The Roles of Type 2 Cytotoxic T Cells in Inflammation, Tissue Remodeling, and Prostaglandin (PG) D2 Production Are Attenuated by PGD2 Receptor 2 Antagonism.

Human type 2 cytotoxic T (Tc2) cells are enriched in severe eosinophilic asthma and can contribute to airway eosinophilia. PGD2 and its receptor PGD2 receptor 2 (DP2) play important roles in Tc2 cell activation, including migration, cytokine production, and survival. In this study, we revealed novel, to our knowledge, functions of the PGD2/DP2 axis in Tc2 cells to induce tissue-remodeling effects and IgE-independent PGD2 autocrine production. PGD2 upregulated the expression of tissue-remodeling genes in Tc2 cells that enhanced the fibroblast proliferation and protein production required for tissue repair and myofibroblast differentiation. PGD2 stimulated Tc2 cells to produce PGD2 using the routine PGD2 synthesis pathway, which also contributed to TCR-dependent PGD2 production in Tc2 cells. Using fevipiprant, a specific DP2 antagonist, we demonstrated that competitive inhibition of DP2 not only completely blocked the cell migration, adhesion, proinflammatory cytokine production, and survival of Tc2 cells triggered by PGD2 but also attenuated the tissue-remodeling effects and autocrine/paracrine PGD2 production in Tc2 induced by PGD2 and other stimulators. These findings further confirmed the anti-inflammatory effect of fevipiprant and provided a better understanding of the role of Tc2 cells in the pathogenesis of asthma.

The Prostaglandin D2 Receptor CRTH2 Promotes IL-33-Induced ILC2 Accumulation in the Lung.

Group 2 innate lymphoid cells (ILC2s) are rare innate immune cells that accumulate in tissues during allergy and helminth infection, performing critical effector functions that drive type 2 inflammation. ILC2s express ST2, the receptor for the cytokine IL-33, and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), a receptor for the bioactive lipid prostaglandin D2 (PGD2). The IL-33-ST2 and the PGD2-CRTH2 pathways have both been implicated in promoting ILC2 accumulation during type 2 inflammation. However, whether these two pathways coordinate to regulate ILC2 population size in the tissue in vivo remains undefined. In this study, we show that ILC2 accumulation in the murine lung in response to systemic IL-33 treatment was partially dependent on CRTH2. This effect was not a result of reduced ILC2 proliferation, increased apoptosis or cell death, or differences in expression of the ST2 receptor in the absence of CRTH2. Rather, data from adoptive transfer studies suggested that defective accumulation of CRTH2-deficient ILC2s in response to IL-33 was due to altered ILC2 migration patterns. Whereas donor wild-type ILC2s preferentially accumulated in the lungs compared with CRTH2-deficient ILC2s following transfer into IL-33-treated recipients, wild-type and CRTH2-deficient ILC2s accumulated equally in the recipient mediastinal lymph node. These data suggest that CRTH2-dependent effects lie downstream of IL-33, directly affecting the migration of ILC2s into inflamed lung tissues. A better understanding of the complex interactions between the IL-33 and PGD2-CRTH2 pathways that regulate ILC2 population size will be useful in understanding how these pathways could be targeted to treat diseases associated with type 2 inflammation.

Impact of high-altitude therapy on type-2 immune responses in asthma patients.

