Mast cells in infection and immunity

Single cell RNA-sequencing suggests a novel lipid associated mast cell population following weight cycling

Our recent study showed weight cycled mice have increased adipose mast cells compared to obese mice by single cell RNA-sequencing. Here, we aimed to confirm and elucidate these changes. Further analysis of our dataset showed that our initial mast cell cluster could subcluster into two unique populations: one with very high expression of classical mast cell markers and another with elevated lipid handling and antigen presentation genes. This new mast cell cluster accounted for most of the mast cells in the weight cycled group although it was not possible to detect the different populations by new studies with flow cytometry or Toluidine blue staining in mice, possibly due to a downregulation in classical mast cell genes. Interestingly, a pilot study in humans did suggest the existence of two mast cell populations in subcutaneous adipose tissue from obese women that appear similar to the murine populations detected by sequencing; one of which was significantly correlated with weight variance. Together, these data suggest that weight cycling may induce a unique population of mast cells similar to lipid associated macrophages. Future studies will focus on isolation of these cells to better determine their lineage, differentiation, and functional roles.

Mast cells selectively produce inflammatory mediators and impact the early response to Chlamydia reproductive tract infection

Introduction

Chlamydia trachomatis (C. trachomatis) is a Gram-negative obligate intracellular bacterium that causes reproductive tract complications in women, including ectopic pregnancies and tubal factor infertility. We hypothesized that mast cells, which are common at mucosal barriers, may contribute to responses to Chlamydia infection and aimed to define human mast cell responses to C. trachomatis.

Methods

Human cord blood-derived mast cells (CBMCs) were exposed to C. trachomatis to assess bacterial uptake, mast cell degranulation, gene expression, and production of inflammatory mediators. The role of formyl peptide receptors and Toll-like receptor 2 (TLR2) were investigated using pharmacological inhibitors and soluble TLR2. Mast cell-deficient mice and littermate controls were used to examine the in vivo role of mast cells in influencing the immune response to Chlamydia infection in the female reproductive tract.

Results

C. trachomatis bacteria were taken up by human mast cells but did not replicate efficiently inside CBMCs. C. trachomatis-activated mast cells did not degranulate but maintained viability and exhibited cellular activation with homotypic aggregation and upregulation of ICAM-1. However, they significantly enhanced the gene expression of IL1B, CCL3, NFKB1, CXCL8, and IL6. Inflammatory mediators were produced, including TNF, IL-1β, IL-1RA, IL-6, GM-CSF, IL-23, CCL3, CCL5, and CXCL8. Endocytic blockade resulted in reduced gene expression of IL6, IL1B, and CCL3, suggesting C. trachomatis induced mast cell activation in both extracellular and intracellular locations. The IL-6 response to C. trachomatis was reduced when CBMCs were treated with C. trachomatis coated with soluble TLR2. Mast cells derived from TLR2-deficient mice also demonstrated a reduced IL-6 response to C. muridarum. Five days following C. muridarum infection, mast cell-deficient mice showed attenuated CXCL2 production and significantly reduced numbers of neutrophils, eosinophils, and B cells in the reproductive tract when compared with mast cell-containing littermates.

Discussion

Taken together, these data demonstrate that mast cells are reactive to Chlamydia spp. through multiple mechanisms that include TLR2-dependent pathways. Mast cells also play an important role in shaping in vivo immune responses in Chlamydia reproductive tract infection through both effector cell recruitment and modification of the chemokine microenvironment.

Sex Differences in Mast Cell-Associated Disorders: A Life Span Perspective

Mast cells are critical innate immune effectors located throughout the body that are crucial for host defense mechanisms via orchestrating immune responses to a variety of host and environmental stimuli necessary for survival. The role of mast cells in brain development and behavior, meningeal function, and stress-related disorders has also been increasingly recognized. While critical for survival and development, excessive mast cell activation has been linked with an increasing number of inflammatory, stress-associated, and neuroimmune disorders including allergy/anaphylaxis, autoimmune diseases, migraine headache, and chronic pain disorders. Further, a strong sex bias exists for mast cell-associated diseases with females often at increased risk. Here we review sex differences in human mast cell-associated diseases and animal models, and the underlying biological mechanisms driving these sex differences, which include adult gonadal sex hormones as well the emerging organizational role of perinatal gonadal hormones on mast cell activity and development.

Exacerbation of Chronic Spontaneous Urticaria Symptoms in COVID-19 Patients, Case Report

Chronic spontaneous urticaria (CSU) is characterized by wheals lasting more than 6 weeks and can be accompanied by angioedema. Treatment of the disease varies depending on the severity and includes first-line therapeutics such as non-sedative antihistamines. Second- and third-line treatments are used in severe and uncontrolled form of CSU. Environmental exposure and infections could trigger worsening symptoms. The goal of this study is to assess the effect of SARS-CoV-2 infection on CSU symptoms and the efficacy of the second- and third-line therapeutics for CSU management in COVID-19 patients. Our findings show that SARS-CoV-2 infection exacerbates CSU symptoms. Worsening of disease was indicated by decreased Urticaria Control Test (UCT) and increased Urticaria Activity Score (UAS). Treatment management was modified by switching to second- and third-line therapeutics; however, therapeutic control was achieved only in one patient. Our data demonstrates that SARS-CoV-2 infection contributes to the severity of CSU. Symptoms of CSU are more challenging to manage and require changes in treatment protocol, including second- and third-line therapeutics. We believe that severe inflammation triggered by SARS-CoV-2 infection contributes to the worsening of CSU symptoms.

Determinants of Innate Immunity in Visceral Leishmaniasis and Their Implication in Vaccine Development

Leishmaniasis is endemic to the tropical and subtropical regions of the world and is transmitted by the bite of an infected sand fly. The multifaceted interactions between Leishmania, the host innate immune cells, and the adaptive immunity determine the severity of pathogenesis and disease development. Leishmania parasites establish a chronic infection by subversion and attenuation of the microbicidal functions of phagocytic innate immune cells such as neutrophils, macrophages and dendritic cells (DCs). Other innate cells such as inflammatory monocytes, mast cells and NK cells, also contribute to resistance and/or susceptibility to Leishmania infection. In addition to the cytokine/chemokine signals from the innate immune cells, recent studies identified the subtle shifts in the metabolic pathways of the innate cells that activate distinct immune signal cascades. The nexus between metabolic pathways, epigenetic reprogramming and the immune signaling cascades that drive the divergent innate immune responses, remains to be fully understood in Leishmania pathogenesis. Further, development of safe and efficacious vaccines against Leishmaniasis requires a broader understanding of the early interactions between the parasites and innate immune cells. In this review we focus on the current understanding of the specific role of innate immune cells, the metabolomic and epigenetic reprogramming and immune regulation that occurs during visceral leishmaniasis, and the strategies used by the parasite to evade and modulate host immunity. We highlight how such pathways could be exploited in the development of safe and efficacious Leishmania vaccines.

