Prostaglandin D2 as a mediator of allergic asthma

The impact of bacterial infection on mast cell degranulation

In developed countries, the prevalence of allergy is on the rise. Although the causes are unknown, it seems that (1) the disappearance of microbiota may play a role in the increase of allergies and (2) exposure to bacterial infections during childhood decreases the incidence of allergies. Although several cell types are involved in the development of allergy, mast cells play a major role in orchestrating inflammation. Upon activation, mast cell secretory granules fuse with the plasma membrane, resulting in the release of a number of inflammatory mediators. In addition to allergy, mast cells contribute to the innate immune response against a variety of bacteria. This is accomplished through the secretion of cytokines and other soluble mediators. Interestingly, there is growing evidence that mast cells exposed to bacteria down-regulate degranulation in response to IgE/Allergen stimulation. This inhibitory effect seems to require direct contact between bacteria and mast cells, but the intracellular mechanism by which bacterial contact suppresses allergic responses is unknown. Here, we review different aspects of mast cell physiology and discuss hypotheses as to how bacteria may influence mast cell degranulation.

Prostaglandins and chronic inflammation

Chronic inflammation is the basis of various chronic illnesses including cancer and vascular diseases. However, much has yet to be learned how inflammation becomes chronic. Prostaglandins (PGs) are well established as mediators of acute inflammation, and recent studies in experimental animals have provided evidence that they also function in transition to and maintenance of chronic inflammation. One role PGs play in such processes is amplification of cytokine signaling. As such, PGs can facilitate acquired immunity and induce long-lasting immune inflammation. PGs also contribute to chronic inflammation by making a positive feedback loop and/or by inducing chemokines and recruiting inflammatory cells to alternate active cell populations at affected sites. PGs also contribute to tissue remodeling as seen in angiogenesis and fibrosis. Although such roles of PGs should be verified in human diseases, these findings suggest that PG signaling is a promising therapeutic target of chronic inflammatory diseases.

Overview of animal models of asthma

Asthma is an inflammatory disease characterized by airways obstruction, airways hyperresponsiveness, excessive mucous secretion and cough. Guinea pig airways display many anatomical, physiological and pharmacological attributes of human airways, making this species ideal for modeling the asthmatic condition. This unit provides an overview of animal models of asthma, including definitions, descriptions of available animal models, and discussion of numerous critical issues to consider before designing a model to study this complex disease.

Niacin and biosynthesis of PGD₂by platelet COX-1 in mice and humans

The clinical use of niacin to treat dyslipidemic conditions is limited by noxious side effects, most commonly facial flushing. In mice, niacin-induced flushing results from COX-1-dependent formation of PGD₂ and PGE₂ followed by COX-2-dependent production of PGE₂. Consistent with this, niacin-induced flushing in humans is attenuated when niacin is combined with an antagonist of the PGD₂ receptor DP1. NSAID-mediated suppression of COX-2-derived PGI₂ has negative cardiovascular consequences, yet little is known about the cardiovascular biology of PGD₂. Here, we show that PGD₂ biosynthesis is augmented during platelet activation in humans and, although vascular expression of DP1 is conserved between humans and mice, platelet DP1 is not present in mice. Despite this, DP1 deletion in mice augmented aneurysm formation and the hypertensive response to Ang II and accelerated atherogenesis and thrombogenesis. Furthermore, COX inhibitors in humans, as well as platelet depletion, COX-1 knockdown, and COX-2 deletion in mice, revealed that niacin evoked platelet COX-1-derived PGD₂ biosynthesis. Finally, ADP-induced spreading on fibrinogen was augmented by niacin in washed human platelets, coincident with increased thromboxane (Tx) formation. However, in platelet-rich plasma, where formation of both Tx and PGD₂ was increased, spreading was not as pronounced and was inhibited by DP1 activation. Thus, PGD₂, like PGI₂, may function as a homeostatic response to thrombogenic and hypertensive stimuli and may have particular relevance as a constraint on platelets during niacin therapy.

Role of G protein-coupled receptors in inflammation

G protein-coupled receptors (GPCRs) play important roles in inflammation. Inflammatory cells such as polymorphonuclear leukocytes (PMN), monocytes and macrophages express a large number of GPCRs for classic chemoattractants and chemokines. These receptors are critical to the migration of phagocytes and their accumulation at sites of inflammation, where these cells can exacerbate inflammation but also contribute to its resolution. Besides chemoattractant GPCRs, protease activated receptors (PARs) such as PAR1 are involved in the regulation of vascular endothelial permeability. Prostaglandin receptors play different roles in inflammatory cell activation, and can mediate both proinflammatory and anti-inflammatory functions. Many GPCRs present in inflammatory cells also mediate transcription factor activation, resulting in the synthesis and secretion of inflammatory factors and, in some cases, molecules that suppress inflammation. An understanding of the signaling paradigms of GPCRs in inflammatory cells is likely to facilitate translational research and development of improved anti-inflammatory therapies.

Prostanoids as regulators of innate and adaptive immunity

Potent, oxygenated lipid molecules called prostanoids regulate a wide variety of physiological responses and pathological processes. Prostanoids are produced by various cell types and act on target cells through specific G protein-coupled receptors. Although prostanoids have historically been considered acute inflammation mediators, studies using specific receptor knockout mice indicate that prostanoids, in fact, regulate various aspects of both innate and adaptive immunity. Each prostanoid, depending on which receptor it acts on, exerts specific effects on immune cells such as macrophages, dendritic cells, and T and B lymphocytes, often in concert with microbial ligands and cytokines, to affect the strength, quality, and duration of immune responses. Prostanoids are also relevant to immunopathology, from inflammation to autoimmunity and cancer. Here, we review the role of prostanoids in regulating immunity, their involvement in immunopathology, and areas of insight that may lead to new therapeutic opportunities.

