Contingent genetic regulatory events in T lymphocyte activation

Two distinct Ca2+ influx pathways activated by the bradykinin B2 receptor

The hormone-induced depletion of cellular Ca stores provides a signal for the Ca2+ influx into electrically non-excitable cells; however, the underlying molecular mechanisms remain elusive. Therefore, we analyzed bradykinin-activated Ca2+ influx into human foreskin fibroblast cells, HF-15, by fura-2 and 45Ca labeling to discriminate between Ca2+ influx into the fura-sensitive compartment and Ca uptake into fura-insensitive Ca stores. Bradykinin-activated Ca2+ influx into the fura-sensitive compartment was blocked by inhibitors of NO synthases. These inhibitors also suppressed bradykinin-activated increases in cGMP, indicating that the NO-dependent increase in cGMP is involved in the activation of the Ca2+ influx into the fura-sensitive compartment. The cGMP-dependent kinase inhibitors KT5823 and Rp-8-(parachlorophenylthio)-cGMP (Rp-8-pCPT-cGMPS) blocked bradykinin-activated Ca2+ influx into the fura-sensitive compartment, suggesting that a cGMP-dependent kinase step participates in the activation of this Ca2+ influx pathway. In addition to the NO/cGMP-mediated Ca2+ influx into the fura-sensitive compartment, bradykinin enhanced 45Ca uptake into Ca stores that were not accessible to fura-2. This enhanced 45Ca uptake was insensitive to blockers of the NO/cGMP pathway, indicating that the 45Ca uptake pathway is distinct from the NO-dependent Ca2+ influx into the fura-sensitive compartment. Furthermore, bradykinin enhanced 45Ca uptake into proliferating but not into quiescent HF-15 fibroblasts. Hence, bradykinin stimulates two distinct Ca2+ influx pathways in HF-15 cells, (a) Ca2+ influx into the fura-sensitive compartment which is NO/cGMP-dependent and (b) Ca uptake into Ca stores which bypasses the cytoplasm, which is NO insensitive and which is linked to cell proliferation.

Inhibition by fenamates of calcium influx and proliferation of human lymphocytes

1. Flufenamic and tolfenamic acids have recently been shown to inhibit receptor-mediated calcium influx in human neutrophils. The present work was designed to study the effects of these two nonsteroidal anti-inflammatory drugs on human peripheral blood lymphocyte activation. 2. Peripheral blood mononuclear cells (PBMNCs; containing 90% lymphocytes) were stimulated by mitogen concanavalin A (Con A) or by a combination of an inhibitor of microsomal Ca(2+)-adenosine triphosphatase thapsigargin (TG) and phorbol myristate acetate (PMA). The effects of the two fenamates on cell proliferation were compared with respective changes in calcium metabolism. 3. Flufenamic and tolfenamic acids (10-100 microM) inhibited both Con A and TG + PMA-induced [3H]-thymidine incorporation in a dose-dependent manner. At the same concentration range, the two fenamates inhibited the increase in intracellular free calcium concentration induced by Con A or TG + PMA. This effect was due to inhibition of calcium influx whereas calcium release from intracellular stores remained unaltered. 4. The inhibition of divalent cation influx was confirmed by showing that fenamates inhibited TG + PMA-induced Mn2+ influx. 5. The inhibitory effects of fenamates on PBMNC proliferation and Ca2+ influx were qualitatively similar with those of SK&F 96365, an earlier known inhibitor of receptor-mediated calcium entry. Ketoprofen, a chemically different prostaglandin synthetase inhibitor did not show similar suppressive effects on PBMNCs. 6. The data suggest that flufenamic and tolfenamic acids suppress proliferation of human peripheral blood lymphocytes by a mechanism which involves inhibition of Ca2+ influx and is not related to inhibition of prostanoid synthesis.

The conserved lymphokine element-0 in the IL5 promoter binds to a high mobility group-1 protein

The conserved lymphokine elements-0 (CLE0) in the IL5 promoter is essential for the expression of IL-5. Here, we report the cloning and expression of a cDNA encoding a novel CLE0-binding protein, CLEBP-1 from a mouse Th2 clone, D10.G4.1. Interestingly, it was found that the CLEBP1 cDNA sequence was almost identical to the sequences of known high mobility group-1 (HMG1) cDNAs. When expressed as a recombinant fusion protein in Escherichia coli, CLEBP-1 was shown to bind to the IL5-CLE0 element in electrophoretic mobility-shift assays (EMSA) and southwestern blot analysis. The CLEBP-1 fusion protein cross-reacts with and-HMG-1/2 in Western blot analysis. It also binds to the CLE0 elements of IL4, GMCSF and GCSF genes. CLEBP-1 and closely related HMG-1 and HMG-2 proteins may play key roles in facilitating the expression of the lymphokine genes that contain CLE0 elements.

Abnormality of Oct-1 DNA binding in T cells from Sjögren's syndrome patients

Primary Sjögren's syndrome (SS) is an autoimmune rheumatic disease characterized by T cell hypoactivity. To understand the diminished T cell response to activation signals, we measured nucleoprotein DNA-binding activities regulating gene expression during T cell activation using the electrophoretic mobility shift assay. Peripheral blood lymphocytes from 9/19 SS patients were found to be defective in their ability to bind an october sequence (Oct-1). This Oct-1-binding phenotype remained stable in culture for up to 3 days prior to activation. This abnormality was not seen in resting T cells nor T cells from patients with systemic lupus erythematosus, rheumatoid arthritis (RA), or SS accompanied by RA. The SS Oct-1 DNA-binding abnormality correlated significantly with an inability of cells to exit the Gzero/G1 cell cycle phase when stimulated in vitro. Importantly, nucleoprotein extracts showing decreased DNA-binding activity had normal amounts of Oct-1 proteins as determined by immunoprecipitation, implying a functional defect in the Oct-1 protein. Moreover, defective DNA binding was corrected by treatment with acid phosphatase.

Telomerase regulation during entry into the cell cycle in normal human T cells

Telomerase activity is involved in telomere length maintenance. Leukocytes, unlike many human somatic tissues, have detectable telomerase activity. These cells provide a normal human cell type in which to study telomerase. We studied the regulation of telomerase activity and the telomerase RNA component as leukocytes were stimulated to enter the cell cycle. In primary human leukocytes stimulated with phytohemagglutinin, telomerase activity increased > 10-fold as naturally quiescent cells entered the cell cycle. Antibodies to the T cell receptor (TCR)/CD3 complex and the costimulatory CD28 receptor induced telomerase activity in a T cell-enriched population of cells. Rapamycin, an immunosuppressant that blocks TCR/CD3 signal transduction pathways and cdk2 activation, blocked telomerase induction. Hydroxyurea, an inhibitor of S phase, did not block cdk2 kinase activity or telomerase activation. In summary, telomerase is regulated in G1 phase as normal human T cells enter the cell cycle.