Histamine activates HinK to promote the virulence of Pseudomonas aeruginosa

During infections, bacteria stimulate host cells to produce and release histamine, which is a key mediator of vital cellular processes in animals. However, the mechanisms underlying the bacterial cell's ability to sense and respond to histamine are poorly understood. Herein, we show that HinK, a LysR-type transcriptional regulator, is required to evoke responses to histamine in Pseudomonas aeruginosa, an important human pathogen. HinK directly binds to and activates the promoter of genes involved in histamine uptake and metabolism, iron acquisition, and Pseudomonas quinolone signal (PQS) biosynthesis. The transcriptional regulatory activity of HinK is induced when histamine is present, and it occurs when HinK binds with imidazole-4-acetic acid (ImAA), a histamine metabolite whose production in P. aeruginosa depends on the HinK-activated histamine uptake and utilization operon hinDAC-pa0222. Importantly, the inactivation of HinK inhibits diverse pathogenic phenotypes of P. aeruginosa. These results suggest that histamine acts as an interkingdom signal and provide insights into the mechanism used by pathogenic bacteria to exploit host regulatory signals to promote virulence.

Divergent Mast Cell Responses Modulate Antiviral Immunity During Influenza Virus Infection

Influenza A virus (IAV) is a respiratory pathogen that infects millions of people each year. Both seasonal and pandemic strains of IAV are capable of causing severe respiratory disease with a high risk of respiratory failure and opportunistic secondary infection. A strong inflammatory cytokine response is a hallmark of severe IAV infection. The widespread tissue damage and edema in the lung during severe influenza is largely attributed to an overexuberant production of inflammatory cytokines and cell killing by resident and infiltrating leukocytes. Mast cells (MCs) are a sentinel hematopoietic cell type situated at mucosal sites, including the lung. Poised to react immediately upon detecting infection, MCs produce a vast array of immune modulating molecules, including inflammatory cytokines, chemokines, and proteases. As such, MCs have been implicated as a source of the immunopathology observed in severe influenza. However, a growing body of evidence indicates that MCs play an essential role not only in inducing an inflammatory response but in suppressing inflammation as well. MC-derived immune suppressive cytokines are essential to the resolution of a number of viral infections and other immune insults. Absence of MCs prolongs infection, exacerbates tissue damage, and contributes to dissemination of the pathogen to other tissues. Production of cytokines such as IL-10 and IL-6 by MCs is essential for mitigating the inflammation and tissue damage caused by innate and adaptive immune cells alike. The two opposing functions of MCs-one pro-inflammatory and one anti-inflammatory-distinguish MCs as master regulators of immunity at the site of infection. Amongst the first cells to respond to infection or injury, MCs persist for the duration of the infection, modulating the recruitment, activation, and eventual suppression of other immune cells. In this review, we will discuss the immune modulatory roles of MCs over the course of viral infection and propose that the immune suppressive mediators produced by MCs are vital to minimizing immunopathology during influenza infection.

Mobilization and Activation of the Innate Immune Response to Dengue Virus

Dengue virus is an important human pathogen, infecting an estimated 400 million individuals per year and causing symptomatic disease in a subset of approximately 100 million. Much of the effort to date describing the host response to dengue has focused on the adaptive immune response, in part because of the well-established roles of antibody-dependent enhancement and T cell original sin as drivers of severe dengue upon heterotypic secondary infection. However, the innate immune system is a crucial factor in the host response to dengue, as it both governs the fate and vigor of the adaptive immune response, and mediates the acute inflammatory response in tissues. In this review, we discuss the innate inflammatory response to dengue infection, focusing on the role of evolutionarily conserved innate immune cells, their effector functions, and clinical course.

Emerging Roles of Mast Cells in the Regulation of Lymphatic Immuno-Physiology

Mast cells (MCs) are abundant in almost all vascularized tissues. Furthermore, their anatomical proximity to lymphatic vessels and their ability to synthesize, store and release a large array of inflammatory and vasoactive mediators emphasize their significance in the regulation of the lymphatic vascular functions. As a major secretory cell of the innate immune system, MCs maintain their steady-state granule release under normal physiological conditions; however, the inflammatory response potentiates their ability to synthesize and secrete these mediators. Activation of MCs in response to inflammatory signals can trigger adaptive immune responses by dendritic cell-directed T cell activation. In addition, through the secretion of various mediators, cytokines and growth factors, MCs not only facilitate interaction and migration of immune cells, but also influence lymphatic permeability, contractility, and vascular remodeling as well as immune cell trafficking through the lymphatic vessels. In summary, the consequences of these events directly affect the lymphatic niche, influencing inflammation at multiple levels. In this review, we have summarized the recent advancements in our understanding of the MC biology in the context of the lymphatic vascular system. We have further highlighted the MC-lymphatic interaction axis from the standpoint of the tumor microenvironment.

Impact of Photobiomodulation and Condition Medium on Mast Cell Counts, Degranulation, and Wound Strength in Infected Skin Wound Healing of Diabetic Rats

Background: Numerous people suffer from diabetes mellitus (DM) and resultant diabetic foot ulcers (DFU), which lack effective treatment. Photobiomodulation (PBM) has accelerated wound healing in diabetic animals and patients in some studies. However, there is scant information on the number and activation state of skin mast cells (MCs) in PBM-treated diabetic wounds. Objective: We intend to assess the influence of the number of MCs and degranulation in the remodeling step of an infected wound model on wound strength and its microbial flora in a type 1 DM (T1DM) rat model by administration of PBM, condition medium (CM) derived from human bone marrow mesenchymal stem cells (hBMMSCs), and the combination of PBM+CM. Methods: We prepared CM by culturing hBMMSCs. T1DM was induced in 72 rats and, after 1 month, we created one excisional wound in each rat. All wounds were infected with methicillin-resistant Staphylococcus aureus (MRSA). We divided the rats into four groups: (n = 18): (i) control; (ii) PBM; (iii) CM, and (iv) PBM+CM. On days 4, 7, and 15, we conducted microbiological, tensiometrical, and stereological analyses. The type of MCs (T1MCs, T2MCs, or T3MCs) and total number of MCs (TOMCs) were counted by light microscopy. Results: On day 15, the PBM+CM, PBM, and CM groups had significantly increased wound strength compared with the control group. There was a significant decrease in colony-forming units (CFU) at all time points in the PBM+CM and PBM groups. The PBM+CM and PBM groups had more stable MCs (T1MCs), less significant degranulated MCs (T2MCs), less significant disintegrated MCs (T3MCs), and less significant TOMCs compared with the control group at all time points. Conclusions: PBM+CM and PBM treatments significantly increased the healing process in an ischemic and MRSA-infected wound model of T1DM rats. PBM+CM and PBM significantly decreased both TOMCs and their degranulation, and significantly decreased CFU.

