T helper cell type 2 cytokines coordinately regulate immunoglobulin E-dependent cysteinyl leukotriene production by human cord blood-derived mast cells: profound induction of leukotriene C(4) synthase expression by interleukin 4

Epithelium-derived kallistatin promotes CD4+ T-cell chemotaxis to TH2-type inflammation in chronic rhinosinusitis

BACKGROUND

The function of kallistatin in airway inflammation, particularly chronic rhinosinusitis with nasal polyps (CRSwNP), has not been elucidated.

OBJECTIVE

We sought to investigate the role of kallistatin in airway inflammation.

METHODS

Kallistatin and proinflammatory cytokine expression levels were detected in nasal polyps. For the in vivo studies, we constructed the kallistatin-overexpressing transgenic mice to elucidate the role of kallistatin in airway inflammation. Furthermore, the levels of plasma IgE and proinflammatory cytokines in the airways were evaluated in the kallistatin-/- rat in vivo model under a type 2 inflammatory background. Finally, the Notch signaling pathway was explored to understand the role of kallistatin in CRSwNP.

RESULTS

We showed that the expression of kallistatin was significantly higher in nasal polyps than in the normal nasal mucosa and correlated with IL-4 expression. We also discovered that the nasal mucosa of kallistatin-overexpressing transgenic mice expressed higher levels of IL-4 expression, associating to TH2-type inflammation. Interestingly, we observed lower IL-4 levels in the nasal mucosa and lower total plasma IgE of the kallistatin-/- group treated with house dust mite allergen compared with the wild-type house dust mite group. Finally, we observed a significant increase in the expression of Jagged2 in the nasal epithelium cells transduced with adenovirus-kallistatin. This heightened expression correlated with increased secretion of IL-4, attributed to the augmented population of CD4+CD45+Notch1+ T cells. These findings collectively may contribute to the induction of TH2-type inflammation.

CONCLUSIONS

Kallistatin was demonstrated to be involved in the CRSwNP pathogenesis by enhancing the TH2 inflammation, which was found to be associated with more expression of IL-4, potentially facilitated through Jagged2-Notch1 signaling in CD4+ T cells.

Cultures of Human Skin Mast Cells, an Attractive In Vitro Model for Studies of Human Mast Cell Biology

Studies of mast cell biology are dependent on relevant and validated in vitro models. Here, we present detailed information concerning the phenotype of both freshly isolated human skin mast cells (MCs) and of in vitro cultures of these cells that were obtained by analyzing their total transcriptome. Transcript levels of MC-related granule proteins and transcription factors were found to be remarkably stable over a 3-week culture period. Relatively modest changes were also seen for important cell surface receptors including the high-affinity receptor for IgE, FCER1A, the low-affinity receptor for IgG, FCGR2A, and the receptor for stem cell factor, KIT. FCGR2A was the only Fc receptor for IgG expressed by these cells. The IgE receptor increased by 2-5-fold and an approximately 10-fold reduction in the expression of FCGR2A was observed most likely due to the cytokines, SCF and IL-4, used for expanding the cells. Comparisons of the present transcriptome against previously reported transcriptomes of mouse peritoneal MCs and mouse bone marrow-derived MCs (BMMCs) revealed both similarities and major differences. Strikingly, cathepsin G was the most highly expressed granule protease in human skin MCs, in contrast to the almost total absence of this protease in both mouse MCs. Transcript levels for the majority of cell surface receptors were also very low compared to the granule proteases in both mouse and human MCs, with a difference of almost two orders of magnitude. An almost total absence of T-cell granzymes was observed in human skin MCs, indicating that granzymes have no or only a minor role in human MC biology. Ex vivo skin MCs expressed high levels of selective immediate early genes and transcripts of heat shock proteins. In validation experiments, we determined that this expression was an inherent property of the cells and not the result of the isolation process. Three to four weeks in culture results in an induction of cell growth-related genes accompanying their expansion by 6-10-fold, which increases the number of cells for in vitro experiments. Collectively, we show that cultured human skin MCs resemble their ex vivo equivalents in many respects and are a more relevant in vitro model compared to mouse BMMCs for studies of MC biology, in particular human MC biology.

Glucocorticoids, their uses, sexual dimorphisms, and diseases: new concepts, mechanisms, and discoveries

The normal stress response in humans is governed by the hypothalamic-pituitary-adrenal (HPA) axis through heightened mechanisms during stress, raising blood levels of the glucocorticoid hormone cortisol. Glucocorticoids are quintessential compounds that balance the proper functioning of numerous systems in the mammalian body. They are also generated synthetically and are the preeminent therapy for inflammatory diseases. They act by binding to the nuclear receptor transcription factor glucocorticoid receptor (GR), which has two main isoforms (GRα and GRβ). Our classical understanding of glucocorticoid signaling is from the GRα isoform, which binds the hormone, whereas GRβ has no known ligands. With glucocorticoids being involved in many physiological and cellular processes, even small disruptions in their release via the HPA axis, or changes in GR isoform expression, can have dire ramifications on health. Long-term chronic glucocorticoid therapy can lead to a glucocorticoid-resistant state, and we deliberate how this impacts disease treatment. Chronic glucocorticoid treatment can lead to noticeable side effects such as weight gain, adiposity, diabetes, and others that we discuss in detail. There are sexually dimorphic responses to glucocorticoids, and women tend to have a more hyperresponsive HPA axis than men. This review summarizes our understanding of glucocorticoids and critically analyzes the GR isoforms and their beneficial and deleterious mechanisms and the sexual differences that cause a dichotomy in responses. We also discuss the future of glucocorticoid therapy and propose a new concept of dual GR isoform agonist and postulate why activating both isoforms may prevent glucocorticoid resistance.

Mepolizumab in chronic rhinosinusitis with nasal polyposis

Chronic rhinosinusitis with nasal polyposis (CRSwNP) is a heterogeneous upper airway disease that is prevalent globally. Recent research into the molecular basis of the disease has led to the development of biologics as a new therapeutic option for severe and recalcitrant forms of CRSwNP. Mepolizumab is a monoclonal antibody targeting IL-5, one of the signature cytokines of the type 2 immune response and which plays an important role in the pathogenesis of CRSwNP. Here we present the latest evidence behind mepolizumab, examining disease pathophysiology and pharmacology, as well as data from clinical trials, real-life studies and meta-analyses. As we welcome this promising step forward into precision medicine, we discuss practical issues and future perspectives on mepolizumab and biologics for CRSwNP.

Dupilumab increases aspirin tolerance in NSAID-exacerbated respiratory disease

BACKGROUND

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) comprises the triad of chronic rhinosinusitis with nasal polyps, asthma and intolerance to NSAIDs. Dupilumab treatment, targeting the interleukin-4 (IL-4) receptor α, significantly reduces polyp burden as well as asthma symptoms. Here we aimed to investigate the effect of dupilumab on aspirin intolerance, burden of disease and nasal cytokine profiles in patients with N-ERD.

