Understanding exocytosis in immune and inflammatory cells: The molecular basis of mediator secretion

A dual role for diacylglycerol kinase generated phosphatidic acid in autoantibody-induced neutrophil exocytosis

Dysregulated release of neutrophil azurophilic granules causes increased tissue damage and amplified inflammation during autoimmune disease. Antineutrophil cytoplasmic antibodies (ANCAs) are implicated in the pathogenesis of small vessel vasculitis and promote adhesion and exocytosis in neutrophils. ANCAs activate specific signal transduction pathways in neutrophils that have the potential to be modulated therapeutically to prevent neutrophil activation by ANCAs. We have investigated a role for diacylglycerol kinase (DGK) and its downstream product phosphatidic acid (PA) in ANCA-induced neutrophil exocytosis. Neutrophils incubated with the DGK inhibitor R59022, before treatment with ANCAs, exhibited a reduced capacity to release their azurophilic granules, demonstrated by a component release assay and flow cytometry. PA restored azurophilic granule release in DGK-inhibited neutrophils. Confocal microscopy revealed that R59022 did not inhibit translocation of granules, indicating a role for DGK during the process of granule fusion at the plasma membrane. In investigating possible mechanisms by which PA promotes neutrophil exocytosis, we demonstrated that exocytosis can only be restored in R59022-treated cells through simultaneous modulation of membrane fusion and increasing cytosolic calcium. PA and its associated pathways may represent viable drug targets to reduce tissue injury associated with ANCA-associated vasculitic diseases and other neutrophilic inflammatory disorders.

Regulation of mucosal mast cell activation by short interfering RNAs targeting syntaxin4

Mucosal mast cells (MMCs) have an important role in allergic inflammation, and effective antagonists are required for their regulation. To discover a possible mechanism of controlling the activation of MMCs, we investigated the expression and function of syntaxin4, one of the soluble membrane N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, in RBL-2H3 cells, which is a rat mucosal mast cell line. Syntaxin4 silencing was induced by transfection of short interfering RNAs (siRNAs). Syntaxin4 was knocked down in mast cells at both the mRNA and protein levels. The release of granule contents that are involved in inflammation, such as histamine and hexosaminidase, was significantly suppressed by the gene silencing of syntaxin4. Silencing of this gene was also induced in the trachea and bronchi of rats by intratracheal application of the siRNAs using an atelocollagen delivery system. The activation of MMCs, which was monitored by the level of rat mast cell protease-II (RMCPII) in the bronchoalveolar lavage fluid (BALF), was inhibited, and asthmatic airway constriction was prevented by administration of the syntaxin/atelocollagen complex. These results indicate that siRNAs targeting syntaxin4 can stabilize mucosal mast cells and may have beneficial therapeutic effects on the asthmatic response.

Absence of Tec family kinases interleukin-2 inducible T cell kinase (Itk) and Bruton's tyrosine kinase (Btk) severely impairs Fc epsilonRI-dependent mast cell responses

Mast cells are critical effector cells in the pathophysiology of allergic asthma and other IgE-mediated diseases. The Tec family of tyrosine kinases Itk and Btk serve as critical signal amplifiers downstream of antigen receptors. Although both kinases are expressed and activated in mast cells following FcεRI stimulation, their individual contributions are not clear. To determine whether these kinases play unique and/or complementary roles in FcεRI signaling and mast cell function, we generated Itk and Btk double knock-out mice. Analyses of these mice show decreased mast cell granularity and impaired passive systemic anaphylaxis responses. This impaired response is accompanied by a significant elevation in serum IgE in Itk/Btk double knock-out mice. In vitro analyses of bone marrow-derived mast cells (BMMCs) indicated that Itk/Btk double knock-out BMMCs are defective in degranulation and cytokine secretion responses downstream to FcεRI activation. These responses were accompanied by a significant reduction in PLCγ2 phosphorylation and severely impaired calcium responses in these cells. This defect also results in altered NFAT1 nuclear localization in double knock-out BMMCs. Network analysis suggests that although they may share substrates, Itk plays both positive and negative roles, while Btk primarily plays a positive role in mast cell FcεRI-induced cytokine secretion.

Crucial role for autophagy in degranulation of mast cells

BACKGROUND

Autophagy plays a crucial role in controlling various biological responses including starvation, homeostatic turnover of long-lived proteins, and invasion of bacteria. However, a role for autophagy in development and/or function of mast cells is unknown.

OBJECTIVE

To investigate a role for autophagy in mast cells, we generated bone marrow-derived mast cells (BMMCs) from mice lacking autophagy related gene (Atg) 7, an essential enzyme for autophagy induction.

METHODS

Bone marrow-derived mast cells were generated from bone marrow cells of control and IFN-inducible Atg7-deficient mice, and morphologic and functional analyses were performed.

RESULTS

We found that conversion of type I to type II light chain (LC3)-II, a hallmark of autophagy, was constitutively induced in mast cells under full nutrient conditions, and LC3-II localized in secretory granules of mast cells. Although deletion of Atg7 did not impair the development of BMMCs, Atg7(-/-) BMMCs showed severe impairment of degranulation, but not cytokine production on FcεRI cross-linking. Intriguingly, LC3-II but not LC3-I was co-localized with CD63, a secretory lysosomal marker, and was released extracellularly along with degranulation in Atg7(+/+) but not Atg7(-/-) BMMCs. Moreover, passive cutaneous anaphylaxis reactions were severely impaired in mast cell-deficient WBB6F1-W/W(V) mice reconstituted with Atg7(-/-) BMMCs compared with Atg7(+/+) BMMCs.

CONCLUSION

These results suggest that autophagy is not essential for the development but plays a crucial role in degranulation of mast cells. Thus, autophagy might be a potential target to treat allergic diseases in which mast cells are critically involved.

Pyk2 is required for neutrophil degranulation and host defense responses to bacterial infection

The appropriate regulation of neutrophil activation is critical for maintaining host defense and limiting inflammation. Polymorphonuclear neutrophils (PMNs) express a number of cytoplasmic tyrosine kinases that regulate signaling pathways leading to activation. One of the most highly expressed, but least studied, kinases in PMNs is proline rich kinase 2 (Pyk2). By analogy to the related focal adhesion kinase, Pyk2 has been implicated in regulating PMN adhesion and migration; however, its physiologic function has yet to be described. Using pyk2(-/-) mice, we found that this kinase was required for integrin-mediated degranulation responses, but was not involved in adhesion-induced cell spreading or activation of superoxide production. Pyk2-deficient PMNs also manifested reduced migration on fibrinogen-coated surfaces. The absence of Pyk2 resulted in a severe reduction in paxillin and Vav phosphorylation following integrin ligation, which likely accounts for the poor degranulation and cell migration. Pyk2(-/-) mice were unable to efficiently clear infection with Staphylococcus aureus in a skin abscess model, owing in part to the poor release of granule contents at the site of infection. However, Pyk2-deficient PMNs responded normally to soluble agonists, demonstrating that this kinase functions mainly in the integrin pathway. These data demonstrate the unrealized physiologic role of this kinase in regulating the adhesion-mediated release of PMN granule contents.

Patients with allergic rhinitis and allergic asthma share the same pattern of eosinophil and neutrophil degranulation after allergen challenge

Background

Patients with allergic rhinitis and allergic asthma demonstrate comparable local and systemic eosinophil inflammation, and yet they present with different clinical pictures. Less is even known about the contribution of neutrophil inflammation in allergic diseases. The aim of the study was to examine the propensity and selectivity of granule release from primed systemic eosinophils and neutrophils in allergic rhinitis and allergic asthma after seasonal and experimental allergen exposure. We hypothesize that the dissimilar clinical manifestations are due to diverse eosinophil and neutrophil degranulation.