Teleost Basophils Have IgM-Dependent and Dual Ig-Independent Degranulation Systems

Recently, mammalian basophils have been highlighted as having roles in allergy and antiparasitic immunity; however, there is little information about the functions and evolutionary origin of basophils, because they are the least abundant leukocyte in most vertebrates. In this study, we characterized the teleost basophils that are abundant in the peripheral blood of fugu (Takifugu rubripes). Fugu basophils have two distinct granules: reddish-purple and dark violet ones. Teleost fish do not have IgG and IgE, but we found that fugu IgM bound on the surface of the basophils, and the cross-linked IgM induced degranulation of both types of granules. This indicates that teleost basophils can be activated in an Ab-dependent manner. Furthermore, papain induced the degranulation of the reddish-purple granules, which contain histamine, and the released granules stimulated the migration of various leukocytes. In contrast, chitin elicited the degranulation of the dark violet granules, which resulted in CD4⁺ T cell-specific migration. Thus, fugu basophils control immune responses via two distinct Ab-independent mechanisms. In addition, fugu basophils endocytosed soluble Ag and expressed MHC class II and B7-H1/DC. These findings suggested that fugu basophils can interact with T cells as APCs. Thus, the Ab-dependent basophil activation predates the emergence of IgG and IgE, and fish basophils exhibit different dynamics and features of degranulation to distinct stimuli compared with mammalian basophils. Some features of teleost basophils are more similar to those of mammalian mast cells than to those of mammalian basophils.

The distribution and heterogeneity of mast cells in tongue from five different avian species

This study was conducted with the aim of determining the morphology, distribution and heterogeneity of mast cells in the tongues of seagull (Larus fuscus), common buzzard (Buteo buteo), goose (Anser anser), white stork (Ciconia ciconia) and Gerze rooster. The study used five samples of tongue material from each of the healthy adult avian species. The samples were fixed in 10% neutral-buffered formalin (NBF) solution, then, after routine tissue follow-up, the samples blocked with paraplast. Cross-sections with 5-6 μm of thickness were stained with the 0.5% toluidine blue and alcian blue/safranin O (AB/SO). In all five avian species, it was found that the mast cells were in different sizes and round, oval or spindle-shaped based on their place of distribution. Mast cell numbers were determined in stained with toluidine blue, examined ×40 objectives in a 1 mm² area. It was observed that mast cell density in subepithelial lamina propria and microscopic papilla was higher in the tongues of all species. Mast cell distribution and heterogeneity varied through the tongue, and there were more mast cells in the dorsal side of the tongue than the ventral side. The highest amount of mast cells was found in the tongue of the Gerze rooster among all five species. In the tongue cross-sections stained with the combined method of alcian blue/safranin O (AB/SO), the mast cells were stained as AB (+), SO (+) and AB/SO (+) (mixed).

Self-Assembling Peptide Nanoscaffold That Activates Human Mast Cells

Engineering biomaterials to manipulate the immune response to elicit specific therapeutic outcomes is a burgeoning field of research. Mast cells play a distinct and central role in the innate immune response, and are characterized by their rapid release of a myriad of proinflammatory mediators in response to stimulation. These mediators are central to protective actions such as wound healing, angiogenesis, and host defense against pathogens and animal venoms. Considering that mast cells are widely distributed in tissues that interface with the external environment, and are loaded with large amounts of preformed protective compounds, they are ideal targets for novel immunotherapies. Here we report that, by using an engineered nanoscaffold, human mast cells can be contact activated in cell and primary human skin tissue culture using a specific receptor-ligand mechanism. The IgE independent PAMP-12 peptide activates human mast cells through the recently identified Mas-related G-protein coupled receptor member X2 (MRGPRX₂) receptor. The PAMP-12 motif was conjugated, via a glycine spacer, with the self-assembling peptide (RADA)₄ and mixed with unmodified (RADA)₄ to form a nanofiber matrix; mast cell activation was influenced directly by this ratio. Moreover, conjugating the PAMP-12 motif within the matrix was shown to only activate local, tissue-resident mast cells. The result of ex vivo human skin tissue tests confirmed that the engineered nanoscaffold successfully activated skin-resident mast cells by contact. Thus, this nanoscaffold design may provide a new platform to modulate localized mast cell functions thereby facilitating their protective role in the skin.

Role of Mast Cells in clearance of Leishmania through extracellular trap formation

Mast Cells (MCs) are one of the first immune cells encountered by invading pathogens. Their presence in large numbers in the superficial dermis, where Leishmania is encountered, suggests that they may play a critical role in immune responses to Leishmania. In this study the interactions of Leishmania donovani, the causative agent of visceral Leishmaniasis, and Leishmania tropica, the causative agent of cutaneous Leishmaniasis with MCs were studied. Co-culture of Leishmania with Peritoneal Mast Cells (PMCs) from BALB/c mice and Rat Basophilic Leukaemia (RBL-2H3) MCs led to significant killing of L. tropica and to a lesser extent of L. donovani. Also, while there was significant uptake of L. tropica by MCs, L. donovani was not phagocytosed. There was significant generation of Reactive Oxygen Species (ROS) by MCs on co-culture with these species of Leishmania which may contribute to their clearance. Interactions of MCs with Leishmania led to generation of MC extracellular traps comprising of DNA, histones and tryptase probably to ensnare these pathogens. These results clearly establish that MCs may contribute to host defences to Leishmania in a differential manner, by actively taking up these pathogens, and also by mounting effector responses for their clearance by extracellular means.

The effects of mosquito saliva on dengue virus infectivity in humans

Arboviruses such as Dengue, Chikungunya, and Zika viruses represent a major public health problem due to globalization and propagation of susceptible vectors worldwide. Arthropod vector-derived salivary factors have the capacity to modulate human cells function by enhancing or suppressing viral replication and, therefore, modify the establishment of local and systemic viral infection. Here, we discuss how mosquito saliva may interfere with Dengue virus (DENV) infection in humans. Identification of saliva factors that enhance infectivity will allow the production of vector-based vaccines and therapeutics that would interfere with viral transmission by targeting arthropod saliva components. Understanding the role of salivary proteins in DENV transmission will provide tools to control not only Dengue but also other arboviral diseases transmitted by the same vectors.

Blockade of CD14 aggravates experimental shigellosis

Shigella infections lead to severe inflammation associated with destruction of colonic mucosa. We assessed the effect of in vivo blockade of CD14 on the outcome of experimental Shigella infection in rabbits. A total of 17 rabbits were divided into two groups: 8 received a single i.v. dose of anti-rabbit CD14 monoclonal antibody prior to infection with an invasive Shigella flexneri strain; the remainder served as controls. The anti-CD14-treated rabbits exhibited more severe tissue destruction and a 50-fold increase in bacterial invasion of the intestinal mucosa when compared to controls. Similar numbers of polymorphonuclear leukocytes were recruited to the intestinal mucosa in both groups despite the massive bacterial invasion seen in the CD14-blocked group. No statistically significant differences were seen in levels of IL-1β nor in the ratio of IL-1RA/IL-1β for either group. In contrast, higher quantities of TNF-α were observed in the CD14-blocked group. To conclude, anti-CD14 treatment had a detrimental effect on the capacity of Shigella-infected animals to clear the infection.

