Cyclic nucleotides in mitogen-induced lymphocyte proliferation

Stress and reactivation of latent herpes simplex virus: a fusion of behavioral medicine and molecular biology

Since 1978, the study of health and behavior has become a major focus of scientists in psychology, psychiatry, nursing, neuroscience, and in traditional medical science disciplines. Investigation of psychological or behavioral influences on biological systems has established that biobehavioral processes such as stress play an important role in disease processes. An excellent example of the interactions between stress and health outcomes is the reactivation of latent herpes simplex virus (HSV) leading to recurrent lesions. This article describes what is currently known about HSV latency and reactivation and considers some mechanisms by which stress-induced changes in the host's immune and nervous systems might allow for either the establishment or reactivation of latent viral infections.

Impaired cytosolic free calcium response in splenic T-cells from mice fed with ethanol-containing diet

Calcium-dependent signal transduction pathways of T-cell proliferation have been extensively studied in the past years. However, little is known about effects of ethanol on the calcium-dependent signal transduction pathway in T-cell proliferation. Thus, a murine model was used to determine effects of ethanol in vivo on T-cell proliferation and the intracellular free calcium concentration [Ca2+]i in response to Concanavalin A (Con A) and recombinant IL2 (rIL2) in T-cells. Splenic cells from young C57BL/6 mice, that had been fed on 3 different diets (ethanol-, maltose substitute- and standard liquid-diet) for 7-8 weeks were tested for their proliferative responses to Con A and rIL2. Concurrently, measurement was also made of [Ca2+]i in the nylon-wool-enriched resting T-cells induced by Con A and in Con-A-activated blast T-cells induced by rIL2. Our results showed that [Ca2+]i increases were seen in the splenic T-cells from three different groups of mice following Con A, but not rIL2 stimulation. However, this increase was much smaller in the splenic T-cells from ethanol-fed mice as compared to mice on maltose- or standard-diet. Furthermore, we also demonstrated that the impaired [Ca2+]i increase was seen in the T-cells of the same ethanol-fed mice having decreased the proliferative response to Con A. This reduced proliferation did not result from the presence of excessive suppressor T-cell activity. Finally, we also demonstrated that both the number of IL2 binding sites/cell and the Kd values of the low- and high-affinity IL2R on the T-cells from ethanol-fed mice were unaltered. Because evidence indicates that (1) a normal level of [Ca2+]i increase is a prerequisite for the production of IL2 by mitogen-stimulated T-cells, and (2) T-cells from ethanol-fed mice have normal capacities to produce IL2 that is the crucial growth factor controlling T-cells to progress through the cell cycle, these lines of evidence taken together with the results of this study suggest that the impairment in [Ca2+]i increases in T-cells from ethanol-fed mice may not be the primary factor contributing to the diminished T-cell proliferation in the same mice.

Regulation of interleukin-2 responses by phosphatidic acid

Interleukin-2 (IL-2) plays a central role in the immune system by regulating the proliferation and differentiation of T lymphocytes. However, the molecular mechanism of the signal transduction through the IL-2 receptor is poorly understood. We have studied the role of phosphatidic acid (PA) on IL-2 signal transduction using cloned T lymphocytes. IL-2 stimulated a transient increase in the PA concentration in resting CTLL-2 cells prelabeled with [3H]palmitic acid. This effect was detected as early as 1 min after IL-2 addition and peaked at 5 min. IL-2 similarly increased phospholipase D activity in intact CTLL-2 cells, as inferred by phosphatidylethanol production. By contrast, IL-2 did not affect [3H]palmitic acid-labeled diacylglycerol levels. Furthermore, exogenous addition of several natural or synthetic PA to T cells mimicked IL-2 activity. Thus, PA were able to induce DNA synthesis on CTLL-2 cells, although this effect was only 10%-20% of that observed with IL-2. PA showed a synergistic effect with low doses of IL-2. In addition, PA was able to induce c-myc RNA transcription in CTLL-2 cells as well as IL-2 receptor (CD25) expression on the cell membrane with equal potency as saturating doses of IL-2. It is likely that IL-2-induced PA accumulation is a consequence of phospholipase D activation. This hypothesis is further supported by the fact that the addition of exogenous phospholipase D but not phosphatidylinositol-specific phospholipase C also reproduced the IL-2 or PA effects mentioned above. In summary, our results suggest a role of phospholipase D activation and PA formation as second messengers of IL-2 activity.

