The rat c-kit ligand, stem cell factor, induces c-kit receptor-dependent mouse mast cell activation in vivo. Evidence that signaling through the c-kit receptor can induce expression of cellular function

New Insight into Intestinal Mast Cells Revealed by Single-Cell RNA Sequencing

Mast cells (MCs) are tissue-resident immune cells distributed in all tissues and strategically located close to blood and lymphatic vessels and nerves. Thanks to the expression of a wide array of receptors, MCs act as tissue sentinels, able to detect the presence of bacteria and parasites and to respond to different environmental stimuli. MCs originate from bone marrow (BM) progenitors that enter the circulation and mature in peripheral organs under the influence of microenvironment factors, thus differentiating into heterogeneous tissue-specific subsets. Even though MC activation has been traditionally linked to IgE-mediated allergic reactions, a role for these cells in other pathological conditions including tumor progression has recently emerged. However, several aspects of MC biology remain to be clarified. The advent of single-cell RNA sequencing platforms has provided the opportunity to understand MCs' origin and differentiation as well as their phenotype and functions within different tissues, including the gut. This review recapitulates how single-cell transcriptomic studies provided insight into MC development as well as into the functional role of intestinal MC subsets in health and disease.

Transmembrane stem factor nanodiscs enhanced revascularization in a hind limb ischemia model in diabetic, hyperlipidemic rabbits

Therapies to revascularize ischemic tissue have long been a goal for the treatment of vascular disease and other disorders. Therapies using stem cell factor (SCF), also known as a c-Kit ligand, had great promise for treating ischemia for myocardial infarct and stroke, however clinical development for SCF was stopped due to toxic side effects including mast cell activation in patients. We recently developed a novel therapy using a transmembrane form of SCF (tmSCF) delivered in lipid nanodiscs. In previous studies, we demonstrated tmSCF nanodiscs were able to induce revascularization of ischemia limbs in mice and did not activate mast cells. To advance this therapeutic towards clinical application, we tested this therapy in an advanced model of hindlimb ischemia in rabbits with hyperlipidemia and diabetes. This model has therapeutic resistance to angiogenic therapies and maintains long term deficits in recovery from ischemic injury. We treated rabbits with local treatment with tmSCF nanodiscs or control solution delivered locally from an alginate gel delivered into the ischemic limb of the rabbits. After eight weeks, we found significantly higher vascularity in the tmSCF nanodisc-treated group in comparison to alginate treated control as quantified through angiography. Histological analysis also showed a significantly higher number of small and large blood vessels in the ischemic muscles of the tmSCF nanodisc treated group. Importantly, we did not observe inflammation or mast cell activation in the rabbits. Overall, this study supports the therapeutic potential of tmSCF nanodiscs for treating peripheral ischemia.

Transmembrane Stem Factor Nanodiscs Enhanced Revascularization in a Hind Limb Ischemia Model in Diabetic, Hyperlipidemic Rabbits

Therapies to revascularize ischemic tissue have long been a goal for the treatment of vascular disease and other disorders. Therapies using stem cell factor (SCF), also known as a c-Kit ligand, had great promise for treating ischemia for myocardial infarct and stroke, however clinical development for SCF was stopped due to toxic side effects including mast cell activation in patients. We recently developed a novel therapy using a transmembrane form of SCF (tmSCF) delivered in lipid nanodiscs. In previous studies, we demonstrated tmSCF nanodiscs were able to induce revascularization of ischemia limbs in mice and did not activate mast cells. To advance this therapeutic towards clinical application, we tested this therapy in an advanced model of hindlimb ischemia in rabbits with hyperlipidemia and diabetes. This model has therapeutic resistance to angiogenic therapies and maintains long term deficits in recovery from ischemic injury. We treated rabbits with local treatment with tmSCF nanodiscs or control solution delivered locally from an alginate gel delivered into the ischemic limb of the rabbits. After eight weeks, we found significantly higher vascularity in the tmSCF nanodisc-treated group in comparison to alginate treated control as quantified through angiography. Histological analysis also showed a significantly higher number of small and large blood vessels in the ischemic muscles of the tmSCF nanodisc treated group. Importantly, we did not observe inflammation or mast cell activation in the rabbits. Overall, this study supports the therapeutic potential of tmSCF nanodiscs for treating peripheral ischemia.

Tyrosine kinase inhibitors as an alternative treatment in canine mast cell tumor

The current gold standard treatment for canine mast cell tumors (MCT) uses vinblastine sulfate (VBL) as chemotherapy, although tyrosine kinase inhibitors (TKI) have recently been shown to be worthy candidates for treatment. This systematic review aimed to analyze the overall survival (OS), progression-free survival (PFS), overall response rate (ORR), and complete (CR) or partial response (PR) in dogs with MCT treated with TKI compared to standard VBL treatment. The systematic review was registered in the Open Science Framework (OSF) database under the identifier 10.17605/OSF.IO/WYPN4 (https://osf.io/). An electronic search was performed in nine databases. References from eligible studies were also selected to find more registers. A total of 28 studies met the eligibility criteria, and one more was recovered from the references of eligible studies, totaling 29 selected studies. The overall response rate, complete response, and partial response were higher in dogs treated with tyrosine kinase inhibitors than in dogs treated with vinblastine. The overall survival and progression-free survival of vinblastine-treated dogs were higher compared to tyrosine kinase inhibitors-treated dogs. Dogs with mutated KIT treated with tyrosine kinase inhibitors have longer overall survival and progression-free survival compared to those treated with vinblastine. It is important to consider the limitation of the study which should temper the interpretation of the results, videlicet, the extracted data lacked sample standardization and included variables such as animal characteristics, mutation detection methods, tumor characteristics, and treatment types which may have influenced the outcome of the study.

Systematic review registration

https://osf.io/, identifier: 10.17605/OSF.IO/WYPN4.

Transmembrane Stem Factor Nanodiscs Enhanced Revascularization in a Hind Limb Ischemia Model in Diabetic, Hyperlipidemic Rabbits

Therapies to revascularize ischemic tissue have long been a goal for the treatment of vascular disease and other disorders. Therapies using stem cell factor (SCF), also known as a c-Kit ligand, had great promise for treating ischemia for myocardial infarct and stroke, however clinical development for SCF was stopped due to toxic side effects including mast cell activation in patients. We recently developed a novel therapy using a transmembrane form of SCF (tmSCF) delivered in lipid nanodiscs. In previous studies, we demonstrated tmSCF nanodiscs were able to induce revascularization of ischemia limbs in mice and did not activate mast cells. To advance this therapeutic towards clinical application, we tested this therapy in an advanced model of hindlimb ischemia in rabbits with hyperlipidemia and diabetes. This model has therapeutic resistance to angiogenic therapies and maintains long term deficits in recovery from ischemic injury. We treated rabbits with local treatment with tmSCF nanodiscs or control solution delivered locally from an alginate gel delivered into the ischemic limb of the rabbits. After eight weeks, we found significantly higher vascularity in the tmSCF nanodisc-treated group in comparison to alginate treated control as quantified through angiography. Histological analysis also showed a significantly higher number of small and large blood vessels in the ischemic muscles of the tmSCF nanodisc treated group. Importantly, we did not observe inflammation or mast cell activation in the rabbits. Overall, this study supports the therapeutic potential of tmSCF nanodiscs for treating peripheral ischemia.

