Molecular signaling mechanisms in T-lymphocyte activation pathways: a review and future prospects

Self-organizing map analysis of toxicity-related cell signaling pathways for metal and metal oxide nanoparticles

The response of a murine macrophage cell line exposed to a library of seven metal and metal oxide nanoparticles was evaluated via High Throughput Screening (HTS) assay employing luciferase-reporters for ten independent toxicity-related signaling pathways. Similarities of toxicity response among the nanoparticles were identified via Self-Organizing Map (SOM) analysis. This analysis, applied to the HTS data, quantified the significance of the signaling pathway responses (SPRs) of the cell population exposed to nanomaterials relative to a population of untreated cells, using the Strictly Standardized Mean Difference (SSMD). Given the high dimensionality of the data and relatively small data set, the validity of the SOM clusters was established via a consensus clustering technique. Analysis of the SPR signatures revealed two cluster groups corresponding to (i) sublethal pro-inflammatory responses to Al2O3, Au, Ag, SiO2 nanoparticles possibly related to ROS generation, and (ii) lethal genotoxic responses due to exposure to ZnO and Pt nanoparticles at a concentration range of 25-100 μg/mL at 12 h exposure. In addition to identifying and visualizing clusters and quantifying similarity measures, the SOM approach can aid in developing predictive quantitative-structure relations; however, this would require significantly larger data sets generated from combinatorial libraries of engineered nanoparticles.

Potassium Channel Blockers Inhibit Adoptive Transfer of Experimental Allergic Encephalomyelitis by Myelin-Basic-Protein-Stimulated Rat T Lymphocytes

Agents which block T cell K(+) currents can prohibit both proliferative and effector cell functions in T cells activated by mitogens or phorbol esters. This study examined the effects of some of these blocking agents on the immune responsiveness of guinea pig myelin basic protein (GPMBP)-reactive Lewis rat T lymphocytes, which are capable of mediating the adoptive transfer of experimental allergic encephalomyelitis (EAE), an accepted animal model for multiple sclerosis. Both the proliferative functions (DNA synthesis and cell blastogenesis) and the EAE transfer activities of GPMBP-reactive lymphocytes were examined following GPMBP-induced activation in the presence of agents shown to block the outwardly rectifying K(+) current in these cells. At concentrations which completely inhibited DNA synthesis, as measured by [(3)H]thymidine incorporation, and cell blastogenesis, tetraethylammonium (TEA), 4-aminopyridine (4-AP) and methoxyverapamil (D60) completely blocked the subsequent adoptive transfer of EAE into naive syngeneic Lewis rats. The concentrations at which these blockers produced a 50% reduction in DNA synthesis were estimated to be 16, 1.6 and 32 &mgr;M for TEA, 4-AP and D-600, respectively, which were roughly equivalent to the EC(50) to block the K(+) current. Apamine, a potent Ca(2+)-activated K(+) channel blocker, at a concentration several orders of magnitude higher than is necessary to block Ca(2+)-activated K(+) channels, reduced the maximal K(+) conductance in GPMBP-reactive T cell K(+) channels by about 20%, but did not alter either [H(3)H]thymidine incorporation or the adoptive transfer of EAE. These results indicate that delayed rectifier K(+) channel blockers may prevent the activation of GPMBP-reactive T cells, thus prohibiting encephalitogenic effector cell functions. Copyright 1997 S. Karger AG, Basel

Depletion of glutathione by benzo(a)pyrene metabolites, ionomycin, thapsigargin, and phorbol myristate in human peripheral blood mononuclear cells

