Murine mast cells secrete a unique profile of cytokines and prostaglandins in response to distinct TLR2 ligands

Role of gut-derived bacterial lipopolysaccharide and peripheral TLR4 in immobilization stress-induced itch aggravation in a mouse model of atopic dermatitis

Psychological stress and intestinal leakage are key factors in atopic dermatitis (AD) recurrence and exacerbation. Here, we demonstrate the mechanism underlying bacterial translocation across intestinal epithelial barrier damaged due to stress and further aggravation of trimellitic anhydride (TMA)-induced itch, which remain unclear, in AD mice. Immobilization (IMO) stress exacerbated scratching bouts and colon histological damage, and increased serum corticosterone and lipopolysaccharide (LPS). Orally administered fluorescein isothiocyanate (FITC)-dextran and surgically injected (into the colon) Cy5.5-conjugated LPS were detected in the serum and skin after IMO stress, respectively. The relative abundance of aerobic or facultative anaerobic bacteria was increased in the colon mucus layer, and Lactobacillus murinus, E. coli, Staphylococcus nepalensis, and several strains of Bacillus sp. were isolated from the spleens and mesenteric lymph nodes. Oral antibiotics or intestinal permeability blockers, such as lubiprostone (Lu), 2,4,6-triaminopyrimidine (TAP) and ML-7, inhibited IMO stress-associated itch; however, it was reinduced through intradermal or i.p. injection of LPS without IMO stress. I.p. injection of TAK-242 (resatorvid), a TLR4 inhibitor, abrogated IMO stress-associated itch, which was also confirmed in TLR4-KO mice. IMO stress alone did not cause itch in naïve mice. IMO stress-induced itch aggravation in TMA-treated AD mice might be attributed to the translocation of gut-derived bacterial cells and LPS, which activates peripheral TLR4 signaling.

IL-10 Modulates the Expression and Activation of Pattern Recognition Receptors in Mast Cells

Mast cells (MCs) are involved in several immune-related responses, including those in bacterial infections, autoimmune diseases, inflammatory bowel diseases, and cancer, among others. MCs identify microorganisms by pattern recognition receptors (PRRs), activating a secretory response. Interleukin (IL)-10 has been described as an important modulator of MC responses; however, its role in PRR-mediated activation of MC is not fully understood. We analyzed the activation of TLR2, TLR4, TLR7 and Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in mucosal-like MCs (MLMCs) and peritoneum-derived cultured MCs (PCMCs) from IL-10^-/- and wild-type (WT) mice. IL-10^-/- mice showed a reduced expression of TLR4 and NOD2 at week 6 and TLR7 at week 20 in MLMC. In MLMC and PCMC, TLR2 activation induced a reduced secretion of IL-6 and TNFα in IL-10^-/- MCs. TLR4- and TLR7-mediated secretion of IL-6 and TNFα was not detected in PCMCs. Finally, no cytokine release was induced by NOD2 ligand, and responses to TLR2 and TLR4 were lower in MCs at 20 weeks. These findings indicate that PRR activation in MCs depends on the phenotype, ligand, age, and IL-10.

Focus on mast cells in the tumor microenvironment: Current knowledge and future directions

Mast cells (MCs) are crucial cells participating in both innate and adaptive immune processes that play important roles in protecting human health and in the pathophysiology of various diseases, such as allergies, cardiovascular diseases, and autoimmune diseases. In the context of tumors, MCs are a non-negligible population of immune cells in the tumor microenvironment (TME). In most tumor types, MCs accumulate in both the tumor tissue and the surrounding tissue. MCs interact with multiple components of the TME, affecting TME remodeling and the tumor cell fate. However, controversy persists regarding whether MCs contribute to tumor progression or trigger an anti-tumor immune response. This review focuses on the context of the TME to explore the specific properties and functions of MCs and discusses the crosstalk that occurs between MCs and other components of the TME, which affect tumor angiogenesis and lymphangiogenesis, invasion and metastasis, and tumor immunity through different mechanisms. We also anticipate the potential role of MCs in cancer immunotherapy, which might expand upon the success achieved with existing cancer therapies.

Fetal Tissue-Derived Mast Cells (MC) as Experimental Surrogate for In Vivo Connective Tissue MC

Bone-marrow-derived mast cells are matured from bone marrow cells in medium containing 20% fetal calf serum (FCS), interleukin (IL)-3 and stem-cell factor (SCF) and are used as in vitro models to study mast cells (MC) and their role in health and disease. In vivo, however, BM-derived hematopoietic stem cells account for only a fraction of MC; the majority of MC in vivo are and remain tissue resident. In this study we established a side-by-side culture with BMMC, fetal skin MC (FSMC) or fetal liver MC (FLMC) for comparative studies to identify the best surrogates for mature connective tissue MC (CTMC). All three MC types showed comparable morphology by histology and MC phenotype by flow cytometry. Heterogeneity was detected in the transcriptome with the most differentially expressed genes in FSMC compared to BMMC being Hdc and Tpsb2. Expression of ST2 was highly expressed in BMMC and FSMC and reduced in FLMC, diminishing their secretion of type 2 cytokines. Higher granule content, stronger response to FcεRI activation and significantly higher release of histamine from FSMC compared to FLMC and BMMC indicated differences in MC development in vitro dependent on the tissue of origin. Thus, tissues of origin imprint MC precursor cells to acquire distinct phenotypes and signatures despite identical culture conditions. Fetal-derived MC resemble mature CTMC, with FSMC being the most developed.

Pathophysiological Role of TLR4 in Chronic Relapsing Itch Induced by Subcutaneous Capsaicin Injection in Neonatal Rats

Despite the high prevalence of chronic dermatitis and the accompanied intractable itch, therapeutics that specifically target itching have low efficacy. Increasing evidence suggests that TLRs contribute to immune activation and neural sensitization; however, their roles in chronic itch remain elusive. Here, we show that the RBL-2H3 mast cell line expresses TLR4 and that treatment with a TLR4 antagonist opposes the LPS dependent increase in mRNA levels of Th2 and innate cytokines. The pathological role of TLR4 activation in itching was studied in neonate rats that developed chronic itch due to neuronal damage after receiving subcutaneous capsaicin injections. Treatment with a TLR4 antagonist protected these rats with chronic itch against scratching behavior and chronic dermatitis. TLR4 antagonist treatment also restored the density of cutaneous nerve fibers and inhibited the histopathological changes that are associated with mast cell activation after capsaicin injection. Additionally, the expression of IL-1β, IL-4, IL-5, IL-10, and IL-13 mRNA in the lesional skin decreased after TLR4 antagonist treatment. Based on these data, we propose that inhibiting TLR4 alleviated itch in a rat model of chronic relapsing itch, and the reduction in the itch was associated with TLR4 signaling in mast cells and nerve fibers.

Do Mast Cells Contribute to the Antifungal Host Defense?

