Mast cells in innate immunity

The development of murine bone marrow-derived mast cells expressing functional human MRGPRX2 for ex vivo and in vivo studies

Introduction

A subtype of human mast cells (MCs) found in the skin and to a lesser extent in the lung and gut express a novel G protein-coupled receptor (GPCR) known as Mas-related GPCR-X2 (MRGPRX2, mouse counterpart MrgprB2). In addition to drug-induced pseudoallergy and cutaneous disorders, MrgprB2 contributes to ulcerative colitis, IgE-mediated lung inflammation and systemic anaphylaxis. Interestingly, most agonists activate MRGPRX2 with higher potency than MrgprB2. In this study, we sought to replace mouse MrgprB2 with human MRGPRX2 and to study receptor function ex vivo and in vivo.

Methods

MrgprB2-/- bone marrow (BM) cells were transduced with retrovirus encoding MRGPRX2 and differentiated into BMMCs (MRGRPX2-BMMCs) ex vivo. Cell surface MRGPRX2 expression was determined by flow cytometry. Effects of substance P (SP) and LL-37 on Ca2+ mobilization, degranulation and TNF-α generation were determined. MRGPRX2-BMMCs were engrafted intraperitoneally into MC-deficient Wsh/Wsh mice. After 6-8 weeks, immunofluorescence staining was performed on peritoneal lavage cells (PLCs), and sections of small intestine and colon with anti c-Kit and anti-MRGPRX2 antibodies. SP-induced degranulation in PLCs obtained from engrafted mice was determined.

Results

MRGPRX2-BMMCs expressed cell surface MRGPRX2 and responded to both SP and LL-37 for Ca2+ mobilization, degranulation and TNF-α generation. Furthermore, Wsh/Wsh mice engrafted with MRGPRX2-BMMCs expressed the receptor in peritoneal, intestinal and colonic MCs. In addition, PLCs from engrafted mice responded to SP for degranulation.

Conclusion

Replacing mouse MrgprB2 with functional human MRGPRX2 in primary BMMCs and their engraftment in MC-deficient mice demonstrated the expression of this receptor in different tissues, which provides unique opportunities to study receptor signaling ex vivo and disease phenotype in vivo.

Association Between Atopic Dermatitis in Pregnant Women and Preterm Births: The Japan Environment and Children's Study

OBJECTIVES

This study aimed to evaluate the association between atopic dermatitis in pregnant women and preterm births, accounting for maternal ritodrine hydrochloride administration status.

METHODS

Data of 83,796 women with singleton pregnancies at and after 22 weeks of gestation (enrolled between 2011 and 2014) were analyzed. These data were obtained from the Japan Environment and Children's Study. Atopic dermatitis was defined based on self-reported questionnaire responses obtained during the first trimester. The primary outcome measures were preterm births before 37, 32, and 28 weeks of gestation. Using a multivariable logistic regression model, odds ratios for preterm births in pregnant women with atopic dermatitis were calculated, with women without atopic dermatitis included in the reference group. This analysis considered confounding factors and maternal ritodrine hydrochloride administration.

RESULTS

Among pregnant women with atopic dermatitis, the adjusted odds ratios (95% confidence intervals) for preterm births before 37, 32, and 28 weeks of gestation were 0.89 (0.81-0.98), 0.98 (0.74-1.30), and 0.88 (0.50-1.55), respectively. This trend remained consistent after excluding participants who received ritodrine hydrochloride.

CONCLUSIONS FOR PRACTICE

Atopic dermatitis in pregnant women was significantly associated with a decreased incidence of preterm births before 37 weeks of gestation, even after accounting for the effects of maternal ritodrine hydrochloride administration.

On Connective Tissue Mast Cells as Protectors of Life, Reproduction, and Progeny

The connective tissue mast cell (MC), a sentinel tissue-residing secretory immune cell, has been preserved in all vertebrate classes since approximately 500 million years. No physiological role of the MC has yet been established. Considering the power of natural selection of cells during evolution, it is likely that the MCs exert essential yet unidentified life-promoting actions. All vertebrates feature a circulatory system, and the MCs interact readily with the vasculature. It is notable that embryonic MC progenitors are generated from endothelial cells. The MC hosts many surface receptors, enabling its activation via a vast variety of potentially harmful exogenous and endogenous molecules and via reproductive hormones in the female sex organs. Activated MCs release a unique composition of preformed and newly synthesized bioactive molecules, like heparin, histamine, serotonin, proteolytic enzymes, cytokines, chemokines, and growth factors. MCs play important roles in immune responses, tissue remodeling, cell proliferation, angiogenesis, inflammation, wound healing, tissue homeostasis, health, and reproduction. As recently suggested, MCs enable perpetuation of the vertebrates because of key effects-spanning generations-in ovulation and pregnancy, as in life-preserving activities in inflammation and wound healing from birth till reproductive age, thus creating a permanent life-sustaining loop. Here, we present recent advances that further indicate that the MC is a specific life-supporting and progeny-safeguarding cell.

The causes and consequences of trained immunity in myeloid cells

Conventionally, immunity in humans has been classified as innate and adaptive, with the concept that only the latter type has an immunological memory/recall response against specific antigens or pathogens. Recently, a new concept of trained immunity (a.k.a. innate memory response) has emerged. According to this concept, innate immune cells can exhibit enhanced responsiveness to subsequent challenges, after initial stimulation with antigen/pathogen. Thus, trained immunity enables the innate immune cells to respond robustly and non-specifically through exposure or re-exposure to antigens/infections or vaccines, providing enhanced resistance to unrelated pathogens or reduced infection severity. For example, individuals vaccinated with BCG to protect against tuberculosis were also protected from malaria and SARS-CoV-2 infections. Epigenetic modifications such as histone acetylation and metabolic reprogramming (e.g. shift towards glycolysis) and their inter-linked regulations are the key factors underpinning the immune activation of trained cells. The integrated metabolic and epigenetic rewiring generates sufficient metabolic intermediates, which is crucial to meet the energy demand required to produce proinflammatory and antimicrobial responses by the trained cells. These factors also determine the efficacy and durability of trained immunity. Importantly, the signaling pathways and regulatory molecules of trained immunity can be harnessed as potential targets for developing novel intervention strategies, such as better vaccines and immunotherapies against infectious (e.g., sepsis) and non-infectious (e.g., cancer) diseases. However, aberrant inflammation caused by inappropriate onset of trained immunity can lead to severe autoimmune pathological consequences, (e.g., systemic sclerosis and granulomatosis). In this review, we provide an overview of conventional innate and adaptive immunity and summarize various mechanistic factors associated with the onset and regulation of trained immunity, focusing on immunologic, metabolic, and epigenetic changes in myeloid cells. This review underscores the transformative potential of trained immunity in immunology, paving the way for developing novel therapeutic strategies for various infectious and non-infectious diseases that leverage innate immune memory.

