Differential regulation of IFN-gamma, IL-10 and inducible nitric oxide synthase in human T cells by cyclic AMP-dependent signal transduction pathway

JNK signaling involved in the effects of cyclic AMP on IL-1beta plus IFNgamma-induced inducible nitric oxide synthase expression in hepatocytes

cAMP significantly inhibits IL-1beta+IFNgamma-induced iNOS gene expression in hepatocytes, but the signaling pathways responsible for the effect are not known. PKA inhibitors, H89, PKI, and KT5720, had no effect on the recovery of the inhibitory effects of cAMP on cytokine-induced hepatocyte iNOS expression and activity. The JNK inhibitor, SP 600125, effectively reversed the inhibitory effects of cAMP on iNOS expression and significantly increased iNOS promoter activity. A cAMP analogue, dbcAMP, significantly induced JNK signaling and increased AP-1 binding activity in hepatocytes. The JNK activator, anisomycin, inhibited iNOS expression and transcription in hepatocytes as well as AP-1 binding activity; and SP600125 reversed this effect of anisomycin. Overexpression of c-Jun in hepatocytes inhibited IL-1beta+IFNgamma-induced nitrite accumulation and iNOS promoter activity while dominant negative c-Jun partially reversed the inhibitory effects of cAMP on nitrite accumulation. We conclude that JNK signaling plays an important role in the inhibitory effects of cAMP on IL-1beta+IFNgamma-induced iNOS gene expression in cultured hepatocytes.

Synthesis and evaluation of a fluorine-18 labeled antisense oligonucleotide as a potential PET tracer for iNOS mRNA expression

Inducible NO synthase (iNOS) is overexpressed in inflammatory bowel diseases. An antisense oligonucleotide with good hybridization properties for iNOS mRNA was selected using RT-PCR. The oligonucleotide was reliably labeled with fluorine-18 using N-(4-[(18)F]fluorobenzyl)-2-bromoacetamide. Cellular uptake and efflux of oligonucleotide complexed with FuGENE-6 were rapid, unlike naked oligonucleotide, which hardly accumulated. However, neither uptake nor efflux showed any selectivity for iNOS expressing cells. The oligonucleotide showed a high level of non-specific binding, which may have obscured its specific hybridization to iNOS mRNA.

Adenosine inhibits activation-induced T cell expression of CD2 and CD28 co-stimulatory molecules: role of interleukin-2 and cyclic AMP signaling pathways

Adenosine is an immunosuppressive molecule that is associated with the microenvironment of solid tumors. Mouse T cells activated with anti-CD3 antibody in the presence of adenosine with or without coformycin (to prevent adenosine breakdown by adenosine deaminase) exhibited decreased tyrosine phosphorylation of some intracellular proteins and were inhibited in their ability to proliferate and synthesize interleukin (IL)-2. In addition, adenosine interfered with activation-induced expression of the co-stimulatory molecules CD2 and CD28. Activation-induced CD2 and CD28 expression was also diminished when T cells were activated in the presence of anti-IL-2 and anti-CD25 antibodies to neutralize IL-2 bioactivity. Collectively, these data suggest that CD2 and CD28 up-regulation following T cell activation is IL-2-dependent; and that adenosine inhibits activation-induced T cell expression of CD2 and CD28 by interfering with IL-2-dependent signaling. The inhibitory effect of adenosine on activation-induced CD2 and CD28 expression could not be attributed to cyclic AMP (cAMP) accumulation resulting from the stimulation of adenylyl cyclase-coupled adenosine receptors, even though cAMP at concentrations much higher than those generated following adenosine stimulation was inhibitory for both CD2 and CD28 expression. We conclude that adenosine interferes with IL-2-dependent T cell expression of co-stimulatory molecules via a mechanism that does not involve the accumulation of intracellular cAMP.

Effects of histamine on Th1/Th2 cytokine balance

Atopic asthma is a chronic inflammatory disorder of the airways where upon exposure to allergens, the body mounts an immune response. This disease is associated with an increase in the number of Th2 (T helper type 2) cells and Th2 cytokines and a decrease in the number of Th1 (T helper type 1) cells and Th1 cytokines. Histamine plays an important role in the pathogenesis of atopic asthma through differential regulation of T helper lymphocytes. Histamine enhances the secretion of Th2 cytokines such as IL-4 (interleukin-4), IL-5, IL-10 and IL-13 and inhibits the production of Th1 cytokines IL-2 and IFNgamma (interferon-gamma) and monokine IL-12. It has been shown that histamine can modulate the cytokine network through upregulation of PGE(2) (prostaglandin E(2)) and NO (nitric oxide). Histamine also affects cytokine production via H2 receptors and through the activation of PKA (protein kinase A). We have also demonstrated that the Jak-STAT (Janus kinase-signal transducers and activators of transcription) pathway is involved in histamine-mediated regulation of Th2 cytokines IL-5, IL-10, IL-13 and Th1 cytokine IFNgamma. While standard treatment of asthma consists of beta-receptor agonists and inhaled corticosteroids, the elucidation of histamine's control over the cytokine network and the Th1/Th2 balance provides a basis for the potential use of antihistamines in the prevention and treatment of atopic asthma. Several other anti-allergic agents to modulate the Th1/Th2 balance are under current investigation based on this paradigm. These include cytokines, cytokine antagonists, anti-IgE, and vaccinations. As more advances are made in our understanding of histamine and its control over the Th1/Th2 balance, the use of new therapeutic targets such as these will play a prominent role in disease management.

Impaired secretion of IL-10 by T cells from patients with common variable immunodeficiency--involvement of protein kinase A type I

Common variable immunodeficiency (CVID) is a heterogeneous group of B cell deficiency syndromes. T cell abnormalities are present in a high proportion of patients with CVID, suggesting impaired T cell-mediated stimulation of B cells. Based on the importance of IL-10 for B cell function and the involvement of the cAMP/protein kinase A type I (PKAI) system in IL-10 synthesis, we examined IL-10 secretion in T cells from CVID patients and controls, particularly focusing on possible modulatory effects of the cAMP/PKAI system. Our main findings were: 1) anti-CD3 and anti-CD3/anti-CD28 activated T cells from CVID patients secreted less IL-10 than healthy controls. This defect was not related to varying proportions of T cell subsets (e.g., CD4(+)/CD8(+), CD45RA(+)/RO(+), or CD28(-) T cells); 2) PKAI activation through the cAMP agonist 8-CPT-cAMP markedly inhibited IL-10 secretion from T cells through CD3 and CD28 activation in both patients and controls, but the sensitivity for cAMP-dependent inhibition was increased in CVID; 3) selective PKAI inhibition by Rp-8-Br-cAMPS markedly increased IL-10 secretion in anti-CD3 and anti-CD3/anti-CD28-stimulated T cells in both patients and controls. Even at the lowest concentrations of Rp-8-Br-cAMPS, IL-10 secretion in CVID patients reached levels comparable to those in controls. Our findings suggest impaired secretion of IL-10 by T cells from CVID patients, suggesting a possible link between T cell deficiency and impaired B cell function in CVID. The involvement of the cAMP/PKAI system in this defect suggests a novel target for therapeutic immunomodulation in CVID.

Intact noradrenaline transporter is needed for the sympathetic fine-tuning of cytokine balance

Earlier studies demonstrated that cytokine production is under the tonic control of noradrenaline. As the level and/or the duration of noradrenaline action is regulated by the noradrenaline transporter (NET), which is also a target of antidepressant treatment, we studied its role in the regulation of the cytokine response during inflammation. The endotoxin-evoked tumour necrosis factor-alpha (TNF-alpha) and interleukin-10 response was studied in genetically produced noradrenaline transporter-deficient (NET-KO) mice and by treatment with desipramine, a monoamine uptake-blocker antidepressant. NET-KO mice responded to endotoxin with significantly lower TNF-alpha and interleukin-10 production in comparison to their wild-type counterparts. Functional involvement of both alpha- and beta-adrenoceptors could be demonstrated in our model systems, using 7,8-methylenedioxy-14 alpha-hydroxy-alloberbane.HCl (CH-38083) and propranolol; however, the differences between the two phenotypes remained, suggesting a limited role of alpha-adrenoceptors in the observed changes. Acute treatment of both wild-type and NET-KO mice with desipramine significantly decreased the TNF-alpha response and significantly increased interleukin-10 production, indicating the role of an intact noradrenaline transporter in anti-inflammatory responses.