Previous studies in this laboratory have shown that polycyclic aromatic hydrocarbons (PAHs) alter Ca2+ homeostasis and inhibit activation of both B and T lymphocytes obtained from rodents and humans. In the present studies, we demonstrate that alpha-naphthoflavone (ANF), an inhibitor of cytochrome P4501A activity, reduced the Ca2+ elevation produced by BaP in human peripheral blood mononuclear cell (HPBMC) lymphocytes. These results suggested that BaP metabolites may play a role in intracellular Ca2+ homeostasis in human lymphocytes. Reactive oxidative intermediates of BaP produced in HPMBC are known to be highly carcinogenic and have also been shown to be immunosuppressive. We examined the effects of benzo(a)pyrene (BaP), 7,12-dimethylbenz(a)anthracene (DMBA), benzo(e)pyrene (BeP), and anthracene, as well as certain BaP metabolites, on the levels of intracellular Ca2+ and glutathione in HPBMC. While BaP, DMBA, BeP, and anthracene did not cause a statistically significant decrease in GSH in HPBMC at concentrations of 1 or 10 microM following a 6-, 48-, or 72-hr exposure, reactive BaP metabolites including 4,5-epoxide BaP and 7,8-diol-9,10-epoxide BaP consistently produced a 20-30% depletion of glutathione in HPBMC following a 6-hr treatment period. These BaP metabolites also elevated intracellular Ca2+ in HPBMC during a 6-hr incubation. Results of these experiments suggest that metabolism of BaP to certain epoxide metabolites may be responsible for sulfhydryl damage leading to transient GSH depletion and Ca2+ elevation. These results are consistent with the hypothesis that sulfhydryl damage by certain PAH metabolites may lead to altered Ca2+ homeostasis, leading to inhibition of cell activation and proliferation in HPBMC.

Intracellular calcium levels are differentially regulated in T lymphocytes triggered by anti-CD2 and anti-CD3 monoclonal antibodies

Antigen and/or mitogen-driven T-cell activation is mediated by a rise in intracellular free Ca2+, as second messenger. A regulatory key role for this process is represented by membrane-associated [Ca2+/Mg2+] ATP-ase that is mainly devoted to extrusion of intracellular ion excess. In the present study we have investigated the kinetics of CA2+ fluxes in both resting and already activated (Jurkat T-cell line) T lymphocytes after CD3 and CD2 (T11(2) and T11(3)) triggering and focused our attention on plasma membrane [Ca2+/Mg2+] ATP-ase activity. In both resting T cells and Jurkat cell line, the CD2 stimulation was able to determine a rise in intracellular free Ca2+ higher than that observed after CD3 triggering. In addition, this calcium signal was independent of negative feedback control exerted by [Ca2+/Mg2+] ATP-ase, as well as of IP3 generation. Thus the CD2 molecular system may, together with cell-adhesion properties, act as an amplifier of Ca2+ signals that, if delivered in the context of other molecular systems, such as CD3 or MHC class II antigens, are essentially devoted to the polyclonal co-stimulatory recruitment of a larger cellular repertoire.

Ethanol-specific impairment of T-lymphocyte activation is caused by a transitory block in signal-transduction pathways

BACKGROUND

Immune system derangement is characteristic of alcoholic liver cirrhosis. However, in vitro studies have never clarified the alcohol-induced T-lymphocyte dysfunction. The aim of this study was to examine any discrete phenotypical and functional abnormalities and possible impairment in transmembrane signal-transduction pathways that, if present on lymphocytes of patients with alcoholic cirrhosis, would also be reproducible after in vitro ethanol exposure of normal T cells.

METHODS

Lymphocytes from 25 patients were analyzed for their in vitro proliferative functions, intracellular Ca2+ fluxes, and inositol 1,4,5-triphosphate (IP3) generation. The same procedures were applied to normal T cells exposed in vitro to ethanol.

RESULTS

Lymphocytes failed to respond to anti-CD3 and anti-CD2 after in vitro stimulation, with decreased intracellular Ca2+ mobilization and IP3 generation but showed normal proliferative response to phytohemagglutinin. In vitro ethanol incubation of normal T lymphocytes resulted in rearrangement of the membrane CD45 antigen, favoring the expression of high-molecular-weight isoforms, and showed a poor blastogenic response to anti-CD3 and anti-CD2 with a decrease in intracellular Ca2+ mobilization and IP3 production. After a 6-month period of ethanol withdrawal, some patients had normalization of phenotypic and functional alterations.

CONCLUSIONS

The T-lymphocyte response to specific polyclonal activators may be severely impaired in alcohol abusers. However, it seems reversible after a period of controlled ethanol withdrawal.

