Trigger Mast Cell Research Articles

Environmental house calls can reduce symptoms of chemical intolerance: a demonstration of personalized exposure medicine.

The goals of this investigation were to 1) identify and measure exposures inside homes of individuals with chemical intolerance (CI), 2) provide guidance for reducing these exposures, and 3) determine whether our environmental house calls (EHCs) intervention could reduce both symptoms and measured levels of indoor air contaminants. CI is an international public health and clinical concern, but few resources are available to address patients' often disabling symptoms. Numerous studies show that levels of indoor air pollutants can be two to five (or more) times higher than outdoor levels. Fragranced consumer products, including cleaning supplies, air fresheners, and personal care products, are symptom triggers commonly reported by susceptible individuals. A team of professionals trained and led by a physician/industrial hygienist and a certified indoor air quality specialist conducted a series of 5 structured EHCs in 37 homes of patients reporting CI. We report three case studies demonstrating that an appropriately structured home intervention can teach occupants how to reduce indoor air exposures and associated symptoms. Symptom improvement, documented using the Quick Environmental Exposure and Sensitivity Inventory Symptom Star, corresponded with the reduction of indoor air volatile organic compounds, most notably fragrances. These results provide a deeper dive into 3 of the 37 cases described previously in Perales et al. (2022). We address the long-standing dilemma that worldwide reports of fragrance sensitivity have not previously been confirmed by human or animal challenge studies. Our ancient immune systems' 'first responders', mast cells, which evolved 500 million years ago, can be sensitized by synthetic organic chemicals whose production and use havegrown exponentially since World War II. We propose that these chemicals, which include now-ubiquitous fragrances, trigger mast cell degranulation and inflammatory mediator release in the olfactory-limbic tract, thus altering cerebral blood flow and impairing mood, memory, and concentration (often referred to as 'brain fog'). The time has come to translate these research findings into clinical and public health practice.

(091) EXPOSURE OF THE VESTIBULE TO A POSSIBLE ALLERGIC TRIGGER AT A VERY YOUNG AGE: LIFELONG NEUROPROLIFERATIVE VESTIBULODYNIA

Abstract Introduction Vestibular fibroblasts from patients with neuroproliferative vestibulodynia (NPV) versus age-matched controls produced higher proinflammatory cytokine levels of various interleukins when provoked with candida albicans in vitro. In genetically susceptible patients, this enhanced cytokine synthesis is hypothesized, in part, to lead to neuroproliferation in vestibular tissue resulting in allodynia/hyperalgesia. Patients with acquired NPV, who initially experienced pain-free penetration in their early adult reproductive life, may experience persistent severe vestibular burning following an allergic reaction to a topical agent applied to the non-keratinized vestibular epithelium. In contrast, patients with lifelong NPV present with the classic history of inability to insert a tampon at menarche (mean age 12.4 years). Patients with lifelong NPV may have unknowingly been exposed to an allergen early in their childhood, potentially even triggered from ointments used in infancy to protect from diaper rash, resulting in local vestibular mast cell accumulation in genetically susceptible patients. Agents commonly used to prevent are zinc oxide 40%, (Desitin) with inactive ingredients petrolatum, cod liver oil, lanolin, talc, glycerin, sorbitan sesquioleate, beeswax, tocopheryl acetate and fragrance and A+D ointment that includes petroleum jelly, lanolin, lavender oil, light liquid paraffin, vitamin A and vitamin D. It is possible an allergic reaction could result from any of these ingredients when applied to the non-keratinized vestibular epithelium. Objective We wished to better understand the possible triggering event in patients with lifelong NPV. Methods A chart review was performed of patients who presented between January 2019 and June 2023 who were clinically suspected to have lifelong NPV based on a history of inability to use tampons and inability to have pain-free penetration and histopathlogically confirmed to have NPV. Information was obtained from a parent or caregiver who regularly changed patient’s diapers as to what agents were utilized to manage diaper rash. Results Our patient cohort included 14 individuals with vulvas, mean age 25 (range 18-37) years. One patient prone to diaper rash was treated with A+D baby diaper rash ointment and Flanders buttocks ointment (zinc oxide, white petrolatum, white beeswax, Peruvian balsam). One patient had a “bad” yeast infection as a baby and received “topical antibiotics”. Five patients claimed Desitin and Vaseline were used while six patients claimed Desitin alone, two of whom cryied every time they Desitin was applied. One patient from Puerto Rico, received “a sock filled with cornstarch that dabbed the vaginal area and crevices after wiping the area clean”. Conclusions The endodermal vestibular epithelium is not protected by a keratin layer, including in babies at a very young age. In genetically susceptible babies, an allergic reaction to an active/inactive agent used to prevent or treat diaper rash could have potentially triggered mast cell accumulation in the baby’s vestibule leading to increased synthesis of cytokines and growth factors resulting in neuroproliferation consistent with lifelong NPV, evidenced by the inability to place a tampon at menarche. More research into this concern is needed. Disclosure No.

