Mast cells in the promotion and limitation of chronic inflammation

Inhibitory effect of hot-water extract of quince (Cydonia oblonga) on immunoglobulin E-dependent late-phase immune reactions of mast cells

We evaluated the effect of a crude hot-water extract (HW) of quince (Cydonia oblonga Miller) fruit on immunoglobulin E (IgE)-dependent late-phase immune reactions of mast cells using in vitro system. Mast cell-like RBL-2H3 cells were treated with quince HW and late-phase reaction was then induced by stimulation with IgE + Antigen. Quince HW reduced the elevation of interleukin-13 and tumor necrosis factor-α expression level. Furthermore, quince HW suppressed these cytokine expressions of mouse bone marrow-derived mast cells (BMMCs), a normal mast cell model. Leukotriene C(4) and prostaglandin D(2) production in BMMCs after 1 and 6 h of stimulation, respectively, were also reduced by treating the cells with quince HW. We found that the induction of intracellular cyclooxygenase (COX)-2 expression but not COX-1 expression in BMMCs was reduced by quince HW. These results suggest that quince HW has an inhibitory effect on broad range of the late-phase immune reactions of mast cells.

What's new in asthma pathophysiology and immunopathology?

Research on asthma pathophysiology over the past decade has expanded the complex repertoire involved in the pathophysiology of asthma to include inflammatory, immune and structural cells, as well as a wide range of mediators. Studies have identified a role for connective and other mesenchymal tissues involved in airway remodeling. Recent findings have implicated the innate immune response in asthma and have revealed interesting patterns of interaction between the innate and adaptive immune response and the associated complex chronic inflammatory reaction. New immune cell populations have also been added to this repertoire, including Tregs, natural killer T cells and Th17 cells. The role of the eosinophil, a prominent pathological feature in most asthma phenotypes, has also been expanding to include roles such as tissue modifiers and immune regulators via a number of fascinating and hitherto unexplored mechanistic pathways. In addition, new and significant roles have been proposed for airway smooth muscle cells, fibroblasts, epithelial and endothelial cells. Tissue remodeling is now considered an integral element of asthma pathophysiology. Finally, an intricate network of mediators, released from both immune and inflammatory cells, including thymus stromal lymphopoietin and matrix metalloproteinases, have added to the complex milieu of asthma immunity and inflammation. These findings have implications for therapy and the search for novel strategies towards better disease management. Sadly, and perhaps due to the complex nature of asthma, advances in therapeutic discoveries and developments have been limited. Thus, understanding the precise roles played by the numerous dramatis personae in this odyssey, both individually and collectively within the context of asthma pathophysiology, continues to pose new challenges. It is clear that the next stage in this saga is to embark on studies that transcend reductionist approaches to involve system analysis of the complex and multiple variables involved in asthma, including the need to narrow down the phenotypes of this condition based on careful analysis of the organs (lung and airways), cells, mediators and other factors involved in bronchial asthma.

The non-selective monovalent cationic channels TRPM4 and TRPM5

Transient Receptor Potential (TRP) proteins are non-selective cationic channels with a consistent Ca(2+)-permeability, except for TRPM4 and TRPM5 that are not permeable to this ion. However, Ca(2+) is a major regulator of their activity since both channels are activated by a rise in internal Ca(2+). Thus TRPM4 and TRPM5 are responsible for most of the Ca(2+)-activated non-selective cationic currents (NSC(Ca)) recorded in a large variety of tissues. Their activation induces cell-membrane depolarization that modifies the driving force for ions as well as activity of voltage gated channels and thereby strongly impacts cell physiology. In the last few years, the ubiquitously expressed TRPM4 channel has been implicated in insulin secretion, the immune response, constriction of cerebral arteries, the activity of inspiratory neurons and cardiac dysfunction. Conversely, TRPM5 whose expression is more restricted, has until now been mainly implicated in taste transduction.

Mast cells, angiogenesis and cancer

Mast cells (MCs) were first described by Paul Ehrlich 1 in his doctoral thesis. MCs have long been implicated in the pathogenesis of allergic reactions and certain protective responses to parasites. As most tumors contain inflammatory cell infiltrates, which often include plentiful MCs, the question as to the possible contribution of MCs to tumor development has progressively been emerging. In this chapter, the specific involvement of MCs in tumor biology and tumor fate will be considered, with particular emphasis on the capacity of these cells to stimulate tumor growth by promoting angiogenesis and lymphangiogenesis. Data from experimental carcinogenesis and from different tumor settings in human pathology will be summarized. Information to be presented will suggest that MCs may serve as a novel therapeutic target for cancer treatment.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

An essential role for mast cells as modulators of neutrophils influx in collagen-induced arthritis in the mouse

Mast cells are involved in immune disorders so that many of the proinflammatory and tissue destructive mediators produced by these cells have been implicated in the pathogenesis of rheumatoid arthritis. This scenario prompted us to investigate the correlation between mast cell degranulation and neutrophil influx within the digits and knees joints of arthritic mice assessing what could be the functional role(s) of joint mast cells in the response to collagen immunization. DBA/1J mice were submitted to collagen-induced arthritis and disease was assessed on day 21, 32 and 42 post-immunization. Pharmacological treatment with the glucocorticoid prednisolone, commonly used in the clinic, and nedocromil, a mast cell stabilizer, was performed from day 21 to 30. Arthritis develop after immunization, gradually increased up to day 42. Neutrophil infiltration peaked on day 32 and 21, in the digits and knees, respectively, showing an unequal pattern of recruitment between these tissues. This difference emerged for mast cells: they peaked in the digits on day 21, but a higher degree of degranulation could be measured in the knee joints. Uneven modulation of arthritis occurred after treatment of mice with prednisolone or nedocromil. Neutrophils migration to the tissue was reduced after both therapies, but only prednisolone augmented mast cell migration to the joints. Nedocromil exerted inhibitory properties both on mast cell proliferation and migration, more effectively on the digit joints. Thus, collagen induced an inflammatory process characterized by tissue mast cells activation and degranulation, suggesting a potential driving force in propagating inflammatory circuits yielding recruitment of neutrophils. However, the different degree of affected joint involvement suggests a time-related implication of digits and knees during collagen-induced arthritis development. These results provide evidence for local alterations whereby mast cells contribute to the initiation of inflammatory arthritis and may be targeted in intervention strategies.

