Prostaglandin I2-IP signaling blocks allergic pulmonary inflammation by preventing recruitment of CD4+ Th2 cells into the airways in a mouse model of asthma

Tissue-Specific Molecular Markers and Heterogeneity in Type 2 Innate Lymphoid Cells

Innate lymphoid cells (ILCs) are the most recently described group of lymphoid subpopulations. These tissue-resident cells display a heterogeneity resembling that observed on different groups of T cells, hence their categorization as cytotoxic NK cells and helper ILCs type 1, 2 and 3. Each one of these groups is highly diverse and expresses different markers in a context-dependent manner. Type 2 innate lymphoid cells (ILC2s) are activated in response to helminth parasites and regulate the immune response. They are involved in the etiology of diseases associated with allergic responses as well as in the maintenance of tissue homeostasis. Markers associated with their identification differ depending on the tissue and model used, making the study and understanding of these cells a cumbersome task. This review compiles evidence for the heterogeneity of ILC2s as well as discussion and analyses of molecular markers associated with their identity, function, tissue-dependent expression, and how these markers contribute to the interaction of ILC2s with specific microenvironments to maintain homeostasis or respond to pathogenic challenges.

Eicosanoid receptors as therapeutic targets for asthma

Eicosanoids comprise a group of oxidation products of arachidonic and 5,8,11,14,17-eicosapentaenoic acids formed by oxygenases and downstream enzymes. The two major pathways for eicosanoid formation are initiated by the actions of 5-lipoxygenase (5-LO), leading to leukotrienes (LTs) and 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), and cyclooxygenase (COX), leading to prostaglandins (PGs) and thromboxane (TX). A third group (specialized pro-resolving mediators; SPMs), including lipoxin A4 (LXA4) and resolvins (Rvs), are formed by the combined actions of different oxygenases. The actions of the above eicosanoids are mediated by approximately 20 G protein-coupled receptors, resulting in a variety of both detrimental and beneficial effects on airway smooth muscle and inflammatory cells that are strongly implicated in asthma pathophysiology. Drugs targeting proinflammatory eicosanoid receptors, including CysLT1, the receptor for LTD4 (montelukast) and TP, the receptor for TXA2 (seratrodast) are currently in use, whereas antagonists of a number of other receptors, including DP2 (PGD2), BLT1 (LTB4), and OXE (5-oxo-ETE) are under investigation. Agonists targeting anti-inflammatory/pro-resolving eicosanoid receptors such as EP2/4 (PGE2), IP (PGI2), ALX/FPR2 (LXA4), and Chemerin1 (RvE1/2) are also being examined. This review summarizes the contributions of eicosanoid receptors to the pathophysiology of asthma and the potential therapeutic benefits of drugs that target these receptors. Because of the multifactorial nature of asthma and the diverse pathways affected by eicosanoid receptors, it will be important to identify subgroups of asthmatics that are likely to respond to any given therapy.

Prostaglandin regulation of type 2 inflammation: From basic biology to therapeutic interventions

Type 2 immunity is critical for the protective and repair responses that mediate resistance to parasitic helminth infection. This immune response also drives aberrant inflammation during atopic diseases. Prostaglandins are a class of critical lipid mediators that are released during type 2 inflammation and are integral in controlling the initiation, activation, maintenance, effector functions, and resolution of Type 2 inflammation. In this review, we explore the roles of the different prostaglandin family members and the receptors they bind to during allergen‐ and helminth‐induced Type 2 inflammation and the mechanism through which prostaglandins promote or suppress Type 2 inflammation. Furthermore, we discuss the potential role of prostaglandins produced by helminth parasites in the regulation of host–pathogen interactions, and how prostaglandins may regulate the inverse relationship between helminth infection and allergy. Finally, we discuss opportunities to capitalize on our understanding of prostaglandin pathways to develop new therapeutic options for humans experiencing Type 2 inflammatory disorders that have a significant prostaglandin‐driven component including allergic rhinitis and asthma.

Prostaglandin I2 and T Regulatory Cell Function: Broader Impacts

T regulatory cells (Tregs) are an important member of the adaptive immune system and function to reduce and resolve inflammation. Prostaglandin I₂ (PGI₂) is a lipid mediator that has potent anti-inflammatory effects on immune cells. Several studies have investigated the interplay between PGI₂ and Tregs. Together, the data from these studies demonstrate that PGI₂ promotes the formation and function of Tregs. This suggests that therapeutic supplementation of PGI₂ may be a treatment for various autoimmune or inflammatory diseases through enhancement of Treg function.

Prostaglandin I2 signaling licenses Treg suppressive function and prevents pathogenic reprogramming

Tregs restrain both the innate and adaptive immune systems to maintain homeostasis. Allergic airway inflammation, characterized by a Th2 response that results from a breakdown of tolerance to innocuous environmental antigens, is negatively regulated by Tregs. We previously reported that prostaglandin I2 (PGI2) promoted immune tolerance in models of allergic inflammation; however, the effect of PGI2 on Treg function was not investigated. Tregs from mice deficient in the PGI2 receptor IP (IP KO) had impaired suppressive capabilities during allergic airway inflammatory responses compared with mice in which PGI2 signaling was intact. IP KO Tregs had significantly enhanced expression of immunoglobulin-like transcript 3 (ILT3) compared with WT Tregs, which may contribute to the impairment of the IP KO Treg's ability to suppress Th2 responses. Using fate-mapping mice, we reported that PGI2 signaling prevents Treg reprogramming toward a pathogenic phenotype. PGI2 analogs promoted the differentiation of naive T cells to Tregs in both mice and humans via repression of β-catenin signaling. Finally, a missense variant in IP in humans was strongly associated with chronic obstructive asthma. Together, these data support that PGI2 signaling licenses Treg suppressive function and that PGI2 is a therapeutic target for enhancing Treg function.

Eicosanoid Control Over Antigen Presenting Cells in Asthma

Asthma is a common lung disease affecting 300 million people worldwide. Allergic asthma is recognized as a prototypical Th2 disorder, orchestrated by an aberrant adaptive CD4+ T helper (Th2/Th17) cell immune response against airborne allergens, that leads to eosinophilic inflammation, reversible bronchoconstriction, and mucus overproduction. Other forms of asthma are controlled by an eosinophil-rich innate ILC2 response driven by epithelial damage, whereas in some patients with more neutrophilia, the disease is driven by Th17 cells. Dendritic cells (DCs) and macrophages are crucial regulators of type 2 immunity in asthma. Numerous lipid mediators including the eicosanoids prostaglandins and leukotrienes influence key functions of these cells, leading to either pro- or anti-inflammatory effects on disease outcome. In this review, we will discuss how eicosanoids affect the functions of DCs and macrophages in the asthmatic lung and how this leads to aberrant T cell differentiation that causes disease.

