Stem cell factor and interleukin-4 increase responsiveness of mast cells to substance P

KIT as a master regulator of the mast cell lineage

The discovery in 1987/1988 and 1990 of the cell-surface receptor KIT and its ligand, stem cell factor (SCF), were critical achievements in efforts to understand the development and function of multiple distinct cell lineages. These include hematopoietic progenitors, melanocytes, germ cells, and mast cells, which all are significantly affected by loss-of-function mutations of KIT or SCF. Such mutations also influence the development and/or function of additional cells, including those in parts of the CNS and the interstitial cells of Cajal (that control gut motility). Many other cells can express KIT constitutively or during immune responses, including dendritic cells, eosinophils, ILC2 cells, and taste cells. Yet the biological importance of KIT in many of these cell types largely remains to be determined. We here review the history of work investigating mice with mutations affecting the W locus (that encodes KIT) or the Sl locus (that encodes SCF), focusing especially on the influence of such mutations on mast cells. We also briefly review efforts to target the KIT/SCF pathway with anti-SCF or anti-KIT antibodies in mouse models of allergic disorders, parasite immunity, or fibrosis in which MCs are thought to play significant roles.

Annexin A1 Mimetic Peptide Ac2-26 Modulates the Function of Murine Colonic and Human Mast Cells

Mast cells (MCs) are main effector cells in allergic inflammation and after activation, they release stored (histamine, heparin, proteases) and newly synthesized (lipid mediators and cytokines) substances. In the gastrointestinal tract the largest MC population is located in the lamina propria and submucosa whereas several signals such as the cytokine IL-4, seem to increase the granule content and to stimulate a remarkable expansion of intestinal MCs. The broad range of MC-derived bioactive molecules may explain their involvement in many different allergic disorders of the gastrointestinal tract. Annexin A1 (AnxA1) is a 37 KDa glucocorticoid induced monomeric protein selectively distributed in certain tissues. Its activity can be reproduced by mimetic peptides of the N-terminal portion, such as Ac2-26, that share the same receptor FPR-L1. Although previous reports demonstrated that AnxA1 inhibits MC degranulation in murine models, the effects of exogenous peptide Ac2-26 on intestinal MCs or the biological functions of the Ac2-26/FPR2 system in human MCs have been poorly studied. To determine the effects of Ac2-26 on the function of MCs toward the possibility of AnxA1-based therapeutics, we treated WT and IL-4 knockout mice with peptide Ac2-26, and we examined the spontaneous and compound 48/80 stimulated colonic MC degranulation and cytokine production. Moreover, in vitro, using human mast cell line HMC-1 we demonstrated that exogenous AnxA1 peptide is capable of interfering with the HMC-1 degranulation in a direct pathway through formyl peptide receptors (FPRs). We envisage that our results can provide therapeutic strategies to reduce the release of MC mediators in inflammatory allergic processes.

Secretion of Mast Cell Inflammatory Mediators Is Enhanced by CADM1-Dependent Adhesion to Sensory Neurons

Neuroimmune interactions are important in the pathophysiology of many chronic inflammatory diseases, particularly those associated with alterations in sensory processing and pain. Mast cells and sensory neuron nerve endings are found in areas of the body exposed to the external environment, both are specialized to sense potential damage by injury or pathogens and signal to the immune system and nervous system, respectively, to elicit protective responses. Cell adhesion molecule 1 (CADM1), also known as SynCAM1, has previously been identified as an adhesion molecule which may couple mast cells to sensory neurons however, whether this molecule exerts a functional as well as structural role in neuroimmune cross-talk is unknown. Here we show, using a newly developed in vitro co-culture system consisting of murine bone marrow derived mast cells (BMMC) and adult sensory neurons isolated from dorsal root ganglions (DRG), that CADM1 is expressed in mast cells and adult sensory neurons and mediates strong adhesion between the two cell types. Non-neuronal cells in the DRG cultures did not express CADM1, and mast cells did not adhere to them. The interaction of BMMCs with sensory neurons was found to induce mast cell degranulation and IL-6 secretion and to enhance responses to antigen stimulation and activation of FcεRI receptors. Secretion of TNFα in contrast was not affected, nor was secretion evoked by compound 48/80. Co-cultures of BMMCs with HEK 293 cells, which also express CADM1, while also leading to adhesion did not replicate the effects of sensory neurons on mast cells, indicative of a neuron-specific interaction. Application of a CADM1 blocking peptide or knockdown of CADM1 in BMMCs significantly decreased BMMC attachment to sensory neurites and abolished the enhanced secretory responses of mast cells. In conclusion, CADM1 is necessary and sufficient to drive mast cell-sensory neuron adhesion and promote the development of a microenvironment in which neurons enhance mast cell responsiveness to antigen, this interaction could explain why the incidence of painful neuroinflammatory disorders such as irritable bowel syndrome (IBS) are increased in atopic patients.

