IgE-mediated Mast Cell Research Articles

Propolis inhibits IgE-mediated mast cell activation by suppressing SYK/MAPK signaling pathway

Abstract Mast cells play a critical role in the effector phase of immediate hypersensitivity and allergic reactions. Propolis exerts multiple biological effects and exhibits immunomodulatory and antioxidant properties. However, its role in antidinitrophenyl (DNP) immunoglobulin E (IgE)-activated mast cells has not been investigated. In this study, we examined the mechanism underlying the inhibitory effect of propolis (Unibee powder propolis, Uniquebiotech, Co., Ltd., Iksan) on DNP-IgE-mediated mast cell degranulation, with a specific focus on histamine and cytokines release, using rat peritoneal mast cells. Propolis protected mast cell degranulation and inhibited histamine release triggered by anti-DNP IgE in rat peritoneal mast cells (RPMC) in vitro. Interestingly, propolis also decreased the level of TNF-a, IL-4, and IL-13 released from anti-DNP IgE-activated RPMC. Moreover, the SYK and its downstream-MAPK signaling pathway also were suppressed in the anti-DNP IgE-activated RPMC by the incubation with propolis. Together, these results suggest that propolis extract effectively inhibits IgE-mediated mast cell anaphylaxis-like reactions. This research was supported by the 2022 Collaborative R&BD Program of The Food Industry Promotional Agency of Korea. This research was supported by the 2022 Collaborative R&BD Program of The Food Industry Promotional Agency of Korea.

Isoprenylation Inhibition Suppresses IL-33-mediated Mast Cell Activation of Allergic Asthma

Abstract Allergic asthma is an inflammatory disease of the airway associated with sensitization to allergens and symptoms such as sneezing, wheezing, and airway hyperresponsiveness. The severity of this disease varies between sex, age, and race; therefore, understanding signaling mechanisms is integral to developing targeted therapeutics. Mast cells (MC), an important effector cell in allergic disease, can be activated by interleukin (IL)-33, an alarmin released after contact with cellular stressors including common allergens. In response to IL-33, MC release inflammatory cytokines and lipid mediators. We previously found that statins suppress IgE-mediated MC activation by inhibiting protein isoprenylation. Therefore, we hypothesized that directly targeting the isoprenylation enzymes farnesyl transferase (FT) and geranylgeranyl transferase (GGT) would suppress IL-33-mediated MC function. We show that the dual transferase inhibitor FGTI-2734 decreased IL-33-mediated inflammatory cytokine secretion, effects that were mimicked by simvastatin. In contrast to the dual inhibitor, suppressing only FT or GGT had no effect on cytokine secretion. These data suggest that inhibiting farnesyl and geranylgeranyl transferases is a potential treatment for IL-33-mediated mast cell activation and allergic disease. Supported by grants from NIH (RO1 AI138495 and RO1 AI164710)

