Human Mast Cell Degranulation Research Articles

Intracellular adenosine inhibits IgE-dependent degranulation of human skin mast cells (177.19)

Abstract Adenosine is a purine nucleoside that modulates the immediate release (degranulation) of allergic mediators from mast cells. We show that adenosine at relatively high concentrations (IC50=245 µM) inhibits IgE-dependent degranulation of human skin mast cells by a non-toxic intracellular mechanism. We demonstrate that pre-treatment with the specific inhibitor of equilibrative nucleoside transporter 1 (ENT1/SLC29A1), NBMPR, dose-dependently prevented the inhibitory effect of adenosine. In contrast, blocking adenosine A2a receptor (A2aAR) signaling with the specific antagonist ZM241385 was ineffective. Thus, blocking the influx of extracellular adenosine, but not A2aAR signals, was necessary and sufficient to prevent the adenosine-mediated inhibition of degranulation. The inhibitory effect of adenosine was not due to acute toxicity since human skin mast cells cultured up to 3 days with adenosine at concentrations as high as 0.5 mM remained completely viable and activation-competent. Importantly, the inhibitory action of intracellular adenosine was specific for FcϵRI-induced signaling pathways since degranulation induced by Complement Factor 5a, Substance P, or calcium ionophore A23187 was not affected. Moreover, activation (phosphorylation) of the FcϵRI-proximal and critical signaling molecule Syk was significantly inhibited in adenosine-treated mast cells. Overall, these findings provide the first evidence of an inhibitory anti-allergic effect of intracellular adenosine.

Inhibitory effects of resveratrol on human mast cell degranulation, cytokine, chemokine and leukotriene release

Resveratrol, a polyphenol abundant in peanuts, red wine and the skin of grapes, has been shown to have anti-cancer, anti-oxidant and anti-inflammatory activities, and may also have beneficial effects on allergic inflammation. We investigated the effects of resveratrol on human mast cell activation in comparison to the anti-allergy drug tranilast. In LAD2 mast cells, both resveratrol and tranilast inhibited degranulation induced by the mast cell activators substance P, IgE/anti-IgE, and compound 48/80. Resveratrol inhibition was immediate, preventing degranulation when added simultaneously to physiological stimuli, and the effect was sustained for up to 24 hrs. The inhibitory effect was not cAMP dependent, but may be attributable to calcium modulation, as resveratrol, and to a lesser extent tranilast, prevented substance P-induced increases in intracellular calcium. Resveratrol attenuated substance P-induced TNF and MCP-1 production and inhibited IgE-mediated release of cysteinyl leukotrienes, whereas tranilast was ineffective. Furthermore, both resveratrol and tranilast reduced expression of the high affinity IgE receptor, FceRI, on LAD2 cells. The effects of resveratrol on mast cell activation were more marked in human primary CD34+-derived mast cells (HuMC), and the polyphenol was significantly more efficacious than tranilast in these cells. In conclusion, resveratrol inhibited key aspects of human mast cell activation to physiological stimuli, and was comparable, if not more efficacious than the anti-allergy drug tranilast. Thus, resveratrol may be an effective therapeutic agent for the treatment of allergic disease.

S36 The adhesion receptor CADM1 promotes human mast cell viability

Introduction and ObjectivesCell adhesion molecule 1 (CADM1) contributes to cell–cell adhesion, proliferation and adhesion-induced degranulation in human lung mast cells. Previously we found that it is expressed as three alternatively...

Immunologic Studies in Humans.

Immunologic Studies in Humans.

Catestatin, a neuroendocrine antimicrobial peptide, induces human mast cell migration, degranulation and production of cytokines and chemokines

Catestatin, a neuroendocrine antimicrobial peptide, induces human mast cell migration, degranulation and production of cytokines and chemokines

G protein coupled receptor specificity for C3a and compound 48/80-induced degranulation in human mast cells: Roles of Mas-related genes MrgX1 and MrgX2

