Regulation of mast cell responses in health and disease

Interaction of DJ-1 with Lyn is essential for IgE-mediated stimulation of human mast cells

BACKGROUND

DJ-1 is a redox-sensitive protein with multiple roles in cell homeostasis, levels of which are altered in patients with mast cell (MC)-related disorders. However, whether DJ-1 can regulate human MC function is unknown.

OBJECTIVE

We sought to investigate the potential role of DJ-1 in the responses of human MCs to antigen stimulation.

METHODS

DJ-1 was silenced in human CD34⁺-derived MCs and in the LAD2 MC line by using lentiviral short hairpin RNA constructs. Release of β-hexosaminidase, prostaglandin D₂, and GM-CSF and changes in reactive oxygen species levels were measured after FcεRI engagement. Enzymatic assays, sucrose density gradient centrifugation, immunoprecipitation, dot and Western blotting, and confocal imaging were performed for signaling, cellular localization, and coassociation studies.

RESULTS

DJ-1 knockdown substantially reduced mediator release, as well as Lyn kinase and spleen tyrosine kinase activation and signaling through mechanisms that appeared largely unrelated to DJ-1 antioxidant activity. Following FcεRI activation, nonoxidized rather than oxidized DJ-1 translocated to lipid rafts, where it associated with Lyn, an interaction that appeared critical for maximal Lyn activation and initiation of signaling. Using purified recombinant proteins, we demonstrated that DJ-1 directly bound to Lyn but not to other Src kinases, and this interaction was specific for human but not mouse proteins. In addition, DJ-1 reduced Src homology 2 domain-containing phosphatase 2 phosphatase activity by scavenging reactive oxygen species, thus preventing spleen tyrosine kinase dephosphorylation and perpetuating MC signaling.

CONCLUSION

We demonstrate a novel role for DJ-1 in the early activation of Lyn by FcεRI, which is essential for human MC responses and provides the basis for an alternative target in allergic disease therapy.

Polydatin inhibits mast cell-mediated allergic inflammation by targeting PI3K/Akt, MAPK, NF-κB and Nrf2/HO-1 pathways

Polydatin(PD) shows anti-allergic inflammatory effect, and this study investigated its underlying mechanisms in in vitro and in vivo models. IgE-mediated passive cutaneous anaphylaxis (PCA) and passive systemic anaphylaxis (PSA) models were used to confirm PD effect in vivo. Various signaling pathway proteins in mast cell were examined. RT-PCR, ELISA and western blotting were applied when appropriate. Activity of Lyn and Fyn kinases in vitro was measured using the Kinase Enzyme System. PD dose-dependently reduced the pigmentation of Evans blue in the PCA model and decreased the concentration of serum histamine in PSA model, and attenuated the degranulation of mast cells without generating cytotoxicity. PD decreased pro-inflammatory cytokine expression (TNF-α, IL-4, IL-1β, and IL-8). PD directly inhibited activity of Lyn and Syk kinases and down-regulated downstream signaling pathway including MAPK, PI3K/AKT and NF-kB. In addition, PD also targets Nrf2/HO-1 pathway to inhibit mast cell-derived allergic inflammatory reactions. In conclusion, the study demonstrates that PD is a possible therapeutic candidate for allergic inflammatory diseases. It directly inhibited activity of Lyn and Syk kinases and down-regulates the signaling pathway of MAPK, PI3K/AKT and NF-κB, and up-regulates the signaling pathway of Nrf2/HO-1 to inhibit the degranulation of mast cells.

Relation between mast cells concentration and serotonin expression in chagasic megacolon development

Chagas' disease is still reaching about 10 million people in the world. In South America, one of the most severe forms of this disease is the megacolon, characterized by severe constipation, dilated sigmoid colon and rectum and severe malnutrition. Previous data suggested that mast cells and serotonin (5-hydroxytryptamine [5-HT]) expression could be involved in intestinal homeostasis control, avoiding the chagasic megacolon development. The aim at this study was to characterize the presence of mast cells and expression of serotonin in chagasic patients with and without megacolon and evaluate the relation between mast cells, serotonin and megacolon development. Our results demonstrated that patients without megacolon feature a large amount of serotonin and few mast cells, while patients with megacolon feature low serotonin expression and a lot of mast cells. We believe that serotonin may be involved in the inflammatory process control, triggered by mast cells, and the presence of this substance in large quantities of the intestine could represent a mechanism of megacolon prevention.

LAT is essential for the mast cell stabilising effect of tHGA in IgE-mediated mast cell activation

Mast cells play a central role in the pathogenesis of allergic reaction. Activation of mast cells by antigens is strictly dependent on the influx of extracellular calcium that involves a complex interaction between signalling molecules located within the cells. We have previously reported that tHGA, an active compound originally isolated from a local shrub known as Melicope ptelefolia, prevented IgE-mediated mast cell activation and passive systemic anaphylaxis by suppressing the release of interleukin-4 (IL-4) and tumour necrosis factor (TNF)-α from activated rat basophilic leukaemia (RBL)-2H3 cells. However, the mechanism of action (MOA) as well as the molecular target underlying the mast cell stabilising effect of tHGA has not been previously investigated. In this study, DNP-IgE-sensitised RBL-2H3 cells were pre-treated with tHGA before challenged with DNP-BSA. To dissect the MOA of tHGA in IgE-mediated mast cell activation, the effect of tHGA on the transcription of IL-4 and TNF-α mRNA was determined using Real Time-Polymerase Chain Reaction (qPCR) followed by Calcium Influx Assay to confirm the involvement of calcium in the activation of mast cells. The protein lysates were analysed by using Western Blot to determine the effect of tHGA on various important signalling molecules in the LAT-PLCγ-MAPK and PI3K-NFκB pathways. In order to identify the molecular target of tHGA in IgE-mediated mast cell activation, the LAT and LAT2 genes in RBL-2H3 cells were knocked-down by using RNA interference to establish a LAT/LAT2 competition model. The results showed that tHGA inhibited the transcription of IL-4 and TNF-α as a result of the suppression of calcium influx in activated RBL-2H3 cells. The results from Western Blot revealed that tHGA primarily inhibited the LAT-PLCγ-MAPK pathway with partial inhibition on the PI3K-p65 pathway without affecting Syk. The results from RNAi further demonstrated that tHGA failed to inhibit the release of mediators associated with mast cell degranulation under the LAT/LAT2 competition model in the absence of LAT. Collectively, this study concluded that the molecular target of tHGA could be LAT and may provide a basis for the development of a mast cell stabiliser which targets LAT.

Differential Ca2+ mobilization and mast cell degranulation by FcεRI- and GPCR-mediated signaling

Mast cells play a primary role in allergic diseases. During an allergic reaction, mast cell activation is initiated by cross-linking IgE-FcεRI complex by multivalent antigen resulting in degranulation. Additionally, G protein-coupled receptors also induce degranulation upon activation. However, the spatio-temporal relationship between Ca²⁺ mobilization and mast cell degranulation is not well understood. We investigated the relationship between oscillations in Ca²⁺ level and mast cell degranulation upon stimulation in rat RBL-2H3 cells. Nile red and Fluo-4 were used as probes for monitoring histamine and intracellular Ca²⁺ levels, respectively. Histamine release and Ca²⁺ oscillations in real-time were monitored using total internal reflection fluorescence microscopy (TIRFM). Mast cell degranulation followed immediately after FcεRI and GPCR-mediated Ca²⁺ increase. FcεRI-induced Ca²⁺ increase was higher and more sustained than that induced by GPCRs. However, no significant difference in mast cell degranulation rates was observed. Although intracellular Ca²⁺ release was both necessary and sufficient for mast cell degranulation, extracellular Ca²⁺ influx enhanced the process. Furthermore, cytosolic Ca²⁺ levels and mast cell degranulation were significantly decreased by downregulation of store-operated Ca²⁺ entry (SOCE) via Orai1 knockdown, 2-aminoethyl diphenylborinate (2-APB) or tubastatin A (TSA) treatment. Collectively, this study has demonstrated the role of Ca²⁺ signaling in regulating histamine degranulation.

