Prostaglandin I2 analogs inhibit Th1 and Th2 effector cytokine production by CD4 T cells

Roles of prostaglandins in immunosuppression

Prostaglandins (PGs) play a crucial and multifaceted role in various physiological processes such as intercellular signaling, inflammation regulation, neurotransmission, vasodilation, vasoconstriction, and reproductive functions. The diversity and biological significance of these effects are contingent upon the specific types or subtypes of PGs, with each PG playing a crucial role in distinct physiological and pathological processes. Particularly within the immune system, PGs are essential in modulating the function of immune cells and the magnitude and orientation of immune responses. Hence, a comprehensive comprehension of the functions PG signaling pathways in immunosuppressive regulation holds substantial clinical relevance for disease prevention and treatment strategies. The manuscript provides a review of recent developments in PG signaling in immunosuppressive regulation. Furthermore, the potential clinical applications of PGs in immunosuppression are also discussed. While research into the immunosuppressive effects of PGs required further exploration, targeted therapies against their immunosuppressive pathways might open new avenues for disease prevention and treatment.

Lipid metabolism-related genes are involved in the occurrence of asthma and regulate the immune microenvironment

BACKGROUND

Lipid metabolism plays a pivotal role in asthma pathogenesis. However, a comprehensive analysis of the importance of lipid metabolism-related genes (LMRGs) in regulating the immune microenvironment in asthma remains lacking. The transcriptome matrix was downloaded from the Gene Expression Omnibus (GEO) dataset. Differentially expressed analysis and weighted gene coexpression network analysis (WGCNA) were conducted on the GSE74986 dataset to select hub LMRGs, and gene set enrichment analysis (GSEA) was conducted to explore their biological functions. The CIBERSORT algorithm was used to determine immune infiltration in the asthma and control groups, and the correlation of diagnostic biomarkers and immune cells was performed via Spearman correlation analysis. Subsequently, a competitive endogenous RNA (ceRNA) network was constructed to investigate the hidden molecular mechanism of asthma. The expression levels of the hub genes were further validated in the GSE143192 dataset, and RT‒qPCR and immunofluorescence were performed to verify the reliability of the results in the OVA asthma model. Lastly, the ceRNA network was confirmed by qRT-PCR and RNAi experiments in the characteristic cytokine (IL-13)-induced asthma cellular model.

RESULTS

ASAH1, ACER3 and SGPP1 were identified as hub LMRGs and were mainly involved in protein secretion, mTORC1 signaling, and fatty acid metabolism. We found more infiltration of CD8+ T cells, activated NK cells, and monocytes and less M0 macrophage infiltration in the asthma group than in the healthy control group. In addition, ASAH1, ACER3, and SGPP1 were negatively correlated with CD8+ T cells and activated NK cells, but positively correlated with M0 macrophages. Within the ceRNA network, SNHG9-hsa-miR-615-3p-ACER3, hsa-miR-212-5p and hsa-miR-5682 may play crucial roles in asthma pathogenesis. The low expression of ASAH1 and SGPP1 in asthma was also validated in the GSE74075 dataset. After SNHG9 knockdown, miR-615-3p expression was significantly upregulated, while that of ACER3 was significantly downregulated.

CONCLUSION

ASAH1, ACER3 and SGPP1 might be diagnostic biomarkers for asthma, and are associated with increased immune system activation. In addition, SNHG9-hsa-miR-615-3p-ACER3 may be viewed as effective therapeutic targets for asthma. Our findings might provide a novel perspective for future research on asthma.

Immunometabolism in the pathogenesis of asthma

Bronchial asthma is a heterogeneous disease characterised by chronic airway inflammation. A variety of immune cells such as eosinophils, mast cells, T lymphocytes, neutrophils and airway epithelial cells are involved in the airway inflammation and airway hyperresponsiveness in asthma pathogenesis, resulting in extensive and variable reversible expiratory airflow limitation. However, the precise molecular mechanisms underlying the allergic immune responses, particularly immunometabolism, remains unclear. Studies have detected enhanced oxidative stress, and abnormal metabolic progresses of glycolysis, fatty acid and amino acid in various immune cells, inducing dysregulation of innate and adaptive immune responses in asthma pathogenesis. Immunometabolism mechanisms contain multiple signalling pathways, providing novel therapy targets for asthma. This review summarises the current knowledge on immunometabolism reprogramming in asthma pathogenesis, as well as potential therapy strategies.