Increased epithelial expression of HLA-DQ and HLA-DP molecules in salivary glands from patients with Sjögren's syndrome compared with obstructive sialadenitis

Salivary gland specimens from 10 patients with primary Sjögren's syndrome (pSS) were examined by two-colour immunofluorescence with various combinations of monoclonal and polyclonal antibody reagents of the following specificities: human leucocyte antigen (HLA) class I and II (DR, DP and DQ), CD3, CD45 (leucocyte common antigen), various cytokeratins, and factor VIII-related antigen. Tissue specimens from 10 normal glands and 10 glands with obstructive sialadenitis (no known autoimmunity) served as controls. Only some intercalated ducts and scattered acini of the normal major glands expressed HLA class II determinants (< 5% of total epithelial area); the relative proportion of positive elements indicated differential expression (DR > DP > DQ). SS glands contained substantial T cell infiltrates and increased numbers of activated (DR+) T cells; adjacent epithelium showed extensive differential expression of HLA class II determinants (DR > DP > DQ). Glands with obstructive sialadenitis showed similarly increased epithelial expression of HLA-DR but with surprisingly small amounts of concomitant HLA-DP and -DQ expression. Epithelial HLA class II expression probably depends on cytokines as an inductive event, which is not unique for SS but particularly prominent in this disorder. Our results suggest that epithelial expression of HLA-DP or -DQ, rather than -DR, might be a prerequisite for the autoimmune process of SS to develop in genetically susceptible individuals.

Immunomodulatory effects of therapeutic gold compounds. Gold sodium thiomalate inhibits the activity of T cell protein kinase C

Previous studies have shown that the gold compounds, gold sodium thiomalate (GST) and auranofin (AUR), which are effective in the treatment of rheumatoid arthritis, inhibit functional activities of a variety of cells, but the biochemical basis of their effect is unknown. In the current studies, human T cell proliferation and interleukin 2 production by Jurkat cells were inhibited by GST or AUR at pharmacologically relevant concentrations. Because it has been documented that protein kinase C (PKC) is involved in T cell activation, the capacity of gold compounds to inhibit PKC partially purified from Jurkat cells was assayed in vitro. GST was found to inhibit PKC in a dose-dependent manner, but AUR caused no significant inhibition of PKC at pharmacologically relevant concentrations. The inhibitory effect of GST on PKC was abolished by 2-mercaptoethanol. To investigate the effect of GST on the regulation of PKC in vivo, the levels of PKC activity in Jurkat cells were examined. Cytosolic PKC activity decreased slowly in a concentration- and time-dependent manner as a result of incubation of Jurkat cells with GST. To ascertain whether GST inhibited PKC translocation and down-regulation, PKC activities associated with the membrane and cystosolic fractions were evaluated after phorbol myristate acetate (PMA) stimulation of GST incubated Jurkat cells. Translocation of PKC was markedly inhibited by pretreatment of Jurkat cells with GST for 3 d, but the capacity of PMA to down-regulate PKC activity in Jurkat cells was not altered by GST preincubation. The functional impact of GST-mediated downregulation of PKC in Jurkat cells was examined by analyzing PMA-stimulated phosphorylation of CD3. Although GST preincubated Jurkat cells exhibited an increased density of CD3, PMA-stimulated phosphorylation of the gamma chain of CD3 was markedly inhibited. Specificity for the inhibitory effect of GST on PKC was suggested by the finding that GST did not alter the mitogen-induced increases in inositol trisphosphate levels in Jurkat cells. Finally, the mechanism of the GST-induced inhibition of PKC was examined in detail, using purified PKC subspecies from rat brain. GST inhibited type II PKC more effectively than type III PKC, and also inhibited the enzymatic activity of the isolated catalytic fragment of PKC. The inhibitory effect of GST on PKC activity could not be explained by competition with phospholipid or nonspecific interference with the substrate. These data suggest that the immunomodulatory effects of GST may result from its capacity to inhibit PKC activity.

Avian scleroderma: evidence for qualitative and quantitative T cell defects

T cell activation is dependent upon calcium influx and protein kinase C activation, with subsequent lymphocyte proliferation dependent upon IL-2. Abnormalities in T cell proliferation, including abnormal calcium influx and defective protein kinase C activation, have been identified in aged mice and humans and many autoimmune diseases including diabetes, lupus and scleroderma. Since UCD line 200 chickens, which spontaneously develop a scleroderma-like disease, have both thymic defects and a diminished peripheral blood lymphocyte response to IL-2, we have further investigated T cell function in these birds. Interestingly, line 200 T cells respond poorly in vitro to a variety of diversely acting T cell mitogens including concanavalin A, phytohemagglutinin and anti-chicken CD3 monoclonal antibody. Moreover, they do not respond well even to phorbol myristate acetate in conjunction with ionomycin. Addition of exogenous IL-2-containing supernatant concurrently with mitogenic stimulation also had no significant effect. Analysis of intracellular free calcium demonstrated that the lymphocytes from diseased birds had a reduced influx of calcium (or release for intracellular stores) following stimulation. These data clearly reflect a unique defect in T cell activation associated with avian scleroderma. Analysis of chicken CD3, CD4 and CD8 expression revealed a 39% decrease in peripheral blood CD4+ cells in scleroderma birds, although this decrease was not sufficient to explain the 80-90% decrease observed in proliferation assays and calcium influx. Our data support the hypothesis that avian scleroderma is mediated via abnormal function of lymphocyte co-stimulatory molecules or intracellular calcium regulators.