In vitro effects of eicosanoids derived from different 20-carbon fatty acids on T helper type 1 and T helper type 2 cytokine production in human whole-blood cultures

BACKGROUND

Different series prostaglandins (PGs) and leukotrienes (LTs) are synthesized from different 20 carbon fatty acid precursors. The effects of the different series of PGs and LTs on production of T helper type 1 (Th1) and Th2 cytokines by human cells are not well established.

OBJECTIVE

To characterize the influence of PGs and LTs produced from different fatty acid precursors on the Th1 and Th2 cytokine profile in mitogen-stimulated human whole-blood cultures.

METHODS

Blood from healthy adult males was diluted and cultured with concanavalin A in the presence or absence of a range of concentrations of various PGs or LTs. Cytokine concentrations in culture supernatants were analysed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

PGE1, PGE2 and PGE3 significantly and dose-dependently decreased the concentrations of the Th1 cytokines IL-2 and IFN-gamma by up to 50% and 70%, respectively. The three PGs exhibited similar potency towards IFN-gamma production. At the highest concentration used (10-6 m) PGE1, but not PGE2 or PGE3, increased the concentration of the Th2 cytokine IL-4 by about 70%. IL-10 production was not affected by PGs. The ratio of the concentrations of IFN-gamma to IL-4 was significantly decreased at PGE concentrations of 10-7 and 10-6 M with all three PGEs having similar effects. LTB4, LTC4 and LTC5 did not significantly affect production of the cytokines studied.

CONCLUSION

PGE produced from different fatty acids significantly decrease Th1 cytokine production resulting in a shift in the Th1, Th2 balance in favour of a Th2 response. PGE produced from different fatty acid precursors are equipotent in their effects on human T lymphocytes. Thus, although changes in the pattern of dietary fatty intakes may contribute to the increased prevalence of atopic disease, this would probably not be mediated through substitution of one PGE with another from a different series. It may, however, be mediated through a change in the total amount of PGE produced at the site of antigen presentation.

Influence of antidepressants on intracellular levels of cyclic adenosine monophosphate in human peripheral blood mononuclear cells

This study examines the effects of paroxetine and imipramine on intracellular concentrations of cyclic adenosine monophosphate (cAMP) in human peripheral blood mononuclear cells. It was found that imipramine and paroxetine had no effect on basal cAMP-levels. Stimulation with lipopolysaccharides and phytohaemagglutinin increased intracellular cAMP concentrations. However, pre-incubation with imipramine or paroxetine, did not influence this increase. These data do not support the hypothesis that cAMP may be related to the in vitro anti-inflammatory effects of antidepressants.

Antidepressant treatment of cytokine-induced mood disorders

Significant evidence suggests that the immune system is capable of profoundly affecting central nervous system (CNS) functioning in ways that may contribute to the development and expression of neuropsychiatric disorders, including disorders of mood. This paper reviews evidence that the production of proinflammatory cytokines, whether in the context of therapeutic administration (e.g. interferon-α-2b for hepatitis C infection) or medical illness, induces a state of sickness behavior that closely resembles major depression. Antidepressants have been shown to abolish or attenuate cytokine-induced sickness behavior in laboratory animals and to protect against the development of major depression in the context of therapeutic cytokine administration in humans. Potential mechanisms by which antidepressants ameliorate depressive and/or sickness symptoms in the context of immune activation include direct effects on immune cell functioning, as well as modulatory effects on monoamine neurotransmitters, intracellular second messenger pathways and the neuroendocrine system, in particular the hypothalamic-pituitary-adrenal axis.

The negative immunoregulatory effects of serotonin (5-HT) moduline, an endogenous 5-HT1B receptor antagonist with anti-anxiety properties

BACKGROUND

Serotonin (5-HT) has negative immunoregulatory effects by reducing the interferon-gamma (IFNgamma)/interleukin-10 (IL-10) production ratio by stimulated immune cells. Leukocytes have functional 5-HT1B receptors. 5-HT moduline, an endogenous 5-HT1B receptor antagonist, may antagonize the 5-HT1B agonist-induced proliferation of immune cells.

AIMS

To examine the effects of 5-HT moduline on the stimulated production of IFNgamma, tumor necrosis factor alpha (TNFalpha) and IL-10.

RESULTS

5-HT moduline, 10(-6) M and 10(-5)M, significantly reduced the production of IFNgamma and the IFNgamma/IL-10 ratio. 5-HT moduline 10(-5)M significantly reduced the production of TNFalpha. The combination of 5-HT, 15 microg/mL, with 5-HT moduline, 10(-6)M and 10(-5)M, further decreases the IFNgamma/IL-10 production ratio.

INTERPRETATION

5-HT moduline has negative immunoregulatory effects.

Relative contribution of NF-kappaB and AP-1 in the modulation by curcumin and pyrrolidine dithiocarbamate of the UVB-induced cytokine expression by keratinocytes

Following ultraviolet B treatment, expression of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-8 by NCTC 2544 keratinocyte cell line was significantly enhanced both at the mRNA and protein level. The UVB also increased the IL-10 steady-state mRNAs level. Radiation-induced cytokine overexpression was accompanied by NF-kappaB and AP-1 transcription factors activation as assessed by electrophoretic mobility shift assays. To investigate in keratinocytes the relative contributions of those transcription factors on UVB-mediated cytokine induction, cell cultures were supplemented with curcumin and pyrrolidine dithiocarbamate (PDTC), agents known to modulate NF-kappaB and AP-1 activation. Both compounds significantly inhibited NF-kappaB activation by UVB, but AP-1 activation was unaffected by curcumin while PDTC further stimulated its activation. In parallel, curcumin decreased, in a dose-dependent manner, the UVB-mediated overexpression of all three pro-inflammatory cytokines and only exhibited a moderate enhancing influence on IL-10 expression. In turn, the inhibitory influence of PDTC on radiation-induced TNF-alpha and IL-6 expression is much lower and in contrast to curcumin, it stimulated IL-8. Taken together, our data indicated that control of proinflammatory cytokine expression induced by UVB in keratinocytes required the selective inhibition of NF-kappaB activation. Simultaneous AP-1 activation by agents like PDTC might, partially or totally, depending on cytokine-type, counterbalanced the inhibitory effect exerted on UVB-induced NF-kappaB activation in keratinocytes.

Contribution of the ADP-ribosylating and receptor-binding properties of cholera-like enterotoxins in modulating cytokine secretion by human intestinal epithelial cells

When epithelial cells first encounter cholera toxin (Ctx) produced by Vibrio cholerae they secrete not only chloride ions responsible for causing diarrhoea, but also a number of cytokines that may contribute to the toxin's potent immunomodulatory properties. Much less is known about the ability of the heat-labile enterotoxin of Escherichia coli (Etx), a close homologue of Ctx, to elicit cytokine secretion by epithelial cells. This study shows that treatment of human intestinal epithelial T84 cells with Etx induces expression of IL-6, IL-10, IL-1R antagonist, as well as IL-1alpha and IL-1beta and low levels of IL-8. Such induction was totally dependent on the intrinsic ADP-ribosylating activity of the toxin A-subunit, and could be mimicked by cAMP-elevating agents, such as forskolin and dibutyryl cAMP. By comparison, neither an enzymically inactive mutant of Etx nor EtxB was able to induce cytokine secretion. The behaviour of Ctx and CtxB was very similar to that of Etx and EtxB, respectively. The spectrum of cytokines released by Etx and Ctx indicates that the toxins may create a local microenvironment that strongly biases the immune response towards an anti-inflammatory and a polarized Th2 response.

