IL-1 beta induces IL-6 expression in human orbital fibroblasts: identification of an anatomic-site specific phenotypic attribute relevant to thyroid-associated ophthalmopathy

Human orbital fibroblasts exhibit a unique inflammatory phenotype. In the present study, we report that these fibroblasts, when treated with IL-1beta, express high levels of IL-6, a cytokine involved in B cell activation and the regulation of adipocyte metabolism. The magnitude of this induction is considerably greater than that in dermal fibroblasts and involves up-regulation of IL-6 mRNA levels. IL-1beta activates both p38 and ERK 1/2 components of the MAPK pathways. Disrupting these could attenuate the IL-6 induction. The up-regulation involves enhanced IL-6 gene promoter activity and retardation of IL-6 mRNA decay by IL-1beta. Dexamethasone completely blocked the effect of IL-1beta on IL-6 expression. Orbital fibroblasts also express higher levels of IL-6R than do skin-derived cells. When treated with rIL-6 (10 ng/ml), STAT3 is transiently phosphorylated. Thus, the exaggerated capacity of orbital fibroblasts to express high levels of both IL-6 and its receptor in an anatomic site-selective manner could represent an important basis for immune responses localized to the orbit in Graves' disease.     

Induction by IL-1 beta of tissue inhibitor of metalloproteinase-1 in human orbital fibroblasts: modulation of gene promoter activity by IL-4 and IFN-gamma

Thyroid-associated ophthalmopathy (TAO), an autoimmune component of Graves' disease, is associated with profound connective tissue remodeling and fibrosis that appear to involve the selective activation of orbital fibroblasts. Accumulation of extracellular matrix molecules is a hallmark of this process. Here we report that orbital fibroblasts treated with IL-1beta express high levels of tissue inhibitor of metalloproteinase-1 (TIMP-1), an important modulator of matrix metalloproteinase activity. These high levels are associated with increased TIMP-1 activity. The induction is mediated at the pretranslational level and involves activating the TIMP-1 gene promoter. IL-1beta activates the ERK 1/2 pathway in these fibroblasts and interrupting this signaling either with PD98059, a chemical inhibitor of MEK, or by transfecting cells with a dominant negative ERK 1 plasmid results in the attenuation of TIMP-1 induction. Surprisingly, treatment with IL-4 or IFN-gamma could also block the IL-1beta induction by attenuating TIMP-1 gene promoter activity. These findings suggest that TIMP-1 expression in orbital fibroblasts following activation with IL-1beta could represent an important therapeutic target for modifying the proteolytic environment. This might alter the natural course of tissue remodeling in TAO.     

TNF-alpha modulates hepatic Na+-K+ ATPase activity via PGE2 and EP2 receptors

The effect of TNF-alpha on liver Na(+)-K(+) ATPase was studied in Sprague-Dawley rats and in HepG2 cells. TNF-alpha was injected intraperitoneally to rats and 4h later the liver was isolated and the activity and protein expression of hepatic Na(+)-K(+) ATPase studied. The cytokine caused a significant down-regulation of the ATPase and a decrease in its activity. This effect disappeared in presence of indomethacin, an inhibitor of COX enzymes, and PGE2 injected to the animals imitated the effect of TNF-alpha. The observed in vivo effects of TNF and PGE2 on the pump appeared again when HepG2 cells were treated with the cytokine or the prostaglandin. The application of different agonist and antagonist to EP receptors showed that the effect of PGE2 is mediated via EP2 receptors. It was concluded that TNF-alpha induces in hepatocytes, PGE2 production which in turn reduces the activity and protein expression of the Na(+)-K(+) ATPase by activating EP2 receptors.     

PGE(2) induces COX-2 expression in podocytes via the EP(4) receptor through a PKA-independent mechanism

