Stem cell factor has a suppressive activity to IgE-mediated chemotaxis of mast cells

5-Bromo-3,4-dihydroxybenzaldehyde from Polysiphonia morrowii attenuate IgE/BSA-stimulated mast cell activation and passive cutaneous anaphylaxis in mice

The present study investigates the anti-allergic activity of the marine algal bromophenol, 3-bromo-4,5-dihydroxybenzaldehyde (BDB), isolated from Polysiphonia morrowii Harvey in immunoglobulin (Ig)E/bovine serum albumin (BSA)-stimulated mouse bone marrow-derived cultured mast cells (BMCMCs) and a passive cutaneous anaphylaxis (PCA) mice ear model. BDB effectively inhibited β-hexosaminidase release (IC₅₀ = 80.12 µM), in IgE/BSA-stimulated BMCMCs without a cytotoxic response. Also, BDB down-regulated the expression or secretion of cytokines, interleukin (IL)-1β, IL-4, IL-5, IL-6, IL-10, IL-13, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α and the chemokine (thymus and activation-regulated chemokine (TARC). The above effects could be attributed to the dose-dependent decrease of FcεRI expression on the surface of BMCMCs and its stable IgE binding. Moreover, BDB suppressed the nuclear factor (NF)-κB and spleen tyrosine kinase (SYK)-linker for T-cell activation (LAT)-GRB2 associated binding protein 2 (Gab2) signaling axis activated by IgE/BSA stimulation. Furthermore, oral administration of BDB to IgE-sensitized mice effectively attenuated IgE-triggered PCA reaction. Collectively, the anti-allergic effects of BDB suggest its potential applicability as a candidate for in-depth test trials.

Changing the threshold-Signals and mechanisms of mast cell priming

Mast cells play a key role in allergy and other inflammatory diseases involving engagement of multivalent antigen with IgE bound to high-affinity IgE receptors (FcεRIs). Aggregation of FcεRIs on mast cells initiates a cascade of signaling events that eventually lead to degranulation, secretion of leukotrienes and prostaglandins, and cytokine and chemokine production contributing to the inflammatory response. Exposure to pro-inflammatory cytokines, chemokines, bacterial and viral products, as well as some other biological products and drugs, induces mast cell transition from the basal state into a primed one, which leads to enhanced response to IgE-antigen complexes. Mast cell priming changes the threshold for antigen-mediated activation by various mechanisms, depending on the priming agent used, which alone usually do not induce mast cell degranulation. In this review, we describe the priming processes induced in mast cells by various cytokines (stem cell factor, interleukins-4, -6 and -33), chemokines, other agents acting through G protein-coupled receptors (adenosine, prostaglandin E₂ , sphingosine-1-phosphate, and β-2-adrenergic receptor agonists), toll-like receptors, and various drugs affecting the cytoskeleton. We will review the current knowledge about the molecular mechanisms behind priming of mast cells leading to degranulation and cytokine production and discuss the biological effects of mast cell priming induced by several cytokines.

Platelet-Eosinophil Interactions As a Potential Therapeutic Target in Allergic Inflammation and Asthma

The importance of platelet activation during hemostasis is well understood. An understanding of these mechanisms has led to the use of several classes of anti-platelet drugs to inhibit aggregation for the prevention of thrombi during cardiovascular disease. It is now also recognized that platelets can function very differently during inflammation, as part of their role in the innate immune response against pathogens. This dichotomy in platelet function occurs through distinct physiological processes and alternative signaling pathways compared to that of hemostasis (leading to platelet aggregation) and is manifested as increased rheological interactions with leukocytes, the ability to undergo chemotaxis, communication with antigen-presenting cells, and direct anti-pathogen responses. Mounting evidence suggests platelets are also critical in the pathogenesis of allergic diseases such as asthma, where they have been associated with antigen presentation, bronchoconstriction, bronchial hyperresponsiveness, airway inflammation, and airway remodeling in both clinical and experimental studies. In particular, platelets have been reported bound to eosinophils in the blood of patients with asthma and the incidence of these events increases after both spontaneous asthma attacks in a biphasic manner, or after allergen challenge in the clinic. Platelet depletion in animal models of allergic airway inflammation causes a profound reduction in eosinophil recruitment to the lung, suggesting that the association of platelets with eosinophils is indeed an important event during eosinophil activation. Furthermore, in cases of severe asthma, and in animal models of allergic airways inflammation, platelet–eosinophil complexes move into the lung through a platelet P-selectin-mediated, eosinophil β1-integrin activation-dependent process, while platelets increase adherence of eosinophils to the vascular endothelium in vitro, demonstrating a clear interaction between these cell types in allergic inflammatory diseases. This review will explore non-thrombotic platelet activation in the context of allergy and the association of platelets with eosinophils, to reveal how these phenomena may lead to the discovery of novel therapeutic targets.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