METHODS

In this open-label trial, adult patients with confirmed N-ERD were treated with dupilumab for 6 months. Clinical parameters (e.g. total polyp scores, quality of life questionnaires, smell test, spirometry), oral aspirin provocation testing and blood, nasal and urine sampling were monitored at regular intervals for up to 6 months after starting dupilumab therapy.

RESULTS

Of the 31 patients included in the study, 30 completed both aspirin provocation tests. After 6 months of treatment with dupilumab, 23% of patients (n=7 of 30) developed complete aspirin tolerance and an additional 33% of patients (n=10 of 30) tolerated higher doses. Polyp burden was significantly reduced (total polyp score: -2.68±1.84, p<0.001), while pulmonary symptoms (asthma control test: +2.34±3.67, p<0.001) and olfactory performance improved (University of Pennsylvania Smell Identification Test: +11.16±9.54, p<0.001) in all patients after therapy. Patients with increased aspirin tolerance showed a significant decrease in urinary leukotriene E4 levels and their improvement in clinical parameters was associated with a reduction of eotaxin-1, C-C motif chemokine ligand 17, IL-5, IL-17A and IL-6.

CONCLUSION

In this study, 57% of N-ERD patients tolerated higher doses of aspirin under dupilumab therapy.

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-1β, 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-1β, 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.

Immune sensing of food allergens promotes aversive behaviour

In addition to its canonical function in protecting from pathogens, the immune system can also promote behavioural alterations ^1â€"3 . The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Using a mouse food allergy model, here we show that allergic sensitization drives antigen-specific behavioural aversion. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus, and central amygdala. Food aversion requires IgE antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote aversion requires leukotrienes and growth and differentiation factor 15 (GDF15). In addition to allergen-induced aversion, we find that lipopolysaccharide-induced inflammation also resulted in IgE-dependent aversive behaviour. These findings thus point to antigen-specific behavioural modifications that likely evolved to promote niche selection to avoid unfavourable environments.

Drug repositioning of anti-microbial agent nifuratel to treat mast cell-mediated allergic responses

Objectives: Our objective was to assess the effects and mechanisms of nifuratel on IgE-mediated mast cell (MC) degranulation and anaphylaxis in both in vitro and in vivo settings.Methods: The anti-allergic activity of nifuratel was evaluated in mast cell cultures and the passive cutaneous anaphylaxis (PCA) model. The effects of nifuratel on signaling pathways stimulated by antigen in mast cells were measured by immunoblotting, immunoprecipitation, in vitro protein tyrosine kinase assay, and other molecular biological methods.Results: Nifuratel reversibly inhibited antigen-induced degranulation of MCs (IC50, approximately 0.34 μM for RBL-2H3 cells; approximately 0.94 μM for BMMCs) and suppressed the secretion of inflammatory cytokines IL-4 (IC50, approximately 0.74 μM) and TNF-α (IC50, approximately 0.48 μM). Mechanism studies showed that nifuratel inhibited the phosphorylation of Syk by antigen via the inhibition of recruitment of cytosolic Syk to the ɣ subunit of FcεRI, and decreased the activation of Syk downstream signaling proteins LAT, Akt, and MAPKs. Finally, nifuratel dose-dependently suppressed the IgE-mediated passive cutaneous anaphylaxis in mice (ED50, approximately 22 mg/kg).Conclusion: Our findings suggest that nifuratel inhibits pathways essential for the activation of mast cells to suppress anaphylaxis, thereby indicating that the anti-microbial drug, nifuratel, could be a potential drug candidate for IgE-mediated allergic disorders.

Leukotriene D4 accelerates antigen-mediated mast cell responses via the cysteinyl leukotriene 1 receptor

Cysteinyl leukotrienes (CysLTs), released from mast cells (MCs), are important mediators in allergy. Type 1 receptors for CysLTs (CysLT1R) are involved in accelerating IgE-mediated MC activation. In this study, we aimed to elucidate the mechanisms underlying CysLT1R-mediated MC activation. The CysLT1R agonist/antagonist was applied to two types of major MC models-RBL-2H3 cells and bone marrow-derived MCs (BMMCs). The use of CysLT1R and CysLT2R inhibitors revealed that CysLT1R plays a major role in the acceleration of MC activation. The administration of the CysLT1R agonist leukotriene D4 upregulated IgE-mediated Akt and ERK phosphorylation and subsequently enhanced TNF-α expression, suggesting that CysLT1R regulates the downstream pathway of MC activation. However, these observations were not corroborated by CysLT1R knockdown using shRNA, suggesting a differential regulatory mechanism between the temporal and constitutive inhibitions of CysLT. In conclusion, CysLT1R enhances MC activation by accelerating IgE-induced signal transduction, which enables the co-regulation of rapid degranulation and delayed synthesis of inflammatory mediators in MCs.

The roles of eosinophils and interleukin-5 in the pathophysiology of chronic rhinosinusitis with nasal polyps

Chronic rhinosinusitis with nasal polyps (CRSwNP) is generally associated with eosinophilic tissue infiltration linked to type 2 inflammation and characterized by elevated levels of interleukin (IL)-5 and other type 2 inflammatory mediators. Although distinct and overlapping contributions of eosinophils and IL-5 to CRSwNP pathology are still being explored, they are both known to play an important role in NP inflammation. Eosinophils secrete numerous type 2 inflammatory mediators including granule proteins, enzymes, cytokines, chemokines, growth factors, lipids, and oxidative products. IL-5 is critical for the differentiation, migration, activation, and survival of eosinophils but is also implicated in the biological functions of mast cells, basophils, innate lymphoid cells, B cells, and epithelial cells. Results from clinical trials of therapeutics that target type 2 inflammatory mediators (including but not limited to anti-IL-5, anti-immunoglobulin-E, and anti-IL-4/13) may provide further evidence of how eosinophils and IL-5 contribute to CRSwNP. Finally, the association between eosinophilia/elevated IL-5 and greater rates of NP recurrence after endoscopic sinus surgery (ESS) suggests that these mediators may have utility as biomarkers of NP recurrence in diagnosing and assessing the severity of CRSwNP. This review provides an overview of eosinophil and IL-5 biology and explores the literature regarding the role of these mediators in CRSwNP pathogenesis and NP recurrence following ESS. Based on current published evidence, we suggest that although eosinophils play a key role in CRSwNP pathophysiology, IL-5, a cytokine that activates these cells, also represents a pertinent and effective treatment target in patients with CRSwNP.

Biological Therapy of Severe Asthma and Nasal Polyps

Chronic rhinosinusitis is a common disease worldwide and can be categorized into chronic rhinosinusitis with nasal polyps and chronic rhinosinusitis without nasal polyps. Chronic rhinosinusitis with nasal polyps is common in patients with asthma and, particularly, severe asthma. Severe asthma is effectively treated with biologics and the coexistence of severe asthma with chronic rhinosinusitis with nasal polyps presents a phenotype that is more likely to respond to such treatment. In this review, we focus on the link between asthma and nasal polyps, and we review the treatment effect of various monoclonal antibodies in patients with severe asthma and nasal polyps as well as in patients with nasal polyps without asthma or with mild-to-moderate asthma. With the enhancement of our armamentarium with new monoclonal antibodies the right choice of biologic becomes an important target and one that is difficult to achieve due to the lack of comparative head-to-head studies.