Effect of LTB4 on the inhibition of natural cytotoxic activity by PGE2

NK activity is regulated by arachidonic acid metabolites. More precisely PGE2 and LTB4 decreases and increases respectively non-MHC-restricted cytotoxicity in humans. We have observed similar data in mice since NK activity was inhibited by PGE2 (10(-6) to 10(-8) M) and enhanced by LTB4 (10(-8) to 10(-12) M). On the other hand when PGE2 and LTB4 were combined during the same assay the lysis percentage was smaller than the one which was induced by PGE2 alone. Because PGE2 increases intracellular cyclic AMP and that LTB4 augments cyclic GMP we used a cAMP inducer (forskolin) and a cGMP analogue (8 Br-cGMP) instead of eicosanoids and we observed similar data (i.e., a decrease of natural killing) as when PGE2 was combined with LTB4. When splenocytes are cultured for 1-4 days alone, cytotoxic activity decreases unless they are cultured in the presence of indomethacin. Cytotoxic activity of spleen cells cultured in the presence of PGE2 or LTB4 is respectively decreased or increased. However, splenocytes that were cultured alone for at least 24 hr were no longer sensitive to inhibition by PGE2 but were still PGE2-sensitive when cultured in the presence of LTB4.

Inhibitory effect of thyrotropin releasing hormone on spontaneous proliferation of mouse spleen lymphocytes in vitro

The effects of thyrotropin releasing hormone (TRH) and of TRH-like tripeptide pGlu-His-Gly-OH (colon mitosis inhibitor, CMI) on spontaneous proliferation of murine splenocytes were investigated in vitro. The 3H-thymidine incorporation into splenocyte DNA was used as an index of proliferation. It was found that TRH suppressed the proliferation of splenocytes. In contrast, CMI was ineffective by itself but used together with TRH blocked the effect of the latter.

The effect of nerve growth factor on DNA synthesis, cyclic AMP and cyclic GMP accumulation by mouse spleen lymphocytes

Nerve growth factor (NGF), a trophic neuropeptide, is known to stimulate development, and to be important in the maintenance and survival of sympathetic and sensory neurons. Considering the presence of specific receptors on the surface of spleen cells, the effect of 2.5s nerve growth factor on 3H-thymidine uptake, cAMP and cGMP accumulation in mouse spleen lymphocytes has been studied. It was found that NGF added in vitro at the concentrations between 4 x 10(-7) and 4 x 10(-8) M significantly inhibited the incorporation of 3H-thymidine into lymphocytes DNA and increased cAMP levels in a dose-dependent manner but had no effect on cGMP levels. The maximal stimulation of cAMP synthesis occurred between 5 and 30 min after the NGF addition to the culture medium. When NGF was administered in vivo a significant dose-dependent inhibition of the lymphocytes proliferation was observed. These results indicate that an early increase of cAMP concentration is responsible for the antiproliferative action of NGF on mouse spleen lymphocytes and suggest that NGF could play an important role in the regulation of immune system function.

Early induction of ornithine decarboxylase occurs simultaneously with inositol phosphate accumulation in concanavalin A-stimulated rat thymocytes

Stimulation of rat thymocytes with the lectin ConA produced an early peak of ornithine decarboxylase (ODC) activity within 10 min. This ODC induction appeared as early as the well-known inositol phosphate accumulation following mitogenic stimulation, and may be part of the signal transduction mechanism. The distribution of counts among the inositol phosphates was constant during the overall time of Concanavalin A (ConA) stimulation. We conclude that early induction of pre-existing ODC may be independent of protein kinase C action.

Influence of PGE2- and cAMP-modulating agents on human glioblastoma cell killing by interleukin-2-activated lymphocytes

Human glioblastoma cells secrete factors, such as prostaglandin E (PGE) and transforming growth factor beta type 2, which are capable of suppressing several immune functions. The present study investigated the effect of PGE2 and agents known to increase intracellular cyclic adenosine monophosphate (cAMP) levels on 1) the induction of lymphokine-activated killer (LAK) cell activity from the peripheral blood lymphocytes (PBL) of both normal and glioma patients and on 2) the cytolytic activities of tumor-infiltrating lymphocytes (TIL's) isolated from malignant gliomas after expansion in vitro with interleukin-2 (IL-2). Cytolytic activity was measured against autologous and allogeneic tumor cells and the natural killer-resistant Daudi cell line. The results demonstrate that PGE2 and agents known to increase intracellular cAMP levels can significantly suppress the IL-2-dependent generation of cytolytic activity from the PBL of normal and glioma patients and from glioblastoma-derived TIL's. The inhibitory effects of these agents could not be reduced by higher concentrations of IL-2 or by cyclic guanosine monophosphate. Although the suppressive effect of PGE2 was most significant during the early stages of LAK cell generation, an inhibitory effect was still evident when PGE2 was added directly to the cytotoxicity assay. Secretion of PGE2 by glioblastoma cells in vivo may regulate both the generation of an immune response and the effectiveness of adoptively transferred immune cells.