Neuroendocrinology of mast cells: Challenges and controversies

Mast cells (MC) are hemotopoietically derived tissue immune cells that are ubiquitous in the body, including neuroendocrine organs such as the hypothalamus, pineal, pituitary, ovaries, pancreas and uterus where their action is not well understood. Mast cells have historically been associated with allergies because of their rich content of histamine and tryptase, but more recently with regulation of immunity and inflammation due to their synthesis and release of numerous cytokines and chemokines. Mast cells are located perivascularly and express numerous receptors for diverse ligands such as allergens, pathogens, neurotransmitters, neuropeptides and hormones including acetylcholine, calcitonin gene-related peptide (CGRP), corticosteroids, corticotropin-releasing hormone (CRH), β-endorphin, epinephrine, 17β-oestradiol, gonadotrophins, hemokinin-A (HKA), leptin, melatonin, neurotensin (NT), parathyroid hormone (PTH), substance P (SP) and vasoactive intestinal peptide (VIP). Moreover, MC can synthesize and release most of their neurohormonal triggers, including adrenocorticotropin hormone (ACTH), CRH, endorphins, HKA, leptin, melatonin, NT, SP and VIP. Animal experiments have shown that diencephalic MC increase in number during courting in doves, while stimulation of brain and nasal MC leads to activation of the hypothalamic-pituitary-adrenal (HPA) axis. Recent evidence indicates that MC reactivity exhibits diurnal variations, and it is interesting that melatonin appears to regulate MC secretion. However, the way MC change their phenotype or secrete specific molecules selectively at different pathophysiological settings still remains unknown. Mast cells developed over 500 million years ago and may have served as the original prototype neuroimmunoendocrine cell and then evolved into a master regulator of such interactions, especially as most of the known diseases involve neuroinflammation that worsens with stress.

Prostaglandin D2-supplemented "functional eicosanoid testing and typing" assay with peripheral blood leukocytes as a new tool in the diagnosis of systemic mast cell activation disease: an explorative diagnostic study

BACKGROUND

Systemic mast cell activation disease (MCAD) is characterized by an enhanced release of mast cell-derived mediators, including eicosanoids, which induce a broad spectrum of clinical symptoms. Accordingly, the diagnostic algorithm of MCAD presupposes the proof of increased mast cell mediator release, but only a few mediators are currently established as routine laboratory parameters. We thus initiated an explorative study to evaluate in vitro typing of individual eicosanoid pattern of peripheral blood leukocytes (PBLs) as a new diagnostic tool in MCAD.

METHODS

Using the "functional eicosanoid testing and typing" (FET) assay, we investigated the balance (i.e. the complex pattern of formation, release and mutual interaction) of prostaglandin E2 (PGE2) and peptido-leukotrienes (pLT) release from PBLs of 22 MCAD patients and 20 healthy individuals. FET algorithms thereby consider both basal and arachidonic acid (AA)-, acetylsalicylic acid (ASA)-, and substance P (SP)-triggered release of PGE2 and pLT. The FET assay was further supplemented by analyzing prostaglandin D2 (PGD2), as mast cell-specific eicosanoid.

RESULTS

We observed marked PGE2-pLT imbalances for PBLs of MCAD patients, as indicated by a markedly enhanced mean FET value of 1.75 ± 0.356 (range: 1.14-2.36), compared to 0.53 ± 0.119 (range: 0.36-0.75) for healthy individuals. In addition, mean PGD2 release from PBLs of MCAD patients was significantly, 6.6-fold higher than from PBLs of healthy individuals (946 ± 302.2 pg/ml versus 142 ± 47.8 pg/ml; P < 0.001). In contrast to healthy individuals, PGD2 release from PBLs of MCAD patients was markedly triggered by SP (mean: 1896 ± 389.7 pg/ml; P < 0.001), whereas AA and ASA caused individually varying effects on both PGD2 and pLT release.

CONCLUSIONS

The new in-vitro FET assay, supplemented with analysis of PGD2, demonstrated that the individual patterns of eicosanoid release from PBLs can unambiguously distinguish MCAD patients from healthy individuals. Notably, in our analyses, the FET value and both basal and triggered PGD2 levels were not significantly affected by MCAD-specific medication. Thus, this approach may serve as an in-vitro diagnostic tool to estimate mast cell activity and to support individualized therapeutic decision processes for patients suffering from MCAD.

Antigen binding characteristics of immunoglobulin free light chains: crosslinking by antigen is essential to induce allergic inflammation

Beside the production of complete immunoglobulins IgG, IgE, IgA, IgM and IgD, consisting of tetrameric heterodimers of immunoglobulin heavy and light chains, B cells also secrete immunoglobulin free light chains (Ig-fLC). Previous studies showed that Ig-fLCs are able to induce immediate hypersensitivity reactions. It is apparent that recognition and binding of antigen are crucial steps in the onset of these inflammatory responses. In this study, the binding characteristics of Ig-fLC to antigen were further investigated using various biochemical approaches. In addition, we investigated whether antigen-mediated crosslinking of Ig-fLC is required to initiate allergic skin inflammation in vivo. Our study shows that binding of Ig-fLCs to antigen can be measured with different experimental setups. Surface plasmon resonance analysis showed real-time antigen binding characteristics. Specific antigen binding by Ig-fLCs was further detected using immunoblotting and ELISA. Using the ELISA-based assay, a binding affinity of 76.9±3.8 nM was determined for TNP-specific Ig-fLC. Antigen-induced ear swelling in mice passively sensitized with trinitrophenol-specific Ig-fLC was inhibited when multivalent antigen was combined with excess of monovalent antigen during challenge. We conclude that Ig-fLCs are able to interact with antigen, a prerequisite for antigen-specific cellular activation. In analogy to antigen-specific Fc receptor-induced mast cell activation, crosslinking of Ig-fLCs is necessary to initiate a local allergic response.