The Link between Prostanoids and Cardiovascular Diseases

Cardiovascular diseases are the leading cause of global deaths, and many risk factors contribute to their pathogenesis. In this context, prostanoids, which derive from arachidonic acid, have attracted attention for their involvement in cardiovascular homeostasis and inflammatory processes. Prostanoids are the target of several drugs, but it has been shown that some of them increase the risk of thrombosis. Overall, many studies have shown that prostanoids are tightly associated with cardiovascular diseases and that several polymorphisms in genes involved in their synthesis and function increase the risk of developing these pathologies. In this review, we focus on molecular mechanisms linking prostanoids to cardiovascular diseases and we provide an overview of genetic polymorphisms that increase the risk for cardiovascular disease.

Metabolism Characteristics of Mycoplasma pneumoniae Infection in Asthmatic Children

PURPOSE

Studies have shown that Mycoplasma pneumoniae (Mp) infection can aggravate symptoms in asthmatics. However, the mechanism by which Mp infection exacerbates asthma remains unclear. Metabolomics can help identify the mechanism of Mp aggravating asthma in children, thereby providing more a potential target for improving clinical treatment programs. In this article, we analyzed the metabolic level of patients to explain how Mp aggravates asthma in children.

METHODS

We divided the subjects into the asthma, Mp infection, asthma combined with Mp infection and healthy groups. Patients' peripheral blood was collected for metabolic and interaction analysis. Cytokine levels were measured via serum and exhaled breath condensate (EBC).

RESULTS

A total of 150 participating subjects were divided into four groups after exclusion. We found out that there were different metabolic pathways between the healthy and disease groups. The major pathways of both asthma and asthma combined with Mp infection were valine, leucine and isoleucine biosynthesis; malate-aspartate shuttle was the main differential pathway for Mp infection. Moreover, even though three disease groups involved 81 metabolites at the same time, compared with asthma combined with Mp infection, 2 single disease groups still involved different amino acid pathways (phenylalanine, tyrosine and tryptophan biosynthesis; valine, leucine and isoleucine biosynthesis). Interaction analysis showed that Mp infection in asthmatic patients not only activated cytokines, but also activated Toll-like receptors (TLRs) 2 and 6. Finally, the levels of interleukin (IL)-4, IL-8, IL-13 and tumor necrosis factor-α in EBC with asthma combined with Mp infection were significantly higher than the 2 single disease groups.

CONCLUSIONS

Mp infection in asthmatic children can cause changes in the levels of various amino acids in the body, which were enriched in the pathways such as valine, leucine and isoleucine biosynthesis. Palmitic acid can activate TLR2, and iloprost reduces IL-10 levels, ultimately leading to the increased airway inflammation.

Eicosanoids in inflammation in the blood and the vessel

Polyunsaturated fatty acids (PUFAs) are structural components of membrane phospholipids in cells. PUFAs regulate cellular function through the formation of derived lipid mediators termed eicosanoids. The oxygenation of 20-carbon PUFAs via the oxygenases cyclooxygenases, lipoxygenases, or cytochrome P450, generates a class of classical eicosanoids including prostaglandins, thromboxanes and leukotrienes, and also the more recently identified hydroxy-, hydroperoxy-, epoxy- and oxo-eicosanoids, and the specialized pro-resolving (lipid) mediators. These eicosanoids play a critical role in the regulation of inflammation in the blood and the vessel. While arachidonic acid-derived eicosanoids are extensively studied due to their pro-inflammatory effects and therefore involvement in the pathogenesis of inflammatory diseases such as atherosclerosis, diabetes mellitus, hypertension, and the coronavirus disease 2019; in recent years, several eicosanoids have been reported to attenuate exacerbated inflammatory responses and participate in the resolution of inflammation. This review focused on elucidating the biosynthesis and the mechanistic signaling of eicosanoids in inflammation, as well as the pro-inflammatory and anti-inflammatory effects of these eicosanoids in the blood and the vascular wall.

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.

Prostanoids and Resolution of Inflammation - Beyond the Lipid-Mediator Class Switch

Bioactive lipid mediators play a major role in regulating inflammatory processes. Herein, early pro-inflammatory phases are characterized and regulated by prostanoids and leukotrienes, whereas specialized pro-resolving mediators (SPM), including lipoxins, resolvins, protectins, and maresins, dominate during the resolution phase. While pro-inflammatory properties of prostanoids have been studied extensively, their impact on later phases of the inflammatory process has been attributed mainly to their ability to initiate the lipid-mediator class switch towards SPM. Yet, there is accumulating evidence that prostanoids directly contribute to the resolution of inflammation and return to homeostasis. In this mini review, we summarize the current knowledge of the resolution-regulatory properties of prostanoids and discuss potential implications for anti-inflammatory, prostanoid-targeted therapeutic interventions.

