Enzymes of the mast cell granule

Anti-microbial cetylpyridinium chloride suppresses mast cell function by targeting tyrosine phosphorylation of Syk kinase

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 Ca2+ 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 Ca2+ 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.

p16Ink4a-induced senescence in cultured mast cells as a model for ageing reveals significant morphological and functional changes

BACKGROUND

Mast cells (MCs) are tissue resident cells of the immune system, mainly known for their role in allergy. However, mounting evidence indicates their involvement in the pathology of age-related diseases, such as Alzheimer's disease, Parkinson's disease, and cancer. MC numbers increase in aged tissues, but how ageing affects MCs is poorly understood.

RESULTS

We show that MC ageing is associated with the increased expression of the cell cycle inhibitor p16 Ink4a, a marker and inducer of cellular senescence. Relying on this observation and the tight association of ageing with senescence, we developed a model of inducible senescence based on doxycycline-induced expression of p16Ink4a in cultured bone marrow derived MCs (BMMCs). Using this model, we show that senescent MCs upregulate IL-1β, TNF-α and VEGF-A. We also demonstrate that senescence causes marked morphological changes that impact MC function. Senescent MCs are larger, contain a larger number of secretory granules (SGs) and have less membrane protrusions. Particularly striking are the changes in their SGs, reflected in a significant reduction in the number of electron dense SGs with a concomitant increase in lucent SGs containing intraluminal vesicles. The changes in SG morphology are accompanied by changes in MC degranulation, including a significant increase in receptor-triggered release of CD63-positive extracellular vesicles (EVs) and the exteriorisation of proteoglycans, as opposed to a gradual inhibition of the release of β-hexosaminidase.

CONCLUSIONS

The inducible expression of p16Ink4a imposes MC senescence, providing a model for tracking the autonomous changes that occur in MCs during ageing. These changes include both morphological and functional alterations. In particular, the increased release of small EVs by senescent MCs suggests an enhanced ability to modulate neighbouring cells.

The endolysosomal system in conventional and unconventional protein secretion

Most secreted proteins are transported through the "conventional" endoplasmic reticulum-Golgi apparatus exocytic route for their delivery to the cell surface and release into the extracellular space. Nonetheless, formative discoveries have underscored the existence of alternative or "unconventional" secretory routes, which play a crucial role in exporting a diverse array of cytosolic proteins outside the cell in response to intrinsic demands, external cues, and environmental changes. In this context, lysosomes emerge as dynamic organelles positioned at the crossroads of multiple intracellular trafficking pathways, endowed with the capacity to fuse with the plasma membrane and recognized for their key role in both conventional and unconventional protein secretion. The recent recognition of lysosomal transport and exocytosis in the unconventional secretion of cargo proteins provides new and promising insights into our understanding of numerous physiological processes.

Antimicrobial cetylpyridinium chloride suppresses mast cell function by targeting tyrosine phosphorylation of Syk kinase

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, we showed that low-micromolar CPC inhibits rat mast cell function by inhibiting antigen (Ag)-stimulated Ca 2+ mobilization, microtubule polymerization, and degranulation. In this study, we extend the findings to human mast cells (LAD2) and present data indicating that CPC's mechanism of action centers on its positively-charged quaternary nitrogen in its pyridinium headgroup. CPC's inhibitory effect is 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 does not affect Lyn kinase phosphorylation. Thus, CPC's root mechanism is electrostatic disruption of particular tyrosine phosphorylation events essential for signaling. This work outlines the biochemical mechanisms underlying the effects of CPC on immune signaling and allows the prediction of CPC effects on cell types, like T cells, that share similar signaling elements.

Description and Characterization of Three-Dimensional Human Mast Cell Progenitor Spheroids In Vitro

Human mast cells (MC) are an essential component of the immune system as they uniquely store and release a wide range of soluble mediators through IgE and non-IgE mechanisms. Several tissue sources can be used to differentiate functional MC for in vitro and in vivo studies. Here we describe an improved method for obtaining large numbers of human MC from adipose tissue with advantages over current methods. We analyzed donor parameters (e.g. age, race) on MC-isolation following adipose and skin tissue digestion from healthy donors. Adipose and skin-derived MC were morphologically and immunophenotypically similar in all donors regardless of age. However, donor-dependent variations in MC numbers were observed following tissue digestion. In addition, we identified and characterized three-dimensional structures from which mature MC emerged in vitro using peripheral blood and human tissue sources. MC progenitor spheroids (MCPS) appeared approximately one week following progenitor isolation and were consistently observed to have mature MC attached, emerging, or nearby when cultured in a stem cell factor-containing medium. The overall characteristics of the MCPS were similar from each tissue source. We propose that these MCPS serve as the common source of human MC in vitro.

Insights into the Characteristics and Functions of Mast Cells in the Gut

Mast cells have vital functions in allergic responses and parasite ejection, while the underlying mechanisms remain unclear. Meanwhile, MCs are essential for the maintenance of GI barrier function, and their interactions with neurons, immune cells, and epithelial cells have been related to various gastrointestinal (GI) disorders. An increasing number of investigations are being disclosed, with a lack of inner connections among them. This review aims to highlight their properties and categorization and further delve into their participation in GI diseases via interplay with neurons and immune cells. We also discuss their roles in diseases like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). Based on the evidence, we advocated for their potential application in clinical practices and advocated future research prospects.

Adapted tissue assay for the assessment of ileal granulocyte degranulation following in ovo inoculation with select bacteria or coccidial challenge in chickens

A previously described heterophil degranulation assay was adapted for use with ileal mucosal tissue via quantification of β-D-glucuronidase and assay end product 4-methylumbelliferone (4-MU). Three initial experiments evaluated the effect of in ovo inoculations of Citrobacter freundii (CF) or mixed lactic acid bacteria (LAB) on ileal granulocyte degranulation. Inoculations were administered on embryonic d18, body weights (BW) were recorded on day of hatch (DOH) and d10 to calculate body weight gain (BWG), and ileal mucosal scrapings were collected on DOH or d10 for the 4-MU assay. In all experiments, treatments were statistically analyzed relative to control groups. Treatments minimally affected BWG in all in ovo experiments (p > 0.05) relative to respective control groups. Similarly, ileal degranulation in in ovo treatments did not statistically differ (p > 0.05). Based on BWG, in ovo treatments may have induced low-level inflammation unable to elicit detectable changes via the 4-MU assay. Four subsequent experiments were conducted to evaluate effects of Eimeria maxima (EM) on ileal degranulation. Treatments included non-inoculated controls and low, medium, or high EM infection. Across all four experiments, final BW or BWG over the inoculation period were suppressed (p < 0.05) in EM groups relative to respective controls with the exception of EM-low (p = 0.094) and EM-medium (p = 0.096) in one trial. Ileal mucosal scrapings for the 4-MU assay were collected on day of peak lesions. Resulting values were reduced (p < 0.05) for EM treated birds in three experiments with the exception of EM-medium (p = 0.247). No differences were observed in one experiment (p = 0.351), which may have been attributed to a variation in strain of infecting Eimeria. Although refinement for low level inflammation is warranted, results indicate successful adaptation of the 4-MU assay for use with intestinal tissue during significant gastrointestinal inflammation.