Mast cells, angiogenesis, and tumour growth

Accumulation of mast cells (MCs) in tumours was described by Ehrlich in his doctoral thesis. Since this early account, ample evidence has been provided highlighting participation of MCs to the inflammatory reaction that occurs in many clinical and experimental tumour settings. MCs are bone marrow-derived tissue-homing leukocytes that are endowed with a panoply of releasable mediators and surface receptors. These cells actively take part to innate and acquired immune reactions as well as to a series of fundamental functions such as angiogenesis, tissue repair, and tissue remodelling. The involvement of MCs in tumour development is debated. Although some evidence suggests that MCs can promote tumourigenesis and tumour progression, there are some clinical sets as well as experimental tumour models in which MCs seem to have functions that favour the host. One of the major issues linking MCs to cancer is the ability of these cells to release potent pro-angiogenic factors. This review will focus on the most recent acquisitions about this intriguing field of research. This article is part of a Special Issue entitled: Mast cells in inflammation.

Immunohistochemical expression of mast cell tryptase in giant cell fibroma and inflammatory fibrous hyperplasia of the oral mucosa

This study analysed the immunohistochemical expression of mast cell tryptase in giant cell fibromas (GCFs). In addition, the possible interaction of mast cells with stellate giant cells, as well as their role in fibrosis and tumour progression, was investigated. For this purpose, the results were compared with cases of inflammatory fibrous hyperplasia (IFH) and normal oral mucosa. Thirty cases of GCF, 30 cases of IFH and 10 normal mucosa specimens used as control were selected. Immunoreactivity of mast cells to the anti-tryptase antibody was analysed quantitatively in the lining epithelium and in connective tissue. In the epithelial component (p=0.250) and connective tissue (p=0.001), the largest mean number of mast cells was observed in IFHs and the smallest mean number in GCFs. In connective tissue, the mean percentage of degranulated mast cells was higher in GCFs than in IFHs and normal mucosa specimens (p<0.001). Analysis of the percentage of degranulated mast cells in areas of fibrosis and at the periphery of blood vessels also showed a larger mean number in GCFs compared to IFHs and normal mucosa specimens (p<0.001). The percent interaction between mast cells and stellate giant cells in GCFs was 59.62%. In conclusion, although mast cells were less numerous in GCFs, the cells exhibited a significant interaction with stellate giant cells present in these tumours. In addition, the results suggest the involvement of mast cells in the induction of fibrosis and modulation of endothelial cell function in GCFs.

Physiological roles of the TRPM4 channel extracted from background currents

Calcium-activated nonselective cationic currents have been known for 30 years, but their physiological implications have remained unresolved until the recent cloning of the TRPM4 ion channel. Since then, TRPM4 has been identified as a key modulator of numerous calcium-dependent mechanisms such as the immune response, insulin secretion, cerebral artery constriction, respiratory rhythm, and cardiac conduction.

Chronic pruritus--pathogenesis, clinical aspects and treatment

Chronic pruritus is a major symptom in numerous dermatological and systemic diseases. Similar to chronic pain, chronic pruritus can have a dramatic impact on the quality of life and can worsen the general condition of the patient considerably. The pathogenesis of itch is diverse and involves a complex network of cutaneous and neuronal cells. In recent years, more and more itch-specific mediators and receptors, such as interleukin-31, gastrin-releasing peptide receptor or histamine H4 receptor have been identified and the concept of itch-specific neurons has been further characterized. Understanding of the basic principles is important for development of target-specific treatment of patients with chronic pruritus. In this review, we summarize the current knowledge about the pathophysiological principles of itch and provide an overview about current and future treatment options.

A Notch ligand, Delta-like 1 functions as an adhesion molecule for mast cells

Mast cells (MCs) accumulate in chronic inflammatory sites; however, it is not clear which adhesion molecules are involved in this process. Recently, the expression of Notch ligands was reported to be upregulated in inflammatory sites. Although Notch receptors are known as signaling molecules that can activate integrins, their contributions to the adhesion of MCs have not been studied. In this study, we demonstrated that mouse MCs efficiently adhered to stromal cells forced to express a Notch ligand, Delta-like 1 (Dll1). Surprisingly, the adhesion was a consequence of direct cell-cell interaction between MCs and Dll1-expressing stromal cells rather than activation of downstream effectors of Notch receptor(s)-Dll1. The adhesion of MCs to Dll1-expressing stromal cells remained even when the cell metabolism was arrested. The recognition was blocked only by inhibition of Notch receptor(s)-Dll1 interaction by addition of soluble DLL1, or mAbs against Dll1 or Notch2. Taken together, these results indicate that Notch receptor(s) and Dll1 directly promote the adhesion of MCs to stromal cells by acting as adhesion molecules. This appreciation that Notch receptor-ligand interactions have an adhesion function will provide an important clue to molecular basis of accumulation of MCs to inflammatory sites.

Peanut-induced intestinal allergy is mediated through a mast cell-IgE-FcepsilonRI-IL-13 pathway

BACKGROUND

Although implicated in the disease, the specific contributions of FcepsilonRI and IL-13 to the pathogenesis of peanut-induced intestinal allergy are not well defined.

OBJECTIVES

We sought to determine the contributions of FcepsilonRI, IL-13, and mast cells to the development of intestinal mucosal responses in a murine model of peanut-induced intestinal allergy.

METHODS

Sensitized wild-type (WT), FcepsilonRI-deficient (FcepsilonRI(-/-)), and mast cell-deficient (Kit(W-sh/W-sh)) mice received peanut orally every day for 1 week. Bone marrow-derived mast cells (BMMCs) from WT, FcepsilonRI(-/-), IL-4(-/-), IL-13(-/-), and IL-4/IL-13(-/-) mice were differentiated and transferred into WT, FcepsilonRI(-/-), and Kit(W-sh/W-sh) recipients. BMMCs from WT and UBI-GFP/BL6 mice were differentiated and transferred into WT and Kit(W-sh/W-sh) mice. Blockade of IL-13 was achieved by using IL-13 receptor alpha2 (IL-13Ralpha2)-IgG fusion protein.

