Upregulated expression of substance P in basophils of the patients with chronic spontaneous urticaria: induction of histamine release and basophil accumulation by substance P

Navigating the blurred path of mixed neuroimmune signaling

Evolution has created complex mechanisms to sense environmental danger and protect tissues, with the nervous and immune systems playing pivotal roles. These systems work together, coordinating local and systemic reflexes to restore homeostasis in response to tissue injury and infection. By sharing receptors and ligands, they influence the pathogenesis of various diseases. Recently, a less-explored aspect of neuroimmune communication has emerged: the release of neuropeptides from immune cells and cytokines/chemokines from sensory neurons. This article reviews evidence of this unique neuroimmune interplay and its impact on the development of allergy, inflammation, itch, and pain. We highlight the effects of this neuroimmune signaling on vital processes such as host defense, tissue repair, and inflammation resolution, providing avenues for exploration of the underlying mechanisms and therapeutic potential of this signaling.

Basophils in pruritic skin diseases

Basophils are rare cells in the peripheral blood which have the capability to infiltrate into the skin. Invasion of basophils has been detected in pruritic skin diseases, including atopic dermatitis, bullous pemphigoid, chronic spontaneous urticaria and contact dermatitis. In the skin, basophils are important players of the inflammatory immune response, as they release Th2 cytokines, including interleukin (IL)-4 and IL-13, subsequently inducing the early activation of T-cells. Further, basophils release a multitude of mediators, such as histamine and IL-31, which both play an important role in the initiation of the pruritic response via activation of sensory nerves. Chronic pruritus significantly affects the quality of life and the working capability of patients, though its mechanisms are not fully elucidated yet. Since basophils and neurons share many receptors and channels, bidirectional interaction mechanisms, which drive the sensation of itch, are highlighted in this review.

Expression of CCR8 and CCX-CKR on Basophils in Chronic Urticaria Is Amplified by IgE-Mediated Activation

Recruitment to the local tissue and alerted phenotype are the hallmarks of basophils in chronic urticaria (CU). Chemokine receptors such as chemokine (C-C motif) receptor 4 (CCR4) or CCR8 have been studied in skin diseases, e.g., atopic dermatitis, but not in CU. In this study, we aimed to define CU's basophil homing potential and receptor profile and the effect of Omalizumab treatment on these. Unstimulated and activated (anti-IgE, fMLP, C5a, and Substance P) whole blood basophils from 11 Omalizumab-treated CU patients and 10 healthy subjects were investigated with flow cytometry. Unstimulated basophils in CU showed higher expression of the skin-associated (CCR8) and scavenger (CCX-CKR) receptors and lower expression of the lung-associated (CCR3) receptor in contrast to healthy ones. IgE-mediated activation increased the percentage of CCR8 and CCX-CKR in CU compared to healthy group and elevated the expression of the lung-associated chemokine receptor, XCR1, in all groups. A trend of augmented expression of the coagulation cascade (CD87) and fMLP (FPR1) receptors was seen on basophils in CU, while a tendency of reduced expression was seen for itch (IL-31RA) and immunotolerance (CD109) receptors. fMLP and C5a increased the expression of CCR4, CCR8, CCX-CKR, and CD87 and decreased CCR2 and CCR3, though no changes between the groups were found. In conclusion, CU basophils exhibit skin-homing potential amplified by IgE-mediated stimulation.

Neuro-Immuno-Psychological Aspects of Chronic Urticaria

Urticaria is a condition characterized by the development of itchy wheals (hives), angioedema, or both. The pathophysiology of chronic spontaneous urticaria (CSU) is still poorly understood. It is suggested that there is no dominant and independent mechanism of CSU; however, there are different immunological and non-immunological abnormalities that act simultaneously or/and follow each other resulting in clinical symptoms. The latest hypothesis points out that mast cells (MCs) to be activated via autoantibodies in autoallergic or autoimmune mechanism mediators released from degranulated MCs are responsible for the vasoactive and neurospecific effect in CSU. According to many clinical observations, it is suggested that psychological stress can be both a triggering factor in the onset of CSU and a modulating one in the course of the disease and therapy effectiveness. Of importance, the mechanistic background of the psychological stress response in the skin has not yet been fully elucidated. However, of note, a variety of inflammatory mediators, neuropeptides, and neurotransmitters facilitate this phenomenon. This review presents recent findings on the neuro-immuno-psychological aspects of CSU, highlighting an emerging role of neuro-immune interactions. It also points out the usefulness of psychological tools employment for the baseline diagnosis of perceived stress level and the presence of its symptoms. Furthermore, it proposes the implementation of non-invasive interventions to reduce psychological stress and anxiety. A bio-psycho-social approach including psychological support and patient education seems to be as important as traditional pharmacotherapy for CSU. It facilitates the effective control of active disease and a prolonged remission time in this disease.