Natural Products in the Prevention of Metabolic Diseases: Lessons Learned from the 20th KAST Frontier Scientists Workshop

The incidence of metabolic and chronic diseases including cancer, obesity, inflammation-related diseases sharply increased in the 21st century. Major underlying causes for these diseases are inflammation and oxidative stress. Accordingly, natural products and their bioactive components are obvious therapeutic agents for these diseases, given their antioxidant and anti-inflammatory properties. Research in this area has been significantly expanded to include chemical identification of these compounds using advanced analytical techniques, determining their mechanism of action, food fortification and supplement development, and enhancing their bioavailability and bioactivity using nanotechnology. These timely topics were discussed at the 20th Frontier Scientists Workshop sponsored by the Korean Academy of Science and Technology, held at the University of Hawaii at Manoa on 23 November 2019. Scientists from South Korea and the U.S. shared their recent research under the overarching theme of Bioactive Compounds, Nanoparticles, and Disease Prevention. This review summarizes presentations at the workshop to provide current knowledge of the role of natural products in the prevention and treatment of metabolic diseases.

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.

Lipid metabolism in asthma: Immune regulation and potential therapeutic target

Asthma is a chronic inflammatory disease of the lungs that poses a considerable health and socioeconomic burden. Several risk factors work synergistically to affect the progression of asthma. Lipid metabolism, especially in distinct cells such as T cells, macrophages, granulocytes, and non-immune cells, plays an essential role in the pathogenesis of asthma, as lipids are potent signaling molecules that regulate a multitude of cellular response. In this review, we focused on the metabolic pathways of lipid molecules, especially fatty acids and their derivatives, and summarized their roles in various cells during the pathogenesis of asthma along with the current pharmacological agents targeting lipid metabolism.

Induced Prostanoid Synthesis Regulates the Balance between Th1- and Th2-Producing Inflammatory Cytokines in the Thymus of Diet-Restricted Mice

Multiple external and internal factors have been reported to induce thymic involution. Involution involves dramatic reduction in size and function of the thymus, leading to various immunodeficiency-related disorders. Therefore, clarifying and manipulating molecular mechanisms governing thymic involution are clinically important, although only a few studies have dealt with this issue. In the present study, we investigated the molecular mechanisms underlying thymic involution using a murine acute diet-restriction model. Gene expression analyses indicated that the expression of T helper 1 (Th1)-producing cytokines, namely interferon-γ and interleukin (IL)-2, was down-regulated, while that of Th2-producing IL-5, IL-6, IL-10 and IL-13 was up-regulated, suggesting that acute diet-restriction regulates the polarization of naïve T cells to a Th2-like phenotype during thymic involution. mRNAs for prostanoid biosynthetic enzymes were up-regulated by acute diet-restriction. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses detected the increased production of prostanoids, particularly prostaglandin D₂ and thromboxane B₂, a metabolite of thromboxane A₂, in the diet-restricted thymus. Administration of non-steroidal anti-inflammatory drugs, namely aspirin and etodolac, to inhibit prostanoid synthesis suppressed the biased expression of Th1- and Th2-cytokines as well as molecular markers of Th1 and Th2 cells in the diet-restricted thymus, without affecting the reduction of thymus size. In vitro stimulation of thymocytes with phorbol myristate acetate (PMA)/ionomycin confirmed the polarization of thymocytes from diet-restricted mice toward Th2 cells. These results indicated that the induced production of prostanoids during diet-restriction-induced thymic involution is involved in the polarization of naïve T cells in the thymus.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Prognostic value of prostaglandin I2 synthase and its correlation with tumor-infiltrating immune cells in lung cancer, ovarian cancer, and gastric cancer

BACKGROUND

Prostaglandin I2 synthase (PTGIS) is a crucial gene for the synthesis of prostaglandin I2, which has multiple roles in inflammation and immune modulation. However, studies on the prognostic value of PTGIS and its correlation with tumor-infiltrating immune cells in multiple cancers are still rare.

RESULTS

Multiple datasets of the Oncomine database showed that PTGIS was expressed at low levels in lung cancer and ovarian cancer compared to the levels in normal tissues. Kaplan-Meier plotter showed that high PTGIS was associated with poor overall survival and progression-free survival in lung, ovarian, and gastric cancers. Moreover, PTGIS expression was significantly positively correlated with infiltrating levels of macrophages and was strongly associated with a variety of immune markers, especially tumor-associated macrophages (TAMs) and T-regulatory cells (Tregs).

