IgE-mediated Mast Cell Activation Research Articles

Statin treatment suppresses IgE-mediated mast cell activation in vitro and in vivo (HYP4P.316)

Abstract Statin drugs are HMG-CoA reductase inhibitors used in the treatment of hypercholesterolemia and cardiovascular disease. They have also been shown to suppress the immune response. Given the critical role that mast cells play in allergic and inflammatory diseases, we assessed the effect of statin drugs on mast cell function. We demonstrate that Fluvastatin suppresses IgE-mediated degranulation and production of pro-inflammatory cytokines and chemokines, without altering IL-10 secretion. These effects were reversed by the addition of mevalonic acid, and mimicked by geranyl geranyl tranferase blockade, suggesting that Fluvastatin inhibits lipid modifications to small G proteins downstream of HMG CoA reductase. In vivo studies further showed that Fluvastatin suppressed IgE-mediated anaphylaxis. Interestingly, Fluvastatin-mediated suppression was completely absent in 129/SvJ mast cells, which showed a 2-fold induction of HMG CoA reductase upon statin treatment. Human mast cells from eight donors showed a range of responses to Fluvastatin, indicating that genetic background may influence statin-mediated suppression. These data demonstrate the possible use of statins, a widely-prescribed group of drugs, as a possible therapy for mast cell-associated disorders.

TGFb inhibits IL-33-mediated mast cell activation (INC6P.316)

Abstract TGFβ is involved in many pathological considtions, including autoimmune disorders, cancer, and cardiovascular and allergic diseases. We have previously found that TGFβ can suppress IgE-mediated mast cell activation. IL-33 is a recently discovered member of the IL-1 family that plays a critical role in mast cell activation and enhances IgE-mediated activation. In this study, we investigated the effects of TGFβ on IL-33-mediated mast cell activation. Bone marrow-derived mast cells cultured in TGFβ -1, -2, or -3 showed reduced IL-33-mediated production of TNF, IL-6, IL-13 and MCP-1, in a concentration-dependent manner. Furthermore, TGFβ also reduced expression of the T1/ST2 receptor as well as IL-33-mediated ERK activation. The role of IL-33 in the pathogenesis of allergic diseases is incompletely understood. These findings, consistent with our previously reported effects of TGFβ on IgE-mediated activation, demonstrate that TGFβ can provide broad and substantial inhibitory signals to activated mast cells.

Dexamethasone suppresses IL-33-mediated mast cell activation (CCR3P.215)

Abstract Dexamethasone, a glucocorticosteroid known for its anti-inflammatory and immunosuppressive activities, has been shown to inhibit IgE-mediated mast cell activation. The present research investigates the role of this drug in suppressing IL-33-mediated mast cell activation. IL-33 is a novel cytokine of the IL-1 family that elicits mast cells to produce inflammatory cytokines independently of IgE-FceRI signals. We have found that micromolar concentrations of dexamethasone are capable of suppressing IL-33-mediated cytokine production, regardless of genetic background. Dexamethasone also suppressed IL-33-induced cytokine production in mouse peritoneal mast cells. Inhibition was maximal when dexamethasone was added simultaneously with IL-33. Intracellular staining demonstrated that dexamethasone significantly reduces T1/ST2 expression in mast cells. However, cytokine suppression was shown to be independent of this downregulation of the IL-33 receptor. Thus, dexamethasone is capable of suppressing IL-33-mediated mast cell activation during the innate and adaptive immune responses. Further studies on the mechanism of dexamethasone are necessary for the understanding of those pathways and the development of more effective strategies for the treatment of inflammatory conditions.