INSIGHTS INTO THE REGULATION OF MAST CELL FUNCTION IN TYPE 2 INFLAMMATION

Type 2 inflammation (T2I) underlies the pathogenesis of asthma, chronic rhinosinusitis with nasal polyps, and eosinophilic esophagitis. Mast cells (MCs) are tissue resident hematopoietic effector cells thought to play major roles in T2I. Two subtypes of human MCs are recognized based on immunohistochemical differences. MCs expressing tryptase but not chymase (MCT) reside within mucosal epithelial surfaces, and MCs expressing tryptase, chymase, and cathepsin G (MCTC) reside in submucosal, perivascular and intraneural locations. During T2I, MCs (particularly MCT) increase markedly by unclear mechanisms. Single cell genomic studies reveal that traditional histochemical categorization vastly underestimates the extent of MC functional heterogeneity. MCT and MCTC likely reflect endpoints of a developmental continuum, emerging from a transitional stage of development in which MCs expand through in situ proliferation. This mechanism, likely driven by interleukin 4 and other cytokines, is unique among granulocytes and carries substantial implications for pathogenesis and therapy of T2I-associated diseases.

Mepolizumab targets multiple immune cells in aspirin-exacerbated respiratory disease

BACKGROUND

Eosinophilic asthma and nasal polyposis are hallmarks of aspirin-exacerbated respiratory disease (AERD), and IL-5 inhibition has been shown to provide therapeutic benefit. However, IL-5Rα is expressed on many cells in addition to eosinophils, and the mechanisms by which IL-5 inhibition leads to clinical benefit in eosinophilic asthma and nasal polyposis are unlikely to be due exclusively to antieosinophil effects.

OBJECTIVE

We sought to identify the mechanisms by which anti-IL-5 treatment with mepolizumab improves respiratory inflammation in AERD.

METHODS

The clinical characteristics, circulating granulocytes, nasal scraping transcripts, eosinophilic cationic protein, tryptase, and antibody levels, and urinary and nasal eicosanoid levels were measured for 18 subjects with AERD who were taking mepolizumab and compared with those of 18 matched subjects with AERD who were not taking mepolizumab.

RESULTS

Subjects taking mepolizumab had significantly fewer peripheral blood eosinophils and basophils, and those cells that remained had higher surface CRTH2 expression than did the cells from subjects not taking mepolizumab. Nasal prostaglandin F_2α, prostaglandin D₂ metabolites, leukotriene B₄, and thromboxane levels were lower in subjects taking mepolizumab, as were urinary levels of tetranor-prostaglandin D₂ and leukotriene E₄. The nasal epithelial cell transcripts that were overexpressed among subjects with AERD who were taking mepolizumab were enriched for genes involved in tight junction formation and cilium organization. Nasal and urinary prostaglandin E₂, tryptase, and antibody levels were not different between the 2 groups.

CONCLUSION

IL-5 inhibition in AERD decreases production of inflammatory eicosanoids and upregulates tight junction-associated nasal epithelial cell transcripts, likely due to decreased IL-5 signaling on tissue mast cells, eosinophils, and epithelial cells. These direct effects on multiple relevant immune cells contribute to the mechanism of benefit afforded by mepolizumab.

Aspirin Actions in Treatment of NSAID-Exacerbated Respiratory Disease

Non-steroidal Anti-inflammatory drugs (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyposis, chronic rhinosinusitis, adult-onset asthma and hypersensitive reactions to cyclooxygenase-1 (COX-1) inhibitors. Among the available treatments for this disease, a combination of endoscopic sinus surgery followed by aspirin desensitization and aspirin maintenance therapy has been an effective approach. Studies have shown that long-term aspirin maintenance therapy can reduce the rate of nasal polyp recurrence in patients with N-ERD. However, the exact mechanism by which aspirin can both trigger and suppress airway disease in N-ERD remains poorly understood. In this review, we summarize current knowledge of aspirin effects in N-ERD, cardiovascular disease, and cancer, and consider potential mechanistic pathways accounting for the effects of aspirin in N-ERD.

Emerging role of cysteinyl LTs in cancer

Cysteinyl leukotrienes (CysLTs) are inflammatory lipid mediators that play a central role in the pathophysiology of several inflammatory diseases. Recently, there has been an increased interest in determining how these lipid mediators orchestrate tumour development and metastasis through promoting a pro-tumour micro-environment. Up-regulation of CysLTs receptors and CysLTs production is found in a number of cancers and has been associated with increased tumorigenesis. Understanding the molecular mechanisms underlying the role of CysLTs and their receptors in cancer progression will help investigate the potential of targeting CysLTs signalling for anti-cancer therapy. This review gives an overview of the biological effects of CysLTs and their receptors, along with current knowledge of their regulation and expression. It also provides a recent update on the molecular mechanisms that have been postulated to explain their role in tumorigenesis and on the potential of anti-CysLTs in the treatment of cancer.

The role of aspirin desensitization followed by oral aspirin therapy in managing patients with aspirin-exacerbated respiratory disease: A Work Group Report from the Rhinitis, Rhinosinusitis and Ocular Allergy Committee of the American Academy of Allergy, Asthma & Immunology

Aspirin-exacerbated respiratory disease (AERD) is characterized by the clinical triad of chronic rhinosinusitis with nasal polyps, asthma, and an intolerance to medications that inhibit the cycloxgenase-1 enzyme. Patients with AERD on average have more severe respiratory disease compared with patients with chronic rhinosinusitis with nasal polyps and/or asthma alone. Although patients with AERD traditionally develop significant upper and lower respiratory tract symptoms on ingestion of cycloxgenase-1 inhibitors, most of these same patients report clinical benefit when desensitized to aspirin and maintained on daily aspirin therapy. This Work Group Report provides a comprehensive review of aspirin challenges, aspirin desensitizations, and maintenance aspirin therapy in patients with AERD. Identification of appropriate candidates, indications and contraindications, medical and surgical optimization strategies, protocols, medical management during the desensitization, and recommendations for maintenance aspirin therapy following desensitization are reviewed. Also included is a summary of studies evaluating the clinical efficacy of aspirin therapy after desensitization as well as a discussion on the possible cellular and molecular mechanisms explaining how this therapy provides unique benefit to patients with AERD.

Aspirin sensitivity: Lessons in the regulation (and dysregulation) of mast cell function

The idiosyncratic activation of mast cells (MCs) in response to administration of nonselective COX inhibitors is a cardinal feature of aspirin-exacerbated respiratory disease (AERD). Older studies using MC-stabilizing drugs support a critical role for MCs and their products in driving the severe eosinophilic inflammation and respiratory dysfunction that is typical of AERD. Because patients with AERD react to all nonselective COX inhibitors regardless of their chemical structure, the mechanism of MC activation is not caused by classical, antigen-induced cross-linking of IgE receptors. Recent studies in both human subjects and animal models have revealed a complex and multifactorial process culminating in dysregulation of MC function and an aberrant dependency on COX-1-derived prostaglandin E₂ to maintain a tenuous homeostasis. This article reviews the factors most likely to contribute to MC dysregulation in patients with AERD and the potential diagnostic and therapeutic implications.