Retinoic Acid Negatively Impacts Proliferation and MCTC Specific Attributes of Human Skin Derived Mast Cells, but Reinforces Allergic Stimulability

The Vitamin-A-metabolite retinoic acid (RA) acts as a master regulator of cellular programs. Mast cells (MCs) are primary effector cells of type-I-allergic reactions. We recently uncovered that human cutaneous MCs are enriched with RA network components over other skin cells. Yet, direct experimental evidence on the significance of the RA-MC axis is limited. Here, skin-derived cultured MCs were exposed to RA for seven days and investigated by flow-cytometry (BrdU incorporation, Annexin/PI, FcεRI), microscopy, RT-qPCR, histamine quantitation, protease activity, and degranulation assays. We found that while MC size and granularity remained unchanged, RA potently interfered with MC proliferation. Conversely, a modest survival-promoting effect from RA was noted. The granule constituents, histamine and tryptase, remained unaffected, while RA had a striking impact on MC chymase, whose expression dropped by gene and by peptidase activity. The newly uncovered MRGPRX2 performed similarly to chymase. Intriguingly, RA fostered allergic MC degranulation, in a way completely uncoupled from FcεRI expression, but it simultaneously restricted MRGPRX2-triggered histamine release in agreement with the reduced receptor expression. Vitamin-A-derived hormones thus re-shape skin-derived MCs numerically, phenotypically, and functionally. A general theme emerges, implying RA to skew MCs towards processes associated with (allergic) inflammation, while driving them away from the skin-imprinted MC_TC (“MCs containing tryptase and chymase”) signature (chymase, MRGPRX2). Collectively, MCs are substantial targets of the skin retinoid network.

KTN0158, a Humanized Anti-KIT Monoclonal Antibody, Demonstrates Biologic Activity against both Normal and Malignant Canine Mast Cells

Purpose: KTN0158 is a novel anti-KIT antibody that potently inhibits wild-type and mutant KIT. This study evaluated the safety, biologic activity, and pharmacokinetic/pharmacodynamics profile of KTN0158 in dogs with spontaneous mast cell tumors (MCT) as a prelude to human clinical applications.Experimental Design: Cell proliferation, KIT phosphorylation, and mast cell degranulation were evaluated in vitro KTN0158 was administered to 4 research dogs to assess clinical effects and cutaneous mast cell numbers. Thirteen dogs with spontaneous MCT were enrolled into a prospective phase I dose-escalating open-label clinical study of KTN0158 evaluating 3 dose levels and 2 schedules and with weekly assessments for response and clinical toxicities.Results: KTN0158 was a potent inhibitor of human and dog KIT activation and blocked mast cell degranulation in vitro In dogs, KTN0158 was well tolerated and reduced cutaneous mast cell numbers in a dose-dependent manner. Clinical benefit of KTN0158 administration in dogs with MCT (n = 5 partial response; n = 7 stable disease) was observed regardless of KIT mutation status, and decreased KIT phosphorylation was demonstrated in tumor samples. Histopathology after study completion demonstrated an absence of neoplastic cells in the primary tumors and/or metastatic lymph nodes from 4 dogs. Reversible hematologic and biochemical adverse events were observed at doses of 10 and 30 mg/kg. The MTD was established as 10 mg/kg.Conclusions: KTN0158 inhibits KIT phosphorylation, demonstrates an acceptable safety profile in dogs, and provides objective responses in canine MCT patients with and without activating KIT mutations, supporting future clinical evaluation of KTN0158 in people. Clin Cancer Res; 23(10); 2565-74. ©2016 AACR.

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.

Inhibitory Effect of Loranthus parasiticus on IgE-Mediated Allergic Responses in RBL-2H3 Cells

The mistletoe Loranthus parasiticus has been used as a compound for traditional medicine in Northeast Asia for a long time and is known to possess neuroprotective action. Nonetheless, the effect of Loranthus parasiticus on allergic responses remains unknown. In the present study, we evaluated whether the water extract of Loranthus parasiticus (LPE) could inhibit IgE-mediated allergic responses in RBL-2H3 cells. LPE inhibited the release of β-hexosaminidase (IC₅₀, 184.5 μg/mL) and the formation of tumor necrosis factor-α (IC₅₀, 84.27 μg/mL), interleukin-4 (IC₅₀, 93.43 μg/mL), prostaglandin E₂ (IC₅₀, 84.10 μg/mL), prostaglandin D₂, and leukotriene C₄ (IC₅₀, 43.27 μg/mL) in a concentration-dependent manner. Moreover, LPE inhibited phosphorylation of Syk, PLCγ1/2, PKCδ, ERK, JNK, p38, and Akt. In the late phase, LPE decreased 5-lipoxygenase phosphorylation and COX-2 expression but not cPLA₂ phosphorylation. Additionally, LPE included total phenolic compounds (10.72 mg/g dry weight) and total flavonoids (56.20 mg/g dry weight). These results suggest that the phenolic compounds or flavonoids contained in LPE may be associated with antiallergic activity. The phenolic compounds and flavonoids in LPE are antiallergic phytochemicals capable of inhibiting the activation of the FcεRI signaling cascade in mast cells. Such effects may provide further information for the development of a phytomedicine for allergic diseases.

Association study of genetic variants in PLA2G4A, PLCG1, LAT, SYK, and TNFRS11A genes in NSAIDs-induced urticaria and/or angioedema patients

NSAIDs-induced urticaria and/or angioedema (NIUA) is the most frequent entity of hypersensitivity reactions to NSAIDs. The underlying cause is considered to be because of a nonspecific immunological mechanism in which mast cells are key players. We studied the association of nine single nucleotide polymorphisms in five genes involved in mast cell activation (SYK, LAT1, PLCG1, PLA2G4A, and TNFRSF11A) in 450 NIUA patients and 500 controls. We identified several statistically significant associations when stratifying patients by symptoms: PLA2G4A rs12746200 (urticaria vs. controls, Pc=0.005). PLCG1 rs2228246 (angioedema vs. controls; Pc=0.044), and TNFRS11A rs1805034 (urticaria+angioedema vs. controls; Pc=0.041). The frequency of haplotype PLCG1 rs753381-rs2228246 (C-G) in angioedema-NIUA patients was lower than that in controls (Pc=0.040). In addition, the haplotype frequency of TNFRS11A rs1805034-rs35211496 (C-T) was higher among urticaria-NIUA and urticaria+angioedema-NIUA patients than the controls (Pc=0.045 and 0.046). Our results shed light on the involvement of variants in genes related to non-immunological mast cell activation in NIUA.