Cyclooxygenase-2 (COX-2)-dependent prostaglandin E(2) (PGE(2)) synthesis correlates with the onset of proteinuria and increased glomerular capillary pressure (P(gc)) glomerular disease models. We previously showed that an in vitro surrogate for P(gc) (cyclical mechanical stretch) upregulates the expression of both COX-2 and the PGE(2) responsive E-Prostanoid receptor, EP(4) in cultured mouse podocytes. In the present study we further delineate the signaling pathways regulating podocyte COX-2 induction. Time course experiments carried out in conditionally-immortalized mouse podocytes revealed that PGE(2) transiently increased phosphorylated p38 MAPK levels at 10 min, and induced COX-2 protein expression at 4 h. siRNA-mediated knockdown of EP(4) receptor expression, unlike treatment with the EP(1) receptor antagonist SC 19220, completely abrogated PGE(2)-induced p38 phosphorylation and COX-2 upregulation suggesting the involvement of the EP(4) receptor subtype. PGE(2)-induced COX-2 induction was abrogated by inhibition of either p38 MAPK or AMP activated protein kinase (AMPK), and was mimicked by AICAR, a selective AMPK activator, and by the cAMP-elevating agents, forskolin (FSK) and IBMX. Surprisingly, neither PGE(2) nor FSK/IBMX-dependent p38 activation and COX-2 expression were blocked by PKA inhibitors or mimicked by 8-cPT-cAMP a selective EPAC activator, but were instead abrogated by Compound C, suggesting the involvement of AMPK. These results indicate that in addition to mechanical stretch, PGE(2) initiates a positive feedback loop in podocytes that drives p38 MAPK activity and COX-2 expression through a cAMP/AMPK-dependent, but PKA-independent signaling cascade. This PGE(2)-induced signaling network activated by increased P(gc) could be detrimental to podocyte health and glomerular filtration barrier integrity.     

PGE2 exerts its effect on the LPS-induced release of TNF-alpha, ET-1, IL-1alpha, IL-6 and IL-10 via the EP2 and EP4 receptor in rat liver macrophages

Lipopolysaccharide (LPS) induces a release of tumor necrosis factor (TNF)-alpha, endothelin (ET)-1, interleukin (IL)-1alpha, IL-6 and IL-10 in rat liver macrophages (Kupffer cells). Prostaglandin (PG)E2 inhibits the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and enhances the release of the anti-fibrogenic mediators IL-6 and IL-10. This effect of PGE2 is mimicked by specific agonists for the PGE2 receptors EP2 and EP4; whereas, agonists for the PGE2 receptors EP1 and EP3 are inactive. Rat liver macrophages express mRNA encoding the PGE2 receptors EP2 and EP4 but not the PGE2 receptors EP1 and EP3. These data suggest that PGE2 exerts its anti-fibrogenic effect through the EP2 and EP4 receptor by inhibiting the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and by enhancing the release of the anti-fibrogenic mediators IL-6 and IL-10 in liver macrophages.     

Central PGE2 exhibits anxiolytic-like activity via EP1 and EP4 receptors in a manner dependent on serotonin 5-HT1A, dopamine D1 and GABAA receptors

We found that centrally administered prostaglandin (PG) E(2) exhibited anxiolytic-like activity in the elevated plus-maze and open field test in mice. Agonists selective for EP(1) and EP(4) receptors, among four receptor subtypes for PGE(2), mimicked the anxiolytic-like activity of PGE(2). The anxiolytic-like activity of PGE(2) was blocked by an EP(1) or EP(4) antagonist, as well as in EP(4) but not EP(1) knockout mice. Central activation of either EP(1) or EP(4) receptors resulted in anxiolytic-like activity. The PGE(2)-induced anxiolytic-like activity was inhibited by antagonists for serotonin 5-HT(1A), dopamine D(1) and GABA(A) receptors. Taken together, PGE(2) exhibits anxiolytic-like activity via EP(1) and EP(4) receptors, with downstream involvement of 5-HT(1A), D(1) and GABA(A) receptor systems.     

Functional domains essential for Gs activity in prostaglandin EP2 and EP3 receptors

