Mast Cells, FcεRI, and IL-13 Are Required for Development of Airway Hyperresponsiveness after Aerosolized Allergen Exposure in the Absence of Adjuvant

Norisoboldine exerts antiallergic effects on IgE/ovalbumin-induced allergic asthma and attenuates FcεRI-mediated mast cell activation

Allergic asthma is an inflammatory lung disorder, and mast cells play crucial roles in the development of this allergic disease. Norisoboldine (NOR), the major isoquinoline alkaloid present in Radix Linderae, has received considerable attention because it has anti-inflammatory effects. Herein, the aim of this study was to explore the antiallergic effects of NOR on allergic asthma in mice and mast cell activation. In a murine model of ovalbumin (OVA)-induced allergic asthma, oral administration at 5 mg/kg body weight (BW) of NOR produced strong reductions in serum OVA-specific immunoglobulin E (IgE) levels, airway hyperresponsiveness, and bronchoalveolar lavage fluid (BALF) eosinophilia, while an increase in CD4+Foxp3+ T cells of the spleen was detected. Histological studies demonstrated that NOR treatment significantly ameliorated the progression of airway inflammation including the recruitment of inflammatory cells and mucus production by decreasing levels of histamine, prostaglandin D2 (PGD2), interleukin (IL)-4, IL-5, IL-6, and IL-13 in BALF. Furthermore, our results revealed that NOR (3 ∼ 30 μM) dose-dependently reduced expression of the high-affinity receptor for IgE (FcεRI) and the production of PGD2 and inflammatory cytokines (IL-4, IL-6, IL-13, and TNF-α), and also decreased degranulation of bone marrow-derived mast cells (BMMCs) activated by IgE/OVA. In addition, a similar suppressive effect on BMMC activation was observed by inhibition of the FcεRI-mediated c-Jun N-terminal kinase (JNK) signaling pathway using SP600125, a selective JNK inhibitor. Collectively, these results suggest that NOR may have therapeutic potential for allergic asthma at least in part through regulating the degranulation and the release of mediators by mast cells.

Nasopharyngeal microbial profiles associated with the risk of airway allergies in early childhood

BACKGROUND

Airway microbiota may play an important role in regulating the immune response related to allergic respiratory diseases. A molecular-based approach was used to analyze the association between nasopharyngeal microbiota, serum immunoglobin (Ig)E levels, and childhood respiratory allergies.

METHODS

Nasopharyngeal swabs were collected from children aged 36 months with three phenotypes, including allergic respiratory diseases plus atopy, atopy alone, and healthy controls for microbiome analysis using Illumina-based 16S rRNA gene sequencing.

RESULTS

In total, 87 children were enrolled, including 36 with allergic respiratory diseases plus atopy, 21 with atopy alone, and 30 healthy controls. Proteobacteria (45.7%), Firmicutes (29.3%), and Actinobacteria (15.3%) were the most prevalent phyla in the study population. Compared with healthy controls, a lower Chao1 index was found in children with allergies (P < 0.035), indicating that bacterial richness was inversely associated with airway allergies. Additionally, in comparison with healthy controls, the genera Acinetobacter, Moraxella, Asaia, and Rhodococcus were more abundant and positively correlated with total serum IgE levels in children with allergies (P < 0.01), whereas the genera Enterococcus and Rickettsia were inversely correlated with total IgE levels, and also appeared to be negatively associated with airway allergies (P < 0.01).

CONCLUSIONS

The composition of the nasopharyngeal microbiota alteration may have an influence on childhood respiratory allergies. The inverse association between bacterial richness and allergies postulated that children living in a microbially hygienic environment may increase their risk of developing respiratory allergies.

Perimenstrual Asthma in Adolescents: A Shared Condition in Pediatric and Gynecological Endocrinology

Asthma is a frequent medical condition in adolescence. The worsening of the most common symptoms perimenstrually is defined as perimenstrual asthma (PMA). The cause of PMA remains unclear, but a role for hormonal milieu is plausible. Data on PMA in adolescents are limited, and its management is not fully established. We aimed to discuss the PMA phenomenon in young females from pathophysiology to preventive strategies, focusing on the relationship with the hormonal pattern. The fluctuation of estrogens at ovulation and before menstruation and the progesterone secretion during the luteal phase and its subsequent withdrawal seem to be the culprits, because the deterioration of asthma is cyclical during the luteal phase and/or during the first days of the menstrual cycle. Conventional asthma therapies are not always effective for PMA. Preventive strategies may include innovative hormonal contraception. Even a possible beneficial effect of other hormonal treatments, including estrogens, progestogens, and androgens, as well as leukotriene receptor antagonists and explorative approach using microbial-directed therapy, is considered. The underlying mechanisms, through which sex-hormone fluctuations influence asthma symptoms, represent a challenge in the clinical management of such a distressing condition. Further studies focused on young females are mandatory to promote adolescent health.

Comparative analysis of the role of mast cells in murine asthma models using Kit-sufficient mast cell-deficient animals

BACKGROUND

Asthma is a frequent chronic disease that can potentially severely affect the respiratory capacity and well-being of patients. Mast cells (MCs) are regarded as major players in human asthma due to their capacity to release crucial inflammatory mediators following allergen exposure. However, unambiguous characterization of their role in animal models has long been hindered by the unavailability of specific MC-deficient models lacking confounding MC-unrelated effects. This study aims to examine the role of MCs in Kit-sufficient MC-deficient Cpa3^{Cre /+} mice.

METHODS

We used a variety of models of acute and chronic asthma employing distinct routes and regimes of sensitization. These sensitizations were done via the peritoneal cavity, the skin, or the lung. Additionally, different allergens, i.e. ovalbumin and house dust mite extract, were used.

RESULTS

Our results show that the absence of MCs had no impact on the severity of allergic airway inflammation in any of the tested mouse models, as measured by leukocyte infiltration in the airways, cytokine expression, antibody production, airway hyper-responsiveness and mucus production.

CONCLUSION

This indicates that MCs do not play a major role in murine allergic airway inflammation.

Catalpol exerts antiallergic effects in IgE/ovalbumin-activated mast cells and a murine model of ovalbumin-induced allergic asthma

Immunoglobulin E (IgE) and mast cells play important roles in the pathogenesis of allergic asthma. Catalpol, an iridoid glycoside, exerts many biological functions including anti-inflammatory activities. Herein, we investigated catalpol to determine both its antiallergic effects on IgE/ovalbumin (OVA)-stimulated mouse bone marrow-derived mast cells and its therapeutic actions in murine allergic asthma. We found that catalpol dramatically suppressed IgE/OVA-induced mast cell degranulation. Meanwhile, 5 ~ 100 μM of catalpol neither affected the expression level of the high-affinity receptor of IgE (FcεRI) by mast cells nor induced mast cell apoptosis. In addition, mRNA expression levels of inflammatory enzymes including cyclooxygenase (COX)-1, COX-2, and 5-lipoxygenase were downregulated. Administration of catalpol also suppressed production of prostaglandin D₂ (PGD₂), interleukin (IL)-6, and IL-13, while not affecting tumor necrosis factor (TNF)-α production. Further, catalpol pretreatment significantly attenuated the FcεRI-mediated Akt signaling pathway. In mice with IgE/OVA-induced asthma, oral administration of catalpol remarkably suppressed the production of OVA-specific IgE, the development of airway hyperresponsiveness (AHR), and the infiltration of eosinophils and neutrophils into the lungs. Histological studies demonstrated that catalpol substantially inhibited the recruitment of mast cells and increased mucus production in lung tissues. Catalpol-treated mice had significantly lower levels of helper T cell type 2 (Th2) cytokines (IL-4, IL-5, and IL-13), PGD₂, eotaxin-1, and C-X-C chemokine ligand-1 (CXCL1) in bronchoalveolar lavage fluid (BALF) than did the allergic group. Collectively, these results indicated that the suppressive effects of catalpol on degranulation and mediator generation by mast cells were beneficial in treating allergic asthma.