In vitro effects of cAMP-elevating agents and glucocorticoid either alone or in combination on the production of nitric oxide, interleukin-12 and interleukin-10 in IFN-gamma- and LPS-activated mouse peritoneal macrophages

The effects of cAMP-elevating agents, N6-2'-O-dibutyryl cAMP (Bu2cAMP), and glucocorticoid (dexamethasone) on the production of inflammatory mediators--nitric oxide and interleukin-12 (IL-12) and anti-inflammatory mediator interleukin-10 (IL-10) were demonstrated in murine peritoneal macrophages. Inducible nitric oxide synthase (iNOS) and iNOS mRNA were detected by northern blot and western blot, respectively. The cAMP elevating agents Bu2cAMP and prostaglandin E2 each alone did not show any effect on NO production but along with IFN-gamma and lipolysaccharide (LPS) they slightly enhanced NO production. Dexamethasone inhibited NO production in IFN-gamma- and LPS-treated cells; cAMP elevating agents interfered with the NO production inhibited by dexamethasone. Inhibition was revealed at the mRNA level as well as at protein level. Bu2cAMP or dexamethasone either alone or synergistically inhibited IL-12 production; Bu2cAMP interfered with dexamethasone-mediated inhibition of IL-10 production in IFN-gamma- and LPS-treated macrophages. The use of glucocorticoids along with cAMP elevating agents was beneficial in lowering the level of inflammatory mediator IL-12 and producing high levels of the anti-inflammatory mediator IL-10 active in cell protection. On the other hand, interference of Bu2cAMP with dexamethasone-mediated NO inhibition may have adverse effect. Therefore, adverse effects due to cAMP-mediated interference (inhibition) with NO synthesis may occur in many inflammatory diseases during combined drug therapy by glucocorticoids and cAMP elevating agents.

Differential regulation of T cell receptor-mediated Th1 cell IFN-gamma production and proliferation by divergent cAMP-mediated redox pathways

Culture of an H-2(s)-restricted, bovine myelin basic protein (BMBP)-specific murine Th1 clone with the adenyl cyclase agonist forskolin (FSK) or isobutylmethylxanthine (IBMX), an inhibitor of cAMP catabolism, before culture with anti-CD3 or BMBP and antigen-presenting cells (APC) suppressed antigen or anti-CD3-induced proliferation and production of interferon-gamma (IFN-gamma). Other H-2(s)-derived or H-2(b)-derived clones specific for BMBP or keyhole limpet hemocyanin (KLH) were similarly affected. FSK did not affect the expression of CD4 or the T cell receptor (TCR) but did diminish levels of the phosphorylated (activated) mitogen-activated protein (MAP) kinases early response kinase-1 (ERK-1) and ERK-2. Immunoblotting of lysates from an FSK-treated Th1 clone with antibodies to a carboxy-terminal epitope of p56(lck), a signal transduction enzyme upstream from ERK-1 and ERK2, did not detect p56(lck) unless the lysates were reduced prior to electrophoresis. Immunoblotting of nonreduced lysates with antibodies to an amino-terminal epitope demonstrated p56(lck) with a lower apparent molecular weight, characteristic of oxidized proteins. Reduction restored the detection of p56(lck) by anticarboxy-terminal p56(lck) and to mobilities indistinguishable from controls detected by the antiamino-terminal p56(lck). N-acetylcysteine or catalase prevented FSK-induced suppression of antigen-induced proliferation and the loss of carboxy-terminal epitopes of p56(lck). An inhibitor of cAMP-dependent protein kinase A (PKA) or nitric oxide synthase (NOS) did not affect FSK-induced inhibition of antigen-induced proliferation. In contrast, inhibitors of PKA or NOS, but not catalase, prevented FSK-induced suppression of IFN-gamma production. Moreover, immunoblots of lysates precipitated with anti-p56(lck), phosphotyrosine, or CD4 demonstrated that in FSK-treated, anti-CD3-stimulated cells, p56(lck) is not associated with CD4 zeta chain, nor is p56(lck) or zeta chain phosphorylated. In vitro kinase assays demonstrated that p56(lck) from FSK-treated cells does not have kinase activity. Taken together, the results suggest that an elevation of intracellular cAMP (in the absence of antigen) creates an oxidative environment that oxidizes and inactivates p56(lck) by an H(2)O(2)-dependent, PKA-independent mechanism and inhibits the production of IFN-gamma by an NO, PKA-dependent mechanism. Thus, antigen-induced proliferation and IFN-gamma production in a Th1 clone are controlled separately by different cAMP-dependent, redox-based mechanisms.

Adenosine 3',5'-cyclic monophosphate (cAMP)-dependent inhibition of IL-5 from human T lymphocytes is not mediated by the cAMP-dependent protein kinase A

IL-5 is implicated in the pathogenesis of asthma and is predominantly released from T lymphocytes of the Th2 phenotype. In anti-CD3 plus anti-CD28-stimulated PBMC, albuterol, isoproterenol, rolipram, PGE2, forskolin, cholera toxin, and the cAMP analog, 8-bromoadenosine cAMP (8-Br-cAMP) all inhibited the release of IL-5 and lymphocyte proliferation. Although all of the above compounds share the ability to increase intracellular cAMP levels and activate protein kinase (PK) A, the PKA inhibitor H-89 failed to ablate the inhibition of IL-5 production mediated by 8-Br-cAMP, rolipram, forskolin, or PGE2. Similarly, H-89 had no effect on the cAMP-mediated inhibition of lymphocyte proliferation. Significantly, these observations occurred at a concentration of H-89 (3 microM) that inhibited both PKA activity and CREB phosphorylation in intact cells. Additional studies showed that the PKA inhibitors H-8, 8-(4-chlorophenylthio) adenosine-3',5'-cyclic monophosphorothioate Rp isomer, and a myristolated PKA inhibitor peptide also failed to block the 8-Br-cAMP-mediated inhibition of IL-5 release from PBMC. Likewise, a role for PKG was considered unlikely because both activators and inhibitors of this enzyme had no effect on IL-5 release. Western blotting identified Rap1, a downstream target of the cAMP-binding proteins, exchange protein directly activated by cAMP/cAMP-guanine nucleotide exchange factors 1 and 2, in PBMC. However, Rap1 activation assays revealed that this pathway is also unlikely to be involved in the cAMP-mediated inhibition of IL-5. Taken together, these results indicate that cAMP-elevating agents inhibit IL-5 release from PBMC by a novel cAMP-dependent mechanism that does not involve the activation of PKA.

Administration of pentoxifylline during allergen sensitization dissociates pulmonary allergic inflammation from airway hyperresponsiveness

Asthma, a chronic inflammatory disease characterized by intermittent, reversible airflow obstruction and airway hyperresponsiveness (AHR), is classically characterized by an excess of Th2 cytokines (IL-13, IL-4) and depletion of Th1 cytokines (IFN-gamma, IL-12). Recent studies indicating an important role for Th1 immunity in the development of AHR with allergic inflammation suggest that Th1/Th2 balance may be important in determining the association of AHR with allergic inflammation. We hypothesized that administration of pentoxifylline (PTX), a phosphodiesterase inhibitor known to inhibit Th1 cytokine production, during allergen (OVA) sensitization and challenge would lead to attenuation of AHR in a murine model of allergic pulmonary inflammation. We found that PTX treatment led to attenuation of AHR when administered at the time of allergen sensitization without affecting other hallmarks of pulmonary allergic inflammation. Attenuation of AHR with PTX treatment was found in the presence of elevated bronchoalveolar lavage fluid levels of the Th2 cytokine IL-13 and decreased levels of the Th1 cytokine IFN-gamma. PTX treatment during allergen sensitization leads to a divergence of AHR and pulmonary inflammation following allergen challenge.

Oral salbutamol decreases IL-12 in patients with secondary progressive multiple sclerosis

IL-12 is a key cytokine for Th1 cell development and may be important in the pathogenesis of multiple sclerosis (MS). The beta2-agonist salbutamol is known to decrease IL-12 production in monocytes of normal individuals through increased intracellular cAMP. In a prospective open-label study, we investigated by flow cytometry the effect of a 2-week long oral salbutamol treatment on monocyte IL-12 production in 21 secondary progressive MS patients. Baseline IL-12 production was higher in patients than in healthy controls. The treatment induced a significant decrease in the percentage of IL-12-producing monocytes and dendritic cells that lasted up to 1 week after treatment interruption. This first report on the use of salbutamol in MS shows that this drug has immunomodulatory properties both in vivo and in vitro, and may be beneficial in the treatment of MS.