Subphenotypes of nonsteroidal antiinflammatory disease-exacerbated respiratory disease identified by latent class analysis

BACKGROUND

Induced sputum (IS) allows to measure mediators of asthmatic inflammation in bronchial secretions. NSAID-exacerbated respiratory disease (NERD) is recognized as a distinct asthma phenotype, usually with a severe course, eosinophilic airway inflammation, and increased production of pro-inflammatory eicosanoids. A more insightful analysis of NERD patients has shown this phenotype to be nonhomogeneous.

OBJECTIVE

We aimed to identify possible subphenotypes in a cohort of NERD patients with the means of latent class analysis (LCA).

METHODS

A total of 95 asthma patients with aspirin hypersensitivity underwent sputum induction. High-performance liquid chromatography or gas chromatography coupled with mass spectrometry was used to profile eicosanoids in induced sputum supernatant (ISS). Sixteen variables covering clinical characteristics, IS inflammatory cells, and eicosanoids were considered in the LCA.

RESULTS

Three classes (subphenotypes) were distinguished within the NERD cohort. Class 1 subjects had mild-to-moderate asthma, an almost equal distribution of inflammatory cell patterns, the lowest concentrations of eicosanoids, and logLTE4 /logPGE2 ratio. Class 2 represented severe asthma with impaired lung function despite high doses of steroids. High sputum eosinophilia was in line with higher pro-inflammatory LTE4 in ISS and the highest logLTE4 /logPGE2 ratio. Class 3 subjects had mild-to-moderate asthma and were also characterized by eosinophilic airway inflammation, yet increased production of pro- (LTE4 , PGD2 and 11-dehydro-TBX2 ) was balanced by anti-inflammatory PGE2 . The value of logLTE4 /logPGE2 was between values calculated for classes 1 and 3, similarly to disease control and severity.

CONCLUSIONS

LCA revealed three distinct NERD subphenotypes. Our results support a more complex pathobiology of aspirin hypersensitivity. Considering NERD heterogeneity, the relationship between inflammatory pathways and clinical manifestations of asthma may lead to more individualized treatment in difficult to treat patients in the future.

Proinflammatory Pathways in the Pathogenesis of Asthma

There are multiple proinflammatory pathways in the pathogenesis of asthma. These include both innate and adaptive inflammation, in addition to inflammatory and physiologic responses mediated by eicosanoids. An important component of the innate allergic immune response is ILC2 activated by interleukin (IL)-33, thymic stromal lymphopoietin, and IL-25 to produce IL-5 and IL-13. In terms of the adaptive T-lymphocyte immunity, CD4+ Th2 and IL-17-producing cells are critical in the inflammatory responses in asthma. Last, eicosanoids involved in asthma pathogenesis include prostaglandin D₂ and the cysteinyl leukotrienes that promote smooth muscle constriction and inflammation that propagate allergic responses.

RPTPε promotes M2-polarized macrophage migration through ROCK2 signaling and podosome formation

Cysteinyl-leukotrienes (cys-LTs) have well-characterized physiopathological roles in the development of inflammatory diseases. We have previously found that protein tyrosine phosphatase ε (PTPε) is a signaling partner of CysLT₁R, a high affinity receptor for leukotriene D4 (LTD₄). There are two major isoforms of PTPε, receptor-like (RPTPε) and cytoplasmic (cyt-)PTPε, both of which are encoded by the PTPRE gene but from different promoters. In most cells, their expression is mutually exclusive, except in human primary monocytes, which express both isoforms. Here, we show differential PTPε isoform expression patterns between monocytes, M1 and M2 human monocyte-derived macrophages (hMDMs), with the expression of glycosylated forms of RPTPε predominantly in M2-polarized hMDMs. Using PTPε-specific siRNAs and expression of RPTPε and cyt-PTPε, we found that RPTPε is involved in monocyte adhesion and migration of M2-polarized hMDMs in response to LTD₄ Altered organization of podosomes and higher phosphorylation of the inhibitory Y-722 residue of ROCK2 was also found in PTPε-siRNA-transfected cells. In conclusion, we show that differentiation and polarization of monocytes into M2-polarized hMDMs modulates the expression of PTPε isoforms and RPTPε is involved in podosome distribution, ROCK2 activation and migration in response to LTD₄.

Airway epithelium-shifted mast cell infiltration regulates asthmatic inflammation via IL-33 signaling

Asthma is a heterogeneous syndrome that has been subdivided into physiologic phenotypes and molecular endotypes. The most specific phenotypic manifestation of asthma is indirect airway hyperresponsiveness (AHR), and a prominent molecular endotype is the presence of type 2 inflammation. The underlying basis for type 2 inflammation and its relationship to AHR are incompletely understood. We assessed the expression of type 2 cytokines in the airways of subjects with and without asthma who were extensively characterized for AHR. Using quantitative morphometry of the airway wall, we identified a shift in mast cells from the submucosa to the airway epithelium specifically associated with both type 2 inflammation and indirect AHR. Using ex vivo modeling of primary airway epithelial cells in organotypic coculture with mast cells, we show that epithelial-derived IL-33 uniquely induced type 2 cytokines in mast cells, which regulated the expression of epithelial IL33 in a feed-forward loop. This feed-forward loop was accentuated in epithelial cells derived from subjects with asthma. These results demonstrate that type 2 inflammation and indirect AHR in asthma are related to a shift in mast cell infiltration to the airway epithelium, and that mast cells cooperate with epithelial cells through IL-33 signaling to regulate type 2 inflammation.

Asthma from immune pathogenesis to precision medicine

Asthma is characterized by multiple immunological mechanisms (endotypes) determining variable clinical presentations (phenotypes). The identification of endotypic mechanisms is crucial to better characterize patients and to identify tailored therapeutic approaches with novel biological agents targeting specific immunological pathways. This review focused on summarizing the major immunological mechanisms involved in the pathogenesis of asthma, as well as on discussing the emergence of phenotypic features of the disease. Novel biological agents and other drugs targeting specific endotypes are discussed, as their use represent a precision medicine approach to the disease that is nowadays mandatory particularly for treating more severe patients.

Biological therapies for atopic dermatitis: An update

Severe atopic dermatitis, which affects both adults and children, is a debilitating disorder with a significant decline of patients' quality of life. Although aetiopathogenic factors are currently a topic of study and interpretation, the main features of atopic eczema are skin barrier disturbance and immune dysregulation. Severe refractory disease that fails to improve with conventional therapy may benefit from biologic therapy. Progress in understanding immunopathology of atopic dermatitis have allowed identification of therapeutic molecular targets in the field of biological therapy. We reviewed the different biological treatments with a focus on novel targeted agents: Systemic immunotherapy (Omalizumab, Dupilumab, Lebrikizumab, Tralokinumab, Nemolizumab, Ustekinumab, Fezakinumab, Tezepelumab, Apremilast, allergen specific immunotherapy), and topical agents (Tofacitinib, Crisaborole).

