Signal transduction by Fc receptors: the Fc epsilon RI case

Inhibition of immediate-type allergic reactions by Prunella vulgaris in a murine model

We studied the effect of aqueous extract of Prunella vulgaris (Labiatae) (PVAE) on immediate-type allergic reactions. PVAE (0.005 to 1 g/kg) dose-dependently inhibited systemic anaphylactic shock induced by compound 48/ 80 in rats. When PVAE was given as pretreatment, at concentrations ranging from 0.005 to 1 g/kg, the serum histamine levels induced by compound 48/ 80 were reduced in a dose-dependent manner. PVAE (0.001 to 1 g/kg) inhibited the passive cutaneous anaphylaxis activated by anti-dinitrophenyl (DNP) IgE antibody dose dependently. PVAE also inhibited the histamine release induced by compound 48/80 or anti-DNP IgE from the rat peritoneal mast cells (RPMC). The level of cyclic AMP in RPMC, when PVAE was added, significantly increased, compared with that of normal control. Moreover, PVAE (0.01 and 0.1 mg/ml) had a significant inhibitory effect on anti-DNP IgE-mediated tumor necrosis factor-alpha production from RPMC. These results indicate that PVAE inhibits immediate-type allergic reactions in rats.

Regulation of mast cell survival by IgE

Mast cells play critical roles in hypersensitivity and in defense against certain parasites. We provide evidence that mouse mast cell survival and growth are promoted by monomeric IgE binding to its high-affinity receptor, Fc epsilon RI. Monomeric IgE does not promote DNA synthesis but suppresses the apoptosis induced by growth factor deprivation. This antiapoptotic effect occurs in parallel with IgE-induced increases in Fc epsilon RI surface expression but requires the continuous presence of IgE. This process does not involve the FasL/Fas death pathway or several Bcl-2 family proteins and induces a distinctly different signal than Fc epsilon RI cross-linking. The ability of IgE to enhance mast cell survival and Fc epsilon RI expression may contribute to amplified allergic reactions.

Monomeric IgE stimulates signaling pathways in mast cells that lead to cytokine production and cell survival

Although IgE binding to mast cells is thought to be a passive presensitization step, we demonstrate herein that monomeric IgE (mIgE) in the absence of antigen (Ag) stimulates multiple phosphorylation events in normal murine bone marrow-derived mast cells (BMMCs). While mIgE does not induce degranulation or leukotriene synthesis, it leads to a more potent production of cytokines than IgE + Ag. Moreover, mIgE prevents the apoptosis of cytokine-deprived BMMCs, likely by maintaining Bcl-X(L) levels and producing autocrine-acting cytokines. The addition of Ag does not increase this IgE-induced survival. Since IgE concentrations as low as 0.1 microg/ml enhance BMMC survival, elevated plasma IgE levels in humans with atopic disorders may contribute to the elevated mast cell numbers seen in these individuals.

Inhibition of antigen-induced mediator release from IgE-sensitized cells by a monoclonal anti-Fc epsilon RI alpha-chain receptor antibody: implications for the involvement of the membrane-proximal alpha-chain region in Fc epsilon RI-mediated cell activation

The interaction between human IgE and its high affinity receptor, FcepsilonRI, is a critical event in mediating the allergic response. Aggregation of the alpha-chain of FcepsilonRI (FcepsilonRIalpha) occurs via cross-linking of receptor-bound IgE by Ag, resulting in cell activation and the release of mediators of hypersensitivity. Recently, we mapped the epitopes of two anti-FcepsilonRIalpha mAbs, 15/1 and 5H5F8. In contrast to 15/1, mAb 5H5F8 does not inhibit IgE binding to FcepsilonRIalpha. Here we demonstrate both 5H5F8 binding to FcepsilonRI(+) cells as well as a high level of IgE binding to 5H5F8-saturated cells. At the same time 5H5F8 strongly inhibits hexosaminidase release and Ca(2+) flux after Ag triggering from human IgE-sensitized RBL-2H3 cells stably transfected with human FcepsilonRIalpha. Further, 5H5F8 and its Fab inhibit sulfidoleukotriene and histamine release from primary human peripheral blood leukocytes, including cells bearing endogenous IGE: Furthermore, we confirm that 5H5F8 maps to a linear peptide sequence in close proximity to the cell membrane. Two chemically synthesized peptides containing the 5H5F8 epitope sequence PREKY were selected for detailed analysis of 5H5F8 and 5H5F8 Fab binding and were found to produce K(d) values of similar magnitude to that observed for binding to recombinant FcepsilonRIalpha. These peptides may prove useful as targets for the identification of antagonists of FcepsilonRIalpha-mediated biological activity. Moreover, our data indicate that FcepsilonRIalpha-mediated activation may involve a novel alpha-chain epitope in an early step of the cell-triggering pathway leading to cellular activation.

Exposure of RBL-2H3 mast cells to Ag(+) induces cell degranulation and mediator release

There is a growing need to understand the impact of environmental sulfhydryl group-reactive heavy metals on the immune system. Here we show that Ag(+) induces mast cell degranulation, as does the aggregation of the high affinity immunoglobulin E receptor (FcepsilonRI). Micromolar quantities of Ag(+) specifically induced degranulation of mast cell model rat basophilic leukemia (RBL-2H3) cells without showing cytotoxicity. The Ag(+)-mediated degranulation could be observed as rapidly as 5 min after the addition of the ions. Ag(+) also induced a rapid change in tyrosine phosphorylation of multiple cellular proteins including the focal adhesion kinase but not Syk kinase. The Syk-selective inhibitor piceatannol and the Src family-selective tyrosine kinase inhibitor PP1 dose-dependently inhibited FcepsilonRI-mediated degranulation, whereas neither compound inhibited the Ag(+)-mediated degranulation. Furthermore, likewise FcepsilonRI aggregation, Ag(+) also induced leukotriene secretion. These results show that Ag(+) activates RBL-2H3 mast cells through a tyrosine phosphorylation-linked mechanism, which is distinct from that involved in FcepsilonRI-mediated activation.

Synaptotagmin I expression in mast cells of normal human tissues, systemic mast cell disease, and a human mast cell leukemia cell line

Synaptotagmin I (STG I) is a Ca(2+) sensor and one of the synaptic vesicle proteins that mediate exocytosis. To determine the mechanism of release of large granules from mast cells, we studied by immunohistochemistry the presence of STG I in mast cells in normal human tissues simultaneously with the mast cell markers mast cell tryptase (tryptase) and c-kit. The tumor cells of systemic mast cell disease (SMCD) and a human mast cell leukemia cell line (HMC-1) were also examined. Human mast cells in normal tissues and the tumor cells of SMCD expressed STG I as well as mast cell tryptase (tryptase) and c-kit. STG I mRNA and its products in HMC-1 were examined by RT-PCR analysis and immunocytochemistry, respectively. STG I expression in HMC-1 cells was compared with that in cells stimulated and non-stimulated by phorbol 12-myristate 13-acetate and also with that in NB-1 and PC12 cells, known to express STG I. STG I mRNA was detected in both non-stimulated and stimulated HMC-1 cells and in NB-1 and PC12 cells. STG I immunoreactivity was weaker than NB-1 or PC12 immunoreactivity. However, it increased in the stimulated HMC-1 cells. Mast cells expressed STG I in various states. STG I may mediate exocytosis of large granules in mast cells.

