IgE-dependent Mast Cell Activation Research Articles

Butyrate, Valerate, and Niacin Ameliorate Anaphylaxis by Suppressing IgE-Dependent Mast Cell Activation: Roles of GPR109A, PGE2, and Epigenetic Regulation.

Short-chain fatty acids (SCFAs) are produced by the intestinal microbiota during the fermentation of dietary fibers as secondary metabolites. Several recent studies reported that SCFAs modulate the development and function of immune-related cells. However, the molecular mechanisms by which SCFAs regulate mast cells (MCs) remain unclear. In the current study, we analyzed the function and gene expression of mouse MCs in the presence of SCFAs invitro and invivo. We found that the oral administration of valerate or butyrate ameliorated passive systemic anaphylaxis and passive cutaneous anaphylaxis in mice. The majority of SCFAs, particularly propionate, butyrate, valerate, and isovalerate, suppressed the IgE-mediated degranulation of bone marrow-derived MCs, which were eliminated by the Gi protein inhibitor pertussis toxin and by the knockdown of Gpr109a. A treatment with the HDAC inhibitor trichostatin A also suppressed IgE-mediated MC activation and reduced the surface expression level of FcεRI on MCs. Acetylsalicylic acid and indomethacin attenuated the suppressive effects of SCFAs on degranulation. The degranulation degree was significantly reduced by PGE2 but not by PGD2. Furthermore, SCFAs enhanced PGE2 release from stimulated MCs. The SCFA-mediated amelioration of anaphylaxis was exacerbated by COX inhibitors and an EP3 antagonist, but not by an EP4 antagonist. The administration of niacin, a ligand of GPR109A, alleviated the symptoms of passive cutaneous anaphylaxis, which was inhibited by cyclooxygenase inhibitors and the EP3 antagonist. We conclude that SCFAs suppress IgE-mediated activation of MCs invivo and invitro involving GPR109A, PGE2, and epigenetic regulation.

Cell-type-specific role of P2Y2 receptor in HDM-driven model of allergic airway inflammation.

Allergic airway inflammation (AAI) is a chronic respiratory disease that is considered a severe restriction in daily life and is accompanied by a constant risk of acute aggravation. It is characterized by IgE-dependent activation of mast cells, infiltration of eosinophils, and activated T-helper cell type 2 (Th2) lymphocytes into airway mucosa. Purinergic receptor signaling is known to play a crucial role in inducing and maintaining allergic airway inflammation. Previous studies in an ovalbumin (OVA)-alum mouse model demonstrated a contribution of the P2Y2 purinergic receptor subtype (P2RY2) in allergic airway inflammation. However, conflicting data concerning the mechanism by which P2RY2 triggers AAI has been reported. Thus, we aimed at elucidating the cell-type-specific role of P2RY2 signaling in house dust mite (HDM)-driven model of allergic airway inflammation. Thereupon, HDM-driven AAI was induced in conditional knockout mice, deficient or intact for P2ry2 in either alveolar epithelial cells, hematopoietic cells, myeloid cells, helper T cells, or dendritic cells. To analyze the functional role of P2RY2 in these mice models, flow cytometry of bronchoalveolar lavage fluid (BALF), cytokine measurement of BALF, invasive lung function measurement, HDM re-stimulation of mediastinal lymph node (MLN) cells, and lung histology were performed. Mice that were subjected to an HDM-based model of allergic airway inflammation resulted in reduced signs of acute airway inflammation including eosinophilia in BALF, peribronchial inflammation, Th2 cytokine production, and bronchial hyperresponsiveness in mice deficient for P2ry2 in alveolar epithelial cells, hematopoietic cells, myeloid cells, or dendritic cells. Furthermore, the migration of bone-marrow-derived dendritic cells and bone-marrow-derived monocytes, both deficient in P2ry2, towards ATP was impaired. Additionally, we found reduced levels of MCP-1/CCL2 and IL-8 homologues in the BALF of mice deficient in P2ry2 in myeloid cells and lower concentrations of IL-33 in the lung tissue of mice deficient in P2ry2 in alveolar epithelial cells. In summary, our results show that P2RY2 contributes to HDM-induced airway inflammation by mediating proinflammatory cytokine production in airway epithelial cells, monocytes, and dendritic cells and drives the recruitment of lung dendritic cells and monocytes.

Allergic Rhinitis: Pathophysiology and Treatment Focusing on Mast Cells.

