Mast cells: versatile regulators of inflammation, tissue remodeling, host defense and homeostasis

The role of mast cells in atrial natriuretic peptide-induced cutaneous inflammation

Atrial natriuretic peptide (ANP) is widely distributed throughout the heart, skin, gastrointestinal and genital tracts, and nervous and immune systems. ANP acts to mediate vasodilation and induces mast cell activation in both human and rats in vitro. However, the mechanisms of ANP-induced mast cell activation, the extent to which ANP can induce tissue swelling, mast cell degranulation, and granulocyte infiltration in mouse skin are not fully understood. This issue was investigated by treatment with ANP in rat peritoneal mast cells (RPMCs) and mouse peritoneal mast cells (MPMCs) in vitro and by injection of ANP into the skin of congenic normal WBB6F1/J-Kit+/Kit+ +/+, genetically mast cell-deficient WBB6F1/J-Kit(W)/Kit(W-v) (W/W(v)) and mast cell-engrafted W/W(v) (BMCMC→W/W(v)) mice in vivo. ANP induced the release of histamine and TNF-α from RPMCs and enhanced serotonin release from MPMCs, in a dose-dependent fashion, as well as reduced cAMP level of RPMCs in vitro. In +/+ mice, ANP induced significant tissue swelling, mast cell degranulation, and granulocyte infiltration in a dose-dependent manner, whereas not in genetically mast cell-deficient W/W(v) mice. However, ANP-induced cutaneous inflammation has been restored in BMCMC→W/W(v) mice. These data indicate that mast cells play a key role in the ANP-induced cutaneous inflammation.

Ischemia/reperfusion injury: The role of immune cells

Ischemia/reperfusion (I/R) injury is an inflammatory condition that is characterized by innate immunity and an adaptive immune response. This review is focused on the acute inflammatory response in I/R injury, and also the adaptive immunological mechanisms in chronic ischemic disease that lead to increased vulnerability during acute events, in relation to the cell types that have been shown to mediate innate immunity to an adaptive immune response in I/R, specifically myocardial infarction. Novel aspects are also highlighted in respect to the mechanisms within the cardiovascular system and cardiovascular risk factors that may be involved in the inflammatory response accompanying myocardial infarction. Experimental myocardial I/R has suggested that immune cells may mediate reperfusion injury. Specifically, monocytes, macrophages, T-cells, mast cells, platelets and endothelial cells are discussed with reference to the complement cascade, toll-like receptors, cytokines, oxidative stress, renin-angiotensin system, and in reference to the microvascular system in the signaling mechanisms of I/R. Finally, the findings of the data summarized in this review are most important for possible translation into clinical cardiology practice and possible avenues for drug development.

Mast cell stabilization decreases cardiomyocyte and LV function in dogs with isolated mitral regurgitation

BACKGROUND

Mast cells are increased in isolated mitral regurgitation (MR) in the dog and may mediate extracellular matrix loss and left ventricular (LV) dilatation. We tested the hypothesis that mast cell stabilization would attenuate LV remodeling and improve function in the MR dog.

METHODS AND RESULTS

MR was induced in adult dogs randomized to no treatment (MR, n = 5) or to the mast cell stabilizer, ketotifen (MR + MCS, n = 4) for 4 months. LV hemodynamics were obtained at baseline and after 4 months of MR and magnetic resonance imaging (MRI) was performed at sacrifice. MRI-derived, serial, short-axis LV end-diastolic (ED) and end-systolic (ES) volumes, LVED volume/mass ratio, and LV 3-dimensional radius/wall thickness were increased in MR and MR + MCS dogs compared with normal dogs (n = 6) (P < .05). Interstitial collagen was decreased by 30% in both MR and MR + MCS versus normal dogs (P < .05). LV contractility by LV maximum time-varying elastance was significantly depressed in MR and MR + MCS dogs. Furthermore, cardiomyocyte fractional shortening was decreased in MR versus normal dogs and further depressed in MR + MCS dogs (P < .05). In vitro administration of ketotifen to normal cardiomyocytes also significantly decreased fractional shortening and calcium transients.

CONCLUSIONS

Chronic mast cell stabilization did not attenuate eccentric LV remodeling or collagen loss in MR. However, MCS therapy had a detrimental effect on LV function because of a direct negative inotropic effect on cardiomyocyte function.

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.