The fungal kingdom includes a group of microorganisms that are widely distributed in the environment, and therefore the exposure to them is almost constant. Furthermore, fungal components of the microbiome, i.e., mycobiome, could serve as a reservoir of potentially opportunistic pathogens. Despite close encounters with fungi, defense mechanisms that develop during fungal infections remain unexplored. The strategic location of mast cells (MCs) close to the external environment places them among the first cells to encounter pathogens along with the other innate immune cells. MCs are directly involved in the host defense through the ability to destroy pathogens or indirectly by activating other immune cells. Most available data present MCs’ involvement in antibacterial, antiviral, or antiparasitic defense mechanisms. However, less is known about their contribution in defense mechanisms against fungi. MCs may support immune responses to fungi or their specific molecules through initiated degranulation, synthesis and release of cytokines, chemokines, mediators, and generation of reactive oxygen species (ROS), as well as immune cells’ recruitment, phagocytosis, or provision of extracellular DNA traps. This review summarizes current knowledge on host defense mechanisms against fungi and MCs’ involvement in those processes. It also describes the effects of fungi or fungus-derived constituents on MCs’ activity.

IgE-activated mast cells enhance TLR4-mediated antigen-specific CD4+ T cell responses

Mast cells are potent mediators of allergy and asthma, yet their role in regulating adaptive immunity remains ambiguous. On the surface of mast cells, the crosslinking of IgE bound to FcεRI by a specific antigen recognized by that IgE triggers the release of immune mediators such as histamine and cytokines capable of activating other immune cells; however, little is known about the mast cell contribution to the induction of endogenous, antigen-specific CD4⁺ T cells. Here we examined the effects of specific mast cell activation in vivo on the initiation of an antigen-specific CD4⁺ T cell response. While CD4⁺ T cells were not enhanced by FcεRI stimulation alone, their activation was synergistically enhanced when FcεRI activation was combined with TLR4 stimulation. This enhanced activation was dependent on global TLR4 stimulation but appeared to be less dependent on mast cell expressed TLR4. This study provides important new evidence to support the role of mast cells as mediators of the antigen-specific adaptive immune response.

New Pathways for the Skin's Stress Response: The Cholinergic Neuropeptide SLURP-1 Can Activate Mast Cells and Alter Cytokine Production in Mice

Background: The alpha7 nicotinic acetylcholine receptor (Chrna7) plays an essential anti-inflammatory role in immune homeostasis and was recently found on mast cells (MC). Psychosocial stress can trigger MC hyperactivation and increases pro-inflammatory cytokines in target tissues such as the skin. If the cholinergic system (CS) and Chrna7 ligands play a role in these cascades is largely unknown.

Objective: To elucidate the role of the CS in the response to psychosocial stress using a mouse-model for stress-triggered cutaneous inflammatory circuits.

Methods: Key CS markers (ACh, Ch, SLURP-1, SLURP-2, Lynx1, Chrm3, Chrna7, Chrna9, ChAT, VAChT, Oct3, AChE, and BChE) in skin and its MC (sMC), MC activation, immune parameters (TNFα, IL1β, IL10, TGFβ, HIF1α, and STAT3) and oxidative stress were analyzed in skin from 24 h noise-stressed mice and in cultured MC (cMC) from C57BL/6 or Chrna7-Knockout mice.

Results: First, Chrna7 and SLURP-1 mRNA were exclusively upregulated in stressed skin. Second, histomorphometry located Chrna7 and SLURP-1 in nerves and sMC and demonstrated upregulated contacts and increased Chrna7+ sMC in stressed skin, while 5 ng/mL SLURP-1 degranulated cMC. Third, IL1β+ sMC were high in stressed skin, and while SLURP-1 alone had no significant effect on cMC cytokines, it upregulated IL1β in cMC from Chrna7-KO and in IL1β-treated wildtype cMC. In addition, HIF1α+ sMC were high in stressed skin and Chrna7-agonist AR-R 17779 induced ROS in cMC while SLURP-1 upregulated TNFα and IL1β in cMC when HIF1α was blocked.

Conclusions: These data infer that the CS plays a role in the regulation of stress-sensitive inflammatory responses but may have a surprising pro-inflammatory effect in healthy skin, driving IL1β expression if SLURP-1 is involved.

Toll-Like Receptor Agonists as Adjuvants for Allergen Immunotherapy

Toll-like receptors (TLRs) are essential components of innate immunity and provide defensive inflammatory responses to invading pathogens. Located within the plasma membranes of cells and also intracellular endosomes, TLRs can detect a range of pathogen associated molecular patterns from bacteria, viruses and fungi. TLR activation on dendritic cells can propagate to an adaptive immune response, making them attractive targets for the development of both prophylactic and therapeutic vaccines. In contrast to conventional adjuvants such as aluminium salts, TLR agonists have a clear immunomodulatory profile that favours anti-allergic T lymphocyte responses. Consequently, the potential use of TLRs as adjuvants in Allergen Immunotherapy (AIT) for allergic rhinitis and asthma remains of great interest. Allergic Rhinitis is a Th2-driven, IgE-mediated disease that occurs in atopic individuals in response to exposure to otherwise harmless aeroallergens such as pollens, house dust mite and animal dander. AIT is indicated in subjects with allergic rhinitis whose symptoms are inadequately controlled by antihistamines and nasal corticosteroids. Unlike anti-allergic drugs, AIT is disease-modifying and may induce long-term disease remission through mechanisms involving upregulation of IgG and IgG4 antibodies, induction of regulatory T and B cells, and immune deviation in favour of Th1 responses that are maintained after treatment discontinuation. This process takes up to three years however, highlighting an unmet need for a more efficacious therapy with faster onset. Agonists targeting different TLRs to treat allergy are at different stages of development. Synthetic TLR4, and TLR9 agonists have progressed to clinical trials, while TLR2, TLR5 and TLR7 agonists been shown to have potent anti-allergic effects in human in vitro experiments and in vivo in animal studies. The anti-allergic properties of TLRs are broadly characterised by a combination of enhanced Th1 deviation, regulatory responses, and induction of blocking antibodies. While promising, a durable effect in larger clinical trials is yet to be observed and further long-term studies and comparative trials with conventional AIT are required before TLR adjuvants can be considered for inclusion in AIT. Here we critically evaluate experimental and clinical studies investigating TLRs and discuss their potential role in the future of AIT.