BACKGROUND: Asthma patients present with distinct immunological profiles, with a predominance of type 2 endotype. The aim of this study was to investigate the impact of high-altitude treatment on the clinical and immunological response in asthma. METHODS: Twenty-six hospitalized asthma patients (nine eosinophilic allergic; EA, nine noneosinophilic allergic; NEA and eight noneosinophilic nonallergic; NN) and nine healthy controls in high altitude for 21 days were enrolled in the study. We assessed eosinophils, T cells, Tregs, and innate lymphoid cells (ILC) from peripheral blood using flow cytometry. RESULTS: The number of eosinophils (both resting and activated) and chemoattractant receptor homolog expressed on Th2 cells (CRTH2)-expressing CD4+ and CD8+ T cells decreased significantly in EA patients after altitude treatment. The frequency of CRTH2+ Tregs as decreased significantly in all the asthma phenotypes as well as the frequency of ILC2 was significantly reduced in EA after altitude treatment. After 21 days of altitude therapy, CRTH2-expressing ILC2, CD4+ and CD8+ T cells and Treg cells showed attenuated responses to exogenous PGD2. Furthermore, PGD2 signaling via CRTH2 was found to diminish the suppressive function of CRTH2+ Tregs which partially normalized during high-altitude treatment. Improved asthma control was particularly evident in allergic asthma patients and correlated with decreased frequencies of CRTH2+ Treg cells in EA patients. Serum IL-5 and IL-13 decreased during climate treatment in asthma patients with high baseline levels. CONCLUSIONS: Asthma treatment in high altitude reduced the type 2 immune response, corrected the increased CRTH2 expression and its dysregulated functions.

A phase 2 study to evaluate the safety, efficacy and pharmacokinetics of DP2 antagonist GB001 and to explore biomarkers of airway inflammation in mild-to-moderate asthma.

BACKGROUND: GB001 is an oral antagonist of the prostaglandin D2 receptor that may inhibit recruitment and activation of airway eosinophils, reducing airway inflammation. OBJECTIVE: To assess GB001 safety, efficacy and pharmacokinetics from a Phase 2 study and explore the association between type 2 biomarkers (fractional exhaled nitric oxide and blood eosinophils) and asthma control markers following GB001 administration. METHODS: A randomized, placebo-controlled, double-blind study evaluating 36 patients with mild-to-moderate atopic asthma. Patients receiving fluticasone propionate ≤500 mcg/day or equivalent were randomized (2:1) to GB001 (30 mg) or placebo once daily for 28 days. Safety, pharmacokinetics, forced expiratory volume in 1 second, asthma control questionnaire and rescue medication use were assessed. Clinical outcomes were analysed post hoc by baseline fractional exhaled nitric oxide (<35 and ≥35 ppb) and blood eosinophil (<250 and ≥250 cells/µL) subgroups. RESULTS: GB001 was well tolerated and rapidly absorbed with a 14.5-hour terminal half-life. Overall, GB001 demonstrated greater improvement relative to placebo in forced expiratory volume in 1 second at Day 28 (102 mL [95% CI: -110, 314]). Greater effects on forced expiratory volume in 1 second were observed in the high baseline fractional exhaled nitric oxide and blood eosinophil subgroups (207 mL [95% CI: -283, 698];133 mL [95% CI: -422, 687], respectively). These effects were observed as early as Day 2 (229 mL [95% CI: -170, 628]; 163 mL [95% CI: -223, 550] for the high baseline fractional exhaled nitric oxide and blood eosinophil subgroups, respectively) and were sustained through treatment completion. CONCLUSION AND CLINICAL RELEVANCE: GB001 was well tolerated, with the estimated half-life supporting once-daily (QD) dosing. GB001 may have a rapid and sustained effect on lung function, particularly in patients with type 2 phenotype. Further studies are needed to confirm these findings.

New Targeted Therapies for Uncontrolled Asthma.

Mechanistic studies have improved our understanding of molecular and cellular components involved in asthma and our ability to treat severe patients. An mAb directed against IgE (omalizumab) has become an established add-on therapy for patients with uncontrolled allergic asthma and mAbs specific for IL-5 (reslizumab, mepolizumab), IL-5R (benralizumab), and IL-4R (dupilumab) have been approved as add-on treatments for uncontrolled eosinophilic (type 2) asthma. While these medications have proven highly effective, some patients with severe allergic and/or eosinophilic asthma, as well as most patients with severe non-type-2 disease, have poorly controlled disease. Agents that have recently been evaluated in clinical trials include an antibody directed against thymic stromal lymphopoietin, small molecule antagonists to the chemoattractant receptor-homologous molecule expressed on TH2 cells (CRTH2) and the receptor for stem cell factor on mast cells (KIT), and a DNA enzyme directed at GATA3. Antibodies to IL-33 and its receptor, ST2, are being evaluated in ongoing clinical studies. In addition, a number of antagonists directed against other potential targets are under consideration for future trials, including IL-25, IL-6, TNF-like ligand 1A, CD6, and activated cell adhesion molecule (ALCAM). Clinical data from ongoing and future trials will be important in determining whether these new medications will offer benefits in place of or in addition to existing therapies for asthma.