An indoxyl compound 5-bromo-4-chloro-3-indolyl 1,3-diacetate, CAC-0982, suppresses activation of Fyn kinase in mast cells and IgE-mediated allergic responses in mice

Mast cells, constituents of virtually all organs and tissues, are critical cells in IgE-mediated allergic responses. The aim of this study was to investigate the effect and mechanism of an indoxyl chromogenic compound, 5-bromo-4-chloro-3-indolyl 1,3-diacetate, CAC-0982, on IgE-mediated mast cell activation and allergic responses in mice. CAC-0982 reversibly suppressed antigen-stimulated degranulation in murine mast cells (IC50, ~3.8μM) and human mast cells (IC50, ~3.0μM). CAC-0982 also inhibited the expression and secretion of IL-4 and TNF-α in mast cells. Furthermore, CAC-0982 suppressed the mast cell-mediated allergic responses in mice in a dose-dependent manner (ED50 27.9mg/kg). As for the mechanism, CAC-0982 largely suppressed the phosphorylation of Syk and its downstream signaling molecules, including LAT, Akt, Erk1/2, p38, and JNK. Notably, the tyrosine kinase assay of antigen-stimulated mast cells showed that CAC-0982 inhibited Fyn kinase, one of the upstream tyrosine kinases for Syk activation in mast cells. Taken together, these results suggest that CAC-0982 may be used as a new treatment for regulating IgE-mediated allergic diseases through the inhibition of the Fyn/Syk pathway in mast cells.

Is the analysis of histamine and/or interleukin-4 release after isocyanate challenge useful in the identification of patients with IgE-mediated isocyanate asthma?

Isocyanates are a well-known and frequent cause of occupational asthma. The implementation of specific inhalation challenges (SICs) is the gold standard in asthma diagnosis supporting occupational case history, lung function testing, specific skin prick tests and the detection of specific IgE. However, the diagnosis is not always definitive. An interesting new approach, analyses of individual genetic susceptibilities, requires discrimination between a positive SIC reaction arising from IgE-mediated immune responses and one from other pathophysiological mechanisms. Hence, additional refinement tools would be helpful in defining sub-classes of occupational asthma and diagnosis. We used total IgE levels, specific IgE and SIC results for sub-classification of 27 symptomatic isocyanate workers studied. Some mutations in glutathione S-transferases (GSTs) are suspected either to enhance or to decrease the individual risk in the development of isocyanate asthma. Our patient groups were assessed for the point mutations GSTP1*I105V and GSTP1*A114V as well as deletions (null mutations) of GSTM1 and GSTT1. There seems to be a higher risk in developing IgE-mediated reactions when GSTM1 is deleted, while GSTT1 deletions were found more frequently in the SIC positive group. Blood samples taken before SIC, 30–60min and 24h after SIC, were analyzed for histamine and IL-4, classical markers for the IgE-mediated antigen-specific activation of basophils or mast cells. We suggest that the utility of histamine measurements might provide an additional useful marker reflecting isocyanate-induced cellular reactions (although the sampling times require optimization). The promising measurement of IL-4 is not feasible at present due to the lack of a reliable, validated assay.

Application of cultured human mast cells (CHMC) for the design and structure-activity relationship of IgE-mediated mast cell activation inhibitors.

Here we report the optimization of small molecule inhibitors of human mast cell degranulation via anti-IgE-mediated tryptase release following cross-linking and activation of IgE-loaded FcεR1 receptors. The compounds are selective upstream inhibitors of FcεR1-dependent human mast cell degranulation and proved to be devoid of activity in downstream ionomycin mediated degranulation. Structure-activity relationship (SAR) leading to compound 26 is outlined.

Mast cell-MrgprB2: sensing secretagogues or a means to overreact?