FKBP-12 is not an inhibitor of protein kinase C

It was recently noted that the amino acid sequence of FK506 binding protein (FKBP-12) is nearly identical to that of an endogenous inhibitor of protein kinase C, PKCI-2. To follow up on this observation, we have tested the hypothesis that FKBP-12 is an inhibitor of PKC. The kinase activity of rat brain protein kinase C (PKC) was not inhibited by the presence of up to 700 micrograms recombinant human FKBP-12 per ml, in either the presence or absence of FK506. FKBP-12 also did not affect PMA-induced phosphorylation of an endogenous PKC substrate, an 80 kDa protein, in permeabilized cells. To test whether FKBP-12 could account for endogenous PKC inhibitory activity in cells, Jurkat cell lysate was chromatographed on an anion exchange column. A peak of PKC inhibitory activity was eluted at approximately 200 mM NaCl. As shown by both Western blots and FK506 binding activity, FKBP-12 was eluted only in the flow-through and wash fractions. These results demonstrate that FKBP-12 is clearly distinct from endogenous PKC inhibitory activity.

Beta-endorphin effects on membrane transduction in human lymphocytes

The endogenous opioid beta-endorphin (beta E) enhances, decreases or has negligible effects on cytotoxic and proliferative responses of lymphocytes. In order to characterize the mechanisms by which beta E modulates lymphocyte functions, we have examined the effects of beta E on certain membrane transduction events. We have shown that beta E inhibits phosphoinositol phosphate metabolism, and that it can enhance or inhibit the phosphorylation of the gamma chain of CD3 in a dose-dependent manner. We present the hypothesis that beta E contemporaneously modulates several membrane transduction processes, some of which may be counteracting and thereby producing the observed mixed effects on many lymphocyte functional responses. The biochemical status of the donor's lymphocytes also contributes to the variability in beta E-mediated effects on CMI outcomes.

Beta-endorphin blunts phosphatidylinositol formation during in vitro activation of isolated human lymphocytes: preliminary report

We have previously described the regulatory effect of beta-endorphin on three human cytotoxic cell populations. We confirmed the variable nature of these effects on human natural killer cell (NK) activity, showed mixed effects on the generation of cytotoxic T lymphocyte (CTL) activity, and demonstrated the reproducible suppression of lymphokine-activated killer cell (LAK) activity. We and others also observed mixed effects of beta-endorphin on the proliferative response to mitogens and in mixed leukocyte reactions. In the study reported here, we test the effects of beta-endorphin on the formation of phosphatidylinositol during cell activation. 32P-radiolabeled peripheral blood mononuclear cells obtained from normal adult donors and CD2-depleted subpopulations were activated with phytohemagglutinin or in a NK, LAK, or CTL protocol in the absence or presence of recombinant beta-endorphin. The total lipidic extract was analyzed by thin-layer chromatography and autoradiography. The results of these studies indicate that beta-endorphin blunts the formation of phosphatidylinositol by about 20% in the four systems studied and in all the donors tested. This effect is dose-dependent and is blocked in part by the opioid antagonist, naltrexone, suggesting involvement of the opioid receptor.

Spectrofluorimetric and image recordings of spontaneous and lectin-induced cytosolic calcium oscillations in Jurkat T cells