A283 ROLE OF IMMUNOGLOBULIN E IN ABDOMINAL PAIN DUE TO INTERACTIONS BETWEEN DIET AND STRESS IN A MODEL OF IBS

Abstract Background Food and stress are common triggers of symptoms in IBS patients. We previously showed in a murine model of IBS that exposure to a food antigen during a period of psychological stress leads to visceral hypersensitivity in both the ileum and colon upon re-exposure to the food antigen. This was inhibited by blocking mast cells and histamine receptors, suggesting that mast cell activation is involved in this increased pain signaling. However, it is unknown if immunoglobulin E (IgE) is involved in the activation of mast cells leading to visceral hypersensitivity. Purpose Determine the role of IgE in the increased pain signaling in ileum and colon of mice re-exposed to ovalbumin after an initial exposure to ovalbumin during chronic stress. Method Balb/c mice underwent water avoidance stress (WAS) for 10 days and were exposed to ovalbumin (OVA) from days 2-10. Five weeks later, mice were re-exposed to ovalbumin for two weeks (WAS/OVA+OVA mice). Mice were injected with anti-mouse IgE or isotype control antibody (1 mg/kg, i.p.) just prior and during ovalbumin re-exposure. Ex-vivo extracellular afferent recordings from nerves innervating the ileum were obtained to assess changes in mechanosensitivity. Ileum and colonic supernatants were also collected. Dorsal root ganglion neurons (DRG) from control mice (n = 12) were incubated with ileal and colonic supernatants. The excitability of these neurons was assessed by measuring the rheobase (minimum current required to evoke an action potential; lower rheobase=increased excitability) using perforated patch clamp. Data were analyzed by unpaired t-test or two-way ANOVA with Sidak’s post hoc test. Result(s) WAS/OVA+OVA mice treated with anti-IgE antibody had decreased mechanosensitivity of ileal nerves following lumen distention compared to WAS/OVA+OVA mice treated with isotype control antibody (7.7 ± 0.65 vs 12.9 ± 1.04 Hz, p = 0.034, n = 9 and 8 mice, respectively). Ileal supernatants from anti-IgE treated WAS/OVA+OVA mice evoked lower excitability (higher rheobase) in DRG neurons than neurons incubated with supernatants from isotype control treated WAS/OVA+OVA mice (rheobase: 89.2 ± 4.7 vs 71.9 ± 5.1 pA, p= 0.018). Colonic supernatants showed similar effects of the anti-IgE treatment (rheobase: 95.5 ± 4.4 vs 76.7 ± 5.4 pA, p = 0.01). Conclusion(s) IgE is involved in the increased pain signaling observed in both ileum and colon induced by antigen re-exposure following an initial stress-food antigen interaction. This suggests that IgE-mediated mast cell activation in response to food antigens may be a mechanism of meal-induced pain in IBS patients. Please acknowledge all funding agencies by checking the applicable boxes below Other Please indicate your source of funding; Department of Medicine, Translational Medicine Grant, Queen's University Disclosure of Interest None Declared

An advanced in vitro human mucosal immune model to predict food sensitizing allergenicity risk: A proof of concept using ovalbumin as model allergen.

The global demand of sustainable food sources leads to introduction of novel foods on the market, which may pose a risk of inducing allergic sensitization. Currently there are no validated in vitro assays mimicking the human mucosal immune system to study sensitizing allergenicity risk of novel food proteins. The aim of this study was to introduce a series of sequential human epithelial and immune cell cocultures mimicking key immune events after exposure to the common food allergen ovalbumin from intestinal epithelial cell (IEC) activation up to mast cell degranulation. This in vitro human mucosal food sensitizing allergenicity model combines crosstalk between IEC and monocyte-derived dendritic cells (moDC), followed by coculture of the primed moDCs with allogenic naïve CD4+ T cells. During subsequent coculture of primed CD4+ T cells with naïve B cells, IgE isotype-switching was monitored and supernatants were added to primary human mast cells to investigate degranulation upon IgE crosslinking. Mediator secretion and surface marker expression of immune cells were determined. Ovalbumin activates IEC and underlying moDCs, both resulting in downstream IgE isotype-switching. However, only direct exposure of moDCs to ovalbumin drives Th2 polarization and a humoral B cell response allowing for IgE mediated mast cell degranulation, IL13 and IL4 release in this sequential DC-T cell-B cell-mast cell model, indicating also an immunomodulatory role for IEC. This in vitro coculture model combines multiple key events involved in allergic sensitization from epithelial cell to mast cell, which can be applied to study the allergic mechanism and sensitizing capacity of proteins.

Acute activation of SERCA with CDN1163 attenuates IgE-mediated mast cell activation through selective impairment of ROS and p38 signaling.

Mast cells are granulocytic immune sentinels present in vascularized tissues that drive chronic inflammatory mechanisms characteristic of allergic pathologies. IgE-mediated mast cell activation leads to a rapid mobilization of Ca2+ from intracellular stores, which is essential for the release of preformed mediators via degranulation and de novo synthesized proinflammatory cytokines and chemokines. Given its potent signaling capacity, the dynamics of Ca2+ localization are highly regulated by various pumps and channels controlling cytosolic Ca2+ concentrations. Among these is sarco/endoplasmic reticulum Ca2+ -ATPase (SERCA), which functions to maintain low cytosolic Ca2+ concentrations by actively transporting cytosolic Ca2+ ions into the endoplasmic reticulum. In this study, we characterized the role of SERCA in allergen-activated mast cells using IgE-sensitized bone marrow-derived mast cells (BMMCs) treated with the SERCA activating compound, CDN1163, and simultaneously stimulated with allergen through FcεRI under stem cell factor (SCF) potentiation. Acute treatment with CDN1163 was found to attenuate early phase mast cell degranulation along with reactive oxygen species (ROS) production. Additionally, treatment with CDN1163 significantly reduced secretion of IL-6, IL-13, and CCL3, suggesting a role for SERCA in the late phase mast cell response. The protective effects of SERCA activation via CDN1163 treatment on the early and late phase mast cell response may be driven by the selective suppression of p38 MAPK signaling. Together, these findings implicate SERCA as an important regulator of the mast cell response to allergen and suggest SERCA activity may offer therapeutic potential targeting allergic pathologies, warranting further investigation.