KIT as a master regulator of the mast cell lineage

The discovery in 1987/1988 and 1990 of the cell surface receptor KIT and its ligand, stem cell factor (SCF), was a critical achievement in efforts to understand the development and function of multiple distinct cell lineages. These include hematopoietic progenitors, melanocytes, germ cells, and mast cells, which all are significantly affected by loss-of-function mutations of KIT or SCF. Such mutations also influence the development and/or function of additional cells, including those in parts of the central nervous system and the interstitial cells of Cajal (which control gut motility). Many other cells can express KIT constitutively or during immune responses, including dendritic cells, eosinophils, type 2 innate lymphoid cells, and taste cells. Yet the biological importance of KIT in many of these cell types largely remains to be determined. We here review the history of work investigating mice with mutations affecting the white spotting locus (which encodes KIT) or the steel locus (which encodes SCF), focusing especially on the influence of such mutations on mast cells. We also briefly review efforts to target the KIT/SCF pathway with anti-SCF or anti-Kit antibodies in mouse models of allergic disorders, parasite immunity, or fibrosis in which mast cells are thought to play significant roles.

Anti-KIT monoclonal antibody CDX-0159 induces profound and durable mast cell suppression in a healthy volunteer study

Background

Mast cells (MC) are powerful inflammatory immune sentinel cells that drive numerous allergic, inflammatory, and pruritic disorders when activated. MC‐targeted therapies are approved in several disorders, yet many patients have limited benefit suggesting the need for approaches that more broadly inhibit MC activity. MCs require the KIT receptor and its ligand stem cell factor (SCF) for differentiation, maturation, and survival. Here we describe CDX‐0159, an anti‐KIT monoclonal antibody that potently suppresses MCs in human healthy volunteers.

Methods

CDX‐0159‐mediated KIT inhibition was tested in vitro using KIT‐expressing immortalized cells and primary human mast cells. CDX‐0159 safety and pharmacokinetics were evaluated in a 13‐week good laboratory practice (GLP)‐compliant cynomolgus macaque study. A single ascending dose (0.3, 1, 3, and 9 mg/kg), double‐blinded placebo‐controlled phase 1a human healthy volunteer study (n = 32) was conducted to evaluate the safety, pharmacokinetics, and pharmacodynamics of CDX‐0159.

Results

CDX‐0159 inhibits SCF‐dependent KIT activation in vitro. Fc modifications in CDX‐0159 led to elimination of effector function and reduced serum clearance. In cynomolgus macaques, multiple high doses were safely administered without a significant impact on hematology, a potential concern for KIT inhibitors. A single dose of CDX‐0159 in healthy human subjects was generally well tolerated and demonstrated long antibody exposure. Importantly, CDX‐0159 led to dose‐dependent, profound suppression of plasma tryptase, a MC‐specific protease associated with tissue MC burden, indicative of systemic MC suppression or ablation.

Conclusion

CDX‐0159 administration leads to systemic mast cell ablation and may represent a safe and novel approach to treat mast cell‐driven disorders.

Mast Cells in Inflammation and Disease: Recent Progress and Ongoing Concerns

Mast cells have existed long before the development of adaptive immunity, although they have been given different names. Thus, in the marine urochordate Styela plicata, they have been designated as test cells. However, based on their morphological characteristics (including prominent cytoplasmic granules) and mediator content (including heparin, histamine, and neutral proteases), test cells are thought to represent members of the lineage known in vertebrates as mast cells. So this lineage presumably had important functions that preceded the development of antibodies, including IgE. Yet mast cells are best known, in humans, as key sources of mediators responsible for acute allergic reactions, notably including anaphylaxis, a severe and potentially fatal IgE-dependent immediate hypersensitivity reaction to apparently harmless antigens, including many found in foods and medicines. In this review, we briefly describe the origins of tissue mast cells and outline evidence that these cells can have beneficial as well as detrimental functions, both innately and as participants in adaptive immune responses. We also discuss aspects of mast cell heterogeneity and comment on how the plasticity of this lineage may provide insight into its roles in health and disease. Finally, we consider some currently open questions that are yet unresolved.

Genetic Regulation of Tryptase Production and Clinical Impact: Hereditary Alpha Tryptasemia, Mastocytosis and Beyond

Tryptase is a serine protease that is predominantly produced by tissue mast cells (MCs) and stored in secretory granules together with other pre-formed mediators. MC activation, degranulation and mediator release contribute to various immunological processes, but also to several specific diseases, such as IgE-dependent allergies and clonal MC disorders. Biologically active tryptase tetramers primarily derive from the two genes TPSB2 (encoding β-tryptase) and TPSAB1 (encoding either α- or β-tryptase). Based on the most common gene copy numbers, three genotypes, 0α:4β, 1α:3β and 2α:2β, were defined as "canonical". About 4-6% of the general population carry germline TPSAB1-α copy number gains (2α:3β, 3α:2β or more α-extra-copies), resulting in elevated basal serum tryptase levels. This condition has recently been termed hereditary alpha tryptasemia (HαT). Although many carriers of HαT appear to be asymptomatic, a number of more or less specific symptoms have been associated with HαT. Recent studies have revealed a significantly higher HαT prevalence in patients with systemic mastocytosis (SM) and an association with concomitant severe Hymenoptera venom-induced anaphylaxis. Moreover, HαT seems to be more common in idiopathic anaphylaxis and MC activation syndromes (MCAS). Therefore, TPSAB1 genotyping should be included in the diagnostic algorithm in patients with symptomatic SM, severe anaphylaxis or MCAS.

Mast cells as a unique hematopoietic lineage and cell system: From Paul Ehrlich's visions to precision medicine concepts

The origin and functions of mast cells (MCs) have been debated since their description by Paul Ehrlich in 1879. MCs have long been considered 'reactive bystanders' and 'amplifiers' in inflammatory processes, allergic reactions, and host responses to infectious diseases. However, knowledge about the origin, phenotypes and functions of MCs has increased substantially over the past 50 years. MCs are now known to be derived from multipotent hematopoietic progenitors, which, through a process of differentiation and maturation, form a unique hematopoietic lineage residing in multiple organs. In particular, MCs are distinguishable from basophils and other hematopoietic cells by their unique phenotype, origin(s), and spectrum of functions, both in innate and adaptive immune responses and in other settings. The concept of a unique MC lineage is further supported by the development of a distinct group of neoplasms, collectively referred to as mastocytosis, in which MC precursors expand as clonal cells. The clinical consequences of the expansion and/or activation of MCs are best established in mastocytosis and in allergic inflammation. However, MCs have also been implicated as important participants in a number of additional pathologic conditions and physiological processes. In this article, we review concepts regarding MC development, factors controlling MC expansion and activation, and some of the fundamental roles MCs may play in both health and disease. We also discuss new concepts for suppressing MC expansion and/or activation using molecularly-targeted drugs.