Lactic Acid Suppresses IL-33-Mediated Mast Cell Inflammatory Responses via Hypoxia-Inducible Factor-1α-Dependent miR-155 Suppression

Lactic acid (LA) is present in tumors, asthma, and wound healing, environments with elevated IL-33 and mast cell infiltration. Although IL-33 is a potent mast cell activator, how LA affects IL-33-mediated mast cell function is unknown. To investigate this, mouse bone marrow-derived mast cells were cultured with or without LA and activated with IL-33. LA reduced IL-33-mediated cytokine and chemokine production. Using inhibitors for monocarboxylate transporters (MCT) or replacing LA with sodium lactate revealed that LA effects are MCT-1- and pH-dependent. LA selectively altered IL-33 signaling, suppressing TGF-β-activated kinase-1, JNK, ERK, and NF-κB phosphorylation, but not p38 phosphorylation. LA effects in other contexts have been linked to hypoxia-inducible factor (HIF)-1α, which was enhanced in bone marrow-derived mast cells treated with LA. Because HIF-1α has been shown to regulate the microRNA miR-155 in other systems, LA effects on miR-155-5p and miR-155-3p species were measured. In fact, LA selectively suppressed miR-155-5p in an HIF-1α-dependent manner. Moreover, overexpressing miR-155-5p, but not miR-155-3p, abolished LA effects on IL-33-induced cytokine production. These in vitro effects of reducing cytokines were consistent in vivo, because LA injected i.p. into C57BL/6 mice suppressed IL-33-induced plasma cytokine levels. Lastly, IL-33 effects on primary human mast cells were suppressed by LA in an MCT-dependent manner. Our data demonstrate that LA, present in inflammatory and malignant microenvironments, can alter mast cell behavior to suppress inflammation.

Ameliorative effects of Artemisia argyi Folium extract on 2,4‑dinitrochlorobenzene‑induced atopic dermatitis‑like lesions in BALB/c mice

Artemisia argyi Folium has been used to treat skin diseases, including eczema and dermatitis, in South Korean medicine. The present study investigated the curative effects of Artemisia argyi Folium extract (AAFE) on 2,4‑dinitrochlorobenzene (DNCB)‑induced atopic dermatitis (AD)‑like skin lesions in a BALB/c mouse model. Briefly, the dorsal skin of the BALB/c mice was sensitized three times with DNCB, whereas the ears were challenged twice. Repeated treatment with DNCB induced AD‑like lesions. The effects of AAFE on AD‑like lesions were evaluated by clinical observation, histopathological analysis, immunohistochemistry and enzyme‑linked immunosorbent assay. In addition, reverse transcription‑polymerase chain reaction and western blotting were performed. Treatment with AAFE reduced AD‑like lesions, as determined by clinical observation, histopathological analysis, and detection of the serum levels of histamine, immunoglobulin E and cytokines. With regards to its mechanism of action, AAFE inhibited the phosphorylation of Lck/yes‑related novel tyrosine kinase (Lyn), spleen tyrosine kinase (Syk), mitogen‑activated protein kinases (MAPKs), phosphoinositide 3‑kinase (PI3K)/Akt and IκBα, which have essential roles in the production of various cytokines in lymph nodes. The suppressive activity of AAFE may be due to the inhibition of a series of immunopathological events, including the release of proinflammatory cytokines. The results of the present study strongly suggest that AAFE exerts an anti‑AD effect by inhibiting the Lyn, Syk, MAPKs, PI3K/Akt and IκBα pathways. Therefore, AAFE may be considered an effective herbal remedy for the treatment of AD.

New Developments in Mast Cell Biology: Clinical Implications

Mast cells (MCs) are present in connective tissue and at mucosal surfaces in all classes of vertebrates. In health, they contribute to tissue homeostasis, host defense, and tissue repair via multiple receptors regulating the release of a vast stockpile of proinflammatory mediators, proteases, and cytokines. However, these potentially protective cells are a double-edged sword. When there is a repeated or long-term stimulus, MC activation leads to tissue damage and dysfunction. Accordingly, MCs are implicated in the pathophysiologic aspects of numerous diseases covering all organs. Understanding the biology of MCs, their heterogeneity, mechanisms of activation, and signaling cascades may lead to the development of novel therapies for many diseases for which current treatments are lacking or are of poor efficacy. This review will focus on updates and developments in MC biology and their clinical implications, with a particular focus on their role in respiratory diseases.

P2X7 receptors induce degranulation in human mast cells

Mast cells play important roles in host defence against pathogens, as well as being a key effector cell in diseases with an allergic basis such as asthma and an increasing list of other chronic inflammatory conditions. Mast cells initiate immune responses through the release of newly synthesised eicosanoids and the secretion of pre-formed mediators such as histamine which they store in specialised granules. Calcium plays a key role in regulating both the synthesis and secretion of mast-cell-derived mediators, with influx across the membrane, in particular, being necessary for degranulation. This raises the possibility that calcium influx through P2X receptors may lead to antigen-independent secretion of histamine and other granule-derived mediators from human mast cells. Here we show that activation of P2X7 receptors with both ATP and BzATP induces robust calcium rises in human mast cells and triggers their degranulation; both effects are blocked by the P2X7 antagonist AZ11645373, or the removal of calcium from the extracellular medium. Activation of P2X1 receptors with αβmeATP also induces calcium influx in human mast cells, which is significantly reduced by both PPADS and NF 449. P2X1 receptor activation, however, does not trigger degranulation. The results indicate that P2X7 receptors may play a significant role in contributing to the unwanted activation of mast cells in chronic inflammatory conditions where extracellular ATP levels are elevated.

Roles of basophils and mast cells in cutaneous inflammation

Mast cells and basophils are associated with T helper 2 (Th2) immune responses. Newly developed mast cell-deficient mice have provided evidence that mast cells initiate contact hypersensitivity via activating dendritic cells. Studies using basophil-deficient mice have also revealed that basophils are responsible for cutaneous Th2 skewing to haptens and peptide antigens but not to protein antigens. Recently, several studies reported the existence of innate lymphoid cells (ILCs), which differ from classic T cells in that they lack the T cell receptor. Mast cells and basophils can interact with ILCs and play some roles in the pathogenesis of Th2 responses. Basophil-derived interleukin (IL)-4 enhances the expression of the chemokine CCL11, as well as IL-5, IL-9, and IL-13 in ILC2s, leading to the accumulation of eosinophils in allergic reactions. IL-33-stimulated mast cells can play a regulatory role in the development of ILC2-mediated non-antigen-specific protease-induced acute inflammation. In this review, we discuss the recent advances in our understanding of mast cells and basophils in immunity and inflammation.

Inhibitory effect of baicalin on allergic response in ovalbumin-induced allergic rhinitis guinea pigs and lipopolysaccharide-stimulated human mast cells

OBJECTIVE

Baicalin, a flavonoid compound purified from the dry roots of Scutellaria baicalensis Georgi, has generally been used for the treatment of various allergic diseases. However, there is little information about the anti-inflammatory effects of baicalin for allergic rhinitis. This study aims to investigate the anti-allergic effect of baicalin on allergic response in ovalbumin (OVA)-induced allergic rhinitis guinea pigs and lipopolysaccharide (LPS)-stimulated human mast cells.

