Coagulation factors induce human skin mast cell and basophil degranulation via activation of complement 5 and the C5a receptor

Pathophysiological Mechanisms of the Onset, Development, and Disappearance Phases of Skin Eruptions in Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is a typical example of an intractable skin disease with no clear cause and significantly affects daily life of patients. Because CSU is a human-specific disease and lacks proper animal model, there are many questions regarding its pathophysiological dynamics. On the other hand, most clinical symptoms of urticaria are notable as dynamic appearance of skin eruptions called wheals. In this study, we explored dynamics of wheal by dividing it into three phases using a mathematical model: onset, development, and disappearance. Our results suggest that CSU onset is critically associated with endovascular dynamics triggered by basophils positive feedback. In contrast, the development phase is regulated by mast cell dynamics via vascular gap formation. We also suggest a disappearance mechanism of skin eruptions in CSU through an extension of the mathematical model using qualitative and quantitative comparisons of wheal expansion data of real patients with urticaria. Our results suggest that the wheal dynamics of the three phases and CSU development are hierarchically related to endovascular and extravascular pathophysiological networks.

Therapies for Chronic Spontaneous Urticaria: Present and Future Developments

Chronic spontaneous urticaria (CSU) is a complex dermatological condition characterized by recurrent wheals and/or angioedema lasting for more than six weeks, significantly impairing patients' quality of life. According to European guidelines, the first step in treatment involves second-generation H1-antihistamines (sgAHs), which block peripheral H1 receptors to alleviate symptoms. In cases with inadequate responses, the dose of antihistamines can be increased by up to fourfold. If symptoms persist despite this adjustment, the next step involves the use of omalizumab, a monoclonal anti-IgE antibody, which has shown efficacy in the majority of cases. However, a subset of patients remains refractory, necessitating alternative treatments such as immunosuppressive agents like cyclosporine or azathioprine. To address these unmet needs, several new therapeutic targets are being explored. Among them, significant attention is being given to drugs that block Bruton's tyrosine kinase (BTK), such as remibrutinib, which reduces mast cell activation. Therapies like dupilumab, which target the interleukin-4 (IL-4) and IL-13 pathways, are also under investigation. Additionally, molecules targeting the Mas-related G protein-coupled receptor X2 (MRGPRX2), and those inhibiting the tyrosine kinase receptor Kit, such as barzolvolimab, show promise in clinical studies. These emerging treatments offer new options for patients with difficult-to-treat CSU and have the potential to modify the natural course of the disease by targeting key immune pathways, helping to achieve longer-term remission. Further research is essential to better elucidate the pathophysiology of CSU and optimize treatment protocols to achieve long-term benefits in managing this condition. Altogether, the future of CSU treatments that target pathogenetic mechanisms seems promising.

Endotypes, phenotypes, and biomarkers in chronic spontaneous urticaria: Evolving toward personalized medicine

Chronic spontaneous urticaria (CSU) is an inflammatory disorder that manifests with hives, angioedema, or both and lasts more than or equal to 6 weeks. Although certain elements of CSU pathogenesis are well defined, others remain unclear. We discuss our current understanding of the underlying CSU endotypes, distinct clinical phenotypes, and predictive biomarkers. It is increasingly recognized that CSU comprises a spectrum of different underlying pathogenic mechanisms and distinct clinical presentations. Broadly, 2 endotypes that drive CSU pathogenesis have been identified, namely type I (autoallergic) and type IIb (autoimmune). However, a subpopulation shows evidence of both types, and some patients show evidence of neither. Multiple identified biomarkers have been associated with these endotypes or with disease features, such as CSU severity and duration. There is a lack of connectivity among the identified biomarkers, genetic risk loci, phenotypes, and corresponding endotypes, and each of these is frequently considered independently of the others. These identifiable features also have been associated with response, or lack thereof, to available therapies. Future investigations should optimize the endotyping of CSU using point-of-care, noninvasive, accessible biomarkers and assess the differences in response to therapy. With multiple treatments in late-stage development, establishing clearly defined CSU endotypes will facilitate future treatment decision-making and tailored treatment approaches and will inform optimal trial design.

