Stem cell factor and interleukin-4 induce murine bone marrow cells to develop into mast cells with connective tissue type characteristics in vitro

Slow integrin-dependent migration organizes networks of tissue-resident mast cells

Immune cell locomotion is associated with amoeboid migration, a flexible mode of movement, which depends on rapid cycles of actin polymerization and actomyosin contraction1. Many immune cells do not necessarily require integrins, the major family of adhesion receptors in mammals, to move productively through three-dimensional tissue spaces2,3. Instead, they can use alternative strategies to transmit their actin-driven forces to the substrate, explaining their migratory adaptation to changing external environments4-6. However, whether these generalized concepts apply to all immune cells is unclear. Here, we show that the movement of mast cells (immune cells with important roles during allergy and anaphylaxis) differs fundamentally from the widely applied paradigm of interstitial immune cell migration. We identify a crucial role for integrin-dependent adhesion in controlling mast cell movement and localization to anatomical niches rich in KIT ligand, the major mast cell growth and survival factor. Our findings show that substrate-dependent haptokinesis is an important mechanism for the tissue organization of resident immune cells.

Type I Interferon α/β Receptor-Mediated Signaling Negatively Regulates Antiviral Cytokine Responses in Murine Bone-Marrow-Derived Mast Cells and Protects the Cells from Virus-Induced Cell Death

Mast cells (MCs) are critical for initiating inflammatory responses to pathogens including viruses. Type I interferons (IFNs) that exert their antiviral functions by interacting with the type I IFN receptor (IFNAR) play a central role in host cellular responses to viruses. Given that virus-induced excessive toxic inflammatory responses are associated with aberrant IFNAR signaling and considering MCs are an early source of inflammatory cytokines during viral infections, we sought to determine whether IFNAR signaling plays a role in antiviral cytokine responses of MCs. IFNAR-intact, IFNAR-blocked, and IFNAR-knockout (IFNAR^−/−) bone-marrow-derived MCs (BMMCs) were treated in vitro with a recombinant vesicular stomatitis virus (rVSVΔm51) to assess cytokine production by these cells. All groups of MCs produced the cytokines interleukin-6 and tumor necrosis factor-α in response to rVSVΔm51. However, production of the cytokines was lowest in IFNAR-intact cells as compared with IFNAR^−/− or IFNAR-blocked cells at 20 h post-stimulation. Surprisingly, rVSVΔm51 was capable of infecting BMMCs, but functional IFNAR signaling was able to protect these cells from virus-induced death. This study showed that BMMCs produced pro-inflammatory cytokines in response to rVSVΔm51 and that IFNAR signaling was required to down-modulate these responses and protect the cells from dying from viral infection.

The role of galanin in the differentiation of mucosal mast cells in mice

Mast cells are generally classified into two phenotypically distinct populations: mucosal-type mast cells (MMCs) and connective tissue-type mast cells (CTMCs). However, the molecular basis determining the different characteristics of the mast cell subclasses still remains unclear. Unfortunately, the number of mast cells that can be obtained from tissues is limited, which makes it difficult to study the function of each mast cell subclass. Here, we report the generation and characterization of MMCs and CTMCs derived from mouse BM mast cells (BMMCs). We found that the expression of galanin receptor 3 was elevated in MMCs when compared to the expression in CTMCs. Moreover, intraperitoneal injection of a galanin antagonist reduced MMCs and inhibited the inflammation of dextran sodium sulfate-induced colitis in mice. Therefore, these results suggest that galanin promotes MMC differentiation in vivo, and provide important insights into the molecular mechanisms underlying the differentiation of mast cell subclasses.

Controlling Mast Cell Activation and Homeostasis: Work Influenced by Bill Paul That Continues Today

Mast cells are tissue resident, innate immune cells with heterogenous phenotypes tuned by cytokines and other microenvironmental stimuli. Playing a protective role in parasitic, bacterial, and viral infections, mast cells are also known for their role in the pathogenesis of allergy, asthma, and autoimmune diseases. Here, we review factors controlling mast cell activation, with a focus on receptor signaling and potential therapies for allergic disease. Specifically, we will discuss our work with FcεRI and FγR signaling, IL-4, IL-10, and TGF-β1 treatment, and Stat5. We conclude with potential therapeutics for allergic disease. Much of these efforts have been influenced by the work of Bill Paul. With many mechanistic targets for mast cell activation and different classes of therapeutics being studied, there is reason to be hopeful for continued clinical progress in this area.

How mast cells make decisions

Mast cells (MCs) are present in various tissues and are responsible for initiating many of the early inflammatory responses to extrinsic challenges. Recent studies have demonstrated that MCs can tailor their responses, depending on the stimulus encountered and the tissue in which they are stimulated. In this issue of the JCI, Gaudenzio and colleagues examine the mechanistic differences between MC responses observed after engagement of Fcε receptor I and those seen after MC stimulation via the recently identified G protein-coupled receptor MRGPRX2. By showing that discrete cellular activation patterns affect the phenotype of the MC response in vivo and in vitro, the authors provide important information about how MCs differentially process various stimuli into distinct degranulation programs.

Mast cell production and response to IL-4 and IL-13

IL-4 was identified as the first cytokine to be produced by mast cells and is responsible for promoting mast cell IL-13 production. IL-4 and IL-13 play a prominent role in stimulating and maintaining the allergic response. As closely related genes, IL-4 and IL-13 share a common receptor subunit, IL-4Rα, necessary for signaling. Here we summarize the literature on mast cell activation associated with IL-4 and IL-13 production, including downstream signaling. We also describe the positive and negative roles each cytokine plays in mast cell immunity and detail the differences that exist between mouse and human mast cell responses to IL-4 and IL-13.

Mast cell function: a new vision of an old cell

Since first described by Paul Ehrlich in 1878, mast cells have been mostly viewed as effectors of allergy. It has been only in the past two decades that mast cells have gained recognition for their involvement in other physiological and pathological processes. Mast cells have a widespread distribution and are found predominantly at the interface between the host and the external environment. Mast cell maturation, phenotype and function are a direct consequence of the local microenvironment and have a marked influence on their ability to specifically recognize and respond to various stimuli through the release of an array of biologically active mediators. These features enable mast cells to act as both first responders in harmful situations as well as to respond to changes in their environment by communicating with a variety of other cells implicated in physiological and immunological responses. Therefore, the critical role of mast cells in both innate and adaptive immunity, including immune tolerance, has gained increased prominence. Conversely, mast cell dysfunction has pointed to these cells as the main offenders in several chronic allergic/inflammatory disorders, cancer and autoimmune diseases. This review summarizes the current knowledge of mast cell function in both normal and pathological conditions with regards to their regulation, phenotype and role.