Methods

Nine birch pollen allergic patients with rhinitis, eight with asthma and four controls were studied during pollen season and after nasal and bronchial allergen challenge. Eosinophils and neutrophils were incubated in vitro with assay buffer and opsonized Sephadex particles for spontaneous and C3b-induced granule protein release. The released amount of eosinophil cationic protein (ECP), eosinophil peroxidase (EPO) and myeloperoxidase (MPO) was measured by specific radioimmunoassay.

Results

C3b-induced degranulation resulted in increased release of ECP and MPO from primed blood eosinophils and neutrophils in both allergic rhinitis and allergic asthma during pollen season and after both nasal and bronchial challenge (p-values 0.008 to 0.043). After bronchial challenge, the ECP release was significantly higher in the rhinitic group compared to the asthmatic group [19.8 vs. 13.2%, (p = 0.010)]. The propensity for EPO release was weak in all challenge models but followed the same pattern in both allergic groups.

Conclusions

Systemically activated eosinophils and neutrophils have similar patterns of degranulation after allergen exposure in allergic rhinitis and allergic asthma. The released amount of ECP, EPO and MPO was similar in all allergen challenge models in both allergic groups. Our results indicate that other mechanisms than the magnitude of eosinophil and neutrophil inflammation or the degranulation pattern of the inflammatory cells determines whether or not an allergic patient develops asthma.

Small-interfering RNA-mediated identification and regulation of the ternary SNARE complex mediating RBL-2H3 mast cell degranulation

Dysregulation of mast cell function contributes to allergic and autoimmune disease that affects more than 70 million persons in the United States alone. Identifying novel mast cell targets that mediate disease or disease progression is required for the development of innovative therapeutics for the treatment of allergy/asthma and autoimmune disease. RNA interference technologies offer hope both as basic research tools for target identification and as potential, novel, specific therapeutics. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of evolutionarily conserved proteins that have been postulated to mediate the transport and fusion of inflammatory mediator-laden vesicles to the membrane in mast cells leading to their subsequent exocytosis. The functional role(s) of specific SNARE family member complexes in mast cell degranulation has not been fully elucidated. Here, we characterize the functional importance of SNARE complexes in FcεRI receptor-mediated degranulation of RBL-2H3 cells utilizing RNA interference. We demonstrate that ternary SNARE complexes of synaptosomal-associated protein-23, Syntaxin 4 and vesicle-associated membrane protein-7 (VAMP-7) or VAMP-8 are directly involved in mast cell degranulation. Additionally, we evaluate the siRNAs directed against these molecules as potential therapeutic agents for disease intervention. These studies have identified specific SNARE proteins and complexes that serve as novel targets for the development of siRNA therapies to treat allergic and autoimmune disease.

Identification of phosphoproteins associated with human neutrophil granules following chemotactic peptide stimulation

Regulated exocytosis of neutrophil intracellular storage granules is necessary for neutrophil participation in the inflammatory response. The signal transduction pathways that participate in neutrophil exocytosis are complex and poorly defined. Several protein kinases, including p38 MAPK and the nonreceptor tyrosine kinases, Hck and Fgr, participate in this response. However, the downstream targets of these kinases that regulate exocytosis are unknown. The present study combined a novel inhibitor of neutrophil exocytosis with proteomic techniques to identify phosphopeptides and phosphoproteins from a population of gelatinase and specific granules isolated from unstimulated and fMLF-stimulated neutrophils. To prevent loss of granule-associated phosphoproteins upon exocytosis, neutrophils were pretreated with a TAT-fusion protein containing a SNARE domain from SNAP-23 (TAT-SNAP-23), which inhibited fMLF-stimulated CD66b-containing granule exocytosis by 100±10%. Following TAT-SNAP-23 pretreatment, neutrophils were stimulated with the chemotactic peptide fMLF for 0 min, 1 min, and 2 min. Granules were isolated by gradient centrifugation and subjected to proteolytic digestion with trypsin or chymotrypsin to obtain peptides from the outer surface of the granule. Phosphopeptides were enriched by gallium or TiO2 affinity chromatography, and phosphopeptides and phosphorylation sites were identified by reversed phase high performance liquid chromatography-electrospray ionization-tandem MS. This resulted in the identification of 243 unique phosphopeptides corresponding to 235 proteins, including known regulators of vesicle trafficking. The analysis identified 79 phosphoproteins from resting neutrophils, 81 following 1 min of fMLF stimulation, and 118 following 2 min of stimulation. Bioinformatic analysis identified a potential Src tyrosine kinase motif from a phosphopeptide corresponding to G protein coupled receptor kinase 5 (GRK5). Phosphorylation of GRK5 by Src was confirmed by an in vitro kinase reaction and by precursor ion scanning for phospho-tyrosine specific immonium ions containing Tyr251 and Tyr253. Immunoprecipitation of phosphorylated GRK5 from intact cells was reduced by a Src inhibitor. In conclusion, targets of signal transduction pathways were identified that are candidates to regulate neutrophil granule exocytosis.

The PH domain adaptor protein Bam32/DAPP1 functions in mast cells to restrain FcɛRI-induced calcium flux and granule release

Mast cell activation triggered by IgE binding to its high affinity receptor FcɛRI is highly dependent on signaling via phosphoinositde 3-kinases (PI3K). The phosphoinositide phosphatase SHIP controls mast cell activation by regulating accumulation of D3 phosphoinositide second messengers generated by PI3K. The PH domain adaptor protein Bam32/DAPP1 binds specifically to the D3 phosphoinositides PI(3,4,5)P3 and PI(3,4)P2 (the substrate and product of SHIP respectively). In B cells, Bam32 is phosphorylated by Src family kinases including Lyn, and is required for antigen receptor-induced activation; however the function of Bam32 in mast cells is unknown. Here we report that Bam32 is expressed in mast cells, is recruited to the plasma membrane upon stimulation and functions in FcɛRI signaling. Examination of bone marrow-derived mast cells (BMMC) isolated from Bam32-deficient mice revealed enhanced FcɛRI-induced degranulation and IL-6 production, indicating that Bam32 may function to restrain signaling via FcɛRI. These enhanced degranulation responses were PI3K-dependent, as indicated by blockade with PI3K inhibitors wortmannin or IC87114. While Bam32-deficient BMMC showed reduced FcɛRI-induced activation of mitogen-activated protein kinases ERK and JNK, FcɛRI-induced calcium flux and phosphorylation of PLCγ1 and Akt were increased. Bam32-deficient BMMC showed significantly reduced phosphorylation of Lyn and SHIP, indicating reduced activity of inhibitory signaling pathways. Together our results identify Bam32 as a novel regulator of mast cell activation, potentially functioning in membrane-proximal integration of positive and negative signaling pathways.

Cell secretion mediated by granule-associated vesicle transport: a glimpse at evolution

Regulated secretion allows extrusion of cell products stored in specialized membrane-bound organelles called secretory granules or secretory vesicles. Regulated secretion provides basic functions in living organisms, and in a phylogenetic perspective, it is recognizable in the most primitive eukaryotic forms. This article is an attempt to trace the evolutionary history of a special type of secretory pattern, which has been referred to as vesicle-mediated degranulation or piecemeal degranulation (PMD). First described in the early 70s of the last century in inflammatory cells, such as the basophils, mast cells, and eosinophils, this regulated secretory route has subsequently been recognized in endocrine cells, in particular in the chromaffin cells of the adrenal medulla. This vesicle-mediated degranulation is held to mobilize small and specific aliquots of granule-associated material for selective paracrine or endocrine transport to the cell exterior. PMD has been identified in many vertebrate classes. By contrast, no data are available for invertebrates. We speculate that this pattern of cell secretion emerged early in phylogenesis, when the first metazoans appeared. In this review article, we will first revise the concept of vesicle-mediated degranulation in the light of the most recent experimental discoveries and theoretical implications. Then, the distribution of this secretory mode among vertebrates and its molecular basis will be highlighted. Finally, the potential occurrence of PMD in invertebrates, its biological significance from an evolutionary perspective and the future direction of investigations will be briefly sketched.