Mice as an Animal Model for Japanese Encephalitis Virus Research: Mouse Susceptibility, Infection Route, and Viral Pathogenesis

Japanese encephalitis virus (JEV), a zoonotic flavivirus, is principally transmitted by hematophagous mosquitoes, continually between susceptible animals and incidentally from those animals to humans. For almost a century since its discovery, JEV was geographically confined to the Asia-Pacific region with recurrent sizable outbreaks involving wildlife, livestock, and people. However, over the past decade, it has been detected for the first time in Europe (Italy) and Africa (Angola) but has yet to cause any recognizable outbreaks in humans. JEV infection leads to a broad spectrum of clinical outcomes, ranging from asymptomatic conditions to self-limiting febrile illnesses to life-threatening neurological complications, particularly Japanese encephalitis (JE). No clinically proven antiviral drugs are available to treat the development and progression of JE. There are, however, several live and killed vaccines that have been commercialized to prevent the infection and transmission of JEV, yet this virus remains the main cause of acute encephalitis syndrome with high morbidity and mortality among children in the endemic regions. Therefore, significant research efforts have been directed toward understanding the neuropathogenesis of JE to facilitate the development of effective treatments for the disease. Thus far, multiple laboratory animal models have been established for the study of JEV infection. In this review, we focus on mice, the most extensively used animal model for JEV research, and summarize the major findings on mouse susceptibility, infection route, and viral pathogenesis reported in the past and present, and discuss some unanswered key questions for future studies.

The relationship between ovarian hormones and mast cell distribution in the ovaries of dromedary camel (Camelus dromedaries) during the follicular wave

Background and Aim: Mast cells (MCs) play an essential role in regulating tissue homeostasis through various non-allergic immune reactions. This study aimed to describe the salient features of MCs during different phases of the estrous cycle and evaluate the relationship between ovarian hormones and the presence of MCs in camel ovaries. Materials and Methods: Genital tracts (n = 28) of healthy, non-pregnant camels were collected from a local slaughterhouse. The follicular wave stage was determined according to structures on the ovaries using an ultrasound device. Stages were classified as "growing" (n = 12, FØ = 0.3–0.8 cm), "mature" (n = 9, FØ = 0.9–2.2 cm), or "regression" phase (n = 7, FØ >2.5). Blood samples were collected at slaughter to determine serum estradiol-17β and progesterone levels using an immunoassay. Safranin-O, periodic acid/Schiff, alcian blue, or methylene blue stains were used to detect MCs. Results: Follicular numbers at the growing, mature, and regression phases were determined to be 36, 14, and 7 follicles, respectively. Mast cells were widely but sparsely distributed within the ovarian tissue (9.3 MCs in the growing phase, 10.7 in the mature phase, and 7.0 in the regression phase). Typical histological features of MCs were observed in ovarian stromal tissue. Some MCs were found in the interstitial tissue, either near the follicular wall or the interstitial gland. Mast cells were present at a higher density during the mature phase than in the growing and regression phases in the ovarian matrix. A significantly reduced presence of MCs was found in the regression phase than in both the growing and mature phases (p < 0.05). A very strong positive correlation was observed between serum estradiol-17β concentrations and MC density in the ovaries (r = 0.9; p < 0.001). In addition, a strong negative correlation (r = –0.65; p = 0.03) was observed between the presence of MCs and serum progesterone concentrations. Conclusion: These findings suggest that the follicular wave phase and the associated hormonal concentration induce changes in the number of MCs in the camel ovary.

Leishmania major-Infected Phlebotomus duboscqi Sand Fly Bites Enhance Mast Cell Degranulation

Leishmania parasites infect mammalian hosts through the bites of sand fly vectors. The response by mast cells (MC) to the parasite and vector-derived factors, delivered by sand fly bites, has not been characterized. We analyzed MC numbers and their mediators in BALB/c mice naturally infected in the ear with Leishmania major through the bite of the sand fly vector Phlebotomus duboscqi and compared them to non-infected sand fly bites. MC were found at the bite sites of infective and non-infected sand flies throughout 48 h, showing the release of granules with intense TNF-α, histamine, and tryptase staining. At 30 min and 48 h, the MC numbers were significantly higher (p < 0.001) in infected as compared to non-infected bites or controls. Neutrophil recruitment was intense during the first 6 h in the skin of infected and non-infected sand fly bites and decreased thereafter. An influx of neutrophils also occurred in lymph nodes, where a strong TNF-α stain was observed in mononuclear cells. Our data show that MC orchestrate an early inflammatory response after infected and non-infected sand fly bites, leading to neutrophilic recruitment, which potentially provides a safe passage for the parasite within the mammalian host.

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.

Do mast cells contribute to the continued survival of vertebrates?

This study is an attempt to shed light on why the connective tissue mast cell (MC) is preserved in all species with a blood circulatory system, i.e., the vertebrates since >500 million years, which suggests that the MC performs as yet not understood indispensible life-promoting actions. The literature survey focuses on data in published papers on MC functions in immunological and nonimmunological reactions, host protection, pregnancy, inflammation, and wound healing. All data are thus accessible to the reader. The MC is a secretory cell with a unique mediator profile. A distinctive role for MCs is defined not only by their extensive mediator composition but also by their prominent ability to affect the vasculature to expedite selective cell recruitment and permeability changes and to set the stage for an appropriate acquired response. MCs, harboring a wide range of surface membrane receptors, are activated by the major female sex hormones as well as by diverse potentially adverse stimuli. MC activation/degranulation creates a presumably unique triad tissue response in physiological and pathological situations alike: extracellular matrix degradation and tissue remodeling, de novo cell proliferation, and de novo angiogenesis. As shown in the literature, MC-activation is crucial for successful female reproduction in the mouse, implying one of possibly several yet unidentified physiological roles of MCs. Moreover, the activated MC aids newborns to survive to reproductive age owing to its key beneficial actions in inflammation and wound healing. Thus, a not previously described life-perpetuating loop spanning generations are apparently formed, which, hypothetically, could contribute to the continued survival of the vertebrates.

Comprehensive analysis of somatic mutator-derived and immune infiltrates related lncRNA signatures of genome instability reveals potential prognostic biomarkers involved in non-small cell lung cancer

Background: The function and features of long non-coding RNAs (lncRNAs) are already attracting attention and extensive research on their role as biomarkers of prediction in lung cancer. However, the signatures that are both related to genomic instability (GI) and tumor immune microenvironment (TIME) have not yet been fully explored in previous studies of non-small cell lung cancer (NSCLC). Method: The clinical characteristics, RNA expression profiles, and somatic mutation information of patients in this study came from The Cancer Genome Atlas (TCGA) database. Cox proportional hazards regression analysis was performed to construct genomic instability-related lncRNA signature (GIrLncSig). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed to predict the potential functions of lncRNAs. CIBERSORT was used to calculate the proportion of immune cells in NSCLC. Result: Eleven genomic instability-related lncRNAs in NSCLC were identified, then we established a prognostic model with the GIrLncSig ground on the 11 lncRNAs. Through the computed GIrLncSig risk score, patients were divided into high-risk and low-risk groups. By plotting ROC curves, we found that patients in the low-risk group in the test set and TCGA set had longer overall survival than those in the high-risk group, thus validating the survival predictive power of GIrLncSig. By stratified analysis, there was still a significant difference in overall survival between high and low risk groups of patients after adjusting for other clinical characteristics, suggesting the prognostic significance of GIrLncSig is independent. In addition, combining GIrLncSig with TP53 could better predict clinical outcomes. Besides, the immune microenvironment differed significantly between the high-risk and the low-risk groups, patients with low risk scores tend to have upregulation of immune checkpoints and chemokines. Finally, we found that high-risk scores were associated with increased sensitivity to chemotherapy. Conclusion: we provided a new perspective on lncRNAs related to GI and TIME and revealed the worth of them in immune infiltration and immunotherapeutic response. Besides, we found that the expression of AC027288.1 is associated with PD-1 expression, which may be a potential prognostic marker in immune checkpoint inhibitor response to improve the prediction of clinical survival in NSCLC patients.