Allergic rhinitis (AR) is a common rhinopathy that affects up to 30% of the adult population. It is defined as an inflammation of the nasal mucosa, develops in allergic individuals, and is detected mostly by a positive skin-prick test. AR is characterized by a triad of nasal congestion, rhinorrhea, and sneezing. Mast cells (MCs) are innate immune system effector cells that play a pivotal role in innate immunity and modulating adaptive immunity, rendering them as key cells of allergic inflammation and thus of allergic diseases. MCs are typically located in body surfaces exposed to the external environment such as the nasal mucosa. Due to their location in the nasal mucosa, they are in the first line of defense against inhaled substances such as allergens. IgE-dependent activation of MCs in the nasal mucosa following exposure to allergens in a sensitized individual is a cardinal mechanism in the pathophysiology of AR. This review is a comprehensive summary of MCs’ involvement in the development of AR symptoms and how classical AR medications, as well as emerging AR therapies, modulate MCs and MC-derived mediators involved in the development of AR.

TH9-derived IL-9 promotes CCR2-dependent mast cell accumulation in the allergic lung

Abstract Allergic asthma is a chronic lung disease characterized by airway hyperresponsiveness and cellular infiltration that is exacerbated by IgE-dependent mast cell activation. Our work in mouse models of allergic airway inflammation identified interleukin-9 (IL-9)-producing T helper 9 (TH9) cells as important effector cells in promoting mast cell accumulation in the lungs. However, the precise mechanism of IL-9-mediated mast cell expansion remains unclear. Here, we demonstrate that intranasal recombinant IL-9 expands, while blockade of IL-9 reduces, mast cell progenitor numbers in the lungs and the bone marrow. These findings suggests that there are systemic effects of local IL-9 production in the allergic lung. Using adoptive transfer models and newly generated mice with an inactivation of the IL-9 gene restricted to T cells generated by CD4-Cre/loxP-mediated targeting of the IL-9 gene, we show that TH9 cells promote mast cell progenitor and mature mast cell recruitment from the bone marrow to the lungs in a chemokine receptor 2-dependent manner. Our research further demonstrates that T cell-derived IL-9 is critical for mast cell-mediated airway hyperresponsiveness. Together, these findings define a contribution of T cell-derived IL-9 in promoting mast cell expansion and function in allergic airway inflammation. Therefore, IL-9 may be a promising therapeutic target for targeting mast cell-specific pathologies. Supported by grants from NIH (R01 AI129241, T32 AI060519)

Diverse immune mechanisms of allergen immunotherapy for allergic rhinitis with and without asthma

Allergen immunotherapy (AIT) is an effective treatment for allergic rhinitis, inducing long-term clinical tolerance to the sensitizing allergen. Clinical tolerance induction can be achieved when AIT is administered for at least 3 years. AIT is associated with the modulation of innate and adaptive immune systems. This comprises inhibition of IgE-dependent activation of mast cells and basophils in the local target organ, suppression of TH2 cells, immune deviation toward TH1 cells, induction of T and B regulatory cells, and production of allergen-neutralizing antibodies. However, recent developments in their underpinning mechanisms have revealed that AIT, administered subcutaneously or sublingually, induces immune regulation through novel cell targets and molecular mechanisms. This comprehensive review discusses how immune tolerance driven by subcutaneous immunotherapy and sublingual immunotherapy is associated with the induction of a novel regulatory subset of innate lymphoid cells and suppression of proinflammatory TH2, allergen-specific TH2 (TH2A), and T follicular helper cells. Moreover, they are associated with exhaustion of TH2A cells and differential expression of nasal and systemic IgA antibodies. Uncovering the underpinning mechanisms of a successful AIT and immune tolerance induction will allow the development of targeted therapeutics for allergic rhinitis with and without asthma.

Regulation of Trafficking and Signaling of the High Affinity IgE Receptor by FcεRIβ and the Potential Impact of FcεRIβ Splicing in Allergic Inflammation.

