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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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Ethnopharmacological Relevance: Food allergies have increasingly become a disease that affects global health and need for corresponding therapeutic drugs urgently. As a traditional Chinses medicine with a wide range of pharmacological effects, however, there was no clear research confirming therapeutic effect and pharmacological substances of Corydalis yanhusuo (YHS) on food allergies. Mast cells (MCs) are the main effector cells which mediate allergic and pseudo-allergic reactions., Materials and Methods: In this study, we investigated the effect of YHS extract on treating food allergy and its underlying mechanism. The inhibitory effect of YHS on MCs activation in vitro was evaluated by Ca 2+ influx, degranulation, and cytokine release detection. The in vivo effect was investigated using the passive cutaneous anaphylaxis (PCA), active systemic allergy as well as OVA-induced food allergy mice. Western blot was performed to reveal the signaling pathway., Results: YHS extract showed an inhibitory effect on MCs activation and food allergy both in vitro and in vivo. PLC/PKC/STAT3 signaling pathway was suppressed by YHS extract in the disease. HPLC analysis revealed YHS extract contains corydaline and tetrahydropalmatine, and both compounds inhibited MCs activation induced by C48/80 in vitro., Conclusion: YHS extract inhibited the MCs activation and food allergy via PLC/PKC/STAT3 pathway., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “Corydalis yanhusuo extract and its pharmacological substances alleviate food allergy by inhibiting mast cells activation via PLC/PKC/STAT3 pathway.”, (Copyright © 2024 Elsevier B.V. All rights reserved.)

The pro-tumor effects of mast cell (MC) in the tumor microenvironment (TME) are becoming increasingly clear. Recently, MC were shown to contribute to tumor malignancy by supporting the migration of tumor-associated macrophages (TAMs), suggesting a relationship with tumor immunity. In the current study, we aimed to examine the correlation between MC infiltration and neoadjuvant chemoradiotherapy (nCRT) response for locally advanced rectal cancer (LARC). Ninety-five LARC patients who recieved nCRT were enrolled in this study. Protein levels of the MC marker tryptase and TAM marker CD206 were evaluated with immunohistochemistry (IHC). The correlation between MC infiltration and prognostic factors was evaluated. The effects of MCs on the malignant potential were examined using in vitro proliferation and invasion assays with a colorectal cancer (CRC) cell line (HCT-116). Following nCRT, 31.6% of resected LARC patient specimens were positive for MC infiltration by tryptase IHC analysis. MC infiltration was significantly correlated with nCRT response. The 5-year disease-free survival (DFS) rate was significantly lower in the MC-positive group compared with the MC-negative group (52.3% vs. 76.8%). Univariate and multivariate analyses revealed that MC infiltration was the independent prognostic indicator for DFS. MC infiltration was significantly correlated with CD206 expression, and therefore TAMs. In vitro experiments suggested that tumor activated mast cells could promote CRC cell malignant behavior via production of macrophage inhibitory factor. MC infiltration in LARC patients was positively correlated with TAM infiltration and resistance to nCRT, and was also an independent poor prognostic indicator., Competing Interests: Declarations. Ethics approval and consent to participate: The study protocol was approved by the Tokushima University Hospital Institutional Ethics Committee (TOCMS: 3215–3, 1900), and informed consent was obtained from all participating patients. The informed consent for this research was obtained from all participating patients. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Upon stimulation and activation, mast cells (MCs) release soluble mediators, including histamine, proteases, and cytokines. These mediators are often stored within cytoplasmic granules in MCs and may be released in a granulated form. The secretion of cytokines and chemokines occurs within hours following activation, with the potential to result in chronic inflammation. In addition to their role in allergic inflammation, MCs are components of the tumor microenvironment (TME). MicroRNAs (miRNAs) are small RNA molecules that do not encode proteins, but regulate post-transcriptional gene expression by binding to the 3' non-coding regions of mRNAs. This plays a crucial role in the function of MC, including the key processes of MC proliferation, maturation, apoptosis, and activation. It has been demonstrated that miRNAs are also present in extracellular vesicles (EVs) secreted by MCs. EVs derived from MCs mediate intercellular communication by carrying miRNAs, affecting various diseases including allergic diseases, intestinal disorders, neuroinflammation, and tumors. These findings provide important insights into the therapeutic mechanisms and targets of miRNAs in MCs that affect diseases. This review discusses the relevance of miRNA production by MCs in regulating their own activity and the effect of miRNAs putatively produced by other cells in the control of MC activity and their participation in selected pathologies., Competing Interests: Declarations. Conflict of Interests: The authors declare no competing interests., (© 2025. The Author(s).)

In mammals, many Hymenopteran stings are characterized by pain, redness, and swelling - three manifestations consistent with nociceptive nerve fiber activation. The effect of a Western honeybee (Apis mellifera) venom on the activation of sensory C-fibers in mouse skin was studied using an innervated isolated mouse skin preparation that allows for intra-arterial delivery of chemicals to the nerve terminals in the skin. Our data show that honeybee venom stimulated mouse cutaneous nociceptive-like C-fibers, with an intensity (action potential discharge frequency) similar to that seen with a maximally-effective concentration of capsaicin. The venom had a stronger effect on chloroquine-sensitive C-fibers compared to chloroquine-insensitive C-fibers, an effect that was recapitulated with a wasp (Vespula spp.) venom. Blocking TRPV1 and TRPA1 channels did not influence the honeybee venom-induced C-fiber activation. The effect of the venoms on chloroquine-sensitive and -insensitive subpopulation of C-fiber terminals was mimicked by melittin but not apamin; two of peptide venom components. Chloroquine-sensitive C-fibers are stimulated as a consequence of mast cell activation. Melittin degranulated mast cells in mouse skin by a non-IgE and non-MrgprB2 mechanism, and this may explain the stronger activation of the chloroquine-sensitive C-fibers., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Introduction: The role of mast cells (MCs) in clear cell renal carcinoma (ccRCC) is unclear, and comprehensive single-cell studies of ccRCC MCs have not yet been performed., Methods: To investigate the heterogeneity and effects of MCs in ccRCC, we studied single-cell transcriptomes from four ccRCC patients, integrating both single-cell sequencing and bulk tissue sequencing data from online sequencing databases, followed by validation via spatial transcriptomics and multiplex immunohistochemistry (mIHC)., Results: We identified four MC signature genes (TPSB2, TPSAB1, CPA3, and HPGDS). MC density was significantly greater in ccRCC tissues than in normal tissues, but MC activation characteristics were not significantly different between ccRCC and normal tissues. Activated and resting MCs were defined as having high and low expression of MC receptors and mediators, respectively, whereas proliferating MCs had high expression of proliferation-related genes. The overall percentage of activated MCs in ccRCC tissues did not change significantly but shifted toward a more activated subpopulation (VEGFA + MCs), with a concomitant decrease in proliferative MCs (TNF + MCs) and resting MCs. An analysis of the ratio of TNF + /VEGFA + MCs in tumors revealed that MCs exerted antitumor effects on ccRCC. However, VEGFA + MC was produced in large quantities in ccRCC tissues and promoted tumor angiogenesis compared with adjacent normal tissues, which aroused our concern. In addition, MC signature genes were associated with a better prognosis in the KIRC patient cohort in the TCGA database, which is consistent with our findings. Furthermore, the highest level of IL1B expression was observed in macrophages in ccRCC samples, and spatial transcriptome analysis revealed the colocalization of VEGFA + MCs with IL1B + macrophages at the tumor-normal interface., Discussion: In conclusion, this study revealed increased MC density in ccRCC. Although the proportion of activated MCs was not significantly altered in ccRCC tissues compared with normal tissues, this finding highlights a shift in the MC phenotype from CTSG high MCs to more activated VEGFA+MCs, providing a potential therapeutic target for inhibiting ccRCC progression., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2025 Song, Jiao, Qin, Zhang, Qin and Ma.)

Background: Sepsis is a systemic inflammatory response caused by infection. When this inflammatory response spreads to the lungs, it can lead to acute lung injury (ALI) or more severe acute respiratory distress syndrome (ARDS). Pulmonary fibrosis is a potential complication of these conditions, and the early occurrence of pulmonary fibrosis is associated with a higher mortality rate. The underlying mechanism of ARDS-related pulmonary fibrosis remains unclear., Methods: To evaluate the role of mast cell in sepsis-induced pulmonary fibrosis and elucidate its molecular mechanism. We investigated the level of mast cell and epithelial-mesenchymal transition(EMT) in LPS-induced mouse model and cellular model. We also explored the influence of cromolyn sodium and mast cell knockout on pulmonary fibrosis. Additionally, we explored the effect of MC-derived IL-13 on the EMT and illustrated the relationship between mast cell and pulmonary fibrosis., Results: Mast cell was up-regulated in the lung tissues of the pulmonary fibrotic mouse model compared to control groups. Cromolyn sodium and mast cell knockout decreased the expression of EMT-related protein and IL-13, alleviated the symptoms of pulmonary fibrosis in vivo and in vitro. The PI3K/AKT/mTOR signaling was activated in fibrotic lung tissue, whereas Cromolyn sodium and mast cell knockout inhibited this pathway., Conclusion: The expression level of mast cell is increased in fibrotic lungs. Cromolyn sodium intervention and mast cell knockout alleviate the symptoms of pulmonary fibrosis probably via the PI3K/AKT/mTOR signaling pathway. Therefore, mast cell inhibition is a potential therapeutic target for sepsis-induced pulmonary fibrosis., Competing Interests: Declarations. Ethics approval and consent to participate: This study was approved by the Institutional Animal Care and Use Committee (IACUC) of Nanjing Medical University (No. 2207016). Consent for publication: Not applicable. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Patients with Hymenoptera venom allergy (HVA), especially those with severe anaphylaxis, frequently have concomitant clonal mast cell disease (MCD) in the form of systemic mastocytosis or monoclonal mast cell activation syndrome. Detection of clonal MCD is important because it will have significant consequences for managing HVA. Therefore, we recommend patients with HVA be systematically screened for clonal MCD. The pretest probability of clonal MCD can be assessed in a stepwise fashion starting with examination of the skin for typical monomorphic maculopapular cutaneous mastocytosis lesions; measurement of the baseline serum tryptase (BST) and tryptase genotyping for patients with BST greater than 11 ng/mL; followed by the Red Española de Mastocitosis score, which is calculated using anaphylaxis clinical features, BST, and the patient's sex. A bone marrow biopsy should be performed in patients with monomorphic maculopapular cutaneous mastocytosis, a Red Española de Mastocitosis score of 2 or greater, or an elevated BST based on tryptase genotype. Patients with HVA and a clonal MCD should be treated with immunotherapy directed against the Hymenoptera venom for which they are sensitized. For this high-risk subgroup of patients with HVA, it is recommended to continue immunotherapy for more than 5 years or indefinitely and to carry at least three epinephrine autoinjectors. Future studies should determine whether KIT D816V-selective tyrosine kinase inhibitors are effective at preventing or reducing the severity of Hymenoptera-venom triggered anaphylaxis in patients with clonal MCD., (Published by Elsevier Inc.)