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

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

Natural isoflavone formononetin inhibits IgE-mediated mast cell activation and allergic inflammation by increasing IgE receptor degradation.

Immunoglobulin (Ig)E-associated mast cell (MC) activation triggers pro-inflammatory signals that underlie type I allergic diseases. Here, we examined the effects of the natural isoflavone formononetin (FNT) on IgE-mediated MC activation and associated mechanisms of high-affinity IgE receptor (FcεRI) signal inhibition. The effects of FNT on the mRNA expression of inflammatory factors, release of histamine and β-hexosaminidase (β-hex), and expression of signaling proteins and ubiquitin (Ub)-specific proteases (USPs) were analyzed in two sensitized/stimulated MC lines. FcεRIγ-USP interactions were detected by co-immunoprecipitation (IP). FNT dose-dependently inhibited β-hex activity, histamine release, and inflammatory cytokine expression in FcεRI-activated MCs. FNT suppressed IgE-induced NF-κB and MAPK activity in MCs. The oral administration of FNT attenuated passive cutaneous anaphylaxis (PCA) reactions and ovalbumin (OVA)-induced active systemic anaphylaxis (ASA) reactions in mice. FNT reduced the FcεRIγ chain expression, via increased proteasome-mediated degradation, and induced FcεRIγ ubiquitination by inhibiting USP5 and/or USP13. FNT and USP inhibition may be useful for suppressing IgE-mediated allergic diseases.

Chemical composition-based characterization of the anti-allergic effect of Guominkang Formula on IgE-mediated mast cells activation and passive cutaneous anaphylaxis.

Guominkang (GMK), a Chinese medicine formula, has been used to treat allergic diseases in clinical settings for many years. To evaluate the antiallergic effect and molecular mechanism of action of GMK extract, RBL-2H3 cell models and passive cutaneous anaphylaxis (PCA) mouse models were established. High performance liquid chromatography (HPLC) and ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) analyses were performed to characterize the chemical composition of GMK. A total of 94 compounds were identified or tentatively identified from GMK. Three of them, emodin, ursolic acid, and hamaudol, were identified for the first time as potential active compounds in GMK, since they inhibited the degranulation of mast cells. The anti-allergic effect of hamaudol was the first to be discovered. GMK could markedly mitigate the shade of Evans Blue extravasation and ear incrassation in PCA mouse models. Additionally, GMK significantly inhibited the degranulation of mast cells, suppressed mast cell degranulation by reducing Ca2+ influx and the levels of TNF-α, IL-4, and histamine, and markedly inhibited the phosphorylation of Lyn, Syk, PLCγ1, IκBα, and NF-κB p65. Molecular docking results indicated that hamaudol and emodin had strong interaction with FcɛRI and NF-κB related proteins, while ursolic acid only interacted with NF-κB associated proteins. These results suggest GMK suppresses the activation of MCs both in vivo and in vitro. The underlying mechanism of its anti-allergic activity is associated with the inhibition of FcɛRI and NF-κB activation.

521 Deciphering Pathomechanisms in Solar Urticaria

Solar Urticaria (SU) is a rare, chronic inducible urticaria characterised by an itching or burning erythemal flare with or without whealing, that can develop within minutes of exposure to ultraviolet radiation (UVR) and/or visible light. It is hypothesised that an unidentified endogenous photo-allergen may be the trigger, leading to IgE-mediated mast cell degranulation. However, the evolution of the response and mechanisms involved are not well understood. We undertook a UVR provocation study with transcriptome analysis to examine early events in SU pathophysiology.