John AL, Ginhoux F. Fetal mast cells mediate postnatal allergic responses dependent on maternal IgE

Mast cells (MCs) are central effector cells in allergic reactions that are often mediated by immunoglobulin E (IgE). Allergies commonly start at an early age, and both MCs and IgE are detectable in fetuses. However, the origin of fetal IgE and whether fetal MCs can degranulate in response to IgE-dependent activation are presently unknown. Here, we show that human and mouse fetal MCs phenotypically mature through pregnancy and can be sensitized by maternal IgE. IgE crossed the placenta, dependent on the fetal neonatal Fc receptor (FcRN), and sensitized fetal MCs for allergen-specific degranulation. Both passive and active prenatal sensitization conferred allergen sensitivity, resulting in postnatal skin and airway inflammation after the first allergen encounter. We report a role for MCs within the developing fetus and demonstrate that fetal MCs may contribute to antigen-specific vertical transmission of allergic disease.

Mast Cells and Their Progenitors in Allergic Asthma

Mast cells and their mediators have been implicated in the pathogenesis of asthma and allergy for decades. Allergic asthma is a complex chronic lung disease in which several different immune cells, genetic factors and environmental exposures influence the pathology. Mast cells are key players in the asthmatic response through secretion of a multitude of mediators with pro-inflammatory and airway-constrictive effects. Well-known mast cell mediators, such as histamine and bioactive lipids are responsible for many of the physiological effects observed in the acute phase of allergic reactions. The accumulation of mast cells at particular sites of the allergic lung is likely relevant to the asthma phenotype, severity and progression. Mast cells located in different compartments in the lung and airways have different characteristics and express different mediators. According to in vivo experiments in mice, lung mast cells develop from mast cell progenitors induced by inflammatory stimuli to migrate to the airways. Human mast cell progenitors have been identified in the blood circulation. A high frequency of circulating human mast cell progenitors may reflect ongoing pathological changes in the allergic lung. In allergic asthma, mast cells become activated mainly via IgE-mediated crosslinking of the high affinity receptor for IgE (FcεRI) with allergens. However, mast cells can also be activated by numerous other stimuli e.g. toll-like receptors and MAS-related G protein-coupled receptor X2. In this review, we summarize research with implications on the role and development of mast cells and their progenitors in allergic asthma and cover selected activation pathways and mast cell mediators that have been implicated in the pathogenesis. The review places an emphasis on describing mechanisms identified using in vivo mouse models and data obtained by analysis of clinical samples.

Adoptive transfer of Trichinella spiralis-activated macrophages can ameliorate both Th1- and Th2-activated inflammation in murine models

Trichinella spiralis is a zoonotic nematode and food borne parasite and infection with T. spiralis leads to suppression of the host immune response and other immunopathologies. Alternative activated macrophages (M2) as well as T_reg cells, a target for immunomodulation by the helminth parasite, play a critical role in initiating and modulating the host immune response to parasite. The precise mechanism by which helminths modulate host immune response is not fully understood. To determine the functions of parasite-induced M2 macrophages, we compared the effects of M1 and M2 macrophages obtained from Trichinella spiralis-infected mice with those of T. spiralis excretory/secretory (ES) protein-treated macrophages on experimental intestinal inflammation and allergic airway inflammation. T. spiralis infection induced M2 macrophage polarization by increasing the expression of CD206, ARG1, and Fizz2. In a single application, we introduced macrophages obtained from T. spiralis-infected mice and T. spiralis ES protein-treated macrophages into mice tail veins before the induction of dextran sulfate sodium (DSS)-induced colitis, ovalbumin (OVA)-alum sensitization, and OVA challenge. Colitis severity was assessed by determining the severity of colitis symptoms, colon length, histopathologic parameters, and Th1-related inflammatory cytokine levels. Compared with the DSS-colitis group, T. spiralis-infected mice and T. spiralis ES protein-treated macrophages showed significantly lower disease activity index (DAI) at sacrifice and smaller reductions of body weight and proinflammatory cytokine level. The severity of allergic airway inflammation was assessed by determining the severity of symptoms of inflammation, airway hyperresponsiveness (AHR), differential cell counts, histopathologic parameters, and levels of Th2-related inflammatory cytokines. Severe allergic airway inflammation was induced after OVA-alum sensitization and OVA challenge, which significantly increased Th2-related cytokine levels, eosinophil infiltration, and goblet cell hyperplasia in the lung. However, these severe allergic symptoms were significantly decreased in T. spiralis-infected mice and T. spiralis ES protein-treated macrophages. Helminth infection and helminth ES proteins induce M2 macrophages. Adoptive transfer of macrophages obtained from helminth-infected mice and helminth ES protein-activated macrophages is an effective treatment for preventing and treating airway allergy in mice and is promising as a therapeutic for treating inflammatory diseases.

Notch ligand Delta-like1 enhances degranulation and cytokine production through a novel Notch/Dok-1/MAPKs pathway in vitro

Food allergy includes sensitization phase and effect phase, and effect cells degranulate and secrete cytokines in the effect phase, causing allergic clinical symptoms. We have demonstrated that Notch signaling plays an important role in the sensitization phase, but its role in effect phases still remains unclear. In this study, we investigated the role of Notch signaling in degranulation and cytokine production of the effect phase response. A RBL-2H3 cell model was used and Notch signaling was induced by priming with Notch ligands. Our results showed after priming with Notch ligand, Delta-like1(Dll1)-Fc, β-hexosaminidase release, and cytokines production, including TGF-β, IL-1β, IL-4, IL-6, and IL-13, were increased significantly, and the enhancement was abolished after DAPT treatment, a γ-secretase inhibitor, indicating that Dll1 Notch signaling enhanced RBL-2H3 cell degranulation and cytokine production. Western blot analysis showed that Dll1 Notch signaling augmented high-affinity IgE receptors-mediated phosphorylation of MAPKs through suppressing the expression of downstream tyrosine kinases 1 (Dok-1). Besides, a passive systemic anaphylaxis mouse model was used to confirm the role of Notch signaling. And our data showed that allergic clinical features of mice were alleviated, and the level of degranulation was decreased significantly after inhibiting Notch signaling in vivo. Therefore, we demonstrated Notch ligand Dll1 enhanced RBL-2H3 cell degranulation and cytokine production through a novel Notch/Dok-1/MAPKs pathway, suggesting Notch signaling played a key role in the effect phase of food allergy.

Importance of the leukotriene B4-BLT1 and LTB4-BLT2 pathways in asthma

For several decades, the leukotriene pathways have been implicated as playing a central role in the pathophysiology of asthma. The presence and elevation of numerous metabolites in the blood, sputum, and bronchoalveolar lavage fluid from asthmatics or experimental animals adds support to this notion. However, targeting of the leukotriene pathways has had, in general, limited success. The single exception in asthma therapy has been targeting of the cysteinyl leukotriene receptor 1, which clinically has proven effective but only in certain clinical situations. Interference with 5-lipoxygenase has had limited success, in part due to adverse drug effects. The importance of the LTB4-BLT1 pathway in asthma pathogenesis has extensive experimental support and findings, albeit limited, from clinical samples. The LTB4-BLT1 pathway was shown to be important as a neutrophil chemoattractant. Despite observations made more than two decades ago, the LTB4-BLT1 pathway has only recently been shown to exhibit important activities on subsets of T lymphocytes, both as a chemoattractant and on lymphocyte activation, as well as on dendritic cells, the major antigen presenting cell in the lung. The role of BLT2 in asthma remains unclear. Targeting of components of the LTB4-BLT1 pathway offers innovative therapeutic opportunities especially in patients with asthma that remain uncontrolled despite intensive corticosteroid treatment.