Uncovering the Mast Cell Response to Mycobacterium tuberculosis

The immunologic mechanisms that contribute to the response to Mycobacterium tuberculosis infection still represent a challenge in the clinical management and scientific understanding of tuberculosis disease. In this scenario, the role of the different cells involved in the host response, either in terms of innate or adaptive immunity, remains key for defeating this disease. Among this coordinated cell response, mast cells remain key for defeating tuberculosis infection and disease. Together with its effector’s molecules, membrane receptors as well as its anatomical locations, mast cells play a crucial role in the establishment and perpetuation of the inflammatory response that leads to the generation of the granuloma during tuberculosis. This review highlights the current evidences that support the notion of mast cells as key link to reinforce the advancements in tuberculosis diagnosis, disease progression, and novel therapeutic strategies. Special focus on mast cells capacity for the modulation of the inflammatory response among patients suffering multidrug resistant tuberculosis or in co-infections such as current COVID-19 pandemic.

Apigenin Inhibits the Histamine-Induced Proliferation of Ovarian Cancer Cells by Downregulating ERα/ERβ Expression

Background

Apigenin (APG), a natural flavonoid, can affect the development of a variety of tumors, but its role in ovarian cancer remains unclear. There has been an increasing amount of evidence supporting the vital role played by mast cells and the bioactive mediators they release, as components of the tumor microenvironment, in the progression of ovarian cancer (OC); however, the mechanism warrants further exploration.

Methods and Results

In this study, a combination of transcriptomics analysis and application of TCGA database was performed, and we found that the expression of genes related to mast cell degranulation in ovarian cancer tissues changed remarkably. We then explored whether histamine, a major constituent of mast cell degranulation, could affect the development of ovarian cancer through immunohistochemistry analysis and cell proliferation assays. The results showed that a certain concentration of histamine promoted the proliferation of ovarian cancer cells by upregulating the expression of estrogen receptor α (ERα)/estrogen receptor β (ERβ). Additionally, we found that the inhibition of ERα or the activation of ERβ could inhibit the proliferation of ovarian cancer cells induced by histamine through real-time PCR and western blot assays. Finally, we demonstrated the attenuation effect imparted by apigenin in histamine-mediated ovarian cancer via the PI3K/AKT/mTOR signaling pathway.

Conclusion

Our research revealed that apigenin decelerated ovarian cancer development by downregulating ER-mediated PI3K/AKT/mTOR expression, thus providing evidence of its applicability as a potentially effective therapeutic agent for ovarian cancer treatment.

Bidirectional communication between mast cells and the gut-brain axis in neurodegenerative diseases: Avenues for therapeutic intervention

Although the global incidence of neurodegenerative diseases has been steadily increasing, especially in adults, there are no effective therapeutic interventions. Neurodegeneration is a heterogeneous group of disorders that is characterized by the activation of immune cells in the central nervous system (CNS) (e.g., mast cells and microglia) and subsequent neuroinflammation. Mast cells are found in the brain and the gastrointestinal tract and play a role in "tuning" neuroimmune responses. The complex bidirectional communication between mast cells and gut microbiota coordinates various dynamic neuro-cellular responses, which propagates neuronal impulses from the gastrointestinal tract into the CNS. Numerous inflammatory mediators from degranulated mast cells alter intestinal gut permeability and disrupt blood-brain barrier, which results in the promotion of neuroinflammatory processes leading to neurological disorders, thereby offsetting the balance in immune-surveillance. Emerging evidence supports the hypothesis that gut-microbiota exert a pivotal role in inflammatory signaling through the activation of immune and inflammatory cells. Communication between inflammatory cytokines and neurocircuits via the gut-brain axis (GBA) affects behavioral responses, activates mast cells and microglia that causes neuroinflammation, which is associated with neurological diseases. In this comprehensive review, we focus on what is currently known about mast cells and the gut-brain axis relationship, and how this relationship is connected to neurodegenerative diseases. We hope that further elucidating the bidirectional communication between mast cells and the GBA will not only stimulate future research on neurodegenerative diseases but will also identify new opportunities for therapeutic interventions.

Delving Into the Origin of Destructive Inflammation in COVID-19: A Betrayal of Natural Host Defense Peptides?

In contrast to other pathogenic agents that directly destroy host cells and tissues, the lethal power of SARS-CoV-2 resides in the over-reactive immune response triggered by this virus. Based on numerous evidences indicating that the lipid composition of host membranes is dramatically affected by COVID-19, and in the fact that our endogenous antimicrobial peptides (AMPs) are sensitive to the membrane composition of pathogenic agents, we propose that such destructive immune response is due to the direct action of AMPs. In a scenario where most host cell membranes are dressed by a pathogenic lipid composition, AMPs can indiscriminately attack them. This is why we use the "AMP betrayal" term to describe this mechanism. Previously proposed cytokine/bradykinin storm mechanisms are not incompatible with this new proposal. Interestingly, the harmful action of AMPs could be prevented by new therapies aimed to reestablish the lipid composition or to inhibit the action of specific peptides.

Effect of zymosan on feed passage in the digestive tract in chicks

1. The purpose of the present study was to examine whether zymosan, which is a component of fungi, affects feed passage through the digestive tract in chicks (Gallus gallus).2. Intraperitoneal (IP) injection of 2.5 mg zymosan significantly reduced the crop-emptying rate and this effect was similar to that of 100 µg lipopolysaccharide (LPS). Zymosan affected phenol red transit from the proventriculus.3. Zymosan significantly affected the gene expression of interleukin-1β (IL-1β), IL-6, IL-8 and histidine decarboxylase in various regions of the digestive tract.4. The present study suggested that zymosan retarded feed passage through the digestive tract in chick and interleukins and histamine may be participating in this process.

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.

The Role of Mast Cells in Bone Metabolism and Bone Disorders

Mast cells (MCs) are important sensor and effector cells of the immune system that are involved in many physiological and pathological conditions. Increasing evidence suggests that they also play an important role in bone metabolism and bone disorders. MCs are located in the bone marrow and secrete a wide spectrum of mediators, which can be rapidly released upon activation of mature MCs following their differentiation in mucosal or connective tissues. Many of these mediators can exert osteocatabolic effects by promoting osteoclast formation [e.g., histamine, tumor necrosis factor (TNF), interleukin-6 (IL-6)] and/or by inhibiting osteoblast activity (e.g., IL-1, TNF). By contrast, MCs could potentially act in an osteoprotective manner by stimulating osteoblasts (e.g., transforming growth factor-β) or reducing osteoclastogenesis (e.g., IL-12, interferon-γ). Experimental studies investigating MC functions in physiological bone turnover using MC-deficient mouse lines give contradictory results, reporting delayed or increased bone turnover or no influence depending on the mouse model used. By contrast, the involvement of MCs in various pathological conditions affecting bone is evident. MCs may contribute to the pathogenesis of primary and secondary osteoporosis as well as inflammatory disorders, including rheumatoid arthritis and osteoarthritis, because increased numbers of MCs were found in patients suffering from these diseases. The clinical observations could be largely confirmed in experimental studies using MC-deficient mouse models, which also provide mechanistic insights. MCs also regulate bone healing after fracture by influencing the inflammatory response toward the fracture, vascularization, bone formation, and callus remodeling by osteoclasts. This review summarizes the current view and understanding of the role of MCs on bone in both physiological and pathological conditions.