The PGI2 Analog Cicaprost Inhibits IL-33-Induced Th2 Responses, IL-2 Production, and CD25 Expression in Mouse CD4+ T Cells

IL-33 has pleiotropic functions in immune responses and promotes the development of allergic diseases and asthma. IL-33 induces Th2 differentiation and enhances type 2 cytokine production by CD4⁺ T cells. However, the regulation of IL-33-driven type 2 cytokine responses is not fully defined. In this study, we investigated the effect of PGI₂, a lipid mediator formed in the cyclooxygenase pathway of arachidonic acid metabolism, on naive CD4⁺ T cell activation, proliferation, and differentiation by IL-33. Using wild-type and PGI₂ receptor (IP) knockout mice, we found that the PGI₂ analog cicaprost dose-dependently inhibited IL-33-driven IL-4, IL-5, and IL-13 production by CD4⁺ T cells in an IP-specific manner. In addition, cicaprost inhibited IL-33-driven IL-2 production and CD25 expression by CD4⁺ T cells. Furthermore, IP knockout mice had increased IL-5 and IL-13 responses of CD4⁺ T cells to Alternaria sensitization and challenge in mouse lungs. Because IL-33 is critical for Alternaria-induced type 2 responses, these data suggest that PGI₂ not only inhibits IL-33-stimulated CD4⁺ Th2 cell responses in vitro but also suppresses IL-33-induced Th2 responses caused by protease-containing allergens in vivo.

Prostaglandins in asthma and allergic diseases

Prostaglandins are synthesized through the metabolism of arachidonic acid via the cyclooxygenase pathway. There are five primary prostaglandins, PGD₂, PGE₂, PGF₂, PGI₂, and thromboxane B₂, that all signal through distinct seven transmembrane, G-protein coupled receptors. The receptors through which the prostaglandins signal determines their immunologic or physiologic effects. For instance, the same prostaglandin may have opposing properties, dependent upon the signaling pathways activated. In this article, we will detail how inhibition of cyclooxygenase metabolism and regulation of prostaglandin signaling regulates allergic airway inflammation and asthma physiology. Possible prostaglandin therapeutic targets for allergic lung inflammation and asthma will also be reviewed, as informed by human studies, basic science, and animal models.

Multi-Walled Carbon Nanotubes Augment Allergic Airway Eosinophilic Inflammation by Promoting Cysteinyl Leukotriene Production

Multi-walled carbon nanotubes (MWCNT) have been reported to promote lung inflammation and fibrosis. The commercial demand for nanoparticle-based materials has expanded rapidly and as demand for nanomaterials grows, so does the urgency of establishing an appreciation of the degree of health risk associated with their increased production and exposure. In this study, we examined whether MWCNT inhalation elicited pulmonary eosinophilic inflammation and influenced the development of allergic airway inflammatory responses. Our data revealed that instillation of FA21 MWCNT into the airways of mice resulted in a rapid increase, within 24 h, in the number of eosinophils present in the lungs. The inflammatory response elicited was also associated with an increase in the level of cysteinyl leukotrienes (cysLTs) present in the bronchoalveolar lavage fluid. CysLTs were implicated in the airway inflammatory response since pharmacological inhibition of their biosynthesis using the 5-lipoxygenase inhibitor Zileuton resulted in a marked reduction in the severity of inflammation observed. Moreover, FA21 MWCNT entering the airways of mice suffering from house dust mite (HDM)-elicited allergic lung inflammation markedly exacerbated the intensity of the airway inflammation. This response was characterized by a pulmonary eosinophilia, lymphocyte infiltration, and raised cysLT levels. The severity of pulmonary inflammation caused by either inhalation of MWCNT alone or in conjunction with HDM allergen correlated with the level of nickel present in the material, since preparations that contained higher levels of nickel (FA21, 5.54% Ni by weight) were extremely effective at eliciting or exacerbating inflammatory or allergic responses while preparations containing lower amounts of nickel (FA04, 2.54% Ni by weight) failed to initiate or exacerbate pulmonary inflammation. In summary, instillation of high nickel MWCNT into the lungs promoted eosinophilic inflammation and caused an intense exacerbation of pre-existing allergic airway inflammation by facilitating cysLT biosynthesis. These findings suggest that exposure to airborne MWCNT is likely to have adverse inflammatory effects in individuals suffering from atopic asthma and, in this context, further investigation of the therapeutic effects of pharmacological agents that block leukotriene synthesis is warranted.

Role of lipid mediators and control of lymphocyte responses in type 2 immunopathology

Type 2 immunopathology is a cardinal feature of allergic diseases and involves cooperation between adaptive immunity and innate effector responses. Virtually all cell types relevant to this pathology generate leukotriene and/or prostaglandin mediators that derive from arachidonic acid, express receptors for such mediators, or both. Recent studies highlight prominent functions for these mediators in communication between the innate and adaptive immune systems, as well as amplification or suppression of type 2 effector responses. This review focuses on recent advances and insights, and highlights existing and potential therapeutic applications of drugs that target these mediators or their receptors, with a special emphasis on their regulation of the innate and adaptive lymphocytes relevant to type 2 immunopathology.

Effects of prostaglandin lipid mediators on agonist-induced lung endothelial permeability and inflammation

Prostaglandins (PG), the products of cyclooxygenase-mediated conversion of arachidonic acid, become upregulated in many situations including allergic response, inflammation, and injury, and exhibit a variety of biological activities. Previous studies described barrier-enhancing and anti-inflammatory effects of PGE₂ and PGI₂ on vascular endothelial cells (EC). Yet, the effects of other PG members on EC barrier and inflammatory activation have not been systematically analyzed. This study compared effects of PGE₂, PGI₂, PGF_2α, PGA₂, PGJ₂, and PGD₂ on human pulmonary EC. EC permeability was assessed by measurements of transendothelial electrical resistance and cell monolayer permeability for FITC-labeled tracer. Anti-inflammatory effects of PGs were evaluated by analysis of expression of adhesion molecule ICAM1 and secretion of soluble ICAM1 and cytokines by EC. PGE₂, PGI₂, and PGA₂ exhibited the most potent barrier-enhancing effects and most efficient attenuation of thrombin-induced EC permeability and contractile response, whereas PGI₂ effectively suppressed thrombin-induced permeability but was less efficient in the attenuation of prolonged EC hyperpermeability caused by interleukin-6 or bacterial wall lipopolysaccharide, LPS. PGD₂ showed a modest protective effect on the EC inflammatory response, whereas PGF_2α and PGJ₂ were without effect on agonist-induced EC barrier dysfunction. In vivo, PGE₂, PGI₂, and PGA₂ attenuated LPS-induced lung inflammation, whereas PGF_2α and PGJ₂ were without effect. Interestingly, PGD₂ exhibited a protective effect in the in vivo model of LPS-induced lung injury. This study provides a comprehensive analysis of barrier-protective and anti-inflammatory effects of different prostaglandins on lung EC in vitro and in vivo and identifies PGE₂, PGI₂, and PGA₂ as prostaglandins with the most potent protective properties.

