Mechanisms by which dupilumab normalizes eicosanoid metabolism and restores aspirin-tolerance in AERD: A hypothesis.

Aspirin-exacerbated respiratory disease (AERD) is associated with overproduction of proinflammatory cysteinyl leukotrienes (CysLTs), defective generation of anti-inflammatory prostaglandin E2 (PGE2), and reduced expression of the EP2 receptor for PGE2. Reduced PGE2 synthesis results from the downregulation of inducible COX-2. Because PGE2 signaling via EP2 inhibits the 5-lipoxygenase/leukotriene C4 synthase-dependent pathway, the deficient levels of both PGE2 and EP2 likely contribute to the excessive baseline production of cysteinyl leukotrienes in patients with AERD compared with in patients with aspirin-tolerant asthma. The COX-2 pathway is regulated by an autocrine metabolic loop involving IL-1ß, IL-1 receptor type I, EP2, COX-2, membrane-bound PGE2 prostaglandin E2 synthase-1, and PGE2. Previous studies reported that this metabolic loop is dysregulated in patients with AERD. When the downexpressed EP2 receptor is normalized, the entire loop returns to its normal function. Cotreatment of airway cells from healthy subjects with IL-4 and IFN-γ induces alterations in the metabolic loop similar to those seen in patients with AERD. In these patients, IL-4, which is produced in excess in airways of patients with AERD, likely contributes to the alteration of normal functioning of the autocrine metabolic loop involving IL-1ß, IL-1 receptor type I, EP2, COX-2, membrane-bound PGE2 prostaglandin E2 synthase-1, and PGE2. We hypothesized that by blocking IL-4 action, dupilumab normalizes EP2 expression and restores the normal functioning of the COX-2 pathway autocrine metabolic loop, thereby normalizing the synthesis of PGE2 and restoring aspirin tolerance.

Efficacy and safety of dupilumab in patients with uncontrolled severe chronic rhinosinusitis with nasal polyps and a clinical diagnosis of NSAID-ERD: Results from two randomized placebo-controlled phase 3 trials.

BACKGROUND: About one-tenth of patients with difficult-to-treat chronic rhinosinusitis with nasal polyps (CRSwNP) have comorbid non-steroidal anti-inflammatory drug-exacerbated respiratory disease (NSAID-ERD). Dupilumab, a fully human monoclonal antibody that blocks the shared interleukin (IL)-4/IL-13 receptor component, is an approved add-on treatment in severe CRSwNP. This post hoc analysis evaluated dupilumab efficacy and safety in patients with CRSwNP with/without NSAID-ERD. METHODS: Data were pooled from the phase 3 SINUS-24 and SINUS-52 studies in adults with uncontrolled severe CRSwNP who received dupilumab 300 mg or placebo every 2 weeks. CRSwNP, nasal airflow, lung function, and asthma control outcomes at Week 24 were evaluated, and treatment-subgroup interactions were assessed for patients with and without NSAID-ERD. RESULTS: Of 724 patients, 204 (28.2%) had a diagnosis of NSAID-ERD. At Week 24, least squares mean treatment differences demonstrated significant improvements in nasal polyp score, nasal congestion (NC), Lund-Mackay computed tomography, 22-item Sinonasal Outcome Test (SNOT-22), Total Symptom Score (TSS), rhinosinusitis severity visual analog scale, peak nasal inspiratory flow (PNIF), six-item Asthma Control Questionnaire score, and improvement in smell with dupilumab versus placebo (all p < .0001) in patients with NSAID-ERD. Treatment comparisons demonstrated significantly greater improvements with dupilumab in patients with versus without NSAID-ERD for NC (p = .0044), SNOT-22 (p = .0313), TSS (p = .0425), and PNIF (p = .0123). CONCLUSIONS: In patients with uncontrolled severe CRSwNP, dupilumab significantly improved objective measures and patient-reported symptoms to a greater extent in the presence of comorbid NSAID-ERD than without. Dupilumab was well tolerated in patients with/without NSAID-ERD.

Food-dependent NSAID-induced hypersensitivity (FDNIH) reactions: Unraveling the clinical features and risk factors.

