Piecemeal degranulation as a general secretory mechanism?

Purified granulocytes in extracorporeal cell therapy: A multifaceted approach to combat sepsis-induced immunoparalysis

BACKGROUND

Immune cell dysfunction plays a central role in sepsis-induced immunoparalysis. Targeted treatment using healthy donor immune cell transfusions, particularly granulocyte concentrates (GC) potentially induces tissue damage. Initial trials using GC in an extracorporeal immune cell perfusion system provided evidence for beneficial effects with fewer side effects, by separating patient and donor immune cell compartments. A multicenter clinical trial is exploring feasibility and effects of a 6-h treatment (NCT06143137). This ex vivo study examines technical feasibility and cellular effects of an extended treatment interval up to 24 h.

METHODS

Standard GC were purified to increase the potential storage time and subsequently implemented in the extracorporeal immune cell perfusion system. Parameters assessed included cell viability, phagocytosis activity, oxidative burst, cytokine release, and metabolic parameters of purified. GC during an extended circulation time of up to 24 h.

RESULTS

After storage of 72 h granulocytes were viable throughout the study period and exhibited preserved functionality and metabolic activity. The findings highlight a time-dependent nature of cytokine release by neutrophils in the extracorporeal circuit, as cytokine secretion patterns showed IL-8 peaking within 6 h, while MCP-1, IL-6, IL-1β, and TNF-α increased after 24 h of circulation.

CONCLUSION

Purified GC remain functional after 72 h of storage and additional 24 h in the circulating treatment model. Cytokine secretion patterns revealed a significant increase, especially between 10 and 24 h of treatment. Extending treatment time holds promise for enhancing immune response against sepsis-induced immunoparalysis. These findings provide valuable insights for optimizing immune-targeted therapeutic interventions.

Recurrent infections drive persistent bladder dysfunction and pain via sensory nerve sprouting and mast cell activity

Urinary tract infections (UTIs) account for almost 25% of infections in women. Many are recurrent (rUTI), with patients frequently experiencing chronic pelvic pain and urinary frequency despite clearance of bacteriuria after antibiotics. To elucidate the basis for these bacteria-independent bladder symptoms, we examined the bladders of patients with rUTI. We noticed a notable increase in neuropeptide content in the lamina propria and indications of enhanced nociceptive activity. In mice subjected to rUTI, we observed sensory nerve sprouting that was associated with nerve growth factor (NGF) produced by recruited monocytes and tissue-resident mast cells. Treatment of rUTI mice with an NGF-neutralizing antibody prevented sprouting and alleviated pelvic sensitivity, whereas instillation of native NGF into naïve mice bladders mimicked nerve sprouting and pain behavior. Nerve activation, pain, and urinary frequency were each linked to the presence of proximal mast cells, because mast cell deficiency or treatment with antagonists against receptors of several direct or indirect mast cell products was each effective therapeutically. Thus, our findings suggest that NGF-driven sensory sprouting in the bladder coupled with chronic mast cell activation represents an underlying mechanism driving bacteria-independent pain and voiding defects experienced by patients with rUTI.

Eosinophils of patients with localized and diffuse cutaneous leishmaniasis: Differential response to Leishmania mexicana, with insights into mechanisms of damage inflicted upon the parasites by eosinophils

Eosinophils are mainly associated with parasitic infections and allergic manifestations. They produce many biologically active substances that contribute to the destruction of pathogens through the degranulation of microbicidal components and inflammatory tissue effects. In leishmaniasis, eosinophils have been found within inflammatory infiltrate with protective immunity against the parasite. We analyzed the responses of eosinophils from patients with localized (LCL) and diffuse (DCL) cutaneous leishmaniasis, as well as from healthy subjects, when exposed to Leishmania mexicana. All DCL patients exhibited blood eosinophilia, along with elevated eosinophil counts in non-ulcerated nodules. In contrast, only LCL patients with prolonged disease progression showed eosinophils in their blood and cutaneous ulcers. Eosinophils from DCL patients secreted significantly higher levels of IL-6, IL-8, and IL-13, compared to eosinophils from LCL patients. Additionally, DCL patients displayed higher serum levels of anti-Leishmania IgG antibodies. We also demonstrated that eosinophils from both LCL and DCL patients responded to L. mexicana promastigotes with a robust oxidative burst, which was equally intense in both patient groups and significantly higher than in healthy subjects. Coincubation of eosinophils (from donors with eosinophilia) with L. mexicana promastigotes in vitro revealed various mechanisms of parasite damage associated with different patterns of granule exocytosis: 1) localized degranulation on the parasite surface, 2) the release of cytoplasmic membrane-bound "degranulation sacs" containing granules, 3) release of eosinophil extracellular traps containing DNA and granules with major basic protein. In conclusion, eosinophils damage L. mexicana parasites through the release of granules via diverse mechanisms. However, despite DCL patients having abundant eosinophils in their blood and tissues, their apparent inability to provide protection may be linked to the release of cytokines and chemokines that promote a Th2 immune response and disease progression in these patients.

miRNA-132-5p mediates a negative feedback regulation of IL-8 secretion through S100A8/A9 downregulation in neutrophil-like HL-60 cells

Background

Neutrophils are an important source of pro-inflammatory and immunomodulatory cytokines. This makes neutrophils efficient drivers of interactions with immune and non-immune cells to maintain homeostasis and modulate the inflammatory process by notably regulating the release of cytokines. Ca2+-dependent regulatory mechanism encompassing cytokine secretion by neutrophils are not still identified. In this context, we propose to define new insights on the role of Ca2+-binding proteins S100A8/A9 and on the regulatory role of miRNA-132-5p, which was identified as a regulator of S100A8/A9 expression, on IL-8 secretion.

Methods

Differentiated HL-60 cells, a human promyelocytic leukemia cell line that can be induced to differentiate into neutrophil-like cells, were used as a model of human neutrophils and treated with N- formyl-methionyl-leucyl-phenylalanine (fMLF), a bacterial peptide that activates neutrophils. shRNA knockdown was used to define the role of selected targets (S100A8/A9 and miRNA-132-5p) on IL-8 secretion.

Results and discussion

Different types of cytokines engage different signaling pathways in the secretion process. IL-8 release is tightly regulated by Ca2+ binding proteins S100A8/A9. miRNA-132-5p is up-regulated over time upon fMLF stimulation and decreases S100A8/A9 expression and IL-8 secretion.

Conclusion

These findings reveal a novel regulatory loop involving S100A8/A9 and miRNA-132-5p that modulates IL-8 secretion by neutrophils in inflammatory conditions. This loop could be a potential target for therapeutic intervention in inflammatory diseases.