LILRB4, from the immune system to the disease target

Leukocyte immunoglobulin (Ig)-like receptor B4 (LILRB4) is a member of leukocyte Ig-like receptors (LILRs), which associate with membrane adaptors to signal through multiple cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Under physiological conditions, LILRB4 plays a very important role in the function of the immune system through its expression on various immune cells, such as T cells and plasma cells. Under pathological conditions, LILRB4 affects the processes of various diseases, such as the transformation and infiltration of tumors and leukemias, through various signaling pathways. Differential expression of LILRB4 is present in a variety of immune system diseases, such as Kawasaki disease, systemic lupus erythematosus (SLE), and sepsis. Recent studies have shown that LILRB4 also plays a role in mental illness. The important role of LILRB4 in the immune system and its differential expression in a variety of diseases make LILRB4 a potential prophylactic and therapeutic target for a variety of diseases.

The histone deacetylase inhibitor valproic acid attenuates phospholipase Cγ2 and IgE-mediated mast cell activation

Mast cell activation through the high-affinity IgE receptor (FcεRI) plays a central role in allergic reactions. FcεRI-mediated activation triggers multiple signaling pathways leading to degranulation and synthesis of different inflammatory mediators. IgE-mediated mast cell activation can be modulated by different molecules, including several drugs. Herein, we investigated the immunomodulatory activity of the histone deacetylase inhibitor valproic acid (VPA) on IgE-mediated mast cell activation. To this end, bone marrow-derived mast cells (BMMC) were sensitized with IgE and treated with VPA followed by FcεRI cross-linking. The results indicated that VPA reduced mast cell IgE-dependent degranulation and cytokine release. VPA also induced a significant reduction in the cell surface expression of FcεRI and CD117, but not other mast cell surface molecules. Interestingly, VPA treatment inhibited the phosphorylation of PLCγ2, a key signaling molecule involved in IgE-mediated degranulation and cytokine secretion. However, VPA did not affect the phosphorylation of other key components of the FcεRI signaling pathway, such as Syk, Akt, ERK1/2, or p38. Altogether, our data demonstrate that VPA affects PLCγ2 phosphorylation, which in turn decreases IgE-mediated mast cell activation. These results suggest that VPA might be a key modulator of allergic reactions and might be a promising therapeutic candidate.

Expression profiling of c-kit and its impact after esiRNA silencing during gonadal development in catfish

Receptor, c-Kit is a member of a family of growth factor receptors that have tyrosine kinase activity, and are involved in the transduction of growth regulatory signals across plasma membrane by activation of its ligand, kitl/scf. The present study analyzed mRNA and protein expression profiles of c-kit in the gonads of catfish, Clarias gariepinus, using real time PCR, in situ hybridization and immunohistochemistry. Tissue distribution analysis revealed higher expression mainly in the catfish gonads. Ontogeny studies showed minimal expression during early developmental stages and highest during 50-75 days post hatch, and the dimorphic expression in gonads decreased gradually till adulthood, which might suggest an important role for this gene around later stages of sex differentiation and gonadal development. Expression of c-kit was analyzed at various phases of gonadal cycle in both male and female, which showed minimal expression during the resting phase, and higher expression during the pre-spawning phase in male compared to females. In vitro and in vivo induction using human chorionic gonadotropin elevated the expression of c-kit indicating the regulatory influence of hypothalamo-hypophyseal axis. In vivo transient gene silencing using c-kit-esiRNA in adult catfish during gonadal recrudescence showed a decrease in c-kit expression, which affected the expression levels of germ cell meiotic marker sycp3, as well as several factors and steroidogenic enzyme genes that are involved in germ cell development. Decrease in the levels of 11-ketotestosterone and testosterone in serum were also observed after esiRNA silencing. The findings suggests that c-kit has an important role in the process of germ cell proliferation, development and maturation during gonadal development and recrudescence in catfish.

Mast Cell-Intervertebral disc cell interactions regulate inflammation, catabolism and angiogenesis in Discogenic Back Pain

Low back pain (LBP) is a widespread debilitating disorder of significant socio-economic importance and intervertebral disc (IVD) degeneration has been implicated in its pathogenesis. Despite its high prevalence the underlying causes of LBP and IVD degeneration are not well understood. Recent work in musculoskeletal degenerative diseases such as osteoarthritis have revealed a critical role for immune cells, specifically mast cells in their pathophysiology, eluding to a potential role for these cells in the pathogenesis of IVD degeneration. This study sought to characterize the presence and role of mast cells within the IVD, specifically, mast cell-IVD cell interactions using immunohistochemistry and 3D in-vitro cell culture methods. Mast cells were upregulated in painful human IVD tissue and induced an inflammatory, catabolic and pro-angiogenic phenotype in bovine nucleus pulposus and cartilage endplate cells at the gene level. Healthy bovine annulus fibrosus cells, however, demonstrated a protective role against key inflammatory (IL-1β and TNFα) and pro-angiogenic (VEGFA) genes expressed by mast cells, and mitigated neo-angiogenesis formation in vitro. In conclusion, mast cells can infiltrate and elicit a degenerate phenotype in IVD cells, enhancing key disease processes that characterize the degenerate IVD, making them a potential therapeutic target for LBP.

Inflammatory targets of therapy in sickle cell disease

Sickle cell disease (SCD) is a monogenic globin disorder characterized by the production of a structurally abnormal hemoglobin (Hb) variant Hb S, which causes severe hemolytic anemia, episodic painful vaso-occlusion, and ultimately end-organ damage. The primary disease pathophysiology is intracellular Hb S polymerization and consequent sickling of erythrocytes. It has become evident for more than several decades that a more complex disease process contributes to the myriad of clinical complications seen in patients with SCD with inflammation playing a central role. Drugs targeting specific inflammatory pathways therefore offer an attractive therapeutic strategy to ameliorate many of the clinical events in SCD. In addition, they are useful tools to dissect the molecular and cellular mechanisms that promote individual clinical events and for developing improved therapeutics to address more challenging clinical dilemmas such as refractoriness to opioids or hyperalgesia. Here, we discuss the prospect of targeting multiple inflammatory pathways implicated in the pathogenesis of SCD with a focus on new therapeutics, striving to link the actions of the anti-inflammatory agents to a defined pathobiology, and specific clinical manifestations of SCD. We also review the anti-inflammatory attributes and the cognate inflammatory targets of hydroxyurea, the only Food and Drug Administration-approved drug for SCD.

Mast Cell Accumulation and Degranulation in Rat Bladder with Partial Outlet Obstruction

INTRODUCTION

Benign prostatic hyperplasia causes partial bladder outlet obstruction (pBOO), and many patients with pBOO are affected by not only voiding symptoms but also storage symptoms. We previously suggested that enhancement of 5-hydroxytryptamine (5-HT)-induced bladder contraction in the pBOO bladder may be one cause of storage symptoms. However, little is known about the presence of 5-HT in rat bladders. In this study, we hypothesized that mast cells are a source of 5-HT and investigated the distribution of mast cells and 5-HT in the bladders of rats with pBOO.

METHODS

The bladders of female Sprague-Dawley rats were subjected to pBOO and sham operations for 1 week, were isolated, and were fixed for light or electron microscopy. Mast cells and 5-HT in the bladders were detected by toluidine blue staining and immunohistochemical staining, respectively. The mast cells were counted under a light microscope. Degranulated mast cells were observed under an electron microscope and counted under a light microscope.

RESULTS

Mast cells were present in the mucosa/submucosa region in sham rat bladders. Their number was increased in the detrusor muscle/subserosa/serosa region, especially the subserosal layer, in pBOO rat bladders. The localization of mast cells almost matched that of 5-HT-positive cells in consecutive sections. Degranulated mast cells were present in sham and pBOO rat bladders, but the proportion of degranulated mast cells was significantly increased in every region in pBOO rat bladders compared with that in sham rat bladders.

