Biomedical subjects

G Bismuth

Publications and source records attributed to G Bismuth.

At least 55 records · Page 3Linked to original sources

PubMed1992

Interferon-alpha downregulates the abnormal intracytoplasmic free calcium concentration of tumor cells in hairy cell leukemia.

Hairy cell leukemia (HCL) is a B-cell tumor affecting the preplasma stage of B-cell differentiation. One important feature of the disease is its exquisite sensitivity to interferon-alpha (IFN-alpha) therapy. Because we showed earlier that the CD20 molecule is consistently hyperphosphorylated in hairy cells and because previous studies showed that CD20 is involved in regulating intracytoplasmic free calcium concentrations ([Ca2+]i) in normal B lymphocytes, we measured [Ca2+]i in tumor cell samples from patients with HCL and studied the effect of IFN-alpha on this parameter. Using the Ca(2+)-sensitive fluorophore fura-2, we observed that hairy cells display a slightly but consistently higher [Ca2+]i than normal 48-hour-activated B cells or other leukemic cells. Furthermore, both in vitro preincubation of cell samples with IFN-alpha and in vivo administration of this cytokine reduced the [Ca2+]i in hairy cells. This effect was observed together with a decrease in transmembrane Ca2+ influx. However, preincubation with IFN-gamma had no effect. The in vivo correlation between the diminution of CD20 phosphorylation and [Ca2+]i in tumor cell samples from patients at the beginning of IFN-alpha therapy suggests that these two parameters are connected.

Antigens, CD↗

PubMed1992

Expression, molecular association, and functions of C3 complement receptors CR1 (CD35) and CR2 (CD21) on the human T cell line HPB-ALL.

We have investigated the expression, molecular association, ligand binding properties, and ability to transduce intracellular signals of CR1 and CR2 C3 receptors on cells of the human HPB-ALL T cell line. CR1 and CR2 on HPB-ALL cells bound polymeric C3b and C3dg and several anti-CR1 and anti-CR2 mAb recognizing different epitopes of the receptors on normal peripheral blood cells. Immunoprecipitated CR1 and CR2 exhibited similar m.w. to those of the receptors on normal peripheral blood T and B lymphocytes. CR1 and CR2 were partially associated in the form of CR1/CR2 complexes in the cell membrane as assessed by the ability of the receptors to cocap and cointernalize and to form a detergent-sensitive complex upon immunoprecipitation analysis. Triggering of CR2 with mAb OKB7 that recognizes an epitope associated with the ligand binding site of the receptor induced an increase in intracellular free calcium concentration in HPB-ALL cells. The signal provided by mAb OKB7 did not synergize with that triggered by anti-CD3 mAb UCHT1. Triggering of CR1 did not result in changes in intracellular free calcium concentration. Our observations have significance for the biology of normal human T cells because the majority of peripheral blood T cells that express CR1 also expressed CR2 and because a change in (Ca2+)i was induced by mAb OKB7 in purified normal T cells. These functions may be relevant for the regulatory role of C3 fragments on the immune response to T-dependent Ag and for the penetration into T cells of lymphocytotropic viruses.

Antigens, Differentiation, B-Lymphocyte↗

PubMed1992

Internalization of HIV glycoprotein gp120 is associated with down-modulation of membrane CD4 and p56lck together with impairment of T cell activation.