Mast cell conditions and drug allergy: when to suspect and how to manage.

Patients with mast cell disorders frequently experience symptoms from excessive mediator release like histamine and tryptase, ranging from mild flushing to severe anaphylactic responses. Hypersensitivity reactions (HRs) to drugs are a major cause of anaphylaxis in these patients, who often worry about triggering mast cell degranulation when taking medications. The aim of this review is to explore the complex interactions between mast cell disorders and drug HRs, focusing on the clinical challenges of managing these conditions effectively to enhance understanding and guide safer clinical practices. Among the drugs most commonly associated with hypersensitivity reactions in patients with mast cell disorders are non-steroidal anti-inflammatory drugs, antibiotics, and perioperative agents. Recent studies have highlighted the role of Mas-related G-protein coupled receptor member X2 (MRGPRX2) - a receptor involved in non-immunoglobulin E mediated mast cell degranulation - in exacerbating HRs. Investigations reveal varied drug tolerance among patients, underscoring the need for individual risk assessments. Tailored diagnostic approaches are crucial for confirming drug allergies and assessing tolerance in patients with mastocytosis, preventing unnecessary medication avoidance and ensuring safety before acute situations arise.

Novel IgE crosslinking-induced luciferase expression method using human-rat chimeric IgE receptor-carrying mast cells

BackgroundThe measurement of antigen-specific serum IgE is common in clinical assessments of type I allergies. However, the interaction between antigens and IgE won't invariably trigger mast cell activation. We previously developed the IgE crosslinking-induced luciferase expression (EXiLE) method using the RS-ATL8 mast cell line; however, the method may not be sensitive enough in some cases. MethodsIn this study, we introduced an NF-AT-regulated luciferase reporter gene into the RBL-2H3 rat mast cell line and expressed a chimeric high-affinity IgE receptor (FcεRI) α chain gene, comprising an extracellular domain from humans and transmembrane/intracellular domains from rats. ResultsWe generated multiple clones expressing the chimeric receptor. Based on their responsiveness and proliferation, we selected the HuRa-40 clone. This cell line exhibited significantly elevated human α chain expression compared to RS-ATL8 cells, demonstrating a 10-fold enhancement of antigen-specific reactivity. Reproducibility across different batches and operators was excellent. Moreover, we observed a detectable response inhibition by an anti-allergy drugs (omalizumab and cyclosporin A). ConclusionsHuRa-40 cells—which carry the human-rat chimeric IgE receptor—comprise a valuable reporter cell line for the EXiLE method. Their versatility extends to various applications and facilitates high-throughput screening of anti-allergy drugs.

Biomarkers of Autoimmune Chronic Spontaneous Urticaria.

Chronic spontaneous urticaria and chronic inducible urticaria (CSU/CindU) are caused by mast cell and basophil activation leading to degranulation and the release of histamine and several other mediators. Three kinds of factors can trigger mast cells in CSU: (1) activation of stimulating receptor(s) on the mast cell membrane, (2) upregulation of certain receptor(s), and (3) intracellular dysregulation in signaling with overexpression of the spleen tyrosine kinase (SYK) or reduced activation of the inhibitory Src homology 2 (SH2)-containing inositol phosphatases (SHIP)-related pathways. In CSU, two major endotypes exist based on the primary receptor activating mechanism: type I hypersensitivity (IgE-mediated, directed against auto-allergens) and type IIb (autoimmune, via IgG autoantibodies directed against IgE or the IgE-receptor). Their treatment responses vary. We discuss in vitro and in vivo biomarkers. Patients with auto-allergic CSU have clinical characteristics that can distinguish them partly from those with autoimmune CSU. Most importantly, their disease generally presents a less aggressive course, a better response to second generation (up-dosed) antihistamines and a good response to omalizumab, if necessary. Meanwhile, autoimmune CSU/CindU patients fare less well and often need immunosuppressive drugs. Biomarkers that might help endotype CSU/CindU patients and select the most appropriate treatment, dose, and duration, e.g., for autoallergic CSU, high total IgE and IgE against auto-allergens; for autoimmune CSU, low IgE, basopenia, and IgG against autoantigens like thyroid peroxidase and a positive autologous serum skin test (but sometimes also positive in autoallergy). Some biomarkers are easily accessible but of low specificity; others are highly specific but more futuristic.