CONCLUSION

These results suggest that mast cells contain 5-HT and are more abundant locally in the subserosal layer of pBOO rat bladders. 5-HT released from mast cells could stimulate 5-HT2 receptors on the detrusor muscle, and this may underlie storage symptoms.

FUNDING

Asahi Kasei Pharma Corp.

Novel basophil- or eosinophil-depleted mouse models for functional analyses of allergic inflammation

Basophils and eosinophils play important roles in various host defense mechanisms but also act as harmful effectors in allergic disorders. We generated novel basophil- and eosinophil-depletion mouse models by introducing the human diphtheria toxin (DT) receptor gene under the control of the mouse CD203c and the eosinophil peroxidase promoter, respectively, to study the critical roles of these cells in the immunological response. These mice exhibited selective depletion of the target cells upon DT administration. In the basophil-depletion model, DT administration attenuated a drop in body temperature in IgG-mediated systemic anaphylaxis in a dose-dependent manner and almost completely abolished the development of ear swelling in IgE-mediated chronic allergic inflammation (IgE-CAI), a typical skin swelling reaction with massive eosinophil infiltration. In contrast, in the eosinophil-depletion model, DT administration ameliorated the ear swelling in IgE-CAI whether DT was administered before, simultaneously, or after, antigen challenge, with significantly lower numbers of eosinophils infiltrating into the swelling site. These results confirm that basophils and eosinophils act as the initiator and the effector, respectively, in IgE-CAI. In addition, antibody array analysis suggested that eotaxin-2 is a principal chemokine that attracts proinflammatory cells, leading to chronic allergic inflammation. Thus, the two mouse models established in this study are potentially useful and powerful tools for studying the in vivo roles of basophils and eosinophils. The combination of basophil- and eosinophil-depletion mouse models provides a new approach to understanding the complicated mechanism of allergic inflammation in conditions such as atopic dermatitis and asthma.

Stem cell factor gene transfer promotes cardiac repair after myocardial infarction via in situ recruitment and expansion of c-kit+ cells

RATIONALE

There is growing evidence that the myocardium responds to injury by recruiting c-kit(+) cardiac progenitor cells to the damage tissue. Even though the ability of exogenously introducing c-kit(+) cells to injured myocardium has been established, the capability of recruiting these cells through modulation of local signaling pathways by gene transfer has not been tested.

OBJECTIVE

To determine whether stem cell factor gene transfer mediates cardiac regeneration in a rat myocardial infarction model, through survival and recruitment of c-kit(+) progenitors and cell-cycle activation in cardiomyocytes, and explore the mechanisms involved.

METHODS AND RESULTS

Infarct size, cardiac function, cardiac progenitor cells recruitment, fibrosis, and cardiomyocyte cell-cycle activation were measured at different time points in controls (n=10) and upon stem cell factor gene transfer (n=13) after myocardial infarction. We found a regenerative response because of stem cell factor overexpression characterized by an enhancement in cardiac hemodynamic function: an improvement in survival; a reduction in fibrosis, infarct size and apoptosis; an increase in cardiac c-kit(+) progenitor cells recruitment to the injured area; an increase in cardiomyocyte cell-cycle activation; and Wnt/β-catenin pathway induction.

CONCLUSIONS

Stem cell factor gene transfer induces c-kit(+) stem/progenitor cell expansion in situ and cardiomyocyte proliferation, which may represent a new therapeutic strategy to reverse adverse remodeling after myocardial infarction.

Stem cell factor programs the mast cell activation phenotype

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

Surgical Therapy of End-Stage Heart Failure: Understanding Cell-Mediated Mechanisms Interacting with Myocardial Damage

Worldwide, cardiovascular disease results in an estimated 14.3 million deaths per year, giving rise to an increased demand for alternative and advanced treatment. Current approaches include medical management, cardiac transplantation, device therapy, and, most recently, stem cell therapy. Research into cell-based therapies has shown this option to be a promising alternative to the conventional methods. In contrast to early trials, modern approaches now attempt to isolate specific stem cells, as well as increase their numbers by means of amplifying in a culture environment. The method of delivery has also been improved to minimize the risk of micro-infarcts and embolization, which were often observed after the use of coronary catheterization. The latest approach entails direct, surgical, transepicardial injection of the stem cell mixture, as well as the use of tissue-engineered meshes consisting of embedded progenitor cells.

Modulation of mast cell adhesion, proliferation, and cytokine secretion on electrospun bioresorbable vascular grafts

Mast cells synthesize several potent angiogenic factors and can also stimulate fibroblasts, endothelial cells, and macrophages. An understanding of how they participate in wound healing and angiogenesis is important to further our knowledge about in situ vascular prosthetic regeneration. The adhesion, proliferation, and cytokine secretion of bone marrow-derived murine mast cells (BMMC) on electrospun polydioxanone, polycaprolactone, and silk scaffolds, as well as tissue culture plastic, has been investigated in the presence or absence of IL-3, stem cell factor, IgE and IgE with a crosslinking antigen, dinitrophenol-conjugated albumin (DNP). It was previously believed that only activated BMMCs exhibit adhesion and cytokine secretion. However, this study shows nonactivated BMMC adhesion to electrospun scaffolds. Silk scaffold was not found to be conducive for mast cell adhesion and cytokine secretion. Activation by IgE and DNP significantly enhanced mast cell adhesion, proliferation, migration, and secretion of tumor necrosis factor alpha, macrophage inflammatory protein-1α, and IL-13. This indicates that mast cells might play a role in the process of biomaterial integration into the host tissue, regeneration, and possibly angiogenesis.

Involvement of mast cells in eosinophilic esophagitis

BACKGROUND

Eosinophilic esophagitis (EE) is an emerging disorder with poorly understood pathogenesis.

OBJECTIVE

Whereas prior studies have primarily focused on the role of eosinophils in disease diagnosis and pathogenesis, this study investigates the involvement of mast cells.

METHODS

Total and degranulated mast cell counts were correlated to microarray and RT-PCR data to generate transcriptome expression profiles related to mast cell number and degranulation in patients with EE and healthy control subjects.

RESULTS

Esophageal mastocytosis and mast cell degranulation were readily apparent in patients with EE compared with control subjects (P < .01), as assessed by staining for total mast cells and the presence of extracellular mast cell tryptase (P < .01). Microarray analysis revealed that mast cell levels correlated with the dysregulation of 0.8% (301 genes) of the genome, which was partially distinct from the genes that correlated with tissue eosinophilia. The expression of transcripts for the mast cell proteases carboxypeptidase A3 and tryptase, but not chymase, correlated with mast cell levels and distinguished patients with EE from control subjects. Suprabasilar mast cell counts (P < .01) and degranulation (P < .01) were proportional with KIT ligand mRNA expression. Treatment of patients with EE with swallowed fluticasone propionate normalized levels of mast cells and the mast cell-related transcriptome in responder patients.