METHODS

Using in vivo models, we evaluated the effect of baicalin on allergic rhinitis symptoms via recording the number of nasal rubs and sneezes. The levels of histamine, OVA-specific immunoglobulin E(IgE), eosinophil cationic protein (ECP) and inflammatory cytokines were measured using enzyme-linked immunosorbent assay (ELISA). The histological changes of nasal mucosa were observed by light microscope after HE staining. In vitro, the release of histamine and β-hexosaminidase of compound 48/80-induced human mast cells were measured by ELISA and PNP-NAG colorimetry, respectively. The productions of inflammatory cytokines of LPS-stimulated human mast cells were determined using ELISA. Western blot was used to test the protein expression of JAK2, p-JAK2, STAT5, p-STAT5, IKKβ, p-IKKβ, IκBα, p-IκBα and NF-κB (p65) of LPS-stimulated human mast cells.

RESULTS

The oral administration of baicalin at doses of 50 and 200 mg/kg improved allergic rhinitis symptoms and the histological changes of nasal mucosa and decreased the serum levels of histamine, ECP, interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α and OVA-specific IgE in OVA-induced allergic rhinitis guinea pigs. In vitro, baicalin suppressed the release of histamine and β-hexosaminidase in compound 48/80-induced human mast cells. In addition, baicalin also inhibited the productions of inflammatory cytokines such as IL-1β, IL-6, IL-8 and TNF-α and suppressed the phosphorylation of JAK2, STAT5, IKKβ, IκBα and the nuclear translocation of NF-κB (p65) subunit in LPS-stimulated human mast cells.

CONCLUSIONS

These results suggest that baicalin can effectively prevent allergic response in OVA-induced allergic rhinitis guinea pigs and inhibit inflammatory response via blocking JAK2-STAT5 and NF-κB signaling pathways in LPS-stimulated human mast cells. Considered together,the results show that baicalin may be a useful drug in the treatment of allergic rhinitis.

Phenotypic variability in human skin mast cells

Mast cells (MCs) are unique constituents of the human body. While inter-individual differences may influence the ways by which MCs operate in their skin habitat, they have not been surveyed in a comprehensive manner so far. We therefore set out to quantify skin MC variability in a large cohort of subjects. Pathophysiologically relevant key features were quantified and correlated: transcripts of c-kit, FcεRIα, FcεRIβ, FcεRIγ, histidine decarboxylase, tryptase, and chymase; surface expression of c-Kit, FcεRIα; activity of tryptase, and chymase; histamine content and release triggered by FcεRI and Ca(2+) ionophore. While there was substantial variability among subjects, it strongly depended on the feature under study (coefficient of variation 33-386%). Surface expression of FcεRI was positively associated with FcεRIα mRNA content, histamine content with HDC mRNA, and chymase activity with chymase mRNA. Also, MC signature genes were co-regulated in distinct patterns. Intriguingly, histamine levels were positively linked to tryptase and chymase activity, whereas tryptase and chymase activity appeared to be uncorrelated. FcεRI triggered histamine release was highly variable and was unrelated to FcεRI expression but unexpectedly tightly correlated with histamine release elicited by Ca(2+) ionophore. This most comprehensive and systematic work of its kind provides not only detailed insights into inter-individual variability in MCs, but also uncovers unexpected patterns of co-regulation among signature attributes of the lineage. Differences in MCs among humans may well underlie clinical responses in settings of allergic reactions and complex skin disorders alike.

Inflammasome components ASC and AIM2 modulate the acute phase of biomaterial implant-induced foreign body responses

Detailing the inflammatory mechanisms of biomaterial-implant induced foreign body responses (FBR) has implications for revealing targetable pathways that may reduce leukocyte activation and fibrotic encapsulation of the implant. We have adapted a model of poly(methylmethacrylate) (PMMA) bead injection to perform an assessment of the mechanistic role of the ASC-dependent inflammasome in this process. We first demonstrate that ASC^−/− mice subjected to PMMA bead injections had reduced cell infiltration and altered collagen deposition, suggesting a role for the inflammasome in the FBR. We next investigated the NLRP3 and AIM2 sensors because of their known contributions in recognising damaged and apoptotic cells. We found that NLRP3 was dispensable for the fibrotic encapsulation; however AIM2 expression influenced leukocyte infiltration and controlled collagen deposition, suggesting a previously unexplored link between AIM2 and biomaterial-induced FBR.

The Hot-Water Extract of Smilacis Chinae Rhizome Suppresses 2,4-Dinitrochlorobenzene and House Dust Mite-Induced Atopic Dermatitis-Like Skin Lesions in Mice

Smilacis Chinae Rhizome (SCR) has been used as an oriental folk medicine for various biological activities. However, its effect on atopic dermatitis (AD) remains undetermined to date. We assessed the effect of orally administered hot-water extract of SCR on AD-like skin lesions in mice and its underlying mechanisms. AD-like murine model was prepared by repeated alternate application of house dust mite (Dermatophagoides farinae) extract (DFE) and 2,4-dinitrochlorobenzene (DNCB) for 4 weeks, topically to the ears. Daily oral administration of SCR for 3 and 4 weeks significantly reduced inflammatory ear thickening, with the effect being enhanced at the earlier start and longer period of administration. This effect was accompanied by a significant decrease in both Th2 and Th1 serum antibodies (total IgE, DFE-specific IgE, and IgG2a). Histological analysis showed that SCR markedly decreased the epidermal/dermal ear thickening and the dermal infiltration of inflammatory cells. Furthermore, SCR suppressed DFE/DNCB-induced expression of IL-4, IL-13, IL-17, IL-18, TSLP, and IFN-γ genes in the ear tissue. Taken together, our observations demonstrate that chronic oral administration of SCR exerts beneficial effect in mouse AD model, suggesting that SCR has the therapeutic potential as an orally active treatment of AD by modulating both Th1 and Th2 responses.

Controlling Arteriogenesis and Mast Cells Are Central to Bioengineering Solutions for Critical Bone Defect Repair Using Allografts

Although most fractures heal, critical defects in bone fail due to aberrant differentiation of mesenchymal stem cells towards fibrosis rather than osteogenesis. While conventional bioengineering solutions to this problem have focused on enhancing angiogenesis, which is required for bone formation, recent studies have shown that fibrotic non-unions are associated with arteriogenesis in the center of the defect and accumulation of mast cells around large blood vessels. Recently, recombinant parathyroid hormone (rPTH; teriparatide; Forteo) therapy have shown to have anti-fibrotic effects on non-unions and critical bone defects due to inhibition of arteriogenesis and mast cell numbers within the healing bone. As this new direction holds great promise towards a solution for significant clinical hurdles in craniofacial reconstruction and limb salvage procedures, this work reviews the current state of the field, and provides insights as to how teriparatide therapy could be used as an adjuvant for healing critical defects in bone. Finally, as teriparatide therapy is contraindicated in the setting of cancer, which constitutes a large subset of these patients, we describe early findings of adjuvant therapies that may present future promise by directly inhibiting arteriogenesis and mast cell accumulation at the defect site.

IL-6 promotes an increase in human mast cell numbers and reactivity through suppression of suppressor of cytokine signaling 3

BACKGROUND

IL-6, levels of which are reported to be increased in association with mastocytosis, asthma, and urticaria, is used in conjunction with stem cell factor to generate CD34(+) cell-derived primary human mast cell (HuMC) cultures. Despite these associations, the effects on and mechanisms by which prolonged exposure to IL-6 alters HuMC numbers and function are not well understood.

OBJECTIVES

We sought to study the effect of IL-6 on HuMC function, the mechanisms by which IL-6 exerts its effects, and the relationship of these findings to mastocytosis.

