Stem cell factor potentiates histamine secretion by multiple mechanisms, but does not affect tumour necrosis factor-alpha release from rat mast cells

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.

Anaphylaxis and mast cell disease: what is the risk?

Mastocytosis is a proliferative disorder of the hematopoietic mast cell progenitor that results from expansion of a clone carrying the D816V c-kit mutation. Based on the dramatic increase in incidence of anaphylaxis in patients with mastocytosis, recent studies analyzed the presence of clonal mast cell markers, including D816V c-kit mutation, in patients with recurrent IgE- and non-IgE-mediated anaphylaxis. These studies demonstrated the presence of an aberrant mast cell clone in a significant proportion of patients with unexplained anaphylaxis, or anaphylaxis due to hymenoptera venom. Clonal mast cell disease should be suspected in particular in patients presenting with profound cardiovascular manifestations such as hypotension and syncope in the absence of urticaria.

Histamine index and clinical expression of rheumatoid arthritis activity

BACKGROUND/AIM

Many arguments prove the pathophysiologic role of histamine in the process of remodeling and joint destruction in rheumatoid arthritis. The aim of our study was to find out if there was a relation between histamine concentration in synovial fluid and blood with clinical expression of disease activity.

METHODS

Histamine concentration in synovial fluid and blood was determinated in 19 patients with rheumatoid arthritis. Histamine concentration measurement was based on the Shore's fluorometric method. Histamine index (HI) was evaluated as a ratio between histamine concentration in synovial fluid and blood. Disease activity score, DAS 28 (3), with three variables (erythrocyte sedimentation rate, the number of swelled joints and the number of tender joints) was also evaluated.

RESULTS

Our results showed that there was no significant difference in concentration of histamine in synovial fluid and blood related to disease activity. However, there was a significiant difference in the histamine index which was increased proportionally with disease activity.

CONCLUSION

Our study indicates that histamine index could be useful in estimation of rheumatoid arthritis activity.

CD4 expression on activated NK cells: ligation of CD4 induces cytokine expression and cell migration

NK cells play an important role in the innate immune response. We have isolated NK cells from human lymphoid tissues and found that these cells express the CD4 molecule on their surface at levels higher than those found on peripheral blood NK cells. To study the functional role of the CD4 molecule on NK cells, we developed an in vitro system by which we are able to obtain robust CD4 expression on NK cells derived from blood. CD4+ NK cells efficiently mediate NK cell cytotoxicity, and CD4 expression does not appear to alter lytic function. CD4+ NK cells are more likely to produce the cytokines gamma-IFN and TNF-alpha than are CD4- NK cells. Ligation of CD4 further increases the number of NK cells producing these cytokines. NK cells expressing CD4 are also capable of migrating toward the CD4-specific chemotactic factor IL-16, providing another function for the CD4 molecule on NK cells. Thus, the CD4 molecule is present and functional on NK cells and plays a role in innate immune responses as a chemotactic receptor and by increasing cytokine production, in addition to its well-described function on T cells as a coreceptor for Ag responsive cell activation.