CONCLUSIONS

High expression of PTGIS could promote the infiltration of TAMs and Tregs in the tumor microenvironment and deteriorate outcomes of patients with lung, ovarian, and gastric cancers. These findings suggest that PTGIS could be taken as a potential biomarker of prognosis and tumor-infiltrating immune cells.

METHODS

PTGIS expression was investigated in different datasets of the Oncomine database, and its expression levels in various tumors and corresponding normal tissues were analyzed by the Tumor Immune Estimation Resource (TIMER). Then, the clinical prognostic value of PTGIS was assessed with online public databases. In addition, we initially explored the correlation between PTGIS and tumor-infiltrating immune cells by TIMER and Gene Expression Profiling Interactive Analysis (GEPIA).

Immune Modulation to Enhance Bone Healing-A New Concept to Induce Bone Using Prostacyclin to Locally Modulate Immunity

Within an aging population, fracture incidences will rise and with the augmented risks of impaired healing the overall risk of delayed bone regeneration will substantially increase in elderly patients. Thus, new strategies to rescue fracture healing in the elderly are highly warranted. Modulating the initial inflammatory phase toward a reduced pro-inflammation launches new treatment options for delayed or impaired healing specifically in the elderly. Here, we evaluated the capacity of the prostacyclin analog Iloprost to modulate the inflammatory phase toward a pro-regenerative milieu using in vitro as well as in vivo model systems. In vitro, Iloprost administration led to a downregulation of potential unfavorable CD8+ cytotoxic T cells as well as their pro-inflammatory cytokine secretion profile. Furthermore, Iloprost increased the mineralization capacity of osteogenic induced mesenchymal stromal cells through both direct as well as indirect cues. In an in vivo approach, Iloprost, embedded in a biphasic fibrin scaffold, decreased the pro-inflammatory and simultaneously enhanced the anti-inflammatory phase thereby improving bone healing outcome. Overall, our presented data confirms a possible strategy to modulate the early inflammatory phase in aged individuals toward a physiological healing by a downregulation of an excessive pro-inflammation that otherwise would impair healing. Further confirmation in phase I/II trials, however, is needed to validate the concept in a broader clinical evaluation.

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.

Altered cytokine profile under control of the serotonergic system determines the regulation of CYP2C11 and CYP3A isoforms

The aim of this study is to assess a potential mechanism by which the serotonergic system can control the expression and activity of cytochrome (CYP) 2C11 and CYP3A isoforms during liver insufficiency. A rat model of diethylnitrosamine (DEN)-induced liver insufficiency was developed by administering 50 mg/kg of DEN twice a week for 7 weeks. Dysfunction of the serotonergic system was evoked by feeding the rats with a tryptophan-free diet for three weeks. Dysfunction of the serotonergic system during liver insufficiency decreased the level of proinflammatory cytokines (TGF-β and IL-1β) and increased the level of an anti-inflammatory cytokine (IL-4). Simultaneously, activation of the repressive mechanism IL-4/JAK1/STAT6/SOCS1 of the JAK2/STAT5b-mediated signal transduction pathway and the pERK1/2/GR/STAT6 signal transduction pathway resulted in the suppression of the CYP2C11 and CYP3A isoforms. Moreover, dysfunction of the serotonergic system during liver insufficiency equalized the level of testosterone to the basal level, did not change the steady state of the corticosterone level and significantly enhanced the reduced level of growth hormone. An altered cytokine profile under control of the serotonergic system determines the regulation of CYP2C11 and CYP3A isoforms during liver insufficiency through mechanisms based on posttranscriptional and posttranslational processes.

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.

Targeted overexpression of prostacyclin synthase inhibits lung tumor progression by recruiting CD4+ T lymphocytes in tumors that express MHC class II

Lung-specific overexpression of prostacyclin synthase (PGIS) decreases tumor initiation in murine lung cancer models. Prostacyclin analogs prevent lung tumor formation in mice and reverse bronchial dysplasia in former smokers. However, the effect of prostacyclin on lung cancer progression has not been well studied. We investigated the effects of pulmonary PGIS overexpression in an orthotopic immunocompetent mouse model of lung cancer using two murine lung cancer cell lines. Pulmonary PGIS overexpression significantly inhibited CMT167 lung tumor growth, increased CXCL9 expression, and increased CD4+ tumor-infiltrating lymphocytes. Immunodepletion of CD4+ T cells abolished the inhibitory effect of pulmonary PGIS overexpression on CMT167 lung tumor growth. In contrast, pulmonary PGIS overexpression failed to inhibit growth of a second murine lung cancer cell line, Lewis Lung Carcinoma (LLC) cells, and failed to increase CXCL9 expression or CD4+ T lymphocytes in LLC lung tumors. Transcriptome profiling of CMT167 cells and LLC cells recovered from tumor-bearing mice demonstrated that in vivo, CMT167 cells but not LLC cells express MHC class II genes and cofactors necessary for MHC class II processing and presentation. These data demonstrate that prostacyclin can inhibit lung cancer progression and suggest that prostacyclin analogs may serve as novel immunomodulatory agents in a subset of lung cancer patients. Moreover, expression of MHC Class II by lung cancer cells may represent a biomarker for response to prostacyclin.

