Timing of prostaglandin exposure is critical for the inhibition of LPS- or IFN-gamma-induced macrophage NO synthesis by PGE2

The role of PGE2 and EP receptors on lung's immune and structural cells; possibilities for future asthma therapy

Asthma is the most common airway chronic disease with treatments aimed mainly to control the symptoms. Adrenergic receptor agonists, corticosteroids and anti-leukotrienes have been used for decades, and the development of more targeted asthma treatments, known as biological therapies, were only recently established. However, due to the complexity of asthma and the limited efficacy as well as the side effects of available treatments, there is an urgent need for a new generation of asthma therapies. The anti-inflammatory and bronchodilatory effects of prostaglandin E2 in asthma are promising, yet complicated by undesirable side effects, such as cough and airway irritation. In this review, we summarize the most important literature on the role of all four E prostanoid (EP) receptors on the lung's immune and structural cells to further dissect the relevance of EP2/EP4 receptors as potential targets for future asthma therapy.

Obesity activates immunomodulating properties of mesenchymal stem cells in adipose tissue with differences between localizations

Mesenchymal stem cells from healthy adipose tissue are adipocytes progenitors with immunosuppressive potential that are used for years in cell therapy. Whether adipose stem cells (ASC) may prevent inflammation in early obesity is not known. To address this question, we performed a kinetic study of high-fat (HF) diet induced obesity in mice to follow the immune regulating functions of adipose stem cells (ASC) isolated from the subcutaneous (SAT) and the visceral adipose tissue (VAT). Our results show that, early in obesity and before inflammation was detected, HF diet durably and differently activated ASC from SAT and VAT. Subcutaneous ASC from HF-fed mice strongly inhibited the proliferation of activated T lymphocytes, whereas visceral ASC selectively inhibited TNFα expression by macrophages and simultaneously released higher concentrations of IL6. These depot specific differences may contribute to the low-grade inflammation that develops with obesity in VAT while inflammation in SAT is delayed. The mechanisms involved differ from those already described for naïve cells activation with inflammatory cytokines and probably engaged metabolic activation. These results evidence that adipose stem cells are metabolic sensors acquiring an obesity-primed immunocompetent state in answer to depot-specific intrinsic features with overnutrition, placing these cells ahead of inflammation in the local dialog with immune cells.

Anti-inflammatory properties of convolutamydine A and two structural analogues

AIMS

Convolutamydine A is an oxindole alkaloid that can be isolated from a marine bryozoan. Due to the variety of biological effects, two analogues were synthesized and their anti-inflammatory properties were evaluated.

MAIN METHODS

The anti-inflammatory effects of convolutamydine A and its analogues (ISA003 and ISA147) were investigated in a formalin-induced licking behaviour model, where mice received an intraplantar injection of formalin and their licking behaviour was evaluated for 30min. Additionally, inflammatory parameters were evaluated in a subcutaneous air pouch (SAP) model of carrageenan-induced inflammation. Exudates were collected for leukocyte counts; measurement of protein, prostaglandin E2 (PGE2) and cytokines by ELISA; and analysis of nitric oxide (NO) using a nitrate conversion protocol. Cyclooxygenase-2 (COX2) and inducible nitric oxide synthase (iNOS) from RAW 264.7 cells were quantified by immunoblotting.

KEY FINDINGS

Convolutamydine A and its two analogues inhibited the formalin-induced licking response at doses as low as 0.01mg/kg. An inhibitory effect was also observed on leukocyte migration and the production of NO, PGE2 and cytokines (IL-6 and TNF-α). The reduction in inflammatory parameters did not appear to be correlated with a direct reduction in the number of cells in the SAP, because a reduction in NO and PGE2 production by cultured macrophages was observed in addition to the inhibition of iNOS and COX2 enzyme expression.

SIGNIFICANCE

These results indicate that convolutamydine A and its two analogues have significant anti-inflammatory effects. These substances can be improved to generate lead compounds for the synthesis of new anti-inflammatory drugs.

Characterization of the inflammatory response during Ehrlich ascitic tumor development

INTRODUCTION

Ehrlich tumor is a mammary adenocarcinoma with aggressive behavior. Inoculated in mice peritoneal cavity, the Ehrlich tumor grows in ascitic form (EAT). Since inflammation modulates tumor progression we further investigated the inflammatory response during EAT growth.

METHODS

Balb/C mice were intraperitoneal inoculated with 5×10(5) Ehrlich cells and after every 2days, blood samples were collected for hemoglobin, hematocrit, platelets and leukocytes counts. The ascitic fluid was collected for protein concentration and cell count. Phenotype analysis of the peritoneal cells was made by FACS, prostaglandin E2 (PGE2) and cytokines by ELISA, nitric oxide (NO) by nitrate conversion protocol, and cyclooxygenase-1 (COX1), COX2 and inducible nitric oxide synthase (iNOS) by immunoblotting.

RESULTS

Following EAT inoculation into the peritoneal cavity there was a rapid increase in ascitis volume and protein concentration. The cell number in ascitis remained stable until day 8 (lag phase) followed by a sharp increase. As tumor progressed, blood leukocytes increased and erythrocyte decreased. Phenotypic analysis showed that during the lag phase the percentage of F4/80(+) cells remained similar to control levels and around 7% of this population was also positive for the GR1 marker. These double-positive cells (probably inflammatory monocytes) markedly increased at day 6. The percentage of F4/80-GR1(+)cells (probably neutrophils) was low and did not significantly vary during tumor progression. CD4(+) and CD8(+) cells were not detected in the time points analyzed. iNOS and COX1 expression increased after day 2 reaching peak levels on day 10. COX2 enzyme expression did not change significantly over time. Sustained increase in PGE2 and NO levels was observed. IL-10 and MCP-1 peaked at day 14 and IL-1β increased progressively till day 10. IFN-γ levels were low till day 10, increasing progressively after that.