PGI2 Controls Pulmonary NK Cells That Prevent Airway Sensitization to House Dust Mite Allergen

In allergic asthma, inhalation of airborne allergens such as the house dust mite (HDM) effectively activates both innate and adaptive immunity in the lung mucosa. To determine the role of the eicosanoid PGI₂ and its receptor IP during allergic airway sensitization, HDM responses in mice lacking a functional IP receptor (i.e., PGI₂ IP receptor-deficient [IP^-/-]) were compared with wild type (WT) mice. Surprisingly, IP^-/- mice had increased numbers of pulmonary CD3^-NK1.1⁺Ly49b⁺ NK cells producing IFN-γ that was inversely associated with the number of type 2 innate lymphoid cells (ILC2s) expressing IL-33Rα and IL-13 compared with WT animals. This phenomenon was associated with elevated CX₃CL1 levels in the airways of IP^-/- mice and treatment with a neutralizing Ab to CX₃CL1 reduced IFN-γ production by the lung NK cells. Remarkably, IP^-/- mice were less responsive to HDM challenge than WT counterparts because intranasal instillation of the allergen induced markedly reduced levels of airway eosinophils, CD4⁺ lymphocyte infiltration, and mucus production, as well as depressed levels of CCL2 chemokine and Th2 cytokines. NK cells were responsible for such attenuated responses because depletion of NK1.1⁺ cells in IP^-/- mice restored both the HDM-induced lung inflammation and ILC2 numbers, whereas transfer of CD3^-NK1.1⁺ NK cells into the airways of WT hosts suppressed the inflammatory response. Collectively, these data demonstrate a hitherto unknown role for PGI₂ in regulating the number and properties of NK cells resident in lung tissue and reveal a role for NK cells in limiting lung tissue ILC2s and preventing allergic inflammatory responses to inhaled HDM allergen.

Prostaglandin I2 Suppresses Proinflammatory Chemokine Expression, CD4 T Cell Activation, and STAT6-Independent Allergic Lung Inflammation

Allergic airway diseases are immune disorders associated with heightened type 2 immune responses and IL-5 and IL-13 production at the site of inflammation. We have previously reported that cyclooxygenase (COX) inhibition by indomethacin augmented allergic airway inflammation in a STAT6-independent manner. However, the key COX product(s) responsible for restraining indomethacin-mediated STAT6-independent allergic inflammation is unknown. In this study, using the mouse model of OVA-induced allergic airway inflammation, we identified that PGI2 receptor (IP) signaling was critical for indomethacin-induced, STAT6-independent proallergic effects. We demonstrated that IP deficiency increased inflammatory cell infiltration, eosinophilia, and IL-5 and IL-13 expression in the lung in a STAT6-independent manner. The augmented STAT6-independent allergic inflammation correlated with enhanced primary immune responses to allergic sensitization and elevated production of multiple inflammatory chemokines (CCL11, CCL17, CCL22, and CXCL12) in the lung after allergen challenge. We also showed that the PGI2 analogue cicaprost inhibited CD4 T cell proliferation and IL-5 and IL-13 expression in vitro, and IP deficiency diminished the stimulatory effect of indomethacin on STAT6-independent IL-5 and IL-13 responses in vivo. The inhibitory effects of PGI2 and the IP signaling pathway on CD4 T cell activation, inflammatory chemokine production, and allergic sensitization and airway inflammation suggest that PGI2 and its analogue iloprost, both Food and Drug Administration-approved drugs, may be useful in treating allergic diseases and asthma. In addition, inhibiting PGI2 signaling by drugs that either block PGI2 production or restrain IP signaling may augment STAT6-independent pathways of allergic inflammation.

Prostaglandin I2 Signaling and Inhibition of Group 2 Innate Lymphoid Cell Responses

RATIONALE

Group 2 innate lymphoid cells (ILC2s) robustly produce IL-5 and IL-13, cytokines central to the asthma phenotype; however, the effect of prostaglandin (PG) I2 on ILC2 function is unknown.

OBJECTIVES

To determine the effect of PGI2 on mouse and human ILC2 cytokine expression in vitro and the effect of endogenous PGI2 and the PGI2 analog cicaprost on lung ILC2s in vivo.

METHODS

Flow-sorted bone marrow ILC2s of wild-type (WT) and PGI2 receptor-deficient (IP(-/-)) mice were cultured with IL-33 and treated with the PGI2 analog cicaprost. WT and IP(-/-) mice were challenged intranasally with Alternaria alternata extract for 4 consecutive days to induce ILC2 responses, and these were quantified. Prior to A. alternata extract, challenged WT mice were treated with cicaprost. Human flow-sorted peripheral blood ILC2s were cultured with IL-33 and IL-2 and treated with the PGI2 analog cicaprost.

MEASUREMENT AND MAIN RESULTS

We demonstrate that PGI2 inhibits IL-5 and IL-13 protein expression by IL-33-stimulated ILC2s purified from mouse bone marrow in a manner that was dependent on signaling through the PGI2 receptor IP. In a mouse model of 4 consecutive days of airway challenge with an extract of A. alternata, a fungal aeroallergen associated with severe asthma exacerbations, endogenous PGI2 signaling significantly inhibited lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5- and IL-13-expressing ILC2s, as well as the mean fluorescence intensity of IL-5 and IL-13 staining. In addition, exogenous administration of a PGI2 analog inhibited Alternaria extract-induced lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5- and IL-13-expressing ILC2s and the mean fluorescence intensity of IL-5 and IL-13 staining. Finally, a PGI2 analog inhibited IL-5 and IL-13 expression by human ILC2s that were stimulated with IL-2 and IL-33.

CONCLUSIONS

These results suggest that PGI2 may be a potential therapy to reduce the ILC2 response to protease-containing aeroallergens, such as Alternaria.

Cyclooxygenase inhibition abrogates aeroallergen-induced immune tolerance by suppressing prostaglandin I2 receptor signaling

BACKGROUND

The prevalence of allergic diseases has doubled in developed countries in the past several decades. Cyclooxygenase (COX)-inhibiting drugs augmented allergic diseases in mice by increasing allergic sensitization and memory immune responses. However, whether COX inhibition can promote allergic airway diseases by inhibiting immune tolerance is not known.

OBJECTIVE

To determine the role of the COX pathway and prostaglandin I2 (PGI2) signaling through the PGI2 receptor (IP) in aeroallergen-induced immune tolerance.

METHODS

Wild-type (WT) BALB/c mice and IP knockout mice were aerosolized with ovalbumin (OVA) to induce immune tolerance prior to immune sensitization with an intraperitoneal injection of OVA/alum. The COX inhibitor indomethacin or vehicle was administered in drinking water to inhibit enzyme activity during the sensitization phase. Two weeks after sensitization, the mice were challenged with OVA aerosols. Mouse bronchoalveolar lavage fluid was harvested for cell counts and TH2 cytokine measurements.

RESULTS

WT mice treated with indomethacin had greater numbers of total cells, eosinophils, and lymphocytes, and increased IL-5 and IL-13 protein expression in BAL fluid compared to vehicle-treated mice. Similarly, IP knockout mice had augmented inflammation and TH2 cytokine responses compared to WT mice. In contrast, the PGI2 analog cicaprost attenuated the anti-tolerance effect of COX inhibition.

CONCLUSION

COX inhibition abrogated immune tolerance by suppressing PGI2 IP signaling, suggesting that PGI2 signaling promotes immune tolerance and that clinical use of COX-inhibiting drugs may increase the risk of developing allergic diseases.