Although human mast cells express G protein coupled receptors for the anaphylatoxin C3a, previous studies indicated that C3a causes mast cell degranulation, at least in part, via a C3a receptor-independent mechanism similar to that proposed for polycationic molecules such as compound 48/80. The purpose of the present study was to delineate the receptor specificity of C3a-induced degranulation in human mast cells. We found that C3a, a C3a receptor “superagonist” (E7) and compound 48/80 induced Ca2+ mobilization and degranulation in a differentiated human mast cell line, LAD2. However, C3a and E7 caused Ca2+ mobilization in an immature mast cell line, HMC-1 but compound 48/80 did not. We have previously shown that LAD2 cells express MrgX1 and MrgX2 but HMC-1 cells do not. To delineate the receptor specificity for C3a and compound 48/80 further, we generated stable transfectants expressing MrgX1 and MrgX2 in a rodent mast cell line, RBL-2H3 cells. We found that compound 48/80 caused degranulation in RBL-2H3 cells expressing MrgX1 and MrgX2 but C3a did not. By contrast, E7 activated RBL-2H3 cells expressing MrgX2 but not MrgX1. These findings demonstrate that in contrast to previous reports, C3a and compound 48/80 do not use a shared mechanism for mast cell degranulation. It shows that while compound 48/80 utilizes MrgX1 and MrgX2 for mast cell degranulation C3a does not. It further reveals the novel finding that the previously characterized synthetic peptide, C3a receptor “superagonist” E7 activates human mast cells via two mechanisms; one involving the C3a receptor and the other MrgX2.

Mast Cells and Neutrophils Release IL-17 through Extracellular Trap Formation in Psoriasis

IL-17 and IL-23 are known to be absolutely central to psoriasis pathogenesis because drugs targeting either cytokine are highly effective treatments for this disease. The efficacy of these drugs has been attributed to blocking the function of IL-17-producing T cells and their IL-23-induced expansion. However, we demonstrate that mast cells and neutrophils, not T cells, are the predominant cell types that contain IL-17 in human skin. IL-17(+) mast cells and neutrophils are found at higher densities than IL-17(+) T cells in psoriasis lesions and frequently release IL-17 in the process of forming specialized structures called extracellular traps. Furthermore, we find that IL-23 and IL-1β can induce mast cell extracellular trap formation and degranulation of human mast cells. Release of IL-17 from innate immune cells may be central to the pathogenesis of psoriasis, representing a fundamental mechanism by which the IL-23-IL-17 axis mediates host defense and autoimmunity.

Distinct and Shared Roles of β-Arrestin-1 and β-Arrestin-2 on the Regulation of C3a Receptor Signaling in Human Mast Cells

BackgroundThe complement component C3a induces degranulation in human mast cells via the activation of cell surface G protein coupled receptors (GPCR; C3aR). For most GPCRs, agonist-induced receptor phosphorylation leads to the recruitment of β-arrestin-1/β-arrestin-2; resulting in receptor desensitization and internalization. Activation of GPCRs also leads to ERK1/2 phosphorylation via two temporally distinct pathways; an early response that reflects G protein activation and a delayed response that is G protein independent but requires β-arrestins. The role of β-arrestins on C3aR activation/regulation in human mast cells, however, remains unknown.Methodology/Principal FindingsWe utilized lentivirus short hairpin (sh)RNA to stably knockdown the expression of β-arrestin-1 and β-arrrestin-2 in human mast cell lines, HMC-1 and LAD2 that endogenously expresses C3aR. Silencing β-arrestin-2 attenuated C3aR desensitization, blocked agonist-induced receptor internalization and rendered the cells responsive to C3a for enhanced NF-κB activity as well as chemokine generation. By contrast, silencing β-arrestin-1 had no effect on these responses but resulted in a significant decrease in C3a-induced mast cell degranulation. In shRNA control cells, C3a caused a transient ERK1/2 phosphorylation, which peaked at 5 min but disappeared by 10 min. Knockdown of β-arrestin-1, β-arrestin-2 or both enhanced the early response to C3a and rendered the cells responsive for ERK1/2 phosphorylation at later time points (10–30 min). Treatment of cells with pertussis toxin almost completely blocked both early and delayed C3a-induced ERK1/2 phosphorylation in β-arrestin1/2 knockdown cells.Conclusion/SignificanceThis study demonstrates distinct roles for β-arrestins-1 and β-arrestins-2 on C3aR desensitization, internalization, degranulation, NF-κB activation and chemokine generation in human mast cells. It also shows that both β-arrestin-1 and β-arrestin-2 play a novel and shared role in inhibiting G protein-dependent ERK1/2 phosphorylation. These findings reveal a new level of complexity for C3aR regulation by β-arrestins in human mast cells.