Chronic pruritus: from pathophysiology to drug design

Pruritus, the most common symptom in dermatology, is an innate response capable of protecting skin against irritants. Nonetheless, when it lasts more than six weeks it is assumed to be a chronic pathology having a negative impact on people's lives. Chronic pruritus (CP) can occur in common and rare skin diseases, having a high prevalence in global population. The existing therapies are unable to counteract CP or are associated with adverse effects, so the development of effective treatments is a pressing issue. The pathophysiological mechanisms underlying CP are not yet completely dissected but, based on current knowledge, involve a wide range of receptors, namely neurokinin 1 receptor (NK1R), Janus kinase (JAK), and transient receptor potential (TRP) ion channels, especially transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1). This review will address the relevance of these molecular targets for the treatment of CP and molecules capable of modulating these receptors that have already been studied clinically or have the potential to possibly alleviate this pathology. According to scientific and clinical literature, there is an increase in the expression of these molecular targets in the lesioned skin of patients experiencing CP when compared with non-lesioned skin, highlighting their importance for the development of potential efficacious drugs through the design of antagonists/inhibitors.

Inflammation and Organ Injury the Role of Substance P and Its Receptors

Tightly controlled inflammation is an indispensable mechanism in the maintenance of cellular and organismal homeostasis in living organisms. However, aberrant inflammation is detrimental and has been suggested as a key contributor to organ injury with different etiologies. Substance P (SP) is a neuropeptide with a robust effect on inflammation. The proinflammatory effects of SP are achieved by activating its functional receptors, namely the neurokinin 1 receptor (NK1R) receptor and mas-related G protein-coupled receptors X member 2 (MRGPRX2) and its murine homolog MRGPRB2. Upon activation, the receptors further signal to several cellular signaling pathways involved in the onset, development, and progression of inflammation. Therefore, excessive SP-NK1R or SP-MRGPRX2/B2 signals have been implicated in the pathogenesis of inflammation-associated organ injury. In this review, we summarize our current knowledge of SP and its receptors and the emerging roles of the SP-NK1R system and the SP-MRGPRX2/B2 system in inflammation and injury in multiple organs resulting from different pathologies. We also briefly discuss the prospect of developing a therapeutic strategy for inflammatory organ injury by disrupting the proinflammatory actions of SP via pharmacological intervention.

Control of myeloid cell functions by nociceptors

The immune system has evolved to protect the host from infectious agents, parasites, and tumor growth, and to ensure the maintenance of homeostasis. Similarly, the primary function of the somatosensory branch of the peripheral nervous system is to collect and interpret sensory information about the environment, allowing the organism to react to or avoid situations that could otherwise have deleterious effects. Consequently, a teleological argument can be made that it is of advantage for the two systems to cooperate and form an “integrated defense system” that benefits from the unique strengths of both subsystems. Indeed, nociceptors, sensory neurons that detect noxious stimuli and elicit the sensation of pain or itch, exhibit potent immunomodulatory capabilities. Depending on the context and the cellular identity of their communication partners, nociceptors can play both pro- or anti-inflammatory roles, promote tissue repair or aggravate inflammatory damage, improve resistance to pathogens or impair their clearance. In light of such variability, it is not surprising that the full extent of interactions between nociceptors and the immune system remains to be established. Nonetheless, the field of peripheral neuroimmunology is advancing at a rapid pace, and general rules that appear to govern the outcomes of such neuroimmune interactions are beginning to emerge. Thus, in this review, we summarize our current understanding of the interaction between nociceptors and, specifically, the myeloid cells of the innate immune system, while pointing out some of the outstanding questions and unresolved controversies in the field. We focus on such interactions within the densely innervated barrier tissues, which can serve as points of entry for infectious agents and, where known, highlight the molecular mechanisms underlying these interactions.

Molecular Mechanisms of Neurogenic Inflammation of the Skin

The skin, including the hypodermis, is the largest body organ and is in constant contact with the environment. Neurogenic inflammation is the result of the activity of nerve endings and mediators (neuropeptides secreted by nerve endings in the development of the inflammatory reaction in the skin), as well as interactions with other cells such as keratinocytes, Langerhans cells, endothelial cells and mast cells. The activation of TRPV-ion channels results in an increase in calcitonin gene-related peptide (CGRP) and substance P, induces the release of other pro-inflammatory mediators and contributes to the maintenance of cutaneous neurogenic inflammation (CNI) in diseases such as psoriasis, atopic dermatitis, prurigo and rosacea. Immune cells present in the skin (mononuclear cells, dendritic cells and mast cells) also express TRPV1, and their activation directly affects their function. The activation of TRPV1 channels mediates communication between sensory nerve endings and skin immune cells, increasing the release of inflammatory mediators (cytokines and neuropeptides). Understanding the molecular mechanisms underlying the generation, activation and modulation of neuropeptide and neurotransmitter receptors in cutaneous cells can aid in the development of effective treatments for inflammatory skin disorders.