Signal Transduction Pathways Activated by Innate Immunity in Mast Cells: Translating Sensing of Changes into Specific Responses

Mast cells (MCs) constitute an essential cell lineage that participates in innate and adaptive immune responses and whose phenotype and function are influenced by tissue-specific conditions. Their mechanisms of activation in type I hypersensitivity reactions have been the subject of multiple studies, but the signaling pathways behind their activation by innate immunity stimuli are not so well described. Here, we review the recent evidence regarding the main molecular elements and signaling pathways connecting the innate immune receptors and hypoxic microenvironment to cytokine synthesis and the secretion of soluble or exosome-contained mediators in this cell type. When known, the positive and negative control mechanisms of those pathways are presented, together with their possible implications for the understanding of mast cell-driven chronic inflammation. Finally, we discuss the relevance of the knowledge about signaling in this cell type in the recognition of MCs as central elements on innate immunity, whose remarkable plasticity converts them in sensors of micro-environmental discontinuities and controllers of tissue homeostasis.

Analysis of Mrgprb2 Receptor-Evoked Ca 2+ Signaling in Bone Marrow Derived (BMMC) and Peritoneal (PMC) Mast Cells of TRPC-Deficient Mice

Mast cells are a heterogeneous group of immune cells. The simplest and commonly accepted classification divides them in two groups according to their protease content. We have compared the action of diverse secretagogues on bone marrow derived (BMMC) and peritoneal (PMC) mast cells which represent classical models of mucosal and connective tissue type mast cells in mice. Whereas, antigen stimulation of the FcεRI receptors was similarly effective in triggering elevations of free intracellular Ca²⁺ concentration ([Ca²⁺]_i) in both BMMC and PMC, robust [Ca²⁺]_i rise following Endothelin-1 stimulation was observed only in a fraction of BMMC. Leukotriene C4 activating cysteinyl leukotriene type I receptors failed to evoke [Ca²⁺]_i rise in either mast cell model. Stimulation of the recently identified target of many small-molecule drugs associated with systemic pseudo-allergic reactions, Mrgprb2, with compound 48/80, a mast cell activator with unknown receptor studied for many years, triggered Ca²⁺ oscillations in BMMC and robust [Ca²⁺]_i rise in PMCs similarly to that evoked by FcεRI stimulation. [Ca²⁺]_i rise in PMC could also be evoked by other Mrgprb2 agonists such as Tubocurarine, LL-37, and Substance P. The extent of [Ca²⁺]_i rise correlated with mast cell degranulation. Expression analysis of TRPC channels as potential candidates mediating agonist evoked Ca²⁺ entry revealed the presence of transcripts of all members of the TRPC subfamily of TRP channels in PMCs. The amplitude and AUC of compound 48/80-evoked [Ca²⁺]_i rise was reduced by ~20% in PMC from Trpc1/4/6^−/− mice compared to Trpc1/4^−/− littermatched control mice, whereas FcεRI-evoked [Ca²⁺]_i rise was unaltered. Whole-cell patch clamp recordings showed that the reduction in compound 48/80-evoked [Ca²⁺]_i rise in Trpc1/4/6^−/− PMC was accompanied by a reduced amplitude of Compound 48/80-induced cation currents which exhibited typical features of TRPC currents. Together, this study demonstrates that PMC are an appropriate mast cell model to study mechanisms of Mrgprb2 receptor-mediated mast cell activation, and it reveals that TRPC channels contribute at least partially to Mrgprb2-mediated mast cellactivation but not following FcεRI stimulation. However, the channels conducting most of the Ca²⁺ entry in mast cells triggered by Mrgprb2 receptor stimulation remains to be identified.

Imidacloprid exposure suppresses cytokine production and neutrophil infiltration in TLR2-dependent activation of RBL-2H3 cells and skin inflammation of BALB/c mice

Imidacloprid suppressed TNF-α and IL-6 production and neutrophil infiltration, without altering mast cell degranulation.

Mast Cells as a Double-Edged Sword in Immunity: Their Function in Health and Disease. First of Two Parts

Mast cells (MCs) have recently been re-interpreted in the context of the immune scenario in the sense that their pro-allergic role is no longer exclusive. In fact, MCs even in steady state conditions maintain homeostatic functions, producing mediators and intensively cross-talking with other immune cells. Here, emphasis will be placed on the array of receptors expressed by MCs and the variety of cytokines they produce. Then, the bulk of data discussed will provide readers with a wealth of information on the dual ability of MCs not only to defend but also to offend the host. This double attitude of MCs relies on many variables, such as their subsets, tissues of residency and type of stimuli ranging from microbes to allergens and food antigens. Finally, the relationship between MCs with basophils and eosinophils will be discussed.

Size- and cell type-dependent cellular uptake, cytotoxicity and in vivo distribution of gold nanoparticles

Background

Gold nanoparticles (AuNPs) have shown great promise in biomedical applications. However, the interaction of AuNPs with biological systems, its underlying mechanisms and influencing factors need to be further elucidated.

Purpose

The aim of this study was to systematically investigate the effects of particle size on the uptake and cytotoxicity of AuNPs in normal cells and cancer cells as well as their biological distribution in vivo.

Results

Our data demonstrated that the uptake of AuNPs increased in HepG2 cancer cells but decreased in L02 normal cells, with the increase of particle size (5-50 nm). In both cancer cells and normal cells, small (5 nm) AuNPs exhibited greater cytotoxicity than large ones (20 and 50 nm). Interestingly, 5 nm AuNPs induced both apoptosis and necrosis in HepG2 cells through the production of reactive oxygen species (ROS) and the activation of pro-caspase3, whereas it mainly induced necrosis in L02 cells through the overexpression of TLR2 and the release of IL-6 and IL-1a cytokines. Among them, 50 nm AuNPs showed the longest blood circulation and highest distribution in liver and spleen, and the treatment of 5 nm AuNPs  but not 20 nm and 50 nm AuNPs resulted in the increase of neutrophils and slight hepatotoxicity in mice.

Conclusion

Our results indicate that the particle size of AuNPs and target cell type are critical determinants of cellular uptake, cytotoxicity and underlying mechanisms, and biological distribution in vivo, which deserves careful consideration in the future biomedical applications.

Toll-like receptor-induced cytokines as immunotherapeutic targets in cancers and autoimmune diseases

Immune cells of the myeloid and lymphoid lineages express Toll-like receptors (TLRs) to recognize pathogenic components or cellular debris and activate the immune system through the secretion of cytokines. Cytokines are signaling molecules that are structurally and functionally distinct from one another, although their secretion profiles and signaling cascades often overlap. This situation gives rise to pleiotropic cell-to-cell communication pathways essential for protection from infections as well as cancers. Nonetheless, deregulated signaling can have detrimental effects on the host, in the form of inflammatory or autoimmune diseases. Because cytokines are associated with numerous autoimmune and cancerous conditions, therapeutic strategies to modulate these molecules or their biological responses have been immensely beneficial over the years. There are still challenges in the regulation of cytokine function in patients, even in those who take approved biological therapeutics. In this review, our purpose is to discuss the differential expression patterns of TLR-regulated cytokines and their cell type specificity that is associated with cancers and immune-system-related diseases. In addition, we highlight key structural features and molecular recognition of cytokines by receptors; these data have facilitated the development and approval of several biologics for the treatment of autoimmune diseases and cancers.

