Activation of the cAMP cascade inhibits an early event involved in murine macrophage Ia expression

Prostaglandin E₂ suppresses allergic sensitization and lung inflammation by targeting the E prostanoid 2 receptor on T cells

BACKGROUND

Endogenous prostanoids have been suggested to modulate sensitization during experimental allergic asthma, but the specific role of prostaglandin (PG) E₂ or of specific E prostanoid (EP) receptors is not known.

OBJECTIVE

Here we tested the role of EP2 signaling in allergic asthma.

METHODS

Wild-type (WT) and EP2(-/-) mice were subjected to ovalbumin sensitization and acute airway challenge. The PGE2 analog misoprostol was administered during sensitization in both genotypes. In vitro culture of splenocytes and flow-sorted dendritic cells and T cells defined the mechanism by which EP2 exerted its protective effect. Adoptive transfer of WT and EP2(-/-) CD4 T cells was used to validate the importance of EP2 expression on T cells.

RESULTS

Compared with WT mice, EP2(-/-) mice had exaggerated airway inflammation in this model. Splenocytes and lung lymph node cells from sensitized EP2(-/-) mice produced more IL-13 than did WT cells, suggesting increased sensitization. In WT but not EP2(-/-) mice, subcutaneous administration of misoprostol during sensitization inhibited allergic inflammation. PGE₂ decreased cytokine production and inhibited signal transducer and activator of transcription 6 phosphorylation by CD3/CD28-stimulated CD4(+) T cells. Coculture of flow cytometry-sorted splenic CD4(+) T cells and CD11c(+) dendritic cells from WT or EP2(-/-) mice suggested that the increased IL-13 production in EP2(-/-) mice was due to the lack of EP2 specifically on T cells. Adoptive transfer of CD4(+) EP2(-/-) T cells caused greater cytokine production in the lungs of WT mice than did transfer of WT CD4(+) T cells.

CONCLUSION

We conclude that the PGE2-EP2 axis is an important endogenous brake on allergic airway inflammation and primarily targets T cells and that its agonism represents a potential novel therapeutic approach to asthma.

The resolution of inflammation and cancer

Inflammation has long been thought to contribute to the development of cancer; however there is also clear evidence that the immune system can recognize and eliminate cancer cells. Current research suggests that cancer-associated inflammation has a dual role in tumor progression; inflammatory mediators promote the malignant activity of cancer cells by acting as growth factors and also stimulate angiogenesis, however, cancer-associated inflammation is also linked with immune-suppression that allows cancer cells to evade detection by the immune system. In this review we will discuss the dual role of inflammation in cancer and how endogenous anti-inflammatory mechanisms may equally be important in carcinogenesis.

Low-dose methotrexate therapy for intravenous immunoglobulin-resistant Kawasaki disease

PURPOSE

The aim of this study was to evaluate the efficacy of low-dose oral methotrexate (MTX) as a treatment for patients with Kawasaki disease (KD) which was resistant to intravenous immunoglobulin (IVIG).

PATIENTS AND METHODS

The patients who had persistent or recrudescent fever after treatment with IVIG were subsequently treated with low-dose oral MTX [10mg/body surface area (BSA)] once weekly.

RESULTS

Seventeen patients developed persistent or recrudescent fever after treatment of KD with IVIG and were consequently given MTX. The proportion of children with coronary artery lesions (CALs) was 76%. The median value of maximum body temperatures decreased significantly within 24 hours of MTX therapy (38.6 degrees C vs. 37.0 degrees C, p < 0.001). The median CRP (C-reactive protein) level was found to be significantly lower 1 week after administering the first dose of MTX (8.9mg/dL vs. 1.2mg/dL, p < 0.001). The median duration of fever before MTX treatment was shorter in CALs (-) group than in CALs (+) group (7 days vs. 10 days, p = 0.023). No adverse effects of MTX were observed.

CONCLUSION

MTX treatment for IVIG-resistant KD resulted in quick resolution of fever and rapid improvement of inflammation markers without causing any adverse effects. MTX therapy should further be assessed in a multicenter, placebo-blinded trial to evaluate whether it also improves coronary artery outcome.