Prostagladin D2 is a mast cell-derived antiangiogenic factor in lung carcinoma

It is well established that prostaglandins (PGs) are involved in tumor angiogenesis and growth, yet the role of prostaglandin D(2) (PGD(2)) remains virtually unknown. Here, we show that host hematopoietic PGD(2) synthase (H-PGDS) deficiency enhances Lewis lung carcinoma (LLC) progression, accompanied by increased vascular leakage, angiogenesis, and monocyte/mast cell infiltration. This deficiency can be rescued by hematopoietic reconstitution with bone marrow from H-PGDS-naive (WT) mice. In tumors on WT mice, c-kit(+) mast cells highly express H-PGDS. Host H-PGDS deficiency markedly up-regulated the expression of proangiogenic factors, including TNF-α in the tumor. In mast cell-null Kit(W-sh/W-sh) mice, adoptive transfer of H-PGDS-deficient mast cells causes stronger acceleration in tumor angiogenesis and growth than in WT mast cells. In response to LLC growth, H-PGDS-deficient mast cells produce TNF-α excessively. This response is suppressed by the administration of a synthetic PGD(2) receptor agonist or a degradation product of PGD(2), 15-deoxy-Δ(12,14)-PGJ(2). Additional TNF-α deficiency partially counteracts the tumorigenic properties seen in H-PGDS-deficient mast cells. These observations identify PGD(2) as a mast cell-derived antiangiogenic factor in expanding solid tumors. Mast cell-derived PGD(2) governs the tumor microenvironment by restricting excessive responses to vascular permeability and TNF-α production.

Lipid-cytokine-chemokine cascades orchestrate leukocyte recruitment in inflammation

Chemoattractants are pivotal mediators of host defense, orchestrating the recruitment of immune cells into sites of infection and inflammation. Chemoattractants display vast chemical diversity and include bioactive lipids, proteolytic fragments of serum proteins, and chemokines (chemotactic cytokines). All chemoattractants induce chemotaxis by activating seven-transmembrane-spanning GPCRs expressed on immune cells, establishing the concept that all chemoattractants are related in function. However, although chemoattractants have overlapping functions in vitro, recent in vivo data have revealed that they function, in many cases, nonredundantly in vivo. The chemically diverse nature of chemoattractants contributes to the fine control of leukocyte trafficking in vivo, with sequential chemoattractant use guiding immune cell recruitment into inflammatory sites. Lipid mediators frequently function as initiators of leukocyte recruitment, attracting the first immune cells into tissues. These initial responding immune cells produce cytokines locally, which in turn, induce the local release of chemokines. Local chemokine production then markedly amplifies subsequent waves of leukocyte recruitment. These new discoveries establish a paradigm for leukocyte recruitment in inflammation--described as lipid-cytokine-chemokine cascades--as a driving force in the effector phase of immune responses.

Group V phospholipase A2 in bone marrow-derived myeloid cells and bronchial epithelial cells promotes bacterial clearance after Escherichia coli pneumonia

Group V-secreted phospholipase A(2) (GV sPLA(2)) hydrolyzes bacterial phospholipids and initiates eicosanoid biosynthesis. Here, we elucidate the role of GV sPLA(2) in the pathophysiology of Escherichia coli pneumonia. Inflammatory cells and bronchial epithelial cells both express GV sPLA(2) after pulmonary E. coli infection. GV(-/-) mice accumulate fewer polymorphonuclear leukocytes in alveoli, have higher levels of E. coli in bronchoalveolar lavage fluid and lung, and develop respiratory acidosis, more severe hypothermia, and higher IL-6, IL-10, and TNF-α levels than GV(+/+) mice after pulmonary E. coli infection. Eicosanoid levels in bronchoalveolar lavage are similar in GV(+/+) and GV(-/-) mice after lung E. coli infection. In contrast, GV(+/+) mice have higher levels of prostaglandin D(2) (PGD(2)), PGF(2α), and 15-keto-PGE(2) in lung and express higher levels of ICAM-1 and PECAM-1 on pulmonary endothelial cells than GV(-/-) mice after lung infection with E. coli. Selective deletion of GV sPLA(2) in non-myeloid cells impairs leukocyte accumulation after pulmonary E. coli infection, and lack of GV sPLA(2) in either bone marrow-derived myeloid cells or non-myeloid cells attenuates E. coli clearance from the alveolar space and the lung parenchyma. These observations show that GV sPLA(2) in bone marrow-derived myeloid cells as well as non-myeloid cells, which are likely bronchial epithelial cells, participate in the regulation of the innate immune response to pulmonary infection with E. coli.

Extended release niacin-laropiprant in patients with hypercholesterolemia or mixed dyslipidemias improves clinical parameters

The progression of atherosclerosis remains a major cause of morbidity and mortality. Plaque formation is an immunological response driven by a number of risk factors, and reduction of risk is the primary goal of treatment. The role of LDL-C is well established and statins have proved effective drugs, although the relative risk reduction is only around 30%. The importance of other factors-notably low HDL-C and high TGs-has become increasingly clear and the search for alternative strategies continues. Niacin is particularly effective in achieving normalization of HDL-C but is clinically underutilized due to the side effect of cutaneous flushing. The discovery that flushing is mediated by mechanisms distinct from the lipid-lowering effects has led to the development of combination drugs with reduced side effects. This review considers the evidence regarding the clinical efficacy of extended-release niacin and the DP1 antagonist laropiprant in the treatment of hypercholesterolemia and mixed dyslipidemias.

D-type prostanoid receptor enhances the signaling of chemoattractant receptor-homologous molecule expressed on T(H)2 cells

BACKGROUND

Prostaglandin (PG) D(2) is substantially involved in allergic responses and signals through the 7 transmembrane-spanning/G protein-coupled receptors, chemoattractant receptor-homologous molecule expressed on T(H)2 cells (CRTH2), and D-type prostanoid (DP) receptor.

OBJECTIVE

Although the proinflammatory function of CRTH2 is well recognized and CRTH2 is hence considered an important emerging pharmacotherapeutic target, the role of the DP receptor in mediating the biological effects of PGD(2) in patients with allergic inflammation has remained unclear.

METHODS

The cross-talk of CRTH2 and DP receptors was investigated by using both a recombinant HEK293 cell model and human eosinophils in Ca(2+) mobilization assays, coimmunoprecipitation, Western blotting, radioligand binding, and immunofluorescence.

RESULTS

We show that CRTH2 and DP receptors modulate one another's signaling properties and form CRTH2/DP heteromers without altering their ligand-binding capacities. We find that the DP receptor amplifies the CRTH2-induced Ca(2+) release from intracellular stores and coincidentally forfeits its own signaling potency. Moreover, desensitization or pharmacologic blockade of the DP receptor hinders CRTH2-mediated signal transduction. However, CRTH2 internalization occurs independently of the DP receptor. In cells that express both receptors, pharmacologic blockade of Gα(q/11) proteins abolishes the Ca(2+) response to both CRTH2 and DP agonists, whereas inhibition of Gα(i) proteins selectively attenuates the CRTH2-mediated response but not the DP signal.