Small-Molecule Host-Defense Peptide Mimetic Antibacterial and Antifungal Agents Activate Human and Mouse Mast Cells via Mas-Related GPCRs

Host-defense peptides (HDPs) have an important therapeutic potential against microbial infections but their metabolic instability and cellular cytotoxicity have limited their utility. To overcome these limitations, we utilized five small-molecule, nonpeptide HDP mimetics (smHDPMs) and tested their effects on cytotoxicity, antimicrobial activity, and mast cell (MC) degranulation. None of the smHDPMs displayed cytotoxicity against mouse 3T3 fibroblasts or human transformed liver HepG2 cells. However, one compound had both antifungal and antibacterial activity. Surprisingly, all five compounds induced degranulation in a human MC line, LAD2, and this response was substantially reduced in Mas-related G protein-coupled receptor (GPCR)-X2 (MRGPRX2)-silenced cells. Furthermore, all five compounds induced degranulation in RBL-2H3 cells expressing MRGPRX2 but this response was abolished in cells expressing naturally occurring loss-of-function missense variants G165E (rs141744602) and D184H (rs372988289). Mrgprb2 is the likely mouse ortholog of human MRGPRX2, which is expressed in connective tissue MCs (CTMCs) such as cutaneous and peritoneal MCs (PMCs). All five smHDPMs induced degranulation in wild-type PMCs but not in cells derived from Mrgprb2⁻/⁻ mice. These findings suggest that smHDPMs could serve as novel targets for the treatment of drug-resistant fungal and bacterial infections because of their ability to harness CTMCs’ host defense functions.

Changing the threshold-Signals and mechanisms of mast cell priming

Mast cells play a key role in allergy and other inflammatory diseases involving engagement of multivalent antigen with IgE bound to high-affinity IgE receptors (FcεRIs). Aggregation of FcεRIs on mast cells initiates a cascade of signaling events that eventually lead to degranulation, secretion of leukotrienes and prostaglandins, and cytokine and chemokine production contributing to the inflammatory response. Exposure to pro-inflammatory cytokines, chemokines, bacterial and viral products, as well as some other biological products and drugs, induces mast cell transition from the basal state into a primed one, which leads to enhanced response to IgE-antigen complexes. Mast cell priming changes the threshold for antigen-mediated activation by various mechanisms, depending on the priming agent used, which alone usually do not induce mast cell degranulation. In this review, we describe the priming processes induced in mast cells by various cytokines (stem cell factor, interleukins-4, -6 and -33), chemokines, other agents acting through G protein-coupled receptors (adenosine, prostaglandin E₂ , sphingosine-1-phosphate, and β-2-adrenergic receptor agonists), toll-like receptors, and various drugs affecting the cytoskeleton. We will review the current knowledge about the molecular mechanisms behind priming of mast cells leading to degranulation and cytokine production and discuss the biological effects of mast cell priming induced by several cytokines.

The development of methods for primary mast cells in vitro and ex vivo: An historical review

Mast cells (MCs) are tissue-based stationary effector cells that form the immune system's first-line defense against various challenges. They are developed from the bone marrow-derived progenitors to complete their differentiation and maturation in the tissues where they eventually establish residence. MCs have been implicated in many diseases, such as allergy, parasitic infection, and neoplastic disorders. Immortalized MC lines, such as RBL-2H3, HMC-1, and LAD-2, are useful for investigating the biological functions of MC only to some extents due to the restriction of degranulation evaluation, in vivo injection and other factors. Over the past few decades, technologies for acquiring primarily MCs have been continually optimized, and novel protocols have been proposed. However, no relevant publications have analyzed and summarized these techniques. In this review, the classical approaches for extracting MCs are generalized, and new methods with potential values are introduced. We also evaluate the advantages and applicability of diverse MC models. Since MCs exhibit substantial plasticity and functional diversity due to different origins, it is both necessary and urgent to select a reliable and suitable source of MCs for a particular study.

Toll-like receptors in immunity and inflammatory diseases: Past, present, and future

The immune system is a very diverse system of the host that evolved during evolution to cope with various pathogens present in the vicinity of environmental surroundings inhabited by multicellular organisms ranging from achordates to chordates (including humans). For example, cells of immune system express various pattern recognition receptors (PRRs) that detect danger via recognizing specific pathogen-associated molecular patterns (PAMPs) and mount a specific immune response. Toll-like receptors (TLRs) are one of these PRRs expressed by various immune cells. However, they were first discovered in the Drosophila melanogaster (common fruit fly) as genes/proteins important in embryonic development and dorso-ventral body patterning/polarity. Till date, 13 different types of TLRs (TLR1-TLR13) have been discovered and described in mammals since the first discovery of TLR4 in humans in late 1997. This discovery of TLR4 in humans revolutionized the field of innate immunity and thus the immunology and host-pathogen interaction. Since then TLRs are found to be expressed on various immune cells and have been targeted for therapeutic drug development for various infectious and inflammatory diseases including cancer. Even, Single nucleotide polymorphisms (SNPs) among various TLR genes have been identified among the different human population and their association with susceptibility/resistance to certain infections and other inflammatory diseases. Thus, in the present review the current and future importance of TLRs in immunity, their pattern of expression among various immune cells along with TLR based therapeutic approach is reviewed.

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TLRs are first described PRRs that revolutionized the biology of host-pathogen interaction and immune response

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The discovery of different TLRs in humans proved milestone in the field of innate immunity and inflammation

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The pattern of expression of all the TLRs expressed by human immune cells

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An association of various TLR SNPs with different inflammatory diseases

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Currently available drugs or vaccines based on TLRs and their future in drug targeting along with the role in reproduction, and regeneration

Immune Characterization of Bone Marrow-Derived Models of Mucosal and Connective Tissue Mast Cells

Purpose

It is well appreciated that mast cells (MCs) demonstrate tissue-specific imprinting, with different biochemical and functional properties between connective tissue MCs (CTMCs) and mucosal MCs (MMCs). Although in vitro systems have been developed to model these different subsets, there has been limited investigation into the functional characteristics of the 2 major MC subsets. Here, we report the immunologic characterization of 2 MCs subsets developed in vitro from bone marrow progenitors modeling MMCs and CTMCs.

Methods

We grew bone marrow for 4 weeks in the presence of transforming growth factor (TGF)-β, interleukin (IL)-9, IL-3, and stem cell factor (SCF) to generate MMCs, and IL-4, IL-3, and SCF to generate CTMCs.

Results

CTMCs and MMCs differed in growth rate and protease content, but their immune characteristics were remarkably similar. Both subsets responded to immunoglobulin E (IgE)-mediated activation with signaling, degranulation, and inflammatory cytokine release, although differences between subsets were noted in IL-10. CTMCs and MMCs showed a similar toll-like receptor (TLR) expression profile, dominated by expression of TLR4, TLR6, or both subsets were responsive to lipopolysaccharide (LPS), but not poly(I:C). CTMCs and MMCs express receptors for IL-33 and thymic stromal lymphopoietin (TSLP), and respond to these cytokines alone or with modified activation in response to IgE cross-linking.

