Disease modification in chronic spontaneous urticaria.

Chronic spontaneous urticaria (CSU) is a debilitating, inflammatory skin condition characterized by infiltrating immune cells. Available treatments are limited to improving the signs and symptoms. There is an unmet need to develop therapies that target disease-driving pathways upstream of mast cell activation to inhibit or delay the progression of CSU and associated comorbidities. Here, we aim to define disease modification due to a treatment intervention and criteria that disease-modifying treatments (DMTs) must meet in CSU. We have defined disease modification in CSU as a favorable treatment-induced change in the underlying pathophysiology and, therefore, the disease course, which is clinically beneficial and enduring. A DMT must fulfil the following criteria: (1) prevents or delays the progression of CSU, (2) induces long-term, therapy-free clinical remission, which is the sustained absence of CSU signs and symptoms without the need for treatment, and (3) affects the underlying mechanism of CSU, as demonstrated by an effect on disease-driving signals and/or a biomarker. DMTs in CSU should slow disease progression, achieve long-lasting disease remission, target disease-driving mechanisms, reduce mast cell-activating IgE autoantibodies, target cytokine profile polarization, and normalize the gut microbiome and barrier. Treating CSU at the immune system level could provide valuable alternatives to pharmacotherapy in CSU management. Specific DMTs in CSU are yet to be developed, but some show potential benefits, such as inhibitors of Bruton's Tyrosine Kinase, IL-4 and IL-13. Future therapies could prevent CSU signs and symptoms, achieve long-term clinical benefits after discontinuing treatment, and prevent associated concomitant disorders.

A Novel Method for Total IgE Purification from Human Serum.

For Ab purification, high-affinity chromatography is commonly used. This technique results in high-purity Abs, but it requires highly specific knowledge and equipment. Commercial kits for purification of IgE are not available. Therefore, we established a (to our knowledge) novel method for the purification of total IgE from human serum. Sera from 19 allergic and nonallergic patients were included. After depletion of polyclonal IgG, total serum IgE was captured using anti-human IgE Abs coupled to beads, eluted from the beads, and incubated with protein G-coupled beads to increase the final purity. Purity analysis and Ab detection were performed by Western blot. Total serum IgE and purified IgE concentrations were analyzed using ELISA. To determine their functionality, primary human mast cells were sensitized with purified IgE and activated with anti-IgE or a relevant allergen. CD63+ expression and histamine release were used as readout parameters. Concentrations of purified total IgE corresponded with the levels of total serum IgE. Minor fractions of IgE remained attached to the beads, confirming an effective elution of IgE Abs. Only minimal amounts of IgG were found in the purified IgE fractions, confirming a high purity of IgE. Mast cells sensitized with purified IgE and subsequent activation with anti-IgE Ab or a relevant allergen showed increased expression of CD63+ and increased histamine release. This (to our knowledge) novel method represents a highly effective and widely accessible approach for purification of human serum IgE, which can improve the use of IgE-based in vivo and in vitro models and contribute to allergy research.

Altered Sweat Composition Due to Changes in Tight Junction Expression of Sweat Glands in Cholinergic Urticaria Patients.

In cholinergic urticaria (CholU), small, itchy wheals are induced by exercise or passive warming and reduced sweating has been reported. Despite the described reduced muscarinic receptor expression, sweat duct obstruction, or sweat allergy, the underlying pathomechanisms are not well understood. To gain further insights, we collected skin biopsies before and after pulse-controlled ergometry and sweat after sauna provocation from CholU patients as well as healthy controls. CholU patients displayed partially severely reduced local sweating, yet total sweat volume was unaltered. However, sweat electrolyte composition was altered, with increased K+ concentration in CholU patients. Formalin-fixed, paraffin-embedded biopsies were stained to explore sweat leakage and tight junction protein expression. Dermcidin staining was not found outside the sweat glands. In the secretory coils of sweat glands, the distribution of claudin-3 and -10b as well as occludin was altered, but the zonula occludens-1 location was unchanged. In all, dermcidin and tight junction protein staining suggests an intact barrier with reduced sweat production capability in CholU patients. For future studies, an ex vivo skin model for quantification of sweat secretion was established, in which sweat secretion could be pharmacologically stimulated or blocked. This ex vivo model will be used to further investigate sweat gland function in CholU patients and decipher the underlying pathomechanism(s).

Autoreactive IgE: Pathogenic role and therapeutic target in autoimmune diseases.