Neural Regulation of Innate Immunity in Inflammatory Skin Diseases

As the largest barrier organ of the body, the skin is highly innervated by peripheral sensory neurons. The major function of these sensory neurons is to transmit sensations of temperature, pain, and itch to elicit protective responses. Inflammatory skin diseases are triggered by the aberrant activation of immune responses. Recently, increasing evidence has shown that the skin peripheral nervous system also acts as a regulator of immune responses, particularly innate immunity, in various skin inflammatory processes. Meanwhile, immune cells in the skin can express receptors that respond to neuropeptides/neurotransmitters, leading to crosstalk between the immune system and nervous system. Herein, we highlight recent advances of such bidirectional neuroimmune interactions in certain inflammatory skin conditions.

Pruritogens in pemphigoid diseases: Possible therapeutic targets for a burdensome symptom

Pruritus is a hallmark feature in pemphigoid diseases, where it can be severe and greatly impact the quality of life of affected patients. Despite being a key symptom, the exact pathophysiological mechanisms involved in pruritus in pemphigoid are yet to be fully elucidated and effective therapies addressing them are limited. This review summarizes the present understanding of pruritus specific to pemphigoid diseases, especially the pruritogens that induce it, and the therapeutic options that have been explored so far. The majority of the available evidence is on bullous pemphigoid and epidermolysis bullosa acquisita. Histamine derived from basophils correlates with pruritus severity, with omalizumab demonstrating promising efficacy in pruritus for bullous pemphigoid. IL-4/-13 contribute to itch in bullous pemphigoid with dupilumab being evaluated in clinical trials. Other pruritogens of interest include substance P, tryptase, and thymic stromal lymphopoetin, with therapies targeting them requiring further investigation. Scratching behaviors contribute directly to blister formation through various mechanisms, such as pathological autoantibody recruitment, T helper cell type 1 polarization, and exposure of intracellular autoantigens. Treatments addressing these pathways may contribute to decreasing disease severity. Additional studies are needed to fully characterize how pruritus is regulated in pemphigoid diseases, to help pave the way to develop novel and effective therapeutics that will not only address pruritic symptoms but also decrease disease severity.

Upregulated expression of substance P and NK1R in blood monocytes and B cells of patients with allergic rhinitis and asthma

Increased expression of substance P (SP) and neurokinin-1 receptor (NK1R) has been noticed in patients with allergic rhinitis (AR) and allergic asthma (AA). However, little is known of the expression of SP and NK1R in monocytes and B cells of AR and AA. In the present study, the expression levels of SP and NK1R were determined by flow cytometry and mouse AR and AA models. The results showed that both percentages of SP+ monocytes and SP+ B cells, and mean fluorescence intensity (MFI) of SP in monocytes were elevated in the blood of AA and AR combined with AA (ARA) patients. Similarly, the percentages of NK1R+ monocytes were elevated in the blood of AR, AA, and ARA patients. Allergens Artemisia sieversiana wild allergen extract (ASWE), house dust mite extract (HDME), and Platanus pollen allergen extract (PPE) increased the expression density of SP molecules (determined by MFI) in an individual monocyte of AR patients. HDME and PPE appeared to enhance SP and NK1R expression in the B cells of ARA and AR patients. In the mouse AR and AA models, the percentages of NK1R+ monocytes and B cells were elevated in blood following OVA (ovalbumin) sensitization and challenge. Knocking out the FcεRI molecule completely abolished the OVA-induced upregulation of expression of NK1R in monocytes and B cells of AA mice. In conclusion, upregulated expressions of SP and NK1R may contribute to the pathogenesis of airway allergy.

Further Understanding of Neuro-Immune Interactions in Allergy: Implications in Pathophysiology and Role in Disease Progression

The complicated interaction between the central and the autonomic (sympathetic, parasympathetic, and enteric) nervous systems on the one hand and the immune system and its components, on the other hand, seems to substantially contribute to allergy pathophysiology, uncovering an under-recognized association that could have diagnostic and therapeutic potentials. Neurons connect directly with and regulate the function of many immune cells, including mast cells, the cells that have a leading role in allergic disorders. Proinflammatory mediators such as cytokines, neurotrophins, chemokines, and neuropeptides are released by immune cells, which stimulate sensory neurons. The release of neurotransmitters and neuropeptides caused by the activation of these neurons directly impacts the functional activity of immune cells and vice versa, playing a decisive role in this communication. Successful application of Pavlovian conditioning in allergic disorders supports the existence of a psychoneuroimmunological interplay in classical allergic hypersensitivity reactions. Activation of neuronal homeostatic reflexes, like sneezing in allergic rhinitis, coughing in allergic asthma, and vomiting in food allergy, offers additional evidence of a neuroimmunological interaction that aims to maintain homeostasis. Dysregulation of this interaction may cause overstimulation of the immune system that will produce profound symptoms and exaggerated hemodynamic responses that will lead to severe allergic pathophysiological events, including anaphylaxis. In this article, we have systematically reviewed and discussed the evidence regarding the role of the neuro-immune interactions in common allergic clinical modalities like allergic rhinitis, chronic rhinosinusitis, allergic asthma, food allergy, atopic dermatitis, and urticaria. It is essential to understand unknown – to most of the immunology and allergy experts – neurological networks that not only physiologically cooperate with the immune system to regulate homeostasis but also pathogenetically interact with more or less known immunological pathways, contribute to what is known as neuroimmunological inflammation, and shift homeostasis to instability and disease clinical expression. This understanding will provide recognition of new allergic phenotypes/endotypes and directions to focus on specialized treatments, as the era of personalized patient-centered medicine, is hastening apace.