Artificial exocytotic system that secretes intravesicular contents upon Ca2+ influx

Exocytosis is a crucial process of secreting various signaling molecules such as neurotransmitters, hormones, and other chemical mediators into the extracellular space. Exocytotic release is caused by membrane fusion of intracellular vesicles with the plasma membrane triggered by an increase in intracellular Ca(2+). In the present study, we developed an artificial system of exocytosis that secretes intravesicular contents upon Ca(2+) influx. We prepared artificial secretory cells using cell-sized giant unilamellar liposomal vesicles (GUVs) that contain small liposomes (SUVs) that correspond to secretory vesicles. To observe exocytosis-like secretion in an artificial system, we labeled both an intra-SUV solution and an SUV membrane with a soluble fluorescent dye and a rhodamine-labeled phospholipid, respectively. To induce membrane fusion between SUVs and a GUV as observed in exocytosis, the Ca(2+) concentration of intra-GUV was elevated by incorporating ionomycin (a Ca(2+) ionophore) into the GUV membrane. We succeeded in inducing exocytosis-like secretion by Ca(2+) elevation in a GUV together with the osmolarity difference between the intra-GUV and extra-GUV solutions.

Human eosinophils recognize endogenous danger signal crystalline uric acid and produce proinflammatory cytokines mediated by autocrine ATP

Eosinophils are multifunctional leukocytes involved in various inflammatory processes, as well as tissue remodeling and immunoregulation. During inflammation and infection, injured cells and damaged tissues release uric acid and monosodium urate (MSU) crystals as important endogenous danger signals. Uric acid is also implicated in the immunogenic effects of an authentic Th2 adjuvant, aluminum hydroxide. Eosinophils often localize at sites of Th2-type chronic inflammation; therefore, we hypothesized that eosinophils may react to endogenous danger signals. We found that human eosinophils migrate toward soluble uric acid and MSU crystals in a gradient-dependent manner. Eosinophils incubated with MSU crystals, but not those incubated with uric acid solution, produced elevated levels of IL-6 and IL-8/CXCL8. Other cytokines and chemokines, including IL-1beta, IL-10, IL-17, IFN-gamma, CCL2, CCL3, CCL4, TNF-alpha, G-CSF, GM-CSF, fibroblast growth factor, vascular endothelial growth factor, and TGF-beta, were also produced by eosinophils incubated with MSU crystals. Eosinophils exposed to MSU crystals rapidly (i.e., within 1 min of exposure) released ATP into the extracellular milieu. Importantly, this autocrine ATP was necessary for eosinophils to produce cytokines in response to MSU crystals, and P2 nucleotide receptors, in particular P2Y(2), are likely involved in this positive feedback loop. Finally, at higher concentrations, MSU crystals promoted P2R-dependent release of a granule protein (eosinophil-derived neurotoxin) and cell death. Thus, human eosinophils may respond to particulate damage-associated endogenous danger signals. These responses by eosinophils to tissue damage may explain the self-perpetuating nature of chronic inflammation in certain human diseases, such as asthma.

Heat shock protein 70B' (HSP70B') expression and release in response to human oxidized low density lipoprotein immune complexes in macrophages

Heat shock proteins (HSPs) have been implicated in the activation and survival of macrophages. This study examined the role of HSP70B', a poorly characterized member of the HSP70 family, in response to oxidatively modified LDL (oxLDL) and immune complexes prepared with human oxLDL and purified human antibodies to oxLDL (oxLDL-IC) in monocytic and macrophage cell lines. Immunoblot analysis of cell lysates and conditioned medium from U937 cells treated with oxLDL alone revealed an increase in intracellular HSP70B' protein levels accompanied by a concomitant increase in HSP70B' extracellular levels. Fluorescence immunohistochemistry and confocal microscopy, however, demonstrated that oxLDL-IC stimulated the release of HSP70B', which co-localized with cell-associated oxLDL-IC. In HSP70B'-green fluorescent protein-transfected mouse RAW 264.7 cells, oxLDL-IC-induced HSP70B' co-localized with membrane-associated oxLDL-IC as well as the lipid moiety of internalized oxLDL-IC. Furthermore, the data demonstrated that HSP70B' is involved in cell survival, and this effect could be mediated by sphingosine kinase 1 (SK1) activation. An examination of regularly implicated cytokines revealed a significant relationship between HSP70B' and the release of the anti-inflammatory cytokine interleukin-10 (IL-10). Small interfering RNA knockdown of HSP70B' resulted in a corresponding decrease in SK1 mRNA levels and SK1 phosphorylation as well as increased release of IL-10. In conclusion, these findings suggest that oxLDL-IC induce the synthesis and release of HSP70B', and once stimulated, HSP70B' binds to the cell-associated and internalized lipid moiety of oxLDL-IC. The data also implicate HSP70B' in key cellular functions, such as regulation of SK1 activity and release of IL-10, which influence macrophage activation and survival.

Physiological function and molecular basis of STIM1-mediated calcium entry in immune cells

Calcium signals in immune cells regulate a variety of physiological responses such as cell activation, differentiation, gene transcription, and effector functions. Surface receptor stimulation induces an increase in the concentration of cytosolic calcium ions (Ca2+), which are derived mainly from two sources, intracellular endoplasmic reticulum (ER) Ca2+ stores and the extracellular space. The major cascade for Ca2+ entry in immune cells is through store-operated Ca2+ entry (SOCE) and Ca2+ release-activated Ca2+ (CRAC) channels. Activation of SOCE is triggered by depletion of intracellular ER Ca2+ stores, but the molecular mechanism was a long-standing issue. With the recent molecular identification of the ER Ca2+ sensor [stromal interacting molecule-1 (STIM1)] and a pore-forming subunit of the CRAC channel (Orai1), our understanding of the SOCE activation pathway has increased dramatically. These advances have now made it possible to shed some light on important questions: what is the physiological significance of SOCE, and what is its molecular basis? This review focuses on the recent progress in the field and the exciting opportunities for understanding how SOCE influences diverse immune functions.

Functional role of eosinophils in gastrointestinal inflammation

Eosinophilic gastrointestinal (GI) diseases (EGIDs) are characterized by a rich eosinophilic inflammation of the GI tract. Clinical and experimental studies suggest that eosinophils have a pathogenic role in EGIDs; however, the function of eosinophils in these diseases remains an enigma. This article describes eosinophil immunoregulatory and effector function and discusses the possible involvement of these pathways in EGIDs.

Gene expression patterns in peripheral blood correlate with the extent of coronary artery disease

Systemic and local inflammation plays a prominent role in the pathogenesis of atherosclerotic coronary artery disease, but the relationship of whole blood gene expression changes with coronary disease remains unclear. We have investigated whether gene expression patterns in peripheral blood correlate with the severity of coronary disease and whether these patterns correlate with the extent of atherosclerosis in the vascular wall.

Patients were selected according to their coronary artery disease index (CADi), a validated angiographical measure of the extent of coronary atherosclerosis that correlates with outcome. RNA was extracted from blood of 120 patients with at least a stenosis greater than 50% (CADi≥23) and from 121 controls without evidence of coronary stenosis (CADi = 0).

160 individual genes were found to correlate with CADi (rho>0.2, P<0.003). Prominent differential expression was observed especially in genes involved in cell growth, apoptosis and inflammation. Using these 160 genes, a partial least squares multivariate regression model resulted in a highly predictive model (r² = 0.776, P<0.0001). The expression pattern of these 160 genes in aortic tissue also predicted the severity of atherosclerosis in human aortas, showing that peripheral blood gene expression associated with coronary atherosclerosis mirrors gene expression changes in atherosclerotic arteries.

In conclusion, the simultaneous expression pattern of 160 genes in whole blood correlates with the severity of coronary artery disease and mirrors expression changes in the atherosclerotic vascular wall.