Cytokine transcriptional events during helper T cell subset differentiation

The molecular basis for changes in cytokine expression during T helper (Th) cell subset differentiation is not well understood. We have characterized transcriptional events related to cytokine gene expression in populations of naive T cell receptor-transgenic T cells as they are driven in vitro toward Th1 or Th2 phenotypes by interleukin (IL)-12 or IL-4 treatment, respectively. Quantitative reverse transcriptase-polymerase chain reaction analysis of cytokine transcripts indicates that interferon (IFN) gamma, IL-4, and IL-2 mRNA are expressed with distinct kinetics after naive T cells are stimulated with antigen and either IL-4 or IL-12. IFN-gamma mRNA appears as early as 6 h in IL-12-treated cultures, IL-4 appears only after 48 h in IL-4-treated cultures, and IL-2 is equivalently expressed in both types of cultures. Analyses were performed to determine if there were any differences in activation of IL-2 or IL-4 transcription factors that accompanied Th1 versus Th2 differentiation. These studies demonstrated that signal transducer and activator of transcription 6 (STAT6) binds to a sequence in the IL-4 promoter and that this STAT6-binding site can support IL-4-dependent transcription of a linked heterologous promoter. Prolonged activation of STAT6 is characteristic of populations undergoing Th2 differentiation. Furthermore, STAT6 is activated in an autocrine manner when differentiated Th2 populations are stimulated by antigen receptor ligation. Th1 populations derived from IL-12 plus antigen treatment of naive T cells remain responsive to IL-4 as indicated by induction of STAT6 and IL-4 mRNA. These data indicate that Th1 and Th2 differentiation represents the combination of different, apparently independently regulated transcriptional events. Furthermore, among transcription factors that bind to the IL-4 or IL-2 promoters, STAT6 is the one whose activation distinguishes Th2 versus Th1 development.

Gfi-1 encodes a nuclear zinc finger protein that binds DNA and functions as a transcriptional repressor

The Gfi-1 proto-oncogene encodes a zinc finger protein with six C2H2-type, C-terminal zinc finger motifs and is activated by provirus integration in T-cell lymphoma lines selected for interleukin-2 independence in culture and in primary retrovirus-induced thymomas. Gfi-1 expression in adult animals is restricted to the thymus, spleen, and testis and is enhanced in mitogen-stimulated splenocytes. In this report, we show that Gfi-1 is a 55-kDa nuclear protein that binds DNA in a sequence-specific manner. The Gfi-1 binding site, TAAATCAC(A/T)GCA, was defined via random oligonucleotide selection utilizing a bacterially expressed glutathione S-transferase-Gfi-1 fusion protein. Binding to this site was confirmed by electrophoretic mobility shift assays and DNase I footprinting. Methylation interference analysis and electrophoretic mobility shift assays with mutant oliginucleotides defined the relative importance of specific bases at the consensus binding site. Deletion of individual zinc fingers demonstrated that only zinc fingers 3, 4, and 5 are required for sequence-specific DNA binding. Potential Gfi-1 binding sites were detected in a large number of eukaryotic promoter-enhancers, including the enhancers of several proto-oncogenes and cytokine genes and the enhancer of the human cytomegalovirus (HCMV) major immediate-early promoter, which contains two such sites. HCMV major immediate-early-chloramphenicol acetyltransferase reporter constructs, transfected into NIH 3T3 fibroblasts, were repressed by Gfi-1, and the repression was abrogated by mutation of critical residues in the two Gfi-1 binding sites. These results suggest that Gfi-1 may play a role in HCMV biology and may contribute to oncogenesis and T-cell activation by repressing the expression of genes that inhibit these processes.

Calcium-dependent ADP-ribosylation of high-mobility-group I (HMGI) proteins

Micrococcal nuclease digestion of nuclei from mouse Lewis lung carcinoma cells releases a protein mixture into the supernatant that lacks histone H1 and contains a full complement of high-mobility-group I (HMGI) proteins (i.e. I, Y and I-C). This implies that all three HMGI proteins are localized at the nuclease-sensitive regions of active chromatin. It is also shown that if Ca2+ ions are present in the nuclear incubation buffer (with or without exogenous nuclease), all three HMGI proteins become ADP-ribosylated. We propose that this modification of HMGI family proteins is part of the general poly(ADP-ribosyl)ation that accompanies DNA damage in apoptosis and other processes.

In vitro T cell activation in elderly individuals: failure in CD69 and CD71 expression

A large number of T cell dysfunctions have been observed in the elderly. The most widely observed is the inability of these cells to proliferate at a level comparable to T cells from young individuals after stimulation by mitogens. To better characterize T cell impairment, we have focused on the in vitro T cell activation, analyzing by flow cytometry the activation molecules CD69 and CD71 on mitogen-stimulated lymphocytes from young and elderly subjects. The results show that the percentages of CD69+ and CD71 + T cells were significantly decreased in cultures from elderly subjects when compared to values obtained culturing cells from young individuals. The differences observed seem not due to differences in CD4 and CD8 rates in the "old' cells that underwent activation, since, following activation, the pattern of CD4 and CD8 phenotypes was the same in both groups of subjects. Signals from CD69 are relevant in controlling cytokine gene expression because its stimulation leads to interleukin-2 production and increases its receptor expression. The interaction of this cytokine with its cellular receptor is an essential requirement for T lymphocytes to express CD71 and to start proliferation. Thus, a key role in the age-associated impairment of T cell activation could be played by an ineffective modulation of CD69 expression suggesting a defect in the signal transduction pathway of the T cell receptor-CD3 complex in elderly.

An electrophysiological study of calcium entry during normal human T-lymphocyte activation

Our aim was to observe whether normal human T-cells respond to mitogenic stimulation with large whole-cell inward currents (composed of identifiable single-channel contributions) when [Ca2+]i is not markedly lowered but instead kept normal or moderately low, as has been reported in human leukaemic Jurkat T-cell line and T-cell clones [Kuno et al. (1986) Nature 323, 269-73; Kuno and Gardner (1987) Nature 326, 301-304; Gardner (1990) Annu. Rev. Immunol. 8, 231-252]. Whole-cell patch recordings showed no such currents in cells otherwise normally responding to depolarisation with the macroscopic IK described in T-lymphocytes and thus deemed viable, in agreement with the notion that Ca2+ influx in normal T-cells enterily depends on depletion of internal stores [Putney (1986) Cell Calcium 7, 1-12; Putney (1990) Cell Calcium 11, 611-624].

Translational control of interleukin 2 messenger RNA as a molecular mechanism of T cell anergy

T cell stimulation by triggering through the T cell receptor (TCR) in the absence of costimulatory signals or by calcium ionophore induces unresponsiveness in T cells to further stimulation, a phenomenon known as anergy. In freshly isolated T cells, calcium ionophore induces expression of interleukin (IL)-2 messenger (mRNA), but this mRNA is not translated and not loaded with ribosomes. In addition, while plate-bound anti-CD3 stimulation of resting T cells leads to IL-2 mRNA expression and IL-2 secretion, in cells pretreated with calcium ionophore before anti-CD3 stimulation, the IL-2 mRNA remains polysome unloaded and no IL-2 is produced. These observations show that IL-2 expression is controlled at the translational level, by differential ribosome loading. Furthermore, our data suggest that translational control of IL-2 mRNA may be a molecular mechanism by which anergy is attained.