Tyrosine phosphorylation of the linker for activator of T cells in mast cells by stimulation with the high affinity IgE receptor

Aggregation of the high affinity IgE receptors (FcepsilonRI) on basophils and mast cells, members of the immune receptor family, initiates a cascade of events that results in the release of inflammatory mediators. This pathway involves the activation of several protein-tyrosine kinases, including Lyn, Syk, Btk, and Fak that induce the tyrosine phosphorylation of various proteins. The linker for activation of T cells (LAT), was originally found as a ZAP-70 tyrosine kinase substrate that linked T cell receptors to cellular activation, and was expressed in T cells, NK cells and mast cells. Here we show that LAT expressed in the RBL-2H3 rat mast cell line is tyrosine-phosphorylated after aggregation of FcepsilonRI. The tyrosine phosphorylation of the LAT was dramatically enhanced after receptor aggregation. Furthermore, a tyrosine-phosphorylated 80-kDa protein associated with LAT transiently after receptor aggregation. GST fusion proteins containing parts of PLCgamma or PI3 kinase can bind LAT. These results suggest that LAT plays an important role not only in T cell, but also in mast cell activation, and that the association among these signaling molecules is critical for FcepsilonRI-mediated intracellular signal transduction in mast cells.

T cell epitope-containing hypoallergenic recombinant fragments of the major birch pollen allergen, Bet v 1, induce blocking antibodies

Allergen-specific immunotherapy represents one of the few curative approaches toward type I allergy. Up to 25% of allergic patients are sensitized against the major birch pollen allergen, Bet v 1. By genetic engineering we produced two recombinant (r) Bet v 1 fragments comprising aa 1-74 and aa 75-160 of Bet v 1, which, due to a loss of their native-like fold, failed to bind IgE Abs and had reduced allergenic activity. Here we show that both fragments covering the full Bet v 1 sequence induced human lymphoproliferative responses similar to rBet v 1 wild type. The C-terminal rBet v 1 fragment induced higher lymphoproliferative responses than the N-terminal fragment and represented a Th1-stimulating segment with high IFN-gamma production, whereas the N-terminal fragment induced higher IL-4, IL-5, and IL-13 secretion. Immunization of mice and rabbits with rBet v 1 fragments induced IgG Abs, which cross-reacted with complete Bet v 1 and Bet v 1-related plant allergens and strongly inhibited the IgE binding of allergic patients to these allergens. Thus, our results demonstrate that hypoallergenic T cell epitope-containing rBet v 1 fragments, despite lacking IgE epitopes, can induce Abs in vivo that prevent the IgE binding of allergic patients to the wild-type allergen. The overall demonstration of the immunogenic features of the hypoallergenic rBet v 1 fragments will now enable clinical studies for safer and more efficient specific immunotherapy.

Roles of mast cells and basophils in innate and acquired immunity

There have been several recent advances in knowledge about mast cells and basophils in immune responses, of which some are particularly important: a role has been found for heparin in the storage of certain proteases and other mediators in mast cell cytoplasmic granules; an important role for mast cells in the development of several chronic aspects of an asthma model in mice has been discovered; and a new approach has been developed, based on the generation of mast cells from embryonic stem cells in vitro, to investigate mast cell function in vitro or in vivo.

Phosphorylation of Syk activation loop tyrosines is essential for Syk function. An in vivo study using a specific anti-Syk activation loop phosphotyrosine antibody

Syk is an important protein-tyrosine kinase in immunoreceptor signaling. FcepsilonRI aggregation in mast cells induces tyrosine phosphorylation and increased enzymatic activity of Syk. The two adjacent tyrosines in the Syk activation loop are thought to be important for the propagation of FcepsilonRI signaling. To evaluate the phosphorylation of these tyrosines in vivo and further understand the relationship of Syk tyrosine phosphorylation with its function, an antibody was developed specific for phosphorylated tyrosines in the activation loop of Syk. FcepsilonRI aggregation on mast cells induced the phosphorylation of both tyrosine residues of the activation loop. The kinase activity of Syk played the major role in phosphorylating its activation loop tyrosines both in vivo and in vitro. In FcepsilonRI-stimulated mast cells, the total Syk tyrosine phosphorylation paralleled the phosphorylation of its activation loop tyrosines and downstream propagation of signals for histamine release. In contrast, the cell surface binding of anti-ganglioside monoclonal antibody AA4 induced only strong general tyrosine phosphorylation of Syk and minimal histamine release and weak phosphorylation of activation loop tyrosines. These results demonstrate that phosphorylation of the activation loop tyrosines is important for mediating receptor signaling and is a better marker of Syk function than is total Syk tyrosine phosphorylation.

A human monoclonal IgE antibody defines a highly allergenic fragment of the major timothy grass pollen allergen, Phl p 5: molecular, immunological, and structural characterization of the epitope-containing domain

Almost 90% of grass pollen-allergic patients are sensitized against group 5 grass pollen allergens. We isolated a monoclonal human IgE Fab out of a combinatorial library prepared from lymphocytes of a grass pollen-allergic patient and studied its interaction with group 5 allergens. The IgE Fab cross-reacted with group 5A isoallergens from several grass and corn species. By allergen gene fragmentation we mapped the binding site of the IgE Fab to a 11.2-kDa N-terminal fragment of the major timothy grass pollen allergen Phl p 5A. The IgE Fab-defined Phl p 5A fragment was expressed in Escherichia coli and purified to homogeneity. Circular dichroism analysis revealed that the rPhl p 5A domain, as well as complete rPhl p 5A, assumed a folded conformation consisting predominantly of an alpha helical secondary structure, and exhibited a remarkable refolding capacity. It reacted with serum IgE from 76% of grass pollen-allergic patients and revealed an extremely high allergenic activity in basophil histamine release as well as skin test experiments. Thus, the rPhl p 5A domain represents an important allergen domain containing several IgE epitopes in a configuration optimal for efficient effector cell activation. We suggest the rPhl p 5A fragment and the corresponding IgE Fab as paradigmatic tools to explore the structural requirements for highly efficient effector cell activation and, perhaps later, for the development of generally applicable allergen-specific therapy strategies.

The unfolding/denaturation of immunogammaglobulin of isotype 2b and its F(ab) and F(c) fragments

The unfolding and further denaturation of IgG and its F(ab) and F(c) fragments were studied both on a macroscopic and molecular level, using differential scanning calorimetry and circular dichroism spectroscopy, respectively. It was shown that the structural integrity of the F(ab) and F(c) units was retained after fragmentation of the IgG. The F(ab) fragment denatured at approximately 61 degrees C and the F(c) fragment at 71 degrees C. The structural transitions observed in the whole IgG is the sum effect of those determined for the isolated F(ab) and F(c) fragments.

Diphenyleneiodonium prevents reactive oxygen species generation, tyrosine phosphorylation, and histamine release in RBL-2H3 mast cells

Mast cells play a central role in immediate allergic reactions mediated by immunoglobulin E. It has recently been reported that mast cells generate intracellular reactive oxygen species (ROS) in response to stimulation with divergent physiologically relevant stimulants. However, the physiological role of ROS is poorly understood. Here we demonstrate that mast cell model rat basophilic leukemia (RBL-2H3) cells generate ROS in response to antigen and the calcium-ionophore A23187 via activation of diphenyleneiodonuim (DPI)-sensitive enzyme and that blockade of ROS generation by DPI suppresses histamine release induced by either stimulant. Increased tyrosine phosphorylation of pp125(FAK) and a 77-kDa protein coprecipitating specifically with the kinase occurred in parallel with the secretion, and blockade of ROS generation by DPI also suppressed the tyrosine phosphorylation of both proteins. These findings suggest that ROS generated by a flavoenzyme-dependent mechanism may be involved in histamine release through the pp125(FAK) pathway.

