane specific capacitance was found to vary from 12 (+/-1.5) mF/m2 prior to stimulation to 10 (+/-1.5) and 16 (+/-3.5) mF/m2 at 24 and 48 h after stimulation, respectively, and to remain unchanged up to 96 h after stimulation. Scanning electron microscopy studies of the cells revealed an increased complexity in cell membrane morphology following stimulation, suggesting that the observed change in the membrane capacitance was dominated by the alteration of cell surface structures. The average electrical conductivity of the cell interior decreased from approximately 1.1 S/m prior to stimulation to approximately 0.8 S/m at 24 h after stimulation and showed little change thereafter. The average dielectric permittivity of the cell interior remained almost unchanged throughout the course of the cell stimulation. The percentage of T-lymphocytes in the S and G2/M phases increased from approximately 4% prior to stimulation to approximately 11 and approximately 34% at 24 and 48 h after stimulation, respectively. The large change in membrane specific capacitance between the 24 and 48 h time period coincided with the large alteration in the cell cycle distribution where the S and G2/M populations increased by approximately 23%. These data, together with an analysis of the variation of the membrane capacitance during the cell cycle based on the cell cycle-dependent membrane lipid accumulation, show that there is a correlation between membrane capacitance and cell cycle phases that reflects alterations in the cell plasma membrane. (+info)
Transcriptional regulation of interleukin-2 gene expression is impaired by copper deficiency in Jurkat human T lymphocytes.
(4/1925)
Copper deficiency reduces secretion of the cytokine interleukin-2 (IL-2) by activated rodent splenocytes, human peripheral blood mononuclear cells and Jurkat cells, a human T lymphocyte cell line. Previous studies showed that low Cu status also decreased the level of IL-2 mRNA in activated Jurkat cells by 50%. Synthesis of this cytokine is regulated by alterations in transcription of the IL-2 gene and the stability of IL-2 mRNA. To determine if Cu status influenced promoter activity of the IL-2 gene, Jurkat cells were transfected with a luciferase reporter gene construct containing the entire 300 bp human IL-2 promoter/enhancer sequence. Cu deficiency was induced by incubating stably transfected cells with the Cu chelator 2,3,2-tetraamine for 35 h prior to activating cells with phytohemagglutinin-P and phorbol myristate acetate. Luciferase activity in lysates of Cu-deficient cells was approximately 50% lower in several multiclonal and clonal cell lines of stably transfected cells than in replicate cultures that were not exposed to chelator. The relative levels of endogenous IL-2 bioactivity and luciferase activity were highly correlated in the transfected cell lines. The chelator-mediated reduction in reporter gene activity was dose-dependent at levels of 5-40 micromol 2,3,2-tetraamine/L. The addition of a slight molar excess of Cu, but not Zn or Fe, to medium containing 2,3,2-tetraamine prevented the decline in luciferase activity. IL-2 mRNA stability in parental Jurkat cells was independent of Cu status. These data indicate that decreased cellular Cu attenuates IL-2 synthesis in T lymphocytes by inhibiting transcription of the IL-2 gene. (+info)
Regulation of lymphotoxin production by the p21ras-raf-MEK-ERK cascade in PHA/PMA-stimulated Jurkat cells.
(5/1925)
Although the production of lymphotoxin (LT) from activated Th1 lymphocytes has been reported extensively, the intracellular signaling mechanisms that regulate this T cell function remain totally undefined. We have examined whether the p21ras-raf-1-mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK) kinase (MEK)-ERK cascade plays a role in regulating the production of LT, because the activity of these signaling molecules is up-regulated in activated T lymphocytes. Transfection of Jurkat leukemic T cells with a dominant negative mutant of p21ras (ras17N or ras15A), raf-1 (raf 1-130), or ERK1 (Erk1-K71R) resulted in the suppression of the mitogen/phorbol ester-stimulated production/secretion of LT. This suppression was accompanied by a parallel inhibition of mitogen-stimulated ERK activation. The selective antagonist of MEK1 activation, PD98059, also attenuated the mitogen-stimulated or anti-CD3 Ab and phorbol ester-stimulated production of LT from Jurkat cells or peripheral blood T lymphocytes. This study provides, for the first time, direct evidence that the p21ras-raf-MEK-ERK cascade plays a vital role in regulating the production of LT. (+info)
Suppression of lymphocyte transformation by plasma from owl monkeys acutely infected with Plasmodium falciparum.