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.

Human skin melanocyte migration towards stromal cell-derived factor-1α demonstrated by optical real-time cell mobility assay: modulation of their chemotactic ability by α-melanocyte-stimulating hormone

To identify potential regulators of normal human melanocyte behaviour, we have developed an in vitro human melanocyte migration assay, using the optically accessible, real-time cell motility assay device TAXIScan. Coating of the glass surface with an extracellular matrix that served as scaffolding molecule was essential to demonstrate efficient melanocyte migration. Among several chemokines tested, stromal cell-derived factor (SDF)-1α/CXCL12 was the most effective driver of human normal skin melanocytes. Incubation of melanocytes with α-melanocyte-stimulating hormone (MSH) before the assay specifically enhanced CXCR4 expression and consequently chemotaxis towards SDF-1α/CXCL12. These results suggest that α-MSH acts on melanocytes to produce melanin as well as stimulates the cells to migrate to the site where they work through CXCR4 up-regulation, which is a new dynamic mode of action of α-MSH on melanocyte physiology.

Mast cells can contribute to axon-glial dissociation and fibrosis in peripheral nerve

Expression of the human epidermal growth factor receptor (EGFR) in murine Schwann cells results in loss of axon-Schwann cell interactions and collagen deposition, modeling peripheral nerve response to injury and tumorigenesis. Mast cells infiltrate nerves in all three situations. We show that mast cells are present in normal mouse peripheral nerve beginning at 4 weeks of age, and that the number of mast-cells in EGFR(+) nerves increases abruptly at 5-6 weeks of age as axons and Schwann cells dissociate. The increase in mast cell number is preceded and accompanied by elevated levels of mRNAs encoding the mast-cell chemoattractants Rantes, SCF and VEGF. Genetic ablation of mast cells and bone marrow reconstitution in W(41) x EGFR(+) mice indicate a role for mast cells in loss of axon-Schwann cell interactions and collagen deposition. Pharmacological stabilization of mast cells by disodium cromoglycate administration to EGFR(+) mice also diminished loss of axon-Schwann cell interaction. Together these three lines of evidence support the hypothesis that mast cells can contribute to alterations in peripheral nerves.

Mast cell chemotaxis - chemoattractants and signaling pathways

Migration of mast cells is essential for their recruitment within target tissues where they play an important role in innate and adaptive immune responses. These processes rely on the ability of mast cells to recognize appropriate chemotactic stimuli and react to them by a chemotactic response. Another level of intercellular communication is attained by production of chemoattractants by activated mast cells, which results in accumulation of mast cells and other hematopoietic cells at the sites of inflammation. Mast cells express numerous surface receptors for various ligands with properties of potent chemoattractants. They include the stem cell factor (SCF) recognized by c-Kit, antigen, which binds to immunoglobulin E (IgE) anchored to the high affinity IgE receptor (FcεRI), highly cytokinergic (HC) IgE recognized by FcεRI, lipid mediator sphingosine-1-phosphate (S1P), which binds to G protein-coupled receptors (GPCRs). Other large groups of chemoattractants are eicosanoids [prostaglandin E₂ and D₂, leukotriene (LT) B₄, LTD₄, and LTC₄, and others] and chemokines (CC, CXC, C, and CX3C), which also bind to various GPCRs. Further noteworthy chemoattractants are isoforms of transforming growth factor (TGF) β1–3, which are sensitively recognized by TGF-β serine/threonine type I and II β receptors, adenosine, C1q, C3a, and C5a components of the complement, 5-hydroxytryptamine, neuroendocrine peptide catestatin, tumor necrosis factor-α, and others. Here we discuss the major types of chemoattractants recognized by mast cells, their target receptors, as well as signaling pathways they utilize. We also briefly deal with methods used for studies of mast cell chemotaxis and with ways of how these studies profited from the results obtained in other cellular systems.