An Agent-Based Model of a Hepatic Inflammatory Response to Salmonella: A Computational Study under a Large Set of Experimental Data

We present an agent-based model (ABM) to simulate a hepatic inflammatory response (HIR) in a mouse infected by Salmonella that sometimes progressed to problematic proportions, known as "sepsis". Based on over 200 published studies, this ABM describes interactions among 21 cells or cytokines and incorporates 226 experimental data sets and/or data estimates from those reports to simulate a mouse HIR in silico. Our simulated results reproduced dynamic patterns of HIR reported in the literature. As shown in vivo, our model also demonstrated that sepsis was highly related to the initial Salmonella dose and the presence of components of the adaptive immune system. We determined that high mobility group box-1, C-reactive protein, and the interleukin-10: tumor necrosis factor-α ratio, and CD4+ T cell: CD8+ T cell ratio, all recognized as biomarkers during HIR, significantly correlated with outcomes of HIR. During therapy-directed silico simulations, our results demonstrated that anti-agent intervention impacted the survival rates of septic individuals in a time-dependent manner. By specifying the infected species, source of infection, and site of infection, this ABM enabled us to reproduce the kinetics of several essential indicators during a HIR, observe distinct dynamic patterns that are manifested during HIR, and allowed us to test proposed therapy-directed treatments. Although limitation still exists, this ABM is a step forward because it links underlying biological processes to computational simulation and was validated through a series of comparisons between the simulated results and experimental studies.

Uterine Mast Cells and Immunoglobulin-E Antibody Responses During Clearance of Tritrichomonas foetus

We showed earlier that Tritrichomonas foetus-specific bovine immunoglobulin (Ig)G1 and IgA antibodies in uterine and vaginal secretions are correlated with clearance of this sexually transmitted infection. Eosinophils have been noted in previous studies of bovine trichomoniasis but the role of mast cells and IgE responses have not been reported. The hypothesis that IgE and mast cell degranulation play a role in clearance was tested in 25 virgin heifers inseminated experimentally and infected intravaginally with T. foetus strain D1 at estrus and cultured weekly. Groups were euthanatized at 3, 6, 9, or 12 weeks, when tissues were fixed and secretions were collected for culture and antibody analysis. Immunohistochemistry using a monoclonal antibody to a soluble lipophosphoglycan (LPG)-containing surface antigen (TF1.17) demonstrated antigen uptake by uterine epithelial cells. Lymphoid nodules were detected below antigen-positive epithelium. Little IgG2 antibody was detected but IgG1, IgA, IgM, and IgE T. foetus-specific antibodies increased in uterine secretions at weeks 6 and 9 after infection. This was inversely proportional to subepithelial mast cells numbers and most animals cleared the infection by the sampling time after the lowest mast cell count. Furthermore, soluble antigen was found in uterine epithelium above inductive sites (lymphoid nodules). Cross-linking of IgE on mast cells by antigen and perhaps LPG triggering appears to have resulted in degranulation. Released cytokines may account for production of predominantly Th2 (IgG1 and IgE) and IgA antibody responses, which are related to clearance of the infection.

Nanotube Formation: A Rapid Form of "Alarm Signaling"?

PURPOSE

Tunneling nanotubes (TNTs) are extremely thin (50-200 nm), actin-containing cell surface protrusions up to a few microns in length that can develop rapidly and connect various cell types. Mast cells (MCs) are unique immunomodulatory cells that are found perivascularly in all tissues. MCs communicate with many other cell types through the release of inflammatory, neurosensitizing, and vasoactive molecules, through which they are involved in the pathogenesis of many inflammatory diseases. We, therefore, investigated the possibility that MCs may form TNTs and communicate among themselves and with glioblastoma cells.

METHODS

Laboratory Allergic Diseases (LAD)-2 human MCs were cultured in medium supplemented with 100 U/mL penicillin/streptomycin and 100 ng/mL recombinant human stem cell factor. They were incubated with 20 nmol/L deep red probe for 20 minutes and 50 nmol/L green probe for 30 minutes. Human glioblastoma cells were incubated with 20 nmol/L deep red probe only, moved to glass-bottom culture dishes, and observed using a substance P 2 confocal microscope. LAD2 MCs were stimulated with 2 µmol/L of the peptide substance P for 30 minutes at 37ºC. Confocal digital images were processed.

FINDINGS

MCs can rapidly (within 5 minutes) form TNTs, which appear to transport mitochondrial and secretory granule particles among themselves and with cocultured glioblastoma cells.

IMPLICATIONS

MCs are now accepted as having an important role in many diseases with an inflammatory component. TNTs provide a rapid and direct way for MCs to "alarm" other cell types with specificity not present when mediators are secreted into the tissue microenvironment. The identification of TNTs and their cargo could be important in the diagnosis and possible treatment of many inflammatory diseases.

NOD1 and NOD2 Interact with the Phagosome Cargo in Mast Cells: A Detailed Morphological Evidence

Mast cells (MC) play a key role in triggering the inflammatory process and share some functions with professional phagocytes. It is not clear whether or not the phagocytic process in MC follows the same route and has the same meaning of that of professional phagocytes. Herein we analyze in detail the structure of the phagosome in rat peritoneal mast cells (RPMC). The ultrastructural analysis of the phagosome, containing either model particles or bacteria, reveals that these vacuoles are very tight, and in several areas, their membrane seems to have dissolved. RPMC express NOD1 and NOD2 proteins whose role is to recognize intracellular foreign components and induce the production of pro-inflammatory mediators. Following Escherichia coli ingestion, both these molecules are found on the phagosome membrane and on ingested pathogens, together with phagosome maturation markers. These findings suggest that in RPMC the ingested cargo can, through interruptions of the phagosome membrane, interact directly with NODs, which act as switches in the process of cytokine production.

Mast cells are dispensable in a genetic mouse model of chronic dermatitis

Chronic inflammatory skin diseases, such as atopic dermatitis, affect a large percentage of the population, but the role of different immune cells in the pathogenesis of these disorders is largely unknown. Recently, we found that mice lacking fibroblast growth factor receptor 1 (Fgfr1) and Fgfr2 (K5-R1/R2 mice) in the epidermis have a severe impairment in the epidermal barrier, which leads to the development of a chronic inflammatory skin disease that shares many features with human atopic dermatitis. Using Fgfr1-/Fgfr2-deficient mice, we analyzed the consequences of the loss of mast cells. Mast cells accumulated and degranulated in the skin of young Fgfr1-/Fgfr2-deficient mice, most likely as a consequence of increased expression of the mast cell chemokine Ccl2. The increase in mast cells occurred before the development of histological abnormalities, indicating a functional role of these cells in the inflammatory skin phenotype. To test this hypothesis, we mated the Fgfr1-/Fgfr2-deficient mice with mast cell-deficient CreMaster mice. Surprisingly, loss of mast cells did not or only mildly affect keratinocyte proliferation, epidermal thickness, epidermal barrier function, accumulation and activation of different immune cells, or expression of different proinflammatory cytokines in the skin. These results reveal that mast cells are dispensable for the development of chronic inflammation in response to a defect in the epidermal barrier.

