Mast Cell Responses Research Articles

IL-33 signaling is dispensable for the IL-10-induced enhancement of mast cell responses during food allergy

BackgroundThe IL-33/ST2 axis plays a pivotal role in the development of IgE-mediated mast cell (MC) responses during food allergy. We recently demonstrated that the pleiotropic cytokine, IL-10, not only exerts proinflammatory effects on IgE-mediated MC activation, but also promotes IL-33-induced MC responses. However, whether IL-33 is necessary for IL-10’s proinflammatory effects has not been examined.MethodsTo therefore determine the role of the IL-33/ST2 axis in this pathway, we assessed the effects of IL-10 on IgE-mediated MC activation and food allergy development in wild-type (WT) and ST2-/- mice.ResultsIL-10 stimulation significantly enhanced IL-33 gene expression, ST2 receptor expression, cytokine production, mMCP-1 secretion, and proliferation in IgE and antigen-activated bone marrow-derived MCs (BMMCs) from WT mice. ST2-/- BMMCs exhibited reduced cytokine secretion in response to IgE-dependent activation. However, IL-10 enhanced cytokine production, mMCP-1 secretion, and proliferation in these cells as well. To further assess the role of IL-10, food allergy was induced in WT and ST2-/- mice subjected to antibody-mediated IL-10 depletion. IL-10-depleted WT mice exhibited a significant attenuation in MC-mediated responses to OVA challenge. While ST2-/- mice also exhibited a profound suppression of MC responses, IL-10 depletion had no additional effects. However, ST2-/-/IL-10-/- mice exhibited further decreases in OVA-IgE and antigen-specific MC activation compared to ST2-/- mice.ConclusionOur data demonstrates that IL-10 can enhance MC responses in both WT and ST2-/- mice, further corroborating its proinflammatory effects on MCs and suggesting that they are not regulated by IL-33 signaling.

Multiplex basophil activation tests for allergy diagnosis: present and future applications.

The basophil activation test (BAT) has become a major cellular in vitro test for evaluating the allergenic activity of specific IgEs. The impact of the BAT is due to the ability of blood basophil granulocytes to present IgE on the high-affinity FcεRI receptor and to mirror the mast cell response that elicits an acute allergic reaction. The BAT proved to be able to identify allergic patients at risk of reacting to a low dose of the allergen and/or developing life-threatening reactions and thus can significantly improve the current management of allergic patients. However, to improve the diagnostic utility for identifying the allergenic activity of different genuinely sensitizing allergens and lower the procedure and labour requirements, developing a multiplex BAT approach incorporating multiple allergen components would be highly anticipated. Recently, the novel multiplex BAT was described utilizing two major innovative steps. The first step was the fluorescent labeling of allergens. The second step was applying fluorescently labeled allergens in flow cytometry assessment to analyze the activation of basophil subpopulations gated according to the binding of different allergens or to evaluate the fluorescence intensity of multiple allergens on the surface of basophils. These novel cellular multiplex approaches will advance our understanding of IgE-mediated responses. Integration of multiplex BAT, in addition to multiplex IgE assays into practice, will personalize the measurement of allergenic IgE activity and can help estimate the likelihood of clinical relevance and risks for multiple allergens when testing individual allergic patients.

Sex hormones and allergies: exploring the gender differences in immune responses.

Allergies are closely associated with sex-related hormonal variations that influence immune function, leading to distinct symptom profiles. Similar sex-based differences are observed in other immune disorders, such as autoimmune diseases. In allergies, women exhibit a higher prevalence of atopic conditions, such as allergic asthma and eczema, in comparison to men. However, age-related changes play a significant role because men have a higher incidence of allergies until puberty, and then comes a switch ratio of prevalence and severity in women. Investigations into the mechanisms of how the hormones influence the development of these diseases are crucial to understanding the molecular, cellular, and pathological aspects. Sex hormones control the reproductive system and have several immuno-modulatory effects affecting immune cells, including T and B cell development, antibody production, lymphoid organ size, and lymphocyte death. Moreover, studies have suggested that female sex hormones amplify memory immune responses, which may lead to an excessive immune response impacting the pathogenesis, airway hyperresponsiveness, inflammation of airways, and mucus production of allergic diseases. The evidence suggests that estrogens enhance immune humoral responses, autoimmunity, mast cell reactivity, and delayed IV allergic reactions, while androgens, progesterone, and glucocorticoids suppress them. This review explores the relationship between sex hormones and allergies, including epidemiological data, experimental findings, and insights from animal models. We discuss the general properties of these hormones, their effects on allergic processes, and clinical observations and therapeutic results. Finally, we describe hypersensitivity reactions to these hormones.