Polyunsaturated Fatty Acid-derived lipid mediators and T cell function

Fatty acids are involved in T cell biology both as nutrients important for energy production as well as signaling molecules. In particular, polyunsaturated fatty acids are known to exhibit a range of immunomodulatory properties that progress through T cell mediated events, although the molecular mechanisms of these actions have not yet been fully elucidated. Some of these immune activities are linked to polyunsaturated fatty acid-induced alteration of the composition of cellular membranes and the consequent changes in signaling pathways linked to membrane raft-associated proteins. However, significant aspects of the polyunsaturated fatty acid bioactivities are mediated through their transformation to specific lipid mediators, products of cyclooxygenase, lipoxygenase, or cytochrome P450 enzymatic reactions. Resulting bioactive metabolites including prostaglandins, leukotrienes, and endocannabinoids are produced by and/or act upon T leukocytes through cell surface receptors and have been shown to alter T cell activation and differentiation, proliferation, cytokine production, motility, and homing events. Detailed appreciation of the mode of action of these lipids presents opportunities for the design and development of therapeutic strategies aimed at regulating T cell function.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

A single injection of a sustained-release prostacyclin analog (ONO-1301MS) suppresses airway inflammation and remodeling in a chronic house dust mite-induced asthma model

ONO-1301, a novel prostacyclin agonist with thromboxane A2 synthase inhibitory activity, is a useful agent for ameliorating airway allergic inflammation; however, its short-action feature implies a requirement for the frequent administration of this drug. Therefore, we investigated the effects of ONO-1301-loaded poly (d,l-lactic-co-glycolic acid) microspheres (ONO-1301MS; to release ONO-1301 for 3 weeks) on the airway inflammation and remodeling in chronic house dust mite (HDM)-induced model. Balb/c mice were exposed to an HDM extract intranasally for 5 days/week for 5 consecutive weeks. The mice received a single subcutaneous injection of ONO-1301MS or vehicle after 3 weeks of HDM exposure, followed by 2 additional weeks of HDM exposure. Forty-eight hours after the last HDM exposure, airway hyperresponsiveness to methacholine was assessed and bronchoalveolar lavage was performed. Lung specimens were excised and stained to check for goblet cell metaplasia, airway smooth muscle hypertrophy, and submucosal fibrosis. Mice receiving ONO-1301MS showed significantly lower airway hyperresponsiveness, airway eosinophilia, and induced T helper 2 cytokine production compared with mice receiving the vehicle. Histological findings such as goblet cell metaplasia, airway smooth muscle hypertrophy, and submucosal fibrosis were decreased in ONO-1301MS-treated mice compared with vehicle-treated mice. A single administration of ONO-1301MS achieved sustained elevation of its circulating level for 3 weeks. These data suggest that a single administration of ONO-1301MS may suppress airway hyperresponsiveness, airway allergic inflammation, and development of airway remodeling in chronic HDM-induced asthma model. This agent may be effective as an anti-inflammatory and remodeling drug in the practical treatment of asthma.

PGI₂ signaling inhibits antigen uptake and increases migration of immature dendritic cells

PGI₂ signaling through IP inhibits allergen-induced inflammatory responses in mice. We reported previously that PGI₂ analogs decreased proinflammatory cytokine and chemokine production by mature BMDCs. However, whether PGI₂ modulates the function of immature DCs has not been investigated. We hypothesized that PGI2 negatively regulates immature DC function and investigated the effect of PGI2 analogs on immature BMDC antigen uptake and migration in vitro and in vivo. Immature BMDCs were obtained from WT and IPKO mice, both on a C57BL/6 background. The PGI2 analog cicaprost decreased FITC-OVA uptake by immature BMDCs. In addition, cicaprost increased immature BMDC podosome dissolution, pro-MMP-9 production, cell surface CCR7 expression, and chemotactic migration toward CCL19 and CCL21, as well as chemokinesis, in an IP-specific fashion. These in vitro results suggested that cicaprost promotes migration of immature DCs from mucosal surface to draining LNs. This concept was supported by the finding that migration of immature GFP⁺ BMDCs to draining LNs was enhanced by pretreatment with cicaprost. Further, migration of immature lung DCs labeled with PKH26 was enhanced by intranasal cicaprost administration. Our results suggest PGI2-IP signaling increases immature DC migration to the draining LNs and may represent a novel mechanism by which this eicosanoid inhibits immune responses.

Regulation of T helper cell subsets by cyclooxygenases and their metabolites

Cyclooxygenases and their metabolites are important regulators of inflammatory responses and play critical roles in regulating the differentiation of T helper cell subsets in inflammatory diseases. In this review, we highlight new information on regulation of T helper cell subsets by cyclooxygenases and their metabolites. Prostanoids influence cytokine production by both antigen presenting cells and T cells to regulate the differentiation of naïve CD4(+) T cells to Th1, Th2 and Th17 cell phenotypes. Cyclooxygenases and PGE2 generally exacerbate Th2 and Th17 phenotypes, while suppressing Th1 differentiation. Thus, cycloxygenases may play a critical role in diseases that involve immune cell dysfunction. Targeting of cyclooxygenases and their eicosanoid products may represent a new approach for treatment of inflammatory diseases, tumors and autoimmune disorders.

Iloprost inhalation in mild asthma

OBJECTIVE

To determine the feasibility of administering iloprost by inhalation in patients with mild atopic asthma.

METHODS

Volunteers underwent supervised inhalation of iloprost in the clinic with measurement of spirometry and blood pressure for 2 hours. The volunteers then inhaled iloprost four times daily at a dose of 2.5 or 5 μg for 14 days. Spirometry, asthma questionnaires, peak flow diaries, measurement of methacholine responsiveness, and exhaled nitric oxide concentrations were obtained prior to and after the treatment period.

RESULTS

Chronic inhalation of iloprost (2.5-5 μg) did not alter spirometry or methacholine responsiveness.

CONCLUSION

Inhaled iloprost in carefully selected volunteers with mild asthma appears to be a suitable intervention to explore the effects of prostacyclin in human asthma.

PGI2 as a regulator of inflammatory diseases

Prostacyclin, or PGI₂, is an end product derived from the sequential metabolism of arachidonic acid via cyclooxygenase and PGI synthase (PGIS). The receptor for PGI₂, IP, can be found on a variety of cell types and signaling through this receptor exhibits broad physiological effects. Historically, PGI₂ has been understood to play a role in cardiovascular health, specifically having powerful vasodilatory effects via relaxation of smooth muscle and inhibiting of platelet aggregation. For these reasons, PGI₂ has a long history of use for the treatment of pulmonary arterial hypertension (PAH). Only recently, its importance as an immunomodulatory agent has been investigated. PGI₂ regulates both the innate and adaptive immune systems and its effects are, for the most part, thought to be anti-inflammatory or immunosuppressive in nature, which may have implications for its further clinical use.

Prostaglandin I2 signaling drives Th17 differentiation and exacerbates experimental autoimmune encephalomyelitis

Background

Prostaglandin I₂ (PGI₂), a lipid mediator currently used in treatment of human disease, is a critical regulator of adaptive immune responses. Although PGI₂ signaling suppressed Th1 and Th2 immune responses, the role of PGI₂ in Th17 differentiation is not known.