Perfluorooctanoic Acid Promotes Recruitment and Exocytosis of Rodlet Cells in the Renal Hematopoietic Tissue of Common Carp

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous environmental contaminants, with perfluorooctanoic acid (PFOA) being a prominent member. PFOA poses a risk to aquatic ecosystems and human health due to its presence in water, environmental persistence, and bioaccumulation. Since rodlet cells (RCs) have emerged as potential biomarkers for chemical stressors, this study aimed to investigate the effects of sub-chronic PFOA exposure on RCs in the renal hematopoietic tissue of common carp. Three groups of fish were used: an unexposed control group and two groups exposed to environmentally relevant (200 ng L-1) and elevated (2 mg L-1) PFOA concentrations. Light and transmission electron microscopy were employed to assess RCs' distribution patterns and exocytosis, while biometry quantified RCs in the hematopoietic tissue. The results showed that, even at environmentally relevant concentrations, PFOA significantly influenced RCs' distribution patterns, leading to increased occurrence and cluster formation, as well as heightened exocytosis activity. This research highlights PFOA's immunotoxicity in fish and suggests the potential of RCs as sentinel cells in the immunological response to environmental contaminants. These findings enhance our understanding of PFAS toxicity and emphasise the importance of monitoring their impact on fish as representative vertebrates and reliable animal models.

Rab44 regulates murine mast cell-driven anaphylaxis through kinesin-1-dependent secretory granule translocation

BACKGROUND

Mast cells (MCs) are key effectors of the allergic response. Following the cross-linking of IgE receptors (FcεRIs), they release crucial inflammatory mediators through degranulation. Although degranulation depends critically on secretory granule (SG) trafficking towards the plasma membrane, the molecular machinery underlying this transport has not been fully characterized.

OBJECTIVE

Here, we analyzed the function of Rab44, a large atypical Rab GTPase highly expressed in MC, in MC degranulation process.

METHODS

Murine KO mouse models (KO^Rab44 and DKO^Kif5b/Rab44) were used to perform passive cutaneous anaphylaxis (PCA) experiments and analyze granule translocation in derived bone-marrow-derived MCs (BMMCs) during degranulation.

RESULTS

We demonstrate that mice lacking Rab44 (KO^Rab44) in their BMMCs are impaired in their ability to translocate and degranulate SGs at the plasma membrane upon FcεRI stimulation. Accordingly, KO^Rab44 mice were less sensitive to IgE-mediated passive cutaneous anaphylaxis in vivo. A lack of Rab44 did not impair early FcεRI-stimulated signaling pathways, microtubule reorganization, lipid mediator or cytokine secretion. Mechanistically, Rab44 appears to interact with and function as part of the previously described kinesin-1-dependent transport pathway.

CONCLUSIONS

Our results highlight a novel role of Rab44 as a regulator of SG transport during degranulation and anaphylaxis acting through the kinesin-1-dependent microtubule transport machinery. Rab44 can thus be considered as a potential target for modulating MC degranulation and inhibiting IgE-mediated allergic reactions.

Ultrastructure and histochemistry of the subepithelial glands of the nasal septal island in dromedaries with special reference to the possible functions

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The NSI subepithelial glands in dromedaries had unique anatomical features.

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Their ultrastructural features are typical for APUD cells.

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They may have the structures required for synthesis of active peptides, amines and chemical mediators.

The nasal septal island (NSI) is a sensory patch of neuroepithelium located within the soft tissue of the nasal septum in dromedaries. The island has unique anatomical features, including the specialized subepithelial glands. The aim of the present study was to describe the microscopic features and ultrastructure of these subepithelial glands and to speculate the possible functions. A total of 10 camel heads were used for the study. Unlike the serous and mucous airway glands, the NSI glands’ ultrastructural features were typical for cells of the (Amine Precursor Uptake and Decarboxylation, APUD) system. These features were included, membrane bound secretory vesicles of varying electron density, smooth endoplasmic reticulum in the form of vesicles; electron dense mitochondria, abundant rough endoplasmic reticulum and free ribosomes. Alcian-PAS identifiable mucus granules were not observed, except for few clusters of cells, located at the luminal surface. The probable functions were discussed on basis of cellular morphology and context. In a conclusion, the NSI subepithelial glands in dromedaries had unique anatomical structures, and as many other APUD cells, they had the machinery required for synthesis of a variable number of biologically active peptides, amines and chemical mediators.

Neutrophils in Tumorigenesis: Missing Targets for Successful Next Generation Cancer Therapies?

Neutrophils—once considered as simple killers of pathogens and unexciting for cancer research—are now acknowledged for their role in the process of tumorigenesis. Neutrophils are recruited to the tumor microenvironment where they turn into tumor-associated neutrophils (TANs), and are able to initiate and promote tumor progression and metastasis. Conversely, anti-tumorigenic properties of neutrophils have been documented, highlighting the versatile nature and high pleiotropic plasticity of these polymorphonuclear leukocytes (PMN-L). Here, we dissect the ambivalent roles of TANs in cancer and focus on selected functional aspects that could be therapeutic targets. Indeed, the critical point of targeting TAN functions lies in the fact that an immunosuppressive state could be induced, resulting in unwanted side effects. A deeper knowledge of the mechanisms linked to diverse TAN functions in different cancer types is necessary to define appropriate therapeutic strategies that are able to induce and maintain an anti-tumor microenvironment.

Cytoskeletal Transport, Reorganization, and Fusion Regulation in Mast Cell-Stimulus Secretion Coupling

Mast cells are well known for their role in allergies and many chronic inflammatory diseases. They release upon stimulation, e.g., via the IgE receptor, numerous bioactive compounds from cytoplasmic secretory granules. The regulation of granule secretion and its interaction with the cytoskeleton and transport mechanisms has only recently begun to be understood. These studies have provided new insight into the interaction between the secretory machinery and cytoskeletal elements in the regulation of the degranulation process. They suggest a tight coupling of these two systems, implying a series of specific signaling effectors and adaptor molecules. Here we review recent knowledge describing the signaling events regulating cytoskeletal reorganization and secretory granule transport machinery in conjunction with the membrane fusion machinery that occur during mast cell degranulation. The new insight into MC biology offers novel strategies to treat human allergic and inflammatory diseases targeting the late steps that affect harmful release from granular stores leaving regulatory cytokine secretion intact.

The Impact of Hypoxia on Neutrophil Degranulation and Consequences for the Host

Neutrophils are key effector cells of innate immunity, rapidly recruited to defend the host against invading pathogens. Neutrophils may kill pathogens intracellularly, following phagocytosis, or extracellularly, by degranulation and the release of neutrophil extracellular traps; all of these microbicidal strategies require the deployment of cytotoxic proteins and proteases, packaged during neutrophil development within cytoplasmic granules. Neutrophils operate in infected and inflamed tissues, which can be profoundly hypoxic. Neutrophilic infiltration of hypoxic tissues characterises a myriad of acute and chronic infectious and inflammatory diseases, and as well as potentially protecting the host from pathogens, neutrophil granule products have been implicated in causing collateral tissue damage in these scenarios. This review discusses the evidence for the enhanced secretion of destructive neutrophil granule contents observed in hypoxic environments and the potential mechanisms for this heightened granule exocytosis, highlighting implications for the host. Understanding the dichotomy of the beneficial and detrimental consequences of neutrophil degranulation in hypoxic environments is crucial to inform potential neutrophil-directed therapeutics in order to limit persistent, excessive, or inappropriate inflammation.