CONCLUSION

Our data demonstrate the capacity of DP receptors to amplify the biological response to CRTH2 activation. Therefore the CRTH2/DP heteromer might not only represent a functional signaling unit for PGD(2) but also a potential target for the development of heteromer-directed therapies to treat allergic diseases.

Recent research and developmental strategy of anti-asthma drugs

Extensive research over the past decade has provided information about the pharmacotherapy of bronchial asthma (BA). Anti-asthma drugs are classified into two categories: relievers (for the relief of asthma attack symptoms) and controllers (for the prevention of asthma symptoms). This paper aims to review the recent advancements of anti-asthma drugs that are controller medicines. The controllers mainly act on immune and inflammatory responses in BA development. 1) Immunomodulators. Drugs that act on the immune response are classified into two categories: immunosuppressors and immunomodulators, including immunopotentiators. The immunomodulation of the Th1 and Th2 imbalance is the first strategy of the controller because allergic BA is thought to be caused by Th2-polarized immunity. Suplatast is a novel immunomodulator that can adjust the imbalance in the Th1/Th2 immune response and shows clear clinical efficacy against BA. The immunomodulator approach has shifted from a more theoretical and conceptual model to one supported by evidence of clinical efficacy.2) Anti-inflammatory agents. Corticosteroids,mast cell stabilizers and autacoid inhibitors are anti-inflammatory agents for BA. The clinical superiority of the combined therapy of inhaled corticosteroids and long-acting beta2 agonists is evident. This combined therapy shows a potent synergic anti-inflammatory effect compared to the effect by corticosteroids alone. Currently, the anti-inflammatory agents for BA under development are drugs affecting lipid mediators. The prostaglandin (PG) D2 antagonist, PGE2, EP3 agonist and PGI2 agonist are being considered in addition to well-established leukotriene and thromboxane A2 inhibitors. New development strategies and therapeutics for controllers are described in this review.

Analysis of two major intracellular phospholipases A(2) (PLA(2)) in mast cells reveals crucial contribution of cytosolic PLA(2)α, not Ca(2+)-independent PLA(2)β, to lipid mobilization in proximal mast cells and distal fibroblasts

Mast cells release a variety of mediators, including arachidonic acid (AA) metabolites, to regulate allergy, inflammation, and host defense, and their differentiation and maturation within extravascular microenvironments depend on the stromal cytokine stem cell factor. Mouse mast cells express two major intracellular phospholipases A(2) (PLA(2)s), namely group IVA cytosolic PLA(2) (cPLA(2)α) and group VIA Ca(2+)-independent PLA(2) (iPLA(2)β), and the role of cPLA(2)α in eicosanoid synthesis by mast cells has been well documented. Lipidomic analyses of mouse bone marrow-derived mast cells (BMMCs) lacking cPLA(2)α (Pla2g4a(-/-)) or iPLA(2)β (Pla2g6(-/-)) revealed that phospholipids with AA were selectively hydrolyzed by cPLA(2)α, not by iPLA(2)β, during FcεRI-mediated activation and even during fibroblast-dependent maturation. Neither FcεRI-dependent effector functions nor maturation-driven phospholipid remodeling was impaired in Pla2g6(-/-) BMMCs. Although BMMCs did not produce prostaglandin E(2) (PGE(2)), the AA released by cPLA(2)α from BMMCs during maturation was converted to PGE(2) by microsomal PGE synthase-1 (mPGES-1) in cocultured fibroblasts, and accordingly, Pla2g4a(-/-) BMMCs promoted microenvironmental PGE(2) synthesis less efficiently than wild-type BMMCs both in vitro and in vivo. Mice deficient in mPGES-1 (Ptges(-/-)) had an augmented local anaphylactic response. These results suggest that cPLA(2)α in mast cells is functionally coupled, through the AA transfer mechanism, with stromal mPGES-1 to provide anti-anaphylactic PGE(2). Although iPLA(2)β is partially responsible for PGE(2) production by macrophages and dendritic cells, it is dispensable for mast cell maturation and function.

Prostaglandin D₂ induces contractions through activation of TP receptors in peripheral lung tissue from the guinea pig

Prostaglandin D(2) (PGD(2)), released through mast cell activation, is used as a non-invasive biomarker in patients with asthma. Since PGD(2) can elicit opposing effects on airway tone via activation of the PGD(2) receptors DP(1) and DP(2) as well as the thromboxane receptor TP, the aim of this study was to characterize the receptors that are activated by PGD(2) in the guinea pig lung parenchyma. PGD(2) and the thromboxane analog U46619 induced concentration-dependent contractions. U46619 was more potent and caused stronger effect than PGD(2). The specific TP receptor antagonist SQ-29548 and the combined TP and DP(2) receptor antagonist BAYu3405 concentration-dependently shifted the curves for both agonists to the right. The DP(1) receptor agonist BW245 induced a weak relaxation at high concentrations, whereas the DP(1) receptor antagonist BWA868C did not affect the PGD(2) induced contractions. The specific DP(2) receptor agonist 13,14-dihydro-15-keto-PGD(2) showed neither contractile nor relaxant effect in the parenchyma. Furthermore, studies in precision-cut lung slices specified that airways as well as pulmonary arteries and veins contracted to both PGD(2) and U46619. When the lung parenchyma from ovalbumin sensitized guinea pigs were exposed to ovalbumin, both thromboxane B(2) and PGD(2) were released. Ovalbumin also induced maximal contractions at similar level as PGD(2) in the parenchyma, which was partly reduced by SQ-29548. These data show that PGD(2) should be recognized as a TP receptor agonist in the peripheral lung inducing contraction on airways, arteries and veins. Therefore, a TP receptor antagonist can be useful in combination treatment of allergic responses in asthma.