ELEVATED HISTAMINE LEVELS WITH NORMAL TRYPTASE IN ANAPHYLAXIS

<h3>Introduction</h3> The most commonly described pathway of anaphylaxis involves IgE mediated mast cell activation. Here we present three patients with elevated histamine, normal tryptase, and normal IgE. These findings suggest a non-mast-cell mediated pathway of anaphylaxis. All patients were placed on a low-histamine diet (LHD) following their anaphylaxis episodes with subsequent decrease in histamine and resolution of anaphylactic episodes. <h3>Cases Description</h3> The first patient was a 25-year-old male who presented to the emergency department with a histamine level of 6.0 (ng/mL). The patient experienced a second anaphylaxis episode a week later. Repeat histamine was 6.5. The patient was placed on a LHD, and follow-up testing demonstrated histamine of 1.6. The second patient was a 51-year-old male who presented to the emergency department for anaphylaxis. Laboratory studies after the event found histamine of 13.2, and the patient was subsequently placed on a LHD. Follow-up testing demonstrated histamine of 5.8. The third patient was a 33-year-old female that developed anaphylaxis after a patch test. Laboratory studies revealed histamine of >28.6. The patient was instructed to start a LHD. Subsequent testing demonstrated histamine of 10.8. <h3>Discussion</h3> Persistent elevation of histamine levels in the absence of elevated tryptase or IgE suggests a non-mast-cell mediated pathway of histamine release. Further studies should be performed in similar cases examining the potential of LHD as a treatment for anaphylaxis with elevated histamine and normal tryptase as LHD resulted in a decrease in histamine level and resolution of anaphylactic episodes.

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

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

Hereditary alpha-tryptasemia: Brief overview of current knowledge and proposal of indications

Human tryptases are serine proteases, which are synthesized nearly exclusively by mast cells (MCs). Immature pro-tryptases, under the form of α- and β-monomers are constantly released by MCs, can be measured in the serum of normal individuals and constitute the basal serum tryptase (bST) level, usually below 6μg/L. By contrast, tetramers of tryptases, which are the mature forms of the enzyme, are normally retained in the secretory granules of MCs. These mature (α- and β-tetramers of tryptase) are only released when MC are activated by different stimuli, leading to a transient increase in serum tryptase level. Such event occurs for instance after IgE-mediated MC degranulation (immediate hypersensitivity reaction). The mature tryptases, through their various biological activities, account for the pathophysiology of immediate hypersensitivity. Of note, recent studies have reported that around 5% of the general population present with increased bST levels related to a genetic trait called hereditary α-tryptasemia (HαT). While there is still a debate on the fact that HαT+ patients may present more frequently various clinical phenotypes, it is now clearly established that the clinical phenotype of patients with primary (clonal) MC disorders, including mastocytosis, is modified by the presence of the HαT trait. In addition, HαT penetrance seems clearly increased in such patients (up to 18% of the cases), leading to the conclusion that HαT is a disease penetrance and phenotype modifier. In the present manuscript, we will describe briefly the genetic patterns of HαT and the clinical phenotypes encountered in HαT+ patients harboring or not a clonal MC disorder. Finally, we will describe the situations when the search for HαT in human can be considered and the preferred method to be used for such investigation.

Nano-silica particles synergistically IgE-mediated mast cell activation exacerbating allergic inflammation in mice.