House Dust Mite-Induced Allergic Airway Disease Is Independent of IgE and FcεRIα

IgE contributes to disease exacerbations but not to baseline airway hyperresponsiveness (AHR) in human asthma. In rodent allergic airway disease (AAD), mast cell and IgE dependence for the induction of AHR has only been observed when mice are immunized with a relatively weak allergen without adjuvant. To evaluate the role of IgE in murine AAD that is induced by a potent allergen, we inoculated BALB/c and FVB/N background wild-type and IgE- or FcεRIα-deficient mice intratracheally with large or limiting doses of house dust mite extract (HDM) and evaluated AHR, pulmonary eosinophilia, goblet cell metaplasia, serum IgE, and lung mastocytosis. We found that neither IgE nor FcεRIα contributed to AAD, even in mice inoculated with the lowest dose of HDM, which readily induced detectable disease, but did not increase serum IgE or pulmonary mast cell levels. In contrast, high doses of HDM strikingly increased serum IgE and pulmonary mast cells, although both AHR and airway mast cell degranulation were equally elevated in wild-type and IgE-deficient mice. Surprisingly, allergen challenge of mice with severe AAD and pulmonary mastocytosis failed to acutely increase airway resistance, lung Newtonian resistance, or hysteresis. Overall, this study shows that, although mice may not reliably model acute asthma exacerbations, mechanisms that are IgE and FcεRIα independent are responsible for AHR and airway inflammation when low doses of a potent allergen are inhaled repetitively.

Spectrum of T-lymphocyte activities regulating allergic lung inflammation

Despite advances in the treatment of asthma, optimization of symptom control remains an unmet need in many patients. These patients, labeled severe asthma, are responsible for a substantial fraction of the disease burden. In these patients, research is needed to define the cellular and molecular pathways contributing to disease which in large part are refractory to corticosteroid treatment. The causes of steroid-resistant asthma are multifactorial and result from complex interactions of genetics, environmental factors, and innate and adaptive immunity. Adaptive immunity, addressed here, integrates the activities of distinct T-cell subsets and by definition is dynamic and responsive to an ever-changing environment and the influences of epigenetic modifications. These T-cell subsets exhibit different susceptibilities to the actions of corticosteroids and, in some, corticosteroids enhance their functional activation. Moreover, these subsets are not fixed in lineage differentiation but can undergo transcriptional reprogramming in a bidirectional manner between protective and pathogenic effector states. Together, these factors contribute to asthma heterogeneity between patients but also in the same patient at different stages of their disease. Only by carefully defining mechanistic pathways, delineating their sensitivity to corticosteroids, and determining the balance between regulatory and effector pathways will precision medicine become a reality with selective and effective application of targeted therapies.

Airway Microbial Diversity is Inversely Associated with Mite-Sensitized Rhinitis and Asthma in Early Childhood

Microbiota plays an important role in regulating immune responses associated with atopic diseases. We sought to evaluate relationships among airway microbiota, serum IgE levels, allergic sensitization and their relevance to rhinitis and asthma. Microbial characterization was performed using Illumina-based 16S rRNA gene sequencing of 87 throat swabs collected from children with asthma (n = 32) and rhinitis (n = 23), and from healthy controls (n = 32). Data analysis was performed using QIIME (Quantitative Insights Into Microbial Ecology) v1.8. Significantly higher abundance of Proteobacteria was found in children with rhinitis than in the healthy controls (20.1% vs. 16.1%, P = 0.009). Bacterial species richness (Chao1 index) and diversity (Shannon index) were significantly reduced in children with mite sensitization but not in those with food or IgE sensitization. Compared with healthy children without mite sensitization, the mite-sensitized children with rhinitis and asthma showed significantly lower Chao1 and Shannon indices. Moraxella and Leptotrichia species were significantly found in the interaction of mite sensitization with rhinitis and asthma respectively. Airway microbial diversity appears to be inversely associated with sensitization to house dust mites. A modulation between airway dysbiosis and responses to allergens may potentially cause susceptibility to rhinitis and asthma in early childhood.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Inhalation of inactivated‑Mycobacterium phlei prevents asthma‑mediated airway hyperresponsiveness and airway eosinophilia in mice by reducing IL‑5 and IL‑13 levels

The present study aimed to investigate whether inhalation of inactivated‑Mycobacterium phlei could prevent airway hyperresponsiveness and airway eosinophilia. A total of 24 male Balb/c mice were randomly divided into three groups: Normal control group (group A), asthma model group (group B) and the intervention group (group C), (8 mice/group). Group A mice were sensitized and with challenged saline and group B with ovalbumin (OVA). Group C mice were administered with aerosol Mycobacterium phlei once daily prior to the allergen challenge. Airway responsiveness in each group was assessed. All the animals were sacrificed and lung tissues, blood samples and bronchoalveolar lavage fluid (BALF) were harvested. Cell fractionation and differential cells were counted in serum and BALF. HE staining and alcian blue/periodic acid Schiff staining were used to measure airway eosinophilic inflammation and mucus production. The levels of the cytokines IL‑5, IL‑13 and IgE were measured in lung and BALF as determined by ELISA and reverse transcription‑quantitative polymerase chain reaction assays. The results indicated that inactivated‑Mycobacterium phlei suppressed the airway hyperresponsiveness and mitigated airway eosinophilia induced by a methacholine challenge, and significantly reduced the levels of cytokines IL‑5 and IL‑13 in lung tissue and IgE level in BALF when compared with the OVA‑sensitized mice. In conclusion, inhalation of inactivated‑Mycobacterium phlei could reduce OVA‑induced airway hyperresponsiveness and may be a potential alternative therapy for allergic airway diseases.

TRPV1 Antagonist Suppresses Allergic Conjunctivitis in a Murine Model

PURPOSE

To determine the immunologic functions of TRPA1 or TRPV1 in allergic conjunctivitis (AC).

METHODS

Mice were sensitized with ovalbumin (OVA), after which TRPA1 antagonist or TRPV1 antagonist was administered before topical OVA challenge. Expression of TRPV1 or TRPA1 in AC was examined by western blotting and multicolor immunofluorescence. Clinical signs, OVA-specific IgE, infiltration of inflammatory cells into conjunctivae (CJs), and Th2 cytokine in draining lymph nodes (LNs) were evaluated by microscopy, flow cytometry, and ELISA.

RESULTS

TRPV1 expression was increased in CJs and LNs from AC mice, but TRPA1 expression was only increased in LNs. TRPV1 antagonist but not TRPA1 antagonist attenuated the clinical signs of AC and OVA-specific IgE in sera. TRPV1 antagonist furthermore inhibited the infiltration of inflammatory cells into CJ and the production of Th2 cytokines in LNs.

CONCLUSION

TRPV1 antagonist but not TRPA1 antagonist may ameliorate AC by suppressing the Th2 response in LNs.

Mouse and human FcR effector functions

Mouse and human FcRs have been a major focus of attention not only of the scientific community, through the cloning and characterization of novel receptors, and of the medical community, through the identification of polymorphisms and linkage to disease but also of the pharmaceutical community, through the identification of FcRs as targets for therapy or engineering of Fc domains for the generation of enhanced therapeutic antibodies. The availability of knockout mouse lines for every single mouse FcR, of multiple or cell-specific--'à la carte'--FcR knockouts and the increasing generation of hFcR transgenics enable powerful in vivo approaches for the study of mouse and human FcR biology. This review will present the landscape of the current FcR family, their effector functions and the in vivo models at hand to study them. These in vivo models were recently instrumental in re-defining the properties and effector functions of FcRs that had been overlooked or discarded from previous analyses. A particular focus will be made on the (mis)concepts on the role of high-affinity IgG receptors in vivo and on results from antibody engineering to enhance or abrogate antibody effector functions mediated by FcRs.