Human mast cell degranulation and preformed TNF secretion require mitochondrial translocation to exocytosis sites: Relevance to atopic dermatitis

Mast cells derive from hematopoietic cell precursors and participate in tissue allergic, immune, and inflammatory processes. They secrete many mediators, including preformed TNF, in response to allergic, neuropeptide, and environmental triggers. However, regulation of mast cell degranulation is not well understood. We investigated the role of mitochondrial dynamics in degranulation of human cultured mast cells. Human umbilical cord blood-derived mast cells (hCBMCs) and Laboratory of Allergic Diseases 2 (LAD2) mast cells were examined by confocal and differential interference contrast microscopy during activation by IgE/antigen and substance P (SP). Mast cells in control and atopic dermatitis (AD) skin were evaluated by transmission electron microscopy. LAD2 cells were pretreated with mitochondrial division inhibitor, a dynamin-related protein 1 (Drp1) inhibitor, and small interfering RNA for Drp1, which is necessary for mitochondrial fission and translocation. Calcineurin and Drp1 gene expression was analyzed in stimulated LAD2 cells and AD skin biopsies. Stimulation of hCBMCs with IgE/antigen or LAD2 cells with SP leads to rapid (30 minutes) secretion of preformed TNF. Degranulation is accompanied by mitochondrial translocation from a perinuclear location to exocytosis sites. Extracellular calcium depletion prevents these effects, indicating calcium requirement. The calcium-dependent calcineurin and Drp1 are activated 30 minutes after SP stimulation. Reduction of Drp1 activity by mitochondrial division inhibitor and decrease of Drp1 expression using small interfering RNA inhibit mitochondrial translocation, degranulation, and TNF secretion. Mitochondrial translocation is also evident by transmission electron microscopy in skin mast cells from AD biopsies, in which gene expression of calcineurin, Drp1, and SP is higher than in normal skin. Human mast cell degranulation requires mitochondrial dynamics, also implicated in AD.

Disparity in FcεRI-Induced Degranulation of Primary Human Lung and Skin Mast Cells Exposed to Adenosine

Inhaled and intravenously administered adenosine induces mast cell-mediated (histamine-dependent) bronchospasm in asthmatics without causing urticaria. A differential response to adenosine by human lung and skin mast cells is shown: low concentrations potentiate FcεRI-induced degranulation of human lung mast cells but not that of skin mast cells. Human lung mast cells were found to express ∼ 3-fold more A3AR messenger RNA (mRNA) than skin mast cells, suggesting the involvement of the G(i)-linked A3AR. Indeed, the adenosine-induced potentiation was sensitive to inhibition by pertussis toxin and, furthermore, could be induced with an A3AR-specific agonist. This study reveals a previously unrecognized disparity in the response to adenosine by primary human mast cells from lung and skin that might explain why adenosine induces a pulmonary but not dermatologic allergy-like response in vivo. In addition, we identify the A3AR as a potentiating receptor of FcεRI-induced degranulation, thereby implicating it in the in vivo bronchoconstrictive response to adenosine in asthmatics.

Catestatin, a neuroendocrine antimicrobial peptide, induces human mast cell migration, degranulation and production of cytokines and chemokines

Catestatin, a neuroendocrine peptide with effects on human autonomic function, has recently been found to be a cutaneous antimicrobial peptide. Human catestatin exhibits three single nucleotide polymorphisms: Gly364Ser, Pro370Leu and Arg374Gln. Given reports indicating that antimicrobial peptides and neuropeptides induce mast cell activation, we postulated that catestatin might stimulate numerous functions of human mast cells, thereby participating in the regulation of skin inflammatory responses. Catestatin and its naturally occurring variants caused the human mast cell line LAD2 and peripheral blood-derived mast cells to migrate, degranulate and release leukotriene C(4) and prostaglandins D(2) and E(2). Moreover, catestatins increased intracellular Ca(2+) mobilization in mast cells, and induced the production of pro-inflammatory cytokines/chemokines such as granulocyte-macrophage colony-stimulating factor, monocyte chemotactic protein-1/CCL2, macrophage inflammatory protein-1α/CCL3 and macrophage inflammatory protein-1β/CCL4. Our evaluation of possible cellular mechanisms suggested that G-proteins, phospholipase C and the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) are involved in catestatin-induced mast cell activation as evidenced by the inhibitory effects of pertussis toxin (G-protein inhibitor), U-73122 (phospholipase C inhibitor) and U0126 (ERK inhibitor), respectively. We also found that human mast cells express the α7 subunit of the nicotinic acetylcholine receptor at both the mRNA and protein levels. Given that silencing the α7 receptor mRNA and an α7-specific inhibitor did not affect catestatin-mediated activation of mast cells, however, we concluded that this receptor is not likely to be functional in human mast cell stimulation by catestatins. Our finding that the neuroendocrine antimicrobial peptide catestatin activates human mast cells suggests that this peptide might have immunomodulatory functions, and provides a new link between neuroendocrine and cutaneous immune systems.