COX-1 mediates IL-33-induced extracellular signal-regulated kinase activation in mast cells: Implications for aspirin sensitivity

BACKGROUND

Classical FcεRI-induced mast cell (MC) activation causes synthesis of arachidonic acid (AA)-derived eicosanoids (leukotriene [LT] C₄, prostaglandin [PG] D₂, and thromboxane A₂), which mediate vascular leak, bronchoconstriction, and effector cell chemotaxis. Little is known about the significance and regulation of eicosanoid generation in response to nonclassical MC activation mechanisms.

OBJECTIVES

We sought to determine the regulation and significance of MC-derived eicosanoids synthesized in response to IL-33, a cytokine critical to innate type 2 immunity.

METHODS

We used an ex vivo model of mouse bone marrow-derived mast cells and an IL-33-dependent in vivo model of aspirin-exacerbated respiratory disease (AERD).

RESULTS

IL-33 potently liberates AA and elicits LTC₄, PGD₂, and thromboxane A₂ production by bone marrow-derived mast cells. Unexpectedly, the constitutive function of COX-1 is required for IL-33 to activate group IVa cytosolic phospholipase A₂ with consequent AA release for synthesis of all eicosanoids, including CysLTs. In contrast, COX-1 was dispensable for FcεRI-driven CysLT production. Inhibition of COX-1 prevented IL-33-induced phosphorylation of extracellular signal-related kinase, an upstream effector of cytosolic phospholipase A₂, which was restored by exogenous PGH₂, implying that the effects of COX-1 required its catalytic function. Administration of a COX-1-selective antagonist to mice completely prevented the generation of both PGD₂ and LTC₄ in a model of AERD in which MC activation is IL-33 driven.

CONCLUSIONS

MC-intrinsic COX-1 amplifies IL-33-induced activation in the setting of innate type 2 immunity and might help explain the phenomenon of therapeutic desensitization to aspirin by nonselective COX inhibitors in patients with AERD.

Leukotriene biosynthetic enzymes as therapeutic targets

Leukotrienes are powerful immune-regulating lipid mediators with established pathogenic roles in inflammatory allergic diseases of the respiratory tract - in particular, asthma and hay fever. More recent work indicates that these lipids also contribute to low-grade inflammation, a hallmark of cardiovascular, neurodegenerative, and metabolic diseases as well as cancer. Biosynthesis of leukotrienes involves oxidative metabolism of arachidonic acid and proceeds via a set of soluble and membrane enzymes that are primarily expressed by cells of myeloid origin. In activated immune cells, these enzymes assemble at the endoplasmic and perinuclear membrane, constituting a biosynthetic complex. This Review describes recent advances in our understanding of the components of the leukotriene-synthesizing enzyme machinery, emerging opportunities for pharmacological intervention, and the development of new medicines exploiting both antiinflammatory and pro-resolving mechanisms.

Aspirin exacerbated respiratory disease: Current topics and trends

Aspirin-exacerbated respiratory disease is a chronic and treatment-resistant disease, characterized by the presence of eosinophilic rhinosinusitis, nasal polyposis, bronchial asthma, and nonsteroidal anti-inflammatory drugs hypersensitivity. Alterations in arachidonic acid metabolism may induce an imbalance between pro-inflammatory and anti-inflammatory substances, expressed as an overproduction of cysteinyl leukotrienes and an underproduction of prostaglandin E2. Although eosinophils play a key role, recent studies have shown the importance of other cells and molecules in the development of the disease like mast cells, basophils, lymphocytes, platelets, neutrophils, macrophages, epithelial respiratory cells, IL-33 and thymic stromal lymphopoietin, making each of them promissory diagnostic and treatment targets. In this review, we summarize the most important clinical aspects of the disease, including the current topics about diagnosis and treatment, like provocation challenges and aspirin desensitization. We also discuss recent findings in the pathogenesis of the disease, as well as future trends in diagnosis and treatment, including monoclonal antibodies and a low salicylate diet as a treatment option.

Mechanisms of Benefit with Aspirin Therapy in Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) is a clinical syndrome characterized by severe persistent asthma, hyperplastic eosinophilic sinusitis with nasal polyps, and an intolerance to aspirin and other NSAIDs that preferentially inhibit COX-1. For more than 30 years, aspirin desensitization has proven to be of significant long-term benefit in carefully selected patients with AERD. Despite this, the exact mechanisms behind the therapeutic effects of aspirin desensitization remain poorly understood. In this article, we review the current understanding of the mechanisms of aspirin desensitization and discuss future areas of investigation.

Lipid Mediators of Allergic Disease: Pathways, Treatments, and Emerging Therapeutic Targets

Bioactive lipids are critical regulators of inflammation. Over the last 75 years, these diverse compounds have emerged as clinically-relevant mediators of allergic disease pathophysiology. Animal and human studies have demonstrated the importance of lipid mediators in the development of asthma, allergic rhinitis, urticaria, anaphylaxis, atopic dermatitis, and food allergy. Lipids are critical participants in cell signaling events which influence key physiologic (bronchoconstriction) and immune phenomena (degranulation, chemotaxis, sensitization). Lipid-mediated cellular mechanisms including: (1) formation of structural support platforms (lipid rafts) for receptor signaling complexes, (2) activation of a diverse family of G-protein coupled receptors, and (3) mediating intracellular signaling cascades by acting as second messengers. Here, we review four classes of bioactive lipids (platelet activating factor, the leukotrienes, the prostanoids, and the sphingolipids) with special emphasis on lipid synthesis pathways and signaling, atopic disease pathology, and the ongoing development of atopy treatments targeting lipid mediator pathways.

Eosinophils and Mast Cells in Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) involves overexpression of proinflammatory mediators, including 5-lipoxygenase and leukotriene C₄ synthase (LTC₄S), resulting in constitutive overproduction of cysteinyl leukotrienes. Mast cells and eosinophils have roles in mediating many of the observed effects. Increased levels of both interleukin-4 (IL-4) and interferon (IFN)-γ are present in the tissue of patients with AERD. Previous studies showed that IL-4 is primarily responsible for the upregulation of LTC₄S by mast cells. Our studies show that IFN-γ, but not IL-4, drives this process in eosinophils. This article examines the overall role that eosinophils and mast cells contribute to the pathophysiology of AERD.

Aspirin-exacerbated respiratory disease: pathophysiological insights and clinical advances

Asthma and chronic rhinosinusitis are heterogeneous airway diseases of the lower and upper airways, respectively. Molecular and cellular studies indicate that these diseases can be categorized into unique endotypes, which have therapeutic implications. One such endotype is aspirin-exacerbated respiratory disease (AERD), which encompasses the triad of asthma, aspirin (or nonsteroidal anti-inflammatory drug) hypersensitivity, and nasal polyposis. AERD has unique pathophysiological features that distinguish it from aspirin-tolerant asthma and other forms of chronic rhinosinusitis. This review details molecular and cellular features of AERD and highlights current and future therapies that are based on these insights.