We previously demonstrated that long term treatment of the Ag-specific CD4+ T cell clone P28D with soluble HIV envelope glycoprotein gp120 results in a marked impairment of CD3/TCR-mediated responses. In this report, to further understand these inhibitory effects, the binding properties and internalization of gp120 have been investigated, in parallel with functional studies, in long term incubations of P28D cells with gp120. Immunofluorescence studies show that surface-bound gp120 level is maximal within 1 h of incubation at 37 degrees C and then gradually decreases. This decrease is accompanied by a progressive down-modulation of membrane CD4 (30-35% loss over a 18-h incubation period) without concomitant alteration of the CD4 mRNA steady-state level. Similar experiments performed with 125I-labeled gp120 demonstrate that the glycoprotein is progressively internalized (up to 35% internalized material after 18 h) and that it accumulates inside the cells. Confocal microscopy studies show that internalized gp120 is concentrated in localized intracellular compartments. CD4 also accumulates in compartments with a similar localization and is stained with mAb OKT4 but not with mAb OKT4a. Concomitantly to internalization of gp120 and disappearance of membrane CD4, a correlated loss of the CD4-associated tyrosine kinase p56lck is evidenced. Interestingly, a progressive impairment of the P28D responses to specific Ag or to anti-CD3 mAb is also observed. Inhibitions of T cell proliferation increase with the degree of both CD4 and p56lck down-modulation. Removal of exogenous gp120 results in a rapid and spontaneous release of internalized gp120 into a degraded form. A progressive restoration of CD4 and p56lck levels is also noticed. In parallel, CD3/TCR-mediated responses of clone P28D are fully recovered. Altogether, our results suggest that HIV-1 glycoprotein gp120 is able to down-modulate membrane CD4 presumably by a cointernalization process and to further down-modulate the associated p56lck. This dual phenomenon is presumably involved in the direct immunosuppressive effect of gp120 on the CD3/TCR-mediated activation pathway.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1992

Imaging early steps of human T cell activation by antigen-presenting cells.

In this work the Ca2+ response and the morphological changes elicited by Ag in human CD4+ T cells are described at the single cell level. The APC used to present the diphtheria toxoid Ag to a human diphtheria toxoid-specific T cell clone were murine L cell fibroblast transfectants expressing MHC class II molecules. The increase of the intracellular Ca2+ concentration, [Ca2+]i, which is one of the earliest steps of the response to TCR stimulation, was followed by fluorimetry with fura-2 on an imaging system. This response was a specific consequence of successful Ag presentation, because it only took place when fibroblasts expressed both class II MHC molecules and Ag. CD4 molecules were also involved in this intercellular interaction, because the Ca2+ response could be inhibited by preincubating the T cells with an anti-CD4 antibody. The response induced by APC started after a delay of at least 6 min, after which large Ca2+ oscillations took place, with a pseudo period of 100 s at 35 degrees C. The frequency of these oscillations decreased with temperature. The oscillations became progressively more damped during the first 30 to 40 min of cell-to-cell interaction, after which they completely stopped; however, [Ca2+]i remained well above its resting level for more than 1 h after the contact. The Ca2+ oscillations were entirely dependent on Ca2+ influx because they immediately disappeared when external calcium was removed. Similar oscillations were observed when the cells were stimulated with an anti-CD3 antibody. After stimulation with APC, many T cells abandoned their spherical shape and tended to flatten and elongate. This aspect of the T cell response was not observed after stimulation with an anti-CD3 antibody. In the presence of cytochalasin B, the morphologic changes elicited by the APC were blocked, whereas the Ca2+ response was slightly enhanced. However, when T cells were loaded with the Ca2+ chelator BAPTA, both Ca2+ and morphologic changes were inhibited, suggesting that the Ca2+ response plays a permissive role for the morphologic changes.

Animals↗

PubMed1991

Cyclic AMP- and inositol phosphate-independent inhibition of Ca2+ influx by cholera toxin in CD3-stimulated Jurkat T cells. A study with a cholera toxin-resistant cell variant and the Ca2+ endoplasmic reticulum-ATPase inhibitor thapsigargin.