The impact of atmospheric ultrafine particulate matter on IgE-mediated type 1 hypersensitivity reaction

The effect of atmospheric ultrafine particulate matter (UPM) on respiratory allergic diseases has been investigated for decades; however, the precise molecular mechanisms underlying these effects remain poorly understood. In this study, we used a simulated UPM (sUPM) generated via the spark discharge method to refine black carbon, a core particle that closely mimics real-world UPM, including the size (i.e., size of agglomerates: 165 nm) and organic carbon/elemental carbon ratio (i.e., 2.62). When 25 μg/mouse of dispersed sUPM was instilled into the lungs of mice, it promoted the infiltration and degranulation response of pulmonary mast cells, and exposure to sUPM in an immunoglobulin E (IgE)-mediated passive anaphylaxis model intensified the degranulation response of peripheral mast cells. These effects of sUPM were demonstrated to amplify the downstream signaling mechanism of the high-affinity IgE receptor (FcεRI) mediated by IgE when tested using rat basophil leukemia (RBL)−2H3 and mouse bone marrow-derived mast cells (BMMCs) collected from the bone marrow of BALB/c mice. These results indicate that airborne UPM can exacerbate type 1 hypersensitivity reactions by enhancing the IgE-mediated signaling pathways within mast cells. Furthermore, this study provided mechanistic evidence on exacerbated allergic pulmonary diseases induced by UPM inhalation.

Interleukin-33 mediated regulation of microRNAs in human cord blood-derived mast cells: Implications for infection, immunity, and inflammation.

Mast cell (MCs) activation is the driving force of immune responses in several inflammatory diseases, including asthma and allergies. MCs are immune cells found throughout the body and are equipped with numerous surface receptors that allow them to respond to external signals from parasites and bacteria as well as to intrinsic signals such as cytokines. Upon activation, MCs release various mediators and proteases that contribute to inflammation. This study aimed to identify microRNAs (miRNAs) that regulate MC response to interleukin-33 and their target genes using a model of human cord blood-derived mast cells (hCBMCs). hCBMCs were induced with 10 and 20 ng of recombinant human interleukin-33 (rhIL-33) for 6 and 24 h, respectively. Total RNA was extracted from these cells and miRNA profiling was performed using high-throughput microarrays. Differential expression of miRNAs and target analysis were performed using Transcriptome Analysis Console and Ingenuity Pathway Analysis. The most significant miRNAs in each condition were miR-6836-5p (fold change = 1.76, p = 3E-03), miR-6883-5p (fold change = -2.13, p = 7E-05), miR-1229-5p (fold change = 2.46, p = 8E-04), and miR-3613-5p (fold change = 66.7, p = 1E-06). Target analysis revealed that these miRNAs regulate mast cell responsiveness and degranulation by modulating the expression of surface receptors, adaptors, and signaling molecules in response to rhIL-33 stimulation. This study is the first miRNA profiling and target analysis of hCBMCs that will further enhance our understanding of the role of miRNAs in the immune response in a timely manner and their relevance for the development of a new therapeutic target for inflammatory disorders.

The importance of mast cell histamine secretion in IgG-mediated systemic anaphylaxis.