Glucagon-like peptide 1 signaling inhibits allergen-induced lung IL-33 release and reduces group 2 innate lymphoid cell cytokine production in vivo

BACKGROUND

IL-33 is one of the most consistently associated gene candidates for asthma identified by using a genome-wide association study. Studies in mice and in human cells have confirmed the importance of IL-33 in inducing type 2 cytokine production from both group 2 innate lymphoid cells (ILC2s) and T_H2 cells. However, there are no pharmacologic agents known to inhibit IL-33 release from airway cells.

OBJECTIVE

We sought to determine the effect of glucagon-like peptide 1 receptor (GLP-1R) signaling on aeroallergen-induced airway IL-33 production and release and on innate type 2 airway inflammation.

METHODS

BALB/c mice were challenged intranasally with Alternaria extract for 4 consecutive days. GLP-1R agonist or vehicle was administered starting either 2 days before the first Alternaria extract challenge or 1 day after the first Alternaria extract challenge.

RESULTS

GLP-1R agonist treatment starting 2 days before the first Alternaria extract challenge decreased IL-33 release in the bronchoalveolar lavage fluid and dual oxidase 1 (Duox1) mRNA expression 1 hour after the first Alternaria extract challenge and IL-33 expression in lung epithelial cells 24 hours after the last Alternaria extract challenge. Furthermore, GLP-1R agonist significantly decreased the number of ILC2s expressing IL-5 and IL-13, lung protein expression of type 2 cytokines and chemokines, the number of perivascular eosinophils, mucus production, and airway responsiveness compared with vehicle treatment. GLP-1R agonist treatment starting 1 day after the first Alternaria extract challenge also significantly decreased eosinophilia and type 2 cytokine and chemokine expression in the airway after 4 days of Alternaria extract challenge.

CONCLUSION

These results reveal that GLP-1R signaling might be a therapy to reduce IL-33 release and inhibit the ILC2 response to protease-containing aeroallergens, such as Alternaria.

Iloprost Affects Macrophage Activation and CCL2 Concentrations in a Microdialysis Model in Rats

PURPOSE

The hypothesis that locally-released iloprost, a synthetic prostacyclin analog, affects macrophage phenotype at a microdialysis implant in the subcutaneous space of rats was tested. Macrophage activation towards alternatively-activated phenotypes using pharmaceutical release is of interest to improve integration of implants and direct the foreign body reaction toward a successful outcome.

METHODS

Macrophage cell culture was used to test iloprost macrophage activation in vitro. Microdialysis sampling probes were implanted into the subcutaneous space of Sprague-Dawley rats to locally deliver iloprost in awake- and freely-moving rats. Monocyte chemoattractant protein -1 (CCL2) was quantified from collected dialysates using ELISA. Immunohistochemical staining was used to determine the presence of CD163⁺ macrophages in explanted tissues.

RESULTS

Iloprost reduced CCL2 concentrations in NR8383 macrophages stimulated with lipopolysaccharide. CCL2 concentrations in collected dialysates were similarly reduced in the presence of iloprost. Iloprost caused an increase in CD163⁺ cells in explanted tissue surrounding implanted microdialysis probes at two days post probe implantation.

CONCLUSIONS

Localized delivery of iloprost caused macrophage activation at the tissue interface of a microdialysis subcutaneous implant in rat. This model system may be useful for testing other potential macrophage modulators in vivo.

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.

Challenges and opportunities in treating inflammation associated with pulmonary hypertension

INTRODUCTION

Inflammatory cells are present in the lungs from patients with many, if not all, forms of severe pulmonary hypertension.

AREAS COVERED

Historically the first inflammatory cell identified in the pulmonary vascular lesions was the mast cell. T and B lymphocytes, as well as macrophages, are present in and around the pulmonary arterioles and many patients have elevated blood levels of interleukin 1 and 6; some patients show elevated levels of leukotriene B4. An overlap between collagen-vascular disease-associated pulmonary arterial hypertension (PAH) and idiopathic PAH exists, yet only a few studies have been designed that evaluate the effect of anti-inflammatory treatments. Here we review the pertinent data that connect PAH and inflammation/autoimmune dysregulation and evaluate experimental models of severe PAH with an emphasis on the Sugen/athymic rat model of severe PAH. Expert commentary: We postulate that there are several inflammatory phenotypes and predict that there will be several anti-inflammatory treatment strategies for severe PAH.