Mast cell signaling and its role in urticaria

Chronic urticaria is a mast cell (MC)-driven disease characterized by the development of itching wheals and/or angioedema. In the last decades, outstanding progress has been made in defining the mechanisms involved in MC activation, and novel activating and inhibitory receptors expressed in MC surface were identified and characterized. Besides an IgE-mediated activation through high-affinity IgE receptor cross-linking, other activating receptors, including Mas-related G-protein-coupled receptor-X2, C5a receptor, and protease-activated receptors 1 and 2 are responsible for MC activation. This would partly explain the reason some subgroups of chronic spontaneous urticaria (CSU), the most frequent form of urticaria in the general population, do not respond to IgE target therapies, requiring other therapeutic approaches for improving the management of the disease. In this review, we shed some light on the current knowledge of the immunologic and nonimmunologic mechanisms regulating MC activation in CSU, considering the complex inflammatory scenario underlying CSU pathogenesis, and novel potential MC-targeted therapies, including surface receptors and cytoplasmic signaling proteins.

Emerging Therapeutics in Chronic Urticaria

Chronic urticaria (CU) is a common and long-lasting mast cell-mediated skin disease associated with psychiatric and autoimmune comorbidities, high economic costs, and considerable impact on quality of life. Available therapies show limited efficacy in many CU patients, which may be related to distinct underlying pathophysiology. Targeted and disease-modifying treatments with higher and broader efficacy are needed and are under development for CU. These novel drugs, small molecules, and monoclonal antibodies target mast cells and their receptors, signaling pathways, or mediators and other immune cells. In this article, the authors focus on the most promising emerging therapeutics in advanced development and discuss their potential place in future management of CU.

PTGS2: A potential immune regulator and therapeutic target for chronic spontaneous urticaria

AIMS

Chronic spontaneous urticaria (CSU) is a common and debilitating skin disease that is difficult to control with existing treatments, and the pathogenesis of CSU has not been fully revealed. The aim of this study was to explore the underlying mechanisms of CSU and identify potential treatments.

MATERIALS AND METHODS

Microarray datasets of CSU were obtained from Gene Expression Omnibus database. Differentially expressed genes between skin lesions of CSU and normal controls (LNS-DEGs) were identified, and the enrichment analyses of LNS-DEGs were performed. Hub genes of LNS-DEGs were selected by protein-protein interaction analysis. The co-expression and transcriptional regulatory networks of hub genes were conducted using GeneMANIA and TRRUST database, respectively. CIBERSORT was utilized for immune cell infiltration analysis. Experimental validation was performed by β-hexosaminidase release examination and passive cutaneous anaphylaxis (PCA) mouse model.

KEY FINDINGS

A total of 247 LNS-DEGs were identified, which were enriched in cell migration, cell chemotaxis, and inflammatory pathways such as TNF and interleukin (IL) -17 signaling pathway. Among LNS-DEGs, seven upregulated (PTGS2, CCL2, IL1B, CXCL1, IL6, VCAM1, ICAM1) and one downregulated hub gene (PECAM1) were selected. Immune infiltration analysis identified eight different immune cells, such as activated/resting mast cells and neutrophils. Furthermore, PTGS2, encoding cyclooxygenase 2 (COX2), was selected for further validation. COX2 inhibitor, celecoxib, significantly inhibited mast cell degranulation, and reduced vascular permeability and inflammatory cytokine expression in PCA mouse model.

SIGNIFICANCE

PTGS2 may be a potential regulator of immunity and inflammation in CSU. Targeting PTGS2 is a new perspective for CSU treatment.