Anti-Inflammatory effects of antidepressants through suppression of the interferon-gamma/interleukin-10 production ratio

There is some evidence that major depression--in particular, treatment-resistant depression (TRD)--is accompanied by activation of the inflammatory response system and that proinflammatory cytokines may play a role in the etiology of depression. This study was carried out to examine the effects of antidepressive agents, i.e., imipramine, venlafaxine, L-5-hydroxytryptophan, and fluoxetine on the production of interferon-gamma (IFN-gamma), a proinflammatory cytokine, and interleukin-10 (IL-10), a negative immunoregulatory cytokine. Diluted whole blood of fluoxetine-treated patients with TRD (mean age, 50.6+/-3.9 years) and age-matched healthy controls (mean age, 51.6+/-1.7 years) and younger healthy volunteers (mean age, 35.4+/-9.6 years) was stimulated with phytohemagglutinin (1 microg/mL) and lipopolysaccharide (5 microg/mL) for 48 hours with and without incubation with the antidepressants at 10-6 M and 10(-5) M. IFN-gamma and IL-10 were quantified by means of enzyme-linked immunoassays. The ratio of IFN-gamma to IL-10 production by immunocytes was computed because this ratio is of critical importance in determining the capacity of immunocytes to activate or inhibit monocytic and T-lymphocytic functions. All four antidepressive drugs significantly increased the production of IL-10. Fluoxetine significantly decreased the production of IFN-gamma. All four antidepressants significantly reduced the IFN-gamma/IL-10 ratio. There were no significant differences in the antidepressant-induced changes in IFN-gamma or IL-10 between younger and older healthy volunteers and TRD patients. Tricyclic antidepressants, selective serotonin reuptake inhibitors, and serotonin-noradrenaline reuptake inhibitors, as well as the immediate precursor of serotonin, have a common, negative immunoregulatory effect by suppressing the IFN-gamma/IL-10 production ratio. It is suggested that the therapeutic efficacy of antidepressants may be related to their negative immunoregulatory effects.

Cytotoxic T cells and mycobacteria

How the immune system kills Mycobacterium tuberculosis is still a puzzle. The classical picture of killing due to phagocytosis by activated macrophages may be only partly correct. Based on recent evidence, we express here the view that cytotoxic T lymphocytes also make an important contribution and suggest that DNA vaccines might be a good way to enhance this.

Prolonged desipramine treatment increases the production of interleukin-10, an anti-inflammatory cytokine, in C57BL/6 mice subjected to the chronic mild stress model of depression

BACKGROUND

Depression is associated with activation of the inflammatory response system (IRS). In humans, antidepressants significantly increase the production of interleukin-10 (IL-10), a negative immunoregulatory cytokine. The aims of the present study were to examine the effects of desipramine, a tricyclic antidepressant, on the IRS in C57BL/6 mice with and without exposure to chronic mild stress (CMS).

METHODS

We examined the effects of desipramine on the cytotoxic activity of natural killer (NK) cells, the proliferative responses of lymphocytes after stimulation with IL-1, IL-2, lipopolysaccharide (LPS), concanavaline-A (Con-A), phytohaemagglutinin-P (PHA), pokeweed mitogen (PWM), and anti-CD3 monoclonal antibodies, the production of IL-2, IL-4, IL-10 and interferon-gamma (IFNgamma) by T lymphocytes and the ability of B cells to proliferate after stimulation by lipopolysaccharide (LPS).

RESULTS

Prolonged treatment of C57BL/6 mice subjected to CMS with desipramine increases the ability of T cells to produce IL-10 and the ability of B cells to proliferate after stimulation with LPS; and significantly decreases the cytotoxic activity of NK cells and the proliferative responses of lymphocytes after stimulation with Con-A, PHA and anti-CD3 monoclonal antibodies. Repeated administration of desipramine to non-stressed mice increases the activity of T lymphocytes, lowers that of B lymphocytes, increases the production of IL-10 by T cells and has no significant effect on the activity of NK cells.

CONCLUSION

Prolonged desipramine treatment of stressed and non-stressed C57BL/6 mice induces an increase in the production of IL-10, an anti-inflammatory cytokine.

Regulation of the IL-10 production by human T cells

Interleukin (IL)-10, an immunomodulatory cytokine predominantly produced by monocytes/macrophages and T cells, inhibits several functions of dendritic cells (DC), monocytes and T cells including their cytokine production, but it stimulates B cell immunoglobulin (Ig) production and cytotoxic T lymphocyte (CTL) generation. A precise knowledge of the mechanisms that control the IL-10 production is therefore highly important for understanding the immunoregulation. The IL-10 production was studied in cultures of freshly isolated human T cells. A rise in intracellular calcium as well as the common gamma-chain containing cytokine receptor triggering or CD28 triggering were found to be important signals for IL-10 induction. CD80, CD58, rIL-12 and rIFN-alpha all had efficacious and independent costimulatory activities on the IL-10 production, while PGE2 was inhibitory. Dependence on autocrine IL-2 signalling was shown by the effects of anti-IL-2 and anti-IL-2R monoclonal antibodies (MoAb), but the IL-10 production proceeded partly IL-2-independent when CD80 provided costimulation. Sensitivity to inhibition by CsA was not removed by CD80 or CD58 costimulation and/or by addition of rIL-12 or rIFN-alpha, pointing to the absolute requirement for calcineurin activity. These data reveal important differences in the regulatory pathways between IL-10 (a cytokine-inhibitory interleukin) and IL-2 (a cytokine-inducing interleukin), which can potentially be exploited therapeutically. The fact that CsA blocks the production of IL-10, which itself has important immunosuppressive properties, should be taken into account in defining immunosuppressive treatment schedules which include the use of CsA.

The immunoregulatory effects of antidepressants

There is some evidence that major depression is accompanied by activation of the inflammatory-response system (IRS). It has been hypothesized that increased production of proinflammatory cytokines may play a role in the etiology of major depression. If increased production of proinflammatory cytokines is at all involved in the etiology of depression, one would expect antidepressive treatments to have negative immunoregulatory effects. This paper reviews the effects of antidepressants, such as tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), heterocyclic antidepressants (HCAs), serotonin-noradrenaline reuptake inhibitors (SNRIs), lithium, l-5-hydroxytroptophan (L-5-HTP), reversible inhibitors of MAO-A (RIMA) on the production of proinflammatory cytokines, e.g. interferon-gamma (IFNgamma), and negative immunoregulatory cytokines and agents, e.g. interleukin-10 (IL-10). In depressed patients, prolonged treatment with antidepressants and mood stabilizers normalizes signs of activation of the IRS, such as increased serum IL-6 and acute phase protein concentrations. In vitro, it has been shown that various types of antidepressive drugs, including TCAs (imipramine; clomipramine); SSRIs (citalopram, fluoxetine, sertraline); lithium; SNRIs (venlafaxine); HCAs (trazodone); RIMAs (moclobemide) and L-5-HTP significantly suppress the ratio of IFNgamma/IL-10 production by peripheral blood immunocytes. These antidepressant drugs appear to have a common effect on the IRS, i.e. in vitro they increase the production of IL-10 by peripheral blood leukocytes. Thus, the results suggest that antidepressants have negative immunoregulatory effects. It may be speculated that antidepressants exert some of their antidepressant effects through their negative immunoregulatory capacities. Copyright 2001 John Wiley & Sons, Ltd.

