IgE-mediated Mast Cell Activation Research Articles

A highly selective KIT inhibitor MOD000001 suppresses IgE-mediated mast cell activation

BackgroundThe KIT receptor tyrosine kinase and its ligand, stem cell factor (SCF) control proliferation and survival of mast cells. Thus, targeting KIT signaling may show promise for the treatment of allergic diseases involving mast cells. Recently, we discovered a new compound MOD000001 as a potential small-molecule KIT kinase inhibitor by using an in silico approach. ObjectiveThis study determined whether MOD000001 is highly-selective to KIT, inhibits KIT signaling in mast cells, and affects IgE-mediated mast cell activation. MethodsThe interaction of MOD000001 with 468 human kinases and its inhibitory activity against KIT were profiled and evaluated by using KinomeScan and cell-free kinase assays, respectively. The effects of MOD000001 on SCF-dependent signaling were examined by using primary mouse and human mast cells. The effects of MOD000001 on SCF-induced degranulation and passive cutaneous anaphylactic (PCA) reaction were examined in mice. ResultsMOD000001 interacted with KIT and inhibited KIT kinase activity with high selectivity. MOD000001 suppressed SCF-induced KIT signaling in mouse and human mast cells and in mice. PCA reaction was suppressed in mice treated with MOD000001 both for a short-term (1 week) and a long-term (7 weeks). Mice treated with MOD000001 for a long-term, but not for a short-term, showed skin mast cell reduction. ConclusionsMOD000001 is a highly selective KIT inhibitor that can suppress IgE-mediated mast cell activation in vivo. MOD000001 may do so by reducing tissue mast cell numbers or by other unknown mechanisms. The findings suggest potential benefits of MOD000001 for allergic diseases involving IgE-mediated mast cell activation.

Identification of pyruvic and maleic acid as potential markers for disease activity and prognosis in chronic urticaria

BackgroundPopulation-based studies have highlighted the link between chronic urticaria (CU) and metabolic syndrome, and metabolic alterations have been revealed in CU. However, to our knowledge, a comprehensive metabolomics study on a large cohort of CU patients has not been reported. ObjectiveTo explore the underlying metabolic subtypes and novel metabolite biomarkers for CU diagnosis and therapy. MethodsPlasma samples from 80 CU patients and 82 healthy controls (HCs) were collected for metabolomics quantification and performed bioinformatics analysis. Another independent cohort consisting of 144 CU patients was studied to validate the findings. Bone marrow-derived mast cells (BMMCs) and IgE-induced passive cutaneous anaphylaxis (PCA) mice were utilized for in vitro and in vivo experiments, respectively. ResultsWe observed clear metabolomics difference between CU and HC. Meanwhile, differential metabolites N6-acetyl-l-lysine, L-aspartate, maleic acid and pyruvic acid were used to respectively construct random forest classifiers, and achieved AUCs greater than 0.85, suggesting their potential as diagnostic biomarkers of CU. More importantly, by exploring the underlying metabolic subtypes of CU, we found that the low abundance of pyruvic acid and maleic acid was significantly related to the activity of CU, poor efficacy of second-generation H1-antihistamines (sgAHs), and short relapse-free time. The results were validated in the independent cohort. Moreover, supplementation with pyruvate or maleate could significantly attenuate IgE-mediated mast cells activation in vitro and in vivo. ConclusionsThe combination of plasma pyruvic acid and maleic acid may be effective biomarkers for predicting the disease activity, therapeutic efficacy as well as prognosis for CU patients.

A novel natural Syk inhibitor suppresses IgE-mediated mast cell activation and passive cutaneous anaphylaxis

Spleen tyrosine kinase (Syk) plays a crucial role as a target for allergy treatment due to its involvement in immunoreceptor signaling. The purpose of this study was to identify natural inhibitors of Syk and assess their effects on the IgE-mediated allergic response in mast cells and ICR mice. A list of eight compounds was selected based on pharmacophore and molecular docking, showing potential inhibitory effects through virtual screening. Among these compounds, sophoraflavanone G (SFG) was found to inhibit Syk activity in an enzymatic assay, with an IC50 value of 2.2 μM. To investigate the conformational dynamics of the SYK-SFG system, we performed molecular dynamics simulations. The stability of the binding between SFG and Syk was evaluated using root mean square deviation (RMSD) and root mean square fluctuation (RMSF). In RBL-2H3 cells, SFG demonstrated a dose-dependent suppression of IgE/BSA-induced mast cell degranulation, with no significant cytotoxicity observed at concentrations below 10.0 μM within 24 h. Furthermore, SFG reduced the production of TNF-α and IL-4 in RBL-2H3 cells. Mechanistic investigations revealed that SFG inhibited downstream signaling proteins, including phospholipase Cγ1 (PLCγ1), as well as mitogen-activated protein kinases (AKT, Erk1/2, p38, and JNK), in mast cells in a dose-dependent manner. Passive cutaneous anaphylaxis (PCA) experiments demonstrated that SFG could reduce ear swelling, mast cell degranulation, and the expression of COX-2 and IL-4. Overall, our findings identify naturally occurring SFG as a direct inhibitor of Syk that effectively suppresses mast cell degranulation both in vitro and in vivo.