Responses of human mast cells and epithelial cells following exposure to influenza A virus

As a part of innate immune defense, the role of mast cells during viral replication has been incompletely understood. In this study, we characterized and compared the responses of the human mast cell line, LAD2, and human lung epithelial cell line, Calu-3, against three influenza A virus strains; A/PR/8/34 (H1N1), A/WS/33 (H1N1) and A/HK/8/68 (H3N2). We found that there were strain-dependent mast cell responses, and different profiles of cytokine, chemokine and antiviral gene expression between the two cell types. All three strains did not induce histamine or β-hexosaminidase release in LAD2. A/HK/8/68 induced release of prostaglandin D2 in LAD2, whereas A/PR/8/34 and A/WS/33 did not. We found that, among those examined, only CCL4 (by A/PR/8/34) was statistically significantly released from LAD2 cells. Furthermore, there was increased mRNA expression of viral recognition receptors (RIG-I and MDA5) and antiviral protein, viperin, but levels and kinetics of the expression were different among the cell types, as well as by the strains examined. Our findings highlight the variability in innate response to different strains of influenza A virus in two human cell types, indicating that further investigation is needed to understand better the role of mast cells and epithelial cells in innate immunity against influenza A viruses.

Lipocalin 2: A New Antimicrobial in Mast Cells

Mast cells (MCs) play a significant role in the innate immune defense against bacterial infection through the release of cytokines and antimicrobial peptides. However, their antimicrobial function is still only partially described. We therefore hypothesized that MCs express additional antimicrobial peptides. In this study, we used FANTOM 5 transcriptome data to identify for the first time that MCs express lipocalin 2 (LCN2), a known inhibitor of bacterial growth. Using MCs derived from mice which were deficient in LCN2, we showed that this antimicrobial peptide is an important component of the MCs' antimicrobial activity against Escherichia coli (E. coli). Since sphingosine-1-phosphate receptors (S1PRs) on MCs are known to regulate their function during infections, we hypothesized that S1P could activate LCN2 production in MCs. Using an in vitro assay, we demonstrated that S1P enhances MCs antimicrobial peptide production and increases the capacity of MCs to directly kill S. aureus and E. coli via an LCN2 release. In conclusion, we showed that LCN2 is expressed by MCs and plays a role in their capacity to inhibit bacterial growth.

Although Abundant in Tumor Tissue, Mast Cells Have No Effect on Immunological Micro-milieu or Growth of HPV-Induced or Transplanted Tumors

High numbers of mast cells populate the stroma of many types of neoplasms, including human papilloma virus-induced benign and malignant tumors in man and mouse. Equipped with numerous pattern recognition receptors and capable of executing important pro-inflammatory responses, mast cells are considered innate sentinels that significantly impact tumor biology. Mast cells were reported to promote human papilloma virus (HPV)-induced epithelial hyperproliferation and neo-angiogenesis in an HPV-driven mouse model of skin cancer. We analyzed HPV-induced epithelial hyperplasia and squamous cell carcinoma formation, as well as growth of tumors inoculated into the dermis, in mice lacking skin mast cells. Unexpectedly, the absence of mast cells had no effect on HPV-induced epithelial growth or angiogenesis, on growth kinetics of inoculated tumors, or on the immunological tumor micro-milieu. Thus, the conspicuous recruitment of mast cells into tumor tissues cannot necessarily be equated with important mast cell functions in tumor growth.

Japanese encephalitis virus neuropenetrance is driven by mast cell chymase

Japanese encephalitis virus (JEV) is a leading cause of viral encephalitis. However, the mechanisms of JEV penetration of the blood-brain-barrier (BBB) remain poorly understood. Mast cells (MCs) are granulated innate immune sentinels located perivascularly, including at the BBB. Here we show that JEV activates MCs, leading to the release of granule-associated proteases in vivo. MC-deficient mice display reduced BBB permeability during JEV infection compared to congenic wild-type (WT) mice, indicating that enhanced vascular leakage in the brain during JEV infection is MC-dependent. Moreover, MCs promoted increased JEV infection in the central nervous system (CNS), enhanced neurological deficits, and reduced survival in vivo. Mechanistically, chymase, a MC-specific protease, enhances JEV-induced breakdown of the BBB and cleavage of tight-junction proteins. Chymase inhibition reversed BBB leakage, reduced brain infection and neurological deficits during JEV infection, and prolonged survival, suggesting chymase is a novel therapeutic target to prevent JEV encephalitis.

How Japanese encephalitis virus (JEV) penetrates the blood-brain barrier (BBB) remains unclear. Here, using a genetic mouse model and a virulent JEV strain, the authors show that perivascular mast cells (MC) mediate JEV neuroinvasion and identify the MC-protease chymase as a potential therapeutic target.

Angiogenic Host Defense Peptide AG-30/5C and Bradykinin B2 Receptor Antagonist Icatibant Are G Protein Biased Agonists for MRGPRX2 in Mast Cells

AG-30/5C is an angiogenic host defense peptide that activates human mast cells (MC) via an unknown mechanism. Using short hairpin RNA-silenced human MC line LAD2 and stably transfected RBL-2H3 cells, we demonstrate that AG-30/5C induces MC degranulation via Mas-related G protein-coupled receptor X2 (MRGPRX2). Most G protein-coupled receptors signal via parallel and independent pathways mediated by G proteins and β-arrestins. AG-30/5C and compound 48/80 induced similar maximal MC degranulation via MRGPRX2, which was abolished by pertussis toxin. However, compound 48/80 induced a robust β-arrestin activation as determined by transcriptional activation following arrestin translocation (Tango), but AG-30/5C did not. Overnight culture of MC with compound 48/80 resulted in reduced cell surface MRGPRX2 expression, and this was associated with a significant decrease in subsequent MC degranulation in response to compound 48/80 or AG-30/5C. However, AG-30/5C pretreatment had no effect on cell surface MRGPRX2 expression or degranulation in response to compound 48/80 or AG-30/5C. Icatibant, a bradykinin B₂ receptor antagonist, promotes MC degranulation via MRGPRX2 and causes pseudoallergic drug reaction. Icatibant caused MC degranulation via a pertussis toxin-sensitive G protein but did not activate β-arrestin. A screen of the National Institutes of Health Clinical Collection library led to the identification of resveratrol as an inhibitor of MRGPRX2. Resveratrol inhibited compound 48/80-induced Tango and MC degranulation in response to compound 48/80, AG-30/5C, and Icatibant. This study demonstrates the novel finding that AG-30/5C and Icatibant serve as G protein-biased agonists for MRGPRX2, but compound 48/80 signals via both G protein and β-arrestin with distinct differences in receptor regulation.