Methodology/Principal Findings

In mouse CD4⁺CD62L⁺ naïve T cell culture, the PGI₂ analogs iloprost and cicaprost increased IL-17A and IL-22 protein production and Th17 differentiation in vitro. This effect was augmented by IL-23 and was dependent on PGI₂ receptor IP signaling. In mouse bone marrow-derived CD11c⁺ dendritic cells (BMDCs), PGI₂ analogs increased the ratio of IL-23/IL-12, which is correlated with increased ability of BMDCs to stimulate naïve T cells for IL-17A production. Moreover, IP knockout mice had delayed onset of a Th17-associated neurological disease, experimental autoimmune encephalomyelitis (EAE), and reduced infiltration of IL-17A-expressing mononuclear cells in the spinal cords compared to wild type mice. These results suggest that PGI₂ promotes in vivo Th17 responses.

Conclusion

The preferential stimulation of Th17 differentiation by IP signaling may have important clinical implications as PGI₂ and its analogs are commonly used to treat human pulmonary hypertension.

Effect of prostaglandin I2 analogs on cytokine expression in human myeloid dendritic cells via epigenetic regulation

Prostaglandin I(2) (PGI(2)) analog is regarded as a potential candidate for treating asthma. Human myeloid dendritic cells (mDCs) play a critical role in the pathogenesis of asthma. However, the effects of PGI(2) analog on human mDCs are unknown. In the present study, circulating mDCs were isolated from six healthy subjects. The effects of PGI(2) analogs iloprost and treprostinil on cytokine production, maturation and T-cell stimulatory function of human mDCs were investigated. Tumor necrosis factor (TNF)-α and interleukin (IL)-10 were measured by enzyme-linked immunosorbent assay. The expression of costimulatory molecules was investigated by flow cytometry. T-cell stimulatory function was investigated by measuring interferon (IFN)-γ, IL-13 and IL-10 production by T cells cocultured with iloprost-treated mDCs. Intracellular signaling was investigated by Western blot and chromatin immunoprecipitation. We found that iloprost and treprostinil induced IL-10, but suppressed TNF-α production in polyinosinic-polycytidylic acid (poly I:C)-stimulated mDCs. This effect was reversed by the I-prostanoid (IP), E-prostanoid (EP) receptor antagonists or intracellular free calcium (Ca(2+)) chelator. Forskolin, an adenyl cyclase activator, conferred a similar effect. Iloprost and treprostinil increased intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels, and iloprost also increased intracellular Ca(2+). Iloprost suppressed poly I:C-induced mitogen-activated protein kinase (MAPK) phospho-p38 and phospho-activating transcription factor (ATF)2 expression. Iloprost downregulated poly I:C-induced histone H3K4 trimethylation in the TNFA gene promoter region via suppressing translocation of histone 3 lysine 4 (H3K4)-specific methyltransferases MLL (mixed lineage leukemia) and WDR5 (WD repeat domain 5). Iloprost-treated mDCs inhibited IL-13, IFN-γ and IL-10 production by T cells. In conclusion, PGI(2) analogs enhance IL-10 and suppress TNF-α expression through the IP/EP2/EP4 receptors-cAMP and EP1 receptor-Ca(2+) pathway. Iloprost suppressed TNF-α expression via the MAPK-p38-ATF2 pathway and epigenetic regulation by downregulation of histone H3K4 trimethylation.

A novel prostacyclin agonist protects against airway hyperresponsiveness and remodeling in mice

Airway remodeling in bronchial asthma results from chronic, persistent airway inflammation. The effects of the reversal of airway remodeling by drug interventions remain to be elucidated. We investigated the effects of ONO-1301, a novel prostacyclin agonist with thromboxane inhibitory activity, on the prevention and reversibility of airway remodeling in an experimental chronic asthma model. Mice sensitized and challenged to ovalbumin (OVA) three times a week for 5 consecutive weeks were administered ONO-1301 or vehicle twice a day from the fourth week of OVA challenges. Twenty-four hours after the final OVA challenge, airway hyperresponsiveness (AHR) was assessed, and bronchoalveolar lavage was performed. Lung specimens were excised for staining to detect goblet-cell metaplasia, airway smooth muscle, and submucosal fibrosis. Mice administered ONO-1301 showed limited increases in AHR compared with mice administered the vehicle. The histological findings of airway remodeling were improved in ONO-1301-treated mice compared with vehicle-treated mice. Presumably, these therapeutic effects of ONO-1301 are attributable to the up-regulation of production of hepatocyte growth factor (HGF) in lung tissue, because the neutralization of HGF by antibodies prevented the effects of ONO-1301 on AHR and airway remodeling. Mice administered ONO-1301 showed similar levels of AHR and airway remodeling as mice administered montelukast, a cysteinyl-leukotriene-1 receptor antagonist, and lower levels were observed in mice administered dexamethasone. These data suggest that ONO-1301 exerts the effect of reversing airway remodeling, at least in part through an elevation of HGF in the lungs, and may be effective as an anti-remodeling drug in the treatment of asthma.

Prostaglandin I₂promotes the development of IL-17-producing γδ T cells that associate with the epithelium during allergic lung inflammation

γδ T cells rapidly produce cytokines and represent a first line of defense against microbes and other environmental insults at mucosal tissues and are thus thought to play a local immunoregulatory role. We show that allergic airway inflammation was associated with an increase in innate IL-17-producing γδ T (γδ-17) cells that expressed the αEβ7 integrin and were closely associated with the airway epithelium. Importantly, PGI(2) and its receptor IP, which downregulated airway eosinophilic inflammation, promoted the emergence of these intraepithelial γδ-17 cells into the airways by enhancing IL-6 production by lung eosinophils and dendritic cells. Accordingly, a pronounced reduction of γδ-17 cells was observed in the thymus of naive mice lacking the PGI(2) receptor IP, as well as in the lungs during allergic inflammation, implying a critical role for PGI(2) in the programming of "natural" γδ-17 cells. Conversely, iloprost, a stable analog of PGI(2), augmented IL-17 production by γδ T cells but significantly reduced airway inflammation. Together, these findings suggest that PGI(2) plays a key immunoregulatory role by promoting the development of innate intraepithelial γδ-17 cells through an IL-6-dependent mechanism. By enhancing γδ-17 cell responses, stable analogs of PGI(2) may be exploited in the development of new immunotherapeutic approaches.

PGI2 as a regulator of CD4+ subset differentiation and function

Prostaglandin (PG)I(2) has important regulatory functions on the innate and adaptive immune systems. Recent experimental evidence reveals that PGI(2) modulates the development and function of CD4+ T cells subsets, including Th1, Th2, and Th17 cell responses. In vitro and in vivo studies support that PGI(2) generally has an inhibitory effect on Th1 and Th2 activation, differentiation, and cytokine production. In contrast, PGI(2) seems to enhance Th17-favoring polarization conditions, resulting in Th17 cytokine production. Therefore, PGI(2) may either promote or inhibit individual CD4+ cell subsets and impact adaptive immune responses.

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.