Background: Mast cells are implicated in the pathogenesis and severity of asthma in children and adults. The release of proinflammatory mediators and cytokines from activated mast cells (MC) is associated with Type 2 (T2) cell-skewed inflammation., Methods: We obtained the airway tissues of Balb/c mice with or without intra-tracheal diesel exhaust particles (DEP) instillation to measure the extent of tryptase + MCs infiltration and interleukin (IL)-33 expression. Cultured human mast cells (HMC-1) were stimulated with DEP to determine the role of aryl hydrocarbon receptor (AhR) in mediating the synthesis and release of IL-33 and type-2 cytokines., Results: In the control animals, most of the MC accumulated in the submucosal vessels without expression of IL-33. Intra-tracheal DEP installation increased the number of IL-33 +  MC infiltrating in the epithelial and sub-epithelial areas of mice. Human MC exposed to DEP upregulated mRNA and protein expression of IL-33. These effects were abolished by knockdown of expression of the AhR or AhR nuclear translocator (ARNT) by small interfering (si)RNA transfection. DEP also activated nuclear factor-kappa B (NF-κB) to facilitate nuclear translocation of the AhR. DEP increased MC migration and induced the synthesis and release of IL-4, IL-5, and IL-13 in MCs, and these effects were abolished by anti-ST2 antibodies., Conclusions: Airborne pollutants may activate MCs to produce IL-33 via the AhR/NF-κB pathway, leading to type 2 cytokines production and enhancing MC airway epithelium-shifted migration through the autocrine or paracrine IL-33/ST2 axis., Competing Interests: Declarations. Ethics approval and consent to participate: Experimental protocols involving animals were approved by the Animal Care and Use Committee of Taipei Medical University (LAC-2020-0397). Consent for publication: Not applicable. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Background: Berberine, an isoquinoline alkaloid, is known for anti-inflammatory activities. However, the research on the anti-inflammatory mechanism of berberine is not comprehensive. Recently, studies have shown that MrgprB2 (Mas-related G-protein-coupled receptor B2) in mice and MrgprX2 (Mas-related G-protein-coupled receptor X2) in humans play vital roles in inflammation. Therefore, this study aims to investigate whether the anti-inflammatory activity of berberine is related to MrgprB2 receptor., Methods: The anti-inflammatory activity of BH (berberine hydrochloride) was evaluated by hindpaw edema analysis, pathological analysis and RT-qPCR. Transgenic mice (MrgprB2 -/- mice), HEK293T cell transfection, calcium imaging, electrophysiology, molecular docking and other methods were employed to investigate the potential relationship between the anti-inflammatory activity of BH and the MrgprB2 receptor., Results: The results demonstrated that BH significantly alleviated C48/80 (compound 48/80)-induced local inflammation in vivo. This was evidenced by a decrease in paw edema, reduced infiltration of inflammatory cells, inhibition of mast cell activation, and down-regulation of inflammatory factors such as CXCL13 (CXC subfamily 13) and TNF-α (tumor necrosis factor-α). It was also found that knockout of MrgprB2 receptor could block the anti-inflammatory activity of BH in mice. Furthermore, calcium imaging revealed that BH effectively inhibited the activity of MrgprB2 receptor in overexpressed HEK293T cells in vitro. Additionally, it was observed that BH also inhibited MrgprB2-mediated voltage-dependent current changes in mouse peritoneal mast cells. Molecular docking results further indicated that BH had affinity with MrgprX2 protein., Conclusions: The anti-inflammatory mechanism of BH may be partially attributed to the inhibition of MrgprB2 receptor-mediated mast cell activation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Primary human mast cells (MC) obtained through culturing of blood-derived MC progenitors are the preferred model for the ex vivo study of MRGPRX2- vs. IgE-mediated MC activation. In order to assess the impact of culture conditions on functional MRGPRX2 expression, we cultured CD34 + -enriched PBMC from peripheral whole blood (PB) and buffy coat (BC) samples in MethoCult medium containing stem cell factor (SCF) and interleukin (IL)-3, modified through variations in seeding density and adding or withholding IL-6, IL-9 and fetal bovine serum (FBS). Functional expression of MRGPRX2 was assessed after 4 weeks via flow cytometry. We found similar proportions of CD34 + MC-committed progenitors in BC and PB. Higher seeding densities (≥ 1x10 5 cells/mL) and exposure to IL-9 and FBS suppressed functional MRGPRX2 expression at 4 weeks, while leaving MC yield largely unaffected. IL-6 had no impact on MRGPRX2 expression. MRGPRX2-expressing MC upregulated CD63 upon stimulation with polyclonal anti-IgE, substance P and compound 48/80 at 4 weeks. Ketotifen and dasatinib but not cromolyn sodium inhibited both IgE- and MRGPRX2-dependent pathways. Our results confirm the feasibility of functional MC activation studies on PB-derived MC after a short 4-week culture and highlight the impact of culture conditions on functional MRGPRX2 expression., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Ieven, Goossens, Roosens, Jonckheere, Cremer, Dilissen, Persoons, Dupont, Schrijvers, Vandenberghe, Breynaert and Bullens.)

Cetylpyridinium chloride (CPC) is a quaternary ammonium antimicrobial used in numerous personal care products, human food, cosmetic products, and cleaning solutions. Yet, there is minimal published data on CPC effects on eukaryotes, immune signaling, and human health. Previously, it was shown that low-micromolar CPC inhibits rat mast cell function by inhibiting antigen (Ag)-stimulated Ca 2+ mobilization, microtubule polymerization, and degranulation. In the current study, these findings are extended to human mast cells (LAD2); this paper presents data indicating that a mechanism of action for CPC might center on its positively-charged quaternary nitrogen in its pyridinium headgroup. The inhibitory effect of CPC was independent of signaling platform receptor architecture. Tyrosine phosphorylation events are a trigger of Ca 2+ mobilization necessary for degranulation. CPC inhibits global tyrosine phosphorylation in Ag-stimulated mast cells. Specifically, CPC inhibits tyrosine phosphorylation of specific key players Syk kinase and LAT, a substrate of Syk. In contrast, CPC did not affect Lyn kinase phosphorylation. Thus, a root mechanism for CPC effect might be electrostatic disruption of particular tyrosine phosphorylation events essential for signaling. This work presented here outlines biochemical mechanisms underlying the effects of CPC on immune signaling.

Purpose: The presence of wheals or hives has been viewed as a hallmark symptom of urticaria, a highly debilitating disease. This study explores our experience with omalizumab in patients with apparent mast-cell mediated pruritus in the absence of hives., Materials and Methods: This is a retrospective case series examining all patients with mast cell-mediated pruritus in the absence of hives from April 2022 to May 2024 at a tertiary referral clinic at Icahn School of Medicine at Mount Sinai in New York. Peak pruritus-numerical rating scale (PP-NRS) itch score changes over time were recorded and analyzed., Results: Six patients (67% women; mean [SD] age, 47.67 [13.52] years) were included in the analysis. The median [IQR] pruritus PP-NRS itch score before omalizumab injection was 9 [6 - 10] and the final median [IQR] PP-NRS itch score was 2.5 [0 - 5]. The mean [SD] reduction in the PP-NRS itch score was 6 [3.16]., Conclusions: This study suggests that patients with evidence of mast cell-mediated pruritus can be identified based on clinical features and may benefit from omalizumab therapy.

Chronic wasting disease (CWD) is a transmissible and fatal prion disease that affects cervids. While both oral and nasal routes of exposure to prions cause disease, the spatial and temporal details of how prions enter the central nervous system (CNS) are unknown. Carotid bodies (CBs) are structures that are exposed to blood-borne prions and are densely innervated by nerves that are directly connected to brainstem nuclei, known to be early sites of prion neuroinvasion. All CBs examined contained mast cells expressing the prion protein which is consistent with these cells playing a role in neuroinvasion following prionemia.