IgG can mediate murine and human systemic anaphylaxis (SA). The roles of mast cells (MCs) and histamine in IgG-mediated anaphylaxis are controversial for mice and have not been studied invivo for humans. We are now investigating these issues. Actively or passively sensitized wild-type and immune-deficient mice were induced to develop anaphylaxis by intravenous antigen challenge. Anaphylaxis was characterized by evaluating hypothermia, hypomobility, histamine, and MC protease responses. In contrast to our previous results with protein-immunized mice from a conventional colony, IgG-mediated passive SA in our specific pathogen-free colony mice depended considerably on histamine produced by connective tissue MCs (CTMCs) in response to FcγRIII crosslinking. This was found for C57BL/6 and young male and female BALB/c mice, including BALB/c mice newly arrived from 3 vendors. IgG-mediated anaphylaxis was less histamine dependent in old than young mice. Although both mucosal MC (MMC) and CTMC responses were severely depleted in c-kit-deficient mice, MMC responses depended considerably more than CTMC responses on c-kit for maintenance. In immunologically naive mice, FcγRIII crosslinking strongly activated a subset of CTMCs but had little ability to activate MMCs. Invivo LPS+ poly I:C treatment decreased histamine dependence of IgG-mediated anaphylaxis, while a strong TH2 immune response increased FcγRIII crosslinking-induced MMC activation. IgG-mediated activation of human MCs in reconstituted immunodeficient mice induced histamine-dependent anaphylaxis. IgG-dependent SA can be mediated largely by histamine released by mouse CTMCs and human MCs; histamine dependence is influenced by mouse age, sex, and immune and infectious history, as well as the anaphylaxis model studied.

Photobiological response of mast cells to green and red light-emitting diodes (LEDs) in cutaneous burns.

This study assessed the effects of red and green LEDs on mast cells (MCs) in third-degree burns in 75 Wistar rats, divided into control, red LED (RED), and green LED (GREEN) groups. Animals were irradiated daily with RED (630 nm, 300 mW, 0.779 W/cm2, 9 J/cm2, 30 s) and GREEN (520 nm, 180 mW, 0.467 W/cm2, 60 J/cm2, 30 s). Histological sections stained with toluidine blue were analyzed for total and subtype MCs. Standardized MC counting was performed across the viable lesion area, considering lesion margins, through intact connective tissue and the integrity of skin appendages. No statistically significant differences in MCs 2 (with released granules and intact cell border) were found between groups. Irradiated groups showed increased total MCs at 7, 14, and 21 days (p < 0.05), with a decrease in MCs 1 (intact MCs) at all time points compared to control (p < 0.05). Significant changes in MCs 3 (with massive degranulation and partial or complete disintegration of the cell border) degranulation were noted in RED at 7, 14, and 21 days (p < 0.009) and in GREEN at 14 (p < 0.009) and 32 days (p < 0.028). Results suggest red and green LEDs modulate MC recruitment and degranulation in third-degree burns.

Mast cells as indicators of foreign particle biocompatibility

The key problem of introducing nanoparticles into clinical practice for diagnostic and therapeutic purposes is their safety. Connective tissue, an important component of which are mast cells, reacts actively in response to foreign particles. The reaction of mast cells can be an indicator of the biocompatibility of foreign particles. The study was conducted on male Wistar rats. Iron-carbon nanoparticles in the FeC modification stabilized in an aqueous medium using an auxiliary substance were used. Tissue examination (liver, lungs, heart, thymus, kidneys) was performed 1, 7 and 30 days after injection. After the injection of nanoparticles, the largest quantity of them is found in the liver and lungs, a smaller quantity is found in the heart, kidneys and thymus. The liver and lungs are the main organs of excretion of nanoparticles due to phagocytes. The accumulation of nanoparticles in the liver leads to the development of destructive processes and to the activation of compensatory and adaptive mechanisms in the form of cellular and intracellular regeneration of hepatocytes. In organs with a low content of nanoparticles, structural changes are poorly expressed. The mast cells of the studied organs react differently to the introduction of nanoparticles. The first to react are the mast cells of the liver by reducing the quantity and increasing degranulation. The population of lung mast cells reacts unidirectionally by sharply activating degranulation without changing the amount. An increase in the secretory activity of mast cells in the lungs and liver indicates the participation of mast cells in the regulation of particle elimination through intercellular signaling pathways of interaction with the system of phagocytic mononuclear cells. Heart mast cells are involved in maintaining the inflammatory process in the early period of the experiment, contribute to the return of myocardial parameters to homeostatic norm in the late period of the experiment. Mast cells can be considered as indicators of biocompatibility nanoparticles. The absence of an inflammatory process and the preservation of the structural and functional characteristics of the tissues where nanoparticles accumulate, as well as the reaction of mast cells in them, indicate the relative safety of the particles under study.