In this report, we describe a Jurkat cell variant, termed JCT8, the selection of which is based upon its resistance to cell-growth inhibition mediated by the holotoxin of Vibrio cholerae, cholera toxin (CT). JCT8 cells exhibit normal cAMP production in response to various cAMP inducers, including CT, together with conserved ADP ribosylation in vitro of G-protein Gs alpha by the A subunit of the toxin. However, after a 4-h pretreatment with CT, JCT8 cells have a conserved expression of cell-surface CD3 molecules. These effects are in contrast to those elicited by the toxin in long term PGE2-desensitized Jurkat cells, which remain as sensitive as the wild type to the inhibitory action of CT on cell growth and CD3 cell-surface expression, despite poor responsiveness to CT with regard to cAMP production. In JCT8 cells, Ca2+ mobilization induced via the CD3/TCR is maintained after CT treatment contrasting with its complete suppression in the wild-type and in the PGE2-desensitized cells. However, as in the other cell types, CT still suppresses Ca2+ influx in JCT8 cells. Increase in inositol phosphates by CD3 stimulation of JCT8 cells, including of inositol 1,4,5-triphosphate (I(1,4,5)P3), is only partially antagonized by CT. This suggests either that in JCT8 cells there is a different susceptibility of Ca2+ mobilization and influx to partial inhibition by CT of CD3-triggered phospholipase C (PLC)-induced phosphoinositide hydrolysis or that an additional and PLC-independent suppressive effect of the toxin on Ca2+ influx may exist. To investigate this particular point further, we use Thapsigargin, a Ca(2+)-endoplasmic reticulum ATPase inhibitor that can mobilize in human T lymphocytes I(1,4,5)P3-dependent intracellular Ca2+ pools by a PLC-independent pathway. We demonstrate that the Ca2+ influx triggered in the wild-type Jurkat cells or in JCT8 cells by Thapsigargin is antagonized by CT. The present data are therefore consistent with the idea that CT specifically impairs in the Jurkat T cell model the entry of Ca2+ from extracellular spaces by a mechanism independent not only from cAMP but also in part from inhibition by the toxin of phosphoinositide hydrolysis.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1991

Nitrendipine-induced inhibition of calcium influx in a human T-cell clone: role of cell depolarization.

An increase in intracellular calcium concentration stimulated by anti-CD2 or CD3 antibodies has been measured with Fura-2 in P28 cells, a human CD4+ T cell clone. This intracellular calcium increase was sensitive to membrane potential changes, being increased when the cells were hyperpolarized and decreased when they were depolarized. The intracellular calcium increase was inhibited by nitrendipine (1-50 microM). Nitrendipine also induced a depolarization of the cells, due to the blockade of a potassium conductance. The inhibition of the calcium increase caused by nitrendipine could be partially reversed by hyperpolarizing the cells with valinomycin. It is concluded that the effects of nitrendipine on potassium channels may account for a large part of the inhibition that nitrendipine exerts on the calcium increase elicited by CD2 or CD3 stimulation.

Antibodies, Monoclonal↗

PubMed1991

NF-kappa B activation by tumor necrosis factor alpha in the Jurkat T cell line is independent of protein kinase A, protein kinase C, and Ca(2+)-regulated kinases.

NF-kappa B is a DNA-binding regulatory factor able to control transcription of a number of genes, including human immunodeficiency virus (HIV) genes. In T cells, NF-kappa B is activated upon cellular treatment by phorbol esters and the cytokine tumor necrosis factor alpha (TNF alpha). In the present work, we investigated the molecular events leading to NF-kappa B activation by TNF alpha in a human T cell line (Jurkat) and its subclone JCT6, which presents a deficiency in the PKA transduction pathway. We found that in both cell lines, both phorbol ester and TNF alpha were able to activate NF-kappa B. Phorbol activation was positively modulated by Ca2+ influx while TNF alpha activation was not. Furthermore, while PMA activation was inhibited by the PKC inhibitor staurosporin, the TNF alpha effect was unchanged. TNF alpha did not activate cAMP production and its signal was not modulated by cAMP activators. Moreover, cAMP activators did not activate NF-kappa B in Jurkat cells. Thus, TNF alpha-induced NF-kappa B activation was found to be mediated by none of the major signal-mediating kinases such as protein kinase C (PKC), protein kinase A, or Ca(2+)-regulated kinases. Furthermore, we found that cytoplasmic acidification facilitated NF-kappa B activation by both TNF alpha and PKC, by a mechanism that increases NF-kappa B/I kappa B dissociation without affecting the NF-kappa B translocation step.

Calcium↗

PubMed1991

Ca(2+)-induced Ca2+ release amplifies the Ca2+ response elicited by inositol trisphosphate in macrophages.