Calcium signaling and regulation of neutrophil functions: Still a long way to go

Neutrophils are the most abundant leukocytes in blood and disruption in their functions often results in an increased risk of serious infections and inflammatory autoimmune diseases. Following recent discoveries in their influence over disease progression, a resurgence of interest for neutrophil biology has taken place. The multitude of signaling pathways activated by the engagement of numerous types of receptors, with which neutrophils are endowed, reflects the functional complexity of these cells. It is therefore not surprising that there remains a huge lack in the understanding of molecular mechanisms underlining neutrophil functions. Moreover, studies on neutrophils are undoubtedly limited by the difficulty to efficiently edit the cell's genome. Over the past 30 years, compelling evidence has clearly highlighted that Ca²⁺ -signaling is governing the key processes associated with neutrophil functions. The confirmation of the role of an elevation of intracellular Ca²⁺ concentration has come from studies on NADPH oxidase activation and phagocytosis. In this review, we give an overview and update of our current knowledge on the role of Ca²⁺ mobilization in the regulation of pro-inflammatory functions of neutrophils. In particular, we stress the importance of Ca²⁺ in the formation of NETs and cytokine secretion in the light of newest findings. This will allow us to embrace how much further we have to go to understand the complex dynamics of Ca²⁺ -dependent mechanisms in order to gain more insights into the role of neutrophils in the pathogenesis of inflammatory diseases. The potential for therapeutics to regulate the neutrophil functions, such as Ca²⁺ influx inhibitors to prevent autoimmune and chronic inflammatory diseases, has been discussed in the last part of the review.

Inhibition of Allergic Reactivity through Targeting FcεRI-Bound IgE with Humanized Low-Affinity Antibodies

Options for effective prevention and treatment of epidemic allergic diseases remain limited, and particularly so for IgE-mediated food allergies. We previously found that mouse low-affinity anti-human IgE mAbs with K_D in the 10^-6-10^-8 M range were capable of blocking allergic reactivity without triggering immediate allergic mediator release. In this study, we humanized three parent low affinity allergic response inhibitor (LARI) mouse anti-human IgE mAbs and characterized their biological and immunological features, refined the lead candidate for further clinical development, examined their safety profiles, determined their therapeutic efficiency, and explored the mechanism of action potentially responsible for their therapeutic effects. LARI profoundly blocked cat- and peanut-allergic IgE-mediated basophil activation, inhibited acute release of both prestored and newly synthesized mediator from human mast cells, suppressed peanut-specific IgE-mediated passive cutaneous anaphylaxis, and attenuated dansyl IgE-mediated systemic anaphylaxis in human FcεRIα transgenic mice. Safety testing demonstrated that concentrations of LARI well above therapeutic levels failed to trigger immediate release of prestored and newly synthesized allergic mediators, failed to promote robust cytokine/chemokine production from allergic effector cells, and did not elicit allergic reactivity in an animal model of cutaneous and systemic anaphylaxis. Mechanistic studies revealed that LARI downregulated surface FcεRI receptors and IgE via internalization of the IgE/FcεRI, promoted a partial mediator depletion pathway leading to slow release of small amount of mediators, and functioned as a partial antagonist to inhibit FcεRI signaling phosphorylation of Syk, Akt, Erk, and p38 MAPK. These studies demonstrate that targeting surface-bound IgE with LARI profoundly suppresses human allergic reactivity while displaying an excellent safety profile.

Mast cells and mast cell tryptase enhance migration of human lung fibroblasts through protease-activated receptor 2

BACKGROUND

Mast cells may activate fibroblasts and contribute to remodeling processes in the lung. However, the mechanism behind these actions needs to be further investigated. Fibroblasts are major regulators of on-going remodeling processes. Protease activated receptor 2 (PAR2) expressed by fibroblasts may be activated by serine proteases, such as the mast cell mediator tryptase. The objective in this study was to investigate the effects of mast cells and specifically mast cell tryptase on fibroblast migration and the role of PAR2 activation.

METHODS

Human lung fibroblasts (HFL-1) were cultured together with human peripheral blood-derived mast cells or LAD2 mast cells and stimulated with either conditioned medium from LAD2 cells or tryptase. Analyses of immunological stimulation of mast cells by IgE/anti IgE in the co-culture system were also performed. The importance of PAR2 activation by mast cells and mast cell tryptase for the migratory effects of fibroblasts was investigated by pre-treatment with the PAR2 antagonist P2pal-18S. The expression of PAR2 was analyzed on fibroblasts and mast cells.

RESULTS

The migratory capacity of HFL-1 cells was enhanced by blood-derived mast cells (p < 0.02), LAD2 cells (p < 0.001), conditioned medium (p < 0.05) and tryptase (p < 0.006). P2pal-18S decreased the induced migration caused by mast cells (p < 0.001) and tryptase (p < 0.001) and the expression of PAR2 was verified in HFL-1 cells. Mast cells immunologically stimulated with IgE/Anti IgE had no further effects on fibroblast migration.

CONCLUSIONS

Mast cells and the mast cell mediator tryptase may have crucial roles in inducing lung fibroblast migration via PAR-2 activation, which may contribute to remodeling processes in chronic lung diseases.

Prueba de activación de basófilos: aspectos técnicos, metodológicos y su utilidad clínica

Introducción. La prueba de activación de basófilos (PAB) se considera una técnica confiable y segura para el diagnóstico de problemas alérgicos.Objetivo. Profundizar en el estado del arte de la PAB y su utilidad clínica.Materiales y métodos. Se realizó una revisión narrativa de la literatura mediante la búsqueda electrónica en las bases de datos y metabuscadores Ovid Medline, Google Scholar y PubMed, sin limitar la búsqueda por fecha, idioma o tipo de artículo. Se buscaron artículos sobre los detalles técnicos de la PAB y su utilidad clínica en el manejo de las enfermedades alérgicas.Resultados. De los marcadores de activación, CD63 ha sido el más estudiado y es el que mejor representa un evento de degranulación anafiláctica, mientras que CD203c es representativo de varias formas de degranulación. La superioridad de uno sobre otro como prueba diagnóstica depende del problema alérgico estudiado. En cuanto a los métodos de detección de basófilos, su selección con un único marcador, CCR3, se propone como una opción con buena relación de costo-efectividad.Conclusiones. La PAB es una herramienta prometedora para evaluar en clínica las reacciones alérgicas de forma segura. Es necesario una mayor estandarización de protocolos para obtener resultados más reproducibles.