The pathogenesis of cianidanol-induced fever

Recently, there has been a variety of reports of adverse drug reactions during therapy with the flavonoid Cianidanol (Ci), a cytoprotective radical scavenger, especially involving haemolytic anaemia and drug fever. To elucidate whether the fever was due to a direct, antigen-independent interaction of Ci with immune competent cells, its effect on macrophage (M phi) function and early biochemical events during lymphocyte activation has been examined. A direct interaction of Ci with M phi was demonstrated, resulting in increased secretion of interleukin-1 (IL-1). The influence of Ci on lymphocyte activation was assessed by measuring levels of cyclic AMP and GMP. At high concentrations of Ci, cAMP levels were increased, and at low Ci concentrations cGMP levels were elevated. Both findings are correlated with lymphocyte proliferation and function, which is increased at low and decreased at high concentrations of Ci. The synthesis of prostaglandin E2 by M phi, an important factor in M phi-mediated suppression, was reduced by increasing doses of Ci, which inhibited M phi-cyclooxygenase. Ci did not affect phospholipase A2 activity. These findings indicate that flavonoid-induced fever may be due to allergic as well as pseudo-allergic mechanisms, the latter probably caused by increased antigen-independent release of IL-1, the endogenous mediator of fever.

A study of cyclic nucleotides as second messengers after interleukin 2 stimulation of human T lymphocytes

Interleukin 2 (IL-2) was shown to induce a small but significant increase in the level of cGMP after 20 min stimulation and a subsequent fall after 1 h in activated T lymphocytes. No change in the level of cAMP was observed. Addition of the cyclic nucleotide analogues dbcAMP or dbcGMP did not stimulate DNA synthesis. On the contrary, IL-2-induced [3H]thymidine incorporation was inhibited by these drugs. Further, the phosphodiesterase inhibitor theophylline inhibited proliferation of activated T lymphocytes. Our results indicate that neither cAMP nor cGMP act as 'second messengers' for IL-2 but support the theory that cAMP is a negative regulator of cell proliferation.

Immunomodulatory action of somatostatin

The influence of somatostatin (SST) on spontaneous proliferation and cyclic AMP level in mouse spleen lymphocytes and on inhibition of human leukocyte migration was studied. The rate of [3H]thymidine incorporation was used as an index of proliferation. It was found that lower concentrations of SST/10(-9) and 10(-8)M, inhibited the splenocyte proliferation. In contrast, a higher SST concentration, 10(-7)M, exerted a stimulatory effect. SST in concentrations from 10(-9) to 10(-6)M did not influence cyclic AMP levels in mouse splenocytes; a significant decrease of cyclic AMP was found after the exposure to superactive SST analog RC-102-2H in concentrations 10(-8) and 10(-7)M. SST, 10(-7)M, and RC-102-2H, 10(-7)M, significantly enhanced the migration inhibition of human leukocytes induced by the exposure of leukocytes to cardiac antigen or phytohemagglutinin. The data provide evidence for an immunomodulatory action of SST.

Modulation of human concanavalin A-induced lymphocyte proliferative response by physiological concentrations of beta-endorphin