CONCLUSION

Herein we have identified local mastocytosis and mast cell degranulation in the esophagi of patients with EE; identified an esophageal mast cell-associated transcriptome that is significantly divergent from the eosinophil-associated transcriptome, with carboxypeptidase A3 mRNA levels serving as the best mast cell surrogate marker; and provided evidence for the involvement of KIT ligand in the pathogenesis of EE.

Molecular and functional characterization of kita and kitla of the goldfish (Carassius auratus L.)

Kit ligand and its type III tyrosine kinase receptor Kit promotes the survival, proliferation and differentiation of progenitor cells involved in mammalian myelopoiesis. In this study we report on the molecular and functional characterization of kit receptor A (kita) and kit ligand A (kitla) from the goldfish. Both kita and kitla were ubiquitously expressed in goldfish tissues, with higher mRNA levels observed in the kidney and spleen, the major hematopoietic organs of fish. Furthermore, both kita and kitla expressions decreased in a time-dependent manner in goldfish primary kidney macrophage (PKM) cultures, as progenitor to macrophage development progressed, and the highest expressions of both the receptor and ligand were observed in sorted progenitor cell populations. Activation of mature macrophage cultures increased both kita and kitla expressions. Kit ligand A induced chemotactic response, proliferation and survival of PKM cells in a dose-dependent manner, but did not induce differentiation of early PKM cells. These results are consistent with the role of kita and kitla during myelopoiesis of higher vertebrates and suggest a conserved mechanism of macrophage development throughout vertebrates.

CCR1 expression and signal transduction by murine BMMC results in secretion of TNF-alpha, TGFbeta-1 and IL-6

Chemokine receptors (CCRs) are important co-stimulatory molecules found on many blood cells and associated with various diseases. The expression and function of CCRs on mast cells has been quite controversial. In this study, we report for the first time that murine bone marrow-derived mast cells (BMMC) express messenger RNA and protein for CCR1. BMMC cultured in the presence of murine recombinant stem cell factor and murine IL-3 expressed CCR1 after 5-6 weeks. We also report for the first time that mBMMC(CCR1+) cells endogenously express neurokinin receptor-1 and intercellular adhesion molecule-1. To examine the activity of CCR1 on these BMMC, we simultaneously stimulated two receptors: CCR1 by its ligand macrophage inflammatory protein-1alpha and the IgE receptor FcepsilonRI by antigen cross-linking. We found that co-stimulation enhanced BMMC degranulation compared with FcepsilonRI stimulation alone, as assessed by beta-hexosaminidase activity (85 versus 54%, P < 0.0001) and Ca(2+) influx (223 versus 183 nM, P < 0.05). We also observed significant increases in mast cell secretion of key growth factors, cytokines and chemokine mediators upon CCR1-FcepsilonRI co-stimulation. These factors include transforming growth factor beta-1, tumor necrosis factor-alpha and the cytokine IL-6. Taken together, our data indicate that CCR1 plays a key role in BMMC function. These findings contribute to our understanding of mechanisms for immune cell trafficking during inflammation.

Mast cells modulate transport of CD23/IgE/antigen complex across human intestinal epithelial barrier

BACKGROUND

Food allergy and chronic intestinal inflammation are common in western countries. The complex of antigen/IgE is taken up into the body from the gut lumen with the aid of epithelial cell-derived CD23 (low affinity IgE receptor II) that plays an important role in the pathogenesis of intestinal allergy. This study aimed to elucidate the role of mast cell on modulation of antigen/IgE complex transport across intestinal epithelial barrier.

METHODS

Human intestinal epithelial cell line HT29 cell monolayer was used as a study platform. Transepithelial electric resistance (TER) and permeability to ovalbumin (OVA) were used as the markers of intestinal epithelial barrier function that were recorded in response to the stimulation of mast cell-derived chemical mediators.

RESULTS

Conditioned media from naïve mast cell line HMC-1 cells or monocyte cell line THP-1 cells significantly upregulated the expression of CD23 and increased the antigen transport across the epithelium. Treatment with stem cell factor (SCF), nerve growth factor (NGF), retinoic acid (RA) or dimethyl sulphoxide (DMSO) enhanced CD23 expression in HT29 cells. Conditioned media from SCF, NGF or RA-treated HMC-1 cells, and SCF, NGF, DMSO or RA-treated THP-1 cells enhanced immune complex transport via enhancing the expression of the CD23 in HT29 cells and the release of inflammatory mediator TNF-α. Nuclear factor kappa B inhibitor, tryptase and TNF-α inhibited the increase in CD23 in HT29 cells and prevents the enhancement of epithelial barrier permeability.

CONCLUSIONS

Mast cells play an important role in modulating the intestinal CD23 expression and the transport of antigen/IgE/CD23 complex across epithelial barrier. (Tu YH, Oluwole C, Struiksma S, Perdue MH, Yang PC. Mast cells modulate transport of CD23/IgE/antigen complex across human intestinal epithelial barrier.

Bombesin can minimize impairments of interstitial cells of Cajal induced by FK506 in small bowel transplantation

PURPOSE

Interstitial cells of Cajal (ICC) are known as intestinal pacemaker cells and express c-kit on their membrane. Previously, we reported that FK506 had neurotoxicity to enteric ganglia, and bombesin (BBS) preserved them against FK506. The aim of this study was to investigate whether ICC was impaired by FK506 and whether ICC was preserved by BBS against FK506.

METHODS

Twelve rats underwent allogeneic SBTx heterotopically and were divided into 2 groups as follows: group A underwent SBTx with FK506 and group B with FK506/BBS. All rats were administered FK506 daily. Either BBS or normal saline was infused continuously from day 14 to 28. Analysis of ICC was performed immunohistochemically with c-kit. Interstitial cells of Cajal were evaluated by counting the number of c-kit-positive clusters in each graft.

RESULTS

The expression of c-kit accumulated around 60% of PGP9.5-positive enteric ganglia. The number of c-kit-positive clusters in group A was 22.3 +/- 5.5 clusters per cross section (C/CS) and that in group B was 36.3 +/- 5.1 C/CS. Interstitial cells of Cajal were well preserved in group B. There was a significant difference between groups A and B (P <.001).

CONCLUSION

Interstitial cells of Cajal were impaired by FK506 in allografts, and BBS could minimize the impairment of ICC against FK506.

The use of experimental murine models to assess novel agents of hematopoietic stem and progenitor cell mobilization

The recent explosion in the understanding of the cellular and molecular mechanisms underlying hematopoietic stem and progenitor cell (HSPC) mobilization has facilitated development of novel therapeutic agents, targeted at improving mobilization kinetics as well as HSPC yield. With the development of new agents comes the challenge of choosing efficient and relevant preclinical studies for the testing of the HSPC mobilization efficacy of these agents. This article reviews the use of the mouse as a convenient small animal model of HSPC mobilization and transplantation, and outlines the range of murine assays that can be applied to assess novel HSPC mobilizing agents. Techniques to demonstrate murine HSPC mobilization are discussed, as well as the role of murine assays to confirm human HSPC mobilization, and techniques to investigate the biologic phenotype of HSPC mobilized by these novel agents. Technical aspects regarding mobilization regimens and control arms, and choice of experimental animals are also discussed.