BACKGROUND: In up to 70%-80% of patients with a suspected non-steroidal anti-inflammatory drug hypersensitivity (NSAIDH), challenge tests with the culprit drug yield negative results. On the other hand, there could be a NSAIDH overdiagnosis when anaphylaxis is the clinical manifestation. We hypothesize that some negative NSAID challenge tests and an overdiagnosis of NSAIDH occur in patients with food-dependent NSAID-induced hypersensitivity (FDNIH). METHODS: We studied 328 patients with a suspected acute NSAIDH. FDNIH was diagnosed in patients meeting all the following: (1) tolerance to the food ingested more temporally closed before the reaction, later the episode, (2) respiratory or cutaneous symptoms or anaphylaxis related to NSAID, (3) positive skin prick test to foods and/or specific IgE to food allergens (Pru p 3, Tri a 19, Pen a 1) involved in the reaction, and (4) negative oral provocation test to the culprit NSAID. RESULTS: 199 patients (60%) were diagnosed with NSAIDH and 52 (16%) with FDNIH. Pru p 3 was involved in 44 cases (84.6%) and Tri a 19 in 6 cases (11%). FDNIH subjects were younger (p < .001), with a higher prevalence of rhinitis (p < .001) and previous food allergy (p < .001), together with a higher proportion of subjects sensitized to pollens (p < .001) and foods (p < .001). Using just four variables (Pru p 3 sensitization, Tri a 19 sensitization, anaphylaxis, and any NSAID different from pyrazolones), 95.3% of cases were correctly classified, with a sensitivity of 92% and specificity of 96%. CONCLUSION: Evaluation of FDNIH should be included in the diagnostic workup of NSAIDH.

Integrated mRNA and microRNA transcriptome profiling during differentiation of human nasal polyp epithelium reveals an altered ciliogenesis.

BACKGROUND: Human adult basal stem/progenitor cells (BSCs) obtained from chronic rhinosinusitis with nasal polyps (CRSwNP) when differentiated in an air-liquid interface (ALI) usually provide a pseudostratified airway epithelium with similar abnormalities than original in vivo phenotype. However, the intrinsic mechanisms regulating this complex process are not well defined and their understanding could offer potential new therapies for CRSwNP (incurable disease). METHODS: We performed a transcriptome-wide analysis during in vitro mucociliary differentiation of human adult BSCs from CRSwNP, compared to those isolated from control nasal mucosa (control-NM), in order to identify which key mRNA and microRNAs are regulating this complex process in pathological and healthy conditions. RESULTS: A number of genes, miRs, biological processes, and pathways were identified during mucociliary differentiation of both CRSwNP and control-NM epithelia, and notably, we have demonstrated for the first time that genetic transcriptional program responsible of ciliogenesis and cilia function is significantly impaired in CRSwNP epithelium, presumably produced by an altered expression of microRNAs, particularly of those miRs belonging to mir-34 and mi-449 families. CONCLUSIONS: This study provides for the first time a novel insight into the molecular basis of sinonasal mucociliary differentiation, demonstrating that transcriptome related to ciliogenesis and cilia function is significantly impaired during differentiation of CRSwNP epithelium due to an altered expression of microRNAs.

Duration of the efficacy of omalizumab after treatment discontinuation in 'real life' severe asthma.

Efficacy of omalizumab in severe asthma is well documented; however, the optimal duration of the treatment remains unclear. In an open prospective study, we sought to assess the persistence of response in subjects withdrawing from omalizumab treatment. We evaluated 49 patients who voluntarily accepted to discontinue omalizumab treatment after 6 years of therapy. Asthma relapse was defined as any severe asthma exacerbation associated with loss of asthma control. Twelve patients relapsed in the first year of follow-up, and 7 within 13 and 48 months. These results suggest that the effects of 6 years of omalizumab may persist after discontinuation of therapy in 60% of patients for at least 4 years.

Follow-up of patients with uncontrolled asthma: clinical features of asthma patients according to the level of control achieved (the COAS study).

Our aim was to study the asthma control achieved in patients with uncontrolled asthma who had received appropriate treatment according to the Global Initiative for Asthma (GINA) 2010 (valid at the time the study was designed), and to analyse the factors associated with a lack of asthma control.This was a multicentre study in routine clinical practice performed in patients with uncontrolled asthma according to GINA 2010. At visit 1, we recorded demographics, asthma characteristics and spirometry. We assessed asthma control using GINA 2010 criteria and the Asthma Control Test (ACT). Treatment was optimised according to GINA 2010. At visit 2, 3 months later, we reassessed spirometry, asthma control and factors associated with failure to achieve control.We recruited 1299 patients with uncontrolled asthma (mean age 46.5±17.3 years, 60.7% women, 25.8% obese). The mean percentage of predicted forced expiratory volume in 1 s was 76.4±12.8% and the mean post-bronchodilator increase was 14.9±6.8%. We observed poor agreement between ACT and GINA 2010 when evaluating asthma control (kappa = -0.151). At visit 2, asthma in 71.2% of patients was still not fully controlled. Patients whose asthma remained uncontrolled were older, had a higher body mass index, greater disease severity, longer disease evolution and worse lung function.After treatment optimisation, most patients did not achieve optimal control according to GINA 2010. Risk factors for failure to achieve asthma control were time of disease evolution, severity, age, weight and lung function impairment (excluded in the GINA 2014).