The effects of physiological concentrations of beta-endorphin on the proliferative response to concanavalin A of human peripheral blood mononuclear cells from a large series of healthy donors are reported. These effects are also compared with those obtained employing beta-endorphin and phytohemagglutinin under the same experimental conditions. The donors (32), aged between 20 and 48 years, chosen among military personnel of the Italian Air Force, underwent clinical and laboratory investigations to exclude any detectable disturbance in their psychophysical fitness. Our results show that beta-endorphin is not mitogenic per se and is unable to modify the response of mononuclear cells to phytohemagglutinin irrespective of the concentration of opioid or mitogen used. beta-Endorphin is also unable to alter the PBMC response to low concentrations of concanavalin A, but significantly increases such a response when higher concentrations of concanavalin A and concentrations of beta-endorphin similar to those found in human plasma under physiological conditions are used. The effect is not reverted by naloxone, the specific opiate antagonist. When the activity of beta-endorphin on the mononuclear cell response to concanavalin A is examined at the single donor level, it is noted that some of the donors fail to show the opioid-dependent increase. The baseline levels of the response to concanavalin A of such subjects, compared to those of the donors whose response is augmented by the opioid, are significantly higher, thus demonstrating that beta-endorphin can selectively modulate concanavalin A-induced mitogenesis with a behavior depending on the individual characteristics of the donor's response. The process involves non-opioid cell receptors.

Phosphatidylethanolamine methyltransferase and cAMP, cGMP phosphodiesterases in lymphocytes and monocytes in sarcoidosis

Among the various hypotheses proposed to explain immune cell defect in sarcoidosis, we examined thoroughly that of Faguet who described abnormalities of signal transmission at lymphocyte membrane level. Phosphatidylethanolamine methyltransferase and cAMP cGMP phosphodiesterases were studied in blood lymphocytes and monocytes from 8 subjects with sarcoidosis disease. Phosphatidylethanolamine methyltransferase (PMT1) plays an important regulatory role in membrane signal transmission. cAMP and cGMP phosphodiesterases (PDE) regulate cytoplasmic cyclic nucleotide levels and so participate in the modulation of the cell cycle. We observed a decreased PMT1 activity in lymphocytes and monocytes and a decreased cAMP and cGMP PDE activities in monocytes. It is not now possible to say if these abnormalities are primary or secondary. Whatever the origin of this dysfunctioning, these results evoke simultaneous disturbances of membrane signal transmission and cell cycle in monocytes and membrane abnormalities in lymphocytes. These abnormalities could explain some immune cell defects in sarcoidosis disease.

Interleukin II increases cyclic GMP levels in immature thymocytes and mitogen-primed T-lymphocytes

Interleukin II, also called T-cell growth factor, induces proliferation of immature peanut agglutinin positive murine thymocytes (PNA+) and renders them responsive to concanavalin A. It also, as shown by others, provides a second signal to induce phytohemagglutinin-primed mature human T-lymphocytes to enter DNA synthesis. Both actions are associated with early increases (2-60 min) in cellular levels of cyclic 3'5' guanosine monophosphate (cyclic GMP) without change of cyclic 3'5' adenosine monophosphate (cyclic AMP) levels. Cyclic GMP is postulated to represent part of the mechanism by which IL-2 acts.

Potentiation of interleukin-2 activity by levamisole and imidazole

Levamisole, a known antihelminthic drug, was able to affect IL-2 dependent proliferation of several T lymphocyte clones. Although levamisole did not replace IL-2 and had no effect at saturating IL-2 concentrations, it reduced by 2- to 4-fold the dose of IL-2 required to give 50% of the maximal DNA synthesis, the optimal concentration of levamisole being between 1 to 3 X 10(-4) M. This effect of levamisole was not due to an alteration of the kinetics of thymidine incorporation. Imidazole and other imidazole ring containing compounds, but not thiol-containing compounds, had similar effects to those of levamisole, suggesting a role of the imidazole ring in the potentiation of IL-2 activity.

Effects of tri-n-butyltin chloride on energy metabolism, macromolecular synthesis, precursor uptake and cyclic AMP production in isolated rat thymocytes

The inhibitor of oxidative phosphorylation tri-n-butyltin chloride (TBTC) causes membrane damage and disintegration of isolated rat thymocytes at concentrations higher than 1 microM. From a concentration of 0.1 microM, TBTC disturbs energy metabolism as indicated by an increase in methylglucose uptake, glucose consumption and lactate production and by a decrease in cellular ATP levels. Over the same TBTC concentration range, the incorporation of DNA, RNA and protein precursors are markedly reduced. Moreover the production of cyclic AMP upon stimulation of the cells with prostaglandin E1 is effectively inhibited. These effects cannot be explained by an inhibition of nucleoside kinase activity, amino acid uptake or adenylate cyclase activity. The effects of TBTC on macromolecular synthesis and cyclic AMP production are possibly due to a disturbance of the cellular energy state.