Increased expressions of CD123, CD63, CD203c, and Fc epsilon receptor I on blood leukocytes of allergic asthma

Background: Altered basophil identification markers have been discovered to associate with allergic asthma (AA) in recent years. However, little is known about the expression of basophil markers in blood granulocytes.

Aim: To parallel test blood basophils in peripheral blood mononuclear cell (PBMC) and granulocyte populations of patients with AA and AA combined with allergic rhinitis (ARA)

Methods: The expressions of surface molecules were determined via flow cytometry. CD123 expressing cells in blood were isolated using a cell sorting technique, and mouse AA models were employed for in vivo study.

Results: The numbers of CD123⁺HLA-DR⁻ cells in the granulocytes of AA and ARA patients markedly increased. However, only 49.7% of CD123⁺HLA-DR⁻ cells in granulocytes and 99.0% of CD123⁺HLA-DR⁻ cells in PBMCs were basophils. Almost all CD123⁺HLA-DR⁻ cells expressed CD63 regardless in granulocytes or PBMC. The numbers of CD63, Fc epsilon receptor I (FcεRI), and CD203c expressing cells markedly enhanced in CD123⁺HLA-DR⁻ granulocytes of AA and ARA patients. Mean fluorescence intensity (MFI) of CD63 and CD203c expressions on CD123⁺HLA-DR⁻ PBMC and granulocytes of AA and ARA patients dramatically elevated. House dust mite extract (HDME) and Artemisia sieversiana wild allergen extract (ASWE) enhanced the numbers of CD63⁺CD123⁺HLA-DR⁻ granulocytes and PBMC and the MFI of CD203c expression on CD123⁺HLA-DR⁻ granulocyte of AA and ARA patients. Histamine, tryptase, and PGD2 enhanced proportions of CD123⁺ KU812 cells. ASWE- and HDME-induced AA mice showed upregulated CD63 expression on basophils. In conclusion, upregulated expressions of CD123, CD203c, CD63, and FcεRIα in PBMC and granulocytes of patients with AA and ARA suggest that CD123⁺HLA-DR⁻ cells may contribute to the development of AA and ARA.

Insights into urticaria in pediatric and adult populations and its management with fexofenadine hydrochloride

OBJECTIVE

The present narrative review provides a comprehensive update of the current knowledge on urticaria, both in adult and pediatric populations, and on the safety and efficacy of fexofenadine hydrochloride (HCl) as a treatment option.

DATA SOURCE

A literature search was conducted on Embase and Medline.

STUDY SELECTION

Clinical studies published in English and published between 1999 and 2020 were selected.

RESULTS

Although the exact pathogenesis of urticaria is not fully understood, multiple pathways of mast cell activation are discussed to explain the existence of phenotypically different clinical manifestations of urticaria. An overview of the worldwide prevalence of chronic urticaria, including disease burden and patient's quality of life is provided. The impact of urticaria on patient's life differs on the basis of whether its form is acute or chronic, but pharmacological approaches are most often needed to control the disabling symptoms. A summary of the current management of urticaria recommended by different guidelines across countries (Global; European; American; Australian; Asian; Japanese) is presented. Non-sedating, second-generation H₁-antihistamines are the preferred choice of treatment across several guidelines worldwide. Herein, the efficacy and safety of fexofenadine HCl, a representative second-generation H₁-antihistamine approved for the treatment of urticaria, is discussed. The occurrence of urticaria manifestations in COVID-19 patients is also briefly presented.

CONCLUSION

The burden of acute and chronic urticaria is high for patients. Second generation anti-histamines such as fexofenadine HCl can help managing the symptoms.

Serum level of hemokinin-1 is significantly lower in patients with chronic spontaneous urticaria than in healthy subjects

BACKGROUND

We previously reported upregulation of expression of Mas-related G protein-coupled receptor X2 (MRGPRX2) on mast cells (MCs) in the skin of patients with severe chronic spontaneous urticaria (CSU). Serum levels of substance P (SP) were reportedly significantly elevated, in correlation with the severity of CSU. Hemokinin-1 (HK-1) reportedly induced histamine release from LAD2 cells via MRGPRX2. We aimed to investigate HK-1's role in CSU.

