Similar effects of cyclosporine and verapamil on lymphokine, interleukin 2 receptor, and proto-oncogene expression

Since calcium channel blocking agents and CsA exert an antiproliferative effect upon T cell mitogenesis, we have compared and characterized their immunosuppressive properties at the level of gene activation. Verapamil (greater than or equal to 30 microM), which blocks T cell mitogenesis and a rise in cytosolic calcium, was added to cultures of peripheral blood mononuclear cells stimulated with phytohemagglutinin (5 micrograms/ml) and phorbol myristate acetate (5 ng/ml). Northern blot analysis was performed using cDNA probes for the p55 interleukin 2 receptor (Tac; IL-2R), interleukin 2 and c-myc at 20 hr of culture. Accumulation of IL-2 encoding mRNA within the cytoplasm was completely abrogated by verapamil. However, IL-2R and c-myc encoding mRNA were clearly detectable in verapamil-treated cell cultures. Surface expression of the Tac protein in mitogen-activated T cells was also not blocked by verapamil as shown by FACS analysis. In companion experiments with CsA, verapamil only partially inhibits the intracellular processes leading to T cell activation. A calcium-independent pathway may exist for the expression of IL-2R and c-myc, while an increase of intracellular Ca2+ may provide the additional signal for IL-2 gene expression. Although the in vitro concentrations of verapamil used in these experiments are in excess of common clinically therapeutic levels, the results help clarify the mode of CsA action and may provide a new tool to dissect the early events of T cell activation.

Preferential enhancement by 2-mercaptoethanol of IL-2 responsiveness of T blast cells from old over young mice is associated with potentiated protein kinase C translocation

Certain thiol compounds have been shown to enhance the T cell-dependent immune response of mice in vivo and the proliferation of T cells in vitro. The magnitude of augmentation is often greater in old than young mice. We hypothesized that the metabolic process that is preferentially up-regulated by thiol compounds in T cells from old mice may reflect a rate-limiting process which contributes to immunosenescence in aging mice. Because IL-2 dependent T cell proliferation in vitro is positively correlated with the strength of T cell-dependent immune response in vivo, we investigated the effects of 2-ME on (a) IL-2 synthesis in vitro, (b) the IL-2-IL-2R binding interaction, and (c) the translocation of PKC from the cytosol to the membrane in Con A-activated splenic T cells from young and old C57BL/6 and C57BL/s mice. The results demonstrated that 2ME does not preferentially enhance the synthesis or secretion of IL-2. Neither the binding affinity of IL-2 to the IL-2R nor the number of receptors on activated T cell blasts differed between young and old mice. At the post-receptor binding level, the magnitude of the translocation of PKC from the cytosol to the membrane was significantly greater in the T blast cells from old than young mice. The preferential enhancement of IL-2-dependent proliferation of T cells from old mice by 2ME is therefore associated with a potentiated translocation of PKC. This would suggest that the metabolic event involved in the translocation of PKC in T cells is vulnerable to aging.

Different mechanisms account for the suppression of interleukin 2 production and the suppression of interleukin 2 receptor expression in Trypanosoma brucei-infected mice

Lymph node cell populations derived from Trypanosoma brucei-infected mice failed to produce interleukin 2 (IL 2) in response to a potent mitogenic trigger and suppress the potential of normal lymph node cells to secrete IL 2 in co-culture assays. This suppression is promptly restored by the addition of indomethacin, which blocks prostaglandin synthesis, but is not markedly affected by the addition of catalase, which degrades H2O2. The suppression of the IL 2 receptor expression, on the other hand, is not restored by the addition of indomethacin, nor by the simultaneous supply of both indomethacin and catalase. This discrepancy is not caused by an extreme susceptibility of the receptor expression to low prostaglandin (PG) concentrations, but rather by the presence of suppressive cells that operate through a PG-independent mechanism. This suppressive mechanism accounts for the loss of the IL 2 receptors on both the Ly-2+ and the L3T4+ T cell compartment. The indomethacin-treated co-cultures, which manifest a normal IL 2 production but lack the IL 2 receptors, manifest an impaired DNA synthesis and contain a decreased number of T cell blasts.