DISCUSSION

These data extended the characterization of the inflammatory response during Ehrlich ascitis tumor growth, further validating it as a useful model for antitumor drugs screening.

Anti-inflammatory activity of Odina wodier Roxb, an Indian folk remedy, through inhibition of toll-like receptor 4 signaling pathway

Inflammation is part of self-limiting non-specific immune response, which occurs during bodily injury. In some disorders the inflammatory process becomes continuous, leading to the development of chronic inflammatory diseases including cardiovascular diseases, diabetes, cancer etc. Several Indian tribes used the bark of Odina wodier (OWB) for treating inflammatory disorders. Thus, we have evaluated the immunotherapeutic potential of OWB methanol extract and its major constituent chlorogenic acid (CA), using three popular in vivo antiinflammatory models: Carrageenan- and Dextran-induced paw edema, Cotton pellet granuloma, and Acetic acid-induced vascular permeability. To elucidate the possible anti-inflammatory mechanism of action we determine the level of major inflammatory mediators (NO, iNOS, COX-2-dependent prostaglandin E2 or PGE2), and pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-12). Further, we determine the toll-like receptor 4 (TLR4), Myeloid differentiation primary response gene 88 (MyD88), c-Jun N-terminal kinases (JNK), nuclear factor kappa-B cells (NF-κB), and NF-kB inhibitor alpha (IK-Bα) by protein and mRNA expression, and Western blot analysis in drug treated LPS-induced murine macrophage model. Moreover, we determined the acute and sub-acute toxicity of OWB extract in BALB/c mice. Our study demonstrated a significant anti-inflammatory activity of OWB extract and CA along with the inhibition of TNF-α, IL-1β, IL-6 and IL-12 expressions. Further, the expression of TLR4, NF-κBp65, MyD88, iNOS and COX-2 molecules were reduced in drug-treated groups, but not in the LPS-stimulated untreated or control groups, Thus, our results collectively indicated that the OWB extract and CA can efficiently inhibit inflammation through the down regulation of TLR4/MyD88/NF-kB signaling pathway.

Post-exposure therapeutic efficacy of COX-2 inhibition against Burkholderia pseudomallei

Burkholderia pseudomallei is a Gram-negative, facultative intracellular bacillus and the etiologic agent of melioidosis, a severe disease in Southeast Asia and Northern Australia. Like other multidrug-resistant pathogens, the inherent antibiotic resistance of B. pseudomallei impedes treatment and highlights the need for alternative therapeutic strategies that can circumvent antimicrobial resistance mechanisms. In this work, we demonstrate that host prostaglandin E2 (PGE₂) production plays a regulatory role in the pathogenesis of B. pseudomallei. PGE₂ promotes B. pseudomallei intracellular survival within macrophages and bacterial virulence in a mouse model of pneumonic melioidosis. PGE₂-mediated immunosuppression of macrophage bactericidal effector functions is associated with increased arginase 2 (Arg2) expression and decreased nitric oxide (NO) production. Treatment with a commercially-available COX-2 inhibitor suppresses the growth of B. pseudomallei in macrophages and affords significant protection against rapidly lethal pneumonic melioidosis when administered post-exposure to B. pseudomallei-infected mice. COX-2 inhibition may represent a novel immunotherapeutic strategy to control infection with B. pseudomallei and other intracellular pathogens.

Burkholderia pseudomallei is the etiologic agent of melioidosis, a severe disease endemic in Southeast Asia and Northern Australia. B. pseudomallei is also classified as a Tier 1 select agent due to the threat of malicious use of the organism. Treatment of melioidosis is complicated by the inherent multidrug resistance of B. pseudomallei, leading to high case fatality rates or disease relapse. New therapeutic strategies are urgently needed to improve patient survival and to protect against a deliberate release of B. pseudomallei. Immunotherapeutics that can enhance the host immune response and delay disease progression represent a significant area of research interest. A number of immunomodulatory agents delivered locally to the lung prior to B. pseudomallei infection have afforded significant protection against pulmonary disease in animal models of melioidosis; however, their protective capacity significantly wanes upon post-exposure administration. In this work, we identify the PGE₂ pathway as an immunotherapeutic target in pulmonary melioidosis and show that post-exposure COX-2 inhibition provides significant protection against lethal B. pseudomallei lung infection in mice. Further research examining FDA-approved COX-2 inhibitors as post-exposure prophylaxis for B. pseudomallei is warranted, as this may represent a safe, affordable, and efficacious immunotherapeutic strategy.

Role of PPARγ in COX-2 activation in mycobacterial pulmonary inflammation

Preliminary studies show that intranasal (i.n.) administration of BCG in mice induces M1 activation of alveolar macrophages (M∅) that increase TNF-α production and cyclooxygenase-2 (COX-2) expression but reduce constitutive peroxisome proliferator-activated receptor gamma (PPARγ) expression. However, COX-2 is catalytically inactive for prostaglandin E(2) release, unlike COX-2 that is active in M1 activation in vitro by BCG. In this study, we determined the role of PPARγ for BCG-induced M1 activation in vivo and in vitro. We found that treatment of mice with GW9662, a PPARγ antagonist, prior to i.n. BCG, partially restored PPARγ expression, and decreased TNF-α production and COX-2 expression. But COX-2 was still inactive. The decreased effects on TNF-α and COX-2 were also observed when alveolar M∅ were treated in vitro with GW9662/BCG, but COX-2 was still active. Our results indicate that PPARγ upregulates M1 activation of alveolar M∅, but inactive COX-2 formation is independent of PPARγ in mycobacterial pulmonary inflammation.