Immunopathogenesis of urticaria: a clinical perspective on histamine and cytokine involvement

BACKGROUND

Urticaria is a clinical condition characterized by the appearance of wheals (hives), angioedema, or both. Over the last several decades, a better understanding of the mechanisms at play in the immunopathogenesis of urticaria has underscored the existence of numerous urticaria subtypes. Separating the different kinds of urticaria explicitly helps find the best detection method for the management of this skin disorder. Subtypes of urticaria also include both spontaneous and physical types. The conventional ones include spontaneous urticaria, constituting both acute and chronic urticaria. Therefore, a broad and effective therapy is essential for the diagnosis and treatment of urticaria.

METHODS

To understand the immunopathogenesis of urticaria, various databases, including PubMed, Scopus, and Web of Science, were used to retrieve original articles and reviews related to urticaria. While information on several clinical trials were obtained from clinicaltrials.gov database.

RESULTS

This article highlights the immunopathogenesis involved in the intricate interaction between cellular infiltration, immune reactions, coagulation cascades, and autoantibodies that underlie urticaria's pathophysiology.

CONCLUSION

The recent progress in understanding urticaria can help to understand the intricate characteristics in the immunopathogenesis of urticaria and could play a beneficial role in the management of urticaria.

Mathematical-based morphological classification of skin eruptions corresponding to the pathophysiological state of chronic spontaneous urticaria

BACKGROUND

Chronic spontaneous urticaria (CSU) is one of the most intractable human-specific skin diseases. However, as no experimental animal model exists, the mechanism underlying disease pathogenesis in vivo remains unclear, making the establishment of a curative treatment challenging.

METHODS

A novel approach combining mathematical modelling, in vitro experiments and clinical data analysis was used to infer the pathological state of CSU patients from geometric features of the skin eruptions.

RESULTS

Based on our hierarchical mathematical modelling, the eruptions of CSU were classified into five categories, each with distinct histamine, basophils, mast cells and coagulation factors network signatures. The analysis of 105 real CSU patients with this classification by six individual dermatologists achieved 87.6% agreement. Furthermore, our network analysis revealed that the coagulation status likely determines boundary/area pattern of wheals, while the state of spontaneous histamine release from mast cells may contribute to the divergence of size and outline of the eruptions.

CONCLUSIONS

Our multi-faceted approach was accurate in defining pathophysiological states of disease based on geometric features offering the potential to improve the accuracy of CSU diagnosis and better management of the disease in the clinic.

Time Course of Priming Effect of TF Inducers on Synergistic TF Expression and Intra-Cellular Gap Formation of Human Vascular Endothelial Cells via the Extrinsic Coagulation Cascade

Chronic spontaneous urticaria (CSU) is characterized by daily recurring wheal and flare with itch for more than 6 weeks. The extrinsic coagulation system has been shown to be activated in correlation with CSU severity. We have reported that tissue factor (TF), a trigger of the extrinsic coagulation cascade, is synergistically expressed on vascular endothelial cells by simultaneous stimulation with TF inducers (TFI), followed by activation of the extrinsic coagulation cascade and hyper permeability in vitro. However, vascular endothelial cells are not likely to be simultaneously stimulated by multiple TFIs under physiological conditions. Therefore, in order to know whether sequential, rather than simultaneous, stimuli with interval may induce synergistic activation of TF, we investigated the time course of the priming effects of each TFI for synergistic TF expression in vascular endothelial cells (HUVECs). We stimulated HUVECs with a TFI (first stimulation) and then stimulated cells with another TFI at indicated time points (second stimulation) and detected TF expression and activity. The TF expression induced by simultaneous stimulation diminished in a few hours. However, both synergistic enhancement of TF expression and activation level of the coagulation cascade were detected even when the second stimulation was added 18 or 22 h after the first stimulation. Thus, the priming effect of TFI for synergistic TF expression may persist for a half day or longer.