T cell activation by concanavalin A in the presence of cyclosporin A: immunosuppressor withdrawal induces NFATp translocation and interleukin-2 gene transcription

Cyclosporin A (CSA), an immunosuppressive agent used in organ transplantation and to treat some autoimmune diseases, blocks the Ca2+-dependent steps involved in T cell receptor triggering leading to interleukin (IL)-2 production. Considering that the early steps of T cell activation are insensitive to CSA, we asked whether the initial activation achieved in presence of this immunosuppressor could affect the capacity of the T cell to respond to a mitogenic restimulation. We found that T cells activated by concanavalin A (ConA) for 48 h in the presence of CSA retain the capacity to proliferate in response to ConA once the immunosuppressor is removed. These cells are able to transcribe anew the IL-2 gene, without the requirement of new protein synthesis, and to up-regulate the alpha chain of the IL-2 receptor. Furthermore, we present the first direct evidence that the nuclear factor AP-1 is present in the nucleus of the T cells primed for 48 h in presence of CSA and that withdrawal of the immunosuppressor leads to the translocation of NFATp from the cytoplasm to the nucleus.

Activation signals of T lymphocytes in microgravity

Human peripheral blood lymphocytes and monocytes were activated with concanavalin A with or without exogenous recombinant interleukin 1 (IL-1) alone or IL-1 + interleukin 2 (IL-2) under microgravity conditions to test the hypothesis that lack of production of IL-1 by monocytes is the cause of the near total loss of activation observed earlier on several Spacelab flights. The 60 min failure of the on-board 1 x g reference centrifuge at the time of the addition of the activator renders the in-flight data at 1 x g unreliable. However, the data from a previous experiment on SLS-1 show that there is no difference between the results from the in-flight 1 x g centrifuge and 1 x g on ground. The comparison between the data of the cultures at 0 x g in space and of the synchronous control at 1 x g on ground show that exogenous IL-1 and IL-2 do not prevent the loss of activity (measured as the mitotic index) at 0 x g; production of interferon-gamma, however, is partially restored. In contrast to a previous experiment in space, the production of IL-1 is not inhibited.

A simple immunomagnetic bead-based technique for the detection of surface molecules capable of inducing T cell functional polarisation

Activated T cells can release lymphokines selectively towards the site of contact with the target cell. In this way the specificity of the target-effector cell interaction can be maintained in spite of signalling being mediated by soluble factors (Mosmann, 1988, Immunol. Today 9, 306). However, this polarised phenotype is not expressed in resting T cells; rather it appears to be induced in the first minutes following T cell activation. In order to analyse single molecules for their ability to induce T cell polarisation, we devised a technique based on targeting different T cell surface molecules with specific antibodies immobilised on to immunomagnetic beads. The polarised phenotype was determined from observation of the microtubule organising centre being oriented towards the site of interaction with the bead. When applied to T cell lines, the technique permitted the classification of CD3 as a polarisation-inducing molecule, while no polarisation was found when targeting CD2, CD6 and CD8 molecules. This technique has a number of potential applications since it can, in principle, be applied to any cell surface molecule or cell type. Technical details and the sensitivity of the procedure are discussed.

S-adenosylmethionine decarboxylase gene expression in rat hepatoma cells: regulation by insulin and by inhibition of protein synthesis

We have investigated expression of the S-adenosylmethionine decarboxylase (AdoMetDC) gene in H4-II-E rat hepatoma cells treated with growth factors (epidermal growth factor and transforming growth factor beta 1) and inducers (cAMP and insulin). Treatment with insulin caused a marked increase in both RNA level and enzyme activity. The stability of AdoMetDC mRNA was not altered by insulin treatment: the accumulation of mRNA in hepatoma cells therefore seems to be due to an increase in the transcription rate. Cycloheximide was found to be a strong inducer of AdoMetDC mRNA transcription and the effects of insulin and cycloheximide were additive, suggesting that they increase expression by separate mechanisms. Chloramphenicol acetyltransferase assays in rat hepatoma cells using 5' flanking regions of different lengths revealed that the promoter region extending 337 bp upstream from the transcription start site contains elements involved in insulin response.

An enhanced immune response in mice lacking the transcription factor NFAT1

Transcription factors of the NFAT family are thought to play a major role in regulating the expression of cytokine genes and other inducible genes during the immune response. The role of NFAT1 was investigated by targeted disruption of the NFAT1 gene. Unexpectedly, cells from NFAT1 -/- mice showed increased primary responses to Leishmania major and mounted increased secondary responses to ovalbumin in vitro. In an in vivo model of allergic inflammation, the accumulation of eosinophils and levels of serum immunoglobulin E were increased in NFAT1 -/- mice. These results suggest that NFAT1 exerts a negative regulatory influence on the immune response.

Laboratory indicators for monitoring HIV disease

Immunological monitoring of disease progression following HIV infection and seroconversion illness, latency and AIDS, not only helps in the basic investigation of the natural history of the viral infection in man, but also can assist in prognosis and treatment of AIDS-defining illnesses. However, outside clinical trials, these tests should be selected and used in clinical practice only if they are validated as relevant and effective. The absolute CD4+ T-helper lymphocyte count, measured by flow cytometry, has emerged as the best available investigation, but needs care in sampling due to diurnal and circadian rhythms, effects of age, pregnancy, therapy, intercurrent infections and technique. Sampling should provide a baseline and trends-monthly intervals initially, then quarterly in uncomplicated cases. Thresholds may be given for counts (e.g. 200/microliter) below which prophylaxis against pneumocystis pneumonia should be administered, and repeating persistently low counts (e.g. below 50/microliter) is seldom helpful in practice. Serum levels of beta-2 microglobulin, neopterin and immunoglobulins rarely add information. Physicians and laboratories should have testing guidelines based on clinical audit of best practice, based in turn on scientific understanding of the immunological processes involved.

Rel-deficient T cells exhibit defects in production of interleukin 3 and granulocyte-macrophage colony-stimulating factor

The c-rel protooncogene encodes a subunit of the NF-kappa B-like family of transcription factors. Mice lacking Rel are defective in mitogenic activation of B and T lymphocytes and display impaired humoral immunity. In an attempt to identify changes in gene expression that accompany the T-cell stimulation defects associated with the loss of Rel, we have examined the expression of cell surface activation markers and cytokine production in mitogen-stimulated Rel-/- T cells. The expression of cell surface markers including the interleukin 2 receptor alpha (IL-2R alpha) chain (CD25), CD69 and L-selectin (CD62) is normal in mitogen-activated Rel-/- T cells, but cytokine production is impaired. In Rel-/- splenic T cell cultures stimulated with phorbol 12-myristate 13-acetate and ionomycin, the levels of IL-3, IL-5, granulocyte- macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor alpha (TNF-alpha), and gamma interferon (IFN-gamma) were only 2- to 3-fold lower compared with normal T cells. In contrast, anti-CD3 and anti-CD28 stimulated Rel-/- T cells, which fail to proliferate, make little or no detectable cytokines. Exogenous IL-2, which restitutes the proliferative response of the anti-CD3- and anti-CD28-treated Rel-/- T cells, restores production of IL-5, TNF-alpha, and IFN-gamma, but not IL-3 and GM-CSF expression to approximately normal levels. In contrast to mitogen-activated Rel-/- T cells, lipopolysaccharide-stimulated Rel-/- macrophages produce higher than normal levels of GM-CSF. These findings establish that Rel can function as an activator or repressor of gene expression and is required by T lymphocytes for production of IL-3 and GM-CSF.