Glycyrrhizic acid suppresses Cox-2-mediated anti-inflammatory responses during Leishmania donovani infection

OBJECTIVES

The aim of the present study was to characterize glycyrrhizic acid (GA) and assess its immunomodulatory potential in a model of experimental visceral leishmaniasis.

METHODS

The antileishmanial activity of GA was tested in an amastigote-macrophage model and its non-cytotoxic dose was measured by a cell viability assay. To understand the effector mechanism of GA-treated macrophages against leishmanial parasites, real-time PCR analysis of inducible nitric oxide synthase 2 (iNOS2) was carried out followed by measurement of nitric oxide generation by Griess reagent. The effect of GA on the production of cytokines, such as interleukin (IL)-12, tumour necrosis factor (TNF)-α, IL-10 and transforming growth factor (TGF)-β, was measured by ELISA (protein) and real-time PCR. The expression of iNOS2 and cyclooxygenase-2 (Cox-2) was studied by western blotting. The parasite burden of the liver and spleen following GA treatment was determined by the stamp-smear method, and T cell proliferation was assessed via [³H]thymidine uptake, measured by a liquid scintillation counter.

RESULTS

Results showed that GA treatment caused an enhanced expression of iNOS2 along with inhibition of Cox-2 in Leishmania donovani-infected macrophages. GA treatment in infected macrophages enhanced the expression of IL-12 and TNF-α, concomitant with a down-regulation of IL-10 and TGF-β. GA increased macrophage effector responses via inhibition of Cox-2-mediated prostaglandin E2 release in L. donovani-infected macrophages. GA also decreased hepatic and splenic parasite burden and increased T cell proliferation in Leishmania-infected BALB/c mice.

CONCLUSIONS

These results provide a mechanistic understanding of GA-mediated protection against leishmanial parasites within the host.

Distinct protein kinase A anchoring proteins direct prostaglandin E2 modulation of Toll-like receptor signaling in alveolar macrophages

Toll-like receptors (TLRs) direct a proinflammatory program in macrophages. One mediator whose generation is induced by TLR ligation is prostaglandin E(2) (PGE(2)), which is well known to increase intracellular cAMP upon G protein-coupled receptor ligation. How PGE(2)/cAMP shapes the nascent TLR response and the mechanisms by which it acts remain poorly understood. Here we explored PGE(2)/cAMP regulation of NO production in primary rat alveolar macrophages stimulated with the TLR4 ligand LPS. Endogenous PGE(2) synthesis accounted for nearly half of the increment in NO production in response to LPS. The enhancing effect of PGE(2) on LPS-stimulated NO was mediated via cAMP, generated mainly upon ligation of the E prostanoid 2 receptor and acting via protein kinase A (PKA) rather than via the exchange protein activated by cAMP. Isoenzyme-selective cAMP agonists and peptide disruptors of protein kinase A anchoring proteins (AKAPs) implicated PKA regulatory subunit type I (RI) interacting with an AKAP in this process. Gene knockdown of potential RI-interacting AKAPs expressed in alveolar macrophages revealed that AKAP10 was required for PGE(2) potentiation of LPS-induced NO synthesis. AKAP10 also mediated PGE(2) potentiation of the expression of cytokines IL-10 and IL-6, whereas PGE(2) suppression of TNF-α was mediated by AKAP8-anchored PKA-RII. Our data illustrate the pleiotropic manner in which G protein-coupled receptor-derived cAMP signaling can influence TLR responses in primary macrophages and suggest that AKAP10 may coordinate increases in gene expression.

M. bovis BCG induced expression of COX-2 involves nitric oxide-dependent and -independent signaling pathways

In a multifaceted immunity to mycobacterial infection, induced expression of cyclooxygenase-2 (COX-2) by Mycobacterium bovis bacillus Calmette-Guerin (BCG) may act as an important influencing factor for the effective host immunity. We here demonstrate that M. bovis BCG-triggered TLR2-dependent signaling leads to COX-2 and PGE2 expression in vitro in macrophages and in vivo in mice. Further, the presence of PGE2 could be demonstrated in sera or cerebrospinal fluid of tuberculosis patients. The induced COX-2 expression in macrophages is dependent on NF-kappaB activation, which is mediated by inducible NO synthase (iNOS)/NO-dependent participation of the members of Notch1-PI-3K signaling cascades as well as iNOS-independent activation of ERK1/2 and p38 MAPKs. Inhibition of iNOS activity abrogated the M. bovis BCG ability to trigger the generation of Notch1 intracellular domain (NICD), a marker for Notch1 signaling activation, as well as activation of the PI-3K signaling cascade. On the contrary, treatment of macrophages with 3-morpholinosydnonimine, a NO donor, resulted in a rapid increase in generation of NICD, activation of PI-3K pathway, as well as the expression of COX-2. Stable expression of NICD in RAW 264.7 macrophages resulted in augmented expression of COX-2. Further, signaling perturbations suggested the involvement of the cross-talk of Notch1 with members with the PI-3K signaling cascade. These results implicate the dichotomous nature of TLR2 signaling during M. bovis BCG-triggered expression of COX-2. In this perspective, we propose the involvement of iNOS/NO as one of the obligatory, early, proximal signaling events during M. bovis BCG-induced COX-2 expression in macrophages.