Potential Local Mechanisms for Exercise-Induced Hypoalgesia in Response to Blood Flow Restriction Training.

Overall, there is a great need within sports medicine to ensure that athletes can return from injury in an efficient, yet thorough manner. It is crucial to not avoid necessary difficulties in this process but also to ensure time-efficient rehabilitation. One of the more promising techniques to achieve timely recovery is blood flow restriction (BFR) training. BFR training is a growing and novel development that could be a vital tool to lighten the burden of recovery from injury in athletes. BFR utilizes a pneumatic tourniquet to limit blood flow in specific areas of the body. The use of BFR has been shown to potentially enhance the analgesic effects of exercise-induced hypoalgesia (EIH). By limiting pain, athletes will be less burdened by mobility and loading exercises required for them to effectively return to play. In a field where time away from sports can have massive implications, the need for tools to assist in the acceleration of the rehabilitation process is vital. Much of the work that has already been done in the field has been able to exploit the benefits of EIHand further enhance the body's capabilities through BFR. Studies have compared EIH at low- and high-intensity settings utilizing BFR with both resistance and aerobic exercise. The results of these studies show comparable beta-endorphin levels with high-intensity exercise without BFR and low-intensity exercise with BFR. Low-intensity training with BFR had greater local pain relief, perhaps indicating the promising effects of BFR in enhancing EIH. By reviewing the current literature on this topic, we hope that further progress can be made to better understand the mechanism behind BFR and its ability to enhance EIH. Currently, local metabolites are a major focus for the potential mechanism behind these effects. Mas-related G-protein-coupled receptors (Mrgprs) contribute to local pain pathways via mast cell degranulation. Similarly, chemokine receptor 2/chemokine ligand 2 (CCR2/CCL2) triggers mast cell degranulation and inflammation-induced pain. Finally, pain-reducing effects have been linked to anti-inflammatory IL-10 signaling and anaerobic metabolites via transient receptor potential vanilloid 1 (TRPV1). Through a better understanding of these metabolites and their mechanisms, it is possible to further exploit the use of BFR to not only serve athletes recovering from injury but also apply this information to better serve all patients.

SARS-CoV-2 vaccine excipients polyethylene glycol and trometamol do not induce mast cell degranulation, in an in vitro model for non-IgE-mediated hypersensitivity.

The development of vaccines against SARS-CoV2 brought about several challenges, including the management of hypersensitivity reactions to these formulations. The search for underlying mechanisms involved in these adverse events initially focused on excipients which may trigger mast cell activation responses via non-IgE pathways: polyethylene glycol and trometamol. We sought to determine whether these components, in their pure form, were capable of stimulating mast cells directly. To test this hypothesis, we used an in vitro model for non-IgE-mediated activation that has previously shown degranulation responses induced via MRGPRX2 with known drug agonists of the receptor. Human LAD2 mast cells were incubated with different concentrations (1, 10, 50 mg/ml) of trometamol and of purified polyethylene glycol/Macrogol (molecular weights: 2,000, 3,350, 4,000, and 6,000). Mast cell degranulation was assessed using a beta-hexosaminidase read-out. Interestingly, degranulation responses for all reagents tested showed no significant differences from those obtained from the negative control (basal degranulation). Receptor-silencing assays were therefore not conducted. In summary, purified PEG and trometamol did not induce mast cell degranulation in this in vitro model for the study of non-IgE mechanisms of drug hypersensitivity, previously shown to be useful in the investigation of MRGPRX2 ligands. Studies using complete vaccine formulations, lipid conjugates, and receptor gene variants are needed to further clarify mechanisms of vaccine hypersensitivity.