Basophil Characteristics as a Marker of the Pathogenesis of Chronic Spontaneous Urticaria in Relation to the Coagulation and Complement Systems

Chronic spontaneous urticaria (CSU) is a common skin disorder characterized by daily or almost daily recurring skin edema and flare with itch and pruritus anywhere on the body for more than 6 weeks. Although basophil- and mast cell-released inflammatory mediators, such as histamine, play important roles in the pathogenesis of CSU, the detailed underlying mechanism is not clear. Since several auto-antibodies, IgGs which recognize IgE or the high-affinity IgE receptor (FcεRI) and IgEs against other self-antigens, are detected in CSU patients, they are considered to activate both mast cells in the skin and basophils circulating in the blood. In addition, we and other groups demonstrated that the coagulation and complement system also contribute to the development of urticaria. Here, we summarized the behaviors, markers and targets of basophils in relation to the coagulation-complement system, and for the treatment of CSU.

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.

Remibrutinib inhibits hives effector cells stimulated by serum from chronic urticaria patients independently of FcεR1 expression level and omalizumab clinical response

BACKGROUND

Despite advances in the treatment of chronic urticaria, in a significant percentage of the patients symptoms are not fully controlled with conventional approaches. New strategies under development include blocking intracellular mediators of mast cell and basophil activation.

OBJECTIVE

We aim to investigate the effects of the Bruton's tyrosine kinase (BTK) inhibitor remibrutinib on human blood basophils and CD34+ -derived mast cells activation induced by serum obtained from chronic urticaria patients.

METHODS

Twenty-two patients with chronic spontaneous urticaria (mean age 52 years, 27% women) and 22 patients with chronic inducible urticaria (46 years, 27% women) were included in the study together with a sex-matched control group. Patients were classified as responders or non-responders to anti-IgE therapy on the basis of their clinical data, FcεR1a expression on blood basophils and total IgE levels. Changes on CD63 expression-as an activation marker-, were used to evaluate in vitro the response of basophils and mast cells to serum exposure and the inhibitory effects of remibrutinib.

RESULTS

Remibrutinib inhibits degranulation induced by IgE cross-linking in mast cells and basophils and also the activation triggered by factors present in the sera of spontaneous and inducible chronic urticaria patients. Patient's serum induces a greater degranulation of effector cells than controls. Activation of mast cells and basophils by patient sera and remibrutinib effects were not related to omalizumab responsiveness.

CONCLUSION

Remibrutinib inhibits activation of human basophils and mast cells induced in vitro by exposure to the serum of chronic urticaria patients independently of their response to omalizumab.

Chronic spontaneous urticaria: Focus on pathophysiology to unlock treatment advances

Chronic spontaneous urticaria (CSU) is a debilitating skin disease characterized by intensely itchy wheals, angioedema, or both. Symptoms recur spontaneously, on a near-daily basis, over >6 weeks; many patients experience flare-ups over several years and, consequently, reduced quality of life. Differences between the inflammatory profiles of the skin of CSU patients (wheals and nonlesional sites) and healthy controls indicate that key drivers such as mast cells, eosinophils, and basophils interact, release vasoactive mediators, and prime the skin, leaving patients predisposed to symptoms. Many cytokines and chemokines involved in these inflammatory networks and their corresponding intracellular signaling cascades have been identified. These insights informed the development of therapies such as omalizumab, dupilumab, and Bruton's tyrosine kinase (BTK) inhibitors, marking a renewed focus on pathogenesis in CSU clinical research. Despite progress, current therapies provide symptomatic control but do not appear to redress the inflammatory balance in the skin permanently. A deeper understanding of CSU pathogenesis will permit a more targeted approach to developing novel treatments with curative intent. Here, we review what is known about the pathogenesis of CSU and consider how this can be used to identify rational targets to improve patient care further.

Biologics for chronic spontaneous urticaria: toward a personalized treatment

INTRODUCTION

Chronic spontaneous urticaria (CSU) is characterized by the recurrent occurrence of short-lived wheals with or without angioedema for more than 6 weeks. Although its pathogenesis is not completely defined, several mechanisms seem involved, including autoimmunity and autoallergy with complement and coagulation activation. Various biologics are currently available or under investigation to counteract different CSU pathomechanisms.