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.

The B Cell Response and Formation of Allergenic and Anti-Allergenic Antibodies in Food Allergy.

Food allergies are a growing public health concern worldwide, especially in children and young adults. Allergen-specific IgE plays a central role in the pathogenesis of food allergies, but their titers poorly correlate with allergy development. Host immune systems yield allergen-specific immunoglobulin (Ig)A, IgE and IgG subclasses with low or high affinities and differential Fc N-glycosylation patterns that can affect the allergic reaction to food in multiple ways. High-affinity IgE is required to induce strong mast cell activation eventually leading to allergic anaphylaxis, while low-affinity IgE can even inhibit the development of clinically relevant allergic symptoms. IgA and IgG antibodies can inhibit IgE-mediated mast cell activation through various mechanisms, thereby protecting IgE-positive individuals from allergy development. The production of IgE and IgG with differential allergenic potential seems to be affected by the signaling strength of individual B cell receptors, and by cytokines from T cells. This review provides an overview of the diversity of the B cell response and the diverse roles of antibodies in food allergy.

Elevated baseline soluble FcεRI may be linked to early response to omalizumab treatment in chronic spontaneous urticaria.

Omalizumab, an anti-IgE monoclonal antibody, is an effective treatment in chronic spontaneous urticaria (CSU). Predictors of fast and good response for omalizumab treatment have not yet been identified and characterized. To evaluate whether soluble FcεRI (sFcεRI), a marker of IgE-mediated mast cell activation, predicts the time of response to omalizumab in CSU. Sera of 67 CSU patients were obtained before omalizumab treatment and analysed for sFcεRI levels by ELISA (2 ng/mL was used as cut-off for elevated sFcɛRI). Treatment response during the first 4 weeks was assessed with the urticaria activity score (UAS7), urticaria control test (UCT) and the rolling UAS7 (rUAS7). Elevated pre-treatment sFcɛRI levels were detected in more than 70% of patients with completely controlled disease (UCT = 16) and well-controlled disease (UCT = 12-15) and were significantly associated with disease control (χ2 = 4.94, p < 0.05). More than half of the patients (14/25) with low levels had poor disease control (UCT < 12). Of the patients who achieved complete and marked UAS7 response, respectively, 75% and 63% had elevated baseline sFcɛRI levels. Post-treatment UAS7 scores were lower in patients with elevated sFcɛRI levels reaching statistical significance at Week 3 (p < 0.05). Patients with elevated baseline sFcɛRI levels achieved rUAS7 ≤ 6 and = 0 earlier than those with lower levels (Days 9 vs. 13 and Days 12 vs. 14, respectively). Elevated sFcεRI serum levels predict early and good response to treatment with omalizumab, which may help to better design treatment options for CSU patients.

To eat or not to eat: type 2 immunity controls food avoidance behavior

Growing evidence suggests that food allergies are regulated by neuroimmune interactions. However, the underlying molecular mechanisms remain unclear. Plum et al. and Florsheim et al. identify IgE-mediated mast cell activation, leukotrienes, and growth differentiating factor 15 (GDF15) as key regulators of the avoidance response to food allergens in mice.

Inhibiting Isoprenylation Suppresses FcεRI-Mediated Mast Cell Function and Allergic Inflammation.

IgE-mediated mast cell activation is a driving force in allergic disease in need of novel interventions. Statins, long used to lower serum cholesterol, have been shown in multiple large-cohort studies to reduce asthma severity. We previously found that statins inhibit IgE-induced mast cell function, but these effects varied widely among mouse strains and human donors, likely due to the upregulation of the statin target, 3-hydroxy-3-methylgutaryl-CoA reductase. Statin inhibition of mast cell function appeared to be mediated not by cholesterol reduction but by suppressing protein isoprenylation events that use cholesterol pathway intermediates. Therefore, we sought to circumvent statin resistance by targeting isoprenylation. Using genetic depletion of the isoprenylation enzymes farnesyltransferase and geranylgeranyl transferase 1 or their substrate K-Ras, we show a significant reduction in FcεRI-mediated degranulation and cytokine production. Furthermore, similar effects were observed with pharmacological inhibition with the dual farnesyltransferase and geranylgeranyl transferase 1 inhibitor FGTI-2734. Our data indicate that both transferases must be inhibited to reduce mast cell function and that K-Ras is a critical isoprenylation target. Importantly, FGTI-2734 was effective invivo, suppressing mast cell-dependent anaphylaxis, allergic pulmonary inflammation, and airway hyperresponsiveness. Collectively, these findings suggest that K-Ras is among the isoprenylation substrates critical for FcεRI-induced mast cell function and reveal isoprenylation as a new means of targeting allergic disease.