The adaptor 3BP2 is required for KIT receptor expression and human mast cell survival.

SH3-binding protein 2 (3BP2) is a cytoplasmic adaptor protein that acts as a positive regulator in mast cell FcεRI-dependent signaling. The KIT receptor whose ligand is the stem cell factor is necessary for mast cell development, proliferation, and survival as well as for optimal IgE-dependent signal. Activating mutations in KIT have been associated with several diseases including mastocytosis. In the present work, we found that 3BP2 silencing impairs KIT signaling pathways, thus affecting phosphoinositide 3-kinase and MAPK pathways in human mast cells (huMCs) from HMC-1, LAD2 (huMC lines), and CD34(+)-derived mast cells. Unexpectedly, silencing of 3BP2 reduces KIT expression in normal huMCs as well as in HMC-1 cells where KIT is mutated, thus increasing cellular apoptosis and caspase-3/7 activity. 3BP2 silencing reduces KIT transcription expression levels. Interestingly, 3BP2 silencing decreased microphthalmia-associated transcription factor (MITF) expression, a transcription factor involved in KIT expression. Reconstitution of 3BP2 in knockdown cells leads to reversal of KIT expression as well as survival phenotype. Accordingly MITF reconstitution enhances KIT expression levels in 3BP2-silenced cells. Moreover, downregulation of KIT expression by miRNA-221 overexpression or the proteasome inhibitor bortezomib also reduced 3BP2 and MITF expression. Furthermore, KIT tyrosine activity inhibition reduced 3BP2 and MITF expression, demonstrating again a tight and reciprocal relationship between these molecules. Taken together, our results show that 3BP2 regulates huMC survival and participates in KIT-mediated signal transduction by directly controlling KIT receptor expression, suggesting its potential as a therapeutic target in mast cell-mediated inflammatory diseases and deregulated KIT disorders.

Respiratory, ocular and skin health in recreational and competitive swimmers: Beneficial effect of a new method to reduce chlorine oxidant derivatives.

BACKGROUND: Chlorine by-products may irritate the eyes, nose, skin and airways of swimmers and may cause chronic airway inflammation. OBJECTIVE: To assess the salutary effects on swimmers health of a new method of water disinfection. METHODS: Recreational (n=320) and competitive swimmers (n=53) participated in the study. The first part of the study (Phase A) was carried out while using the current standard method. The second part (Phase B) began 8 weeks after the new method had been introduced. Total oxidants in air and chlorine species in water were assessed by standard methods. All swimmers completed a questionnaire on health complaints. Exhaled breath condensate (EBC) was used to monitor the levels of leukotriene B4 (LTB4) and cysteinyl leukotrienes (CysLTs) in airway from competitive swimmers. RESULTS: The new system resulted in a 75% and 39% reduction in the concentration of total oxidants and of nitrogen trichloride respectively in the air of the swimming pool. With the new system recreational swimmers experienced fewer symptoms of cough and irritation of the eyes, nose and skin. A decrease in eye irritation symptoms was also noted by competitive swimmers. The baseline concentration of CysLTs in EBC decreased significantly in Phase B with respect to Phase A. CONCLUSIONS: The new method markedly reduced the levels of irritant oxidant substances in the pool atmosphere that resulted in a reduction of eye, nose, skin and cough complaints in recreational swimmers, and eye irritation in competitive swimmers. It was also associated with reduced CysLT levels in the airways of competitive swimmers.

Low E-prostanoid 2 receptor levels and deficient induction of the IL-1ß/IL-1 type I receptor/COX-2 pathway: Vicious circle in patients with aspirin-exacerbated respiratory disease.