Food allergy herbal formula 2 protection against peanut anaphylactic reaction is via inhibition of mast cells and basophils

Mast cells and basophils are key effector cells of IgE-mediated anaphylactic reactions. The Chinese herbal formula, food allergy herbal formula 2 (FAHF-2), protects against peanut anaphylaxis in mice. However, the mechanisms underlying this effect are not fully elucidated. To investigate whether FAHF-2 inhibits mast cell/basophil numbers and IgE-mediated activation. Mice with peanut allergy (PNA mice) were treated with FAHF-2 intragastrically for 7 weeks and challenged intragastrically with peanut 1 day and 4 weeks posttreatment. Peripheral blood basophil numbers and peritoneal mast cell numbers and FcεRI expression were determined. Direct effects of FAHF-2 on the murine mast cell line MC/9, and effects of 4fractions and 3 compounds isolated from FAHF-2 on rat basophilic leukemia cells (RBL-2H3) and human skin mast cells degranulation and on the IgE-mediated spleen tyrosine kinase signaling pathway, were determined. Although all sham-treated PNA mice developed anaphylaxis, FAHF-2-treated PNA mice were protected against anaphylaxis after peanut challenge at 1 day and 4 weeks posttherapy. Reduction of peripheral blood basophils began after 1 week of treatment and continued for at least 4 weeks posttherapy. The number and FcεRI expression of peritoneal mast cells were also significantly decreased 4 weeks posttherapy. FAHF-2-treated MC/9 cells showed significantly reduced IgE-induced FcεRI expression, FcεRI γ mRNA subunit expression, proliferation, and histamine release on challenge. Fraction 2 from FAHF-2 inhibited RBL-2H3 cell and human mast cell degranulation. Three compounds from fraction 2-berberine, palmatine, and jatrorrhizine-inhibited RBL-2H3 cell degranulation via suppressing spleen tyrosine kinase phosphorylation. Food allergy herbal formula 2 reduction of basophils and mast cell numbers as well as suppression of IgE-mediated mast cell activation may contribute to FAHF-2's persistent protection against peanut anaphylaxis.

A granular variant of CD63 is a regulator of repeated human mast cell degranulation

Mast cells are secretory immune cells whose degranulation can provoke acute allergic reactions. It is presently unclear, however, whether an individual mast cell can repeatedly degranulate or turns dysfunctional after a single antigen stimulus. This work thus aims to better define the mast cell life cycle, with particular focus on new target structures for therapeutic or diagnostic approaches in allergy. Monoclonal antibodies were raised against degranulated cord blood-derived human mast cells. A subset of these antibodies that exclusively recognized degranulated mast cells, but did not cross-react with quiescent mast cells or other hematopoietic cell types, became key reagents in subsequent experiments. We identified a granular variant of tetraspanin CD63 as an exclusive molecular marker of degranulated human mast cells. Mutant analyses indicate that a cysteine cluster around residue C170 and protein glycosylation at residue N172 account for the antibody specificity. Here, we show that mast cells, which underwent an initial FcεRI-mediated degranulation, can be degranulated for at least another cycle in vitro. Repeated degranulation, however, requires an IgE/antigen stimulus that differs from the preceding one. Furthermore, the new variant-specific anti-CD63 antibodies effectively impair repeated cycles of mast cell degranulation. Our findings indicate that mast cells are stable, multiple-use cells, which are capable of surviving and delivering several consecutive hits. Surface expression of the novel CD63 variant is a distinguishing feature of such primed cells. Reagents directed against this molecular hallmark may thus become valuable diagnostic and therapeutic agents.

Evidence for PI3K-dependent CXCR3 agonist-induced degranulation of human cord blood-derived mast cells

The chemokine receptor CXCR3, which has three known variants (CXCR3-A, CXCR3-B and CXCR3-Alt), has been implicated in the recruitment of mast cells to tissues in many different chronic diseases with its agonists found in elevated levels in several pulmonary diseases. All three variants of CXCR3 were detected in cord blood-derived mast cells at the mRNA level. Using an antibody that is unable to distinguish individual CXCR3 isoforms, we detected a marked down-regulation of intracellular protein during maturation from progenitor cells, with no concomitant changes in the modest surface expression of CXCR3. The known CXCR3 agonists CXCL9, CXCL10 and CXCL11 as well as the reported CXCR3-B agonist CXCL4, were able to induce Akt and ERK1/2 phosphorylation, as well as partial degranulation. Responses to all agonists were inhibited by pre-treatment with selective CXCR3 antagonists and pertussis toxin. Use of novel isoform-selective inhibitors, indicates that the p110γ isoform of PI3K is required for degranulation and signaling responses to CXCR3 agonists.