Eosinophil cationic protein (ECP) is processed during secretion

The eosinophil granulocyte is an inflammatory cell involved in allergic diseases such as asthma and rhinitis. Eosinophil cationic protein (ECP) is a basic and potentially cytotoxic granule protein that is released from the eosinophil upon activation. The aim was to study secretion of molecular variants of ECP from blood eosinophils with the hypothesis that the stored noncytotoxic ECP is altered into cytotoxic species upon release from the cell. Eosinophil granulocytes were purified to >95% from venous blood from birch pollen allergic subjects, with symptoms of rhinitis, and from healthy control subjects during the birch pollen season. The cells were stimulated with IL-5, GM-CSF, or serum-opsonized Sephadex particles. Concentration of ECP in cells or supernatants was measured by means of a fluoroenzyme immunoassay, and ECP heterogeneity was studied using an affinity capture assay with the surface-enhanced laser desorption/ionization-time of flight mass spectrometry technique. Extracts of unstimulated eosinophils contained 10 major ECP variants, with molecular masses ranging from 16.1 to 17.7 kDa. Stimulation with particles mainly induced the secretion of two molecular variants at 16.1 and 16.3 kDa, while cytokine stimulation gave rise to a different secretion profile. ECP variants in the pellet extracts remained unaffected by cell activation. The modifications of secreted ECP were partly explained by differences in N-linked glycosylations. Secretion of ECP from eosinophils involves protein modification. The molecular masses of released ECP have acquired the masses of the cytotoxic species.

Quantal release of serotonin from platelets

Even though platelets are known to play a critical role in hemostasis, mediated in part by their uptake, storage, and release of serotonin, there are many unexplored aspects of this process. Herein, single-cell amperometry is employed to characterize the dynamic secretion of serotonin from platelet dense-body granules. On the basis of a three-dimensional random walk simulation that estimates detection efficiency with varied spacing between the carbon-fiber microelectrode and the platelet, it is clear that the detected charge likely represents complete oxidation of the released granule contents and, thus, is a good method to calculate the serotonin concentration in each granule. Using the measured charge and volume estimates based on transmission electron microscopy (TEM) data, the granular concentration of serotonin is approximately 0.5 M. The simulated spike widths are significantly narrower than most of the measured amperometric spikes, clearly indicating that the stored serotonin is highly associated with an aggregate rather than freely diffusible within the dense-body granule. Additionally, by varying extracellular buffer temperature and pH to adjust the driving forces for serotonin delivery from the dense-body granules to the extracellular space, it is clear that, although platelet chemical messenger storage and secretion is similar to that of other secretory cells, there are some important distinctions.

Ragweed pollen-mediated IgE-independent release of biogenic amines from mast cells via induction of mitochondrial dysfunction

Normal functions of mitochondria are required for physiological dynamics of cells, while their dysfunction contributes to development of various disorders including those of immune system. Here we demonstrate that exposure of mast cells to ragweed pollen extract increases production of H(2)O(2) via mitochondrial respiratory complex III. These mitochondrial ROS (mtROS) enhance secretion of histamine and serotonin from mast cells, but not enzymes such as beta-hexosaminidase, independently from FcvarepsilonRI-generated stimuli. The release of biogenic amines is associated with inhibition of secretory granules' H(+)-ATPase activity, activation of PKC-delta and microtubule-dependent motility, and it is independent from intracellular free Ca(2+) levels. To asses differences from IgE-mediated mast cell degranulation we show that mtROS decrease antigen-triggered beta-hexosaminidase release, while they are synergistic with antigen-induced IL-4 production in sensitized cells. Taken together, these data indicate that mitochondrial dysfunction can act independently from adaptive immunity, as well as augments Th2-type responses. Pharmacological maintenance of physiological mitochondrial function could have clinical benefits in prevention and treatment of allergic diseases.

New developments in mast cell biology

Mast cells can function as effector and immunoregulatory cells in immunoglobulin E-associated allergic disorders, as well as in certain innate and adaptive immune responses. This review focuses on exciting new developments in the field of mast cell biology published in the past year. We highlight advances in the understanding of FcvarepsilonRI-mediated signaling and mast cell-activation events, as well as in the use of genetic models to study mast cell function in vivo. Finally, we discuss newly identified functions for mast cells or individual mast cell products, such as proteases and interleukin 10, in host defense, cardiovascular disease and tumor biology and in settings in which mast cells have anti-inflammatory or immunosuppressive functions.

Primary granule exocytosis in human neutrophils is regulated by Rac-dependent actin remodeling

The actin cytoskeleton regulates exocytosis in all secretory cells. In neutrophils, Rac2 GTPase has been shown to control primary (azurophilic) granule exocytosis. In this report, we propose that Rac2 is required for actin cytoskeletal remodeling to promote primary granule exocytosis. Treatment of neutrophils with low doses (< or = 10 microM) of the actin-depolymerizing drugs latrunculin B (Lat B) or cytochalasin B (CB) enhanced both formyl peptide receptor- and Ca(2+) ionophore-stimulated exocytosis. Higher concentrations of CB or Lat B, or stabilization of F-actin with jasplakinolide (JP), inhibited primary granule exocytosis measured as myeloperoxidase release but did not affect secondary granule exocytosis determined by lactoferrin release. These results suggest an obligatory role for F-actin disassembly before primary granule exocytosis. However, lysates from secretagogue-stimulated neutrophils showed enhanced actin polymerization activity in vitro. Microscopic analysis showed that resting neutrophils contain significant cortical F-actin, which was redistributed to sites of primary granule translocation when stimulated. Exocytosis and actin remodeling was highly polarized when cells were primed with CB; however, polarization was reduced by Lat B preincubation, and both polarization and exocytosis were blocked when F-actin was stabilized with JP. Treatment of cells with the small molecule Rac inhibitor NSC23766 also inhibited actin remodeling and primary granule exocytosis induced by Lat B/fMLF or CB/fMLF, but not by Ca(2+) ionophore. Therefore, we propose a role for F-actin depolymerization at the cell cortex coupled with Rac-dependent F-actin polymerization in the cell cytoplasm to promote primary granule exocytosis.

Acetamide-45 inhibited hyperresponsiveness and airway inflammation in mice partly depending on phosphodiesterase activity suppression

AIM

Asthma is characterized as a chronic inflammatory disorder of the airways. Phosphodiesterases (PDE), which hydrolyze cAMP, are considered to play important roles in asthma. We previously reported that acetamide-45 could inhibit cAMP-PDE activity, and histamine- and methacholine-induced contractions of isolated guinea pig trachea. The purpose of this study is to determine whether this agent could suppress allergic-induced airway hyperresponsiveness (AHR) and airway inflammation in allergic mice.

METHODS

A mouse model for asthma was used to investigate acetamide-45 on the airway lesions compared with glucocorticoids. The study was conducted on mice sensitized and challenged with ovalbumin and the whole body plethysmography was carried out to assess AHR. The bronchoalveolar lavage (BAL) histopathology was examined.

RESULTS

We found that acetamide-45 significantly inhibited the enhanced hyperresponsiveness and eosinophil recruitment in airways with elimination of cAMP-PDE activity in lung tissue. Elevated IL-4 and IL-5 in bronchoalveolar lavage fluid (BALF) in asthmatic mice were markedly decreased.

CONCLUSION

Our results indicate that the agent has a potential role in inflammatory disease.

Proteomic map of peripheral blood mononuclear cells

In the field of proteomics extensive efforts have been focused on the knowledge of proteins expressed by different cell types. In particular, enormous progress has been done in the characterization of blood cellular components. In this work, we have established a public 2-DE database for human peripheral blood mononuclear cells (PBMCs) proteins. Two hundred and forty-six spots corresponding to 174 different proteins have been identified on 2-DE gels from PBMCs isolated from six healthy individuals. All the identified proteins have been classified in thirteen categories on the basis of their differential functions or cellular localization and annotated at the http://physiology.unile.it/proteomics. The role of several proteins has been discussed in relation to their biological function. We intend to show the potentiality of PBMCs to investigate the proteomics changes possibly associated with a large number of pathologies such as autoimmune, neurodegenerative and cancer diseases.