Intracellular variations in Ca2+ concentrations have been measured in single Jurkat T lymphocyte variants (77 6.8 and E6.1) using Fura-2 as a probe. Under basal conditions, the cytosolic Ca2+ level is stable but some cells show spontaneous Ca2+ oscillations (frequency, 0.30 +/- 0.06 Hz). These oscillations are sensitive to the external concentration of Ca2+ since they can no longer be observed when the bathing solution is replaced (superfusion) with a Ca(2+)-free medium or when a Ca2+ chelator (EGTA) is added. Various changes in the cytosolic concentration of Ca2+ ([Ca2+]i) can be observed when the cells are exposed to the mitogenic lectin phytohemagglutinin (PHA, 80 nM). For instance, in the case of non-oscillating cells, the lectin induces either a rapid increase in [Ca2+]i that is followed by a sustained response (plateau) or it triggers Ca2+ spikes. In the case of experiments done in Ca(2+)-free medium, only the initial spike was observed. In the case of spontaneously oscillating cells, PHA induces a rapid increase in [Ca2+]i that is followed by a plateau where oscillations are absent. In every case, the PHA-dependent Ca2+ response is abrogated in a Ca(2+)-free medium. Computer simulations based on the model of Goldbeter et al. [27] show that the various Ca2+ responses of Jurkat cells are related to the cytosolic level of free Ca2+. Video imaging analyses show that the cellular Ca2+ responses are not homogeneous whether the observations are made in spontaneously oscillating Jurkat cells or when they are exposed to PHA.

Alterations in mitogen-induced calcium mobilization and intracellular free calcium produced by 7,12-dimethylbenz(a)anthracene in the Jurkat human T cell line

The purpose of these studies was to assess the effects of 7,12-dimethylbenz(a)anthracene (DMBA), an immunosuppressive polycyclic aromatic hydrocarbon (PAH), on Ca+2 mobilization induced by phytohemagglutinin (PHA) in the Jurkat human T cell line. Intracellular levels of free cytosolic Ca+2 were examined by flow cytometry using Indo-1 loaded cells. At doses of 3-30 microM, DMBA was found to produce a dose and time-dependent inhibition of Ca+2 mobilization in Jurkat following in vitro exposure. The decrease in Ca+2 mobilization was correlated with an increase in baseline levels of cytoplasmic free Ca+2. Two non-immunosuppressive PAH, benzo(e)pyrene and anthracene, failed to inhibit PHA-induced Ca+2 mobilization or alter baseline levels of free Ca+2. These results suggest that DMBA may produce immunosuppression by inhibiting Ca+2 mobilization or by altering Ca+2 homeostasis in activated T cells.

Basis for defective proliferation of peripheral blood T cells to anti-CD2 antibodies in primary Sjögren's syndrome

Anti-CD2-induced T cell proliferation was analyzed in the peripheral blood samples of 31 primary and 8 secondary untreated Sjögren's syndrome patients. Anti-CD2-stimulated PBMC proliferation was very low in about one-third of primary Sjögren's syndrome samples, despite the number of CD2+ cells being similar in primary and secondary Sjögren's syndrome and normal PBMC samples. The depressed response to anti-CD2 was mainly found in anti-Ro+/La+ patients. Experiments on purified T cells demonstrated that a defect at the T cell level was responsible for the anti-CD2 unresponsiveness. Cell proliferation failure was associated with poor IL-2 and IL-2 receptor mRNA expression and, consequently, IL-2 and IL-2 receptor synthesis. Since defective anti-CD2-induced mitogenesis could be reversed by phorbol myristate acetate, but not calcium ionophore A23187, it is probably correlated with impaired protein kinase C activation. Comparison of anti-CD2-triggered PBMC proliferation in treated and untreated patients and a long-term study of nine patients showed that the defect is a stable characteristic in primary Sjögren's syndrome patients, but that it can be reversed by pharmacological immunosuppression.

Activation of cord T lymphocytes. II. Cellular and molecular analysis of the defective response induced by anti-CD3 monoclonal antibody

Despite the fact that the percentage of circulating CD3-positive cells is similar in cord and adult blood, the proliferative response induced by anti-CD3 monoclonal antibody (mAb) was impaired in the majority of human cord peripheral blood mononuclear cell (PBMC) samples we tested. The cell proliferative defect was associated with low interleukin 2 (IL 2) gene expression and scant IL 2 production. However, interleukin 2 receptor was fully expressed at both the mRNA and protein levels. Such a finding is consistent with the observation that exogenous recombinant IL 2 is able to boost the anti-CD3-mediated response of cord PBMC. Furthermore, when anti-CD3 and phorbol myristate acetate (PMA) were added together, they exerted a very marked synergistic effect on both the proliferation of, and IL 2 production by, cord PBMC. The addition of allogeneic antigen presenting cells plus soluble anti-CD3 or Sepharose-coupled anti-CD3 mAb to the cord T cell cultures had no significant effect on proliferation, whereas both elicited good mitogenesis of adult T cells. Moreover, addition of exogenous recombinant interleukin 1 to anti-CD3-stimulated T cells failed to trigger any proliferation in either adult or cord samples. Since the combination of PMA and calcium ionophore A23187 is effective in triggering optimal proliferation of cord T cells, the defect would seem to be associated with a failure in transmembrane transduction of the activation signals provided by the anti-CD3 stimulus for the cord T cell.