Lapachol suppresses cell proliferation and secretion of interleukin-6 and plasminogen activator inhibitor-1 of fibroblasts derived from hypertrophic scars

Objectives

The pathogenesis and therapy of hypertrophic scar have not yet been established. Our aim was to investigate the antiproliferative and antisecretory effects of lapachol, isolated from the stem bark of Avicennia rumphiana Hall. f., on hypertrophic scar fibroblasts.

Methods

The effects of lapachol on hypertrophic scar fibroblast proliferation were measured using the MTT assay, cell-cycle analyses and lactate dehydrogenase assays. The type I collagen α-chain (COL1A1), interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) mRNA and/or protein levels of hypertrophic scar-fibroblasts were quantitated by real-time PCR and ELISA.

Key findings

Lapachol at 25 and 50 µm significantly inhibited the in vitro proliferation of hypertrophic scar fibroblasts, but not fibroblasts from non-lesional skin sites. In addition, lapachol had no apparent effect on cell cycle and lactate dehydrogenase activity in conditioned medium from lapachol-treated hypertrophic scar fibroblasts was nearly equal to that in medium from vehicle-treated cells. Lapachol treatment also inhibited COL1A1 and PAI-1 mRNA levels in hypertrophic scar fibroblasts, but did not affect IL-6 mRNA levels. The protein levels of IL-6 and PAI-1 in conditioned medium from hypertrophic scar fibroblasts treated with 50 µm lapachol were lower than those from vehicle-treated hypertrophic scar fibroblasts.

Conclusions

Lapachol decreased the proliferation rate of hypertrophic scar fibroblasts. As IL-6 and PAI-1 secretion was also lowered in lapachol-treated hypertrophic scar fibroblasts, our findings suggested that lapachol may have suppressed extracellular matrix hyperplasia in wound healing and possibly alleviated the formation of hypertrophic scar.

The transmembrane adaptor protein NTAL signals to mast cell cytoskeleton via the small GTPase Rho

The transmembrane adaptor protein NTAL (non-T-cell activation linker) participates in signalosome assembly in hematopoietic cells, but its exact role in cell physiology remains enigmatic. We report here that BM-derived mast cells from NTAL-deficient mice, responding to Ag alone or in combination with SCF, exhibit reduced spreading on fibronectin, enhanced filamentous actin depolymerization and enhanced migration towards Ag relative to WT cells. No such differences between WT and NTAL(-/-) BM-derived mast cells were observed when SCF alone was used as activator. We have examined the activities of two small GTPases, Rac and Rho, which are important regulators of actin polymerization. Stimulation with Ag and/or SCF enhanced activity of Rac(1,2,3) in both NTAL(-/-) and WT cells. In contrast, RhoA activity decreased and this trend was much faster and more extensive in NTAL(-/-) cells, indicating a positive regulatory role of NTAL in the recovery of RhoA activity. After restoring NTAL into NTAL(-/-) cells, both spreading and actin responses were rescued. This is the first report of a crucial role of NTAL in signaling, via RhoA, to mast cell cytoskeleton.