Multiplex messenger assay: simultaneous, quantitative measurement of expression of many genes in the context of T cell activation

The hybridization signature approach, using colony filters and labeled complex probes, can provide high throughput measurement of gene activity. We describe here the implementation of this method to follow the expression levels of 47 genes in resting and activated T cells, as well as in epithelial cells. Using 4-fold spotting of colonies, imaging plate detection and various correction and normalization procedures, the technique is sensitive enough to quantify expression levels for sequences present at 0.005% abundance in the probe. Comparison with Northern blotting shows good consistency between the two methods. Upon activation of a T cell clone by an anti-CD3 antibody variations ranging from 2- to 20-fold are measured, some of which had not been reported previously. This 'multiplex messenger assay' method, performed using available commercial apparatus, can be used in many cases where simultaneous assessment of mRNA levels for many genes is of interest.

Corticostatins/defensins inhibit in vitro NK activity and cytokine production by human peripheral blood mononuclear cells

Corticostatins/defensins are a family of cationic peptides recently isolated from phagocytotic cells of the myeloid lineage. Natural killer (NK) cells are spontaneously cytotoxic large granular lymphocytes that are involved in immunosurveillance against cancer and infections. Their activity is modulated by hormones of the hypothalamic-pituitary-adrenal axis. We wished to determine whether two human corticostatins/defensins, HP-1 and HP-4, are able to change in vitro the spontaneous NK activity of human peripheral blood mononuclear cells (PBMC) and the responses either to the stimulatory cytokines immune interferon (IFN-gamma) or interleukin 2 (IL-2) and to the inhibitory hormone cortisol. NK cell activity was measured in a 4-h direct cytotoxicity assay with K562 cells as a target. HP-1 and HP-4 (10 (-8) -10 (-9) M) significantly inhibited the spontaneous and cytokine-inducible NK activity, and increased the cortisol-dependent inhibition. Radioimmunoassay of HPLC purified fractions obtained from sonicated NK cells showed HP-1 in the two cell preparations examined. We also evaluated the effects of HP-1 and HP-4 (10 (-8) M -10(-9) M) upo IFN-gamma and interleukin 6 (IL-6) production by PBMC stimulated with phytohemagglutinin (PHA) or concanavalin A (ConA). IFN-gamma was titrated with the biological assay using WISH cells as indicators and vescicular stomatitis virus (VSV) as the challenge virus. IL-6 was measured using an enzyme amplified sensitivity immunoassay. Both HP-1 and HP-4 significantly reduced cytokine production. Our data indicate that corticostatins/defensins are novel modulators of lymphocyte functions in vitro. Their immunodepressing properties could add complexity and plasticity to hypothalamic-pituitary-adrenal-cytokine circuits in vivo.

Nuclear appearance of a factor that binds the CD28 response element within the interleukin-2 enhancer correlates with interleukin-2 production

Activation of T lymphocytes requires the combined signaling of the T cell receptor and costimulatory molecules such as CD28. The ability of T cells to produce interleukin-2 (IL-2) is a critical control point in T lymphocyte activation. The IL-2 enhancer contains a functional motif named CD28 response element (CD28RE) that serves a role as a target for mitogenic T cell activation signals. The CD28RE sequence reveals similarity to the consensus kappaB binding motif. Here we demonstrate that CD28RE binds an inducible protein with a molecular mass of approximately 35 kDa called nuclear factor of mitogenic-activated T cells (NF-MATp35) that is clearly different from the known NF- kappaB/Rel family members. Induction of NF-MATp35 was shown to depend on de novo protein synthesis and was restricted to T cells that received a mitogenic combination of T cell stimuli, not necessarily including CD28 signaling. Nonmitogenic T cell stimulation did not result in appearance of NF-MATp35. These results indicate that mitogenic combinations of T cell activation signals are integrated at the level of NF-MATp35 induction. Similar to its effect on IL-2 production, cyclosporin A inhibited the induction of NF-MATp35. Taken together, these data demonstrate that the nuclear appearance of NF-MATp35 shows excellent correlation with IL-2 production, which is a unique characteristic among nuclear factors implicated in the control of IL-2 gene expression.

T cell antigen receptor signal transduction pathways

The T cell antigen receptor (TCR) regulates the activation and growth of T lymphocytes. The initial membrane proximal event triggered by the TCR is activation of protein tyrosine kinases with the resultant phosphorylation of cellular proteins. This biochemical response couples the TCR to a divergent array of signal transduction molecules including enzymes that regulate lipid metabolism, GTP binding proteins, serine/threonine kinases, and adapter molecules. The ultimate aim of studies of intracellular signaling mechanisms is to understand the functional consequences of a particular biochemical event for receptor function. The control of cytokine gene expression is one of the mechanism that allows the TCR to control immune responses. Accordingly, one object of the present review is to discuss the role of the different TCR signal transduction pathways in linking the TCR to nuclear targets: the transcription factors that control the expression of cytokine genes.

How is expression of the interleukin-5 gene regulated?

Eosinophilia is a uniquely specific phenomenon regulated by interleukin-5 (IL-5), suggesting specific control for IL-5 expression. However in eosinophilia IL-5 is often co-expressed with other lymphokines such as IL-4, indicating that common, as well as independent, control mechanisms must exist. IL-5 gene expression is regulated at the transcriptional level. The molecular analysis of the IL-5 promoter region reveals the presence of positive regulatory sites that are common to many lymphokine genes. Results from immunosuppression studies suggest that the key control mechanism of IL-5 regulation may not depend on specific regulatory factors but on how gene expression is activated.

Protein kinase C-theta isoenzyme selective stimulation of the transcription factor complex AP-1 in T lymphocytes

T-lymphocyte stimulation requires activation of several protein kinases, including the major phorbol ester receptor protein kinase C (PKC), ultimately leading to induction of lymphokines, such as interleukin-2 (IL-2). The revelant PKC isoforms which are involved in the activation cascades of nuclear transcription factors involved in IL-2 production have not yet been clearly defined. We have examined the potential role of two representative PKC isoforms in the induction of the IL-2 gene, i.e., PKC-alpha and PKC-theta, the latter being expressed predominantly in hematopoietic cell lines, particularly T cells. Similar to that of PKC-alpha, PKC-theta overexpression in murine EL4 thymoma cells caused a significant increase in phorbol 12-myristate 13-acetate (PMA)-induced transcriptional activation of full-length IL-2-chloramphenicol acetyltransferase (CAT) and NF-AT-CAT but not of NF-IL2A-CAT or NF-kappaB promoter-CAT reporter gene constructs. Importantly, the critical AP-1 enhancer element was differentially modulated by these two distinct PKC isoenzymes, since only PKC-theta but not PKC-alpha overexpression resulted in an approximately 2.8-fold increase in AP-1-collagenase promoter CAT expression in comparison with the vector control. Deletion of the AP-1 enhancer site in the collagenase promoter rendered it unresponsive to PKC-theta. Expression of a constitutively active mutant PKC-theta A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-theta K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-RasS17N completely inhibited the PKC-O A148E-induced signal, PKC-O. Expression of a constitutively active mutant PKC-O A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-O K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-enRasS17N completely inhibited in the PKC-O A148E-induced signal, identifying PKC-theta as a specific constituent upstream of or parallel to Ras in the signaling cascade leading to AP transcriptional activation.