Aspirin induces IL-4 production: augmented IL-4 production in aspirin-exacerbated respiratory disease

Aspirin hypersensitivity is a hallmark of aspirin-exacerbated respiratory disease (AERD), a clinical syndrome characterized by the severe inflammation of the respiratory tract after ingestion of cyclooxygenase-1 inhibitors. We investigated the capacity of aspirin to induce interleukin-4 (IL-4) production in inflammatory cells relevant to AERD pathogenesis and examined the associated biochemical and molecular pathways. We also compared IL-4 production in peripheral blood mononuclear cells (PBMCs) from patients with AERD vs aspirin-tolerant asthma (ATA) upon exposure to aspirin. Aspirin induced IL-4 expression and activated the IL-4 promoter in a report assay. The capacity of aspirin to induce IL-4 expression correlated with its activity to activate mitogen-activated protein kinases, to form DNA-protein complexes on P elements in the IL-4 promoter and to synthesize nuclear factor of activated T cells, critical transcription factors for IL-4 transcription. Of clinical importance, aspirin upregulated IL-4 production twice as much in PBMCs from patients with AERD compared with PBMCs from patients with ATA. Our results suggest that IL-4 is an inflammatory component mediating intolerance reactions to aspirin, and thus is crucial for AERD pathogenesis.

Factors driving the aspirin exacerbated respiratory disease phenotype

BACKGROUND

Aspirin-exacerbated respiratory disease (AERD) is explained in part by overexpression of 5-lipoxygenase and leukotriene C4 synthase (LTC4S), resulting in constitutive overproduction of cysteinyl leukotrienes (CysLTs) and driving the surge in CysLT production that occurs with aspirin ingestion. Similarly, AERD is characterized by the overexpression of CysLT receptors. Increased levels of both interleukin (IL)-4 and interferon (IFN)-γ are present in the tissue of AERD subjects. Previous studies demonstrated that IL-4 is primarily responsible for the up-regulation of LTC4S by mast cells.

METHODS

Literature review.

RESULTS

Our previous studies demonstrated that IFN-γ, but not IL-4, drives this process in eosinophils. These published studies also extend to both IL-4 and IFN-γ the ability to up-regulate CysLT receptors. Prostaglandin E2 (PGE2) acts to prevent CysLT secretion by inhibiting mast cell and eosinophil activation. PGE2 concentrations are reduced in AERD, and our published studies confirm that this reflects diminished expression of cyclooxygenase (COX)-2. A process again that is driven by IL-4. Thus, IL-4 and IFN-γ together play an important pathogenic role in generating the phenotype of AERD. Finally, induction of LTC4S and CysLT1 receptors by IL-4 reflects in part the IL-4-mediated activation of signal transducer and activator of transcription 6 (STAT6). Our previous studies demonstrated that aspirin blocks trafficking of STAT6 into the nucleus and thereby prevents IL-4-mediated induction of these transcripts, thereby suggesting a modality by which aspirin desensitization could provide therapeutic benefit for AERD patients.

CONCLUSION

This review will examine the evidence supporting this model.

Mast cell production and response to IL-4 and IL-13

IL-4 was identified as the first cytokine to be produced by mast cells and is responsible for promoting mast cell IL-13 production. IL-4 and IL-13 play a prominent role in stimulating and maintaining the allergic response. As closely related genes, IL-4 and IL-13 share a common receptor subunit, IL-4Rα, necessary for signaling. Here we summarize the literature on mast cell activation associated with IL-4 and IL-13 production, including downstream signaling. We also describe the positive and negative roles each cytokine plays in mast cell immunity and detail the differences that exist between mouse and human mast cell responses to IL-4 and IL-13.

Association of Leukotriene C4 Synthase A-444C Polymorphism with Asthma and Asthma Phenotypes in Romanian Population

INTRODUCTION

Leukotriene C4 synthase (LTC4S) gene -444A/C polymorphism has been implicated in susceptibility to asthma, but a large number of studies have reported inconclusive results. The aim of this study was to investigate the association between the -444A/C polymorphism of LTC4S gene and asthma, asthma phenotypes (aspirin intolerant/tolerant asthma) and different characteristics of the patients.

MATERIAL AND METHODS

We included 106 patients with asthma (60 with aspirin tolerant asthma - ATA, 46 with aspirin intolerant asthma - AIA) and 103 controls. All the subjects were genotyped for LTC4S-444 A/C by Real-Time PCR. We assessed the association of LTC4S promoter polymorphism with asthma and its phenotypes and with clinical and biological characteristics of asthmatic patients.

RESULTS

We did not find a significant association between the studied polymorphism and asthma, but the minor allele tended to be more frequent in AIA patients. We found a significant association between the minor allele C and lower levels of serum total immunoglobulin E and eosinophils, suggesting a possible role of -444A/C LTC4S polymorphism as modulating factor of allergic inflammation in asthma.

CONCLUSION

The results show that LTC4S -444A/C SNP is not associated with susceptibility to asthma in Romanian patients, but could influence asthma phenotype, namely aspirin intolerant asthma.

Synthesis of leukotrienes in porcine uteri with endometritis induced by infection with Escherichia coli

Leukotrienes (LTs) are lipid mediators that play a significant role in the inflammatory process. Their production in inflamed uteri is not fully understood. The present experiment aimed to determine LTB4 and LTC4 amounts, 5-lipooxygenase (5-LO), LTA4 hydrolase (LTAH) and LTC4 synthase (LTCS) mRNA levels and protein expression in inflamed porcine uteri. On Day 3 of the oestrous cycle (Day 0 of the study), either Escherichia coli suspension or saline were infused into uterine horns. Collection of uterine tissues and washings took place eight or sixteen days later. In gilts suffering from endometritis increased LTB4 and LTC4 levels in the endometrium and washings and 5-LO mRNA levels in the myometrium on Days 8 and 16, 5-LO protein levels in the endometrium and myometrium on Day 8, LTAH mRNA and protein levels in the endometrium and myometrium on Days 8 and 16, respectively. Although LTCS mRNA and protein expression in the myometrium and LTCS protein expression in the endometrium were enhanced on Day 16 after Escherichia coli inoculation, LTCS mRNA levels decreased on Day 8 in both tissues. Our study shows the upregulation of LT production in inflamed porcine uteri, which suggests the importance of these factors to the process of uterine inflammation.