METHODS

HuMCs were cultured in stem cell factor with or without IL-6. Responses to FcεRI aggregation and expression of proteases and receptors, including the soluble IL-6 receptor (sIL-6R), were then quantitated. Epigenetic changes in suppressor of cytokine signaling 3 (SOCS3) were determined by using methylation-specific PCR. Serum samples from healthy control subjects and patients with mastocytosis were assayed for IL-6, tryptase, and sIL-6R.

RESULTS

IL-6 enhanced mast cell (MC) proliferation, maturation, and reactivity after FcεRI aggregation. IL-6 reduced expression of SOCS3, which correlated with methylation of the SOCS3 promoter and increased expression and activation of signal transducer and activator of transcription 3. IL-6 also suppressed constitutive production of sIL-6R, and serum levels of sIL-6R were similarly reduced in patients with mastocytosis.

CONCLUSION

IL-6 increases MC proliferation and formation of a more reactive phenotype enabled by suppressing proteolytic cleavage of sIL-6R from IL-6R and downregulation of the SOCS3 autoinhibitory pathway. We suggest IL-6 blockade might ameliorate MC-related symptoms and pathology in patients with MC-related diseases associated with increased IL-6 levels, including mastocytosis.

c-kit plays a critical role in induction of intravenous tolerance in experimental autoimmune encephalomyelitis

c-kit (CD117) is a tyrosine kinase receptor found in various types of immune cells. It has been shown that c-kit plays a role in the pathogenesis of multiple sclerosis, an inflammatory demyelinating disorder of the CNS. Recent data have suggested an immunoregulatory effect of c-kit. We therefore examined the role of c-kit in autoantigen-induced i.v. tolerance in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Our results show that induction of intravenous tolerance against EAE in B6 mice is characterized by increased numbers of CD117(+) cells and altered mast cell-associated molecules in the periphery and in the CNS. W(-sh) (c-kit-deficient) mice were resistant to i.v autoantigen-induced tolerance, with increased proinflammatory cytokine production in the periphery. I.v. autoantigen in WT mice suppressed the production of proinflammatory cytokines IFN-γ and IL-6 and up-regulated the expression of FoxP3, a transcription factor of Tregs; however, in W(-sh) mice, IFN-γ and IL-6 were increased with a failure of FoxP3 induction upon i.v. autoantigen injection and is thus a mechanism for resistance to i.v. tolerance induction in these mice. We conclude that c-kit signaling has a regulatory role in i.v. tolerance and could be a target for potential immunotherapy in autoimmune disorders.

Butyrate suppresses murine mast cell proliferation and cytokine production through inhibiting histone deacetylase

Beyond their nutritional impact to colonic epithelial cells, the intestinal microbiota metabolite butyrate has pleotropic effects to host cells and is known for its beneficial effects on intestinal homeostasis and metabolism. However, it remains unclear how it modulates mast cell function. Here, we demonstrate that butyrate profoundly inhibited proliferation of mouse mastocytoma P815 cells through inducing cell cycle arrest and apoptosis, as well as decreasing c-Kit activation. In addition, butyrate increased early- and late-stage apoptotic P815 cells. In murine bone marrow-derived mast cells (BMMC), butyrate-suppressed FcεRI-dependent tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) release without affecting β-Hexosaminidase, but that was associated with decreased mitogen-activated protein kinase extracellular signal-regulated kinase 1/2, p38 and c-Jun N-terminal kinases activation. Butyrate treatment substantially enhanced histone 3 acetylation in both P815 and BMMC and decreased FcεRI-dependent mRNA expression of tnf-α and il-6 in BMMC, mimicking the effect of Trichostatin A, a known histone deacetylase inhibitor. Chromatin immunoprecipitation revealed that butyrate enhanced acetylation of the tnf-α and il-6 promoter regions but blocked RNA polymerase II binding to the promoters of tnf-α and il-6 genes, indicating suppressed transcription initiation. These phenotypes mimicked those of Trichostatin A treatment. In conclusion, butyrate inhibits cell proliferation and increases cell apoptosis in mastocytoma P815 cells and suppresses FcεRI-dependent cytokine production in murine primary BMMC, which are likely mediated by HDAC inhibition.

Mast cells in airway diseases and interstitial lung disease

Mast cells are major effector cells of inflammation and there is strong evidence that mast cells play a significant role in asthma pathophysiology. There is also a growing body of evidence that mast cells contribute to other inflammatory and fibrotic lung diseases such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. This review discusses the role that mast cells play in airway diseases and highlights how mast cell microlocalisation within specific lung compartments and their cellular interactions are likely to be critical for their effector function in disease.

Signal transduction and chemotaxis in mast cells

Mast cells play crucial roles in both innate and adaptive arms of the immune system. Along with basophils, mast cells are essential effector cells for allergic inflammation that causes asthma, allergic rhinitis, food allergy and atopic dermatitis. Mast cells are usually increased in inflammatory sites of allergy and, upon activation, release various chemical, lipid, peptide and protein mediators of allergic reactions. Since antigen/immunoglobulin E (IgE)-mediated activation of these cells is a central event to trigger allergic reactions, innumerable studies have been conducted on how these cells are activated through cross-linking of the high-affinity IgE receptor (FcεRI). Development of mature mast cells from their progenitor cells is under the influence of several growth factors, of which the stem cell factor (SCF) seems to be the most important. Therefore, how SCF induces mast cell development and activation via its receptor, KIT, has been studied extensively, including a cross-talk between KIT and FcεRI signaling pathways. Although our understanding of the signaling mechanisms of the FcεRI and KIT pathways is far from complete, pharmaceutical applications of the knowledge about these pathways are underway. This review will focus on recent progresses in FcεRI and KIT signaling and chemotaxis.

Rhamnus davurica leaf extract inhibits Fyn activation by antigen in mast cells for anti-allergic activity

BACKGROUND

Complementary and alternative herbal medicines are recently considered as a promising approach for treating various diseases. We screened approximately 100 plant extracts for anti-allergic activity. Rhamnus davurica leaf extract showed the most potent inhibitory effect on the activation of RBL-2H3 mast cells. Although Rhamnus davurica extract has been used to treat pruritus, dysuresia, and constipation as a traditional herbal medicine in some Asian countries, an anti-allergic effect of Rhamnus davurica has not yet been demonstrated. We aimed to investigate the effect and mechanism of the leaf extract of Rhamnus davurica (LERD) on mast cells in vitro and allergic responses in vivo.

METHODS

The effects of LERD on the activation of mast cells and mast cell-mediated passive cutaneous anaphylaxis (PCA) were measured in mice and two types of mast cells, mouse bone marrow-derived mast cells (BMMCs) and RBL-2H3 cells in vitro. A mechanistic study of its inhibitory effect was performed by using degranulation assay, reverse transcriptase-polymerase chain reaction, enzyme-linked immunosorbent assay, and western blotting analysis.

RESULTS

LERD reversibly suppressed antigen-stimulated degranulation in BMMCs and RBL-2H3 cells, and also inhibited mRNA expression and secretion of TNF-α and IL-4 in a dose-dependent manner. In a PCA animal model, LERD significantly inhibited antigen-induced allergic response and degranulation of ear tissue mast cells. As for the mechanism of action, LERD inhibited the activation of Syk, which is the pivotal signaling protein for mast cell activation by antigen. Furthermore, LERD also impeded the activations of well-known downstream proteins such as LAT, Akt and three MAP kinases (Erk, p38 and JNK). In an in vitro kinase assay, LERD suppressed the activation of Fyn in antigen-stimulated mast cells.