Clostridium difficile toxin B inhibits the secretory response of human mast cell line-1 (HMC-1) cells stimulated with high free-Ca²⁺ and GTPγS

Clostridium difficile toxins A and B (TcdA and TcdB) belong to the class of large clostridial cytotoxins and inactivate by glucosylation some low molecular mass GTPases of the Rho-family (predominantly Rho, Rac and Cdc42), known as regulators of the actin cytoskeleton. TcdA and B also represent the main virulence factors of the anaerobic gram-positive bacterium that is the causal agent of pseudomembranous colitis. In our study, TcdB was chosen instead of TcdA for the well-known higher cytotoxic potency. Inactivation of Rho-family GTPases by this toxin in our experimental conditions induced morphological changes and reduction of electron-dense mast cell-specific granules in human mast cell line-1 (HMC-1) cells, but not cell death or permeabilisation of plasma-membranes. Previously reported patch-clamp dialysis experiments revealed that high intracellular free-Ca(2+) and GTPγS concentrations are capable of inducing exocytosis as indicated by significant membrane capacitance (Cm) increases in HMC-1 cells. In this study, we investigated the direct effects of TcdB upon HMC-1 cell "stimulated" Cm increase, as well as on "constitutive" secretion of hexosaminidase and interleukin-16 (IL-16). Compared to untreated control cells, HMC-1 cells incubated with TcdB for 3-24h exhibited a significant reduction of the mean absolute and relative Cm increase in response to free-Ca(2+) and GTPγS suggesting an inhibition of secretory processes by TcdB. In conclusion, the HMC-1 cell line represents a suitable model for the study of direct effects of C. difficile toxins on human mast cell secretory activity.

New insights into the antimicrobial effect of mast cells against Enterococcus faecalis

Enterococcus faecalis has emerged as an important cause of life-threatening multidrug-resistant bacterial infections in the hospital setting. The pathogenesis of enterococcal infections has remained a relatively neglected field despite their obvious clinical relevance. The objective of this study was to characterize the interactions between mast cells (MCs), an innate immune cell population abundant in the intestinal lamina propria, and E. faecalis. This study was conducted with primary bone marrow-derived murine MCs. The results demonstrated that MCs exerted an antimicrobial effect against E. faecalis that was mediated both by degranulation, with the concomitant discharge of the antimicrobial effectors contained in the granules, and by the release of extracellular traps, in which E. faecalis was snared and killed. In particular, the cathelicidin LL-37 released by the MCs had potent antimicrobial effect against E. faecalis. We also investigated the specific receptors involved in the recognition of E. faecalis by MCs. We found that Toll-like receptors (TLRs) are critically involved in the MC recognition of E. faecalis, since MCs deficient in the expression of MyD88, an adaptor molecule required for signaling by most TLRs, were significantly impaired in their capacity to degranulate, to reduce E. faecalis growth as well as to release tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) after encountering this pathogen. Furthermore, TLR2 was identified as the most prominent TLR involved in the recognition of E. faecalis by MCs. The results of this study indicate that MCs may be important contributors to the host innate immune defenses against E. faecalis.

Anti-inflammatory BmAFI of Brugia malayi modulates IgE, histamine and histamine receptor responses in Mastomys coucha

We recently reported that BmAFI, an anti-inflammatory fraction of Brugia malayi adult worm supports parasite development in the hostile peritoneal cavity (p.c.) of Mastomys coucha through a modified Th2 type of response that includes IL-13 and IgE response and anti-inflammatory IL-10 cytokine milieu. In the present study we investigated IgE related responses such as histamine release and modulation of histamine receptors 1 and 2 (HR1 and HR2) by presensitization with BmAFI of M. coucha infected with B. malayi. Sensitization with BmAFI alone enhanced IgE, histamine and HR2, but decreased HR1. Exposure of these animals to infection produced an IgE response that was inversely related to the parasite burden, and decreased histamine conc., and HR1 and HR2 expression. However, there was an early small increase in HR1 expression for a short period after exposure to infection. As expected, BmAFI sensitization supported parasite survival and development in the hostile p.c. of the host. These findings further establish that BmAFI decreases inflammatory/Th1 response and modulates Th2 responses to favour survival and development of the parasite in the hostile p.c. of the host and that IgE and histamine play an important role in this.

Up-regulation of matrix metalloproteinases-2 and -9 via an Erk1/2/NF-κB pathway in murine mast cells infected with Toxoplasma gondii

Mast cells are key effectors in inflammation and contain proteinases that are released on activation. This study investigates associations between extracellular signal-regulated kinase (Erk)1/2, nuclear factor (NF)-κB, matrix metalloproteinase (MMP)-2 and MMP-9 in mast cells infected with Toxoplasma gondii tachyzoites. T. gondii infection led to increased mast cell degranulation. Phosphorylated (p)-Erk1/2 and p-NF-κB were increased significantly in mast cells infected with T. gondii. Pretreatment with the Erk kinase inhibitor PD98059 significantly decreased the expression of p-Erk1/2, p-NF-κB, MMP-2 and MMP-9. Treatment with MG132, an indirect NF-κB inhibitor, effectively reduced p-IκBα, p-NF-κB, MMP-2 and MMP-9 expression. Collectively, these data show that suppression of an Erk1/2/NF-κB signalling pathway caused a reduction in MMP-2 and -9 activities. Inhibiting this signalling pathway for MMP-2 and MMP-9 expression might offer a potential way to control early T. gondii infection. This pathway for the generation of MMP-2 and MMP-9 is important for mast cell secretion and the NF-κB/Erk1/2 signalling pathway may be key in MMP-2 and MMP-9 production in host defense against toxoplasmosis.

Polyphenols differentially inhibit degranulation of distinct subsets of vesicles in mast cells by specific interaction with granule-type-dependent SNARE complexes

Anti-allergic effects of dietary polyphenols were extensively studied in numerous allergic disease models, but the molecular mechanisms of anti-allergic effects by polyphenols remain poorly understood. In the present study, we show that the release of granular cargo molecules, contained in distinct subsets of granules of mast cells, is specifically mediated by two sets of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, and that various polyphenols differentially inhibit the formation of those SNARE complexes. Expression analysis of RBL-2H3 cells for 11 SNARE genes and a lipid mixing assay of 24 possible combinations of reconstituted SNAREs indicated that the only two active SNARE complexes involved in mast cell degranulation are Syn (syntaxin) 4/SNAP (23 kDa synaptosome-associated protein)-23/VAMP (vesicle-associated membrane protein) 2 and Syn4/SNAP-23/VAMP8. Various polyphenols selectively or commonly interfered with ternary complex formation of these two SNARE complexes, thereby stopping membrane fusion between granules and plasma membrane. This led to the differential effect of polyphenols on degranulation of three distinct subsets of granules. These results suggest the possibility that formation of a variety of SNARE complexes in numerous cell types is controlled by polyphenols which, in turn, might regulate corresponding membrane trafficking.