An intron transcriptional enhancer element regulates IL-4 gene locus accessibility in mast cells

The cell type-specific expression of a gene is dependent on developmentally regulated modifications in chromatin structure that allow accessibility of basal and inducible transcription factors. In this study, we demonstrate that a cis-acting element in the second intron of the murine IL-4 gene has a dual function in regulating transcription in mast cells as well as chromatin accessibility of the IL-4 gene locus through its influence on the methylation state of the gene. Previous studies have shown that mast cell-restricted transcription factors GATA-1/2 and PU.1 associate with the intron element and regulate its activity. In this study, we use DNase I footprinting and mutational analyses to identify two additional sites that contribute to the element's ability to enhance transcription. One of these sites associates preferentially with STAT5a and STAT5b. We also demonstrate that deletion of the element or mutation of the GATA binding site in the context of a stably integrated IL-4 genomic construct prevents maintenance of a demethylated locus in IL-4-producing mast cells. These data indicate that, analogous to Ig and TCR intron regulatory elements, the intron enhancer has an essential role in maintaining developmentally regulated demethylation at the IL-4 gene locus. In addition, they indicate that members of the GATA family of transcription factors likely play an important role in these processes.

In vivo immunological function of mast cells derived from embryonic stem cells: an approach for the rapid analysis of even embryonic lethal mutations in adult mice in vivo

An important goal of tissue engineering is to achieve reconstitution of specific functionally active cell types by transplantation of differentiated cell populations derived from normal or genetically altered embryonic stem cells in vitro. We find that mast cells derived in vitro from wild-type or genetically manipulated embryonic stem cells can survive and orchestrate immunologically specific IgE-dependent reactions after transplantation into mast cell-deficient Kit(W)/Kit(W-v) mice. These findings define a unique approach for analyzing the effects of mutations of any genes that are expressed in mast cells, including embryonic lethal mutations, in vitro or in vivo.

Redundant and opposing functions of two tyrosine kinases, Btk and Lyn, in mast cell activation

Protein-tyrosine kinases play crucial roles in mast cell activation through the high-affinity IgE receptor (FcepsilonRI). In this study, we have made the following observations on growth properties and FcepsilonRI-mediated signal transduction of primary cultured mast cells from Btk-, Lyn-, and Btk/Lyn-deficient mice. First, Lyn deficiency partially reversed the survival effect of Btk deficiency. Second, FcepsilonRI-induced degranulation and leukotriene release were almost abrogated in Btk/Lyn doubly deficient mast cells while singly deficient cells exhibited normal responses. Tyrosine phosphorylation of cellular proteins including phospholipases C-gamma1 and C-gamma2 was reduced in Btk/Lyn-deficient mast cells. Accordingly, FcepsilonRI-induced elevation of intracellular Ca2+ concentrations and activation of protein kinase Cs were blunted in the doubly deficient cells. Third, in contrast, Btk and Lyn demonstrated opposing roles in cytokine secretion and mitogen-activated protein kinase activation. Lyn-deficient cells exhibited enhanced secretion of TNF-alpha and IL-2 apparently through the prolonged activation of extracellular signal-related kinases and c-Jun N-terminal kinase. Potentially accounting for this phenomenon and robust degranulation in Lyn-deficient cells, the activities of protein kinase Calpha and protein kinase CbetaII, low at basal levels, were enhanced in these cells. Fourth, cytokine secretion was severely reduced and c-Jun N-terminal kinase activation was completely abrogated in Btk/Lyn-deficient mast cells. The data together demonstrate that Btk and Lyn are involved in mast cell signaling pathways in distinctly different ways, emphasizing that multiple signal outcomes must be evaluated to fully understand the functional interactions of individual signaling components.

Inhibition of mast cell-mediated anaphylaxis by sochungryong-tang

According to traditional Asian philosophy, sochungryong-tang (S-Tang) is a prescription for treating exterior syndrome. In this study, we investigated the effect of S-Tang on mast cell-mediated anaphylaxis. S-Tang completely inhibited compound 48/80-induced systemic anaphylactic shock at a dose of 100 mg/kg. When S-Tang was given as pretreatment at concentrations ranging from 1 to 1000 mg/kg, the serum histamine levels induced by compound 48/80 were reduced in a dose-dependent manner. S-Tang inhibited the local anaphylaxis activated by anti-dinitrophenyl (DNP) IgE antibody, and also inhibited the histamine release from the rat peritoneal mast cells by compound 48/80 or anti-DNP IgE. These results indicate that S-Tang may contain substances with actions that inhibit mast cell degranulation.

Calmodulin regulates the disassembly of cortical F-actin in mast cells but is not required for secretion

Secretion is dependent on a rise in cytosolic Ca(2+)concentration and is associated with dramatic changes in actin organization. The actin cortex may act as a barrier between secretory vesicles and plasma membrane. Thus, disassembly of this cortex should precede late steps of exocytosis. Here we investigate regulation of both the actin cytoskeleton and secretion by calmodulin. Ca(2+), together with ATP, induces cortical F-actin disassembly in permeabilized rat peritoneal mast cells. This effect is strongly inhibited by removing endogenous calmodulin (using calmodulin inhibitory peptides), and increased by exogenous calmodulin. Neither treatment, however, affects secretion. Low concentrations ( approximately 1 microM) of a specific inhibitor of myosin light chain kinase, ML-7, prevent F-actin disassembly, but not secretion. In contrast, a myosin inhibitor affecting both conventional and unconventional myosins, BDM, decreases cortical disassembly as well as secretion. Observations of fluorescein-calmodulin, introduced into permeabilized cells, confirmed a strong (Ca(2+)-independent) association of calmodulin with the actin cortex. In addition, fluorescein-calmodulin enters the nuclei in a Ca(2+)-dependent manner. In conclusion, calmodulin promotes myosin II-based contraction of the membrane cytoskeleton, which is a prerequisite for its disassembly. The late steps of exocytosis, however, require neither calmodulin nor cortical F-actin disassembly, but may be modulated by unconventional myosin(s).

Thapsigargin-induced degranulation of mast cells is dependent on transient activation of phosphatidylinositol-3 kinase

Thapsigargin, which elevates cytosolic calcium levels by inhibiting the sarcoplasmic/endoplasmic reticulum calcium-dependent ATPase, was tested for its ability to degranulate bone marrow-derived mast cells (BMMCs) from src homology 2-containing inositol phosphatase +/+ (SHIP+/+) and SHIP-/- mice. As was found previously with steel factor, thapsigargin stimulated far more degranulation in SHIP-/- than in SHIP+/+ BMMCs, and this was blocked with the phosphatidylinositol-3 (PI-3) kinase inhibitors, LY294002 and wortmannin. In contrast to steel factor, however, this heightened degranulation of SHIP-/- BMMCs was not due to a greater calcium influx into these cells, nor was the thapsigargin-induced calcium influx inhibited by LY294002, suggesting that the heightened thapsigargin-induced degranulation of SHIP-/- BMMCs was due to a PI-3 kinase-regulated step distinct from that regulating calcium entry. An investigation of thapsigargin-stimulated pathways in both cell types revealed that MAPK was heavily but equally phosphorylated. Interestingly, the protein kinase C inhibitor, bisindolylmaleimide (compound 3), totally blocked thapsigargin-induced degranulation in both SHIP+/+ and SHIP-/- BMMCs. As well, thapsigargin stimulated a PI-3 kinase-dependent, transient activation of protein kinase B, and this activation was far greater in SHIP-/- than in SHIP+/+ BMMCs. Consistent with this, thapsigargin was found to be a potent survival factor, following cytokine withdrawal, for both cell types and was more potent with SHIP-/- cells. These studies have both identified an additional PI-3 kinase-dependent step within the mast cell degranulation process, possibly involving 3-phosphoinositide-dependent protein kinase-1 and a diacylglycerol-independent protein kinase C isoform, and shown that the tumor-promoting activity of thapsigargin may be due to its activation of protein kinase B and subsequent promotion of cell survival.