Protein kinase C and T cell activation

Understanding the intracellular mechanisms by which binding of ligands, such as hormones and growth factors, to their specific receptors elicits the appropriate cellular response has long been a topic of great interest. Considerable excitement was generated when it was recognised that several receptor-ligand interactions operate via the hydrolysis of inositol phospholipids. This yields, at least, two 'second messengers', namely, inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], which causes the release of Ca2+ from intracellular stores, and 1,2-diacylglycerol (ac2Gro), which activates the serine/threonine-specific enzyme, protein kinase C(PKC), reviewed in [1] and [2]. The pertinent question that follows is, how do PKC activation and elevation of the intracellular Ca2+ concentration evoke cell responses? In this review, attention has been focused on PKC, and the consequences of its activation in resting human T cells. Evidence that PKC activity is, at least partially, responsible for activation of resting human T cells will be examined, and some of the more recent research investigating how PKC activation elicits this cell response will be described.

Increased intracellular Ca2+ is necessary for maximal expression of the proto-oncogene c-jun in the Jurkat T-cell line

The time course and signal-transduction requirements for proto-oncogene c-jun expression in T-cells were investigated. Expression of c-jun mRNA was evident at 30 min after stimulation. Both the activation of Ca2+/phospholipid-dependent kinase as well as an increased intracellular free Ca2+ concentration were necessary for the maximal induction of c-jun mRNA and synthesis of Jun protein 1 h after stimulation.

Activation of human T lymphocytes by phorbol-12,13-dibutyrate and ionomycin

The calcium ionophore ionomycin and the phorbol ester phorbol-12,13-dibutyrate (PDBu) are shown to have a synergistic effect upon interleukin 2 (IL-2) production, interleukin 2 receptor expression, and T-lymphocyte proliferation. The proliferative response was inhibited by addition of a monoclonal antibody directed against the IL-2R (Tac antigen) demonstrating that PDBu and ionomycin induce T-cell growth through an IL-2-dependent autocrine pathway. Sequential stimulation with PDBu and ionomycin failed to induce IL-2 production, IL-2R expression, and consequently proliferation of the T cells, indicating that T-cell activation requires simultaneous activation of protein kinase C (PKC) and elevation of cytosolic calcium. Exposure of T cells to both agents for different times resulted in IL-2 production, IL-2R expression, and proliferation in proportion to the duration of incubation with at least 4 h required for maximal T-cell activation. Further, in the presence of PDBu maximal T-cell activation was found to require stimulation with ionomycin for 4 h, indicating that a sustained increase in free cytoplasmic calcium of several hours' duration is essential for T-cell activation. In contrast T cells incubated with ionomycin were induced to produce IL-2 and express IL-2Rs upon brief exposure to PDBu with a 2-h incubation period being sufficient for maximal T-cell activation. Thus transient activation of PKC seems to be sufficient for activation of the IL-2 gene and IL-2R gene. However, maximal T-cell activation requires activation of PKC for at least 2 h.

T-cell response to phorbol ester PMA and calcium ionophore A23187 in Down's syndrome

The proliferative response of purified T cells to anti-CD2 monoclonal antibodies (T112 plus T113) was found to be markedly reduced in 12 subjects with Down's syndrome (DS). The addition of phorbol ester PMA, which activates Ca2+/phospholipid-dependent enzyme protein kinase C, or calcium ionophore A23187, which increases intracytosolic free Ca2+ concentration, enhanced, but did not normalize, the defective anti-CD2-mediated T-cell mitogenesis. In contrast, the proliferation of resting lymphocytes from trisomic patients was comparable to that of the control cells when PMA and A23187 were used as co-blastogenic reagents. Because PMA and A23187 together bypass the early activation pathways and promote T-cell growth through the direct induction of membrane interleukin 2 (IL-2) receptor expression and IL-2 synthesis and secretion, it could reasonably be hypothesized that the faulty DS T-cell activation induced by antigen or mitogen is due to a deranged transmembrane signal transduction, rather than a defect in the later intracellular events.