CONCLUSION

This study demonstrated for the first time that LERD has anti-allergic effects through inhibiting the Fyn/Syk pathway in mast cells. Therefore, this study provides scientific evidence for LERD to be used as an herbal medicine or health food for patients with allergic diseases.

Toxicity of eosinophil MBP is repressed by intracellular crystallization and promoted by extracellular aggregation

Eosinophils are white blood cells that function in innate immunity and participate in the pathogenesis of various inflammatory and neoplastic disorders. Their secretory granules contain four cytotoxic proteins, including the eosinophil major basic protein (MBP-1). How MBP-1 toxicity is controlled within the eosinophil itself and activated upon extracellular release is unknown. Here we show how intragranular MBP-1 nanocrystals restrain toxicity, enabling its safe storage, and characterize them with an X-ray-free electron laser. Following eosinophil activation, MBP-1 toxicity is triggered by granule acidification, followed by extracellular aggregation, which mediates the damage to pathogens and host cells. Larger non-toxic amyloid plaques are also present in tissues of eosinophilic patients in a feedback mechanism that likely limits tissue damage under pathological conditions of MBP-1 oversecretion. Our results suggest that MBP-1 aggregation is important for innate immunity and immunopathology mediated by eosinophils and clarify how its polymorphic self-association pathways regulate toxicity intra- and extracellularly.

Approaches for analyzing the roles of mast cells and their proteases in vivo

The roles of mast cells in health and disease remain incompletely understood. While the evidence that mast cells are critical effector cells in IgE-dependent anaphylaxis and other acute IgE-mediated allergic reactions seems unassailable, studies employing various mice deficient in mast cells or mast cell-associated proteases have yielded divergent conclusions about the roles of mast cells or their proteases in certain other immunological responses. Such "controversial" results call into question the relative utility of various older versus newer approaches to ascertain the roles of mast cells and mast cell proteases in vivo. This review discusses how both older and more recent mouse models have been used to investigate the functions of mast cells and their proteases in health and disease. We particularly focus on settings in which divergent conclusions about the importance of mast cells and their proteases have been supported by studies that employed different models of mast cell or mast cell protease deficiency. We think that two major conclusions can be drawn from such findings: (1) no matter which models of mast cell or mast cell protease deficiency one employs, the conclusions drawn from the experiments always should take into account the potential limitations of the models (particularly abnormalities affecting cell types other than mast cells) and (2) even when analyzing a biological response using a single model of mast cell or mast cell protease deficiency, details of experimental design are critical in efforts to define those conditions under which important contributions of mast cells or their proteases can be identified.

Mast cells and basophils in cutaneous immune responses

Mast cells and basophils share some functions in common and are generally associated with T helper 2 (Th2) immune responses, but taking basophils as surrogate cells for mast cell research or vice versa for several decades is problematic. Thus far, their in vitro functions have been well studied, but their in vivo functions remained poorly understood. New research tools for their functional analysis in vivo have revealed previously unrecognized roles for mast cells and basophils in several skin disorders. Newly developed mast cell-deficient mice provided evidence that mast cells initiate contact hypersensitivity via activating dendritic cells. In addition, studies using basophil-deficient mice have revealed that basophils were responsible for cutaneous Th2 skewing to haptens and peptide antigens but not to protein antigens. Moreover, human basophils infiltrate different skin lesions and have been implicated in the pathogenesis of skin diseases ranging from atopic dermatitis to autoimmune diseases. In this review, we will discuss the recent advances related to mast cells and basophils in human and murine cutaneous immune responses.

Are mast cells still good biomarkers for bladder pain syndrome/interstitial cystitis?

PURPOSE

ESSIC identifies mast cell infiltrates of detrusor muscle as a diagnostic criterion for bladder pain syndrome/interstitial cystitis. However, an increased mast cell count is also characteristic of overactive bladder syndrome. The lack of uniformity in mast cell detection methods hampers data comparison. Using state-of-the-art techniques we investigated whether mast cells differ among bladder conditions.

MATERIALS AND METHODS

We analyzed bladder biopsies from 56 patients, including 31 with bladder pain syndrome/interstitial cystitis with (12) or without (19) Hunner lesions, 13 with overactive bladder syndrome and 12 without bladder symptoms to determine the quantity, location, distribution and activation of mast cells using immunohistochemistry with anti-mast cell tryptase. Patients were allocated to study groups by key bladder symptoms commonly used to define conditions (pain and major urgency).

RESULTS

Subepithelial mast cell localization (p <0.001) and an increased detrusor mast cell count (p = 0.029) were characteristic of bladder pain syndrome/interstitial cystitis with Hunner lesions. The optimal cutoff of 32 detrusor mast cells per mm(2) achieved only 68% accuracy with 38% positive predictive value. No difference was observed between bladder pain syndrome/interstitial cystitis without Hunner lesions and overactive bladder syndrome. Patient groups differed in lymphocyte infiltration (p = 0.001), nodular lymphocyte aggregates (p <0.001) and urothelium integrity (p <0.001).

CONCLUSIONS

Subepithelial mast cell distribution was characteristic of bladder pain syndrome/interstitial cystitis with Hunner lesions. Detrusor mastocytosis had poor predictive value for bladder pain syndrome/interstitial cystitis. Mast cell assessment did not distinguish bladder pain syndrome/interstitial cystitis without Hunner lesions from overactive bladder syndrome.

New insights on the signaling and function of the high-affinity receptor for IgE

Clustering of the high-affinity receptor for immunoglobulin E (FcεRI) through the interaction of receptor-bound immunoglobulin E (IgE) antibodies with their cognate antigen is required to couple IgE antibody production to cellular responses and physiological consequences. IgE-induced responses through FcεRI are well known to defend the host against certain infectious agents and to lead to unwanted allergic responses to normally innocuous substances. However, the cellular and/or physiological response of individuals that produce IgE antibodies may be markedly different and such antibodies (even to the same antigenic epitope) can differ in their antigen-binding affinity. How affinity variation in the interaction of FcεRI-bound IgE antibodies with antigen is interpreted into cellular responses and how the local environment may influence these responses is of interest. In this chapter, we focus on recent advances that begin to unravel how FcεRI distinguishes differences in the affinity of IgE-antigen interactions and how such discrimination along with surrounding environmental stimuli can shape the (patho) physiological response.

The role of mouse mast cell proteases in the proliferative phase of wound healing in microdeformational wound therapy

BACKGROUND

Stored in the secretory granules of cutaneous mouse mast cells are mouse mast cell proteases (mMCP-4, -5, and -6). Using transgenic mouse lines that lacked these enzymes, it was shown that mMCP-4 and mMCP-5 modulate the outcome of burn-induced skin injury. Whether or not these proteases also play a role in the repair of surgically damaged skin, with or without microdeformational wound therapy, remains to be determined.

METHODS

Wild-type C57BL/6 mice and transgenic C57BL/6 mouse lines lacking mMCP-4, -5, or -6 were subjected to surgical wounding of their skin. Wounds were splinted with a stabilizing patch, and the mice received either microdeformational wound therapy (n = 5) or occlusive dressing (n = 5) for 7 days. Wound healing parameters were assessed in the proliferative phase.