Virgin and memory T cells have different requirements for activation via the CD2 molecule

T cells can be divided into unprimed virgin (T0) and primed memory (T') subpopulations by their expression of different isoforms of the leukocyte common antigen. We have separated the CD4+ T cells into T0 and T' subpopulations and examined their capacity to respond to activation signals via the CD2 receptor molecule. On stimulation with a mitogenic combination of anti-CD2 antibodies, the T' population was induced to express IL-2 receptor, increased levels of the 4F2 antigen and to proliferate, whereas the response of the T0 populations was reflected solely by a minimal increase in the 4F2 antigen. The addition of IL-2 or monocytes to T0 cells stimulated with anti-CD2 antibodies did not enhance their expression of the IL-2 receptor or proliferation. However, T0 cells stimulated with the triad of anti-CD2 antibodies, monocytes, and IL-2 responded with high levels of IL-2 receptor expression and proliferation. The T0 subpopulation could also be induced to respond when cultured with anti-CD2 antibodies and phorbol myristate acetate. The results suggest that in order to respond to stimulation via the CD2 molecule, virgin T helper cells require additional signals that can be jointly provided by monocytes and IL-2. In contrast, memory T helper cells can be activated via CD2 signal transduction alone.

Short-term somatostatin infusion affects T lymphocyte responsiveness in humans

Peripheral blood lymphocytes (PBL) function was analysed in 16 young men with duodenal ulcers after one-hour intravenous infusion of somatostatin (SMS) at a dose of 250 micrograms/h. Proliferative responses of PBL from SMS-treated patients were significantly diminished compared with pre-treatment values, after stimulation with PHA, PWM or Con A. Spontaneous IL-2R expression was moderately increased after SMS infusion but PHA-induced IL-2R expression was not affected by this drug. Alloantigen and autoantigen stimulation of PBL showed no significant changes in the proliferative response after SMS infusion. NK cell activity was similarly unaffected. These observations establish a link between SMS exposure and possible development of immune dysfunction.

Functional consequences of monocyte IL-2 receptor expression. Induction of IL-1 beta secretion by IFN gamma and IL-2

The generation of an immune response involves the interaction of monocytes and T cells, but the events which regulate this interaction are not well understood. Culture of human peripheral blood monocytes in vitro induces low level surface expression of the p55 protein of the IL-2R and the expression of this receptor can be enhanced significantly by exposure to IFN-gamma. The addition of IL-2 to IFN-gamma-treated monocytes was shown to augment subsequent IL-1 beta secretion in the presence or absence of LPS. These effects could be partially blocked by anti-p55-IL-2R mAb. Nuclear "run on" assays and Northern analysis to probe for IL-1 beta transcripts showed enhanced IL-1 beta gene transcription and mRNA accumulation by monocytes treated with IFN-gamma and IL-2 but not in cultures that were obtained from monocytes treated with IL-2 alone. These results suggest that the T cell lymphokines IFN-gamma and IL-2 may act in a sequential fashion on monocytes to amplify the immune response by establishing a positive feedback circuit.

Cyclosporin A mediated immunosuppression in vitro: effect on high affinity interleukin-2 receptor expression and -turnover

The effect of in vitro administration of Cyclosporin A (CsA) during mitogen, antigen and alloantigen activation of human T-lymphocytes on high affinity interleukin-2 (IL-2) receptor expression and -turnover and IL-2 production was investigated. The presence of CsA reduced 3H-thymidine incorporation and binding of radiolabelled human recombinant (ala125) IL-2 to high-affinity receptors in a dose-dependent fashion, although a pronounced inter- and intra-individual variation in sensitivity to CsA mediated immunosuppression was observed. Maximum inhibition was obtained when antigen and CsA were added to culture medium simultaneously. Preincubation with CsA did not influence the response. Although the number of IL-2 receptors was reduced, the turnover of the remaining high affinity IL-2 receptors on CsA treated cells was unaffected. Thus, binding, internalization and degradation were qualitatively unaltered by CsA administration. Finally, T cell activation in the presence of CsA reduced radioimmuno detectable IL-2 in cell culture supernatants to about 20%. CsA, added during antigen activation, reduced the number of Tac antigen presenting cells, but anti-Tac was unable to detect variations in the expression of high affinity IL-2 receptors. The present data indicate that CsA mediates immunosuppression by affecting early events during T-cell activation, and that variations in high affinity IL-2 receptor expression and IL-2 production are secondary to this affection.