Tenascin, an extracellular matrix protein, exerts immunomodulatory activities

Tenascin is a nonubiquitous extracellular matrix protein mainly expressed during morphogenesis in embryonal life. In adults it reappears in malignant tumors and during inflammation and tissue repair. Extracellular matrix proteins can alter cell morphology, adhesion, motility, differentiation, and growth. Since cells of the immune system can express receptors for extracellular matrix, we investigated the effects of tenascin on human monocytes and T and B lymphocytes. Tenascin inhibited monocyte adhesion to fibronectin and enhanced the LFA-1 (lymphocyte function-associated antigen 1)-dependent clustering of Epstein-Barr virus-transformed B cells. The physiological consequences of the effects of tenascin were studied in several T-cell activation models. Tenascin inhibited T-cell activation induced by a soluble antigen (tetanus toxoid), alloantigens, or the mitogen concanavalin A. However, T-cell activation with phytohemagglutinin, crosslinked anti-CD3 antibody, or a mixture of ionomycin and phorbol ester was not inhibited by tenascin. Tenascin did not prevent interleukin 2-dependent T-cell growth or the cytolytic activity of an antigen-specific CD4+ T-cell clone. These results suggest that tenascin alters the adhesion properties of human monocytes, B cells, and T cells. The in vitro immunosuppressive activity of tenascin might be due to abrogation of an accessory cell function at an early stage of the interaction between antigen-presenting cells and T cells.

Induction of high-affinity interleukin 2 receptors on human T lymphocytes. The role of calcium and protein kinase C

The relationship between free cytoplasmic calcium, activation of protein kinase C (PKC) and expression of high-affinity interleukin 2 receptors (HA-IL-2R) on human T lymphocytes was studied. Induction of HA-IL-2R by phytohaemagglutinin (PHA) was associated with an increase in free cytoplasmic calcium and a transient increase in membrane-associated PKC. However, whereas addition of EGTA inhibited induction of receptors by PHA, addition of the PKC-inhibitor H7 did not. 12-o-tetradecanoyl-phorbol-13-acetate (PMA) and 1-oleoyl-2-acetyl-rac-glycerol (OAG) were both found to activate and translocate PKC. However, only PMA induced expression of HA-IL-2R. Not surprisingly, the effect of PMA was independent of extracellular calcium, but was inhibited by H7. Furthermore, a correlation between the number of HA-IL-2R and free cytoplasmic calcium upon stimulation with ionomycin was observed. Associated with the rise in intracellular calcium, the ionophore caused a slight increase in membrane-associated PKC. Also, addition of H7 inhibited expression of HA-IL-2R. Finally, OAG and ionomycin acted synergistically on expression of HA-IL-2R. In conclusion, induction of HA-IL-2R requires at least two different signals and neither activation of PKC nor an increase in free cytoplasmic calcium is sufficient. However, these two signals may act synergistically. There is evidence for both a PKC- and calcium-independent pathway.

Complexing of the CD-3 subunit by a monoclonal antibody activates a microtubule-associated protein 2 (MAP-2) serine kinase in Jurkat cells

Treatment of Jurkat T-cells with anti-CD-3 monoclonal antibodies resulted in the rapid and transient activation of a serine kinase which utilized the microtubule-associated protein, MAP-2, as a substrate in vitro. The kinase was also activated on treatment of Jurkat cells with phytohaemagglutinin, but with a different time course. The activation of the MAP-2 kinase by anti-CD-3 antibodies was dose-dependent, with maximal activity observed at concentrations of greater than 500 ng/ml. Normal human E-rosette-positive T-cells also exhibited induction of MAP-2 kinase activity during anti-CD-3 treatment. The enzyme was optimally active in the presence of 2 mM-Mn2+; lower levels of activity were observed with Mg2+, even at concentrations up to 20 mM. The kinase was partially purified by passage over DE-52 Sephacel with the activity eluting as a single peak at 0.25 M-NaCl. The molecular mass was estimated to be 45 kDa by gel filtration. The activation of the MAP-2 kinase was probably due to phosphorylation of this enzyme as treatment with alkaline phosphatase diminished its activity. These data demonstrate that the stimulation of T-cells through the CD-3 complex results in the activation of a novel serine kinase which may be critically involved in signal transduction in these cells.