Btk-dependent Rac activation and actin rearrangement following FcepsilonRI aggregation promotes enhanced chemotactic responses of mast cells

Mast cells infiltrate the sites of inflammation associated with chronic atopic disease and during helminth and bacterial infection. This process requires receptor-mediated cell chemotaxis across a concentration gradient of their chemotactic ligands. In vivo, mast cells are likely to be exposed to several such agents, which can cooperate in a synergistic manner to regulate mast cell homing. Here, we report that chemotaxis of mouse bone-marrow-derived mast cells (BMMCs) in response to the chemoattractants stem-cell factor (SCF) and prostaglandin (PG)E(2), is substantially enhanced following antigen-dependent ligation of the high-affinity receptor for IgE (FcεRI). These responses were associated with enhanced activation of phosphoinositide 3-kinase (PI3K), and downstream activation of the tyrosine protein kinase Btk, with subsequent enhanced phospholipase (PL)Cγ-mediated Ca(2+) mobilization, Rac activation and F-actin rearrangement. Antigen-induced chemotaxis, and the ability of antigen to amplify responses mediated by SCF, adenosine and PGE(2) were suppressed following inhibition of PI3K, and were impaired in BMMCs derived from Btk(-/-) mice. There were corresponding decreases in the PLCγ-mediated Ca(2+) signal, Rac activation and F-actin rearrangement, which, as they are essential for BMMC chemotaxis, accounts for the impaired migration of Btk-deficient cells. Taken together, these data demonstrate that, by regulating signaling pathways that control F-actin rearrangement, Btk is crucial for the ability of antigen to amplify mast-cell chemotactic responses.

Necrotic neurons enhance microglial neurotoxicity through induction of glutaminase by a MyD88-dependent pathway

Background

Microglia are macrophage-like cells that constantly sense the microenvironment within the central nervous system (CNS). In the event of neuronal stress or injury, microglial cells rapidly react and change their phenotype. This response may lead to a deleterious type of microglial activation, which is often associated with neuroinflammation and neurotoxicity in several neuropathological conditions. We investigated the molecular mechanisms underlying triggering of microglial activation by necrotic neuronal damage.

Methods

Primary cultures of microglia were used to study the effect of necrotic neurons on microglial inflammatory responses and toxicity towards cerebellar granule neurons (CGN). The mouse hippocampal cell line, HT22, was used in this study as the main source of necrotic neurons to stimulate microglia. To identify the signal transduction pathways activated in microglia, primary microglial cultures were obtained from mice deficient in Toll-like receptor (TLR) -2, -4, or in the TLR adapter protein MyD88.

Results

Necrotic neurons, but not other necrotic cell types, induced microglial activation which was characterized by up-regulation of: i) MHC class II; ii) co-stimulatory molecules, i.e. CD40 and CD24; iii) β2 integrin CD11b; iii) pro-inflammatory cytokines, i.e. interleukin 6 (IL-6), IL-12p40 and tumor-necrosis factor (TNF); iv) pro-inflammatory enzymes such as nitric oxide synthase (iNOS, type II NOS), indoleamine 2,3-dioxygenase (IDO) and cyclooxygenase-2 (COX-2) and increased microglial motility. Moreover, microglia-conditioned medium (MCM) obtained from cultures of activated microglia showed increased neurotoxicity mediated through the N-methyl-D-aspartate receptor (NMDAR). The activation of microglia by necrotic neurons was shown to be dependent on the TLR-associated adapter molecule myeloid differentiation primary response gene (MyD88). Furthermore, MyD88 mediated enhanced neurotoxicity by activated microglia through up-regulation of the expression and activity of glutaminase, an enzyme that produces glutamate, which is an NMDAR agonist.

Conclusion

These results show that necrotic neurons activate in microglia a MyD88-dependent pathway responsible for a pro-inflammatory response that also leads to increased neurotoxic activity through induction of glutaminase. This finding contributes to better understanding the mechanisms causing increased neuroinflammation and microglial neurotoxicity in a neurodegenerative environment.