Persistent inactivation of macrophage cyclooxygenase-2 in mycobacterial pulmonary inflammation

The induction of cyclooxygenase-2 (COX-2) in tissue macrophages (MØ) increases prostaglandin E(2) (PGE(2)) release, potentially down-regulating granulomatous inflammation. In response to Mycobacteria, local MØ express COX-2, which is either nuclear envelope (NE)-associated or NE-dissociated. Persistent mycobacterial pulmonary inflammation is characterized by alveolar MØ expressing NE-dissociated (inactive) COX-2 without release of PGE(2). In this study, we examined COX-2 in alveolar MØ after intranasal exposure to heat-killed Mycobacterium bovis BCG (HK-BCG). After administration, whole lungs of C57Bl/6 mice were lavaged with saline; COX-2 expression and PGE(2) release by alveolar MØ and tumor necrosis factor (TNF)-alpha and nitric oxide levels in the lung lavage were monitored. Normal alveolar MØ had undetectable levels of COX-2 on Western blots. However, 1 day after intranasal administration, almost all alveolar MØ had phagocytosed HK-BCG and expressed NE-dissociated COX-2 without any increase in the release of PGE(2). At 28 days after intranasal administration, 68% of alveolar MØ still contained both BCG and the NE-dissociated form of COX-2. NE-associated (active) COX-2 was not observed in alveolar MØ. In contrast, 7 days after intraperitoneal injection of HK-BCG, peritoneal MØ containing HK-BCG were no longer detected. At 28 days after intranasal administration, TNF-alpha and nitrite levels in the lung lavage fluid were significantly higher than those in controls. Our results indicate that mycobacterial pulmonary inflammation is associated with suppressed PGE(2) production by alveolar MØ, with expression of COX-2 dissociated from the NE.

Cross-Regulation of iNOS and COX-2 by its Products in Murine Macrophages Under Stress Conditions

Exposure of macrophages to heat shock induces rapid synthesis of heat shock proteins (HSPs) which are important for cell homeostasis. Prostaglandins (PGs) and nitric oxide (NO) are important cell regulatory molecules. We have therefore investigated the interactions between these molecules in the LPS-induced expression of iNOS and COX-2 and in the mitochondrial activity of macrophages. Cultures of the murine macrophage cell line, J774, were exposed to heat shock (43 degrees C, 30 min) and stimulated with LPS (1 microg/ml), concomitantly or after 8h of cell recovery. NO production was measured by Griess reaction; PGE(2) by ELISA; HSP70, iNOS and COX-2 by immunobloting; mitochondrial activity by MTT assay. Heat shock induced HSP70, but not iNOS or COX-2 whereas LPS induced iNOS and COX-2 but not HSP70. When heat shock and LPS were given concomitantly, iNOS but not COX-2 expression was reduced. When a period of 8h was given between heat shock and LPS stimulation, iNOS, COX-2, PGE(2) and NO levels were significantly increased. Under these conditions, the expression of COX-2 was reduced by L-NAME (NO-synthesis inhibitor) and of iNOS by nimesulide (PGs-synthesis inhibitor). Such cross-regulation was not observed in cells at 37 degrees C. These treatments significantly reduced MTT levels in cells at 37 degrees C but not in cells submitted to heat shock. These results suggest that HSPs and cross-regulation of iNOS and COX-2 by their products might be of relevance in the control of cell homeostasis during stress conditions.

Genome-wide identification and characterization of transcripts translationally regulated by bacterial lipopolysaccharide in macrophage-like J774.1 cells

Although Escherichia coli LPS is known to elicit various proinflammatory responses in macrophages, its effect on the translational states of transcripts has not yet been explored on a genome-wide scale. To address this, we investigated the mRNA profiles in polysomal and free messenger ribonucleoprotein particle (mRNP) fractions of mouse macrophage-like J774.1 cells, using Affymetrix Mouse Genome 430 2.0 GeneChips. Comparison of the mRNA profiles in total cellular, polysomal, and free mRNP fractions enabled us to identify transcripts that were modulated at the translational level by LPS: among 19,791 transcripts, 115 and 418 were up- and downregulated at 1, 2, or 4 h after LPS stimulation (100 ng/ml) in a translation-dependent manner. Interestingly, gene ontology-based analysis suggested that translation-dependent downregulated genes frequently include those encoding proteins in the mitochondrial respiratory chain. In fact, the mRNA levels of some transcripts for complexes I, IV, and V in the mitochondrial respiratory chain were translationally downregulated, eventually contributing to the decline of their protein levels. Moreover, the amount of metabolically labeled cytochrome oxidase subunit Va in complex IV was decreased without any change of its mRNA level in total cellular fraction after LPS stimulation. Consistently, the total amounts and activities of complexes I and IV were attenuated by LPS stimulation, and the attenuation was independent of nitric oxide. These results demonstrated that translational suppression may play a critical role in the LPS-mediated attenuation of mitochondrial oxidative phosphorylation in a nitric oxide-independent manner in J774.1 cells.

Catalytically inactive cyclooxygenase 2 and absence of prostaglandin E2 biosynthesis in murine peritoneal macrophages following in vivo phagocytosis of heat-killed Mycobacterium bovis bacillus Calmette-Guérin

Over 25 years ago, it was observed that peritoneal macrophages (Mphi) isolated from mice given heat-killed Mycobacterium bovis bacillus Calmette-Guérin (HK-BCG) i.p. did not release PGE(2). However, when peritoneal Mphi from untreated mice are treated with HK-BCG in vitro, cyclooxygenase 2 (COX-2), a rate-limiting enzyme for PGE(2) biosynthesis, is expressed and the release of PGE(2) is increased. The present study of peritoneal Mphi obtained from C57BL/6 mice and treated either in vitro or in vivo with HK-BCG was undertaken to further characterize the cellular responses that result in suppression of PGE(2) release. The results indicate that Mphi treated with HK-BCG in vivo express constitutive COX-1 and inducible COX-2 that are catalytically inactive, are localized subcellularly in the cytoplasm, and are not associated with the nuclear envelope (NE). In contrast, Mphi treated in vitro express catalytically active COX-1 and COX-2 that are localized in the NE and diffusely in the cytoplasm. Thus, for local Mphi activated in vivo by HK-BCG, the results indicate that COX-1 and COX-2 dissociated from the NE are catalytically inactive, which accounts for the lack of PGE(2) production by local Mphi activated in vivo with HK-BCG. Our studies further indicate that the formation of catalytically inactive COX-2 is associated with in vivo phagocytosis of HK-BCG, and is not dependent on extracellular mediators produced by in vivo HK-BCG treatment. This attenuation of PGE(2) production may enhance Mphi-mediated innate and Th1-acquired immune responses against intracellular infections which are suppressed by PGE(2).