Transcriptional regulation of the interleukin-2 gene in normal human peripheral blood T cells. Convergence of costimulatory signals and differences from transformed T cells

To study transcriptional regulation in normal human T cells, we have optimized conditions for transient transfection. Interleukin-2 (IL-2) promoter-reporter gene behavior closely parallels the endogenous gene in response to T cell receptor and costimulatory signals. As assessed with mutagenized promoters, the most important IL-2 cis-regulatory elements in normal T cells are the proximal AP-1 site and the NF- kappaB site. Both primary activation, with phytohemagglutinin or antibodies to CD3, and costimulation, provided by pairs of CD2 antibodies or B7-positive (B cells) or B7-negative (endothelial) accessory cells, are mediated through the same cis-elements. Interestingly, the nuclear factor of activated T cell sites are much less important in normal T cells than in Jurkat T cells. We conclude that IL-2 transcriptional regulation differs in tumor cell lines compared with normal T cells and that different costimulatory signals converge on the same cis-elements in the IL-2 promoter.

The functional consequences of partial calcineurin inhibition in human peripheral blood mononuclear leucocytes

Calcium-dependent signal transduction is essential to the induction of cytokine expression by stimuli acting through the T cell receptor. In vitro, the immunosuppressant cyclosporine (CyA) blocks this pathway by inhibition of calcineurin (CN) phosphatase activity. But in vivo, patients on CyA have only 50% inhibition of CN and can mount cytokine responses. To simulate this state of partial inhibition, we studied the responses of human peripheral blood mononuclear leucocytes (PBL) in vitro at low CyA concentrations. PBL were challenged in vitro with calcium ionophores or anti-CD3 monoclonal antibody. The induction of IFN-gamma (interferon-gamma) and IL-2 (interleukin 2) steady-state mRNA was studied by Northern blotting and reverse transcriptase-polymerase chain reaction. IFN-gamma was assessed in a radiolabelled antibody binding assay or by ELISA (enzyme-linked immunosorbent assay). CN was assessed by dephosphorylation of a 32P-serine labelled 19 amino acid substrate. CyA inhibited CN with an IC50 (concentration giving 50% inhibition) of 10 ng/ml (95% confidence interval, CI = 8-13 ng/ml). Likewise, the induction of IFN-gamma and IL-2 mRNA by calcium ionophore A23187 was inhibited with IC50 of 14 ng/ml (95% CI = 8-27 ng/ml) and 32 ng/ml (95% CI = 5-178 ng/ml), respectively, while the IC50 for inhibition of IFN-gamma protein secretion was 8 ng/ml (95% CI = 9-18 ng/ml). Partial inhibition of CN also altered the threshold for IFN-gamma induction. CyA 10 ng/ml inhibited IFN-gamma induction by anti-CD3 monoclonal antibody OKT3 significantly more at low OKT3 concentrations (10 ng/ml, mean +/- SEM = 72 +/- 9% inhibition) compared to high OKT3 concentrations (1000 ng/ml, 47 +/- 6%, p < 0.01). Similar results were seen using high and low concentrations of A23187. Finally, cells pretreated with CyA recovered the ability to respond to high concentrations of A23187 (5 microM) faster than low concentrations (0.5 microM). We conclude that the principal defect in lymphocytes with partial CN inhibition is a reduction in maximum cytokine output which is closely related to the degree of CN inhibition. In addition, there is significantly greater inhibition of weak stimuli compared to maximal stimuli. These defects may explain why patients on CyA can have a reduction in immune responsiveness but still retain protection from infection.

Regulation of [Ca2+]i rise activated by doxepin-sensitive H1-histamine receptors in Jurkat cells, cloned human T lymphocytes

To clarify the presence of histamine receptor and its transmembrane mechanism in human T lymphocytes, we investigated the effects of agonists or antagonists of histamine receptor subtypes and bacterial toxins on intracellular concentration of Ca2+ [Ca2+]i), [3H]pyrilamine binding and c-fos mRNA expression in Jurkat cells, cloned human T lymphocytes. H1-agonists (histamine and 2-methylhistamine) caused a transient rise of [Ca2+], and H1-antagonists (pyrilamine and doxepin) inhibited the histamine-induced [Ca2+]i rise more potently than the H2-antagonist (cimetidine) on the H3-antagonist (impromidine). Binding parameters of [3H]pyrilamine binding were Kd = 5.53 nM and Bmax = 2,647 sites/cell. Pretreatment with B.pertussis, V.cholera. or C.botulinum toxin did not influence histamine-induced [Ca2+]i rise. Western Blot analysis using antibodies against subunits of GTP-binding proteins indicated that Gq/G11 richly existed in Jurkat cells. Histamine induced mRNA expression of an immediate early gene c-fos. Pretreatment with a protein kinase C activator, phorbol 12-myristate 13-acetate, caused almost complete inhibition of histamine-induced [Ca2+]i rise, but did not do so by activators of cAMP- and cGMP-dependent protein kinases.

In vivo anergized CD4+ T cells express perturbed AP-1 and NF-kappa B transcription factors

Anergy is a major mechanism to ensure antigen-specific tolerance in T lymphocytes in the adult. In vivo, anergy has mainly been studied at the cellular level. In this study, we used the T-cell-activating superantigen staphylococcal enterotoxin A (SEA) to investigate molecular mechanisms of T-lymphocyte anergy in vivo. Injection of SEA to adult mice activates CD4+ T cells expressing certain T-cell receptor (TCR) variable region beta-chain families and induces strong and rapid production of interleukin 2 (IL-2). In contrast, repeated injections of SEA cause CD4+ T-cell deletion and anergy in the remaining CD4+ T cells, characterized by reduced expression of IL-2 at mRNA and protein levels. We analyzed expression of AP-1, NF-kappa B, NF-AT, and octamer binding transcription factors, which are known to be involved in the regulation of IL-2 gene promoter activity. Large amounts of AP-1 and NF-kappa B and significant quantities of NF-AT were induced in SEA-activated CD4+ spleen T cells, whereas Oct-1 and Oct-2 DNA binding activity was similar in both resting and activated T cells. In contrast, anergic CD4+ T cells contained severely reduced levels of AP-1 and Fos/Jun-containing NF-AT complexes but expressed significant amounts of NF-kappa B and Oct binding proteins after SEA stimulation. Resolution of the NF-kappa B complex demonstrated predominant expression of p50-p65 heterodimers in activated CD4+ T cells, while anergic cells mainly expressed the transcriptionally inactive p50 homodimer. These alterations of transcription factors are likely to be responsible for repression of IL-2 in anergic T cells.