Survival strategies of Entamoeba histolytica: Modulation of cell-mediated immune responses

Tissue invasion and disease associated with the protozoan Entamoeba histolytica has long been connected with suppression of host cellular immunity. Dampening of the host's defences may facilitate survival of amoebae in extraintestinal sites and development of the characteristic amoebic abscesses. In recent years, several studies have begun to clarify, at the cellular level, the specific effects E. histolytica has on immune cell accessory and effector cell functions. Here, Darren Campbell and Kris Chadee discuss the parasite's multiple modulatory effects on macrophages and T cells and how this manipulation of immune defences may enable the parasite to remain viable in the host. They suggest the putative amoebic molecules involved and potential modulation by the cytokines: interleukins IL-4 and IL-10 and transforming growth factor-beta.

Identification and characterization of a cyclooxygenase-like enzyme from Entamoeba histolytica

The intestinal protozoan parasite Entamoeba histolytica remains a significant cause of morbidity and mortality worldwide. However, almost nothing is known about the molecules secreted by the parasite that modulate host immune responses or epithelial barrier function in the colon. Herein, we describe the isolation and characterization of a cyclooxygenase (COX)-like enzyme in E. histolytica that is responsible for the biosynthesis of prostaglandin (PG)E2. PGE2 produced by ameba was constitutive but highly dependent on exogenous arachidonic acid substrate. COX-like activity and the immunoreactive protein were localized to the nuclear fraction of E. histolytica. The COX-like protein (72 kDa) was microsequenced and cloned by reverse transcriptase PCR. Ameba COX showed little homology with COX-1/2 enzymes from different species at the nucleotide and amino acid levels. Surprisingly, the arachidonate-binding domain and heme-coordinating and catalytic sites, which are conserved in other species, were absent in ameba. Ameba COX expressed in Escherichia coli demonstrated COX-like enzyme activity in vitro by converting arachidonic acid into PGE2 but not into PGD2 or PGF2alpha. COX activity was inhibited with 1 mM aspirin but not with indomethacin or COX-1/2-specific inhibitors. Taken together, these studies reveal that E. histolytica produces PGE2, by means of a previously undescribed ancestral COX-like enzyme, which could play a major role in pathogenesis and immune evasion.

Regulation of IL-18 production by IFN gamma and PGE2 in mouse microglial cells: involvement of NF-kB pathway in the regulatory processes

Interleukin (IL)-18, a recently identified proinflammatory cytokine, has been implicated in a variety of pathological conditions such as rheumatoid arthritis, insulin-dependent diabetes mellitus, and inflammatory liver injury. Microglial cells are the primary cellular source of IL-18 in the brain. Along with other inflammatory mediators in the central nervous system (CNS), IL-18 may play an important role in the pathogenesis of various neurodegenerative diseases. To understand how lymphokines and lipid mediators participate in the regulation of microglial IL-18 production, we assessed the effects of interferon (IFN)gamma, one of the major macrophage-activating lymphokines, and prostaglandin (PG)E(2), a lipid mediator produced in the brain, on IL-18 production and the expression of the IL-18 processing enzyme, caspase-1, in mouse microglial cells. IFNgamma increased lipopolysaccharide (LPS)-induced IL-18 production and caspase-1 expression, while PGE(2) inhibited LPS-induced IL-18 production. A similar pattern of IL-18 regulation by IFNgamma and PGE(2) was observed at the mRNA level. The regulation of microglial activation by IFNgamma and PGE(2) was accompanied by differential modulation of LPS-induced NF-kB activation. While IFNgamma enhanced LPS-induced NF-kB activation, PGE(2) suppressed its activation. These results indicate that IFNgamma and PGE(2) are the important regulators of proinflammatory microglial activation in CNS, and suggest the involvement of NF-kB pathway in these regulatory processes.

Downregulation of CIITA function by protein kinase a (PKA)-mediated phosphorylation: mechanism of prostaglandin E, cyclic AMP, and PKA inhibition of class II major histocompatibility complex expression in monocytic lines

Prostaglandins, pleiotropic immune modulators that induce protein kinase A (PKA), inhibit gamma interferon induction of class II major histocompatibility complex (MHC) genes. We show that phosphorylation of CIITA by PKA accounts for this inhibition. Treatment with prostaglandin E or 8-bromo-cyclic AMP or transfection with PKA inhibits the activity of CIITA in both mouse and human monocytic cell lines. This inhibition is independent of other transcription factors for the class II MHC promoter. These same treatments also greatly reduced the induction of class II MHC mRNA by CIITA. PKA phosphorylation sites were identified using site-directed mutagenesis and phosphoamino acid analysis. Phosphorylation at CIITA serines 834 and 1050 accounts for the inhibitory effects of PKA on CIITA-driven class II MHC transcription. This is the first demonstration that the posttranslational modification of CIITA mediates inhibition of class II MHC transcription.