Stimulation of 2',3'-cyclic nucleotide 3'-phosphodiesterase in human lymphocytes by Robinia pseudoacacia lectin

2',3'-Cyclic nucleotide 3'-phosphodiesterase (CNP) activity was studied in human peripheral blood lymphocytes. Incubation of human lymphocytes with optimum mitogenic concentrations of Robinia pseudoacacia lectin produced an increase in CNP activity. This increase was not detected before 24 h of incubation. Furthermore, whereas unfractionated lymphocytes exhibited activation of CNP, this was not observed in B and T cell subpopulations.

Influence of beta-endorphin on phytohemagglutinin-induced lymphocyte proliferation and on the expression of mononuclear cell surface antigens in vitro

Recent evidence suggests that opiates can modulate the immune responses. In particular it has been shown that beta-endorphin and morphine are able to depress some T lymphocyte functions in humans. In the present study, experiments were designed to evaluate the effect of beta-endorphin phytohemagglutinin-induced lymphocyte proliferation and determine the mechanism of this action. The ability of naloxone to block the effect of beta-endorphin was also investigated, and the influence of beta-endorphin on the expression of mononuclear cell surface antigens using the OKT3, OKT4, OKT8, anti-HLA-DR and anti-beta 2-microglobulin monoclonal antibodies was evaluated. Phytohemagglutinin-induced lymphocyte proliferation was significantly inhibited by beta-endorphin. This effect occurred when beta-endorphin was added to cells at the beginning of the culture period (30 min before, simultaneously or 30 min after phytohemagglutinin), but not when added after 48 h of incubation. The preincubation of cells with BEP for 1 h, 4 h or 24 h did not affect lymphocyte activation by phytohemagglutinin. A ten-fold excess of naloxone, added to cultures 30 min prior to beta-endorphin, did not block the inhibitory effect. Incubation with beta-endorphin had different effects on each surface antigen tested. The OKT8+ and beta 2-microglobulin+ cells did not show significant variations. The OKT4+ cells significantly decreased, after 4 h of incubation with beta-endorphin, both in mononuclear cell and in purified T lymphocyte cultures and, after 24 h, in mononuclear cell cultures only. The OKT3+ cells decreased, in mononuclear cell cultures only, after 24 h beta-endorphin incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Second messenger function of arachidonic acid lipoxygenation products in human natural killer cell lysis?

Human natural killer (NK) cells were tested in the presence of several fatty acid oxygenase inhibitors such as nordihydroguaiaretic acid (NDGA), 5,8,11,14-eicosatetraynoic acid, 3-amino-1-m-(trifluoromethyl)-phenyl-2-pyrazoline (BW 755C), and indomethacin. All drugs inhibited NK lysis at the post-target cell-binding level at concentrations that also suppressed lipoxygenation of arachidonic acid, suggesting that such reactivity may be required for effector cell triggering. NDGA gave a 50% NK cell inhibition in the range of 10-30 microM and also suppressed antibody-dependent and lectin-dependent systems. Further evidence of the involvement of arachidonic acid lipoxygenation was found as NK activity could be reconstituted to NDGA-suppressed effector cells with several metabolites such as LTB4, LTB4 analogues, and hydroxyeicosatetraenoic acids lipoxygenated at C-5, C-12, and C-15. Cyclic nucleotides such as cGMP and cAMP could also reconstitute activity with optimal effects at approximately 10(-8) M. The combined evidence is compatible with a model for triggering lysis in which lipoxygenation products have a second messenger function. Whether arachidonic acid lipoxygenation is necessary for effector cells at all different activation/differentiation stages and whether the lipoxygenation products activate guanylic cyclase, protein kinase C, or some other target molecule remain to be further investigated.

Products of the lipoxygenase pathway in human natural killer cell cytotoxicity

As earlier data suggested the importance of lipoxygenase activation for expression of human NK cell cytotoxicity, four different lipoxygenase inhibitors were tested for suppression of natural killer (NK) cell lysis. All inhibitors were found active at nontoxic concentrations with 50% inhibition at approximately 15 microM for nordihydroguaiaretic acid (NDGA). NK cell lysis could be reconstituted to NDGA-suppressed cells with leukotriene B4 (LTB4), the all-trans isomers 6-trans-LTB4 and 12-epi-6-trans-LTB4, and 20-COOH-LTB4. LTB4 reconstitution was best in the concentration range 1-100 pM and near control levels at both higher and lower concentrations. Herpesvirus Ateles-transformed killer T cells could also be inhibited by NDGA. These data indicate that lipoxygenase activity is required for human NK cell lysis and that several different LTB4-related products can restore NK activity in inhibited cells; they also suggest that the lipoxygenase pathway is present in the killer cell population.