Tumor necrosis factor alpha gene regulation in activated T cells involves ATF-2/Jun and NFATp

The human tumor necrosis factor alpha (TNF-alpha) gene is one of the earliest genes expressed upon the activation of a T or B cell through its antigen receptor. Previous experiments have demonstrated that in stimulated T cells, a TNF-alpha promoter element, kappa 3, which binds NFATp, is required for the cyclosporin A-sensitive transcriptional activation of the gene. Here, we demonstrate that a cyclic AMP response element (CRE), which lies immediately upstream of the kappa 3 site, is also required for induction of TNF-alpha gene transcription in T cells stimulated by calcium ionophore or T-cell receptor ligands. The CRE binds ATF-2 and Jun proteins in association with NFATp bound to kappa 3. These proteins bind noncooperatively in vitro; however, the transcriptional activity of the CRE/kappa 3 composite site is dramatically higher than the activity of the kappa 3 site alone, indicating that the two sites cooperate in vivo. This study is the first demonstration of a role for ATF-2 in TNF-alpha gene transcription and of a functional interaction between ATF-2/Jun and NFATp. This novel pairing of NFATp with ATF-2/Jun may account for the specific and immediate pattern of TNF-alpha gene transcription in stimulated T cells.

Signal transduction by CD28 costimulatory receptor on T cells. B7-1 and B7-2 regulation of tyrosine kinase adaptor molecules

This study compares the biochemical responses in T cells activated with the CD28 ligands B7-1 and B7-2. The patterns of tyrosine phosphorylation induced in T cells by these two CD28 ligands are identical, but clearly different from the tyrosine phosphorylation induced by the T cell receptor (TCR). The TCR regulates protein complexes mediated by the adapter Grb2 both in vivo and in vitro. In contrast, there is no apparent regulation of in vivo Grb2 complexes in response to B7-1 or B7-2. Rather, B7-1 and B7-2 both induce tyrosine phosphorylation of a different adaptor protein, p62. The regulation of p62 is a unique CD28 response that is not shared with the TCR. These data indicate that B7-1 and B7-2 induce identical tyrosine kinase signal transduction pathways. The data show also that the TCR and CD28 couple to different adapter proteins, which could explain the divergence of TCR and CD28 signal transduction pathways during T cell activation.

CD28 signal transduction pathways. A comparison of B7-1 and B7-2 regulation of the map kinases: ERK2 and Jun kinases

The present study compares the mitogen-activated protein (MAP) kinase responses in T cells activated with the CD28 ligands B7-1 (CD80) and B7-2/B70 (CD86). Ligands B7-1 and B7-2 do not activate the Raf-1/ERK2 cascade, but share the ability to activate related Jun kinases. These natural ligands for CD28 had no stimulatory effect alone on Jun kinase activation, but the data show that B7-1 and B7-2 could both co-operate with intracellular Ca2+ increase and protein kinase C (PKC) activation to stimulate Jun kinases. The present study shows that the interaction of CD28 with its ligands B7-1 and B7-2 can induce identical signal transduction through the MAP kinase cascades.

Calcium signals and protein tyrosine kinases are required for the induction of c-jun in Jurkat cells stimulated by the T cell-receptor complex and oxidative signals

The regulation of c-jun plays an important role in T cell activation, proliferation, and expression of interleukin-2. In the present study, we determined whether Ca2+ signals and the activity of protein tyrosine kinases (PTKs) were required for the induction of c-jun in Jurkat cells stimulated with cross-linked anti-T cell receptor/CD3 antibodies or exposed to oxidative stress in the form of micromolar concentrations of H2O2. Jurkat cells exhibited rapid elevations in intracellular calcium [Ca2+]i levels in response to H2O2 and cross-linked anti-CD3 antibodies that mainly reflected the influx of extracellular Ca2+. The Ca2+ flux in response to oxidative signals was distinguished by an exquisite sensitivity to inhibition with Ni2+, suggesting the involvement of cation channels. PTK activity was needed for [Ca2+]i elevations in response to both oxidative and anti-CD3 signals, although H2O2 induction of [Ca2+]i increases was more resistant to inhibition by genistein than anti-CD3 [Ca2+]i responses. Both oxidative signals and anti-CD3 stimulation induced increased levels of c-jun and c-fos mRNA. The increased expression of c-jun with H2O2 was preceded by [Ca2+]i increases and accompanied by activation of c-Jun aminoterminal kinases (JNKs), as well as increased AP-1 binding activity. Induction of c-jun with oxidative signals and anti-CD3 was also shown to be crucially dependent on [Ca2+]i elevations because the chelation of [Ca2+]i with BAPTA resulted in a dose-dependent inhibition of c-jun expression. Furthermore, inhibition studies demonstrated that the optimal induction of c-jun mRNA in response to oxidative signals required PTK as well as protein kinase C (PKC). Thus, these findings suggest that both [Ca2+]i signals and the activity of PTKs are essential for the optimal expression of c-jun in response to TCR/CD3 signals and changes in redox potentials.

Kinetics of transcription factors regulating the RANTES chemokine gene reveal a developmental switch in nuclear events during T-lymphocyte maturation

RANTES is a chemoattractant cytokine (chemokine) whose gene is expressed immediately after stimulation of several cell types but upregulated late (3 to 5 days) after activation in normal T lymphocytes. Here we describe two cis-acting elements in the human RANTES promoter that act in T lymphocytes. One site interacts with NFIL6, which is activated within the first 24 h after T-cell activation. The second site binds an apparently novel complex that is upregulated later, between days 3 and 5. These data provide an explanation for the immediate-early expression of RANTES in some cell types and identify apparently novel factors contributing to late RANTES transcription in T cells. The results reveal a developmental switch occurring during normal T-cell maturation coincident with the onset of terminal differentiation and the binding of late-acting factors to sequences of the RANTES promoter.

Human endogenous retroviruses: nature, occurrence, and clinical implications in human disease

Retroviral diagnostics have become standard in human laboratory medicine. While current emphasis is placed on the human exogenous viruses (human immunodeficiency virus and human T-cell leukemia virus), evidence implicating human endogenous retroviruses (HERVs) in various human disease entities continues to mount. Literature on the occurrence of HERVs in human tissues and cells was analyzed. Substantial evidence documents that retrovirus particles were clearly demonstrable in various tissues and cells in both health and disease and were abundant in the placenta and that their occurrence could be implicated in some of the reproductive diseases. The characteristics of HERVs are summarized, mechanisms of replication and regulation are outlined, and the consistent hormonal responsiveness of HERVs is noted. Clear evidence implicating HERV gene products as participants in glomerulonephritis in some cases of systemic lupus erythematosus is adduced. Data implicating HERVs as etiologic factors in reproductive diseases, in some of the autoimmune diseases, in some forms of rheumatoid arthritis and connective tissue disease, in psoriasis, and in some of the inflammatory neurologic diseases are reviewed. The current major needs are to improve methods for HERV detection, to identify the most appropriate HERV prototypes, and to develop diagnostic reagents so that the putative biologic and pathologic roles of HERVs can be better evaluated.