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.

STAT6 Signaling Attenuates Interleukin-17-Producing γδ T Cells during Acute Klebsiella pneumoniae Infection

γδ T cells are prevalent at mucosal and epithelial surfaces and are a critical first line of defense against bacterial and fungal pathogens. γδ17 cells are a subset of γδ T cells which, in the presence of IL-23 and IL-1β, produce large quantities of interleukin-17A (IL-17A), a cytokine crucial to these cells' antibacterial and antifungal function. STAT6, an important transcription factor in Th2 differentiation and inhibition of Th1 differentiation, is expressed at high levels in the T cells of people with parasitic infections and asthma. Our group and others have shown that STAT6 attenuates IL-17A protein expression by CD4(+) T cells. By extension, we hypothesized that STAT6 activation also inhibits innate γδ17 cell cytokine secretion. We show here that γδ17 cells expressed the type I IL-4 receptor (IL-4R), and IL-4 increased STAT6 phosphorylation in γδ T cells. IL-4 inhibited γδ17 cell production of IL-17A. IL-4 also decreased γδ17 cell expression of IL-23R as well as Sgk1. To determine whether STAT6 signaling regulates γδ17 cell numbers in vivo, we used a model of Klebsiella pneumoniae in mice deficient in STAT6. We chose K. pneumoniae for our in vivo model, since K. pneumoniae increases IL-17A expression and γδ17 numbers. K. pneumoniae infection of STAT6 knockout mice resulted in a statistically significant increase in the number of γδ17 cells compared to that of wild-type mice. These studies are the first to demonstrate that γδ17 cells express the type I IL-4R and that STAT6 signaling negatively regulates γδ17 cells, a cell population that plays a front-line role in mucosal immunity.

Prostanoids in Asthma and COPD: Actions, Dysregulation, and Therapeutic Opportunities

Pathophysiologic gaps in the actions of currently available treatments for asthma and COPD include neutrophilic inflammation, airway remodeling, and alveolar destruction. All of these processes can be modulated by cyclic adenosine monophosphate-elevating prostaglandins E2 and I2 (also known as prostacyclin). These prostanoids have long been known to elicit bronchodilation and to protect against bronchoconstriction provoked by a variety of stimuli. Much less well known is their capacity to inhibit inflammatory responses involving activation of lymphocytes, eosinophils, and neutrophils, as well as to attenuate epithelial injury and mesenchymal cell activation. This profile of actions identifies prostanoids as attractive candidates for exogenous administration in asthma. By contrast, excessive prostanoid production and signaling might contribute to both the increased susceptibility to infections that drive COPD exacerbations and the inadequate alveolar repair that characterizes emphysema. Inhibition of endogenous prostanoid synthesis or signaling, thus, has therapeutic potential for these types of patients. By virtue of their pleiotropic capacity to modulate numerous pathophysiologic processes relevant to the expression and natural history of airway diseases, prostanoids emerge as attractive targets for therapeutic manipulation.

Serum levels of tumor necrosis factor-related apoptosis-inducing ligand correlate with the severity of pulmonary hypertension

Pulmonary hypertension (PH) is a rapidly progressive disease that eventually leads to right heart failure and death. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptors (TRAIL-Rs) play an important role in the survival, migration, and proliferation of vascular smooth muscle cells. However, the association between serum TRAIL levels and PH is unknown. In this study, we assayed the serum soluble TRAIL (sTRAIL) levels in 78 patients with PH and 80 controls. The sTRAIL concentrations were elevated in the PH patients compared with the controls (138.76 ± 6.60 pg/mL vs. 80.14 ± 3.38 pg/mL, p < 0.0001). The presence of sTRAIL levels of >103 pg/mL could discriminate PH patients from healthy individuals, with a sensitivity of 75.6% and specificity of 81.2%. Moreover, elevated sTRAIL concentrations were associated with eventual pathological complications; this is consistent with the finding that sTRAIL levels decreased in patients who responded to treatment. In a hypoxia-induced PH mouse model, sTRAIL levels were significantly higher compared with those in normoxia mice, and clearly decreased when the mice were treated with treprostinil. The sTRAIL levels were positively correlated with right ventricular systolic pressure and the index of right ventricular hypertrophy. In conclusion, serum sTRAIL could be a biomarker for diagnosis and effective therapy for PH patients.