Histological changes in the urothelium and suburothelium of human overactive bladder following intradetrusor injections of botulinum neurotoxin type A for the treatment of neurogenic or idiopathic detrusor overactivity

BACKGROUND

We examined, for the first time in a prospective study, the histological changes in the urothelium and suburothelium of patients with neurogenic (NDO) or idiopathic detrusor overactivity (IDO) after one or repeat treatments with intradetrusor BoNTA.

METHODS

Flexible cystoscopic bladder biopsies were obtained from patients with urodynamically proven intractable spinal NDO or IDO before and 4 and 16 wk after one or repeat treatments with intradetrusor injections of BOTOX1 (NDO 300 U, IDO 200 U). Specimens were stained for haematoxylin-eosin and analysed blindly for inflammatory changes, fibrosis, hyperplasia, and dysplasia in the urothelium and suburothelium. Statistical comparisons were significant at p values less than 0.05.

RESULTS

Signs of chronic inflammation were found in 59.1% of baseline biopsies (65.6% of NDO vs. 50% of IDO, p=0.049), 67.6% of post-first biopsies and 86.4% after repeat injections. The two groups were comparable for degree of baseline inflammation, which did not change significantly after first injection and up to 16 wk after a third injection. Mild fibrosis was found in 2.2% of biopsies examined, equally before and after treatment, but not after repeat injections. No dysplasia or hyperplasia was identified. Eosinophils were identified more frequently in biopsies taken after repeat injections compared with the post-first injection and baseline biopsies (chi2=8.23, p=0.018). No difference existed between NDO and IDO bladders.

CONCLUSIONS

BoNTA injections do not appear to be producing significant inflammatory changes, fibrosis, or dysplastic changes in human bladder urothelium/suburothelium after a single injection and in a limited number of repeat treatment biopsies. The presence of eosinophils might be treatment-related, because they were mostly found in post-treatment biopsies.

Fully automated microchip system for the detection of quantal exocytosis from single and small ensembles of cells

A lab-on-a-chip device that enables positioning of single or small ensembles of cells on an aperture in close proximity to a mercaptopropionic acid (MPA) modified sensing electrode has been developed and characterized. The microchip was used for the detection of Ca(2+)-dependent quantal catecholamine exocytosis from single as well as small assemblies of rat pheochromocytoma (PC12) cells. The frequency of events increased considerably upon depolarization of the PC12 cell membrane using a high extracelluar concentration of potassium. The number of recorded events could be correlated with the number of cells immobilized on the electrode. Quantal characteristics, such as the number of released molecules per recorded event, are equivalent to data obtained using conventional carbon fiber microelectrodes. The detection sensitivity of the device allows for the detection of less than 10 000 dopamine molecules in a quantal release. The distribution of peak rise-time and full width at half maximum was constant during measurement periods of several minutes demonstrating the stability of the MPA modified surface.

JunB is required for IgE-mediated degranulation and cytokine release of mast cells

Mast cells are effector cells of IgE-mediated immune responses frequently found at the vicinity of blood vessels, the margins of diverse tumors and at sites of potential infection and inflammation. Upon IgE-mediated stimulation, mast cells produce and secrete a broad spectrum of cytokines and other inflammatory mediators. Recent work identified JunB, a member of the AP-1 transcription factor family, as critical regulator of basal and induced expression of inflammatory mediators in fibroblasts and T cells. To study the impact of JunB on mast cell biology, we analyzed JunB-deficient mast cells. Mast cells lacking JunB display a normal in vivo maturation, and JunB-deficient bone marrow cells in vitro differentiated to mast cells show no alterations in proliferation or apoptosis. But these cells exhibit impaired IgE-mediated degranulation most likely due to diminished expression of SWAP-70, Synaptotagmin-1, and VAMP-8, and due to impaired influx of extracellular calcium. Moreover, JunB-deficient bone marrow mast cells display an altered cytokine expression profile in response to IgE stimulation. In line with these findings, the contribution of JunB-deficient mast cells to angiogenesis, as analyzed in an in vitro tube formation assay on matrigel, is severely impaired due to limiting amounts of synthesized and secreted vascular endothelial growth factor. Thus, JunB is a critical regulator of intrinsic mast cell functions including cross-talk with endothelial cells.

Mechanisms of eosinophilia in the pathogenesis of hypereosinophilic disorders

The increased numbers of activated eosinophils in the blood and tissues that typically accompany hypereosinophilic disorders result from a variety of mechanisms. Exciting advances in translating discoveries achieved from mouse models and molecular strategies to the clinic have led to a flurry of new therapeutics specifically designed to target eosinophil-associated diseases. So far, this form of hypothesis testing in humans in vivo through pharmacology generally has supported the paradigms generated in vitro and in animal models, raising hopes that a spectrum of novel therapies soon may become available to help those who have eosinophil-associated diseases.

Pro-inflammatory feedback activation cycle evoked by attack of Vibrio cholerae cytolysin on human neutrophil granulocytes

Vibrio cholerae cytolysin (VCC) is a pore-forming toxin that is secreted in precursor form (pro-VCC) and requires proteolytic cleavage in order to attain membrane-permeabilizing properties. Pro-VCC can be activated both in solution and membrane-bound state. Processing of membrane-bound pro-VCC can in turn be achieved through the action of both cell-associated and soluble proteases. The current investigation describes the interaction of VCC with human neutrophil granulocytes. It is shown that pro-VCC binds to these cells and is cleaved by cell-bound serine proteases. Membrane permeabilization leads to granulocyte activation, as witnessed by the generation of reactive oxygen metabolites and liberation of granule constituents. A mutant toxin with unaltered binding properties but devoid of pore-forming activity did not elicit these effects. The secreted proteases cleave and activate further bound- and non-bound pro-VCC. A positive feedback loop is thus created that results in enhanced cytotoxicity towards both the targeted granulocytes and towards bystander cells that are not primarily killed by the protoxin. Thus, activation of neutrophil granulocytes by VCC fuels a positive feedback cycle that will cripple immune defence, augment inflammation, and enhance the cytotoxic action of the toxin on neighbouring tissue cells.

Robust syntaxin-4 immunoreactivity in mammalian horizontal cell processes

Horizontal cells mediate inhibitory feed-forward and feedback communication in the outer retina; however, mechanisms that underlie transmitter release from mammalian horizontal cells are poorly understood. Toward determining whether the molecular machinery for exocytosis is present in horizontal cells, we investigated the localization of syntaxin-4, a SNARE protein involved in targeting vesicles to the plasma membrane, in mouse, rat, and rabbit retinae using immunocytochemistry. We report robust expression of syntaxin-4 in the outer plexiform layer of all three species. Syntaxin-4 occurred in processes and tips of horizontal cells, with regularly spaced, thicker sandwich-like structures along the processes. Double labeling with syntaxin-4 and calbindin antibodies, a horizontal cell marker, demonstrated syntaxin-4 localization to horizontal cell processes; whereas, double labeling with PKC antibodies, a rod bipolar cell (RBC) marker, showed a lack of co-localization, with syntaxin-4 immunolabeling occurring just distal to RBC dendritic tips. Syntaxin-4 immunolabeling occurred within VGLUT-1-immunoreactive photoreceptor terminals and underneath synaptic ribbons, labeled by CtBP2/RIBEYE antibodies, consistent with localization in invaginating horizontal cell tips at photoreceptor triad synapses. Vertical sections of retina immunostained for syntaxin-4 and peanut agglutinin (PNA) established that the prominent patches of syntaxin-4 immunoreactivity were adjacent to the base of cone pedicles. Horizontal sections through the OPL indicate a one-to-one co-localization of syntaxin-4 densities at likely all cone pedicles, with syntaxin-4 immunoreactivity interdigitating with PNA labeling. Pre-embedding immuno-electron microscopy confirmed the subcellular localization of syntaxin-4 labeling to lateral elements at both rod and cone triad synapses. Finally, co-localization with SNAP-25, a possible binding partner of syntaxin-4, indicated co-expression of these SNARE proteins in the same subcellular compartment of the horizontal cell. Taken together, the strong expression of these two SNARE proteins in the processes and endings of horizontal cells at rod and cone terminals suggests that horizontal cell axons and dendrites are likely sites of exocytotic activity.