We have studied the rise in intracellular calcium concentration ([Ca2+]i) elicited in macrophages stimulated by platelet-activating factor (PAF) by using fura-2 measurements in individual cells. The [Ca2+]i increase begins with a massive and rapid release of Ca2+ from intracellular stores. We have examined the mechanism of this Ca2+ release, which has been generally assumed to be triggered by inositol trisphosphate (IP3). First, we confirmed that IP3 plays an important role in the initiation of the PAF-induced [Ca2+]i rise. The arguments are 1) an increase in IP3 concentration is observed after PAF stimulation; 2) injection of IP3 mimics the response to PAF; and 3) after introduction of heparin in the cell with a patch-clamp electrode, the PAF response is abolished. Second, we investigated the possibility of an involvement of Ca(2+)-induced Ca2+ release (CICR) in the development of the Ca2+ response. Ionomycin was found to elicit a massive Ca2+ response that was inhibited by ruthenium red or octanol and potentiated by caffeine. The PAF response was also inhibited by ruthenium red or octanol and potentiated by caffeine, suggesting that CICR plays a physiological role in these cells. Because our results indicate that in this preparation IP3 production is not sensitive to [Ca2+]i, CICR appears as a primary mechanism of positive feedback in the Ca2+ response. Taken together, the results suggest that the response to PAF involves an IP3-induced [Ca2+]i rise followed by CICR.

Animals↗

PubMed1990

Helper or cytolytic functions can be selectively induced in bifunctional T cell clones.

By using bifunctional T cell populations, we have shown in this report that elicitation of helper versus cytolytic function depends on the stimulatory signal at the membrane. Interestingly enough, the transduction of these signals is likely to be achieved via different metabolic pathways. Thus, helper function is associated with intracellular Ca2+ mobilization and PLC activation, while cytolysis can occur even in the absence of detectable levels of these second messengers. These results indicate that selective activation through the same membrane-transducing molecule may orientate T cell function through qualitatively or quantitatively different second messengers. This would be an important part of immune regulation.

Antibodies, Monoclonal↗

PubMed1990

Stage specific phosphoinositides turnover capacity of human intrathymic T cells following CD2-triggering.

Triggering of distinct CD2 epitopes on human T lymphocytes increases their phosphatidylinositol (PI) cycle-related metabolism. In this work, we investigated the relationship between this signal transduction pathway following surface CD2 antigen triggering and intrathymic T cell development. Therefore, various thymocyte subsets were incubated with co-mitogenic CD2I+III mAb. The cells were then tested for their various phosphoinositides levels as well as their ability to proliferate in response to recombinant interleukin-2 (rIL-2). Our results indicate that immature CD4- CD8- cells have high PI metabolism while more mature CD4+CD8+ and unfractionated thymocytes display significantly lower PI-turnover. Mature CD4+CD8- and CD4-CD8+ thymocytes regain this transduction capacity. Thus, PI-turnover following CD2- triggering is linked to the developmental fate of thymocyte subclasses.

Antigens, CD↗

PubMed1990

CD2 triggering stimulates a phospholipase A2 activity beside the phospholipase C pathway in human T lymphocytes.

In previous studies we demonstrated the triggering of the phospholipase C (PLC) pathway during the activation of an Ag-specific human CD4+ T lymphocyte clone by a mitogenic pair of CD2 (X11,D66) mAb. Similar conditions were applied to investigate a possible involvement of a phospholipase A2 (PLA2) acting as an additional alternative pathway during human T cell activation. Our results show that arachidonic acid or its derivatives are released after CD2 triggering. This release is largely independent of PLC activation and is mediated by a PLA2 because: 1) phosphatidylcholine is the preferential source of [3H]arachidonate release; 2) [3H]arachidonic acid release and phosphatidylcholine hydrolysis are blocked by two inhibitors of solubilized PLA2, mepacrine, and 4-p-bromophenacylbromide; and 3) we evidenced a PLA2 activity in cell homogenates. Extracellular calcium appears to play a critical role because the effects of CD2 mAb were inhibited in a Ca2(+)-depleted medium. In contrast, protein kinase C is not implicated since PMA, a protein kinase C activator, neither stimulated arachidonic acid release nor modulated CD2-induced arachidonic acid release. Cyclic AMP which has been proved to regulate the activity of the PLC in T lymphocytes does not appear to play an important role in the regulation of PLA2 activity since PGE2 has only a minimal effect on [3H]-arachidonate release. Altogether, these findings suggest that CD2 triggering stimulates a PLA2 activity in T lymphocytes via an extracellular Ca2(+)-dependent PLC protein kinase C independent mechanism.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1990