Recurrent headache as the main symptom of acquired cerebral toxoplasmosis in nonhuman immunodeficiency virus-infected subjects with no lymphadenopathy: the parasite may be responsible for the neurogenic inflammation postulated as a cause of different types of headaches

Headache and/or migraine, a common problem in pediatrics and internal medicine, affect about 5% to 10% children and adolescents, and nearly 30% of middle-aged women. Headache is also one of the most common clinical manifestations of acquired Toxoplasma gondii infection of the central nervous system (CNS) in immunosuppressed subjects. We present 11 apparently nonhuman immunodeficiency virus-infected children aged 7 to 17 years (8 girls, 3 boys) and 1 adult woman with recurrent severe headaches in whom latent chronic CNS T. gondii infection not manifested by enlarged peripheral lymph nodes typical for toxoplasmosis, was found. In 7 patients, the mean serum IgG Toxoplasma antibodies concentration was 189 +/- 85 (SD) IU/mL (range 89 to 300 IU/mL), and in 5 other subjects, the indirect fluorescent antibody test titer ranged from 1:40 to 1:5120 IU/mL (n= <1:10 IU/mL). Some of the patients suffered also from atopic dermatitis (AD) and were exposed to cat and/or other pet allergens, associated with an increased IL-4 and decreased IFN-gamma production. These cytokine irregularities caused limited control of cerebral toxoplasmosis probably because IL-4 down-regulated both the production of IFN-gamma and its activity, and stimulated production of a low NO-producing population of monocytes, which allowed cysts rupture, increased parasite multiplication and finally reactivation of T. gondii infection. The immune studies performed in 4 subjects showed a decreased percentage of T lymphocytes, increased total number of lymphocytes B and serum IgM concentration, and impaired phagocytosis. In addition, few of them had also urinary tract diseases known to produce IL-6 that can mediate immunosuppressive functions, involving induction of the anti-inflammatory cytokine IL-10. These disturbances probably resulted from the host protective immune reactions associated with the chronic latent CNS T. gondii infection/inflammation. This is consistent with significantly lower enzyme indoleamine 2,3-dioxygenase (IDO) activity reported in atopic than in nonatopic individuals, and an important role that IDO and tryptophan degradation pathways plays in both, the host resistance to T. gondii infection and its reactivation. Analysis of literature information on the subjects with different types of headaches caused by foods, medications, and other substances, may suggest that their clinical symptoms and changes in laboratory data result at least in part from interference of these factors with dietary tryptophan biotransformation pathways. Several of these agents caused headache attacks through enhancing NO production via the conversion of arginine to citrulline and NO by the inducible nitric oxide synthase enzyme, which results in the high-output pathway of NO synthesis. This increased production of NO is, however, quickly down-regulated by NO itself because this biomolecule can directly inactivate NOS, may inhibit Ia expression on IFN-gamma-activated macrophages, which would limit antigen-presenting capability, and block T-cell proliferation, thus decreasing the antitoxoplasmatic activity. Moreover, NO inhibits IDO activity, thereby suppressing kynurenine formation, and at least one member of the kynurenine pathway, 3-hydroxyanthranilic acid, has been shown to inhibit NOS enzyme activity, the expression of NOS mRNA, and activation of the inflammatory transcription factor, nuclear factor-kB. In addition, the anti-inflammatory cytokines IL-4 and IL-10, TGF-beta, and a cytokine known as macrophage deactivating factor, have been shown to directly modulate NO production, sometimes expressing synergistic activity. On the other hand, IL-4 and TGF-beta can suppress IDO activity in some cells, for example human monocytes and fibroblasts, which is consistent with metabolic pathways controlled by IDO being a significant contributor to the proinflammatory system. Also, it seems that idiopathic intracranial hypertension, pseudotumor cerebri, and aseptic meningitis, induced by various factors, may result from their interference with IDO and inducible nitric oxide synthase activities, endogenous NO level, and cytokine irregularities which finally affect former T. gondii status 2mo in the brain. All these biochemical disturbances caused by the CNS T. gondii infection/inflammation may also be responsible for the relationship found between neurologic symptoms, such as headache, vertigo, and syncope observed in apparently immunocompetent children and adolescents, and physical and psychiatric symptoms in adulthood. We therefore believe that tests for T. gondii should be performed obligatorily in apparently immunocompetent patients with different types of headaches, even if they have no enlarged peripheral lymph nodes. This may help to avoid overlooking this treatable cause of the CNS disease, markedly reduce costs of hospitalization, diagnosis and treatment, and eventually prevent developing serious neurologic and psychiatric disorders.

Differential subcellular localization of COX-2 in macrophages phagocytosing heat-killed Mycobacterium bovis BCG

Cyclooxygenase-2 (COX-2)-mediated prostaglandin E(2) (PGE(2)) biosynthesis by macrophages downregulates microbicidal activities in innate and acquired immune responses against intracellular bacteria. Previous studies in mice showed that intraperitoneal administration of heat-killed Mycobacterium bovis bacillus Calmette-Guérin (HK-BCG) resulted in induction of splenic PGE(2)-releasing macrophages in 7-14 days. In contrast, HK-BCG induced catalytically inactive COX-2 at relatively high levels in the macrophages within 1 day. In the present study, we found that COX-2 was localized subcellularly in the nuclear envelope (NE) 7 and 14 days after HK-BCG treatment, whereas COX-2 was dissociated from the NE 1 day after treatment. At 1 day after treatment, the majority of COX-2-positive macrophages had phagocytosed HK-BCG. In contrast, no intracellular HK-BCG was detected 7 and 14 days after treatment in COX-2-positive macrophages, where COX-2 was associated with the NE. However, when macrophages phagocytosed HK-BCG in vitro, all COX-2 was associated with the NE. Thus the administration of HK-BCG induces the biphasic COX-2 expression of an NE-dissociated catalytically inactive or an NE-associated catalytically active form in splenic macrophages. The catalytically inactive COX-2-positive macrophages develop microbicidal activities effectively, since they lack PGE(2) biosynthesis.