BackgroundAllergic respiratory diseases have increased dramatically due to air pollution over the past few decades. However, studies are limited on the effects of inorganic components and particulate matter with different particle sizes in smog on allergic diseases, and the possible molecular mechanism of inducing allergies has not been thoroughly studied.MethodsFour common mineral elements with different particle sizes in smog particles were selected, including Al2O3, TiO2, Fe2O3, and SiO2. We studied the relationship and molecular mechanism of smog particle composition, particle size, and allergic reactions using mast cells, immunoglobulin E (IgE)-mediated passive cutaneous anaphylaxis (PCA) model, and an ovalbumin (OVA)-induced asthmatic mouse model in vitro and in vivo, combined with transmission electron microscopy, scanning transmission X-ray microscopy analysis, and transcriptome sequencing.ResultsOnly 20 nm SiO2 particles significantly increased β-hexosaminidase release, based on dinitrophenol (DNP)-human serum albumin (HSA) stimulation, from IgE-sensitized mast cells, while other particles did not. Meanwhile, the PCA model showed that Evan’s blue extravasation in mice was increased after treatment with nano-SiO2 particles. Nano-SiO2 particles exposure in the asthmatic mouse model caused an enhancement of allergic airway inflammation as manifested by OVA-specific serum IgE, airway hyperresponsiveness, lung inflammation injury, mucous cell metaplasia, cytokine expression, mast cell activation, and histamine secretion, which were significantly increased. Nano-SiO2 particles exposure did not affect the expression of FcϵRI or the ability of mast cells to bind IgE but synergistically activated mast cells by enhancing the mitogen-activated protein kinase (MAPK) signaling pathway, especially the phosphorylation levels of the extracellular signal-regulated kinase (ERK)1/2. The ERK inhibitors showed a significant inhibitory effect in reducing β-hexosaminidase release.ConclusionOur results indicated that nano-SiO2 particles stimulation might synergistically activate IgE-sensitized mast cells by enhancing the MAPK signaling pathway and that nano-SiO2 particles exposure could exacerbate allergic inflammation. Our experimental results provide useful information for preventing and treating allergic diseases.

Roles of Mast Cells in Cutaneous Diseases.

Mast cells are present in all vascularized tissues of the body. They are especially abundant in tissues that are in frequent contact with the surrounding environment and act as potential sources of inflammatory and/or regulatory mediators during development of various infections and diseases. Mature mast cells’ cytoplasm contains numerous granules that store a variety of chemical mediators, cytokines, proteoglycans, and proteases. Mast cells are activated via various cell surface receptors, including FcϵRI, toll-like receptors (TLR), Mas-related G-protein-coupled receptor X2 (MRGPRX2), and cytokine receptors. IgE-mediated mast cell activation results in release of histamine and other contents of their granules into the extracellular environment, contributing to host defense against pathogens. TLRs, play a crucial role in host defense against various types of pathogens by recognizing pathogen-associated molecular patterns. On the other hand, excessive/inappropriate mast cell activation can cause various disorders. Here, we review the published literature regarding the known and potential inflammatory and regulatory roles of mast cells in cutaneous inflammation, including atopic dermatitis, psoriasis, and contact dermatitis GVHD, as well as in host defense against pathogens.

Allergen-Specific IgA Antibodies Block IgE-Mediated Activation of Mast Cells and Basophils.

Mast cells and basophils have long been implicated in the pathogenesis of IgE-mediated hypersensitivity reactions. They express the high-affinity IgE receptor, FcϵRI, on their surface. Antigen-induced crosslinking of IgE antibodies bound to that receptor triggers a signaling cascade that results in activation, leading to the release of an array of preformed vasoactive mediators and rapidly synthesized lipids, as well as the de novo production of inflammatory cytokines. In addition to bearing activating receptors like FcεRI, these effector cells of allergy express inhibitory ones including FcγR2b, an IgG Fc receptor with a cytosolic inhibitory motif that activates protein tyrosine phosphatases that suppress IgE-mediated activation. We and others have shown that food allergen-specific IgG antibodies strongly induced during the course of oral immunotherapy (OIT), signal via FcγR2b to suppress IgE-mediated mast cell and basophil activation triggered by food allergen challenge. However, the potential inhibitory effects of IgA antibodies, which are also produced in response to OIT and are present at high levels at mucosal sites, including the intestine where food allergens are encountered, have not been well studied. Here we uncover an inhibitory function for IgA. We observe that IgA binds mouse bone marrow-derived mast cells (BMMCs) and peritoneal mast cells. Binding to BMMCs is dependent on calcium and sialic acid. We also found that IgA antibodies inhibit IgE-mediated mast cell degranulation in an allergen-specific fashion. Antigen-specific IgA inhibits IgE-mediated mast cell activation early in the signaling cascade, suppressing the phosphorylation of Syk, the proximal protein kinase mediating FcεRI signaling, and suppresses mast cell production of cytokines. Furthermore, using basophils from a peanut allergic donor we found that IgA binds to basophils and that activation by exposure to peanuts is effectively suppressed by IgA. We conclude that IgA serves as a regulator of mast cell and basophil degranulation, suggesting a physiologic role for IgA in the maintenance of immune homeostasis at mucosal sites.