Roles of Mas-related G protein-coupled receptor X2 on mast cell-mediated host defense, pseudoallergic drug reactions, and chronic inflammatory diseases

Mast cells (MCs), which are granulated tissue-resident cells of hematopoietic lineage, contribute to vascular homeostasis, innate/adaptive immunity, and wound healing. However, MCs are best known for their roles in allergic and inflammatory diseases, such as anaphylaxis, food allergy, rhinitis, itch, urticaria, atopic dermatitis, and asthma. In addition to the high-affinity IgE receptor (FcεRI), MCs express numerous G protein-coupled receptors (GPCRs), which are the largest group of membrane receptor proteins and the most common targets of drug therapy. Antimicrobial host defense peptides, neuropeptides, major basic protein, eosinophil peroxidase, and many US Food and Drug Administration-approved peptidergic drugs activate human MCs through a novel GPCR known as Mas-related G protein-coupled receptor X2 (MRGPRX2; formerly known as MrgX2). Unique features of MRGPRX2 that distinguish it from other GPCRs include their presence both on the plasma membrane and intracellular sites and their selective expression in MCs. In this article we review the possible roles of MRGPRX2 on host defense, drug-induced anaphylactoid reactions, neurogenic inflammation, pain, itch, and chronic inflammatory diseases, such as urticaria and asthma. We propose that host defense peptides that kill microbes directly and activate MCs through MRGPRX2 could serve as novel GPCR targets to modulate host defense against microbial infection. Furthermore, mAbs or small-molecule inhibitors of MRGPRX2 could be developed for the treatment of MC-dependent allergic and inflammatory disorders.

Role of IL-4 receptor α-positive CD4(+) T cells in chronic airway hyperresponsiveness

BACKGROUND

TH2 cells and their cytokines are associated with allergic asthma in human subjects and with mouse models of allergic airway disease. IL-4 signaling through the IL-4 receptor α (IL-4Rα) chain on CD4(+) T cells leads to TH2 cell differentiation in vitro, implying that IL-4Rα-responsive CD4(+) T cells are critical for the induction of allergic asthma. However, mechanisms regulating acute and chronic allergen-specific TH2 responses in vivo remain incompletely understood.

OBJECTIVE

This study defines the requirements for IL-4Rα-responsive CD4(+) T cells and the IL-4Rα ligands IL-4 and IL-13 in the development of allergen-specific TH2 responses during the onset and chronic phase of experimental allergic airway disease.

METHODS

Development of acute and chronic ovalbumin (OVA)-induced allergic asthma was assessed weekly in CD4(+) T cell-specific IL-4Rα-deficient BALB/c mice (Lck(cre)IL-4Rα(-/lox)) and respective control mice in the presence or absence of IL-4 or IL-13.

RESULTS

During acute allergic airway disease, IL-4 deficiency did not prevent the onset of TH2 immune responses and OVA-induced airway hyperresponsiveness or goblet cell hyperplasia, irrespective of the presence or absence of IL-4Rα-responsive CD4(+) T cells. In contrast, deficiency of IL-13 prevented allergic asthma, irrespective of the presence or absence of IL-4Rα-responsive CD4(+) T cells. Importantly, chronic allergic inflammation and airway hyperresponsiveness were dependent on IL-4Rα-responsive CD4(+) T cells. Deficiency in IL-4Rα-responsive CD4(+) T cells resulted in increased numbers of IL-17-producing T cells and, consequently, increased airway neutrophilia.

CONCLUSION

IL-4-responsive T helper cells are dispensable for acute OVA-induced airway disease but crucial in maintaining chronic asthmatic pathology.

Cbl-b Deficiency in Mice Results in Exacerbation of Acute and Chronic Stages of Allergic Asthma

Mice sensitized to ovalbumin (OVA) develop allergic airway disease (AAD) with short-term daily OVA aerosol challenge; inflammation resolves with long-term OVA aerosol exposure, resulting in local inhalational tolerance (LIT). Cbl-b is an E3 ubiquitin ligase involved with CD28 signaling; Cbl-b^−/− effector T cells are resistant to regulatory T cell-mediated suppression in vitro and in vivo. The present study utilized Cbl-b^−/− mice to investigate the role of Cbl-b in the development of AAD and LIT. Cbl-b^−/− mice exhibited increased airway inflammation during AAD, which failed to resolve with long-term OVA aerosol exposure. Exacerbation of inflammation in Cbl-b^−/− mice correlated with increased proinflammatory cytokine levels and expansion of effector T cells in the BAL during AAD, but did not result in either a modulation of lymphocyte subsets in systemic tissues or in OVA-specific IgE in serum. These results implicate a role for Cbl-b in the resolution of allergic airway inflammation.

Abrogation of airway hyperresponsiveness but not inflammation by rho kinase insufficiency

BACKGROUND

Major features of allergic asthma include airway hyperresponsiveness (AHR), eosinophilic inflammation, and goblet cell metaplasia. Rho kinase (ROCK) is a serine/threonine protein kinase that regulates the actin cytoskeleton. By doing so, it can modulate airway smooth muscle cell contraction and leucocyte migration and proliferation. This study was designed to determine the contributions of the two ROCK isoforms, ROCK1 and ROCK2, to AHR, inflammation and goblet cell metaplasia in a mast cell-dependent model of allergic airways disease.

METHODS AND RESULTS

Repeated intranasal challenges with OVA caused AHR, eosinophilic inflammation, and goblet cell hyperplasia in wild-type (WT) mice. OVA-induced AHR was partially or completely abrogated in mice haploinsufficient for ROCK2 (ROCK2(+/-) ) or ROCK1 (ROCK1(+/-) ), respectively. In contrast, there was no effect of ROCK insufficiency on allergic airways inflammation, although both ROCK1 and ROCK2 insufficiency attenuated mast cell degranulation. Goblet cell hyperplasia, as indicated by PAS staining, was not different in ROCK1(+/-) vs. WT mice. However, in ROCK2(+/-) mice, goblet cell hyperplasia was reduced in medium but not large airways. Maximal acetylcholine-induced force generation was reduced in tracheal rings from ROCK1(+/-) and ROCK2(+/-) vs. WT mice. The ROCK inhibitor, fasudil, also reduced airway responsiveness in OVA-challenged mice, without affecting inflammatory responses.

CONCLUSION

In a mast cell model of allergic airways disease, ROCK1 and ROCK2 both contribute to AHR, likely through direct effects on smooth muscle cell and effects on mast cell degranulation. In addition, ROCK2 but not ROCK1 plays a role in allergen-induced goblet cell hyperplasia.

Potential effector and immunoregulatory functions of mast cells in mucosal immunity

Mast cells (MCs) are cells of hematopoietic origin that normally reside in mucosal tissues, often near epithelial cells, glands, smooth muscle cells, and nerves. Best known for their contributions to pathology during IgE-associated disorders such as food allergy, asthma, and anaphylaxis, MCs are also thought to mediate IgE-associated effector functions during certain parasite infections. However, various MC populations also can be activated to express functional programs--such as secreting preformed and/or newly synthesized biologically active products--in response to encounters with products derived from diverse pathogens, other host cells (including leukocytes and structural cells), damaged tissue, or the activation of the complement or coagulation systems, as well as by signals derived from the external environment (including animal toxins, plant products, and physical agents). In this review, we will discuss evidence suggesting that MCs can perform diverse effector and immunoregulatory roles that contribute to homeostasis or pathology in mucosal tissues.