Inhibition of calcium release-activated calcium current by Rac/Cdc42-inactivating clostridial cytotoxins in RBL cells

Using large clostridial cytotoxins as tools, the role of Rho GTPases in activation of RBL 2H3 hm1 cells was studied. Clostridium difficile toxin B, which glucosylates Rho, Rac, and Cdc42 and Clostridium sordellii lethal toxin, which glucosylates Rac and Cdc42 but not Rho, inhibited the release of hexosaminidase from RBL cells mediated by the high affinity antigen receptor (FcepsilonRI). Additionally, toxin B and lethal toxin inhibited the intracellular Ca(2+) mobilization induced by FcepsilonRI-stimulation and thapsigargin, mainly by reducing the influx of extracellular Ca(2+). In patch clamp recordings, toxin B and lethal toxin inhibited the calcium release-activated calcium current by about 45%. Calcium release-activated calcium current, the receptor-stimulated Ca(2+) influx, and secretion were inhibited neither by the Rho-ADP-ribosylating C3-fusion toxin C2IN-C3 nor by the actin-ADP-ribosylating Clostridium botulinum C2 toxin. The data indicate that Rac and Cdc42 but not Rho are not only involved in late exocytosis events but are also involved in Ca(2+) mobilization most likely by regulating the Ca(2+) influx through calcium release-activated calcium channels activated via FcepsilonRI receptor in RBL cells.

Transient translocation and activation of protein phosphatase 2A during mast cell secretion

Okadaic acid inhibits secretion from mast cells, suggesting a regulatory role for protein Ser/Thr phosphatases type I (PP1) and/or 2A (PP2A) in the secretory process. In unstimulated RBL-2H3 cells, okadaic acid pretreatment inhibited PP2A activity in both cytosol and membrane fractions, but inhibition of secretion correlated with inhibition of membrane-bound rather than cytosolic PP2A activity. Okadaic acid had very little effect on PP1 activity. Stimulation of RBL-2H3 cells by antigen led to the activity and amount of PP2A in the membrane fraction increasing nearly 2-fold. In contrast, there was little change in the activity or distribution of PP1. Importantly, the translocation of PP2A was transient, coinciding with or marginally preceding the peak rate of secretion, suggesting a link between PP2A translocation, activity, and secretion. Phorbol 12-myristate 13-acetate plus the calcium ionophore A23187 induced a slower, prolonged rate of secretion that coincided with a similarly protracted translocation of PP2A to the membrane fraction. PP2A translocation is not the only event required for secretion as translocation was also induced by phorbol 12-myristate 13-acetate, without resulting in secretion. These results indicate that increased protein dephosphorylation in the membrane fraction mediated by PP2A is required for mast cell secretion. To our knowledge, this is the first demonstration of a signal-mediated, rapid, transient translocation and activation of PP2A in membranes in any system.

Sequential requirements of the N-terminal palmitoylation site and SH2 domain of Src family kinases in the initiation and progression of FcepsilonRI signaling

Initial biochemical signaling originating from high-affinity immunoglobulin E receptor (FcepsilonRI) has been ascribed to Src family kinases. To understand the mechanisms by which individual kinases drive the signaling, we conducted reconstitution experiments: FcepsilonRI signaling in RBL2H3 cells was first suppressed by a membrane-anchored, gain-of-function C-terminal Src kinase and then reconstructed with Src family kinases whose C-terminal negative regulatory sequence was replaced with a c-myc epitope. Those constructs derived from Lyn and Fyn, which are associated with detergent-resistant membranes (DRMs), physically interacted with resting FcepsilonRI and reconstructed clustering-induced signaling that leads to calcium mobilization and ERK1 and -2 activation. c-Src-derived construct, which was excluded from DRMs, failed to interact with FcepsilonRI and to restore the signaling, whereas creation of palmitoylatable Cys3 enabled it to interact with DRMs and with FcepsilonRI and to restore the signaling. Deletion of Src homology 3 (SH3) domain from the Lyn-derived construct did not alter its ability to transduce the series of signaling. Deletion of SH2 domain did not affect its association with DRMs and with FcepsilonRI nor clustering-induced tyrosine phosphorylation of FcepsilonRI beta and gamma subunits, but it almost abrogated the next step of tyrosine phosphorylation of Syk and its recruitment to FcepsilonRI. These findings suggest that Lyn and Fyn could, but c-Src could not, drive FcepsilonRI signaling and that N-terminal palmitoylation and SH2 domain are required in sequence for the initial interaction with FcepsilonRI and for the signal progression to the molecular assembly.

Mast cells and basophils

Mast cells and basophils are effector cells in IgE-associated immune responses, such as those that contribute to asthma and other allergic diseases and to host resistance to parasites. Recent work shows that mast cells can also participate in innate immunity to bacterial infection and that the expression of such mast cell-dependent natural immunity can be significantly enhanced by long-term treatment of mice with the kit ligand, stem cell factor. However, mast cells may also influence many other biologic responses, including tissue remodeling and angiogenesis. This review discusses certain recent findings about the differentiation, phenotype, and function of basophils and mast cells, as well as briefly considering evolving concepts about the roles of these cells in health and disease.

Role of protein phosphatases in the regulation of human mast cell and basophil function

Many extracellular stimuli mediate physiological change in target cells by altering the phosphorylation state of proteins. These alterations result from the dynamic interplay of protein kinases, which mediate phosphorylations, and protein phosphatases, which catalyse dephosphorylations. The antigen-mediated aggregation of high-affinity receptors for IgE on mast cells and basophils triggers rapid changes in the phosphorylation of many proteins and culminates in the generation of inflammatory mediators involved in allergic inflammatory diseases such as asthma. Although protein kinases have an established role in this process, less is known about the involvement of protein phosphatases. This imbalance has been redressed in recent years by the availability of phosphatase inhibitors, such as okadaic acid, that facilitate investigations of the role of protein phosphatases in intact cells. Here we review a number of studies in which inhibitors of protein phosphatases have been used to shed light on the potential importance of these enzymes in the regulation of human mast cell and human basophil function.

Protein kinase C activator PMA reduces the Ca(2+) response to antigen stimulation of adherent RBL-2H3 mucosal mast cells by inhibiting depletion of intracellular Ca(2+) stores

Activation of protein kinase C has been shown to reduce the Ca(2+) responses of a variety of cell types. In most cases, the reduction is due to inhibition of Ca(2+) influx, but acceleration of Ca(2+) efflux and inhibition of Ca(2+) store depletion by protein kinase C activation have also been described. For adherent RBL-2H3 mucosal mast cells, results from whole-cell patch clamp experiments suggest that protein kinase C activation reduces Ca(2+) influx, while experiments with intact, fura-2-loaded cells suggest that Ca(2+) influx is not affected. Here we present single-cell data from Ca(2+) imaging experiments with adherent RBL-2H3 cells, showing that antigen-stimulated Ca(2+) responses of phorbol 12-myristate 13-acetate (PMA)-treated cells are more transient than those of control cells. PMA also reduced the response to antigen in the absence of extracellular Ca(2+), indicating that depletion of intracellular Ca(2+) stores is inhibited. If PMA was added after stores had been depleted by thapsigargin, a small decrease in [Ca(2+)](i) was observed, consistent with a slight inhibition of Ca(2+) influx. However, the major effect of PMA on the antigen-stimulated Ca(2+) response is to inhibit depletion of intracellular Ca(2+) stores. We also show that inhibition of protein kinase C did not enhance the Ca(2+) response to antigen, suggesting that inhibition of the Ca(2+) response by activation of protein kinase C does not contribute to the physiological response to antigen.