Ca2+ influx in human T lymphocytes is induced independently of inositol phosphate production by mobilization of intracellular Ca2+ stores. A study with the Ca2+ endoplasmic reticulum-ATPase inhibitor thapsigargin.

Thapsigargin (TG), a sesquiterpene lactone and non-phorbol 12-myristate 13-acetate tumor promoter, stimulates a rapid increase in intracellular free Ca2+ [( Ca2+]i) in human T lymphocytes clone P28. The [Ca2+]i response to TG is sustained in the presence of 1 mM extracellular Ca2+, while it becomes transient in Ca2(+)-free medium suggesting that TG activates both the release of Ca2+ from intracellular stores and the entry of Ca2+ from extracellular spaces. TG-induced Ca2+ influx is completely abolished after cell depolarization caused by increased extracellular concentrations of K+. The rise in [Ca2+]i stimulated by TG occurs in the absence of detectable production of inositol phosphates. Moreover, TG does not alter the early biochemical events of T cell activation triggered through the CD2 or the CD3 T cell antigens. Indeed, both inositol phosphate production and intracellular pH increase induced by specific monoclonal antibodies (mAb) remain unchanged after TG treatment. These data suggest that in human T lymphocytes TG releases Ca2+ from an intracellular pool by a mechanism which is independent of the phospholipase C metabolic pathway. Preincubation with TG of T cell clone P28 empties both the CD2 and the CD3-sensitive intracellular Ca2+ pool(s). Conversely, prestimulation of T cell clone P28 by CD3 or CD2-specific mAb inhibits the Ca2(+)-mobilizing effect of TG. Thus it appears that TG and CD2- or CD3-specific mAb mobilize Ca2+ from common Ca2+ pool(s). Taken together, these results demonstrate that Ca2+ influx in human T cells may be linked to mobilization of intracellular Ca2+ pools and by a mechanism independent of phosphoinositide hydrolysis. They further indicate that the release of intracellular Ca2+ pool(s) may play a major role in the opening of cell membrane Ca2+ channels observed during the CD2- or CD3-induced stimulation of human T lymphocytes.

Antibodies, Monoclonal↗

PubMed1990

A human TCR-Ig chimeric protein used to generate a TCR alpha chain variable region-specific mAb.

In a recent report, a construction containing the alpha chain-variable region (V alpha) coding sequence of a cDNA clone derived from a diphtheria toxoid-specific human T cell (P28), fused to a human immunoglobulin kappa light chain constant region (Ck), was used stably to transfect a murine myeloma cell. In the present study, these transfected cells were employed as an immunogen to raise a mAb, termed 1C5V alpha, specific both for the V alpha Ck chimeric protein secreted by the transfectant and the P28 T cell antigen receptor-V alpha region. mAb 1C5V alpha specifically immunoprecipitates the V alpha Ck protein as a family of 32-35 kDa bands present in the 35S-methionine-labeled culture supernatant from the transfected cells. It specifically binds clone P28. Surface molecules recognized by mAb 1C5V alpha are physically linked to the CD3 molecules since cell treatment with either 1C5V alpha or anti-CD3 mAbs caused the simultaneous down-regulation of the CD3/TCR molecular complex. This link is further supported by immunoprecipitation experiments. Thus, both the 1C5V alpha and the anti-CD3 mAbs precipitate the 16-28 kDa CD3 molecules and the disulfide-linked form of P28 TCR from 125I-labeled P28 T cells. Studies performed in order to define whether a stimulus directly acting on the TCR-V alpha region may trigger the intracellular events observed during human T cell activation showed that (a) mAb 1C5V alpha efficiently triggers the phospholipase C transduction pathway revealed by an accelerated phosphoinositides turn-over and an increased production of phosphorylated derivatives of inositol phosphates; (b) mAb 1C5V alpha induces an up-regulation of IL2R mRNA, accompanied by a slight increase of IL2 and IFN alpha mRNA transcripts evidently amplified in the presence of PMA; (c) soluble mAb 1C5V alpha is strongly mitogenic together with PMA. These results provide the first evidence for the structural authenticity of a secreted water-soluble chimeric form of the variable region of a human TCR alpha chain. They further demonstrate that such chimeric proteins may be valuable tool to further dissect the various functional structure of the human TCR.