The mechanistic basis of prostacyclin and its stable analogues in pulmonary arterial hypertension: Role of membrane versus nuclear receptors

Pulmonary arterial hypertension (PAH) is a progressive disease of distal pulmonary arteries in which patients suffer from elevated pulmonary arterial pressure, extensive vascular remodelling and right ventricular failure. To date prostacyclin (PGI2) therapy remains the most efficacious treatment for PAH and is the only approved monotherapy to have a positive impact on long-term survival. A key thing to note is that improvement exceeds that predicted from vasodilator testing strongly suggesting that additional mechanisms contribute to the therapeutic benefit of prostacyclins in PAH. Given these agents have potent antiproliferative, anti-inflammatory and endothelial regenerating properties suggests therapeutic benefit might result from a slowing, stabilization or even some reversal of vascular remodelling in vivo. This review discusses evidence that the pharmacology of each prostacyclin (IP) receptor agonist so far developed is distinct, with non-IP receptor targets clearly contributing to the therapeutic and side effect profile of PGI2 (EP3), iloprost (EP1), treprostinil (EP2, DP1) along with a family of nuclear receptors known as peroxisome proliferator-activated receptors (PPARs), to which PGI2 and some analogues directly bind. These targets are functionally expressed to varying degrees in arteries, veins, platelets, fibroblasts and inflammatory cells and are likely to be involved in the biological actions of prostacylins. Recently, a highly selective IP agonist, selexipag has been developed for PAH. This agent should prove useful in distinguishing IP from other prostanoid receptors or PPAR binding effects in human tissue. It remains to be determined whether selectivity for the IP receptor gives rise to a superior or inferior clinical benefit in PAH.

The role of prostaglandins in allergic lung inflammation and asthma

Prostaglandins (PGs) are products of the COX pathway of arachidonic acid metabolism. There are five primary PGs, PGD₂, PGE₂, PGF₂, PGI₂ and thromboxane A₂, all of which signal through distinct seven transmembrane, G-protein coupled receptors. Some PGs may counteract the actions of others, or even the same PG may have opposing physiologic or immunologic effects, depending on the specific receptor through which it signals. In this review, we examine the effects of COX activity and the various PGs on allergic airway inflammation and physiology that is associated with asthma. We also highlight the potential therapeutic benefit of targeting PGs in allergic lung inflammation and asthma based on basic science, animal model and human studies.

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.

Deficiency of gp91phox inhibits allergic airway inflammation

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a multienzyme complex, is the major source for production of reactive oxygen species (ROS). ROS are increased in allergic diseases, such as asthma, but the role of ROS in disease pathogenesis remains uncertain. We hypothesized that mice unable to generate ROS via the NADPH oxidase pathway would have decreased allergic airway inflammation. To test this hypothesis, we studied gp91phox(-/-) mice in a model of allergic airway inflammation after sensitization and challenge with ovalbumin. Serum, bronchoalveolar lavage fluid, and lungs were then examined for evidence of allergic inflammation. We found that mice lacking a functional NADPH oxidase complex had significantly decreased ROS production and allergic airway inflammation, compared with wild-type (WT) control animals. To determine the mechanism by which allergic inflammation was inhibited by gp91phox deficiency, we cultured bone marrow-derived dendritic cells from WT and gp91phox(-/-) mice and activated them with LPS. IL-12 expression was significantly increased in the gp91phox(-/-) bone marrow-derived dendritic cells, suggesting that the cytokine profile produced in the absence of gp91phox enhanced the conditions leading to T helper (Th) type 1 differentiation, while inhibiting Th2 polarization. Splenocytes from sensitized gp91phox(-/-) animals produced significantly less IL-13 in response to ovalbumin challenge in vitro compared with splenocytes from sensitized WT mice, suggesting that NADPH oxidase promotes allergic sensitization. In contrast, inflammatory cytokines produced by T cells cultured from WT and gp91phox(-/-) mice under Th0, Th1, Th2, and Th17 conditions were not significantly different. This study demonstrates the importance of NADPH oxidase activity and ROS production in a murine model of 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.