Mast cells are unique immunocytes that reside predominantly at anatomical sites exposed to the environment, such as the skin, gastrointestinal tract and lung. Their strategic location and potential to participate in diverse physiological and pathological processes, as a result of their activation by any of an array of receptors, indicates that they can act as key contributors of innate and adaptive immune responses, inflammation and tissue remodelling.1, 2 Despite their beneficial functions of maintaining homeostasis1 and acting as sentinels in host defence, mast cells have earned notoriety as troublesome cells owing to their detrimental contributions in IgE-mediated allergic disorders. In such settings mast-cell activation is initiated when antigen cross-links antigen-specific IgE antibodies bound to high-affinity FceRI receptors.2 In addition to this classical mode of activation, mast cells also respond to basic secretagogues, including Substance P, mastoparan and compound 48/80, as well as a range of peptidergic drugs associated with adverse reactions.3, 4, 5 Basic polycationic peptides are thought to activate pertussis toxin-sensitive G proteins (that is, Gi2 and Gi3) in a receptor-independent manner on the mast cell surface.6 These in turn propagate signalling via pathways involving phospholipase C-γ, phosphatidylinositol 3-kinase and phospholipase A2, which then promote Ca2+ mobilisation that leads to exocytosis of preformed granule-associated mediators (for example, histamine) and the synthesis of arachidonic acid metabolites.6 However, the specific molecular mechanisms underlying basic secretagogue or peptide-induced activation of mast cell G proteins or a receptor, particularly those involved in drug-associated anaphylactoid/pseudoallergic reactions, have been poorly understood until now.

Adenine suppresses IgE-mediated mast cell activation

Nucleobase adenine is produced by dividing human lymphoblasts mainly from polyamine synthesis and inhibits immunological functions of lymphocytes. We investigated the anti-allergic effect of adenine on IgE-mediated mast cell activation in vitro and passive cutaneous anaphylaxis (PCA) in mice. Intraperitoneal injection of adenine to IgE-sensitized mice attenuated IgE-mediated PCA reaction in a dose dependent manner, resulting in a median effective concentration of 4.21mg/kg. In mast cell cultures, only adenine among cytosine, adenine, adenosine, ADP and ATP dose-dependently suppressed FcɛRI (a high affinity receptor for IgE)-mediated degranulation with a median inhibitory concentration of 1.6mM. It also blocked the production of LTB4, an inflammatory lipid mediator, and inflammatory cytokines TNF-α and IL-4. In addition, adenine blocked thapsigargin-induced degranulation which is FcɛRI-independent but shares FcɛRI-dependent signaling events. Adenine inhibited the phosphorylation of signaling molecules important to FcɛRI-mediated allergic reactions such as Syk, PLCγ2, Gab2, Akt, and mitogen activated protein kinases ERK and JNK. From this result, we report for the first time that adenine inhibits PCA in mice and allergic reaction by inhibiting FcɛRI-mediated signaling events in mast cells. Therefore, adenine may be useful for the treatment of mast cell-mediated allergic diseases. Also, the upregulation of adenine production may provide another mechanism for suppressing mast cell activity especially at inflammatory sites.

IgE and Mast Cells: The Endogenous Adjuvant.

Mast cells and immunoglobulin E (IgE) are most familiar as the effectors of type I hypersensitivity reactions including anaphylaxis. It is becoming clear however that this pair has important immunomodulatory effects on innate and adaptive cells of the immune system. In this purview, they act as endogenous adjuvants to ignite evolving immune responses, promote the transition of allergic disease into chronic illness, and disrupt the development of active mechanisms of tolerance to ingested foods. Suppression of IgE-mediated mast cell activation can be exerted by molecules targeting IgE, FcɛRI, or signaling kinases including Syk, or by IgG antibodies acting via inhibitory Fcγ receptors. Recent reports indicate that such interventions have promise in the development of strategies to treat allergic disease.

Spiraeoside inhibits mast cells activation and IgE-mediated allergic responses by suppressing phospholipase C-γ-mediated signaling.