Autoimmunity is the break of tolerance to self-antigens that leads to organ-specific or systemic diseases often characterized by the presence of pathogenic autoreactive antibodies (AAb) produced by plasmablast and/or plasma cells. AAb are prevalent in the general population and not systematically associated with clinical symptoms. In contrast, in some individuals, these AAb are pathogenic and drive the development of signs and symptoms of antibody-mediated autoimmune diseases (AbAID). AAb production, isotype profiles, and glycosylations are promoted by pro-inflammatory triggers linked to genetic, environmental, and hormonal parameters. Recent evidence supports a role for pathogenic AAb of the IgE isotype in a number of AbAID. Autoreactive IgE can drive the activation of mast cells, basophils, and other types of FcεRI-bearing cells and may play a role in promoting autoantibody production and other pro-inflammatory pathways. In this review, we discuss the current knowledge on the pathogenicity of autoreactive IgE in AbAID and their status as therapeutic targets. We also highlight unresolved issues including the need for assays that reproducibly quantify IgE AAbs, to validate their diagnostic and prognostic value, and to further study their pathophysiological contributions to AbAID.

A novel approach for studying mast cell-driven disorders: Mast cells derived from induced pluripotent stem cells.

BACKGROUND: Mast cells (MCs) are considered the main effectors in allergic reactions and well known for their contribution to the pathogenesis of various inflammatory diseases, urticaria, and mastocytosis. To study their functions in vitro, human primary MCs are isolated directly from several tissues or differentiated from hematopoietic progenitors. However, these techniques bear several disadvantages and challenges including low proliferation capacity, donor-dependent heterogeneity, and the lack of a continuous cell source. OBJECTIVE: To address this, we developed a novel strategy for the rapid and efficient differentiation of MCs from human-induced pluripotent stem cells (hiPSCs). METHODS: A 4-step protocol for the generation of hiPSC-derived MCs, based on the use of 3 hiPSC lines, was established and validated by comparison with human skin MCs and peripheral hematopoietic stem cell-derived MCs. RESULTS: hiPSC-MCs share phenotypic and functional characteristics of human skin MCs and peripheral hematopoietic stem cell-derived MCs. They display stable expression of the MC-associated receptors CD117, FcεRIα, and Mas-related G protein-coupled receptor X2 and degranulate in response to IgE/anti-IgE and substance P. CONCLUSIONS: This novel hiPSC-based approach provides a sustainable and homogeneous source for a rapid and highly productive generation of phenotypically mature, functional MCs, and its principle allows for the investigation of disease- and patient-specific MC populations.

Mast cells, cortistatin, and its receptor, MRGPRX2, are linked to the pathogenesis of chronic prurigo.

BACKGROUND: Chronic prurigo (CPG) is characterized by intensive itch and interactions among nerves, neuropeptides, and mast cells (MCs). The role of some neuropeptides such as cortistatin (CST) and its receptor, Mas-related G protein-coupled receptor X2 (MRGPRX2), in CPG remains poorly investigated. OBJECTIVES: We evaluated first whether CST activates human skin MCs, and second whether CST and MRGPRX2 are expressed in the skin of CPG patients, and by which cells. METHODS: Skin prick tests and microdialysis with CST were performed in 6 and 1 healthy volunteers, respectively. Degranulation of human skin MCs was assessed using ß-hexosaminidase and histamine release assays. Skin samples from 10 patients with CPG and 10 control subjects were stained for CST, MCs, and MRGPRX2 (protein and mRNA) using immunohistochemistry, immunofluorescence, and/or in situ hybridization. Flow cytometry was used to assess CST in human skin MCs. MRGPRX2 levels were measured in serum by ELISA. RESULTS: CST induced concentration-dependent degranulation of human skin MCs in vivo and ex vivo. Skin lesions of CPG patients exhibited markedly higher numbers of CST-expressing cells, CST-expressing MCs, MRGPRX2-expressing cells, and MRGPRX2 mRNA-expressing cells than nonlesional skin. MCs were the main MRGPRX2 mRNA-expressing cells in the lesions of most CPG patients (70%). Stimulation of human skin MCs with anti-IgE led to a release of CST. The number of MRGPRX2-expressing cells correlated with disease severity (r = 0.649, P = .04). MRGPRX2 serum levels in CPG patients correlated with disease severity (r = 0.704, P = .023) and quality-of-life impairment (r = 0.687, P = .028). CONCLUSIONS: CST and MRGPRX2 may contribute to the pathogenesis of CPG and should be evaluated in further studies as potential biomarkers and novel therapeutic targets.

Chronic urticaria and the pathogenic role of mast cells.