The extracellular signal-regulated kinase mitogen-activated protein kinase/ribosomal S6 protein kinase 1 cascade phosphorylates cAMP response element-binding protein to induce MUC5B gene expression via D-prostanoid receptor signaling

Mucus hypersecretion is a prominent feature of respiratory diseases, and MUC5B is a major airway mucin. Mucin gene expression can be affected by inflammatory mediators, including prostaglandin (PG) D(2,) an inflammatory mediator synthesized by hematopoietic PGD synthase (H-PGDS). PGD(2) binds to either D-prostanoid receptor (DP1) or chemoattractant receptor homologous molecule expressed on T-helper type 2 cells (CRTH2). We investigated the mechanisms by which PGD(2) induces MUC5B gene expression in airway epithelial cells. Western blot analysis showed that H-PGDS was highly expressed in nasal polyps. Similar results were obtained for PGD(2) expression. In addition, we could clearly detect the expressions of both H-PGDS and DP1 in nasal epithelial cells but not CRTH2. We demonstrated that PGD(2) increased MUC5B gene expression in normal human nasal epithelial cells as well as in NCI-H292 cells in vitro. S5751, a DP1 antagonist, inhibited PGD(2)-induced MUC5B expression, whereas a CRTH2 antagonist (OC0459) did not. These data suggest that PGD(2) induced MUC5B expression via DP1. Pretreatment with extracellular signal-regulated kinase (ERK) inhibitor (PD98059) blocked both PGD(2)-induced ERK mitogen-activated protein kinase (MAPK) activation and MUC5B expression. Proximity ligation assays showed direct interaction between RSK1 and cAMP response element-binding protein (CREB). Stimulation with PGD(2) caused an increase in intracellular cAMP levels, whereas intracellular Ca(2+) did not have such an effect. PGD(2)-induced MUC5B mRNA levels were regulated by CREB via direct interaction with two cAMP-response element sites (-921/-914 and -900/-893). Finally, we demonstrated that PGD(2) can induce MUC5B overproduction via ERK MAPK/RSK1/CREB signaling and that DP1 receptor may have suppressive effects in controlling MUC5B overproduction in the airway.

Discovery of selective indole-based prostaglandin D₂ receptor antagonist

A series of N-benzoyl-2-methylindole-3-acetic acids were synthesized and biologically evaluated as prostaglandin (PG) D₂ receptor antagonists. Some of the selected compounds significantly inhibited OVA-induced vascular permeability in guinea pig conjunctiva after oral dosing. Structure-activity relationship study is presented.

Hematopoietic prostaglandin D synthase (HPGDS): a high stability, Val187Ile isoenzyme common among African Americans and its relationship to risk for colorectal cancer

Intestinal tumors in Apc(Min/+) mice are suppressed by over-production of HPGDS, which is a glutathione transferase that forms prostaglandin D(2) (PGD(2)). We characterized naturally occurring HPGDS isoenzymes, to see if HPGDS variation is associated with human colorectal cancer risk. We used DNA heteroduplex analysis and sequencing to identify HPGDS variants among healthy individuals. HPGDS isoenzymes were produced in bacteria, and their catalytic activities were tested. To determine in vivo effects, we conducted pooled case-control analyses to assess whether there is an association of the isoenzyme with colorectal cancer. Roughly 8% of African Americans and 2% of Caucasians had a highly stable Val187lle isoenzyme (with isoleucine instead of valine at position 187). At 37°C, the wild-type enzyme lost 15% of its activity in 1h, whereas the Val187Ile form remained >95% active. At 50°C, the half life of native HPGDS was 9min, compared to 42 min for Val187Ile. The odds ratio for colorectal cancer among African Americans with Val187Ile was 1.10 (95% CI, 0.75-1.62; 533 cases, 795 controls). Thus, the Val187Ile HPGDS isoenzyme common among African Americans is not associated with colorectal cancer risk. Other approaches will be needed to establish a role for HPGDS in occurrence of human intestinal tumors, as indicated by a mouse model.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Prostaglandins and inflammation

Prostaglandins are lipid autacoids derived from arachidonic acid. They both sustain homeostatic functions and mediate pathogenic mechanisms, including the inflammatory response. They are generated from arachidonate by the action of cyclooxygenase isoenzymes, and their biosynthesis is blocked by nonsteroidal antiinflammatory drugs, including those selective for inhibition of cyclooxygenase-2. Despite the clinical efficacy of nonsteroidal antiinflammatory drugs, prostaglandins may function in both the promotion and resolution of inflammation. This review summarizes insights into the mechanisms of prostaglandin generation and the roles of individual mediators and their receptors in modulating the inflammatory response. Prostaglandin biology has potential clinical relevance for atherosclerosis, the response to vascular injury and aortic aneurysm.

Relaxant effect of prostaglandin D(2)--receptor DP agonist on liver myofibroblast contraction

Increased intrahepatic resistance causes portal hypertension in cirrhosis. Liver myofibroblasts (MFs) are now regarded as the principle cells involved in sinusoidal blood flow regulation. Many other prostaglandin-receptor agonists have been reported to regulate liver MF contraction, but the role of the prostaglandin D(2)-receptor DP is unknown. In this study, we investigated the effect of a synthetic agonist of prostanoid DP receptor, BW245C, on contractile properties of primary rat liver MFs. Collagen gel contraction assay revealed that BW245C alone (1 and 10 µM) did not induce contraction but induced cell relaxation. Pretreatment with BW245C (10 µM, 30 min) attenuated bradykinin (100 nM)-induced liver MF contraction. Elevation of [Ca(2+)](i) induced by bradykinin (100 nM) was partially suppressed by BW245C pretreatment (10 µM, 3 min). BW245C (1 and 10 µM) significantly increased intracellular cAMP level in a dose-dependent manner. Pretreatment with forskolin (30 - 300 nM, 30 min) and dibutyryl-cAMP (3 - 30 µM, 30 min) significantly reduced bradykinin-induced contraction. Furthermore, a protein kinase A (PKA) inhibitor KT5720 (10 nM to 1 µM, 30 min) blocked the relaxant effect of BW245C. These results suggest that prostanoid DP receptor agonism inhibits bradykinin-induced [Ca(2+)](i) elevation and contraction through cAMP-PKA signal activation in rat liver MFs.

Functional haplotypes in the PTGDR gene fail to associate with asthma in two Australian populations

BACKGROUND AND OBJECTIVE

Haplotypes in the promoter region of the prostanoid DP receptor (PTGDR) gene have been shown to functionally influence gene transcription and to be associated with asthma in two previous case-control studies in Caucasians. This study tested the association of PTGDR haplotypes with asthma phenotypes in two large Caucasian-Australian populations. These results were incorporated in a meta-analysis with previously published data to determine the overall role for these haplotypes in the risk of asthma.