The type IV phosphodiesterase specific inhibitor mesopram inhibits experimental autoimmune encephalomyelitis in rodents

Experimental autoimmune encephalomyelitis (EAE) is an autoimmune disease with pathological features reminiscent of those seen in multiple sclerosis and thus serves as an animal model for this disease. Inhibition of type IV phosphodiesterase (PDE IV) in animals with this disease has been shown to result in amelioration of disease symptoms. Here we describe the immunomodulatory activity of the novel potent and selective PDE IV inhibitor mesopram. In vitro, mesopram selectively inhibits the activity of type 1 helper T (Th1) cells without affecting cytokine production or proliferation of type 2 helper T (Th2) cells. Administration of mesopram to rodents inhibits EAE in various models. Clinically, EAE is completely suppressed by mesopram in Lewis rats. This is accompanied by a reduction of inflammatory lesions in spinal cord and brain. RT-PCR analysis revealed a marked reduction in the expression of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in the brains of these animals. Furthermore, the ex vivo production of Th1 cytokines by activated spleen cells derived from mesopram-treated animals is significantly reduced compared to vehicle-treated controls. Amelioration of the clinical symptoms is also observed during chronic EAE in mesopram-treated SJL mice as well as in relapsing-remitting EAE in SWXJ mice using a therapeutic treatment regimen. These data demonstrate the anti-inflammatory activity of mesopram and provide a rationale for its clinical development.

Cholera toxin increases intracellular pH in B lymphoma cells and decreases their antigen-presenting ability

Cholera toxin (CT) can function as a potent adjuvant in the mucosal immune response. However, we have found that treatment of A20-HL murine B lymphoma cells with CT severely inhibits the presentation of ovalbumin (OVA) to cells of the T cell clone 42-6A specific for OVA(323-339)/I-Ad, whereas it does not affect the presentation of OVA(323-339) peptide. CT treatment did not affect the expression of B7-1, B7-2, ICAM-1, LFA-1 or MHC class II on, or the internalization of OVA into A20-HL cells. In CT-treated A20-HL cells, degradation of OVA was decreased, and intracellular pH was raised to a level approximately equivalent to that in CH3NH2-treated cells. Treatment with CH3NH2 is known to raise the pH in endocytic structures and thus inhibits antigen processing. Treatment of A20-HL cells with dibutyryl-cAMP similarly increased intracellular pH. The increase in intracellular pH following CT treatment was inhibited by a cAMP inhibitor, 2',3'-dideoxyadenosine. These results strongly suggest that CT treatment of A20-HL cells inhibits their antigen-presenting cell function by triggering the cAMP cascade, increasing intracellular pH, and reducing the degradation of OVA.

Prostaglandin E receptor subtypes in cultured rat microglia and their role in reducing lipopolysaccharide-induced interleukin-1beta production

Prostaglandins (PGs) are potent modulators of brain function under normal and pathological conditions. The diverse effects of PGs are due to the various actions of specific receptor subtypes for these prostanoids. Recent work has shown that PGE2, while generally considered a proinflammatory molecule, reduces microglial activation and thus has an antiinflammatory effect on these cells. To gain further insight to the mechanisms by which PGE2 influences the activation of microglia, we investigated PGE receptor subtype, i.e., EP1, EP2, EP3, and EP4, expression and function in cultured rat microglia. RT-PCR showed the presence of the EP1 and EP2 but not EP3 and EP4 receptor subtypes. Sequencing confirmed their identity with previously published receptor subtypes. PGE2 and the EP1 agonist 17-phenyl trinor PGE2 but not the EP3 agonist sulprostone elicited reversible intracellular [Ca2+] increases in microglia as measured by fura-2. PGE2 and the EP2/EP4-specific agonists 11-deoxy-PGE1 and 19-hydroxy-PGE2 but not the EP4-selective agonist 1-hydroxy-PGE1 induced dose-dependent production of cyclic AMP (cAMP). Interleukin (IL)-1beta production, a marker of activated microglia, was also measured following lipopolysaccharide exposure in the presence or absence of the receptor subtype agonists. PGE2 and the EP2 agonists reduced IL-1beta production. IL-1beta production was unchanged by EP1, EP3, and EP4 agonists. The adenylyl cyclase activator forskolin and the cAMP analogue dibutyryl cAMP also reduced IL-1beta production. Thus, the inhibitory effects of PGE2 on microglia are mediated by the EP2 receptor subtype, and the signaling mechanism of this effect is likely via cAMP. These results show that the effects of PGE2 on microglia are receptor subtype-specific. Furthermore, they suggest that specific and selective manipulation of the effects of PGs on microglia and, as a result, brain function may be possible.