Mast cells are tissue-resident immune cells that function in both innate and adaptive immunity through the release of both preformed granule-stored mediators, and newly generated proinflammatory mediators that contribute to the generation of both the early and late phases of the allergic inflammatory response. Although mast cells can be activated by a vast array of mediators to contribute to homeostasis and pathophysiology in diverse settings and contexts, in this review, we will focus on the canonical setting of IgE-mediated activation and allergic inflammation. IgE-dependent activation of mast cells occurs through the high affinity IgE receptor, FcεRI, which is a multimeric receptor complex that, once crosslinked by antigen, triggers a cascade of signaling to generate a robust response in mast cells. Here, we discuss FcεRI structure and function, and describe established and emerging roles of the β subunit of FcεRI (FcεRIβ) in regulating mast cell function and FcεRI trafficking and signaling. We discuss current approaches to target IgE and FcεRI signaling and emerging approaches that could target FcεRIβ specifically. We examine how alternative splicing of FcεRIβ alters protein function and how manipulation of splicing could be employed as a therapeutic approach. Targeting FcεRI directly and/or IgE binding to FcεRI are promising approaches to therapeutics for allergic inflammation. The characteristic role of FcεRIβ in both trafficking and signaling of the FcεRI receptor complex, the specificity to IgE-mediated activation pathways, and the preferential expression in mast cells and basophils, makes FcεRIβ an excellent, but challenging, candidate for therapeutic strategies in allergy and asthma, if targeting can be realized.

The regulatory mechanisms of IgE-dependent and independent mast cell activation and allergic responses

The regulatory mechanisms of IgE-dependent and independent mast cell activation and allergic responses

Tuning IgE: IgE-Associating Molecules and Their Effects on IgE-Dependent Mast Cell Reactions

The recent emergence of anti-immunoglobulin E (IgE) drugs and their candidates for humans has endorsed the significance of IgE-dependent pathways in allergic disorders. IgE is distributed locally in the tissues or systemically to confer a sensory mechanism in a domain of adaptive immunity to the otherwise innate type of effector cells, namely, mast cells and basophils. Bound on the high-affinity IgE receptor FcεRI, IgE enables fast memory responses against revisiting threats of venoms, parasites, and bacteria. However, the dysregulation of IgE-dependent reactions leads to potentially life-threatening allergic diseases, such as asthma and anaphylaxis. Therefore, reactivity of the IgE sensor is fine-tuned by various IgE-associating molecules. In this review, we discuss the mechanistic basis for how IgE-dependent mast cell activation is regulated by the IgE-associating molecules, including the newly developed therapeutic candidates.

Na+/H+ exchanger regulatory factor 1 (NHERF1) enhances MRGPRX2-mediated mast cell anaphylaxis

Abstract Anaphylaxis is a severe life-threatening allergic reaction that is caused by mast cell hyperactivity. Two different mast cell receptors play critical roles in mediating anaphylaxis: 1) the IgE receptor that is stimulated by IgE-bound allergen and 2) the MRGPRX2 receptor that can bind to several cationic molecules and FDA-approved drugs resulting in mast cell activation. Activated mast cells degranulate to release proinflammatory mediators. We have recently identified that Na+/H+ exchanger regulatory factor 1 (NHERF1) regulates IgE-dependent mast cell activation in vitro and promotes passive cutaneous anaphylaxis (PCA) and passive systemic anaphylaxis (PSA) in vivo. In the current study, we investigated the role of this adapter molecule in affecting IgE-independent mast cell activation via the MrgprB2 (mouse orthologue of human MRGPRX2) receptor using a novel mouse strain, Cpa3-Cre+ NHERF1fl/fl that lacks NHERF1 in mast cells. PCA and PSA to compound 48/80 (a known MrgprB2 agonist) were significantly attenuated in the Cpa3-Cre+ NHERF1fl/fl mice as compared to control Cpa3-Cre− NHERF1fl/fl mice. In agreement with our in vivo data, peritoneal mast cells isolated from Cpa3-Cre+ NHERF1fl/fl mice showed a significant reduction in mast cell degranulation to the MrgprB2 ligands, compound 48/80 and substance P. Additionally, NHERF1-silenced human LAD2 mast cells showed decreased degranulation to these ligands as well. Collectively, our data suggests that NHERF1 promotes mast cell activation though the MRGPRX2/MrgprB2 receptor and determining the mechanisms through which NHERF1 modulates MRGPRX2 responses will lend insights into the development of new therapeutics for anaphylaxis and other allergic diseases.

Immunological Responses and Biomarkers for Allergen-Specific Immunotherapy Against Inhaled Allergens

Long-term efficacy that occurs with allergen immunotherapy of proven value is associated with decreases in IgE-dependent activation of mast cells and tissue eosinophilia. This suppression of type 2 immunity is accompanied by early induction of regulatory T cells, immune deviation in favor of TH1 responses, and induction of local and systemic IgG, IgG4, and IgA antibodies. These "protective" antibodies can inhibit allergen-IgE complex formation and consequent mast cell triggering and IgE-facilitated TH2-cell activation. Recent studies have highlighted the importance of innate responses mediated by type 2 dendritic cells and innate lymphoid cells in allergic inflammation. These cell types are under the regulation of cytokines such as thymic stromal lymphopoietin and IL-33 derived from the respiratory epithelium. Novel subsets of regulatory cells induced by immunotherapy include IL-35-producing regulatory T cells, regulatory B cells, a subset of T follicular regulatory cells, and IL-10-producing group 2 innate lymphoid cells. These mechanisms point to biomarkers that require testing for their ability to predict clinical response to immunotherapy and to inform novel approaches for better efficacy, safety, and long-term tolerance.