RESULTS

FcepsilonRI(-/-) mice showed decreased intestinal inflammation (mast cell and eosinophil numbers) and goblet cell metaplasia and reduced levels of IL4, IL6, IL13, and IL17A mRNA expression in the jejunum. Transfer of WT BMMCs to FcepsilonRI(-/-) recipients restored their ability to develop intestinal allergic responses unlike transfer of FcepsilonRI(-/-), IL-13(-/-), or IL-4/IL-13(-/-) BMMCs. FcepsilonRI(-/-) mice exhibited lower IL-13 levels and treatment of WT mice with IL-13 receptor alpha2 prevented peanut-induced intestinal allergy and inflammation.

CONCLUSIONS

These data indicate that the development of peanut-induced intestinal allergy is mediated through a mast cell-dependent IgE-FcepsilonRI-IL-13 pathway. Targeting IL-13 might be a potential treatment for IgE-mediated peanut-induced allergic responses in the intestine.

Lipopolysaccharide from Porphyromonas Gingivalis Stimulates Rat Mast Cells to Cysteinyl Leukotriene Generation and Upregulates Toll-like Receptor −2 and −4 Expression

Mast cells are found in all tissues of the oral cavity and it is suggested that they take part in the development of oral inflammation. As Porhyromonas gingivalis is widely recognized as a major pathogen in the development and progression of gingivitis and periodontitis, the aim of our study is to determine the effect of P. gingivalis lipopolysaccharide (LPS) on mast cell degranulation, cysteinyl leukotriene (cysLT) generation, and migration, as well as Toll-like receptor (TLR)−2 and −4 expression. Experiments were carried out in vitro on rat peritoneal mast cells. LPS-induced mast cell histamine release was estimated by a spectrofluorometric method and cysLT generation by ELISA test. Mast cell migration in response to this antigen was examined according to Boyden's modified method and TLR expression was determined by flow cytometry. We found that P. gingivalis LPS did not induce mast cell degranulation and histamine release. However, activation of mast cells with this bacterial antigen resulted in generation and release of significant amounts of cysLTs. We also documented that LPS from P. gingivalis did not stimulate mast cell migration, even in the presence of laminin, whereas it strongly upregulated TLR2 and TLR4 expression on mast cells. Observations that P. gingivalis LPS activates mast cells to generate and release proinflammatory mediators such as cysLTs and modulates TLR2 and TLR4 expression indicates that these cells might be involved in the emergency of inflammatory processes evolved in response to P. gingivalis infection.

Partial hepatectomy, partial portal vein stenosis and mesenteric lymphadenectomy increase splanchnic mast cell infiltration in the rat

It is currently believed that portal hypertension induces an inflammatory response in which mast cells may be involved. The aim of this study was to verify the involvement of the intestinal submucosal and mesenteric lymph node mast cells in the splanchnic inflammatory response related to portal hypertension. Mast cell infiltration in the intestine (duodenum, jejunum, ileum, caecum and distal colon) and in the mesenteric lymph node complex (MLC) was measured using a stereological method in sham-operated rats (SO; n = 12), in two experimental models of portal hypertension, chronic (triple partial portal vein ligation, TPVL; n = 12) and transient (microsurgical partial hepatectomy; n = 12) and in rats in which the MLC was resected (n = 12). The small and large bowel submucosal infiltration increases in MLC-resected rats (p = 0.0001), in TPVL rats (p = 0.0001) and in rats with partial hepatectomy (p = 0.0001). An extensive mast cell infiltration in the MLC (p = 0.0001) was found in TPVL rats and in rats with partial hepatectomy (347.40+/-45.25 and 351.92+/-99.28/mm(3), respectively) in relation to sham-operated rats (135.27+/-30.28/mm(3)). We conclude that mast cells could be involved in the splanchnic alterations developed in the surgical experimental models of portal hypertension studied.

I787 provides signals for c-Kit receptor internalization and functionality that control mast cell survival and development

Mast cell (MC) differentiation, survival, and activation are controlled by the membrane tyrosine kinase c-Kit upon interaction with stem cell factor (SCF). Here we describe a single point mutation induced by N-ethyl-N-nitrosurea (ENU) mutagenesis in C57BL/6J mice-an A to T transversion at position 2388 (exon 17) of the c-Kit gene, resulting in the isoleucine 787 substitution by phenylalanine (787F), and analyze the consequences of this mutation for ligand binding, signaling, and MC development. The Kit(787F/787F) mice carrying the single amino acid exchange of c-Kit lacks both mucosal and connective tissue-type MCs. In bone marrow-derived mast cells (BMMCs), the 787F mutation does not affect SCF binding and c-Kit receptor shedding, but strongly impairs SCF-induced cytokine production, degranulation enhancement, and apoptosis rescue. Interestingly, c-Kit downstream signaling in 787F BMMCs is normally initiated (Erk1/2 and p38 activation as well as c-Kit autophosphorylation) but fails to be sustained thereafter. In addition, 787F c-Kit does not efficiently mediate Cbl activation, leading to the absence of subsequent receptor ubiquitination and impaired c-Kit internalization. Thus, I787 provides nonredundant signals for c-Kit internalization and functionality.

Effects of mast cell modulation on early host response to implanted synthetic meshes

INTRODUCTION

Mast cells (MCs) and their products (e.g., histamine, serotonin, heparin, prostaglandins, cytokines, etc.) play key roles in controlling local inflammation, wound healing, and foreign body reactions in vivo. Investigation of the role of MCs in mediating local tissue responses to synthetic hernia meshes has been very limited to date. We aimed to determine the effects of MCs/MC products in mice undergoing synthetic mesh implantation.

MATERIALS AND METHODS

Circular samples (5 mm) of heavyweight microporous polypropylene (Trelex), midweight microporous polypropylene (ProLite), lightweight macroporous polypropylene with poliglecaprone (Ultrapro), and 3-dimensional macroporous polyester (Parietex) meshes were implanted subcutaneously in C57BL/6 J mice with and without cromolyn (MC stabilizer/suppressant) treatment (50 mg/kg, daily IP). Two weeks post-implantation, all meshes were explanted and evaluated histologically using H&E and trichrome stains.