Effect of dexamethasone on mechanisms responsible for regulation of polyclonal B-cell response

The effect of dexamethasone (Dex) on the differentiation of pokeweed mitogen (PWM), or Staphylococcus aureus Cowan I (SAC)-stimulated human peripheral blood mononuclear cells (PBMC), into immunoglobulin secreting cells (ISC) was studied with special emphasis on the regulatory role of IL-2 in these systems. Dex, known to reduce endogenous IL-2 production and expression of IL-2 receptors, reduced the proliferation of pokeweed mitogen-activated T-cells, and the proliferation was restored by exogenous recombinant interleukin 2 (rIL-2). Furthermore, Dex enhanced in PWM and in SAC-stimulated cultures, the number of ISC. Addition of rIL-2 resulted in a further increase of ISC in SAC-stimulated cultures, whereas in PWM-stimulated cultures the enhancing effect of Dex was reversed. When IL-2 receptors were blocked by a monoclonal anti-IL-2 receptor antibody rIL-2 was no longer suppressive. Addition of monocytes to PWM-stimulated cultures resulted in suppression or the number of ISC, which was even more pronounced when monocytes were pretreated with rIL-2. In contrast to ISC, neither a suppressive effect of rIL-2 nor an enhancing effect of Dex was observed when PWM-stimulated cultures were evaluated for cells with intracytoplasmic immunoglobulin (plasma cells). From these results we conclude that Dex, by blocking IL-2 production and receptor expression, interferes with IL-2 mediated induction and/or activation of suppressor mechanisms.

Restricted expression of mitogen-induced high affinity IL-2 receptors in aging mice

Several lines of indirect evidence suggest that the number and/or affinity of IL-2R expressed by activated T lymphocytes declines with age and that this decline is implicated in the age-related proliferative impairment of Ag or mitogen-stimulated T cells. In an attempt to provide a direct demonstration of such a defect, various experimental approaches were used to analyze the expression of high and low affinity IL-2R as well as their functional properties in relation to age in purified populations of murine T lymphocytes. IL-2R were induced by Con A-activation which involves a transmembrane signaling mechanism or by exposure to phorbol dibutyrate (PDBu) which bypasses such a pathway. Consistent with the previously reported age-related defect in signal transduction, a major deficiency in the expression of high affinity IL-2R was observed in mitogen-activated cells derived from aged animals. As expected, PDBu-induction circumvented the transmembrane signaling defect and resulted in the restoration of a measurable amount of high affinity IL-2R expressed by cells from aged mice early after activation. The functional properties of the IL-2R expressed as a consequence of Con A or PDBu induction were investigated by assessing the proliferative response induced through the high affinity IL-2R as compared to that mediated by the beta-chain alone. Although Con A-induction resulted in a decreased expression of high affinity IL-2R by T lymphocytes derived from aged mice, the ability of these receptors as well as that of their beta-chain component to transmit a proliferative signal was identical in both age groups. In contrast, PDBu induced in both cell populations the expression of functionally aberrant IL-2R, unable to signal for proliferation unless excessively high concentrations of rIL-2 were available. The quantitative minimal estimate of the frequency of Con A-activated, IL-2-responsive cells showed a fourfold age-associated decrease, confirming the inability of a subpopulation of T lymphocytes from aged mice to express a sufficient density of high affinity IL-2R as a consequence of mitogenic activation.

IL-2-PE40 is cytotoxic for activated T lymphocytes expressing IL-2 receptors

IL-2-PE40 is a chimeric molecule in which IL-2 is attached to the amino end of modified Pseudomonas exotoxin molecule lacking cell recognition domain. This molecule was extremely toxic for Con A-stimulated spleen cells from mice. Moreover, IL-2-PE40 has suppressive effect against Ag-activated cells; it inhibits the generation of cytotoxic T lymphocyte activity in a MLC. IL-2-PE40 could be a useful agent in IL-2R targeting therapy including immunosuppressive therapy for allograft rejection or some autoimmune diseases.

Molecular analysis of the dissociation between IL-2 production and proliferation in a response of a T cell clone to the antigen presented by B cells

Using B cells as APC, antigen specific responses of two murine T cell clones, 34-7F and 35-8H, were analyzed. 34-7F cells produced IL-2 but failed to proliferate, whereas 35-8H cells both produced IL-2 and proliferate. The antigenic stimulation increased intracellular free Ca2+ concentration in both clones, but enhanced inositol phospholipid metabolism only in 35-8H cells. The treatment of 34-7F cells with PMA, an activator of protein kinase C, synergized with the antigenic stimulation to induce the proliferation of the T cells. Thus, the failure of 34-7F cells to proliferate in the Ag response appears to result from the absence of an increase in inositol phospholipid metabolism. The absence is likely due to the defect in B cells as APC, inasmuch as the antigenic stimulation of 34-7F cells with whole spleen cells induced increases in inositol phospholipid metabolism and proliferation. The PMA treatment synergized with the Ag on B cells to enhance IL-2R expression, which was not inhibited by the addition of nifedipine, a calcium channel blocker. The agent inhibited the IL-2 production. Taken together, the results in the present experiments suggest the association of IL-2 production with increases in intracellular free Ca2+ concentration but not in inositol phospholipid metabolism, and that of IL-2R expression with increases in the metabolism but not in intracellular free Ca2+ concentration.