Pathogenesis, clinical features, and treatment advances in mastocytosis

Systemic mastocytosis (SM) is characterized by the abnormal growth and accumulation of mast cells (MC) in one or more organs. The interaction between the cytokine stem cell factor (SCF) and its cognate receptor, the c-kit receptor tyrosine kinase (KIT), plays a central role in regulating MC growth and differentiation. Whereas germline and somatically acquired activating mutations of KIT have been identified in SM, the issue as to whether individual KIT mutation(s) are necessary and sufficient to cause MC transformation remains unclear based on currently available data. Activating mutations of platelet-derived growth factor receptor-alpha (FIP1 L1-PDGFRA) are identified in a significant number of SM cases that have associated eosinophilia. To date, as with gastrointestinal stromal tumors, activating mutations of KIT and PDGFRA appear to be alternative and mutually exclusive genetic events in SM. The World Health Organization has specified criteria for classification of SM into six major subtypes: cutaneous mastocytosis, indolent systemic mastocytosis (ISM), systemic mastocytosis with an associated clonal hematological non-mast-cell disorder (SM-AHNMD), aggressive systemic mastocytosis (ASM), mast cell leukemia, and mast cell sarcoma. The ability to molecularly classify individual SM cases based on the presence or absence of specific mutations allows for molecularly targeted therapy in a growing number of cases. Imatinib mesylate therapy might result in complete remission of SM cases with wild-type KIT, certain KIT mutations, such as F522C, or the FIP1L1-PDGFRA fusion gene, but not of D816V-KIT-bearing SM. For the latter, interferon-alpha and 2-CdA are potential first- and second-line therapeutic options. Other drugs under investigation include novel tyrosine kinase inhibitors, as well as NF-kappaB inhibitors, which might display greater selectivity towards D816V-KIT as compared to wild type KIT. The pathogenesis of mastocytosis, its major clinical subtypes, and recent treatment advances are discussed in this chapter.

Clonality and molecular pathogenesis of mastocytosis

Mast cell is a hematopoietic lineage dependent on Kit signaling for growth, differentiation, and survival. Mast cells are found in excessive numbers in tissues in a heterogeneous group of disorders collectively known as mastocytosis. Last decade has witnessed important advancements in our understanding of the molecular pathology of mastocytosis. First, systemic mastocytosis has been found to be associated with activating codon 816 mutations of the c-kit gene. Second, this mutation was used as a tracking marker to elucidate the clonal nature of mastocytosis. These findings have resulted in consideration of systemic mastocytosis as a clonal neoplastic disorder of a hematopoietic progenitor cell. Improved knowledge of the mechanisms causing pathological mast cell growth will lead to the discovery of novel treatment options including drugs targeting the mutated Kit protein.

IL-16 activates plasminogen-plasmin system and promotes human eosinophil migration into extracellular matrix via CCR3-chemokine-mediated signaling and by modulating CD4 eosinophil expression

Increased eosinophil counts are a major feature of asthmatic airways. Eosinophil recruitment requires migration through epithelium and tissue extracellular matrix by activation of proteases. We assessed the capacity of IL-16, a CD4(+) cell chemotactic factor, to induce migration of eosinophils through a reconstituted basement membrane and evaluated the proteases, mediators, and receptors involved in this migration. IL-16 added to lower chambers of Invasion Chambers elicited eosinophil migration through Matrigel. This effect was decreased by inhibition of the plasminogen-plasmin system (Abs against urokinase plasminogen activator receptor or plasminogen depletion), but not by anti-matrix metalloproteinase-9 Abs. Abs against CD4 also inhibited IL-16-induced eosinophil migration. At the baseline level, few eosinophils (4.6% positive cells with a mean fluorescence of 0.9) expressed surface membrane CD4, while most permeabilized eosinophils (68% positive cells with a mean fluorescence of 18) express the CD4 Ag. TNF-pretreatment increased surface membrane CD4(+) expression by 6-fold as previously described, and increased IL-16-induced cell migration by 2.2-fold. Incubation of eosinophils with IL-16 also increased surface membrane CD4 expression by 5.4-fold, supporting the role of CD4 as receptor for IL-16. Abs against CCR3, eotaxin, or RANTES blocked IL-16-induced migration. In conclusion, IL-16 promotes eosinophil migration in vitro, by activating the plasminogen-plasmin system and increasing the membrane expression of its receptor. This effect is initiated via CD4 and mediated via the release of CCR3 ligand chemokines. Interestingly, most eosinophils express intracellular CD4. Hence, IL-16 may play an important role in the recruitment of blood eosinophils to the bronchial mucosa of asthmatics.