RESULTS

Chronic inflammation was focused around individual mesh fibers; inter-fiber inflammation and fibrosis diminished as mesh porosity increased. MC accumulation was seen at the periphery of inflammatory reactions, and in association with mesh-induced fibrosis and neovascularization. Cromolyn treatment resulted in significantly decreased fibrotic responses to all four meshes and reduced inflammation induced by Trelex, ProLite, and Parietex meshes but not Ultrapro.

CONCLUSION

We demonstrated that MCs play important roles in mesh-induced host tissue reactions. Blocking MC degranulation decreased early inflammation and fibrosis induced by most synthetic meshes in this study. Further evaluation and understanding of the role of MCs in mesh-induced tissue reactions will provide new therapeutic approaches to enhance the biocompatibility of surgical meshes and ultimately improve clinical outcomes in patients undergoing hernia repair with synthetic biomaterials.

Leukotriene B(4) BLT receptor signaling regulates the level and stability of cyclooxygenase-2 (COX-2) mRNA through restricted activation of Ras/Raf/ERK/p42 AUF1 pathway

Recent studies suggest that active resolution of the inflammatory response in animal models of arthritis may involve leukotriene B(4) (LTB(4))-dependent stimulation of "intermediate" prostaglandin production, which in turn favors the synthesis of "downstream" anti-inflammatory and pro-resolving lipoxins, resolvins, and protectins. We explored a putative mechanism involving LTB(4)-dependent control of cyclooxygenase-2 (COX-2) expression, the rate-limiting step in inflammatory prostaglandin biosynthesis. Indeed, LTB(4) potently up-regulated/stabilized interleukin-1beta-induced COX-2 mRNA and protein expression under conditions of COX-2 inhibitor-dependent blockade of PGE(2) release in human synovial fibroblasts (EC(50) = 16.5 + or - 1.7 nm for mRNA; 19 + or - 2.4 nm for protein, n = 4). The latter response was pertussis toxin-sensitive, and semi-quantitative reverse transcription-PCR confirmed the quantitative predominance of the BLT2 receptor. Transfection experiments, using human COX-2 promoter plasmids and chimeric luciferase-COX-2 mRNA 3'-untranslated region (3'-UTR) reporter constructs, revealed that LTB(4) exerted its stabilizing effect at the post-transcriptional level through a 116-bp adenylate/uridylate-rich sequence in the proximal region of the COX-2 3'-UTR. Using luciferase-COX-2 mRNA 3'-UTR reporter constructs and Ras/c-Raf expression and mutant constructs, we showed that the Ras/c-Raf/MEK1/2/ERK1/2 signaling pathway mediated LTB(4)-dependent COX-2 mRNA stabilization. Knockdown experiments with specific short hairpin RNAs confirmed that LTB(4) stabilization of COX-2 mRNA was apparently mediated through the RNA-binding protein, p42 AUF1. The nuclear export of p42 AUF1 was driven by c-Raf/MEK1/2/ERK1/2 signaling and sensitive to leptomycin B treatment, suggesting a CRM1-dependent mechanism. We conclude that LTB(4) may support the resolution phase of the inflammatory response by stabilizing COX-2, ensuring a reservoir of ambient pro-resolution lipid mediators.

Advances in mast cell biology: new understanding of heterogeneity and function

Mast cells are classically viewed as effector cells of IgE-mediated allergic diseases. However, over the last decade our understanding has been enriched about their roles in host defense, innate and adaptive immune responses, and in homeostatic responses, angiogenesis, wound healing, tissue remodeling, and immunoregulation. Despite impressive progress, there are large gaps in our understanding of their phenotypic heterogeneity, regulatory mechanisms involved, and functional significance. This review summarizes our knowledge of mast cells in innate and acquired immunity, allergic inflammation and tissue homeostasis, as well as some of the regulatory mechanisms that control mast cell development, phenotypic determination, and function, particularly in the context of mucosal surfaces.

Targeting CD44 in mast cell regulation

IMPORTANCE OF THE FIELD

Accumulating evidence suggests that mast cells are involved in a wide variety of immune responses including chronic inflammation, immune tolerance and tumor immunity. Mast cells originate from hematopoietic stem cells and undergo terminal differentiation in the tissues, in which they are ultimately resident. Heterogeneity of tissue mast cells is, therefore, one of the key concepts for a better understanding of various immune responses.

AREAS COVERED IN THIS REVIEW

This review describes the candidate genes involved in regulation of cutaneous mast cell differentiation, with a particular attention to CD44, which is the primary receptor for hyaluronan.

WHAT THE READER WILL GAIN

CD44 is involved in various aspects of cutaneous inflammation. Regarding mast cells, CD44 is upregulated upon differentiation and maturation of mast cells, and plays a critical role in regulation of cutaneous mast cell number. Since both degradation and decrease of hyaluronan are often observed upon chronic inflammation, CD44 might be involved in modulation of local immune responses through regulation of cutaneous mast cell functions.

TAKE HOME MESSAGE

Understanding of cutaneous immune responses should require clarification of local mast cell functions, a part of which is regulated by extracellular matrix components and their membrane receptors.

Signaling of c-kit in dendritic cells influences adaptive immunity

The binding of the receptor tyrosine kinase, c-kit, to its ligand, stem cell factor (SCF), mediates numerous biological functions. Important roles for c-kit in hematopoiesis, melanogenesis, erythropoiesis, spermatogenesis, and carcinogenesis are well documented. Similarly, activation of granulocytes, mast cells, and of eosinophils in particular, by c-kit ligation has long been known to result in degranulation with concomitant release of pro-inflammatory mediators, including cytokines. However, recent work from a number of laboratories, including our own, highlights previously unappreciated functions for c-kit in immunologic processes. These novel findings strongly suggest that signaling through the c-kit-SCF axis could have a significant impact on the pathogenesis of diseases associated with an immunologic component. In our own studies, c-kit upregulation on dendritic cells via T helper (Th)2- and Th17-inducing stimuli led to c-kit activation and immune skewing toward these T helper subsets and away from Th1 responses. Others have shown that dendritic cell treatment with inhibitors of c-kit activation, such as imatinib mesylate (Gleevec), favored breaking of T-cell tolerance, skewing of responses toward production of Th1 cytokines, and activation of natural killer cells. These data all indicate that deeper understanding of, and ability to control, the c-kit-SCF axis could lead to improved treatment modalities aimed at redirecting unwanted and/or deleterious immune responses in a wide variety of conditions.