Deficiency of CRTH2, a Prostaglandin D2 Receptor, Aggravates Bleomycin-induced Pulmonary Inflammation and Fibrosis.

Chemoattractant receptor homologous with T-helper cell type 2 cells (CRTH2), a receptor for prostaglandin D2, is preferentially expressed on T-helper cell type 2 lymphocytes, group 2 innate lymphoid cells, eosinophils, and basophils, and elicits the production of type 2 cytokines, including profibrotic IL-13. We hypothesized that lack of CRTH2 might protect against fibrotic lung disease, and we tested this hypothesis using a bleomycin-induced lung inflammation and fibrosis model in CRTH2-deficient (CRTH2-/-) or wild-type BALB/c mice. Compared with wild-type mice, CRTH2-/- mice treated with bleomycin exhibited significantly higher mortality, enhanced accumulation of inflammatory cells 14-21 days after bleomycin injection, reduced pulmonary compliance, and increased levels of collagen and total protein in the lungs. These phenotypes were associated with decreased levels of IFN-γ, IL-6, IL-10, and IL-17A in BAL fluid. Adoptive transfer of splenocytes from wild-type, but not CRTH2-/-, mice 2 days before injection of bleomycin resolved the sustained inflammation as well as the increased collagen and protein accumulation in the lungs of CRTH2-/- mice. We consider that the disease model is driven by γδT cells that express CRTH2; thus, the adoptive transfer of γδT cells could ameliorate bleomycin-induced alveolar inflammation and fibrosis.

Leptin Elicits LTC4 Synthesis by Eosinophils Mediated by Sequential Two-Step Autocrine Activation of CCR3 and PGD2 Receptors.

Leptin is a cytokine, produced mainly by mature adipocytes, that regulates the central nervous system, mainly to suppress appetite and stimulate energy expenditure. Leptin also regulates the immune response by controlling activation of immunomodulatory cells, including eosinophils. While emerging as immune regulatory cells with roles in adipose tissue homeostasis, eosinophils have a well-established ability to synthesize pro-inflammatory molecules such as lipid mediators, a key event in several inflammatory pathologies. Here, we investigated the impact and mechanisms involved in leptin-driven activation of eicosanoid-synthesizing machinery within eosinophils. Direct in vitro activation of human or mouse eosinophils with leptin elicited synthesis of lipoxygenase as well as cyclooxygenase products. Displaying selectivity, leptin triggered synthesis of LTC4 and PGD2, but not PGE2, in parallel to dose-dependent induction of lipid body/lipid droplets biogenesis. While dependent on PI3K activation, leptin-driven eosinophil activation was also sensitive to pertussis toxin, indicating the involvement of G-protein coupled receptors on leptin effects. Leptin-induced lipid body-driven LTC4 synthesis appeared to be mediated through autocrine activation of G-coupled CCR3 receptors by eosinophil-derived CCL5, inasmuch as leptin was able to trigger rapid CCL5 secretion, and neutralizing anti-RANTES or anti-CCR3 antibodies blocked lipid body assembly and LTC4 synthesis induced by leptin. Remarkably, autocrine activation of PGD2 G-coupled receptors DP1 and DP2 also contributes to leptin-elicited lipid body-driven LTC4 synthesis by eosinophils in a PGD2-dependent fashion. Blockade of leptin-induced PGD2 autocrine/paracrine activity by a specific synthesis inhibitor or DP1 and DP2 receptor antagonists, inhibited both lipid body biogenesis and LTC4 synthesis induced by leptin stimulation within eosinophils. In addition, CCL5-driven CCR3 activation appears to precede PGD2 receptor activation within eosinophils, since neutralizing anti-CCL5 or anti-CCR3 antibodies inhibited leptin-induced PGD2 secretion, while it failed to alter PGD2-induced LTC4 synthesis. Altogether, sequential activation of CCR3 and then PGD2 receptors by autocrine ligands in response to leptin stimulation of eosinophils culminates with eosinophil activation, characterized here by assembly of lipidic cytoplasmic platforms synthesis and secretion of the pleiotropic lipid mediators, PGD2, and LTC4.