Targeting active sites of inflammation using inherent properties of tissue-resident mast cells

Mast cells play a pivotal role in initiating and directing host's immune response. They reside in tissues that primarily interface with the external environment. Activated mast cells respond to environmental cues throughout acute and chronic inflammation through releasing immune mediators via rapid degranulation, or long-term de novo expression. Mast cell activation results in the rapid release of a variety of unique enzymes and reactive oxygen species. Furthermore, the increased density of mast cell unique receptors like mas related G protein-coupled receptor X2 also characterizes the inflamed tissues. The presence of these molecules (either released mediators or surface receptors) are particular to the sites of active inflammation, and are a result of mast cell activation. Herein, the molecular design principles for capitalizing on these novel mast cell properties is discussed with the goal of manipulating localized inflammation. STATEMENT OF SIGNIFICANCE: Mast cells are immune regulating cells that play a crucial role in both innate and adaptive immune responses. The activation of mast cells causes the release of multiple unique profiles of biomolecules, which are specific to both tissue and disease. These unique characteristics are tightly regulated and afford a localized stimulus for targeting inflammatory diseases. Herein, these important mast cell attributes are discussed in the frame of highlighting strategies for the design of bioresponsive functional materials to target regions of inflammations.

Lactic acid suppresses MRGPRX2 mediated mast cell responses

MAS related G-protein coupled receptor X2 (MRGPRX2) is a G-protein coupled receptor (GPCR) expressed in human mast cells that has been implicated to play an important role in causing pseudo-allergic reactions as well as exacerbating inflammation during asthma and other allergic diseases. Lactic acid, a byproduct of glucose metabolism, is abundantly present in inflamed tissues and has been shown to regulate functions of several immune cells. Because the endogenous ligands for MRGPRX2 (substance P and LL-37) are elevated during pathologic conditions, such as cancer and asthma, and given that lactic acid levels are also enhanced in these patients, we explored the role of lactic acid in regulating mast cells response via MRGPRX2 and MrgprB2, the mouse orthologue of the human receptor. We found that lactic acid suppressed both the early (Ca²⁺ mobilization and degranulation) and late (chemokine/cytokine release) phases of mast cell activation; this data was confirmed in LAD2, human skin and mouse peritoneal mast cells. In LAD2 cells, the reduction in degranulation and chemokine/cytokine production mediated by lactic acid was dependent on pH. In agreement with our in vitro studies, lactic acid also reduced passive systemic anaphylaxis to compound 48/80 (a known MRGPRX2/MrgprB2 ligand) and skin inflammation in a mouse model of rosacea that is dependent on MrgprB2 expression on skin mast cells. Our data thus suggest that lactic acid may serve to inhibit mast cell-mediated inflammation during asthma and reduce immune response during cancer by affecting mast cell activation through MRGPRX2.

The Role of Skin Mast Cells in Acupuncture Induced Analgesia in Animals: A Preclinical Systematic Review and Meta-analysis

While mast cells (MCs) are previously well-known as a pathological indicator of pain, their role in alleviating pain is recently emerged in acupuncture research. Thus, this study systematically reviews the role of MC in acupuncture analgesia. Animal studies on MC changes associated with the acupuncture analgesia were searched in PubMed and EMBASE. The MC number, degranulation ratio and pain threshold changes were collected as outcome measures for meta-analyses. Twenty studies were included with 13 suitable for meta-analysis, most with a moderate risk of bias. A significant MC degranulation after acupuncture was indicated in the normal and was significantly higher in the pain model. In the subgroup analysis by acupuncture type, manual (MA) and electrical (EA, each P < .00001) but not sham acupuncture had significant MC degranulation. Meta-regression revealed the linear proportionality between MC degranulation and acupuncture-induced analgesia (P < .001), which was found essential in MA (P < .00001), but not in EA (P = .45). MC mediators, such as adenosine and histamine, are involved in its mechanism. Taken together, skin MC is an essential factor for acupuncture-induced analgesia, which reveals a new aspect of MC as a pain alleviator. However, its molecular mechanism requires further study. PERSPECTIVE: This systematic review synthesizes data from studies that examined the contribution of skin MC in acupuncture analgesia. Current reports suggest a new role for skin MC and its mediators in pain alleviation and explain a peripheral mechanism of acupuncture analgesia, with suggesting the need of further studies to confirm these findings.

Genetic Regulation of Tryptase Production and Clinical Impact: Hereditary Alpha Tryptasemia, Mastocytosis and Beyond

Tryptase is a serine protease that is predominantly produced by tissue mast cells (MCs) and stored in secretory granules together with other pre-formed mediators. MC activation, degranulation and mediator release contribute to various immunological processes, but also to several specific diseases, such as IgE-dependent allergies and clonal MC disorders. Biologically active tryptase tetramers primarily derive from the two genes TPSB2 (encoding β-tryptase) and TPSAB1 (encoding either α- or β-tryptase). Based on the most common gene copy numbers, three genotypes, 0α:4β, 1α:3β and 2α:2β, were defined as "canonical". About 4-6% of the general population carry germline TPSAB1-α copy number gains (2α:3β, 3α:2β or more α-extra-copies), resulting in elevated basal serum tryptase levels. This condition has recently been termed hereditary alpha tryptasemia (HαT). Although many carriers of HαT appear to be asymptomatic, a number of more or less specific symptoms have been associated with HαT. Recent studies have revealed a significantly higher HαT prevalence in patients with systemic mastocytosis (SM) and an association with concomitant severe Hymenoptera venom-induced anaphylaxis. Moreover, HαT seems to be more common in idiopathic anaphylaxis and MC activation syndromes (MCAS). Therefore, TPSAB1 genotyping should be included in the diagnostic algorithm in patients with symptomatic SM, severe anaphylaxis or MCAS.