Stem cell factor induces eosinophil activation and degranulation: mediator release and gene array analysis

Eosinophils are effector cells that play an important role in the damage induced by the allergic process by releasing inflammatory mediators and proteolytic factors after activation. Stem cell factor (SCF) is a primary cytokine involved in hematopoiesis and mast cell differentiation, proliferation, and activation. Studies have also indicated that SCF is directly involved in pathogenesis of allergic airway inflammation. In the present study, we examined the ability of SCF to activate murine eosinophils for increased mediator release and up-regulation of chemokines. Initial data demonstrated that eosinophils have significant levels of surface c-kit protein, SCF receptor. SCF-activated eosinophils degranulate and release eosinophil peroxidase and leukotriene C(4) in a dose-dependent manner. In addition, SCF was further shown to induce the release of CC chemokines, RANTES, macrophage-derived chemokine (MDC), macrophage inflammatory protein-1beta (MIP-1beta), and C10 from eosinophils. To identify the extent of SCF-induced activation of eosinophils, we also performed gene array analysis using an array containing 1153 genes related to inflammation, including cytokines and their receptors, growth factors, structural and cytoskeletal genes, signal transduction genes as well as several other classes related to immune/inflammatory responses. The gene analysis indicated that more than 150 genes were significantly up-regulated in eosinophils after SCF stimulation. The gene array results were verified using a quantitative real-time polymerase chain reaction analysis to identify the expression of several chemokine and chemokine receptor genes. Altogether, these studies indicate that SCF is a potent eosinophil degranulator and activator that may play a number of roles during an inflammatory/immune response.

Stem cell factor enhances IgE-mediated histamine and TNF-alpha release from dispersed canine cutaneous mast cells

Stem cell factor (SCF), the c-kit receptor ligand, plays a critical role in mast cell (MC) development and differentiation. In addition, SCF has recently been found to both modulate and induce MC activation. To investigate the effect of SCF on canine cutaneous MC function, we have characterized the ability of SCF to modulate the release by mature canine MC of preformed (histamine) and newly generated (TNF-alpha) mediators. Mature MC were isolated from skin and cultured in the absence or presence of exogenous SCF (6 ng/ml) for up to 5 days and then challenged with anti-IgE (1 microg/ml) alone for 30 min or with a combination of SCF (50 ng/ml) and anti-IgE. SCF alone failed to trigger either histamine or TNF-alpha release at any time. However, we observed that SCF used as a co-stimulus significantly potentiated histamine and TNF-alpha release in canine MC activated through Fc epsilon RI regardless of whether or not SCF was added to the medium during culturing. Thus, the mean histamine release (%) and TNF-alpha production (pg/ml) were found to be significantly higher if cells were maintained in culture in SCF-supplemented medium compared with cells cultured in the absence of exogenous SCF. We also observed that MC responsiveness to immunological stimulation increased with culture time, the percentage of histamine released being higher in cells cultured for at least 3 days when compared to freshly isolated MC. Taken together these findings suggest that canine skin MC releasability can be enhanced independently either through prolonged incubation with SCF and/or through anti-IgE and SCF co-stimulation.

The action of tumor necrosis factor-alpha on rat mast cells

Taking into account that cytokine tumor necrosis factor-alpha (TNF-alpha) and mast cells (MC) both are involved in inflammation, it seems of great importance to recognize their relationships. Therefore, we have studied whether recombinant human TNF-alpha (rHuTNF-alpha) can cause histamine secretion from rat peritoneal MC. We have also examined the effect of this cytokine on MC reactivity. We have established that TNF-alpha stimulates rat MC to histamine release in a concentration-dependent manner. TNF-alpha-induced histamine secretion was evoked by concentrations > 10-16 M and reached the maximum rate at a concentration of 10-10 M (histamine release 17.1% +/- 1.9%, mean +/- SEM). We have also noticed that pretreatment of MC with TNF-alpha (in a concentration of 10-16 M) significantly inhibited concanavalin A (ConA)-stimulated release of histamine, with the percent release decreasing to 51% of the control value. Treatment of mast cells with TNF-alpha resulted in a decrease of compound 48/80-dependent histamine release as well (the percent released histamine fell to 85% of the control value). This altered MC responsiveness was reversible. After 120 min of resting time, the MC reactivity came back to the initial values. We have concluded that TNF-alpha appears to be a direct stimulus for MC to release histamine, and it may regulate MC secretory function.