Cardiac mast cells cause atrial fibrillation through PDGF-A-mediated fibrosis in pressure-overloaded mouse hearts

Atrial fibrillation (AF) is a common arrhythmia that increases the risk of stroke and heart failure. Here, we have shown that mast cells, key mediators of allergic and immune responses, are critically involved in AF pathogenesis in stressed mouse hearts. Pressure overload induced mast cell infiltration and fibrosis in the atrium and enhanced AF susceptibility following atrial burst stimulation. Both atrial fibrosis and AF inducibility were attenuated by stabilization of mast cells with cromolyn and by BM reconstitution from mast cell-deficient WBB6F1-KitW/W-v mice. When cocultured with cardiac myocytes or fibroblasts, BM-derived mouse mast cells increased platelet-derived growth factor A (PDGF-A) synthesis and promoted cell proliferation and collagen expression in cardiac fibroblasts. These changes were abolished by treatment with a neutralizing antibody specific for PDGF alpha-receptor (PDGFR-alpha). Consistent with these data, upregulation of atrial Pdgfa expression in pressure-overloaded hearts was suppressed by BM reconstitution from WBB6F1-KitW/W-v mice. Furthermore, injection of the neutralizing PDGFR-alpha-specific antibody attenuated atrial fibrosis and AF inducibility in pressure-overloaded hearts, whereas administration of homodimer of PDGF-A (PDGF-AA) promoted atrial fibrosis and enhanced AF susceptibility in normal hearts. Our results suggest a crucial role for mast cells in AF and highlight a potential application of controlling the mast cell/PDGF-A axis to achieve upstream prevention of AF in stressed hearts.

Presence and quantification of mast cells in the gingiva of cats with tooth resorption, periodontitis and chronic stomatitis

OBJECTIVE

Mast cells are tissue-dwelling granule-containing immune cells that play a pivotal role in the pathogenesis of inflammation and other processes. The three most common orodental disorders in cats are periodontitis, feline resorptive lesions (FRL), and chronic gingivostomatitis (FCGS). The presence and density of mast cells in the gingiva has been established in healthy cats but not in cats affected by FRL, FCGS or periodontitis. The aim of the present study was to document and quantify the presence of mast cells in the gingiva adjacent to teeth affected by FRL, FCGS or chronic periodontitis.

METHODS

Samples from the gingiva of 32 cats affected by FRL, FCGS or periodontitis were obtained and compared to samples obtained from 7 specific pathogen-free (SPF) cats. Evaluation of mast cells and the inflammatory infiltrate were performed on hematoxylin and eosin, and toluidine blue stained sections.

RESULTS

Mast cells densities were significantly increased in gingival tissues adjacent to teeth affected by FRL, FCGS or periodontitis in comparison to SPF samples. There were no significant differences between gingival tissues of the FRL, FCGS and periodontitis groups. However, the relative inflammatory score in the FRL group was significantly lower as compared to the FCGS or periodontitis groups, yet with similar density of mast cells.

CONCLUSION

In the gingiva of cats affected with FRL, FCGS or periodontitis, there is an increase in the number of mast cells. The high number of mast cells in the FRL group and concurrent mild inflammatory reaction suggests the notion that mast cells may potentially play role in the pathogenesis of FRL.

Splanchnic Th(2) and Th(1) cytokine redistribution in microsurgical cholestatic rats

BACKGROUND

Long-term extrahepatic cholestasis in the rat induces ductular proliferation and fibrosis in the liver, portal hypertension, splenomegaly, portosystemic collateral circulation, and ascites. These splanchnic alterations could have an inflammatory pathophysiology.

MATERIAL AND METHODS

We measured serum levels of hepatobiliary injury markers and the acute phase proteins, alpha-1-major acid protein (alpha(1)-MAP) and alpha-1-acid glycoprotein (alpha(1)-GPA) in rats 6 wk after microsurgical extrahepatic cholestasis. We also assayed Th(1) (TNF-alpha and IL-1beta) and Th(2) (IL-4 and IL-10) cytokine levels in the liver, ileum, spleen, and mesenteric lymph complex by enzyme-linked immunosorbent assay (ELISA) techniques. Liver fibrosis was measured by Sirius red stain and by using an image system computer-assisted method and mast cell liver infiltration by Giemsa stain.

RESULTS

The cholestatic rats showed an increase (P<0.001) in serum levels of bile acids, total and direct bilirubin, AST, ALT, AST/ALT index, gamma-GT, alkaline phosphatase, alpha(1)- MAP, alpha(1)-GPA, and LDH (P<0.05) in relation to sham-operated rats. TNF-alpha, IL-1beta, IL-4, and IL-10 increased in the ileum (P<0.01) and mesenteric lymph complex (P<0.001), and decreased in the liver (P<0.001). A marked bile proliferation associated with fibrosis (P<0.001) and mast cell infiltration was also shown in the liver of cholestatic rats.

CONCLUSION

The splanchnic redistribution of cytokines, with an increase of Th(1) and Th(2) production in the small bowel and in the mesenteric lymph complex, supports the key role of inflammatory mechanisms in rats with secondary biliary fibrosis.

Mast cells contribute to the stromal microenvironment in mammary gland branching morphogenesis

The stromal microenvironment regulates mammary gland branching morphogenesis. We have observed that mast cells are present in the mammary gland throughout its postnatal development and, in particular, are found around the terminal end buds and ductal epithelium of the pubertal gland. Mast cells contribute to allergy, inflammatory diseases, and cancer development but have not been implicated in normal development. Genetic and pharmacological disruption of mast cell function in the mammary gland revealed that mast cells are involved in rapid proliferation and normal duct branching during puberty, and this effect is independent of macrophage recruitment, which also regulates mammary gland development. For mast cells to exert their effects on normal morphogenesis required activation of their serine proteases and degranulation. Our observations reveal a novel role for mast cells during normal pubertal development in the mammary gland.