Inhibitory effect of prostaglandin I2 on bone marrow kinetics of eosinophils in the guinea pig

Enhanced eosinophil trafficking from bone marrow to the tissue is a hallmark of allergic diseases. We have shown previously that PGI(2) markedly attenuates the locomotion of human eosinophils in vitro. Here, we set out to determine the effect of PGI(2) on the trafficking of bone marrow eosinophils in the guinea pig. Shape change of bone marrow eosinophils was determined by flow cytometry, and chemotaxis assays were performed using a transwell migration system. Eosinophil release from bone marrow of guinea pigs was investigated in the isolated, perfused hind-limb preparation. We found that PGI(2) prevented the mobilization of eosinophils from bone marrow and attenuated the shape change and chemotactic responses of bone marrow eosinophils. These effects were mimicked by iloprost and were prevented by the IP antagonist CAY10441 and the adenylyl cyclase inhibitor SQ22536. Immunohistochemical staining of bone marrow confirmed the expression of IPs by bone marrow eosinophils. The rate-limiting enzyme of PGI(2) formation, PGIS, was found in large mononuclear cells. These data show that IP activation negatively modulates the mobilization and locomotion of bone marrow eosinophils and might therefore also protect against exaggerated recruitment of eosinophils to inflammatory sites.

[Novel immunopathological approaches to pulmonary arterial hypertension]

Inflammation is important for the initiation and the maintenance of vascular remodeling in the most commun animal models of pulmonary hypertension (PH), and its therapeutical targeting blocks PH development in these models. In human, pulmonary vascular lesions of PH are also the source of an intense chemokine production, linked to inflammatory cell recruitment. However, arteritis is uncommon in PH patients. Of note, current PH treatments have immunomodulatory properties. In addition, some studies have shown a correlation between levels of circulating inflammatory mediators and patients' survival. The study of autoimmunity in the pathophysiology of pulmonary arterial hypertension is becoming an area of intense investigation. New immunopathological approaches to PH should allow the development of innovative treatments for this very severe condition.

Prostaglandin I(2) analogues suppress TNF-α expression in human monocytes via mitogen-activated protein kinase pathway

OBJECTIVE AND DESIGN

Although treatment for asthma control has improved a lot recently, refractory asthma is still a challenge for clinicians. Evidence revealed that anti-tumor necrosis factor (TNF)-α therapy may have potential in treating refractory asthma. Recently in an animal model, prostaglandin I(2) (PGI(2)) analogues can suppress the cardinal feature of asthma. However, whether PGI(2) analogues can regulate TNF-α expression in monocytes and the mechanism is not well-known.

MATERIALS AND METHODS

The human monocytes were pretreated with beraprost, iloprost and treprostinil, three PGI(2) analogues, before stimulation with lipopolysaccharide (LPS). TNF-α concentration of the cell supernatants was measured by ELISA. Intracellular signaling was investigated by Western blot.

RESULTS

PGI(2) analogues suppressed LPS-induced TNF-α expression in THP-1 cells. CAY10449, an I prostanoid receptor antagonist, could reverse these effects. Beraprost increased intracellular cAMP level in THP1 cells. Forskolin, an adenylyl cyclase activator, could confer similar effect. LPS-induced TNF-α expression in THP-1 cells could be reversed by mitogen-activator protein kinase (MAPK)-p38, extracellular signal-related kinase (ERK) and c-Jun N-terminal kinase (JNK) inhibitors. Western blot revealed that beraprost suppressed MAPK phospho-p38, phosphor-JNK and phosphor-ERK expression.

CONCLUSION

PGI(2) analogues suppressed LPS-induced TNF-α expression in THP-1 cells via the IP receptor-cAMP and the MAPK pathways. PGI(2) analogues may have potentiality to treat asthma.

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.

Prostaglandin I(2) analogues enhance growth-related oncogene-alpha expression in human monocyte-derived dendritic cells

Chemokines for neutrophils such as growth-related oncogene-alpha (GRO-alpha) are important in patients with refractory or severe asthma. Prostaglandin I(2) (PGI(2)) analogues were regarded as potential treatments for asthma. Dendritic cells (DCs) are the professional antigen-presenting cells and play a critical role in regulating immune response. However, it is unknown whether PGI(2) analogues have regulatory effects on GRO-alpha expression in human monocyte-derived DCs (MDDCs). The human MDDCs were pretreated with iloprost and treprostinil (two PGI(2) analogues) or forskolin, a cyclic adenosine monophosphate (cAMP) activator, before stimulation with lipopolysaccharide (LPS). In some cases, I prostanoid (IP) receptor and E prostanoid (EP) antagonists were pretreated before PGI(2) analogue treatment. To investigate the intracellular signaling, nuclear factor (NF)-kappaB inhibitor and the mitogen-activated protein kinase (MAPK) inhibitors were pretreated before PGI(2) analogue treatment. GRO-alpha was measured by enzyme-linked immunosorbent assay. Intracellular signaling was also investigated by Western blot. Iloprost and treprostinil enhanced LPS-induced GRO-alpha expression in MDDCs. This effect could be reversed by an I prostanoid receptor antagonist, CAY10449, but not EP receptor antagonists. Forskolin conferred a similar modulating effect as that noted in iloprost- and treprostinil-treated MDDCs. PGI(2) analogue-enhanced LPS-induced GRO-alpha expression was reduced by MAPK-p38 inhibitor, SB203580. PGI(2) analogues enhanced LPS-induced phospho-p38 expression. PGI(2) analogues enhanced LPS-induced GRO-alpha expression via the IP receptor-cAMP and p38-MAPK pathways in human MDDCs, which may further recruit neutrophil accumulation and adversely affect patients with refractory or severe asthma because of airway neutrophilia. These effects should be considered for PGI(2) analogues as candidates for the treatment of asthma.

Effects of PGI2 analogues on Th1- and Th2-related chemokines in monocytes via epigenetic regulation

Chemokines play important roles in asthma. Prostaglandin I(2) (PGI(2)) analogue is recently suggested as a candidate for treating asthma. However, the effects of PGI(2) analogues on the expression of Th1- and Th2-related chemokines are unknown. To this end, we investigated the in vitro effects of PGI(2) analogues on the expression of Th1-related chemokine interferon-γ-inducible protein-10 (IP-10/CXCL10) and Th2-related chemokine macrophage-derived chemokine (MDC/CCL22) in human monocytes. The human monocytes were pretreated with iloprost and treprostinil before lipopolysaccharide (LPS) stimulation. IP-10 and MDC were measured by ELISA. Intracellular signaling was investigated by cyclic adenosine monophosphate (cAMP) assay, western blot and chromatin immunoprecipitation. PGI(2) analogues enhanced MDC, but suppressed IP-10 expression in LPS-stimulated monocytes. These effects were reversed by the I prostanoid (IP) receptor antagonist (CAY10449), peroxisomal proliferators-activated receptor (PPAR)-α antagonist (GW6741) and PPAR-γ antagonist (GW9662). PGI(2) analogues increased intracellular cAMP levels. Forskolin, an adenyl cyclase activator, conferred similar effects. PGI(2) analogue-enhanced MDC expression was reduced by nuclear factor (NF) κB inhibitor (BAY 117085) and mitogen-activated protein kinase (MAPK)-p38 inhibitor (SB203580). PGI(2) analogues up-regulated phospho-p65 and phospho-p38 but down-regulated phospho-ERK expression. Iloprost enhanced H3 acetylation in MDC promoter area and suppressed H3 acetylation, H3K4, and H3K36 trimethylation in IP-10 promoter area. PGI(2) analogues enhanced MDC expression via the I prostanoid-receptor-cAMP, PPAR-α and PPAR-γ, NFκB-p65, MAPK-p38-ATF2 pathways and increasing histone acetylation, and suppressed IP-10 expression via the IP-receptor-cAMP, PPAR-γ, MAPK-ERK-ELK1 pathways and inhibiting histone acetylation and trimethylation in LPS-stimulated monocytes. PGI(2) analogues may therefore increase Th2 recruitment and inflammation.