Calcium mediates cell shape change in human peritoneal mesothelial cells

Mast cells in the peritoneal membrane (PM) may degranulate to release preformed inflammatory mediators including histamine which is capable of diffusing into the surrounding interstitium, modulating cells in their vicinity including, human peritoneal mesothelial cells (hPMC). The present study aimed to investigate the quorum intracellular calcium ([Ca²⁺_i]) response to histamine compared to the membrane soluble ionophore, A23187, in adherent cultured hPMC. To examine [Ca²⁺_i] handling, Fura - 2 loaded cells were exposed to histamine and A23187. Agonist induced transient [Ca²⁺_i] event(s) (TCE) were defined and compared including, resting calcium, peak height, recovery and transient kinetics. Changes in cell shape were examined with immunocytochemistry of the cortical actin (CA) and microtubule (MT) cytoskeleton. To investigate whether histamine induced changes in cell shape were mediated by [Ca²⁺_i], mobilization of [Ca²⁺_i] was prevented with 20 μmol/l of the calcium chelator 1,2-bis-(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). Histamine produced a dose dependent increase of [Ca²⁺_i], maximal at 1.0 mmol/l which recovered to the pre-challenge resting value. Transient multiplicity with repeated challenge was evident below a histamine threshold of 10^-2 mmol/l. Morphometric analysis of MTs and CA showed significant cell elongation plus histamine and A23187. The histamine induced cell elongation was eliminated with [Ca²⁺_i] clamping. This data indicated that increased [Ca²⁺_i] was essential for cell elongation and the formation of stress fibres and therefore has a pivotal role in the regulation of the PM barrier.

Thalamic mast cell activity is associated with sign-tracking behavior in rats

Mast cells are resident immune cells in the thalamus that can degranulate and release hundreds of signaling molecules (i.e., monoamines, growth factors, and cytokines) both basally and in response to environmental stimuli. Interestingly, mast cell numbers in the brain show immense individual variation in both rodents and humans. We used a Pavlovian conditioned approach (PCA) procedure to examine whether mast cells are associated with individual variation in the attribution of incentive-motivational value to reward-related cues. During the PCA procedure, a lever response-independently predicts the delivery of a food pellet into a magazine, and over training sessions three conditioned responses (CRs) develop: sign-tracking (lever-directed CRs), goal-tracking (magazine-directed CRs), and an intermediate response (both CRs). In Experiment 1, we measured thalamic mast cell number/activation using toluidine blue and demonstrated that sign-trackers have increased degranulated (activated) but not granulated (inactive) mast cells. In Experiment 2, we infused the mast cell inhibitor, cromolyn (200µg/rat; i.c.v.), immediately before five daily PCA training sessions and demonstrated that mast cell inhibition selectively impairs the acquisition of sign-tracking behavior. Taken together, these results demonstrate that thalamic mast cells contribute to the attribution of incentive-motivational value to reward-related cues and suggest that mast cell inhibition may be a novel target for addiction treatment.

Blocking Allergic Reaction through Targeting Surface-Bound IgE with Low-Affinity Anti-IgE Antibodies

Allergic disorders have now become a major worldwide public health issue, but the effective treatment options remain limited. We report a novel approach to block allergic reactivity by targeting the surface-bound IgE of the allergic effector cells via low-affinity anti-human IgE Abs with dissociation constants in the 10^-6 to 10^-8 M range. We demonstrated that these low-affinity anti-IgE mAbs bind to the cell surface-bound IgE without triggering anaphylactic degranulation even at high concentration, albeit they would weakly upregulate CD203c expression on basophils. This is in contrast to the high-affinity anti-IgE mAbs that trigger anaphylactic degranulation at low concentration. Instead, the low-affinity anti-IgE mAbs profoundly block human peanut- and cat-allergic IgE-mediated basophil CD63 induction indicative of anaphylactic degranulation; suppress peanut-, cat-, and dansyl-specific IgE-mediated passive cutaneous anaphylaxis; and attenuate dansyl IgE-mediated systemic anaphylaxis in human FcεRIα transgenic mouse model. Mechanistic studies reveal that the ability of allergic reaction blockade by the low-affinity anti-IgE mAbs was correlated with their capacity to downregulate the surface IgE and FcεRI level on human basophils and the human FcεRIα transgenic mouse bone marrow-derived mast cells via driving internalization of the IgE/FcεRI complex. Our studies demonstrate that targeting surface-bound IgE with low-affinity anti-IgE Abs is capable of suppressing allergic reactivity while displaying an excellent safety profile, indicating that use of low-affinity anti-IgE mAbs holds promise as a novel therapeutic approach for IgE-mediated allergic diseases.

Mast cell secretome: Soluble and vesicular components

Mast cells are multifunctional master cells implicated in both innate and adaptive immune responses. Their role has been best characterized in allergy and anaphylaxis; however, emerging evidences support their contribution to a wide variety of human diseases. Mast cells, being capable of both degranulation and subsequent recovery, have recently attracted substantial attention as also being rich sources of secreted extracellular vesicles (including exosomes and microvesicles). Along with secreted de novo synthesized soluble molecules and secreted preformed granules, the membrane-enclosed extracellular vesicles represent a previously unexplored part of the mast cell secretome. In this review article we summarize available data regarding the different soluble molecules and membrane-enclosed structures secreted by mast cells. Furthermore, we provide an overview of the release mechanisms including degranulation, piecemeal degranulation, transgranulation, and secretion of different types of extracellular vesicles. Finally, we aim to give a summary of the known biological functions associated with the different mast cell-derived secretion products. The increasingly recognized complexity of mast cell secretome may provide important novel clues to processes by which mast cells contribute to the development of different pathologies and are capable of orchestrating immune responses both in health and disease.

SNAP23-Dependent Surface Translocation of Leukotriene B4 (LTB4) Receptor 1 Is Essential for NOX2-Mediated Exocytotic Degranulation in Human Mast Cells Induced by Trichomonas vaginalis-Secreted LTB4

Trichomonas vaginalis is a sexually transmitted parasite that causes vaginitis in women and itself secretes lipid mediator leukotriene B₄ (LTB₄). Mast cells are important effector cells of tissue inflammation during infection with parasites. Membrane-bridging SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes are critical for fusion during exocytosis. Although T. vaginalis-derived secretory products (TvSP) have been shown to induce exocytosis in mast cells, information regarding the signaling mechanisms between mast cell activation and TvSP is limited. In this study, we found that SNAP23-dependent surface trafficking of LTB₄ receptor 1 (BLT1) is required for nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2)-mediated exocytotic degranulation of mast cells induced by TvSP. First, stimulation with TvSP induced exocytotic degranulation and reactive oxygen species (ROS) generation in HMC-1 cells. Next, TvSP-induced ROS generation and exocytosis were strongly inhibited by transfection of BLT1 small interfering RNA (siRNA). TvSP induced trafficking of BLT1 from the cytosol to the plasma membrane. We also found that knockdown of SNAP23 abrogated TvSP-induced ROS generation, exocytosis, and surface trafficking of BLT1 in HMC-1 cells. By coimmunoprecipitation, there was a physical interaction between BLT1 and SNAP23 in TvSP-stimulated HMC-1 cells. Taken together, our results suggest that SNAP23-dependent surface trafficking of BLT1 is essential for exocytosis in human mast cells induced by T. vaginalis-secreted LTB₄ Our data collectively demonstrate a novel regulatory mechanism for SNAP23-dependent mast cell activation of T. vaginalis-secreted LTB₄ involving surface trafficking of BLT1. These results can help to explain how the cross talk mechanism between parasite and host can govern deliberately tissue inflammatory responses.