Urushiol-induced allergic contact dermatitis (ACD) is a chronic inflammatory skin disease in which skin barrier dysfunction leads to pruritus and eczematous lesions. ACD is triggered by immune imbalance. Aloe emodin is an anthraquinone derivative extracted from rhubarb, aloe and other traditional Chinese medicines. It has a wide range of pharmacological effects, including anti-inflammatory, anti-tumor, and anti-allergic effects. The purpose of our study was to demonstrate the effectiveness of aloe-emodin on urushiol-induced acute pruritus and allergic contact dermatitis. The results showed that urushiol could stimulate keratinocytes to release chemokines CXCL1, CXCL2, CCL2, TSLP, and TNF-α, which recruit or activate mast cells. Aloe-emodin treatment inhibited inflammatory-response-induced mast cell degranulation in skin lesions and suppressed the expression of inflammatory cytokines, such as interleukin-4, and interleukin-6. Therefore, the results indicate that aloe-emodin can improve urushiol-induced acute pruritus and allergic contact dermatitis in mice by inhibiting mast cell degranulation., Competing Interests: Declaration of competing interest The authors declare that they have no competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 European Federation of Immunological Societies. Published by Elsevier B.V. All rights reserved.)

Background: Bidirectional interactions between eosinophils and mast cells (MCs) have been reported in various allergic diseases. Bone marrow (BM) eosinophilia, and to a lesser extent blood eosinophilia, is common in systemic mastocytosis (SM), but its significance remains unknown., Objective: We described blood and BM eosinophil characteristics in SM., Methods: A large collection of BM biopsy samples was analyzed using immunohistochemical staining and whole-slide imaging. Eosinophil and extracellular granules were detected by eosinophil peroxidase (EPX) staining and MCs by KIT staining. Complementary analyses were conducted using flow cytometry and immunofluorescence., Results: Eosinophil infiltrates and large areas of eosinophil degranulation were observed within or around BM MC infiltrates in SM. EPX staining surface, highlighting intact eosinophils and eosinophil degranulation, was higher in nonadvanced SM (n = 37 BM biopsy samples) compared with both controls (n = 8, P = .0003) and advanced SM (n = 24, P = .014). In nonadvanced SM, positive correlations were observed between serum tryptase levels and percentages of eosinophil counts in BM aspirations (Spearman r coefficient r = 0.38, P = .038), eosinophils count in BM biopsy samples (r = 0.45, P = .007), EPX staining (r = 0.37, P = .035), and eosinophil degranulation (r = 0.39, P = .023). Eosinophil counts in BM biopsy samples also correlated with MC counts (r = 0.47, P = .006) and KIT staining surface (r = 0.49, P = .003). BM MCs expressed IL-5 receptor and other usual eosinophil cytokine/chemokine receptors, and blood eosinophils displayed several increased surface markers compared with controls, suggesting an activated state., Conclusion: Our data suggest possible cross talk between MCs and eosinophils, supporting MC tryptase release and MC activation-related symptoms. This suggests a rationale for targeting eosinophils in nonadvanced SM not fully controlled by other therapies., Competing Interests: Disclosure statement Funding provided by GSK (ISS 10889). The authors are solely responsible for final content and interpretation. Disclosure of potential conflict of interest: O. Hermine received research funds from Blueprint, AB Science, Alexion, and BMS; and is cofounder and shareholder of Innatherys and AB Science. D. Launay received consulting fees from AstraZeneca. G. Lefèvre received consulting fees from AstraZeneca, GSK, and Sanofi; and research funds from AstraZeneca and GSK. J. Rossignol received consulting fees from Blueprint and research funds from Novartis. D. Staumont-Salle received consulting fees from AstraZeneca, GSK, Novartis, and Sanofi-Regeneron. The rest of the authors declare that they have no relevant conflicts of interest., (Copyright © 2024 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Mas-related G protein-coupled receptor X2 (MRGPRX2) is a newly identified receptor on mast cells that contribute to IgE-independent pseudo-allergy. Ursolic acid (UA), a pentacyclic triterpenoid, has been reported for its anti-allergy effects. However, the protective mechanism against pseudo-allergic reactions remains unclear. This study aims to investigate the effects of UA on pseudo-allergic reactions both in vivo and in vitro, focusing on the therapeutical mechanism underlying its effect on mast cells. In present study, UA reduced degranulation and chemokines production induced by MRGPRX2 agonists, including compound 48/80 (C48/80) and substance P (SP), in LAD2 cells in vitro. UA also alleviated C48/80 and SP-induced systemic anaphylaxis and passive cutaneous anaphylaxis (PCA) in vivo. Furthermore, UA demonstrated strong binding affinity to the MRGPRX2 protein, leading to a decrease in calcium influx in both LAD2 cells and MRGPRX2-HEK293 cells stimulated with C48/80 and SP. Moreover, UA effectively suppressed phosphorylation levels within phospholipase C-γ (PLCγ) pathway and nuclear factor kappa-B (NF-κB) pathway of MRGPRX2 downstream proteins. Our findings indicated that UA exerts an attenuating effect in pseudo-allergic reactions by suppressing MRGPRX2-mediated mast cell activation, targeting PLCγ pathway and NF-κB pathway. These results suggest that UA may serve as a promising therapeutic agent for MRGPRX2-dependent pseudo-allergic reactions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 European Federation of Immunological Societies. Published by Elsevier B.V. All rights reserved.)

A recent article in Cell reported a new peculiar interaction between mast cells (MCs) and neutrophils. Upon IgE/Ag-mediated degranulation, MCs produce leukotriene B4, which attracts migrating neutrophils. Some neutrophils are able to establish close contact with MCs and end up trapped inside the MC, forming a cell-in-cell structure. While the neutrophil eventually dies inside the vacuole, the MC benefits from the remains of its prisoner, using it as a nutrient reserve and reusing its antimicrobial weapons., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Leukocyte Biology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Mast cells are hematopoietic-derived immune cells that possess numerous cytoplasmic granules containing immune mediators such as cytokines and histamine. Antigen stimulation triggers mast cell granule exocytosis, releasing granule contents in a process known as degranulation. We have shown that Rho GTPase signaling is an essential component of granule exocytosis, however, the proteins that regulate Rho GTPases during this process are not well defined. Here we examined the role of Rho guanine-nucleotide dissociation inhibitors (RhoGDIs) in regulating Rho GTPase signaling using RBL-2H3 cells as a mast cell model. We found that RBL-2H3 cells express two RhoGDI isoforms which are primarily localized to the cytosol. Knockdown of RhoGDI1 and RhoGDI2 greatly reduced the levels of all Rho GTPases tested: RhoA, RhoG, Rac1, Rac2, and Cdc42. The reduction in Rho GTPase levels was accompanied by an increase in their membrane-localized fraction and an elevation in the levels of active Rho GTPases. All RhoGDI knockdown strains had altered resting cell morphology, although each strain was activation competent when stimulated. Live cell imaging revealed that the RhoGDI1/2 double knockdown (DKD) strain maintained its activated state for prolonged periods of time compared to the other strains. Only the RhoGDI1/2 DKD strain showed a significant increase in granule exocytosis. Conversely, RhoGDI overexpression in RBL-2H3 cells did not noticeably affect Rho GTPases or degranulation. Based on these results, RhoGDIs act as negative regulators of Rho GTPases during mast cell degranulation, and inhibit exocytosis by sequestering Rho GTPases in the cytosol., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Leukocyte Biology.)

Purpose of Review: Clinical interest in non-IgE activation of mast cells has been growing since the description of the human MRGPRX2 receptor. Its participation in many allergic and inflammatory conditions such as non histaminergic itch, urticaria, asthma and drug hypersensitivity has been growing. We present here an updated review of its structure, expression and biology to help understand conditions and diseases attributed to its activation and/or overpexression and the search for agonists and antagonists of clinical utility., Recent Findings: The description of patients presenting anaphylaxis when exposed to one or multiple MRGPRX2 agonists such as general anesthetics, antibiotics, opiods and other agents has provided evidence of potential heterogeneity in humans. This review provides the most recent developments into the receptor structure, tissue expression and signaling pathways including the potential enhancement of IgE-mediated mast cell activation. New insight into its agonists and antagonists is described and future developments to adress its modulations., Competing Interests: Declarations. Competing Interests: Mariana Castells is Editor in Chief and did not play any part in the assignment of this manuscript to Associate Editors or peer reviewers and is separated and blinded from the editorial system from submission inception to decision. Carole Oskeritzian has grant funding from The National Institutes of Health/National Institute for General Medical Sciences. Carole Oskeritzian has grant funding from The National Institutes of Health/National Institute for General Medical Sciences. Michael Madden declares that he has no conflict of interest. Human and Animal Rights and Informed Consent: This article does not contain any studies with human or animal subjects performed by any of the authors., (© 2024. The Author(s).)