A monoclonal antibody to Siglec-8 suppresses non-allergic airway inflammation and inhibits IgE-independent mast cell activation

In addition to their well characterized role in mediating IgE-dependent allergic diseases, aberrant accumulation and activation of mast cells (MCs) is associated with many non-allergic inflammatory diseases, whereby their activation is likely triggered by non-IgE stimuli (e.g., IL-33). Siglec-8 is an inhibitory receptor expressed on MCs and eosinophils that has been shown to inhibit IgE-mediated MC responses and reduce allergic inflammation upon ligation with a monoclonal antibody (mAb). Herein, we evaluated the effects of an anti-Siglec-8 mAb (anti-S8) in non-allergic disease models of experimental cigarette-smoke-induced chronic obstructive pulmonary disease and bleomycin-induced lung injury in Siglec-8 transgenic mice. Therapeutic treatment with anti-S8 inhibited MC activation and reduced recruitment of immune cells, airway inflammation, and lung fibrosis. Similarly, using a model of MC-dependent, IL-33-induced inflammation, anti-S8 treatment suppressed neutrophil influx, and cytokine production through MC inhibition. Transcriptomic profiling of MCs further demonstrated anti-S8-mediated downregulation of MC signaling pathways induced by IL-33, including TNF signaling via NF-κB. Collectively, these findings demonstrate that ligating Siglec-8 with an antibody reduces non-allergic inflammation and inhibits IgE-independent MC activation, supporting the evaluation of an anti-Siglec-8 mAb as a therapeutic approach in both allergic and non-allergic inflammatory diseases in which MCs play a role.

Blocking of mast cell-mediated passive anaphylaxis to peanut using covalent heterobivalent inhibitor in a humanized mouse model

Abstract Anaphylaxis to peanut allergen is a severe hypersensitive allergic reaction characterized by life-threatening symptoms. Anaphylaxis is mediated by IgE-dependent mast cell activation that leads to the release of inflammatory mediators. In a previous report, we described the design of a covalent heterobivalent inhibitor (cHBI) that selectively forms covalent bonds with allergen specific-IgE (sIgE) on mast cells and abates allergic reactions in ex-vivo peanut challenges. Here, we utilized a humanized mouse model to recapitulate key features of anaphylaxis to peanut in humans, and we examined the efficacy of cHBI in blocking the anaphylactic reaction in this model. NSGS (NOD-scid Il2rgnull IL-3/GM-CSF/SCF) mice engrafted with human hematopoietic stem cells were treated with an allergen-specific human IgE monoclonal antibody and then challenged with a peanut allergen. We found that the peanut-challenged humanized mice can develop rapid anaphylaxis and mast cell degranulation following challenge. The anaphylactic reaction was characterized by a substantial decline of core body temperatures and upregulation of human mast cell degranulation markers. Additionally, we found that the severity of the anaphylactic reaction is hIgE dose-dependent. Most importantly, cHBI protected the mice from developing an anaphylactic reaction demonstrating the ability of cHBI to block IgE-mediated allergic reactions in the humanized mice. Overall, our results show that the humanized mouse model is a novel model to study human mast cell IgE-mediated allergic reactions and demonstrate that cHBI is an effective potential therapeutic inhibitor for food allergy.

Resveratrol inhibits IL-33\u2013mediated mast cell activation by targeting the MK2/3\u2013PI3K/Akt axis