The effects of histamine on interferon gamma production are dependent on the stimulatory signals

Histamine regulates the immune response by enhancing TH2 cytokine production and by inhibiting TH1 cytokine production. We assessed the mechanisms of histamine's action on helper T cell subsets by evaluating the role of protein kinase A (PKA) in the histamine-mediated effects on IFN gamma production. The splenocytes and TH1 murine cloned cells (pGL10) were pretreated with histamine at a concentration range of 10(-8)-10(-5) M for 1 h and then were activated with anti-CD3, PHA, PMA + ionomycin, or ionomycin for 24 h. The levels of IFN gamma were measured in the supernatants by ELISA. The inhibitory effects of histamine were the most prominent in anti-CD3-stimulated splenocytes (61%). The effects of histamine on IFN gamma production from TH1 cells depended on the mode of cell activation. The activation of cells with anti-CD3 resulted in 27% inhibition of IFN gamma production whereas the activation with ionomycin produced 70% suppression. The inhibitory effects of histamine were completely reversed by cimetidine in a dose-dependent manner in both TH1 cells and in splenocytes. PKA played a role in the inhibition of IFN gamma by histamine when the cells were activated via TCR, and the PKA inhibitors Rp-cAMPS (10(-5) M) and H8 (10(-5) M) reversed the inhibitory effects of histamine on IFN gamma production. However, when the cells were stimulated with ionomycin, the PKA inhibitors did not affect histamine-mediated suppression of IFN gamma production.

Regulation of interleukin-10 secretion by histamine in TH2 cells and splenocytes

Interleukin-10 is a potent suppressive factor that down-regulates cellular immune response via inhibition of the production of TH1 cytokines. Histamine shifts the TH1/TH2 balance from TH1 to TH2 cytokines making the effects of histamine on IL-10 secretion an important factor in this switch. This study was designed to assess the role of histamine in the regulation of IL-10 production and the involvement of PKA and STAT factors in this process. TH2 cells (D10.G4.1) and AKR/j splenocytes were pretreated with histamine at a concentration range of 10(-8)-10(-5) M for 1 h and then activated with PMA + ionomycin or anti-CD3 for 24 h. The supernatants were collected and tested for IL-10 content by ELISA. Histamine stimulated IL-10 production in TH2 cells in a dose-dependent manner that was reversed by both H1- and H2-receptor antagonists and by PKA inhibitors H8 and Rp-cAMPS. Tyrphostin also reversed the stimulation of IL-10 secretion by histamine, indicating that STAT factors were involved in this process. The up-regulation of IL-10 production by histamine in splenocytes was accompanied by inhibitory effects of histamine on IFN gamma production. The pretreatment of splenocytes with histamine in the presence of anti-IL-10 abrogated histamine-mediated inhibition of IFN gamma production suggesting that the effects of histamine on IFN gamma secretion were regulated by IL-10 in multi-cell system.

Effects of prostaglandin E2 and nitric oxide inhibitors on the expression of interleukin-10, interleukin-12 and MHC class-II molecules in Mycobacterium microti-infected and interferon-gamma-treated mouse peritoneal macrophages

Mycobacterium microti-infected mouse peritoneal macrophages produced high amounts of prostaglandin E2 (PGE2) and nitric oxide (NO) when activated with interferon-gamma (IFN-gamma). In order to understand the relation between PGE2 and NO production and the expression of interleukin-12 (IL-12), interleukin-10 (IL-10) and MHC class-II (Ia) molecules by M. microti-infected and IFN-gamma-stimulated macrophages, we analyzed the level of these molecules in the presence or absence of PGE2 and NO inhibitors. Addition of NG-methyl-L-arginine (L-NMA) and indomethacin (IM) caused a significant increase in IL-12 level (2.6- and 1.9-fold, respectively) whereas IL-10 level decreased by 88 and 56%, respectively, relative to M. microti-infected and IFN-gamma-treated control macrophages. Enhanced PGE2 and NO upregulated IL-10 expression and down-regulated IL-12 and MHC class-II (Ia) expression in M. microti-infected and IFN-gamma-treated mouse peritoneal macrophages.

The effect of repeated amitriptyline and desipramine administration on cytokine release in C57BL/6 mice

This study examines the effects of repeated amitriptyline and desipramine administration (10 mg/kg, IP) on the immunoreactivity of saline-injected C57BL/6 mice, as evaluated by the ability of splenocytes to reduce a tetrazolium salt to formazan (MTT test), to proliferate, and to produce cytokines, such as interleukin (IL)-1, IL-2, IL-4, IL-6, IL-10 and interferon gamma (IFN-gamma). Desipramine and amitriptyline administered for one or two weeks enhance the biochemical (estimated by MTT test) and proliferative activities of splenocytes. One and two weeks administration of desipramine significantly reduces the secretion of IL-4, an anti-inflammatory cytokine. Amitriptyline administration for four weeks stimulates the proliferative activity of splenocytes and enhances IL-2 bioactivity, whereas four weeks desipramine aministration does not change these parameters in comparison to saline treated control mice. Prolonged desipramine administration (seven and 28 days) significantly increased the bioactivity of IL-1. Four weeks of prolonged administration of amitriptyline and desipramine induces a significant increase in the secretion of IL-10, a cytokine with immunosuppressive and anti-inflammatory activities. The results show that the immunoregulatory effects of tricyclic antidepressants in C57BL/6 mice depend on the drugs used and on the duration of administration.

Differential effects of pentoxifylline, a non-specific phosphodiesterase inhibitor, on the production of IL-10, IL-12 p40 and p35 subunits by murine peritoneal macrophages

Pentoxifylline (PTX), a methylxanthine derivative, has been reported to be an effective drug in inhibiting TNF-alpha responses during septic shock. The inhibition of TNF-alpha production seems to be correlated with increased intracellular cAMP levels. PTX also affects the production of other cytokines such as IL-1, IL-6, IL-10, IL-12, and IFN-gamma. However, inhibition, as well as enhancement of cytokine production, has been observed in vitro, depending on the PTX concentration and cell type used.IL-12 is a heterodimeric cytokine that plays an important role in the development of Th1-mediated inflammatory responses. IL-12 along with TNF-alpha and other proinflammatory cytokines has shown to be responsible for the pathological reaction, which may lead to septic shock. For biological activity, the expression of both subunits of IL-12, p35 and p40, is required. Moreover, the p40 chain of IL-12 specifically inhibits the effects of the IL-12 heterodimer. In this study, we investigated the effects of PTX on the production of both proinflammatory (TNF-alpha, IL-6, IL-12) and anti-inflammatory (IL-10) cytokines by murine macrophages (Mφ). We have found that PTX, at concentrations below 100 microg/ml, selectively inhibited the production of TNF-alpha. Forskolin, a cAMP-elevating agent, similarly affected the production of the cytokines tested. However, at higher concentrations, PTX inhibited the production of TNF-alpha, IL-10, and IL-12 p35, but surprisingly, PTX enhanced the production of IL-12 p40. Concentrations of IL-10 were negatively correlated with the concentrations of IL-12 p40 subunit. These results further confirm the relevance of the use of PTX in clinical trials of immunological disorders characterised by inappropriate Th1 type immune responses.

Induction of functional CD154 (CD40 ligand) in neonatal T cells by cAMP-elevating agents

A deficiency of neonatal T lymphocytes to express CD154 antigen in response to ionomycin and phorbol 12-myrsistate 13-acetate (PMA) stimulation or after CD3 cross-linking has been described. In the present report we describe that CD45RA+ newborn cells are able to synthesize and express CD154 at similar or even higher levels than adult cells in response to ionomycin and cAMP-elevating agents which trigger the protein kinase A (PKA) -mediated metabolic pathway. Peak CD154 protein concentrations in newborn cells were found between 4 and 8 hr after stimulation with ionomycin and dibutyryl cAMP. These agents, however, did not induce expression of the early activation antigen CD69. Surface levels of CD154 did not correlate with specific mRNA concentration, indicating that dibutyryl cAMP up-regulates CD154 by acting at a post-transcriptional stage. The CD154 antigen induced by PKA activation of newborn cells was functional, since upon binding to CD40 on B lymphocytes in the presence of interleukin-4 (IL-4), it promoted immunoglobulin heavy-class switching to IgE. We also found a different pattern of cytokine production between neonatal and adult CD4+ T cells. In response to ionomycin and dibutyryl cAMP, cord blood cells were more prone than adult lymphocytes to secrete the T helper type 2-derived immunosuppressive cytokines IL-4 and IL-10. Taking into account that the feto-maternal environment is rich in cAMP-elevating agents, the reduced risk of graft versus host disease associated with cord blood trasplantation, as compared with the risk with adult bone marrow cell transplants, may be due to the bias of neonatal cells to differentiate towards the T helper type 2 functional cell subset.