Nanoimaging granule dynamics and subcellular structures in activated mast cells using soft X-ray tomography

Mast cells play an important role in allergic responses. During activation, these cells undergo degranulation, a process by which various kinds of mediators stored in the granules are released. Granule homeostasis in mast cells has mainly been studied by electron microscopy (EM), where the fine structures of subcellular organelles are partially destroyed during sample preparation. Migration and fusion of granules have not been studied in detail in three dimensions (3D) in unmodified samples. Here, we utilized soft X-ray tomography (SXT) coupled with fluorescence microscopy to study the detailed structures of organelles during mast cell activation. We observed granule fission, granule fusion to plasma membranes, and small vesicles budding from granules. We also detected lipid droplets, which became larger and more numerous as mast cells were activated. We observed dramatic morphological changes of mitochondria in activated mast cells and 3D-reconstruction revealed the highly folded cristae inner membrane, features of functionally active mitochondria. We also observed giant vesicles containing granules, mitochondria, and lipid droplets, which we designated as granule-containing vesicles (GCVs) and verified their presence by EM in samples prepared by cryo-substitution, albeit with a less clear morphology. Thus, our studies using SXT provide significant insights into mast cell activation at the organelle level.

Ultrastructural Examination of the Host Cellular Response in the Gills of Atlantic Salmon, Salmo salar, with Amoebic Gill Disease

Gills from Atlantic salmon with experimentally induced amoebic gill disease ( Neoparamoeba spp.) were examined with transmission electron microscopy to assess pathology and host-cell responses. Amoebae were found either on the surface epithelium or with pseudopodia extending deeply into invaginations of epithelial cells. The amoebae had various densities along the plasma membrane and contained electron-dense deposits within their cytoplasm. Surface epithelial cells sloughed from the gills and had features consistent with apoptosis, including rounded shape, loss of surface microridges, and hypercondensation of nuclear chromatin. Affected areas of gills had fusion of secondary lamellae with interlamellar spaces occupied by mitotic epithelial cells and eosinophils. Eosinophils contained abundant fusiform-shaped granules that measured approximately 1 μm long and 360 nm wide. The granule consisted of an electron-dense matrix with a central inclusion that was less electron-dense, consisting of particulate and fibrillar material. In many instances, the central inclusion appeared empty and 90% of the eosinophils had morphology suggestive of piecemeal degranulation. Also observed within affected areas were a few neutrophils, mucous cells releasing mucus, and a small number of dendritic-like cells.

The role of mast cells in functional GI disorders

Functional gastrointestinal disorders (FGIDs) are characterized by chronic complaints arising from disorganized brain-gut interactions leading to dysmotility and hypersensitivity. The two most prevalent FGIDs, affecting up to 16-26% of worldwide population, are functional dyspepsia and irritable bowel syndrome. Their etiopathogenic mechanisms remain unclear, however, recent observations reveal low-grade mucosal inflammation and immune activation, in association with impaired epithelial barrier function and aberrant neuronal sensitivity. These findings come to challenge the traditional view of FGIDs as pure functional disorders, and relate the origin to a tangible organic substrate. The mucosal inflammatory infiltrate is dominated by mast cells, eosinophils and intraepithelial lymphocytes in the intestine of FGIDs. It is well established that mast cell activation can generate epithelial and neuro-muscular dysfunction and promote visceral hypersensitivity and altered motility patterns in FGIDs, postoperative ileus, food allergy and inflammatory bowel disease. This review will discuss the role of mucosal mast cells in the gastrointestinal tract with a specific focus on recent advances in disease mechanisms and clinical management in irritable bowel syndrome and functional dyspepsia.

Regulation of Neutrophil Degranulation and Cytokine Secretion: A Novel Model Approach Based on Linear Fitting

Neutrophils participate in the maintenance of host integrity by releasing various cytotoxic proteins during degranulation. Due to recent advances, a major role has been attributed to neutrophil-derived cytokine secretion in the initiation, exacerbation, and resolution of inflammatory responses. Because the release of neutrophil-derived products orchestrates the action of other immune cells at the infection site and, thus, can contribute to the development of chronic inflammatory diseases, we aimed to investigate in more detail the spatiotemporal regulation of neutrophil-mediated release mechanisms of proinflammatory mediators. Purified human neutrophils were stimulated for different time points with lipopolysaccharide. Cells and supernatants were analyzed by flow cytometry techniques and used to establish secretion profiles of granules and cytokines. To analyze the link between cytokine release and degranulation time series, we propose an original strategy based on linear fitting, which may be used as a guideline, to (i) define the relationship of granule proteins and cytokines secreted to the inflammatory site and (ii) investigate the spatial regulation of neutrophil cytokine release. The model approach presented here aims to predict the correlation between neutrophil-derived cytokine secretion and degranulation and may easily be extrapolated to investigate the relationship between other types of time series of functional processes.

Identification of a New Exo-Endocytic Mechanism Triggered by Corticotropin-Releasing Hormone in Mast Cells

The key role of mast cells (MC), either in development of inflammatory pathologies or in response to environmental stress, has been widely reported in recent years. Previous studies have described the effects of corticotropin-releasing hormone (CRH), which is released from inflamed tissues by cellular stress signals, on MC degranulation, a process possibly driven by selective secretion of mediators (piecemeal degranulation). In this study, we introduce a novel granular exo-endocytic pathway induced by CRH on peritoneal MC. We found that CRH triggers substantial exocytosis, which is even stronger than that induced by Ag stimulation and is characterized by large quantal size release events. Membrane fluorescence increases during stimulation in the presence of FM1-43 dye, corroborating the strength of this exocytosis, given that discrete upward fluorescence steps are often observed and suggesting that secretory granules are preferentially released by compound exocytosis. Additionally, the presence of a depot of large tubular organelles in the cytoplasm suggests that the exocytotic process is tightly coupled to a fast compound endocytosis. This CRH-stimulated mechanism is mediated through activation of adenylate cyclase and an increase of cAMP and intracellular Ca(2+), as evidenced by the fact that the effect of CRH is mimicked by forskolin and 8-bromo-cAMP. Thus, these outcomes constitute new evidence for the critical role of MC in pathophysiological conditions within a cellular stress environment and an alternative membrane trafficking route mediated by CRH.