The role of mast cells in cutaneous wound healing in streptozotocin-induced diabetic mice

Mast cells (MCs) reside in cutaneous tissue, and an increment of MCs is suggested to induce vascular regression in the process of wound healing. To clarify participation of MCs in diabetic cutaneous wound healing, we created an excisional wound on diabetic mice 4 weeks after streptozotocin injections and subsequently investigated the healing processes for 49 days, comparing them with control mice. The rate of wound closure was not markedly different between the diabetic and control mice. In the proliferative phase at days 7 and 14, neovascularization in the wound was weaker in diabetic mice than in control mice. In the remodeling phase at day 21 and afterward, rapid vascular regression occurred in control mice; however, neovascularization was still observed in diabetic mice where the number of vessels in granulation tissues was relatively higher than in control mice. In the remodeling phase of the control mice, MCs within the wound began to increase rapidly and resulted in considerable accumulation, whereas the increment of MCs was delayed in diabetic mice. In addition, the number of fibroblast growth factor (FGF)- or vascular endothelial growth factor (VEGF)-immunopositive hypertrophic fibroblast-like spindle cells and c-Kit-positive/VEGFR2-positive/FcεRIα-negative endothelial progenitor cells (EPCs) were higher in diabetic wounds. In conclusion, neovascularization in the proliferative phase and vascular regression in the remodeling phase were impaired in diabetic mice. The delayed increment of MCs and sustained angiogenic stimuli by fibroblast-like spindle cells and EPCs may inhibit vascular regression in the remodeling phase and impair the wound-healing process in diabetic mice.

Mast Cell Subsets and Their Functional Modulation by the Acanthocheilonema viteae Product ES-62

ES-62, an immunomodulator secreted by filarial nematodes, exhibits therapeutic potential in mouse models of allergic inflammation, at least in part by inducing the desensitisation of FcεRI-mediated mast cell responses. However, in addition to their pathogenic roles in allergic and autoimmune diseases, mast cells are important in fighting infection, wound healing, and resolving inflammation, reflecting that mast cells exhibit a phenotypic and functional plasticity. We have therefore characterised the differential functional responses to antigen (via FcεRI) and LPS and their modulation by ES-62 of the mature peritoneal-derived mast cells (PDMC; serosal) and those of the connective tissue-like mast cells (CTMC) and the mucosal-like mast cells derived from bone marrow progenitors (BMMC) as a first step to produce disease tissue-targeted therapeutics based on ES-62 action. All three mast cell populations were rendered hyporesponsive by ES-62 and whilst the mechanisms underlying such desensitisation have not been fully delineated, they reflect a downregulation of calcium and PKCα signalling. ES-62 also downregulated MyD88 and PKCδ in mucosal-type BMMC but not PDMC, the additional signals targeted in mucosal-type BMMC likely reflecting that these cells respond to antigen and LPS by degranulation and cytokine secretion whereas PDMC predominantly respond in a degranulation-based manner.

Lipid mediator metabolic profiling demonstrates differences in eicosanoid patterns in two phenotypically distinct mast cell populations

Mast cells are inflammatory cells that play key roles in health and disease. They are distributed in all tissues and appear in two main phenotypes, connective tissue and mucosal mast cells, with differing capacities to release inflammatory mediators. A metabolic profiling approach was used to obtain a more comprehensive understanding of the ability of mast cell phenotypes to produce eicosanoids and other lipid mediators. A total of 90 lipid mediators (oxylipins) were characterized using liquid chromatography-tandem mass spectrometry (LC-MS/MS), representing the cyclooxygenase (COX), lipoxygenase (LO), and cytochrome P450 (CYP) metabolic pathways. In vitro-derived murine mucosal-like mast cells (MLMC) and connective tissue-like mast cells (CTLMC) exhibited distinct mRNA expression patterns of enzymes involved in oxylipin biosynthesis. Oxylipins produced by 5-LO and COX pathways were the predominant species in both phenotypes, with 5-LO products constituting 90 ± 2% of the CTLMCs compared with 58 ± 8% in the MLMCs. Multivariate analyses demonstrated that CTLMCs and MLMCs secrete differing oxylipin profiles at baseline and following calcium ionophore stimulation, evidencing specificity in both a time- and biosynthetic pathway-dependent manner. In addition to the COX-regulated prostaglandin PGD(2) and 5-LO-regulated cysteinyl-leukotrienes (e.g., LTC(4)), several other mediators evidenced phenotype-specificity, which may have biological implications in mast cell-mediated regulation of inflammatory responses.

Antigen binding characteristics of immunoglobulin free light chains: crosslinking by antigen is essential to induce allergic inflammation

Beside the production of complete immunoglobulins IgG, IgE, IgA, IgM and IgD, consisting of tetrameric heterodimers of immunoglobulin heavy and light chains, B cells also secrete immunoglobulin free light chains (Ig-fLC). Previous studies showed that Ig-fLCs are able to induce immediate hypersensitivity reactions. It is apparent that recognition and binding of antigen are crucial steps in the onset of these inflammatory responses. In this study, the binding characteristics of Ig-fLC to antigen were further investigated using various biochemical approaches. In addition, we investigated whether antigen-mediated crosslinking of Ig-fLC is required to initiate allergic skin inflammation in vivo. Our study shows that binding of Ig-fLCs to antigen can be measured with different experimental setups. Surface plasmon resonance analysis showed real-time antigen binding characteristics. Specific antigen binding by Ig-fLCs was further detected using immunoblotting and ELISA. Using the ELISA-based assay, a binding affinity of 76.9±3.8 nM was determined for TNP-specific Ig-fLC. Antigen-induced ear swelling in mice passively sensitized with trinitrophenol-specific Ig-fLC was inhibited when multivalent antigen was combined with excess of monovalent antigen during challenge. We conclude that Ig-fLCs are able to interact with antigen, a prerequisite for antigen-specific cellular activation. In analogy to antigen-specific Fc receptor-induced mast cell activation, crosslinking of Ig-fLCs is necessary to initiate a local allergic response.

Differentiation of mast cell subpopulations from mouse embryonic stem cells

Mast cells can generally be divided into two major groups, connective tissue mast cells and mucosal mast cells. We and others have previously shown that these mast cell populations can be developed in vitro from mouse bone marrow stem cells using a combination of specific growth factors and cytokines. Mast cell differentiation from mouse embryonic stem (ES) cells is an important alternative method when developing mast cells from an embryonic lethal genetic deficiency or to reduce the use and handling of experimental animals. In this study, we have used protocols prior known to induce connective tissue like mast cells (CTLMC) (SCF and IL-4) and mucosal like mast cells (MLMC) (SCF, IL-3, IL-9 and TGF-β) from mouse bone marrow progenitor cells and employed these protocols to study if phenotype specific mast cells can be developed from ES cells. We here demonstrate that mast cells of the different phenotypes, CTLMC and MLMC, can be derived from mouse ES cells. The mast cell populations were characterized by chymase expression, receptor expression and their difference in activation pattern and in activation-induced survival.