METHODS

Three PTGDR promoter-region single nucleotide polymorphisms (SNP) were genotyped in 368 individuals from the Western Australian Twin Child Health study and 2988 individuals from the Busselton Health Study. Logistic regression and transition disequilibrium tests were used to assess whether SNP genotypes and three SNP haplotypes were associated with doctor-diagnosed asthma or intermediate quantitative traits. Longitudinal data from the Busselton Health Study were used to examine whether PTGDR influences changes in lung function over time. Meta-analysis incorporated the findings of this study with those of two previous studies in Caucasian populations.

RESULTS

Cross-sectional associations between PTGDR haplotypes and asthma phenotypes were non-significant (P > 0.05) in both populations. Longitudinal analyses of PTGDR and lung function were also non-significant. Meta-analysis, however, suggested that haplotype TCT was significantly associated with decreased risk of asthma (OR = 0.76; P = 0.02) while haplotype CCC was not significantly associated with asthma (OR = 1.30; P = 0.07).

CONCLUSIONS

These results suggest that despite the non-significant findings in the present study populations, PTGDR promoter haplotypes may account for a small but significant proportion of the risk of asthma in Caucasian populations.

Mast cells play a key role in Th2 cytokine-dependent asthma model through production of adhesion molecules by liberation of TNF-α

Mast cells are well recognized as key cells in allergic reactions, such as asthma and allergic airway diseases. However, the effects of mast cells and TNF-α on T-helper type 2 (Th2) cytokine-dependent asthma are not clearly understood. Therefore, an aim of this study was to investigate the role of mast cells on Th2 cytokine-dependent airway hyperresponsiveness and inflammation. We used genetically mast cell-deficient WBB6F1/J-Kitw/Kitw-v (W/Wv), congenic normal WBB6F1/J-Kit+/Kit+ (+/+), and mast cell-reconstituted W/Wv mouse models of allergic asthma to investigate the role of mast cells in Th2 cytokine-dependent asthma induced by ovalbumin (OVA). And we investigated whether the intratracheal injection of TNF-α directly induce the expression of ICAM-1 and VCAM-1 in W/Wv mice. This study, with OVA-sensitized and OVA-challenged mice, revealed the following typical histopathologic features of allergic diseases: increased inflammatory cells of the airway, airway hyperresponsiveness, and increased levels of TNF-α, intercellular adhesion molecule (ICAM)-1, and vascular cellular adhesion molecule (VCAM)-1. However, the histopathologic features and levels of ICAM-1 and VCAM-1 proteins in W/Wv mice after OVA challenges were significantly inhibited. Moreover, mast cell-reconstituted W/Wv mice showed restoration of histopathologic features and recovery of ICAM-1 and VCAM-1 protein levels that were similar to those found in +/+ mice. Intratracheal administration of TNF-α resulted in increased ICAM-1 and VCAM-1 protein levels in W/Wv mice. These results suggest that mast cells play a key role in a Th2 cytokine-dependent asthma model through production of adhesion molecules, including ICAM-1 and VCAM-1, by liberation of TNF-α.

Discovery of AMG 853, a CRTH2 and DP Dual Antagonist

Prostaglandin D2 (PGD2) plays a key role in mediating allergic reactions seen in asthma, allergic rhinitis, and atopic dermatitis. PGD2 exerts its activity through two G protein-coupled receptors (GPCRs), prostanoid D receptor (DP or DP1), and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2 or DP2). We report the optimization of a series of phenylacetic acid derivatives in an effort to improve the dual activity of AMG 009 against DP and CRTH2. These efforts led to the discovery of AMG 853 (2-(4-(4-(tert-butylcarbamoyl)-2-(2-chloro-4-cyclopropylphenyl sulfonamido)phenoxy)-5-chloro-2-fluorophenyl)acetic acid), which is being evaluated in human clinical trials for asthma.

Prostanoid DP receptor antagonists suppress symptomatic asthma-like manifestation by distinct actions from a glucocorticoid in rats

While inhaled glucocorticoids are the best treatment for the majority of chronic asthmatics, there is a small group who do not respond to these drugs or whose disease can only be controlled by high doses of oral glucocorticoids with risks of severe side effects. Therefore, a safe novel anti-asthmatic agent which has a different mechanism from that of glucocorticoids is needed for the management of asthma. We have previously shown that an orally active prostanoid DP receptor antagonist, S-5751, had potent anti-inflammatory effects in guinea pig and sheep asthma models. In this study, using a rat asthma like model, we found that lung neutrophilia and proinflammatory cytokine secretion as well as bronchial hyperresponsiveness and lung eosinophilia were induced by repeated antigen-inhalations after antigen-sensitization. These symptoms are similar to the pathogenesis of symptomatic asthma. Orally-administered prostanoid DP receptor antagonists S-5751 and pinagladin significantly suppressed not only bronchial hyperresponsiveness and lung eosinophilia but also neutrophilia and mucus secretion in the lung, while oral prednisolone inhibited only bronchial hyperresponsiveness and eosinophil infiltration. In addition, prostanoid DP receptor antagonists significantly suppressed interleukin (IL)-1β, IL-6 and CXCL1 mRNA in contrast to suppression of IL-4 and CCL11 mRNA by prednisolone. The majority of prostanoid DP receptor-expressing cells in both rat and human asthmatic lungs are infiltrative macrophages and/or monocytes. These results suggest that prostanoid DP receptor antagonists utilize different mechanisms from glucocorticoids, and that they would be a novel alternative and/or combination drug for asthma therapy.