The interaction of cell surface hormone receptors with heterotrimeric G proteins is crucial for hormonal actions. The domains of the receptor, which interact with and activate G protein, have been extensively studied. However, precise molecular mechanisms underlying regulation of the receptor-induced G protein activation are still poorly understood. Prostaglandin E(2) (PGE(2)) receptors comprise of four subtypes, EP1, EP2, EP3 and EP4. Among them, EP2 and EP4 couple to Gs and EP3 to Gi. To assess the functional domains essential for Gs activation in prostanoid receptors, EP2, EP3beta and each intracellular loop- (IC-) interchanged EP2/EP3 chimeras were tested for agonist binding and functional responses. In EP2 receptor, substitution of IC1 or IC3 resulted in loss of binding activity, while substitution of IC2, N- (IC2N) or C-terminal half region of IC2 (IC2C) had no effects on the binding activity. Wild-type EP2 and IC2C-substituted EP2 showed agonist-induced Gs activity, but IC2- and IC2N-substituted EP2 failed to elicit Gs activity upon agonist stimulation. On the other hand, in EP3 receptor substitution of IC1 resulted in loss of PGE(2) binding, while substitution of IC2, IC3, IC2N or IC2C had no effects on binding activity. Wild-type EP3beta, IC3- or IC2C-substituted EP3 failed to show Gs activity upon agonist stimulation, but IC2- or IC2N-substituted EP3 chimera showed agonist-dependent Gs activity. These results indicated that the second intracellular loop of the EP2 plays an essential role in activation of Gs.     

Role of EP(2) and EP(3) PGE(2) receptors in control of murine renal hemodynamics

The kidney plays a central role in long-term regulation of arterial blood pressure and salt and water homeostasis. This is achieved in part by the local actions of paracrine and autacoid mediators such as the arachidonic acid-prostanoid system. The present study tested the role of specific PGE(2) E-prostanoid (EP) receptors in the regulation of renal hemodynamics and vascular reactivity to PGE(2). Specifically, we determined the extent to which the EP(2) and EP(3) receptor subtypes mediate the actions of PGE(2) on renal vascular tone. Renal blood flow (RBF) was measured by ultrasonic flowmetry, whereas vasoactive agents were injected directly into the renal artery of male mice. Studies were performed on two independent mouse lines lacking either EP(2) or EP(3) (-/-) receptors and the results were compared with wild-type controls (+/+). Our results do not support a unique role of the EP(2) receptor in regulating overall renal hemodynamics. Baseline renal hemodynamics in EP(2)-/- mice [RBF EP(2)-/-: 5.3 +/- 0.8 ml. min(-1). 100 g kidney wt(-1); renal vascular resistance (RVR) 19.7 +/- 3.6 mmHg. ml(-1). min. g kidney wt] did not differ statistically from control mice (RBF +/+: 4.0 +/- 0.5 ml. min(-1). 100 g kidney wt(-1); RVR +/+: 25.4 +/- 4.9 mmHg. ml(-1). min. 100 g kidney wt(-1)). This was also the case for the peak RBF increase after local PGE(2) (500 ng) injection into the renal artery (EP(2)-/-: 116 +/- 4 vs. +/+: 112 +/- 2% baseline RBF). In contrast, we found that the absence of EP(3) receptors in EP(3)-/- mice caused a significant increase (43%) in basal RBF (7.9 +/- 0.8 ml. min(-1). g kidney wt(-1), P < 0.05 vs. +/+) and a significant decrease (41%) in resting RVR (11.6 +/- 1.4 mmHg. ml(-1). min. g kidney wt(-1), P < 0.05 vs. +/+). Local administration of 500 ng of PGE(2) into the renal artery caused more pronounced renal vasodilation in EP(3)-/- mice (128 +/- 2% of basal RBF, P < 0.05 vs. +/+). We conclude that EP(3 )receptors mediate vasoconstriction in the kidney of male mice and its actions are tonically active in the basal state. Furthermore, EP(3) receptors are capable of buffering PGE(2)-mediated renal vasodilation.     

Local stimulation of the adenosine A2B receptors induces an increased release of IL-6 in mouse striatum: an in vivo microdialysis study

Both adenosine and interleukin-6 (IL-6) have been implicated in the pathophysiology of, e.g., epileptic seizures, traumatic brain injury, and affective disorders. Stimulation of adenosine A_2B receptors on astrocytes in vitro leads to the increased synthesis and secretion of IL-6. We investigated whether or not activation of adenosine receptors evokes an increase of IL-6 release also in vivo . 5'- N -ethylcarboxamidoadenosine, a non-specific adenosine-agonist or vehicle was administered into the striatum of freely moving mice by reverse microdialysis. A statistical significant increase of the IL-6 concentration in the perfusate was detected already 60 min after 5'- N -ethylcarboxamidoadenosine administration. IL-6 increased progressively and reached a maximum after 240 min. This effect appears to be mediated through adenosine A_2B receptors since it was counteracted by the specific A_2B receptor antagonist MRS1706 but not by the specific A₁ receptor antagonist DPCPX. We conclude that adenosine via activation of A_2B receptors evokes IL-6 release also in vivo .     