Inhibition of immediate-type allergic reaction by Rosa davurica Pall. in a murine model

We studied the effect of Rosa davurica Pall. (Rosaceae) fruits (RdF) on immediate-type allergic reactions. RdF completely inhibited compound 48/80-induced systemic anaphylactic shock at the dose of 1 g/kg. When RdF was given as pretreatment, at concentrations ranging from 0.0001 to 1 g/kg, the serum histamine levels induced by compound 48/80 were reduced in a dose-dependent manner. RdF inhibited the passive cutaneous anaphylaxis activated by anti-dinitrophenyl (DNP) IgE antibody dose dependently. RdF also inhibited the histamine release induced by compound 48/80 or anti-DNP IgE from the rat peritoneal mast cells (RPMC). Moreover, RdF had a significant inhibitory effect on anti-DNP IgE-induced tumor necrosis factor-alpha production from RPMC. These results indicate that RdF may contain compounds with actions that inhibit mast cell degranulation in the rat.

Altered expression and action of the low-affinity IgE receptor FcepsilonRII (CD23) in asthmatic airway smooth muscle

BACKGROUND

Changes in cell surface expression of certain immunoglobulin Fc receptors have been demonstrated in leukocytes isolated from the lungs of atopic asthmatic individuals. This, together with emerging evidence that Fc receptors can also be expressed and activated in non-bone marrow-derived cell types, including airway smooth muscle (ASM), raises the hypothesis that the atopic asthmatic ASM phenotype is associated with an altered endogenous expression and action of specific Fc receptors present in the ASM itself.

OBJECTIVE

The current study addressed the above hypothesis by examining (1) whether the expression of certain key Fc receptor subtypes for IgE and IgG is altered in ASM tissue isolated from human atopic asthmatic individuals and (2) whether this altered Fc receptor expression is comparably induced in naive human ASM tissue and cultured cells after their passive sensitization with human atopic asthmatic serum or IgE immune complexes.

METHODS

Messenger RNA and cell surface protein expression of the individual IgG receptor subtypes FcgammaRI, FcgammaRII, and FcgammaRIII, as well as the IgE receptor subtypes FcepsilonRI and FcepsilonRII, were examined in human ASM tissue isolated from atopic asthmatic and control (nonatopic/nonasthmatic) individuals. In addition, we examined the effects of passive sensitization of ASM tissue and cultured ASM cells with control serum, atopic asthmatic serum, or exogenously administered IgE immune complexes on Fc receptor expression and action (ie, induction of proinflammatory cytokine release).

RESULTS

The observations demonstrate that (1) human ASM tissue expresses messenger RNA and surface protein for FcepsilonRII, as well as for all the Fcgamma receptor subtypes, (2) in contrast to unaltered Fcgamma subtype expression, however, relative to control human ASM, FcepsilonRII is significantly up-regulated in inherently asthmatic ASM tissue, (3) up-regulated expression of FcepsilonRII represents, at least in part, an inducible phenomenon that is largely attributed to IgE immune complex-coupled activation of the receptor, and (4) the latter action is associated with FcepsilonRII-induced autologous elaboration of the proinflammatory cytokine, IL-1beta, by the atopic sensitized ASM.

CONCLUSION

These observations provide new evidence that human ASM tissue expresses FcepsilonRII in addition to all 3 subtypes of Fcgamma receptors and that the expression of FcepsilonRII is selectively increased in atopic asthmatic ASM, a phenomenon associated with IgE immune complex/FcepsilonRII-mediated elaboration of IL-1beta by the ASM itself.

Electron spin resonance characterization of liquid ordered phase of detergent-resistant membranes from RBL-2H3 cells

The dynamic structure of detergent-resistant membranes (DRMs) isolated from RBL-2H3 cells was characterized using two different acyl chain spin-labeled phospholipids (5PC and 16PC), a headgroup labeled sphingomyelin (SM) analog (SD-Tempo) and a spin-labeled cholestane (CSL). It was shown, by comparison to dispersions of SM, dipalmitoylphosphatidylcholine (DPPC), and DPPC/cholesterol of molar ratio 1, that DRM contains a substantial amount of liquid ordered phase: 1) The rotational diffusion rates (R( perpendicular)) of 16PC in DRM between -5 degrees C and 45 degrees C are nearly the same as those in molar ratio DPPC/Chol = 1 dispersions, and they are substantially greater than R( perpendicular) in pure DPPC dispersions in the gel phase studied above 20 degrees C; 2) The order parameters (S) of 16PC in DRM at temperatures above 4 degrees C are comparable to those in DPPC/Chol = 1 dispersions, but are greater than those in DPPC dispersions in both the gel and liquid crystalline phases. 3) Similarly, R( perpendicular) for 5PC and CSL in DRM is greater than in pure SM dispersions in the gel phase, and S for these labels in DRM is greater than in the SM dispersions in both the gel and liquid crystalline phases. 4) R( perpendicular) of SD-Tempo in DRM is greater than in dispersions of SM in both gel and liquid phases, consistent with the liquid-like mobility in the acyl chain region in DRM. However, S of SD-Tempo in DRM is substantially less than that of this spin label in SM in gel and liquid crystalline phases (in absolute values), indicating that the headgroup region in DRMs is less ordered than in pure SM. These results support the hypothesis that plasma membranes contain DRM domains with a liquid ordered phase that may coexist with a liquid crystalline phase. There also appears to be a coexisting region in DRMs in which the chain labels 16PC and 5PC are found to cluster. We suggest that other biological membranes containing high concentrations of cholesterol also contain a liquid ordered phase.

Interleukin-3 or immunoglobulin E promotes expression of protein kinase C delta gene in murine mast cells

We reported previously that protein kinase C delta (PKCdelta) is the main isoenzyme in various types of murine mast cells. In the present study we investigated the regulation of expression of PKCdelta gene in murine mast cells in vitro and in vivo. The mRNA expressions of PKCdelta were promoted in response to interleukin-3 (IL-3) or immunoglobulin E (IgE) in mouse mastocytoma P-815 cells. In addition we have evaluated the mast cells which express PKCdelta mRNA in IgE-dependent passive cutaneous anaphylaxis reaction, using in situ hybridization with the antisense riboprobe in skin. These results indicate that mast cell activation can induce a marked promotion in steady state levels of PKCdelta mRNA.

Genetically engineered and synthetic allergen derivatives: candidates for vaccination against type I allergy

Type I allergy, a hypersensitivity disease affecting almost 20% of the population worldwide, is based on the IgE recognition of otherwise harmless antigens (i.e., allergens). Allergen-induced crosslink of effector cell-bound IgE antibodies leads to the release of biological mediators and thus to immediate disease symptoms (allergic rhinitis, conjunctivitis and asthma). Specific immunotherapy, the only causative treatment of Type I allergy, is based on the administration of increasing doses of allergens to allergic patients in order to yield allergen-specific non-responsiveness. Major disadvantages are 1. that current forms of allergen immunotherapy are performed with allergens difficult to standardize which cannot be matched to the patients reactivity profile and 2. that the administration of active allergen preparations can cause anaphylactic side effects. Through the application of molecular biological techniques many relevant environmental allergens have been produced as active recombinant proteins which allow component-resolved allergy diagnosis and thus represent the basis for patient-tailored forms of immunotherapy. Here we review molecular strategies which have been recently applied to generate genetically engineered and synthetic hypoallergenic allergen derivatives for patient-tailored and safe vaccination against Type I allergy.