Distinct locomotive patterns of granulocytes, monocytes and lymphocytes in a stable concentration gradient of chemokines

The pattern of leukocyte locomotion can be changed in many pathological situations, but its accurate analysis is difficult because of technological limitation. In the present study, by using a newly developed time-lapse videomicroscopic technique, we have analyzed the locomotive patterns of leukocytes in a stable concentration gradient of chemokines. Granulocytes, monocytes, and lymphocytes were purified from adult human peripheral blood. Locomotive behavior of the leukocytes was analyzed by an optical assay using a microchannel producing a stable concentration gradient of chemokines. Videomicroscopic analysis showed distinct locomotive patterns of granulocytes, monocytes, and lymphocytes. Granulocytes were intrinsically motile, vigorously moving in random direction without any chemokine stimulation. Upon stimulation with CXCL8/IL-8, the speed of migration was increased from 13.3 +/- 2.8 to 19.4 +/- 2.5 microm/min (P = 0.002, n = 100) and they moved toward the chemokine, although many cells still wandered very much. Stimulation with CCL5/RANTES or CXCL12/SDF-1alpha induced similar changes in locomotive pattern. On the other hand, most lymphocytes did not polarize or move spontaneously without chemokine stimulation. Stimulation with CXCL12 induced directional migration in 37% of the lymphocytes at a speed of 9.6 +/- 1.6 microm/min (n = 100). The movement pattern of monocytes was similar to that of granulocytes in that they tend to become polarized and move spontaneously, but they moved at a very slow speed ranging from 3.9 to 4.2 microm/min even with chemokine stimulation. The new optical assay may be useful for many diagnostic as well as basic studies.

Recent advances in the understanding of mastocytosis: the role of KIT mutations

Mastocytosis is a heterogeneous disorder characterised by the expansion and accumulation of mast cells in different organs and tissues. Mast cell physiology is closely dependent on activation of the stem cell factor/Kit signalling pathways and accumulating evidences confirm the physiopathological key role of activating KIT mutations (typically D816V) in mastocytosis and their relationship with the clinical manifestations of the disease. This paper reviews the most recent advances in the understanding of the molecular mechanisms associated with KIT mutations in mastocytosis, including recent data about the use of new therapies targeting the Kit molecule and its associated downstream signalling pathways.

Hepatocyte growth factor attenuates eotaxin and PGD2-induced chemotaxis of human eosinophils

BACKGROUND

Hepatocyte growth factor (HGF) is known to influence a number of cell types, and regulate various biologic activities including cell migration, proliferation, and survival. In a recent study, we found that, in vivo, HGF suppresses allergic airway inflammation, i.e. the infiltration of inflammatory cells including eosinophils into the airway, and further, that HGF reduces Th2 cytokine levels; however, the directly physiologic role of HGF with eosinophils remains unclear. In this study, we investigate the potential of recombinant HGF to regulate the factor-induced chemotaxis of human eosinophils.

METHODS

Eosinophils were isolated from subjects with mild eosinophilia by modified CD16-negative selection. After culture with or without recombinant HGF, esoinophil chemotaxis was measured by Boyden chamber and KK chamber.

RESULTS

Treatment with HGF prevented eotaxin or prostaglandin D(2) (PGD(2))-induced chemotaxis of eosinophils. Moreover, we demonstrated that extracellular signal-regulated kinase (ERK) 1/2 and p38 mitogen-activated protein kinases as well as the enhancement of Ca(2+) influx, which are indispensable for eosinophil chemotaxis, were attenuated by HGF treatment.

CONCLUSION

Taken together, these data suggest that in allergic diseases, HGF not only mediates eosinophils through the inhibition of Th2 cytokines, but also regulates the function of eosinophils directly, provides further insight into the cellular and molecular pathogenesis of allergic reactions.