Authentic and Ectopically Expressed MRGPRX2 Elicit Similar Mechanisms to Stimulate Degranulation of Mast Cells

The identification of the Mas-related G-protein-coupled receptors (Mrgpr) as targets of diverse stimuli of mast cells (MCs), including neuropeptides and pseudo-allergy causing drugs, has placed these receptors at a prime position in MC research. However, the species-dependent diversity of these receptors raises the need for an adequate model for investigating the human MRGPRX2 receptor. RBL-2H3 cells, stably transfected with MRGPRX2 (RBL-MRGPRX2), are increasingly used for this purpose. Therefore, we investigated whether ectopically expressed MRGPRX2, in rat MCs, recapitulates its authentic signaling. To this purpose, we performed a broad comparative study of the responses of human LAD-2 MCs that express MRGPRX2 endogenously, and RBL-MRGPRX2 cells to compound 48/80, substance P and vancomycin, three proto-type ligands of MRGPRX2. We demonstrate that both models share similar dose-response relationships, kinetics and sensitivities to a wide range of signaling targeting drugs. Therefore, our results indicate that ectopically expressed MRGPRX2 preserves the signaling pathways employed to evoke human MC degranulation, which we show to rely on ERK1/2 MAP kinases, phospholipase C (PLC) and autophagy-related signaling. Importantly, we also show that the underlying mechanisms of MRGPRX2-triggered MC degranulation in either LAD-2 or RBL-MRGPRX2 cells are different from those elicited by its rodent orthologs.

Infectious Complications of Biological and Small Molecule Targeted Immunomodulatory Therapies

The past 2 decades have seen a revolution in our approach to therapeutic immunosuppression. We have moved from relying on broadly active traditional medications, such as prednisolone or methotrexate, toward more specific agents that often target a single receptor, cytokine, or cell type, using monoclonal antibodies, fusion proteins, or targeted small molecules. This change has transformed the treatment of many conditions, including rheumatoid arthritis, cancers, asthma, and inflammatory bowel disease, but along with the benefits have come risks. Contrary to the hope that these more specific agents would have minimal and predictable infectious sequelae, infectious complications have emerged as a major stumbling block for many of these agents. Furthermore, the growing number and complexity of available biologic agents makes it difficult for clinicians to maintain current knowledge, and most review articles focus on a particular target disease or class of agent. In this article, we review the current state of knowledge about infectious complications of biologic and small molecule immunomodulatory agents, aiming to create a single resource relevant to a broad range of clinicians and researchers. For each of 19 classes of agent, we discuss the mechanism of action, the risk and types of infectious complications, and recommendations for prevention of infection.

Mast cell activation markers for in vitro study

Mast cells (MCs) are well known for their role in allergic conditions. This cell can be activated by various types of secretagogues, ranging from a small chemical to a huge protein. Mast cell activation by secretagogues triggers the increase in intracellular calcium (iCa²⁺) concentration, granule trafficking, and exocytosis. Activated mast cells release their intra-granular pre-stored mediator or the newly synthesized mediator in the exocytosis process, in the form of degranulation or secretion. There are at least three types of exocytosis in mast cells, which are suggested to contribute to the release of different mediators, i.e.,, piecemeal, kiss-and-run, and compound exocytosis. The status of mast cells, i.e., activated or resting, is often determined by measuring the concentration of the released mediator such as histamine or β-hexosaminidase. This review summarizes several mast cell components that have been and are generally used as mast cell activation indicator, from the classical histamine and β-hexosaminidase measurement, to eicosanoid and granule trafficking observation. Basic principle of the component determination is also explained with their specified research application and purpose. The information will help to predict the experiment results with a certain study design.

Pharmacotherapy in Mast Cell Leukemia

INTRODUCTION

Mast cell leukemia (MCL) is one of the most aggressive forms of Systemic Mastocytosis (SM), a complex family of rare diseases, for which standard therapies are very few. MCL represents only <1% cases of SM and this is the reason why there are no specific clinical trials to better explore this disease. As a consequence, MCL is treated and grouped within other forms of SM, being all KIT-driven diseases; however, its KIT dysregulation leads to uncontrolled activation of mast cells (MCs), which correlates with forms of myeloid acute leukemia (AML).

AREAS COVERED

Different therapeutic approaches can be followed in the treatment of MCL. The authors look at both symptomatic therapies along with other approaches including targeted therapy. Further, the authors provide their expert opinion.

EXPERT OPINION

In the scenario of mast cell leukemia treatment, the key approach to achieve clinical results is, more than other similar pathologies, personalizing the therapy. It could be interesting or desirable to introduce for instance KIT mutant forms as minor criteria for the diagnosis of advanced SM, considering the small patient population with MCL and the relatively large panel of activating mutations for KIT and other important proteins involved in MCs' regulation.

Mast Cells Are Directly Activated by Cancer Cell-Derived Extracellular Vesicles by a CD73- and Adenosine-Dependent Mechanism

We have recently shown that mast cells (MCs), which constitute an important part of the tumor microenvironment (TME), can be directly activated by cancer cells under conditions that recapitulate cell to cell contact. However, MCs are often detected in the tumor periphery rather than intratumorally. Therefore, we investigated the possibility of MC activation by cancer cell–derived extracellular vesicles (EVs). Here we show that exposure of MCs to EVs derived from pancreatic cancer cells or non–small cell lung carcinoma results in MC activation, evident by the increased phosphorylation of the ERK1/2 MAP kinases. Further, we show that, similarly to activation by cancer cell contact, activation by EVs is dependent on the ecto enzyme CD73 that mediates extracellular formation of adenosine and on signaling by the A3 adenosine receptor. Finally, we show that activation by either cell contact or EVs upregulates expression of angiogenic and tissue remodeling genes, including IL8, IL6, VEGF, and amphiregulin. Collectively, our findings indicate that both intratumorally localized MCs and peripheral MCs are activated and reprogrammed in the TME either by contact with the cancer cells or by their released EVs.

Antimicrobial agent triclosan suppresses mast cell signaling via phospholipase D inhibition

Humans are exposed to the antimicrobial agent triclosan (TCS) through use of TCS-containing products. Exposed tissues contain mast cells, which are involved in numerous biological functions and diseases by secreting various chemical mediators through a process termed degranulation. We previously demonstrated that TCS inhibits both Ca²⁺ influx into antigen-stimulated mast cells and subsequent degranulation. To determine the mechanism linking the TCS cytosolic Ca²⁺ depression to inhibited degranulation, we investigated the effects of TCS on crucial signaling enzymes activated downstream of the Ca²⁺ rise: protein kinase C (PKC; activated by Ca²⁺ and reactive oxygen species [ROS]) and phospholipase D (PLD). We found that TCS strongly inhibits PLD activity within 15 minutes post-antigen, a key mechanism of TCS mast cell inhibition. In addition, experiments using fluorescent constructs and confocal microscopy indicate that TCS delays antigen-induced translocations of PKCβII, PKCδ and PKC substrate myristoylated alanine-rich C-kinase. Surprisingly, TCS does not inhibit PKC activity or overall ability to translocate, and TCS actually increases PKC activity by 45 minutes post-antigen; these results are explained by the timing of both TCS inhibition of cytosolic Ca²⁺ (~15+ minutes post-antigen) and TCS stimulation of ROS (~45 minutes post-antigen). These findings demonstrate that it is incorrect to assume that all Ca²⁺ -dependent processes will be synchronously inhibited when cytosolic Ca²⁺ is inhibited by a toxicant or drug. The results offer molecular predictions of the effects of TCS on other mammalian cell types, which share these crucial signal transduction elements and provide biochemical information that may underlie recent epidemiological findings implicating TCS in human health problems.