Prostaglandin I2-IP signalling regulates human Th17 and Treg cell differentiation

Prostaglandin I2 (PGI2) is an important immunoregulatory lipid mediator. In this study, we analysed the effects of the PGI2 analogue (Iloprost) on the differentiation of Th17 cells and Tregs from human naïve CD4(+) T cells. PGI2 receptors (IP) are expressed on human naïve CD4(+) T cells. Via IP binding, the PGI2 analogue decreased the proportion of Tregs and Foxp3 mRNA expression but increased the percentage of Th17 cells, RORC mRNA and IL-17A production. The regulatory effects of Iloprost correlated with elevated intracellular cAMP levels. The effects were mimicked by a cAMP agonist (db-cAMP) but attenuated by a protein kinase A inhibitor (H-89). STAT3 and STAT5 signalling play direct and crucial roles in the development of Th17 and Tregs, respectively. The PGI2 analogue enhanced the activation of STAT3 in response to IL-6, whereas it decreased STAT5 activation in response to IL-2. Moreover, db-cAMP imitated the above effects of Iloprost, which were weakened by H-89. These results demonstrate that the PGI2-IP interaction promoted the phosphorylation of STAT3 and reduced the phosphorylation of STAT5, likely via the upregulation of cAMP-PKA signalling, thus facilitated Th17 differentiation and suppressed Treg differentiation. Together with previous results, these data suggest that prostanoids play an important role in the pathogenesis of autoimmune diseases, such as rheumatoid arthritis.

Lipid mediators and allergic diseases

OBJECTIVE

To review the basic science and translational relevance of lipid mediators in the pathobiology of allergic diseases.

DATA SOURCES

PubMed was searched for articles using the key terms lipid mediator, prostaglandin, prostanoid, leukotriene, thromboxane, asthma, and allergic inflammation.

STUDY SELECTIONS

Articles were selected based on their relevance to the goals of this review. Articles with a particular focus on clinical and translational aspects of basic science discoveries were emphasized.

RESULTS

Lipid mediators are bioactive molecules generated from cell membrane phospholipids. They play important roles in many disease states, particularly in inflammatory and immune responses. Lipid mediators and their receptors are potentially useful as diagnostic markers of disease and therapeutic targets.

CONCLUSIONS

Several useful therapeutic agents have been developed based on a growing understanding of the lipid mediator pathways in allergic disease, notably the cysteinyl leukotriene receptor type 1 antagonists and the 5-lipoxygenase inhibitor, zileuton. Additional receptor agonists and antagonists relevant to these pathways are in development, and it is likely that future pharmacologic treatments for allergic disease will become available as our understanding of these molecules continues to evolve.

Proinflammatory and immunoregulatory roles of eicosanoids in T cells

Eicosanoids are inflammatory mediators primarily generated by hydrolysis of membrane phospholipids by phospholipase A2 to ω-3 and ω-6 C20 fatty acids that next are converted to leukotrienes (LTs), prostaglandins (PGs), prostacyclins (PCs), and thromboxanes (TXAs). The rate-limiting and tightly regulated lipoxygenases control synthesis of LTs while the equally well-controlled cyclooxygenases 1 and 2 generate prostanoids, including PGs, PCs, and TXAs. While many of the classical signs of inflammation such as redness, swelling, pain, and heat are caused by eicosanoid species with vasoactive, pyretic, and pain-inducing effects locally, some eicosanoids also regulate T cell functions. Here, we will review eicosanoid production in T cell subsets and the inflammatory and immunoregulatory functions of LTs, PGs, PCs, and TXAs in T cells.

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.

[Functions of prostaglandin receptors in contact dermatitis and application to drug discovery]

Contact dermatitis is an inflammatory skin disease caused by toxic factors that activate the skin innate immunity (irritant contact dermatitis) or by a T cell-mediated hypersensitivity reaction (allergic contact dermatitis). These inflammatory skin diseases are sometimes still not easy to control. Therefore, the development of new effective drugs with fewer side effects is anticipated. In the skin under pathophysiological conditions, multiple prostaglandins are produced and their receptors are expressed in time- and/or cell-dependent manners. However, the precise role of prostaglandins and their receptors in contact dermatitis has not been fully understood. Recently, studies using mice with a disruption of each prostaglandin receptor gene, as well as receptor-selective compounds revealed that prostaglandin receptors have manifold functions, sometimes resulting in opposite outcomes. Here, we review new advances in the roles of prostaglandin receptors in contact hypersensitivity as a cutaneous immune response model, and also discuss the clinical potentials of receptor-selective drugs.

Effects of sub-acute exposure to rhodium (as Rh (III) chloride hydrate) on cytokines in female Wistar rats

Quantitative changes in different cytokines were determined in serum of female Wistar rats exposed to Rhodium (III) chloride hydrate to evaluate its early effects on the immune system. Findings revealed an inhibitory effect of Rh salt since each cytokine, with the exceptions of IL-1α and IL-2 levels observed at the highest doses of exposure, was reduced compared to the controls and interestingly, the lowest doses induced the greatest inhibition. This generalized decrease of cytokine levels was not related to a specific cytokine pathway, and may suggest an anti-inflammatory role of Rh salt.

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.