Quantitative analysis of eosinophil chemotaxis tracked using a novel optical device -- TAXIScan

We have reported previously the development of an optically accessible, horizontal chemotaxis apparatus, in which migration of cells in the channel from a start line can be traced with time-lapse intervals using a CCD camera (JIM 282, 1-11, 2003). To obtain statistical data of migrating cells, we have developed quantitative methods to calculate various parameters in the process of chemotaxis, employing human eosinophil and CXCL12 as a model cell and a model chemoattractant, respectively. Median values of velocity and directionality of each cell within an experimental period could be calculated from the migratory pathway data obtained from time-lapse images and the data were expressed as Velocity-Directionality (VD) plot. This plot is useful for quantitatively analyzing multiple migrating cells exposed to a certain chemoattractant, and can distinguish chemotaxis from random migration. Moreover precise observation of cell migration revealed that each cell had a different lag period before starting chemotaxis, indicating variation in cell sensitivity to the chemoattractant. Thus lag time of each cell before migration, and time course of increment of the migrating cell ratio at the early stages could be calculated. We also graphed decrement of still moving cell ratio at the later stages by calculating the duration time of cell migration of each cell. These graphs could distinguish different motion patterns of chemotaxis of eosinophils, in response to a range of chemoattractants; PGD(2), fMLP, CCL3, CCL5 and CXCL12. Finally, we compared parameters of eosinophils from normal volunteers, allergy patients and asthma patients and found significant difference in response to PGD(2). The quantitative methods described here could be applicable to image data obtained with any combination of cells and chemoattractants and useful not only for basic studies of chemotaxis but also for diagnosis and for drug screening.

Leukotriene B4Receptors BLT1 and BLT2: Expression and Function in Human and Murine Mast Cells

Leukotriene B4 (LTB4) is a potent activator and chemoattractant for leukocytes and is implicated in several inflammatory diseases. The actions of LTB4 are mediated by two cell surface receptors, BLT1, which is predominantly expressed in peripheral blood leukocytes, and BLT2, which is expressed more ubiquitously. Recently, BLT1 expression and LTB4-dependent chemotaxis have been reported in immature mast cells (MCs). We now show the first evidence for BLT2 mRNA expression, in addition to BLT1, in murine bone marrow-derived MCs (mBMMCs) and in a human MC line (HMC-1). Protein expression of BLT1 was confirmed by mAb staining in HMC-1 cells and shown to be predominantly intracellular. Both HMC-1 cells and mBMMCs migrated to LTB4 in a dose-dependent manner in chemotaxis assays. Migration to LTB4 could be inhibited by either a BLT1- or BLT2-selective antagonist. Significant dose-dependent migration of mBMMCs also was observed to 12-(S)-hydroxyeicosotetraenoic acid, a BLT2-selective agonist, demonstrating functional BLT2 activity in these cells. Stimulation of mBMMCs with LTB4 induced transient, dose-dependent, ERK phosphorylation and changes in Akt phosphorylation. Dose-dependent ERK phosphorylation also was observed in response to 12-(S)-hydroxyeicosotetraenoic acid, indicating signaling downstream of BLT2. Pretreatment of mBMMCs with stem cell factor significantly down-regulated expression of BLT1 and BLT2 mRNA and inhibited their migration to LTB4. This study demonstrates expression of functional LTB4 receptors, both BLT1 and BLT2, in murine and human MCs and a regulatory role for stem cell factor in their expression. These receptors may mediate recruitment and accumulation of MCs in response to LTB4 production in areas of inflammation.

Stem cell factor expression, mast cells and inflammation in asthma

The Kit ligand SCF or stem cell factor (SCF) is a multipotent growth factor, acting as an important growth factor for human mast cells. SCF induces chemotaxis and survival of the mast cell, as well as proliferation and differentiation of immature mast cells from CD34(+) progenitors. Additionally, SCF enhances antigen-induced degranulation of human lung-derived mast cells, and induces a mast cell hyperplasia after subcutaneous administration. SCF expression increases in the airways of asthmatic patients, and this is reversed after treatment with glucocorticoids. A role for SCF may thus be hypothesized in diseases associated with a local increase in the number and/or activation of mast cells, as occurring in the airways in asthma. SCF will be reviewed as a potential therapeutic target in asthma, to control the regulation of mast cell number and activation. We here report the main pathways of SCF synthesis and signalling, and its potential role on airway function and asthma.