METHODS

The concentrations of HK-1 and SP were measured using ELISAs. Skin- and synovium-derived cultured MCs were generated by culturing dispersed skin and synovial cells, respectively, with stem cell factor. MRGPRX2 expression in the MCs was reduced using a lentiviral shRNA silencing technique.

RESULTS

Anti-SP Ab used in the SP ELISA showed 100% cross-reactivity to HK-1, but anti-HK-1 Ab showed 0% cross-reactivity to SP. The serum level of HK-1 was significantly lower in patients with CSU (n = 151) than in non-atopic healthy control (NC) subjects (n = 114). The EC₅₀ of histamine release from MCs induced by HK-1 (5056 nM) was 12-fold higher than by SP (426 nM). Brief pretreatment of MCs with HK-1 at concentrations of 3.0-10 μM significantly reduced histamine release by 0.1 μM SP. However, brief incubation of MCs with HK-1 did not elicit rapid MRGPRX2 internalization.

CONCLUSIONS

In NC subjects, high HK-1 concentrations may desensitize MGRPRX2-mediated MC activation, thereby preventing MC degranulation by SP.

Involvement of Neuro-Immune Interactions in Pruritus With Special Focus on Receptor Expressions

Pruritus is a common, but very challenging symptom with a wide diversity of underlying causes like dermatological, systemic, neurological and psychiatric diseases. In dermatology, pruritus is the most frequent symptom both in its acute and chronic form (over 6 weeks in duration). Treatment of chronic pruritus often remains challenging. Affected patients who suffer from moderate to severe pruritus have a significantly reduced quality of life. The underlying physiology of pruritus is very complex, involving a diverse network of components in the skin including resident cells such as keratinocytes and sensory neurons as well as transiently infiltrating cells such as certain immune cells. Previous research has established that there is a significant crosstalk among the stratum corneum, nerve fibers and various immune cells, such as keratinocytes, T cells, basophils, eosinophils and mast cells. In this regard, interactions between receptors on cutaneous and spinal neurons or on different immune cells play an important role in the processing of signals which are important for the transmission of pruritus. In this review, we discuss the role of various receptors involved in pruritus and inflammation, such as TRPV1 and TRPA1, IL-31RA and OSMR, TSLPR, PAR-2, NK1R, H1R and H4R, MRGPRs as well as TrkA, with a focus on interaction between nerve fibers and different immune cells. Emerging evidence shows that neuro-immune interactions play a pivotal role in mediating pruritus-associated inflammatory skin diseases such as atopic dermatitis, psoriasis or chronic spontaneous urticaria. Targeting these bidirectional neuro-immune interactions and the involved pruritus-specific receptors is likely to contribute to novel insights into the underlying pathogenesis and targeted treatment options of pruritus.

In Chronic Spontaneous Urticaria, Comorbid Depression Linked to Higher Disease Activity, and Substance P Levels

Background: Patients with chronic spontaneous urticaria often exhibit psychiatric comorbidities including depression that contribute to the impairment of their quality of life. How CSU and depression are linked isn't well-understood. Substance P has been shown to be increased in patients with CSU and is held to contribute to the pathogenesis of depression. Methods: We measured disease activity in 30 CSU patients without depression and 30 CSU patients with depression by using the urticaria activity score. The severity of depression was assessed with the Beck Depression Inventory. We measured SP levels in these patients as well as in 30 healthy control subjects. In patients with comorbid depression, we correlated SP levels with CSU disease activity and the severity of depression. Results: In CSU patients, disease activity and the severity of depression were positively linked. UAS7 values were higher in CSU patients with comorbid depression as compared to those without (p < 0.05). SP levels were higher in CSU patients with depression than in those without (p < 0.001), but was similar in all CSU patients compared to healthy controls. SP levels weren't correlated with UAS7 values in CSU patients with depression, whereas they were weakly but significantly correlated with BDI scores (p < 0.05). Conclusion: Our results suggest that, in CSU patients with comorbid depression, CSU disease activity affects the severity of depression. CSU patients with high disease activity should be explored for comorbid depression.

Upregulation of the expression of Toll-like receptor 9 in basophils in patients with allergic rhinitis: An enhanced expression by allergens