Compound 48/80 reduces the crop-emptying rate, likely through a histamine-associated pathway in chicks

Infectious conditions are associated with reduced food passage through the digestive tract in both mammals and chicks; however, the precise mechanism mediating this response in chicks remains unclear. The purpose of the present study was to determine if mast cells, a blood cell type which plays an important role in the immune system, might affect food passage through the digestive tract in chicks. Specifically, we performed intraperitoneal (IP) injections of compound 48/80, an inducer of mast cell degranulation, and measured crop emptying. The IP injection of compound 48/80 significantly reduced the crop-emptying rate, but it did not affect the proventriculus to small intestine transit rate or the number of defecations. We also found that IP-injected histamine, which is secreted by mast cells, also reduced the crop-emptying rate. In addition, IP injection of 2-pyridylethylamine (histamine H1 receptor agonist), but not dimaprit, (R)-(-)-α-methylhistamine, and VUF8430 (histamine H2, H3, and H4 receptor agonists, respectively), reduced the crop-emptying rate, implying that histamine reduces the crop emptying rate via the histamine H1 receptor. Finally, we found that IP injection of compound 48/80 reduced mRNA expression of histidine decarboxylase, a rate-limiting enzyme for histamine synthesis, in the esophagus and proventriculus at 1 h and the proventriculus and duodenum at 3 h after the injection. In sum, the present study suggests that the degranulation of mast cells causes a reduction in the crop-emptying rate, possibly via the histamine pathway in chicks.

Transcriptomic analysis of short-term 17α-ethynylestradiol exposure in two Californian sentinel fish species sardine (Sardinops sagax) and mackerel (Scomber japonicus)

Endocrine disrupting chemicals (EDCs) are substances which disrupt normal functioning of the endocrine system by interfering with hormone regulated physiological pathways. Aquatic environments provide the ultimate reservoir for many EDCs as they enter rivers and the ocean via effluent discharges and accumulate in sediments. One EDC widely dispersed in municipal wastewater effluent discharges is 17α-ethynylestradiol (EE2), which is one of the most widely prescribed medicines. EE2 is a bio-active estrogen employed in the majority of oral contraceptive pill formulations. As evidence of the health risks posed by EDCs mount, there is an urgent need to improve diagnostic tools for monitoring the effects of pollutants. As the cost of high throughput sequencing (HTS) diminishes, transcriptional profiling of an organism in response to EDC perturbation presents a cost-effective way of screening a wide range of endocrine responses. Coastal pelagic filter feeding fish species analyzed using HTS provide an excellent tool for EDC risk assessment in the marine environment. Unfortunately, there are limited genome sequence data and annotation for many of these species including Pacific sardine (Sardinops sagax) and chub mackerel (Scomber japonicus), which limits the utility of molecular tools such as HTS to interrogate the effects of endocrine disruption. In this study, we carried out RNA sequencing (RNAseq) of liver RNA harvested from wild sardine and mackerel exposed for 5 h under laboratory conditions to a concentration of 12.5 pM EE2 in the tank water. We developed an analytical framework for transcriptomic analyses of species with limited genomic information. EE2 exposure altered expression patterns of key genes involved in important metabolic and physiological processes. The systems approach presented here provides a powerful tool for obtaining a comprehensive picture of endocrine disruption in aquatic organisms.

Unimpaired Responses to Vaccination With Protein Antigen Plus Adjuvant in Mice With Kit-Independent Mast Cell Deficiency

Innate inflammatory responses are crucial for induction and regulation of T cell and antibody responses. Mast cell (MC)-deficient Kit mutant mice showed impaired adaptive immunity, suggesting that MCs provide essential adjuvant activities, and pharmacological MC activation was proposed as a new adjuvant principle. However, the Kit mutations result in complex alterations of the immune system in addition to MC deficiency. We revisited the role of MCs in vaccination responses using Mcpt5-Cre R26^DTA/DTA and Cpa3^Cre/+ mice that lack connective tissue MCs or all MCs, respectively, but feature an otherwise normal immune system. These animals showed no impairment of T and B cell responses to intradermal vaccination with protein antigen plus complete Freund’s adjuvant. Moreover, we demonstrate that the adjuvant effects of the MC secretagogue c48/80 in intradermal or mucosal immunization are independent of the presence of MCs. We hence find no evidence for a regulation by MCs of adaptive immune responses to protein antigens. The finding that immunological MC functions differ from those suggested by experiments in Kit mutants, emphasizes the importance of rigorous tests in Kit-independent MC-deficiency models.

Pike intestinal reaction to Acanthocephalus lucii (Acanthocephala): immunohistochemical and ultrastructural surveys

Background

The Northern pike, Esox lucius, is a large, long-lived, top-predator fish species and occupies a broad range of aquatic environments. This species is on its way to becoming an important model organism and has the potential to contribute new knowledge and a better understanding of ecology and evolutionary biology. Very few studies have been done on the intestinal pathology of pike infected with helminths. The present study details the first Italian record of adult Acanthocephalus lucii reported in the intestine of E. lucius.

Results

A total of 22 pike from Lake Piediluco (Central Italy) were examined, of which 16 (72.7%) were infected with A. lucii. The most affected areas of gastrointestinal tract were the medium and distal intestine. The intensity of infection ranged from 1 to 18 parasites per host. Acanthocephalus lucii penetrated mucosal and submucosal layers which had a high number of mast cells (MCs) with an intense degranulation. The cellular elements involved in the immune response within the intestine of pike were assessed by ultrastructural techniques and immunohistochemistry using antibodies against met-enkephalin, immunoglobulin E (IgE)-like receptor (FCεRIγ), histamine, interleukin-6, interleukin-1β, substance P, lysozyme, serotonin, inducible-nitric oxide synthase (i-NOS), tumor necrosis factor-α (TNF-α) and the antimicrobial peptide piscidin 3 (P3). In intestines of the pike, several MCs were immunopositive to 9 out of the 11 aforementioned antibodies and infected fish had a higher number of positive MCs when compared to uninfected fish.

Conclusions

Pike intestinal tissue response to A. lucii was documented. Numerous MCs were seen throughout the mucosa and submucosal layers. In infected and uninfected intestines of pike, MCs were the dominant immune cell type encountered; they are the most common granulocyte type involved in several fish-helminth systems. Immunopositivity of MCs to 9 out of 11 antibodies is of great interest and these cells could play an important key role in the host response to an enteric helminth. This is the first report of A. lucii in an Italian population of E. lucius and the first account on positivity of MCs to piscidin 3 and histamine in a non-perciform fish.

The Role of Mast Cells in Tuberculosis: Orchestrating Innate Immune Crosstalk?

Tuberculosis causes more annual deaths globally than any other infectious disease. However, progress in developing novel vaccines, diagnostics, and therapies has been hampered by an incomplete understanding of the immune response to Mycobacterium tuberculosis (Mtb). While the role of many immune cells has been extensively explored, mast cells (MCs) have been relatively ignored. MCs are tissue resident cells involved in defense against bacterial infections playing an important role mediating immune cell crosstalk. This review discusses specific interactions between MCs and Mtb, their contribution to both immunity and disease pathogenesis, and explores their role in orchestrating other immune cells against infections.