CD4+ T cell and eosinophil adhesion is mediated by specific ICAM-3 ligation and results in eosinophil activation

T cells and eosinophils, which are found in close proximity in asthmatic lungs, express many surface receptors that are counterligands. These data suggest that direct interactions between these cell types could play an important role in regulating airway inflammation in asthma. We examined the effect of selective adhesion between counterligands on human eosinophils and CD4+ T cells to determine 1) the existence of specific adhesive interactions and 2) if augmented specific adhesion to CD4+ T cells also caused augmented secretion of leukotriene C4 (LTC4) from eosinophils. A new method for binding of human CD4+ T cells to microwell plates was developed, which allowed for specific quantitative assessment of eosinophil adhesion to individual CD4+ T cells in culture. Adhesion of CD4+ T cells to eosinophils was minimal in unstimulated cells but increased after activation of T cells by PMA. Augmented adhesion was regulated substantially through binding of ICAM-3 and only minimally by ICAM-1. We further evaluated whether this specific adhesion up-regulated stimulated secretion of LTC4 from eosinophils. Adhesion with CD4+ T cells augmented eosinophil secretion of LTC4 caused by FMLP plus cytochalasin. Blockade of ICAM-3, as well as ICAM-1, inhibited completely the augmented secretion of eosinophil LTC4. We demonstrate that eosinophils and CD4+ T cells are capable of ligand-specific adhesion that is mediated predominantly by ICAM-3 ligation and that this binding causes augmented eosinophil secretion.

Interferon-gamma regulates the interaction of RBL-2H3 cells with fibronectin through production of nitric oxide

Interferon-gamma (IFN-gamma) is an important regulatory cytokine in cell proliferation, differentiation, adhesion, mediator release, and gene induction. This diversity of effector roles is achieved by a variety of incompletely understood mechanisms. In the mast cell (MC), IFN-gamma downregulates mediator synthesis and secretion. The present study demonstrates and characterizes for the first time IFN-gamma inhibition of adhesion of the MC analogue RBL-2H3 to the extracellular matrix protein fibronectin (FN). Inhibition requires preincubation of the cells with IFN-gamma for 20 hr, and is statistically significant at 100 U/ml IFN-gamma. Flow cytometry indicates that cell surface expression of very late antigen-4 (VLA-4), VLA-5, and the vitronectin receptor (VNR) remain constant following IFN-gamma treatment, indicating the inhibitory effect of IFN-gamma on adhesion to FN is not achieved through a reduction in integrin receptors for FN. Fluorescent labelling with Texas red phalloidin demonstrated rearrangement of the actin cytoskeleton in response to IFN-gamma was not significant. The tyrosine phosphatase inhibitor vanadate, and the nitric oxide (NO) synthase inhibitor L-NAME, reduced the IFN-gamma effect on adhesion to FN by 62 and 70%, respectively, demonstrating that the IFN-gamma effect is dependent upon the production of NO, potentially though a tyrosine phosphatase dependent mechanism. The NO donors sodium nitroprusside and S-nitrosoglutathione mimicked the effect of IFN-gamma. Thus, following stimulation with IFN-gamma, NO plays an autocrine role in the MC, and is able to modulate integrin function. This adds to the pathways NO is able to inhibit in the mast cell, shows that endogenous NO is able to inhibit these pathways, and suggests NO is impinging upon an element common to many signalling mechanisms in the MC.

Mast cells are an important cellular source of tumour necrosis factor alpha in human intestinal tissue

BACKGROUND

Several inflammatory disorders of the intestine are characterised by enhanced expression of tumour necrosis factor alpha (TNF-alpha). Monocytes and macrophages have been suggested as a major cellular source of TNF-alpha in human gut, whereas mast cells, although known to be capable of producing TNF-alpha, have been poorly examined in this respect.