The role of myeloid cells in the promotion of tumour angiogenesis

The use of various transgenic mouse models and analysis of human tumour biopsies has shown that bone marrow-derived myeloid cells, such as macrophages, neutrophils, eosinophils, mast cells and dendritic cells, have an important role in regulating the formation and maintenance of blood vessels in tumours. In this Review the evidence for each of these cell types driving tumour angiogenesis is outlined, along with the mechanisms regulating their recruitment and activation by the tumour microenvironment. We also discuss the therapeutic implications of recent findings that specific myeloid cell populations modulate the responses of tumours to agents such as chemotherapy and some anti-angiogenic therapies.

Activation of protein kinase D1 in mast cells in response to innate, adaptive, and growth factor signals

Little is known about the serine/threonine kinase protein kinase D (PKD)1 in mast cells. We sought to define ligands that activate PKD1 in mast cells and to begin to address the contributions of this enzyme to mast cell activation induced by diverse agonists. Mouse bone marrow-derived mast cells (BMMC) contained both PKD1 mRNA and immunoreactive PKD1 protein. Activation of BMMC through TLR2, Kit, or FcepsilonRI with Pam(3)CSK(4) (palmitoyl-3-cysteine-serine-lysine-4), stem cell factor (SCF), and cross-linked IgE, respectively, induced activation of PKD1, as determined by immunochemical detection of autophosphorylation. Activation of PKD1 was inhibited by the combined PKD1 and protein kinase C (PKC) inhibitor Gö 6976 but not by broad-spectrum PKC inhibitors, including bisindolylmaleimide (Bim) I. Pam(3)CSK(4) and SCF also induced phosphorylation of heat shock protein 27, a known substrate of PKD1, which was also inhibited by Gö 6976 but not Bim I in BMMC. This pattern also extended to activation-induced increases in mRNA encoding the chemokine CCL2 (MCP-1) and release of the protein. In contrast, both pharmacologic agents inhibited exocytosis of beta-hexosaminidase induced by SCF or cross-linked IgE. Our findings establish that stimuli representing innate, adaptive, and growth factor pathways activate PKD1 in mast cells. In contrast with certain other cell types, activation of PKD1 in BMMC is largely independent of PKC activation. Furthermore, our findings also indicate that PKD1 preferentially influences transcription-dependent production of CCL2, whereas PKC predominantly regulates the rapid exocytosis of preformed secretory granule mediators.

Mast cells in the promotion and limitation of chronic inflammation

Observations of increased numbers of mast cells at sites of chronic inflammation have been reported for over a hundred years. Light and electron microscopic evidence of mast cell activation at such sites, taken together with the known functions of the diverse mediators, cytokines, and growth factors that can be secreted by appropriately activated mast cells, have suggested a wide range of possible functions for mast cells in promoting (or suppressing) many features of chronic inflammation. Similarly, these and other lines of evidence have implicated mast cells in a variety of adaptive or pathological responses that are associated with persistent inflammation at the affected sites. Definitively characterizing the importance of mast cells in chronic inflammation in humans is difficult. However, mice that genetically lack mast cells, especially those which can undergo engraftment with wildtype or genetically altered mast cells, provide a means to investigate the importance of mast cells and specific mast cell functions or products in diverse models of chronic inflammation. Such work has confirmed that mast cells can significantly influence multiple features of chronic inflammatory responses, through diverse effects that can either promote or, perhaps more surprisingly, suppress aspects of these responses.

Inhibition of pathologic inflammation by leukocyte Ig-like receptor B4 and related inhibitory receptors

Leukocyte immunoglobulin (Ig)-like receptor B4 (LILRB4)(previously termed gp49B1) is a member of the Ig superfamily expressed constitutively on the surface of mast cells, neutrophils, and macrophages. LILRB4 inhibits IgE-dependent activation of mast cells in vitro through its two immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that recruit the src homology domain type-2-containing tyrosine phosphatase 1 into the cell membrane. Accordingly, Lilrb4(-/-) mice exhibit greater incidence and severity of IgE- and mast cell-dependent anaphylactic inflammation compared with mice that express LILRB4. In addition, mast cell-dependent inflammation induced by the interaction of stem cell factor (SCF) with its receptor Kit is also more severe in Lilrb4(-/-) mice, indicating that the counterregulatory function of LILRB4 extends beyond inflammation induced by Fc receptors, which signal through ITIMs, to responses initiated through a receptor tyrosine kinase. Indeed, pathologic inflammatory responses induced by activation of neutrophils with lipopolysaccharide (LPS) alone or with tissue-specific autoantibodies are greatly exacerbated in Lilrb4(-/-) mice. The rapid upregulation of LILRB4 expression on neutrophils in Lilrb4(+/+) mice in response to LPS suggests it is an innate counterregulatory response designed to reduce pathologic inflammation. Nevertheless, LILRB4 also serves a similar purpose for inflammation induced by the humoral adaptive immune response that is manifested through effector cells bearing Fc receptors.

Kit is essential for PMA-inflammation–induced mast-cell accumulation in the skin

Cutaneous mast cells have important pathogenic roles in skin inflammation, but the signals regulating mast-cell numbers in healthy and inflamed skin are not fully understood. Mast-cell development depends on the receptor tyrosine kinase Kit as shown by a greater than 95% reduction of mast-cell numbers in hypomorphic (KitW/Wv) mutant mice that are widely used as a mast-cell deficiency model. Mast-cell numbers are normally very low in KitW/Wv mice, but numbers can strongly increase under inflammatory conditions. It remains elusive whether this inflammation-driven mast-cell accumulation is mediated by signals transmitted via the KitWv receptor or by other, Kit-independent stimuli. We show here, using viable Kit- null mice (KitW/W), that Kit is essential for mast-cell accumulation in phorbol-12-myristate-13-acetate (PMA)–treated, chronically inflamed skin. This increase in mast- cell numbers is strongly attenuated in KitW/Wv mice lacking mature lymphocytes (T, B, and natural killer [NK] cells). These data, together with reconstitution experiments, point at a role for lymphocytes in the regulation of mast-cell compartments under limiting Kit signaling. We conclude that inflammation-induced cutaneous mast-cell accumulation is dependent on Kit signaling strength, and, under limiting Kit signals, on cells of the adaptive immune system.

Stem cell factor expression, mast cells and inflammation in asthma

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

Inhibition of SCF attenuates peribronchial remodeling in chronic cockroach allergen-induced asthma

The progression and severity of chronic asthma likely depends upon the intensity of the damage and remodeling of the tissue. We have developed a chronic model of allergic asthma using multiple cockroach allergen challenges. Using this clinically relevant allergen we have established significant peribronchial fibrosis and mucus overproduction. These remodeling events are accompanied by intense peribronchial inflammation, including lymphocytes and eosinophils. A cytokine that has been identified as having a prominent role in short-term allergic events, stem cell factor (SCF), appears to have a significant role in this late-stage process. Using our polyclonal antibody specific for SCF administered into the airways of mice during the final allergen challenges, we find a significant effect on the chronic peribronchial allergen-induced fibrotic remodeling. This was characterized by reduced inflammation, especially eosinophils, as well as reduced hydroxyproline levels in anti-SCF compared to control antibody-treated animals. In addition, when we examined chemokines associated with the chronic disease and neutralized SCF in vivo we observed a corresponding decrease in CCL6 and CCL17. Using an inhibitor, imatinib mesylate, that blocks SCF/c-kit-associated RTK, we find similar results as with anti-SCF for attenuating AHR and fibrotic changes, suggesting that a potential clinical treatment for chronic asthma already exists related to this pathway. These results further support the potential use of SCF/c-kit inhibition for targeting chronic severe asthmatic responses.