Mast cells are responsible for IgE-mediated allergic responses through the secretion of various inflammatory cytokines and mediators. Therefore, the pharmacological regulation of mast cell activation is an important goal in the development of novel anti-allergic drugs. In this study, we found that spiraeoside (SP) inhibits mast cell activation and allergic responses in vivo. SP dose-dependently inhibited the degranulation induced by IgE-antigen (Ag) stimulation in RBL-2H3 mast cells without cytotoxic effects. At the molecular level, SP reduced the Ag-induced phosphorylation and subsequent activation of phospholipase C-γ2 (PLC-γ2). Moreover, SP inhibited the phosphorylation of spleen tyrosine kinase (Syk), linker for activation of T cells (LAT), and downstream MAPKs, such as ERK1/2, p38, and JNK, eventually attenuating expression of TNF-α and IL-4. Finally, we found that SP significantly inhibited IgE-mediated passive cutaneous anaphylaxis (PCA) in mice. Taken together, our results strongly suggest that SP suppresses IgE-mediated mast cell activation and allergic responses by inhibiting Lyn-induced PLC-γ2/MAPK signaling in mast cells.

Correction: Tumor Suppressor p53 Functions as a Negative Regulator in IgE-Mediated Mast Cell Activation

Correction: Tumor Suppressor p53 Functions as a Negative Regulator in IgE-Mediated Mast Cell Activation

Severe hypersensitivity reactions to iodinated contrast media: clinical and immunological features in a cohort of patients

Iodinated contrast media (ICM) are diagnostic agents used in millions of X-ray procedures yearly. Although current agents are usually well tolerated, mild immediate hypersensitivity reactions (IHR) occur in about 0.15% to 3% of administrations and severe IHRs in 0.01% to 0.04%. Despite this low incidence these reactions are an important clinical problem because the increasingly large amount of administrations per year worldwide. New data indicate that many of the immediate reactions are caused by an IgE-mediated activation of mast cells in the organs affected. Methods A retrospective review of adverse reactions to ICM between 2011 and 2012 in a tertiary hospital was carried out. Allergy study was performed in all patients who developed immediate hypersensitivity reactions. Skin tests for contrast media (Iomeprol, Iobitridol, Iohexol, Iodixanol, Amidotrizoato) were performed. We analysed the characteristics of patients who had severe reactions (Grade III-IV de Muller). Results 73,962 radiological contrast studies were performed during 2011 and 2012. 80 (0.011%) patients showed immediate hypersensitivity reactions to contrast media, 4 of them had severe reactions to ICM. Three patients, 2 males and 1 female, ages ranging from 60 to 78 years, were studied in Allergy unit. One patient had atopy. Two patients were on antihypertensive treatment (beta-blockers, angiotensin II receptor blockers, calcium channel blockers). All patients had at least 1 previous study with iodinated contrast in the past that had been well tolerated. Iomeprol was the contrast media involved in all the patients, incidence of 0.008% (Poisson 95% CI: 0.004% to 0.015%), no fatality. Skin tests (Skin Prick Test in one patient, and Intradermal test on the other two) were positive for Iomeprol. 2/3 showed negativity for the other contrasts tested and 1/3 showed also a positive response to Iohexol. Both positives results were confirmed with basophil activation test. Conclusion Incidence of severe immediate reactions to iodinated contrast media is very low. They are IgE mediated at least in 75% of cases in our cohort. There was at least one previous exposure to iodinated contrast before developing the reaction.

Basophil activation tests: a diagnostic break-through in opiate allergy.