Changes in gene expression associated with IFN-beta and IL-2-induced augmentation of human natural killer cell function

NK function can be augmented by a variety of agents, including the cytokines IL-2 and IFN. The mechanisms associated with IL-2- and IFN-mediated augmentation of NK function are largely unknown. In order to learn more about the regulation of NK activity, we have studied changes in gene expression that occur upon treatment of a cloned line of NK cells (NK 3.3) with rIL-2 and rIFN-beta. Both IL-2 and IFN-beta induced rapid augmentation of lysis mediated by NK 3.3, which was significant within 1 h, peaked at 6 h of treatment, and declined by 12 h. This enhancement of lytic function was independent of proliferation and associated with a corresponding increase in steady state levels of RNA coding for both the nuclear proto-oncogene c-myb and for the IL-2R. These changes were specific in that RNA levels of another nuclear proto-oncogene, c-myc, were increased by IL-2 but not by IFN-beta, whereas HLA class I RNA levels were relatively unchanged by either IL-2 or IFN-beta treatment. Treatment of NK 3.3 with the combination of IL-2 and IFN enhanced both lysis and c-myb expression in an additive fashion. These findings suggest that c-myb may play a regulatory role in the cytolytic activity of NK cells.

Isoprinosine potentiation of human peripheral blood mononuclear cell response to mitogens: kinetics and effect on expression of the IL-2 receptor and the activity of interleukin 2

Isoprinosine, a synthetic purine derivative, enhanced the proliferative response of peripheral blood mononuclear cells to the lectin phytohaemagglutinin, and to the monoclonal antibody OKT3. The drug did not potentiate the activation of cells following oxidation by sodium periodate. Isoprinosine had no effect on the expression of receptors for interleukin-2. Increased interleukin-2 activity was detected in three out of nine supernatants from PHA activated mononuclear cells which were cultured in the presence of isoprinosine. Kinetic experiments involving addition or removal of the drug at various time intervals indicated that potentiation of the proliferative response required the presence of the drug at both early and late stages of cell activation. Inhibition of mononuclear cell activation by cyclosporine A was not affected by isoprinosine. These results suggest that enhancement of mononuclear cell proliferation by isoprinosine involves events in both early and late stages of the activation cycle.

IL-4 bypasses the immune suppressive effect of cyclosporin A during the in vitro induction of murine cytotoxic T lymphocytes

We have analyzed at the clonal level the effect of IL-4 on the immune suppressive action of cyclosporin A (CsA) during the in vitro primary activation of anti-MHC alloantigen-reactive murine CD8+ CTL. Although neither IL-4 nor IL-2 alone were able to overcome the CsA-mediated suppression, the addition of IL-4 in the presence of IL-2 restored in a dose-dependent manner the induction of cytolytic activity. On the other hand, CsA greatly impaired proliferative responses of alloantigen-reactive CD8 T cells, thereby operationally dissecting proliferative responsiveness from acquisition of cytolytic activity during primary activation of alloantigen-reactive CD8+ T cells. The existence of a CsA-resistant induction pathway for Ag-specific CD8+ T cell-mediated cytolytic activity may be of relevance for experimental and clinical organ transplantation.

Two different molecular pathways account for low IL-2 receptor and c-myc mRNA expression by lpr Lyt-2- L3T4- T cells

We have previously shown that Lyt-2- L3T4- T cells from the lymph nodes of MRL/lpr/lpr mice could respond to 12-O-tetradecanoylphorbol-2-acetate (TPA) and A23187 by proliferation, IL-2 secretion, and IL-2R (IL-2R) expression. However, the optimal response was significantly less than that of normal T cells. To understand the molecular mechanisms underlying the relatively inert nature of these cells, the expression of the T cell early competence genes, IL-2R and c-myc, was examined by Northern blot analysis and nuclear run-on assays. In resting lpr Lyt-2- L3T4- T cells, IL-2R mRNA was not detected, whereas the expression of c-myc mRNA was slightly enhanced compared to that of normal T cells. TPA and A23187 synergistically induced both IL-2R and c-myc mRNA expression by the lpr Lyt-2- L3T4- T cells, as well as by normal T cells. However, the amounts of specific mRNA induced in the former were much less than those in the latter. Cycloheximide treatment caused the TPA/A23187-stimulated lpr cells to express large amounts of c-myc mRNA, but not IL-2R mRNA. The deficient expression of c-myc and its correction by cycloheximide treatment were also observed in Con A-stimulated lpr Lyt-2- L3T4- T cells. Run-on transcription assays revealed that the enhancing effect of cycloheximide was most likely at the posttranscriptional level. These findings suggest that two separate mechanisms differentiated by their sensitivity to cycloheximide can inhibit the accumulation of mRNA for early competence genes in lpr Lyt-2- L3T4- T cells. These mechanisms may prevent the full activation of the lpr T cells and lead to abnormal differentiation of these cells.