The signs and symptoms of chronic urticaria (CU) are caused by the activation and degranulation of skin mast cells (MCs). Recent studies have added to our understanding of how and why skin MCs are involved and different in CU. Also, novel and relevant mechanisms of MC activation in CU have been identified and characterized. Finally, the use of MC-targeted and MC mediator-specific treatments has helped to better define the role of the skin environment, the contribution of specific MC mediators, and the relevance of MC crosstalk with other cells in the pathogenesis of CU. Here, we review these recent findings and their impact on our understanding of CU, with a focus on chronic spontaneous urticaria (CSU). Also, we highlight open questions, issues of controversy, and unmet needs, and we suggest what studies should be performed moving forward.

Bruton's tyrosine kinase inhibition-An emerging therapeutic strategy in immune-mediated dermatological conditions.

Bruton's tyrosine kinase (BTK), a member of the Tec kinase family, is critically involved in a range of immunological pathways. The clinical application of BTK inhibitors for B-cell malignancies has proven successful, and there is strong rationale for the potential benefits of BTK inhibitors in some autoimmune and allergic conditions, including immune-mediated dermatological diseases. However, the established risk-to-benefit profile of "first-generation" BTK inhibitors cannot be extrapolated to these emerging, non-oncological, indications. "Next-generation" BTK inhibitors such as remibrutinib and fenebrutinib entered clinical development for chronic spontaneous urticaria (CSU); rilzabrutinib and tirabrutinib are being studied as potential treatments for pemphigus. Promising data from early-phase clinical trials in CSU suggest potential for these agents to achieve strong pathway inhibition, which may translate into measurable clinical benefits, as well as other effects such as the disruption of autoantibody production. BTK inhibitors may help to overcome some of the shortcomings of monoclonal antibody treatments for immune-mediated dermatological conditions such as CSU, pemphigus, and systemic lupus erythematosus. In addition, the use of BTK inhibitors may improve understanding of the pathophysiological roles of mast cells, basophils, and B cells in such conditions.

Mas-related G protein-coupled receptor X2 and its activators in dermatologic allergies.

The Mas-related G protein-coupled receptor X2 (MRGPRX2) is a multiligand receptor responding to various exogenous and endogenous stimuli. Being highly expressed on skin mast cells, MRGPRX2 triggers their degranulation and release of proinflammatory mediators, and it promotes multicellular signaling cascades, such as itch induction and transmission in sensory neurons. The expression of MRGPRX2 by skin mast cells and the levels of the MRGPRX2 agonists (eg, substance P, major basic protein, eosinophil peroxidase) are upregulated in the serum and/or skin of patients with inflammatory and pruritic skin diseases, such as chronic spontaneous urticaria or atopic dermatitis. Therefore, MRGPRX2 and its agonists might be potential biomarkers for the progression of cutaneous inflammatory diseases and the response to treatment. In addition, they may represent promising targets for prevention and treatment of signs and symptoms in patients with skin diseases or drug reactions. To assess this possibility, this review explores the role and relevance of MRGPRX2 and its activators in cutaneous inflammatory disorders and chronic pruritus.

A group of cationic amphiphilic drugs activates MRGPRX2 and induces scratching behavior in mice.

BACKGROUND: Mas gene-related G protein-coupled receptors (MRGPRs) are a G protein-coupled receptor family responsive to various exogenous and endogenous agonists, playing a fundamental role in pain and itch sensation. The primate-specific family member MRGPRX2 and its murine orthologue MRGPRB2 are expressed by mast cells mediating IgE-independent signaling and pseudoallergic drug reactions. OBJECTIVES: Our aim was to increase knowledge about the function and regulation of MRGPRX2/MRGPRB2, which is of major importance in prevention of drug hypersensitivity reactions and drug-induced pruritus. METHODS: To identify novel MRGPR (ant)agonists, we screened a library of pharmacologically active compounds by utilizing a high-throughput calcium mobilization assay. The identified hit compounds were analyzed for their pseudoallergic and pruritogenic effects in mice and human. RESULTS: We found a class of commonly used drugs activating MRGPRX2 that, to a large extent, consists of antidepressants, antiallergic drugs, and antipsychotics. Three-dimensional pharmacophore modeling revealed structural similarities of the identified agonists, classifying them as cationic amphiphilic drugs. Mast cell activation was investigated by using the 3 representatively selected antidepressants clomipramine, paroxetine, and desipramine. Indeed, we were able to show a concentration-dependent activation and MRGPRX2-dependent degranulation of the human mast cell line LAD2 (Laboratory of Allergic Diseases-2). Furthermore, clomipramine, paroxetine, and desipramine were able to induce degranulation of human skin and murine peritoneal mast cells. These substances elicited dose-dependent scratching behavior following intradermal injection into C57BL/6 mice but less so in MRGPRB2-mutant mice, as well as wheal-and-flare reactions following intradermal injections in humans. CONCLUSION: Our results contribute to the characterization of structure-activity relationships and functionality of MRGPRX2 ligands and facilitate prediction of adverse reactions such as drug-induced pruritus to prevent severe drug hypersensitivity reactions.