The influence of tetracyclines on T cell activation

Minocycline has been shown to have an anti-inflammatory effect in patients with rheumatoid arthritis (RA). Since there is evidence that RA is a T cell-mediated disease, we investigated the effect of minocycline on human T cell clones derived from the synovium of an RA patient. The T cells, when activated via the T cell receptor (TCR)/CD3 complex, were suppressed functionally by minocycline, resulting in a dose-dependent inhibition of T cell proliferation and reduction in production of IL-2, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha). Besides an inhibition of IL-2 production, minocycline exerted its effect on T cell proliferation by induction of a decreased IL-2 responsiveness. We showed that the chelating capacity of minocycline plays a crucial role in the inhibitory effect on T cell function, since the inhibitory effect on T cell proliferation could be annulled by addition of exogenous Ca2+. However, minocycline did not markedly influence the typical TCR/CD3-induced intracellular Ca2+ mobilization. Taken together, the results clearly indicate that minocycline has immunomodulating effects on human T cells.

Protein kinase C modulates cytosolic free calcium by stimulating calcium pump activity in Jurkat T cells

Although protein kinase C (PKC) activation has been shown to inhibit Ca2+ influx in T lymphocytes, the role of PKC on Ca2+ sequestration or extrusion processes has not been fully explored. We examined the effect of CD3 stimulation and PKC activators on cytosolic Ca2+ (Ca2+i) extrusion and 45Ca2+ efflux in human leukemic Jurkat T cells. Treatment of Fura-2 loaded cells with phorbol 12-myristate 13-acetate (PMA) or thymeleatoxin (THYM) resulted in a decrease in Ca2+i both in the presence and absence of extracellular Ca2+, whereas inactive phorbol esters had no effect. PKC activators added at the peak of a Ca2+i transient induced by anti-CD3 mAb, ionomycin or thapsigargin (TG) stimulated the rate and extent of return of Ca2+i to basal levels by 17-53%. PKC stimulation of the Ca2+i decline was not enhanced by the presence of Na+, indicating that PKC activators increase Ca2+ pump activity rather than a Na+/Ca2+ exchange mechanism. As CD3 receptor activation enhanced the Ca2+i decline in TG-treated cells, antigen-mediated activation of phospholipase C (PLC) signaling includes enhanced Ca2+ extrusion at the plasma membrane. The effect of PKC activators on parameters of Ca2+i extrusion were further explored. PMA significantly increased the rate of Ca2+ extrusion in TG-treated cells from 0.28 +/- 0.02 to 0.35 +/- 0.03 s-1 (mean +/- SEM) and stimulated the initial rate of 45Ca2+ efflux by 69% compared to inactive phorbol ester treated cells. The effects of PKC activation on the Ca2+i decline were eliminated by PKC inhibitors, PKC down regulation (24 h PMA pretreatment), ATP-depletion and conditions that inhibited the Ca2+ pump. In contrast, pretreatment of cells with okadaic acid enhanced the PMA-stimulated response. We suggest that Jurkat T cells contain a PKC-sensitive Ca2+ extrusion mechanism likely to be the Ca2+ pump. In lymphocytes, receptor/PLC-linked PKC activation modulates Ca2+i not only by inhibiting Ca2+ influx but also by stimulating plasma membrane Ca2+i extrusion.

Simultaneous quantitation of multiple cytokine mRNAs by RT-PCR utilizing plate based EIA methodology

Cytokines are small protein hormones produced during an immune response that are responsible for mediation and regulation of many aspects of immunity. Measurement of cytokines by several different methods has led to a broader understanding of the immune response. This paper describes a sensitive, reproducible, and quantitative RT-PCR assay for the simultaneous measurement of multiple cytokines. The main features of the methodology are: RNA competitors which control for all aspects of the process from RNA extraction, through reverse transcription (RT) and PCR amplification; a general cloning vector, pQPCR1, for building RNA competitors that does not require prior analyte cDNA cloning; and analysis by plate based EIA. This RT-PCR-EIA system is shown to be more sensitive than agarose gel electrophoresis followed by EtBr staining, measuring PCR product in the sub-nanogram range. It also extends the linear dynamic range of detection to a four log fold range of analyte concentration. The assay is reproducible, with coefficients of variation (CVs) in the 10-20% range. Moreover, the cloning vector is designed to accommodate multiple primer templates, thus allowing simultaneous quantitation of many different analytes from a single RT reaction. The described system is versatile and adapts to numerous analytes.

Identification of an ionomycin/cyclosporin A-responsive element within the human T cell receptor gamma enhancer

Activation through the Ca2+/calcineurin pathway is essential to the transcription of many cytokine genes. The conserved cis-acting sequence, GGAAAA, and transcription factors binding to this sequence are involved in the response to increased intracellular Ca2+ concentrations. Here we report the identification and importance of the same sequence in a non-cytokine gene, the human T cell receptor gamma (TCRG) enhancer. Results from site-directed mutations and electrophoretic mobility shift assays strongly suggest that this sequence mediates the ionomycin-induced activation of the TCRG enhancer. Our studies provide an explanation for a previous observation that TCRG mRNA levels, but not mRNA levels for T cell receptor alpha and -beta, are increased by ionomycin treatment.

Interferon-gamma induces T lymphocyte proliferation in multiple sclerosis via a Ca(2+)-dependent mechanism

The intracellular mechanisms underlying T lymphocyte activation leading to demyelination in multiple sclerosis (MS) have not yet been clarified. We have recently reported that interferon (IFN)-gamma activates a novel trans-plasmalemma Ca2+ influx on T lymphocytes (mainly CD4+) from patients with MS which induces intracellular Ca2+ ([Ca2+]i) elevation. Since Ca2+ is an essential second messenger in regulating transcription of T lymphocyte activation genes, we have evaluated how [Ca2+]i elevation due to the activity of this particular influx affects T lymphocyte proliferative behaviour in 12 influx-positive relapsing-remitting MS (RR-MS) patients. Fourteen influx-negative RR-MS patients and 14 healthy donors were used as controls. In lymphocytes from healthy controls, a significant correlation (r = 0.62; P < 0.001) was found between [Ca2+]i levels and proliferation rate after phytohemagglutinin (PHA) stimulation. Sustained proliferation was induced in T lymphocytes by > or = 10 micrograms/ml of PHA, a dose leading to a [Ca2+]i increase of at least 45% over basal level. Similar [Ca2+]i elevations were obtained when > or = 10 micrograms/ml of PHA were used on cells from RR-MS patients. However, T lymphocytes from RR-MS patients, but not from healthy donors, proliferated also in response to 1 micrograms/ml of PHA, indicating a state of preactivation. Moreover, 1 microgram/ml of PHA used in combination with suboptimal doses of IFN-gamma (5 UI/ml) doubled the proliferation rate of influx-positive MS cells, but not influx-negative MS cells or cells from healthy donors compared to the values obtained using PHA alone (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Ruthenium Red potently inhibits immune responses both in vitro and in vivo