The immunoglobulin-like modules Cepsilon3 and alpha2 are the minimal units necessary for human IgE-FcepsilonRI interaction

Atopic allergy is a genetically determined immunodisorder that affects almost 20% of the population worldwide. Immediate symptoms of type I allergy are caused by the release of biologic mediators from effector cells induced by IgE-allergen complexes that cross-link the high-affinity receptor for IgE (FcepsilonRI). Chronic disease manifestations result from allergen-specific T-cell activation, a process that is enhanced when allergens are presented via FcepsilonRI-bound IgE. We report the baculovirus expression, as soluble recombinant proteins, of the minimal units required for human IgE and FcepsilonRI interaction: Cepsilon3 represents the third constant domain of the IgE heavy chain, and alpha2 is the membrane-proximal Ig-like module from FcepsilonRIalpha. Native overlay experiments showed binding of human FcepsilonRIalpha to recombinant Cepsilon3 and of natural or recombinant human IgE to recombinant alpha2. Moreover, recombinant Cepsilon3 inhibited binding of natural IgE antibodies to alpha2, and preincubation of human IgE with alpha2 inhibited anti-IgE-triggered histamine release from human basophils. Isolated Cepsilon3 and alpha2 can now be used for the molecular and structural analysis of the IgE-FcepsilonRI interaction, as well as for diagnostic and therapeutic applications.

FcepsilonRI-mediated antigen endocytosis turns interferon-gamma-treated mouse mast cells from inefficient into potent antigen-presenting cells

Previous studies in our laboratory have shown that bone-marrow-derived mast cells (BMMC) could present immunogenic peptides, from soluble antigens endocytosed through fluid phase, only if they were subjected to a 48-hr treatment with interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF). In contrast to GM-CSF, interferon-gamma (IFN-gamma) which highly upregulates major histocompatibility complex (MHC) class II expression, completely inhibits the generation of immunogenic peptides. We have used this model to study the role of FcepsilonRI-mediated antigen internalization in the regulation of the antigen-presenting function of IFN-gamma-treated mast cells. Here, we report that FcepsilonRI can reverse the IFN-gamma-treated mast cells from inefficient to highly efficient antigen-presenting cells. Inhibition of the antigen presenting capacity by piceatannol, a protein tyrosine kinase (PTK) syk inhibitor, indicates that this is an active process resulting from immunoglobulin E (IgE)-antigen-FcepsilonRI engagement which involves tyrosines found in the immunoreceptor tyrosine-based activation motif (ITAM) embedded in the cytoplasmic tail of the FcepsilonRI beta and gamma chains. Antigen-presenting function was also shown to require the activation of phosphatidyl inositol 3 (PI3) kinase, downstream of PTK syk phosphorylation, since this activity was completely blocked by wortmannin, a PI3 kinase inhibitor. These data suggest that signalling generated by FcepsilonRI provides mast cells with IgE-mediated enhanced antigen presentation to T cells and emphasize a so far unknown immunoregulatory mast-cell function that might take place in inflammatory sites.

Inhibition of IgE-mediated triggering of mast cells by complement-derived peptides interacting with the Fc epsilon RI

Mucosal type mast cells, in contrast to the serosal type ones, do not respond to cationic agents, or to the complement-derived peptides C3a and C5a. Earlier we have found that while C3a does not activate the rat mucosal type mast cells (line RBL-2H3), it strongly inhibits the IgE-mediated triggering of these cells, by interfering with the Fc epsilon RI-initiated signaling pathway. In the present study we further investigated the mechanism of this process. It is shown, that C3a interacts with the beta-chain of the Fc epsilon RI complex. Binding of the complement peptide to the cells apparently causes a decrease in the proximity of the IgE-binding Fc epsilon RI. Investigating certain sequences of C3a we found that the inhibition is caused by the C-terminal sequences of the complement-peptide, ranging from positions 56 to 77 and also by a shorter sequence, ranging from positions 56 to 64. The inhibitory effect of these peptides was observed both in the case of RBL-2H3 cells and mouse bone marrow derived mast cells.

IgE Enhances Fcε Receptor I Expression and IgE-Dependent Release of Histamine and Lipid Mediators from Human Umbilical Cord Blood-Derived Mast Cells: Synergistic Effect of IL-4 and IgE on Human Mast Cell Fcε Receptor I Expression and Mediator Release

We investigated the effects of IgE versus IL-4 on FcεRI surface expression in differentiated human mast cells derived in vitro from umbilical cord blood mononuclear cells. We found that IgE (at 5 μg/ml) much more strikingly enhanced surface expression of FcεRI than did IL-4 (at 0.1–100 ng/ml); similar results were also obtained with differentiated mouse mast cells. However, IL-4 acted synergistically with IgE to enhance FcεRI expression in these umbilical cord blood-derived human mast cells, as well as in mouse peritoneal mast cells derived from IL-4−/− or IL-4+/+ mice. We also found that: 1) IgE-dependent enhancement of FcεRI expression was associated with a significantly enhanced ability of these human mast cells to secrete histamine, PGD2, and leukotriene C4 upon subsequent passive sensitization with IgE and challenge with anti-IgE; 2) preincubation with IL-4 enhanced IgE-dependent mediator secretion in these cells even in the absence of significant effects on FcεRI surface expression; 3) when used together with IgE, IL-4 enhanced IgE-dependent mediator secretion in human mast cells to levels greater than those observed in cells that had been preincubated with IgE alone; and 4) batches of human mast cells generated in vitro from umbilical cord blood cells derived from different donors exhibited differences in the magnitude and pattern of histamine and lipid mediator release in response to anti-IgE challenge, both under baseline conditions and after preincubation with IgE and/or IL-4.

Ca2+ and phorbol ester effect on the mast cell phosphoprotein induced by cromolyn

Several phosphoproteins are involved in stimulus-secretion coupling. The beta and gamma subunits of immunoglobulin E binding protein (FC epsilonRI) and three other protein bands get phosphorylated during stimulation of mast cell secretion. These additional proteins of 42, 59 and 68 kDa are also phosphorylated when secretion is stimulated by compound 48/80 (C48/80). A 78 kDa band, however, is phosphorylated as secretion wanes after stimulation with C48/80 and by the anti-allergic drug disodium cromoglycate (cromolyn). Phosphorylation was blocked by protein kinase C inhibitors. We investigated the isozyme involved by first showing that a cation ionophore prevented the phosphorylation of the 78 kDa protein, while a Ca2+ chelator did not affect phosphorylation even though it enhanced the inhibitory effect of cromolyn. This protein was identified as moesin by immunoprecipitation. Protein kinase C activators had no effect on 78 kDa protein phosphorylation either in the presence or absence of Ca2+ ions, but prevented its phosphorylation by cromolyn. Protein phosphatase inhibitors prolonged the duration, but not the amount of phosphate incorporated in the 78 kDa protein band while cromolyn had no effect on protein phosphatase action in vitro. The insensitivity of the 78 kDa protein phosphorylation to calcium and protein kinase C activators suggests that an atypical protein kinase C isozyme may be involved. Western blot analysis identified the presence of isozymes alpha, beta, delta and zeta, of which only the latter fits the profile suggested by the present findings.