A novel function for SNAP29 (synaptosomal-associated protein of 29 kDa) in mast cell phagocytosis

Mast cells play a critical role in the innate immune response to bacterial infection. They internalize and kill a variety of bacteria and process antigen for presentation to T cells via MHC molecules. Although mast cell phagocytosis appears to play a significant role during bacterial infection, little is known about the proteins involved in its regulation. In this study, we demonstrate that the SNARE protein SNAP29 is involved in mast cell phagocytosis. SNAP29 is localized in the endocytic pathway and is transiently recruited to Escherichia coli (E. coli)-containing phagosomes. Interestingly, overexpression of SNAP29 significantly increases the internalization and killing of E. coli, while it does not affect mast cell exocytosis of inflammatory mediators. To our knowledge, these data are the first to demonstrate a novel function of SNAP29 in mast cell phagocytosis and have implications in protection against bacterial infection.

SNARE complex-mediated degranulation in mast cells

Mast cell function and dysregulation is important in the development and progression of allergic and autoimmune disease. Identifying novel proteins involved in mast cell function and disease progression is the first step in the design of new therapeutic strategies. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of proteins demonstrated to mediate the transport and fusion of secretory vesicles to the membrane in mast cells, leading to the subsequent release of the vesicle cargo through an exocytotic mechanism. The functional role[s] of specific SNARE family member complexes in mast cell degranulation has not been fully elucidated. Here, we review recent and historical data on the expression, formation and localization of various SNARE proteins and their complexes in murine and human mast cells. We summarize the functional data identifying the key SNARE family members that appear to participate in mast cell degranulation. Furthermore, we discuss the utilization of RNA interference (RNAi) methods to validate SNARE function and the use of siRNA as a therapeutic approach to the treatment of inflammatory disease. These studies provide an overview of the specific SNARE proteins and complexes that serve as novel targets for the development of new therapies to treat allergic and autoimmune disease.

Mast cells act as phagocytes against the periodontopathogen Aggregatibacter actinomycetemcomitans

BACKGROUND

Evidence to date shows that mast cells play a critical role in immune defenses against infectious agents, but there have been no reports about involvement of these cells in eliminating periodontopathogens. In this study, the phagocytic ability of mast cells against Aggregatibacter actinomycetemcomitans compared with macrophages is evaluated.

METHODS

In vitro phagocytic assays were conducted using murine mast cells and macrophages, incubated with A. actinomycetemcomitans, either opsonized or not, with different bacterial load ratios. After 1 hour, cells were stained with acridine orange and assessed by confocal laser-scanning electron microscopy.

RESULTS

Phagocytic ability of murine mast cells against A. actinomycetemcomitans was confirmed. In addition, the percentage of mast cells with internalized bacteria was higher in the absence of opsonization than in the presence of opsonization. Both cell types showed significant phagocytic activity against A. actinomycetemcomitans. However, the percentage of mast cells with non-opsonized bacteria was higher than that of macrophages with opsonized bacteria in one of the ratios (1:10).

CONCLUSIONS

This is the first report about the participation of murine mast cells as phagocytes against A. actinomycetemcomitans, mainly in the absence of opsonization with human serum. Our results may indicate that mast cells act as professional phagocytes in the pathogenesis of biofilm-associated periodontal disease.

The role of mast cells in allergic inflammation

The histochemical characteristics of human basophils and tissue mast cells were described over a century ago by Paul Ehrlich. When mast cells are activated by an allergen that binds to serum IgE attached to their FcɛRI receptors, they release cytokines, eicosanoids and their secretory granules. Mast cells are now thought to exert critical proinflammatory functions, as well as potential immunoregulatory roles, in various immune disorders through the release of mediators such as histamine, leukotrienes, cytokines chemokines, and neutral proteases (chymase and tryptase). The aim of this review is to describe the role of mast cells in allergic inflammation. Mast cells interact directly with bacteria and appear to play a vital role in host defense against pathogens. Drugs, such as glucocorticoids, cyclosporine and cromolyn have been shown to have inhibitory effects on mast cell degranulation and mediator release. This review shows that mast cells play an active role in such diverse diseases as asthma, rhinitis, middle ear infection, and pulmonary fibrosis. In conclusion, mast cells may not only contribute to the chronic airway inflammatory response, remodeling and symptomatology, but they may also have a central role in the initiation of the allergic immune response, that is providing signals inducing IgE synthesis by B-lymphocytes and inducing Th2 lymphocyte differentiation.

Hematopoietic cytokines for cardiac repair: mobilization of bone marrow cells and beyond

Hematopoietic cytokines, traditionally known to influence cellular proliferation, differentiation, maturation, and lineage commitment in the bone marrow, include granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor, stem cell factor, Flt-3 ligand, and erythropoietin among others. Emerging evidence suggests that these cytokines also exert multifarious biological effects on diverse nonhematopoietic organs and tissues. Although the precise mechanisms remain unclear, numerous studies in animal models of myocardial infarction (MI) and heart failure indicate that hematopoietic cytokines confer potent cardiovascular benefits, possibly through mobilization and subsequent homing of bone marrow-derived cells into the infarcted heart with consequent induction of myocardial repair involving multifarious mechanisms. In addition, these cytokines are also known to exert direct cytoprotective effects. However, results from small-scale clinical trials of G-CSF therapy as a single agent after acute MI have been discordant and largely disappointing. It is likely that cardiac repair following cytokine therapy depends on a number of known and unknown variables, and further experimental and clinical studies are certainly warranted to accurately determine the true therapeutic potential of such therapy. In this review, we discuss the biological features of several key hematopoietic cytokines and present the basic and clinical evidence pertaining to cardiac repair with hematopoietic cytokine therapy.

Down-regulation of interleukin-16 in human mast cells HMC-1 by Clostridium difficile toxins A and B

Toxin A (TcdA) and toxin B (TcdB) are the major virulence factors of Clostridium difficile and are the causative agents for clinical symptoms, such as secretory diarrhoea and pseudomembranous colitis. Mast cells are essentially involved in the toxin-induced colonic inflammatory processes. To study the direct effects of these toxins on the expression of inflammatory genes, a DNA microarray containing evaluated probes of 90 selected inflammatory genes was applied to the immature mast cell line HMC-1. TcdA and TcdB induced up-regulation of only a limited number of genes within the early phase of cell treatment. Interleukin-8 (IL-8), transcription factor c-jun and heme oxygenase-1 messenger RNA (mRNA) increased more than 2-fold. In contrast, IL-16, known as a CD4(+) T-cell chemoattractant factor and the chemokine receptor cKit were down-regulated. Stimulation of HMC-1 cells with IL-8 had no effect on IL-16 mRNA level, indicating that both cytokines were independently affected by the toxins. Regulation of both cytokines, however, depended on glucosylation of Rho GTPases as tested by application of enzyme-deficient TcdA or TcdB. Down-regulation of total and secreted IL-16 protein was checked by enzyme-linked immunosorbent assay. The data implicate that TcdA and TcdB affect lymphocyte migration by modulating release of the chemoattractant factor IL-16 from mast cells. In addition, this is the first report showing that Rho GTPases are involved in the regulation of IL-16 expression.