Plexiform neurofibroma genesis: questions of Nf1 gene dose and hyperactive mast cells

PURPOSE OF REVIEW

Tumorigenic cells can co-opt normal functions of nonmalignant hematopoietic cells, promoting tumor progression. Recent mouse and human studies indicate that mast cells underpin inflammation in the plexiform neurofibroma microenvironment of neurofibromatosis type 1. In this model, Nf1 homozygous-deficient Schwann cells recruit hyperactive mast cells, promoting tumorigenesis. Here, we discuss the importance of Nf1 gene dosage, delineate hematopoietic contributions to the plexiform neurofibroma microenvironment, and highlight applications to human treatment.

RECENT FINDINGS

Previous studies found that plexiform neurofibroma formation in a mouse model requires biallelic loss of Nf1 in Schwann cells and an Nf1 heterozygous cellular background. Now, transplantation and pharmacological experiments have indicated that tumor formation specifically requires Nf1 heterozygosity of c-kit-dependent bone marrow.

SUMMARY

Neurofibromatosis type 1 results from autosomal dominant mutations of the NF1 tumor suppressor gene. Although unpredictable second-hit mutations in the remaining NF1 allele precede local manifestations such as tumor formation, human and mouse data indicate that NF1/Nf1 gene haploinsufficiency modulates cellular physiology and disease pathogeneses. In particular, Nf1 haplo insufficient mast cells demonstrate multiple gain-in-functions, and mast cells permeate neurofibroma tissue. Transplantation experiments have shown that these aberrant mast cells critically underpin the tumor microenvironment. Using these findings, clinicians have medically treated a patient with a debilitating plexiform neurofibroma.

Giardia lamblia: interleukin 6 and tumor necrosis factor-alpha release from mast cells induced through an Ig-independent pathway

Giardia lamblia is a common cause of both acute and chronic diarrheal disease in humans worldwide. It has been shown that mast cells, IL-6 and TNF-alpha are substantially involved in the early control of G. lamblia infection in mice. However, no studies have yet been reported concerning the interaction between mast cell and Giardia, as well as the mast cells mediators generated in response to Giardia infection. In this study we demonstrated the direct activation of mast cells by G. lamblia live trophozoites or trophozoite-derived antigens followed by an increase in tryptase expression and a significant release of the preformed mediator histamine. In addition, parasite derived antigens increased TNF-alpha and de novo synthesized cytokine IL-6, at the mRNA and protein level. These results strongly suggest that mast cells might be an important source not only of IL-6 but also of TNF-alpha during Giardia infection, playing an important role in the outcome of the infection.

Fullerene nanomaterials inhibit phorbol myristate acetate-induced inflammation

Inflammation is a natural biological response that occurs when vascular tissues are subjected to harmful stimuli. This process may be beneficial to the host during wound healing and infections but can be detrimental if left unchecked. Oxidative stress, the generation of reactive oxygen species, is thought to be one component of this response. Fullerenes can counteract reactive oxygen species due to their potent antioxidant capabilities. Thus, we hypothesized that these molecules may inhibit inflammation. To test this hypothesis we used an in vivo model of phorbol 12-myristate 13-acetate (PMA)-induced inflammation and examined the effects fullerenes have on mitigating this response. We show that PMA-induced inflammation and oedema is dramatically inhibited when fullerenes are given prior to challenge. Thus, fullerene derivatives may be a novel way to blunt certain inflammatory conditions and facilitate faster recovery of damaged tissue.

Mucosal immunology, eosinophilic esophagitis, and other intestinal inflammatory diseases

The gastrointestinal mucosa constitutes the largest host-environment interface of the body. It uses both innate and adaptive immune mechanisms to provide protection from the diverse onslaught of foods, microbes, and other ingested products. The innate immune system is genetically encoded and evolutionarily ancient, possesses no memory, and lacks diversity. In contrast, the adaptive immune system is quite diverse, develops memory, and undergoes expansion after stimulation. The gastrointestinal mucosa is charged with the difficult task of mounting protective responses against invading microorganisms while simultaneously maintaining an overall state of nonresponsiveness or tolerance to innocuous substances, such as commensal bacteria and food antigens. Perturbation or malfunction of these complex protective mechanisms results in diseases, such as inflammatory bowel diseases, celiac disease, or eosinophilic gastrointestinal diseases.

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.