Upregulation of Kupffer cell beta-adrenoceptors and cAMP levels during the late stage of sepsis

Although a burst of immunoresponsiveness may occur during the early stage of sepsis, late sepsis is characterized by severe immunodepression. In addition, although studies have shown that stimulation of macrophage beta-adrenoceptors results in an increase in cAMP and an associated reduction in macrophage phagocytic activity, it remains unknown whether Kupffer cell beta-adrenoceptor characteristics and cAMP levels are altered during polymicrobial sepsis. To study this, Sprague-Dawley rats were subjected to sepsis by cecal ligation and puncture (CLP). At 5 h (i.e., the early stage of sepsis) or 20 h (late sepsis) after CLP or sham operation, the liver was perfused with collagenase solution and Kupffer cells were isolated. beta-Adrenoceptor characteristics of the isolated Kupffer cells were determined using [125I]iodopindolol, and basal levels of cAMP were measured by radioimmunoassay. The results indicate that while maximum binding capacity (Bmax) of Kupffer cell beta-adrenoceptors was not altered at 5 h, it increased significantly at 20 h after CLP. Similarly, basal levels of cAMP in Kupffer cells did not change at 5 h but increased markedly at 20 h after the onset of sepsis. In contrast, the dissociation constant (Kd, 1/affinity) of Kupffer cell beta-adrenoceptors was not significantly affected by sepsis at both 5 h and 20 h after CLP. Thus, upregulation of beta-adrenoceptors and increase in cAMP levels in Kupffer cells occur during the late stage of polymicrobial sepsis, and this may contribute to the depression of macrophage phagocytic function under such conditions.

Cholera toxin stimulates human B-cell DR antigen biosynthesis at the level of translation

Cholera toxin (CT) exerts many diverse regulatory effects on cells of the immune system and is considered a potent adjuvant on gut mucosal immune responses to orally presented antigens. It has been previously described that CT induces surface DR expression in human resting B-cells. As a further step toward understanding this phenomenon, the molecular mechanisms underlying the regulation of DR expression were investigated. By the use of Western analysis, it is shown that CT increases the total levels of DR protein in highly purified human tonsillar cells. [35S]Methionine incorporation studies show that the aforementioned increase is due to de novo biosynthesis of DR protein at as early as 6 hr after CT stimulation and is completed by 24 hr. [3H]Uridine uptake experiments, nuclear transcription runoff assays, and Northern analysis show that CT does not exert its effect at a transcriptional level, indicating translational regulation. Anti-IgM, which mimics B-cell antigen binding, behaves in a manner similar to CT. The B subunit of CT (B-CT) and prostaglandin E2, either alone or in combination, do not induce DR protein biosynthesis nor do they exert any effect on the transcription of DR beta 1 gene. These results show that cAMP elevation as well as binding of B-CT to GM-1 ganglioside, by themselves, do not lead to DR protein biosynthesis suggesting that other activation pathways may be involved.