Loss of isoprenylation significantly reduces IgE mediated mast cell activation

Abstract Allergic disease is the 6th leading cause of chronic illness in the US and accounts for billions of dollars in healthcare costs annually. Mast cells are tissue resident innate immune cells linked to allergic disease and activated by IgE and other ligands. Upon activation they release histamine, cytokines, chemokines, proteases, and lipid mediators evoking allergic symptoms. New ways of targeting mast cells could greatly benefit allergic disease therapy. Previous findings showed repurposing of statin drugs, such as Fluvastatin, reduced allergic symptoms in vitro and in vivo. We found that Fluvastatin suppresses IgE-mediated mast cell activation by inhibiting isoprenylation of proteins. However, statin effects were dependent on genetic background. To avert genetic background dependency, we tested the hypothesis that a dual farnesyl and geranylgeranyl transferase inhibitor (FGTI 2734) would suppress allergic disease withoutgenetic background limitations. We show that FGTI 2734 reduced IgE-mediated degranulation and cytokine production by bone marrow derived mast cells from multiple genetic backgrounds. Similarly, FGTI 2734 also suppressed IgE-mediated anaphylaxis on multiple genetic backgrounds. These in vivo effects extended to an allergic asthma model, in which FGTI 2734 inhibited pulmonary inflammation. Finally, we show that FGTI-2734 can significantly reduce IgE-induced cytokine production from human skin mast cells. These data show that dual farnesyl and geranylgeranyl transferase inhibitors may be an effective therapeutic treatment for mast cell-associated diseases. Supported by NIH (1RO1AI101153)

Characterization of pathological IgE-mediated mast cell activation in Lyme disease

Abstract Lyme disease, caused by the bacteria Borrelia burgdorferi, is the most common and rapidly growing vector-borne infectious disease in the United States and Europe. High variability in disease burden among Lyme patients suggests that individual immune responses may be key drivers of clinical presentation and patient outcomes. Use of high resolution flow-based immunosorbent profiling revealed that a subset of Lyme patients with persistent symptoms were producing high concentrations of IgE specific to B. burgdorferi. Comparing C57B/6 mice, which are tolerant to B. burgdorferi, and C3H/HeJ mice, which are susceptible to disease, we find high levels of IgE specific for B. burgdorferi in C3H/HeJ but not C57B/6 mice. Furthermore, IgE was found to target Borrelia peptidoglycan in both acute and chronic infection models. Histologic analysis of mouse Lyme arthritic ankle tissue showed mast cells, which release highly immunogenic effectors upon activation by bound IgE, degranulating at significantly higher rates compared to uninfected controls. Forced mast cell degranulation exacerbated Lyme arthritis in infected mice. This data suggests that a subset of Lyme patients with persistent symptoms may have developed an allergic response to conserved bacterial antigens from a B. burgdorferi infection, as opposed to an autoimmune type response. Inclusion of IgE reactivity in diagnostic testing and examination of pathological immune responses to bacterial antigens could assist clinicians in patient care and effective treatments. Research reported in this publication was supported by the Fairbairn family foundation; Bay Area Lyme Foundation; the Younger family foundation; the Robert J. Kleberg, Jr., and Helen C. Kleberg Foundation; the Virginia and D. K. Ludwig Fund for Cancer Research; M.C.T. was supported by Stanford Immunology training grant 5T32AI007290, and the NIH NRSA 1 F32 AI124558-01 award. L.B.T.D. was supported by a Stanford Diversifying Academia Recruiting Excellence fellowship. S.D.G was supported by the California Institute for Regenerative Medicine Bridges 2.0 Training Program grant EDUC2-08397. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Dendritic cell immunoreceptor drives atopic dermatitis by modulating oxidized CaMKII-involved mast cell activation.