Generation and characterization of bone marrow-derived cultured canine mast cells

Disorders of mast cells, particularly mast cell tumors (MCTs), are common in dogs. There now is evidence that many of these disorders exhibit breed predilections, suggesting an underlying heritable component. In comparison to humans and mice, little is known regarding the biology of canine mast cells. To facilitate the study of mast cell biology in other species, bone marrow-derived cultured mast cells (BMCMCs) often are used because these represent a ready source of large numbers of cells. We have developed a protocol to successfully generate canine BMCMCs from purified CD34(+) cells. After 5-7 weeks of culture with recombinant canine stem cell factor (rcSCF), greater than 90% of the cell population consisted of mast cells as evidenced by staining with Wright's-Giemsa, as well as production of chymase, tryptase, IL-8 and MCP-1. These cells expressed cell surface markers typical of mast cells including Kit, Fc epsilonRI, CD44, CD45 and CD18/CD11b. The canine BMCMCs were dependent on rcSCF for survival and proliferation, and migrated in response to rcSCF gradients. Cross-linking of cell surface-bound IgE induced the release of histamine and TNFalpha. Histamine release could also be stimulated by ConA, compound 48/80, and calcium ionophore. In summary, canine BMCMCs possess phenotypic and functional properties similar to mast cells found in vivo. These cells represent a novel, valuable resource for investigating normal canine mast cell biology as well as for identifying factors that lead to mast cell dysregulation in the dog.

Stem cell factor and its receptor c-Kit as targets for inflammatory diseases

Stem cell factor (SCF), the ligand of the c-Kit receptor, is expressed by various structural and inflammatory cells in the airways. Binding of SCF to c-Kit leads to activation of multiple pathways, including phosphatidyl-inositol-3 (PI3)-kinase, phospholipase C (PLC)-gamma, Src kinase, Janus kinase (JAK)/Signal Transducers and Activators of Transcription (STAT) and mitogen activated protein (MAP) kinase pathways. SCF is an important growth factor for mast cells, promoting their generation from CD34+ progenitor cells. In vitro, SCF induces mast cells survival, adhesion to extracellular matrix and degranulation, leading to expression and release of histamine, pro-inflammatory cytokines and chemokines. SCF also induces eosinophil adhesion and activation. SCF is upregulated in inflammatory conditions both in vitro and in vivo, in human and mice. Inhibition of the SCF/c-Kit pathway leads to significant decrease of histamine levels, mast cells and eosinophil infiltration, interleukin (IL)-4 production and airway hyperresponsiveness in vivo. Taken together, these data suggest that SCF/c-Kit may be a potential therapeutic target for the control of mast cell and eosinophil number and activation in inflammatory diseases.

Pharmacologic differentiation of inflammation and fibrosis in the rat bleomycin model

RATIONALE

The model most often used to study the pathogenesis of pulmonary fibroses is the bleomycin (BLM)-induced lung fibrosis model. Several treatments have been efficacious in this model, but not in the clinic.

OBJECTIVES

To describe the time course of inflammation and fibrosis in the BLM model and to study the effect of timing of antiinflammatory and antifibrotic treatments on efficacy.

METHODS AND MEASUREMENTS

Rats were given single intratracheal injections of BLM on Day 0. At specified time points, 10 rats were killed and their lungs studied for proinflammatory cytokines and for profibrotic growth factor mRNA. After a single intratracheal injection of BLM on Day 0, rats were treated from Day 1 or 10 daily with oral prednisolone (10 mg/kg) or oral imatinib mesylate (50 mg/kg) for 21 d.

RESULTS

After BLM administration, the expression of inflammatory cytokines was elevated and returned to background levels at later time points. Profibrotic gene expression peaked between Days 9 and 14 and remained elevated till the end of the experiment, suggesting a "switch" between inflammation and fibrosis in this interval. Antiinflammatory treatment (oral prednisolone) was beneficial when commenced at Day 1, but had no effect if administered from Day 10 onward. However, imatinib mesylate was effective independently of the dosing regime.

CONCLUSIONS

The response of the BLM model to antifibrotic or antiinflammatory interventions is critically dependent on timing after the initial injury.