Regulation of mast cell responses in health and disease

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

A critical role of conventional protein kinase C in morphological changes of rodent mast cells

In mast cells, crosslinking the high-affinity IgE receptor (FcɛRI) results in a dynamic reorganization of the actin cytoskeleton that is associated with membrane ruffling. Although the signaling involved in degranulation has been well described, it is less understood in morphological changes. In this study, we investigated the specific role of conventional protein kinase C (cPKC), a crucial signal for degranulation, in antigen-induced membrane ruffling of mast cells. In RBL-2H3 mast cells, antigen induced a long-lasting membrane ruffling, which was blocked with late-added Gö6976, a specific cPKC inhibitor, indicating that sustained activation of cPKC is required for maintaining the reaction. Immunofluorescence staining of endogenous PKCα/β and real-time imaging of transfected green fluorescent protein-tagged PKCα/β demonstrated that in response to antigen both PKCα and PKCβI quickly translocated to the plasma membrane and were colocalized with actin filaments at the ruffling sites. These reactions were blocked by expression of kinase-negative PKCβI, but not kinase-negative PKCα, and by treatment with a specific PKCβ inhibitor, LY333531. The adhesion, spreading and membrane ruffling of mouse bone marrow-derived mast cells (BMMCs), which are mostly nonadhesive, were promoted by both antigen and thymeleatoxin. Treatment with Gö6976 abolished all these reactions. Antigen-mediated migration of BMMC was also sensitive to Gö6076 and LY333531. In addition, BMMC adhesion by and migration toward stem cell factor were shown to be dependent on cPKC. Thus, cPKC, at least PKCβ subtype, may be critical for the dynamic morphological changes that lead to the migration of mast cells.

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.

Interleukin-4-mediated suppression of histamine synthesis in a murine mast cell line, BNu-2cl3

Since a wide variety of heterogeneity was found in tissue mast cells, recent studies have focused on the process of differentiation and maturation of mast cells. It has been largely accepted that the ability of histamine synthesis is high in the mucosal type mast cells whereas that is low in the tissue-connective type mast cells, although it remains largely unknown how histamine synthesis is regulated during differentiation. Interleukin (IL)-4 is one of the candidate factors that regulate the process of mast cell differentiation. We investigated the effects of IL-4 on histamine synthesis using a murine IL-3-dependent mucosal-type mast cell line, BNu-2cl3. IL-4 drastically suppressed histamine synthesis at the transcriptional levels. Storage of histamine was significantly decreased upon prolonged treatment with IL-4. Down-regulation in expression of histidine decarboxylase by IL-4 was restored by addition of excessive amount of IL-3. Changes in mRNA expression of mouse mast cell proteases (MMCPs) in the cells treated with IL-4 mimicked the differentiation process from mucosal-type to connective tissue-type mast cells; mRNA expression of MMCP2 was decreased, whereas that of MMCP4 and carboxypeptidase A3 were unchanged. These results suggest that IL-4 should play a critical role in suppression of histamine synthesis in mucosal-type mast cells.

Mechanisms of allergy and asthma

Allergies are the result of an inappropriate reaction against innocuous environmental proteins. The prevalence and severity of allergic diseases has increased dramatically during the last decade in developed countries. Allergen-specific T helper (Th) cells play a pivotal role in the pathogenesis of allergic hypersensitivity reactions. These Th cells activate a complex immune reaction that triggers the release of potent mediators and enhances the recruitment of inflammatory cells, which in turn elicit an inflammatory response that leads to the clinical symptoms of allergic disease. The current therapies for allergic diseases focus primarily on control of symptoms and suppression of inflammation, without affecting the underlying cause. However, the knowledge about the pathophysiology of allergic diseases has substantially increased, offering new opportunities for therapeutic intervention. In this review, we will focus on current insights into the mechanism of allergic reactions.

Induction of Ym1/2 in mouse bone marrow-derived mast cells by IL-4 and identification of Ym1/2 in connective tissue type-like mast cells derived from bone marrow cells cultured with IL-4 and stem cell factor

Mast cells play an important role in allergic inflammation by releasing various bioactive mediators. The function of mast cells is enhanced by various stimuli, partly due to the induction of specific genes and their products. Although many inducible genes have been identified, a significant number of genes remain to be identified. Therefore, this study used PCR-selected cDNA subtraction to establish the profile of induced genes in the connective tissue (CT) type-like mast cells derived from bone marrow cells cultured in the presence of IL-4 and stem cell factor. Two hundred and fifty cDNA clones were obtained from the CT type-like mast cells by PCR-selected cDNA subtraction. Among them, Ym1/2, a chitinase-like protein, is one of the most abundantly induced genes. Ym1 is produced by activated macrophages in a parasitic infection, whereas its isotype, Ym2, is highly upregulated in allergic lung disease. In order to differentiate which isotype is expressed in bone marrow cells, specific primers for bone marrow-derived mast cells (BMMC), and CT type-like mast cells were used for RT-PCR. The results showed that Ym1 was constitutively expressed in bone marrow cells and gradually decreased in the presence of IL-3, whereas Ym2 was induced only in the presence of IL-4. CT type-like mast cells from bone marrow cells expressed Ym1 throughout the culture period and Ym2 was induced only by the addition of IL-4 into BMMC, indicating that IL-4 is essential for the expression of Ym1/2 genes.

Neuropeptides activate human mast cell degranulation and chemokine production

During neuronal-induced inflammation, mast cells may respond to stimuli such as neuropeptides in an FcepsilonRI-independent manner. In this study, we characterized human mast cell responses to substance P (SP), nerve growth factor (NGF), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) and compared these responses to human mast cell responses to immunoglobulin E (IgE)/anti-IgE and compound 48/80. Primary cultured mast cells, generated from CD34(+) progenitors in the presence of stem cell factor and interleukin-6 (IL-6), and human cultured mast cells (LAD2) were stimulated with these and other stimuli (gastrin, concanavalin A, radiocontrast media, and mannitol) and their degranulation and chemokine production was assessed. VIP and SP stimulated primary human mast cells and LAD cells to degranulate; gastrin, concanavalin A, radiocontrast media, mannitol, CGRP and NGF did not activate degranulation. While anti-IgE stimulation did not induce significant production of chemokines, stimulation with VIP, SP or compound 48/80 potently induced production of monocyte chemoattractant protein-1, inducible protein-10, monokine induced by interferon-gamma (MIG), RANTES (regulated on activation, normal, T-cell expressed, and secreted) and IL-8. VIP, SP and compound 48/80 also activated release of tumour necrosis factor, IL-3 and granulocyte-macrophage colony-stimulating factor, but not IL-4, interferon-gamma or eotaxin. Human mast cells expressed surface neurokinin 1 receptor (NK1R), NK2R, NK3R and VIP receptor type 2 (VPAC2) but not VPAC1 and activation of human mast cells by IgE/anti-IgE up-regulated expression of VPAC2, NK2R, and NK3R. These studies demonstrate the pattern of receptor expression and activation of mast cell by a host of G-protein coupled receptor ligands and suggest that SP and VIP activate a unique signalling pathway in human mast cells. These results are likely to have direct relevance to neuronally induced inflammatory diseases.