Adenosine receptor A3AR is responsible for augmenting FcϵRI-induced degranulation of human lung mast cells by extracellular adenosine. (86.17)

Abstract Inhaled adenosine induces a bronchoconstrictive response in asthmatics that is attributed to enhanced activation of mast cells in the airways. In this study, we demonstrate that extracellular adenosine augments FcϵRI-mediated degranulation of human mast cells from lung via the adenosine A3 receptor (A3AR). We found that low concentrations (10-7 - 10-6 M) of adenosine and its stable analog NECA enhanced degranulation of mast cells from lung, but not skin. Quantitative real time PCR analysis revealed that lung and skin mast cells expressed equal amounts of A2aAR and A2bAR (A1AR was not detectable), but that lung mast cells expressed a 5-fold greater amount of A3AR mRNA transcripts compared with skin mast cells. This suggested that A3AR was responsible for augmenting degranulation of lung mast cells. Indeed, targeted stimulation with the A3AR-specific agonist HEMADO significantly enhanced mediator release from lung mast cells following FcϵRI crosslinking with an anti-FcϵRIα MAb, but had little effect on skin mast cells. In addition, the enhancing effect of adenosine on lung mast cells could be completely inhibited by inactivating Gi-coupled A3ARs by ADP ribosylation with pertussis toxin. These data provide direct evidence that extracellular adenosine enhances IgE-induced degranulation of human lung mast cells through an A3AR-mediated mechanism; thus supporting a role for A3AR in the bronchoconstrictive response to inhaled adenosine in asthmatics.

Human mast cell degranulation is distinguished from selective secretion of TNF through intracellular calcium, energy and mitochondrial morphology dynamics

The mast cells are unique bone‐marrow derived immune cells that can secrete pre‐stored mediators through degranulation, such as triggered by Substance P (SP) or release de novo synthesized cytokines stimulated by lipopolysaccharide (LPS). However, differences in these modes secretion are largely unknown. We examined energy production, calcium homeostasis and mitochondrial morphological dynamics in LAD2 mast cell degranulation and selective secretion. A) Mast cells degranulation triggered by SP (10 μM) had two times higher energy consumption than LPS (10 ng/ml) treated cells and control cells. Mitochondria ATP pump blocker Oligomycin (2 μM) inhibited 68% of TNF secretion due to degranulation, but has little effects on de novo synthesized TNF release. B) Mast cells have increased intracellular calcium level 10 seconds after SP stimulation, while LPS did not induce significant intracellular calcium increase. C) Mitochondrial uncoupling protein 2 (UCP2) absorbs calcium from intracellular region and protects cells from calcium toxicity. UCP2 mRNA expression level enhanced ten times after 7 hours SP stimulation, but was unchanged with LPS. D) Mitochondria morphology has tight connection with its function. We showed mast cells treated with SP (10 μM) had significant mitochondrial fragmentation, which was no appeared in LPS stimulation. The present findings indicate that secretion from human mast cells can occur through distinct pathways. Mitochondria may play key role in regulating mast cell activation.This work was supported in part by NIH grant R01 AR47652 to TCT.

Counterregulation of β2-adrenoceptor function in human mast cells by stem cell factor

Mast cells contribute to the pathophysiology of asthma with the sustained release of both preformed and newly generated mediators in response to allergens and other diverse stimuli. Stem cell factor (SCF) is the key human mast cell growth factor, but also primes mast cells for mediator release. SCF expression is markedly increased in asthmatic airways. Short-acting beta(2)-adrenoceptor drugs such as albuterol inhibit human lung mast cell (HLMC) degranulation in vitro in the absence of SCF, but their effect in the presence of SCF is not known. The aim of this study was to elucidate the effects of albuterol on HLMC function in the presence of SCF. Mediator release and K(Ca)3.1 ion channel activity were analyzed in purified HLMC. Intracellular signalling and beta(2)-adrenoceptor phosphorylation and internalization were analyzed in the HMC-1 human mast cell line. beta(2)-Adrenoceptor agonist-dependent inhibition of K(Ca)3.1 ion channels and HLMC mediator release was markedly attenuated in the presence of SCF. Remarkably, albuterol actually potentiated IgE-induced histamine release in a dose-dependent manner when both SCF and IgE were present. These effects were related to the SCF-dependent phosphorylation of Tyr350 on the beta(2)-adrenoceptor with immediate uncoupling of the receptor followed by receptor internalization. The potentially beneficial effects of beta(2)-adrenoceptor agonists in asthmatic airways may be blunted as a result of the high concentrations of SCF present.