BACKGROUND: We hypothesized that the 2 reported alterations in aspirin-exacerbated respiratory disease (AERD), reduced expression/production of COX-2/prostaglandin (PG) E2 and diminished expression of E-prostanoid (EP) 2 receptor, are closely linked. OBJECTIVE: We sought to determine the mechanisms involved in the altered regulation of the COX pathway in patients with AERD. METHODS: Fibroblasts were obtained from nasal mucosa; samples of control subjects (NM-C, n = 8) and from nasal polyps from patients with aspirin-exacerbated respiratory disease (NP-AERD, n = 8). Expression of the autocrine loop components regulating PGE2 production and signaling, namely IL-1 type I receptor (IL-1RI), COX-2, microsomal prostaglandin E synthase 1 (mPGES-1), and EP receptors, was assessed at baseline and after stimulation with IL-1ß, PGE2, and specific EP receptor agonists. RESULTS: Compared with NM-C fibroblasts, basal expression levels of IL-1RI and EP2 receptor were lower in NP-AERD fibroblasts. IL-1ß-induced IL-1RI, COX-2, and mPGES-1 expression levels were also lower in these cells. Levels of IL-1RI positively correlated with COX-2 and mPGES-1 expression in both NM-C and NP-AERD fibroblasts. Incubation with either exogenous PGE2 or selective EP2 agonist significantly increased expression of IL-1RI in NM-C fibroblasts and had hardly any effect on NP-AERD fibroblasts. Alterations in IL-1RI, COX-2, and mPGES-1 expression that were found in NP-AERD fibroblasts were corrected when EP2 receptor expression was normalized by transfection of NP-AERD fibroblasts. CONCLUSION: Altered expression of EP2 in patients with AERD contributes to deficient induction of IL-1RI, reducing the capacity of IL-1ß to increase COX-2 and mPGES-1 expression, which results in low PGE2 production. This impairment in the generation of PGE2 subsequently reduces its ability to induce IL-1RI.

Distinct transcriptome profiles differentiate nonsteroidal anti-inflammatory drug-dependent from nonsteroidal anti-inflammatory drug-independent food-induced anaphylaxis.

BACKGROUND: Lipid transfer protein (LTP), an abundant protein in fruits, vegetables, and nuts, is a common food allergen in Mediterranean areas causing diverse allergic reactions. Approximately 40% of food-related anaphylaxis induced by LTPs requires nonsteroidal anti-inflammatory drugs (NSAIDs) as a triggering cofactor. OBJECTIVE: We sought to better understand the determinants of NSAID-dependent and NSAID-independent LTP-induced anaphylaxis (LTP-A). METHODS: Selection of patients was based on a proved clinical history of NSAID-dependent or NSAID-independent anaphylaxis to LTPs, positive skin prick test response to LTPs, and serum LTP IgE. Whole-transcriptome (RNA sequencing) analysis of blood cells from 14 patients with NSAID-related LTP-A (NSAID-LTP-A), 7 patients with LTP-A, and 13 healthy control subjects was performed to identify distinct gene expression signatures. RESULTS: Expression of genes regulating gastrointestinal epithelial renewal was altered in both patient sets, particularly in those with LTP-A, who also presented with gene expression profiles characteristic of an inflammatory syndrome. These included altered B-cell pathways, increased neutrophil activation markers, and increased reactive oxygen species levels. Increased expression of the IgG receptor (CD64) in patients with LTP-A was mirrored by the presence of LTP-specific IgG1 and IgG3. Conversely, patients with NSAID-LTP-A were characterized by reduced expression of IFN-γ-regulated genes and IFN-γ levels, as well as upregulated expression of adenosine receptor 3 (ADORA3) and genes related to adenosine metabolism. CONCLUSIONS: Gene ontology analysis suggests disturbances in gut epithelial homeostasis in both groups with LTP-A, with potential integrity breaches in patients with LTP-A that might explain their distinct inflammatory signatures. Differential regulation in patients with LTP-A and those with NSAID-LTP-A of the IFN-γ pathway, IgG receptors, and ADORA3 might provide the pathogenic basis of their distinct responses.

Role of Art v 3 in pollinosis of patients allergic to Pru p 3.