Animal models of anaphylaxis

PURPOSE OF REVIEW

In this review we will focus on recent advances in the role of mast cells in the pathophysiology of insect allergy and the possible mechanisms of mast cell activation in anaphylaxis.

RECENT FINDINGS

Anaphylactic reactions in the mouse can be induced by several independent pathways involving immunoglobulin E, immunoglobulin free light chains, or immunoglobulin G. There is considerable evidence that mast cells play a central role in anaphylactic reactions to insect stings. Mast cells can be directly activated by components of insect venom or after allergic sensitization. Of interest is the observation that mast cells are not only effector cells in insect allergy, but may also play a protective role in preventing the development of severe anaphylactic responses or by controlling inflammatory reactions by modulation of antigen-specific T-cell responses.

SUMMARY

The contribution of mast cells in anaphylactic responses to insect venom may be heterogeneous. On the one hand, activation of mast cells contributes to the pathology by the release of bioactive and tissue-damaging mediators. However, mast cell activation may neutralize constituents in insect venom and defend against the adverse effects of these toxins or they may modulate inflammation through downregulation of antigen-specific immune responses.

IL-10 confers protection from mast cell degranulation in a mouse model of allergic conjunctivitis

IL-10 is a regulatory cytokine known to inhibit allergic and inflammatory events. Mast cells (MC) are effector cells which when stimulated release histamine, chemokines and cytokines that initiate the allergic inflammatory response. Recent studies have shown that IL-10 regulates MC function by affecting cytokine production and expression of FcvarepsilonR1 in in vitro assays. Using IL-10 knockout (IL10KO) mice, we examined the effect of its absence on MC susceptibility to degranulation by the basic secretagogue, Compound 48/80 (C48/80). C48/80 is a receptor mimetic that directly activates G proteins and stimulates vigorous MC degranulation. For these studies we stimulated conjunctival MC with C48/80 and found that conjunctival MC of IL10KO mice exhibit increased degranulation compared with wild type mice. Reconstitution of IL10KO mice by adding rIL-10 24h prior to challenge with C48/80 conferred increased resistance of MC to the degranulatory effects of C48/80. The protective effect therefore appears to be due to the presence of IL-10. This is the first in vivo rodent study which reports a novel role of IL-10 in stabilizing mast cells from degranulation by a secretagogue, by as of yet an unknown mechanism.

Peritoneal Cell-Derived Mast Cells: An In Vitro Model of Mature Serosal-Type Mouse Mast Cells

Bone marrow-derived mast cells (BMMC) have been used extensively as a mast cell model. BMMC, however, are immature cells that have no known physiological equivalent in tissues. They do not respond to IgG immune complexes. They may therefore not be appropriate for studying the physiopathology of IgE-induced allergies or IgG-induced tissue-specific inflammatory diseases which both depend on mature mast cells. Resident peritoneal mast cells are a minor population of differentiated cells that are not readily purified. They, however, can be expanded in culture to generate large numbers of homogeneous cells. We show here that these peritoneal cell-derived mast cells (PCMC) are mature serosal-type mouse mast cells which retain most morphological, phenotypic, and functional features of peritoneal mast cells. Like peritoneal mast cells, PCMC respond to IgG Abs. IgG immune complex-induced responses depended on FcgammaRIIIA and were negatively regulated by FcgammaRIIB. We found that a moderate FcgammaRIIB-dependent negative regulation, due not to a higher FcgammaRIIIA/FcgammaRIIB ratio, but to a relatively inefficient use of the lipid phosphatase SHIP1, determines this property of PCMC. PCMC also respond to IgE Abs. IgE-induced PCMC responses, however, differed quantitatively and qualitatively from BMMC responses. PCMC secreted no or much lower amounts of lipid mediators, chemokines, and cytokines, but they contained and released much higher amounts of preformed granular mediators. PCMC, but not BMMC, also contained and, upon degranulation, released molecules with a potent proteolytic activity. These properties make PCMC a useful new model for understanding the physiopathology of mast cells in IgE- and IgG-dependent tissue inflammation.

FcεRI Aggregation Promotes Survival of Connective Tissue-Like Mast Cells but Not Mucosal-Like Mast Cells

Mast cells play a critical role in IgE-dependent immediate hypersensitivity reactions. This is facilitated by their capacity to release inflammatory mediators and to undergo activation-induced survival upon cross-linking of the high-affinity IgE-receptor (FcepsilonRI). Due to their heterogeneity, mast cells can be divided into two major groups: the connective tissue mast cells and the mucosal mast cells. We have previously shown that IL-3-dependent bone marrow-derived mast cells can undergo activation-induced survival that is dependent on the prosurvival gene A1. In this study, we have used two different protocols to develop murine connective tissue-like mast cells (CTLMC) and mucosal-like mast cells (MLMC) to investigate their capacity to survive an allergic reaction in vitro. In this study, we demonstrate that FcepsilonRI stimulation promotes survival of CTLMC but not MLMC. Similarly, a prominent induction of A1 is observed only in CTLMC but not MLMC. MLMC have a higher basal level of the proapoptotic protein Bim compared with CTLMC. These findings demonstrate a difference among mast cell populations in their ability to undergo activation-induced survival after FcepsilonRI stimulation, which might explain the slower turnover of CTMC in IgE-dependent reactions.

Effects of Particle Size and Physical Form of Diets on Mast Cell Numbers, Histamine, and Stem Cell Factor Concentration in the Small Intestine of Broiler Chickens

The aim of this study was to investigate the hypothesis that particle size and diet form may affect the growth of mast cells and histamine release from the small intestine of broiler chickens. A total of 288, day-old male broiler chicks were randomly allocated to 1 of 4 corn-soy diets in a 2 x 2 factorial design. The factors included particle size (coarse vs. fine) and physical form (mash vs. pellet). The birds were housed in 90 x 60 cm pens containing 12 birds, and each treatment contained 6 replicate pens of birds from d 1 to 22. On d 22, 6 broilers from each treatment were slaughtered. Tissues from the small intestine (duodenum, jejunum, and ileum) were obtained to quantify mast cells using the toluidine blue staining technique. The results showed that mast cells in the jejunum were concentrated in the upper part of the villus in birds fed the coarsely ground mash diet, whereas mast cells were evenly distributed throughout the intestine in birds fed the other 3 diets. The number of mast cells was significantly lower in the duodenum (P = 0.04), jejunum (P < 0.01), and ileum (P = 0.01) of birds fed coarsely ground diets compared with finely ground diets, and there was no difference in mast cell numbers between birds fed mashed or pelleted diets at any site in the intestine. The histamine content (P = 0.02) and stem cell factor concentration (P = 0.03) were markedly lower in the jejunum of birds that were fed coarsely ground diets compared with finely ground diets. The stem cell factor concentration in the duodenum (P < 0.01) and jejunum (P = 0.05) was higher in birds fed pelleted compared with mash diets. The overall results of this experiment suggest that particle size and diet form affect mast cell number and histamine content in the small intestine by regulation of stem cell factor concentration.