Mast cells in atopic dermatitis

Mast cells play as the major effector cells in immediate hypersensitivity through activation via the high-affinity IgE receptor, Fc epsilon RI, although many other functions have recently been discovered for this cell type. Given the broad array of proinflammatory mediators secreted from Fc epsilon RI-activated mast cells, as well as sensitization to allergens, IgE elevation, and increased mast cells in a majority of atopic dermatitis patients, mast cells are believed to be involved in the pathogenesis of atopic dermatitis. Numerous animal models have been used to study this epidemic disease. Here we review the recent progress to synthesize our current understanding of this disease and potential mechanisms for a mast cell's role in the disease.

Innate immunity and allergy in the skin

The skin as an organ has many functions of which the protection against environmental threats may be the most important. Recent investigations have broadened our understanding of the cellular mechanisms of host defense responses of the skin. Interestingly, the three key effector cells of cutaneous innate immunity, that is keratinocytes, dendritic cells, and mast cells, are also critically involved in the elicitation of allergic reactions. Keratinocytes keep bacteria and other pathogens from invading the host, but they can also promote the development of allergic asthma by releasing thymic stromal lymphopoietin. Dendritic cells in the skin are crucial for the detection and processing of allergens and thus for the development of allergies, but they are also essential in host defense against bacteria, for example by releasing cytokines such as TNF and IL-17. Mast cells, the most important effector cells in immediate hypersensitivity type allergic reactions, effectively combat bacterial infections, for example by releasing antimicrobial peptides.

Exploring the role of mast cells in eosinophilic esophagitis

The mast cell plays a critical role in allergic responses in the gastrointestinal tract and other sites. Emerging evidence indicates that mast cells also participate in the pathogenesis of eosinophilic esophagitis, although their precise role has not been defined. This article reviews the biology of mast cells and examines the potential involvement of the cell as an effector of the inflammatory response and tissue remodeling, and as a cell that has the potential to function as an immunomodulator and limit inflammation.

The foreign body reaction in T-cell-deficient mice

The role(s) of T lymphocytes in the foreign body response has not been thoroughly elucidated. Lymphocytes are known to augment macrophage adhesion and fusion in vitro. Furthermore, T lymphocytes are a possible source of the cytokines, IL-4 and IL-13, which induce macrophage fusion. In this study, we used BALB/c mice and BALB/c (nu/nu) nude mice to investigate foreign body giant cell (FBGC) formation in a T-cell-deficient setting. Mice were implanted with Elasthane 80A (PEU), silicone rubber (SR), or poly(ethylene terephthalate) (PET) for 7, 14, or 21 days using the cage implant system. Exudate cells and IL-4 and IL-13 levels in exudate supernatants were analyzed by flow cytometry and a multiplex immunoassay, respectively, at Days 7, 14, and 21. Macrophage adhesion and fusion on material surfaces were analyzed using optical microscopy. T-cell-deficient mice had lower total leukocyte concentrations at the biomaterial implant site at all time points. Adherent cell density was comparable between normal and T-cell-deficient mice except in the PEU group at Day 21. However, percent fusion, average nuclei per FBGC, and FBGC morphology were comparable between normal and T-cell-deficient mice. IL-4 was not detected in any sample, but IL-13 levels were also comparable between normal and T-cell-deficient mice indicating Th2-polarized T-cells are not the sole source of this cytokine. We have shown that there are pathways that do not require thymus-matured T lymphocytes, which lead to a normal foreign body response to biomaterials in a murine model.

Murine mast cells secrete a unique profile of cytokines and prostaglandins in response to distinct TLR2 ligands

Mast cells (MCs) are important effector cells in host defense against bacteria. In the course of a bacterial infection, MCs can be activated by various mechanisms, i.e. bacterial toxins, endogenously produced infection-associated peptides or via complement receptors, fimbrial adhesion molecules and toll-like receptors (TLRs). While some of these mechanisms are well established, the effects of TLR2 ligand-driven MC activation are far less understood. Here, we show that murine mature connective tissue-type MCs, but not immature bone marrow-derived cultured mast cells, express significant amounts of full length TLR2 on their surface. Activation by various TLR2 ligands only induces the selective release of cytokines in peritoneum-derived cultured mast cells (PCMCs) with preferential secretion of pro-inflammatory cytokines (IL-6 > IL-17 > IFN-gamma TNF > IL-1 > GM-CSF) upon stimulation with lipoteichoic acid (LTA). This response is much lower in PCMCs stimulated with the TLR2/6 agonist macrophage-activating lipopeptide-2 (MALP-2), which most prominently triggers the release of the immunomodulatory cytokine IL-10. Furthermore, only LTA but not MALP-2 induces prostaglandin D2 secretion which is again restricted to the mature MC phenotype. These findings suggest that TLR2 ligand-mediated activation of mature MCs, i.e. tissue-residing cells, which most likely occurs during infection, can selectively raise a potent inflammatory or anti-inflammatory response, depending on TLRs which are engaged.

Mast cells: novel clinical perspectives from recent insights

Mast cells are still generally viewed as mediators of type I allergic or pseudoallergic reactions. Research over the past 10 years revealed that our view was too small and that mast cells are of key importance in innate immunity and also types II, III and IV adaptive immune reactions. Understanding their role in modulating and amplifying of inflammatory responses provides important insights into the pathogenesis of skin diseases such as psoriasis, atopic dermatitis, bullous pemphigoid or the control of infections. This helps us to understand the course of these diseases, their trigger mechanisms, and, the new role of agents, which can modulate the function of mast cells. These insights will help to develop new therapeutic approaches.