Stimulus-specific inhibition of IL-5 by cAMP-elevating agents and IL-10 reveals differential mechanisms of action

Interleukin-5 (IL-5) is a Th2 cytokine, which is implicated in the pathogenesis of eosinophilic diseases such as asthma. Peripheral blood mononuclear cells (PBMC), costimulated with phorbol 12-myristate 13-acetate (PMA) plus phytohemagglutinin (PHA) or activating antibodies to the CD3 and CD28 T-lymphocyte surface markers, produced similar patterns of IL-5 expression. However, in PMA + PHA-treated cells, 8-bromo-cAMP and PGE(2) did not affect IL-5 expression, whereas in CD3 + CD28-stimulated cells, almost total repression was observed. IL-10 failed to inhibit IL-5 mRNA from PMA + PHA-treated cells, yet reduced release by 40%. By contrast, IL-10 totally inhibited CD3 + CD28-induced IL-5 release and inhibited mRNA by 50-60%. These results highlight important biological differences in the induction of IL-5 by the nonspecific stimulus PMA + PHA and the more physiological CD3 + CD28 costimulation. Finally, the potential for downregulating Th2 responses by cAMP-elevating agents or IL-10 is demonstrated and a significant role for posttranscriptional mechanisms in the inhibition by IL-10 is suggested.

Regulation of IL-10 secretion after phagocytosis of Mycobacterium tuberculosis by human monocytic cells

Downregulation of pro-inflammatory events in the immune response to Mycobacterium tuberculosis is critical to prevent host tissue injury. Interleukin (IL-)10 is an important anti-inflammatory cytokine secreted in human tuberculosis but little is known about the control of such IL-10 release. Using an established cellular model, we measured IL-10 secretion after phagocytosis of M. tuberculosis. Phagocytosis of M. tuberculosis but not of inert latex beads by human monocytic (THP-1) cells resulted in IL-10 secretion maximal at 24 h. The magnitude and kinetics of IL-10 secretion were distinct from IL-10 secretion after phagocytosis of yeast-derived zymosan and depended on transcriptional activity and protein synthesis in infected monocytes. IL-10 secretion was decreased in a dose-dependent manner by specific inhibitors of tyrosine kinases, protein kinase (PK) C and PKA. Inhibition of more than one pathway did not result in further synergistic or additive reduction in IL-10 secretion. Finally, specific neutralising antibody directed against IL-10 demonstrated that IL-10 secreted by infected monocytic cells did not block autologous IL-8 secretion.

Liver infiltrating T lymphocytes express interferon gamma and inducible nitric oxide synthase in chronic hepatitis C virus infection

BACKGROUND

Pathogenesis of hepatitis C virus (HCV) associated liver injury is thought to be due to the host antiviral immune response. Using a quantitative, competitive RT-PCR technique, we recently showed that expression of interferon gamma (IFN-gamma) and IFN-gamma inducible type of nitric oxide synthase (iNOS) is increased in homogenised liver tissue of patients with chronic HCV infection.

AIMS

To determine the cellular origin of IFN-gamma and iNOS expression and to examine the hypothesis that T cell derived IFN-gamma secretion induces iNOS in hepatocytes in chronic HCV infection.

METHODS

By applying a non-radioactive in situ hybridisation method combined with indirect immunofluorescence, 33 liver biopsy specimens from patients with chronic HCV infection were studied for cellular expression of IFN-gamma and iNOS mRNA.

RESULTS

In chronic HCV infection, both IFN-gamma and iNOS gene expression were significantly increased. IFN-gamma and iNOS mRNA were observed in CD3+ lymphocytes infiltrating portal tracts and hepatic lobules, but not in hepatocytes.

CONCLUSIONS

Results are consistent with previous reports that IFN-gamma and iNOS transcripts are elevated in chronic HCV infection. In contrast to the hypothesis, IFN-gamma expressing T cells do not induce iNOS in hepatocytes, but probably in T cells. T lymphocytes expressing IFN-gamma and/or iNOS have the potential to participate in autocrine and paracrine pathways that may contribute to the pathobiology of chronic hepatitis C.

Effects of intrinsic nitric oxide on the expression of interleukin-4 and IFN-gamma mRNA in the bronchial and lung tissues of sensitized rats

To investigate the effects of intrinsic nitric oxide (NO) on the expression of interleukin-4 (IL-4) mRNA and interferon-gamma (IFN-gamma) mRNA in the airway inflammation of asthma, the rat models of asthmatic inflammation were established by sensitizing and then challenging the animals with ovalbumin. The 24 animals were randomly divided into control group, sensitized group, sensitized and L-Arg-treated group as well as L-NAME-treated group equally. By using in situ hybridization combined with compute physiological quantitative imaging analysis techniques, the influence of intrinsic NO on the expression of IL-4 mRNA and IFN-gamma mRNA in the airway inflammatory cells was observed. In situ hybridization study demonstrated that IL-4 mRNA expression was obviously increased as compared with that in the control group, mainly distributed in the inflammatory cells in the submucous of airways in the sensitized group. The increase of intensity of IL-4 mRNA expression was positively correlated with the numbers of eosinophil (Eos) and lymphocyte (both with P < 0.05) in the sensitized group. There was no statistically difference in IFN-gamma expression between the control group and the sensitized group. Imaging analysis showed that L-NAME could inhibit the expression of IL-4 mRNA (P < 0.05) and increase the expression of IFN-gamma mRNA (P < 0.05), while L-Arg could increase the expression of IL-4 mRNA in inflammatory cells (P < 0.05). It was indicated that a suitable levels of intrinsic NO can influence the expression of IL-4 mRNA of Th2 lymphocytes and the expression of IFN-gamma mRNA of Th1 lymphocytes and in turn, promote the development of asthmatic airway inflammation.

Effect of Costimulation and the Microenvironment on Antigen Presentation by Leukemic Cells

Costimulatory signals supplied by genetically modified tumor cells can enable T-cell recognition of tumor-associated antigens that were previously silent when presented by unmodified tumor cells. Although the mechanism of the CD80/CD28 costimulation has been studied extensively in the normal T-cell/antigen-presenting cell (APC) interactions, it is unclear how expression of CD80 by tumor cells mediates its effect. We demonstrate here that optimal CD80 expression on a leukemic cell enhances T-cell recognition of alloantigen primarily by lowering the level of T-cell receptor (TCR) stimulation required for activation. CD80 expression by leukemic cells leads to increased survival of activated T cells by inducing upregulation of the antiapoptotic protein BCL-2, but not BCL-XL. The cytokine microenvironment in which T cells are activated is crucial in determining their differentiation and consequently the nature of the immune response generated. Many tumor cells produce immunosuppressive cytokines that may not favor the induction of cell-mediated immunity. In this study, the presence of CD80 on leukemic cells increased T-cell activation in vitro, but this did not result in the production of Th1 cytokines. We show that this is due to a leukemia-derived soluble factor that inhibits the production of Th1 cytokines. Optimal expression of a costimulatory molecule, therefore, enhances the ability of leukemic cells to present antigen by amplifying TCR signals, but the microenvironment generated by leukemic cells may suppress the immune response required for their eradication. Thus, strategies aimed at inducing antileukemic immunity by providing leukemic cells with costimulatory functions must ensure the presence of an appropriate microenvironment.

Modulation of inducible nitric oxide synthase induction by prostaglandin E2 in macrophages: distinct susceptibility in murine J774 and RAW 264.7 macrophages

Prostaglandin E2 (PGE2) is the major cyclooxygenase metabolite in macrophages with complex proinflammatory and immunoregulatory properties. In the present study, we have compared the modulatory role of PGE2/cAMP-dependent signaling on induced nitric oxide (NO) production in two murine macrophages, J774 and RAW 264.7. With no effect on NO release by itself, PGE2 co-addition with lipopolysaccharide (LPS) resulted in a concentration-dependent enhancement in NO release and inducible NO synthase induction in J774, but not in RAW 264.7, macrophages. The potentiation effect of PGE2 in J774 cells was still seen when applied within 9 h after LPS treatment. Whereas RAW 264.7 macrophages release PGE2 with greater extent than J774 macrophages in response to LPS, indomethacin and NS-398, upon abolishing LPS-induced PGE2 release, caused a more obvious inhibition of NO release from J774 than RAW 264.7 cells. Thus, we suggest a higher positive modulatory role of PGE2--either endogenous or exogenous--on NO formation in J774 cells. Supporting these findings, exogenous PGE2 triggers cAMP formation in J774 cells with higher potency and efficacy. Of interest, dBcAMP also elicits higher sensitivity in potentiating NO release in J774 cells. We conclude that the opposite effect of PGE2/cAMP signaling on macrophage NO induction depends on its signaling efficacy and might be associated with the difference in endogenous PGE2 levels.