We have read the manuscript about codeine (3-methylmorphine) anaphylaxis by Hey-Soo Yoo et al.1 with great interest and would like to take the opportunity to raise some issues and communicate our experience. As recently reviewed, despite their frequent and ubiquitous use, genuine IgE-mediated allergy to opiates remains exceedingly rare. Also, correct diagnosis is not straightforward, mainly because of uncertainties associated with measurement of drug-specific IgE antibodies and skin testing.2 Actually, the key to correct diagnosis of opiate allergy lies in elucidating the clinical significance of positive specific IgE (sIgE) results and distinguishing skin test responsiveness resulting from direct histamine release from a true IgE-mediated activation of cutaneous mast cells. From investigations about morphine and pholcodine (3-[2-morpholinyl-ethyl] morphine)-reactive IgE antibodies it is clear that positive IgE results towards these compounds cannot be considered as a proof for opiate allergy. As a matter of fact, sIgE reactivity to opiates has been observed in up to 10% of the general population and over 80% of patients allergic to rocuronium.3,4,5 Mutatis mutandis, this observation applies to skin testing with these potent histamine releasers that, for years, have been used as a positive control in skin testing (for review2). In contrast, opiates seem not to trigger histamine release from human basophils,6,7,8 making these cells highly attractive as a complementary diagnostic instrument to discriminate non-immunologic hypersensitivity reactions from genuine allergy with an underlying IgE-mediated mechanism (for review2). In their manuscript the authors describe a patient who suffered from anaphylaxis due to oral intake of codeine and document their diagnosis with a drug provocation and histamine release tests. However, due to the unavailability of codeine-sIgE tests, they were unable to establish a potential IgE-mediated mechanism. However, several points might be addressed here. First, measurement of pholcodine and morphine sIgE antibodies, that are readily available from Phadia Thermo Fisher Scientific, might have proven to be useful. As a matter of fact, these three opiates are structurally almost identical, except the substituent in position 3. At this position codeine has a methoxy group, morphine a hydroxyl group, and pholcodine a 2-morpholinoethyl group. Second, mutatis mutandis, the recommendation also applies to histamine release and drug provocation tests. Recently, we have described three patients with immediate hypersensitivity reactions to pholcodine in who measurement of drug-specific IgE and basophil activation tests (Figure) lead to the diagnosis of an IgE-mediated pholcodine allergy.9 Because these patients demonstrated a positive sIgE to morphine but negative basophil activation and provocation tests with the closely related structures morphine and pholcodine, the conclusion seems inescapable that the currently available quantification of opiate-sIgE tests should not be used to diagnose or predict clinical outcomes. Moreover, these observations seem to indicate the likelihood of antibody combining site heterogeneity with recognition at the fine structural level of features additional, and adjacent to, the position 3 substituent. Figure Representative plot CD63 appearance and histamine release in response to buffer, anti-IgE as a positive control, pholcodine 10 µg/mL (top), and the structurally almost similar opiates codeine 100 mg/mL and morphine 100 µg/mL (both bottom) ...

Persistence of IgE-associated allergy and allergen-specific IgE despite CD4+ T cell loss in AIDS.

The infection of CD4+ cells by HIV leads to the progressive destruction of CD4+ T lymphocytes and, after a severe reduction of CD4+ cells, to AIDS. The aim of the study was to investigate whether HIV-infected patients with CD4 cell counts <200 cells/µl can suffer from symptoms of IgE-mediated allergy, produce allergen-specific IgE antibody responses and show boosts of allergen-specific IgE production. HIV-infected patients with CD4 counts ≤200 cells/µl suffering from AIDS and from IgE-mediated allergy were studied. Allergy was diagnosed according to case history, physical examination, skin prick testing (SPT), and serological analyses including allergen microarrays. HIV infection was confirmed serologically and the disease was staged clinically. The predominant allergic symptoms in the studied patients were acute allergic rhinitis (73%) followed by asthma (27%) due to IgE-mediated mast cell activation whereas no late phase allergic symptoms such as atopic dermatitis, a mainly T cell-mediated skin manifestation, were found in patients suffering from AIDS. According to IgE serology allergies to house dust mites and grass pollen were most common besides IgE sensitizations to various food allergens. Interestingly, pollen allergen-specific IgE antibody levels in the patients with AIDS and in additional ten IgE-sensitized patients with HIV infections and low CD4 counts appeared to be boosted by seasonal allergen exposure and were not associated with CD4 counts. Our results indicate that secondary allergen-specific IgE production and IgE-mediated allergic inflammation do not require a fully functional CD4+ T lymphocyte repertoire.

Calpain-1 contributes to IgE-mediated mast cell activation.