Interleukin-33 (IL-33)/ST2–mediated mast cell activation plays important roles in the pathophysiology of allergic diseases. Hence, pharmacologically targeting the IL-33/ST2 pathway in mast cells could help to treat such diseases. We found that resveratrol inhibits IL-33/ST2–mediated mast cell activation. Resveratrol suppressed IL-33–induced IL-6, IL-13, and TNF-α production in mouse bone marrow–derived mast cells (BMMCs), mouse fetal skin–derived mast cells, and human basophils. Resveratrol also attenuated cytokine expression induced by intranasal administration of IL-33 in mouse lung. IL-33–mediated cytokine production in mast cells requires activation of the NF-κB and MAPK p38–MAPK-activated protein kinase-2/3 (MK2/3)–PI3K/Akt pathway, and resveratrol clearly inhibited IL-33–induced activation of the MK2/3–PI3K/Akt pathway, but not the NF-κB pathway, without affecting p38 in BMMCs. Importantly, resveratrol inhibited the kinase activity of MK2, and an MK2/3 inhibitor recapitulated the suppressive effects of resveratrol. Resveratrol and an MK2/3 inhibitor also inhibited IgE-dependent degranulation and cytokine production in BMMCs, concomitant with suppression of the MK2/3–PI3K/Akt pathway. These findings indicate that resveratrol inhibits both IL-33/ST2–mediated and IgE-dependent mast cell activation principally by targeting the MK2/3–PI3K/Akt axis downstream of p38. Thus, resveratrol may have potential for the prevention and treatment of broad ranges of allergic diseases.

Suppressive role of PPARγ in the IgE-dependent activation of mast cells.

Mast cells (MCs) play a central role in IgE-dependent immune responses. PPARγ is a nuclear receptor that is essential for adipocyte differentiation and insulin sensitivity. Although PPARγ is expressed in activated MCs, the effect of PPARγ suppression in IgE-mediated activation of MCs is largely unknown. In the current study, we evaluated the effect of PPARγ knockdown on the function of IgE plus antigen (Ag)-stimulated MCs using siRNA-transfected bone marrow-derived MCs (BMMCs). We found that the mRNA expression level of cytokines in IgE/Ag-stimulated BMMCs was significantly increased in PPARγ knockdown BMMCs, and IgE/Ag-mediated degranulation and the protein production level of TNF-α was moderately increased by PPARγ knockdown, whereas the cell surface expression level of FcεRI was not affected by PPARγ knockdown. Oral administration of pioglitazone (PPARγ agonist) significantly suppressed body temperature change of mice in passive systemic anaphylaxis, supporting the inhibitory functions of PPARγ in IgE/Ag-dependent activation of MCs in vivo. IgE-mediated up-regulation of mRNA levels of Ptgs2 (encoding COX-2) was drastically enhanced in PPARγ knockdown BMMCs. Although several prostaglandin (PG) derivatives are known to be ligands for PPARγ, treatment with a COX inhibitor, acetyl salicylic acid, up-regulated the IgE-mediated increase of Il13, Tnf and Ptgs2 mRNA levels in a synergistic manner with PPARγ siRNA. Knockdown of COX-1 and/or COX-2 by siRNA showed that suppression of IgE/Ag-mediated activation was mainly dependent on COX-1. Taken together, these results indicate that PPARγ suppresses IgE/Ag-induced transactivation of cytokine genes and the Ptgs2 gene in MCs in a manner distinguishable from that of PGs.

Dampening of mast cell secondary responses to allergen involves specific signalling and epigenetic changes

Allergic diseases are increasing worldwide. Allergen and IgE dependent mast cell (MC) activation is the major initiator of these clinical symptoms. During this study, the effect of multiple exposures to the same allergen, on MC degranulation was studied. First, MC recovery in terms of surface expression of high affinity receptor FcεRI, and granule content after a primary allergen challenge was confirmed. Overall, previous exposure of MCs to allergen challenge led to a significant reduction in pre-stored mediator release during the secondary challenge at various time points and with various doses of allergen in vitro. The dampened response was not due to any defects in very early steps in signalling involving FcεRI activation. Inhibition of dampening response during secondary challenge by various inhibitors like wortmannin, tranylcypromine and pargyline, indicated the involvement of PI3K signalling and chromatin modifications. Our study provides insight into new therapeutic avenues for treating allergic disorders targeting MCs.

IgE-mediated mast cell activation promotes inflammation and cartilage destruction in osteoarthritis.