Conclusions

The results of this paper show the immunologic characterization of bone marrow-derived MMCs and CTMCs, providing useful protocols for in vitro modeling of MC subsets.

Mast Cells Are Critical Regulators of Bone Fracture-Induced Inflammation and Osteoclast Formation and Activity

Mast cells, important sensor and effector cells of the immune system, may influence bone metabolism as their number is increased in osteoporotic patients. They are also present during bone fracture healing with currently unknown functions. Using a novel c-Kit-independent mouse model of mast cell deficiency, we demonstrated that mast cells did not affect physiological bone turnover. However, they triggered local and systemic inflammation after fracture by inducing release of inflammatory mediators and the recruitment of innate immune cells. In later healing stages, mast cells accumulated and regulated osteoclast activity to remodel the bony fracture callus. Furthermore, they were essential to induce osteoclast formation after ovariectomy. Additional in vitro studies revealed that they promote osteoclastogenesis via granular mediators, mainly histamine. In conclusion, mast cells are redundant in physiologic bone turnover but exert crucial functions after challenging the system, implicating mast cells as a potential target for treating inflammatory bone disorders. © 2017 American Society for Bone and Mineral Research.

Lipopolysaccharide suppresses IgE-mast cell-mediated reactions

BACKGROUND

Clinical and experimental analyses have identified a central role for IgE/FcεRI/mast cells in promoting IgE-mediated anaphylaxis. Recent data from human studies suggest that bacterial infections can alter susceptibility to anaphylaxis.

OBJECTIVE

We examined the effect of LPS exposure on the induction of IgE-mast cell (MC) mediated reactions in mice.

METHODS

C57BL/6 WT, tlr4-/- and IL10-/- mice were exposed to LPS, and serum cytokines (TNF and IL-10) were measured. Mice were subsequently treated with anti-IgE, and the symptoms of passive IgE-mediated anaphylaxis, MC activation, Ca2+ -mobilization and the expression of FcεRI on peritoneal MCs were quantitated.

RESULTS

We show that LPS exposure of C57BL/6 WT mice constraints IgE-MC-mediated reactions. LPS-induced suppression of IgE-MC-mediated responses was TLR-4-dependent and associated with increased systemic IL-10 levels, decreased surface expression of FcεRI on MCs and loss of sensitivity to IgE activation. Notably, LPS-induced desensitization of MCs was short term with MC sensitivity to IgE reconstituted within 48 hours, which was associated with recapitulation of FcεRI expression on the MCs. Mechanistic analyses revealed a requirement for IL-10 in LPS-mediated decrease in MC FcεRI surface expression.

CONCLUSIONS & CLINICAL RELEVANCE

Collectively, these studies suggest that LPS-induced IL-10 promotes the down-regulation of MC surface FcεRI expression and leads to desensitization of mice to IgE-mediated reactions. These studies indicate that targeting of the LPS-TLR-4-IL-10 pathway may be used as a therapeutic approach to prevent adverse IgE-mediated reactions.

Interleukin-17-positive mast cells influence outcomes from BCG for patients with CIS: Data from a comprehensive characterisation of the immune microenvironment of urothelial bladder cancer

The tumour immune microenvironment is considered to influence cancer behaviour and outcome. Using a panel of markers for innate and adaptive immune cells we set out to characterise and understand the bladder tumour microenvironment of 114 patients from a prospective multicentre cohort of newly-diagnosed bladder cancer patients, followed-up for 4.33±1.71 years. We found IL-17-positive cells were significantly increased in primary and concomitant carcinoma in situ (CIS), p<0.0001, a highly malignant lesion which is the most significant single risk factor for disease progression. Further characterisation of the tumour immunophenotype identified IL-17+ cells as predominantly mast cells rather than T-cells, in contrast to most other tumour types. Expression of the IL-17-receptor in bladder tumours, and functional effects and gene expression changes induced by IL-17 in bladder tumour cells in vitro suggest a role in tumour behaviour. Finally, we assessed the effects of IL-17 in the context of patient outcome, following intravesical BCG immunotherapy which is the standard of care; higher numbers of IL-17+ cells were associated with improved event-free survival (p = 0.0449, HR 0.2918, 95% CI 0.08762–0.9721) in patients with primary and concomitant CIS (n = 41), we propose a model of IL-17+ Mast cells mechanism of action. Thus, in the context of bladder CIS, IL-17+ mast cells predict favourable outcome following BCG immunotherapy indicative of a novel mechanism of BCG immunotherapy in UBC and could form the basis of a stratified approach to treatment.

Putative mechanisms of kiwifruit on maintenance of normal gastrointestinal function

Kiwifruits are recognized as providing relief from constipation and symptoms of constipation-predominant irritable bowel syndrome (IBS-C). However, the underlying mechanisms, specifically in regards to gastrointestinal transit time and motility, are still not completely understood. This review provides an overview on the physiological and pathophysiological processes underlying constipation and IBS-C, the composition of kiwifruit, and recent advances in the research of kiwifruit and abdominal comfort. In addition, gaps in the research are highlighted and scientific studies of other foods with known effects on the gastrointestinal tract are consulted to find likely mechanisms of action. While the effects of kiwifruit fiber are well documented, observed increases in gastrointestinal motility caused by kiwifruit are not fully characterized. There are a number of identified mechanisms that may be activated by kiwifruit compounds, such as the induction of motility via protease-activated signaling, modulation of microflora, changes in colonic methane status, bile flux, or mediation of inflammatory processes.

Expression of surface and intracellular Toll-like receptors by mature mast cells

Nowadays, more and more data indicate that mast cells play an important role in host defense against pathogens. That is why it is essential to understand the expression of Toll-like receptors (TLRs) by mast cells, because these molecules play particularly significant role in initiation host defense against microorganisms as they recognize both wide range of microbial pathogen-associated molecular patterns (PAMPs) and various endogenous damage-associated molecular patterns (DAMPs) released in response to infection. Therefore, we examined the constitutive expression of both surface and endosomal TLRs in rat native fully mature tissue mast cells. By the use of qRT-PCR we found that these cells express mRNAs for TLR2, TLR3, TLR4, TLR5, TLR7, and TLR9. The expression of TLR3, TLR4, TLR5, TLR7, and TLR9 transcripts were low and comparable and only the expression of TLR2 transcript was significant. By the use of flow cytometry technique, we clearly documented that mast cells express TLR2, TLR4, and TLR5 on cell surface, while TLR3, TLR7, and TLR9 proteins are located both on the cell membrane and intracellularly. The highest expression was observed for TLR5 and the lowest for surface TLR7. These observations undoubtedly indicate that mature tissue mast cells have a broad set of TLR molecules, thus can recognize and bind bacterial, viral, and fungal PAMPs as well as various endogenous molecules generated in response to infection.