Uric acid accumulation in the kidney triggers mast cell degranulation and aggravates renal oxidative stress

The accumulation of uric acid (UA) in the body can lead to the occurrence of hyperuricemia or uric acid nephropathy. Mast cells (MCs) increase oxidative stress and release renin to promote the production of Ang II. The aim of this study was to investigate the effect of UA on MCs in rat kidneys and the association between MCs and renal injury. Our results show that UA accumulation in the kidney stimulated the degranulation of MCs and the release of renin to promote Ang II production, resulting in renal oxidative stress, mitochondrial structural damage, and microvascular system damage. The expression of urate-related transporters was regulated by the UA level and serum urinary toxins levels were substantially elevated in hyperuricemia. Administration of the MCs membrane stabilizer sodium cromoglycate (SCG) or the angiotensin receptor antagonist Valsartan decreased the production of renin and Ang II and relieved renal oxidative stress, mitigated mitochondrial structural damage and microvascular system damage, and promoted the excretion of UA and urinary toxins by increasing the expression of urate-related transporters. These results demonstrate that the accumulation of UA in the kidney can trigger the degranulation of MCs and promote the development of renal oxidative stress. Administration of SCG and Valsartan ameliorated UA-induced renal injury by inhibiting MCs degranulation and reducing renal oxidative stress by inhibiting renin and Ang II production and accelerating renal clearance of UA and uremic toxins.

Immunologic aspects of migraine: A review of literature.

Migraine headaches are highly prevalent, affecting 15% of the population. However, despite many studies to determine this disease's mechanism and efficient management, its pathophysiology has not been fully elucidated. There are suggested hypotheses about the possible mediating role of mast cells, immunoglobulin E, histamine, and cytokines in this disease. A higher incidence of this disease in allergic and asthma patients, reported by several studies, indicates the possible role of brain mast cells located around the brain vessels in this disease. The mast cells are more specifically within the dura and can affect the trigeminal nerve and cervical or sphenopalatine ganglion, triggering the secretion of substances that cause migraine. Neuropeptides such as calcitonin gene-related peptide (CGRP), neurokinin-A, neurotensin (NT), pituitary adenylate-cyclase-activating peptide (PACAP), and substance P (SP) trigger mast cells, and in response, they secrete pro-inflammatory and vasodilatory molecules such as interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) as a selective result of corticotropin-releasing hormone (CRH) secretion. This stress hormone contributes to migraine or intensifies it. Blocking these pathways using immunologic agents such as CGRP antibody, anti-CGRP receptor antibody, and interleukin-1 beta (IL-1β)/interleukin 1 receptor type 1 (IL-1R1) axis-related agents may be promising as potential prophylactic migraine treatments. This review is going to summarize the immunological aspects of migraine.

Thebaine induces anaphylactic reactions via the MRGPRX2 receptor pathway on mast cells

Morphine derivatives are clinically important anesthetic and sedative drugs, which often show anaphylactic side effects. Mas-related G-protein coupled receptor member X2 (MRGPRX2) triggers mast cell degranulation, which is important process in anaphylactic reactions. MRGPRX2-HEK293 and LAD2 cell membrane chromatographic (CMC) models were used to screen morphine derivatives binding to MRGPRX2. Furthermore, most morphine derivatives significantly enhanced Ca2+ mobilization. More importantly, thebaine was found to effectively promote histamine release. Thebaine induced the increased release of β-hexosaminidase and high secretion level of cytokines, confirming that thebaine could further trigger anaphylactic reactions and promote subsequent inflammatory reactions. Moreover, the ability of thebaine inducing degranulation and the release of allergenic mediators in mast cells was significantly decreased after MRGPRX2 knockdown, which proved that MRGPRX2 is the key media for thebaine-induced anaphylactic reactions. Significant hind paw swelling and hypothermia in mice after injecting thebaine suggested that thebaine could trigger anaphylactic reactions in vivo.

