Urticaria and basophils

IgE-Mediated Activation of Mast Cells and Basophils in Health and Disease

Type 2-mediated immune responses protect the body against environmental threats at barrier surfaces, such as large parasites and environmental toxins, and facilitate the repair of inflammatory tissue damage. However, maladaptive responses to typically nonpathogenic substances, commonly known as allergens, can lead to the development of allergic diseases. Type 2 immunity involves a series of prototype TH2 cytokines (IL-4, IL-5, IL-13) and alarmins (IL-33, TSLP) that promote the generation of adaptive CD4+ helper Type 2 cells and humoral products such as allergen-specific IgE. Mast cells and basophils are integral players in this network, serving as primary effectors of IgE-mediated responses. These cells bind IgE via high-affinity IgE receptors (FcεRI) expressed on their surface and, upon activation by allergens, release a variety of mediators that regulate tissue responses, attract and modulate other inflammatory cells, and contribute to tissue repair. Here, we review the biology and effector mechanisms of these cells, focusing primarily on their role in mediating IgE responses in both physiological and pathological contexts.

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.

Neuroimmune mechanisms of type 2 inflammation in the skin and lung

Type 2 inflammation has a major role in barrier tissues such as the skin and airways and underlies common conditions including atopic dermatitis (AD) and asthma. Cytokines including interleukin 4 (IL-4), IL-5, and IL-13 are key immune signatures of type 2 inflammation and are the targets of multiple specific therapeutics for allergic diseases. Despite shared core immune mechanisms, the distinct structures and functions of the skin and airways lead to unique therapeutic responses. It is increasingly recognized that the nervous system has a major role in sensing and directing inflammatory processes. Indeed, crosstalk between type 2 immune activation and somatosensory functions mediates tissue-specific signatures such as itching in the skin. However, neuroimmune interactions are shaped by distinct neuronal and immune landscapes, and differ between the skin and airways. In the skin, dorsal root ganglia-derived neurons mediate pruritus via type 2 cytokines and neurogenic inflammation by mast cell or basophil activation. Conversely, vagal ganglia-derived neurons regulate airway immune responses by releasing neuropeptides/neurotransmitters such as calcitonin gene-related peptides, neuromedin U, acetylcholine, and noradrenaline. Sensory neuron-derived vasoactive intestinal peptide forms a feedback loop with IL-5, amplifying eosinophilic inflammation in the airways, a mechanism that is absent in the skin. These differences influence the efficacy of cytokine-targeted therapies. For instance, IL-4/IL-13-targeted therapies like dupilumab demonstrate efficacy in AD and allergic airway diseases, whereas IL-5-targeted therapies are effective in eosinophilic asthma but not AD. Understanding these neuroimmune interactions underscores the need for tailored therapeutic approaches to address allergic diseases where barrier tissues are involved.

Beyond the itch: the complex interplay of immune, neurological, and psychological factors in chronic urticaria

Chronic urticaria (CU) arises from a multifaceted interplay of immunological, neurological, and psychological components. Immune dysregulation, mediated through both immunoglobulin E (IgE)-dependent and IgE-independent pathways, plays a pivotal role in CU pathogenesis, involving key effector cells such as mast cells (MCs), basophils, and eosinophils. This dysregulation culminates in the release of histamine, prostaglandins, and other mediators, which precipitate pruritus. The chronicity of the disease leads to sustained pruritic symptoms, contributing to both central and peripheral sensitization. The excitation of the itch circuit is augmented, leading to the release of neurotransmitters and neuropeptides, which subsequently interact with immune cells. Psychological factors such as depression, anxiety, and stress exacerbate CU symptoms and diminish quality of life. These factors disrupt the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS). Furthermore, the act of scratching activates the reward circuit, resulting in the manifestation of the itch-scratching cycle. Current treatments, such as antihistamines, omalizumab, and cyclosporine, demonstrate variable efficacy and are often associated with adverse effects. A holistic approach addressing both psychological and physiological aspects is advocated. This review highlights the critical importance of understanding neuroimmune interactions and the influence of psychosomatic factors in CU. It aims to enhance diagnostic and therapeutic strategies by integrating psychological, neurological, and immunological perspectives.

Association of Circulating Basophil Count with Gastric Cancer Prognosis

PURPOSE

Basophils play a crucial role in immunoglobulin E-mediated allergic reactions and parasitic infections. Recently, a low basophil count was reported to be a poor prognostic indicator in patients with malignant tumors. This study aimed to investigate the cut-off value to evaluate the clinicopathological and prognostic significance of the basophil count in patients with gastric cancer.

METHODS

This study enrolled 1192 gastric cancer patient who underwent surgery without preoperative chemotherapy between 2001 and 2020. The cutoff value was 26/μl based on the receiver of characteristics curves for overall survival, and 606 patients were classified as the low basophil group. The clinicopathological and prognostic significance of the low basophil count was assessed by univariate and multivariate analyses.