Avidin-positive mast cells of the liver when exposed to water-soluble silicon for nine months

Mast cells, due to the mediators contained in them, are active participants in various processes occurring in the body. The reaction of avidin-positive mast cells of the liver to the intake of silicon with drinking water at a concentration of 20 mg/L for nine months was studied. The experiment was conducted on laboratory nonlinear male rats, which were divided into two groups: the control group received bottled drinking water with a silicon concentration of 10 mg/L; the experimental group received the same water, but with the addition of sodium metasilicate nine-hydrate, which was used to adjust the total concentration of silicon in drinking water to 20 mg/L. The mass concentration of silicon in the water of the control and experimental groups was determined using an inductively coupled plasma emission spectrometer 5110 ICP-OES. After nine months, the animals were sacrificed, the liver was extracted and fixed in 10% neutral formalin, processed and embedded in paraffin. After deparaffinization, 6-ìm-thick liver sections were incubated for 30 minutes with green fluorescent-labeled avidin (Avidin, Alexa Fluor® 488 conjugate, Invitrogen, Germany). The preparations were analyzed under a fluorescence microscope at an excitation light wavelength of 495 nm. According to the results of the study, an increase in the number of avidin-positive mast cells due to weakly fluorescent ones was found in the liver of rats of the experimental group, as well as an increase in the median of their area and fluorescence intensity. It was revealed that the change in the median of area of avidin-positive mast cells in the liver of rats of the experimental group is due to a decrease in the number of small cells and an increase in the number of medium and large cells. Positive strong and positive average correlations were established between the cell area and its intensity in the control and experimental groups, respectively. Thus, the study made it possible to expand the data on the effect of water-soluble silicon on the liver and indirectly suggest the occurrence of inflammatory processes in the organ under study.

Adipokine receptor expression in mast cells is altered by specific ligands and proinflammatory cytokines.

Adipokines play essential roles in regulating a range of biological processes, but growing evidence indicates that they are also fundamental in immunological mechanisms and, primarily, inflammatory responses. Adipokines mediate their actions through specific receptors. However, although adipokine receptors are widely distributed in many cell and tissue types, limited data are available on their expression in mast cells (MCs) and, consequently, adipokine's significance in the modulation of MC activity within the tissues. In this study, we demonstrate that rat peritoneal MCs constitutively express the leptin receptor (i.e. LEPR), adiponectin receptors (i.e. ADIPOR1 and ADIPOR2) and the chemerin receptor (i.e. CMKLR1). We also found that LEPR, ADIPOR1, ADIPOR2 and CMKLR1 expression in MCs changes in response to stimulation by their specific ligands and some cytokines with potent proinflammatory properties. Furthermore, the involvement of intracellular signaling molecules in leptin-, adiponectin- and chemerin-induced MC response was analyzed. Overall, our findings suggest that adipokines leptin, adiponectin and chemerin can significantly affect the activity of MCs in various processes, especially during inflammation. These observations may contribute significantly to understanding the relationship between adipokines, immune mechanisms and diseases or conditions with an inflammatory component.

IgE-Mediated Mast Cell Responses to Rocuronium: A Matter of Protonation Status.

IgE-Mediated Mast Cell Responses to Rocuronium: A Matter of Protonation Status.

Glutenin from the Ancient Wheat Progenitor Is Intrinsically Allergenic as It Can Clinically Sensitize Mice for Systemic Anaphylaxis by Activating Th2 Immune Pathway.