Antibodies, Monoclonal↗

PubMed1990

Identification of cross-reactive T cell restriction epitopes located on the DR7 beta 1 and DR beta 4 molecules.

L cell fibroblasts transfected with HLA class II cDNA clones isolated from a cDNA library produced from a DR7 homozygous cell line were used as antigen-presenting cells (APC) for three HLA DR-restricted, diphtheria toxoid-specific T-cell clones in order to assess the antigen-presenting ability of the transfectants and to define the class II restriction of each clone. Class II-expressing transfectants are capable of presenting antigen to antigen-specific T-cell clones, although the transfectants are less efficient at antigen presentation than conventional APC. Paraformaldehyde fixation of transfectants prior to antigen pulsing abrogated antigen presentation, demonstrating that the transfectants require antigen processing. Antigen presentation by transfectants is completely inhibited by CD4-specific monoclonal antibodies (mAb) and one of four DR-specific mAb, whereas antigen presentation by conventional APC is only partially inhibited. Both the DR alpha:DR7 beta 1 and DR alpha:DR beta 4 (DR omega 53) molecules of the DR7 allotype serve as restriction elements for the diphtheria toxoid-specific T-cell clones. One clone is restricted by the DR7 beta 1 molecule, another clone by the DR beta 4(DR omega 53) molecule, and a third clone by a cross-reactive T cell epitope on DR7 beta 1 and DR beta 4(DR omega 53) molecules. The two DR beta 4(DR omega 53)-restricted clones react, however, differently with a panel of HLA-DR DR omega 53-positive human peripheral blood lymphocytes used as APC. Therefore the data presented here clearly document that the DR beta 4 (DR omega 53) chain may serve as restriction elements for DT-specific T-cell clones. They also provide the first evidence for functional cross-reactivity of the products of two different DR beta loci and in addition emphasize the high complexity of the supertypic HLA-DR omega 53 specificity.

Amino Acid Sequence↗

PubMed1990

Human immunodeficiency virus-1 glycoproteins gp120 and gp160 specifically inhibit the CD3/T cell-antigen receptor phosphoinositide transduction pathway.

The interference of the recombinant HIV-1 glycoproteins gp160 and gp120 with the CD3/T cell antigen receptor (TcR)-mediated activation process has been investigated in the CD4+ diphtheria toxoid-specific human P28D T cell clone. Both glycoproteins clearly inhibit the T cell proliferation induced in an antigen-presenting cell (APC)-free system by various cross-linked monoclonal antibodies specific for the CD3 molecule or the TcR alpha chain (up to 80% inhibition). Biochemical studies further demonstrate that exposure of the T cell clone to both glycoproteins (gps) specifically inhibits the CD3/TcR phospholipase C (PLC) transduction pathway, without affecting the CD3/TcR cell surface expression. Thus, inositol phosphate production, phosphatidic acid turnover, intracellular free calcium, and intracellular pH increase induced by CD3/TcR-specific MAbs are specifically impaired in gps-treated P28D T cells. Addition of purified soluble CD4 prevents binding of gps to T cells and overcomes all observed inhibitions. Maximal inhibitions are obtained for long-term exposure of the T cell clone to gps (16 h). No early effect of gps is observed. By contrast, gp160 and gp120 fail to suppress the CD2-triggered functional and biochemical P28D T cell responses. These results demonstrate that, in addition to their postulated role in the alteration of the interaction between CD4 on T lymphocytes and MHC class II molecules on APC, soluble HIV-1 envelope glycoproteins may directly and specifically impair the CD3/TcR-mediated activation of PLC in uninfected T cells via the CD4 molecule.