Role of Varp, a Rab21 exchange factor and TI‐VAMP/VAMP7 partner, in neurite growth

The vesicular soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) tetanus neurotoxin-insensitive vesicle-associated membrane protein (TI-VAMP/VAMP7) was previously shown to mediate an exocytic pathway involved in neurite growth, but its regulation is still largely unknown. Here we show that TI-VAMP interacts with the Vps9 domain and ankyrin-repeat-containing protein (Varp), a guanine nucleotide exchange factor (GEF) of the small GTPase Rab21, through a specific domain herein called the interacting domain (ID). Varp, TI-VAMP and Rab21 co-localize in the perinuclear region of differentiating hippocampal neurons and transiently in transport vesicles in the shaft of neurites. Silencing the expression of Varp by RNA interference or expressing ID or a form of Varp deprived of its Vps9 domain impairs neurite growth. Furthermore, the mutant form of Rab21, defective in GTP hydrolysis, enhances neurite growth. We conclude that Varp is a positive regulator of neurite growth through both its GEF activity and its interaction with TI-VAMP.

Autocrine production of cysteinyl leukotrienes activates human mast cells (139.13)

Abstract Cysteinyl leukotrienes (CysLT) are potent inflammatory lipid mediators which are derived from 5-lipoxygenase activity. CysLTs mediate some of the pathophysiological responses associated with asthma such as bronchoconstriction, vasodilation and increased microvascular permeability, increased mucus secretion, decreased mucociliary clearance, eosinophil migration, and increased eosinophil survival. We now report that peripheral blood CD34+ progenitor-derived human mast cells and the human mast cell line (LAD2) express both CysLT receptors (CysLT1R and CysLT2R), the G protein-coupled receptors that bind CysLTs. LTC4, LTD4 and LTE4 activated LAD2 to produce MIP-1β and MCP-1 and production of these chemokines was inhibited by the CysLT1R inhibitor, monelukast. LAD2 activated by IgE/anti-IgE produced CysLT (980 + 55 pg/million cells) but LAD2 activated by substance P, a neuropeptide that also binds a G protein-coupled receptor, did not produce CysLT. Montelukast had no effect on SP-mediated LAD2 degranulation. CysLT did not induce human mast cell degranulation but montelukast inhibited FcεRI-mediated human mast cell degranulation by approximately 20% suggesting that autocrine production of CysLT potentiated FcεRI-dependent degranulation. IL-4 (10 ng/mL) in the presence of stem cell factor (SCF; 100 ng/mL) significantly upregulated expression of both CysLT1R and CysLT2R (16% and 32% respectively) and potentiated mast cell responses to LTE4 by up to 25%. Overall, these results show that human mast cell activation and degranulation is subject to autocrine CysLT-induced signaling which can be blocked by CysLT1R inhibitors such as montelukast. Funded by the Investigator Initiated Studies Program (IISP) from Merck and Company, Inc.

Systemic administration of an Fcγ–Fcε-fusion protein in house dust mite sensitive nonhuman primates

Crosslinking FcεRI and FcγRIIB receptors inhibits mast cell and basophil activation, decreasing mediator release. In this study, a fusion protein incorporating human Fcγ and Fcε domains, hGE2, was shown to inhibit degranulation of human mast cells and basophils, and to exhibit efficacy in a nonhuman primate model of allergic asthma. hGE2 increased the provocative concentration of dust mite aeroallergen that induced an early phase asthmatic response. The treatment effect lasted up to 4 weeks and was associated with reduction in the number of circulating basophils and decreased expression of FcεRI on repopulating basophils. Repeat hGE2 dosing induced production of serum antibodies against human Fcγ and Fcε domains and acute anaphylaxis-like reactions. Immune serum induced histamine release from human IgE or hGE2-treated cord blood-derived mast cells and basophils in vitro. These results indicate that repeat administration with hGE2 induced an antibody response to the human molecule that resulted in activation rather than inhibition of allergic responses.