Simultaneous reduction of all ORMDL proteins decreases the threshold of mast cell activation

In mammals, the ORMDL family of evolutionarily conserved sphingolipid regulators consists of three highly homologous members, ORMDL1, ORMDL2 and ORMDL3. ORMDL3 gene has been associated with childhood-onset asthma and other inflammatory diseases in which mast cells play an important role. We previously described increased IgE-mediated activation of mast cells with simultaneous deletions of ORMDL2 and ORMDL3 proteins. In this study, we prepared mice with Ormdl1 knockout and thereafter, produced primary mast cells with reduced expression of one, two or all three ORMDL proteins. The lone deletion of ORMDL1, or in combination with ORMDL2, had no effect on sphingolipid metabolism nor IgE-antigen dependent responses in mast cells. Double ORMDL1 and ORMDL3 knockout mast cells displayed enhanced IgE-mediated calcium responses and cytokine production. Silencing of ORMDL3 in mast cells after maturation increased their sensitivity to antigen. Mast cells with reduced levels of all three ORMDL proteins demonstrated pro-inflammatory responses even in the absence of antigen activation. Overall, our results show that reduced levels of ORMDL proteins shift mast cells towards a pro-inflammatory phenotype, which is predominantly dependent on the levels of ORMDL3 expression.

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&amp;BD Program of The Food Industry Promotional Agency of Korea. This research was supported by the 2022 Collaborative R&amp;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

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.

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.

Histamine-Releasing Factor Is a Novel Alarmin Induced by House Dust Mite Allergen, Cytokines, and Cell Death.

Histamine-releasing factor (HRF) is a multifunctional protein with fundamental intracellular functions controlling cell survival and proliferation. HRF is also secreted during allergic reactions and promotes IgE-mediated activation of mast cells and basophils. In this study, we investigated HRF secretion and its relevance to airway inflammation. HRF monomers were constitutively secreted from BEAS-2B human bronchial epithelial cells (HBECs) and converted to oligomers over the course of culture. Stimulation with house dust mite (HDM) extract increased HRF secretion substantially. Several cytokines involved in asthma pathogenesis showed moderate effects on HRF secretion but dramatically enhanced HDM-induced HRF secretion. HDM-induced HRF secretion from BEAS-2B cells and normal HBECs proceeded via TLR2. Consistent with this, multiple TLR2 ligands, including Der p 2, Der p 5, Der p 13, and Der p 21, induced HRF secretion. Der p 10 (tropomyosin) also promoted HRF secretion. Cell death or incubation with adenosine and ATP, compounds released upon cell death, also enhanced HRF secretion. Furthermore, intranasal administration of recombinant HRF elicited robust airway inflammation in HDM-sensitized mice in an FcεRI-dependent manner. Therefore, we conclude that HRF is a novel alarmin that promotes allergic airway inflammation.

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.

The Role of TGFβ and Other Cytokines in Regulating Mast Cell Functions in Allergic Inflammation.

Mast cells (MC) are a key effector cell in multiple types of immune responses, including atopic conditions. Allergic diseases have been steadily rising across the globe, creating a growing public health problem. IgE-mediated activation of MCs leads to the release of potent mediators that can have dire clinical consequences. Current therapeutic options to inhibit MC activation and degranulation are limited; thus, a better understanding of the mechanisms that regulate MC effector functions in allergic inflammation are necessary in order to develop effective treatment options with minimal side effects. Several cytokines have been identified that play multifaceted roles in regulating MC activation, including TGFβ, IL-10, and IL-33, and others that appear to serve primarily anti-inflammatory functions, including IL-35 and IL-37. Here, we review the literature examining cytokines that regulate MC-mediated allergic immune responses.

Anaphylaxis: Mediators, Biomarkers, and Microenvironments.

The life-threatening nature of anaphylactic reactions has increased interest in discovering new biomarkers that could improve diagnosis and prevention. However, the diverse nature of the clinical features and the etiology and pathogenesis of anaphylaxis hinder the identification of valuable molecular indicators of disease. Most studies on anaphylaxis focus on the immune system. Anaphylactic reactions are characterized primarily by IgE-mediated activation of mast cells and basophils and release of mediators. Determination of serum tryptase levels is the main in vitro test used to confirm the reaction, although there are no biomarkers that can predict it. Nevertheless, recent research has postulated that alternative pathways, cell types, and systems are involved. Consequently, various molecular products have been explored and considered potential biomarkers, although none of them are yet used in clinical practice. The products that are altered in patients with anaphylaxis include vasoactive agents, proteases, proteoglycans, lipids, interleukins, cytokines, products of the complement-contact and coagulation systems, circulating proteins, extracellular vesicles, microRNAs, and metabolites. The recognition of biological processes and molecular pathways affecting the microenvironments involved in anaphylaxis will considerably improve clinical practice and the identification of better molecular markers. We offer a broad review of the various mediators described in anaphylaxis, consider their usefulness as potential biomarkers of this pathological event, and examine their role in the molecular basis of the reaction.