Identification of Novel Mast Cell Activators Using Cell-Based High-Throughput Screening

Mast cells (MCs) are known to regulate innate and adaptive immunity. MC activators have recently been described as safe and effective vaccine adjuvants. Many currently known MC activators are inadequate for in vivo applications, however, and research on identifying novel MC activators is limited. In this study, we identified novel MC activators by using high-throughput screening (HTS) assays using approximately 55,000 small molecules. Data sets obtained by the primary HTS assays were statistically evaluated using quality control rules and the B-score calculation, and compounds with B-scores of >3.0 were chosen as mast cell activators (hits). These hits were re-evaluated with secondary and tertiary HTS assays, followed by further statistical analysis. From these hits, we selected 15 compounds that caused degranulation in murine and human MCs, with potential for flexible chemical modification for further study. Among these 15 compounds, ST101036, ST029248, and ST026567 exhibited higher degranulation potency than other hit compounds in both human and mouse MCs. In addition, the 15 compounds identified promote de novo synthesis of cytokines and induce the release of eicosanoids from human and mouse MCs. HTS enabled us to identify small-molecule MC activators with unique properties that may be useful as vaccine adjuvants.

Searching for tryptase in the RBL-2H3 mast cell model: Preparation for comparative mast cell toxicology studies with zebrafish

Mast cells comprise a physiologically and toxicologically important cell type that is ubiquitous among species and tissues. Mast cells undergo degranulation, in which characteristic intracellular granules fuse with the plasma membrane and release many bioactive substances, such as enzymes β-hexosaminidase and tryptase. Activity of mast cells in the toxicology model organism, zebrafish, has been monitored via tryptase release and cleavage of substrate N-α-benzoyl-dl-Arg-p-nitroanilide (BAPNA). An extensively used in vitro mast cell model for studying toxicant mechanisms is the RBL-2H3 cell line. However, instead of tryptase, granule contents such as β-hexosaminidase have usually been employed as RBL-2H3 degranulation markers. To align RBL-2H3 cell toxicological studies to in vivo mast cell studies using zebrafish, we aimed to develop an RBL-2H3 tryptase assay. Unexpectedly, we discovered that tryptase release from RBL-2H3 cells is not detectable, using BAPNA substrate, despite optimized assay that can detect as little as 1 ng tryptase. Additional studies performed with another substrate, tosyl-Gly-Pro-Lys-pNA, and with an enzyme-linked immunosorbent assay, revealed a lack of tryptase protein released from stimulated RBL-2H3 cells. Furthermore, none of the eight rat tryptase genes (Tpsb2, Tpsab1, Tpsg1, Prss34, Gzmk, Gzma, Prss29, Prss41) is expressed in RBL-2H3 cells, even though all are found in RBL-2H3 genomic DNA and even though β-hexosaminidase mRNA is constitutively expressed. Therefore, mast cell researchers should utilize β-hexosaminidase or another reliable marker for RBL-2H3 degranulation studies, not tryptase. Comparative toxicity testing in RBL-2H3 cells in vitro and in zebrafish mast cells in vivo will require use of a degranulation reporter different from tryptase.

Rapid Mast Cell Generation from Gata2 Reporter Pluripotent Stem Cells

Mast cells are tissue-resident immune cells. Their overgrowth/overactivation results in a range of common distressing, sometimes life-threatening disorders, including asthma, psoriasis, anaphylaxis, and mastocytosis. Currently, drug discovery is hampered by use of cancer-derived mast cell lines or primary cells. Cell lines provide low numbers of mature mast cells and are not representative of in vivo mast cells. Mast cell generation from blood/bone marrow gives poor reproducibility, requiring 8–12 weeks of culture. Here we report a method for the rapid/robust production of mast cells from pluripotent stem cells (PSCs). An advantageous Gata2Venus reporter enriches mast cells and progenitors as they differentiate from PSCs. Highly proliferative mouse mast cells and progenitors emerge after 2 weeks. This method is applicable for rapid human mast cell generation, and could enable the production of sufficient numbers of physiologically relevant human mast cells from patient induced PSCs for the study of mast cell-associated disorders and drug discovery.

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Efficient mast cell production is achieved with novel Gata2-reporter PSCs

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14-day Gata2-reporter PSC culture produces mast cells and self-renewing progenitors

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Gata2-reporter mast cells have high protease content and degranulate

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Gata2-reporter iPSC method advances prospects for human mast cell research

Mast cell deficiency attenuates acupuncture analgesia for mechanical pain using c-kit gene mutant rats

Background

Acupuncture therapy plays a pivotal role in pain relief, and increasing evidence demonstrates that mast cells (MCs) may mediate acupuncture analgesia. The present study aims to investigate the role of MCs in acupuncture analgesia using c-kit gene mutant-induced MC-deficient rats.

Materials and methods

WsRC-Ws/Ws rats and their wild-type (WT) littermates (WsRC-+/+) were used. The number of MCs in skin of ST36 area was compared in two rats after immunofluorescence labeling. Mechanical withdrawal latency (MWL), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL) were measured on bilateral plantar for pain threshold evaluation before and after each stimulus. Acupuncture- and moxibustion-like stimuli (43°C, 46°C heat, 1 mA electroacupuncture [EA], 3 mA EA, and manual acupuncture [MA]) were applied randomly on different days.

Results

Fewer MCs were observed in the skin of ST36 in mutant rats compared to WT rats (P<0.001). For pain thresholds, MWL and MWT were higher in WsRC-Ws/Ws compared to WsRC-+/+ on bilateral paws (P<0.05), but TWL was not different between the two rats (P>0.05). Bilateral MWL and MWT in WsRC-+/+ rats increased significantly after each stimulus compared to baseline (P<0.01, P<0.001). In WsRC-Ws/Ws rats, only noxious stimuli could produce anti-nociceptive effects for mechanical pain (46°C, 3 mA EA, MA) (P<0.01, P<0.001). Additionally, the net increases in MWL and MWT induced by most stimuli were greater in WT than in mutant rats (P<0.05). For thermal nociception, either high- or low-intensity stimuli could significantly augment TWL in two rats (P<0.001), and the net increases of TWL evoked by most stimuli were to the same extent in two genetic variants.