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.

Changes in holothurian coelomocyte populations following immune stimulation with different molecular patterns

Echinoderms possess a variety of cells populating the coelomic fluid; these cells are responsible for mounting defense against foreign agents. In the sea cucumber Holothuria glaberrima, four different coelomocyte types were readily distinguished using morphological, histochemical and physiological (phagocytic activity) parameters: lymphocytes, phagocytes, spherulocytes and "giant" cells (listed in order of abundance). Monoclonal antibodies generated against sea cucumber tissues and one polyclonal against sea urchin mayor yolk protein (MYP) were also used to characterize these cell populations. The effects of several pathogen-associated molecular patterns (PAMPs): Lipopolysaccharides from Escherichia. coli (LPS), heat-killed Staphylococcus aureus (SA) and a synthetic dsRNA were studied on coelomocyte cell populations. PAMPs increased the phagocytic activity of the holothurian coelomocytes, and were able to induce selective immune responses in several of these populations, demonstrating the ability of the sea cucumber to respond to a different variety of immune challenges. Overall, these results show the variety of cells that populate the coelomic fluid of the holothurian and demonstrate their involvement in immune reactions. These animals represent an untapped resource for new findings into the evolution and development of the immune response not only in invertebrates but also in phylogenetically shared reactions with vertebrates.

Distribution, density and histochemical profiles of the lung mast cells during the post-hatching period of Japanese quails (Coturnix coturnix japonica)

The distribution, density and histochemical characteristics of mast cells in the lungs of the Japanese quail were investigated during the post-hatching period. In the period starting from the first to the 60th day post-hatching, based on proteoglycan content, three types of mast cells, which were alcian blue-positive, safranin O-positive and alcian blue/safranin O-positive, were found to exist in the lungs. The application of staining with berberine sulphate demonstrated that, similar to the distribution of safranin O-positive cells, the heparin-containing cells were located in the periphery of large blood vessels. The percentages of mast cells in different localization sites of the lungs were found to vary with age in the post-hatching period with toluidine blue staining. The lack of any statistically significant increase/decrease in the number of mast cells per unit area of the right and left lung lobes is partially in favour of the proposal that the mast cell number increases with the growth of the lung volume in the post-hatching period.

Mast cell-orchestrated immunity to pathogens

Although mast cells were discovered more than a century ago, their functions beyond their role in allergic responses remained elusive until recently. However, there is a growing appreciation that an important physiological function of these cells is the recognition of pathogens and modulation of appropriate immune responses. Because of their ability to instantly release several pro-inflammatory mediators from intracellular stores and their location at the host-environment interface, mast cells have been shown to be crucial for optimal immune responses during infection. Mast cells seem to exert these effects by altering the inflammatory environment after detection of a pathogen and by mobilizing various immune cells to the site of infection and to draining lymph nodes. Interestingly, the character and timing of these responses can vary depending on the type of pathogen stimulus, location of pathogen recognition and sensitization state of the responding mast cells. Recent studies using mast cell activators as effective vaccine adjuvants show the potential of harnessing these cells to confer protective immunity against microbial pathogens.

Reconstitution of the mast cell population in W/Wv mice

HYPOTHESIS

Intravenous injection of cultured mast cells (MCs) can reconstitute the MC population in MC-deficient mice. We hypothesize that injected culture-derived MCs do not repopulate all tissues equally.

BACKGROUND

Mast cells are central elements not only in anaphylaxis and allergy but also in immune reactions to bacteria and other pathogens. Their broad involvement in innate immunity requires extensive research in the future. Studies of MC function often use MC-deficient mice to compare with wild-type animals. A very elegant method to prove that the observed changes are due to the lack of MCs is to compare results in wild-type mice, MC-deficient mice, and MC-deficient mice that have been reconstituted with cultured MCs. Reconstitution of the MC population can be achieved by intravenous injection of MCs into MC-deficient mice. Whether the injected MCs repopulate the desired tissues has to be proven before this model is used. Also, the time frame of the reconstitution has to be demonstrated.

METHODS

Mast cell-deficient mice were injected with bone marrow-derived cultured MCs, and the mucosa of middle ear (MEs), nose, and tracheobronchial system was analyzed for MCs 4, 6, 8, 10, and 20 weeks after injection.

RESULTS

Reconstitution of the ME mucosa was complete and persistent for more than 20 weeks. Reconstitution failed in nasal mucosa. In bronchial mucosa, reconstitution was incomplete and transient.

CONCLUSION

This model can be used to investigate effects of MCs in various immune reactions in the ME. Studies should use the time frame 6 to 8 weeks after reconstitution of the MC population. However, the model has limitations for investigations in the respiratory tract.

RhoH plays critical roles in Fc epsilon RI-dependent signal transduction in mast cells

RhoH is an atypical small G protein with defective GTPase activity that is specifically expressed in hematopoietic lineage cells. RhoH has been implicated in regulation of several physiological processes including hematopoiesis, integrin activation, and T cell differentiation and activation. In the present study, we investigated the role of RhoH in mast cells by generating RhoH knockout mice. Despite observing normal development of mast cells in vivo, passive systemic anaphylaxis and histamine release were impaired in these mice. We also observed defective degranulation and cytokine production upon FcepsilonRI ligation in RhoH-deficient bone marrow-derived mast cells. Furthermore, FcepsilonRI-dependent activation of Syk and phosphorylation of its downstream targets, including LAT, SLP76, PLCgamma1, and PLCgamma2 were impaired, however phosphorylation of the gamma-subunit of FcepsilonRI remained intact. We also found RhoH-Syk association that was greatly enhanced by active Fyn. Our results indicate that RhoH regulates FcepsilonRI signaling in mast cells by facilitating Syk activation, possibly as an adaptor molecule for Syk.

Mast cell hyperplasia in the skin of Dsg4-deficient hypotrichosis mice, which are long-living mutants of lupus-prone mice

Desmosomal cadherins are essential cell adhesion molecules expressed in the epidermis. We identified a mutation of a cadherin superfamily member, namely, desmoglein 4 (Dsg4), in early onset of death (EOD)( hage ) mice with hypotrichosis. The mutation was induced by the insertion of an early transposon II-beta into intron 8 of Dsg4. Mast cell hyperplasia was observed in the skin of EOD( hage ) mice. The abnormally expanded population of lpr T cells, i.e., CD4(-)CD8(-)B220(+)Thy1.2(+) alphabetaT cells, in the splenocytes of EOD mice was reduced in EOD( hage ) mice. Therefore, it was suspected that the long-living mutant EOD( hage ) mice were selected from lupus-prone EOD mice because of their immunological immaturity. These findings clearly indicate that Dsg4 is an important molecule for the formation of hair follicles and hypothesize that unorganized hyperplastic hair follicles in anagen due to the Dsg4 mutation provide niches for mast cell precursors in the skin.