Prostaglandin E(2) receptors, EP2 and EP4, differentially modulate TNF-alpha and IL-6 production induced by lipopolysaccharide in mouse peritoneal neutrophils

The expression and function of prostaglandin (PG) E(2) receptors were examined in mouse neutrophils exudated into the peritoneal cavity by casein treatment. Expressions of the EP2 and EP4 receptors were detected in neutrophils by Northern blot, but those of EP1 and EP3 receptors were not detected by RT-PCR. EP2-selective agonist, ONO-AE1-259, and EP4-selective agonist, ONO-AE1-329, stimulated cAMP formation in the cells. PGE(2) affected the TNF-alpha and IL-6 production in lipopolysaccharide (LPS)-treated neutrophils; it suppressed the TNF-alpha production and enhanced the IL-6 production. The PGE(2) effects were mimicked by dibutyryl cAMP. This is the first study of the enhancement of IL-6 production by cAMP-elevating reagents in neutrophils. Using neutrophils from EP2- and EP4-deficient mice in combination with EP2- and EP4-selective agonists, it was found that the augmentation of IL-6 was mediated mainly by the EP2 receptor and the suppression of TNF-alpha by the EP4 receptor and partially by the EP2 receptor. These findings indicate that casein-induced peritoneal neutrophils express Gs-coupled PGE(2) receptors, EP2 and EP4, which might differentially regulate the LPS-induced production of TNF-alpha and IL-6.     

Histamine induces exocytosis and IL-6 production from human lung macrophages through interaction with H1 receptors

Increasing evidence suggests that a continuous release of histamine from mast cells occurs in the airways of asthmatic patients and that histamine may modulate functions of other inflammatory cells such as macrophages. In the present study histamine (10(-9)-10(-6) M) increased in a concentration-dependent fashion the basal release of beta-glucuronidase (EC(50) = 8.2 +/- 3.5 x 10(-9) M) and IL-6 (EC(50) = 9.3 +/- 2.9 x 10(-8) M) from human lung macrophages. Enhancement of beta-glucuronidase release induced by histamine was evident after 30 min and peaked at 90 min, whereas that of IL-6 required 2-6 h of incubation. These effects were reproduced by the H(1) agonist (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)heptane carboxamide but not by the H(2) agonist dimaprit. Furthermore, histamine induced a concentration-dependent increase of intracellular Ca(2+) concentrations ([Ca(2+)](i)) that followed three types of response, one characterized by a rapid increase, a second in which [Ca(2+)](i) displays a slow but progressive increase, and a third characterized by an oscillatory pattern. Histamine-induced beta-glucuronidase and IL-6 release and [Ca(2+)](i) elevation were inhibited by the selective H(1) antagonist fexofenadine (10(-7)-10(-4) M), but not by the H(2) antagonist ranitidine. Inhibition of histamine-induced beta-glucuronidase and IL-6 release by fexofenadine was concentration dependent and displayed the characteristics of a competitive antagonism (K(d) = 89 nM). These data demonstrate that histamine induces exocytosis and IL-6 production from human macrophages by activating H(1) receptor and by increasing [Ca(2+)](i) and they suggest that histamine may play a relevant role in the long-term sustainment of allergic inflammation in the airways.     

Correlation in inflammatory fibroblasts between the number of glucocorticoid receptors and PGE2 release

The anti-inflammatory effects of glucocorticoids are mediated through steroid receptor occupancy and there is a significant correlation between the extent of receptor saturation and the extent of the biological effects. In a previously published study, we found that the number of these receptors was higher in inflammatory fibroblasts than in quiescent ones. PGE2 release, measured at the same time as the number of steroid receptors, was higher when the cells were from inflammatory tissue. Our aim, in the present study, was to determine whether the PGE2 released by cells during inflammatory processes could participate in increasing the number of steroid receptors. Fibroblasts obtained from rat quiescent subcutaneous connective tissue and granulomas were subcultured in monolayers. The specific binding of [3H]dexamethasone was assessed and analyzed by a method described by Kalimi et al. After a freeze-thaw cycle, we observed a decrease in the number of receptors in inflammatory fibroblasts. When the frozen and thawed fibroblasts were subcultured in the presence of PGE2 (10(-8) M), the number of receptors was enhanced in fibroblasts from inflammatory tissue. Cycloheximide (3 X 10(-7) M) prevented this increase. The release of PGE2 decreased after freezing and then increased simultaneously with the number of receptors in inflammatory cells. These findings suggest that PGE2 may play a role in regulating steroid effects on fibroblast function.     