Mast cells play a central role in allergy through secretion of both preformed and newly synthesized mediators. Mast cell mediator secretion is controlled by a complex network of signaling events. Despite intensive studies, signaling pathways in the regulation of mast cell mediator secretion remain incompletely defined. In this study, we examined the role of calpain in IgE-dependent mast cell activation. IgE-mediated activation of mouse bone marrow-derived mast cells enhanced calpain activity. Inhibition of calpain activity by a number of calpain inhibitors reduced IgE-mediated mast cell degranulation both in vitro and in vivo. Calpain inhibitors blocked IgE-mediated TNF and IL-6 production in vitro and reduced late-phase allergic response in vivo. Importantly, mouse calpain-1 null bone marrow-derived mast cells showed reduced IgE-mediated mast cell degranulation in vitro and in vivo, diminished cytokine and chemokine production in vitro, and impaired late-phase allergic response in vivo. Further studies revealed that calpain-1 deficiency led to specific attenuation of IκB-NF-κB pathway and IKK-SNAP23 pathway, whereas calcium flux, MAPK, Akt, and NFAT pathway proceed normally in IgE-activated calpain-1 null mast cells. Thus, calpain-1 is identified as a novel regulator in IgE-mediated mast cell activation and could serve as a potential therapeutic target for the management of allergic inflammation.

Doxycycline exerts multiple anti-allergic effects in vitro and in vivo though modulating PI3K/Akt pathway (HYP6P.269)

Abstract Tetracyclines, belonging to an old antibiotic drug family that possesses a striking variety of non-antibiotic properties, have been successfully applied in a wide range of diseases, including asthma. However, their roles in allergic diseases and underlying anti-allergic mechanisms remain elusive.To explore the roles of doxycycline in allergic pathogenesis, we have focused on its role on B cells, mast cells (MCs) and histamine function using and experimental allergic conjunctivitis (EAC) and passive systemic anaphylaxis (PSA) animal models. Our results demonstrated that treatment with doxycycline significantly reduced IgE release of B cells and IgE-mediated activation of MCs. Furthermore, doxycycline treatment significantly inhibited histamine-stimulated vascular hyperpermeability. Mechanistically, doxycycline-mediated inhibition of B cells, mast cells and histamine may be through modulating PI3K/Akt pathway. Using mouse models of EAC, PSA and histamine-induced systemic anaphylaxis like reaction (HISA), we demonstrated that treatment with doxycycline significantly attenuated allergic symptoms. Doxycycline-mediated anti-allergic effects on EAC, PSA and HISA were abrogated when an Akt activator, SC79 was administrated. Our study has suggested that doxycycline inhibits B cell, mast cell and histamine function and attenuates experimental allergic conjunctivitis and systemic anaphylaxis by modulating PI3K/Akt pathway.

Fluvastatin suppresses IgE-mediated mast cell activation in vitro and in vivo (HYP3P.411)

Abstract Fluvastatin, the HMG-CoA reductase inhibitor known for its role in the treatment of hypercholesterolemia and cardiovascular disease, has more recently been shown to play a role in the immune response. Given the critical role that mast cells play in allergy and inflammatory diseases such as asthma, which effects one third of America’s population, we assessed the effect of Fluvastatin on mast cell function. We demonstrate that Fluvastatin downregulated IgE-mediated cytokine production and mast cell migration. Additionally, in vivo studies showed that Fluvastatin suppressed IgE-mediated anaphylaxis. Interestingly, the effect of Fluvastatin may be restricted to mast cells cultured from mice with a Th1-prone background. Characterizing the role of Fluvastatin on mast cells may prove to be therapeutically important.

Differential effects of cyclosporine A and TGFβ1 on IgE- versus IL-33-mediated mast cell activation (HYP3P.407)