Mas-related G protein-coupled receptor b2 (Mrgprb2) binding to its cationic endogenous and exogenous ligands induces mast cell degranulation and promotes inflammation in mice. However, the physiological roles of its human homologue MRGPRX2 remain unclear. Here we aimed to elucidate the mechanisms by which MRGPRX2 regulates vascular permeability, and generated MRGPRX2 knock-in (MRGPRX2-KI) and Mrgprb2 knockout (Mrgprb2-KO) mice. Substance P (SP) and ciprofloxacin strongly degranulated MRGPRX2-KI peritoneal mast cells (PMCs) better than WT PMCs, whereas Dermatophagoides pteronyssinus (Der p) extract and phenol-soluble modulin α3 (PSMα3) did not degranulate PMCs. SP-stimulated MRGPRX2-KI PMCs released large amounts of histamine and mast cell protease 4 (MCPT4) chymase. Der p extract, PSMα3, and MCPT4, but not histamine, induced SP release from dorsal root ganglion (DRG) cells. However, this effect of Der p extract/PSMα3 was suppressed by a transient receptor potential vanilloid 1 (TRPV1) antagonist. SP-, ciprofloxacin-, Der p extract-, PSMα3-, and MCPT4-induced vascular permeability was highest in MRGPRX2-KI mice, which depended on SP. In addition, SP-, ciprofloxacin- and PSMα3-induced MRGPRX2-dependent vascular hyperpermeability was suppressed by antihistamine and chymase inhibitor. TRPV1 antagonist also inhibited PSMα3-induced MRGPRX2-dependent vascular hyperpermeability. Both Mrgprb2-KO and MRGPRX2-KI did not influence the histamine-induced murine vascular hyperpermeability. Overall, our results suggest that neuronal SP induces MRGPRX2-dependent mast cell degranulation, releasing histamine and chymase, which promote vascular hyperpermeability directly or indirectly via DRG cell activation. Importantly, the worsening cycle (MRGPRX2 → mast cell degranulation → chymase → DRG activation → SP → MRGPRX2) seems to play an important role in human MRGPRX2-depdendent inflammation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be constructed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Nagamine, Kaitani, Izawa, Ando, Yoshikawa, Nakamura, Maehara, Yamamoto, Okamoto, Wang, Yamada, Maeda, Nakano, Shimizu, Ogawa, Okumura and Kitaura.)

COVID-19 is an infectious disease caused by SARS-CoV-2; over the course of the disease, a dysregulated immune response leads to excessive inflammation that damages lung parenchyma and compromises its function. One of the cell lineages classically associated with pathological inflammatory processes is mast cells (MCs). MCs and their mediators have been associated with COVID-19; we previously reported the role of carboxypeptidase A3 (CPA3) in severe COVID-19. However, sequelae of SARS-CoV-2 infection have been poorly studied. In patients who successfully resolve the infection, one of the reported sequelae is pulmonary fibrosis (PF). The etiology and exact mechanisms are unknown, and few studies exist. Therefore, the aim of this study was to evaluate whether MCs are associated with PF development after SARS-CoV-2 infection. Our findings demonstrate that during severe cases of SARS-CoV-2 infection, there is an increased amount of CPA3 + MCs in areas with pneumonia, around thrombotic blood vessels, and in fibrotic tissue. Moreover, higher numbers of CPA3-expressing MCs correlate with fibrotic tissue development (r = 0.8323; p = 0.001170). These results suggest that during COVID-19, exacerbated inflammation favors the recruitment or expansion of MCs and CPA3 expression in the lungs, which favors tissue damage and a failure of repair mechanisms, leading to fibrosis.

Background: Mast cells are key effector cells that elicit immunoglobulin E (IgE)-mediated allergic inflammations. Allergen cross-linking of IgE bound to the high-affinity IgE receptor, FcεRI, on mast cells triggers signaling cascades that activate signal proteins and evoke extracellular Ca 2+ influx, which are crucial for cytokine production. The β2-adrenergic receptor (Adrb2) on mast cells negatively regulates FcεRI signaling, as demonstrated by the inhibition of IgE/antigen (Ag)-induced activation by Adrb2 agonists., Objective: Although β2-adrenergic-related reagents are known to influence mast cell functions, the specific intrinsic role of Adrb2 in these cells is not fully understood, potentially because of off-target effects. In this study, the additional roles of Adrb2 in mast cells were investigated, specifically the involvement of Adrb2 in FcεRI signaling, using Adrb2 -/- mice., Methods: Adrb2 -/- mice were used to investigate the roles of Adrb2 in mast cells by examining bone marrow-derived mast cells (BMMCs) for surface expression of mast cell markers, granule numbers, and gene expression of mast cell proteases. Cytokine production, Ca 2+ influx, and nuclear factor of activated T cells (NFAT) nuclear translocation were measured in Adrb2 -/- and Adrb2 +/+ BMMCs upon IgE/Ag stimulation., Results: Adrb2 -/- did not affect the generation of BMMCs, their surface expression of mast cell markers, granule numbers, or gene expression of mast cell proteases, indicating that the absence of Adrb2 had no adverse effect on mast cell development. However, Adrb2 -/- BMMCs exhibited reduced tumor necrosis factor α (TNFα) production and diminished Ca 2 ⁺ influx upon IgE/Ag stimulation, which correlated with decreased NFAT translocation. Restoration of Adrb2 in Adrb2 -/- BMMCs rescued cytokine production. Notably, FcεRI-mediated phosphorylation of the phospholipase PLCγ1 and mitogen-activated protein kinases (MAPKs) remained unchanged in the absence of Adrb2., Conclusion: These results suggest that Adrb2 has a novel ligand-independent function, increasing Ca 2+ entry in mast cells when stimulated with IgE/Ag., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Although antimicrobial peptides (AMPs) exhibit a range of biological functions, reports on AMPs with therapeutic effects in allergic disorders are limited. In this study, we investigated the anti-allergic effects of Pro10-1D, a 10-meric AMP derived from insect defensin protaetiamycine. Our findings demonstrate that Pro10-1D effectively inhibits antigen-induced degranulation of mast cells (MCs) with IC 50 values of approximately 11.6 μM for RBL-2H3 cells and 2.7 μM for bone marrow-derived MCs. Furthermore, Pro10-1D suppressed the secretion of cytokines with IC 50 values of approximately 2.8 μM for IL-4 and approximately 8.6 μM for TNF-α. Mechanistically, Pro10-1D inhibited the Syk-LAT-PLCγ1 signaling pathway in MCs and decreased the activation of mitogen-activated protein kinases (MAPKs). Pro10-1D demonstrated a dose-dependent reduction in IgE-mediated passive cutaneous anaphylaxis in mice with an ED 50 value of approximately 7.6 mg/kg. Further investigation revealed that Pro10-1D significantly reduced the activity of key kinases Fyn and Lyn, which are critical in the initial phase of the FcεRI-mediated signaling pathway, with IC 50 values of approximately 22.6 μM for Fyn and approximately 1.5 μM for Lyn. Collectively, these findings suggest that Pro10-1D represents a novel therapeutic candidate for the treatment of IgE-mediated allergic disorders by targeting the Lyn/Fyn Src family kinases in MCs.

Acute respiratory distress syndrome (ARDS) is a critical disorder characterized by immune-related damage to epithelial cells; however, its underlying mechanism remains elusive. This study investigated the effects of alterations in microRNA (miRNA) expression in mast cell-derived exosomes on human bronchial epithelial (HBE) cells and ARDS development in cellular and mouse models challenged with lipopolysaccharide. Lipopolysaccharide-treated mast cell-derived exosomes reduced glutathione peroxidase 4 (GPX4) expression and increased long-chain acyl-CoA synthetase 4 (ACSL4), 15-lipoxygenase (ALOX15), and inflammatory mediator levels in HBE cells. miRNA sequencing revealed a reduction in mast cell-derived exosomal miR-744 levels, which was associated with the regulation of ACSL4, ALOX15, and GPX4 expression. This downregulation of exosomal miR-744 expression reduced miR-744 levels and promoted ferroptosis in HBE cells, whereas the experimental upregulation of miR-744 reversed these adverse effects. Down-regulation of miR-744 induced the expression of markers for ferroptosis and inflammation in HBE cells and promoted pulmonary ferroptosis, inflammation, and injury in LPS-stimulated mice. In vivo, treatment with ACSL4, ALOX15, and GPX4 inhibitors mitigated these effects, and experimental miR-744 expression rescued the lipopolysaccharide-induced changes in HBE cells and mouse lungs. Notably, miR-744 levels were reduced in the plasma and exosomes of patients with ARDS. We concluded that decreased mast cell-derived exosomal miR-744 levels trigger epithelial cell ferroptosis, promoting lung inflammation and damage in ARDS. This study provides new mechanistic insights into the development and sustained pulmonary damage associated with ARDS and highlights potential therapeutic strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Background: Histopathologic criteria for diagnosis of cutaneous mastocytosis include 20 mast cells per high-power field or clusters of 15 mast cells. We aimed to determine the specificity of these criteria for cutaneous mastocytosis in comparison with inflammatory disorders of mast cell activation., Methods: Twenty-six cases of spongiotic dermatitis or urticaria were identified from 2021 to 2022. Recuts were stained with mast cell tryptase and slides were reviewed for the presence of 20 mast cells per high-power field and for clusters of 15 mast cells. In addition, seven cases of mastocytosis were reviewed for the same criteria., Results: Twelve of 26 cases (46.1%) of spongiotic dermatitis/urticaria had at least 20 mast cells per high-power field. Three of 26 cases (11.5%) of spongiotic dermatitis/urticaria had a cluster of 15 mast cells. Six of seven cases (85.7%) of mastocytosis had at least 20 mast cells per high-power field; four of seven cases (57.1%) of mastocytosis had a cluster of 15 mast cells., Conclusions: In our study, the finding of 20 mast cells per high-power field was nonspecific as a single criterion for cutaneous mastocytosis. The finding of clusters of 15 mast cells was more specific but not sensitive., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: KIT p.D816 mutation is strongly associated with systemic mastocytosis (SM). Next-generation sequencing (NGS) is now routinely performed in almost all bone marrow sample and KIT mutations are detected from patients who are not known or suspected to have SM. Therefore, we wanted to assess if KIT mutations in this patient population are associated with unsuspected SM., Methods: We searched NGS result in our institution with positive result for KIT mutation from patients with known/suspected myeloid neoplasms. Patients with previously documented history of systemic mastocytosis were excluded. Bone marrow biopsies from patients with KIT mutation were assessed with immunohistochemical stains for CD117 and mast cell tryptase (MST)., Results: Bone marrow biopsies were assessed with immunohistochemical stains for CD117 and mast cell tryptase (n = 49). Most patients had acute myeloid leukemia (AML, n = 38) or chronic myelomonocytic leukemia (CMML, n = 6). Immunohistochemical stains for CD117 and tryptase were performed in all 49 patients. A total of 4 patients (8.2%) showed mast cell nodules where spindled shaped mast cells were present, meeting the WHO criteria for SM. All four patients had KIT p.D816V mutation and had high mutant allelic frequency (∼ 50%) except one patient (1%)., Conclusion: We discovered approximately 8% of patients who had myeloid neoplasms with unexpected KIT mutations fulfilled the diagnostic criteria for systemic mastocytosis after additional immunohistochemical studies. Our data support that application of additional immunohistochemical studies is recommended to identify underrecognized SM when KIT mutations are found by molecular assays., Competing Interests: Disclosure CYO has received research funding from Blueprint Medicines., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Mast cells are commonly found in pancreatic ductal adenocarcinoma (PDAC), yet their role in the disease remains uncertain. Although mast cells have been associated with depression in several diseases, their connection to PDAC in this context remains unclear. This study explored the correlation between mast cells and psychosocial stress in patients with PDAC. Prior to surgery, 40 patients with PDAC (n = 29 primary resected, n = 11 neoadjuvant treated) completed four questionnaires assessing stress and quality of life. Immunostaining was performed on the resected tumor tissue. Spearman analysis was employed to correlate mast cells with distress and neuropeptides serotonin and beta-endorphin serum and tissue levels. Patients with PDAC exhibited elevated levels of distress and worry. Lower number of mast cells within the tumor correlated with greater psychological burden. Among primary resected patients, mast cell count moderately correlated with joy and inversely with worries. Following neoadjuvant chemotherapy, strong inverse correlation was observed between anxiety, depression, and mast cell quantity. No correlation was found between mast cells and serotonin or beta-endorphin levels. In summary, mast cell presence inversely correlates with psychosocial stress, suggesting a link between immune cells and psychological well-being in pancreatic cancer. Targeting mast cells might offer therapeutic avenues for addressing cancer-induced depression and anxiety., (© 2024. The Author(s).)