Targeting mast cells: Uncovering prolific therapeutic role in myriad diseases

The mast cells are integral part of immune system and they have pleiotropic physiological functions in our body. Any type of abnormal stimuli causes the mast cells receptors to spur the otherwise innocuous mast cells to degranulate and release inflammatory mediators like histamine, cytokines, chemokines and prostaglandins. These mediators are involved in various diseases like allergy, asthma, mastocytosis, cardiovascular disorders, etc. Herein, we describe the receptors involved in degranulation of mast cells and are broadly divided into four categories: G-protein coupled receptors, ligand gated ion channels, immunoreceptors and pattern recognition receptors. Although, activation of pattern recognition receptors do not cause mast cell degranulation, but result in cytokines production. Degranulation itself is a complex process involving cascade of events like membrane fusion events and various proteins like VAMP, Syntaxins, DOCK5, SNAP-23, MARCKS. Furthermore, we described these mast cell receptors antagonists or agonists useful in treatment of myriad diseases. Like, omalizumab anti-IgE antibody is highly effective in asthma, allergic disorders treatment and recently mechanistic insight of IgE uncovered; matrix mettaloprotease inhibitor marimistat is under phase III trial for inflammation, muscular dystrophy diseases; ZPL-389 (H4 receptor antagonist) is in Phase 2a Clinical Trial for atopic dermatitis and psoriasis; JNJ3851868 an oral H4 receptor antagonist is in phase II clinical development for asthma, rheumatoid arthritis. Therefore, research is still in inchoate stage to uncover mast cell biology, mast cell receptors, their therapeutic role in myriad diseases.

Live Staphylococcus aureus Induces Expression and Release of Vascular Endothelial Growth Factor in Terminally Differentiated Mouse Mast Cells

Mast cells have been shown to express vascular endothelial growth factor (VEGF), thereby implicating mast cells in pro-angiogenic processes. However, the mechanism of VEGF induction in mast cells and the possible expression of VEGF in fully mature mast cells have not been extensively studied. Here, we report that terminally differentiated peritoneal cell-derived mast cells can be induced to express VEGF in response to challenge with Staphylococcus aureus, thus identifying a mast cell–bacteria axis as a novel mechanism leading to VEGF release. Whereas live bacteria produced a robust upregulation of VEGF in mast cells, heat-inactivated bacteria failed to do so, and bacteria-conditioned media did not induce VEGF expression. The induction of VEGF was not critically dependent on direct cell–cell contact between bacteria and mast cells. Hence, these findings suggest that VEGF can be induced by soluble factors released during the co-culture conditions. Neither of a panel of bacterial cell-wall products known to activate toll-like receptor (TLR) signaling promoted VEGF expression in mast cells. In agreement with the latter, VEGF induction occurred independently of Myd88, an adaptor molecule that mediates the downstream events following TLR engagement. The VEGF induction was insensitive to nuclear factor of activated T-cells inhibition but was partly dependent on the nuclear factor kappa light-chain enhancer of activated B cells signaling pathway. Together, these findings identify bacterial challenge as a novel mechanism by which VEGF is induced in mast cells.

Potential effector and immunoregulatory functions of mast cells in mucosal immunity

Mast cells (MCs) are cells of hematopoietic origin that normally reside in mucosal tissues, often near epithelial cells, glands, smooth muscle cells, and nerves. Best known for their contributions to pathology during IgE-associated disorders such as food allergy, asthma, and anaphylaxis, MCs are also thought to mediate IgE-associated effector functions during certain parasite infections. However, various MC populations also can be activated to express functional programs--such as secreting preformed and/or newly synthesized biologically active products--in response to encounters with products derived from diverse pathogens, other host cells (including leukocytes and structural cells), damaged tissue, or the activation of the complement or coagulation systems, as well as by signals derived from the external environment (including animal toxins, plant products, and physical agents). In this review, we will discuss evidence suggesting that MCs can perform diverse effector and immunoregulatory roles that contribute to homeostasis or pathology in mucosal tissues.

Human mast cell activation with viruses and pathogen products

Mast cells have been demonstrated to have critical roles in host defense against a number of types of pathogens. In order to better understand how mast cells participate in effective immune responses, it is important to evaluate their ability to respond directly to pathogens and their products. In the current chapter we provide a methodology to evaluate human mast cell responses to a number of bacterial and fungal pathogen products and to mammalian reovirus as a model of acute viral infection. These methods should provide key information necessary to aid in the effective design of experiments to evaluate human mast cell responses to a number of other organisms. However, it is important to carefully consider the biology of the mast cell subsets and pathogens involved and the optimal experimental conditions necessary to evaluate mediators of interest.

Asthma and Mast Cell Biology

Asthma is a chronic inflammatory disease of the lung and its pathophysiology is initiated by mast cell activation in response to the antigen binding to IgE receptor as well as by TH2 cell activation. Mast cells are well established effector cells in asthma where they exacerbate the inflammatory response, playing a key role in early phase, degranulating and increasing histamine. Human mast cells possess high affinity IgE receptors and are ubiquitous but predominantly localized in mucosal and connective tissue and are distributed along blood vessels. There are two types of mast cells: connective tissue mast cells (TC) and mucosal mast cells (T mast cells). TC mast cells contain more heparin, whereas T mast cells contain more chondroitin sulfate. In asthma, mast cell activation can trigger degranulation, releasing secretory granule complex and preformed mediators, such as histamine and proteases, along with the synthesis of leukotrines and prostaglandins, and induction of cytokines and chemokines. Leukotrine inhibitors and omalizumab, which inhibits IgE, both relieve the asthma exacerbation when administered to humans and permit to reduce the use of other drugs. The release of cytokines by mast cells, such as TNF-alpha, IL-1, IL-6 and IL-33, participate in the pathogenesis of asthma. Stress worsens asthma, and this effect is also mediated by mast cell activation through the release of cytokines. Administration of IL-33 in experimental animals provokes pathological effects in the mucosal tissues and augments antibody IgE and IgA in blood vessels. Here, we report the impact of mast cell biology in asthma pathogenesis.

Inhibiting mast cell degranulation by HO-1 affects dendritic cell maturation in vitro

OBJECTIVE AND DESIGN

Mast cell (MC) degranulation can break peripheral immune tolerance. However, its mechanism remains unclear. Our goal was to study the stabilization of MC membranes by heme oxygenase-1 (HO-1) in order to influence dendritic cell (DC) function.

MATERIAL

Mast cells and dendritic cells were prepared from 8-week-old to 10-week-old C57BL/6 mice; spleen mononuclear cells (SMCs) were prepared from 8-week-old to 10-week-old C57BL/6 and Balb/c mice.