Dietary fish oil enhances circulating interferon-gamma in mice during listeriosis without altering in vitro production of this cytokine

The objective of this study was to investigate the impact of feeding mice a diet rich in n-3 polyunsaturated fatty acids (PUFA) from fish oil on the interferon-gamma (IFN-gamma) response during an active infection with Listeria monocytogenes. Weanling female C3H/Hen mice were fed experimental diets containing 20% by weight one of the following fats: soybean oil, lard, or a mixture of menhaden fish oil and corn oil (17:3, w/w). After 4 weeks, mice were injected with 10(5) live L. monocytogenes, and the concentration of IFN-gamma in serum and spleen was determined 0, 2, 4, and 7 days postinfection by enzyme-linked immunosorbent assay (ELISA). Fish oil-fed mice showed significantly higher IFN-gamma in their blood at 2 and 4 days postchallenge compared with mice fed the soybean oil-containing or lard-containing diets (p < 0.001). A higher concentration of IFN-gamma was also found in the spleen homogenate of fish oil-fed mice on day 4 postchallenge (p < 0.005). To examine in vitro IFN-gamma production, splenocytes were isolated from fish oil-fed and soybean oil-fed mice on day 4 postchallenge and cultured with concanavalin A (1 microgram/ml and 10 micrograms/ml) for 24 and 48 h. There were no significant differences in the IFN-gamma concentration in cell culture supernatants between these diet treatments. This study demonstrated that the elevation in the concentration of IFN-gamma in blood and spleen during murine listeriosis is accentuated and prolonged by dietary n-3 PUFA, and these effects may not be due to changes in IFN-gamma production.

Stimulation of macrophages with IFN gamma or TNF alpha shuts off the suppressive effect played by PGE2

PGE2 has been shown to be able to interfere with various lymphocyte and macrophage functions, but its effects on macrophage activation are still unclear. In this study, carried out on peritoneal macrophages obtained from healthy, tumour-bearing and Corynebacterium parvum-treated mice, we demonstrated that PGE2 is involved in the down-regulation of macrophage activation, but it cannot exert its inhibiting effect when macrophages are further stimulated with activating cytokines, such as IFN gamma and TNF alpha. Our findings provide new insight into how macrophage tumoricidal activity may be induced and maintained even in presence of significant levels of PGE2.

Inhibition of IFN-gamma induction of class II MHC genes by cAMP and prostaglandins

Triggering of the cyclic AMP (cAMP) signal transduction pathway inhibits the the interferon gamma (IFN-gamma)-mediated induction of class II major histocompatibility (MHC) genes. We have investigated the mechanism of the inhibition of IFN-gamma induction of the murine A alpha class II MHC gene by cAMP and E series prostaglandins (PGEs). 151 base pairs of the A alpha promoter were sufficient to confer positive regulation by IFN-gamma and negative regulation by cAMP which accurately mirrored the regulation of the endogenous A alpha gene. cAMP also inhibited the IFN-gamma activation of the Fc gamma receptor I (Fc gamma RI) gene promoter, an "early" promoter which is activated immediately after treatment of cells with IFN-gamma. PGEs, which cause an elevation in intracellular cAMP, inhibited the induction of the A alpha promoter, and inhibition was greater in the presence of tumor necrosis factor alpha (TNF alpha). A mutational analysis of the A alpha promoter showed that all four conserved class II promoter elements, the S, X1, X2, and Y boxes, play a role in mediating A alpha promoter activation by IFN-gamma. Mutations in these elements did not diminish the cAMP inhibition of promoter activation by IFN-gamma. Thus, conserved class II promoter sequences which mediate most known examples of positive and negative regulation, including cAMP inhibition of constitutive class II expression, do not mediate cAMP inhibition of IFN-gamma activation of the A alpha promoter. We suggest that this inhibition may be mediated by a novel class II promoter element or by disruption of an early step in the IFN-gamma signal transduction pathway.

Modulation of leukocyte cyclic AMP phosphodiesterase activity by recombinant interferon-gamma: evidence for a differential effect on atopic monocytes

Mechanisms of interferon-gamma (IFN-gamma) effects on monocytes are poorly defined. Evidence for altered IFN-gamma responses and increased monocyte cyclic AMP phosphodiesterase (PDE) activity in atopic dermatitis (AD) suggested a possible relationship. PDE activity in response to IFN-gamma was assessed in normal and atopic monocytes to evaluate the IFN-gamma regulatory role in cell function. Adherence-isolated peripheral blood monocytes were exposed to recombinant human IFN-gamma at 0.1-300 U/ml in Gey's balanced salt solution for varying time periods. Anti-IFN-gamma was used as control. PDE activity was measured by radioenzyme assay using 1 microM cyclic AMP as final substrate concentration. IFN-gamma caused a dose-dependent increase in PDE activity of normal monocytes and the effect was neutralized by anti-IFN-gamma. By contrast, in atopic monocytes, PDE activity was not affected by IFN-gamma at low dose, while at concentrations greater than 200 U/ml, it significantly reduced phosphodiesterase activity. IFN-gamma of PDE activity may alter normal monocyte functions by decreasing cyclic AMP levels. Paradoxical PDE unresponsiveness probably reflects maximal PDE activation in atopic monocytes. This elevated PDE activity is inhibited by high IFN-gamma levels. Reduction of atopic monocyte PDE activity may help to normalize immune function and could account for recent reports of therapeutic efficacy of IFN-gamma in AD.