Chronic wounds significantly burden health care systems worldwide, requiring novel strategies to ease their impact. Many physiological processes underlying wound healing are well studied but the role of mast cells remains controversial. Mast cells are innate immune cells and play an essential role in barrier function by inducing inflammation to defend the host against chemical irritants and infections, among others. Many mast cell-derived mediators have proposed roles in wound healing; however, in vivo evidence using mouse models has produced conflicting results. Recently, studies involving more complex wound models such as infected wounds, diabetic wounds and wounds healing under psychological stress suggest that mast cells play critical roles in these processes. This review briefly summarizes the existing literature regarding mast cells in normal wounds and the potential reasons for the contradictory results. Focus will be placed on examining more recent work emerging in the last 5 years that explores mast cells in more complex systems of wound healing, including infection, psychological stress and diabetes, with a discussion of how these discoveries may inspire future work in the field., (© 2024 The Author(s). Immunology & Cell Biology published by John Wiley & Sons Australia, Ltd on behalf of the Australian and New Zealand Society for Immunology, Inc.)

Clinical flow cytometry laboratories require quality control materials for assay development, validation, and performance monitoring, including new reagent lot qualification. However, finding suitable controls for populations with uncommonly expressed antigens or for rare populations, such as mast cells, can be difficult. To that end, we evaluated synthetic abnormal mast cell particles (SAMCP), developed together with, and manufactured by, Slingshot Biosciences. The SAMCP's were designed to phenotypically mimic abnormal neoplastic mast cells: they were customized to have the same light scatter and autofluorescence properties of mast cells, along with surface antigen levels of CD45, CD33, CD117, CD2, CD25, and CD30 consistent with that seen in mast cell disease. We evaluated several performance characteristics of these particles using ARUP's high sensitivity clinical mast cell assay, including limit of detection, off-target activity and FMO controls, precision, scatter properties of the particles utilizing several different cytometer platforms, and particle antigen stability. The phenotype of the SAMCP mimicked abnormal mast cells, and they could be distinguished from normal native mast cells. FMO controls demonstrated specificity of each of the markers, and no off-target binding was detected. The limit of detection of the particles spiked into normal bone marrow was found to be ≤0.003% in a limiting dilution assay. The mast cell particles were found to perform similarly on Becton Dickinson Lyric, Cytek Aurora, and Beckman Coulter Navios and CytoFLEX platforms. Within run and between run precision were less than 10% CV. SAMCP were stable up to 13 days with minimal loss of antigen fluorescence intensity. The SAMCP's were able to successfully mimic neoplastic mast cells based on the results of our high sensitivity mast cell flow cytometry panel. These synthetic cell particles represent an exciting and innovative technology, which can fulfill vital needs in clinical flow cytometry such as serving as standardized control materials for assay development and performance monitoring., (© 2024 The Author(s). Cytometry Part B: Clinical Cytometry published by Wiley Periodicals LLC on behalf of International Clinical Cytometry Society.)

Introduction: Because MRGPRX2 is now recognized as the mast cell receptor for basic secretagogues, there is currently a tremendous interest in whether MRGRPX2 could play an important role in various pruritic dermatoses such as chronic spontaneous urticaria. Therefore, we sought to identify new potent and selective antagonists to pharmacologically characterize the biological role of MRGPRX2., Methods: Various relevant in vitro , ex vivo , and in vivo model systems were used to investigate the role of MRGPRX2. This included the study of freshly isolated human skin mast cells and human basophils as well as an ex vivo human skin microdialysis preparation. The additivity of MRGPRX2 and FcεR1-mediated degranulation was also investigated. Human MRGPRX2 knock-in mice were generated to interrogate pharmacokinetic/pharmacodynamic relationships because both antagonists studied were shown to be human specific., Results: Two novel and structurally distinct MRGPRX2 antagonists were identified with one, Compound B, being orally active and demonstrating high potency in blocking Substance P-mediated degranulation using freshly isolated human skin mast cells with half maximal inhibitory concentration (IC 50 ) at 0.42 nM. Compound B also potently blocked Substance P-stimulated histamine release from resident mast cells in a human skin explant setup as well as blocking itch in an established behavioral scratching model using MRGPRX2 knock-in mice. Unlike human mast cells, Substance P failed to elicit a functional response in human basophils., Conclusion: These data fully support the investigation of MRGPRX2 receptor antagonists in mast cell-driven allergic skin disorders such as chronic spontaneous urticaria., Competing Interests: CHM, DVP, TR, DAG, SKP, and ZW are all employees of GSK. PSS is the Head of R&D at RefLab, and KB is an employee of RefLab. XD is the scientific co-founder and a consultant of Escient Pharmaceuticals and collaborator with GSK on MRGPRX projects. The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Macphee, Dong, Peng, Paone, Skov, Baumann, Roethke, Goldspink, Pearson and Wu.)

Skin mast cells (MCs) mediate acute allergic reactions in the cutaneous environment and contribute to chronic dermatoses, including urticaria, and atopic or contact dermatitis. The cAMP response element binding protein (CREB), an evolutionarily well conserved transcription factor (TF) with over 4,000 binding sites in the genome, was recently found to form a feedforward loop with KIT, maintaining MC survival. The most selective MC function is degranulation with its acute release of prestored mediators. Herein, we asked whether CREB contributes to the expression and function of the degranulation-competent receptors FcεRI and MRGPRX2. Interference with CREB by pharmacological inhibition (CREBi, 666-15) or RNA interference only slightly affected the expression of these receptors, while KIT was strongly attenuated. Interestingly, MRGPRX2 surface expression moderately increased following CREB-knockdown, whereas MRGPRX2-dependent exocytosis simultaneously decreased. FcεRI expression and function were regulated consistently, although the effect was stronger at the functional level. Preformed MC mediators (tryptase, histamine, β -hexosaminidase) remained comparable following CREB attenuation, suggesting that granule synthesis did not rely on CREB function. Collectively, in contrast to KIT, FcεRI and MRGPRX2 moderately depend on unperturbed CREB function. Nevertheless, CREB is required to maintain MC releasability irrespective of stimulus, insinuating that CREB may operate by safeguarding the degranulation machinery. To our knowledge, CREB is the first factor identified to regulate MRGPRX2 expression and function in opposite direction. Overall, the ancient TF is an indispensable component of skin MCs, orchestrating not only survival and proliferation but also their secretory competence.

Interleukin-33 (IL-33) is an alarmin released by epithelial cells in response to tissue damage. It activates resident immune sentinel cells, which then produce signals commonly associated with type 2 immune responses, particularly affecting infiltrating antigen-specific T cells. Given that mast cells (MCs) are a primary target of IL-33 and can shape T helper (Th) cell responses, we investigated the effect of IL-33 priming on the ability of MCs to influence Th cell cytokine production. To examine the Th cell/MC interaction, we developed human primary MC/memory CD4 + T-cell coculture systems involving both cognate and non-cognate interactions. Our results demonstrated that IL-33-primed MCs, whether as bystander cells cocultured with activated effector T cells or functioning as antigen-presenting cells, promoted IL-9 and increased IL-13 production in Th cells via an OX40L-dependent mechanism. This indicates that MCs sense IL-33-associated danger, prompting them to direct Th cells to produce the key type 2 effector cytokines IL-9 and IL-13., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Battut, Leveque, Valitutti, Cenac, Dietrich and Espinosa.)