BACKGROUND: Food allergy caused by lipid transfer protein (LTP) from peach (Pru p 3) is frequently associated with sensitization to mugwort LTP (Art v 3). Although in vitro cross-reactivity is already well known, it has yet to be elucidated whether a pollen LTP can induce rhinitis. OBJECTIVE: The aim of this study was to investigate whether mugwort LTP could elicit respiratory symptoms and whether a primary food LTP allergy could lead to a respiratory allergy. METHODS: Patients with confirmed Pru p 3 allergy and control subjects were selected. Immediate responses to nasal allergen provocation tests (NAPTs) with Art v 3, Pru p 3, and mugwort were assessed by using the visual analog scale score, total nasal symptom score, and acoustic rhinometry. Tryptase and cysteinyl leukotriene (cysLT) levels were measured in nasal lavage fluid. Immunoblotting, ELISAs, and ELISA inhibition assays were also performed. RESULTS: Fifteen patients and 9 control subjects were selected. NAPT results with Art v 3 and Pru p 3 showed significant changes in acoustic rhinometry, visual analog scale scores, total nasal symptom scores, and cysLT levels (P < .001). Tryptase levels were only increased in NAPTs with Pru p 3. NAPTs with mugwort were used in those patients who were only sensitized to Art v 3, with similar results (P < .05). No significant changes were detected in control subjects. CONCLUSION: The results demonstrated that a pollen LTP can elicit rhinitis in sensitized patients. Findings also suggest that a primary sensitization to Pru p 3 can lead to a respiratory allergy through cross-reactivity.

Prostaglandin E2 receptors in asthma and in chronic rhinosinusitis/nasal polyps with and without aspirin hypersensitivity.

Chronic rhinosinusitis with nasal polyps (CRSwNP) and asthma frequently coexist and are always present in patients with aspirin exacerbated respiratory disease (AERD). Although the pathogenic mechanisms of this condition are still unknown, AERD may be due, at least in part, to an imbalance in eicosanoid metabolism (increased production of cysteinyl leukotrienes (CysLTs) and reduced biosynthesis of prostaglandin (PG) E2), possibly increasing and perpetuating the process of inflammation. PGE2 results from the metabolism of arachidonic acid (AA) by cyclooxygenase (COX) enzymes, and seems to play a central role in homeostasis maintenance and inflammatory response modulation in airways. Therefore, the abnormal regulation of PGE2 could contribute to the exacerbated processes observed in AERD. PGE2 exerts its actions through four G-protein-coupled receptors designated E-prostanoid (EP) receptors EP1, EP2, EP3, and EP4. Altered PGE2 production as well as differential EP receptor expression has been reported in both upper and lower airways of patients with AERD. Since the heterogeneity of these receptors is the key for the multiple biological effects of PGE2 this review focuses on the studies available to elucidate the importance of these receptors in inflammatory airway diseases.

Fluticasone furoate inhibits cytokine secretion from nasal epithelial cells and reduces eosinophil survival in an in vitro model of eosinophilic inflammation.

BACKGROUND: Fluticasone furoate (FF) is an intranasal corticosteroid indicated for the treatment of allergic rhinitis (AR). However, the anti-inflammatory effects of FF in the nasal mucosa have yet to be investigated thoroughly. The aim of this study was to investigate the effect of FF on eosinophil survival and cytokine secretion from nasal mucosa epithelial cells. METHODS: Epithelial cells obtained from nasal mucosa were stimulated with 10% fetal bovine serum (FBS) in the presence of FF (from 10(-12) to 10(-7)M) for 6-24 h. Cytokine [granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-6 and IL-8] concentrations in supernatants were measured by ELISA. Peripheral blood eosinophils were incubated for 4 days with epithelial cell secretions in the presence or absence of FF (from 10(-12) to 10(-7)M) and survival was assessed by Trypan blue dye exclusion. Results are expressed as medians of the minimum effective concentration and IC values. RESULTS: FBS stimulated the secretion of GM-CSF, IL-6 and IL-8. FF significantly inhibited GM-CSF (up to 10(-10)M, IC25 = 12.6 pM), IL-6 (up to 10(-10)M, IC25 = 65.8 pM) and IL-8 (up to 10(-11)M, IC25 = 8.6 pM) secretion induced by FBS (n = 8). Epithelial cell secretions induced eosinophil survival from day 1 to day 4 (n = 6). This effect was significantly inhibited by FF (up to 10(-12)M) at day 3 (IC50 = 3.22 nM) and day 4 (IC50 = 1.29 nM). CONCLUSIONS: The results obtained in this in vitro model suggest that FF may reduce upper airway eosinophilic inflammation through decreasing cytokine secretion from epithelial cells and reducing eosinophil survival.

The adaptor 3BP2 is required for early and late events in FcεRI signaling in human mast cells.