Differential Regulation of Mas-Related G Protein-Coupled Receptor X2-Mediated Mast Cell Degranulation by Antimicrobial Host Defense Peptides and Porphyromonas gingivalis Lipopolysaccharide

Porphyromonas gingivalis is a keystone pathogen that contributes to periodontal pathogenesis by disrupting host-microbe homeostasis and promoting dysbiosis. The virulence of P. gingivalis likely reflects an alteration in the lipid A composition of its lipopolysaccharide (LPS) from the penta-acylated (PgLPS₁₆₉₀) to the tetra-acylated (PgLPS_1435/1449) form. Mast cells play an important role in periodontitis, but the mechanisms of their activation and regulation remain unknown. The expression of epithelium- and neutrophil-derived host defense peptides (HDPs) (LL-37 and human β-defensin-3), which activate mast cells via Mas-related G protein-coupled receptor X2 (MRGPRX2), is increased in periodontitis. We found that MRGPRX2-expressing mast cells are present in normal gingiva and that their numbers are elevated in patients with chronic periodontitis. Furthermore, HDPs stimulated degranulation in a human mast cell line (LAD2) and in RBL-2H3 cells stably expressing MRGPRX2 (RBL-MRGPRX2). PgLPS₁₆₉₀ caused substantial inhibition of HDP-induced mast cell degranulation, but PgLPS_1435/1449 had no effect. A fluorescently labeled HDP (FAM-LL-37) bound to RBL-MRGPRX2 cells, and PgLPS₁₆₉₀ inhibited this binding, but PgLPS_1435/1449 had no effect. These findings suggest that low-level inflammation induced by HDP/MRGPRX2-mediated mast cell degranulation contributes to gingival homeostasis but that sustained inflammation due to elevated levels of both HDPs and MRGPRX2-expressing mast cells promotes periodontal disease. Furthermore, differential regulation of HDP-induced mast cell degranulation by PgLPS₁₆₉₀ and PgLPS_1435/1449 may contribute to the modulation of disease progression.

Emerging Roles for MAS-Related G Protein-Coupled Receptor-X2 in Host Defense Peptide, Opioid, and Neuropeptide-Mediated Inflammatory Reactions

Mast cells (MCs) are tissue-resident immune cells that contribute to host defense but are best known for their roles in allergic and inflammatory diseases. In humans, MCs are divided into two subtypes based on the protease content of their secretory granules. Thus, human lung MCs contain only tryptase and are known as MC_T, whereas skin MCs contain both tryptase and chymase and are known as MC_TC. Patients with severe asthma display elevated MCs in the lung, which undergo phenotypic change from MC_T to MC_TC. Although the human genome contains four Mas related G protein coupled receptor X (MRGPRX) genes, an important feature of MC_TC is that they selectively express MRGPRX2. It is activated by antimicrobial host defense peptides such as human β-defensins and the cathelicidin LL-37 and likely contributes to host defense. MRGPRX2 is also a receptor for the neuropeptide substance P, major basic protein, eosinophil peroxidase, opioids, and many FDA-approved cationic drugs. Increased expression of MRGPRX2 or enhanced downstream signaling likely contributes to chronic inflammatory diseases such as rosacea, atopic dermatitis, chronic urticaria, and severe asthma. In this chapter, I will discuss the expression profile and function of MRGPRX1-4 and review the emerging roles of MRGPRX2 on host defense, chronic inflammatory diseases, and drug-induced pseudoallergic reactions. I will also examine the novel aspects of MRGPRX2 signaling in MCs as it related to degranulation and review the mechanisms of its regulation.

African Trypanosomes Undermine Humoral Responses and Vaccine Development: Link with Inflammatory Responses?

African trypanosomosis is a debilitating disease of great medical and socioeconomical importance. It is caused by strictly extracellular protozoan parasites capable of infecting all vertebrate classes including human, livestock, and game animals. To survive within their mammalian host, trypanosomes have evolved efficient immune escape mechanisms and manipulate the entire host immune response, including the humoral response. This report provides an overview of how trypanosomes initially trigger and subsequently undermine the development of an effective host antibody response. Indeed, results available to date obtained in both natural and experimental infection models show that trypanosomes impair homeostatic B-cell lymphopoiesis, B-cell maturation and survival and B-cell memory development. Data on B-cell dysfunctioning in correlation with parasite virulence and trypanosome-mediated inflammation will be discussed, as well as the impact of trypanosomosis on heterologous vaccine efficacy and diagnosis. Therefore, new strategies aiming at enhancing vaccination efficacy could benefit from a combination of (i) early parasite diagnosis, (ii) anti-trypanosome (drugs) treatment, and (iii) anti-inflammatory treatment that collectively might allow B-cell recovery and improve vaccination.

Innate immunity in cutaneous melanoma

The skin immune system is composed of a vast network of immune cells, including lymphocytes, macrophages, neutrophils, dendritic cells and Langerhans cells, which not only are involved in inflammatory responses but also contribute to homeostatic function and may participate in the various steps of carcinogenesis. Many studies support the notion that innate immunity has a key role in the development, growth and prognosis of cutaneous malignant melanoma (MM), through the release of pro- and/or anti-inflammatory cytokines and tumour growth factors. The tumour environment in a major subset of cutaneous MM shows evidence of a T cell-infiltrated phenotype, but there is less known about the presence and the phenotype of other immune system cells. Response to immunotherapy is largely correlated with the presence of T cells in the tumour microenvironment, while the regulation exerted by stromal components such as macrophages and mast cells has been less investigated. In the current report, we review the recent literature, focusing our attention on the role of macrophages, dendritic cells, mast cells and natural killer cells in orchestrating MM progression, to better understand tumour immunobiology. The identification of new therapeutic targets and the application of approaches aimed at modulating crosstalk between immune and tumour cells, could have a crucial impact on immunotherapy and result in better clinical outcome. We hope this review will be helpful in cutaneous MM research.

Peroxisome proliferator-activated receptor-β/δ modulates mast cell phenotype

The peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is known to have multiple anti-inflammatory effects, typically observed in endothelial cells, macrophages, T cells and B cells. Despite the fact that mast cells are important mediators of inflammation, to date, the role of PPARβ/δ in mast cells has not been examined. Hence, the present study examined the hypothesis that PPARβ/δ modulates mast cell phenotype. Bone-marrow-derived mast cells (BMMCs) and peritoneal mast cells from Pparβ/δ^+/+ mice expressed higher levels of high-affinity IgE receptor (FcεRI) compared with Pparβ/δ^-/- mice. BMMCs from Pparβ/δ^+/+ mice also exhibited dense granules, associated with higher expression of enzymes and proteases compared with Pparβ/δ^-/- mice. Resting BMMCs from Pparβ/δ^+/+ mice secreted lower levels of inflammatory cytokines, associated with the altered activation of phospholipase Cγ1 and extracellular signal-regulated kinases compared with Pparβ/δ^-/- mice. Moreover, the production of cytokines by mast cells induced by various stimuli was highly dependent on PPARβ/δ expression. This study demonstrates that PPARβ/δ is an important regulator of mast cell phenotype.

The bacterial quorum-sensing molecule, N-3-oxo-dodecanoyl-L-homoserine lactone, inhibits mediator release and chemotaxis of murine mast cells

OBJECTIVE

Bacterial colonization relies on communication between bacteria via so-called "quorum-sensing molecules", which include the acyl-homoserine lactone group. Certain acyl-homoserine lactones can modulate mammalian cell function and are thought to contribute to bacterial pathogenicity. Given the role of mast cells in host defense, we investigated the ability of acyl-homoserine lactones to modulate mast cell function.

METHODS

We utilized murine primary mast cell cultures to assess the effect of acyl-homoserine lactones on degranulation and cytokine release in response to different stimuli. We also assessed cell migration in response to chemoattractants. The effect of acyl-homoserine lactones in vivo was tested using a passive cutaneous anaphylaxis model.