Francisella tularensis-infected macrophages release prostaglandin E2 that blocks T cell proliferation and promotes a Th2-like response

Francisella tularensis is a highly infectious bacterial pathogen, and is likely to have evolved strategies to evade and subvert the host immune response. In this study, we show that F. tularensis infection of macrophages alters T cell responses in vitro, by blocking T cell proliferation and promoting a Th2-like response. We demonstrate that a soluble mediator is responsible for this effect and identify it as PGE(2). Supernatants from F. tularensis-infected macrophages inhibited IL-2 secretion from both MHC class I and MHC class II-restricted T cell hybridomas, as well as enhanced a Th2-like response by inducing increased production of IL-5. Furthermore, the soluble mediator blocked proliferation of naive MHC class I-restricted T cells when stimulated with cognate tetramer. Indomethacin treatment partially restored T cell proliferation and lowered IL-5 production to wild-type levels. Macrophages produced PGE(2) when infected with F. tularensis, and treatment of infected macrophages with indomethacin, a cyclooxygenase-1/cyclooxygenase-2 inhibitor, blocked PGE(2) production. To further demonstrate that PGE(2) was responsible for skewing of T cell responses, we infected macrophages from membrane PGE synthase 1 knockout mice (mPGES1(-/-)) that cannot produce PGE(2). Supernatants from F. tularensis-infected membrane PGE synthase 1(-/-) macrophages did not inhibit T cell proliferation. Furthermore, treatment of T cells with PGE(2) recreated the effects seen with infected supernatant. From these data, we conclude that F. tularensis can alter host T cell responses by causing macrophages to produce PGE(2). This study defines a previously unknown mechanism used by F. tularensis to modulate adaptive immunity.

Immunologic response enhances atherosclerosis-type 1 helper T cell (Th1)-to-type 2 helper T cell (Th2) shift and calcified atherosclerosis in Bacillus Calmette-Guerin (BCG)-treated apolipoprotein E-knockout (apo E-/-) mice

Although immunocompetent hosts develop protective type 1 helper T cell (Th1) responses in mycobacterial infections, seroepidemiologic studies show that patients with atherosclerosis commonly express high antibody titers against mycobacterial heat shock protein (HSP) 65 and may develop a nonprotective type 2 helper T cell (Th2) response and advanced disease. These studies were undertaken to define mycobacterial dose requirements and kinetics for development of antibodies to HSP65, the Th1 to Th2 shift of immune response, and calcified atherosclerotic lesion development in the apo E-/- mouse. Fourteen-week apo E-/- female mice were treated intraperitoneally (ip) with heat-killed M. bovis Bacillus Calmette-Guerin (BCG), and 14 days later, cross-sections from the ascending aortas were stained for measurement of lesion size and calcium deposition. At 14 days, 0.01-mg BCG induced Th1 responses against HSP65. In contrast, 1-mg BCG induced splenic PGE2-releasing macrophages with a Th1-to-Th2 shift of responses to HSP65, which was PGE2-dependent. Treatment with 1-mg BCG significantly lowered bone density with increases in marrow osteoclastogenesis and development of calcified lesions in the aorta. At 14 days, 0.01-mg BCG induced Th1-dependent HSP65 responses and did not advance atherosclerosis. In contrast, for 1-mg BCG, a PGE2-dependent Th1-to-Th2 shift of responses to HSP65 and evidence of bone resorption are associated with advanced calcified atherosclerotic lesions.

Dual ligand stimulation of RAW 264.7 cells uncovers feedback mechanisms that regulate TLR-mediated gene expression

To characterize how signaling by TLR ligands can be modulated by non-TLR ligands, murine RAW 264.7 cells were treated with LPS, IFN-gamma, 2-methyl-thio-ATP (2MA), PGE(2), and isoproterenol (ISO). Ligands were applied individually and in combination with LPS, for 1, 2, and 4 h, and transcriptional changes were measured using customized oligo arrays. We used nonadditive transcriptional responses to dual ligands (responses that were reproducibly greater or less than the expected additive responses) as a measure of pathway interaction. Our analysis suggests that cross-talk is limited; <24% of the features with significant responses to the single ligands responded nonadditively to a dual ligand pair. PGE(2) and ISO mainly attenuated, while 2MA enhanced, LPS-induced transcriptional changes. IFN-gamma and LPS cross-regulated the transcriptional response induced by each other: while LPS preferentially enhanced IFN-gamma-induced changes in gene expression at 1 h, IFN-gamma signaling primarily attenuated LPS-induced changes at 4 h. Our data suggest specific cross-talk mechanisms: 1) LPS enhances the expression of IFN-gamma-response genes by augmenting STAT1 activity and by activating NF-kappaB, which synergizes with IFN-gamma-induced transcriptional factors; 2) IFN-gamma attenuates the late LPS transcriptional response by increasing the expression of suppressor of cytokine signaling 1 and cytokine-inducible SH2-containing protein expression; 3) 2MA modulates LPS secondary transcriptional response by increasing IFN-beta and inhibiting IL-10 gene expression; 4) PGE(2) and ISO similarly regulate the LPS transcriptional response. They increase IL-10 transcription, resulting in attenuated expression of known IL-10-suppressed genes.