RESULTS

Cell proliferation in the wounded wild-type mice receiving microdeformational wound therapy was 60 ± 3 percent. Cell proliferation was only 35 ± 5 percent, 25 ± 5 percent, and 45 ± 4 percent for the treated mMCP-4-, mMCP-5-, and mMCP-6-null mice, respectively (p = 0.005). Blood vessel sprouting was higher in the control mice with microdeformational wound therapy (170 ± 40 vessels/high-power field) compared with mouse mast cell protease 6-null mice with microdeformational wound therapy (70 ± 20 vessels/high-power field; p = 0.005), and higher in the control mice with occlusive dressing (110 ± 30 vessels/high-power field) compared with mMCP-4-null mice with occlusive dressing (50 ± 20 vessels/high-power field; p = 0.01). Qualitatively, the granulation tissue of all the protease-deficient groups receiving microdeformational wound therapy was disrupted.

CONCLUSION

Results suggest that mouse mast cell proteases 4, 5, and 6 are mediators of the critical role mast cells play in microdeformational wound therapy in the proliferative phase of healing.

Vesicular trafficking and signaling for cytokine and chemokine secretion in mast cells

Upon activation mast cells (MCs) secrete numerous inflammatory compounds stored in their cytoplasmic secretory granules by a process called anaphylactic degranulation, which is responsible for type I hypersensitivity responses. Prestored mediators include histamine and MC proteases but also some cytokines and growth factors making them available within minutes for a maximal biological effect. Degranulation is followed by the de novo synthesis of lipid mediators such as prostaglandins and leukotrienes as well as a vast array of cytokines, chemokines, and growth factors, which are responsible for late phase inflammatory responses. While lipid mediators diffuse freely out of the cell through lipid bilayers, both anaphylactic degranulation and secretion of cytokines, chemokines, and growth factors depends on highly regulated vesicular trafficking steps that occur along the secretory pathway starting with the translocation of proteins to the endoplasmic reticulum. Vesicular trafficking in MCs also intersects with endocytic routes, notably to form specialized cytoplasmic granules called secretory lysosomes. Some of the mediators like histamine reach granules via specific vesicular monoamine transporters directly from the cytoplasm. In this review, we try to summarize the available data on granule biogenesis and signaling events that coordinate the complex steps that lead to the release of the inflammatory mediators from the various vesicular carriers in MCs.

Autocrine hemokinin-1 functions as an endogenous adjuvant for IgE-mediated mast cell inflammatory responses

BACKGROUND

Efficient development of atopic diseases requires interactions between allergen and adjuvant to initiate and amplify the underlying inflammatory responses. Substance P (SP) and hemokinin-1 (HK-1) are neuropeptides that signal through the neurokinin-1 receptor (NK1R) to promote inflammation. Mast cells initiate the symptoms and tissue effects of atopic disorders, secreting TNF and IL-6 after FcεRI cross-linking by antigen-IgE complexes (FcεRI-activated mast cells [FcεRI-MCs]). Additionally, MCs express the NK1R, suggesting an adjuvant role for NK1R agonists in FcεRI-MC-mediated pathologies; however, in-depth research addressing this relevant aspect of MC biology is lacking.

OBJECTIVE

We sought to investigate the effect of NK1R signaling and the individual roles of SP and HK-1 as potential adjuvants for FcεRI-MC-mediated allergic disorders.

METHODS

Bone marrow-derived mast cells (BMMCs) from C57BL/6 wild-type (WT) or NK1R(-/-) mice were used to investigate the effects of NK1R signaling on FcεRI-MCs. BMMCs generated from Tac1(-/-) mice or after culture with Tac4 small interfering RNA were used to address the adjuvancy of SP and HK-1. WT, NK1R(-/-), and c-Kit(W-sh/W-sh) mice reconstituted with WT or NK1R(-/-) BMMCs were used to evaluate NK1R signaling on FcεRI-MC-mediated passive local and systemic anaphylaxis and on airway inflammation.

RESULTS

FcεRI-activated MCs upregulated NK1R and HK-1 transcripts and protein synthesis, without modifying SP expression. In a positive signaling loop HK-1 promoted TNF and IL-6 secretion by MC degranulation and protein synthesis, the latter through the phosphoinositide 3-kinase/Akt/nuclear factor κB pathways. In vivo NK1R signaling was necessary for the development of passive local and systemic anaphylaxis and airway inflammation.

CONCLUSIONS

FcεRI stimulation of MCs promotes autocrine secretion of HK-1, which signals through NK1R to provide adjuvancy for efficient development of FcεRI-MC-mediated disorders.

Mast cells aggravate sepsis by inhibiting peritoneal macrophage phagocytosis

Controlling the overwhelming inflammatory reaction associated with polymicrobial sepsis remains a prevalent clinical challenge with few treatment options. In septic peritonitis, blood neutrophils and monocytes are rapidly recruited into the peritoneal cavity to control infection, but the role of resident sentinel cells during the early phase of infection is less clear. In particular, the influence of mast cells on other tissue-resident cells remains poorly understood. Here, we developed a mouse model that allows both visualization and conditional ablation of mast cells and basophils to investigate the role of mast cells in severe septic peritonitis. Specific depletion of mast cells led to increased survival rates in mice with acute sepsis. Furthermore, we determined that mast cells impair the phagocytic action of resident macrophages, thereby allowing local and systemic bacterial proliferation. Mast cells did not influence local recruitment of neutrophils and monocytes or the release of inflammatory cytokines. Phagocytosis inhibition by mast cells involved their ability to release prestored IL-4 within 15 minutes after bacterial encounter, and treatment with an IL-4-neutralizing antibody prevented this inhibitory effect and improved survival of septic mice. Our study uncovers a local crosstalk between mast cells and macrophages during the early phase of sepsis development that aggravates the outcome of severe bacterial infection.

Honeycomb-like Structured Film Regulates Mediator Release from Non-Tumor Mast Cells

We previously reported a honeycomb-like structured film (HCF) stimulates mast cell proliferation and multinucleated formation. In this study, we examined the role of HCF in regulating the release of mediators from cultured mast cells. We measured the release of histamine, substance P, tumor necrosis factor (TNF)-α, and leukotriene B4 (LTB-4) from NCL-2 cells (proliferative mouse non-tumor mast cells). After 7 days of culture, HCF selectively down-regulated the release of TNF-α, LTB-4, and (to a lesser extent) substance P, but not histamine. Mast cell attachment to HCF may have a greater effect on release of de novo synthesized molecules.

Mast cells as rapid innate sensors of cytomegalovirus by TLR3/TRIF signaling-dependent and -independent mechanisms

The succinct metaphor, 'the immune system's loaded gun', has been used to describe the role of mast cells (MCs) due to their storage of a wide range of potent pro-inflammatory and antimicrobial mediators in secretory granules that can be released almost instantly on demand to fight invaders. Located at host-environment boundaries and equipped with an arsenal of pattern recognition receptors, MCs are destined to be rapid innate sensors of pathogens penetrating endothelial and epithelial surfaces. Although the importance of MCs in antimicrobial and antiparasitic defense has long been appreciated, their role in raising the alarm against viral infections has been noted only recently. Work on cytomegalovirus (CMV) infection in the murine model has revealed MCs as players in a novel cross-talk axis between innate and adaptive immune surveillance of CMV, in that infection of MCs, which is associated with MC degranulation and release of the chemokine CCL5, enhances the recruitment of protective CD8 T cells to extravascular sites of virus replication, specifically to lung interstitium and alveolar epithelium. Here, we have expanded on these studies by investigating the conditions for MC activation and the consequent degranulation in response to host infection. Surprisingly, the data revealed two temporally and mechanistically distinct waves of MC activation: an almost instant indirect activation that depended on TLR3/TRIF signaling and delayed activation by direct infection of MCs that did not involve TLR3/TRIF signaling. Cell type-specific Cre-recombination that yielded eGFP-expressing reporter virus selectively originating from MCs identified MC as a new in vivo, first-hit target cell of productive murine CMV infection.