Abstract Cyclosporine A (CsA), a potent calcineurin antagonist and immunosuppressant, is known to inhibit IgE-mediated mast cell activation. The present research investigates the role of this drug in suppressing IL-33-mediated mast cell activation. IL-33 is a novel cytokine of IL-1 family that elicits mast cells to produce inflammatory cytokines independently of IgE-FcεRI signals. We have found that low concentrations of CsA (10nM) are capable of suppressing IgE-mediated cytokine production by 50-80% in mouse bone marrow-derived mast cells. By comparison, IL-33-mediated secretion of TNF, IL-6, and MCP-1 was unaffected by CsA under these conditions. These results were consistent among mast cells derived from C57BL/6, 129Sv, C3H, and A/J mouse strains. We have previously reported that TGFβ1 inhibits IgE-mediated cytokine production. Our current experiments showed that TGFβ1 similarly antagonizes IL-33-induced cytokine secretion, and that CsA does not enhance this effect. These data demonstrate that mast cell activation by IL-33, thought to be a key regulator of innate immunity, is responsive to TGFβ1-mediated suppression, but relatively resistant to CsA effects. Understanding how mast cells are regulated by innate signals will shed light on many inflammatory diseases.

Aceriphyllum rossii Extract and Its Active Compounds, Quercetin and Kaempferol Inhibit IgE-mediated Mast Cell Activation and Passive Cutaneous Anaphylaxis

Aceriphyllum rossii contains an abundant source of natural flavonoids with potential antioxidant, anticancer and anti-inflammatory properties. However, the effect of A. rossii extract (ARE) on immunoglobulin E(IgE)-mediated allergic responses remains unknown. In the present study, the effects of ARE and its active compounds, quercetin and kaempferol, on IgE-mediated rat basophilic leukemia mast cell activation and passive cutaneous anaphylaxis (PCA) were investigated. ARE, quercetin, and kaempferol inhibited secretion of β-hexosaminidase and histamine, and reduced the production and mRNA expression of interleukin-4 and tumor necrosis factor-α. ARE also decreased the production of prostaglandin E2 and leukotriene B4 and expression of cyclooxygenase 2 and 5-lipoxygenase. Furthermore, ARE, quercetin, and kaempferol inhibited IgE-mediated phosphorylation of Syk, phospholipase Cγ, protein kinase C (PKC)μ, and the mitogen-activated protein kinases, extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase. ARE, quercetin, and kaempferol markedly suppressed mast cell-dependent PCA in IgE-sensitized mice. These results indicate that ARE and its active constituents, quercetin and kaempferol, may be a useful therapy for immediate-type hypersensitivity.

Mechanisms of vitamin D3 metabolite repression of IgE-dependent mast cell activation

Mast cells have gained notoriety based on their detrimental contributions to IgE-mediated allergic disorders. Although mast cells express the vitamin D receptor (VDR), it is not clear to what extent 1α,25-dihydroxyvitamin D3 (1α,25[OH]2D3) or its predominant inactive precursor metabolite in the circulation, 25-hydroxyvitamin D3 (25OHD3), can influence IgE-mediated mast cell activation and passive cutaneous anaphylaxis (PCA) in vivo. We sought to assess whether the vitamin D3 metabolites 25OHD3 and 1α,25(OH)2D3 can repress IgE-dependent mast cell activation through mast cell-25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) and mast cell-VDR activity. We measured the extent of vitamin D3 suppression of IgE-mediated mast cell degranulation and mediator production in vitro, as well as the vitamin D3-induced curtailment of PCA responses in WBB6F1-Kit(W/W-v) or C57BL/6J-Kit(W-sh/W-sh) mice engrafted with mast cells that did or did not express VDR or CYP27B1. Here we show that mouse and human mast cells can convert 25OHD3 to 1α,25(OH)2D3 through CYP27B1 activity and that both of these vitamin D3 metabolites suppressed IgE-induced mast cell-derived proinflammatory and vasodilatory mediator production in a VDR-dependent manner in vitro. Furthermore, epicutaneously applied vitamin D3 metabolites significantly reduced the magnitude of skin swelling associated with IgE-mediated PCA reactions in vivo; a response that required functional mast cell-VDRs and mast cell-CYP27B1. Taken together, our findings provide a mechanistic explanation for the anti-inflammatory effects of vitamin D3 on mast cell function by demonstrating that mast cells can actively metabolize 25OHD3 to dampen IgE-mediated mast cell activation in vitro and in vivo.