RESULTS

Elderly age (p < 0.001), high C-reactive protein level (p < 0.001), low lymphocyte count (p = 0.044), and low neutrophil count (p < 0.001) are independently associated with low basophil count. The low basophil group demonstrated a significantly worse overall survival than the high basophil group (p = 0.005). Although there was no significant difference in stage I, the low basophil group demonstrated poor overall survival in stage II/III/IV. In stage II, low basophil count was independently associated with poor OS. In stage III/IV, low basophil group tended to have poor overall survival rate. Including all stages, low basophil count was an independent risk factor for poor overall survival (hazard ratio (HR) = 1.29, 95% CI: 1.03-1.61, p = 0.027).

CONCLUSION

Low basophil count was significantly associated with elderly age, high C-reactive protein level, and low neutrophil count (<26/μl). In addition, low basophil count was an independent poor prognostic factor in patients with gastric cancer. Thus, preoperative circulating basophil count assessment may be useful for predicting the postoperative survival of patients with gastric cancer.

The decrease in peripheral blood basophils in a mouse model of IgE-induced inflammation involves their migration to lymph nodes

BACKGROUND

During the active phase of urticaria, a decrease in peripheral blood basophils, known as basopenia, is observed. We previously reported that basopenia occurs as a result of basophils migrating to the skin in a contact dermatitis model where a Th2 response is induced with oxazolone.

OBJECTIVE

Although there is currently no established model for urticaria, given that urticaria is an IgE-mediated immediate-type allergic reaction, we aimed to determine whether an IgE-mediated model could reproduce the decrease in basophils in peripheral blood observed during the active phase of urticaria.

METHODS

Mice were pretreated with 2,4,6-trinitrophenylhaptene (TNP)-specific IgE and basophil dynamics were examined following stimulation with TNP-ovalbumin. Mast cell-deficient WBB6F1-KitW/KitW-v mice were used to investigate the role of mast cells in this IgE-mediated model.

RESULTS

Following stimulation, we observed immediate ear swelling and basopenia after 0.5 hours. However, the number of basophils observed in the skin lesions was low, while a higher number of basophils were observed in the antigen-draining lymph nodes (LN). In mast cell-deficient mice, no increase in basophils in the LN was observed, reflecting reduced antigen influx into the LN, but basophils remained in the skin.

CONCLUSIONS

In the IgE-mediated mouse model, basopenia was observed, which coincided with the induction of inflammation in the skin. The migration of basophils to the LN in this model suggests that the systemic immune system, including the LN, should be considered when exploring the pathogenesis of urticaria in humans.

Chronic Spontaneous Urticaria: Etiology and Pathogenesis

Urticaria, also known as hives, is a common condition thought to affect up to 20% of individuals worldwide in their lifetime. This skin condition is characterized by the appearance of pruritic, erythematous papules or plaques with superficial swelling of the dermis. The major complaint is the symptom of pruritus. Angioedema, which involves a deeper swelling of dermal or mucosal tissues, may accompany urticaria. Urticaria can be classified by both time course of symptoms and the underlying etiology.

Current insights on gut microbiome and chronic urticaria: progress in the pathogenesis and opportunities for novel therapeutic approaches

Chronic urticaria (CU) is a prevalent skin disorder greatly impacting the patients' life quality, in which immune dysregulation mediated by gut microbiome plays a significant role. Several studies have found the gut dysbiosis exists in patients with CU. In addition, infection may also be one of the causes of CU. The primary treatment currently used for CU is the second-generation non-sedating H1-antihistamines (nsAH). However, there are some limitations in current therapies. Based on the latest evidence, this review provides an updated overview of how the gut dysbiosis influences CU development, explores potential therapeutic approaches based on the gut microbiota and summarizes the interaction between gut microbiota and current treatment.

Autoimmune Diseases and Low Baseline IgE in Chronic Spontaneous Urticaria: A Clinical and Therapeutic Prospective Analysis in Real-Life Clinical Practice

BACKGROUND

Autoimmunity contributes to the pathogenesis of chronic spontaneous urticaria (CSU). The subtyping of CSU has revealed an autoimmune form of CSU. Despite autoimmune diseases having been associated with CSU, there are few prospective studies that have evaluated the characteristics and biomarkers of patients with CSU and autoimmune disease in a real-life practice setting.

OBJECTIVE

To evaluate the presence of specific biomarkers for the presence of autoimmune disease in CSU and to analyze the clinical and therapeutic features of patients with CSU and autoimmune disease.

METHODS

The clinical, laboratory, and therapeutic features of patients with CSU at a tertiary-level center were prospectively collected. Data obtained were compared in function of the presence/absence of autoimmune disease and typified according to IgE levels.

RESULTS

Patients with CSU who had associated autoimmune disease corresponded to middle-aged women with a common pattern of blood test findings: both low baseline IgE and high-affinity receptor of IgE expression, basopenia, eosinopenia, higher baseline erythrocyte sedimentation rate and D-dimer, increased presence of antinuclear antibodies, IgG against thyroid peroxidase, and positive autologous serum skin test result. Total baseline IgE less than or equal to 43.8 IU/mL was both the optimal cutoff to predict autoimmune disease in the CSU cohort and a significant risk factor for the presence of autoimmune disease in the regression analysis.

CONCLUSIONS

In real-life clinical practice, characteristics of patients with CSU and autoimmune disease share common features with type IIb autoimmune CSU. Total baseline IgE less than or equal to 43.8 IU/mL has been detected as a possible biomarker of autoimmune disease in patients with CSU.