WD-repeat-propeller-FYVE protein, ProF, binds VAMP2 and protein kinase Czeta

We have recently identified a protein, consisting of seven WD repeats, presumably forming a beta-propeller, and a domain identified in Fab1p, YOTB, VAC1p, and EEA1 (FYVE) domain, ProF. The FYVE domain targets the protein to vesicular membranes, while the WD repeats allow binding of the activated kinases Akt and protein kinase (PK)Czeta. Here, we describe the vesicle-associated membrane protein 2 (VAMP2) as interaction partner of ProF. The interaction is demonstrated with overexpressed and endogenous proteins in mammalian cells. ProF and VAMP2 partially colocalize on vesicular structures with PKCzeta and the proteins form a ternary complex. VAMP2 can be phosphorylated by activated PKCzeta in vitro and the presence of ProF increases the PKCzeta-dependent phosphorylation of VAMP2 in vitro. ProF is an adaptor protein that brings together a kinase with its substrate. VAMP2 is known to regulate docking and fusion of vesicles and to play a role in targeting vesicles to the plasma membrane. The complex may be involved in vesicle cycling in various secretory pathways.

Presence of SNAP-23 and syntaxin 4 in mouse and hamster peritoneal mast cells

Mast cells (MCs) play a crucial role in inflammatory reactions. Their presence and number in the peritoneal cavity is important to overcome and enhance resistance to peritoneal infection. When MCs are activated they release a variety of biological mediators from their granules, such as histamine, that contribute to the appropriate and rapid local immune response. Granular content is released using a process of compound exocytosis, also termed degranulation. SNAP-23 and syntaxin 4 are plasma membrane proteins involved in degranulation of rat MCs. Their presence, however, has not been studied in MCs of other rodent species. The aim of the present study was to investigate using immunocytochemistry whether SNAP-23 and syntaxin 4 are present in peritoneal MCs of the mouse and hamster. In addition, the diameter, percentage and histamine content of these cells were also analyzed. Our results demonstrate that SNAP-23 and syntaxin 4 are present in the mouse and hamster peritoneal MCs, suggesting that proteins involved in the secretory process in MCs are conserved among species. Likewise, we conclude that peritoneal MCs of mouse and hamster are heterogeneous in size, percentage and histamine content.

Diclofenac induces basophil degranulation without increasing CD63 expression in sensitive patients

Diclofenac (Dc) induces an IgE-independent basophil (Ba) degranulation in susceptible individuals. CD63 Ba expression is utilized as an in vitro test for diagnosis of drug hypersensitivity. We tested the ability of Dc to induce CD63 Ba expression by flow cytometry (BAT) and Ba degranulation using light microscopy (HBDT) in patients sensitive to Dc. We studied 14 patients with diclofenac hypersensitivity, also two patients sensitive to Dermatophagoides pteronyssinus (Dp), and 12 normal controls. HBDT was performed by mononuclear cells toluidine blue staining. BAT determined CD63 expression in antiCD63/anti-IgE/anti-CD45-labelled whole blood. In each case, the percentage of activated Ba post-stimulation with 1 and 10 microg/ml Dc was determined. Positive controls included N-formyl-methionyl-leucyl-phenylalanine (fMLP) peptide-induced activation. IgE-mediated Ba activation was induced with a Dp allergenic extract. With Dc 1 microg/ml, mean HBDT in Dc-susceptible individuals was 33.62 +/- 18.35% and 8.49 +/- 4.79% in controls (P = 0.0001). Mean BAT was 2.04 +/- 1.68% and 1.93 +/- 1.40% in controls (P = 0.8). Ba preincubation with Dc did not affect fMLP-induced CD63 expression, neither in Dc-sensitive individuals (P = 0.8) (n = 4) nor in subjects without Dc hypersensitivity (P = 0.25) (n = 4). Ba from the two patients sensitive both to Dc and Dp responded to Dp but not to Dc by BAT: Dc, 1.99 +/- 0.78%; Dp: 60.87 +/- 9.28%; but showed degranulation by HBDT: Dc, 30.53 +/- 1.02%, Dp: 48.78 +/- 22.17%. Dc induces Ba degranulation in sensitive patients in a way that does not induce CD63 expression and is different from IgE-mediated and fMLP-mediated degranulation. Our results suggest that CD63 expression is not a reliable diagnostic method for diclofenac allergy.

Calcium-sensing receptor stimulates secretion of an interferon-γ-induced monokine (CXCL10) and monocyte chemoattractant protein-3 in immortalized GnRH neurons

Biology of GnRH neurons is critically dependent on extracellular Ca(2+) (Ca(2+) (o)). We evaluated differences in gene expression patterns with low and high Ca(2+) (o) in an immortalized GnRH neuron line, GT1-7 cells. Mouse global oligonucleotide microarray was used to evaluate transcriptional differences among the genes regulated by elevated Ca(2+) (o). Our result identified two interferon-gamma (IFNgamma)-inducible chemokines, CXCL9 and CXCL10, and a beta chemokine, monocyte chemoattractant protein-3 (MCP-3/CCL7), being up-regulated in GT1-7 cells treated with high Ca(2+) (o) (3.0 mM) compared with low Ca(2+) (o) (0.5 mM). Up-regulation of these mRNAs by elevated Ca(2+) (o) was confirmed by quantitative PCR. Elevated Ca(2+) (o) stimulated secretion of CXCL10 and MCP-3 but not CXCL9 in GT1-7 cells, and this effect was mediated by an extracellular calcium-sensing receptor (CaR) as the dominant negative CaR attenuated secretion of CXCL10 and MCP-3. CXCL10 and MCP-3 were localized in mouse GnRH neurons in the preoptic hypothalamus. Suppression of K(+) channels (BK channels) with 25 nM charybdotoxin inhibited high-Ca(2+) (o)-stimulated CXCL10 release. Accordingly, CaR activation by a specific CaR agonist, NPS-467, resulted in the activation of a Ca(2+)-activated K(+) channel in these cells. CaR-mediated MCP-3 secretion involves the PI3 kinase pathway in GT1-7 cells. MCP-3 stimulated chemotaxis of astrocytes treated with transforming growth factor-beta (TGFbeta). With TGFbeta-treated astrocytes, we next observed that conditioned medium from GT1-7 cells treated with high Ca(2+) promoted chemotaxis of astrocytes, and this effect was attenuated by a neutralizing antibody to MCP-3. These results implicate CaR as an important regulator of GnRH neuron function in vivo by stimulating secretion of heretofore unsuspected cytokines, i.e., CXCL10 and MCP-3.

SNAREing immunity: the role of SNAREs in the immune system

The trafficking of molecules and membranes within cells is a prerequisite for all aspects of cellular immune functions, including the delivery and recycling of cell-surface proteins, secretion of immune mediators, ingestion of pathogens and activation of lymphocytes. SNARE (soluble-N-ethylmaleimide-sensitive-factor accessory-protein receptor)-family members mediate membrane fusion during all steps of trafficking, and function in almost all aspects of innate and adaptive immune responses. Here, we provide an overview of the roles of SNAREs in immune cells, offering insight into one level at which precision and tight regulation are instilled on immune responses.

Unraveling cell processes: interference imaging interwoven with data analysis

The paper presents results on the application of interference microscopy and wavelet-analysis for cell visualization and studies of cell dynamics. We demonstrate that interference imaging of erythrocytes can reveal reorganization of the cytoskeleton and inhomogenity in the distribution of hemoglobin, and that interference imaging of neurons can show intracellular compartmentalization and submembrane structures. We investigate temporal and spatial variations of the refractive index for different cell types: isolated neurons, mast cells and erythrocytes. We show that the refractive dynamical properties differ from cell type to cell type and depend on the cellular compartment. Our results suggest that low frequency variations (0.1-0.6 Hz) result from plasma membrane processes and that higher frequency variations (20-26 Hz) are related to the movement of vesicles. Using double-wavelet analysis, we study the modulation of the 1 Hz rhythm in neurons and reveal its changes under depolarization and hyperpolarization of the plasma membrane. We conclude that interference microscopy combined with wavelet analysis is a useful technique for non-invasive cell studies, cell visualization, and investigation of plasma membrane properties.