Effect of a single intravenous dose of verapamil on some immune parameters in duodenal ulcer patients

The effect of a single intravenous dose of calcium channel blocking agent verapamil (VER) on immune parameters in humans remains uncertain. In this study the effects of VER on lymphocyte subpopulations, interleukin 1 (IL-1) and 2 (IL-2) production in vitro, autologous mixed lymphocyte reaction (AMLR), IL-2 receptor expression (Tac positive cells) and natural killer (NK) cell activity were assessed. The investigations were undertaken on 12 hospitalized men, aged 19-23 years, with small abdominal complaints. None of them had active duodenal ulcer disease, while in the remaining no signs of organic disease were found. VER was given intravenously in a dose of 0.15 mg/kg and examinations were performed on peripheral blood mononuclear cells (PBL) drawn before and 30 and 150 min following VER injection. The single VER dose induced a significant, but transient increase in T, T helper, T suppressor lymphocytes and monocytes, and decrease in IL-1 and IL-2 generation as well as diminished Tac antigen expression. These data provide evidence that calcium channel blockers may transiently disturb immunoregulation.

Multiple sclerosis: effect of myelin basic protein on interleukin 1, interleukin 2 production and interleukin 2 receptor expression in vitro

The production of interleukin 1 (IL-1) and interleukin 2 (IL-2) by peripheral blood mononuclear cells (PBMC) stimulated with human myelin basic protein (MBP) was assessed in vitro in multiple sclerosis (MS) patients in relapse, patients with other neurological diseases (OND) and healthy subjects. Myelin basic protein significantly increased both IL-1 and IL-2 production by PBMC from MS patients during relapse when compared to OND patients or healthy controls. The most efficient concentration of MBP for the induction of IL-1 and IL-2 was 50 micrograms/ml. The optimal IL-1 production occurred after 48 h of PBMC culture and optimal IL-2 production after 72 h of PBMC culture. Anti-Tac monoclonal antibody (MoAb) was used to study IL-2 receptor expression on the same sample of PBM used for IL-2 study in MS patients in relapse. In addition IL-2 receptor expression was studied in PBMC from chronic progressive MS patients. In both MS groups IL-2 receptor expression on PBMC stimulated with MBP appeared higher than in control groups, but these differences were not statistically significant. IL-2 receptor expression on cerebrospinal fluid lymphocytes (CSF-L) either unstimulated or MBP-stimulated was, however, significantly higher in both MS groups when compared to OND patients. These results confirm the presence of activated lymphocytes in the CSF of MS patients during active stages of disease and suggest that this activation may be related to expansion of MBP specific cells.

Evidence that 8-methoxypsoralen (8-MOP) is a T-lymphocyte immunomodulatory agent

This study was designed to characterize the effects of the anti-psoriatic compound 8-methoxypsoralen (8-MOP) on human lymphocyte function in vitro. Normal human peripheral blood mononuclear cells were stimulated with an optimal (1%) or a suboptimal (0.05%) concentration of phytohemagglutinin (PHA). At the optimal concentration of PHA, 8-MOP (140 microM) caused a delay in lymphocyte proliferation, interleukin-2 (IL-2) production/accumulation and IL-2 receptor expression. Addition of exogenous IL-2 to cultures stimulated with an optimal concentration of PHA did not overcome the delay of lymphocyte proliferation and IL-2 receptor expression. At the suboptimal concentration of PHA, 8-MOP (140 microM) caused a sustained inhibition of lymphocyte proliferation, IL-2 production/accumulation and IL-2 receptor expression. Addition of exogenous IL-2 under these conditions restored the magnitude of lymphocyte proliferation and IL-2 receptor expression. However, the responses displayed the delayed lymphocyte proliferation and IL-2 receptor expression typical of cells incubated with 8-MOP and an optimal concentration of PHA.