Involvement of farnesyl protein transferase (FPTase) in FcarepsilonRI-induced activation of RBL-2H3 mast cells

Changes in farnesyl protein transferase (FPTase) activity and FPTase beta-subunit protein levels were determined in IgE-sensitized RBL-2H3 mast cells in response to polyvalent antigen administration. Ten minutes after the addition of DNP modified BSA to mast cells, whose high affinity receptor for IgE (FcvarepsilonRI) contained bound anti-DNP IgE, FPTase specific activity increased by 54 +/- 28%. Time course studies showed FPTase specific activity doubled during a 20- to 30-min period after antigen-induced cell aggregation. Also, an increase in FPTase beta-subunit protein during this time ( approximately 30%) was observed; this protein increase was not accompanied by a similar increase in FPTase beta-subunit m-RNA levels. The FcvarepsilonRI aggregation had no significant effect on the activities of other enzymes involved with farnesyl diphosphate (FPP) metabolism: FPP synthase, isopentenyl diphosphate isomerase, geranylgeranyl protein transferase, and squalene synthase. Specific inhibition of FPTase activity by manumycin was studied to determine what role FPTase plays in mast cell activation. Manumycin profoundly inhibited hexosaminidase release in activated cells, indicating FPTase is required for signal transduction involved with protein exocytosis from RBL-2H3 mast cells.

Mucosal mast cell secretion processes imaged using three-photon microscopy of 5-hydroxytryptamine autofluorescence

The secretion process of the mucosal mast cell line RBL-2H3 was imaged using infrared three photon excitation (3PE) of serotonin (5-hydroxytryptamine, 5-HT) autofluorescence, a measurement previously difficult because of the technical intractability of deep UV optics. Images of prestimulation 5-HT distributions were analyzed in loaded cell populations (those incubated in a 5-HT-rich medium overnight) and in unloaded populations and were found to be strictly quantifiable by comparison with bulk population high-performance liquid chromatography measurements. Antigenically stimulated cells were observed to characteristically ruffle and spread as granular 5-HT disappeared with no detectable granule movement. Individual cells exhibited highly heterogeneous release kinetics, often with quasi-periodic bursts. Neighboring granule disappearances were correlated, indicative of either spatially localized signaling or granule-granule interactions. In one-half of the granule release events, weak residual fluorescence was visible suggestive of leftover 5-HT still bound to the granule matrix. The terminal stages of secretion (>300 s) consisted primarily of unresolved granules and remainder 5-HT leakage from already released granules.

Terreic acid, a quinone epoxide inhibitor of Bruton's tyrosine kinase

Bruton's tyrosine kinase (Btk) plays pivotal roles in mast cell activation as well as in B cell development. Btk mutations lead to severe impairments in proinflammatory cytokine production induced by cross-linking of high-affinity IgE receptor on mast cells. By using an in vitro assay to measure the activity that blocks the interaction between protein kinase C and the pleckstrin homology domain of Btk, terreic acid (TA) was identified and characterized in this study. This quinone epoxide specifically inhibited the enzymatic activity of Btk in mast cells and cell-free assays. TA faithfully recapitulated the phenotypic defects of btk mutant mast cells in high-affinity IgE receptor-stimulated wild-type mast cells without affecting the enzymatic activities and expressions of many other signaling molecules, including those of protein kinase C. Therefore, this study confirmed the important roles of Btk in mast cell functions and showed the usefulness of TA in probing into the functions of Btk in mast cells and other immune cell systems. Another insight obtained from this study is that the screening method used to identify TA is a useful approach to finding more efficacious Btk inhibitors.

Mast cells as sentinels of innate immunity

Mast cells are widely regarded as important effector cells in immune responses associated with Th2 cells and IgE. Recent work shows that they can also contribute significantly to the expression of innate immunity; furthermore, survival in a model of acute bacterial infection that is dependent on complement and mast cells can be greatly enhanced by long-term treatment of mice with the kit ligand (stem cell factor) at least in part because of the effects of such treatment on mast cell numbers and/or function. These findings not only indicate that mast cells can represent a critical component of host defense in natural immunity but also suggest that mast cell function in this setting can be manipulated for therapeutic ends.

Glycoprotein derived from the hot water extract of mint plant, Perilla frutescens britton

Glycoprotein showing inhibitory activity against mast cell degranulation and hyaluronidase activity was purified from the hot water extract of mint plant (Perilla frutescens Britton). The purified inhibitor gave a single band detected with Coomassie brilliant blue staining and periodic acid-Schiff staining on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The molecular mass was estimated to be 6.0 kDa on SDS-PAGE. The inhibitor did not become inactivated when boiled for 30 min or digested with trypsin, V8 protease, or proteinase K but was inactivated by NaIO(4) oxidation. The inhibitor prevented mast cell degranulation and hyaluronidase activity (IC(50) = 0.42 mg/mL) in a dose-dependent manner. The inhibitor also inhibited the protein kinase C activity. It is possible to purify and characterize a glycoprotein with putative pharmacological properties from mint plants.

The IL-1 Receptor-Related T1 Antigen Is Expressed on Immature and Mature Mast Cells and on Fetal Blood Mast Cell Progenitors

Expression of the T1 gene, also known as ST2, DER4, and Fit-1, has been shown to be associated with cell proliferation. It gives rise to two different mRNAs that encode a receptor-like protein and a soluble molecule representing the ectodomain of the receptor form. Although T1 is a member of the IL-1R family, its biologic function is currently unknown. In this study, we have analyzed the expression of the T1 surface Ag in murine hemopoietic organs. Mast cells (MCs) were shown to be the only identifiable cell lineage that expressed T1 at high levels. T1 expression was found on cultured bone marrow-derived immature MCs. Similarly, freshly isolated connective tissue-type MCs from the i.p. cavity were also shown to express high levels of T1. Interestingly, the earliest detectable committed MC precursor isolated from fetal blood (FB) at day 15.5 of gestation, but not circulating hemopoietic stem cells in FB, also expresses high level of T1. Since FB promastocytes lack expression of the high affinity IgE receptor (FcεRI), T1 expression precedes expression of FcεRI in MC ontogeny. The finding that the T1 Ag is selectively expressed at several stages during development of the MC lineage suggests that this cell surface molecule, in combination with the well-established markers c-Kit and FcεRI, should be valuable for studying the MC lineage.

Characterization of protein serine/threonine phosphatase activities in human lung mast cells and basophils

1. The serine/threonine protein phosphatase (PP) inhibitors, okadaic acid and calyculin, attenuated the IgE-mediated release of histamine from human lung mast cells (HLMC) and basophils in a dose-dependent manner whereas an alternative PP inhibitor, microcystin, was ineffective. Calyculin was more potent than okadaic acid in both cell types. The concentration required to inhibit by 50% (IC50) the release of histamine was 15 (HLMC) and 50 nM (basophils) for calyculin and 200 (HLMC) and 300 nM (basophils) for okadaic acid. 2. Lysates of purified HLMC and basophils dephosphorylated radiolabelled glycogen phosphorylase, a substrate for both PP1 and PP2A. The PP activity in lysates of both cell types was inhibited in a dose-dependent fashion by the PP inhibitors with the following rank order of activity, calyculin (approximate IC50; 0.02-0.1 nM) > or = microcystin (0.1 nM) > okadaic acid (70 nM). 3. The PP1-selective inhibitor, inhibitor-2 (I-2), attenuated the dephosphorylation of glycogen phosphorylase in lysates of both HLMC and basophils. I-2 (20 nM) inhibited the glycogen phosphorylase PP activity by 71+/-3% and 49+/-13% in HLMC and basophil extracts, respectively. There were, approximately, 6 fold greater levels of I-2-sensitive activity in HLMC than in basophils. Qualitatively similar results were obtained with an alternative PP1-selective inhibitor, inhibitor-1 (I-1). 4. Lysates derived from HLMC and basophils dephosphorylated radiolabelled casein which is a PP2A-restricted substrate. HLMC lysates contained, approximately, 2.5 fold higher levels of casein PP activity than basophil lysates. 5. These data indicate that HLMC and basophils both contain PP1 and PP2A. The data suggest that, on a per cell basis, HLMC have higher levels of both PP1 and PP2A. Moreover, the ratio of PP1 to PP2A is higher in HLMC than in basophils.