TREATMENT

Mast cells were pretreated with PBS, DMSO, Hemin (50 μl/ml), and Znpp (50 μl/ml) for 8 h.

METHOD

Real-time PCR and western-blot tested the HO-1 of MC mRNA and protein. The co-stimulatory molecules of DCs (CD80, CD86, CD40) were measured by flow cytometry, and levels of TNF-α, IL-6, and IFN-γ were measured by ELISA. We set up a one-way mixed lymphocyte reaction (MLR) model to test the proliferation of SMCs after MC/DC interaction. *P < 0.05 (t test) was taken as the level of statistical significance.

RESULT

MCs pretreated with hemin induced HO-1 mRNA and protein expression, then interacted with DCs; expression of the co-stimulatory molecules was attenuated. The TNF-α, IL-6, and IFN-γ levels in the co-culture system were decreased. These DCs couldn't stimulate the proliferation of SMCs.

CONCLUSION

Inhibiting MC degranulation by HO-1 restrained DC maturation and attenuated the proliferation of SMCs.

Targeting mast cells in inflammatory diseases

Although mast cells have long been known to play a critical role in anaphylaxis and other allergic diseases, they also participate in some innate immune responses and may even have some protective functions. Data from the study of mast cell-deficient mice have facilitated our understanding of some of the molecular mechanisms driving mast cell functions during both innate and adaptive immune responses. This review presents an overview of the biology of mast cells and their potential involvement in various inflammatory diseases. We then discuss some of the current pharmacological approaches used to target mast cells and their products in several diseases associated with mast cell activation.

The immune complex CTA1-DD/IgG adjuvant specifically targets connective tissue mast cells through FcγRIIIA and augments anti-HPV immunity after nasal immunization

We have previously reported that CTA1-DD/IgG immune complexes augment antibody responses in a mast cell-dependent manner following intranasal (IN) immunizations. However, from a safety perspective, mast cell activation could preclude clinical use. Therefore, we have extended these studies and demonstrate that CTA1-DD/IgG immune complexes administered IN did not trigger an anaphylactic reaction. Importantly, CTA1-DD/IgE immune complexes did not activate mast cells. Interestingly, only connective tissue, but not mucosal, mast cells could be activated by CTA1-DD/IgG immune complexes. This effect was mediated by FcγRIIIA, only expressed on connective tissue mast cells, and found in the nasal submucosa. FcγRIIIA-deficient mice had compromised responses to immunization adjuvanted by CTA1-DD/IgG. Proof-of-concept studies revealed that IN immunized mice with human papillomavirus (HPV) type 16 L1 virus-like particles (VLP) and CTA1-DD/IgG immune complexes demonstrated strong and sustained specific antibody titers in serum and vaginal secretions. From a mast cell perspective, CTA1-DD/IgG immune complexes appear to be safe and effective mucosal adjuvants.

Mast cells: multitalented facilitators of protection against bacterial pathogens

Mast cells are crucial effector cells evoking immune responses against bacterial pathogens. The positioning of mast cells at the host-environment interface, and the multitude of pathogen-recognition receptors and preformed mediator granules make these cells potentially the earliest to respond to an invading pathogen. In this review, the authors summarize the receptors used by mast cells to recognize invading bacteria and discuss the function of immune mediators released by mast cells in control of bacterial infection. The interaction of mast cells with other immune cells, including macrophages, dendritic cells and T cells, to induce protective immunity is highlighted. The authors also discuss mast cell-based vaccine strategies and the potential application in control of bacterial disease.

Possible involvement of TLRs and hemichannels in stress-induced CNS dysfunction via mastocytes, and glia activation

In the central nervous system (CNS), mastocytes and glial cells (microglia, astrocytes and oligodendrocytes) function as sensors of neuroinflammatory conditions, responding to stress triggers or becoming sensitized to subsequent proinflammatory challenges. The corticotropin-releasing hormone and glucocorticoids are critical players in stress-induced mastocyte degranulation and potentiation of glial inflammatory responses, respectively. Mastocytes and glial cells express different toll-like receptor (TLR) family members, and their activation via proinflammatory molecules can increase the expression of connexin hemichannels and pannexin channels in glial cells. These membrane pores are oligohexamers of the corresponding protein subunits located in the cell surface. They allow ATP release and Ca²⁺ influx, which are two important elements of inflammation. Consequently, activated microglia and astrocytes release ATP and glutamate, affecting myelinization, neuronal development, and survival. Binding of ligands to TLRs induces a cascade of intracellular events leading to activation of several transcription factors that regulate the expression of many genes involved in inflammation. During pregnancy, the previous responses promoted by viral infections and other proinflammatory conditions are common and might predispose the offspring to develop psychiatric disorders and neurological diseases. Such disorders could eventually be potentiated by stress and might be part of the etiopathogenesis of CNS dysfunctions including autism spectrum disorders and schizophrenia.

Mannose receptor and macrophage galactose-type lectin are involved in Bordetella pertussis mast cell interaction

Mast cells are crucial in the development of immunity against Bordetella pertussis, and the function of TLRs in this process has been investigated. Here, the interaction between mast cells and B. pertussis with an emphasis on the role of CLRs is examined. In this study, two CLRs, MGL and MR, were detected for the first time on the surface of mast cells. The involvement of MR and MGL in the stimulation of mast cells by heat-inactivated BP was investigated by the use of blocking antibodies and specific carbohydrate ligands. The cell wall LOS of BP was also isolated to explore its role in this interaction. Mast cells stimulated with heat-inactivated BP or BP LOS induced TNF-α, IL-6, and IFN-γ secretion, which was suppressed by blocking MR or MGL. Inhibition of CLRs signaling during BP stimulation affected the ability of mast cells to promote cytokine secretion in T cells but had no effect on the cell-surface expression of ICAM1. Blocking MR or MGL suppressed BP-induced NF-κB expression but not ERK phosphorylation. Syk was involved in the CLR-mediated activation of mast cells by BP. Bacterial recognition by immune cells has been predominantly attributed to TLRs; in this study, the novel role of CLRs in the BP-mast cell interaction is highlighted.

Mast cell and macrophage chemokines CXCL1/CXCL2 control the early stage of neutrophil recruitment during tissue inflammation

Neutrophil recruitment is an important early step in controlling tissue infections or injury. Here, we report that this influx depends on both tissue-resident mast cells and macrophages. Mice with mast cell deficiency recruit reduced numbers of neutrophils in the first few hours of intraperitoneal lipopolysaccharide (LPS) stimulation. Conversely, in mice with clodronate-ablated macrophages, neutrophils extravasate, but have limited ability to reach the peritoneal fluid. Tissue macrophages synthesize neutrophil chemoattractants CXCL1/CXCL2 (CXC chemokine ligands 1/2) in response to LPS. Mast cells also produce these chemokines of which a proportion are preformed in granules. Release of the granules and new CXCL1/CXCL2 synthesis is Toll-like receptor 4-dependent. Both in vivo studies with blocking monoclonal antibodies and in vitro chemotaxis experiments show the neutrophil response to mast cells and macrophages to be CXCL1/CXCL2-dependent. The data are in keeping with the model that mast cells, optimally positioned in close proximity to the vasculature, initiate an early phase of neutrophil recruitment by releasing the chemoattractants CXCL1/CXCL2. Having arrived within the stimulated tissue, neutrophils penetrate further in a macrophage-dependent manner. Therefore, we demonstrate a positive role for mast cells in tissue inflammation and define how this comes about with contribution from a second tissue cell, the macrophage.