Heat‐killed BCG induces biphasic cyclooxygenase 2 + splenic macrophage formation—role of IL‐10 and bone marrow precursors

Previous studies have shown that prostaglandin E(2) (PGE(2)) release by splenic F4/80(+) cyclooxygenase (COX)-2(+) macrophages (MØ) isolated from mice, treated with mycobacterial components, plays a major role in the regulation of immune responses. However, splenic MØ, isolated from untreated mice and treated in vitro with lipopolysaccharide and interferon-gamma, express COX-1 and COX-2 within 1 day but release only minimal amounts of PGE(2) following elicitation with calcium ionophore A23187. For further characterization of in vivo requirements for development of PGE(2)-releasing MØ (PGE(2)-MØ), C57Bl/6 [wild-type (WT)], and interleukin (IL)-10-deficient (IL-10(-/-)) mice were treated intraperitoneally with heat-killed Mycobacterium bovis bacillus Calmette-Guerin (HK-BCG). One day following injection, COX-2 was induced in splenic MØ of both mouse strains. However, PGE(2) biosynthesis by these MØ was not increased. Thus, expression of COX-2 is not sufficient to induce PGE(2) production in vivo or in vitro. In sharp contrast, 14 days after HK-BCG treatment, PGE(2) release by COX-2(+) splenic MØ increased as much as sevenfold, and a greater increase was seen in IL-10(-/-) cells than in WT cells. To further determine whether the 14-day splenic PGE(2)-MØ could be derived from bone marrow precursors, we established a chimera in which bone marrow cells were transfused from green fluorescent protein (GFP)-transgenic donors to WT mice. Donors and recipients were treated with HK-BCG simultaneously, and marrow transfusion was performed on Days 1 and 2. On Day 14 after BCG treatment, a significant number of spleen cells coexpressed COX-2 and GFP, indicating that bone marrow-derived COX-2(+) MØ may be responsible for the increased PGE(2) production.

Modulation of macrophage nitric oxide production by prostaglandin D2

BACKGROUND

Nitric oxide and prostaglandins readily become activated in response to inflammatory events. The overproduction of nitric oxide is detrimental to the host. The present study was conducted to examine whether prostaglandin D(2) (PGD(2)) modulates nitric oxide production in macrophages in response to an inflammatory stimulus.

METHODS

Cultures of RAW 264.7 murine macrophages were exposed to Escherichia coli lipopolysaccharide (LPS, 0.01 and 1.0 microg/ml) before and after exposure to PGD(2) (0.01 to 10 nmol). After 24-h incubation, supernatants were collected and nitrite was quantitated by Greiss reaction as a measure of nitric oxide synthesis. Inducible nitric oxide synthase (iNOS) protein was measured by Western blot analysis.

RESULTS

Macrophages exposed to 0.01 and 1.0 microg/ml LPS produced 8.3 +/- 0.2 and 15.0 +/- 1.4 nmol/1.1 x 10(6) cells/24 h of nitrite, respectively. The simultaneous addition of PGD(2) with LPS inhibited nitrite production in a dose-dependent fashion and suppressed iNOS protein expression. A strong time effect was also exhibited when macrophages were incubated with PGD(2) 1 hour before as compared to 7 hours after the addition of LPS (0.01 or 1.0 microg/ml), indicating that the earlier the time PGD(2) was added to the culture media, the greater the inhibition. Prostaglandin D(2) had the capacity to block nitrite synthesis even when added as much as 7 hours after an LPS challenge. Blocking endogenous prostaglandins, using indomethacin (10 microM), suppressed nitrite production.

CONCLUSION

Exogenous PGD(2) caused dose- and time-dependent decreases in LPS-stimulated nitrite production by RAW 264.7 macrophages by hindering iNOS protein expression. Conversely, the endogenous prostaglandins released by these same cells in response to an LPS challenge stimulated nitrite production, which may consequently dampen the inhibitory actions of exogenous PGD(2).

PAF is involved in the Mycoplasma arthritidis superantigen-triggering pathway for iNOS and COX-2 expression in murine peritoneal cells

We investigated the capacity of Mycoplasma arthritidis mitogen (MAM) to induce (a) expression of the inducible enzymes cyclo-oxygenase (COX-2) and nitric oxide synthase (iNOS), (b) production of prostaglandin E2 (PGE2) and nitric oxide (NO), and (c) involvement of platelet-activating factor (PAF) in the MAM-induced activation pathway. Resident peritoneal cells from C3H/HePas mice were incubated with MAM in the presence or absence of a PAF-antagonist (WEB2170) or COX-2 inhibitors (nimesulide or NS398). Enzyme expression was evaluated by immunoblotting, PGE2 by EIA, and NO by Griess reaction. Following MAM-stimulation of peritoneal cells, expression of COX-2 was detected at 3 h (peak levels at 12 h) and of iNOS at 6 h (peak levels at 20 h). PGE2 increased till 20 h, decreasing thereafter, whereas NO increased with time. WEB2170 (5 x 10(-5) M) treatment caused 44% inhibition of NO output and reduced iNOS expression (48% at the peak of expression). Concomitant treatment with WEB2170 and nimesulide (10(-5) M) reversed these inhibitory effects. WEB2170 reduced COX-2 expression (43% at the peak of expression) and prevented the decline in PGE2 levels after 20 h. These results suggest the involvement of PAF in the signaling pathway triggered by MAM that leads to expression of iNOS and COX-2, and show that PAF regulates the production of NO, possibly by controlling levels of PGE2.