Inhibitory effect of anaphylactic reaction of Sosiho-Tang

Mast cells synthesize and secrete chemical mediators which play an central role in anaphylactic reactions. Compound 48/80 is a condensation product of formaldehyde with paramethoxyphenylethylamine that reliably induces the release of chemical mediators in the mast cell granules. Aggregation of the high-affinity Fc receptor also stimulates the mast cells. The objective of the current study was to determine the effect of Sosiho-Tang (SS-Tang) on mast cell-mediated anaphylactic reaction. SS-Tang completely inhibited systemic anaphylaxis induced by compound 48/80 in mice. SS-Tang inhibited local anaphylaxis induced by anti-dinitrophenyl (DNP) IgE. In addition SS-Tang concentration-dependently inhibited histamine release in mast cells induced by compound 48/80 or anti-DNP IgE. These results indicate that SS-Tang may contain compounds with actions that inhibit mast cell degranulation.

Increase in histamine production by inflammatory exudate in the chronic phase of allergic inflammation in rats

In the air pouch-type allergic inflammation in rats, we reported that a sustained histamine production in the late phase is induced by a cytokine-like factor, named histamine-production-increasing factor (HPIF) (1). Recently, we found another type of histamine-production-increasing factor in the pouch fluid at the chronic phase of air pouch-type allergic inflammation. Although it did not increase histamine production by itself, it enhanced the HPIF-induced histamine production by rat bone marrow cells. It also increased GM-CSF-induced histamine production. The activity of this factor increased time-dependently from 3 to 7 days after the antigen challenge. Injection of the 5 day pouch fluid sample containing this factor into the pouch 4 h after the antigen challenge increased histamine contents in the pouch fluid at 24 h, indicating that this factor enhances HPIF-induced histamine production in vivo. Biochemical analysis of the 5 day pouch fluid sample indicated that this factor is a heat-labile and trypsin-sensitive protein of which pI value and molecular weight are 7-8 and about 100 kDa, respectively.

Effects of mitogen-activated protein kinase kinase inhibitor PD 098059 on antigen challenge of guinea-pig airways in vitro

1. It has been shown that activation of protein tyrosine kinases is the earliest detectable signalling response to FcepsilonRI cross-linking on mast cell. Following tyrosine kinase activation, a family of mitogen-activated protein kinases (MAPKs) was found to be activated as well. The present study examined the role of MAPK signalling cascade in in vitro model of allergic asthma using a specific MAPK kinase inhibitor PD 098059. 2. Guinea-pigs were passively sensitized with IgG antibody raised against ovalbumin (OA). Effects of PD 098059 on OA-induced anaphylactic contraction of isolated bronchi and release of histamine and peptidoleukotrienes from chopped lung preparations were studied. 3. PD 098059 (10-50 microM) produced only minor reduction of maximal OA-induced bronchial contraction. In contrast, the rate of relaxation of OA-induced bronchial contraction was markedly faster in the presence of PD 098059 than the vehicle control in a concentration-dependent manner. 4. These observations corroborate well with the inability of PD 098059 (5-50 microM) to substantially block the OA-induced release of histamine and with marked inhibition of OA-induced release of peptidoleukotrienes from lung fragments in the presence of PD 098059. Exogenous arachidonic acid-induced release of peptidoleukotrienes from lung fragments was not blocked by PD 098059. 5. In immunoblotting study, we found that p42MAPK was constitutively expressed in guinea-pig bronchi. However, treatment with OA, histamine or LTD4 did not cause activation of p42MAPK. These findings together with the lack of inhibitory effects of PD 098059 on bronchial contraction induced by histamine or LTD4 suggest that histamine- and LTD4-induced bronchial contractions are not mediated by p42MAPK activation. 6. Taken together, our findings show that inhibition of MAPK signalling cascade by PD 098059 significantly reduced the OA-triggered release of peptidoleukotrienes leading to rapid relaxation of anaphylactic bronchial contraction. On the other hand, p42MAPK did not play a role in histamine- or LTD4-induced bronchial smooth muscle contraction suggesting that PD 098059 exerts its inhibitory effects on OA-induced bronchial contraction primarily through inhibition of peptidoleukotrienes release from mast cells.

Multiple Signaling Pathways for the Activation of JNK in Mast Cells: Involvement of Bruton’s Tyrosine Kinase, Protein Kinase C, and JNK Kinases, SEK1 and MKK7

Stimulation of the high affinity IgE receptor (FcεRI) as well as a variety of stresses induce activation of c-Jun N-terminal protein kinases (JNKs) stress-activated protein kinases in mast cells. At least three distinct signaling pathways leading to JNK activation have been delineated based on the involvements of Bruton’s tyrosine kinase (Btk), protein kinase C (PKC), and the JNK-activating cascades composed of multiple protein kinases. The PKC-dependent pathway, which is inhibited by a PKC inhibitor Ro31-8425 and can be activated by PMA, functions as a major route in FcεRI-stimulated mast cells derived from btk gene knockout mice. On the other hand, wild-type mouse-derived mast cells use both PKC-dependent and PKC-independent pathways for JNK activation. A PKC-independent pathway is regulated by Btk and SEK1 via the PAK→MEKK1→SEK1→JNK cascade, and is sensitive to phosphatidylinositol 3-kinase inhibitors, wortmannin and LY-294002, while the PKC-dependent pathway is affected to a lesser extent by both wortmannin treatment and overexpression of wild-type and dominant negative mutant SEK1 proteins. Another PKC-independent pathway involves Btk and MKK7, a recently cloned direct activator of JNK. Among the stresses tested, UV irradiation seems to activate Btk and JNK via the PKC-independent pathways.

Global environmental pollutant substance vanadium activates mast cells and basophils at the late phase in the presence of hydrogen peroxide

Vanadium is contained in fossil fuel such as coal, oil and sand oil and released in the air through the combustion. We studied the allergic and inflammatory potentials of vanadium as the factor of a recent increase of allergic disease. Vanadium oxide (V(2)O(5)) and orthovanadate (Na(3)VO(4)) released histamine from human basophils, rat mast cells and rat basophilic leukemia (RBL-2H3) cells in the presence of hydrogen peroxide (H(2)O(2)). Activation of RBL-2H3 cells by vanadium/H(2)O(2) was accompanied by leukotriene synthesis, increases of [Ca(2+)](i), multiple protein tyrosine phosphorylations and remarkable morphological changes. Pharmacological study suggests that vanadium/H(2)O(2) activates mast cells at the late phase, bypassing the early signaling components. Thus, vanadium can amplify the allergy in the presence of H(2)O(2) at the inflammation site in the global environment of industrial age.

1,25-Dihydroxyvitamin D3 enhances degranulation of mast cells

The mast cell lines rat basophilic leukemia (RBL) and mouse C57 cells respond to IgE/antigen complexes by degranulation. Treatment of these cells with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), (10-100 nM) for 24-48 h enhanced IgE/antigen-induced exocytosis as monitored by release of hexosaminidase. A short term incubation with the hormone did not affect exocytosis, ruling out a rapid non genomic mechanism. The presence of vitamin D receptors, demonstrated by immunoblotting and the lack of effect of 24,25(OH)2D3 suggest a role for these receptors in the enhancing effect. 1,25(OH)2D3 also enhanced exocytosis induced by the calcium ionophore A23187 in the presence or absence of phorbol ester indicating modulation of events distal to signal transduction. 1,25(OH)2D3 enhanced exocytosis in the presence of cytochalasin D, indicating that the action of the hormone is not due to effects on microfilament structure. The results of this study suggest that 1,25(OH)2D3 may affect the allergic or pro-inflammatory potential of mast cells.