Phagocytosis-independent antimicrobial activity of mast cells by means of extracellular trap formation

These days it has been increasingly recognized that mast cells (MCs) are critical components of host defense against pathogens. In this study, we have provided the first evidence that MCs can kill bacteria by entrapping them in extracellular structures similar to the extracellular traps described for neutrophils (NETs). We took advantage of the ability of MCs to kill the human pathogen Streptococcus pyogenes by a phagocytosis-independent mechanism in order to characterize the extracellular antimicrobial activity of MCs. Close contact of bacteria and MCs was required for full antimicrobial activity. Immunofluorescence and electron microscopy revealed that S pyogenes was entrapped by extracellular structures produced by MCs (MCETs), which are composed of DNA, histones, tryptase, and the antimicrobial peptide LL-37. Disruption of MCETs significantly reduced the antimicrobial effect of MCs, suggesting that intact extracellular webs are critical for effective inhibition of bacterial growth. Similar to NETs, production of MCETs was mediated by a reactive oxygen species (ROS)-dependent cell death mechanism accompanied by disruption of the nuclear envelope, which can be induced after stimulation of MCs with phorbol-12-myristate-13-acetate (PMA), H(2)O(2), or bacterial pathogens. Our study provides the first experimental evidence of antimicrobial extracellular traps formation by an immune cell population other than neutrophils.

Effects of cigarette smoke in mice wound healing is strain dependent

It has been clinically and experimentally shown that cigarette smokers suffer from impaired wound healing, but the mechanisms that lead to the alterations are not well understood. The aim of this study was to investigate if the effects of cigarette smoke exposure on excisional cutaneous wound healing are different depending on the strain (Swiss, BALB/c and C57BL/6 mice) studied. Male mice were exposed to smoke of nine whole cigarettes per day, 3 times/day, daily, for 10 days. In the 11th day a full-thickness excisional wound was performed. Control group was sham-exposed and also had a full-thickness excisional wound. The cigarette smoke exposure protocol was performed until euthanasia. Animals were euthanatized 14 days after wounding. Wound contraction was evaluated 7 and 14 days after lesion. Sections were stained with hematoxylin-eosin, Sirius red or toluidine blue and immunostained for alpha-smooth muscle actin. Smoke exposed animals presented delay in wound contraction, in fibroblastic and inflammatory cells recruitment and in myofibroblastic differentiation; those alterations were strain dependent. Cigarette smoke exposure also affected mast cells recruitment and neoepidermis thickness. In conclusion, the present study demonstrated that the effects of cigarette smoke in mice cutaneous wound healing are related to mice strain studied.

Pharmacological modulation of wound healing in experimental burns

Factors involved in wound healing and their interdependence are not yet fully understood; nevertheless, new prospects for therapy to favor speedy and optimal healing are emerging. Reports about wound healing modulation by local application of simple and natural agents abound even in the recent literature, however, most are anecdotal and lack solid scientific evidence. We describe the effect of silver sulfadiazine and moist exposed burn ointment (MEBO), a recently described burn ointment of herbal origin, on mast cells and several wound healing cytokines (bFGF, IL-1, TGF-beta, and NGF) in the rabbit experimental burn model. The results demonstrate that various inflammatory cells, growth factors and cytokines present in the wound bed may be modulated by application of local agents with drastic effects on their expression dynamics with characteristic temporal and spatial regulation and changes in the expression pattern. Such data are likely to be important for the development of novel strategies for wound healing since they shed some light on the potential formulations of temporally and combinatory optimized therapeutic regimens.

Recombinant soybean protein beta-conglycinin alpha'-subunit expression and induced hypersensitivity reaction in rats

BACKGROUND

The major storage protein in soybean seed is beta-conglycinin and this protein has been identified as being responsible for food-allergic reactions in several species. However, the mechanism through which beta-conglycinin induces an allergic reaction has not yet been elucidated. In addition, assessing the antigenic activity of beta-conglycinin by studying the activity of a subunit has rarely been conducted. Therefore, the objective of the present study was to characterize the antigenic specificity of the beta-conglycinin alpha'-subunit.

METHODS

We established an Escherichia coli expression system to obtain beta-conglycinin alpha'-subunit. The fusion proteins were then used in a rat model to induce a hypersensitive reaction. Immunoblotting, IgE and IgG1 level, histamine release, and passive cutaneous anaphylaxis reactions and intestinal histology were tested to assess the allergenic activity of the beta-conglycinin alpha'-subunit.

RESULTS

Pure beta-conglycinin alpha'-subunit was obtained by expression in E. coli. The recombinant proteins were shown to have the same biological activity as the natural beta-conglycinin alpha'-subunit using immunoblotting analysis. Both the IgE and IgG1 level in serum and the histamine concentration in the intestine were increased while passive cutaneous anaphylactic reactions were induced in Brown Norway rats by intragastric gavage with the alpha'-subunit. Histamine release of mast cells was also elevated in vitro.

CONCLUSIONS

Our results indicate that the beta-conglycinin alpha'-subunit possesses an intrinsic immune-stimulating capacity and that it can induce an allergic reaction. Moreover, this study showed that beta-conglycinin alpha'-subunit-induced anaphylaxis is IgE mediated, and mast cell degranulation and histamine release are associated with anaphylactic symptoms.

Mast cells initiate early anti-Listeria host defences

The Gram-positive bacterium Listeria monocytogenes (L. m.) is the aetiological agent of listeriosis. The early phase listeriosis is characterized by strong innate host responses that play a major role in bacterial clearance. This is emphasized by the fact that mice deficient in T and B cells have a remarkable ability to control infection. Mast cells, among the principal effectors of innate immunity, have largely been studied in the context of hyper-reactive conditions such as allergy and autoimmune diseases. In the present study, we evaluated the significance of mast cells during the early phase of listeriosis. Compared with controls, mice depleted of mast cells showed hundred-fold higher bacterial burden in spleen and liver and were significantly impaired in neutrophil mobilization. Although L. m. interacts with and triggers mast cell degranulation, bacteria were hardly found within such cells. Mainly neutrophils and macrophages phagozytosed L. m. Thus, mast cells control infection not via direct bacterial uptake, but by initiating neutrophils influx to the site of infection. We show that this is initiated by pre-synthesized TNF-alpha, rapidly secreted by mast cell upon activation by L. m. We also show that upon recruitment, neutrophils also become activated and additionally secrete TNF-alpha thus amplifying the anti-L. m. inflammatory response.