Mast cells in atherogenesis: actions and reactions

Mast cells (better known as allergy cells) are proinflammatory effector cells present in the human arterial intima and in evolving atherosclerotic lesions. Experiments in vitro, in vivo experiments in animals, and immunohistologic studies of human coronary samples have uncovered mechanisms by which activated mast cells could participate in the development of the lesions. When activated, mast cells acutely expel a fraction of their cytoplasmic granules, which are filled with a wide selection of heparin-bound preformed mediators. These include histamine, neutral proteases, growth factors, and proinflammatory cytokines. The microenvironmental targets of these effector molecules are various lipoprotein particles in the intimal fluid, components of the extracellular matrix, and intimal cells neighboring the activated mast cells. Importantly, sustained selective release of proinflammatory mediators without degranulation may also occur at sites of chronic inflammation. The activities of the various mediators are suggested to contribute to fatty streak formation and to the generation of unstable plaques susceptible to rupture. Thus, mast cells appear to provide a novel link between inflammation and atherogenesis.

Combination of peritumoral mast cells and T-regulatory cells predicts prognosis of hepatocellular carcinoma

The peritumoral inflammatory environment is critical for the progression of intrahepatic recurrence of hepatocellular carcinoma (HCC) after curative resections. Here, we investigated the relevance of peritumoral mast cells (MCs) to HCC outcomes. Peritumoral tryptase(+) MCs in addition to Foxp3(+) T-regulatory cells (Tregs) were evaluated using immunohistochemistry enumeration in tissue microarrays containing 207 randomly selected HCC patients. Clinicopathological factors and postoperative outcomes were compared between high and low subgroups of MCs or Tregs. Compared to low denstiy, higher peritumoral MCs were associated with poorer clinical outcomes, and independently related to elevated 5-year recurrence incidence (54.1%vs 39.2%, P = 0.026). High-dense MCs were especially related to increased probability of early recurrence (within 2 years) (P = 0.004). We also found that peritumoral Tregs were positively correlated with MCs in density (r = 0.353, P < 0.001) and reversely related to HCC outcomes. Notably, MCs in combination with Tregs displayed better prognostic performances than MCs alone (area under curve [AUC](survival) = 0.629 vs 0.589, AUC(recurrence) = 0.632 vs 0.591). Moreover, MCs were positively correlated to alanine aminotransferase, a serum inflammatory marker (P = 0.014). Therefore, peritumoral MCs are promising prognostic parameters for HCC mainly through inflammation response-related mechanisms, and we propose that MCs and Tregs may cooperate with each other and result in poorer prognosis.

Fc(epsilon)RI and FcgammaRIII/CD16 differentially regulate atopic dermatitis in mice

The high-affinity IgE receptor Fc(epsilon)RI and, in some models, the low-affinity IgG receptor Fc(epsilon)RIIII/CD16 play an essential role in allergic diseases. In human skin, they are present on APCs and effector cells recruited into the inflamed dermis. FcRgamma is a subunit shared, among other FcRs, by Fc(epsilon)RI and CD16 and is essential to their assembly and signal transduction. Using an experimental model reproducing some features of human atopic dermatitis and specific FcR-deficient mice, we have herein delineated the respective contribution of Fc(epsilon)RIand Fc(epsilon)RIII/CD16 to the pathology. We demonstrate that symptoms of atopic dermatitis are completely absent in FcRgamma-deficient animals but only partially inhibited in either Fc(epsilon)RI- or FcgammaRIII/CD16-deficient animals. Absence or attenuation of the pathology is correlated to increased skin expression of regulatory IL-10 and Foxp3. While Fc(epsilon)RI controls both Th1 and Th2 skin response, mast cell recruitment into draining lymph nodes and IgE production, CD16 regulates only Th2 skin response, as well as T cell proliferation and IgG1 production. This isotype-specific regulation by the cognate FcR is associated to a differential regulation of IL-4 and IL-21 expression in the draining lymph nodes. Fc(epsilon)RIand CD16 thus contribute to atopic dermatitis but differentially regulate immune responses associated with the disease. Targeting both IgE/Fc(epsilon)RI and IgG/CD16 interactions might represent an efficient therapeutic strategy for allergic diseases.

Influence of Pseudomonas aeruginosa quorum sensing signal molecule N-(3-oxododecanoyl) homoserine lactone on mast cells

Quorum sensing system is a cell-to-cell communication system that plays a pivotal role in virulence expression in bacteria. Recent advances have demonstrated that the Pseudomonas aeruginosa quorum sensing molecule, N-3-oxododecanoyl homoserine lactone (3OC(12)-HSL), exerts effects on mammalian cells and modulates host immune response. Mast cells (MCs) are strategically located in the tissues that are constantly exposed to external stimulus. Therefore, it is very much possible that 3OC(12)-HSL may interact with MCs. Little is known, however, about specific effects of 3OC(12)-HSL on MCs. To address this, we investigated the influence of 3OC(12)-HSL on cell viability, apoptosis, intracellular calcium and cytokine release in MCs. We found that at high concentrations (100 microM), 3OC(12)-HSL inhibited proliferation and induced apoptosis in P815. The 3OC(12)-HSL treatment significantly increased intracellular calcium release in both P815 and HMC-1. We also observed that 3OC(12)-HSL-induced histamine release and degranulation in HMC-1 cells. Furthermore, 3OC(12)-HSL-induced IL-6 production at lower concentrations (6.25-12.5 microM) but steadily reduced IL-6 production at high concentration (50-100 muM). These data demonstrate that P. aeruginosa 3OC(12)-HSL affects MCs function.

Involvement of CD44 in mast cell proliferation during terminal differentiation

By using the recently established culture system that reproduces the terminal differentiation process of connective tissue-type mast cells, we found significant transcriptional induction of CD44. As CD44 is a primary receptor for hyaluronan (HA), which is one of the major extracellular matrix components, we investigated the role of CD44 in cutaneous mast cells. When co-cultured with fibroblasts, mouse bone marrow-derived cultured mast cells (BMMCs) were found to form clusters in an HA-dependent manner. As compared with BMMCs derived from the wild-type mice, those from the CD44(-/-) mice exhibited impaired growth during the co-cultured period. Furthermore, in the peritoneal cavities and ear tissues, mature mast cells were fewer in number in the CD44(-/-) mice than in the wild-type mice. We investigated roles of CD44 in mast cell proliferation by reconstituting BMMCs into the tissues of mast cell-deficient, Kit(W)/Kit(W-v) mice, and found that the number of metachromatic cells upon acidic toluidine blue staining in the tissues transplanted with CD44(-/-) BMMCs was not significantly changed for 10 weeks, whereas that in the tissues transplanted with the CD44(+/+) BMMCs was significantly increased. These results suggest that CD44 plays a crucial role in the regulation of the cutaneous mast cell number.