Peripheral basophil reactivity, CD203c expression by Cryj1 stimulation, is useful for diagnosing seasonal allergic rhinitis by Japanese cedar pollen

Measuring specific IgE can yield direct, accurate, and objective data. Nevertheless, clinical symptoms of allergy are often inconsistent with these data. Recently, the expression of CD203c, a surface marker of basophils, has been reported as capable of distinguishing allergic patients. This study compared specific IgE in serum and skin tests against antigen to assess CD203c as a biomarker correlated with allergic rhinitis (AR). We asked 3,453 subjects whether they experienced any AR related symptom. All subjects were assessed for six specific IgEs for common aeroallergens. Skin tests were also conducted for six aeroallergens. We observed the reactivity of peripheral basophil by measuring the levels of CD203c by Cryj1 stimulation using flow cytometry. Of the 3,453 participants, 1,987 (57.5%) possessed Japanese cedar pollen (JCP) specific IgE in their serum. Among those 1,987 JCP specific IgE positive participants, 552 (27.8%) had not experienced any allergic symptom during the JCP season. The levels of CD203c in the peripheral basophil by Cryj1 stimulation were significantly higher in SAR-JCP subjects than in non-SAR-JCP subjects (Cryj1 0.5 ng/ml: 2.25 ± 0.90% vs. 60.2 ± 27.4%, p < 0.01, Cryj1 50 ng/ml: 1.89 ± 0.90% vs. 68.0 ± 21.2%, p < 0.01). Our results indicate that the levels of CD203c in peripheral basophils by Cryj1 stimulation is a more objective and reliable marker that better reflects the allergic reaction by SAR-JCP in vivo than measuring specific IgE in serum or skin tests.

Vesicular trafficking and signaling for cytokine and chemokine secretion in mast cells

Upon activation mast cells (MCs) secrete numerous inflammatory compounds stored in their cytoplasmic secretory granules by a process called anaphylactic degranulation, which is responsible for type I hypersensitivity responses. Prestored mediators include histamine and MC proteases but also some cytokines and growth factors making them available within minutes for a maximal biological effect. Degranulation is followed by the de novo synthesis of lipid mediators such as prostaglandins and leukotrienes as well as a vast array of cytokines, chemokines, and growth factors, which are responsible for late phase inflammatory responses. While lipid mediators diffuse freely out of the cell through lipid bilayers, both anaphylactic degranulation and secretion of cytokines, chemokines, and growth factors depends on highly regulated vesicular trafficking steps that occur along the secretory pathway starting with the translocation of proteins to the endoplasmic reticulum. Vesicular trafficking in MCs also intersects with endocytic routes, notably to form specialized cytoplasmic granules called secretory lysosomes. Some of the mediators like histamine reach granules via specific vesicular monoamine transporters directly from the cytoplasm. In this review, we try to summarize the available data on granule biogenesis and signaling events that coordinate the complex steps that lead to the release of the inflammatory mediators from the various vesicular carriers in MCs.

Stress-induced mast cell activation in glabrous and hairy skin

Mast cells play a key role in modulation of stress-induced cutaneous inflammation. In this study we investigate the impact of repeated exposure to stress on mast cell degranulation, in both hairy and glabrous skin. Adult male Wistar rats were randomly divided into four groups: Stress 1 day (n = 8), Stress 10 days (n = 7), Stress 21 days (n = 6), and Control (n = 8). Rats in the stress groups were subjected to 2 h/day restraint stress. Subsequently, glabrous and hairy skin samples from animals of all groups were collected to assess mast cell degranulation by histochemistry and transmission electron microscopy. The impact of stress on mast cell degranulation was different depending on the type of skin and duration of stress exposure. Short-term stress exposure induced an amplification of mast cell degranulation in hairy skin that was maintained after prolonged exposure to stress. In glabrous skin, even though acute stress exposure had a profound stimulating effect on mast cell degranulation, it diminished progressively with long-term exposure to stress. The results of our study reinforce the view that mast cells are active players in modulating skin responses to stress and contribute to further understanding of pathophysiological mechanisms involved in stress-induced initiation or exacerbation of cutaneous inflammatory processes.

The role of inflammation in prostate cancer

In the United States and in "Westernized" countries, the prevalence of both prostate cancer and prostate inflammation is very high, indicating that the two pathologies could be causally related. Indeed, chronic inflammation is now regarded as an "enabling" characteristic of human cancer. Prostate cancer incidence is thought to be mediated in part by genetics, but also by environmental exposures, including the same exposures that may contribute to the development of prostatic inflammation. As our understanding of the role of inflammation in cancer deepens, it is increasingly apparent that "inflammation" as a whole is a complex entity that does not always play a negative role in cancer etiology. In fact, inflammation can play potentially dichotomous (both pro and antitumorigenic) roles depending on the nature and the cellular makeup of the immune response. This chapter will focus on reviewing the current state of knowledge on the role of innate and adaptive immune cells within the prostate tumor microenvironment and their seemingly complex role in prostate cancer in preventing versus promoting initiation and progression of the disease.

Formaldehyde inhalation reduces respiratory mechanics in a rat model with allergic lung inflammation by altering the nitric oxide/cyclooxygenase-derived products relationship

Bronchial hyperresponsiveness is a hallmark of asthma and many factors modulate bronchoconstriction episodes. A potential correlation of formaldehyde (FA) inhalation and asthma has been observed; however, the exact role of FA remains controversial. We investigated the effects of FA inhalation on Ovalbumin (OVA) sensitisation using a parameter of respiratory mechanics. The involvement of nitric oxide (NO) and cyclooxygenase-derived products were also evaluated. The rats were submitted, or not, to FA inhalation (1%, 90 min/day, 3 days) and were OVA-sensitised and challenged 14 days later. Our data showed that previous FA exposure in allergic rats reduced bronchial responsiveness, respiratory resistance (Rrs) and elastance (Ers) to methacholine. FA exposure in allergic rats also increased the iNOS gene expression and reduced COX-1. L-NAME treatment exacerbated the bronchial hyporesponsiveness and did not modify the Ers and Rrs, while Indomethacin partially reversed all of the parameters studied. The L-NAME and Indomethacin treatments reduced leukotriene B₄ levels while they increased thromboxane B₂ and prostaglandin E₂. In conclusion, FA exposure prior to OVA sensitisation reduces the respiratory mechanics and the interaction of NO and PGE₂ may be representing a compensatory mechanism in order to protect the lung from bronchoconstriction effects.

Seasonal changes in the activity of the adrenal medulla of Viscacha (Lagostomus maximus maximus)

Animals living in nontropical climates modify their physiology and behavior to adapt to seasonal environmental changes. Part of this adaptation involves the release of catecholamine from sympathetic nerve endings and the adrenal medulla, which play a major role in regulating energy balance. The aim of this work was to investigate whether adult male viscachas in their natural habitat exhibits structural changes in the adrenal medulla during the annual seasonal cycle. In August-September, chromaffin granules revealed ultrastructural changes suggestive of piecemeal degranulation. Quantitative morphometric analysis by transmission electron microscopy showed a significantly lower percentage of resting chromaffin granules and a higher percentage of altered granules and empty containers in August-September (late winter) compared to February-March (late summer), suggesting an increased secretory process of catecholamines in August-September. The mechanism of piecemeal degranulation might amplify this process, encouraging the adaptive response to winter environmental conditions. Tissue levels of epinephrine, norepinephrine, and dopamine (analyzed by high-performance liquid chromatography) changed throughout the year, reaching maximum values in February-March and minimum values in August-September. These results demonstrate morphological and biochemical seasonal variations of the adrenal medulla, suggesting that epinephrine might promote energy mobilization, which allow the Lagostomus to cope with adverse environmental conditions and thus to survive during winter season.