Immunity-mediated regulation of fecundity in the nematode Heligmosomoides polygyrus--the potential role of mast cells

Previous studies have shown that host immunity regulates the fecundity of nematodes. The present study was aimed at clarifying the reversible nature of fecundity in response to changes of immunological status and to determine which effector cells are responsible for compromising fecundity in Heligmosomoides polygyrus. Enhanced fecundity was observed in immunocompromised SCID and nu/nu mice compared to those in the corresponding wild-type mice, with significantly fewer numbers of intrauterine eggs produced in the wild-type than in the immunodeficient mice. When 14-day-old adult worms from BALB/c mice were transplanted into naïve BALB/c mice, their fecundity increased significantly as early as 24 h post-transplantation, but not when they were transferred into immune mice, suggesting the plastic and reversible nature of fecundity in response to changes in host immunological status. In mast cell-deficient W/W(v) mice, nematode fecundity was significantly higher than in mast cell-reconstituted W/W(v) or +/+ mice. The serum levels of the mast-cell protease mMCP1 were markedly increased in the wild-type as well as the mast cell-reconstituted W/W(v), but not in the W/W(v), SCID, or nu/nu mice during infection. These findings raise the interesting possibility that certain activities of mast cells, either directly or indirectly, regulate parasite fecundity during infection.

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.

Increased differentiation of dermal mast cells in mice lacking the Mpl gene

Thrombopoietin interactions with its receptor, Mpl, play an important role in the regulation of hematopoietic stem/progenitor cell proliferation and differentiation. In this study, we report that the mast cell restricted progenitor cells (MCP) and the mast cell precursors in the bone marrow of wild-type mice express Mpl on their surface. Furthermore, targeted deletion of the Mpl gene in mice decreases the number of MCP while increasing the number of mast cell precursors present in the marrow and spleen. It also increases the number of mast cells present in the dermis, in the peritoneal cavity, and in the gut of the mice. In addition, serosal mast cells from Mpl(null) mice have a distinctive differentiation profile similar to that expressed by wild-type dermal mast cells. These results suggest that not only does ligation of thrombopoietin with the Mpl receptor exert an effect at the mast cell restricted progenitor cell level, but also plays an unexpected yet important role in mast cell maturation.

P2 receptor-mediated signaling in mast cell biology

Mast cells are widely recognized as effector cells of allergic inflammatory reactions. They contribute to the pathogenesis of different chronic inflammatory diseases, wound healing, fibrosis, thrombosis/fibrinolysis, and anti-tumor immune responses. In this paper, we summarized the role of P2X and P2Y receptors in mast cell activation and effector functions. Mast cells are an abundant source of ATP which is stored in their granules and secreted upon activation. We discuss the contribution of mast cells to the extracellular ATP release and to the maintenance of extracellular nucleotides pool. Recent publications highlight the importance of purinergic signaling for the pathogenesis of chronic airway inflammation. Therefore, the role of ATP and P2 receptors in allergic inflammation with focus on mast cells was analyzed. Finally, ATP functions as mast cell autocrine/paracrine factor and as messenger in intercellular communication between mast cells, nerves, and glia in the central nervous system.

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.

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.

Human mast cells adhere to and migrate on epithelial and vascular basement membrane laminins LM-332 and LM-511 via alpha3beta1 integrin

Mast cells (MCs) are multifunctional effectors of the immune system that are distributed in many tissues, often in close association with the basement membrane of blood vessels, epithelium and nerves. Laminins (LMs), a family of large alphabetagamma heterotrimeric proteins, are major components of basement membrane that strongly promote cell adhesion and migration. In this study, we investigated the role of LM isoforms and their integrin receptors in human MC biology in vitro. In functional assays, alpha3-(LM-332) and alpha5-(LM-511) LMs, but not alpha1-(LM-111), alpha2-(LM-211), or alpha4-(LM-411) LMs, readily promoted adhesion and migration of cultured MCs. These activities were strongly enhanced by various stimuli. alpha3-LM was also able to costimulate IL-8 production. Among LM-binding integrins, MCs expressed alpha(3)beta(1), but not alpha(6)beta(1), alpha(7)beta(1), or alpha(6)beta(4), integrins. Blocking Abs to alpha(3)beta(1) integrin caused inhibition of both cell adhesion and migration on alpha3- and alpha5-LMs. Immunohistochemical studies on skin showed that MCs colocalized with epithelial and vascular basement membranes that expressed alpha3- and alpha5-LMs and that MCs expressed alpha(3) integrin but not alpha(6) integrin(s). These results demonstrate a role for alpha3- and alpha5-LMs and their alpha(3)beta(1) integrin receptor in MC biology. This may explain the intimate structural and functional interactions that MCs have with specific basement membranes.