Dual functions of prostaglandin D2 in murine contact hypersensitivity via DP and CRTH2

Prostaglandin D2 (PGD2) exerts its effects through two distinct receptors: the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) and the D prostanoid (DP) receptor. Our previous study demonstrated that CRTH2 mediates contact hypersensitivity (CHS) in mice. However, the function of DP receptor remains to be fully established. In this study, we examine the pathophysiological roles of PGD2 using DP-deficient (DP(-/-)) and CRTH2/DP-deficient (CRTH2(-/-)/DP(-/-)) mice to elucidate receptor-mediated PGD2 action in CHS. We observed profound exacerbation of CHS in DP(-/-) mice. CRTH2(-/-)/DP(-/-) mice showed similar exacerbation, but to a lesser extent. These symptoms were accompanied by increased production of interferon-γ and IL-17. The increase in IL-17 producing γδ T cells was marked and presumably contributed to the enhanced CHS. DP deficiency promoted the in vivo migration of dendritic cells to regional lymph nodes. A DP agonist added to DCs in vitro was able to inhibit production of IL-12 and IL-1β. Interestingly, production of IL-10 in dendritic cells was elevated via the DP pathway, but it was lowered by the CRTH2 pathway. Collectively, PGD2 signals through CRTH2 to mediate CHS inflammation, and conversely, DP signals to exert inhibitory effects on CHS. Thus, we report opposing functions for PGD2 that depend on receptor usage in allergic reactions.

Synthesis and evaluation of 5-lipoxygenase translocation inhibitors from acylnitroso hetero-Diels-Alder cycloadducts

Acylnitroso cycloadducts have proven to be valuable intermediates in the syntheses of a plethora of biologically active molecules. Recently, organometallic reagents were shown to open bicyclic acylnitroso cycloadducts and, more interestingly, the prospect of highly regioselective openings was raised. This transformation was employed in the synthesis of a compound with excellent inhibitory activity against 5-lipoxygenase ((±)-4a, IC(50) 51 nM), an important mediator of inflammation intimately involved in a number of disease states including asthma and cancer. Optimization of the copper-mediated organometallic ring opening reaction was accomplished allowing the further exploration of the biological activity. Synthesis of a number of derivatives with varying affinity for metal binding as well as pendant groups in a range of sizes was accomplished. Analogues were tested in a whole cell assay which revealed a subset of the compounds to be inhibitors of enzyme translocation, a mode of action not previously known and, potentially, extremely important for better understanding of the enzyme and inhibitor development. Additionally, the lead compound was tested in vivo in an established colon cancer model and showed very encouraging anti-tumorogenic properties.

Increased expression of lipocalin-type-prostaglandin D synthase in ulcerative colitis and exacerbating role in murine colitis

The pathogenesis of ulcerative colitis (UC) is unclear, but enhancement of disease activity by usage of nonsteroidal anti-inflammatory drugs suggests involvement of prostanoid in its pathophysiology. However, biological effect of prostaglandin (PG) D(2) on intestinal inflammation remains unknown. We investigated the expression of enzymes for PGD(2) synthesis, prostaglandin D synthase (PGDS), and its relation to the activity of colitis in UC patients. The role of lipocalin-type PGDS (L-PGDS) using a murine colitis model was also assessed. Tissue samples were obtained by colonic biopsies from patients with UC. Expression levels of mRNAs for L-PGDS and hematopoietic-type PGDS were investigated by quantitative RT-PCR. COX-2 and L-PGDS expression was investigated by immunohistochemistry. Localization of L-PGDS expression was also determined by in situ hybridization. In experimental study, mice were treated with dextran sodium sulfate in the drinking water to induce colitis. The degree of colonic inflammation was compared with L-PGDS(-/-) mice and control mice. The level of L-PGDS mRNA expression was increased in UC patients in parallel with disease activity. Colocalization of L-PGDS and cyclooxygenase (COX) 2 was observed in lamina proprial infiltrating cells and muscularis mucosa in UC patients. The level of hematopoietic PGDS mRNA expression did not differ from control mucosa. Dextran sodium sulfate treatment to L-PGDS(-/-) mice showed lower disease activity than control mice. We reported for the first time the presence of L-PGDS in the COX-2-expressing cells in the mucosa of active UC patients and that only L-PGDS increased with disease activity. An animal model study suggests that PGD(2) derived from L-PGDS-expressing cells plays proinflammatory roles in colitis.

Prostaglandin D₂ and T(H)2 inflammation in the pathogenesis of bronchial asthma

Prostaglandin D₂ (PGD₂) is a major prostanoid, produced mainly by mast cells, in allergic diseases, including bronchial asthma. PGD₂-induced vasodilatation and increased permeability are well-known classical effects that may be involved in allergic inflammation. Recently, novel functions of PGD₂ have been identified. To date, D prostanoid receptor (DP) and chemoattractant receptor homologous molecule expressed on T(H)2 cells (CRTH2) have been shown to be major PGD₂-related receptors. These two receptors have pivotal roles mediating allergic diseases by regulating the functions of various cell types, such as T(H)2 cells, eosinophils, basophils, mast cells, dendritic cells, and epithelial cells. This review will focus on the current understanding of the roles of PGD₂ and its metabolites in T(H)2 inflammation and the pathogenesis of bronchial asthma.

Hematopoietic-Prostaglandin D2 synthase through PGD2 production is involved in the adult ovarian physiology

Background

The prostaglandin D2 (PGD2) pathway is involved in numerous biological processes and while it has been identified as a partner of the embryonic sex determining male cascade, the roles it plays in ovarian function remain largely unknown. PGD2 is secreted by two prostaglandin D synthases (Pgds); the male-specific lipocalin (L)-Pgds and the hematopoietic (H)-Pgds.

Methods

To study the expression of the Pgds in the adult ovary, in situ hybridization were performed. Then, to evaluate the role of H-Pgds produced PGD2 in the ovarian physiology, adult female mice were treated with HQL-79, a specific inhibitor of H-Pgds enzymatic activity. The effects on expression of the gonadotrophin receptors FshR and LhR, steroidogenic genes Cyp11A1, StAR and on circulating progesterone and estradiol, were observed.

Results

We report the localization of H-Pgds mRNA in the granulosa cells from the primary to pre-ovulatory follicles. We provide evidence of the role of H-Pgds-produced PGD2 signaling in the FSH signaling through increased FshR and LhR receptor expression. This leads to the activation of steroidogenic Cyp11A1 and StAR gene expression leading to progesterone secretion, independently on other prostanoid-synthetizing mechanisms. We also identify a role whereby H-Pgds-produced PGD2 is involved in the regulation of follicular growth through inhibition of granulosa cell proliferation in the growing follicles.

Conclusions

Together, these results show PGD2 signaling to interfere with FSH action within granulosa cells, thus identifying an important and unappreciated role for PGD2 signaling in modulating the balance of proliferation, differentiation and steroidogenic activity of granulosa cells.