Role of protein kinase A in LPS-induced activation of NF-kappa B proteins of a mouse macrophage-like cell line, J774

The electrophoretic mobility shift assays (EMSA) with the use of the synthetic HIV-1 NF-kappa B motif as a probe, showed that LPS-treatment of J774 cells (a mouse macrophage cell line) leads to the activation of the fast-moving (denoted as B1) and the slow-moving NF-kappa B (denoted as B2). The binding of both B1 and B2 to the NF-kappa B probe was inhibited specifically by either unlabelled NF-kappa B, or competitor probes, but not by unrelated probes. LPS-induced activation of NF-kappa B was inhibited by a protein kinase A (PKA) inhibitor (H-89), but not by a protein kinase C (PKC) inhibitor (H-7). PMA itself failed to activate NF-kappa B and the depletion of PKC did not prevent LPS-induced activation of NF-kappa B. The pre-treatment of J774 cells with dibutyric cAMP, forskolin, prostaglandin E2 or cholera toxin resulted in NF-kappa B activation. Thus, these data suggested a probable involvement of PKA in LPS-induced NF-kappa B activation in macrophages.

Current concepts in DRA gene regulation

The purpose of this review is to provide an interpretative view of work from our laboratory on the DRA gene, and incorporate it with work from other laboratories. Specially, we will deal with: (a) the functional roles of transcription factors in DRA gene regulation; (b) the mechanisms of DRA induction by cytokines; (c) the analysis of DRA gene control in primary untransformed cells, and (d) interactions among transcription factors critical for DRA gene expression.

Suppression of murine collagen-induced arthritis by treatment with a novel thiazole derivative, SM-8849

The antiarthritic activity of a novel thiazole derivative, SM-8849, was compared with that of indomethacin and D-penicillamine, in mice with collagen-induced arthritis. SM-8849 reduced the incidence and severity of disease in collagen-immunized mice, as assessed by clinical observation. This efficacy was also confirmed by radiographic and histologic studies. Indomethacin produced an apparent reduction of the clinical score, but had only a marginal effect on bone destruction. D-penicillamine did not produce any improvement. Unlike indomethacin and D-penicillamine, SM-8849 reduced the serum levels of anti-type II collagen antibodies. Flow cytometric analysis of spleen cells from arthritic mice revealed an increase in T cells expressing activation antigens (class II antigens) in comparison with normal mice. Treatment with SM-8849, but not indomethacin or D-penicillamine, prevented the increase in Ia-bearing T cells. The results suggest that an effect of SM-8849 on immunocompetent cells may be responsible for the antiarthritic activity of the compound, and this would distinguish its action from that of traditional antirheumatic drugs.

Inhibition of expression of major histocompatibility complex class II molecules in macrophages infected with Leishmania donovani occurs at the level of gene transcription via a cyclic AMP-independent mechanism

Among the important pleiotropic responses to gamma interferon (IFN-gamma) during the activation of macrophages (M phi) is the increased expression of major histocompatibility complex class II genes. In the present study, infection with Leishmania donovani was shown to inhibit in parallel the induction by IFN-gamma of H-2 A beta gene transcription, class II mRNA accumulation, and H-2 Ad protein expression in cells of the murine macrophage cell line P388D1. Treatment of P388D1 cells with either the adenylate cyclase activator cholera toxin or the protein kinase A activator N6-2'-O-dibutyryl cyclic AMP (dibutyryl cAMP) similarly inhibited the induction by IFN-gamma of class II protein expression, and in parallel with Leishmania infection, cholera toxin inhibited the induction of mRNA for the H-2 A alpha and H-2 A beta proteins. Concentrations of intracellular cAMP were significantly increased in cholera toxin-treated cells but not in leishmania-infected cells. These findings indicate that at least one mechanism by which Leishmania infection attenuates the activation of M phi by IFN-gamma involves selective, transcriptional inhibition of major histocompatibility complex class II genes via a cAMP-independent mechanism.