Notch signaling enhances FcεRI-mediated cytokine production by mast cells through direct and indirect mechanisms

Th2-type cytokines and TNF-α secreted by activated mast cells upon cross-linking of FcεRI contribute to the development and maintenance of Th2 immunity to parasites and allergens. We have previously shown that cytokine secretion by mouse mast cells is enhanced by signaling through Notch receptors. In this study, we investigated the molecular mechanisms by which Notch signaling enhances mast cell cytokine production induced by FcεRI cross-linking. FcεRI-mediated production of cytokines, particularly IL-4, was significantly enhanced in mouse bone marrow-derived mast cells by priming with Notch ligands. Western blot analysis showed that Notch signaling augmented and prolonged FcεRI-mediated phosphorylation of MAPKs, mainly JNK and p38 MAPK, through suppression of the expression of SHIP-1, a master negative regulator of FcεRI signaling, resulting in the enhanced production of multiple cytokines. The enhancing effect of Notch ligand priming on multiple cytokine production was abolished by knockdown of Notch2, but not Notch1, and FcεRI-mediated production of multiple cytokines was enhanced by retroviral transduction with the intracellular domain of Notch2. However, only IL-4 production was enhanced by both Notch1 and Notch2. The enhancing effect of Notch signaling on IL-4 production was lost in bone marrow-derived mast cells from mice lacking conserved noncoding sequence 2, which is located at the distal 3' element of the Il4 gene locus and contains Notch effector RBP-J binding sites. These results indicate that Notch2 signaling indirectly enhances the FcεRI-mediated production of multiple cytokines, and both Notch1 and Notch2 signaling directly enhances IL-4 production through the noncoding sequence 2 enhancer of the Il4 gene.

TH9 cells are required for tissue mast cell accumulation during allergic inflammation

BACKGROUND

IL-9 is important for the growth and survival of mast cells. IL-9 is produced by T cells, natural killer T cells, mast cells, eosinophils, and innate lymphoid cells, although the cells required for mast cell accumulation during allergic inflammation remain undefined.

OBJECTIVE

We sought to elucidate the role of TH9 cells in promoting mast cell accumulation in models of allergic lung inflammation.

METHODS

Adoptive transfer of ovalbumin-specific TH2 and TH9 cells was used to assess the ability of each subset to mediate mast cell accumulation in tissues. Mast cell accumulation was assessed in wild-type mice and mice with PU.1-deficient T cells subjected to acute and chronic models of allergic inflammation.

RESULTS

Adoptive transfer experiments demonstrated that recipients of TH9 cells had significantly higher mast cell accumulation and expression of mast cell proteases compared with control or TH2 recipients. Mast cell accumulation was dependent on IL-9, but not IL-13, a cytokine required for many aspects of allergic inflammation. In models of acute and chronic allergic inflammation, decreased IL-9 levels in mice with PU.1-deficient T cells corresponded to diminished tissue mast cell numbers and expression of mast cell proteases. Mice with PU.1-deficient T cells have defects in IL-9 production from CD4(+) T cells, but not natural killer T cells or innate lymphoid cells, suggesting a TH cell-dependent phenotype. Rag1(-/-) mice subjected to a chronic model of allergic inflammation displayed reduced mast cell infiltration comparable with accumulation in mice with PU.1-deficient T cells, emphasizing the importance of IL-9 produced by T cells in mast cell recruitment.

CONCLUSION

TH9 cells are a major source of IL-9 in models of allergic inflammation and play an important role in mast cell accumulation and activation.

Approaches for analyzing the roles of mast cells and their proteases in vivo

The roles of mast cells in health and disease remain incompletely understood. While the evidence that mast cells are critical effector cells in IgE-dependent anaphylaxis and other acute IgE-mediated allergic reactions seems unassailable, studies employing various mice deficient in mast cells or mast cell-associated proteases have yielded divergent conclusions about the roles of mast cells or their proteases in certain other immunological responses. Such "controversial" results call into question the relative utility of various older versus newer approaches to ascertain the roles of mast cells and mast cell proteases in vivo. This review discusses how both older and more recent mouse models have been used to investigate the functions of mast cells and their proteases in health and disease. We particularly focus on settings in which divergent conclusions about the importance of mast cells and their proteases have been supported by studies that employed different models of mast cell or mast cell protease deficiency. We think that two major conclusions can be drawn from such findings: (1) no matter which models of mast cell or mast cell protease deficiency one employs, the conclusions drawn from the experiments always should take into account the potential limitations of the models (particularly abnormalities affecting cell types other than mast cells) and (2) even when analyzing a biological response using a single model of mast cell or mast cell protease deficiency, details of experimental design are critical in efforts to define those conditions under which important contributions of mast cells or their proteases can be identified.

Parasitic nematode-induced CD4+Foxp3+T cells can ameliorate allergic airway inflammation

Background

The recruitment of CD4⁺CD25⁺Foxp3⁺T (T_reg) cells is one of the most important mechanisms by which parasites down-regulate the immune system.

Methodology/Principal Findings

We compared the effects of T_reg cells from Trichinella spiralis-infected mice and uninfected mice on experimental allergic airway inflammation in order to understand the functions of parasite-induced T_reg cells. After four weeks of T. spiralis infection, we isolated Foxp3-GFP-expressing cells from transgenic mice using a cell sorter. We injected CD4⁺Foxp3⁺ cells from T. spiralis-infected [Inf(+)Foxp3⁺] or uninfected [Inf(-)Foxp3⁺] mice into the tail veins of C57BL/6 mice before the induction of inflammation or during inflammation. Inflammation was induced by ovalbumin (OVA)-alum sensitization and OVA challenge. The concentrations of the Th2-related cytokines IL-4, IL-5, and IL-13 in the bronchial alveolar lavage fluid and the levels of OVA-specific IgE and IgG1 in the serum were lower in mice that received intravenous application of Inf(+)Foxp3⁺ cells [IV(inf):+(+) group] than in control mice. Some features of allergic airway inflammation were ameliorated by the intravenous application of Inf(-)Foxp3⁺ cells [IV(inf):+(-) group], but the effects were less distinct than those observed in the IV(inf):+(+) group. We found that Inf(+)Foxp3⁺ cells migrated to inflammation sites in the lung and expressed higher levels of T_reg-cell homing receptors (CCR5 and CCR9) and activation markers (Klrg1, Capg, GARP, Gzmb, OX40) than did Inf(-)Foxp3⁺ cells.

Conclusion/Significance

T. spiralis infection promotes the proliferation and functional activation of T_reg cells. Parasite-induced T_reg cells migrate to the inflammation site and suppress immune responses more effectively than non-parasite-induced T_reg cells. The adoptive transfer of Inf(+)Foxp3⁺ cells is an effective method for the treatment and prevention of allergic airway diseases in mice and is a promising therapeutic approach for the treatment of allergic airway diseases.

Many studies have investigated the down-regulation of the immune system by parasite infection. CD4⁺CD25⁺Foxp3⁺T (T_reg) cells are key players in parasite-mediated immune downregulation. Our previous study suggested that T_reg cells recruited by Trichinella spiralis infection were the key cells mediating the amelioration of allergic airway inflammation in mice. In the present study, we investigated the functions of parasite-induced T_reg cells using mice expressing GFP-tagged Foxp3. T. spiralis infection increased the number of T_reg cells. Adoptive transfer of the parasite-induced T_reg cells to mice with allergic airway inflammation ameliorated allergic airway inflammation. The transferred cells were recruited to inflammation sites in the lung. Cells from parasite-infected mice expressed higher levels of T_reg-cell homing receptors and activation markers than did cells from uninfected mice. This study might help explain why immune disorders (often of unknown cause) are more prevalent among people in developed countries (areas with low parasite infection) than among those in developing countries (areas with parasite epidemics). Our finding might improve current cell therapy techniques and facilitate the development of new techniques that use parasites or parasite-borne materials to treat diverse immune disorders.