Conclusion

MCs influence the basic mechanical but not thermal pain threshold. MCs participate in acupuncture analgesia in mechanical but not in thermal nociception, in that MC deficiency may attenuate the mechanical analgesia evoked by high-intensity stimuli and eliminate analgesia provoked by low-intensity stimuli.

Review of various molecular targets on mast cells and its relation to obesity: A future perspective

Mast cells are stimulatory factors in prognosis of various immunogenic and allergic diseases in human body. These cells play an important role in various immunological and metabolic diseases. The aim of present article is to explore the molecular targets to suppress the over expression of mast cells in obesity. The last 20 years literature were searched by various bibliographic data bases like Pubmed, google Scholar, Scopus and web of Science. The data were collected by keywords like "Mast Cell" "obesity" and "role of mast cell or role in obesity". Articles and their abstract were reviewed with a counting of 827 publications, in which 87 publications were considered for study and remaining was excluded because of its specificity to the subject. This review explains the characteristics, molecular targets and role of mast cells in obesity and existing research with mast cells to the area of metabolic diseases.

Structure-based design, synthesis, and binding mode analysis of novel and potent chymase inhibitors

Based on insight from the X-ray crystal structure of human chymase in complex with compound 1, a lactam carbonyl of the diazepane core was exchanged with O-substituted oxyimino group, leading to amidoxime derivatives. This modification resulted in highly potent chymase inhibitors, such as O-phenylamidoxime 5f. X-ray crystal structure analysis indicated that compound 5f induced movement of the Leu99 and Tyr94 side chains at the S2 site, and the increase in inhibitory activity of O-phenyl amidoxime derivatives suggested that the O-phenyl moiety interacted with the Tyr94 residue. Surface plasmon resonance experiments showed that compound 5f had slower association and dissociation kinetics and the calculated residence time of compound 5f to human chymase was extended compared to that of amide compound 1.

Rifampicin Alleviates Atopic Dermatitis-Like Response in vivo and in vitro

Atopic dermatitis (AD) is a common inflammatory skin disorder mediated by inflammatory cells, such as macrophages and mast cells. Rifampicin is mainly used for the treatment of tuberculosis. Recently, it was reported that rifampicin has anti-inflammatory and immune-suppressive activities. In this study, we investigated the effect of rifampicin on atopic dermatitis in vivo and in vitro. AD was induced by treatment with 2, 4-dinitrochlorobenzene (DNCB) in NC/Nga mice. A subset of mice was then treated with rifampicin by oral administration. The severity score and scratching behavior were alleviated in the rifampicin-treated group. Serum immunoglobulin E (IgE) and interleukin-4 (IL-4) levels were also ameliorated in mice treated with rifampicin. We next examined whether rifampicin has anti-atopic activity via suppression of mast cell activation. Rifampicin suppressed the release of β-hexosaminidase and histamine from human mast cell (HMC)-1 cultures stimulated with compound 48/80. Treatment with rifampicin also inhibited secretion of inflammatory mediators, such tumor necrosis factor-α (TNF-α) and prostaglandin D₂ (PGD₂), in mast cells activated by compound 48/80. The mRNA expression of cyclooxygenase 2 (COX-2) was reduced in the cells treated with rifampicin in a concentration-dependent manner. These results suggest that rifampicin can be used to treat atopic dermatitis.

Cirsium maritimum Makino Inhibits the Antigen/Immunoglobulin-E-Mediated Allergic Response In Vitro and In Vivo

We investigated whether Cirsium maritimum Makino can inhibit immunoglobulin-E-mediated allergic response in rat basophilic leukemia (RBL-2H3) cells and passive cutaneous anaphylaxis (PCA) in BALB/c mice. In vitro, the ethyl acetate extract of C. maritimum Makino (ECMM) significantly inhibited β-hexosaminidase release and decreased intracellular Ca²⁺ levels in RBL-2H3 cells. Moreover, ECMM leaves more strongly suppressed the release of β-hexosaminidase than ECMM flowers. ECMM leaves also significantly suppressed the PCA reaction in the murine model. High-performance liquid chromatography and ¹H and ¹³C nuclear magnetic resonance indicated that cirsimaritin, a flavonoid, was concentrated in active fractions of the extract. Our findings suggest that ECMM leaves have a potential regulatory effect on allergic reactions that may be mediated by mast cells. Furthermore, cirsimaritin may be the active anti-allergic component in C. maritimum Makino.

Mast cells are directly activated by contact with cancer cells by a mechanism involving autocrine formation of adenosine and autocrine/paracrine signaling of the adenosine A3 receptor

Mast cells (MCs) constitute an important part of the tumor microenvironment (TME). However, their underlying mechanisms of activation within the TME remain poorly understood. Here we show that recapitulating cell-to-cell contact interactions by exposing MCs to membranes derived from a number of cancer cell types, results in MC activation, evident by the increased phosphorylation of the ERK1/2 MAP kinases and Akt, in a phosphatidylinositol 3-kinase dependent fashion. Activation is unidirectional since MC derived membranes do not activate cancer cells. Stimulated ERK1/2 phosphorylation is strictly dependent on the ecto enzyme CD73 that mediates autocrine formation of adenosine, and is inhibited by knockdown of the A3 adenosine receptor (A3R) as well as by an A3R antagonist or by agonist-stimulated down-regulation of the A3R. We also show that cancer cell mediated triggering upregulates expression and stimulates secretion of interleukin 8 from the activated MCs. These findings provide evidence for a novel mode of unidirectional crosstalk between MCs and cancer cells implicating direct activation by cancer cells in MC reprogramming into a pro tumorigenic profile.

Mast cell secretome: Soluble and vesicular components

Mast cells are multifunctional master cells implicated in both innate and adaptive immune responses. Their role has been best characterized in allergy and anaphylaxis; however, emerging evidences support their contribution to a wide variety of human diseases. Mast cells, being capable of both degranulation and subsequent recovery, have recently attracted substantial attention as also being rich sources of secreted extracellular vesicles (including exosomes and microvesicles). Along with secreted de novo synthesized soluble molecules and secreted preformed granules, the membrane-enclosed extracellular vesicles represent a previously unexplored part of the mast cell secretome. In this review article we summarize available data regarding the different soluble molecules and membrane-enclosed structures secreted by mast cells. Furthermore, we provide an overview of the release mechanisms including degranulation, piecemeal degranulation, transgranulation, and secretion of different types of extracellular vesicles. Finally, we aim to give a summary of the known biological functions associated with the different mast cell-derived secretion products. The increasingly recognized complexity of mast cell secretome may provide important novel clues to processes by which mast cells contribute to the development of different pathologies and are capable of orchestrating immune responses both in health and disease.