(6/1925)
Plasma collected from owl monkeys during the acute phase of Plasmodium falciparum infection was shown to adversely affect several in vitro responses which are considered to be correlates of cell-mediated immune functions of normal monkeys. In the presence of acute-phase plasma, response of normal monkey peripheral blood lymphocytes to stimulation with phytohemagglutinin, concanavalin A, and pokeweed mitogen was severely reduced, as was the ability of peripheral blood lymphocytes to respond to allogenic and xenogenic histocompatible antigens. The transformation response of peripheral blood lymphocytes from normal humans to phytohemagglutinin and concanavalin A was also suppressed. Since acute-phase plasma was not cytotoxic for peripheral blood lymphocytes, decreased responsiveness did not result from cell destruction. Acute-phase plasma appears to block initial steps in lymphocyte transformation. (+info)
Enhanced expression of CTLA-4 (CD152) on CD4+ T cells in HIV infection.
(7/1925)
CTLA-4 (CD152) is a surface molecule of activated T cells with sequence homology to CD28. Both molecules bind to the same ligands, B7.1 (CD80) and B7.2 (CD86) but have antagonistic functions. While CD28 is an important costimulator, CTLA-4 has an essential inhibitory function in maintaining the homeostasis of the immune system. Down-regulation of CD28 predominantly on CD8+ T cells has been described in HIV infection, but analysis of CTLA-4 is complicated by its low expression levels. Here we have used potent signal enhancement to study CTLA-4 on peripheral blood mononuclear cells (PBMC) during HIV infection. CTLA-4 was expressed only on T cells. Expression levels were significantly increased selectively on CD4+ T cells during all stages of HIV infection, while CTLA-4 expression on CD8+ T cells was always low. In contrast, after stimulation with the mitogen phytohaemagglutinin (PHA), CTLA-4 levels were strongly increased on T cells from controls but in T cells from HIV patients this response was severely impaired. Our data suggest that in HIV infection CD4+ and CD8+ T cells may be less responsive to B7 costimuli due to two different mechanisms: increase in CTLA-4 expression by CD4+ cells and down-regulation of CD28 by CD8+ cells. (+info)
Human T cells express the C5a receptor and are chemoattracted to C5a.
(8/1925)
The anaphylatoxin C5a is a potent mediator of inflammation that exerts a broad range of activity on cells of the myeloid lineage. In this study, we present the first evidence that human T cells express the C5a receptor (C5aR) and are chemotactic to C5a. Using FACS analysis, we found that the C5aR was expressed at a low basal level on unstimulated T cells and was strikingly up-regulated upon PHA stimulation in a time- and dose-dependent manner. CD3+ sorted T cells as well as Jurkat T cells were shown to express C5aR mRNA as assessed by RT-PCR. Moreover, semiquantitative RT-PCR analysis demonstrated that C5aR mRNA was down-regulated in purified T cells upon long-term PHA stimulation. To demonstrate that C5a was biologically active on T cells, we investigated the chemotactic activity of C5a and observed that purified CD3+ T cells are chemotactic to C5a at nanomolar concentrations. Finally, using a combination of in situ hybridization and immunohistochemistry, we showed that the T cells infiltrating the central nervous system during experimental allergic encephalomyelitis express the C5aR mRNA. In summary, these results suggest that C5a exerts direct effects on T cells and could be involved in the trafficking of T cells under physiological and pathological conditions, including inflammatory diseases of the central nervous system. (+info)