The role of mast cells in autoinflammation.

The concept of autoinflammation was proposed to define a new class of immune disorders categorized by self-directed inflammation that is driven via activation of innate immune pathways. Within innate immunity, inflammasomes serve as intracellular signaling platforms to endogenous danger molecules and pathogens. Their key function is the cleavage of pro-interleukin-1ß (pro-IL-1ß) into its active form to promote inflammation and programmed cell death. A growing number of inflammasome sensors were described, among which NLR family pyrin domain containing 3 (NLRP3) is the best-studied sensor. Besides macrophages, monocytes, and other innate immune cells, mast cells (MCs) were shown to express functional inflammasomes too. Also, MCs are both, a source and target of IL-1ß. Here we review the functional relevance and role of MC inflammasomes and MC-derived IL-1ß in contributing to the inflammation at the skin, joints, and central nervous system in rare monogenic autoinflammatory conditions and also common inflammatory and degenerative diseases.

A mutation in the kringle domain of human factor XII that causes autoinflammation, disturbs zymogen quiescence, and accelerates activation.

Coagulation factor XII (FXII) drives production of the inflammatory peptide bradykinin. Pathological mutations in the F12 gene, which encodes FXII, provoke acute tissue swelling in hereditary angioedema (HAE). Interestingly, a recently identified F12 mutation, causing a W268R substitution, is not associated with HAE. Instead, FXII-W268R carriers experience cold-inducible urticarial rash, arthralgia, fever, and fatigue. Here, we aimed to investigate the molecular characteristics of the FXII-W268R variant. We expressed wild type FXII (FXII-WT), FXII-W268R, and FXII-T309R (which causes HAE), as well as other FXII variants in HEK293 freestyle cells. Using chromogenic substrate assays, immunoblotting, and ELISA, we analyzed expression media, cell lysates, and purified proteins for FXII activation. Recombinant FXII-W268R forms increased amounts of intracellular cleavage products that are also present in expression medium and display enzymatic activity. The active site-incapacitated variant FXII-W268R/S544A reveals that intracellular fragmentation is largely dependent on autoactivation. Purified FXII-W268R is highly sensitive to activation by plasma kallikrein and plasmin, compared with FXII-WT or FXII-T309R. Furthermore, binding studies indicated that the FXII-W268R variant leads to the exposure of a plasminogen-binding site that is cryptic in FXII-WT. In plasma, recombinant FXII-W268R spontaneously triggers high-molecular-weight kininogen cleavage. Our findings suggest that the W268R substitution influences FXII protein conformation and exposure of the activation loop, which is concealed in FXII-WT. This results in intracellular autoactivation and constitutive low-grade secretion of activated FXII. These findings help to explain the chronically increased contact activation in carriers of the FXII-W268R variant.

Flare Size but Not Intensity Reflects Histamine-Induced Itch.

INTRODUCTION: Flare reactions arise due to the release of vasodilators from sensory nerves caused by antidromic transmission of action potentials after the induction of itch. OBJECTIVE: We investigated the link between flare and itch using 3 models of itch. METHODS: Skin provocations with histamine, capsaicin, and cowhage were performed in 31 subjects. Itch was quantified using the visual analog scale. Flare was assessed using laser speckle contrast imaging (LSCI) and digital photography. RESULTS: The duration, intensity, and area under the curve of histamine-induced itch correlated with the area of increased blood flow measured with LSCI (r = 0.545, p = 0.002; r = 0.575, p = 0.001; and r = 0.649, p < 0.001, respectively). Itch and skin blood flow in response to capsaicin or cowhage did not correlate. CONCLUSION: In histamine-induced skin inflammation, itch and increased blood flow are linked. Thus, the area of histamine-induced flare may be used as a surrogate marker for histamine-induced itch.

The complex role of mast cells in fungal infections.

In addition to their critical role in allergic disorders, mast cells (MCs) are well recognized for their protective effector functions during bacteria and parasite infections. This review describes recent advancements of our understanding of the complex role of MCs in fungal infections. Specifically, we outline key features of the contribution of MCs to infections with six fungal pathogens, namely Sporothrix, Paracoccidioides, Aspergillus, Malassezia, Candida and Dermatophytes. Evidence from studies of these pathogens suggests that MCs can function as positive regulators that detect and contain fungi at the site of infection. However, it appears that the inflammation induced by MCs following fungal infections may not always and only be beneficial to the host. MC responses during fungal infections may primarily benefit the pathogen by facilitating its spreading and contributing to a greater severity of fungal infections. This review also highlights key drivers of MCs activation and effector mechanisms that have been identified for the multidimensional function of MCs in fungal diseases and in allergic diseases combined with fungal infection.