RESULTS

Two of the tested quorum-sensing molecules, N-3-oxo-dodecanoyl-L-homoserine lactone and N-Dodecanoyl-L-homoserine lactone, inhibited IgE dependent and independent degranulation and mediator release from primary mast cells. Further testing of N-3-oxo-dodecanoyl-L-homoserine lactone, the most potent inhibitor and a product of Pseudomonas aeruginosa, revealed that it also attenuated chemotaxis and LPS induced cytokine production. In vivo, N-3-oxo-dodecanoyl-L-homoserine lactone inhibited the passive cutaneous anaphylaxis response in mice.

CONCLUSION

The ability of N-3-oxo-dodecanoyl-L-homoserine lactone to stabilize mast cells may contribute to the pathogenicity of P. aeruginosa but could potentially be exploited therapeutically in allergic disease.

A Role for Human Skin Mast Cells in Dengue Virus Infection and Systemic Spread

Dengue virus (DENV) is a mosquito-borne flavivirus that causes serious global human disease and mortality. Skin immune cells are an important component of initial DENV infection and systemic spread. Here, we show that mast cells are a target of DENV in human skin and that DENV infection of skin mast cells induces degranulation and alters cytokine and growth factor expression profiles. Importantly, to our knowledge, we also demonstrate for the first time that DENV localizes within secretory granules in infected skin mast cells. In addition, DENV within extracellular granules was infectious in vitro and in vivo, trafficking through lymph to draining lymph nodes in mice. We demonstrate an important role for human skin mast cells in DENV infection and identify a novel mechanism for systemic spread of DENV infection from the initial peripheral mosquito injection site.

Activation of human mast cells by retrocyclin and protegrin highlight their immunomodulatory and antimicrobial properties

Preclinical evaluation of Retrocyclins (RC-100, RC-101) and Protegrin-1 (PG-1) antimicrobial peptides (AMPs) is important because of their therapeutic potential against bacterial, fungal and viral infections. Human mast cells (HMCs) play important roles in host defense and wound healing but the abilities of retrocyclins and protegrin-1 to harness these functions have not been investigated. Here, we report that chemically synthesized RC-100 and PG-1 caused calcium mobilization and degranulation in HMCs but these responses were not blocked by an inhibitor of formyl peptide receptor-like 1 (FPRL1), a known receptor for AMPs. However, RC-100 and PG-1 induced degranulation in rat basophilic leukemia (RBL-2H3) cells stably expressing Mas related G protein coupled receptor X2 (MrgX2). Chemical synthesis of these AMPs is prohibitively expensive and post-synthesis modifications (cyclization, disulfide bonds, folding) are inadequate for optimal antimicrobial activity. Indeed, we found that synthetic RC-100, which caused mast cell degranulation via MrgX2, did not display any antimicrobial activity. Green-fluorescent protein (GFP)-tagged RC-101 (analog of RC-100) and GFP-tagged PG-1 purified from transgenic plant chloroplasts killed bacteria and induced mast cell degranulation. Furthermore, GFP-PG1 bound specifically to RBL-2H3 cells expressing MrgX2. These findings suggest that retrocyclins and protegrins activate HMCs independently of FPRL1 but via MrgX2. Harnessing this novel feature of AMPs to activate mast cell's host defense/wound healing properties in addition to their antimicrobial activities expands their clinical potential. Low cost production of AMPs in plants should facilitate their advancement to the clinic overcoming major hurdles in current production systems.

Roles of Mas-related G protein-coupled receptor X2 on mast cell-mediated host defense, pseudoallergic drug reactions, and chronic inflammatory diseases

Mast cells (MCs), which are granulated tissue-resident cells of hematopoietic lineage, contribute to vascular homeostasis, innate/adaptive immunity, and wound healing. However, MCs are best known for their roles in allergic and inflammatory diseases, such as anaphylaxis, food allergy, rhinitis, itch, urticaria, atopic dermatitis, and asthma. In addition to the high-affinity IgE receptor (FcεRI), MCs express numerous G protein-coupled receptors (GPCRs), which are the largest group of membrane receptor proteins and the most common targets of drug therapy. Antimicrobial host defense peptides, neuropeptides, major basic protein, eosinophil peroxidase, and many US Food and Drug Administration-approved peptidergic drugs activate human MCs through a novel GPCR known as Mas-related G protein-coupled receptor X2 (MRGPRX2; formerly known as MrgX2). Unique features of MRGPRX2 that distinguish it from other GPCRs include their presence both on the plasma membrane and intracellular sites and their selective expression in MCs. In this article we review the possible roles of MRGPRX2 on host defense, drug-induced anaphylactoid reactions, neurogenic inflammation, pain, itch, and chronic inflammatory diseases, such as urticaria and asthma. We propose that host defense peptides that kill microbes directly and activate MCs through MRGPRX2 could serve as novel GPCR targets to modulate host defense against microbial infection. Furthermore, mAbs or small-molecule inhibitors of MRGPRX2 could be developed for the treatment of MC-dependent allergic and inflammatory disorders.

Immune Evasion Strategies of Trypanosoma brucei within the Mammalian Host: Progression to Pathogenicity

The diseases caused by African trypanosomes (AT) are of both medical and veterinary importance and have adversely influenced the economic development of sub-Saharan Africa. Moreover, so far not a single field applicable vaccine exists, and chemotherapy is the only strategy available to treat the disease. These strictly extracellular protozoan parasites are confronted with different arms of the host's immune response (cellular as well as humoral) and via an elaborate and efficient (vector)-parasite-host interplay they have evolved efficient immune escape mechanisms to evade/manipulate the entire host immune response. This is of importance, since these parasites need to survive sufficiently long in their mammalian/vector host in order to complete their life cycle/transmission. Here, we will give an overview of the different mechanisms AT (i.e. T. brucei as a model organism) employ, comprising both tsetse fly saliva and parasite-derived components to modulate host innate immune responses thereby sculpturing an environment that allows survival and development within the mammalian host.

Serum concentrations of mast cell tryptase are reduced in heavy drinkers

BACKGROUND

Baseline serum tryptase concentrations are commonly used in clinical practice as a marker of the body's mast cell burden. This study aimed to investigate serum tryptase concentrations in heavy drinkers.

METHODS

Serum tryptase concentrations were determined in 126 heavy drinkers (75% males, median age 47 years) who were admitted to the hospital because of alcohol withdrawal syndrome (n = 60), general symptoms with abnormalities on biochemical tests that indicated acute liver disease (n = 19), complications of advanced liver disease (n = 33), and miscellaneous reasons (n = 14). Results were compared with those of 70 healthy controls (66% males, median age 40 years).

RESULTS

Serum tryptase concentrations were lower in heavy drinkers than in healthy controls (median 2.23 μg/l vs. median 3.25 μg/l, p < 0.001). Ten heavy drinkers (7.9%) had undetectable (<1 μg/l) serum tryptase levels versus none of the healthy controls (p = 0.01). The association of low tryptase levels with heavy drinking was independent of age, gender, and smoking status. Among heavy drinkers, the lowest tryptase concentrations were observed in patients with alcohol withdrawal syndrome and patients with general symptoms with abnormalities on biochemical tests that indicated acute liver disease. Furthermore, serum tryptase concentrations were negatively correlated with markers of acute liver damage or alcohol consumption (serum aspartate aminotransferase and gamma-glutamyl transferase). Atopy (skin prick test positivity) was not associated with serum tryptase concentrations in heavy drinkers.