Polymorphisms of the PTGDR and LTC4S influence responsiveness to leukotriene receptor antagonists in Korean children with asthma

Activation of the prostaglandin D2 receptor (PTGDR) may contribute to pulmonary vasodilation, bronchoconstriction, recruitment of eosinophils, basophils and T-lymphocytes, and enhanced synthesis of leukotriene C4. We investigated whether polymorphisms of the leukotriene C4 synthase (LTC4S) -444A/C and PTGDR -441T/C were associated with clinical phenotypes and responsiveness to leukotriene receptor antagonist (LTRA) in Korean asthmatic children. We enrolled 270 normal and 870 asthmatic children. We prescribed montelukast (5 mg per day) to 100 of asthmatic children, and analyzed the responsiveness to LTRA by exercise challenge tests. Polymorphisms were genotyped by PCR-restriction fragment length polymorphism. As the number of minor alleles of the PTGDR -441T/C and LTC4S -444A/C polymorphisms increased, the log total eosinophil counts increased in atopic asthmatic children (P-value=0.03). We found a significant association between responsiveness to montelukast and the PTGDR polymorphism (P-value=0.038). However, the LTC4S -444A/C and PTGDR -441T/C were not associated with the susceptibility for asthma (LTC4S, AA versus AC+CC, adjusted odds ratio of 0.98 (95% confidence interval, 0.73-1.31); PTGDR, TT versus TC+CC, adjusted odds ratio of 0.90 (95% confidence interval, 0.68-1.19)) or clinical phenotypes (P-value>0.05). The effects of the PTGDR and LTC4S polymorphisms on the enhancement of eosinophil counts were additive in the Korean children with asthma. In addition, the PTGDR polymorphism seems to be associated with the responsiveness to LTRA. Therefore, therapies that target the PTGDR may be useful for modulating the responsiveness to LTRA.

Roles of prostaglandin E2-EP3/EP4 receptor signaling in the enhancement of lymphangiogenesis during fibroblast growth factor-2-induced granulation formation

OBJECTIVE

One of the hallmarks of inflammation is lymphangiogesis that drains the interstitial fluids. During chronic inflammation, angiogenesis is induced by a variety of inflammatory mediators, such as prostaglandins (PGs). However, it remains unknown whether they enhance lymphangiogenesis. We examined the roles of cyclooxygenase-2 (COX-2) and PGE2 receptor signaling in enhancement of lymphangiogenesis during proliferative inflammation.

METHODS AND RESULTS

Lymphangiogenesis estimated by podoplanin/vascular endothelial growth factor (VEGF) receptor-3/LYVE-1 expression was upregulated during proliferative inflammation seen around and into subcutaneous Matrigel plugs containing fibroblast growth factor-2 (125 ng/site). A COX-2 inhibitor (celecoxib) significantly reduced lymphangiogenesis in a dose-dependent manner, whereas topical PGE2 enhanced lymphangiogenesis. Topical injection of fluorescein isothiocyanate-dextran into the Matrigel revealed that lymphatic flow from the Matrigels was COX-2 dependent. Lymphangiogenesis was suppressed in the granulation tissues of mice lacking either EP3 or EP4, suggesting that these molecules are receptors in response to endogenous PGE2. An EP3-selective agonist (ONO-AE-248) increased the expression of VEGF-C and VEGF-D in cultured macrophages, whereas an EP4-selective agonist (ONO-AE1-329) increased VEGF-C expression in cultured macrophages and increased VEGF-D expression in cultured fibroblasts.

CONCLUSIONS

Our findings suggest that COX-2 and EP3/EP4 signaling contributes to lymphangiogenesis in proliferative inflammation, possibly via induction of VEGF-C and VEGF-D, and may become a therapeutic target for controlling lymphangiogenesis.

Bronchial epithelial cell-derived prostaglandin E2 dampens the reactivity of dendritic cells

Airway epithelial cells regulate immune reactivity of local dendritic cells (DCs), thus contributing to microenvironment homeostasis. In this study, we set out to identify factors that mediate this regulatory interaction. We show that tracheal epithelial cells secrete soluble factors that downregulate TNF-α and IL-12p40 secretion by bone marrow-derived DCs but upregulate IL-10 and arginase-1. Size exclusion chromatography identified small secreted molecules having high modulatory activity on DCs. We observed that airway tracheal epithelial cells constitutively release the lipid mediator PGE(2). Blocking the synthesis of PGs within airway epithelial cells relieved DCs from inhibition. Cyclooxygenase-2 was found to be expressed in primary tracheal epithelial cell cultures in vitro and in vivo as shown by microdissection of epithelial cells followed by real-time PCR. Paralleling these findings we observed that DCs treated with an antagonist for E-prostanoid 4 receptor as well as DCs lacking E-prostanoid 4 receptor showed reduced inhibition by airway epithelial cells with respect to secretion of proinflammatory cytokines measured by ELISA. Furthermore, PGE(2) mimicked the effects of epithelial cells on DCs. The results indicate that airway epithelial cell-derived PGE(2) contributes to the modulation of DCs under homeostatic conditions.

Understanding DP receptor antagonism using a CoMSIA approach

A Comparative Molecular Similarity Indices Analysis (CoMSIA) was performed for 2,6-substituted-4-monosubstituted aminopyrimidine antagonists of prostaglandin D(2) receptor (DP). Both two-component (Q(2) = 0.63, R(2) = 0.82, SEE = 0.47 pIC(50)) and three-component (Q(2) = 0.70, R(2) = 0.91, SEE = 0.36 pIC(50)) CoMSIA models were established. Two hydrogen-bond acceptors with spatial separation of about 8Å are shown as optimal for binding. A large hydrophobic center that separates the two acceptors confers to the potency of the 2,6-substituted-4-monosubstituted aminopyrimidine. The models were used to predict IC(50) values for compounds which had functional groups different from those in the training set.