AREAS COVERED

The recent literature dealing with biologics in the treatment of CSU was screened and analyzed; the different treatments were divided into anti-IgE and other than anti-IgE biologics. The latter were subdivided according to their target mechanisms.

EXPERT OPINION

Biologic drugs exert their effects in a very precise and specific manner. A majority of patients (arguably those with type I disease) respond to anti-IgE treatment. Others, possibly with type IIa disease, show a slow response to anti-IgE drugs. Things are much more complicated in anti-IgE-refractory patients. Some respond well to nonspecific immune suppressors, such as corticosteroids and cyclosporin suggesting that an immune-mediated pathogenic mechanism, not involving the high-affinity IgE receptor, is probably active. Several ongoing studies are evaluating biologics and small molecules counteracting other pathomechanisms, including anti-receptor biologics, Bruton tyrosine kinase (BTK) inhibitors, mast cell targets, and specific cytokines.

An update on anaphylaxis and urticaria

Notable scientific developments have taken place in the field of anaphylaxis and urticaria in recent years; they are highlighted in this review. Case-control studies, genome-wide association studies, and large omics analyses have promoted further insights into not only the underlying genetics but also the biomarkers of both anaphylaxis and urticaria. New evidence regarding IgE-dependent and non-IgE-dependent mechanisms of anaphylaxis and urticaria, including the Mas-related G protein-coupled receptor (MRGPR [formerly MRG]) signaling pathway, has been gained. Putative elicitors of anaphylactic reactions in the context of coronavirus disease 2019 (COVID-19) vaccination and impact of the COVID-19 pandemic on the management and course of chronic urticaria have been reported. Clinical progress has also been made regarding the severity grading and risk factors of anaphylaxis, as well as the distinction of phenotypes and elicitors of both diseases. Furthermore, novel treatment approaches for anaphylaxis and subtypes of urticaria have been assessed, with different outcome and potential for a better disease control or prevention.

Dysregulated haemostasis in thrombo-inflammatory disease

Inflammatory disease is often associated with an increased incidence of venous thromboembolism in affected patients, although in most instances, the mechanistic basis for this increased thrombogenicity remains poorly understood. Acute infection, as exemplified by sepsis, malaria and most recently, COVID-19, drives 'immunothrombosis', where the immune defence response to capture and neutralise invading pathogens causes concurrent activation of deleterious prothrombotic cellular and biological responses. Moreover, dysregulated innate and adaptive immune responses in patients with chronic inflammatory conditions, such as inflammatory bowel disease, allergies, and neurodegenerative disorders, are now recognised to occur in parallel with activation of coagulation. In this review, we describe the detailed cellular and biochemical mechanisms that cause inflammation-driven haemostatic dysregulation, including aberrant contact pathway activation, increased tissue factor activity and release, innate immune cell activation and programmed cell death, and T cell-mediated changes in thrombus resolution. In addition, we consider how lifestyle changes increasingly associated with modern life, such as circadian rhythm disruption, chronic stress and old age, are increasingly implicated in unbalancing haemostasis. Finally, we describe the emergence of potential therapies with broad-ranging immunothrombotic functions, and how drug development in this area is challenged by our nascent understanding of the key molecular and cellular parameters that control the shared nodes of proinflammatory and procoagulant pathways. Despite the increasing recognition and understanding of the prothrombotic nature of inflammatory disease, significant challenges remain in effectively managing affected patients, and new therapeutic approaches to curtail the key pathogenic steps in immune response-driven thrombosis are urgently required.