The prostaglandin D2 receptor 2 pathway in asthma: a key player in airway inflammation.

Asthma is characterised by chronic airway inflammation, airway obstruction and hyper-responsiveness. The inflammatory cascade in asthma comprises a complex interplay of genetic factors, the airway epithelium, and dysregulation of the immune response.Prostaglandin D2 (PGD2) is a lipid mediator, predominantly released from mast cells, but also by other immune cells such as TH2 cells and dendritic cells, which plays a significant role in the pathophysiology of asthma. PGD2 mainly exerts its biological functions via two G-protein-coupled receptors, the PGD2 receptor 1 (DP1) and 2 (DP2). The DP2 receptor is mainly expressed by the key cells involved in type 2 immune responses, including TH2 cells, type 2 innate lymphoid cells and eosinophils. The DP2 receptor pathway is a novel and important therapeutic target for asthma, because increased PGD2 production induces significant inflammatory cell chemotaxis and degranulation via its interaction with the DP2 receptor. This interaction has serious consequences in the pulmonary milieu, including the release of pro-inflammatory cytokines and harmful cationic proteases, leading to tissue remodelling, mucus production, structural damage, and compromised lung function. This review will discuss the importance of the DP2 receptor pathway and the current understanding of its role in asthma.

Activation of Th2 cells downregulates CRTh2 through an NFAT1 mediated mechanism.

CRTh2 (encoded by PTGDR2) is a G-protein coupled receptor expressed by Th2 cells as well as eosinophils, basophils and innate lymphoid cells (ILC)2s. Activation of CRTh2, by its ligand prostaglandin (PG)D2, mediates production of type 2 cytokines (IL-4, IL-5 and IL-13), chemotaxis and inhibition of apoptosis. As such, the PGD2-CRTh2 pathway is considered important to the development and maintenance of allergic inflammation. Expression of CRTh2 is mediated by the transcription factor GATA3 during Th2 cell differentiation and within ILC2s. Other than this, relatively little is known regarding the cellular and molecular mechanisms regulating expression of CRTh2. Here, we show using primary human Th2 cells that activation (24hrs) through TCR crosslinking (αCD3/αCD28) reduced expression of both mRNA and surface levels of CRTh2 assessed by flow cytometry and qRT-PCR. This effect took more than 4 hours and expression was recovered following removal of activation. EMSA analysis revealed that GATA3 and NFAT1 can bind independently to overlapping sites within a CRTh2 promoter probe. NFAT1 over-expression resulted in loss of GATA3-mediated CRTh2 promoter activity, while inhibition of NFAT using a peptide inhibitor (VIVIT) coincided with recovery of CRTh2 expression. Collectively these data indicate that expression of CRTh2 is regulated through the competitive action of GATA3 and NFAT1. Though prolonged activation led to NFAT1-mediated downregulation, CRTh2 was re-expressed when stimulus was removed suggesting this is a dynamic mechanism and may play a role in PGD2-CRTh2 mediated allergic inflammation.

Prostaglandin D2 Receptor DP1 Antibodies Predict Vaccine-induced and Spontaneous Narcolepsy Type 1: Large-scale Study of Antibody Profiling.