Stem cell factor programs the mast cell activation phenotype

Mast cells, activated by Ag via FcεRI, release an array of proinflammatory mediators that contribute to allergic disorders, such as asthma and anaphylaxis. The KIT ligand, stem cell factor (SCF), is critical for mast cell expansion, differentiation, and survival, and under acute conditions, it enhances mast cell activation. However, extended SCF exposure in vivo conversely protects against fatal Ag-mediated anaphylaxis. In investigating this dichotomy, we identified a novel mode of regulation of the mast cell activation phenotype through SCF-mediated programming. We found that mouse bone marrow-derived mast cells chronically exposed to SCF displayed a marked attenuation of FcεRI-mediated degranulation and cytokine production. The hyporesponsive phenotype was not a consequence of altered signals regulating calcium flux or protein kinase C, but of ineffective cytoskeletal reorganization with evidence implicating a downregulation of expression of the Src kinase Hck. Collectively, these findings demonstrate a major role for SCF in the homeostatic control of mast cell activation with potential relevance to mast cell-driven disease and the development of novel approaches for the treatment of allergic disorders.

Histamine release and surface CD200R1 staining as sensitive methods for assessing murine mast cell activation

Mast cells are important effector cells of allergy and are involved in the pathology of many other diseases. Measurement of β-hexosaminidase activity, the most commonly used method for evaluation of murine mast cell activity, requires a large number of cells and thus is of limited utility for studying mast cells in mouse models of disease. In this study we evaluated the sensitivity of histamine release as compared to β-hexosaminidase activity in the measurement of mast cell activation. Whereas a minimum of 6×10(4) mast cells per ml were required to detect slight increases in β-hexosaminidase activity after anti-IgE and ionomycin stimulation, substantial increases in histamine release could be detected under the same activating conditions with as few as 480 mast cells per ml. These findings demonstrate that measurement of histamine release is substantially more sensitive than assessment of β-hexosaminidase activity for detecting mast cell activation. Additionally, we describe a novel flow cytometric method for detecting murine mast cell activation. When using 7.5×10(5) peritoneal cells per condition and gating on IgE+c-kit+cells, mast cell expression of surface CD200R1 increased after both IgE and non IgE-mediated activation. This flow cytometric procedure was uncomplicated and rapid, with increases in surface CD200R1 expression appearing after as little as 30 min of stimulation time. Measuring histamine release and surface CD200R1 expression are sensitive approaches for detection of murine mast cell activation. Further, both approaches can be done on unpurified peritoneal cell populations. By requiring low numbers of cells, these approaches are ideal for investigating mast cell activation in murine models of disease.

Effects of IL-3 and SCF on Histamine Production Kinetics and Cell Phenotype in Rat Bone Marrow-derived Mast Cells

BACKGROUND

Rat mast cells were regarded as a good model for mast cell function in immune response.

METHODS

Rat bone marrow mast cells (BMMC) were prepared both by recombinant rat IL-3 (rrIL-3) and by recombinant mouse stem cell factor (rmSCF), and investigated for both proliferation and differentiation in time course. Rat BMMC was induced by culture of rat bone marrow cells (BMCs) in the presence of both rrIL-3 (5 ng/ml) and rmSCF (5 ng/ml). Culture media were changed 2 times per week with the cell number condition of 5x10(4)/ml in 6 well plate. Proliferation was analyzed by cell number and cell counting kit-8 (CCK-8) and differentiation was by rat mast cell protease (RMCP) II and histamine.

RESULTS

Cell proliferation rates reached a maximum at 8 or 11 days of culture and decreased thereafter. However, both RMCP II production and histamine synthesis peaked after 11 days of culture. By real time RT-PCR, the level of histidine decarboxylase mRNA was more than 500 times higher on culture day 11 than on culture day 5. By transmission electron microscopy, the cells were heterogeneous in size and contained cytoplasmic granules. Using gated flow cytometry, we showed that cultured BMCs expressed high levels of FcepsilonRI and the mast cell antigen, ganglioside, on culture day 11.

CONCLUSION

These results indicate that rat BMMCs were generated by culturing BMCs in the presence of rrIL-3 and rmSCF and that the BMMCs have the characteristics of mucosal mast cells.