Targeting mast cells: Uncovering prolific therapeutic role in myriad diseases

The mast cells are integral part of immune system and they have pleiotropic physiological functions in our body. Any type of abnormal stimuli causes the mast cells receptors to spur the otherwise innocuous mast cells to degranulate and release inflammatory mediators like histamine, cytokines, chemokines and prostaglandins. These mediators are involved in various diseases like allergy, asthma, mastocytosis, cardiovascular disorders, etc. Herein, we describe the receptors involved in degranulation of mast cells and are broadly divided into four categories: G-protein coupled receptors, ligand gated ion channels, immunoreceptors and pattern recognition receptors. Although, activation of pattern recognition receptors do not cause mast cell degranulation, but result in cytokines production. Degranulation itself is a complex process involving cascade of events like membrane fusion events and various proteins like VAMP, Syntaxins, DOCK5, SNAP-23, MARCKS. Furthermore, we described these mast cell receptors antagonists or agonists useful in treatment of myriad diseases. Like, omalizumab anti-IgE antibody is highly effective in asthma, allergic disorders treatment and recently mechanistic insight of IgE uncovered; matrix mettaloprotease inhibitor marimistat is under phase III trial for inflammation, muscular dystrophy diseases; ZPL-389 (H4 receptor antagonist) is in Phase 2a Clinical Trial for atopic dermatitis and psoriasis; JNJ3851868 an oral H4 receptor antagonist is in phase II clinical development for asthma, rheumatoid arthritis. Therefore, research is still in inchoate stage to uncover mast cell biology, mast cell receptors, their therapeutic role in myriad diseases.

Interferon at the crossroads of allergy and viral infections

IFN-α/β was first described as a potent inhibitor of viral replication, but it is now appreciated that IFN signaling plays a pleiotropic role in regulating peripheral T cell functions. Recently, IFN-α/β was shown to block human Th2 development by suppressing the transcription factor GATA3. This effect is consistent with the role for IFN-α/β in suppressing allergic inflammatory processes by blocking granulocyte activation and IL-4-mediated B cell isotype switching to IgE. With the consideration of recent studies demonstrating a defect in IFN-α/β secretion in DCs and epithelial cells from individuals with severe atopic diseases, there is an apparent reciprocal negative regulatory loop in atopic individuals, whereby the lack of IFN-α/β secretion by innate cells contributes to the development of allergic Th2 cells. Is it possible to overcome these events by treating with IFN-α/β or by inducing its secretion in vivo? In support of this approach, case studies have documented the therapeutic potential of IFN-α/β in treating steroid-resistant allergic asthma and other atopic diseases. Additionally, individuals with asthma who are infected with HCV and respond to IFN therapy showed a reduction in symptoms and severity of asthma attacks. These findings support a model, whereby allergic and antiviral responses are able to cross-regulate each other, as IgER cross-linking of pDCs prevents IFN-α/β production in response to viral infection. The clinical importance of upper-respiratory viruses in the context of allergic asthma supports the need to understand how these pathways intersect and to identify potential therapeutic targets.

Mast cell function: a new vision of an old cell

Since first described by Paul Ehrlich in 1878, mast cells have been mostly viewed as effectors of allergy. It has been only in the past two decades that mast cells have gained recognition for their involvement in other physiological and pathological processes. Mast cells have a widespread distribution and are found predominantly at the interface between the host and the external environment. Mast cell maturation, phenotype and function are a direct consequence of the local microenvironment and have a marked influence on their ability to specifically recognize and respond to various stimuli through the release of an array of biologically active mediators. These features enable mast cells to act as both first responders in harmful situations as well as to respond to changes in their environment by communicating with a variety of other cells implicated in physiological and immunological responses. Therefore, the critical role of mast cells in both innate and adaptive immunity, including immune tolerance, has gained increased prominence. Conversely, mast cell dysfunction has pointed to these cells as the main offenders in several chronic allergic/inflammatory disorders, cancer and autoimmune diseases. This review summarizes the current knowledge of mast cell function in both normal and pathological conditions with regards to their regulation, phenotype and role.

Does β-hexosaminidase function only as a degranulation indicator in mast cells? The primary role of β-hexosaminidase in mast cell granules

β-Hexosaminidase, which is generally present in the lysosome, is essential for glycoprotein metabolism in the maintenance of cell homeostasis. In mast cells (MCs), large amounts of β-hexosaminidase are present in the granules as opposed to the lysosome, and the biological role of MC β-hexosaminidase has yet to be fully elucidated. Therefore, we investigated the biological role of β-hexosaminidase in MC granules. Bone marrow-derived MCs from C57BL/6 (BL/6-BMMC) or β-hexosaminidase gene-deficient (hexb(-/-)-BMMC) mice were transplanted into MC-deficient (WBB6F1/J-Kit(W)/Kit(W-v) [W/W(v)]) mice to generate MC-reconstituted models. In asthma model experiments, no differences were observed in the symptoms of BL/6, W/W(v), BL/6-BMMC-reconstituted W/W(v), or hexb(-/-)-BMMC-reconstituted W/W(v) mice. In Staphylococcus epidermidis experimental infection model experiments, the severity of symptoms and frequency of death were markedly higher in W/W(v) and hexb(-/-)-BMMC-reconstituted W/W(v) mice than in BL/6 and BL/6-BMMC-reconstituted W/W(v) mice. The growth of S. epidermidis in an in vitro study was clearly inhibited by addition of BL/6-BMMC lysate, but not by addition of hexb(-/-)-BMMC lysate. Moreover, suppression of bacterial proliferation was completely recovered when bacteria were incubated with hexb(-/-)-BMMC lysate plus β-hexosaminidase. Transmission electron microscopy indicated that the cell wall of S. epidermidis was heavily degraded following coincubation of bacteria with BL/6-BMMC lysate, but not following coincubation with hexb(-/-)-BMMC lysate. These findings strongly suggest that MC granule β-hexosaminidase is crucial for defense against bacterial invasion, but is not involved in the allergic response. Our results also suggest that the bactericidal mechanism of β-hexosaminidase involves degradation of bacterial cell wall peptidoglycan.

Characterization of mast cell secretory granules and their cell biology

Exocytosis and secretion of secretory granule (SG) contained inflammatory mediators is the primary mechanism by which mast cells exert their protective immune responses in host defense, as well as their pathological functions in allergic reactions and anaphylaxis. Despite their central role in mast cell function, the molecular mechanisms underlying the biogenesis and secretion of mast cell SGs remain largely unresolved. Early studies have established the lysosomal nature of the mast cell SGs and implicated SG homotypic fusion as an important step occurring during both their biogenesis and compound secretion. However, the molecular mechanisms that account for key features of this process largely remain to be defined. A novel high-resolution imaging based methodology allowed us to screen Rab GTPases for their phenotypic and functional impact and identify Rab networks that regulate mast cell secretion. This screen has identified Rab5 as a novel regulator of homotypic fusion of the mast cell SGs that thereby regulates their size and cargo composition.