Prostaglandin E(2) inhibits IL-18-induced ICAM-1 and B7.2 expression through EP2/EP4 receptors in human peripheral blood mononuclear cells

Costimulatory molecules play important roles in immune responses. In the present study we investigated the effects of PGE(2) on the expression of ICAM-1, B7.1, and B7.2 on monocytes in IL-18-stimulated PBMC using FACS analysis. Addition of PGE(2) to PBMC inhibited ICAM-1 and B7.2 expression elicited by IL-18 in a concentration-dependent manner. We examined the involvement of four subtypes of PGE(2) receptors, EP1, EP2, EP3, and EP4, in the modulatory effect of PGE(2) on ICAM-1 and B7.2 expression elicited by IL-18, using subtype-specific agonists. ONO-AE1-259-01 (EP2R agonist) inhibited IL-18-elicited ICAM-1 and B7.2 expression in a concentration-dependent manner with a potency slightly less than that of PGE(2), while ONO-AE1-329 (EP4R agonist) was much less potent than PGE(2). The EP2/EP4R agonist 11-deoxy-PGE(1) mimicked the effect of PGE(2) with the same potency. ONO-D1-004 (EP1R agonist) and ONO-AE-248 (EP3R agonist) showed no effect on IL-18-elicited ICAM-1 or B7.2 expression. These results indicated that EP2 and EP4Rs were involved in the action of PGE(2). Dibutyryl cAMP and forskolin down-regulated ICAM-1 and B7.2 expression in IL-18-stimulated monocytes. As EP2 and EP4Rs are coupled to adenylate cyclase, we suggest that PGE(2) down-regulates IL-18-induced ICAM-1 and B7.2 expression in monocytes via EP2 and EP4Rs by cAMP-dependent signaling pathways. The fact that anti-B7.2 as well as anti-ICAM-1 Ab inhibited IL-18-induced cytokine production implies that PGE(2) may modulate the immune response through regulation of the expression of particular adhesion molecules on monocytes via EP2 and EP4Rs.     

IL-19 induces production of IL-6 and TNF-alpha and results in cell apoptosis through TNF-alpha

IL-10 is an immunosuppressive cytokine in the immune system. It was in clinical trial as an anti-inflammatory therapy for inflammatory bowel disease and various autoimmune diseases such as psoriasis, rheumatoid arthritis, and multiple sclerosis. IL-19 belongs to the IL-10 family, which includes IL-10, IL-19, IL-20, IL-22, melanoma differentiation-associated gene (MDA-7, IL-24), and AK155 (IL-26). Despite a partial homology in their amino acid sequences, they are dissimilar in their biologic functions. Little is known about the biologic function and gene regulation of IL-19. To understand the gene regulation of human IL-19, we identified a human IL-19 genomic clone and analyzed its promoter region. Five fusion genes containing different regions upstream of exon 1 linked to a luciferase reporter gene were expressed in the canine kidney epithelial-like Madin-Darby canine kidney cells. A fusion gene containing 394 bp showed luciferase activity 7- to 8-fold higher than the negative control of the promoterless fusion gene. We also isolated a full-length mouse cDNA clone. Mouse IL-19 shared 71% amino acid identity with human IL-19. Treatment of monocytes with mouse IL-19 induced the production of IL-6 and TNF-alpha. It also induced mouse monocyte apoptosis and the production of reactive oxygen species. Taken together, our results indicate that mouse IL-19 may play some important roles in inflammatory responses because it up-regulates IL-6 and TNF-alpha and induces apoptosis.     

Induction of complement factor B activity in human fibroblasts by IL-6/IFN-beta 2 and IFN-gamma

Human skin fibroblasts synthesize and secrete complement Factor B, a component of the complement alternative pathway, when stimulated by mediators of inflammation such as lipopolysaccharide and various cytokines. Recombinant IL-6/IFN-beta 2 (E. coli) stimulates Factor B synthesis in fibroblasts but the effect is strongly potentiated by the addition of IFN-gamma. When both cytokines are added, the skin fibroblasts secrete significant amounts of biologically active Factor B detectable in a hemolysis test. This cooperative effect of IL-6, which is made by most tissue cells and monocytes and of IFN-gamma which is made by T-lymphocytes may play a role in local inflammatory processes. IL-6 and IFN-gamma also cooperate in the induction of (2'-5') A synthetase, a mediator of IFN action.     