Microarray analysis on Runx2-deficient mouse embryos reveals novel Runx2 functions and target genes during intramembranous and endochondral bone formation

A major challenge in developmental biology is to correlate genome-wide gene expression modulations with developmental processes in vivo. In this study, we analyzed the role of Runx2 during intramembranous and endochondral bone development, by comparing gene expression profiles in 14.5 dpc wild-type and Runx2 (-/-) mice. A total of 1277, 606 and 492 transcripts were found to be significantly modulated by Runx2 in calvaria, forelimbs and hindlimbs, respectively. Bioinformatics analysis indicated that Runx2 not only controls the processes of osteoblast differentiation and chondrocyte maturation, but may also play a role in axon formation and hematopoietic cell commitment during bone development. A total of 41 genes are affected by the Runx2 deletion in both intramembranous and endochondral bone, indicating common pathways between these two developmental modes of bone formation. In addition, we identified genes that are specifically involved in endochondral ossification. In conclusion, our data show that a comparative genome-wide expression analysis of wild-type and mutant mouse models allows the examination of mutant phenotypes in complex tissues.

IL-4 modulates the histamine content of mast cells in a mast cell/fibroblast co-culture through a Stat6 signaling pathway in fibroblasts

IL-4 plays a crucial role in the pathogenesis of allergic diseases, such as the induction of IgE synthesis and the development of mast cells. To further understand the effect of IL-4 on mast cells in skin, we utilized a mast cell/fibroblast co-culture system as an in vitro model of dermal mast cells. IL-4 induced mast cell growth in the culture with fibroblasts. Immunoblot analysis revealed that IL-4 activated Stat6 in both mast cells and fibroblasts. The over-expression of dominant-negative Stat6 in fibroblasts in the presence of IL-4 decreased the histamine content per mast cell, but not the number of mast cells. In contrast, the over-expression of constitutively-active Stat6 in fibroblasts increased the histamine content per mast cell, indicating that the activation of Stat6 in fibroblasts supports the maturation of mast cells co-cultured with fibroblasts.

IL-15 induces mast cell migration via a pertussis toxin-sensitive receptor

IL-15 induces proliferation, inhibits apoptosis and increases IL-4 production in murine mast cells. There is evidence that these activities are mediated via the uncharacterised receptor, IL-15R-X, rather than the classical three-chain IL-15 receptor. Effects of IL-15 on important aspects of mast cell biology, such as migration and degranulation, are unknown. We report that IL-15 induces migration of murine and human mast cells in a dose-dependent and biphasic manner, with peaks of migration occurring at approximately 10(-15) and approximately 10(-9) M. The potency of the response was similar to that induced by other well-established mast cell chemoattractants. Competition assays performed with murine and human mast cells indicate that both peaks of migration are due to chemotaxis. Pre-treatment of cells with pertussis toxin (PTX), a guanine nucleotide-binding regulatory protein (G-protein) inhibitor, resulted in complete inhibition of murine mast cell migration at approximately 10(-15) M IL-15, and human mast cell migration at approximately 10(-15) and approximately 10(-9) M. This demonstrates that murine and human mast cells express a PTX-sensitive receptor, activated in response to IL-15. Additionally, IL-15 did not induce degranulation in murine mast cells. Locally-produced IL-15 may contribute to mast cell recruitment during inflammatory responses, thereby acting as a linking cytokine between innate and adaptive arms of the immune system.

Establishment and characterization of continuous hematopoietic progenitors-derived pig normal mast cell lines

Mast cells (MCs) are tissue resident, hematopoietic stem cells-derived elements, distributed throughout the body. They are the pivotal mediating cells of allergic reactions. In addition, in mice, MCs play a critical role in the defense against several pathogens, such as bacteria, parasites and viruses. Whereas the biology of rodent and human MCs has been extensively studied using in vitro derived populations, the role of MCs in pigs has not yet been evaluated, given the very low availability of pure porcine MCs populations. In the present report, we describe an original method to obtain continuous factor-dependent normal pig MCs (PMC) lines from fetal hematopoietic progenitors. These Stem Cell Factor (SCF) and Interleukin-3- (IL-3)-dependent PMC lines retain their capacity to growth after conventional freezing methods and exhibit most of the morphological and biochemical properties of normal, although immature, MCs, including metachromatic granules containing sulfated polysaccharides, the expression of c-kit and high-affinity IgE receptors (FcepsilonRI), and the ability to store histamine that is released upon cross-linking of FcepsilonRI. In vitro derived PMC lines might thus be valuable tools to further investigate the reactivity of these elements towards several parasites frequently encountered in pig, such as, but not limited to, Ascaris suum, Trichinella spiralis or Trichuris suis, or towards antigens derived from these pathogens.

Live Cell Imaging to Study Signaling Molecules in Allergic Reactions

Mast cells are widely distributed throughout the body, predominantly near blood vessels and nerves, and express effector functions in allergic reactions, inflammatory diseases, and host defense. The activation of mast cells results in secretion of the preformed chemical mediators in their granules by a regulated process of exocytosis and leads to synthesis and secretion of lipid mediators and cytokines. Their soluble factors contribute to allergic inflammation. Mast cells are associated with hypersensitivity reactions, not only in the classical immunoglobulin E (IgE)-dependent mechanism but also in an IgE-independent manner. In particular, investigations of potential anatomical and functional interactions between mast cells and the nervous system have recently attracted great interest. To understand these molecular mechanisms in mast cell activation, the ability to visualize, track, and quantify molecules and events in living mast cells is an essential and powerful tool. Recent dramatic advances in imaging technology and labeling techniques have enabled us to carry out these tasks with high spatiotemporal resolution using confocal laser scanning microscopes, green fluorescent protein and its derivatives, and image analysis systems. Here we review our investigations of the dynamic processes of intracellular signaling molecules, cellular structure, and interactions with neurons in mast cells to provide basic and valuable information for allergy and clinical immunology using these new imaging methods.