Implication of stem cell factor in human liver regeneration after transplantation and resection

The stem cell factor (SCF), besides regulating hemopoietic stem cells homing and proliferation, has proliferative effects on hepatocytes and may be involved in liver regeneration. We investigate if liver transplantation (LT) and hepatic resection (HR) modify the concentration of soluble SCF (s-SCF) in peripheral blood of 15 LT and 7 HR. s-SCF was measured by ELISA as ng/ml. s-SCF basal levels were higher in LT that in HR (818 +/- 349 vs. 479 +/- 79, p = 0.005). A significant increase of s-SCF, peaking at postoperative day +3, was seen after LT (from 818 +/- 349 to 1212 +/- 461, p = 0.01) and HR (from 479 +/- 79 to 698 +/- 122, p = 0.004). s-SCF peak levels were higher after LT than HR (p = 0.0008). At day +7 s-SCF concentration returned to baseline values. LT have a higher basal s-SCF level than HR. These data show for the first time that liver injury affects s-SCF level and suggest that SCF may be involved also in clinical liver regeneration.

Critical Role for Mast Cells in the Pathogenesis of 2,4-Dinitrobenzene-Induced Murine Colonic Hypersensitivity Reaction

The immunological mechanisms underlying the role of mast cells in the pathogenesis of inflammatory bowel disease (IBD) are poorly defined. In this study, non-IgE mediated colonic hypersensitivity responses in BALB/c mice induced by skin sensitization with dinitrofluorobenzene (DNFB) followed by an intrarectal challenge with dinitrobenzene sulfonic acid featured as a model to study the role of mast cells in the development of IBD. Vehicle- or DNFB-sensitized mice were monitored for clinical symptoms and inflammation 72 h after dinitrobenzene sulfonic acid challenge. DNFB-sensitized mice developed diarrheic stool, increased colonic vascular permeability, hypertrophy of colonic lymphoid follicles (colonic patches), and showed cellular infiltration at the microscopic level. Increased numbers of mast cells were found in the colon of DNFB-sensitized mice located in and around colonic patches associated with elevated levels of mouse mast cell protease-1 in plasma indicating mast cell activation. Colonic patches of DNFB mice, stimulated in vitro with stem cell factor indicated that an increase in TNF-alpha levels in the colon is mainly mast cell originated. Finally, neutrophil infiltration was observed in the colon of DNFB-sensitized mice. Induction of this model in mast cell-deficient WBB6F(1) W/W(v) mice shows a profound reduction of characteristics of the colonic hypersensitivity reaction. Reconstitution with bone marrow-derived mast cells in WBB6F(1) W/W(v) mice fully restored the inflammatory response. This study demonstrates the importance of mast cells in the development of clinical symptoms and inflammation in the presented murine model for IBD.

Mast cells as "tunable" effector and immunoregulatory cells: recent advances

This review focuses on recent progress in our understanding of how mast cells can contribute to the initiation, development, expression, and regulation of acquired immune responses, both those associated with IgE and those that are apparently expressed independently of this class of Ig. We emphasize findings derived from in vivo studies in mice, particularly those employing genetic approaches to influence mast cell numbers and/or to alter or delete components of pathways that can regulate mast cell development, signaling, or function. We advance the hypothesis that mast cells not only can function as proinflammatory effector cells and drivers of tissue remodeling in established acquired immune responses, but also may contribute to the initiation and regulation of such responses. That is, we propose that mast cells can also function as immunoregulatory cells. Finally, we show that the notion that mast cells have primarily two functional configurations, off (or resting) or on (or activated for extensive mediator release), markedly oversimplifies reality. Instead, we propose that mast cells are "tunable," by both genetic and environmental factors, such that, depending on the circumstances, the cell can be positioned phenotypically to express a wide spectrum of variation in the types, kinetics, and/or magnitude of its secretory functions.

Regulation of stem cell factor expression in inflammation and asthma

Stem cell factor (SCF) is a major mast cell growth factor, which could be involved in the local increase of mast cell number in the asthmatic airways. In vivo, SCF expression increases in asthmatic patients and this is reversed after treatment with glucocorticoids. In vitro in human lung fibroblasts in culture, IL-1beta, a pro-inflammatory cytokine, confirms this increased SCF mRNA and protein expression implying the MAP kinases p38 and ERK1/2 very early post-treatment, and glucocorticoids confirm this decrease. Surprisingly, glucocorticoids potentiate the IL-1beta-enhanced SCF expression at short term treatment, implying increased SCF mRNA stability and SCF gene transcription rate. This potentiation involves p38 and ERK1/2. Transfection experiments with the SCF promoter including intron1 also confirm this increase and decrease of SCF expression by IL-1beta and glucocorticoids, and the potentiation by glucocorticoids of the IL-1beta-induced SCF expression. Deletion of the GRE or kappaB sites abolishes this potentiation, and the effect of IL-1beta or glucocorticoids alone. DNA binding of GR and NF-kappaB are also demonstrated for these effects. In conclusion, this review concerns new mechanisms of regulation of SCF expression in inflammation that could lead to potential therapeutic strategy allowing to control mast cell number in the asthmatic airways.

Lack of significant skin inflammation during elimination by apoptosis of large numbers of mouse cutaneous mast cells after cessation of treatment with stem cell factor

We previously reported that subcutaneous (s.c.) administration of stem cell factor (SCF), the ligand for the c-Kit receptor, to the back skin of mice promotes marked local increases in the numbers of cutaneous mast cells (MCs), and that cessation of SCF treatment results in the rapid reduction of cutaneous MC populations by apoptosis. In the present study, we used the 125I-fibrin deposition assay, a very sensitive method for quantifying increased vascular permeability, to assess whether the clearance of large numbers of apoptotic MCs is associated with significant cutaneous inflammation. The s.c. injection of rrSCF164 (30 or 100 microg/kg/day) or rrSCF164-peg (polyethylene glycol-treated SCF, 30 or 100 microg/kg/day) for 23 days increased the numbers of dermal MCs at skin injection sites from 5.1+/-0.7 MCs/mm2 to 36.4+/-4.1, 34.7+/-9.7, 52.5+/-5.8, and 545+/-97 MCs/mm2, respectively. In contrast, MC numbers were markedly lower in mice that had been treated with SCF for 21 days, followed by 2 days of injection with the vehicle alone. Notably, when tested during the period of rapid reduction of skin MCs,125I-fibrin deposition in the skin was very similar to that in mice receiving continuous treatment with SCF or vehicle. We conclude that the rapid elimination of even very large populations of MCs by apoptosis, which also results in the clearance of the considerable quantities of proinflammatory products stored by these cells, does not lead to significant local cutaneous inflammatory responses.