Basophils activation of patients with chronic spontaneous urticaria in response to C5a despite failure to respond to IgE-mediated stimuli

Urticaria is characterized by the occurrence of wheals and flares in response to vasoactive mediators, such as histamine. Various studies have suggested the involvement of basophils in the pathogenesis of chronic spontaneous urticaria (CSU). However, histamine release from peripheral basophils in response to stimuli acting on the high affinity IgE receptor (FcϵRI) is impaired in many patients with CSU (non/low responders). We previously demonstrated that tissue factor (TF)s expressed on vascular endothelial cells in response to a combination of various stimuli, such as that of histamine and lipopolysaccharide (LPS), activates the extrinsic coagulation pathway and produces anaphylatoxin, complement 5a (C5a), which then activates basophils and mast cells via the C5a receptor (C5aR). We have revealed that histamine release was induced in response to C5a and formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLP), regardless of the response to anti-IgE antibody, the reduced numbers of basophils and severity of urticaria. Moreover, we found that spontaneous release of histamine ex vivo from basophils of patients with CSU is higher than that from healthy individuals. These results suggest that basophils and the complement system, which could be activated by coagulation factors, may play a critical role in the pathogenesis of CSU, especially in cases refractory to treatment involving the IgE/FcϵRI pathway.

Increased NMUR1 Expression in Mast Cells in the Synovial Membrane of Obese Osteoarthritis Patients

Obesity is a risk factor for knee osteoarthritis (KOA). Neuromedin U (NMU) and NMU receptors (NMUR1 and NMUR2) are associated with obesity-related disorders and found in mast cells (MCs), which are elevated in osteoarthritis. However, NMU/NMUR expression was not examined in the synovial membrane (SM) or synovial MCs of obese osteoarthritis patients. We compared expression of NMU, NMUR1, NMUR2, and the mast cell (MC) marker, CPA3, in the SM of KOA patients categorized as normal weight (NW; BMI < 25 kg/m2, n = 79), overweight (OW; BMI ≥ 25 and <30 kg/m2, n = 87), and obese (OB; ≥30 kg/m2, n = 40). To study NMU/NMUR expression in MCs, we compared the MC-rich fraction (MC-RF), CD88(+) MC-RF, and CD88(−) MC-RF, extracted using magnetic isolation, with the MC-poor fraction (MC-PF). While NMU and NMUR2 expression were comparable, NMUR1 was significantly elevated in OW and OB compared to NW. Moreover, CPA3 levels were significantly greater in OB than NW. NMUR1 and CPA3 expression were significantly higher in both the CD88(+) and CD88(−) MC-RF than MC-PF. Therefore, NMUR1 expression was elevated in the SM of OB KOA patients, and its expression was found in MCs. Further investigation to analyze the NMU/NMUR1 pathway in MC may provide a link between obesity and KOA pathology.

Urticaria

Urticaria is an inflammatory skin disorder that affects up to 20% of the world population at some point during their life. It presents with wheals, angioedema or both due to activation and degranulation of skin mast cells and the release of histamine and other mediators. Most cases of urticaria are acute urticaria, which lasts ≤6 weeks and can be associated with infections or intake of drugs or foods. Chronic urticaria (CU) is either spontaneous or inducible, lasts >6 weeks and persists for >1 year in most patients. CU greatly affects patient quality of life, and is linked to psychiatric comorbidities and high healthcare costs. In contrast to chronic spontaneous urticaria (CSU), chronic inducible urticaria (CIndU) has definite and subtype-specific triggers that induce signs and symptoms. The pathogenesis of CSU consists of several interlinked events involving autoantibodies, complement and coagulation. The diagnosis of urticaria is clinical, but several tests can be performed to exclude differential diagnoses and identify underlying causes in CSU or triggers in CIndU. Current urticaria treatment aims at complete response, with a stepwise approach using second-generation H1 antihistamines, omalizumab and cyclosporine. Novel treatment approaches centre on targeting mediators, signalling pathways and receptors of mast cells and other immune cells. Further research should focus on defining disease endotypes and their biomarkers, identifying new treatment targets and developing improved therapies.