BACKGROUND: Neuropathological findings support an autoimmune etiology as an underlying factor for loss of orexin-producing neurons in spontaneous narcolepsy type 1 (narcolepsy with cataplexy; sNT1) as well as in Pandemrix influenza vaccine-induced narcolepsy type 1 (Pdmx-NT1). The precise molecular target or antigens for the immune response have, however, remained elusive. METHODS: Here we have performed a comprehensive antigenic repertoire analysis of sera using the next-generation phage display method - mimotope variation analysis (MVA). Samples from 64 children and adolescents were analyzed: 10 with Pdmx-NT1, 6 with sNT1, 16 Pandemrix-vaccinated, 16 H1N1 infected, and 16 unvaccinated healthy individuals. The diagnosis of NT1 was defined by the American Academy of Sleep Medicine international criteria of sleep disorders v3. FINDINGS: Our data showed that although the immunoprofiles toward vaccination were generally similar in study groups, there were also striking differences in immunoprofiles between sNT1 and Pdmx-NT1 groups as compared with controls. Prominent immune response was observed to a peptide epitope derived from prostaglandin D2 receptor (DP1), as well as peptides homologous to B cell lymphoma 6 protein. Further validation confirmed that these can act as true antigenic targets in discriminating NT1 diseased along with a novel epitope of hemagglutinin of H1N1 to delineate exposure to H1N1. INTERPRETATION: We propose that DP1 is a novel molecular target of autoimmune response and presents a potential diagnostic biomarker for NT1. DP1 is involved in the regulation of non-rapid eye movement (NREM) sleep and thus alterations in its functions could contribute to the disturbed sleep regulation in NT1 that warrants further studies. Together our results also show that MVA is a helpful method for finding novel peptide antigens to classify human autoimmune diseases, possibly facilitating the design of better therapies.

Prostaglandin D2 amplifies lupus disease through basophil accumulation in lymphoid organs.

In systemic lupus erythematosus (SLE), autoantibody production can lead to kidney damage and failure, known as lupus nephritis. Basophils amplify the synthesis of autoantibodies by accumulating in secondary lymphoid organs. Here, we show a role for prostaglandin D2 (PGD2) in the pathophysiology of SLE. Patients with SLE have increased expression of PGD2 receptors (PTGDR) on blood basophils and increased concentration of PGD2 metabolites in plasma. Through an autocrine mechanism dependent on both PTGDRs, PGD2 induces the externalization of CXCR4 on basophils, both in humans and mice, driving accumulation in secondary lymphoid organs. Although PGD2 can accelerate basophil-dependent disease, antagonizing PTGDRs in mice reduces lupus-like disease in spontaneous and induced mouse models. Our study identifies the PGD2/PTGDR axis as a ready-to-use therapeutic modality in SLE.

Generation and characterization of an antagonistic monoclonal antibody against an extracellular domain of mouse DP2 (CRTH2/GPR44) receptors for prostaglandin D2.