PGE2 through the EP4 receptor controls smooth muscle gene expression patterns in the ductus arteriosus critical for remodeling at birth

The ductus arteriosus (DA) is a fetal shunt that directs right ventricular outflow away from pulmonary circulation and into the aorta. Critical roles for prostaglandin E(2) (PGE(2)) and the EP4 receptor (EP4) have been established in maintaining both the patency of the vessel in utero and in its closure at birth. Here we have generated mice in which loss of EP4 expression is limited to either the smooth muscle (SMC) or endothelial cells and demonstrated that SMC, but not endothelial cell expression of EP4 is required for DA closure. The genome wide expression analysis of full term wild type and EP4(-/-) DA indicates that PGE(2)/EP4 signaling modulates expression of a number of unique pathways, including those involved in SMC proliferation, cell migration, and vascular tone. Together this supports a mechanism by which maturation and increased contractility of the vessel is coupled to the potent smooth muscle dilatory actions of PGE(2).     

Lps induces IL-6 in the brain and in serum largely through TNF production

We investigated the relative contribution of IL-6 and PGE2 directly induced by LPS and indirectly induced via TNF, using in vivo and in vitro models in the mouse. In these models we have used as tools an anti-TNF antibody and a cyclooxygenase inhibitor, the S enantiomer of ketoprofen (S-KPF). Anti-TNF antibodies inhibited LPS-induced IL-6 production in three different models: IL-6 production by mouse peritoneal macrophages in vitro; serum IL-6 levels induced by intraperitoneal LPS; and brain IL-6 levels induced by an intracerebroventricular injection of LPS. However, in vitro anti-TNF antibodies, did not inhibit LPS-induced PGE2, indicating that this effect is not mediated by TNF. Since PGE2 has an opposite effect on TNF and IL-6 production, inhibiting that of TNF but inducing that of IL-6, we investigated the effect of S-KPF on TNF and IL-6 production in vivo following LPS injection. Both TNF and IL-6 induction was augmented by S-KPF, but anti-TNF antibodies abolished the augmentation of IL-6 production. Thus, the effect of anti-inflammatory drugs on IL-6 production in some models can be secondary to their effect on TNF production.     

Prostaglandin E2 selectively enhances the IgE-mediated production of IL-6 and granulocyte-macrophage colony-stimulating factor by mast cells through an EP1/EP3-dependent mechanism

PGE(2) is an endogenously synthesized inflammatory mediator that is over-produced in chronic inflammatory disorders such as allergic asthma. In this study, we investigated the regulatory effects of PGE(2) on mast cell degranulation and the production of cytokines relevant to allergic disease. Murine bone marrow-derived mast cells (BMMC) were treated with PGE(2) alone or in the context of IgE-mediated activation. PGE(2) treatment alone specifically enhanced IL-6 production, and neither induced nor inhibited degranulation and the release of other mast cell cytokines, including IL-4, IL-10, IFN-gamma, and GM-CSF. IgE/Ag-mediated activation of BMMC induced the secretion of IL-4, IL-6, and GM-CSF, and concurrent PGE(2) stimulation synergistically increased mast cell degranulation and IL-6 and GM-CSF, but not IL-4, production. A similar potentiation of degranulation and IL-6 production by PGE(2), in the context of IgE-directed activation, was observed in the well-established IL-3-dependent murine mast cell line, MC/9. RT-PCR analysis of unstimulated MC/9 cells revealed the expression of EP(1), EP(3), and EP(4) PGE receptor subtypes, including a novel splice variant of the EP(1) receptor. Pharmacological studies using PGE receptor subtype-selective analogs showed that the potentiation of IgE/Ag-induced degranulation and IL-6 production by PGE(2) is mediated through EP(1) and/or EP(3) receptors. Our results suggest that PGE(2) may profoundly alter the nature of the mast cell degranulation and cytokine responses at sites of allergic inflammation through an EP(1)/EP(3)-dependent mechanism.