Characterization and modulation of canine mast cell derived eicosanoids

Mast cells play an important role in both innate and acquired immunity as well as several pathological conditions including allergy, arthritis and neoplasia. They influence these processes by producing a variety of mediators including cytokines, chemokines and eicosanoids. Very little is currently known about the spectrum of inflammatory mediators, particularly eicosanoids (prostaglandins and leukotrienes), produced by canine mast cells. This is important since modulating mast cell derived eicosanoids may help in the treatment of autoimmune and inflammatory disorders. The purpose of this study was to investigate the spectrum of eicosanoids produced by normal canine mast cells and to evaluate the effects of cytokines and non-steroidal anti-inflammatory mediators (NSAIDS) on eicosanoid production and release. Canine bone marrow derived cultured mast cells (cBMCMCs) expressed COX-1, COX-2, and 5-LOX and synthesized and released PGD2, PGE2, LTB4, and LTC4 following activation by a variety of stimuli. The selective COX-2 NSAIDs carprofen (Rimadyl) and deracoxib (Deramaxx) inhibited PGD2 and PGE2 production but only slightly inhibited LTB4 and LTC4. The mixed COX-1/COX-2 inhibitor piroxicam blocked PGD2 and PGE2 production, but upregulated LTC4 following treatment while tepoxilan (Zubrin), a pan COX/LOX inhibitor, markedly reduced the production of all eicosanoids. The LOX inhibitor nordihydroguaiaretic acid (NDGA) prevented LTB4/LTC4 release and BMBMC degranulation. Pre-incubation of cBMCMCs with IL-4 and SCF sensitized these cells to degranulation in response to substance P. In conclusion, canine BMCMCs produce an array of eicosanoids similar to those produced by mast cells from other species. Tepoxilan appeared to be the most effective NSAID for blocking eicosanoid production and thus may be useful for modulating mast cell mediated responses in dogs.

Delineating protease functions during cancer development

Much progress has been made in understanding how matrix remodeling proteases, including metalloproteinases, serine proteases, and cysteine cathepsins, functionally contribute to cancer development. In addition to modulating extracellular matrix metabolism, proteases provide a significant protumor advantage to developing neoplasms through their ability to modulate bioavailability of growth and proangiogenic factors, regulation of bioactive chemokines and cytokines, and processing of cell-cell and cell-matrix adhesion molecules. Although some proteases directly regulate these events, it is now evident that some proteases indirectly contribute to cancer development by regulating posttranslational activation of latent zymogens that then directly impart regulatory information. Thus, many proteases act in a cascade-like manner and exert their functionality as part of a proteolytic pathway rather than simply functioning individually. Delineating the cascade of enzymatic activities contributing to overall proteolysis during carcinogenesis may identify rate-limiting steps or pathways that can be targeted with anti-cancer therapeutics. This chapter highlights recent insights into the complexity of roles played by pericellular and intracellular proteases by examining mechanistic studies as well as the roles of individual protease gene functions in various organ-specific mouse models of cancer development, with an emphasis on intersecting proteolytic activities that amplify programming of tissues to foster neoplastic development.

Human mast cells stimulate activated T cells: implications for multiple sclerosis

Multiple sclerosis is an autoimmune demyelinating disease of the central nervous system mainly mediated by Th1 and/or Th17 cells, which cross the blood-brain barrier. Recent evidence indicates that Th2 cells and mast cells, typically associated with allergic reactions, are also involved. Brain mast cells are critically located perivascularly and secrete numerous proinflammatory and vasoactive molecules that can disrupt the blood-brain barrier, a finding that precedes clinical or pathologic signs of multiple sclerosis. Brain mast cells in multiple sclerosis are activated by neural factors, including substance P, myelin basic protein, and corticotropin-releasing hormone, caused by acute stress, which induce release of several inflammatory mediators. Mast cells can stimulate activated T cells coming in contact with them at the blood-brain barrier, as well as after stimulation with myelin basic protein or substance P. Pretreatment with the flavone luteolin blocks mast cell stimulation and T cell activation, as well as experimental autoimmune encephalitis. Interactions between mast cells and T cells could constitute a new and unique therapeutic target for multiple sclerosis.

Mechanisms of allergy and asthma

Allergies are the result of an inappropriate reaction against innocuous environmental proteins. The prevalence and severity of allergic diseases has increased dramatically during the last decade in developed countries. Allergen-specific T helper (Th) cells play a pivotal role in the pathogenesis of allergic hypersensitivity reactions. These Th cells activate a complex immune reaction that triggers the release of potent mediators and enhances the recruitment of inflammatory cells, which in turn elicit an inflammatory response that leads to the clinical symptoms of allergic disease. The current therapies for allergic diseases focus primarily on control of symptoms and suppression of inflammation, without affecting the underlying cause. However, the knowledge about the pathophysiology of allergic diseases has substantially increased, offering new opportunities for therapeutic intervention. In this review, we will focus on current insights into the mechanism of allergic reactions.