Wheat allergy is a major type of food allergy with the potential for life-threatening anaphylactic reactions. Common wheat, Triticum aestivum (hexaploid, AABBDD genome), was developed using tetraploid wheat (AABB genome) and the ancient diploid wheat progenitor (DD genome)-Aegilops tauschii. The potential allergenicity of gluten from ancient diploid wheat is unknown. In this study, using a novel adjuvant-free gluten allergy mouse model, we tested the hypothesis that the glutenin extract from this ancient wheat progenitor will be intrinsically allergenic in this model. The ancient wheat was grown, and wheat berries were used to extract the glutenin for testing. A plant protein-free colony of Balb/c mice was established and used in this study. The intrinsic allergic sensitization potential of the glutenin was determined by measuring IgE response upon transdermal exposure without the use of an adjuvant. Clinical sensitization for eliciting systemic anaphylaxis (SA) was determined by quantifying the hypothermic shock response (HSR) and the mucosal mast cell response (MMCR) upon intraperitoneal injection. Glutenin extract elicited a robust and specific IgE response. Life-threatening SA associated and a significant MMCR were induced by the glutenin challenge. Furthermore, proteomic analysis of the spleen tissue revealed evidence of in vivo Th2 pathway activation. In addition, using a recently published fold-change analysis method, several immune markers positively and negatively associated with SA were identified. These results demonstrate for the first time that the glutenin from the ancient wheat progenitor is intrinsically allergenic, as it has the capacity to elicit clinical sensitization for anaphylaxis via activation of the Th2 pathway in vivo in mice.

MRGPRX2-mediated mast cell activation by substance P from overloaded human tenocytes induces inflammatory and degenerative responses in tendons

Mast cells are immune cells minimally present in normal tendon tissue. The increased abundance of mast cells in tendinopathy biopsies and at the sites of tendon injury suggests an unexplored role of this cell population in overuse tendon injuries. Mast cells are particularly present in tendon biopsies from patients with more chronic symptom duration and a history of intensive mechanical loading. This study, therefore, examined the cross talk between mast cells and human tendon cells in either static or mechanically active conditions in order to explore the potential mechanistic roles of mast cells in overuse tendon injuries. A coculture of isolated human tenocytes and mast cells (HMC-1) combined with Flexcell Tension System for cyclic stretching of tenocytes was used. Additionally, human tenocytes were exposed to agonists and antagonists of substance P (SP) receptors. Mast cell degranulation was assessed by measuring β-hexosaminidase activity. Transwell and cell adhesion assays were used to evaluate mast cell migration and binding to tendon extracellular matrix components (collagen and fibronectin), respectively. Gene expressions were analyzed using real time qRT-PCR. Our results indicate that mechanical stimulation of human tenocytes leads to release of SP which, in turn, activates mast cells through the Mas-related G-protein-coupled receptor X2 (MRGPRX2). The degranulation and migration of mast cells in response to MRGPRX2 activation subsequently cause human tenocytes to increase their expression of inflammatory factors, matrix proteins and matrix metalloproteinase enzymes. These observations may be important in understanding the mechanisms by which tendons become tendinopathic in response to repetitive mechanical stimulation.

IL-10 Neutralization Attenuates Mast Cell Responses in a Murine Model of Experimental Food Allergy.

IgE-mediated mast cell (MC) activation is a critical component of allergic responses to oral Ags. Several T cell-derived cytokines have been shown to promote MC reactivity, and we recently demonstrated a critical role for the cytokine IL-10 in mediating MC responses during food allergy. In this study, we further validate the role of IL-10 using Ab-mediated IL-10 depletion. IL-10 neutralization significantly attenuated MC responses, leading to decreased MC accumulation and activation, as well as inhibition of MC-mediated symptoms such as allergic diarrhea. This was accompanied by decreased Th2 cytokine gene expression, attenuated systemic T cell responses, and fewer CD4 T cells, B cells, and MCs in the spleen. Our data further confirm the role of IL-10 in driving MC responses and suggest that IL-10-responsive MCs may constitute an important player in allergic responses.

SR-BI regulates the synergistic mast cell response by modulating the plasma membrane-associated cholesterol pool.