Recent progress in phospholipase A₂ research: from cells to animals to humans

Mammalian genomes encode genes for more than 30 phospholipase A₂s (PLA₂s) or related enzymes, which are subdivided into several classes including low-molecular-weight secreted PLA₂s (sPLA₂s), Ca²+-dependent cytosolic PLA₂s (cPLA₂s), Ca²+-independent PLA₂s (iPLA₂s), platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA₂s, and a recently identified adipose-specific PLA. Of these, the intracellular cPLA₂ and iPLA₂ families and the extracellular sPLA₂ family are recognized as the "big three". From a general viewpoint, cPLA₂α (the prototypic cPLA₂ plays a major role in the initiation of arachidonic acid metabolism, the iPLA₂ family contributes to membrane homeostasis and energy metabolism, and the sPLA₂ family affects various biological events by modulating the extracellular phospholipid milieus. The cPLA₂ family evolved along with eicosanoid receptors when vertebrates first appeared, whereas the diverse branching of the iPLA₂ and sPLA₂ families during earlier eukaryote development suggests that they play fundamental roles in life-related processes. During the past decade, data concerning the unexplored roles of various PLA₂ enzymes in pathophysiology have emerged on the basis of studies using knockout and transgenic mice, the use of specific inhibitors, and information obtained from analysis of human diseases caused by mutations in PLA₂ genes. This review focuses on current understanding of the emerging biological functions of PLA₂s and related enzymes.

Lipopolysaccharide induces proinflammatory cytokines and chemokines in experimental otitis media through the prostaglandin D2 receptor (DP)-dependent pathway

Otitis media is one of the most common and intractable ear diseases, and is the major cause of hearing loss, especially in children. Multiple factors affect the onset or development of otitis media. Prostaglandin D₂ is the major prostanoid involved in infection and allergy. However, the role of prostaglandin D₂ and prostaglandin D2 receptors on the pathogenesis of otitis media remains to be determined. Recent studies show that D prostanoid receptor (DP) and chemoattractant receptor-homologous molecule expressed on T helper type 2 (Th2) cells (CRTH2) are major prostaglandin D₂ receptors. In this study, homozygous DP single gene-deficient (DP⁻(/)⁻) mice, CRTH2 single gene-deficient (CRTH2⁻(/)⁻) mice and DP/CRTH2 double gene-deficient (DP⁻(/)⁻ CRTH2⁻(/)⁻) mice were used to investigate the role of prostaglandin D₂ and its receptors in otitis media. We demonstrate that prostaglandin D₂ is induced by lipopolysaccharide (LPS), a major component of Gram-negative bacteria, and that transtympanic injection of prostaglandin D₂ up-regulates macrophage inflammatory protein 2 (MIP-2), interleukin (IL)-1β and IL-6 in the middle ear. We also show that middle ear inflammatory reactions, including infiltration of inflammatory cells and expression of MIP-2, IL-1β and IL-6 induced by LPS, are reduced significantly in DP⁻(/)⁻ mice and DP⁻(/)⁻ CRTH2⁻(/)⁻ mice. CRTH2⁻(/)⁻ mice display inflammatory reactions similar to wild-type mice. These findings indicate that prostaglandin D₂ may play significant roles in LPS-induced experimental otitis media via DP.

An interaction between L-prostaglandin D synthase and arrestin increases PGD2 production

L-type prostaglandin synthase (L-PGDS) produces PGD(2), a lipid mediator involved in neuromodulation and inflammation. Here, we show that L-PGDS and arrestin-3 (Arr3) interact directly and can be co-immunoprecipitated endogenously from MG-63 osteoblasts. Perinuclear L-PGDS/Arr3 co-localization is observed in PGD(2)-producing MG-63 cells and is induced by the addition of the L-PGDS substrate or co-expression of COX-2 in HEK293 cells. Inhibition of L-PGDS activity in MG-63 cells triggers redistribution of Arr3 and L-PGDS to the cytoplasm. Perinuclear localization of L-PGDS is detected in wild-type mouse embryonic fibroblasts (MEFs) but is more diffused in MEFs-arr-2(-/-)-arr-3(-/-). Arrestin-3 promotes PGD(2) production by L-PGDS in vitro. IL-1β-induced PGD(2) production is significantly lower in MEFs-arr-2(-/-)-arr-3(-/-) than in wild-type MEFs but can be rescued by expressing Arr2 or Arr3. A peptide corresponding to amino acids 86-100 of arrestin-3 derived from its L-PGDS binding domain stimulates L-PGDS-mediated PGD(2) production in vitro and in MG-63 cells. We report the first characterization of an interactor/modulator of a PGD(2) synthase and the identification of a new function for arrestin, which may open new opportunities for improving therapies for the treatment of inflammatory diseases.

Emerging roles of prostanoids in T cell-mediated immunity

Three distinct subsets of T helper (Th) cells, Th1, Th2, and Th17, not only contribute to host defense against pathogens, but also cause many types of immune diseases. Differentiation and functions of these T cell subsets are mainly regulated by specific cytokines. Intriguingly, recent studies have revealed that prostanoids including various types of prostaglandins (PGs) and thromboxane (TX) are also involved in these processes. Prostanoids exert their actions by binding to their specific receptors. They include PGD receptor, EP1, EP2, EP3, and EP4 subtypes of PGE receptor, PGF receptor, PGI receptor, and TX receptor. From many in vitro findings, prostanoids, especially PGE(2), were traditionally believed to be an immunosuppressant. However, studies using mice deficient in each type or subtype of prostanoid receptors and their selective agonists and antagonists have revealed that prostanoids collaborate with cytokines, and critically regulate T cell proliferation, differentiation and functions. Recent studies have revealed that PGE(2) facilitates Th1 cell differentiation and Th17 cell expansion in collaboration with IL-12 and IL-23, respectively, and that these PGE(2) actions contribute to development of immune diseases mediated by these Th subsets. Furthermore, studies using the receptor-deficient mice have also revealed that other prostanoids including PGD(2) and PGI(2) contribute to regulation of immune diseases of the Th2 type such as allergic asthma. These findings shed a new light on the roles of prostanoids in T cell-mediated immunity and immune diseases.

Mast cells in allergic asthma and beyond

Mast cells have been regarded for a long time as effector cells in IgE mediated type I reactions and in host defence against parasites. However, they are resident in all environmental exposed tissues and express a wide variety of receptors, suggesting that these cells can also function as sentinels in innate immune responses. Indeed, studies have demonstrated an important role of mast cells during the induction of life-saving antibacterial responses. Furthermore, recent findings have shown that mast cells promote and modulate the development of adaptive immune responses, making them an important hinge of innate and acquired immunity. In addition, mast cells and several mast cell-produced mediators have been shown to be important during the development of allergic airway diseases. In the present review, we will summarize findings on the role of mast cells during the development of adaptive immune responses and highlight their function, especially during the development of allergic asthma.