Primary human airway epithelial cell-dependent inhibition of human lung mast cell degranulation

INTRODUCTION

Chronic mast cell activation is a characteristic feature of asthma. BEAS-2B human airway epithelial cells (AEC) profoundly inhibit both constitutive and IgE-dependent human lung mast cell (HLMC) histamine release. The aim of this study was to examine the regulation of HLMC degranulation by primary AEC from healthy and asthmatic subjects, and investigate further the inhibitory mechanism.

METHODS

HLMC were co-cultured with both BEAS-2B and primary AEC grown as monolayers or air-liquid interface (ALI) cultures.

RESULTS

Both constitutive and IgE-dependent HLMC histamine release were attenuated by BEAS-2B, primary AEC monolayers and ALI cultures. This occurred in the absence of HLMC-AEC contact indicating the presence of a soluble factor. Unlike healthy ALI AEC, asthmatic ALI-AEC did not significantly reduce constitutive histamine release. AEC inhibitory activity was transferable in primary AEC monolayer supernatant, but less active than with Transwell co-culture, suggesting that the inhibitory factor was labile. The AEC inhibitory effects were attenuated by both AEC wounding and pertussis toxin, indicating the involvement of a G(0)/G(i) receptor coupled mechanism. Solid phase extraction of lipids (<10 kDa) removed the AEC inhibitory activity. The lipid derivatives resolving D1 and D2 and lipoxin A(4) attenuated HLMC histamine release in a dose-dependent fashion but were not detectable in co-culture supernatants.

CONCLUSIONS

Primary AEC suppress HLMC constitutive and IgE-dependent histamine secretion through the release of a soluble, labile lipid mediator(s) that signals through the G(0)/G(i) receptor coupled mechanism. Manipulation of this interaction may have a significant therapeutic role in asthma.

Effect of acute heat stress on rat adrenal medulla — a morphological and ultrastructural study

Isolated rat adrenal medulla was analyzed by light and electron microscope after an acute (60 min) exposure to high ambient temperature (38°C). Under these conditions there was a significant rise in plasma adrenaline and noradrenaline. Stereological investigation by light microscopy showed a significant decrease in volume density of cells and an increase in the interstitium. At the ultrastructural level, the profile area of cells, nuclei and cytoplasm of adrenaline cells were significantly decreased. After the heat stress numbers of resting granules in adre naline and noradrenaline cells were significantly reduced, while the numbers of altered granules and empty containers in both types of adrenomedullar cells were significantly increased.

Mast cell adenosine receptors function: a focus on the a3 adenosine receptor and inflammation

Adenosine is a metabolite, which has long been implicated in a variety of inflammatory processes. Inhaled adenosine provokes bronchoconstriction in asthmatics or chronic obstructive pulmonary disease patients, but not in non-asthmatics. This hyper responsiveness to adenosine appears to be mediated by mast cell activation. These observations have marked the receptor that mediates the bronchoconstrictor effect of adenosine on mast cells (MCs), as an attractive drug candidate. Four subtypes (A1, A2a, A2b, and A3) of adenosine receptors have been cloned and shown to display distinct tissue distributions and functions. Animal models have firmly established the ultimate role of the A3 adenosine receptor (A3R) in mediating hyper responsiveness to adenosine in MCs, although the influence of the A2b adenosine receptor was confirmed as well. In contrast, studies of the A3R in humans have been controversial. In this review, we summarize data on the role of different adenosine receptors in mast cell regulation of inflammation and pathology, with a focus on the common and distinct functions of the A3R in rodent and human MCs. The relevance of mouse studies to the human is discussed.

Cytokine release from innate immune cells: association with diverse membrane trafficking pathways

Cytokines released from innate immune cells play key roles in the regulation of the immune response. These intercellular messengers are the source of soluble regulatory signals that initiate and constrain inflammatory responses to pathogens and injury. Although numerous studies describe detailed signaling pathways induced by cytokines and their specific receptors, there is little information on the mechanisms that control the release of cytokines from different cell types. Indeed, the pathways, molecules, and mechanisms of cytokine release remain a "black box" in immunology. Here, we review research findings and new approaches that have begun to generate information on cytokine trafficking and release by innate immune cells in response to inflammatory or infectious stimuli. Surprisingly complex machinery, multiple organelles, and specialized membrane domains exist in these cells to ensure the selective, temporal, and often polarized release of cytokines in innate immunity.

Mechanisms of cytokine secretion: a portfolio of distinct pathways allows flexibility in cytokine activity

Since cytokines are potent immunoregulators that can determine the fate of an immune response, their expression is tightly regulated at the transcriptional level. Recent research, however, has also revealed complex post-translational mechanisms through which cytokine secretion, and thereby cytokine activity, is regulated. Here, we review the progress in our understanding of the portfolio of pathways that regulate cytokine intracellular storage, transport, and release. Like other secreted proteins, cytokines utilize canonical and non-canonical secretory pathways for extracellular release. Illustrated by IL-1β, IL-2, TNF-α, IL-12 and IL-15 secretion as selected examples, we discuss common and alternative cytokine secretion pathways and relate them to the consequences these distinct pathways have for cytokine function, mode of action and stability.

CGRP1 receptor activation induces piecemeal release of protease-1 from mouse bone marrow-derived mucosal mast cells

BACKGROUND

The parasitized or inflamed gastrointestinal mucosa shows an increase in the number of mucosal mast cells (MMC) and the density of extrinsic primary afferent nerve fibers containing the neuropeptide, calcitonin gene-related peptide (CGRP). Currently, the mode of action of CGRP on MMC is unknown.

METHODS

The effects of CGRP on mouse bone marrow-derived mucosal mast cells (BMMC) were investigated by measurements of intracellular Ca(2+)[Ca(2+)](i) and release of mMCP-1.

KEY RESULTS

Bone marrow-derived mucosal mast cells responded to the application of CGRP with a single transient rise in [Ca(2+)](i). The proportion of responding cells increased concentration-dependently to a maximum of 19 ± 4% at 10(-5)mol L(-1) (mean ±SEM; C48/80 100%; EC(50)10(-8) mol L(-1) ). Preincubation with the CGRP receptor antagonist BIBN4096BS (10(-5) mol L(-1)) completely inhibited BMMC activation by CGRP [range 10(-5) to 10(-11) mol L(-1); analysis of variance (ANOVA) P < 0.001], while preincubation with LaCl(3) to block Ca(2+) entry did not affect the response (P = 0.18). The presence of the CGRP1 receptor on BMMC was confirmed by simultaneous immunofluorescent detection of RAMP1 or CRLR, the two components of the CGRP1 receptor, and mMCP-1. Application of CGRP for 1 h evoked a concentration-dependent release of mMCP-1 (at EC(50) 10% of content) but not of β-hexosaminidase and alterations in granular density indicative of piecemeal release.