Lymphotoxin-beta receptor activation by activated T cells induces cytokine release from mouse bone marrow-derived mast cells

Lymphotoxin-beta receptor (LTbetaR) signaling is known to play a key role in embryonic lymphoid organ formation as well as maintenance of lymphoid architecture. Activation of the LTbetaR is induced by either the heterotrimeric lymphotoxin-alpha(1)beta(2) (LTalpha(1)beta(2)) or the homotrimeric LIGHT (homologous to lymphotoxins, exhibits inducible expression, and competes with HSV gpD for herpes virus entry mediator, a receptor expressed by T lymphocyte). Both ligands are expressed on activated lymphocytes. As mast cells reside in close proximity to activated T cells in some inflammatory tissues, we examined the expression of LTbetaR on bone marrow-derived mast cells and asked whether the LTbetaR-ligand interaction would allow communication between mast cells and activated T cells. We found that mast cells express LTbetaR at the mRNA as well as at the protein level. To investigate LTbetaR-specific mast cell activation, the LTbetaR on BMMC from either wild-type or LTbetaR-deficient mice was stimulated with recombinant mouse LIGHT or agonistic mAbs in the presence of ionomycin. LTbetaR-specific release of the cytokines IL-4, IL-6, TNF, and the chemokines macrophage inflammatory protein 2 and RANTES was detected. Moreover, coculture of mast cells with T cells expressing the LTbetaR ligands also entailed the release of these cytokines. Interference with a specific LTbetaR inhibitor resulted in significant suppression of mast cell cytokine release. These data clearly show that LTbetaR expressed on mast cells can transduce a costimulatory signal in T cell-dependent mast cell activation.

Substance P can stimulate prostaglandin D2 and leukotriene C4 generation without granule exocytosis in murine mast cells

Mast cells play a central role in immediate type hypersensitivity and inflammatory events. Activation of mast cells not only can result in the release of preformed granule-associated mediators generally followed by de novo synthesis of lipid-derived substances. In the present study, we show that mast cell can be activated to release lipid mediators in absence of granule exocytosis. Primary cultured murine mast cells were stimulated with substance P and produced leukotriene C4, and prostaglandin D2 without the release of the granule-associated enzyme beta-hexosaminidase. Indomethacin and nordihydroguaiaretic acid caused complete inhibition of arachidonic metabolite generation. Leukotriene C4 and prostaglandin D2 production was blocked by genistein, a specific inhibitor of tyrosine kinases, and bisindolylmaleimide, a protein kinase C inhibitor, indicating a role for both phosphorylation pathways in the substance P-stimulated lipid mediator production. We suggest that the cytokine microenvironment of the mast cell determines whether mast cell stimulation leads to only lipid mediator release or full activation. Analysis of granule-associated mediators only might underestimate the role of mast cell activation under (patho)physiological conditions.

Functional expression of neurokinin 1 receptors on mast cells induced by IL-4 and stem cell factor

It is widely accepted that neurokinin 1 (NK(1)) receptors are not generally expressed on mast cells but little is known about their expression in inflammation. The present study shows expression of NK(1) receptors on bone marrow-derived mast cells (BMMC) under the influence of IL-4 or stem cell factor (SCF). Highest expression was found when both cytokines are present. Six days of coculture with the cytokines IL-4 and SCF showed significant expression of NK(1) receptors (NK(1) receptor(+)/c-kit(+) BMMC; control: 7%, IL-4/SCF: 16%), while 12 days of cytokine coculture increased this expression to 37% positive cells. A longer coculture with IL-4 and SCF did not give an additional effect. Increased expression in IL-4/SCF-treated BMMC was further confirmed using Western blot analysis. Next, we demonstrated the functional relevance of NK(1) receptor expression for mast cell activation, resulting in an enhanced degranulation upon stimulation by substance P. BMMC activation was significantly diminished by the NK(1) receptor antagonist RP67580 (10 micro M) when stimulated with low concentrations of substance P. The inactive enantiomer RP65681 had no effect. In addition, BMMC cultured from bone marrow of NK(1) receptor knockout mice showed significantly decreased exocytosis to low concentrations of substance P. The present study clearly shows that NK(1) receptor-induced activation contributes significantly at low physiological substance P concentrations (<100 micro M). In conclusion, BMMC were shown to express NK(1) receptors upon IL-4/SCF coculture. This expression of NK(1) receptors has been demonstrated to be of functional relevance and leads to an increase in the sensitivity of BMMC to substance P.

IL-9 enhances the growth of human mast cell progenitors under stimulation with stem cell factor

We examined the effects of IL-9 on human mast cell development from CD34(+) cord blood (CB) and peripheral blood cells in serum-deprived cultures. IL-9 apparently enhanced cell production under stimulation with stem cell factor (SCF) from CD34(+) CB cells. A great majority of the cultured cells grown with SCF + IL-9 became positive for tryptase at 4 wk. In methylcellulose cultures of CD34(+) CB cells, IL-9 increased both the number and size of mast cell colonies grown with SCF. Furthermore, SCF + IL-9 caused an exclusive expansion of mast cell colony-forming cells in a 2-wk liquid culture of CD34(+) CB cells, at a level markedly greater than for SCF alone. Clonal cell cultures and RT-PCR analysis showed that the targets of SCF + IL-9 were the CD34(+)CD38(+) CB cells rather than the CD34(+)CD38(-) CB cells. IL-9 neither augmented the SCF-dependent generation of progeny nor supported the survival of 6-wk-cultured mast cells. Moreover, there was no difference in the appearance of tryptase(+) cells and histamine content in the cultured cells between SCF and SCF + IL-9. The addition of IL-9 increased numbers of mast cell colonies grown with SCF from CD34(+) peripheral blood cells in children with or without asthma. It is of interest that mast cell progenitors of asthmatic patients responded to SCF + IL-9 to a greater extent than those of normal controls. Taken together, IL-9 appears to act as a potent enhancer for the SCF-dependent growth of mast cell progenitors in humans, particularly asthmatic patients.

CD34 is a specific marker of mature murine mast cells

OBJECTIVE

CD34 is a 90- to 120-kDa cell surface sialomucin that is widely used for the enrichment of human hematopoietic stem cells (HSCs) because of its selective expression on progenitor cells and absence on mature hematopoietic cells. Recently we found that CD34 is the prototypic member of a family of three proteins with similar structure and gene organization. In light of this observation, we further examined the distribution of CD34 family members in the mouse.

MATERIALS AND METHODS

Hematopoietic cell lines and primary tissues were evaluated for CD34 mRNA expression by Northern blot and protein expression by cell surface immunofluorescence. To confirm specific reactivity of the CD34 antibody, cells from CD34-deficient mice were used as controls.