Autoimmune chronic spontaneous urticaria

Chronic spontaneous urticaria (CSU) is a debilitating mast cell-driven disease characterized by recurrent wheals and/or angioedema. Substantial progress has been made in dissecting the 2 main autoimmune mechanisms that drive the pathogenesis of CSU. Type I autoimmune (autoallergic) CSU is associated with IgE antibodies against autoantigens, for example, thyroid peroxidase and IL-24. Type IIb autoimmune CSU is mediated by autoantibodies that activate mast cells, for example, via IgE and FcεRI, and is present in less than 10% of patients with CSU when strict criteria are used, that is, triple positivity of autologous serum skin test, immunoassays for IgG autoantibodies, and basophil activation tests. A subpopulation of patients with CSU has both types. Type IIb autoimmune CSU is characterized by higher disease severity, concomitant autoimmune diseases, low levels of total IgE, elevated levels of IgG-anti-thyroid peroxidase, basopenia, eosinopenia, poor response to antihistamines and to omalizumab, and a good response to cyclosporine. Novel targeted therapies for CSU are under development such as ligelizumab, an anti-IgE, fenebrutinib and remibrutinib, Bruton's tyrosine kinase inhibitors, and dupilumab, an anti-IL-4Rα. Further studies should investigate the overlap between autoallergic and type IIb autoimmune CSU, optimize the diagnosis of both autoimmune endotypes using easy-to-perform, noninvasive, and inexpensive markers, and assess differences in response to therapy.

The Role of Crosstalk of Immune Cells in Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is defined as recurrent episodes of spontaneous wheal development and/or angioedema for more than six weeks and at least twice a week. The core link in the pathogenesis of CSU is the activation of mast cells, T cells, eosinophils, and other immune cells infiltrating around the small venules of the lesion. Increased vascular permeability, vasodilatation, and recruitment of inflammatory cells directly depend on mast cell mediators’ release. Complex regulatory systems tightly influence the critical roles of mast cells in the local microenvironment. The bias toward Th2 inflammation and autoantibodies derived from B cells, histamine expressed by basophils, and initiation of the extrinsic coagulation pathway by eosinophils or monocytes exerts powerful modulatory influences on mast cells. Cell-to-cell interactions between mast cells and eosinophils/T cells also are regulators of their function and may involve CSU’s pathomechanism. This review summarizes up-to-date knowledge regarding the crosstalk between mast cells and other immune cells, providing the impetus to develop new research concepts and treatment strategies for CSU.

A novel detection method for cross-linking of IgE-receptors by autoantibodies in chronic spontaneous urticaria

BACKGROUND

Autoantibodies (AAbs) against immunoglobulin E (IgE) antibodies (Abs) and their high-affinity receptor alpha subunits (FcεRIα) are key factors in the elicitation of type IIb autoimmune chronic spontaneous urticaria (type IIb aiCSU). In this study, we aimed to develop a new method to detect functional anti-FcεRIα and anti-IgE AAbs, which can crosslink the plural FcεRІα molecules and IgE Abs on the surface of mast cells and basophils, in sera from aiCSU patients using the amplified luminescence proximity homogeneous assay (Alpha).

METHODS

Sera were obtained from 14 aiCSU patients, as diagnosed by recurrent chronic spontaneous urticaria episodes and positive results for the autologous serum skin test and/or histamine release test (HRT). The AAbs to FcεRIα and IgE Abs were determined in sera from aiCSU patients using enzyme-linked immunosorbent assay (ELISA) and Alpha by cross-linking (AlphaCL) of IgE Abs and/or FcεRІα.

RESULTS

Serum anti-FcεRIα and anti-IgE AAb levels were not significantly different between aiCSU patients and healthy subjects in ELISA. Anti-FcεRIα AAbs were detected in 10 of 14 aiCSU patients who displayed positive (5/5) and negative (5/9) results in the HRT for anti-FcεRIα AAbs by AlphaCL, whereas no signals were observed in healthy subjects. Additionally, anti-IgE AAbs were detected in two of four aiCSU patients who displayed positive results in the HRT for anti-IgE AAbs.