Granule maturation in mast cells: histamine in control

Mast cells are derived from committed progenitors that originate in the BM. They mature into histochemically distinguishable, metachromatic mast cells containing numerous cytoplasmic secretory granules. Accumulating evidence demonstrates that mast cell granule maturation is very tightly regulated by many factors including different granule components such as proteoglycans. In this issue of the European Journal of Immunology, Nakazawa et al. [Eur. J. Immunol. 2014. 44: 204-214] highlight a role for mast cell derived histamine as another factor critical for mast cell maturation. Using histidine decarboxylase (HDC) deficient mice that are unable to make histamine, they show poorly formed secretory granules and decreased secretory granule protease expression in peritoneal mast cells. Co-culturing BM-derived mast cells with fibroblasts normally drives granule maturation, but HDC-deficient BM-derived mast cells fail to do so. Exogenously provided histamine partly restores granule differentiation as evidenced by increased tryptase and chymase activity, and this is histamine receptor type H4 -dependent. However, H4 -deficient mice have intact granule formation in peritoneal mast cells, suggesting that when HDC is functional, the intrinsic histamine production is sufficient for most granule maturation processes and H4 is dispensable. This study highlights the role of histamine in the regulation of mast cell maturation, although the cytosolic target remains unknown.

The process of granule exocytosis in non-stimulated atrial granular cells of the snail, Achatina achatina: an ultrastructural, histochemical and immunocytochemical study

Abundant secretory granular cells (GCs) in the Giant African land snail atrium harbor a range of bioactive substances and undergo rapid total degranulation in response to stimulation of the cardiac nerve or stressful influences. Here we have analyzed exocytotic events in the non-stimulated GCs. It was shown that the GCs contain three major distinct types of granules that differ histochemically, immunocytochemically and ultrastructurally, each performing specific functions. The type I granules characteristically filled with electron-lucent homogeneous materials exhibit intense immunoreactivity for bioactive proteins and therefore are considered to be storage granules. Histochemistry using vital staining with Acridine Orange and Gomori acid phosphatase technique has revealed lysosomal-related nature of the electron-dense type II granules. Digestion remnants appearing as fine filamentous materials fill the type III granules. Only the type III granules fuse together and with the plasma membrane form degranulation channels and surface pores, through which the debris is removed from the cell. The finding of granules exhibiting intermediate ultrastructural, histochemical and immunocytochemical features suggests that the major granule types represent most stable states along a granule empting continuum. Thus, under physiological conditions, the GCs continuously produce secretory proteins and so maintain readiness for stress-response, but use protein degradation machinery to prevent massive release of these bioactive substances into hemolymph.

A focus on mast cells and pain

Mast cells (MCs) are immunocytes with secretory functions that act locally in peripheral tissues to modulate local hemodynamics, nociceptor activation and pain. They are also able to infiltrate the central nervous system (CNS), especially the spinal cord and the thalamus, but their cerebral function remains an enigma. A role in regulating the opening of the blood-brain barrier has been proposed. Paracrine-like action of MCs on synaptic transmission might also signal a modulation of the nervous system by the immune system. In this review, we examine the link between MCs and nociceptive process, at the periphery as well as in the CNS.

The tetraspanin CD63 is required for efficient IgE-mediated mast cell degranulation and anaphylaxis

Mast cell (MC) activation through the high-affinity IgE receptor FcεRI leads to the release of mediators involved in immediate-type allergic reactions. Although Abs against the tetraspanins CD63 and CD81 inhibit FcεRI-induced MC degranulation, the intrinsic role of these molecules in FcεRI-induced MC activation is unknown. In MCs, CD63 is expressed at the cell surface and in lysosomes (particularly secretory lysosomes that contain allergic mediators). In this study, we investigated the role of CD63 in MC using a CD63 knockout mouse model. CD63-deficiency did not affect in vivo MC numbers and tissue distribution. Bone marrow-derived MC developed normally in the absence of CD63 protein. However, CD63-deficient bone marrow-derived MC showed a significant decrease in FcεRI-mediated degranulation, but not PMA/ionomycin-induced degranulation, as shown by β-hexosaminidase release assays. The secretion of TNF-α, which is both released from granules and synthesized de novo upon MC activation, was also decreased. IL-6 secretion and production of the lipid mediator leukotriene C₄ were unaffected. There were no ultrastructural differences in granule content and morphology, late endosomal/lysosomal marker expression, FcεRI-induced global tyrosine phosphorylation, and Akt phosphorylation. Finally, local reconstitution in genetically MC-deficient Kit(w/w-v) mice was unaffected by the absence of CD63. However, the sites reconstituted with CD63-deficient MC developed significantly attenuated cutaneous anaphylactic reactions. These findings demonstrate that the absence of CD63 results in a significant decrease of MC degranulation, which translates into a reduction of acute allergic reactions in vivo, thus identifying CD63 as an important component of allergic inflammation.

Regulation of the immune response by soybean isoflavones

Soybeans are rich in immuno-modulatory isoflavones such as genistein, daidzein, and glycitein. These isoflavones are well-known antioxidants, chemopreventive and anti-inflammatory agents. Several epidemiological studies suggest that consumption of traditional soy food containing isoflavones is associated with reduced prevalence of chronic health disorders. Isoflavones are considered to be phytoestrogens because of their ability to bind to estrogen receptors. The literature is extensive on the chemistry, bio-availability, and bio-activity of isoflavones. However, their effects on immune response are yet to be fully understood, but are beginning to be appreciated. We review the role of isoflavones in regulation of the immune response and their potential clinical applications in immune-dysfunction. Special emphasis will be made regarding in vivo studies including humans and animal model systems.

Isoflavones, genistein and daidzein, regulate mucosal immune response by suppressing dendritic cell function

Lipopolysaccharide (LPS), a component of gram-negative bacterial cell walls, has been shown to have a strong adjuvant effect towards inhaled antigens contributing to airway inflammation. Isoflavones are anti-inflammatory molecules present in abundant quantities in soybeans. We investigated the effect of isoflavones on human dendritic cell (DC) activation via LPS stimulation and subsequent DC-mediated effector cell function both in vitro and in a mouse model of upper airway inflammation. Human monocyte-derived DCs (MDDC) were matured with LPS (or TNF-α) +/− isoflavones (genistein or daidzein). The surface expression levels of DC activation markers were analyzed by flow cytometry. Mature DCs +/− isoflavones were washed and cultured with freshly-isolated allogenic naïve CD4⁺ T cells for 5 days or with autologous natural killer (NK) cells for 2 hours. The percentages of proliferating IFN-γ⁺ CD4⁺ T cells and cytokine levels in culture supernatants were assessed. NK cell degranulation and DC cytotoxicity were measured by flow cytometry. Isoflavones significantly suppressed the activation-induced expression of DC maturation markers (CD83, CD80, CD86) and MHC class I but not MHC class II molecules in vitro. Isoflavone treatment inhibited the ability of LPS-DCs to induce IFN-γ in CD4⁺ T cells. NK cell degranulation and the percentage of dead DCs were significantly increased in isoflavone-treated DC-NK co-culture experiments. Dietary isoflavones suppressed the mucosal immune response to intra-nasal sensitization of mice to ovalbumin. Similar results were obtained when isoflavones were co-administered during sensitization. These results demonstrate that soybean isoflavones suppress immune sensitization by suppressing DC-maturation and its subsequent DC-mediated effector cell functions.