This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Histamine-releasing factor (HRF) is a novel alarmin

Abstract Objective We are investigating how HRF secretion is regulated during allergic conditions. Results HRF interacts with a subset of IgE molecules. HRF dimer and oligomers, but not monomer, enhance the antigen sensitivity and magnitude of IgE-dependent mast cell activation. We found that BEAS-2B human bronchial epithelial cells constitutively secrete various forms of HRF (monomer, disulfide-linked dimer/oligomers). Secretion of these forms of HRF was enhanced by allergens such as house dust mites (HDM). HDM-mediated HRF secretion was dramatically enhanced by epithelial-derived cytokines (IL-25, IL-33, TSLP), Th2 cytokines (IL-4, IL-5, IL-13), and proinflammatory cytokines (IL-1b, IL-6, TNF), although the cytokines alone had much less effects. Mechanical injury of BEAS-2B cells and its byproducts (i.e., adenosine and ATP) also enhanced HRF secretion. In contrast, papain and bromelain (occupational allergens) as well as uric acid (NLRP3 inflammasome activator) exhibited limited effects on HRF secretion. Several high-molecular-weight forms (≥150 kDa) of HRF were found in body fluids. Interestingly, rhinovirus infection in humans and nasal instillation of HDM in mice, conditions predisposing asthma exacerbation, induced secretion of these HRF forms into airways. These results suggest that disulfide-linked HRF dimer/oligomers are involved in asthma exacerbation. Conclusion HRF dimer/oligomers secreted by epithelial and other cells enhance allergic inflammation as a novel alarmin.

Recruiting CD33 on mast cells to inhibit IgE-mediated mast cell-dependent anaphylaxis.

IgE-mediated activation of mast cells is a hallmark of an anaphylactic reaction to allergen. In this issue of the JCI, Duan et al. describe an approach for suppressing IgE-dependent mast cell activation, thereby suppressing anaphylaxis. Specifically, the authors show that delivery of liposomes containing both the specific antigen recognized by the mast cell-bound IgE and a high-affinity glycan ligand of the inhibitory receptor CD33 (CD33L) to targeted mast cells inhibits antigen-induced, FcεRI-dependent spleen tyrosine kinase (Syk) phosphorylation and downstream protein tyrosine kinase (PTK) phosphorylation, Ca++ flux, and β-hexosaminidase release (i.e., degranulation). However, this strategy only worked if both the antigen (reactive with the mast cell-bound IgE) and CD33L were on the same liposome. This approach promises to rapidly reduce IgE-dependent mast cell activation in response to challenge with offending allergens.

Mas-related G protein-coupled receptor X2: a novel receptor for non-IgE-dependent activation of mast cells

Mast cells (MC) , a major participant in inflammation and allergy, can initiate an early defense response to foreign invaders. Besides expressing high-affinity IgE receptor, MC also expresse a large number of G protein-coupled receptors (GPCRs) . Various studies have shown that cationic micromolecules represented by substance P and many peptidergic drugs can induce MC degranulation through a novel receptor, Mas-related G protein-coupled receptor X2 (MrgprX2) . MrgprX2 plays an important role in allergy, itching and pseudo-allergic drug reactions. It will help explain some clinical difficulties which can not be explained by classical IgE-dependent activation of MC, and provides potential therapeutic targets for MC-mediated diseases. Key words: Mast cells; Immunoglobulin E; Receptors, G-protein-coupled; Pruritus

IL-10 enhances IgE-independent IL-33-mediated mast cell cytokine production

Abstract IgE antibodies play a critical role in antigen-mediated mast cell activation. However, mast cells can be activated via IgE-independent mechanisms including signaling via the IL-33 receptor ST2. We have previously shown that the Th2-derived cytokine IL-10 can enhance IgE-dependent mucosal mast cell activation and promote mast cell function and survival. However, whether the effects of IL-10 on mast cells are global in nature and not limited to IgE-mediated signaling is not clear. To determine whether IL-10 can prime the activation of mast cells mediated by IgE-independent signals such as IL-33, we assessed the effects of rIL-10 exposure on IL-33-stimulated mast cells and their subsequent activation via IgE. Bone marrow-derived mast cells (BMMCs) from wild-type (WT) and IL-10−/− mice were cultured with rIL-33 with or without rIL-10 and activated with DNP-IgE and antigen. Exposure to IL-10 enhanced cytokine production in both WT and IL-10−/− BMMCs, and this was significantly increased after activation via IgE. IL-10−/−BMMCs exhibited decreased cytokine production, but this was restored upon culture with rIL-10. Interestingly, IL-33 stimulation (and subsequent activation with IgE) induced comparably enhanced levels of cytokine production, specifically IL-13 and IL-6, in both WT and IL-10−/−cells, suggesting that ST2-mediated signals can overcome the lack of IL-10. However, the addition of exogenous IL-10 to IL-33-stimulated cultures further enhanced the levels of these cytokines not only in IgE-activated cells, but also in cells stimulated with IL-33 alone. Our observations therefore suggest that IL-10 can play critical roles in enhancing mast cell function both via IgE-dependent and independent mechanisms.