CCL5 evokes calcium signals in microglia through a kinase-, phosphoinositide-, and nucleotide-dependent mechanism

Microglia, the resident macrophages of the CNS, are responsible for the innate immune response in the brain and participate in the pathogenesis of certain neurodegenerative disorders. Chemokines initiate activation and migration of microglia. The beta-chemokine CCL5 induces an elevation in intracellular calcium concentration ([Ca(2+)](i)) in human microglia. Here, we examined the signal transduction pathway linking activation of chemokine receptor CCR5 to an elevation in [Ca(2+)](i) in cultured microglia by using pharmacological approaches in combination with Fura-2-based digital imaging. The CCL5-induced response required Janus kinase (Jak) activity and the stimulation of an inhibitory G protein. Multiple downstream signaling pathways were involved, including phosphatidylinositol 3-kinase (PI3K), Bruton's tyrosine kinase (Btk), and phospholipase C (PLC)-mediated release of Ca(2+) from inositol 1,4,5-trisphosphate (IP(3))-sensitive stores. Activation of both the kinase and the lipase pathways was required for eliciting the Ca(2+) response. However, the majority of the [Ca(2+)](i) increase was derived from sources activated by NAD metabolites. Cyclic ADP-ribose (cADPR) evoked Ca(2+) release from intracellular stores, and ADPR evoked Ca(2+) influx via a nimodipine-sensitive channel. Thus, a multistep cascade couples CCR5 activation to Ca(2+) increases in human microglia. Because changes in [Ca(2+)](i) affect chemotaxis, secretion, and gene expression, pharmacologic modulation of this pathway may alter inflammatory and degenerative processes in the CNS.

Antiallergic drugs, azelastine hydrochloride and epinastine hydrochloride, inhibit ongoing IgE secretion of rat IgE-producing hybridoma FE-3 cells

We asked whether or not antiallergic drugs, azelastine hydrochloride and epinastine hydrochloride, inhibit IgE secretion from IgE-producing hybridoma FE-3 cells. FE-3 cells were cultured in the presence of azelastine or epinastine for 24 h, washed in phosphate-buffered saline , and then recultured in the medium in the absence of the antiallergic drugs. IgE levels in the cultured medium as well as those in the cytoplasm of FE-3 cells were measured by enzyme-linked immunosorbent assay. mRNA levels of Cepsilon, activation-induced cytidine deaminase (AID), XBP-1, and Bip were estimated by northern blot or reverse transcriptase polymerase chain reaction analysis. The activities of nuclear factor-kappa B (NF-kappaB) were analyzed by electrophoretic mobility shift assay (EMSA). Phosphorylation of I kappa B alpha (IkappaBalpha) was analyzed by immunoprecipitation followed by western blot analysis. IgE levels in the cultured medium and in the microsome fraction were lower on the treatment with 10(-5) M azelastine or epinastine than those on the treatment with vehicle. Cepsilon and AID mRNA levels were lower on the treatment with 10(-5) M azelastine than those on the treatment with vehicle, but were not decreased on the treatment with 10(-5) M epinastine. XBP-1 and Bip mRNA levels were not altered following treatment of the antiallergic drugs. Azelastine at 10(-5) M, but not epinastine, reduced DNA binding activity of NF-kappaB and also diminished IkappaBalpha phosphorylation, leading to sustaining IkappaBalpha protein levels. These findings suggest that azelastine exerts its inhibitory effect on the IgE secretion from FE-3 cells through the inhibition of Cepsilon mRNA expression, and that the inhibitory effect of epinastine is, at least in part, due to suppression of IgE synthesis at the post-transcriptional level.

Differential secretion of cytokines

Eosinophil granules store a vast array of cytokines and chemokines, many of which possess opposing activities. Specific stimuli can induce the release of entire granules or selective mediators through a process termed piecemeal degranulation. Until recently, the mechanisms that governed the decision to opt for either of these processes were unknown. Recent research has identified a mechanism through which differential secretion occurs during piecemeal degranulation. Eotaxin stimulation of eosinophils induces the selective mobilization of the granule-stored alpha chain of the interleukin-4 (IL-4) receptor into secretory vesicles. This process selectively recruits IL-4 to these vesicles and facilitates its differential secretion. There is also recent evidence for a mechanism of differential mobilization and membrane fusion of secretory vesicles versus granules. These two compartments possess a different set of SNARE and Rab molecules as vesicle fusion and transport-docking proteins, respectively. This presumably allows differential regulation of the processes of mobilization and plasma membrane fusion. These findings provide a model to explain the mechanism by which eosinophils, and likely many other cell types, differentially secrete cytokines and chemokines.

A peptide against the N-terminus of myristoylated alanine-rich C kinase substrate inhibits degranulation of human leukocytes in vitro

Leukocytes synthesize a variety of inflammatory mediators that are packaged and stored in the cytoplasm within membrane-bound granules. Upon stimulation, the cells secrete the granule contents via an exocytotic process whereby the granules translocate to the cell periphery, the granule membranes fuse with the plasma membrane, and the granule contents are released extracellularly. We have reported previously that another exocytotic process, release of mucin by secretory cells of the airway epithelium, is regulated by the myristoylated alanine-rich C kinase substrate (MARCKS) (Li Y, Martin LD, Spizz G, Adler KB. MARCKS protein is a key molecule regulating mucin secretion by human airway epithelial cells in vitro. J Biol Chem 2001;276:40982-40990; Singer M, Martin LD, Vargaftig BB, Park J, Gruber AD, Li Y, Adler KB. A MARCKS-related peptide blocks mucus hypersecretion in a mouse model of asthma. Nat Med 2004;10:193-196). In those studies, mucin secretion in vitro and in vivo was attenuated by a synthetic peptide identical to the N-terminus of MARCKS, named the MANS peptide (Li and colleagues, 2001). In this study, we used the MANS peptide to investigate possible involvement of MARCKS in secretion of leukocyte granule proteins. In neutrophils isolated from human blood, phorbol 12-myristate 13-acetate-induced myeloperoxidase release was attenuated in a concentration-dependent manner by MANS but not by equal concentrations of a missense control peptide. In additional studies using human leukocyte cell lines, secretion of eosinophil peroxidase from the eosinophil-like cell line HL-60 clone 15, lysozyme from the monocytic leukemia cell line U937, and granzyme from the lymphocyte natural killer cell line NK-92 were attenuated by preincubation of the cells with MANS but not with the missense control peptide. The results indicate that MARCKS protein may play an important role in the secretion of membrane-bound granules from different leukocytes. MARCKS may be an important component of secretory pathways associated with release of granules by different cell types.

Oxidized LDL immune complexes induce release of sphingosine kinase in human U937 monocytic cells

The transformation of macrophages into foam cells is a critical event in the development of atherosclerosis. The most studied aspect of this process is the uptake of modified LDL through the scavenger receptors. Another salient aspect is the effect of modified LDL immune complexes on macrophages activation and foam cell formation. Macrophages internalize oxidized LDL immune complexes (oxLDL-IC) via the Fc-gamma receptor and transform into activated foam cells. In this study we examined the effect of oxLDL-IC on sphingosine kinase 1 (SK1), an enzyme implicated in mediating pro-survival and inflammatory responses through the generation of the signaling molecule sphingosine-1-phosphate (S1P). Intriguingly, oxLDL-IC, but not oxLDL alone, induced an immediate translocation and release of SK1 into the conditioned medium as evidenced by fluorescence confocal microscopy. Immunoblot analysis of cell lysates and conditioned medium revealed a decrease in intracellular SK1 protein levels accompanied by a concomitant increase in extracellular SK1 levels. Furthermore, measurement of S1P formation showed that the activity of cell-associated SK decreased in response to oxLDL-IC compared to oxLDL alone, whereas the activity of SK increased extracellularly. Blocking oxLDL-IC binding to Fc-gamma receptors resulted in decreased levels of extracellular S1P. The data also show that cell survival of human U937 cells exposed to oxLDL-IC increased compared to oxLDL alone. Exogenously added S1P further increased cell survival induced by oxLDL-IC. Taken together, these findings indicate that S1P may be generated extracellularly in response to modified LDL immune complexes and may therefore promote cell survival and prolong cytokine release by activated macrophages.