TLR4-activated microglia require IFN-γ to induce severe neuronal dysfunction and death in situ.

Microglia (tissue-resident macrophages) represent the main cell type of the innate immune system in the CNS; however, the mechanisms that control the activation of microglia are widely unknown. We systematically explored microglial activation and functional microglia-neuron interactions in organotypic hippocampal slice cultures, i.e., postnatal cortical tissue that lacks adaptive immunity. We applied electrophysiological recordings of local field potential and extracellular K(+) concentration, immunohistochemistry, design-based stereology, morphometry, Sholl analysis, and biochemical analyses. We show that chronic activation with either bacterial lipopolysaccharide through Toll-like receptor 4 (TLR4) or leukocyte cytokine IFN-γ induces reactive phenotypes in microglia associated with morphological changes, population expansion, CD11b and CD68 up-regulation, and proinflammatory cytokine (IL-1ß, TNF-α, IL-6) and nitric oxide (NO) release. Notably, these reactive phenotypes only moderately alter intrinsic neuronal excitability and gamma oscillations (30-100 Hz), which emerge from precise synaptic communication of glutamatergic pyramidal cells and fast-spiking, parvalbumin-positive GABAergic interneurons, in local hippocampal networks. Short-term synaptic plasticity and extracellular potassium homeostasis during neural excitation, also reflecting astrocyte function, are unaffected. In contrast, the coactivation of TLR4 and IFN-γ receptors results in neuronal dysfunction and death, caused mainly by enhanced microglial inducible nitric oxide synthase (iNOS) expression and NO release, because iNOS inhibition is neuroprotective. Thus, activation of TLR4 in microglia in situ requires concomitant IFN-γ receptor signaling from peripheral immune cells, such as T helper type 1 and natural killer cells, to unleash neurotoxicity and inflammation-induced neurodegeneration. Our findings provide crucial mechanistic insight into the complex process of microglia activation, with relevance to several neurologic and psychiatric disorders.

New insights on the signaling and function of the high-affinity receptor for IgE.

Clustering of the high-affinity receptor for immunoglobulin E (FcεRI) through the interaction of receptor-bound immunoglobulin E (IgE) antibodies with their cognate antigen is required to couple IgE antibody production to cellular responses and physiological consequences. IgE-induced responses through FcεRI are well known to defend the host against certain infectious agents and to lead to unwanted allergic responses to normally innocuous substances. However, the cellular and/or physiological response of individuals that produce IgE antibodies may be markedly different and such antibodies (even to the same antigenic epitope) can differ in their antigen-binding affinity. How affinity variation in the interaction of FcεRI-bound IgE antibodies with antigen is interpreted into cellular responses and how the local environment may influence these responses is of interest. In this chapter, we focus on recent advances that begin to unravel how FcεRI distinguishes differences in the affinity of IgE-antigen interactions and how such discrimination along with surrounding environmental stimuli can shape the (patho) physiological response.

Tyrphostin AG126 exerts neuroprotection in CNS inflammation by a dual mechanism.

The putative protein tyrosine kinase (PTK) inhibitor tyrphostin AG126 has proven beneficial in various models of inflammatory disease. Yet molecular targets and cellular mechanisms remained enigmatic. We demonstrate here that AG126 treatment has beneficial effects in experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. AG126 alleviates the clinical symptoms, diminishes encephalitogenic Th17 differentiation, reduces inflammatory CNS infiltration as well as microglia activation and attenuates myelin damage. We show that AG126 directly inhibits Bruton's tyrosine kinase (BTK), a PTK associated with B cell receptor and Toll-like receptor (TLR) signaling. However, BTK inhibition cannot account for the entire activity spectrum. Effects on TLR-induced proinflammatory cytokine expression in microglia involve AG126 hydrolysis and conversion of its dinitrile side chain to malononitrile (MN). Notably, while liberated MN can subsequently mediate critical AG126 features, full protection in EAE still requires delivery of intact AG126. Its anti-inflammatory potential and especially interference with TLR signaling thus rely on a dual mechanism encompassing BTK and a novel MN-sensitive target. Both principles bear great potential for the therapeutic management of disturbed innate and adaptive immune functions.

Correction: Predatory journals: Perception, impact and use of Beall's list by the scientific community-A bibliometric big data study.

[This corrects the article DOI: 10.1371/journal.pone.0287547.].