It was reported that the expression of Toll-like receptor (TLR) 9 may be related to Th2-type allergic inflammation including allergic rhinitis (AR). However, little is known about the expression of TLR9 in the basophils in AR. In the present study, the expression of TLR9 was examined by flow cytometry analysis, and the expression of TLR9 mRNA in KU812 was determined by quantitative real-time PCR. The results showed that the percentage of TLR9⁺ CCR3⁺ cells in blood granulocytes increased by 46% in patients with AR, but not in peripheral blood mononuclear cells (PBMCs). Allergens namely Dermatophagoide allergen extract (DAE) and Platanus pollen allergen extract (PPAE) upregulated the expression of TLR9 in CCR3⁺ granulocytes by 76% and 84%, respectively. DAE and PPAE also enhanced the proportions of TLR9⁺ CD123⁺ HLA-DR^- cells and TLR9⁺ CCR3⁺ CD123⁺ HLA-DR^- cells in granulocytes and PBMCs of patients with AR. In order to investigate the actions of allergens on basophils, KU812 cells were used. It was observed that all KU812 cells expressed TLR9, and the expression intensity of TLR9 in a single KU812 cell was elevated by CpG. IL-37, IL-31, IL-33, Artemisia sieversiana wild allergen extract (ASWAE), DAE, OVA and Der p 1 induced an increase in the expression of TLR9 mRNA and IL-6 production in KU812 cells. It was shown that the percentage of TLR9-expressing basophils increased in the blood of ovalbumin (OVA)-sensitized mice. In conclusion, an increased expression of TLR9 and the production of IL-6 in basophils implicate that the contribution of basophils to AR is likely via TLR9.

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.

Urticaria: recommendations from the Italian Society of Allergology, Asthma and Clinical Immunology and the Italian Society of Allergological, Occupational and Environmental Dermatology

Background

Urticaria is a disorder affecting skin and mucosal tissues characterized by the occurrence of wheals, angioedema or both, the latter defining the urticaria-angioedema syndrome. It is estimated that 12–22% of the general population has suffered at least one subtype of urticaria during life, but only a small percentage (estimated at 7.6–16%) has acute urticaria, because it is usually self-limited and resolves spontaneously without requiring medical attention. This makes likely that its incidence is underestimated. The epidemiological data currently available on chronic urticaria in many cases are deeply discordant and not univocal, but a recent Italian study, based on the consultation of a national registry, reports a prevalence of chronic spontaneous urticaria of 0.02% to 0.4% and an incidence of 0.1–1.5 cases/1000 inhabitants/year.

Methods

We reviewed the recent international guidelines about urticaria and we described a methodologic approach based on classification, pathophysiology, impact on quality of life, diagnosis and prognosis, differential diagnosis and management of all the types of urticaria.

Conclusions

The aim of the present document from the Italian Society of Allergology, Asthma and Clinical Immunology (SIAAIC) and the Italian Society of Allergological, Occupational and Environmental Dermatology (SIDAPA) is to provide updated information to all physicians involved in diagnosis and management of urticaria and angioedema.

Psychological Stress and Chronic Urticaria: A Neuro-immuno-cutaneous Crosstalk. A Systematic Review of the Existing Evidence

PURPOSE

It has been observed that certain patients with chronic spontaneous or idiopathic urticaria (CSU/CIU) have a personal history of a significant stressor before urticaria onset, while the prevalence of any psychopathology among these patients is significantly higher than in healthy individuals. Research has confirmed that skin is both an immediate stress perceiver and a target of stress responses. These complex interactions between stress, skin, and the nervous system may contribute to the onset of chronic urticaria. This systematic review investigated the association between CSU/CIU and neuroimmune inflammation with or without evidence of co-existing psychological stress from in vivo and ex vivo studies in human beings.

METHODS

PubMed and Scopus were searched to September 2019 for reports in human beings describing neuroimmune inflammation, stress, and CSU/CIU. A comprehensive search strategy was used that included all the relevant synonyms for the central concept.

FINDINGS

A total of 674 potentially relevant articles were identified. Only 13 satisfied the predefined inclusion criteria and were included in the systematic review. Five of these 13 studies evaluated the correlation between CSU/CIU, stress, and neuro-immune-cutaneous factors, while the remaining 8 focused on the association between CSU/CIU and these factors without examining any evidence of stress.

IMPLICATIONS

The complex neuro-immune-cutaneous model that involves numerous neuropeptides and neurokinins, inflammatory mediators and cells, hypothalamic-pituitary-adrenal axis hormones, and the skin may better explain the underlying pathophysiological mechanisms involved in the onset of urticaria. In addition, the elevated psychological stress level that has been closely related to CSU/CIU could be attributed to the imbalance or irregularity of this neuro-immune-cutaneous circuit. It is still unclear and must be further investigated whether any psychological stress results in or triggers CSU/CIU onset on top of a preexisting neuroimmune dysregulation. Nevertheless, new psycho-phenotypic or neuro-endotypic CSU/CIU subsets should be considered as the era of personalized treatment strategies emerges. A better understanding of CSU/CIU pathophysiology and consideration of the patient as a whole is vital for identifying targets for new potential treatment options.