Targeted drug screening revealed a compound, Ruthenium Red, which potently blocked proliferation of human T-cells. This compound is not generally cytotoxic or cytostatic, as judged by its lack of effect on the proliferation of a panel of transformed cell lines, but it exhibits true immunosuppressive properties. Ruthenium Red inhibits the T-cell proliferative response (with an IC50 approximately 100 nM) to a wide variety of agents, including viral antigens from herpes simplex virus, tetanus toxoid, alloantigens and IL-2. This compound did not alter the growth of an M-CSF-dependent cell line (M-NFS-60) in response to added growth factor. Time course studies revealed that Ruthenium Red could be added as late as 24 h after the initiation of T-cell stimulation by antigen and still produce maximal inhibition, indicating that later stages of signaling events are being effected. Ruthenium REd was then tested for its ability to abrogate immune response in vivo. It was discovered that this compound dramatically reduced the expansion of lymphocytes in draining lymph nodes of mice immunized with cytochrome c in adjuvants. Furthermore, Ruthenium Red also suppressed specific antibody production in mice following challenge with this antigen. The functional properties of Ruthenium Red have been compared with other immunosuppressive agents and reveal that this compound is most similar to rapamycin in its overall profile. The chemical structure of Ruthenium Red is quite different from these other agents; therefore, it may be extremely useful in helping dissect the activation pathway of T-cells. It will be important to explore further the therapeutic potential of this unique compound.

Novel NFAT sites that mediate activation of the interleukin-2 promoter in response to T-cell receptor stimulation

The transcription factors NFAT and AP-1 have been shown to be essential for inducible interleukin-2 (IL-2) expression in activated T cells. NFAT has been previously reported to bind to two sites in the IL-2 promoter: in association with AP-1 at the distal antigen response element at -280 and at -135. On the basis of DNase I footprinting with recombinant NFAT and AP-1 proteins, gel shift assays, and transfection experiments, we have identified three additional NFAT sites in the IL-2 promoter. Strikingly, all five NFAT sites are essential for the full induction of promoter activity in response to T-cell receptor stimulation. Four of the five NFAT sites are part of composite elements able to bind AP-1 in association with NFAT. These sites display a diverse range of cooperativity and interdependency on NFAT and AP-1 proteins for binding. One of the NFAT sites directly overlaps the CD28-responsive element. We present evidence that CD28 inducibility is conferred by the AP-1 component in NFAT-AP-1 composite elements. These findings provide further insight into the mechanisms involved in the regulation of the IL-2 promoter.

Differential regulation of the synthesis and activity of the major cyclin-dependent kinases, p34cdc2, p33cdk2, and p34cdk4, during cell cycle entry and progression in normal human T lymphocytes

Three major cyclin-dependent kinases, p34cdc2, p33cdk2, and p34cdk4 were examined in normal human T cells stimulated to enter the cell cycle in vitro. None of the three genes was expressed in resting T cells. Transcripts form the cdk4 and cdk2 genes were detectable as early as 3 and 8 hr after stimulation, respectively, whereas cdc2 gene transcripts were not detectable until about 24 hr, shortly before S phase entry. Immunoblot analysis showed that resting T cells contained little p34cdk4, no p34cdc2, and a low level of p33cdk2 protein. Increased amounts of p34cdk4, p33cdk2, and p34cdc2 proteins were seen at about 7, 10, and 30 hr after stimulation, respectively. Immunoprecipitates of each of the kinases were assessed for histone H1 kinase activity. Activity due to p33cdk2 first became detectable in mid-G1 phase and increased dramatically after entry into S phase. Active p34cdc2 kinase was not detected until about 40 hr after stimulation, about 10 hr after the first appearance of the protein. Immunoprecipitates of p34cdk4 possessed almost no H1 histone kinase activity; however, activity was detected as early as 10 hr after cell activation when a protein (p60Rb) derived from the retinoblastoma susceptibility gene product was used as substrate. Cells were synchronized about the G1/S and G2/M borders by aphidicolin and nocodazole. Cells arrested prior to S-phase contained high levels of active p33cdk2 and essentially no active p34cdc2, despite the fact that large amounts of both proteins were present. Cells arrested by nocodazole had high levels of active p34cdc2 and greatly reduced levels of p33cdk2 kinase activity. The results suggest that the major role for the p34cdc2 kinase is at mitosis, whereas that for p33cdk2 is in late G1 and/or S phase. The p34cdk4 protein, present in aphidicolin-blocked cells, was nearly absent from cells arrested at the G2/M border; however, kinase activity was low in cells blocked at both points, suggesting that the major role for p34cdk4 may be in G1 phase.

A mutation in zap-70 protein tyrosine kinase results in a selective immunodeficiency

We have previously described a new type of selective T-cell deficiency characterized by persistent infections reminiscent of severe combined immunodeficiency. We show here that selective T-cell deficiency patients carry a mutation of zap-70 protein tyrosine kinase, resulting in a loss of the activity of this kinase. The thymus of zap-70(-1-1) patients shows the presence of CD4CD8 double-positive cells in the cortex, however, only CD4, and not CD8, single-positive cells are present in the medulla. Peripheral CD4+ T cells from the zap-70(-1-1) patients exhibit markedly reduced tyrosine phosphorylation, fail to produce interleukin-2, and do not proliferate in response to T-cell receptor stimulation by mitogens or antigens. Thus zap-70 kinase appears to be indispensable for the development of CD8 single-positive T cells as well as for the signal transduction and function of single-positive CD4 T cells.

Molecular cloning and characterization of NF-IL3A, a transcriptional activator of the human interleukin-3 promoter

To isolate transcription factors important in the regulation of the human interleukin-3 (IL-3) gene, we screened a lambda gt11 cDNA library, constructed from phytohemagglutinin-stimulated human T-cell RNA, with a probe containing regulatory sequences in the upstream region of the IL-3 gene (located from bp -165 to -128 and referred to as the DNase I footprint A region). We isolated a 0.96-kb cDNA that encoded a basic amino acid domain and a leucine zipper domain and used the "rapid amplification and cloning of 3' ends" technique to isolate the 3' half of the cDNA clone, generating a 1.9-kb full-length cDNA clone. Using in vitro-translated protein, which we call NF-IL3A, we defined the IL-3 promoter sequences bound by NF-IL3A in DNase I footprinting assays as TAATTACGTCTG and, using gel shift assays, defined ATTACG as the minimal sequence required for binding of NF-IL3A in vitro. Proteins that bind to the NF-IL3A binding site are found in both unstimulated and stimulated T-cell lines in similar amounts, although the level of NF-IL3A mRNA increases after T-cell activation in several mature T-cell lines. The NF-IL3A protein is nearly identical to a recently identified transcriptional repressor protein, E4BP4, and NF-IL3A binds specifically to regulatory sequences in both the adenovirus E4 promoter and the human gamma interferon promoter. Cotransfection experiments demonstrate that introduction of an expression vector containing the NF-IL3A cDNA into resting T cells transactivates IL-3 promoter-chloramphenicol acetyltransferase gene plasmids that contain the A region; this effect requires the presence of an intact NF-IL3A binding site. One or more copies of the A region also confer NF-IL3A responsiveness on a heterologous promoter in T cells. NF-IL3A appears to play an important role in the expression of IL-3 by T cells.