Inhibition of spleen tyrosine kinase attenuates allergen-mediated airway constriction

Spleen tyrosine kinase (SYK) is a key activator of signaling pathways downstream of multiple surface receptors implicated in asthma. SYK function has been extensively studied in mast cells downstream of the high-affinity IgE receptor, FcεR1. Preclinical studies have demonstrated a role for SYK in models of allergic inflammation, but a role in airway constriction has not been demonstrated. Here, we have used a potent and selective pharmacological inhibitor of SYK to determine the role of SYK in allergen-mediated inflammation and airway constriction in preclinical models. Attenuation of allergic airway responses was evaluated in a rat passive anaphylaxis model and rat and sheep inhaled allergen challenge models, as well as an ex vivo model of allergen-mediated airway constriction in rats and cynomolgus monkeys. Pharmacological inhibition of SYK dose-dependently blocked IgE-mediated tracheal plasma extravasation in rats. In a rat ovalbumin-sensitized airway challenge model, oral dosing with an SYK inhibitor led to a dose-dependent reduction in lung inflammatory cells. Ex vivo analysis of allergen-induced airway constriction in ovalbumin-sensitized brown Norway rats showed a complete attenuation with treatment of a SYK inhibitor, as well as a complete block of allergen-induced serotonin release. Similarly, allergen-mediated airway constriction was attenuated in ex vivo studies from nonhuman primate lungs. Intravenous administration of an SYK inhibitor attenuated both early- and late-phase allergen-induced increases in airway resistance in an Ascaris-sensitive sheep allergen challenge model. These data support a key role for SYK signaling in mediating allergic airway responses.

Insights into mast cell functions in asthma using mouse models

Therapeutics targeting specific mechanisms of asthma have shown promising results in mouse models of asthma. However, these successes have not transferred well to the clinic or to the treatment of asthma sufferers. We suggest a reason for this incongruity is that mast cell-dependent responses, which may play an important role in the pathogenesis of both atopic and non-atopic asthma, are not a key component in most of the current asthma mouse models. Two reasons for this are that wild type mice have, in contrast to humans, a negligible number of mast cells localized in the smaller airways and in the parenchyma, and that only specific protocols show mast cell-dependent reactions. The development of mast cell-deficient mice and the reconstitution of mast cells within these mice have opened up the possibility to generate mouse models of asthma with a marked role of mast cells. In addition, mast cell-deficient mice engrafted with mast cells have a distribution of mast cells more similar to humans. In this article we review and highlight the mast cell-dependent and -independent responses with respect to airway hyperresponsiveness and inflammation in asthma models using mast cell-deficient and mast cell-engrafted mice.

The receptor LMIR3 negatively regulates mast cell activation and allergic responses by binding to extracellular ceramide

Mast cells (MCs) are key effector cells in allergic reactions. However, the inhibitory mechanism that prevents excessive activation of MCs remains elusive. Here we show that leukocyte mono-immunoglobulin-like receptor 3 (LMIR3; also called CD300f) is a negative regulator of MC activation in vivo. LMIR3 deficiency exacerbated MC-dependent allergic responses in mice, including anaphylaxis, airway inflammation, and dermatitis. Both physical binding and functional reporter assays via an extracellular domain of LMIR3 showed that several extracellular lipids (including ceramide) and lipoproteins were possible ligands for LMIR3. Importantly, MCs were frequently surrounded by extracellular ceramide in vivo. Upon engagement of high-affinity immunoglobulin E receptor, extracellular ceramide-LMIR3 binding inhibited MC activation via immunoreceptor tyrosine-based inhibitory and switch motifs of LMIR3. Moreover, pretreatment with LMIR3-Fc fusion protein or antibody against either ceramide or LMIR3 interfered with this binding in vivo, thereby exacerbating passive cutaneous anaphylaxis. Thus, the interaction between extracellular ceramide and LMIR3 suppressed MC-dependent allergic responses.

n-3 Long-chain PUFA reduce allergy-related mediator release by human mast cells in vitro via inhibition of reactive oxygen species

Increased n-6 and reduced n-3 long-chain PUFA (LC-PUFA) intake in Western diets may contribute to the increased prevalence of allergic diseases. Key effector cells in allergy are mast cells (MC). The aim of the present study was to investigate the effects of n-6 v. n-3 LC-PUFA on MC phenotype. Human MC lines (LAD2 and HMC-1) were incubated for 24 h with either arachidonic acid (AA, n-6 LC-PUFA) or the n-3 LC-PUFA EPA or DHA. The effects of these three LC-PUFA on degranulation, mediator secretion and reactive oxygen species (ROS) generation were assessed. ROS, mitogen-activated protein kinase (MAPK) or NF-κB inhibitors were used to unravel signalling pathways involved in cytokine secretion. AA, EPA or DHA did not reduce IgE-mediated degranulation by LAD2 cells. However, AA increased PGD₂ and TNF-α secretion by ionomycin/phorbol 12-myristate 13-acetate-stimulated HMC-1, whereas EPA and DHA more prominently inhibited IL-4 and IL-13 secretion. Suppression of IL-4 and IL-13 release by LC-PUFA correlated with reduced ROS generation. IL-4 and IL-13 release by activated HMC-1 was abrogated using ROS inhibitors. Inhibition of MAPK signalling, but not NF-κB, downstream of ROS reduced IL-13 secretion by activated HMC-1. Combined incubation of EPA or DHA with MAPK inhibitors further suppressed IL-13 secretion. In conclusion, the n-6 LC-PUFA AA enhanced pro-inflammatory mediator production by MC, while the n-3 LC-PUFA EPA as well as DHA more effectively suppressed ROS generation and IL-4 and IL-13 release. This suggests that dietary supplementation with EPA and/or DHA may alter the MC phenotype, contributing to a reduced susceptibility to develop and sustain allergic disease.

Susceptibility to vaccinia virus infection and spread in mice is determined by age at infection, allergen sensitization and mast cell status

BACKGROUND

Patients, especially young children, with atopic dermatitis are at an increased risk of developing eczema vaccinatum, a severe reaction to the smallpox vaccine, either through direct vaccination or indirect contact with a person recently vaccinated.

METHODS

Using a mouse model of infection, the severity of vaccinia-induced lesions was assessed from their appearance and viral DNA content. The response to vaccinia inoculation was assessed in young and adult mice, allergen-sensitized mice, and in mast cell-deficient mice.

RESULTS

Young age, sensitization to an allergen prior to infection, and a mast cell deficit, accomplished by using mast cell-deficient mice, resulted in more severe viral lesions at the site of inoculation, according to lesion appearance and viral DNA content. All three factors combined demonstrated maximal susceptibility, characterized by the severity of primary lesions and the development of secondary (satellite) lesions, as occurs in eczema vaccinatum in humans. Resistance to the appearance of satellite lesions could be restored by adoptive transfer of bone marrow-derived mast cells from either wild-type or cathelicidin-related antimicrobial peptide-deficient mice. Primary lesions were more severe following the latter transfer, indicating that cathelicidin-related antimicrobial peptide does contribute to the protective activity of mast cells against infection.

CONCLUSIONS

The combination of young age, allergen sensitization and a mast cell deficit resulted in the most severe lesions, including satellite lesions. Understanding the factors determining the relative resistance/sensitivity to vaccinia virus will aid in the development of strategies for preventing and treating adverse reactions which can occur after smallpox vaccination.

The αvβ6 integrin modulates airway hyperresponsiveness in mice by regulating intraepithelial mast cells

Allergic asthma is the most common form of asthma, affecting more than 10 million Americans. Although it is clear that mast cells have a key role in the pathogenesis of allergic asthma, the mechanisms by which they regulate airway narrowing in vivo remain to be elucidated. Here we report that mice lacking αvβ6 integrin are protected from exaggerated airway narrowing in a model of allergic asthma. Expression microarrays of the airway epithelium revealed mast cell proteases among the most prominent differentially expressed genes, with expression of mouse mast cell protease 1 (mMCP-1) induced by allergen challenge in WT mice and expression of mMCP-4, -5, and -6 increased at baseline in β6-deficient mice. These findings were most likely explained by loss of TGF-β activation, since the epithelial integrin αvβ6 is a critical activator of latent TGF-β, and in vitro-differentiated mast cells showed TGF-β-dependent expression of mMCP-1 and suppression of mMCP-4 and -6. In vitro, mMCP-1 increased contractility of murine tracheal rings, an effect that depended on intact airway epithelium, whereas mMCP-4 inhibited IL-13-induced epithelial-independent enhancement of contractility. These results suggest that intraepithelial activation of TGF-β by the αvβ6 integrin regulates airway responsiveness by modulating mast cell protease expression and that these proteases and their proteolytic substrates could be novel targets for improved treatment of allergic asthma.