Sphingosine-1-phosphate and other lipid mediators generated by mast cells as critical players in allergy and mast cell function

Sphingosine-1-phosphate (S1P), platelet activating factor (PAF) and eicosanoids are bioactive lipid mediators abundantly produced by antigen-stimulated mast cells that exert their function mostly through specific cell surface receptors. Although it has long been recognized that some of these bioactive lipids are potent regulators of allergic diseases, their exact contributions to disease pathology have been obscured by the complexity of their mode of action and the regulation of their metabolism. Indeed, the effects of such lipids are usually mediated by multiple receptor subtypes that may differ in their signaling mechanisms and functions. In addition, their actions may be elicited by cell surface receptor-independent mechanisms. Furthermore, these lipids may be converted into metabolites that exhibit different functionalities, adding another layer of complexity to their overall biological responses. In some instances, a second wave of lipid mediator synthesis by both mast cell and non-mast cell sources may occur late during inflammation, bringing about additional roles in the altered environment. New evidence also suggests that bioactive lipids in the local environment can fine-tune mast cell maturation and phenotype, and thus their responsiveness. A better understanding of the subtleties of the spatiotemporal regulation of these lipid mediators, their receptors and functions may aid in the pursuit of pharmacological applications for allergy treatments.

Unravelling adverse reactions to NSAIDs using systems biology

We introduce the reader to systems biology, using adverse drug reactions (ADRs), specifically hypersensitivity reactions to multiple non-steroidal anti-inflammatory drugs (NSAIDs), as a model. To disentangle the different processes that contribute to these reactions - from drug intake to the appearance of symptoms - it will be necessary to create high-throughput datasets. Just as crucial will be the use of systems biology to integrate and make sense of them. We review previous work using systems biology to study related pathologies such as asthma/allergy, and NSAID metabolism. We show examples of their application to NSAIDs-hypersensitivity using current datasets. We describe breakthroughs in high-throughput technology and speculate on their use to improve our understanding of this and other drug-induced pathologies.

New insights on the signaling and function of the high-affinity receptor for IgE

Clustering of the high-affinity receptor for immunoglobulin E (FcεRI) through the interaction of receptor-bound immunoglobulin E (IgE) antibodies with their cognate antigen is required to couple IgE antibody production to cellular responses and physiological consequences. IgE-induced responses through FcεRI are well known to defend the host against certain infectious agents and to lead to unwanted allergic responses to normally innocuous substances. However, the cellular and/or physiological response of individuals that produce IgE antibodies may be markedly different and such antibodies (even to the same antigenic epitope) can differ in their antigen-binding affinity. How affinity variation in the interaction of FcεRI-bound IgE antibodies with antigen is interpreted into cellular responses and how the local environment may influence these responses is of interest. In this chapter, we focus on recent advances that begin to unravel how FcεRI distinguishes differences in the affinity of IgE-antigen interactions and how such discrimination along with surrounding environmental stimuli can shape the (patho) physiological response.

Pro- and anti-inflammatory mediators change leukotriene B4 and leukotriene C4 synthesis and secretion in an inflamed porcine endometrium

We studied the effect of lipopolysaccharide (LPS), proinflammatory cytokines (tumor necrosis factor α [TNF-α] and interleukin [IL]-1β), and anti-inflammatory cytokines (IL-4 and IL-10) on leukotriene (LT) A4 hydrolase and LTC4 synthase (LTCS) protein expression in, and LTB4 and LTC4 secretion from, an inflamed porcine endometrium. On day 3 of the estrous cycle (day 0 of the study), 50 mL of either saline or Escherichia coli suspension (10(9) CFU/mL) was injected into each uterine horn of gilts (n = 12 per group). Endometrial explants, obtained 8 and 16 days later, were incubated for 24 h with LPS (10 or 100 ng/mL of medium), TNF-α, IL-1β, IL-4, and IL-10 (each cytokine: 1 or 10 ng/mL of medium). Although acute endometritis developed in all bacteria-inoculated gilts, a severe form of acute endometritis was diagnosed more often on day 8 of the study than on day 16. The amount of the LTA4 hydrolase (LTAH) protein in the inflamed endometrium on day 8 was greater after applying the lower dose of TNF-α (P < 0.001) and both doses of IL-1β (P < 0.001) and IL-4 (1 ng, P < 0.01 and 10 ng, P < 0.001) than in the saline-treated uteri. A similar situation was observed in the case of the inflamed tissue on day 16 in response to LPS (100 ng, P < 0.01), TNF-α (10 ng, P < 0.05), and IL-4 (1 ng, P < 0.001). The content of LTC4 synthase in the inflamed endometrium on day 8 was reduced by LPS (100 ng, P < 0.05), IL-1β (10 ng, P < 0.05), IL-4 (1 and 10 ng, P < 0.05), and IL-10 (1 ng, P < 0.01) but increased after the application of LPS (100 ng, P < 0.05) and TNF-α (1 and 10 ng, P < 0.001), IL-1β, and IL-4 (1 ng, P < 0.05 and 10 ng, P < 0.001) on day 16. On day 8, endometrial secretion of LTB4 from the saline-injected and E coli-injected organs was similar in response to all of the used mediators. On the other hand, the contents of LTB4 in the medium decreased after incubating the inflamed tissues from day 16 with TNF-α (1 ng, P < 0.05 and 10 ng, P < 0.01), IL-1β (1 ng, P < 0.01), and IL-10 (10 ng, P < 0.05) compared with the saline-treated ones. Secretion of LTC4 from the inflamed uteri on day 8 was elevated by the lower doses of TNF-α (P < 0.01) and IL-10 (P < 0.05), whereas on day 16, such an effect occurred in response to the higher doses of IL-4 (P < 0.01) and IL-10 (P < 0.05). The obtained results show that pro- and anti-inflammatory mediators participate in the synthesis/secretion of LTs from an inflamed porcine endometrium. Our data suggest that inflammatory mediators may indirectly affect the processes regulated by LTs by influencing LT production.

Cysteinyl leukotrienes and their receptors; emerging concepts

Cysteinyl leukotrienes (cys-LTs) are potent mediators of inflammation derived from arachidonic acid through the 5-lipoxygenase/leukotriene C4 synthase pathway. The derivation of their chemical structures and identification of their pharmacologic properties predated the cloning of their classical receptors and the development of drugs that modify their synthesis and actions. Recent studies have revealed unanticipated insights into the regulation of cys-LT synthesis, the function of the cys-LTs in innate and adaptive immunity and human disease, and the identification of a new receptor for the cys-LTs. This review highlights these studies and summarizes their potential pathobiologic and therapeutic implications.

Increased density of intraepithelial mast cells in patients with exercise-induced bronchoconstriction regulated through epithelially derived thymic stromal lymphopoietin and IL-33

BACKGROUND

Exercise-induced bronchoconstriction (EIB) is a prototypical feature of indirect airway hyperresponsiveness. Mast cells are implicated in EIB, but the characteristics, regulation, and function of mast cells in patients with EIB are poorly understood.

OBJECTIVES

We sought to examine mast cell infiltration of the airway epithelium in patients with EIB and the regulation of mast cell phenotype and function by epithelially derived cytokines.

METHODS

Endobronchial biopsy specimens, epithelial brushings, and induced sputum were obtained from asthmatic patients with and without EIB and healthy control subjects. Mast cell proteases were quantified by using quantitative PCR, and mast cell density was quantified by using design-based stereology. Airway epithelial responses to wounding and osmotic stress were assessed in primary airway epithelial cells and ex vivo murine lung tissue. Mast cell granule development and function were examined in cord blood-derived mast cells.