Inhibition of interferon-gamma- and phorbol ester-induced HLA-DR and interleukin-1 production by the expression of a transfected poly(ADP-ribose) synthetase gene in human leukemia THP-1 cells

We have examined a correlation between an expression level of poly(ADP-ribose) synthetase gene and the stage of monocytic differentiation. We selected three human leukemia cell lines, U937, THP-1, and J111, whose differentiation stage was characterized by nitroblue tetrazolium reduction activity, non-specific esterase activity, phagocytic activity and a cell surface marker. Enzyme activity and mRNA level of the synthetase decreased in accompaniment with the progress of monocytic differentiation. When THP-1 cells were treated with either interferon-gamma or phorbol ester, mRNA level of the synthetase decreased and HLA-DR or interleukin-1 was induced, respectively. We transfected expression plasmid of the exogenous synthetase gene to examine whether the down-regulation of the synthetase is a necessary step to induce these proteins. An expression of the exogenous synthetase gene inhibited the interferon-gamma- and phorbol ester-dependent induction of HLA-DR and interleukin-1. The results suggest that down-regulation of the synthetase may be a signal mediator of immunological response such as HLA-DR or interleukin-1 production in monocytes.

Biphasic effect of camp-elevating agents on ICAM-1 expression stimulated by retinoic acid and interferonγ

Incubation of the human glioma cell line HS 683 in the presence of IFN-gamma or retinoic acid strongly stimulates the cell-surface expression of the intercellular adhesion molecule ICAM-1. We have investigated the role of the cAMP-mediated signal transduction pathway in this process and report that pharmacological agents which increased the intracellular levels of cAMP exhibited a biphasic action on ICAM-1 expression in human glioma cell line HS 683. Treatment for 1 hr with 25 microM forskolin or 1 mM isobutylmethylxanthine, or for 12 hr with 100 ng/ml pertussis toxin or 50 micrograms/ml cholera toxin transiently stimulated ICAM-1 expression with a maximal level of expression 8 hr post treatment, after which time ICAM-1 expression returned to the basal level. On the other hand, such pretreatments inhibited the inducing effects of either retinoic acid or IFN-gamma. Indeed, 24 hr after treatment with cAMP-elevating agents, both the retinoic-acid- and the IFN-gamma-induced ICAM-1 expression were inhibited by 60 to 80%, with a maximal 90 to 100% inhibition 72 hr post treatment. This inhibition of the cell-surface expression of ICAM-1 was confirmed at the mRNA level. The intracytoplasmic levels of cAMP were also quantified following treatments with forskolin, retinoic acid or IFN-gamma. In response to forskolin, cAMP levels increased 30-fold within 5 min, whereas a 10-fold increase occurred 60 min following treatment with 10 microM retinoic acid. Interferon gamma, in contrast, did not induce cAMP accumulation. These results were also correlated with an in vitro activation of adenylyl cyclase activity by retinoic acid and inhibition of this activity by IFN-gamma, in a dose-dependent and a GTP-dependent manner. Our results suggest that the suppression of IFN-gamma-induced ICAM-1 expression, obtained upon pre-treatment with cAMP-elevating agents, is due to direct antagonism with IFN-gamma action on adenylyl cyclase. However, the inhibition of retinoic-acid-induced ICAM-1 expression cannot be explained by the same mechanisms. The timing of adenylyl cyclase stimulation and cAMP accumulation, as well as the levels of cAMP accumulation, are probably involved in this inhibition. Our results also emphasize the fact that the induction of ICAM-1 expression is a multi-step process implicating different transductional signals among which cAMP might be involved as a second messenger.