Honeybee venom secretory phospholipase A2 induces leukotriene production but not histamine release from human basophils

The role of basophils in an anaphylactic response is well recognized but is usually masked by mast cells, which contain similar mediators for the induction of generalized vasodilatation and laryngeal constriction. The rapid onset of systemic anaphylactic symptoms, particularly in insect stings and ingested food, suggest that basophils, a circulating pool of cells containing histamine and other potent mediators such as leukotrienes, may be more involved in systemic anaphylaxis than originally thought. We wished to examine if secretory phospholipase A2, a systemic allergen found in honey bee venom (HBV-sPLA2) may activate basophils directly leading to rapid systemic mediator release. Basophils were isolated from human blood and stimulated with increasing concentrations of HBV-sPLA2. We found that physiological concentrations of HBV-sPLA2 induce rapid leukotriene C4 production from purified human basophils within 5 min, while interleukin (IL)-4 expression and production was induced at later time-points. Histamine release was not induced, signifying that HBV-sPLA2 did not induce generalized degranulation. Surface expression of CD63, CD69 and CD11b were up-regulated following HBV-sPLA2 treatment. Stimulation of basophils with anti-immunoglobulin E (IgE) following treatment with HBV-sPLA2 did not induce more leukotriene release. To investigate the mechanism of leukotriene production, 9-12 octadecadiynioc acid, a cyclooxygenase-1 (COX-1) and 15-lipoxygenase inhibitor, was used and this abrogated leukotriene production. These results indicate that HBV-sPLA2 can directly activate human basophils in vitro to induce leukotriene production.

Responses during cell preparation for functional analyses in mouse bone marrow-derived cultured mast cells

Murine bone marrow-derived cultured mast cells (BMMCs) are most widely used in in vitro experiments for evaluation of mast cell functions. The present study has shown that cell preparation procedure, i.e., cell collection by centrifugation and the subsequent adjustment and culture of cell density at the desired concentrations, transiently induced gene expression of plasminogen activator inhibitor-1 (PAI-1) and the AP-1 components (c-fos, c-jun, and junB). The level of PAI-1 gene transcript was closely related to the cell density and the gene expression was enhanced by pretreatment with okadaic acid, an inhibitor of protein phosphatases 1 (PP1) and 2A (PP2A). The cell preparation procedure also caused dephosphorylation of MAP kinases, i.e., ERK, p38, and JNK, resulting from PP1/PP2A activation. In view of the cell responses to the cell preparation procedure itself, care is needed in the interpretation of in vitro data using BMMCs.

Mast cell activation is differentially affected by heat shock

OBJECTIVE

Mast cells play pivotal roles in immediate-type and inflammatory allergic and nonallergic reactions. Cross-linking of the high-affinity receptor for IgE (FcepsilonRI) on mast cells activates a signaling pathway leading to Ca2+ mobilization and is followed by degranulation and the release of histamine and other preformed mediators, as well as de novo synthesis of arachidonic acid metabolites. In a previous study, we have demonstrated that heat shock activates heat shock transcription factor-1 (HSF-1), induces heat shock protein 70 (HSP70), and suppresses cytokine production in bone marrow-derived mast cells (BMMC). In this study, we further investigated the effects of heat shock on the activation of mast cells and the release of mast cell mediators.

METHODS

In mouse mast cells, derived from a culture of bone marrow cells of male BALB/cBy and null HSF-1(-/-)mice, responsiveness to heat shock was monitored by measuring beta-hexosaminidase and leukotriene C4 (LTC4) release.

RESULTS

Using BMMC, we found that heat shock inhibits degranulation of BMMC without affecting leukotriene production. To further elucidate the mechanism of suppression of degranulation, we studied the effects of heat shock on the regulation of signal transduction in more detail. We found that heat shock inhibits calcium mobilization and tyrosine phosphorylation of Syk and SHIP upon IgE receptor activation, but increases the phosphorylation of SHP-1 and -2. Moreover, our results revealed that suppression of tyrosine phosphorylation of Syk and SHIP coincided with an increased tyrosine phosphatase activity.

CONCLUSION

The inhibitory action of heat shock toward mast cell degranulation is likely due to shifting the balance between kinase and phosphatase activity.

Significance of Conversation between Mast Cells and Nerves

More and more studies are demonstrating interactions between the nervous system and the immune system. However, the functional relevance of this interaction still remains to be elucidated. Such associations have been found in the intestine between nerves and mast cells as well as between eosinophils and plasma cells. Similar morphologic associations have been demonstrated in the liver, mesentery, urinary bladder, and skin. Unmyelinated axons especially were found to associate with mast cells as well as Langerhans' cells in primate as well as murine skin. Although there are several pathways by which immune cells interact with the nervous system, the focus in this review will be on the interaction between mast cells and nerves.