Murine fetal skin-derived cultured mast cells: a useful tool for discovering functions of skin mast cells

Mast cells are widely distributed throughout the body, being preferentially localized at host-environment interfaces. They have long been known as major effector cells in IgE-mediated allergic responses. However, accumulating evidence has provided many new insights into their functions. They are now known to be involved in diverse pathological processes, for example, innate and adaptive immunity. Utility of mast cell-deficient mice and mast cell-knock-in mice has provided powerful models to demonstrate compelling evidence for their in vivo relevance. Conversely, primary cultures of tissue-derived mast cells provide excellent models for in vitro studies of functions at both cellular and molecular levels. Because mast cells exhibit phenotypical and functional heterogeneity in different anatomical sites, it is important to obtain tissue-specific mast cells to clarify their function in tissue. In this regard, researchers have established several methods to prepare mast cells from different tissues, which are technically difficult to obtain at high purity and yield. To overcome these difficulties, we have developed a primary culture system to obtain large numbers of mast cells at high purity from murine fetal skin. In this review, we describe characteristics of such mast cells and their utility in mast cell biology.

Mast cells decrease renal fibrosis in unilateral ureteral obstruction

Mast cells regulate both inflammatory responses and tissue repair in human diseases but there are conflicting reports on the role of these cells in the pathogenesis of various kidney diseases. Here we measured mast cell function in unilateral ureteral obstruction, a well-characterized model of renal fibrosis, using Kit(W)/Kit(W-v) mice genetically deficient in mast cells, wild-type mice, and deficient mice reconstituted by adoptive transfer with mast cells from the wild-type animals. Mast cell-deficient mice had higher levels of renal tubular damage, more stromal fibrosis, higher numbers of infiltrating ERHR3-positive macrophages and CD3-positive T cells, and higher tissue levels of profibrotic transforming growth factor-beta1 than wild-type mice or mice reconstituted by adoptive transfer of mast cells 3 weeks after ureteral obstruction. Similarly, while wild-type and adoptively transferred mice had increased alpha-smooth muscle actin and decreased E-cadherin expression, which are indicators of epithelial-mesenchymal transition, the obstructed kidneys of the mast cell-deficient mice had significant attenuation of those indicators. Thus, our study suggests that mast cells protect the kidney against fibrosis by modulation of inflammatory cell infiltration and by transforming growth factor-beta1-driven epithelial-to-mesenchymal transitions.

Mast cells in tumor growth: angiogenesis, tissue remodelling and immune-modulation

There is a growing acceptance that tumor-infiltrating myeloid cells play an active role in tumor growth and mast cells are one of the earliest cell types to infiltrate developing tumors. Mast cells accumulate at the boundary between healthy tissues and malignancies and are often found in close association with blood vessels within the tumor microenvironment. They express many pro-angiogenic compounds, and may play an early role in angiogenesis within developing tumors. Mast cells also remodel extracellular matrix during wound healing, and this function is subverted in tumor growth, promoting tumor spread and metastasis. In addition, mast cells modulate immune responses by dampening immune rejection or directing immune cell recruitment, depending on local stimuli. In this review, we focus on key roles for mast cells in angiogenesis, tissue remodelling and immune modulation and highlight recent findings on the integral role that mast cells play in tumor growth. New findings suggest that mast cells may serve as a novel therapeutic target for cancer treatment and that inhibiting mast cell function may lead to tumor regression.

Notch signaling confers antigen-presenting cell functions on mast cells

BACKGROUND

Notch signaling is involved in cell fate determination along with the development of the immune system. However, very little is known about the role for Notch signaling in mast cells.

OBJECTIVE

We investigated the role of Notch signaling in mast cell functions.

METHODS

After mouse bone marrow-derived mast cells (BMMCs) or peritoneal mast cells (PMCs) were cocultured with mouse Notch ligand-expressing chinese hamster ovary cells for 5 days, we examined the mast cell surface expressions of MHC-II molecules and OX40 ligand (OX40L), Fc epsilon RI-mediated cytokine production, and the effects of the mast cells on proliferation and differentiation of naive CD4(+) T cells in vitro.

RESULTS

We showed that BMMCs and PMCs constitutively expressed Notch1 and Notch2 proteins on the cell surface. We also found that Delta-like 1 (Dll1)/Notch signaling induced the expression of MHC-II and upregulated the expression level of OX40L on the surface of the mast cells. Dll1/Notch signaling augmented Fc epsilon RI-mediated IL-4, IL-6, IL-13, and TNF production by BMMCs. Dll1-stimulated MHC-II(+)OX40L(high) BMMCs promoted proliferation of naive CD4(+) T cells and their differentiation into T(H)2 cells producing IL-4, IL-5, IL-10, and IL-13.

CONCLUSION

Dll1/Notch signaling confers the functions as an antigen-presenting cell on mast cells, which preferentially induce the differentiation of T(H)2.

Our perception of the mast cell from Paul Ehrlich to now

Just over a century ago Paul Ehrlich received the Nobel Prize for his studies of immunity. This review describes one of his legacies, the histochemical description of the mast cell, and the research that has ensued since then. After a long period of largely descriptive studies, which revealed little about the biological role of the mast cell, the field was galvanized in the 1950s by the recognition that the mast cell was the main repository of histamine and a key participant in anaphylactic reactions. Although the mast cell was long-viewed in these terms, recent research has now shown that the mast cell also plays a key role in innate and adaptive immune responses, autoimmune disease, and possibly tissue homeostasis by virtue of its expression of a diverse array of receptors and biologically active products. In addition, the responsiveness of mast cells to immunological and pathological stimulants is highly modulated by the tissue cytokine environment and by synergistic, or inhibitory, interactions among the various mast cell receptor systems. This once enigmatic cell of Paul Ehrlich has proved to be both adaptable and multifunctional.