RESULTS

Although CD34 mRNA was undetectable in all murine progenitor cell lines tested, high level expression was detected for bone marrow-derived mast cells (BMMCs). Likewise, cell surface immunofluorescence confirmed that CD34 is expressed by BMMCs and by in vivo peritoneal mast cells. No protein expression was observed for CD34-deficient mast cells. In addition, our data show that mast cells highly express the stem cell antigen Sca-1 and the well-known stem cell and mast cell antigen c-kit.

CONCLUSIONS

Our results demonstrate that, contrary to current dogma, CD34 is expressed by one mature hematopoietic lineage: mast cells. Our data also demonstrate that antigenically, murine mast cells and their precursors closely resemble HSCs and suggest caution should be used in the phenotypic characterization of HSCs to prevent mast cell contamination of stem cell preparations.

Immunoglobulin-free light chains elicit immediate hypersensitivity-like responses

Immunoglobulin (Ig)-free light chains IgLC are present in serum and their production is augmented under pathological conditions such as multiple sclerosis, rheumatoid arthritis and neurological disorders. Until now, no (patho)physiological function has been ascribed to circulating Ig light chains. Here we show that IgLCs can confer mast cell dependent hypersensitivity in mice. Antigenic stimulation results in plasma extravasation, cutaneous swelling and mast-cell degranulation. We show that IgLCs have a crucial role in development of contact sensitivity, which could be completely prevented by a novel IgLC antagonist. Although IgE and IgG(1) are central to the induction of immediate hypersensitivity reactions, our results show that IgLCs have similar activity. IgLCs may therefore be a novel factor in the humoral immune response to antigen exposure. Our findings open new avenues in investigating the pathogenesis of autoimmune diseases and their treatments.

Enhancement of mast cell survival: a novel function of some secretory phospholipase A(2) isotypes

This study tested the hypothesis that certain secretory phospholipase A(2) (sPLA(2)) isotypes act in a cytokine-like fashion through cell surface receptors to influence mast cell survival. Initial experiments revealed that sPLA(2) activity and sPLA(2) receptor expression are increased, and mast cells lost their capacity to maintain membrane asymmetry upon cytokine depletion. Groups IB and III, but not group IIA PLA(2), prevented the loss of membrane asymmetry. Similarly, group IB prevented nucleosomal DNA fragmentation in mast cells. Providing putative products of sPLA(2) hydrolysis to cytokine-depleted mast cells did not influence survival. Furthermore, catalytic inactivation of sPLA(2) did not alter its capacity to prevent apoptosis. Inhibition of protein synthesis using cycloheximide or actinomycin reversed the antiapoptotic effect of sPLA(2). Additionally, both wild-type and catalytically inactive group IB PLA(2) induced IL-3 synthesis in mast cells. However, adding IL-3-neutralizing Ab did not change Annexin V(FITC) binding and only partially inhibited thymidine incorporation in sPLA(2)-supplemented mast cells. In contrast, IL-3-neutralizing Ab inhibited both Annexin V(FITC) binding and thymidine incorporation in mast cells maintained with IL-3. sPLA(2) enhanced phosphoinositide 3'-kinase activity, and a specific inhibitor of phosphoinositide 3'-kinase reversed the antiapoptotic effects of sPLA(2). Likewise, sPLA(2) increased the degradation of I-kappaBalpha, and specific inhibitors of nuclear factor kappa activation (NF-kappaB) reversed the antiapoptotic effects of sPLA(2). Together, these experiments reveal that certain isotypes of sPLA(2) enhance the survival of mast cells in a cytokine-like fashion by activating antiapoptotic signaling pathways independent of IL-3 and probably via sPLA(2) receptors rather than sPLA(2) catalytic products.

Tachykinins and neuro-immune interactions in asthma

Excitatory non-adrenergic-non-cholinergic neuropeptides, such as the tachykinins substance P and neurokinin A, and its receptors are present in human and animal airways. Tachykinins are biologically active at extremely low concentrations. These peptides can cause potent inflammatory effects and can affect airway function in a way that resembles features of asthma. Local release of tachykinins affects blood vessels (vasodilatation and increased vascular permeability) and bronchial smooth muscle (bronchoconstrition and hyperresponsiveness). Neuropeptide research has revealed that tachykinins also play an important modulatory role in immune reactions. Tachykinins stimulate immune cells, such as mast cells, lymphocytes, and macrophages and are chemotactic for neutrophils and eosinophils. Vice versa, a range of immune cell mediators can also induce the release of tachykinins from excitatory NANC nerve endings in the airways. In the last 20 years, significant advances have been made in investigations of the interaction between immune cells and nervous systems in chronic inflammatory diseases such as asthma.

Vector-driven hyperexpression of a triad of costimulatory molecules confers enhanced T-cell stimulatory capacity to DC precursors

Activation of T cells requires at least two signals: signal 1, via the T-cell receptor, and signal 2, in which a costimulatory molecule on the antigen presenting cell (APC) interacts with a ligand on the T cell. Dendritic cells (DCs) are the most potent APCs in part due to their expression of costimulatory molecules. DCs, however, constitute only a minor percentage of APCs in the body, and the in vitro preparation of DCs is both costly and time consuming. The studies reported here demonstrate that one can utilize other APCs, such as bone marrow progenitor cells (BMPCs) and make them markedly more effective as APCs; this was accomplished by their infection with recombinant poxviruses (either the replication-defective avipox or vaccinia), which contain transgenes for a triad of costimulatory molecules (B7-1, ICAM-1 and LFA-3, designated TRICOM). APCs infected with TRICOM vectors are shown to significantly enhance the activation of both naive and effector CD4(+) and CD8(+) T-cell populations. The use of TRICOM vectors in vaccine strategies is discussed.

Influence of injury and cytokines on synthesis of monocyte chemoattractant protein-1 mRNA in peripheral nervous tissue

The signals and the source of the signals for monocyte/macrophage entry into the injured peripheral nervous tissue are not yet defined. This study was undertaken to determine the distribution of the chemokine monocyte chemoattractant protein-1 mRNA in injured rat and mouse nerves and to investigate the mechanisms that regulate its synthesis in rat Schwann cells. Results from RNase protection assays showed that, following sciatic nerve transection in rats, mRNA for monocyte chemoattractant protein-1 was induced at the site of lesion within 3 h of surgery and in more distal segments from 24 h for at least 8 days. In cultured Schwann cells, tumour necrosis factor-alpha but not interleukin-1 beta, interleukin-6, transforming growth factor-beta 1, platelet-derived growth factor-BB or nerve growth factor induced monocyte chemoattractant protein-1 mRNA in a time- and dose-dependent fashion. The induction of monocyte chemoattractant protein-1 mRNA in Schwann cells treated with tumour necrosis factor-alpha was reduced by inhibitors of nuclear factor-kappa B and the p38 mitogen-activated protein kinase. In mice that lack the two receptors for tumour necrosis factor, the message for JE, a murine homologue of monocyte chemoattractant protein-1, was still induced within 6 h of injury at the lesion site. However, in more distal segments 4 days after transection the concentration of JE mRNA was lower than that of control mice. Tumor necrosis factor-alpha is the only cytokine that was shown to induce monocyte chemoattractant protein-1 mRNA in cultured Schwann cells and is one of the factors that regulate the synthesis of monocyte chemoattractant protein-1 in injured nerves.