Evidence for a restricted rather than generalized stimulatory response of skin-derived human mast cells to substance P

To resolve the controversy regarding substance P (SP) mediated stimulation of mast cells (MC), we demonstrate that SP triggers histamine release from purified human skin MC (sMC), but contrast to stimulation via FcepsilonRI, does not effect the production of TNF-alpha or IL-8. Conversely, both anti-IgE and SP are suppressive in terms of IL-6. By quantitative RT-PCR, the amount of templates at baseline (per 25 ng total RNA) is 2178 (IL-6), 2,665 (IL-8) and 94 (TNF-alpha), and remains unaltered by SP. Contrast to sMC, LAD2 MC respond to SP with stronger histamine release and robust TNF-alpha production in an only partially neurokinin-1R mediated manner, while histamine release of sMC is chiefly mediated by this receptor. We conclude that human sMC are responsive to SP in a selective manner by eliciting degranulation without the induction of cytokines and that SP-triggered cytokine production varies among MC subtypes, likely through differences in signaling mechanisms.

Live Cell Imaging to Study Signaling Molecules in Allergic Reactions

Mast cells are widely distributed throughout the body, predominantly near blood vessels and nerves, and express effector functions in allergic reactions, inflammatory diseases, and host defense. The activation of mast cells results in secretion of the preformed chemical mediators in their granules by a regulated process of exocytosis and leads to synthesis and secretion of lipid mediators and cytokines. Their soluble factors contribute to allergic inflammation. Mast cells are associated with hypersensitivity reactions, not only in the classical immunoglobulin E (IgE)-dependent mechanism but also in an IgE-independent manner. In particular, investigations of potential anatomical and functional interactions between mast cells and the nervous system have recently attracted great interest. To understand these molecular mechanisms in mast cell activation, the ability to visualize, track, and quantify molecules and events in living mast cells is an essential and powerful tool. Recent dramatic advances in imaging technology and labeling techniques have enabled us to carry out these tasks with high spatiotemporal resolution using confocal laser scanning microscopes, green fluorescent protein and its derivatives, and image analysis systems. Here we review our investigations of the dynamic processes of intracellular signaling molecules, cellular structure, and interactions with neurons in mast cells to provide basic and valuable information for allergy and clinical immunology using these new imaging methods.

Mechanisms underlying the inhibitory effects of tachykinin receptor antagonists on eosinophil recruitment in an allergic pleurisy model in mice

The activation of tachykinin NK receptors by neuropeptides may induce the recruitment of eosinophils in vivo. The aim of the present study was to investigate the effects and underlying mechanism(s) of the action of tachykinin receptor antagonists on eosinophil recruitment in a model of allergic pleurisy in mice. Pretreatment of immunized mice with capsaicin partially prevented the recruitment of eosinophils after antigen challenge, suggesting the potential contribution of sensory nerves for the recruitment of eosinophils Local (10-50 nmol per pleural cavity) or systemic (100-300 nmol per animal) pretreatment with the tachykinin NK1 receptor antagonist SR140333 prevented the recruitment of eosinophils induced by antigen challenge of immunized mice. Neither tachykinin NK2 nor NK3 receptor antagonists suppressed eosinophil recruitment. Pretreatment with SR140333 failed to prevent the antigen-induced increase of interleukin-5 concentrations in the pleural cavity. Similarly, SR140333 failed to affect the bone marrow eosinophilia observed at 48 h after antigen challenge of immunized mice. SR140333 induced a significant increase in the concentrations of antigen-induced eotaxin at 6 h after challenge. Antigen challenge of immunized mice induced a significant increase of Leucotriene B4 (LTB4) concentrations at 6 h after challenge. Pretreatment with SR140333 prevented the antigen-induced increase of LTB4 concentrations. Our data suggest an important role for NK1 receptor activation with consequent LTB4 release and eosinophil recruitment in a model of allergic pleurisy in the mouse. Tachykinins appear to be released mainly from peripheral endings of capsaicin-sensitive sensory neurons and may act on mast cells to facilitate antigen-driven release of LTB4.

Functional expression of neurokinin 1 receptors on mast cells induced by IL-4 and stem cell factor

It is widely accepted that neurokinin 1 (NK(1)) receptors are not generally expressed on mast cells but little is known about their expression in inflammation. The present study shows expression of NK(1) receptors on bone marrow-derived mast cells (BMMC) under the influence of IL-4 or stem cell factor (SCF). Highest expression was found when both cytokines are present. Six days of coculture with the cytokines IL-4 and SCF showed significant expression of NK(1) receptors (NK(1) receptor(+)/c-kit(+) BMMC; control: 7%, IL-4/SCF: 16%), while 12 days of cytokine coculture increased this expression to 37% positive cells. A longer coculture with IL-4 and SCF did not give an additional effect. Increased expression in IL-4/SCF-treated BMMC was further confirmed using Western blot analysis. Next, we demonstrated the functional relevance of NK(1) receptor expression for mast cell activation, resulting in an enhanced degranulation upon stimulation by substance P. BMMC activation was significantly diminished by the NK(1) receptor antagonist RP67580 (10 micro M) when stimulated with low concentrations of substance P. The inactive enantiomer RP65681 had no effect. In addition, BMMC cultured from bone marrow of NK(1) receptor knockout mice showed significantly decreased exocytosis to low concentrations of substance P. The present study clearly shows that NK(1) receptor-induced activation contributes significantly at low physiological substance P concentrations (<100 micro M). In conclusion, BMMC were shown to express NK(1) receptors upon IL-4/SCF coculture. This expression of NK(1) receptors has been demonstrated to be of functional relevance and leads to an increase in the sensitivity of BMMC to substance P.