Natural Foxp3(+) regulatory T cells inhibit Th2 polarization but are biased toward suppression of Th17-driven lung inflammation

nTregs prevent autoimmunity and modulate immune and inflammatory responses to foreign antigens. CD4(+)Foxp3(+) nTregs from DO11.10 mice were expanded ex vivo, and their effectiveness in suppressing the development of lung inflammatory responses, elicited by differentiated CD4(+) T cells following antigen inhalation, was examined. Effector DO11.10 CD4(+) Th2 cells, when adoptively transferred into BALB/c mice that subsequently inhaled OVA, elicited a pronounced pulmonary, eosinophilic inflammation. Surprisingly, the cotransfer of expanded nTregs failed to suppress the Th2-mediated airway inflammation. Nevertheless, expanded OVA-specific CD4(+)Foxp3(+) nTregs were highly effective at inhibiting the polarization of naïve CD4(+) T cells into a Th2 phenotype. This suppression was reversed by an antibody to GITR but was not affected by the presence of the soluble OX40L. Further analysis revealed that although nTregs also failed to inhibit the lung neutrophilic inflammation induced by effector CD4(+) Th1 cells, they markedly suppressed pulmonary inflammation elicited by CD4(+) Th17 cells but not AHR. The suppression of the Th17-mediated response was evident from a striking reduction in the proportion of OVA-specific T cells expressing IL-17 and the numbers of neutrophils present in the airways of Th17 recipient mice. Collectively, these results demonstrate that expanded nTregs clearly limit the Th2 polarization process and that Th17-mediated inflammatory responses are particularly prone to the immunoregulatory properties of nTregs. These findings thus indicate that expanded nTregs are restrictive in their ability to suppress airway inflammatory processes and AHR.

An inhalation model of airway allergic response to inhalation of environmental Aspergillus fumigatus conidia in sensitized BALB/c mice

Fungal exposure may elicit a number of pulmonary diseases in man, including allergic asthma. Fungal sensitization is linked to asthma severity, although the basis for this increased pathology remains ambiguous. To create conditions simulating environmental fungal allergen exposure in a human, nose-only inhalation delivery of Aspergillus fumigatus conidia was employed in mice previously sensitized to Aspergillus antigen extract. BALB/c mice were immunized with subcutaneous and intraperitoneal injections of soluble A. fumigatus extract in alum, which was followed by three intranasal inoculations of the same fungal antigens dissolved in saline to elicit global sensitization in a manner similar to other published models. The animals were then challenged with a 10-min inhaled dose of live conidia blown directly from the surface of a mature A. fumigatus culture. After a single challenge with inhaled A. fumigatus conidia, allergic pulmonary inflammation and airway hyperresponsiveness were significantly increased above that of either naïve animals or animals that had been sensitized to A. fumigatus antigens but not challenged with conidia. The architecture of the lung was changed by inhalation of conidia when compared to controls in that there were significant increases in epithelial thickness, goblet cell metaplasia, and peribronchial collagen deposition. Additionally, α-smooth muscle actin staining of histological sections showed visual evidence of increased peribronchial smooth muscle mass after fungal challenge. In summary, the delivery of live A. fumigatus conidia to the sensitized airways of BALB/c mice advances the study of the pulmonary response to fungi by providing a more natural route of exposure and, for the first time, demonstrates the consistent development of fibrosis and smooth muscle changes accompanying exposure to inhaled fungal conidia in a mouse model.

Emerging roles of secreted phospholipase A2 enzymes: Lessons from transgenic and knockout mice

Among the emerging phospholipase A(2) (PLA(2)) superfamily, the secreted PLA(2) (sPLA(2)) family consists of low-molecular-mass, Ca(2+)-requiring extracellular enzymes with a His-Asp catalytic dyad. To date, more than 10 sPLA(2) enzymes have been identified in mammals. Individual sPLA(2)s exhibit unique tissue and cellular localizations and enzymatic properties, suggesting their distinct pathophysiological roles. Despite numerous enzymatic and cell biological studies on this enzyme family in the past two decades, their precise in vivo functions still remain largely obscure. Recent studies using transgenic and knockout mice for several sPLA(2) enzymes, in combination with lipidomics approaches, have opened new insights into their distinct contributions to various biological events such as food digestion, host defense, inflammation, asthma and atherosclerosis. In this article, we overview the latest understanding of the pathophysiological functions of individual sPLA(2) isoforms fueled by studies employing transgenic and knockout mice for several sPLA(2)s.

Endothelium-derived prostaglandin I(2) controls the migration of eosinophils

BACKGROUND

Enhanced eosinophil migration from the blood into the tissue is a hallmark of allergic diseases. Prostaglandin (PG) I(2) is the major prostanoid released by endothelial cells. Mice deficient in PGI(2) receptors (IPs) show exaggerated eosinophilic inflammation in response to allergen.

OBJECTIVE

We set out to determine the role of PGI(2) in eosinophil trafficking.

METHODS

Human lung microvascular endothelial cells and purified human eosinophils were used to study adhesion and transendothelial migration. Morphologic studies were performed with fluorescence microscopy.

RESULTS

PGI(2) markedly attenuated the migration of eosinophils through cell-free filters but had no effect on neutrophil migration. The inhibitory effect of PGI(2) on eosinophils was prevented by the IP antagonist Cay10441 and the adenylyl cyclase inhibitor SQ22536. Similarly, PGI(2) prevented the adhesion of eosinophils to fibronectin and the rapid upregulation and activation of the adhesion molecule CD11b. IP expression on eosinophils was confirmed by means of flow cytometry and Western blotting. Furthermore, when endothelial cells were treated with the COX inhibitor diclofenac to abolish PGI(2) production, adhesion of eosinophils to endothelial monolayers and subsequent transendothelial migration were markedly enhanced. Similarly, the IP antagonist enhanced eosinophil adhesion to endothelial cells. Inhibition of PGI(2) biosynthesis decreased the electrical resistance of endothelial monolayers and compromised the texture of adherent junctions, as visualized by means of VE-cadherin and F-actin staining.

CONCLUSION

We propose that endothelium-derived PGI(2) might be fundamental for the maintenance of the endothelial barrier function against infiltrating cells. These results suggest that selective IP agonists might have beneficial effects in allergic inflammation.