AIMS

To investigate whether human intestinal mast cells can produce TNF-alpha, and which factors regulate TNF-alpha production in these cells.

METHODS

Mast cells were isolated from surgery tissue specimens of patients undergoing bowel resection because of cancer. Immunohistochemical studies were performed in biopsy specimens derived from 13 patients (two healthy controls, four with Crohn's disease, four with ulcerative colitis, three others). TNF-alpha mRNA and protein expression were studied in vitro by polymerase chain reaction, RNAse protection assay, western blot, and enzyme linked immunosorbent assay in isolated purified human intestinal mast cells stimulated by IgE receptor crosslinking, intestinal bacteria, and lipopolysaccharide. Cellular localisation of TNF-alpha was examined by immunohistochemistry.

RESULTS

TNF-alpha mRNA and protein were expressed constitutively in isolated human intestinal mast cells. Expression of TNF-alpha mRNA and release of TNF-alpha protein were substantially enhanced by IgE receptor crosslinking and by coculture of mast cells with intestinal bacteria; lipopolysaccharide had only marginal effects. Immunohistochemical studies revealed that approximately 60% of the lamina propria cells with immunoreactivity for TNF-alpha were mast cells.

CONCLUSIONS

The data show that mast cells are an important source of TNF-alpha in the human intestinal mucosa.

Tumor necrosis factor alpha (TNF-alpha) modulates rat mast cell reactivity

Nowadays there is growing evidence that some cytokines regulate biological functions of the mature mast cells. Therefore, we have studied whether TNF-alpha, the cytokine of multifunctional activities, could directly stimulate rat peritoneal mast cells to histamine secretion and whether it could modulate rat mast cell reactivity in anaphylactic (with ConA) and anaphylactoid (with compound 48/80) reactions. We have established that rat recombinant TNF-alpha does not activate rat mast cells to histamine release. However, TNF-alpha-treatment causes the decrease of spontaneous histamine release up to 85% (TNF-alpha concentration: 2 x 10(-9) M). Pretreatment of mast cells with TNF-alpha inhibits ConA-stimulate release of histamine with the percent release decreasing up to 33.7% of the control value (TNF-alpha concentration: 5 x 10(-9) M) and this decrease is statistically significant. Pretreatment of mast cells with TNF-alpha reduces compound 48/80-dependent histamine release as well and the percent release of histamine fell to 64.7% of the control value. We have concluded that TNF-alpha may play a significant role in regulation of mast cell secretory activity.

Role of intestinal mast cells in modulating gastrointestinal pathophysiology

OBJECTIVE

This article reviews the current understanding of the pathophysiologic role of intestinal mast cells.

DATA SOURCE

Up to date English language publications on mast cell characteristics, heterogeneity and functions were used. Recent articles were used to develop and extend novel concepts about the role of intestinal mast cells.

STUDY SELECTION

Reference sources were selected because of their pertinence to the pathophysiological effects of mast cells in intestinal hypersensitivity. Recent publications on the following topics were emphasized: mast cell proteases in intestinal anaphylaxis; effects of nitric oxide in gastrointestinal pathophysiology; involvement of cytokines derived from mast cells in tissue damage and repair.

RESULTS

Mast cells are clearly implicated in the pathology of intestinal disease. Growing evidence suggests physiological roles for mast cells in the protection of tissues from inflammatory damage, and in intestinal maturation. Mast cells can release cytokines, such as tumour necrosis factor-alpha and interleukin-10, which were originally thought to contribute to inflammatory damage, but which may also have anti-inflammatory properties. Interestingly, mast cell function can be regulated by nitric oxide, and mast cells themselves are sources of this important mediator. Nitric oxide has protective as well as detrimental effects in the intestine.

CONCLUSIONS

Intestinal mast cells have physiologic regulatory effects in addition to their pathologic effects. However, relatively little is known about the mechanisms of these regulatory effects. Mast cells are likely in an ongoing fluctuating balance between physiological functions and pathological effects in normal individuals. Poorly known factors can create an imbalance and lead to pathologic reactions.