Transduction of the IFN-gamma signal for HLA-DR expression in the promonocytic line THP-1 involves a late-acting PKC activity

Interferon gamma (IFN-gamma) is the most potent known lymphokine for activating macrophages and has been shown to induce expression of HLA-DR in THP-1 cells, a monocytic tumor cell line which expresses many of the properties of monocytes, in a dose- and time-dependent manner. Experiments were designed to examine, by FACS analysis and by measurement of messenger RNA levels, the molecular mechanism regulating the expression of HLA-DR molecules. The expression of HLA-DR molecules induced by IFN-gamma was blocked by the protein kinase C (PKC) inhibitors sphingosine, staurosporine, and H7. H7 when added up to 20 hr after the initial stimulation with IFN-gamma prevented the further expression of HLA-DR. The general kinase inhibitors H8, H9, and HA1004, all less potent PKC inhibitors than H7, did not block the IFN-gamma-induced expression of HLA-DR at the concentrations employed. W7, a calmodulin antagonist, but not a PKC inhibitor, was also unable to prevent the IFN-gamma-induced expression of HLA-DR. Treatment of THP-1 with phorbol 12-myristate 13-acetate (PMA), a direct activator of PKC, alone or with Ca2+ ionophore A23187, was unable to induce HLA-DR expression. However, pretreatment with PMA for 24 hr prior to IFN-gamma stimulation decreased the IFN-gamma-induced expression of HLA-DR without decreasing IFN-gamma receptor levels. These results suggest that PKC plays a significant role in the IFN-gamma-induced signal transduction pathway leading to the expression of HLA-DR in cells of the mononuclear phagocytic lineage, and that PKC activity is required throughout the course of events leading to the actual expression of HLA-DR.

The exposure of murine macrophages to alpha 2-macroglobulin 'fast' forms results in the rapid secretion of eicosanoids

The exposure of [3H]arachidonate-radiolabelled murine peritoneal macrophages to alpha 2-macroglobulin-methylamine or alpha 2-macroglobulin-trypsin but not native alpha 2-macroglobulin (alpha 2M) results in the rapid secretion of [3H]eicosanoids. Resident peritoneal macrophages stimulated with 0.1 microM alpha 2M-methylamine exhibited an enhanced secretion within 10 min. The ability of alpha 2M 'fast' forms to stimulate secretion of [3H]eicosanoids was similar to that observed in the presence of the murine macrophage chemoattractant platelet-activating factor. As observed for total [3H]eicosanoid secretion, alpha 2M 'fast' forms also rapidly enhanced the secretion of the cAMP-elevating prostanoid, prostaglandin E2, from resident peritoneal macrophages. Stimulated secretion of prostaglandin E2 in response to 0.1 microM alpha 2M-methylamine was less rapid than that observed using 0.1 microM platelet-activating factor. Similar amounts of secreted prostaglandin E2 were present in media of macrophage cultures after 1 h exposure to the two stimuli. In the presence of 0.1 microM alpha 2M-methylamine, secreted prostaglandin E2 remained elevated, compared to the appropriate buffer control, for at least 24 h. The present results indicate that receptor recognition of alpha 2M 'fast' forms by macrophages results in the rapid stimulation of eicosanoid secretion and suggest that secretion of prostaglandin E2 and other eicosanoids may be involved in the ability of alpha 2 M 'fast' forms to regulate various macrophage functional responses.

Differential modulation by N4, 2'-O-dibutyryl cytidine 3':5'-cyclic monophosphate of neutrophil activation

The cyclic pyrimidine nucleotide, cCMP, is an endogenous substance in mammalian cells but little is known on its functional role. We studied the effects of cCMP, its cell-permeant analogue, N4,2'-O-dibutyryl cytidine 3':5'-cyclic monophosphate (Bt2cCMP), and of butyrate on superoxide (O2-) formation and cytosolic Ca2+ [( Ca2+]i) in human neutrophils. Bt2cCMP inhibited O2- formation and the rise in [Ca2+]i induced by a chemotactic peptide at submaximally effective concentrations. O2- formation induced by platelet-activating factor was potentiated by Bt2cCMP, whereas the cyclic nucleotide had no effect on the rise in [Ca2+]i induced by this agonist. Bt2cCMP enhanced O2- formation induced by tau-hexachlorocyclohexane at a submaximally effective concentration. O2- formation stimulated by complement C5a, concanavalin A, NaF, A 23187, phorbol myristate acetate and arachidonic acid was not affected by Bt2cCMP. cCMP was less effective than Bt2cCMP to inhibit fMet-Leu-Phe-induced O2- formation, and butyrate was without effect on any of the functional parameters studied. Our data show that a cell-permeant analogue of cCMP differentially inhibits and potentiates activation of human neutrophils.