Immunodominant conformational and linear IgE epitopes lie in a single segment of Ara h 2

Contribution of conformational epitopes to the IgE reactivity of peanut allergens Ara h 2 and Ara h 6 is at least as important as that of the linear epitopes. However, little is known about these conformational IgE-binding epitopes. We investigated the distribution of conformational epitopes on chimeric 2S-albumins. Recombinant chimeras were generated by exchanging structural segments between Ara h 2 and Ara h 6. Well-refolded chimeras, as verified by circular dichroism analysis, were then used to determine the epitope specificity of mAbs by performing competitive inhibition of IgG binding. Furthermore, we delineated the contribution of each segment to the overall IgE reactivity of both 2S-albumins by measuring the chimeras' IgE-binding capacity with sera from 21 patients allergic to peanut. We finally assessed chimeras' capacity to trigger mast cell degranulation. Configuration of the conformational epitopes was preserved in the chimeras. Mouse IgG mAbs, raised against natural Ara h 6, and polyclonal human IgE antibodies recognized different conformational epitopes distributed all along Ara h 6. In contrast, we identified human IgG mAbs specific to different Ara h 2 linear or conformational epitopes located in all segments except the C-terminal one. The major conformational IgE-binding epitope of Ara h 2 was located in a segment located between residues 33 and 81 that also contains the major linear hydroxyproline-containing epitope. Accordingly, this segment is critical for the capacity of Ara h 2 to induce mast cell degranulation. Chimeric 2S-albumins provide new insights on the conformational IgE-binding epitopes of Ara h 2 and Ara h 6. Proximity of the immunodominant linear and conformational IgE-binding epitopes probably contributes to the high allergenicpotency of Ara h 2.

Adefovir accumulation in the renal interstitium triggers mast cell degranulation and promotes renal interstitial fibrosis

Organic anion transporters 1 (OAT1) and OAT3 are responsible for transporting adefovir (ADV) into renal tubular epithelial cells. Our previous research found that ADV accumulated in the renal interstitium and caused renal interstitial fibrosis when Oat1/3 were inhibited by OATs inhibitor probenecid for long-term. Mast cells (MCs) in the interstitial space are considered to be key drivers of renal fibrosis. The current work investigated the effect of ADV on MCs in vitro and during the development of interstitial fibrosis in rats. Results indicate that ADV triggers chymase release from cultured RBL-2H3 mast cells in a time-and concentration-dependent manner. Angiotensin II (Ang II) in renal interstitium is generated mainly by chymase, renin and other products released from MCs, and has a direct effect on fibrosis through the angiotensin receptor. The concentrations of Ang II and fibrosis was significantly increased after administration of ADV alone or with probenecid for 4 weeks. The MCs membrane stabilizer sodium cromoglycate (SCG) and the angiotensin receptor antagonist Valsartan (VAL) could ameliorate ADV-induced nephrotoxicity. Additionally, SCG or VAL could reduce the accumulation of ADV in the renal interstitium by upregulating the expression of Oat1/3 and multidrug resistance-associated protein 4. Therefore, ADV accumulation in the renal interstitium could promote the degranulation of interstitial MCs and drive the development of renal fibrosis. SCG or VAL could ameliorate ADV-associated fibrosis by decreasing degranulation of MCs and accelerating renal clearance of ADV.

Mast cell activation syndrome-anesthetic challenges in two different clinical scenarios.

Mast cell activation syndrome (MCAS) includes a group of disorders that result in the inappropriate release of inflammatory mediators from mast cells. These mediators can affect multiple organ systems and lead to significant morbidity, and possible fatality. Although reactions, typically in response to various nonspecific stimuli, are usually mild, they may put those with MCAS at increased risk of anaphylaxis. In this case report, we present two clinical scenarios of MCAS, and identify possible factors triggering mast cell mediator release. We also define a preoperative preventive pathway, outline anesthetic considerations, and discuss the management of immediate hypersensitivity reactions in patients with MCAS. Meticulous preoperative preparation, avoidance of triggers, and development of a plan to treat possible adverse organ responses are paramount of good outcomes.

MRGPRX2 and Adverse Drug Reactions.