Mitochondrial Ca2+ flux is a critical determinant of the Ca2+ dependence of mast cell degranulation

An increase in intracellular Ca2+ ([Ca2+]i) is necessary for mast cell exocytosis, but there is controversy over the requirement for Ca2+ in the extracellular medium. Here, we demonstrate that mitochondrial function is a critical determinant of Ca2+ dependence. In the presence of extracellular Ca2+, mitochondrial metabolic inhibitors, including rotenone, antimycin A, and the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), significantly reduced degranulation induced by immunoglobulin E (IgE) antigen or by thapsigargin, as measured by beta-hexosaminidase release. In the absence of extracellular Ca2+; however, antimycin A and FCCP, but not rotenone, enhanced, rather than reduced, degranulation to a maximum of 76% of that observed in the presence of extracellular Ca2+. This enhancement of extracellular, Ca2+-independent degranulation was concomitant with a rapid collapse of the mitochondrial transmembrane potential. Mitochondrial depolarization did not enhance degranulation induced by thapsigargin, irrespective of the presence or absence of extracellular Ca2+. IgE antigen was more effective than thapsigargin as an inducer of [Ca2+]i release, and mitochondrial depolarization augmented IgE-mediated but not thapsigargin-induced Ca2+ store release and mitochondrial Ca2+ ([Ca2+]m) release. Finally, atractyloside and bongkrekic acid [an agonist and an antagonist, respectively, of the mitochondrial permeability transition pore (mPTP)], respectively, augmented and reduced IgE-mediated Ca2+ store release, [Ca2+]m release, and/or degranulation, whereas they had no effects on thapsigargin-induced Ca2+ store release. These data suggest that the mPTP is involved in the regulation of Ca2+ signaling, thereby affecting the mode of mast cell degranulation. This finding may shed light on a new role for mitochondria in the regulation of mast cell activation.

Novel stabilin-1 interacting chitinase-like protein (SI-CLP) is up-regulated in alternatively activated macrophages and secreted via lysosomal pathway

Mammalian Glyco_18-domain-containing proteins include catalytically active chitinases and chitinase-like proteins with cytokine activity involved in host defense and Th2-type inflammatory reactions. Here, we describe a novel human Glyco_18-domain-containing protein, SI-CLP, as an interacting partner of the endocytic/sorting receptor stabilin-1. Similarly to the chitinase-like cytokines YKL-39, YKL-40, and YM1/2, SI-CLP lacks a chitin-binding domain and catalytic amino acids. Using a novel mAb 1C11, we demonstrated that SI-CLP is sorted into late endosomes and secretory lysosomes in human alternatively activated macrophages. The direct interaction of SI-CLP with stabilin-1, their colocalization in the trans-Golgi network, and the reduced sorting of SI-CLP into lysosomes in macrophages treated with stabilin-1 siRNA suggest that stabilin-1 is involved in intracellular sorting of SI-CLP. Expression of SI-CLP in macrophages was strongly up-regulated by the Th2 cytokine IL-4 and by dexamethasone. This effect was suppressed by IFNgamma but not affected by IL-10. In contrast, expression of YKL-40 was induced by IFNgamma and suppressed by dexamethasone. Macrophages treated with IL-4 secreted SI-CLP, while costimulation with dexamethasone blocked secretion and resulted in intracellular accumulation of SI-CLP. The 1C11 mAb detected SI-CLP in human bronchoalveolar lavage and peripheral-blood leukocytes (PBLs), and can be used to analyze the role of SI-CLP in human disorders.

The role of Rho GTPases and SNAREs in mediator release from granulocytes

Granulocytes are defined as the population of granulated white blood cells (eosinophils, neutrophils, and basophils). These cells are involved in inflammation and contribute to the pathogenesis of allergic and inflammatory diseases. Inflammation is induced by the release of mediators from granulocytes recruited to or resident within tissues, resulting in edema, leukocyte recruitment, and tissue injury. Eosinophils and neutrophils express Rac1 and Rac2 guanosine triphosphatases (GTPases), 2 members of the Rho GTPase subfamily of ras-related GTPases. Rho GTPases are activated by receptors in the cell membrane and are proposed to function as intracellular molecular switches to regulate mediator release, including exocytosis, from granulocytes. Exocytosis involves granule fusion, which requires the binding of intracellular membrane receptors known as SNAP receptor (SNAREs; soluble N-ethylmaleimide-sensitive factor [NSF] attachment protein [SNAP] receptors). Eosinophils and neutrophils express similar SNARE isoforms that are important in granule fusion events. Together, these molecules link together to form a common signaling pathway for mediator release from granulocytes. Identifying these molecules and their function may provide novel targets for the prevention of inflammatory reactions.

Nonpathogenic, Environmental Fungi Induce Activation and Degranulation of Human Eosinophils

Eosinophils and their products are probably important in the pathophysiology of allergic diseases, such as bronchial asthma, and in host immunity to certain organisms. An association between environmental fungal exposure and asthma has been long recognized clinically. Although products of microorganisms (e.g., lipopolysaccharides) directly activate certain inflammatory cells (e.g., macrophages), the mechanism(s) that triggers eosinophil degranulation is unknown. In this study we investigated whether human eosinophils have an innate immune response to certain fungal organisms. We incubated human eosinophils with extracts from seven environmental airborne fungi (Alternaria alternata, Aspergillus versicolor, Bipolaris sorokiniana, Candida albicans, Cladosporium herbarum, Curvularia spicifera, and Penicillium notatum). Alternaria and Penicillium induced calcium-dependent exocytosis (e.g., eosinophil-derived neurotoxin release) in eosinophils from normal individuals. Alternaria also strongly induced other activation events in eosinophils, including increases in intracellular calcium concentration, cell surface expression of CD63 and CD11b, and production of IL-8. Other fungi did not induce eosinophil degranulation, and Alternaria did not induce neutrophil activation, suggesting specificity for fungal species and cell type. The Alternaria-induced eosinophil degranulation was pertussis toxin sensitive and desensitized by preincubating cells with G protein-coupled receptor agonists, platelet-activating factor, or FMLP. The eosinophil-stimulating activity in Alternaria extract was highly heat labile and had an M(r) of approximately 60 kDa. Thus, eosinophils, but not neutrophils, possess G protein-dependent cellular activation machinery that directly responds to an Alternaria protein product(s). This innate response by eosinophils to certain environmental fungi may be important in host defense and in the exacerbation of inflammation in asthma and allergic diseases.

Mechanisms of eosinophil cytokine release

Human eosinophils have been demonstrated to contain a multitude of cytokines and chemokines that exist pre-formed within these cells. This content of pre-formed cytokines, with diverse potential biologic activities, provides eosinophils with capabilities distinct from most other leukocytes. The localization of pre-formed cytokines within eosinophils is both within specific granules and associated with substantial numbers of morphologically distinct cytoplasmic vesicles. Stimulation for release of specific cytokines, such as IL-4, leads to a regulated signal transduction cascade, which is dependent on the formation of leukotriene C4 within eosinophils where it acts as an intracrine mediator. IL-4 release occurs selectively and is by means of vesicular transport. The capabilities of eosinophils not only to rapidly release pre-formed cytokines but also to differentially regulate which cytokines are released endow eosinophils with distinct abilities in innate and acquired immunity.