CONCLUSIONS

A new assay method using AlphaCL can detect anti-FcεRIα and anti-IgE AAbs with FcεRIα- and IgE-crosslinking abilities in sera from aiCSU patients. This simple and practical assay method may be available as a diagnostic tool for urticaria patients.

Chronic Urticaria: Advances in Understanding of the Disease and Clinical Management

Chronic urticaria (CU) is a common skin condition characterized by the recurrence of wheals, with or without angioedema, which lasts for at least 6 weeks. Owing to its pruritus and incurability, this disease adversely affects the patients' physical and mental health and diminishes the quality of life. CU is generally classified into two subtypes based on the relevance of eliciting factors: chronic spontaneous urticaria (CSU) and chronic inducible urticaria (CIndU), the latter of which is further divided into several subtypes. To improve the understanding and clinical management of this highly heterogeneous disorder, the EAACI/GA²LEN/EDF/WAO guideline was developed and published in 2018 based on evidence and expert consensus. The diagnostic and treatment algorithms proposed by the guideline have largely facilitated dermatologists in clinical practice. However, several questions remained unsolved and have been widely investigated in the recent years. First, a better understanding of the association between chronic urticaria and its potential underlying causes or eliciting factors such as autoimmunity, infections, coagulation aberrance, and vitamin D deficiency is warranted. This would lead to updates in the diagnostic and treatment procedures of different subtypes of chronic urticaria. Secondly, treatment for recalcitrant cases, especially those resistant to or intolerant of second-generation antihistamines and (or) omalizumab, calls for novel therapeutic measures or strategies. In the present review, we summarized recent advances in the understanding and management of both CSU and CIndU, with special emphasis on their underlying causes or eliciting factors, pathogenic mechanisms, potential targets for intervention, and advances in treatment strategies.

The Role of Coagulation and Complement Factors for Mast Cell Activation in the Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is a common skin disorder characterized by an almost daily recurrence of wheal and flare with itch for more than 6 weeks, in association with the release of stored inflammatory mediators, such as histamine, from skin mast cells and/or peripheral basophils. The involvement of the extrinsic coagulation cascade triggered by tissue factor (TF) and complement factors, such as C3a and C5a, has been implied in the pathogenesis of CSU. However, it has been unclear how the TF-triggered coagulation pathway and complement factors induce the activation of skin mast cells and peripheral basophils in patients with CSU. In this review, we focus on the role of vascular endothelial cells, leukocytes, extrinsic coagulation factors and complement components on TF-induced activation of skin mast cells and peripheral basophils followed by the edema formation clinically recognized as urticaria. These findings suggest that medications targeting activated coagulation factors and/or complement components may represent new and effective treatments for patients with severe and refractory CSU.

The Pathogenesis of Chronic Spontaneous Urticaria: The Role of Infiltrating Cells

Chronic spontaneous urticaria is characterized by a perivascular non-necrotizing cellular infiltrate around small venules of the skin. It consists primarily of CD4(+) lymphocytes, a prominence of the T helper (Th)2 subtype but also Th1 cells, with Th17 cell-derived cytokines elevated in plasma. There are also neutrophils, eosinophils, basophils, and monocytes. Chemokines derived from mast cells and activated endothelial cells drive the process. Although the role of the cellular infiltrate has not previously been addressed, each constituent can contribute to the overall pathogenesis. It is of interest that CSU responds to corticosteroid, yet, short-term steroids do not affect autoimmunity or degranulation of mast cells, and act on margination of cells along the endothelium and chemotaxis to enter the surrounding dermis. In this review, we address each cell's contribution to the overall inflammatory response, as it is currently understood, with a view toward development of therapeutic options that impede the function of critical cells and/or their secretory products.