Many adverse reactions to therapeutic drugs appear to be allergic in nature, and are thought to be triggered by patient-specific Immunoglobulin E (IgE) antibodies that recognize the drug molecules and form complexes with them that activate mast cells. However, in recent years another mechanism has been proposed, in which some drugs closely associated with allergic-type events can bypass the antibody-mediated pathway and trigger mast cell degranulation directly by activating a mast cell-specific receptor called Mas-related G protein-coupled receptor X2 (MRGPRX2). This would result in symptoms similar to IgE-mediated events, but would not require immune priming. This review will cover the frequency, severity, and dose-responsiveness of allergic-type events for several drugs shown to have MRGPRX2 agonist activity. Surprisingly, the analysis shows that mild-to-moderate events are far more common than currently appreciated. A comparison with plasma drug levels suggests that MRGPRX2 mediates many of these mild-to-moderate events. For some of these drugs, then, MRGPRX2 activation may be considered a regular and predictable feature after administration of high doses.

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

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

Engineering the Fab fragment of the anti-IgE omalizumab to prevent Fab crystallization and permit IgE-Fc complex crystallization.

Immunoglobulin E (IgE) plays a central role in the allergic response, in which cross-linking of allergen by FcεRI-bound IgE triggers mast cell and basophil degranulation and the release of inflammatory mediators. The high-affinity interaction between IgE and FcεRI is a long-standing target for therapeutic intervention in allergic disease. Omalizumab is a clinically approved anti-IgE monoclonal antibody that binds to free IgE, also with high affinity, preventing its interaction with FcεRI. All attempts to crystallize the pre-formed complex between the omalizumab Fab and the Fc region of IgE (IgE-Fc), to understand the structural basis for its mechanism of action, surprisingly failed. Instead, the Fab alone selectively crystallized in different crystal forms, but their structures revealed intermolecular Fab/Fab interactions that were clearly strong enough to disrupt the Fab/IgE-Fc complexes. Some of these interactions were common to other Fab crystal structures. Mutations were therefore designed to disrupt two recurring packing interactions observed in the omalizumab Fab crystal structures without interfering with the ability of the omalizumab Fab to recognize IgE-Fc; this led to the successful crystallization and subsequent structure determination of the Fab/IgE-Fc complex. The mutagenesis strategy adopted to achieve this result is applicable to other intractable Fab/antigen complexes or systems in which Fabs are used as crystallization chaperones.

In Planta Glycan Engineering and Functional Activities of IgE Antibodies.

Human immunoglobulin E (IgE) is the most extensively glycosylated antibody isotype so glycans attached to the seven N-glycosites (NGS) in its Fab and Fc domains may modulate its functions. However, targeted modification of glycans in multiply glycosylated proteins remains a challenge. Here, we applied an in vivo approach that allows the manipulation of IgE N-glycans, using a trastuzumab equivalent IgE (HER2-IgE) as a model. Taking advantage of plant inherent features, i.e., synthesis of largely homogeneous complex N-glycans and susceptibility to glycan engineering, we generated targeted glycoforms of HER2-IgE largely resembling those found in serum IgE. Plant-derived HER2-IgE exhibited N-glycans terminating with GlcNAc, galactose or sialic acid, lacking, or carrying core fucose and xylose. We were able to not only modulate the five NGSs naturally decorated with complex N-glycans, but to also induce targeted glycosylation at the usually unoccupied NGS6, thus increasing the overall glycosylation content of HER2-IgE. Recombinant human cell-derived HER2-IgE exhibited large N-glycan heterogeneity. All HER2-IgE variants demonstrated glycosylation-independent binding to the target antigen and the high affinity receptor FcεRI, and subsequent similar capacity to trigger mast cell degranulation. In contrast, binding to the low affinity receptor CD23 (FcεRII) was modulated by the glycan profile, with increased binding to IgE variants with glycans terminating with GlcNAc residues. Here we offer an efficient in planta approach to generate defined glycoforms on multiply glycosylated IgE, allowing the precise exploration of glycosylation-dependent activities.