Mast cell activation: a complex interplay of positive and negative signaling pathways

Mast cells regulate the immunological responses causing allergy and autoimmunity, and contribute to the tumor microenvironment through generation and secretion of a broad array of preformed, granule-stored and de novo synthesized bioactive compounds. The release and production of mast cell mediators is the result of a coordinated signaling machinery, followed by the FcεRI and FcγR antigen ligation. In this review, we present the latest understanding of FcεRI and FcγR signaling, required for the canonical mast cell activation during allergic responses and anaphylaxis. We then describe the cooperation between the signaling of FcR and other recently characterized membrane-bound receptors (i.e., IL-33R and thymic stromal lymphopoietin receptor) and their role in the chronic settings, where mast cell activation is crucial for the development and the sustainment of chronic diseases, such as asthma or airway inflammation. Finally, we report how the FcR activation could be used as a therapeutic approach to treat allergic and atopic diseases by mast cell inactivation. Understanding the magnitude and the complexity of mast cell signaling is necessary to identify the mechanisms underlying the potential effector and regulatory roles of mast cells in the biology and pathology of those disease settings in which mast cells are activated.

Bone marrow-derived vascular modulatory cells in pulmonary arterial hypertension

Hematopoiesis and vascular homeostasis are closely linked to each other via subsets of circulating bone marrow-derived cells with potent activity to repair endothelial injury and promote angiogenesis. As a consequence, abnormalities in hematopoiesis will eventually affect vascular health. Pulmonary arterial hypertension (PAH) is a vascular disease characterized by severe remodeling of the pulmonary artery wall. Over the past decade, circulating hematopoietic cells have been assigned an increasing role in the remodeling, such that these cells have been used in new therapeutic strategies. More recently, research has been extended to the bone marrow where these cells originate to identify abnormalities in hematopoiesis that may underlie PAH. Here, we review the current literature and identify gaps in knowledge of the myeloid effects on PAH.

Small molecule analogues of the immunomodulatory parasitic helminth product ES-62 have anti-allergy properties

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Small molecule analogues of the helminth immunomodulator ES-62 have been produced.

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Two analogues inhibit mast cell functions and prevent airway hypersensitivity.

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The analogues are drug-like and could be considered for treatment of human allergy.

ES-62, a glycoprotein secreted by the filarial nematode Acanthocheilonema viteae, exhibits anti-inflammatory properties by virtue of covalently attached phosphorylcholine moieties. Screening of a library of ES-62 phosphorylcholine-based small molecule analogues (SMAs) revealed that two compounds, termed 11a and 12b, mirrored the helminth product both in inhibiting mast cell degranulation and cytokine responses in vitro and in preventing ovalbumin-induced Th2-associated airway inflammation and eosinophil infiltration of the lungs in mice. Furthermore, the two SMAs inhibited neutrophil infiltration of the lungs when administered therapeutically. ES-62-SMAs 11a and 12b thus represent starting points for novel drug development for allergies such as asthma.

Abnormal interactions between perifollicular mast cells and CD8+ T-cells may contribute to the pathogenesis of alopecia areata

Alopecia areata (AA) is a CD8+ T-cell dependent autoimmune disease of the hair follicle (HF) in which the collapse of HF immune privilege (IP) plays a key role. Mast cells (MCs) are crucial immunomodulatory cells implicated in the regulation of T cell-dependent immunity, IP, and hair growth. Therefore, we explored the role of MCs in AA pathogenesis, focusing on MC interactions with CD8+ T-cells in vivo, in both human and mouse skin with AA lesions. Quantitative (immuno-)histomorphometry revealed that the number, degranulation and proliferation of perifollicular MCs are significantly increased in human AA lesions compared to healthy or non-lesional control skin, most prominently in subacute AA. In AA patients, perifollicular MCs showed decreased TGFβ1 and IL-10 but increased tryptase immunoreactivity, suggesting that MCs switch from an immuno-inhibitory to a pro-inflammatory phenotype. This concept was supported by a decreased number of IL-10+ and PD-L1+ MCs, while OX40L+, CD30L+, 4–1BBL+ or ICAM-1+ MCs were increased in AA. Lesional AA-HFs also displayed significantly more peri- and intrafollicular- CD8+ T-cells as well as more physical MC/CD8+ T-cell contacts than healthy or non-lesional human control skin. During the interaction with CD8+ T-cells, AA MCs prominently expressed MHC class I and OX40L, and sometimes 4–1BBL or ICAM-1, suggesting that MC may present autoantigens to CD8+ T-cells and/or co-stimulatory signals. Abnormal MC numbers, activities, and interactions with CD8+ T-cells were also seen in the grafted C3H/HeJ mouse model of AA and in a new humanized mouse model for AA. These phenomenological in vivo data suggest the novel AA pathobiology concept that perifollicular MCs are skewed towards pro-inflammatory activities that facilitate cross-talk with CD8+ T-cells in this disease, thus contributing to triggering HF-IP collapse in AA. If confirmed, MCs and their CD8+ T-cell interactions could become a promising new therapeutic target in the future management of AA.

The enzyme Cyp26b1 mediates inhibition of mast cell activation by fibroblasts to maintain skin-barrier homeostasis

Mast cells (MCs) mature locally, thus possessing tissue-dependent phenotypes for their critical roles in both protective immunity against pathogens and the development of allergy or inflammation. We previously reported that MCs highly express P2X7, a receptor for extracellular ATP, in the colon but not in the skin. The ATP-P2X7 pathway induces MC activation and consequently exacerbates the inflammation. Here, we identified the mechanisms by which P2X7 expression on MCs is reduced by fibroblasts in the skin, but not in the other tissues. The retinoic-acid-degrading enzyme Cyp26b1 is highly expressed in skin fibroblasts, and its inhibition resulted in the upregulation of P2X7 on MCs. We also noted the increased expression of P2X7 on skin MCs and consequent P2X7- and MC-dependent dermatitis (so-called retinoid dermatitis) in the presence of excessive amounts of retinoic acid. These results demonstrate a unique skin-barrier homeostatic network operating through Cyp26b1-mediated inhibition of ATP-dependent MC activation by fibroblasts.

Establishment of a mast cell line, NCL-2, without Kit mutation, derived from NC mouse bone marrow

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We established an immortal mast cell line without Kit mutation, NCL-2.

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NCL-2 cells could be maintained without additional growth factors.

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NCL-2 cells expressed FcεRI and released histamine and LTB₄ in response to antigens.

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NCL-2 cells were tumorigenic but much less aggressive than P815 mastocytoma.

Immortal mast cell lines, such as RBL-2H3 and HMC-1 cells, are commonly utilized to investigate the function of mast cells. However, they are tumor cells carrying a gain-of-function mutation of Kit. We established an immortal mast cell line without Kit mutation, NCL-2, derived from NC mouse bone marrow. NCL-2 cells could be maintained without additional growth factors and thus could respond to exogenous growth signals. Moreover, NCL-2 cells expressed FcεRI and KIT, and release histamine and LTB₄ in response to antigen stimulation. This cell line could be a useful tool to analyze proliferation, differentiation, and function of normal mast cells.