Mast cells (MCs) are derived from CD34 + hematopoietic progenitors, consist of different subtypes, and are involved in several inflammatory conditions. However, our understanding of human MC developmental trajectories and subtypes has been limited by a scarcity of suitable cellular model systems. Herein, we developed an in vitro model of human MC differentiation from induced pluripotent stem cells (iPSC) to study human MC differentiation trajectories. Flow cytometry characterization of hemopoietic cells derived from the myeloid cells-forming complex (MCFC) revealed an initial increase in Lin - CD34 + hematopoietic progenitors within Weeks 1-3, followed by an increase in CD34 - CD45RA - SSC l ow and SSC high hematopoietic cells. The Lin - CD34 + hematopoietic progenitors consisted of SSC low CD45RA - CD123 ± c-Kit + FcεRI + populations that were β7-integrin high CD203c + and β7-integrin high CD203c - cells consistent with CMP Fc ε RI+ cells. Flow cytometry and cytologic analyses of the CD34 - Lin - (SSC low ) population revealed hypogranular cell populations, predominantly characterized by CD45RA - CD123 ± c-Kit + FcεRI - β7-integrin low and CD45RA - CD123 ± c-Kit - FcεRI + β7-integrin Mid cells. Analyses of hypergranular SSC high cells identified Lin - CD34 - CD45RA - c-Kit + FcεRI - and Lin - CD34 - cells. scRNA-seq analysis of the cells harvested at week 4 of the MCFC culture revealed the presence of monocyte and granulocyte progenitors (n = 547 cells, 26.7 %), Erythrocyte / unknown (n = 85, 4.1 %), neutrophils / myelocytes (n = 211 cells, 10.2 %), mast cell progenitor 1 (n = 599, 29.1 %), mast cell progenitor 2 (n = 152, 7.4 %), committed mast cell precursor (n = 113, 5.5 %), and MCs (n = 353, 17.1 %). In silico analyses of the MC precursor and mature MC populations revealed transcriptionally distinct MC precursor subtype and mature MC states (CMA1 - c-Kit + subtypes). Culturing MC precursor populations in MC maturation media (mast cell media II) led to homogenous mature MC populations as evidenced by high expression of high-affinity IgE receptor, metachromatic granules, presence of MC granule proteins (Tryptase and Chymase) and activation following substance P stimulation and FcεRI crosslinking. This human iPSC-based approach generates MC precursors and phenotypically mature and functional MC populations. This system will be a useful model to generate human MC populations and broaden our understanding of MC biology and transcriptional regulation of MC differentiation trajectories.+ cells. scRNA-seq analysis of the cells harvested at week 4 of the MCFC culture revealed the presence of monocyte and granulocyte progenitors (n = 547 cells, 26.7 %), Erythrocyte / unknown (n = 85, 4.1 %), neutrophils / myelocytes (n = 211 cells, 10.2 %), mast cell progenitor 1 (n = 599, 29.1 %), mast cell progenitor 2 (n = 152, 7.4 %), committed mast cell precursor (n = 113, 5.5 %), and MCs (n = 353, 17.1 %). In silico analyses of the MC precursor and mature MC populations revealed transcriptionally distinct MC precursor subtype and mature MC states (CMA1 + and CMA1 - subtypes). Culturing MC precursor populations in MC maturation media (mast cell media II) led to homogenous mature MC populations as evidenced by high expression of high-affinity IgE receptor, metachromatic granules, presence of MC granule proteins (Tryptase and Chymase) and activation following substance P stimulation and FcεRI crosslinking. This human iPSC-based approach generates MC precursors and phenotypically mature and functional MC populations. This system will be a useful model to generate human MC populations and broaden our understanding of MC biology and transcriptional regulation of MC differentiation trajectories., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Neutrophils are sentinel immune cells with essential roles for antimicrobial defense. Most of our knowledge on neutrophil tissue navigation derived from wounding and infection models, whereas allergic conditions remained largely neglected. Here, we analyzed allergen-challenged mouse tissues and discovered that degranulating mast cells (MCs) trap living neutrophils inside them. MCs release the attractant leukotriene B4 to re-route neutrophils toward them, thus exploiting a chemotactic system that neutrophils normally use for intercellular communication. After MC intracellular trap (MIT) formation, neutrophils die, but their undigested material remains inside MC vacuoles over days. MCs benefit from MIT formation, increasing their functional and metabolic fitness. Additionally, they are more pro-inflammatory and can exocytose active neutrophilic compounds with a time delay (nexocytosis), eliciting a type 1 interferon response in surrounding macrophages. Together, our study highlights neutrophil trapping and nexocytosis as MC-mediated processes, which may relay neutrophilic features over the course of chronic allergic inflammation., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background/aim: Breast cancers are one of the most common cancers in women and are responsible for many deaths worldwide. Mast cells are inflammatory cells. Their role in cancers is controversial, and there is limited data on systemic mast cell activation in cancer cases. This study aimed to evaluate systemic mast cell activation in an experimentally induced rat model of breast cancer., Materials and Methods: Sprague Dawley female rats were divided into control (n = 6) and mammary tumor (n = 12) groups. In the tumor group, 20 mg 7,12-dimethylbenz[a]anthracene (DMBA) dissolved in 1 mL cottonseed oil was administered intragastrically by gavage, and the rats were followed daily until their mammary tumors reached 3 cm in diameter. The control group received only cottonseed oil. Paraffin sections obtained from the mammary tumor tissue were subjected to hematoxylin-eosin, toluidine blue staining, and proliferating cell nuclear antigen (PCNA) immunohistochemistry. Mesenteric tissues from each subject were also stained with toluidine blue. The number and activation status of mast cells in mammary tumors and mesenteric tissues were evaluated., Results: Toluidine blue staining showed that activated mast cells were commonly found in tumor tissues. Based on the mesenteric tissue analysis, severe degranulation of the mesenteric mast cells was found in the tumor-induced groups compared to the control group., Conclusion: This study demonstrated for the first time that systemic mast cell activation develops in both tumoral and mesenteric tissues in an experimental cancer model. However, it is not known at which stage of tumor development it occurs., (© TÜBİTAK.)

Mast cells serve as crucial effector cells within the innate immune system and are predominantly localized in the skin, airways, gastrointestinal tract, urinary and reproductive tracts, as well as in the brain. Under physiological conditions, brain-resident mast cells secrete a diverse array of neuro-regulatory mediators to actively participate in neuroprotection. Meanwhile, as the primary source of molecules causing brain inflammation, mast cells also function as the "first responders" in brain injury. They interact with neuroglial cells and neurons to facilitate the release of numerous inflammatory mediators, proteases, and reactive oxygen species. This process initiates and amplifies immune-inflammatory responses in the brain, thereby contributing to the regulation of neuroinflammation and blood-brain barrier permeability. This article provides a comprehensive overview of the potential mechanisms through which mast cells in the brain may modulate neuroprotection and their pathological implications in various neurological disorders. It is our contention that the inhibition of mast cell activation in brain disorders could represent a novel avenue for therapeutic breakthroughs., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Huang, Lan and Hu.)

Background: Vitamin K3 (VK3), a fat-soluble synthetic analog of the vitamin K family, has coagulant, anti-inflammatory, antibacterial, and anticancer properties. Pseudo allergy is a IgE-independent immune response associated with mast cells. This study investigated the role of VK3 in IgE-independent mast cell activation., Methods: Substance P (SP) was used to induce LAD2-cell activation in order to analyze the effects of VK3 in vitro. Cutaneous allergy and systemic allergy mouse models were used to analyze the anti-pseudo-allergic effects of VK3. Proteome microarray assays were used to analyze VK3-binding protein. Biolayer interferometry and immunoprecipitation were used to verify interaction between VK3 and its key targets. RNA interference was used to determine the role of GAB1 in LAD2cell activation., Results: VK3 inhibited SP-induced LAD2-cell activation, and resulted in the release of β-hexosaminidase, histamine and cytokines; VK3 inhibited SP-induced pseudo allergic reactions in mice, and serum histamine and TNF-α levels decreased. Degranulation of skin mast cells was reduced; GAB1 in mast cells was stably bound to VK3. GAB1 participated in SP-induced LAD2-cell activation. GAB1 knockdown in LAD2 cells prevented SP-induced β-hexosaminidase release, calcium mobilization and cell skeletal remodeling. VK3 directly binds to GAB1 and reduces its expression to inhibited SP-induced LAD2 cell activation., Conclusion: The anti-pseudo-allergic activity of VK3 was confirmed in vitro and in vivo. VK3 can inhibit SP-induced mast cell activation by directly targeting GAB1. This study provides new insights on the activity of VK3 and the mechanism of pseudoallergic reaction., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Emerging evidence indicates that gut dysbiosis is involved in the pathogenesis of visceral hypersensitivity (VH). However, how gut microbiota contributes to the development of VH is unknown. Here, we sought to examine the signal transduction pathways from gut to dorsal root ganglion (DRG) responsible for this. Therefore, abdominal withdrawal reflex (AWR) scores, fecal output, fecal water content, and total gastrointestinal transit time (TGITT) were assessed in Con rats, VH rats, rats treated with NaB, and VH rats treated with VSL#3. Fecal microbiota and its metabolite (short-chain fatty acids, SCFAs), mast cell degranulation in colon, lincRNA-01028, miR-143, and protease kinase C (PKC) and TRPV1 expression in DRGs were further detected. VH rats showed an increased fecal water content, a shortened TGITT, an increased abundance of Clostridium sensu stricto 1 and increased butyrate in fecal samples, an increased mast cell degranulation, an increased expression of lincRNA-01028, PKC, and TRPV1, and a decreased expression of miR-143 in DRGs compared with control rats, which could be restored by the application of probiotic VSL#3. The above-mentioned detection in rats treated with butyrate was similar to that of VH rats. We further confirm whether butyrate sensitized DRG neurons by a lincRNA-01028, miR-143, and PKC-dependent mechanism via mast cell in vitro . In co-cultures, MCs treated with butyrate elicited a higher TRPV1 current, a higher expression of lincRNA-01028, PKC, and a lower expression of miR-143 in DRG neurons, which could be inhibited by a lincRNA-01028 inhibitor. These findings indicate that butyrate promotes visceral hypersensitivity via mast cell-derived DRG neuron lincRNA-01028-PKC-TRPV1 pathway.IMPORTANCEIrritable bowel syndrome (IBS), characterized by visceral hypersensitivity, is a common gastrointestinal dysfunction syndrome. Although the gut microbiota plays a role in the pathogenesis and treatment of irritable bowel syndrome (IBS), the possible underlying mechanisms are unclear. Therefore, it is of critical importance to determine the signal transduction pathways from gut to DRG responsible for this in vitro and in vivo assay. This study demonstrated that butyrate sensitized TRPV1 in DRG neurons via mast cells in vivo and in vitro by a lincRNA-01028, miR-143, and PKC-dependent mechanism. VH rats similarly showed an increased abundance of Clostridium sensu stricto 1, an increased fecal butyrate, an increased mast cell degranulation, and increased expression of TRPV1 compared with control rats, which could be restored by the application of VSL#3. In conclusion, butyrate produced by the altered intestinal microbiota is associated with increased VH., Competing Interests: The authors declare no conflict of interest.