Augmentation of cytotoxic responses by prostaglandin E2

The cytotoxic-T-lymphocyte activity in the spleen cells after in vivo immunization of C3H mice with allogeneic spleen cells ip was consistently very weak. Substantial cytotoxic responses were obtained, however, when prostaglandins (PGE2, PGE1, or PGI2) were injected ip together with or prior to the immunization. An augmentation of cytotoxic responses against allogeneic stimulator cells was also observed in mixed lymphocyte cultures which were provided with an interleukin 2-containing helper factor. This augmentation was observed when PGE2 was added at the start of the culture but not if added 1 day later. Indomethacin was found to be suppressive in these cultures.

Ethanol dependent interaction between prostaglandins and lipoxygenase products in human peripheral lymphocytes

The effect of lipoxygenase products, 12-L-HETE and 15-L-HPETE, on cyclic AMP levels in human peripheral lymphocytes was examined in the absence and in the presence of a prostaglandin of the E-type (0.6-3.0 microM) or isoprenaline (33 microM). The studies were performed either in the absence or in the presence of 6 per cent ethanol. For comparison the effect of arachidonic acid and linolenic acid were studied. In the absence of ethanol 12-L-HETE and 15-L-HPETE had no significant effect on cyclic AMP accumulation. However, in the presence of ethanol 12-L-HETE (above 1 microM) inhibited prostaglandin E1 but not isoprenaline induced cyclic AMP accumulation. 15-L-HPETE had a biphasic effect on prostaglandin E2 induced cyclic AMP accumulation. Concentrations below 1 microM stimulated, those above inhibited. Virtually complete inhibition was seen at 15 microM. The two other fatty acids inhibited both prostaglandin E2 and isoprenaline induced cyclic AMP accumulation in the presence, but not in the absence of ethanol. The results show that lipoxygense products have little or no effect on cyclic AMP accumulation in human peripheral lymphocytes unless ethanol is present. In the presence of ethanol both 12-L-HETE and 15-L-HPETE appeared to selectively affect the cyclic AMP accumulation stimulated by PGE.

Effect of verapamil on T-lymphocyte activation in vitro

Verapamil, a calcium-inhibitory drug, was found to inhibit T-lymphocyte proliferation in mixed lymphocyte culture and the proliferative response to phytohaemagglutinin and mumps antigen. It also inhibited production of interleukin 2 (IL-2). To exert inhibition, verapamil had to be added early in the culture period. Verapamil also had a relatively small inhibitory effect on IL-2-dependent growth. The effects were clearly seen only at concentrations exceeding the therapeutic serum level of verapamil.

Subchronic inhalation toxicity of isobutyl nitrite in BALB/c mice. II. Immunotoxicity studies

Initial epidemiologic studies of acquired immunodeficiency syndrome (AIDS) occurring in homosexual men identified the use of the inhalants amyl, butyl, and isobutyl nitrite as possible risk factors contributing to the disease. Because of the lack of immunotoxicological data on these chemicals, we studied the effects of subchronic exposure to isobutyl nitrite (IBN) on the immune system. BALB/c mice were exposed to either 50 or 300 ppm IBN for 6.5 h/d, 5 d/wk for up to 18 wk. After 7, 13, or 18 wk of exposure, mice were killed and the following assays were performed. Antibody producing cells were enumerated by a slide plaque assay on animals immunized with sheep red blood cells while still in exposure chambers. The lymphocyte proliferative response to mitogens (phytohemagglutinin, concanavalin A, pokeweed mitogen, and lipopolysaccharide) was tested using several concentrations of each mitogen. Additional mice were immunized with Freund's complete adjuvant 21 d prior to death and were tested for delayed hypersensitivity response to purified protein derivative by a radiometric skin test. Finally, the relative numbers of T cells and T-cell subsets among splenic lymphocytes from exposed and control animals were determined. At the time periods tested there were no discernable immunotoxic effects observed in the exposed animals in any of the assays performed. These results indicate that IBN, at the dosages tested, had no discernable detrimental effect on the immune system of mice.