T-cell response to anti-CD2 monoclonal antibodies in Down's syndrome

Peripheral blood mononuclear cells from 10 subjects with cytogenetically documented Down's syndrome (DS) and from 10 age- and sex-matched healthy controls were assayed for their ability to proliferate in response to phytohaemagglutinin, anti-CD3 (OKT3), or anti-CD2 (T11(2) plus T11(3] monoclonal antibodies. Interleukin 2 (IL-2) receptor expression and IL-2 production in mitogen-pulsed lymphocyte cultures was also investigated in parallel. DS cells responded poorly to all the blastogenic stimuli used in this study. Under certain experimental conditions (anti-CD3 or anti-CD2 antibody stimulation), the patients' lymphocytes expressed low levels of IL-2 surface receptors and failed to produce normal amounts of this lymphokine. Studies are currently in progress in our laboratories to determine whether these defects are due to an impairment of the early signalling events surrounding the complexing of CD3, CD2, or lectin receptors to their respective ligands.

Synergistic interaction between anti-CD3 and IL-2 demonstrated by proliferative response, interferon production, and non-MHC-restricted killing

Anti-CD3 monoclonal antibody acts on normal peripheral blood mononuclear cells to induce T cell proliferation, interferon-gamma production, and non-MHC-restricted cytotoxicity against both NK (CD16+)-sensitive and -resistant target cells. Moreover, anti-CD3 and interleukin 2 (IL-2) act synergistically to give greater proliferative, interferon-gamma (IFN-gamma), and natural cytotoxicity responses than those expected by the simple addition of the individual responses to each stimulus acting alone. This synergistic response is macrophage independent, greatest at low concentrations of anti-CD3, inhibited by anti-IL2 receptor, and depends upon the induction of IL-2 receptors by CD3 activation which are then available to respond to exogenously added IL-2. Natural cytotoxicity induced by anti-CD3 and IL-2 correlates with IFN-gamma production, is inhibited by anti-IFN-gamma, and is still present after depletion of CD16-positive cells by specific monoclonal antibody and complement. The use of anti-CD3 in concert with IL-2 may be worthy of examination in a clinical setting, presumably because CD3/IL-2-generated LAK effector cells could be followed by in vivo administration of potentially lower and less toxic quantities of IL-2 than have been used in the past.

Modulation of high-affinity interleukin 2 receptors on activated human T lymphocytes by activators of protein kinase C

Phorbol myristate acetate (PMA) and 1-oleoyl-2-acetyl-rac-glycerol (OAG) are shown to induce a rapid (within 30 min) down-regulation of the capacity of activated human T lymphocytes to bind interleukin 2. This was associated with a manifold increase in membrane-associated protein kinase C, whereas no change in free cytoplasmic calcium was observed. In contrast, a 10-fold increase in free cytoplasmic calcium by ionomycin had no effect on interleukin 2 binding or subcellular distribution of protein kinase C. The reduction of interleukin 2 binding was caused by a decreased number of high-affinity interleukin 2 receptors, whereas the affinity of the remaining receptors was unchanged. However, PMA and OAG had no effect on the rate of internalization of the interleukin receptor. These data suggest that activation of protein kinase C, but not an increase in free cytoplasmic calcium, leads to a rapid decrease in the number of high-affinity interleukin 2 receptors on activated human T lymphocytes. However, the mechanism and biological importance of this phenomenon have to be further elucidated.

Division of human helper T cells into two sets on the basis of the induction of anti-tumor cytotoxicity by phorbol ester and calcium ionophore

Fourteen noncytotoxic human helper T cell clones were examined for autocrine proliferative responses and cytotoxicity to tumor cells after stimulation with 12-O-tetradecanoylphorbol 13-acetate (TPA) and ionomycin (Io). Although all clones responded to alloantigen, they could be divided into two groups based on their proliferative response or lack of it to TPA/Io. Nonresponders could not be converted to responder status by addition of interleukin (IL) 1 or indomethacin to the cultures. Responder status did not correlate with any of the following properties of the clones: originating donor, recognitive specificity, B cell helper activity, proliferative response to IL 2 or 4, lymphokine secretory capacity or density of expression of antigen receptors, CD4 or HLA class II molecules. Responder status did, however, correlate with the ability of TPA/Io to induce major histocompatibility complex-unrestricted cytolytic activity directed towards natural killer-resistant tumor cells. These results divide human helper cells into two types on the basis of induction of anti-tumor cytotoxicity.