Inhibitory effects of Solidago chilensis Meyen hydroalcoholic extract on acute inflammation

AIM OF THE STUDY

Alcoholic or hydroalcoholic preparations of the plant Solidago chilensis Meyen (Asteraceae) are employed in popular medicines to treat inflammation. The anti-inflammatory effects of the hydroalcoholic extract of aerial parts of the plant (93% ethanol) were investigated and the main components of the extract were identified.

MATERIALS AND METHODS

Ear oedema was induced in male Wistar rats by topical application of the chloroform fraction of latex-extract from Euphorbia milii. Leukocyte mobilisation was quantified after air-pouch inflammation evoked by oyster glycogen. Leukocyte-endothelial interactions and mast cell degranulation were quantified by intravital microscopy. The extract itself was characterised via HPLC-DAD-MS and HPLC-MS/MS.

RESULTS

Topical (12.5-50mg/kg) or intraperitoneal (25 or 50mg/kg) administrations of the extract reduced ear oedema formation (>25% reduction). Intraperitoneal applications of 25mg/kg of extract inhibited the migration of polymorphonuclear cells into the inflamed cavity (about 50%). In addition, the rolling behaviour and adherence of circulating leukocytes to postcapillary venules of the mesentery network was diminished (50%), but the mast cell degranulation in the perivascular area was not affected. The major components of the extract were identified as caffeoylquinic acid derivatives and the flavonoid rutin.

CONCLUSIONS

The data presented herein show local and systemic anti-inflammatory effects of the hydroalcoholic extract of aerial parts of Solidago chilensis, and implicate the inhibition of leukocyte-endothelial interactions as an important mechanism of the extract's action.

Role of sensory innervation in the rat pulmonary neutrophil recruitment induced by staphylococcal enterotoxins type A and B

Rat airways exposure to Staphylococcal enterotoxin A (SEA) and B (SEB) induces marked neutrophil influx. Since sensory neuropeptides play important roles in cell infiltration, in this study we have investigated its contribution in triggering SEA- and SEB-induced pulmonary neutrophil infiltration. Male Wistar rats were exposed intratracheally with SEA (3 ng/trachea) or SEB (250 ng/trachea). Animals received different in vivo pretreatments, after which the neutrophil counts and levels of substance P and IL-1 in bronchoalveolar lavage fluid were evaluated. Alveolar macrophages and peritoneal mast cells were incubated with SEA and SEB to determine the IL-1 and TNF-alpha levels. Capsaicin pretreatment significantly reduced SEA- and SEB-induced neutrophil influx in bronchoalveolar lavage fluid, but this treatment was more effective to reduce SEA responses. Treatments with SR140333 (tachykinin NK(1) receptor antagonist) and SR48968 (tachykinin NK(2) receptor antagonist) decreased SEA-induced neutrophil influx, whereas SEB-induced responses were inhibited by SR140333 only. Cyproheptadine (histamine/5-hydroxytriptamine receptor antagonist) and MD 7222 (5-HT(3) receptor antagonist) reduced SEA- and SEB-induced neutrophil influx. The substance P and IL-1 levels in bronchoalveolar lavage fluid of SEA-exposed rats were significantly higher than SEB. In addition, SEA (but not SEB) significantly released mast cell TNF-alpha. Increased production of TNF-alpha and IL-1 in alveolar macrophages was observed in response to SEA and SEB. In conclusion, sensory neuropeptides contribute significantly to SEA- and SEB-induced pulmonary neutrophil recruitment, but SEA requires in a higher extent the airways sensory innervation, and participation of mast cells and alveolar macrophage products.

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: multifaceted immune cells with diverse roles in health and disease

Mast cells were discovered more than 100 years ago and until recently, have been considered renegades of the host with the sole purpose of perpetuating allergy. The discovery of mast cell-deficient mice that could be reconstituted with mast cells (the so called "mast cell knock-in" mice) has allowed the study of the in vivo functions of mast cells and revealed several new facets of these cells. It is now evident that mast cells have a much broader impact on many physiological and pathologic processes. Mast cells, particularly through their dynamic interaction with the nervous system, have been implicated in wound healing, tissue remodeling, and homeostasis. Perhaps the most progress has been made in our understanding of the role of mast cells in immunity outside the realm of allergy, and host defense. Mast cells play critical roles in both innate and adaptive immunity, including immune tolerance. Greater insight into mast cell biology has prompted studies probing the additional consequences of mast cell dysfunction, which reveal a central role for mast cells in the pathogenesis of autoimmune disorders, cardiovascular disorders, and cancer. Here, we review recent developments in the study of mast cells, which present a complex picture of mast cell functions.