The high-affinity IgE receptor FcεRI is the mast cell (MC) receptor responsible for the involvement of MCs in IgE-associated allergic disorders. Activation of the FcεRI is achieved via crosslinking by multivalent antigen (Ag) recognized by IgE resulting in degranulation and proinflammatory cytokine production. In comparison to the T- and B-cell receptor complexes, for which several co-receptors orchestrating the initial signaling events have been described, information is scarce about FcεRI-associated proteins. Additionally, it is unclear how FcεRI signaling synergizes with input from other receptors and how regulators affect this synergistic response. We found that the HDL receptor SR-BI (gene name: Scarb1/SCARB1) is expressed in MCs, functionally associates with FcεRI, and regulates the plasma membrane cholesterol content in cholesterol-rich plasma membrane nanodomains. This impacted the activation of MCs upon co-stimulation of the FcεRI with receptors known to synergize with FcεRI signaling. Amongst them, we investigated the co-activation of the FcεRI with the receptor tyrosine kinase KIT, the IL-33 receptor, and GPCRs activated by adenosine or PGE2. Scarb1-deficient bone marrow-derived MCs showed reduced cytokine secretion upon co-stimulation conditions suggesting a role for plasma membrane-associated cholesterol regulating respective MC activation. Mimicking Scarb1 deficiency by cholesterol depletion employing MβCD, we identified PKB and PLCγ1 as cholesterol-sensitive proteins downstream of FcεRI activation in bone marrow-derived MCs. When MCs were co-stimulated with stem cell factor (SCF) and Ag, PLCγ1 activation was boosted, which could be mitigated by cholesterol depletion and SR-BI inhibition. Similarly, SR-BI inhibition attenuated the synergistic response to PGE2 and anti-IgE in the human ROSAKIT WT MC line, suggesting that SR-BI is a crucial regulator of synergistic MC activation.

IL-10 differentially promotes mast cell responsiveness to IL-33 resulting in induction of anaphylaxis and suppression of neutrophilia

Abstract Mast cells (MCs) play critical roles in the establishment of allergic diseases. We recently demonstrated an unexpected, proinflammatory role for IL-10 in regulating MC responses. IL-10 enhanced MC activation and promoted IgE-dependent responses during food allergy. However, whether the effects of IL-10 on MCs extend to IgE-independent stimuli is not clear. Herein, we demonstrate that IL-10 plays a critical role in driving IL-33-mediated MC responses. IL-10 stimulation significantly enhanced MC expansion, ST2 expression, IL-6 and IL-13 production, and MC degranulation in IL-33-treated BMMCs. In contrast, it suppressed TNF-a in IL-33-responding cells. These differential effects also extended in vivo. In a model of IL-33-induced neutrophilia, IL-10 enhanced IL-33 responsiveness leading to increased MC activation and suppression of neutrophils via decreased TNF-a. In contrast, during IL-33-induced type 2 inflammation, IL-10 priming exacerbated MC activity, resulting in MC recruitment to various tissues, enhanced ST2 expression and induction of anaphylaxis. Our data elucidate a novel role for IL-10 as an augmenter of IL-33-mediated MC responses, with implications during both allergic diseases and other MC-dependent disorders.

Mast Cell–Neutrophil Communication Regulates Allergic Diseases

Allergic diseases (e.g., food allergies) are a growing problem, with increasing numbers of individuals experiencing them worldwide. Congruently, the adverse reactions (e.g., anaphylaxis) associated with the administration of vaccines against emerging infectious diseases such as coronavirus disease 2019 (COVID-19) have become a familiar problem. Allergic diseases, which have a wide variety of symptoms, are difficult to prevent or cure; treatment is currently limited to therapeutic drugs or allergen immunotherapy. Therefore, elucidating new allergic regulatory factors that control the allergic (i.e., mast cell) responses is important. While investigating the regulatory mechanisms of the wide range of allergic responses of mast cells, we found that the affinity of allergens to immunoglobin E (IgE) regulates allergic inflammation through the differences in the secretory responses of mast cells and the types and interactions of the cells infiltrating the tissues. Here, we present our recent findings regarding the affinity of allergens to IgE in regulating allergic inflammation, heterogeneous secretory granules inducing diverse secretory responses, and mast cells interacting with neutrophils, thereby regulating the various allergic responses.

IL-10 promotes mast cell homeostasis and differentiation towards a mucosal mast cell phenotype