Prostaglandin D2 (PGD2) is a lipid mediator involved in sleep regulation and inflammation. PGD2 interacts with 2 types of G protein-coupled receptors, DP1 and DP2/CRTH2 (chemoattractant receptor homologous molecule expressed on T helper type 2 cells)/GPR44 to show a variety of biological effects. DP1 activation leads to Gs-mediated elevation of the intracellular cAMP level, whereas activation of DP2 decreases this level via the Gi pathway; and it also induces G protein-independent, arrestin-mediated cellular responses. Activation of DP2 by PGD2 causes the progression of inflammation via the recruitment of lymphocytes by enhancing the production of Th2-cytokines. Here we developed monoclonal antibodies (MAbs) against the extracellular domain of mouse DP2 by immunization of DP2-null mutant mice with DP2-overexpressing BAF3, murine interleukin-3 dependent pro-B cells, to reduce the generation of antibodies against the host cells by immunization of mice. Moreover, we immunized DP2-KO mice to prevent immunological tolerance to mDP2 protein. After cell ELISA, immunocytochemical, and Western blot analyses, we successfully obtained a novel monoclonal antibody, MAb-1D8, that specifically recognized native mouse DP2, but neither human DP2 nor denatured mouse DP2, by binding to a particular 3D receptor conformation formed by the N-terminus and extracellular loop 1, 2, and 3 of DP2. This antibody inhibited the binding of 0.5 nM [3H]PGD2 to mouse DP2 (IC50 = 46.3 ± 18.6 nM), showed antagonistic activity toward 15(R)-15-methyl PGD2-induced inhibition of 300 nM forskolin-activated cAMP production (IC50 = 16.9 ± 2.6 nM), and gave positive results for immunohistochemical staining of DP2-expressing CD4+ Th2 lymphocytes that had accumulated in the kidney of unilateral ureteral obstruction model mice. This monoclonal antibody will be very useful for in vitro and in vivo studies on DP2-mediated diseases.

Niacin ameliorates ulcerative colitis via prostaglandin D2-mediated D prostanoid receptor 1 activation.

Niacin, as an antidyslipidemic drug, elicits a strong flushing response by release of prostaglandin (PG) D2 However, whether niacin is beneficial for inflammatory bowel disease (IBD) remains unclear. Here, we observed niacin administration-enhanced PGD2 production in colon tissues in dextran sulfate sodium (DSS)-challenged mice, and protected mice against DSS or 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in D prostanoid receptor 1 (DP1)-dependent manner. Specific ablation of DP1 receptor in vascular endothelial cells, colonic epithelium, and myeloid cells augmented DSS/TNBS-induced colitis in mice through increasing vascular permeability, promoting apoptosis of epithelial cells, and stimulating pro-inflammatory cytokine secretion of macrophages, respectively. Niacin treatment improved vascular permeability, reduced apoptotic epithelial cells, promoted epithelial cell update, and suppressed pro-inflammatory gene expression of macrophages. Moreover, treatment with niacin-containing retention enema effectively promoted UC clinical remission and mucosal healing in patients with moderately active disease. Therefore, niacin displayed multiple beneficial effects on DSS/TNBS-induced colitis in mice by activation of PGD2/DP1 axis. The potential efficacy of niacin in management of IBD warrants further investigation.

Preclinical Safety Profile of a Depleting Antibody against CRTh2 for Asthma: Well Tolerated Despite Unexpected CRTh2 Expression on Vascular Pericytes in the Central Nervous System and Gastric Mucosa.

CRTh2 is expressed on immune cells that drive asthma pathophysiology. Current treatment options for severe asthma are inadequate and therapeutic antibody-mediated depletion of CRTh2-expressing cells represents a promising new therapeutic strategy. Here we report for the first time that CRTh2 is not only expressed on immune cells, but also on microvasculature in the central nervous system (CNS) and gastric mucosa in humans. Microvascular expression of CRTh2 raises a safety concern because a therapeutic antiCRTh2 antibody with enhanced depletion capacity could lead to vascular damage. To evaluate this safety risk, we characterized microvascular expression in human and in transgenic mice expressing human CRTh2 protein (hCRTh2.BAC.Tg) and found that CRTh2 is not localized to microvascular endothelium that is directly exposed to circulating therapeutic antibody, but rather, to pericytes that in the CNS are shielded from direct circulatory exposure by the blood-brain barrier. Immunohistochemical visualization of an intravenously administered antiCRTh2 antibody in transgenic mice revealed localization to microvascular pericytes in the gastric mucosa but not in the CNS, suggesting the blood-brain barrier effectively limits pericyte exposure to circulating therapeutic antibody in the CNS. Repeated dosing with a depleting antiCRTh2 antibody in hCRTh2.BAC.Tg mice revealed linear pharmacokinetics and no drug-related adverse findings in any tissues, including the CNS and gastric mucosa, despite complete depletion of CRTh2 expressing circulating eosinophils and basophils. Collectively, these studies demonstrate that the likelihood of drug-related CNS or gastrointestinal toxicity in humans treated with a therapeutic depleting antiCRTh2 antibody is low despite pericyte expression of CRTh2 in these tissues.