RESULTS

Tryptase and carboxypeptidase A3 expression in epithelial brushings and epithelial mast cell density were selectively increased in the asthma group with EIB. An in vitro scratch wound initiated the release of thymic stromal lymphopoietin, which was greater in epithelial cells derived from asthmatic patients. Osmotic stress induced the release of IL-33 from explanted murine lungs, which was increased in allergen-treated mice. Thymic stromal lymphopoietin combined with IL-33 increased tryptase and carboxypeptidase A3 immunostaining in mast cell precursors and selectively increased cysteinyl leukotriene formation by mast cells in a manner that was independent of in vitro sensitization.

CONCLUSIONS

Mast cell infiltration of the epithelium is a critical determinant of indirect airway hyperresponsiveness, and the airway epithelium might serve as an important regulator of the development and function of this mast cell population.

Dectin-2 regulates the effector phase of house dust mite-elicited pulmonary inflammation independently from its role in sensitization

The myeloid C-type lectin receptor Dectin-2 directs the generation of Th2 and Th17 immune responses to the house dust mite Dermatophagoides farinae through the generation of cysteinyl leukotrienes and proinflammatory cytokines, respectively, but a role for Dectin-2 in effector phase responses has not been described. In this study, we demonstrate that administration of the Dectin-2 mAb solely at the time of D. farinae challenge abrogated eosinophilic and neutrophilic inflammation in the bronchoalveolar lavage fluid and Th1, Th2, and Th17 inflammation in the lung of previously sensitized mice. Furthermore, Dectin-2 null mice (Clec4n(-/-)) sensitized with the adoptive transfer of D. farinae-pulsed wild-type (WT) bone marrow-derived dendritic cells (DCs) also had less D. farinae-elicited pulmonary inflammation, supporting an effector function for Dectin-2. The protection from pulmonary inflammation seen with the Dectin-2 mAb or in Clec4n(-/-) mice was associated with little or no reduction in lung-draining lymph node cells or their cytokine production and with no reduction in serum IgE. WT and Clec4n(-/-) mice recipients, sensitized with D. farinae-pulsed WT bone marrow-derived DCs, had comparable levels of D. farinae-elicited IL-6, IL-23, TNF-α, and cysteinyl leukotrienes in the lung. By contrast, D. farinae-elicited CCL4 and CCL8 production from pulmonary CD11c(+)CD11b(+)Ly6C(+) and CD11c(+)CD11b(+)Ly6C(-)CD64(+) monocyte-derived DCs was reduced in Clec4n(-/-) recipients. Addition of CCL8 at the time of D. farinae challenge abrogated the protection from eosinophilic, neutrophilic, and Th2 pulmonary inflammation seen in Clec4n(-/-) recipients. Taken together, these results reveal that Dectin-2 regulates monocyte-derived DC function in the pulmonary microenvironment at D. farinae challenge to promote the local inflammatory response.

Mechanisms of aspirin desensitization

Aspirin-exacerbated respiratory disease is a clinical syndrome characterized by severe, persistent asthma, hyperplastic eosinophilic sinusitis with nasal polyps, and reactions to aspirin and other nonsteroidal antiinflammatory drugs that preferentially inhibit cyclooxygenase 1. The mechanisms behind the therapeutic effects of aspirin desensitization remain poorly understood. Recent studies suggest that the clinical benefits may occur through direct inhibition of tyrosine kinases and the signal transducer and activator of transcription 6 signaling pathway, which results in inhibition of interleukin 4 production. In this article, the current understanding of the mechanisms of aspirin desensitization is reviewed and future areas of investigation are discussed.

Prominent role of IFN-γ in patients with aspirin-exacerbated respiratory disease

BACKGROUND

Aspirin-exacerbated respiratory disease (AERD) is distinguished from aspirin-tolerant asthma/chronic sinusitis in large part by an exuberant infiltration of eosinophils that are characterized by their overexpression of metabolic pathways that drive the constitutive and aspirin-induced secretion of cysteinyl leukotrienes (CysLTs).

OBJECTIVE

We defined the inflammatory milieu that in part drives CysLT overproduction and, in particular, the role of IFN-γ in the differentiation of eosinophils.

METHODS

Quantitative real-time PCR was performed for TH1 and TH2 signature cytokines on tissue from control subjects, patients with chronic hyperplastic eosinophilic sinusitis, and patients with AERD, and their cellular source was determined. The influence of IFN-γ on maturation, differentiation, and functionality of eosinophils derived from hematopoietic stem cells was determined.

RESULTS

Gene expression analysis revealed that tissue from both aspirin-tolerant subjects and patients with AERD display a TH2 cytokine signature; however, AERD was distinguished from chronic hyperplastic eosinophilic sinusitis by the prominent expression of IFN-γ. Intracellular and immunohistochemical cytokine staining revealed that the major sources of these cytokines were the eosinophils themselves. IFN-γ promoted the maturation of eosinophil progenitors, as measured by increased mRNA and surface expression of CCR3 and sialic acid-binding immunoglobulin-like lectin 8 (Siglec-8). Additionally, IFN-γ increased the expression of genes involved in leukotriene synthesis that led to increased secretion of CysLTs. IFN-γ-matured eosinophil progenitors were also primed, as demonstrated by their enhanced degranulation.

CONCLUSIONS

High IFN-γ levels distinguish AERD from aspirin-tolerant asthma and underlie the robust constitutive and aspirin-induced secretion of CysLTs that characterize this disorder.

The leukotrienes: immune-modulating lipid mediators of disease

The leukotrienes are important lipid mediators with immune modulatory and proinflammatory properties. Classical bioactions of leukotrienes include chemotaxis, endothelial adherence, and activation of leukocytes, chemokine production, as well as contraction of smooth muscles in the microcirculation and respiratory tract. When formed in excess, these compounds play a pathogenic role in several acute and chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. An increasing number of diseases have been linked to inflammation implicating the leukotrienes as potential mediators. For example, recent investigations using genetic, morphological, and biochemical approaches have pointed to the involvement of leukotrienes in cardiovascular diseases including atherosclerosis, myocardial infarction, stroke, and abdominal aortic aneurysm. Moreover, new insights have changed our previous notion of leukotrienes as mediators of inflammatory reactions to molecules that can fine-tune the innate and adaptive immune response. Here, we review the most recent understanding of the leukotriene cascade with emphasis on recently identified roles in immune reactions and pathophysiology.

Interleukin-13 signaling and its role in asthma

Asthma affects nearly 300 million people worldwide. The majority respond to inhaled corticosteroid treatment with or without beta-adrenergic agonists. However, a subset of 5 to 10% with severe asthma do not respond optimally to these medications. Different phenotypes of asthma may explain why current therapies show limited benefits in subgroups of patients. Interleukin-13 is implicated as a central regulator in IgE synthesis, mucus hypersecretion, airway hyperresponsiveness, and fibrosis. Promising research suggests that the interleukin-13 pathway may be an important target in the treatment of the different asthma phenotypes.