Mast cell proteoglycans

Mast cells are versatile effector cells of the immune system, contributing to both innate and adaptive immunity toward pathogens but also having profound detrimental activities in the context of inflammatory disease. A hallmark morphological feature of mast cells is their large content of cytoplasmic secretory granules, filled with numerous secretory compounds, including highly negatively charged heparin or chondroitin sulfate proteoglycans of serglycin type. These anionic proteoglycans provide the basis for the strong metachromatic staining properties of mast cells seen when applying various cationic dyes. Functionally, the mast cell proteoglycans have been shown to have an essential role in promoting the storage of other granule-contained compounds, including bioactive monoamines and different mast cell-specific proteases. Moreover, granule proteoglycans have been shown to regulate the enzymatic activities of mast cell proteases and to promote apoptosis. Here, the current knowledge of mast cell proteoglycans is reviewed.

Decoding the regulation of mast cell exocytosis by networks of Rab GTPases

Exocytosis is a key event in mast cell functions. By this process, mast cells release inflammatory mediators, contained in secretory granules (SGs), which play important roles in immunity and wound healing but also provoke allergic and inflammatory responses. The mechanisms underlying mast cell exocytosis remained poorly understood. An essential step toward deciphering the mechanisms behind exocytosis is the identification of the cellular components that regulate this process. Because Rab GTPases regulate specific trafficking pathways, we screened 44 Rabs for their functional impacts on exocytosis triggered by the FcεRI or combination of Ca ²⁺ ionophore and phorbol ester. Because exocytosis involves the continuous reorganization of the actin cytoskeleton, we also repeated our screen in the presence of cytochalasin D that inhibits actin polymerization. In this paper, we report on the identification of 30 Rabs as regulators of mast cell exocytosis, the involvement of 26 of which has heretofore not been recognized. Unexpectedly, these Rabs regulated exocytosis in a stimulus-dependent fashion, unless the actin skeleton was disrupted. Functional clustering of the identified Rabs suggested their classification as Rabs involved in SGs biogenesis or Rabs that control late steps of exocytosis. The latter could be further divided into Rabs that localize to the SGs and Rabs that regulate transport from the endocytic recycling compartment. Taken together, these findings unveil the Rab networks that control mast cell exocytosis and provide novel insights into their mechanisms of action.

Systemic effects of ingested Lactobacillus rhamnosus: inhibition of mast cell membrane potassium (IKCa) current and degranulation

Exposure of the intestine to certain strains lactobacillus can have systemic immune effects that include the attenuation of allergic responses. Despite the central role of mast cells in allergic disease little is known about the effect of lactobacilli on the function of these cells. To address this we assessed changes in rat mast cell activation following oral treatment with a strain of Lactobacillus known to attenuate allergic responses in animal models. Sprague Dawley rats were fed with L. rhamnosus JB-1 (1×10(9)) or vehicle control for 9 days. Mediator release from peritoneal mast cells (RPMC) was determined in response to a range of stimuli. Passive cutaneous anaphylaxis (PCA) was used to assess mast cell responses in vivo. The Ca(2+) activated K(+) channel (KCa3.1) current, identified as critical to mast cell degranulation, was monitored by whole cell patch-clamp. L. rhamnosus JB-1 treatment lead to significant inhibition of mast cell mediator release in response to a range of stimuli including IgE mediated activation. Furthermore, the PCA response was significantly reduced in treated rats. Patch-clamp studies revealed that RPMC from treated animals were much less responsive to the KCa3.1 opener, DCEBIO. These studies demonstrate that Ingestion of L. rhamnosus JB-1 leads to mast cell stabilization in rats and identify KCa3.1 as an immunomodulatory target for certain lactobacilli. Thus the systemic effects of certain candidate probiotics may include mast cell stabilization and such actions could contribute to the beneficial effect of these organisms in allergic and other inflammatory disorders.

Mast cell adenosine receptors function: a focus on the a3 adenosine receptor and inflammation

Adenosine is a metabolite, which has long been implicated in a variety of inflammatory processes. Inhaled adenosine provokes bronchoconstriction in asthmatics or chronic obstructive pulmonary disease patients, but not in non-asthmatics. This hyper responsiveness to adenosine appears to be mediated by mast cell activation. These observations have marked the receptor that mediates the bronchoconstrictor effect of adenosine on mast cells (MCs), as an attractive drug candidate. Four subtypes (A1, A2a, A2b, and A3) of adenosine receptors have been cloned and shown to display distinct tissue distributions and functions. Animal models have firmly established the ultimate role of the A3 adenosine receptor (A3R) in mediating hyper responsiveness to adenosine in MCs, although the influence of the A2b adenosine receptor was confirmed as well. In contrast, studies of the A3R in humans have been controversial. In this review, we summarize data on the role of different adenosine receptors in mast cell regulation of inflammation and pathology, with a focus on the common and distinct functions of the A3R in rodent and human MCs. The relevance of mouse studies to the human is discussed.

Mast cells: an expanding pathophysiological role from allergy to other disorders

The mast cells are multi-effector cells with wide distribution in the different body parts and traditionally their role has been well-defined in the development of IgE-mediated hypersensitivity reactions including bronchial asthma. Due to the availability of genetically modified mast cell-deficient mice, the broadened pathophysiological role of mast cells in diverse diseases has been revealed. Mast cells exert different physiological and pathophysiological roles by secreting their granular contents, including vasoactive amines, cytokines and chemokines, and various proteases, including tryptase and chymase. Furthermore, mast cells also synthesize plasma membrane-derived lipid mediators, including prostaglandins and leukotrienes, to produce diverse biological actions. The present review discusses the pathophysiological role of mast cells in different diseases, including atherosclerosis, pulmonary hypertension, ischemia-reperfusion injury, male infertility, autoimmune disorders such as rheumatoid arthritis and multiple sclerosis, bladder pain syndrome (interstitial cystitis), anxiety, Alzheimer's disease, nociception, obesity and diabetes mellitus.