Testosterone exerts selective anti-inflammatory effects on human skin mast cells in a cell subset dependent manner

Androgens are known to exert anti-inflammatory effects but their impact on mast cells (MCs) remains to be determined. Here, we show that MCs isolated from human foreskin samples (male) and those from breast skin (female) express the androgen receptor, albeit with a 10-fold difference between the subsets. While fundamental MC properties (FcεRI, c-Kit, tryptase; histamine release upon FcεRI cross-linking) were unaffected or slightly reduced (chymase) by testosterone, the hormone had a more profound impact on the production of cytokines, with IL-6 being a target (reduction by 53%). Interestingly, this effect was limited to breast skin MCs (15 of 16 donors displayed this phenomenon), but was not reproduced by foreskin MCs. Collectively, effector functions of human skin MCs are modulated by androgens in a gene-selective and MC subset-specific fashion. Possibly, MCs from women are more susceptible to testosterone. We also demonstrate that MC IL-6 production is highly variable among individuals.

The role of peroxisome proliferator-activated receptor γ in immune responses to enteroaggregative Escherichia coli infection

Background

Enteroaggregative Escherichia coli (EAEC) is recognized as an emerging cause of persistent diarrhea and enteric disease worldwide. Mucosal immunity towards EAEC infections is incompletely understood due in part to the lack of appropriate animal models. This study presents a new mouse model and investigates the role of peroxisome proliferator-activated receptor gamma (PPARγ) in the modulation of host responses to EAEC in nourished and malnourished mice.

Methods/Principal Findings

Wild-type and T cell-specific PPARγ null C57BL/6 mice were fed protein-deficient diets at weaning and challenged with 5×10⁹cfu EAEC strain JM221 to measure colonic gene expression and immune responses to EAEC. Antigen-specific responses to E. coli antigens were measured in nourished and malnourished mice following infection and demonstrated the immunosuppressive effects of malnutrition at the cellular level. At the molecular level, both pharmacological blockade and deletion of PPARγ in T cells resulted in upregulation of TGF-β, IL-6, IL-17 and anti-microbial peptides, enhanced Th17 responses, fewer colonic lesions, faster clearance of EAEC, and improved recovery. The beneficial effects of PPARγ blockade on weight loss and EAEC clearance were abrogated by neutralizing IL-17 in vivo.

Conclusions

Our studies provide in vivo evidence supporting the beneficial role of mucosal innate and effector T cell responses on EAEC burden and suggest pharmacological blockade of PPARγ as a novel therapeutic intervention for EAEC infection.

Targeting IL-17 and TH17 cells in chronic inflammation

The key role of interleukin-17 (IL-17) and T helper 17 (T(H)17) cells in tissue inflammation, autoimmunity and host defence led to the experimental targeting of these molecules in mouse models of diseases as well as in clinical settings. Moreover, the demonstration that IL-17 and T(H)17 cells contribute to local and systemic aspects of disease pathogenesis, as well as the finding that the IL-17-T(H)17 cell pathway is regulated by IL-23, prompted the identification of inhibitors. These inhibitors include biotechnology products that target IL-23 as well as the leading member of the IL-17 family, IL-17A, and one of its receptors, IL-17 receptor A. Several clinical trials of these inhibitors are underway, and positive results have been obtained in psoriasis, rheumatoid arthritis and ankylosing spondylitis. This Review focuses on the current knowledge of the IL-17-T(H)17 cell pathway to better understand the positive as well as potential negative consequences of targeting them.

Mast cells in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis

Mast cells (MCs) are best known as key immune players in immunoglobulin E (IgE)-dependent allergic reactions. In recent years, several lines of evidence have suggested that MCs might play an important role in several pathological conditions, including autoimmune disorders such as multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model for MS. Since their first description in MS plaques in the late 1800s, much effort has been put into elucidating the contribution of MCs to the development of central nervous system (CNS) autoimmunity. Mouse models of MC-deficiency have provided a valuable experimental tool for dissecting MC involvement in MS and EAE. However, to date there is still major controversy concerning the function of MCs in these diseases. Indeed, although MCs have been classically proposed as having a detrimental and pro-inflammatory role, recent literature has questioned and resized the contribution of MCs to the pathology of MS and EAE. In this review, we will present the main evidence obtained in MS and EAE on this topic, and discuss the critical and controversial aspects of such evidence.

Toll-like receptors expression and NF-κB activation in peritoneal leukocytes in morphine-mediated impairment of zymosan-induced peritonitis in swiss mice

Zymosan-induced peritonitis represents a well-described model of acute inflammation. The binding of zymosan with its specific Toll-like receptors (TLR2 and TLR6) on leukocytes initiates activation and phosphorylation of nuclear factor (NF)-κB, which leads to accumulation of NF-κB p65 subunits in the nucleus and subsequently up-regulation of the proinflammatory cytokine genes expression. Intraperitoneal co-administration of zymosan and morphine significantly inhibits peritonitis in several strains of mice by decreasing the influx of exudatory cells; however, mechanisms of this action still remain unclear. We aimed to verify the effects of morphine on NF-κB and TLRs expression at messenger RNA and protein levels during the early stages of zymosan-induced peritonitis. Peritonitis was induced by a single injection of zymosan A or zymosan supplemented with morphine in Swiss mice. At selected time points, after stimulation, peritoneal leukocytes were harvested. The TLRs and NF-κB expression was assessed by real-time PCR and flow cytometry. In comparison with the mice injected with zymosan only, morphine co-injection significantly decreased the expression of phospho-NF-κB and TLR2 in all investigated immunocompetent cells as well as up-regulated the levels of nitric oxide (NO) in peritoneal fluid. Moreover, supplementation of zymosan with morphine altered the TLR, NF-κB and some proinflammatory cytokines (keratinocyte-derived chemokine, tumor necrosis factor-α) gene expression during ongoing inflammation. We may postulate that after morphine stimulation peritoneal leukocytes recognize less effectively zymosan antigens because of impaired TLRs expression. The lower TLR expression attenuates TLR-mediated signal transduction, which prevents NF-κB activation. Additionally, during zymosan-induced peritonitis, morphine may modulate the NF-κB expression, at least partially, by an up-regulated release of NO, as suggested by others.