Identification and validation of differentially expressed proteins in serum of CSU patients with different duration of wheals using an iTRAQ labeling, 2D-LC-MS/MS

Chronic spontaneous urticaria (CSU) is one of the most common types of chronic urticaria (CU), with symptoms that recur easily, migrate and are refractory. It is unclear whether association between the differentiation of protein expression levels in the serum of CSU patients and the different duration of wheals exists. In the present study the samples were divided according to the duration of the wheals into group A (wheal duration <2 h) and group B (wheal duration 12–24 h). Differentially expressed proteins in sera of CSU patients with different durations of wheals were identified and validated with isobaric tags for relative and absolute quantitation (iTRAQ) in combination with two-dimensional liquid chromatography/tandem mass spectrometry (2D-LC-MS/MS). Three hundred and seventy CSU serum-related proteins were initially identified. Among these proteins, ~30 had significant differences between the groups. According to the classification of biological functions and upregulated/downregulated values, serum amyloid A (SAA), CFL1, TPM4 and monocyte differentiation antigen (CD14) were chosen and validated by enzyme-linked immunosorbent assay (ELISA). The expression levels of CD14 in sera were not significantly different among the groups. SAA, CFL1 and TPM4 were associated with the wheal duration in CSU patients and therefore could be considered as new potential inflammatory biomarkers associated with CSU.

The overlap syndrome of urticaria and gastroesophageal reflux disease

BACKGROUND

One-quarter of systemic symptoms associated with chronic spontaneous urticaria (CSU) are related to gastrointestinal complaints (GICs).

OBJECTIVES

To investigate the prevalence and features of urticaria-overlapping GICs.

METHODS

In this retrospective cross-sectional survey, 1426 consecutive outpatients were observed at our University Department. Only patients suffering from urticaria or GICs with a complete diagnostic work-up including serum total IgE level (Tot-IgE), differential blood count and urticaria activity score (UAS), were evaluated.

RESULTS

Among different GICs, gastroesophageal reflux disease (GERD) was the most frequent syndrome observed (15.4%; 95%CI: 13.6-17.3). The prevalence of overlap syndrome for urticaria and GERD was 5.9% (95%CI: 4.7-7.2). In urticaria-patients, the prevalence of GERD was four-fold higher than in patients without hives (44% vs. 11%, p<0.001). UAS was significantly higher in urticaria and GERD overlap syndromes vs. isolated urticarias. In patients with GERD or acute/chronic urticaria or overlap syndrome, Tot-IgE and eosinophil blood count (EBC) differed significantly, with a stepwise increase in their values; from the subgroup of patients with GERD only, to that with overlap of CSU to GERD. Prevalence values for urticaria overlapping with GERD were three- and two-fold higher in CSU and in long-duration GERD cases respectively compared to acute urticaria or short-duration GERD cases. Similar to Th2 pathology models, CSU and GERD overlap syndrome was significantly and independently associated with Total-IgE ≥100IU/ml or EBC ≥250/mmc compared to CSU or GERD. Endoscopic/bioptic findings of non-erosive reflux disease (NERD) or Barrett's esophagus (BE) were more frequent in chronic overlap syndrome than in GERD-patients.

CONCLUSIONS

GERD was the most frequent GIC in patients with urticaria. Overlap syndrome was more frequent among patients with CSU, where this syndrome was associated with higher values of UAS, Tot-IgE, EBC and frequencies of NERD and BE. These results suggest that overlap syndrome is frequently a chronic syndrome with a Th2-like profile.

Focus on the role of substance P in chronic urticaria

BACKGROUND

Emerging data have strengthened the importance of substance P (SP) as a proinflammatory mediator in human pathology. A role for SP in the pathogenesis of urticaria has long been hypothesized.

METHODS

Literature data regarding the possible role of SP in chronic urticaria/chronic spontaneous urticaria (CSU) have been reviewed and summarized in this manuscript. This review is based on pertinent articles that were retrieved by a selective literature search in the PubMed database. Articles in English published up to July 2018 were taken into consideration.

RESULTS

Recent studies in patients with CSU have demonstrated that circulating levels of SP are significantly elevated, in correlation with disease severity, and that SP-positive basophils are upregulated. SP has been shown to trigger degranulation in basophils derived from CSU patients. Moreover, SP can be involved in pseudoallergic reactions and may act as a histamine-releasing factor in a subset of patients with CSU. Current evidence suggests that the biological activity of SP can be exerted not only through the conventional NK-1 receptor but also through the recently identified Mas-related G protein-coupled receptors. MRGPRX2 can cause mast cell activation and has been found to be upregulated in the skin of patients with severe chronic urticaria.

CONCLUSIONS

Many findings seem to support the pathogenic involvement of SP in chronic urticaria/CSU. However, further studies are necessary to elucidate the role of SP as a mediator in CSU pathogenesis and a potential new therapeutic target.

Possible roles of basophils in chronic itch

Basophils are blood granulocytes and normally constitute <1% of blood peripheral leucocytes. Basophils share some morphological and functional similarities with mast cells, and basophils were once regarded as redundant and negligible circulating mast cells. However, recent studies reveal the indispensable roles of basophils in various diseases, including allergic and pruritic diseases. Basophils may be involved in itch through the mediation of a Th2 immune response, interaction with other cells in the skin and secretion of a wide variety of itch-related mediators, for example histamine, cytokines and chemokines (IL-4, IL-13, IL-31 and TSLP), proteases (cathepsin S), prostaglandins (PGE2 and PGD2), substance P and platelet-activating factor. Not only pruritic skin diseases (eg, atopic dermatitis, irritant contact dermatitis, chronic urticaria, prurigo, papulo-erythroderma of Ofuji, eosinophilic pustular folliculitis, scabies, tick bites and bullous pemphigoid) but also pruritic systemic diseases (eg, primary sclerosing cholangitis and polycythemia vera) may be affected by basophils.