CONCLUSIONS & INFERENCES

We demonstrate that BMMC express functional CGRP1 receptors and that their activation causes mobilization of Ca(2+) from intracellular stores and piecemeal release of mMCP-1. These findings support the hypothesis that the CGRP signaling from afferent nerves to MMC in the gastrointestinal wall is receptor-mediated.

The mechanisms of exocytosis in mast cells

Upon activation through high affinity IgE receptors (FcεRI), mast cells (MCs) can release up to 100% of their content of preformed mediators stored in cytoplasmic secretory granules by compound exocytosis. This causes Type I immediate hypersensitivity reactions and, in the case of inappropriate activation by allergens, the symptoms of allergy. Recent work has uncovered a central role of SNARE (Soluble N-ethylmaleimide-Sensitive Factor (NSF) Attachment Protein (SNAP) Receptors) proteins in regulating the numerous membrane fusion events during exocytosis. This has defined a series of new molecular actors in MC exocytosis that participate in the regulation of membrane fusion and the connection of the fusion machinery with early signaling events. The purpose of this chapter is to describe these proteins and provide a brief overview on their mechanism of action.

Piecemeal degranulation in human eosinophils: a distinct secretion mechanism underlying inflammatory responses

Secretion is a fundamental cell process underlying different physiological and pathological events. In cells from the human immune system such as eosinophils, secretion of mediators generally occurs by means of piecemeal degranulation, an unconventional secretory pathway characterized by vesicular transport of small packets of materials from the cytoplasmic secretory granules to the cell surface. During piecemeal degranulation in eosinophils, a distinct transport vesicle system, which includes large, pleiomorphic vesiculo-tubular carriers is mobilized and enables regulated release of granule-stored proteins such as cytokines and major basic protein. Piecemeal degranulation underlies distinct functions of eosinophils as effector and immunoregulatory cells. This review focuses on the structural and functional advances that have been made over the last years concerning the intracellular trafficking and secretion of eosinophil proteins by piecemeal degranulation during inflammatory responses.

Pathways for Cytokine Secretion

Cytokine secretion is a widely studied process, although little is known regarding the specific mechanisms that regulate cytokine release. Recent findings have shed light on some of the precise molecular pathways that regulate the packaging of newly synthesized cytokines from immune cells. These findings begin to elucidate pathways and mechanisms that underpin cytokine release in all cells. In this article, we review the highlights of some of these novel discoveries.

Mast cells: multifaceted immune cells with diverse roles in health and disease

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

Reduced allergic lung inflammation in rats following formaldehyde exposure: long-term effects on multiple effector systems

Clinical and experimental evidences show that formaldehyde (FA) exposure has an irritant effect on the upper airways. As being an indoor and outdoor pollutant, FA is known to be a causal factor of occupational asthma. This study aimed to investigate the repercussion of FA exposure on the course of a lung allergic process triggered by an antigen unrelated to FA. For this purpose, male Wistar rats were subjected to FA inhalation for 3 consecutive days (1%, 90-min daily), subsequently sensitized with ovalbumin (OVA)-alum via the intraperitoneal route, and 2 weeks later challenged with aerosolized OVA. The OVA challenge in rats after FA inhalation (FA/OVA group) evoked a low-intensity lung inflammation as indicated by the reduced enumerated number of inflammatory cells in bronchoalveolar lavage as compared to FA-untreated allergic rats (OVA/OVA group). Treatment with FA also reduced the number of bone marrow cells and blood leukocytes in sensitized animals challenged with OVA, which suggests that the effects of FA had not been only localized to the airways. As indicated by passive cutaneous anaphylactic reaction, FA treatment did not impair the anti-OVA IgE synthesis, but reduced the magnitude of OVA challenge-induced mast cell degranulation. Moreover, FA treatment was associated to a diminished lung expression of PECAM-1 (platelet-endothelial cell adhesion molecule 1) in lung endothelial cells after OVA challenge and an exacerbated release of nitrites by BAL-cultured cells. Keeping in mind that rats subjected solely to either FA or OVA challenge were able to significantly increase the cell influx into lung, our study shows that FA inhalation triggers long-lasting effects that affect multiple mediator systems associated to OVA-induced allergic lung such as the reduction of mast cells activation, PECAM-1 expression and exacerbation of NO generation, thereby contributing to the decrease of cell recruitment after the OVA challenge. In conclusion, repeated expositions to air-borne FA may impair the lung cell recruitment after an allergic stimulus, thereby leading to a non-responsive condition against inflammatory stimuli likely those where mast cells are involved.

High-resolution three-dimensional imaging of the rich membrane structures of bone marrow-derived mast cells

Atomic force microscopy (AFM) enables high-resolution three-dimensional (3D) imaging of cultured bone marrow-derived mast cells. Cells were immobilized by a quick centrifugation and fixation to preserve their transient cellular morphologies followed by AFM characterization in buffer. This "fix-and-look" approach preserves the structural integrity of individual cells. Well-known membrane morphologies, such as ridges and microvilli, are visualized, consistent with prior electron microscopy observations. Additional information including the 3D measurements of these characteristic features are attained from AFM topographs. Filopodia and lamellopodia, associated with cell spreading, were captured and visualized in three dimensions. New morphologies are also revealed, such as high-density ridges and micro-craters. This investigation demonstrates that the "fix-and-look" approach followed by AFM imaging provides an effective means to characterize the membrane structure of hydrated cells with high resolution. The quantitative imaging and measurements pave the way for systematic correlation of membrane structural features with the biological status of individual cells.

Electron tomography and immunonanogold electron microscopy for investigating intracellular trafficking and secretion in human eosinophils

Electron tomography (ET) has increasingly been used to understand the complexity of membrane systems and protein-trafficking events. By ET and immunonanogold electron microscopy, we recently defined a route for vesicular transport and release of granule-stored products from within activated human eosinophils, cells specialized in the secretion of numerous cytokines and other proteins during inflammatory responses. Here, we highlight these techniques as important tools to unveil a distinct eosinophil vesicular system and secretory pathway.

Mechanisms of eosinophil secretion: large vesiculotubular carriers mediate transport and release of granule-derived cytokines and other proteins

Eosinophils generate and store a battery of proteins, including classical cationic proteins, cytokines, chemokines, and growth factors. Rapid secretion of these active mediators by eosinophils is central to a range of inflammatory and immunoregulatory responses. Eosinophil products are packaged within a dominant population of cytoplasmic specific granules and generally secreted by piecemeal degranulation, a process mediated by transport vesicles. Large, pleiomorphic vesiculotubular carriers were identified recently as key players for moving eosinophil proteins from granules to the plasma membrane for extracellular release. During secretion, these specialized, morphologically distinct carriers, termed eosinophil sombrero vesicles, are actively formed and direct differential and rapid release of eosinophil proteins. This review highlights recent discoveries concerning the organization of the human eosinophil secretory pathway. These discoveries are defining a broader role for large vesiculotubular carriers in the intracellular trafficking and secretion of proteins, including selective receptor-mediated mobilization and transport of cytokines.