Inducible nitric oxide synthase activation by interleukin-17

Interleukin-17 (IL-17) is a proinflammatory T cell cytokine presumably involved in physiological responses to infection, but also in immunopathology of autoimmune disorders such as rheumatoid arthritis. The proinflammatory action of IL-17 depends considerably on its ability to trigger the expression of inducible nitric oxide (NO) synthase (iNOS), an enzyme responsible for the generation of cytotoxic and immunoregulatory free radical NO. Here we discuss the role of IL-17 in the cytokine network controlling iNOS expression, and analyze signaling pathways employed by IL-17 for the initiation of iNOS gene transcription. We also propose biological consequences of IL-17-mediated NO release that could be relevant for the mechanisms or therapy of autoimmune and inflammatory disorders.

Vaccinia virus-induced inhibition of nitric oxide production

BACKGROUND

The role of nitric oxide (NO) in the host defense against viruses has not been well defined. Several studies have implicated NO as responsible for the destruction of a variety of viruses. However, others have reported that certain viruses can impair the ability of macrophages to produce NO. This study was initiated to determine the ability of macrophages to produce NO in response to vaccinia virus infection.

METHODS

RAW 264.7 murine macrophages in minimum essential medium were exposed to virus-containing supernatants for 1 h before stimulation with Escherichia coli lipopolysaccharide (LPS, 0.001 and 1.0 microg/ml). After further 24-h incubations, nitrite concentration, cell viability, and inducible nitric oxide synthase (iNOS) were quantitated.

RESULTS

The viral preparation alone did not stimulate nitric oxide synthesis (measured as nitrite) by macrophages. However, macrophages exposed to 0.001 and 1.0 microg/ml LPS produced 7.7 +/- 0.6 and 16.6 +/- 0.8 nmole/1.1 x 10(6) cells/24-h nitrite, respectively. Production of nitrite caused cell death. Macrophages incubated with vaccinia virus prior to exposure to LPS resulted in a dose-dependent decrease in nitrite production. An 80% inhibition of nitrite was noted when macrophages were exposed to vaccinia virus (m.o.i. 10(-4)) plus LPS (1.0 microg/ml) (P < 0.05). Further study showed that this inhibition was not associated with changes in cell viability or substrate availability, but was associated with a marked reduction in iNOS protein. When the virus was inactivated with UV-irradiation, the same incubation caused a 46% inhibition of nitrite production (P < 0.05 vs active virus). However, this effect occurred without altering the quantity of iNOS protein.

CONCLUSION

These results indicate that active vaccinia virus inhibits the ability of stimulated macrophages to produce NO by hindering iNOS protein expression. Because live viral particles were not entirely required for this inhibition, it is possible that by products of viral infection, such as soluble viral proteins, may also be responsible for this effect.

Contribution of the two Gs-coupled PGE2-receptors EP2-receptor and EP4-receptor to the inhibition by PGE2 of the LPS-induced TNFalpha-formation in Kupffer cells from EP2-or EP4-receptor-deficient mice. Pivotal role for the EP4-receptor in wild type Kupffer cells

BACKGROUND/AIMS

Prostaglandin E2 (PGE2) is known to inhibit the lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNFalpha) formation in Kupffer cells via an increase in cAMP. Four receptor-subtypes have been cloned for PGE2 so far. Two of them, the EP2-receptor and the EP4-receptor are linked to stimulatory Gs-proteins and could mediate the inhibition by PGE2 of TNFalpha-formation.

METHODS

The significance of both receptors for PGE2-dependent inhibition of LPS-induced TNFalpha-formation was studied using Kupffer cells of mice in which either one of the two receptors had been eliminated by homologous recombination.

RESULTS

The mRNAs of both receptors were expressed in wild type mouse Kupffer cells. Exogenous PGE2 inhibited TNFalpha-formation in Kupffer cells lacking either EP2-receptor or EP4-receptor to a similar extent as in control cells, however, 10-fold higher PGE2 concentrations were needed for half maximal inhibition in cells lacking the EP4-receptor than in control or EP2-receptor-deficient cells. The response to endogenous PGE2 was blunted in EP4-receptor-deficient mice only and especially after prolonged incubation.

CONCLUSIONS

The data indicate, that PGE2 can inhibit TNFalpha-formation via both the EP2- and the EP4-receptor and that, however, the EP4-receptor appears to be physiologically more relevant in Kupffer cells since it conferred a high affinity response to PGE2.

Malnutrition alters the innate immune response and increases early visceralization following Leishmania donovani infection

Malnutrition is a risk factor for the development of visceral leishmaniasis. However, the immunological basis for this susceptibility is unknown. We have developed a mouse model to study the effect of malnutrition on innate immunity and early visceralization following Leishmania donovani infection. Three deficient diets were studied, including 6, 3, or 1% protein; these diets were also deficient in iron, zinc, and calories. The control diet contained 17% protein, was zinc and iron sufficient, and was provided ab libitum. Three days after infection with L. donovani promastigotes, the total extradermal (lymph nodes, liver, and spleen) and skin parasite burdens were equivalent in the malnourished (3% protein) and control mice, but in the malnourished group, a greater percentage (39.8 and 4.0%, respectively; P = 0.009) of the extradermal parasite burden was contained in the spleen and liver. The comparable levels of parasites in the footpads in the two diet groups and the higher lymph node parasite burdens in the well-nourished mice indicated that the higher visceral parasite burdens in the malnourished mice were not due to a deficit in local parasite killing but to a failure of lymph node barrier function. Lymph node cells from the malnourished, infected mice produced increased levels of prostaglandin E(2) (PGE(2)) and decreased levels of interleukin-10. Inducible nitric oxide synthase activity was significantly lower in the spleen and liver of the malnourished mice. Thus, malnutrition causes a failure of lymph node barrier function after L. donovani infection, which may be related to excessive production of PGE(2) and decreased levels of IL-10 and nitric oxide.