Altered expression of IL-18 binding protein and IL-18 receptor in basophils and mast cells of asthma patients

IL-18 is likely to contribute to asthma. However, little is known regarding the role of IL-18 binding protein (BP) and IL-18 receptor (R) in asthma. Because the action of IL-18 in the body is regulated by IL-18BP and mast cells and basophils are key cell types involved in asthma, we investigated the expression of IL-18, IL-18BP and IL-18R in basophils and mast cells using flow cytometry and a mouse asthma model. We found that among basophils, approximately 53% and 51% were IL-18⁺ , 85% and 81% were IL-18BP⁺ basophils, and 19.8% and 8.6% were IL-18R⁺ in healthy control (HC) and asthmatic blood, respectively. The allergens tested had little effect on the expression of IL-18 and related factors. Only 3.5%, 14.3% and 2.4% of dispersed mast cells expressed IL-18, IL-18BP and IL-18R, respectively, in asthmatic sputum. In a mouse asthma model, OVA-sensitized mice exhibited decreased IL-18BP⁺ but increased IL-18R⁺ basophils in their blood. IL-18 increased the number of basophils but eliminated IL-18BP⁺ basophils in mouse blood. IL-18 increased the number of mast cells and IL-18R⁺ mast cells in the lung as well as increased the mast cell numbers and IL-18BP⁺ mast cells in the bronchoalveolar lavage fluid (BALF) of OVA-sensitized mice. Thus, basophils and mast cells may be involved in asthma pathogenesis via an IL-18-associated mechanism.

The role of basophils as innate immune regulatory cells in allergy and immunotherapy

Basophils are circulating cells that are associated quite exclusively with allergy response and hypersensitivity reactions but their role in the immune network might be much more intriguing and complex than previously expected. The feasibility of testing their biology in vitro for allergy research and diagnosis, due fundamentally to their quite easy availability in the peripheral blood, made them the major source for assessing allergy in the laboratory assay, when yet many further cells such as mast cells and eosinophils are much more involved as effector cells in allergy than circulating basophils. Interestingly, basophil numbers change rarely in peripheral blood during an atopic response, while we might yet observe an increase in eosinophils and modification in the biology of mast cells in the tissue during an hypersensitivity response. Furthermore, the fact that basophils are very scanty in numbers suggests that they should mainly serve as regulatory cells in immunity, rather than effector leukocytes, as still believed by the majority of physicians. In this review we will try to describe and elucidate the possible role of these cells, known as "innate IL4-producing cells" in the immune regulation of allergy and their function in allergen immunotherapy.

Up-regulated expression of substance P in CD8+ T cells and NK1R on monocytes of atopic dermatitis

BACKGROUND

Large numbers of CD8⁺ T cells were observed in atopic dermatitis (AD) skin, and monocytes from AD patients showed increased prostaglandin E2 production. However, little is known about the expression of substance P (SP) and its receptor NK1R in blood leukocytes of patients with AD.

OBJECTIVE

To explore the expression of SP and NK1R in leukocytes of AD and the influence of allergens on SP and NK1R expression.

METHODS

The expression levels of SP and NK1R in patients with AD were examined by flow cytometry, ELISA and a mouse AD model.

RESULTS

The plasma SP level was 4.9-fold higher in patients with AD than in HC subjects. Both the percentage of SP expression in the population and mean fluorescence intensity (MFI) of SP expression were elevated in CD8⁺ T cells in the blood of AD patients. However, both the CD14⁺NK1R⁺ population and MFI of NK1R expression on CD14⁺ cells were enhanced in the blood of AD patients. Allergens ASWE, HDME and PPE failed to up-regulate SP expression in CD8⁺ T cells. However, allergens ASWE and HDME both enhanced NK1R expression on CD14⁺ blood leukocytes regardless of AD or HC subjects. OVA-sensitized AD mice showed an elevated proportion and MFI of SP-expressing CD8⁺ T cells in the blood, which agrees with the SP expression situation in human AD blood. Injection of SP into mouse skin did not up-regulate NK1R expression on monocytes.

CONCLUSIONS

An elevated plasma SP level, up-regulated expression of SP and NK1R indicate that the SP/NK1R complex is important in the development of AD. Therefore, SP and NK1R antagonist or blocker agents may help to treat patients with AD. Trial registration Registration number: ChiCTR-BOC-16010279; Registration date: Dec., 28, 2016; retrospectively registered.