Prostaglandins from Cytosolic Phospholipase A2α/Cyclooxygenase-1 Pathway and Mitogen-activated Protein Kinases Regulate Gene Expression in Candida albicans-infected Macrophages.

In Candida albicans-infected resident peritoneal macrophages, activation of group IVA cytosolic phospholipase A2(cPLA2α) by calcium- and mitogen-activated protein kinases triggers the rapid production of prostaglandins I2 and E2 through cyclooxygenase (COX)-1 and regulates gene expression by increasing cAMP. InC. albicans-infected cPLA2α(-/-)or COX-1(-/-)macrophages, expression ofI l10,Nr4a2, and Ptgs2 was lower, and expression ofTnfα was higher, than in wild type macrophages. Expression was reconstituted with 8-bromo-cAMP, the PKA activator 6-benzoyl-cAMP, and agonists for prostaglandin receptors IP, EP2, and EP4 in infected but not uninfected cPLA2α(-/-)or COX-1(-/-)macrophages. InC. albicans-infected cPLA2α(+/+)macrophages, COX-2 expression was blocked by IP, EP2, and EP4 receptor antagonists, indicating a role for both prostaglandin I2 and E2 Activation of ERKs and p38, but not JNKs, by C. albicansacted synergistically with prostaglandins to induce expression of Il10,Nr4a2, and Ptgs2. Tnfα expression required activation of ERKs and p38 but was suppressed by cAMP. Results using cAMP analogues that activate PKA or Epacs suggested that cAMP regulates gene expression through PKA. However, phosphorylation of cAMP-response element-binding protein (CREB), the cAMP-regulated transcription factor involved inIl10,Nr4a2,Ptgs2, andTnfα expression, was not mediated by cAMP/PKA because it was similar inC. albicans-infected wild type and cPLA2α(-/-)or COX-1(-/-)macrophages. CREB phosphorylation was blocked by p38 inhibitors and induced by the p38 activator anisomycin but not by the PKA activator 6-benzoyl-cAMP. Therefore, MAPK activation inC. albicans-infected macrophages plays a dual role by promoting the cPLA2α/prostaglandin/cAMP/PKA pathway and CREB phosphorylation that coordinately regulate immediate early gene expression.

The prostaglandin D2 receptor CRTH2 regulates accumulation of group 2 innate lymphoid cells in the inflamed lung.

Group 2 innate lymphoid cells (ILC2s) promote type 2 cytokine-dependent immunity, inflammation, and tissue repair. Although epithelial cell-derived cytokines regulate ILC2 effector functions, the pathways that control the in vivo migration of ILC2s into inflamed tissues remain poorly understood. Here, we provide the first demonstration that expression of the prostaglandin D2 (PGD2) receptor CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells) regulates the in vivo accumulation of ILC2s in the lung. Although a significant proportion of ILC2s isolated from healthy human peripheral blood expressed CRTH2, a smaller proportion of ILC2s isolated from nondiseased human lung expressed CRTH2, suggesting that dynamic regulation of CRTH2 expression might be associated with the migration of ILC2s into tissues. Consistent with this, murine ILC2s expressed CRTH2, migrated toward PGD2 in vitro, and accumulated in the lung in response to PGD2 in vivo. Furthermore, mice deficient in CRTH2 exhibited reduced ILC2 responses and inflammation in a murine model of helminth-induced pulmonary type 2 inflammation. Critically, adoptive transfer of CRTH2-sufficient ILC2s restored pulmonary inflammation in CRTH2-deficient mice. Together, these data identify a role for the PGD2-CRTH2 pathway in regulating the in vivo accumulation of ILC2s and the development of type 2 inflammation in the lung.