Allergens have been identified as potential triggers in patients with atopic dermatitis (AD). Patients with AD are highly sensitive to cockroach allergen. The underlying mechanism, however, remains undetermined. Here, we established a cockroach allergen–induced AD-like mouse model, and we demonstrate that repeated exposure to cockroach allergen led to aggravated mouse skin inflammation, characterized by increased type 2 immunity, type 2 innate lymphoid cells (ILC2s), and mast cells. Increased mast cells were also observed in patients with AD. Mast cell–deficient mice (KitW-sh/W-sh) showed diminished skin inflammation, suggesting that mast cells are required in allergen-induced skin inflammation. Furthermore, DC immunoreceptor (DCIR) is upregulated in skin mast cells of patients with AD and mediates allergen binding and uptake. DCIR–/– mice or reconstituted KitW-sh/W-sh mice with DCIR–/– mast cells showed a significant reduction in AD-like inflammation. Both in vitro and in vivo analyses demonstrate that DCIR–/– mast cells had reduced IgE-mediated mast cell activation and passive cutaneous anaphylaxis. Mechanistically, DCIR regulates allergen-induced IgE-mediated mast cell ROS generation and oxidation of calmodulin kinase II (ox-CaMKII). ROS-resistant CaMKII (MM-VVδ) prevents allergen-induced mast cell activation and inflammatory mediator release. Our study reveals a DCIR/ROS/CaMKII axis that controls allergen-induced mast cell activation and AD-like inflammation.

Flavoring agent dihydrocoumarin alleviates IgE-mediated mast cell activation and allergic inflammation.

Mast cells (MCs) are the main effector cells in the onset of high-affinity receptor for IgE (FcεRI)-mediated allergic diseases. The aim of this study was to test whether dihydrocoumarin (DHC), a food flavoring agent derived from Melilotus officinalis, can block IgE-induced MC activation effects and to examine the potential molecular mechanisms by which DHC affects MC activation. Rat basophilic leukemia cells (RBLs) and mouse bone marrow-derived mast cells (BMMCs) were sensitized with anti-dinitrophenol (DNP) immunoglobulin (Ig)E antibodies, stimulated with DNP-human serum albumin antigen, and treated with DHC. Western blot analyses were performed to detect the expression of signaling proteins. Murine IgE-mediated passive cutaneous anaphylaxis (PCA) and ovalbumin (OVA)-induced active systemic anaphylaxis (ASA) models were used to examine DHC effects on allergic reactions in vivo. DHC inhibited MC degranulation, as evidenced by reduced β-hexosaminidase activity and histamine levels, and reduced morphological changes associated with MC activation, namely cellular elongation and F-actin reorganization. DHC inhibited the activation of MAPK, NF-κB, and AP-1 pathways in IgE-activated MCs. Additionally, DHC could attenuate IgE/Ag-induced allergic reactions (dye extravasation and ear thickening) in PCA as well as OVA challenge-induced reactions in ASA mice (body temperature, serum histamine and IL-4 secretion changes). In conclusion, DHC suppressed MC activation. DHC may represent a new MC-suppressing treatment strategy for the treatment of IgE-mediated allergic diseases.

Fluvastatin enhances IL-33-mediated mast cell IL-6 and TNF production

Statins are HMG-CoA reductase inhibitors prescribed for lowering cholesterol. They can also inhibit inflammatory responses by suppressing isoprenylation of small G proteins. Consistent with this, we previously found that fluvastatin suppresses IgE-mediated mast cell function. However, some studies have found that statins induced pro-inflammatory cytokines in macrophages and NK cells. In contrast to IgE signaling, we show that fluvastatin augments IL-33-induced TNF and IL-6 production by mast cells. This effect required the key mast cell growth factor, stem cell factor (SCF). Treatment of IL-33-activated mast cells with mevalonic acid or isoprenoids reduced fluvastatin effects, suggesting fluvastatin acts at least partly by reducing isoprenoid production. Fluvastatin also enhanced IL-33-induced NF-κB transcriptional activity and promoted neutrophilic peritonitis in vivo, a response requiring mast cell activation. Other statins tested did not enhance IL-33 responsiveness. Therefore, this work supports observations of unexpected pro-inflammatory effects of some statins and suggests mechanisms by which this may occur. Because statins are candidates for repurposing in inflammatory disorders, our work emphasizes the importance of understanding the pleiotropic and possible unexpected effects of these drugs.