The effects of cyclic nucleotides on the proliferation of cultured human T-lymphocytes

The effects of cyclic nucleotides on the proliferation of cultured T-lymphocytes (CTC) stimulated by either phytohemagglutinin (PHA) or lectin-free interleukin-2 (IL-2) were studied. The addition of either N6,O2-dibutyryl cyclic AMP (DB-cAMP), aminophylline or isoproterenol to CTC cultures significantly suppressed the proliferation of CTC stimulated by either PHA or IL-2. This inhibitory effect was maximal when added at initiation of the assay; however, significant depression was still observed when added 24 h later. When DB-cAMP and aminophylline were added together, the inhibitory effects were additive. When DB-cGMP was added to the CTC cultures, inhibition of both PHA- and IL-2-stimulated cultures was also found, but the degree of activity was considerably less than for DB-cAMP or aminophylline. In contrast, when carbachol was added, no inhibition or modulation in proliferation was seen. Lastly, DB-cGMP was not found to antagonize the inhibitory effect of DB-cAMP, but instead to further increase the level of inhibition. In summary, these studies illustrate that cyclic nucleotides modulate the proliferation of IL-2-stimulated CTC as well as PHA-treated cells. This model system should provide an approach to study, in more depth, the mechanism by which cyclic nucleotides or their inducers can modulate the latter stages of the lymphocyte proliferative response, which is mediated by the lymphokine, IL-2.

The effect of theophyllamine on T-lymphocyte activation in vitro

Theophyllamine in similar concentrations as the therapeutic serum level was found to inhibit the proliferative response in mixed lymphocyte cultures (MLC) and cultures stimulated with purified protein derivative of tuberculin (PPD). Theophyllamine inhibited interleukin 2 (IL-2) production of lymphocytes stimulated with phytohemaglutinin (PHA) and IL-2-dependent growth of T-cell lines, but had no effect on PPD pulsing of antigen-presenting cells.

Immunological aspects of psoriasis. VI. Impairment of isoprenaline and theophylline-induced inhibition of mitogen responsiveness

Pharmacological abnormalities occur in the psoriatic epidermis, and if similar abnormalities occur in the peripheral blood mononuclear cells they could impair the immune responses in psoriasis. In a paired control study, we have tested the capacity of histamine, isoprenaline and theophylline (10(-5) and 10(-7) M) to inhibit the mitogen responsiveness of blood mononuclear cells from normal and psoriatic subjects, using phytohaemagglutinin and concanavalin A. In the normal controls, mitogen responsiveness was inhibited by all three pharmacological agents by about 30 to 50%. In cells from psoriatic patients, the response in the presence of histamine was inhibited (as in the controls), but isoprenaline caused no inhibition, and theophylline paradoxically increased the mitogenic responses. These results suggest there is a defect in the pharmacological response of the blood mononuclear cells in psoriasis.

Chromatin structure and nucleic acid synthesis in human lymphocyte activation by phytohemagglutinin

Alterations in chromatin structure were explored as a function of time following phytohemagglutinin (PHA) activation of human lymphocytes. Nuclear refringency (related to chromatin status), ultrastructural changes, and modifications of nucleic acid synthesis were compared. Chromatin dispersion was observed within 20 min of stimulation, with a concomitant increase in [3H]uridine incorporation; both were inhibited by actinomycin D. Recondensation of chromatin had occurred at 60 min when RNA synthesis was still increasing. The early chromatin dispersion thus was a reversible step and one of the most striking cellular events during the first phase of PHA activation. Late chromatin dispersion of blastic cells during the second phase of PHA response (after 24 h) was related to DNA synthesis in mitotic cells. This step was also inhibited by actinomycin D. These results suggest a relationship between the morphological changes in chromatin structure and the induction of RNA and DNA syntheses. The regulation of transcriptional and replicational states of the nucleus is discussed in terms of modifications of chromatin structure, considering PHA-induced calcium and cyclic nucleotide metabolism and interleukin II receptor expression.

Conversion of arachidonic acid in human maternal and neonatal mononuclear leukocytes

The metabolism of exogenous [1-14C]arachidonic acid in neonatal and maternal peripheral mononuclear leukocytes was studied. Both neonatal and maternal leukocytes converted arachidonic acid to hydroxy acids and to prostaglandin E2, but small amounts of PGF2 alpha and thromboxane B2 were also found. In addition a polar arachidonic acid metabolite with conjugated double bonds was identified in the supernatant from both maternal and neonatal leukocytes. This might be a leukotriene, but further attempts at biochemical characterization are necessary in order to confirm this.