Cyclic adenosine monophosphate-responsive elements are involved in the transcriptional activation of the human IL-10 gene in monocytic cells

IL-10 plays an important role in the regulation of immune responses. We and others have demonstrated recently that cyclic adenosine monophosphate (cAMP)-elevating substances up-regulate monocytic IL-10 expression in vitro and in vivo. Computer analysis of the IL-10 promoter/enhancer region localized four putative cAMP-responsive elements (CRE1- 4) with homology to the CRE consensus motif. In electrophoretic mobility shift assays CRE1 and CRE4 bound protein complexes consisting of transcription factors CREB-1 and ATF-1, while CRE3 bound only marginal amounts of CREB-1/ATF-1 in combination with unknown protein(s). CRE2 showed no protein binding activity. In vitro mutation of CRE1 and CRE4 reduced the level of cAMP-stimulated transactivation in reporter gene assays in comparison to the wild-type promoter by 20 % and 50 %, respectively, while mutation of CRE3 had no effect. The main action of CRE4 on cAMP-dependent stimulation is probably based on its adjacent localization to the TATA box and its sequence comprising a perfect half site. Experiments with double and triple mutants and with deleted promoter fragments indicated the participation of additional elements beside the CRE motifs in the cAMP-dependent stimulation. Our data suggest that intracellular cAMP may directly affect expression of the immunoregulatory cytokine IL-10 in monocytic cells via activation of the eukaryotic transcription factors CREB-1 and ATF-1 and their binding to CRE1 and CRE4 in the upstream enhancer of the IL-10 promoter.

Role of protein kinase C in cyclic AMP-mediated suppression of T-lymphocyte activation following burn injury

Major burn injury induces T-lymphocyte dysfunction. Previous studies suggest that prostaglandin (PG) E2, which is elevated post-burn, is the causative factor via a cyclic AMP-dependent process. The present study was conducted to elucidate the mechanism by which cAMP induces T-lymphocyte dysfunction following burn injury. Splenocytes were isolated from mice 7 days after receiving a scald burn covering 25% of their total body surface or sham procedure. ConA-induced proliferation by splenocytes from burned mice was significantly suppressed. Macrophage depletion of the splenocyte cultures abrogated the suppression. Concanavalin A-stimulated proliferation by macrophage-depleted splenocytes was suppressed by PGE2 and dibutyryl cAMP in both groups. The IC50 of these cAMP-elevating agents, however, was approximately 100-fold lower for cells from burned mice, indicating an increased sensitivity to cAMP. PGE2 did not suppress PMA/Ca2+ ionophore-induced T-lymphocyte activation. Addition of PMA to ConA-stimulated cultures prevented the suppression of proliferative responses by PGE2, whereas Ca2+ ionophore had no effect. Thus, the suppression of T-lymphocyte activation following burn injury is macrophage-dependent, related to an increased sensitivity to cAMP and due to an uncoupling of cell surface receptors from protein kinase C activation.

Potentiation of cytokine induced iNOS expression in the human intestinal epithelial cell line, DLD-1, by cyclic AMP

BACKGROUND

Nitric oxide production by the inducible isoform of nitric oxide synthase (iNOS) is thought to play a role in the pathogenesis of inflammatory bowel disease along with other proinflammatory mediators.

AIMS

To examine the effects of cAMP, an intracellular mediator of several proinflammatory mediators, on iNOS expression in the human intestinal epithelial cell line, DLD-1.

METHODS

iNOS activity was assessed by measuring the NO stable oxidative product NO(2)(-). iNOS protein expression and iNOS mRNA levels were determined by western blotting and northern blotting, respectively.

RESULTS

iNOS activity, protein, and mRNA were induced by a combination of interleukin 1beta (0.5-5 ng/ml), interferon gamma (20-200 u/ml), and tumour necrosis factor alpha (10-100 ng/ml). The cytokine induced NOS activity was potentiated by N(6), 2'-O-dibutyryladenosine 3':5'-cyclic monophosphate and 8-bromoadenosine 3':5'-cyclic monophosphate (0.1-1 mM), and the adenylate cyclase activator, forskolin (1-100 microM). This activity was inhibited by the selective iNOS inhibitor, 1400W (0.1-100 microM). These agents increased iNOS protein. The cAMP analogues potentiated iNOS at the transcriptional level as shown by effects of actinomycin D (5 microgram/ml) and northern blot analyses; the nuclear factor (NF) kappaB inhibitor, pyrrolidine dithiocarbamate (10-200 microM), significantly reduced this potentiation. The cAMP potentiated iNOS activity was inhibited by the tyrosine kinase inhibitor, A25 (10-200 microM) and the Janus activated kinase 2 inhibitor, B42 (10-200 microM).

CONCLUSIONS

Increased intracellular cAMP is a potent stimulus of iNOS expression in combination with cytokines in DLD-1 cells, acting at the transcriptional level and involving NF-kappaB and the JAK-STAT pathways. Thus, proinflammatory mediators that increase cAMP levels may augment iNOS expression and NO production.

Differential inhibitory mechanism of cyclic AMP on TNF-alpha and IL-12 synthesis by macrophages exposed to microbial stimuli

Microbial stimuli such as bacterial lipopolysaccharide (LPS) or glycosylphosphatidylinositol-mucins derived from Trypanosoma cruzi trypomastigotes (tGPI-mucins) are effective stimulators of the synthesis of cytokines by macrophages. Here, we evaluated the ability of cyclic AMP mimetic or elevating agents to modulate TNF-alpha and IL-12 synthesis by murine inflammatory macrophages. Cholera Toxin (ChTx) inhibited tGPI-mucins (2.5 nM) or LPS (100 ng ml(-1)) induced TNF-alpha and IL-12(p40) synthesis in a concentration-dependent manner. Similarly, the cyclic AMP mimetics, 8-bromo cyclic AMP or dibutyryl cyclic AMP, or prostaglandin (PG) E2 inhibited the synthesis of both cytokines by macrophages exposed to microbial stimuli. The protein kinase A inhibitor H-89 partially reversed the inhibitory effects of dibutyryl cyclic AMP and PGE2 on both IL-12(p40) and TNF-alpha synthesis. Pretreatment of macrophages with dibutyryl cyclic AMP or ChTx augmented the synthesis of IL-10 triggered by microbial products. Elevation of cyclic AMP inhibited the synthesis of TNF-alpha, but not IL-12(p40), by inflammatory macrophages from IL-10 knockout mice. Kinetic studies showed that synthesis of both TNF-alpha and IL-10 peaked at 8 h and IL-12 at 24 h after stimulation with microbial stimuli. Together, our findings favour the hypothesis that the cyclic AMP inhibitory activity on IL-12(p40) but not on TNF-alpha synthesis is dependent on de novo protein synthesis, most likely involving IL-10, by macrophages stimulated with microbial products. Accordingly, dibutyryl cyclic AMP inhibited IL-12(p40) synthesis only when added before or at the same time of the stimuli. In contrast, the effect of this cyclic AMP analogue on TNF-alpha synthesis was protracted and observed even 2 h after the addition of the stimuli.

Requirement of peptidergic sensory innervation for disease activity in murine models of immune hepatitis and protection by beta-adrenergic stimulation

To investigate the interaction between the peripheral nervous and the immune system in vivo, we used two mouse models of T cell and TNF-alpha dependent liver injury inducible by either concanavalin A or a combination of D-galactosamine and staphylococcal enterotoxin B. Mice depleted of peptidergic sensory nerve fibres by capsaicin were protected from liver injury. Moreover, TNF-alpha production was significantly reduced. Examination of the effect of catecholamines on liver injury showed that the beta2-adrenergic agonist salbutamol prevented, whereas chemical sympathectomy by 6-hydroxydopamine, deteriorated the disease. Hence, strategies reducing the activity of peptidergic sensory nerve fibres or stimulating beta2-adrenoreceptors, may be of benefit in immune-mediated liver disease.