Activation of mast cells induced by agonists of proteinase-activated receptors under normal conditions and during acute inflammation in rats

Functions of thrombin as a modulator of inflammation and tissue repair are mediated by the proteinase-activated receptor (PAR) family. Some of these effects may be induced by activation of mast cells. To characterize the degranulation of rat peritoneal mast cells in response to PAR agonists, the effects of thrombin, trypsin and peptide agonists of PARs (PAR-AP, proteinase-activated receptor-activating peptides) on secretion were investigated. The release of beta-hexosaminidase by thrombin (0.01-1 microM) was concentration-dependent and mediated via PAR(1), as evidenced by cathepsin G (100 microM)-induced inactivation of PAR(1) and thrombin-stimulated PAR(1) desensitization. Trypsin (1 microM) accelerated histamine secretion. The PAR(1)-AP, TRAP (SFFLRN, 1-100 microM) and the PAR(2)-AP SLIGRL (5-100 microM) caused the release of histamine, and beta-hexosaminidase from inflammatory mast cells were obtained from a model of acute peritonitis in rats. Relative to the response to compound 48/80, the thrombin- and TRAP-induced release of beta-hexosaminidase was higher in inflammatory mast cells than in the control. This suggests that additional exposure of PAR(1) on mast cells to PAR agonists or an increase in PARs sensitivity to PAR agonists probably occurred during acute inflammation.

Mast cells: new targets for multiple sclerosis therapy?

Growing evidence suggests that mast cells (MCs) play a crucial role in the inflammatory process and the subsequent demyelination observed in patients suffering from multiple sclerosis (MS). Although no consensus exists on the role of mast cells in multiple sclerosis, recent results from animal models clearly indicate that these cells act at multiple levels to influence both the induction and the severity of disease. In addition to changing our views on the pathophysiology of multiple sclerosis, the concept that mast cells are critical for the outcome of the disease could have an important impact on the development of new therapeutic approaches.

Key role for mast cells in nonatopic asthma

The mechanisms involved in nonatopic asthma are poorly defined. In particular, the importance of mast cells in the development of nonatopic asthma is not clear. In the mouse, pulmonary hypersensitivity reactions induced by skin sensitization with the low-m.w. compound dinitrofluorobenzene (DNFB) followed by an intra-airway application of the hapten have been featured as a model for nonatopic asthma. In present study, we used this model to examine the role of mast cells in the pathogenesis of nonatopic asthma. First, the effect of DNFB sensitization and intra-airway challenge with dinitrobenzene sulfonic acid (DNS) on mast cell activation was monitored during the early phase of the response in BALB/c mice. Second, mast cell-deficient W/W(v) and Sl/Sl(d) mice and their respective normal (+/+) littermate mice and mast cell-reconstituted W/W(v) mice (bone marrow-derived mast cells-->W/W(v)) were used. Early phase mast cell activation was found, which was maximal 30 min after DNS challenge in DNFB-sensitized BALB/c, +/+ mice but not in mast cell-deficient mice. An acute bronchoconstriction and increase in vascular permeability accompanied the early phase mast cell activation. BALB/c, +/+ and bone marrow-derived mast cell-->W/W(v) mice sensitized with DNFB and DNS-challenged exhibited tracheal hyperreactivity 24 and 48 h after the challenge when compared with vehicle-treated mice. Mucosal exudation and infiltration of neutrophils in bronchoalveolar lavage fluid associated the late phase response. Both mast cell-deficient strains failed to show any features of this hypersensitivity response. Our findings show that mast cells play a key role in the regulation of pulmonary hypersensitivity responses in this murine model for nonatopic asthma.

Mast cell-derived TNF-alpha primes sensory nerve endings in a pulmonary hypersensitivity reaction

TNF-alpha is a cytokine associated with inflammatory diseases, including asthma. Increased levels of TNF-alpha were found in the bronchoalveolar lavage fluid of mice undergoing a dinitrofluorobenzene (DNFB)-induced non-IgE-mediated pulmonary hypersensitivity reaction. We report in this work that TNF-alpha increases the susceptibility of sensory neurons to dinitrobenzene sulfonic acid (DNS) and capsaicin, leading to a tracheal vascular hyperpermeability response in DNFB-sensitized and DNS-challenged mice. mAb against TNF-alpha or the TNFR1 inhibited this hyperpermeability response in DNFB-sensitized and DNS-challenged mice. Furthermore, the hyperpermeability response after DNS challenge was abolished in DNFB-sensitized mast cell-deficient WBB6F(1)-W/W(V) mice. These animals showed a remarked decrease of TNF-alpha bronchoalveolar lavage fluid levels after a single DNS challenge. The hyperpermeability response after DNS challenge was regained in mast cell-deficient mice after mast cell reconstitution. These findings indicate a prominent role for TNF-alpha and its TNFR1 in the DNFB-induced tracheal hyperpermeability response. We propose that a priming effect of mast cell-derived TNF-alpha on the sensory neurons could be the mechanism of action of TNF-alpha in the vascular hyperpermeability response in tracheas of mice undergoing a pulmonary hypersensitivity reaction.