Antigens, CD↗

PubMed1988

PGE2-induced cyclic AMP accumulation in human CD4+ T cells is strongly enhanced during the CD2-mediated activatory process.

The effect of a mitogenic combination of two different anti-CD2 monoclonal antibodies on the PGE2-stimulated and basal cAMP production in human CD4+ T cell clones was investigated. The anti-CD2 stimulation strongly potentiates the PGE2-induced cAMP production while both PMA and A23187 produced a less potent effect. On the opposite the anti-CD2 treatment is without any effect on the basal cAMP level contrasting with a marked increase of intracellular cAMP concentrations with A23187 or the combination of A23187 and PMA. These results suggest that activation of CD4+ human T cells via the CD2 molecule significantly influences the cAMP-related transduction pathway. Although PMA and A23187 also modulate the activity of this pathway, their effect in this model is more likely mediated through an amplification of basal cAMP production.

Antibodies, Monoclonal↗

PubMed1988

Activation signals via CD2 molecule and interleukin 2 receptor act in synergy for helper function induction.

The membrane CD2 molecule appears to play an important role in T cell activation. Indeed, T cell stimulation by some combinations of anti-CD2 monoclonal antibodies (mAb) can result in antigen-independent expression of helper function as assessed by proliferation and lymphokine secretion. We report here that T cell stimulation by a combination of two anti-CD2 mAb recognizing GT2 and T11(1) epitopes, respectively, cannot alone induce T helper clones to proliferate when preincubated in culture medium devoid of exogenous interleukin 2 (IL2). The concerted action of both anti-GT2 + T11(1) mAb and exogenous recombinant IL2 is required to induce cloned helper T cells to produce IL 2 and interferon-gamma to significantly increase IL2 receptors (IL2R) and finally to divide by an autocrine mechanism, whereas each signal alone has no effect. This therefore suggests that, under some conditions of CD2 stimulation, two minimal signals may be delivered through CD2 and IL2R and act synergistically to achieve a complete expression of T helper cell functions. Moreover, analysis of phosphatidylinositol and phosphatidic acid metabolic changes mediated by each signal separately or together suggests that, in this model, IL2 increases the phosphoinositide turnover induced by anti-CD2 antibodies up to a level required for helper function acquisition.

Antigens, Differentiation↗

PubMed1988

Triggering of the phosphoinositide transduction pathway by a monoclonal antibody specific for the human gamma/delta T cell receptor.

We have developed a monoclonal antibody (mAb), termed anti-TigammaA, which recognizes an antigenic determinant carried by a variable segment of the T cell receptor (TcR) gamma chain. This determinant, encoded by the V gamma 9 gene, is expressed on approximately 3% of peripheral blood lymphocytes. In the present study, we have found that binding of anti-TigammaA mAb to its specific ligand results in the triggering of the phosphatidylinositol (PI) cycle-related metabolic process. Indeed, an increased labeling of both phosphatidic acid and PI, related to an enhanced turnover of PI cycle-dependent phospholipids, was observed following exposure of 32P orthophosphoric acid-labeled cells to anti-TigammaA mAb. In addition, there was a rapid rise in intracellular free calcium concentrations. Similar experiments have been performed previously on CD3+ TcR alpha/beta- -cells with an anti-CD3 mAB. They predicted that signals produced by the interaction between the second TcR and its ligand(s) would be transmitted via the PI cycle-linked intracellular second messengers. We confirm this hypothesis in an experimental system where stimulation occurs directly through the gamma/delta receptor structure.

Antibodies, Monoclonal↗