Lack of neurokinin-1 receptor expression affects tissue mast cell numbers but not their spatial relationship with nerves

A spatial association between mast cells and nerves has been described in both the gastrointestinal and genitourinary tracts. However, the factors that influence the anatomic relationship between mast cells and nerves have not been completely defined. It has been suggested that the high-affinity receptor for substance P [neurokinin-1 (NK1)] might modulate this interaction. We therefore assessed mast cell-nerve relationships in tissues isolated from wild-type and NK1 receptor knockout (NK1-/-) mice. We now report that, in the complete absence of NK1 receptor expression, there is a significant increase in the number of mast cells without a change in the anatomic relationship between mast cell and nerves in stomach and bladder tissues at the light microscopic level. We next determined whether transplanted mast cells would maintain their spatial distribution, number, and contact with nerve elements. For this purpose, mast cell-deficient Kit(W)/Kit(W-v) mice were reconstituted with wild-type or NK1-/- bone marrow. No differences in mast cell-nerve contact were observed. These results suggest that NK1 receptor expression is important in the regulation of the number of mast cells but is not important in the interaction between mast cells and nerves. Furthermore, the interaction between mast cells and nerves is not mediated through NK1 receptor expression on the mast cell. Further studies are needed to determine the molecular pathway involved in mast cell migration and interaction with nerve elements, but the model of reconstitution of Kit(W)/Kit(W-v) mice with mast cells derived from different genetically engineered mice is a useful approach to further explore these mechanisms.

Treatment of cockroach allergen asthma model with imatinib attenuates airway responses

In the present study it was determined whether a pharmacologic approach to blocking receptor tyrosine kinase-mediated activation during allergic airway responses could be beneficial. To examine these responses, allergic mice were given a single oral dose of imatinib at clinically relevant concentrations, ranging from 0.05 to 50 mg/kg, by oral gavages just before allergen challenge. The reduction in the allergen-induced responses was significant and centered on reducing overall inflammation as well as pulmonary cytokine levels. In particular, the treatment of the mice with imatinib significantly attenuated airway hyperreactivity and peribronchial eosinophil accumulation, and significantly reduced Th2 cytokines, interleukin-4 and interleukin-13. In addition, chemokines previously associated with allergen-induced pulmonary disease, CCL2, CCL5, and CCL6, were significantly reduced in the lungs of the imatinib-treated animals. Together these data demonstrate that the pharmacologic inhibitor imatinib may provide a clinically attractive therapy for allergic, asthmatic responses.

Mast cell degranulation during abdominal surgery initiates postoperative ileus in mice

BACKGROUND & AIMS

Inflammation of the intestinal muscularis following manipulation during surgery plays a crucial role in the pathogenesis of postoperative ileus. Here, we evaluate the role of mast cell activation in the recruitment of infiltrates in a murine model.

METHODS

Twenty-four hours after control laparotomy or intestinal manipulation, gastric emptying was determined. Mast cell degranulation was determined by measurement of mast cell protease-I in peritoneal fluid. Intestinal inflammation was assessed by determination of tissue myeloperoxidase activity and histochemical staining.

RESULTS

Intestinal manipulation elicited a significant increase in mast cell protease-I levels in peritoneal fluid and resulted in recruitment of inflammatory infiltrates to the intestinal muscularis. This infiltrate was associated with a delay in gastric emptying 24 hours after surgery. Pretreatment with mast cell stabilizers ketotifen (1 mg/kg, p.o.) or doxantrazole (5 mg/kg, i.p.) prevented both manipulation-induced inflammation and gastroparesis. Reciprocally, in vivo exposure of an ileal loop to the mast cell secretagogue compound 48/80 (0.2 mg/mL for 1 minute) induced muscular inflammation and delayed gastric emptying. The manipulation-induced inflammation was dependent on the presence of mast cells because intestinal manipulation in mast cell-deficient Kit/Kitv mice did not elicit significant leukocyte recruitment. Reconstitution of Kit/Kitv mice with cultured bone marrow-derived mast cells from congenic wild types restored the manipulation-induced inflammation.

CONCLUSIONS

Our results show that degranulation of connective tissue mast cells is a key event for the establishment of the intestinal infiltrate that mediates postoperative ileus following abdominal surgery.

The meaning of the c-kit proto-oncogene product in malignant transformation in human mammary epithelium

To evaluate the relationship between the c-kit proto-oncogene product and malignant transformation of human breast tissue, we examined the immunohistochemical expression of the c-kit proto-oncogene product in both malignant and non-malignant breast tissues. The immunohistochemical expression of the c-kit proto-oncogene product in 40 primary breast cancer tissues (22 axillary lymph nodes negative, 18 lymph nodes positive), in 18 corresponding axillary lymph nodes, and in 10 distant metastastic tissues were studied using an anti-c-kit proto-oncogene product antibody in comparison with 20 normal and 20 benign breast tissues. The mean values of immunoreactive score (IRS) were compared. The IRS of the c-kit proto-oncogene product in normal mammary epithelia was 5.90 +/- 1.37 (mean +/- s.d.). In benign tissues, the c-kit proto-oncogene product was detected heterogeneously with a reduced IRS (4.05 +/- 1.82). In primary breast cancer tissues, the expression of the c-kit proto-oncogene product was often deleted and the average IRS (0.90 +/- 1.73) was significantly reduced compared to those of the normal breast tissues or benign breast disease tissues, but no significant difference was shown between the breast cancer groups. The c-kit proto-oncogene product may correlate with growth control or the differentiation of normal breast epithelium. This result suggests that the loss of expression of this protein might correlate with malignant breast cancer progression, but it is most likely involved at an early stage of human breast cancer development.

Gastrointestinal stromal tumors in a mouse model by targeted mutation of the Kit receptor tyrosine kinase

Oncogenic Kit mutations are found in somatic gastrointestinal (GI) stromal tumors (GISTs) and mastocytosis. A mouse model for the study of constitutive activation of Kit in oncogenesis has been produced by a knock-in strategy introducing a Kit exon 11-activating mutation into the mouse genome based on a mutation found in a case of human familial GIST syndrome. Heterozygous mutant KitV558Delta/+ mice develop symptoms of disease and eventually die from pathology in the GI tract. Patchy hyperplasia of Kit-positive cells is evident within the myenteric plexus of the entire GI tract. Neoplastic lesions indistinguishable from human GISTs were observed in the cecum of the mutant mice with high penetrance. In addition, mast cell numbers in the dorsal skin were increased. Therefore KitV558Delta/+ mice reproduce human familial GISTs, and they may be used as a model for the study of the role and mechanisms of Kit in neoplasia. Importantly, these results demonstrate that constitutive Kit signaling is critical and sufficient for induction of GIST and hyperplasia of interstitial cells of Cajal.

Stem cell factor attenuates liver damage in a murine model of acetaminophen-induced hepatic injury

Acute liver injury is a common cause of intensive care unit visits. In these studies, we used a murine model of acetaminophen poisoning to examine the role of stem cell factor (SCF) on liver damage. In the initial studies, we identified that the liver produces relatively high constitutive levels of SCF. Upon administration of acetaminophen, the levels of SCF fell dramatically, correlating to damage within the liver. When the liver was allowed to regenerate, the levels of SCF again correlated with the liver regeneration. We next treated mice with anti-SCF before sublethal doses of acetaminophen and significantly increased lethality in anti-SCF-treated animals. When exogenous SCF was given to mice, the lethality was significantly reduced compared with the control acetaminophen-treated animals and the damage within the liver tissue was attenuated. The administration of rSCF reduced the level of steady-state mRNA for cytochrome P450 cyp2E1 enzyme both in vitro and in vivo. These data suggest that SCF functions as an important factor that protects livers from acute damage.