Adaptor molecules are essential in organizing signaling molecules and in coordinating and compartmentalizing their activity. SH3-binding protein 2 (3BP2) is a cytoplasmic adaptor protein mainly expressed by hematopoietic cells that has been shown to act as a positive regulator in T, B, and NK cell signal transduction. 3BP2 is an important regulator of cytotoxic granule release in NK cells. Mast cells (MCs) similarly degranulate following Ag-dependent aggregation of the FcεRI on the cell surface. Activation of these cells induces the release of preformed inflammatory mediators and the de novo synthesis and secretion of cytokines and chemokines. Thus, MCs participate in both innate and acquired responses. We observed that 3BP2 is expressed in human MCs (huMCs) from diverse origins. Moreover, 3BP2 coimmunoprecipitates with essential MC signaling mediators such as Lyn, Syk, and phospholipase C γ; thus, a role for this adaptor in MC function was postulated. In the present work, we used the short hairpin RNA lentiviral targeting approach to silence 3BP2 expression in huMCs. Our findings point to a requirement for 3BP2 in optimal immediate and late MCs responses such as degranulation and IL-8 or GM-CSF secretion. 3BP2 was determined to be necessary for optimal phosphorylation of Syk, linker for activation of T cells, and phospholipase C γ(1), critical signals for calcium release from intracellular stores. Taken together, our results show that by participating in FcεRI- mediated signal transduction 3BP2 is an important regulator of huMC activation. Thus, 3BP2 could be a potential therapeutic target for IgE-dependent MC-mediated inflammatory disease.

Elevated Prostaglandin E2 Synthesis Is Associated with Clinical and Radiological Disease Severity in Cystic Fibrosis.

Background: Previous studies found high but very variable levels of tetranor-PGEM and PGDM (urine metabolites of prostaglandin (PG) E2 and PGD2, respectively) in persons with cystic fibrosis (pwCF). This study aims to assess the role of cyclooxygenase COX-1 and COX-2 genetic polymorphisms in PG production and of PG metabolites as potential markers of symptoms' severity and imaging findings. Methods: A total of 30 healthy subjects and 103 pwCF were included in this study. Clinical and radiological CF severity was evaluated using clinical scoring methods and chest computed tomography (CT), respectively. Urine metabolites were measured using liquid chromatography/tandem mass spectrometry. Variants in the COX-1 gene (PTGS1 639 C>A, PTGS1 762+14delA and COX-2 gene: PTGS2-899G>C (-765G>C) and PTGS2 (8473T>C) were also analyzed. Results: PGE-M and PGD-M urine concentrations were significantly higher in pwCF than in controls. There were also statistically significant differences between clinically mild and moderate disease and severe disease. Patients with bronchiectasis and/or air trapping had higher PGE-M levels than patients without these complications. The four polymorphisms did not associate with clinical severity, air trapping, bronchiectasis, or urinary PG levels. Conclusions: These results suggest that urinary PG level testing can be used as a biomarker of CF severity. COX genetic polymorphisms are not involved in the variability of PG production.

Locally administered prostaglandin E2 prevents aeroallergen-induced airway sensitization in mice through immunomodulatory mechanisms.

Prostaglandin E2 attenuates airway pathology in asthmatic patients and exerts a protective effect in antigen-sensitized mice when administered systemically. We aimed to establish the consequences of intranasal PGE2 administration on airway reactivity to aeroallergens in mice and reveal the underlying immunoinflammatory mechanisms. PGE2 was administered either daily during a 10-day exposure to house dust mite (HDM) extracts or for limited intervals. Airway hyperreactivity was measured by whole-body and invasive plethysmography. The phenotypes of lung immune cells and cytokine production were analysed by flow cytometry and ELISA, respectively. Airway hyperreactivity was sustainably reduced only when PGE2 administration was restricted to the initial 5 days of exposure to HDM. Lung inflammation, IL-4 production, and airway mast cell activity were also prevented under this early short-term treatment with PGE2. Interestingly, a Th2 response was already committed on day 5 of exposure to HDM. This was paralleled by GM-CSF and osteopontin upregulation and a decreased number of plasmacytoid dendritic and T regulatory cells, as well as a trend towards reduced IL-10 expression. Local PGE2 administration prevented the increase of airway IL-13 and osteopontin and kept lung plasmacytoid dendritic cell counts close to baseline. GM-CSF and Tregs were unaffected by the treatment. These findings suggest that the protection provided by PGE2 is a result of the modulation of early lung immunomodulatory mechanisms, and possibly a shift in the balance of dendritic cells towards a tolerogenic profile.