Attenuation of very late antigen-5-mediated adhesion of bone marrow-derived mast cells to fibronectin by peptides with inverted hydropathy to EF-hands

Release of allergic mediators from mast cells is enhanced by very late Ag (VLA)-5-mediated interaction of these cells with fibronectin. In this report, we show that VLA-5-mediated adhesion of bone marrow-derived mast cells to fibronectin can be induced by two different pathways: first, FcepsilonRI clustering, which depends on calmodulin activation and extracellular Ca(2+), and, second, by Mn(2+) stimulation, which is independent of calmodulin activation and antagonized by Ca(2+). Previous studies have shown the presence of several cation-binding domains in VLA-5 that are homologous to the calcium-binding EF-hands of calmodulin. To show a role for EF-hands of different proteins in VLA-5-mediated adhesion, we used calcium-like peptides (CALP), CALP1 and CALP2, designed to bind to EF-hands based on inverted hydropathy. CALP1 and, more potently, CALP2 inhibited FcepsilonRI-induced adhesion to fibronectin via different mechanisms. The target for the effects of CALP1 and 2 on FcepsilonRI-induced adhesion and degranulation was intracellular and likely involved calmodulin. Interestingly only CALP2 was able to inhibit Mn(2+)-induced calmodulin-independent adhesion by interfering with an extracellular target, which is probably VLA-5. We conclude that CALP1 and 2 can inhibit VLA-5-mediated adhesion of mast cells to fibronectin through binding to EF-hands of multiple proteins, and that these peptides can be used as lead compounds for the development of future therapy against allergy.

Excitatory non-adrenergic-non-cholinergic neuropeptides: key players in asthma

Professor David de Wied first introduced the term 'neuropeptides' at the end of 1971. Later peptide hormones and their fragments, endogenous opioid (morphine-like) peptides and a large number of other biogenic peptides became classified as neuropeptides. All of these peptides are united by a number of common features including their origin (nervous system and peptide-secreting cells found in various organs such as skin, gut, lungs), biosynthesis, secretion, metabolism, and enormous effectiveness. Neuropeptides are biologically active at extremely low concentrations. The past decade, neuropeptide research has revealed that neuropeptides also participate strongly in immune reactions. The neuro-immune concept has opened up a whole new research area. In the last 20 years, significant advances have been made in investigations of the interaction between immune and nervous systems in chronic inflammatory diseases such as asthma. The goal of this review is to bring together the functional relevance of excitatory non-adrenergic-non-cholinergic (NANC) nerves and the interaction with the immune system in asthma.

In activated mast cells, IL-1 up-regulates the production of several Th2-related cytokines including IL-9

Mast cells can play detrimental roles in the pathophysiology and mortality observed in anaphylaxis and other Th2-dominated allergic diseases. In contrast, these cells contribute to protective host defense mechanisms against parasitic worm infections. After IgE/Ag activation, mast cells can produce multiple cytokines that may enhance allergic inflammations, while a similar panel of Th2-related cytokines may support immunological strategies against parasites. Here we report that in primary mouse bone marrow-derived mast cells activated by ionomycin or IgE/Ag, the proinflammatory mediator IL-1 (alpha or beta) up-regulated production of IL-3, IL-5, IL-6, and IL-9 as well as TNF, i.e., cytokines implicated in many inflammatory processes including those associated with allergies and helminthic infections. IL-1 did not induce significant cytokine release in the absence of ionomycin or IgE/Ag, suggesting that Ca-dependent signaling was required. IL-1-mediated enhancement of cytokine expression was confirmed at the mRNA level by Northern blot and/or RT-PCR analysis. Our study reveals a role for IL-1 in the up-regulation of multiple mast cell-derived cytokines. Moreover, we identify mast cells as a novel source of IL-9. These results are of particular importance in the light of recent reports that strongly support a central role of IL-9 in allergic lung inflammation and in host defense against worm infections.

Stem cell factor and interleukin-4 increase responsiveness of mast cells to substance P

The response of mast cells (MC) to non-IgE-mediated stimulation is critically dependent on the population of MC examined. The neuropeptide Substance P (SP) has been reported to activate connective tissue-type MC (CTMC), while mucosal MC (MMC) are not activated by SP. We examined the effect of stem cell factor (SCF) plus interleukin-4 (IL-4) on SP-initiated activation of bone marrow-derived MC (BMMC). Mouse MC, derived from a culture of BM cells with IL-3, were subsequently treated with recombinant SCF plus IL-4 for 6 days. Responsiveness to SP was monitored measuring beta-hexosaminidase and lipid mediator release. Histochemical staining, histamine analysis, and granule protease expression were achieved to characterize the cells. In contrast to IL-3 grown cells, SCF/IL-4-exposed cells showed functional responsiveness to release beta-hexosaminidase (42.25% +/- 1.46% at SP concentration of 100 microM) and produce leukotriene C(4) (LTC(4)) (7.4 +/- 1.5 ng/10(6) cells)/prostaglandin D(2) (PGD(2)) (2.0 +/- 0.3 ng/10(6) cells) upon stimulation by SP. The increase in sensitivity of the cells to SP was not due to differentiation into CTMC, as the cells remained heparin negative. Both SCF and IL-4 were needed because SCF or IL-4 alone were insufficient to keep cells viable after 3 to 4 days post coculture. SP-induced secretion from BMMC cultured in medium containing SCF plus IL-4 (25.76% +/- 1.83%) was higher in comparison with cells cultured with SCF plus IL-3 (8.85% +/- 0.68%).These findings indicate that temporal changes in cytokine expression can influence the sensitivity of MC to non-immunologic stimuli. Local cytokine production leading to an increase in MC responsiveness to SP and inducing secretion of granule content and lipid generation may, therefore, propagate and worsen inflammatory conditions.

Regulation of mast cell number and function

Mast cells are complex, multifunctional cells that have unique phenotypes and growth requirements. Regulation in vitro of human mast cell growth and function differs from regulation of rodent mast cells. Human cell yields in vitro vary depending on tissue of origin, use of mononuclear or CD34+ progenitor cells, presence of cytokines, and serum-free versus serum-containing mediums. This article presents a summary of recent advances in the understanding of cytokine regulation of mast cell numbers and function in rodents and humans.