A mast-cell-specific receptor mediates Iopamidol induced immediate IgE-independent anaphylactoid reactions

Iopamidol is a radiographic contrast media which caused a very high incidence of anaphylactic reactions. Mast cells are sentinel cells in host defense reactions during immediate hypersensitivity responses and anaphylactic responses. Mas-related G protein-coupled receptor X2 (MRGPRX2) is a kind of mast cell specific receptor, which triggers mast cell degranulation in anaphylactic reactions. Mice MrgprB2 is a homologous gene of MRGPRX2. We sought to better understand the anaphylactic reactions induced by Iopamidol and the mechanisms involving MRGPRX2. The MRGPRX2-related anaphylactic reactions induced by Iopamidol were investigated using the hindpaw swelling and extravasation assay in vivo and a calcium imaging assay was used for mast cell intracellular calcium responses detection and mast cell release of anaphylactic mediators, such as β-hexosaminidase, histamine and TNF-α, was also detected in vitro. The mast cell deficient KitW-sh/W-sh mice and MrgprB2 knockout mice exhibited a reduced Iopamidol-induced inflammation effect compared with wild type mice. Furthermore, human mast cells that express MRGPRX2 were activated by Iopamidol in a dose-dependent manner, meanwhile MRGPRX2 knockdown mast cells showed reduced intracellular calcium responses and anaphylactic mediators release effect. It could be concluded that Iopamidol-induced anaphylactoid reactions were MRGPRX2 mediated to provoke mast cells Ca2+ mobilization and degranulation.

A Connective Tissue Mast-Cell-Specific Receptor Detects Bacterial Quorum-Sensing Molecules and Mediates Antibacterial Immunity

Quorum-sensing molecules (QSMs) are secreted by bacteria to signal population density. Upon reaching a critical concentration, QSMs induce transcriptional alterations in bacteria, which enable virulence factor expression and biofilm formation. It is unclear whether mammalian hosts can recognize QSMs to trigger responsive antibacterial immunity. We report that mouse mast-cell-specific G-protein-coupled receptor Mrgprb2 and its human homolog MRGPRX2 are receptors for Gram-positive QSMs, including competence-stimulating peptide (CSP)-1. CSP-1 activates Mrgprb2 and MRGPRX2, triggering mast cell degranulation, which inhibits bacterial growth and prevents biofilm formation. Such antibacterial functions are reduced in Mrgprb2-deficient mast cells, while wild-type mast cells fail to inhibit the growth of bacterial strains lacking CSP-1. Mrgprb2-knockout mice exhibit reduced bacterial clearance, while pharmacologically activating Mrgprb2 invivo eliminates bacteria and improves disease score. These findings identify a host defense mechanism that uses QSMs as an "Achilles heel" and suggest MRGPRX2 as a potential therapeutic target for controlling bacterial infections.

Mannitol triggers mast cell–dependent contractions of human small bronchi and prostacyclin bronchoprotection

Clinical research supports that exercise-induced bronchoconstriction (EIB) is caused by hyperosmolar triggering of mast cells. The reaction can be mimicked by inhalation of mannitol, but it has paradoxically previously not been possible to replicate this mode of action of mannitol in isolated airways. We sought to establish an exvivo model of EIB in human small bronchi. Small bronchi (inner diameter, 0.5-2mm) from macroscopically healthy human lung tissue were obtained from 48 patients and mounted in organ baths. Contractions and mediator release were analyzed after challenge with hyperosmolar mannitol (850 mOsm). Ten minutes of exposure to mannitol caused a small initial contraction (12%±1% of maximum) that was followed by a second and much larger contraction (maximum effect [Emax], 47%±5%) when mannitol was washed out. The mast cell stabilizer cromolyn reduced the second contraction (Emax,27%±3%). Furthermore, this main contraction was abolished by the combination of antagonists of histamine and cysteinyl leukotrienes in the presence of indomethacin. Mannitol increased the release of the mast cell mediators histamine (9.0-fold), cysteinyl leukotrienes (4.5-fold), and prostaglandin (PG) D2 (5.4-fold), as well as PGE2 (6.3-fold) and the prostacyclin metabolite 6-keto PGF1α (5.7-fold). In contrast, indomethacin alone enhanced the bronchoconstriction (Emax,68%±6%). Likewise, receptor antagonists for PGE2 (EP2 and EP4) and prostacyclin (IP)also enhanced the mannitol-induced bronchoconstriction (Emax, 67%±5%, 66%±4%, and 68%±3%, respectively). In bronchi precontracted by carbachol, the IP receptor agonist cicaprost induced profound relaxation. This new protocol established an invitro model for studies of EIB in isolated human bronchi. The IP receptor might be a new target for asthma treatment.