Cyclosporin A inhibits activation of inducible nitric oxide synthase in C6 glioma cell line

The effects of immunosuppressant cyclosporin A (CsA) on nitric oxide (NO) production and inducible NO synthase (iNOS) mRNA expression in rat C6 glioma cell line were investigated. CsA applied simultaneously with iNOS activator IFN-gamma caused dose-dependent reduction of NO synthesis in confluent C6 cells, as determined by measuring accumulation of nitrite, an indicator of NO production, in 48 h culture supernatants. IFN-gamma-induced expression of iNOS, but not interferon regulatory factor-1 (IRF-1) mRNA was reduced in CsA-treated cells. The enzymatic activity of iNOS was not changed by CsA, since it failed to affect NO production in cells in which iNOS had already been induced with IFN-gamma and any further induction was blocked by protein synthesis inhibitor cycloheximide (CHX). FK506 was not able to mimic inhibitory effect of CsA on NO production in C6 cells, suggesting calcineurin-independent mechanism of CsA action.

Inhibition of Allergic Airway Inflammation in Mice Lacking Nitric Oxide Synthase 2

We have used mice rendered deficient for nitric oxide synthase 2 (NOS2) production to study the role of inducible nitric oxide (NO) in the pathogenesis of allergic airways disease. Using a model with OVA as aeroallergen, we show that the manifestations of disease, including infiltration of inflammatory cells, particularly eosinophils, loss of structural integrity of the airway walls, microvascular leakage, pulmonary edema, and airway occlusion are markedly less severe in the NOS2 mutants than in wild-type animals. Indeed, NOS2-deficiency resulted in a 55–60% reduction in both circulatory and pulmonary eosinophil numbers following aeroallergen treatment, although eosinophil maturation or efflux from the bone marrow was not suppressed. There were no obvious differences in levels of airway hyperreactivity recorded in OVA-treated wild-type and NOS2-deficient mice. Interestingly, the suppression of allergic inflammation was accompanied by marked increases in T cell production of IFN-γ but not by any obvious reduction in the secretion of either IL-4 or IL-5, nor by major changes in the IgG1 and IgE OVA-specific serum Ig profiles in the mutants. The markedly enhanced production of IFN-γ in NOS2−/− mice was apparently responsible for the suppression of both eosinophilia and disease, as in vivo depletion of this factor restored allergic pathology in these animals. Our data indicate that NOS2 promotes allergic inflammation in airways via down-regulation of IFN-γ activity and suggest that inhibitors of this molecule may represent a worthwhile therapeutic strategy for allergic diseases including asthma.

Modulation of inflammation and immunity by arginine supplements

Arginine holds a key position in the cellular functions and interactions that occur during inflammation and immune responses. The competition for arginine as a substrate between nitric oxide synthase and arginase appears to be at the core of the regulation of the inflammatory process. This review examines some of the recently defined effects of arginine on various inflammatory processes and immune cell functions.

Increased PGE2 production mediates the in vitro inhibitory effect of the human immunodeficiency virus P24 immunosuppressive heptapeptide Ch7

Previous work from our laboratory demonstrated that a synthetic heptapeptide (Ch7), corresponding to a conserved sequence of human immunodeficiency virus (HIV) core protein p24 (amino acids 232-238), was able to specifically abrogate antigen-induced responses in cultures of normal human peripheral blood lymphocytes (PBL). Addition of recombinant human interferon-gamma (IFN-gamma) to Ch7-suppressed cultures restored the capacity to mount an antigen-specific antibody response, suggesting that a cytokine imbalance may be at the basis of the Ch7 immunosuppressive activity. In the present paper we show that the Ch7-dependent in vitro immunosuppression was accompanied by a significant up-regulation of prostaglandin E2 (PGE2) production and induction of interleukin-10 (IL-10)-secreting cells. In the presence of the PGE2 inhibitor indomethacin, IL-10 up-regulation was prevented and the induction of a specific antibody response was partially restored. PGE2 is indeed an important regulator of immune responses with the ability to differentially affect cytokine production. Thus, our results demonstrate that the Ch7 immunosuppressive epitope may primarily act by up-regulating PGE2 production and, through this mediator, by causing a cytokine dysregulation, finally responsible for immune response suppression.

Effect of desipramine on immunological parameters in mice, and their reversal by stress

Immunomodulation of cell-mediated immunity is demonstrated in mice, after administration of desipramine, a noradrenaline-reuptake inhibitor, with or without exposing the mice later to an acute swimming stress. A single i.p. injection of 10 mg/kg desipramine to naive mice increased the relative weight of their spleens, the response of their splenocytes to the mitogen concavaline-A and their ability to produce IL-10, as compared to saline controls. Exposing the desipramine-treated mice to a swimming stress significantly reduced these parameters, as well as the levels of IL-2 and IFN-gamma, as compared to desipramine-treated mice. Stress alone reduced the weight of the spleen, and the ability of splenocytes to produce IFN-gamma. As desipramine and acute stress have stimulatory effect on the sympathetic system, it is suggested that a concomitant administration of the drug and a stressful event of these mice, change the splenocytes' micro-environment of sympathetic transmitters, and inhibit their function. These results may be partially due to impairment in the T-helper cell function by a beta-adrenoreceptor-dependent mechanism.

Calcium-dependent nitric oxide synthase activity in rat thymocytes

We examined the conversion of L-[3H]arginine to L-[3H]citrulline in lysate from rat thymocytes, which was dependent on Ca2+ and cofactors (FAD, BH4, NADPH). Removal of Ca2+ of the medium, reduced the total L-[3H]citrulline formation by about 97%. The L-[3H]citrulline formation was completely inhibited by the NO synthase inhibitors, NG-nitro-L-arginine and NG-monomethyl-L-arginine, with values for IC50 of 1.2 microM and 19.4 microM, respectively. In intact thymocytes, the L-[3H]citrulline formation was dependent on the intracellular Ca2+ ([Ca2+]i) concentration. Increasing the extracellular free-Ca2+ concentration up to 1.5 mM, was accompanied by an increase in [Ca2+]i inside the thymocytes and there was a parallel increase in the intracellular L-[3H]citrulline formation, which reached a maximal value of 371.2 nM of [Ca2+]i. Addition of NG-nitro-L-arginine to the medium, completely inhibited the formation of L-[3H]citrulline. The immunolabeling study revealed that 15% of the thymocytes isolated from rat thymus constitutively expressed the endothelial isoform of NO synthase.

Pentoxifylline potentiates nitric oxide production and growth suppression in interferon-gamma-treated L929 fibroblasts

In this study the effects of the phosphodiesterase inhibitor pentoxifylline (PTX) on nitric oxide (NO) production and proliferation of murine fibrosarcoma cell line L929 were investigated. We showed that both IFN-gamma (200 U/ml)-induced NO production and inhibition of [3H]thymidine uptake by L929 cells were potentiated in a synergistic fashion in the presence of PTX (200 micrograms/ml). These effects of PTX could be a consequence of phosphodiesterase inhibition, since they were mimicked by cAMP analogue dibutyryl cAMP. PTX failed to affect NO production when added to cells in which inducible NO synthase (iNOS) had already been induced with IFN-gamma and any further induction was blocked by cycloheximide (1 ug/ml), indicating that PTX modulates NO synthesis in L929 cells probably on a pretranslational level. Inhibition of iNOS with L-NAME (3 mM), although completely abolishing NO production, did not have any effect on proliferation of IFN-gamma or IFN-gamma + PTX-treated L929 cells, arguing against the possibility that growth suppression of these cells was due to the enhanced NO production. Moreover, the observation that the NO donor sodium nitroprusside (10-250 microM) significantly increased incorporation of [3H]thymidine in L929 fibroblasts suggests a role for NO in the positive regulation of their growth.