The polyamine and histamine metabolic interplay in cancer and chronic inflammation

PURPOSE OF REVIEW

To provide an update on the major research contributing to deciphering the metabolic interplay of polyamines/histamine and its impact in cancer and chronic inflammation.

RECENT FINDINGS

The most recent and relevant findings that might reflect a link between the polyamines/histamine metabolic interplay and the development of cancer and chronic inflammation-related diseases include: the observation that histamine catabolism is downregulated in the colonic mucosa of patients with colonic adenoma; the finding that some polyamine and histamine-related metabolites are different between a breast cancer cell line and a reference mammary epithelial cell line; and the demonstration of the critical role that mast cells (a cell type in which the polyamine/histamine metabolic interplay has been confirmed) play in the development of pancreatic tumors. There is still, however, a lack of specific studies elucidating the exact contribution of the polyamine/histamine metabolic interplay in these clinical settings.

SUMMARY

In mammalian cells, a polyamine/histamine metabolic interplay has been extensively proven; however, its ultimate effect on human health largely depends on the cell type and environment. Information on this topic is currently fragmented in the literature. In order to develop efficient intervention strategies, it will be necessary to establish an integrated and holistic view of the role of the polyamine/histamine metabolic interplay in each pathological state.

Mastocytosis: a disease of the hematopoietic stem cell

INTRODUCTION

Mastocytosis is an unusual clonal disease of the hematopoietic stem cell.

METHODS

This article is based on a selective literature search and on the authors' clinical and pathological experience.

RESULTS

The clinical manifestations of mastocytosis range from cutaneous mastocytosis, a common, prognostically favorable presentation, to mast cell leukemia, a rare, life-threatening disease. The mediator-induced symptoms usually respond well to H1 antihistamines. Therapeutic standards for cytoreduction in the progressive, systemic forms of mastocytosis are still lacking.

DISCUSSION

Because some of the manifestations of mastocytosis are nonspecific and can be mimicked by other diseases, there is a risk of two types of diagnostic error: Mastocytosis may remain undiagnosed when it is actually present, or it may be diagnosed even though morphological and molecular findings rule out mastocytosis. Well-defined criteria should be used to differentiate mastocytosis from other diseases with a similar clinical presentation.

Acute exposure of human skin to ultraviolet or infrared radiation or heat stimuli increases mast cell numbers and tryptase expression in human skin in vivo

BACKGROUND

Mast cells are key effector cells in diverse immunological and pathological processes. It is still unclear why there are more mast cells at peripheral and sun-exposed skin sites than at sun-protected sites.

OBJECTIVES

To investigate changes in mast cell numbers associated with natural ageing and photoageing, and to observe the effects of ultraviolet (UV) and infrared (IR) radiation and heat on the prevalence of mast cells and tryptase expression in human skin in vivo.

METHODS

Sun-exposed and sun-protected skin samples were taken from individuals in four different age groups. UV, IR or heat-treated buttock skin of young volunteers was also obtained. Mast cells were quantified by immunohistochemical staining of mast cell-specific tryptase and chymase. The expression of tryptase was determined by Western blotting.

RESULTS

Both sun-exposed and sun-protected skin showed a gradual decrease in total mast cells (MC(Total)) number with ageing. The number of mast cells in sun-exposed skin was significantly higher than that in sun-protected skin. After UV irradiation (2 minimal erythema doses), MC(Total) and mast cells expressing tryptase and chymase were significantly increased at 24 and 48 h postirradiation. After IR irradiation (3 minimal heating doses) and heat treatment (43 degrees C for 90 min), MC(Total) reached peak induction at 8 and 48 h after stimulation, respectively. Tryptase expression was also clearly upregulated by UV, IR and heat.

CONCLUSIONS

Our data demonstrate that mast cell numbers decreased with ageing in human skin. Also, mast cells may be activated and recruited by UV, IR and heat. These findings should further our understanding of the reason for the high prevalence of mast cells at peripheral sun-exposed skin sites.

Discovery of aryl aminoquinazoline pyridones as potent, selective, and orally efficacious inhibitors of receptor tyrosine kinase c-Kit

Inhibition of c-Kit has the potential to treat mast cell associated fibrotic diseases. We report the discovery of several aminoquinazoline pyridones that are potent inhibitors of c-Kit with greater than 200-fold selectivity against KDR, p38, Lck, and Src. In vivo efficacy of pyridone 16 by dose-dependent inhibition of histamine release was demonstrated in a rodent pharmacodynamic model of mast cell activation.