Involvement of substance P, mast cells, TNF-alpha and ICAM-1 in the infiltration of inflammatory cells in human periapical granulomas

BACKGROUND

Substance P (SP), a potent proinflammatory peptide present in sensory neurons, is believed to be a major mediator of neurogenic inflammation. The aim of this study was to examine the localization and involvement of SP, mast cells and tumor necrosis factor-alpha (TNF-alpha)-positive cells in human periapical granulomas.

METHODS

Sections from seven periapical granulomas were stained using a variety of immunohistochemical methods.

RESULTS

SP-immunoreactive nerve fibers, mast cells and TNF-alpha-positive cells were found localized in the vicinity of blood vessels in all the samples of periapical granulomas. The vascular endothelial cells stained positively for E-selectin and intercellular adhesion molecule-1. SP, TNF-alpha-positive cells and E-selectin could not be detected in clinically healthy periodontal ligament, and served as a negative control.

CONCLUSION

Our findings suggest that SP, mast cells, TNF-alpha-positive cells and E-selectin may modulate the pathogenesis of apical periodontitis and may be responsible for stimulating the formation of granuloma with the resorption of periapical bone.

Tachykinins and neuro-immune interactions in asthma

Excitatory non-adrenergic-non-cholinergic neuropeptides, such as the tachykinins substance P and neurokinin A, and its receptors are present in human and animal airways. Tachykinins are biologically active at extremely low concentrations. These peptides can cause potent inflammatory effects and can affect airway function in a way that resembles features of asthma. Local release of tachykinins affects blood vessels (vasodilatation and increased vascular permeability) and bronchial smooth muscle (bronchoconstrition and hyperresponsiveness). Neuropeptide research has revealed that tachykinins also play an important modulatory role in immune reactions. Tachykinins stimulate immune cells, such as mast cells, lymphocytes, and macrophages and are chemotactic for neutrophils and eosinophils. Vice versa, a range of immune cell mediators can also induce the release of tachykinins from excitatory NANC nerve endings in the airways. In the last 20 years, significant advances have been made in investigations of the interaction between immune cells and nervous systems in chronic inflammatory diseases such as asthma.

SCF-induced airway hyperreactivity is dependent on leukotriene production

Stem cell factor (SCF) is directly involved in the induction of airway hyperreactivity during allergen-induced pulmonary responses in mouse models. In these studies, we examined the specific mediators and mechanisms by which SCF can directly induce airway hyperreactivity via mast cell activation. Initial in vitro studies with bone marrow-derived mast cells indicated that SCF was able to induce the production of bronchospastic leukotrienes, LTC4and LTE4. Subsequently, when SCF was instilled in the airways of naive mice, we were able to observe a similar induction of LTC4and LTE4in the bronchoalveolar lavage (BAL) fluid and lungs of treated mice. These in vivo studies clearly suggested that the previously observed SCF-induced airway hyperreactivity may be related to the leukotriene production after SCF stimulation. To further investigate whether the released leukotrienes were the mediators of the SCF-induced airway hyperreactivity, an inhibitor of 5-lipoxygenase (5-LO) binding to the 5-LO activating protein (FLAP) was utilized. The FLAP inhibitor MK-886, given to the animals before intratracheal SCF administration, significantly inhibited the release of LTC4and LTE4into the BAL fluid. More importantly, use of the FLAP inhibitor nearly abrogated the SCF-induced airway hyperreactivity. In addition, blocking the LTD4/E4, but not LTB4, receptor attenuated the SCF-induced airway hyperreactivity. In addition, the FLAP inhibitor reduced other mast-derived mediators, including histamine and tumor necrosis factor. Altogether, these studies indicate that SCF-induced airway hyperreactivity is dependent upon leukotriene-mediated pathways.

Excitatory non-adrenergic-non-cholinergic neuropeptides: key players in asthma

Professor David de Wied first introduced the term 'neuropeptides' at the end of 1971. Later peptide hormones and their fragments, endogenous opioid (morphine-like) peptides and a large number of other biogenic peptides became classified as neuropeptides. All of these peptides are united by a number of common features including their origin (nervous system and peptide-secreting cells found in various organs such as skin, gut, lungs), biosynthesis, secretion, metabolism, and enormous effectiveness. Neuropeptides are biologically active at extremely low concentrations. The past decade, neuropeptide research has revealed that neuropeptides also participate strongly in immune reactions. The neuro-immune concept has opened up a whole new research area. In the last 20 years, significant advances have been made in investigations of the interaction between immune and nervous systems in chronic inflammatory diseases such as asthma. The goal of this review is to bring together the functional relevance of excitatory non-adrenergic-non-cholinergic (NANC) nerves and the interaction with the immune system in asthma.