CONCLUSIONS

Serum concentrations of mast cell tryptase are lower in heavy drinkers than in healthy controls.

Modulation of host defense peptide-mediated human mast cell activation by LPS

Human β-defensin3 (hBD3) and the cathelicidin LL-37 are host defense peptides (HDPs) that directly kill microbes and display immunomodulatory/wound-healing properties via the activation of chemokine, formylpeptide and epidermal growth factor receptors on leukocytes and epithelial cells. A C-terminal 14 amino acid hBD3 peptide with all Cys residues replaced with Ser (CHRG01) and an LL-37 peptide consisting of residues 17-29 (FK-13) display antimicrobial activity but lack immunomodulatory property. Surprisingly, we found that CHRG01 and FK-13 caused Ca(2+) mobilization and degranulation in human mast cells via a novel G protein-coupled receptor known as Mas-related gene-X2 (MrgX2). At local sites of bacterial infection, the negatively charged LPS likely interacts with cationic HDPs to inhibit their activity and thus providing a mechanism for pathogens to escape host defense mechanisms. We found that LPS caused almost complete inhibition of hBD3 and LL-37-induced Ca(2+) mobilization and mast cell degranulation. In contrast, it had no effect on CHRG01 and FK-13-induced mast cell responses. These findings suggest that HDP derivatives that kill microbes, harness mast cell's host defense and wound-healing properties via the activation of MrgX2 but are resistant to inhibition by LPS could be utilized for the treatment of antibiotic-resistant microbial infections.

The Dermatological Manifestations of Postural Tachycardia Syndrome: A Review with Illustrated Cases

Postural tachycardia syndrome (POTS) is a syndrome of excessive tachycardia with orthostatic challenge, and relief of such symptoms with recumbence. There are several proposed subtypes of the syndrome, each with unique pathophysiology. Numerous symptoms such as excessive tachycardia, lightheadedness, blurry vision, weakness, fatigue, palpitations, chest pain, and tremulousness are associated with orthostatic intolerance. Other co-morbid conditions associated with POTS are not clearly attributable to orthostatic intolerance. These include chronic headache, fibromyalgia, functional gastrointestinal or bladder disorders, cognitive impairment, and sleep disturbances. Dermatological manifestations of POTS are also common and wide ranging, from livedo reticularis to Raynaud's phenomenon, from cutaneous flushing to erythromelalgia. Here, we provide three illustrative cases of POTS with dermatological manifestations. We discuss the potential pathophysiology underlying such dermatological manifestations, and how such mechanisms could in turn help guide development of management.

Addressing the Global Burden of Trauma in Major Surgery

Despite a technically perfect procedure, surgical stress can determine the success or failure of an operation. Surgical trauma is often referred to as the "neglected step-child" of global health in terms of patient numbers, mortality, morbidity, and costs. A staggering 234 million major surgeries are performed every year, and depending upon country and institution, up to 4% of patients will die before leaving hospital, up to 15% will have serious post-operative morbidity, and 5-15% will be readmitted within 30 days. These percentages equate to around 1000 deaths and 4000 major complications every hour, and it has been estimated that 50% may be preventable. New frontline drugs are urgently required to make major surgery safer for the patient and more predictable for the surgeon. We review the basic physiology of the stress response from neuroendocrine to genomic systems, and discuss the paucity of clinical data supporting the use of statins, beta-adrenergic blockers and calcium-channel blockers. Since cardiac-related complications are the most common, particularly in the elderly, a key strategy would be to improve ventricular-arterial coupling to safeguard the endothelium and maintain tissue oxygenation. Reduced O2 supply is associated with glycocalyx shedding, decreased endothelial barrier function, fluid leakage, inflammation, and coagulopathy. A healthy endothelium may prevent these "secondary hit" complications, including possibly immunosuppression. Thus, the four pillars of whole body resynchronization during surgical trauma, and targets for new therapies, are: (1) the CNS, (2) the heart, (3) arterial supply and venous return functions, and (4) the endothelium. This is termed the Central-Cardio-Vascular-Endothelium (CCVE) coupling hypothesis. Since similar sterile injury cascades exist in critical illness, accidental trauma, hemorrhage, cardiac arrest, infection and burns, new drugs that improve CCVE coupling may find wide utility in civilian and military medicine.

rPbPga1 from Paracoccidioides brasiliensis Activates Mast Cells and Macrophages via NFkB

Background

The fungus Paracoccidioides brasiliensis is the leading etiological agent of paracoccidioidomycosis (PCM), a systemic granulomatous disease that typically affects the lungs. Cell wall components of P. brasiliensis interact with host cells and influence the pathogenesis of PCM. In yeast, many glycosylphosphatidylinositol (GPI)-anchored proteins are important in the initial contact with the host, mediating host-yeast interactions that culminate with the disease. PbPga1 is a GPI anchored protein located on the surface of the yeast P. brasiliensis that is recognized by sera from PCM patients.

Methodology/Principal Findings

Endogenous PbPga1 was localized to the surface of P. brasiliensis yeast cells in the lungs of infected mice using a polyclonal anti-rPbPga1 antibody. Furthermore, macrophages stained with anti-CD38 were associated with P. brasiliensis containing granulomas. Additionally, rPbPga1 activated the transcription factor NFkB in the macrophage cell line Raw 264.7 Luc cells, containing the luciferase gene downstream of the NFkB promoter. After 24 h of incubation with rPbPga1, alveolar macrophages from BALB/c mice were stimulated to release TNF-α, IL-4 and NO. Mast cells, identified by toluidine blue staining, were also associated with P. brasiliensis containing granulomas. Co-culture of P. Brasiliensis yeast cells with RBL-2H3 mast cells induced morphological changes on the surface of the mast cells. Furthermore, RBL-2H3 mast cells were degranulated by P. brasiliensis yeast cells, but not by rPbPga1, as determined by the release of beta-hexosaminidase. However, RBL-2H3 cells activated by rPbPga1 released the inflammatory interleukin IL-6 and also activated the transcription factor NFkB in GFP-reporter mast cells. The transcription factor NFAT was not activated when the mast cells were incubated with rPbPga1.

Conclusions/Significance

The results indicate that PbPga1 may act as a modulator protein in PCM pathogenesis and serve as a useful target for additional studies on the pathogenesis of P. brasiliensis.

Paracoccidioidomycosis (PCM), one of the most prevalent mycoses in Latin America, is caused by the thermodimorphic fungus Paracoccidioides brasiliensis. P. brasiliensis is thought to infect the host through the respiratory tract. Cell wall components of P. brasiliensis interact with host cells producing granulomas, thus influencing the pathogenesis of PCM. PbPga1 is an O-glycosylated, GPI-anchored protein that is localized on the yeast cell surface and is up-regulated in the pathogenic yeast form. GPI anchored proteins are involved in cell-cell and cell-tissue adhesion and have a key role in the interaction between fungal and host cells. In the present study, the authors show that both macrophages and mast cells are associated with the P.brasiliensis granulomas. Furthermore, recombinant PbPga1 was able to activate both alveolar macrophages and mast cells via the transcription factor NFkB to release inflammatory mediators. The results of this study indicate that the surface antigen, PbPga1, may play an important role in PCM pathogenesis by activating macrophages and mast cells. Additionally, PbPga1 may be a target for new strategies for detecting and treating PCM.