Prostaglandin E(2) exerts homeostatic regulation of pulmonary vascular remodeling in allergic airway inflammation

Nonselective inhibition of PG synthesis augments inflammation in mouse models of airway disease, but the roles of individual PGs are not completely clarified. To investigate the role of PGE(2) in a mouse model of airway inflammation induced by a natural allergen, we used mice lacking the critical terminal synthetic enzyme, microsomal PGE(2) synthase (mPGES)-1. Mice lacking mPGES-1 (ptges(-/-) mice) and wild-type C57BL/6 controls were challenged intranasally with low doses of an extract derived from the house dust mite Dermatophagoides farinae (Der f). The levels of PGE(2) in the bronchoalveolar lavage fluids of Der f-treated ptges(-/-) mice were approximately 80% lower than the levels in wild-type controls. Der f-induced bronchovascular eosinophilia was modestly enhanced in the ptges(-/-) mice. Both Der f-treated strains showed similar increases in serum IgE and IgG1, as well as comparable levels of Th1, Th2, and Th17 cytokine production by Der f-stimulated spleen cells. These findings indicated that mPGES-1-derived PGE(2) was not required for allergen sensitization or development of effector T cell responses. Unexpectedly, the numbers of vascular smooth muscle cells and the thickness of intrapulmonary vessels were both markedly increased in the Der f-treated ptges(-/-) mice. These vascular changes were suppressed by the administration of the stable PGE(2) analog 16, 16-dimethyl PGE(2), or of selective agonists of the E-prostanoid (EP) 1, EP2, and EP3 receptors, respectively, for PGE(2). Thus, mPGES-1 and its product, PGE(2), protect the pulmonary vasculature from remodeling during allergen-induced pulmonary inflammation, and these effects may be mediated by more than one EP receptor.

A prostacyclin agonist with thromboxane inhibitory activity for airway allergic inflammation in mice

BACKGROUND

ONO-1301 is a novel drug that acts as a prostacyclin agonist with thromboxane A(2) (TxA(2)) synthase inhibitory activity. We investigated the effect of ONO-1301 on development of airway allergic inflammation.

METHODS

Mice sensitized and challenged to ovalbumin (OVA) received ONO-1301, OKY-046 (TxA(2) synthase inhibitor), beraprost, a prostacyclin receptor (IP) agonist, ONO-1301 plus CAY10449 (selective IP antagonist) or vehicle during the challenge period. Twenty-four hours after the OVA challenge, airway hyperresponsiveness (AHR) to methacholine was assessed and bronchoalveolar lavage was performed. Lung specimens were excised for goblet cell staining and analysis of lung dendritic cells (DCs). Bone marrow-derived dendritic cells (BMDCs) were generated, in the presence or absence of drugs, for analysis of DC function.

RESULTS

Mice that received ONO-1301 showed significantly lower AHR, airway eosinophilia, T-helper type 2 cytokine levels, mucus production and lung DCs numbers than vehicle-treated mice. These effects of ONO-1301 were mostly reversed by CAY10449. BMDCs treated with ONO-1301 alone showed lower DC functions, such as expression of costimulatory factors or stimulation to spleen T cells.

CONCLUSIONS

These data suggest that ONO-1301 may suppress AHR and airway allergic inflammation through modulation of DCs, mainly mediated through the IP receptor. This agent may be effective as an anti-inflammatory drug in the treatment of asthma.

Prostacyclin inhibits IFN-gamma-stimulated cytokine expression by reduced recruitment of CBP/p300 to STAT1 in a SOCS-1-independent manner

Increasing evidence indicates that pulmonary arterial hypertension is a vascular inflammatory disease. Prostacyclin (PGI(2)) is widely used to treat pulmonary arterial hypertension and is believed to benefit patients largely through vasodilatory effects. PGI(2) is also increasingly believed to have anti-inflammatory effects, including decreasing leukocyte cytokine production, yet few mechanistic details exist to explain how these effects are mediated at the transcriptional level. Because activated monocytes are critical sources of MCP-1 and other cytokines in cardiovascular inflammation, we examined the effects of iloprost on IFN-gamma- and IL-6-stimulated cytokine production in human monocytes. We found that iloprost inhibited IFN-gamma- and IL-6-induced MCP-1, IL-8, RANTES, and TNF-alpha production in monocytes, indicating wide-ranging anti-inflammatory action. We found that activation of STAT1 was critical for IFN-gamma-induced MCP-1 production and demonstrated that iloprost inhibited STAT1 activation by several actions as follows: 1) iloprost inhibited the phosphorylation of STAT1-S727 in the transactivation domain, thereby reducing recruitment of the histone acetylase and coactivator CBP/p300 to STAT1; 2) iloprost selectively inhibited activation of JAK2 but not JAK1, both responsible for activation of STAT1 via phosphorylation of STAT1-Y701, resulting in reduced nuclear recruitment and activation of STAT1; and 3) SOCS-1, which normally terminates IFN-gamma-signaling, was not involved in iloprost-mediated inhibition of STAT1, indicating divergence from the classical pathway for terminating IFN-gamma-signaling. We conclude that PGI(2) exerts anti-inflammatory action by inhibiting STAT1-induced cytokine production, in part by targeting the transactivation domain-induced recruitment of the histone acetylase CBP/p300.

Selective prostacyclin receptor agonism augments glucocorticoid-induced gene expression in human bronchial epithelial cells

Prostacyclin receptor (IP-receptor) agonists display anti-inflammatory and antiviral activity in cell-based assays and in preclinical models of asthma and chronic obstructive pulmonary disease. In this study, we have extended these observations by demonstrating that IP-receptor activation also can enhance the ability of glucocorticoids to induce genes with anti-inflammatory activity. BEAS-2B bronchial epithelial cells stably transfected with a glucocorticoid response element (GRE) luciferase reporter were activated in a concentration-dependent manner by the glucocorticoid dexamethasone. An IP-receptor agonist, taprostene, increased cAMP in these cells and augmented luciferase expression at all concentrations of dexamethasone examined. Analysis of the concentration-response relationship that described this effect showed that taprostene increased the magnitude of transcription without affecting the potency of dexamethasone and was, thus, steroid-sparing in this simple system. RO3244794, an IP-receptor antagonist, and oligonucleotides that selectively silenced the IP-receptor gene, PTGIR, abolished these effects of taprostene. Infection of BEAS-2B GRE reporter cells with an adenovirus vector encoding a highly selective inhibitor of cAMP-dependent protein kinase (PKA) also prevented taprostene from enhancing GRE-dependent transcription. In BEAS-2B cells and primary cultures of human airway epithelial cells, taprostene and dexamethasone interacted either additively or cooperatively in the expression of three glucocorticoid-inducible genes (GILZ, MKP-1, and p57(kip2)) that have anti-inflammatory potential. Collectively, these data show that IP-receptor agonists can augment the ability of glucocorticoids to induce anti-inflammatory genes in human airway epithelial cells by activating a cAMP/PKA-dependent mechanism. This observation may have clinical relevance in the treatment of airway inflammatory diseases that are either refractory or respond suboptimally to glucocorticoids.