Mast cells in lung inflammation

Mast cells play an important role in the lung in both health and disease. Their primary role is to initiate an appropriate program of inflammation and repair in response to tissue damage initiated by a variety of diverse stimuli. They are important for host immunity against bacterial infection and potentially in the host immune response to non small cell lung cancer. In situations of ongoing tissue damage, the sustained release of numerous pro-inflammatory mediators, proteases and cytokines, contributes to the pathophysiology of lung diseases such as asthma and interstitial lung disease. A key goal is the development of treatments which attenuate adverse mast cell function when administered chronically to humans in vivo. Such therapies may offer a novel approach to the treatment of many life-threatening diseases.

Mast cells and the development of allergic airway disease

Murine models have highlighted the importance of T-cells and T_H2 cytokines in development of allergen-induced airway disease. In contrast, the role of mast cells for the development of allergic airway disease has been controversial. Recent studies in murine models demonstrate a significant contribution of mast cells during the development of airway hyperresponsiveness and airway inflammation. Furthermore these models have allowed identifying certain mast cell-produced mediators (e.g. histamine and leukotriene B4) to be involved in the recruitment of effector T-cells into the lung. Additionally, mast cell-produced TNF can directly activate T_H2 cells and contribute to the development of allergic airway disease. These new findings demonstrate a complex role of mast cells and their mediators, not only as effector cells, but also during sensitization and development of allergic airway disease. Therefore mast cells and certain mast cell-produced mediators might be an interesting target for the prevention and treatment of allergic asthma.

Phospholipase C-β3 regulates FcɛRI-mediated mast cell activation by recruiting the protein phosphatase SHP-1

Mast cells are major effectors in high-affinity IgE receptor (FcɛRI)-dependent allergic reactions. Here we show that phospholipase C (PLC)-β3 is crucial for FcɛRI-mediated mast cell activation. Plcb3(-/-) mice showed blunted FcɛRI-dependent late-phase, but not acute, anaphylactic responses and airway inflammation. Accordingly, FcɛRI stimulation of Plcb3(-/-) mast cells exhibited reduced cytokine production but normal degranulation. Reduced cytokine production in Plcb3(-/-) cells could be accounted for by increased activity of the negative regulatory Src family kinase Lyn and reduced activities of the positive regulatory protein kinases MAPKs. Mechanistically, PLC-β3 constitutively interacts with FcɛRI, Lyn, and SHP-1 (protein phosphatase). SHP-1 probably recognizes its substrates Lyn and MAPKs via the recently described kinase tyrosine-based inhibitory motif, KTIM. Consistent with PLC-β3- and SHP-1-mediated repression of Lyn activity by dephosphorylation at Tyr396, FcɛRI-mediated phenotypes were similar in Plcb3(-/-) and SHP-1 mutant mast cells. Thus, we have defined a PLC-β3- and SHP-1-mediated signaling pathway for FcɛRI-mediated cytokine production.

Genetic variation determines mast cell functions in experimental asthma

Mast cell-deficient mice are a key for investigating the function of mast cells in health and disease. Allergic airway disease induced as a Th2-type immune response in mice is employed as a model to unravel the mechanisms underlying inception and progression of human allergic asthma. Previous work done in mast cell-deficient mouse strains that otherwise typically mount Th1-dominated immune responses revealed contradictory results as to whether mast cells contribute to the development of airway hyperresponsiveness and airway inflammation. However, a major contribution of mast cells was shown using adjuvant-free protocols to achieve sensitization. The identification of a traceable genetic polymorphism closely linked to the Kit(W-sh) allele allowed us to generate congenic mast cell-deficient mice on a Th2-prone BALB/c background, termed C.B6-Kit(W-sh). In accordance with the expectations, C.B6-Kit(W-sh) mice do not develop IgE- and mast cell-dependent passive cutaneous anaphylaxis. Yet, unexpectedly, C.B6-Kit(W-sh) mice develop full-blown airway inflammation, airway hyperresponsiveness, and mucus production despite the absence of mast cells. Thus, our findings demonstrate a major influence of genetic background on the contribution of mast cells in an important disease model and introduce a novel strain of mast cell-deficient mice.

Zebrafish mast cells possess an FcɛRI-like receptor and participate in innate and adaptive immune responses

We previously identified a zebrafish mast cell (MC) lineage and now aim to determine if these cells function analogously in innate and adaptive immunity like their mammalian counterparts. Intraperitoneal (IP) injection of compound 48/80 or live Aeromonas salmonicida resulted in significant MC degranulation evident histologically and by increased plasma tryptase compared with saline-injected controls (p=0.0006, 0.005, respectively). Pre-treatment with ketotifen abrogated these responses (p=0.0004, 0.005, respectively). Cross-reactivity was observed in zebrafish to anti-human high-affinity IgE receptor gamma (FcɛRIγ) and IgE heavy chain-directed antibodies. Whole mount in situ hybridization on 7-day embryos demonstrated co-localization of cpa5, a MC-specific marker, with myd88, a toll-like receptor adaptor, and zebrafish FcɛRI subunit homologs. Zebrafish injected IP with matched dinitrophenyl-sensitized mouse (anti-DNP) IgE and DNP-BSA or trinitrophenyl-sensitized mouse (anti-TNP) IgE and TNP-BSA demonstrated increased plasma tryptase compared with mismatched controls (p=0.03, 0.010, respectively). These results confirm functional conservation and validate the zebrafish model as an in vivo screening tool for novel MC modulating agents.

Mast cells in allergic asthma and beyond

Mast cells have been regarded for a long time as effector cells in IgE mediated type I reactions and in host defence against parasites. However, they are resident in all environmental exposed tissues and express a wide variety of receptors, suggesting that these cells can also function as sentinels in innate immune responses. Indeed, studies have demonstrated an important role of mast cells during the induction of life-saving antibacterial responses. Furthermore, recent findings have shown that mast cells promote and modulate the development of adaptive immune responses, making them an important hinge of innate and acquired immunity. In addition, mast cells and several mast cell-produced mediators have been shown to be important during the development of allergic airway diseases. In the present review, we will summarize findings on the role of mast cells during the development of adaptive immune responses and highlight their function, especially during the development of allergic asthma.

Peanut-induced intestinal allergy is mediated through a mast cell-IgE-FcepsilonRI-IL-13 pathway

BACKGROUND

Although implicated in the disease, the specific contributions of FcepsilonRI and IL-13 to the pathogenesis of peanut-induced intestinal allergy are not well defined.

OBJECTIVES

We sought to determine the contributions of FcepsilonRI, IL-13, and mast cells to the development of intestinal mucosal responses in a murine model of peanut-induced intestinal allergy.

METHODS

Sensitized wild-type (WT), FcepsilonRI-deficient (FcepsilonRI(-/-)), and mast cell-deficient (Kit(W-sh/W-sh)) mice received peanut orally every day for 1 week. Bone marrow-derived mast cells (BMMCs) from WT, FcepsilonRI(-/-), IL-4(-/-), IL-13(-/-), and IL-4/IL-13(-/-) mice were differentiated and transferred into WT, FcepsilonRI(-/-), and Kit(W-sh/W-sh) recipients. BMMCs from WT and UBI-GFP/BL6 mice were differentiated and transferred into WT and Kit(W-sh/W-sh) mice. Blockade of IL-13 was achieved by using IL-13 receptor alpha2 (IL-13Ralpha2)-IgG fusion protein.

RESULTS

FcepsilonRI(-/-) mice showed decreased intestinal inflammation (mast cell and eosinophil numbers) and goblet cell metaplasia and reduced levels of IL4, IL6, IL13, and IL17A mRNA expression in the jejunum. Transfer of WT BMMCs to FcepsilonRI(-/-) recipients restored their ability to develop intestinal allergic responses unlike transfer of FcepsilonRI(-/-), IL-13(-/-), or IL-4/IL-13(-/-) BMMCs. FcepsilonRI(-/-) mice exhibited lower IL-13 levels and treatment of WT mice with IL-13 receptor alpha2 prevented peanut-induced intestinal allergy and inflammation.