Abstract We recently demonstrated an unexpected role for IL-10 in driving mast cell (MC) activation and proliferation. IL-10 stimulation significantly enhanced IgE-mediated MC activation, upregulated FceRI expression, and promoted MC-mediated food allergy. Surprisingly, IL-10 also amplified cytokine production in un-activated MCs and enhanced their proliferation and survival, suggesting a role for IL-10 in MC homeostasis. Herein, we demonstrate that IL-10 can significantly expand MC proliferation and activity during homeostatic conditions. Treatment with IL-10 enhanced the proliferation and survival of both IL-3 and IL-3+SCF cultured bone marrow-derived MCs (BMMCs). This corresponded with a dramatic increase in cytokine production in IL-10-treated cells, along with upregulation of FceRI expression. While SCF was dispensable for the increased FceRI, it significantly enhanced cytokine production compared to cells cultured in IL-3 alone. Further analysis revealed a distinctive mucosal MC phenotype in IL-10-treated cells, characterized by beta7-integrin expression and enhanced secretion of murine MC protease-1. Lastly, autocrine IL-10 also supported MC expansion and function, as blocking IL-10 signaling attenuated MC expansion, inducing apoptosis, and decreasing cytokine production. Taken together, these data suggest an important role for IL-10 in maintaining MC responses during physiological conditions.

Mast Cells are Dependent on Glucose Transporter 1 (GLUT1) and GLUT3 for IgE-mediated Activation

Mast cells (MCs) are known to have a pathological impact in a variety of settings, in particular in allergic conditions. There is also limited evidence implicating MCs in diabetes, raising the possibility that MC function may be influenced by alterations in glucose levels. However, it is not known whether MCs are directly affected by elevated glucose concentrations. Moreover, it is not known which glucose transporters that are expressed by MCs, and whether MCs are dependent on glucose transporters for activation. Here we addressed these issues. We show that MCs express high levels of both glucose transporter 1 (GLUT1/Slc2A1) and GLUT3 (Slc2A3). Further, we show that the inhibition of either GLUT1 or GLUT3 dampens both MC degranulation and cytokine induction in response to IgE receptor crosslinking, and that combined GLUT1 and GLUT3 inhibition causes an even more pronounced inhibition of these parameters. In contrast, the inhibition of GLUT1 or GLUT3, or combined GLUT1 and GLUT3 inhibition, had less impact on the ability of the MCs to respond to activation via compound 48/80. Elevated glucose concentrations did not affect MC viability, and had no stimulatory effect on MC responses to either IgE receptor crosslinking or compound 48/80. Altogether, these findings reveal that MCs are strongly dependent on glucose transport via GLUT1 and/or GLUT3 for optimal responses towards IgE-mediated activation, whereas MC functionality is minimally affected by elevated glucose levels. Based on these findings, antagonists of GLUT1 and GLUT3 may be considered for therapeutic intervention in allergic conditions.

An Overview of the Effects of Tenapanor on Visceral Hypersensitivity in the Treatment of Irritable Bowel Syndrome with Constipation.

Patients with irritable bowel syndrome with constipation (IBS-C) experience persistent abdominal pain, a common symptom leading to greater healthcare utilization and reports of treatment non-response. Clinically significant improvements in abdominal pain were observed in clinical trials of tenapanor, a first-in-class inhibitor of sodium/hydrogen exchanger isoform 3 (NHE3), for the treatment of IBS-C in adults. This narrative review reports the current knowledge about visceral hypersensitivity as a mechanism for abdominal pain in patients with IBS-C and explores the published evidence for hypothesized mechanisms by which tenapanor may reduce visceral hypersensitivity leading to the observed clinical response of decreased abdominal pain. Abdominal pain is experienced through activation and signaling of nociceptive dorsal root ganglia that innervate the gut. These sensory afferent neurons may become hypersensitized through signaling of transient receptor potential cation channel subfamily V member 1 (TRPV1), resulting in reduced action potential thresholds. TRPV1 signaling is also a key component of the proinflammatory cascade involving mast cell responses to macromolecule exposure following permeation through the intestinal epithelium. Indirect evidence of this pathway is supported by observations of higher pain in association with increased intestinal permeability in patients with IBS. Tenapanor reduces intestinal sodium absorption, leading to increased water retention in the intestinal lumen, thereby improving gastrointestinal motility. In animal models of visceral hypersensitivity, tenapanor normalized visceromotor responses and normalized TRPV1-mediated nociceptive signaling. By improving gastrointestinal motility, decreasing intestinal permeability and inflammation, and normalizing nociception through decreased TRPV1 signaling, tenapanor may reduce visceral hypersensitivity, leading to less abdominal pain in patients with IBS-C. Therapies that have demonstrated effects on visceral hypersensitivity may be the future direction for meaningful abdominal pain relief for patients with IBS-C.