Interaction of mast cells (MCs) with fibroblasts is essential for MC maturation within tissue microenvironments, although the underlying mechanism is incompletely understood. Through a phenotypic screening of >30 mouse lines deficient in lipid-related genes, we found that deletion of the lysophosphatidic acid (LPA) receptor LPA 1 , like that of the phospholipase PLA2G3, the prostaglandin D 2 (PGD 2 ) synthase L-PGDS, or the PGD 2 receptor DP1, impairs MC maturation and thereby anaphylaxis. Mechanistically, MC-secreted PLA2G3 acts on extracellular vesicles (EVs) to supply lysophospholipids, which are converted by fibroblast-derived autotaxin (ATX) to LPA. Fibroblast LPA 1 then integrates multiple pathways required for MC maturation by facilitating integrin-mediated MC-fibroblast adhesion, IL-33-ST2 signaling, L-PGDS-driven PGD 2 generation, and feedforward ATX-LPA 1 amplification. Defective MC maturation resulting from PLA2G3 deficiency is restored by supplementation with LPA 1 agonists or PLA2G3-modified EVs. Thus, the lipid-orchestrated paracrine circuit involving PLA2G3-driven lysophospholipid, eicosanoid, integrin, and cytokine signaling fine-tunes MC-fibroblast communication, ensuring MC maturation., Competing Interests: Declaration of interests J.C. has an employment relationship with Neurocrine Biosciences, Inc. as a Distinguished Scholar, unrelated to the current manuscript., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Introduction: The Janus kinase (JAK) family includes four cytoplasmic tyrosine kinases (JAK1, JAK2, JAK3, and TYK2) constitutively bound to several cytokine receptors. JAKs phosphorylate downstream signal transducers and activators of transcription (STAT). JAK-STAT5 pathways play a critical role in basophil and mast cell activation. Previous studies have demonstrated that inhibitors of JAK-STAT pathway blocked the activation of mast cells and basophils., Methods: In this study, we investigated the in vitro effects of ruxolitinib, a JAK1/2 inhibitor, on IgE- and IL-3-mediated release of mediators from human basophils, as well as substance P-induced mediator release from skin mast cells (HSMCs)., Results: Ruxolitinib concentration-dependently inhibited IgE-mediated release of preformed (histamine) and de novo synthesized mediators (leukotriene C 4 ) from human basophils. Ruxolitinib also inhibited anti-IgE- and IL-3-mediated cytokine (IL-4 and IL-13) release from basophils, as well as the secretion of preformed mediators (histamine, tryptase, and chymase) from substance P-activated HSMCs., Discussion: These results indicate that ruxolitinib, inhibiting the release of several mediators from human basophils and mast cells, is a potential candidate for the treatment of inflammatory disorders., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Poto, Cristinziano, Criscuolo, Strisciuglio, Palestra, Lagnese, Di Salvatore, Marone, Spadaro, Loffredo and Varricchi.)

Mast cell activation syndrome (MCAS) is a term applied to several clinical entities that have gained increased attention from patients and medical providers. Although several descriptive publications about MCAS exist, there are many gaps in knowledge, resulting in confusion about this clinical syndrome. Whether MCAS is a primary syndrome or exists as a constellation of symptoms in the context of known inflammatory, allergic, or clonal disorders associated with systemic mast cell activation is not well understood. More importantly, the underlying mechanisms and pathways that lead to mast cell activation in MCAS patients remain to be elucidated. Here we summarize the known literature, identify gaps in knowledge, and highlight research needs. Covered topics include contextualization of MCAS and MCAS-like endotypes and related diagnostic evaluations; mechanistic research; management of typical and refractory symptoms; and MCAS-specific education for patients and health care providers., Competing Interests: Disclosure statement M.C.C. and D.D.M. were supported by the Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not represent the official views of the NIH. Disclosure of potential conflict of interest: M. Castells has received research funding and consulting fees from Blueprint Medicines and consulting fees from Cogent Biosciences. M. P. Giannetti has received research funding and consulting fees from Blueprint Medicines and consulting fees from Cogent Biosciences. M. J. Hamilton has received consulting fees from Blueprint Medicines. P. Novak has received funding from Mona Taliaferro/Bay Shore Recycling, the National Heart, Lung, and Blood Institute (NHLNI; 1OT2HL156812-01), and FBRI (2022A018462); is current or previous shareholder of Moderna, Edidas Medicine, Novavax, and Pfizer; and has received royalties from Oxford University Press. J. Nicoloro-SantaBarbara has received consulting fees from Cogent Biosciences and Blueprint Medicines. S. C. Glover received consulting fees from Blueprint Medicine, Janssen, BMS, AbbVie, and Takeda. S. J. Galli has received research funding from and is scientific advisor to Evommune; and is on the scientific advisory board of Jasper Therapeutics. A. White is on the speakers bureau at Blueprint Medicines; and received consulting fees from Cogent Biosciences and Blueprint Medicines. P. Valent received funding from BMS/Celgene and AOP Orphan; and consultancy fees from Novartis, BMS/Celgene, Blueprint, Pfizer, Cogent, and Stemline. J. H. Butterfield has received a fee for the licensing of HMC-1 cell lines. D. D. Metcalfe has received consulting fees from Visterra. J. D. Milner has received consulting fees from Blueprint Medicines. The rest of the authors declare that they have no relevant conflicts of interest., (Copyright © 2024 American Academy of Allergy, Asthma & Immunology. All rights reserved.)

Age-related macular degeneration (AMD) is a common retinal neurodegenerative disease among the elderly. Neovascular AMD (nAMD), a leading cause of AMD-related blindness, involves choroidal neovascularization (CNV), which can be suppressed by anti-angiogenic treatments. However, current CNV treatments do not work in all nAMD patients. Here we investigate a novel target for AMD. Granzyme B (GzmB) is a serine protease that promotes aging, chronic inflammation and vascular permeability through the degradation of the extracellular matrix (ECM) and tight junctions. Extracellular GzmB is increased in retina pigment epithelium (RPE) and mast cells in the choroid of the healthy aging outer retina. It is further increased in donor eyes exhibiting features of nAMD and CNV. Here, we show in RPE-choroidal explant cultures that exogenous GzmB degrades the RPE-choroid ECM, promotes retinal/choroidal inflammation and angiogenesis while diminishing anti-angiogenic factor, thrombospondin-1 (TSP-1). The pharmacological inhibition of either GzmB or mast-cell degranulation significantly reduces choroidal angiogenesis. In line with our in vitro data, GzmB-deficiency reduces the extent of laser-induced CNV lesions and the age-related deterioration of electroretinogram (ERG) responses in mice. These findings suggest that targeting GzmB, a serine protease with no known endogenous inhibitors, may be a potential novel therapeutic approach to suppress CNV in nAMD., (© 2024. The Author(s).)

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 PGE 2 . 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 PGE 2 and anti-IgE in the human ROSA KIT WT MC line, suggesting that SR-BI is a crucial regulator of synergistic MC activation., (© 2024 The Authors. European Journal of Immunology published by Wiley‐VCH GmbH.)