CONCLUSIONS

These data indicate that the development of peanut-induced intestinal allergy is mediated through a mast cell-dependent IgE-FcepsilonRI-IL-13 pathway. Targeting IL-13 might be a potential treatment for IgE-mediated peanut-induced allergic responses in the intestine.

The many paths to asthma: phenotype shaped by innate and adaptive immunity

Asthma is a very complex and heterogeneous disease that is characterized by airway inflammation and airway hyper-reactivity (AHR). The pathogenesis of asthma is associated with environmental factors, many cell types, and several molecular and cellular pathways. These include allergic, non-allergic and intrinsic pathways, which involve many cell types and cytokines. Animal models of asthma have helped to clarify some of the underlying mechanisms of asthma, demonstrating the importance of T helper type 2 (T(H)2)-driven allergic responses, as well as of the non-allergic and intrinsic pathways, and contributing to understanding of the heterogeneity of asthma. Further study of these many pathways to asthma will greatly increase understanding of the distinct asthma phenotypes, and such studies may lead to new therapies for this important public health problem.

Airway smooth muscle modulation and airway hyper-responsiveness in asthma: new cellular and molecular paradigms

There is growing evidence indicating the existence of a causal relationship between abnormal airway smooth muscle (ASM) function and airway hyper-responsiveness, a poorly understood feature of asthma that can be defined as an excessive bronchospastic response. In recent years, there has been a veritable explosion of articles suggesting that ASM exposed to proasthmatic cytokines can elicit a hyper-responsive state to contractile G-protein-coupled receptor (GPCR) agonists. Aberrant airway responsiveness could result from abnormal calcium signaling, with changes occurring at various levels of GPCR-associated signal transduction. This review presents the latest observations describing novel mechanistic models that could explain the involvement of ASM in airway hyper-responsiveness. This review will discuss the role of ASM in beta(2)-agonist-mediated bronchial hyper-responsiveness and the clinical significance of cell-cell contact between ASM and mast cells recently described to be intimately infiltrated within the ASM tissues in asthmatic patients. The possibility that allergens could trigger airway hyper-responsiveness by directly acting on ASM via activation of immunoglobulin E receptors, FcepsilonRI and FCepsilonRII will also be discussed. These important findings further support the notion that targeting ASM could offer new treatment for many features of asthma, including airway hyper-responsiveness. Future therapeutic intervention includes: the prevention of ASM-inflammatory cell physical and/or functional interaction, the inhibition of Immunoglobulin E receptor-dependent signal transduction, and the abrogation of cytokine-dependent pathways that modulate receptor-associated calcium metabolism.

SHP-1 deficient mast cells are hyperresponsive to stimulation and critical in initiating allergic inflammation in the lung

Phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP-1)-deficient mice display an allergic asthma phenotype that is largely IL-13 and STAT6 dependent. The cell types responsible for the Th2 phenotype have not been identified. We hypothesized that SHP-1 deficiency leads to mast cell dysregulation and increased production and release of mediators and Th2 cytokines, leading to the allergic asthma phenotype. We examined SHP-1 regulation of mast cell differentiation, survival, and functional responses to stimulation using bone marrow-derived mast cells from viable motheaten (mev) mice. We assessed pulmonary phenotypical changes in mev mice on the mast cell-deficient Kit(W-Sh) genetic background. The results showed that SHP-1 deficiency led to increased differentiation and survival, but reduced proliferation, of mast cells. SHP-1-deficient mast cells produced and released increased amounts of mediators and Th2 cytokines IL-4 and -13 spontaneously and in response to H(2)O(2), LPS, and Fc epsilonI cross-linking, involving c-Kit-dependent and -independent processes. The Fc epsilonRI signaling led to binding of SHP-1 to linker for activation of T cells 2 and enhanced linker for activation of T cells 2 phosphorylation in mev bone marrow-derived mast cells. Furthermore, the number of mast cells in the lung tissue of mev mice was increased and mast cell production and release of Th2 cytokines were distinctly increased upon Fc epsilonRI stimulation. When backcrossed to the Kit(W-Sh) background, mev mice had markedly reduced pulmonary inflammation and Th2 cytokine production. These findings demonstrate that SHP-1 is a critical regulator of mast cell development and function and that SHP-1-deficient mast cells are able to produce increased Th2 cytokines and initiate allergic inflammatory responses in the lung.

Regulation of human mast cell and basophil function by anaphylatoxins C3a and C5a

Allergic diseases such as asthma result from inappropriate immunologic responses to common environmental allergens in genetically susceptible individuals. Following allergen exposure, interaction of dendritic cells (DC) with CD4(+) T cells leads to the production of Th2 cytokines, which induce B cells to synthesize IgE molecules (sensitization phase). These IgE molecules bind to their high affinity receptors (FcvarepsilonRI) on the surface of mast cells and basophils and their subsequent cross-linking by allergen results in the release of preformed and newly synthesized mediators, which cause bronchoconstriction, lung inflammation and airway hyperresponsiveness (AHR) in asthma (effector phase). The complement components C3a and C5a levels are increased in the lungs of patients with asthma and are likely generated via the actions of both allergen and mast cell proteases. In vivo studies with rodents have shown that while C3a facilitates allergen sensitization in some models C5a inhibits this response. Despite this difference, both anaphylatoxins promote lung inflammation and AHR in vivo indicating that cells other than DC and T cells likely mediate the functional effects of C3a and C5a in asthma. This review focuses on the contribution of C3a and C5a in the pathogenesis of asthma with a particular emphasis on mast cells and basophils. It discusses the mechanisms by which anaphylatoxins activate mast cells and basophils and the associated signaling pathways via which their receptors are regulated by priming and desensitization.

Mouse mast cell protease 4 is the major chymase in murine airways and has a protective role in allergic airway inflammation

It is widely established that mast cells (MCs) have a harmful role in asthma, for example by secreting various proinflammatory substances stored within their secretory granule. However, in this study, we show that one of the substances stored within MC granule, chymase, in fact has a protective role in allergic airway inflammation, indicating that MCs may possess both harmful and protective activities in connection with this type of disease. Wild-type (WT) mice and mice lacking mouse MC protease 4 (mMCP-4), a chymase that is functionally homologous to human chymase, were sensitized and challenged with OVA, followed by the assessment of airway physiology and inflammatory parameters. Our results show that the airway hyperresponsiveness was significantly higher in mMCP-4(-/-) as compared with WT mice. Moreover, the degree of lung tissue inflammation was markedly higher in mice lacking mMCP-4 than in WT controls. Histological analysis revealed that OVA sensitization/challenge resulted in a marked increased in the thickness of the smooth muscle cell (SMC) layer and, notably, that the degree of SMC layer thickening was more pronounced in mMCP-4(-/-) animals than in WT controls, thus indicating that chymase may have an effect on airway SMCs. In support of this, mMCP-4-positive MCs were located in the close vicinity of the SMC layer, mainly in the upper airways, and mMCP-4 was shown to be the major chymase expressed in these MCs. Taken together, our results indicate that chymase present in the upper airways protects against allergic airway responses, possibly by regulating SMCs.

Understanding asthma using animal models

Asthma is a complex syndrome with many clinical phenotypes in children and adults. Despite the rapidly increasing prevalence, clinical investigation and epidemiological studies of asthma, the successful introduction of new drugs has been limited due to the different disease phenotypes and ethical issues. Mouse models of asthma replicate many of the features of human asthma, including airway hyperreactivity, and airway inflammation. Therefore, examination of disease mechanisms in mice has been used to elucidate asthma pathology and to identify and evaluate new therapeutic agents. In this article, we discuss the various animal models of asthma with a focus on mouse strains, allergens, protocols, and outcome measurements.