The pathophysiology of mast cell (MC)-driven disorders is diverse, ranging from localized reactions to systemic disorders caused by abnormal accumulation and activation in multiorgan systems. Prompt and accurate diagnosis is critically important, both for informing treatment and objective assessment of treatment outcomes. As new therapeutics are being developed to deplete MCs or silence them (eg, by engaging inhibitory receptors that block activation), new biomarkers are needed that can distinguish between MC activation versus burden. Serum tryptase is the gold standard for assessing both MC burden and activation; however, commercial tryptase assays have limitations related to timing of release, lack of discernment between inactive (α) and active (β) forms of tryptase, and interpatient variability of baseline levels. Alternative approaches to measuring MC activation include urinary MC mediators, flow cytometry-based assays or gene expression profiling. Additional markers of MC activation are needed for use in clinical diagnostics, to help selection of treatment of MC diseases, and for assessing outcomes of therapy. We review the spectrum of disorders with known or suspected MC contribution, describe the utility and limitations of current MC markers and assays, and discuss the need for new markers that can differentiate between MC activation and burden., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

This is the first study to describe the subtypes, number and distribution of mast cells (MC) in cat tongue by histochemical and immunohistochemical methods. Six male adult felines' tongue tissue samples consist of the study's material. Samples were fixed in 10% formaldehyde. MC number and distribution in the feline tongue were assessed using toluidine blue. Also, sections taken from blocks were stained in alcian blue/safranin O (AB/SO) combined dyes to determine the MC subtypes. The Streptavidin biotin complex method using anti-chymase and anti-tryptase primary antibodies was used for immunohistochemistry. Metachromatic MCs were mainly observed in the lamina propria close to the multilayered keratinized stratified squamous epithelium. The high number of MCs in this region may be because the dorsal surface of the tongue plays an essential role in the defence system of tongue tissue and, thus, of the body as a whole. Additionally, the number of MCs stained with AB (+) (1.7 ± 0.08) in the feline tongue was statistically higher than those with SO (+) (0.18 ± 0.02). This might be interpreted as an indication that MC heterogeneity may be due not only to their staining properties but also to their localization. It is also conceivable that the high histamine content may be a factor in this. Tryptase-positive MCs were found in the loose connective tissue around blood vessels, between the glands, as solitary cells, or in groups of several cells. Chymase-positive MCs were observed more individually rather than in groups. Moreover, chymase-positive MCs were detected to be located in the filiform papillae subepithelial and in the blood vessels' immediate vicinity. Animals often lick themselves to clean themselves and promote healing. For this reason, it is very important to protect the tongue, which is in direct contact with the external environment, against foreign agents. Considering both the functional and protective properties of the tongue, we concluded that MCs may play a role in oral cavity immunity and protective effect., (© 2024 The Author(s). Anatomia, Histologia, Embryologia published by Wiley‐VCH GmbH.)

Objectives: Mast cell (MC) degranulation is a key process in allergic reactions and inflammatory responses. Aspartate aminotransferase 1 (AAT1)-derived endogenous sulfur dioxide (SO 2 ) is an important regulator of MC function. However, the mechanism underlying its role in MC degranulation remains unclear. This study aimed to investigate the mechanism by which endogenous SO 2 controlled MC degranulation., Methods: HMC-1 and Rat basophilic leukemia cell MC line (RBL-2H3) were used in the cell experiments. SO 2 content was detected by in situ fluorescent probe. MC degranulation represented by the release rate of MC β-hexosaminidase was determined using a colorimetric assay. Sulfenylation of galectin-9 (Gal-9) in MCs and purified protein was detected using a biotin switch assay. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to determine the exact sulfenylation sites of Gal-9 by SO 2 . Animal models of passive cutaneous anaphylaxis (PCA) and hypoxia-driven pulmonary vascular remodeling were used to investigate the effect of SO 2 on mast cell activation in vivo . Site-directed mutation of Gal-9 was conducted to confirm the exact site of SO 2 and support the significance of SO 2 /Gal-9 signal axis in the regulation of MC degranulation., Results: Degranulation was increased in AAT1-knockdowned MCs, and SO 2 supplementation reversed the increase in MC degranulation. Furthermore, deficiency of endogenous SO 2 contributed to IgE-mediated degranulation in vitro. Besides, SO 2 inhibited IgE-mediated and hypoxia-driven MC degranulation in vivo . Mechanistically, LC-MS/MS analysis and site-directed mutation results showed that SO 2 sulfenylated Gal-9 at cysteine 74. Sulfenylation of the 74 th cysteine of Gal-9 protein was required in the SO 2 -inhibited MC degranulation under both physiological and pathophysiological conditions., Conclusion: These findings elucidated that SO 2 inhibited MC degranulation via sulfenylating Gal-9 under both physiological and pathophysiological conditions, which might provide a novel treatment approach for MC activation-related diseases., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Song, Zheng, Li, Fu, Yang, Li, Yu, Lv, Du, Huang and Jin.)

It is not known whether esophageal mast cells may be a cause of unexplained esophageal symptoms. We aimed to determine the prevalence of esophageal mastocytosis in patients without other underlying causes of symptoms and assess the relationship between symptoms and mast cells. In this retrospective study, we identified adults with esophageal symptoms, a normal endoscopy, normal esophageal biopsies, and no definitive diagnosis during clinical evaluation. We quantified mast cell density (mast cells/mm 2 ) in archived esophageal biopsies using tryptase immunohistochemistry, and compared mast cell levels by clinical features and physiologic testing. In the 87 patients identified (mean age 37, 72% female, 63% white, 92% non-Hispanic), common symptoms were dysphagia (76%), heartburn (71%), and chest pain (25%). Overall, the mean esophageal epithelial mast cell count was 83.0 ± 51.8 mast cells/mm 2 ; 60% of patients had ≥ 60 mast/mm 2 , and 17% had ≥ 120 masts/mm 2 . There were no differences in mast cell counts by type of esophageal testing. Mast cell levels did not differ significantly by type of symptoms, atopic status, medications, smoking status, or alcohol use. There were also no major differences in clinical characteristics by mast cell quartiles or thresholds. In conclusion, esophageal mast cell infiltration was common in patients with symptoms unexplained by prior testing, and levels were higher than previously published values for patients with no underlying esophageal condition. Mast cell esophagitis could be a novel cause of unexplained esophageal symptoms in a subset of patients, though it reamins to be determined if such patients benefit from mast cell-targeted treatment., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Background: Pain, an evolutionarily conserved warning system, lets us recognize threats and motivates us to adapt to those threats. Headache pain from migraine affects approximately 15% of the global population. However, the identity of any putative threat that migraine or headache warns us to avoid is unknown because migraine pathogenesis is poorly understood. Here, we show that a stress-induced increase in pituitary adenylate cyclase-activating polypeptide-38 (PACAP38), known as an initiator of allosteric load inducing unbalanced homeostasis, causes headache-like behaviour in male mice via mas-related G protein-coupled receptor B2 (MrgprB2) in mast cells., Methods: The repetitive stress model and dural injection of PACAP38 were performed to induce headache behaviours. We assessed headache behaviours using the facial von Frey test and the grimace scale in wild-type and MrgprB2-deficient mice. We further examined the activities of trigeminal ganglion neurons using in vivo Pirt-GCaMP Ca 2+ imaging of intact trigeminal ganglion (TG)., Results: Repetitive stress and dural injection of PACAP38 induced MrgprB2-dependent headache behaviours. Blood levels of PACAP38 were increased after repetitive stress. PACAP38/MrgprB2-induced mast cell degranulation sensitizes the trigeminovascular system in dura mater. Moreover, using in vivo intact TG Pirt-GCaMP Ca 2+ imaging, we show that stress or/and elevation of PACAP38 sensitized the TG neurons via MrgprB2. MrgprB2-deficient mice showed no sensitization of TG neurons or mast cell activation. We found that repetitive stress and dural injection of PACAP38 induced headache behaviour through TNF-a and TRPV1 pathways., Conclusions: Our findings highlight the PACAP38-MrgprB2 pathway as a new target for the treatment of stress-related migraine headache. Furthermore, our results pertaining to stress interoception via the MrgprB2/PACAP38 axis suggests that migraine headache warns us of stress-induced homeostatic imbalance., (© 2024. The Author(s).)

Initiation of the bradykinin generation cascade is responsible for the occurrence of attacks in some types of angioedema without wheals. Hereditary angioedema due to C1 inhibitor deficiency (HAE-C1-INH) is one such clinical entity. In this paper, we explore the existing evidence that mast cells (MCs) degranulation may contribute to the activation of the kallikrein-kinin system cascade, followed by bradykinin formation and angioedema. We present the multidirectional effects of MC-derived heparin and other polyanions on the major components of the kinin-kallikrein system, particularly on the factor XII activation. Although, bradykinin- and histamine-mediated symptoms are distinct clinical phenomena, they share some common features, such as some similar triggers and a predilection to occur at sites where mast cells reside, namely the skin and mucous membranes. In addition, recent observations indicate a high incidence of hypersensitivity reactions associated with MC degranulation in the HAE-C1-INH patient population. However, not all of these can be explained by IgE-dependent mechanisms. Mast cell-related G protein-coupled receptor-X2 (MRGPRX2), which has recently attracted scientific interest, may be involved in the activation of MCs through a different pathway. Therefore, we reviewed MRGPRX2 ligands that HAE-C1-INH patients may be exposed to in their daily lives and that may affect MCs degranulation. We also discussed the known inter- and intra-individual variability in the course of HAE-C1-INH in relation to factors responsible for possible variability in the strength of the response to MRGPRX2 receptor stimulation. The above issues raise several questions for future research. It is not known to what extent a prophylactic or therapeutic intervention targeting the pathways of one mechanism (mast cell degranulation) may affect the other (bradykinin production), or whether the number of mast cells at a specific body site and their reactivity to triggers such as pressure, allergens or MRGPRX2 agonists may influence the occurrence of HAE-C1-INH attacks at that site., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling editor MR declared a past co-authorship with the author GP., (Copyright © 2024 Porebski, Dziadowiec, Rybka, Kitel and Kwitniewski.)