The Potential Role of Basophils in Urticaria

Thymic stromal lymphopoietin-activated basophil promotes lung inflammation in mouse atopic march model

Background

Atopic dermatitis (AD), a prevalent inflammatory skin disease affecting 10%-20% of the population, is linked to the development of asthma through atopic march (AM). This study aims to explore the role of basophils in OVA-induced lung inflammation in the presence of AD-like skin lesions and investigate the potential contribution of thymic stromal lymphopoietin (TSLP) in activating basophils.

Methods

Mouse AM models were established in C57BL/6 mice using MC903 and OVA epicutaneous sensitization, followed by intranasal OVA challenges. An intraperitoneal OVA-sensitized asthma model was employed as the control group. RNA-Seq analysis was conducted on lung CD45+ immune cells from these models. Histologic examinations, flow cytometry, and ELISA were used to examine the lung and systemic inflammatory response. Basophil depletion was achieved through intraperitoneal administration of anti-FcϵRIα mAb. The role of TSLP was investigated using TSLPR knockout mice.

Results

As in the intraperitoneal sensitization model, AM model also induced eosinophilic lung inflammation in mice, resembling the AM process. The RNA-Seq analysis revealed differential gene expression, with genes related to basophils being prominent in AM model. Increased basophil activation and IL-4 production were observed in OVA epicutaneously sensitized mice. Basophil depletion attenuated the eosinophilic lung inflammation. TSLP levels increased with topical MC903, and TSLPR knockout reduced lung inflammation, suggesting TSLP is involved in basophil activation.

Conclusion

Basophils play a crucial role in OVA-induced lung inflammation in the context of AD-like skin lesions, and TSLP appears to drive basophil activation. Understanding these interactions provides insights for potential therapeutic interventions in AM-associated conditions.

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.

Comorbidities of Chronic Urticaria: A glimpse into a complex relationship

Chronic Urticaria (CU) is a chronic inflammatory, predominantly mast cell-driven disease, characterized by the development of wheals and/or angioedema for more than 6 weeks. It affects approximately 1%-5% of the total population worldwide and imposes a substantial burden on health-related quality of life, significantly affecting patients' daily life. The economic impact on the health system is also not negligible, with an estimated cost per patient per year of approximately 2.000 $ in the United States. Although the underlying pathophysiology is not fully explored, autoimmune mechanisms have been proposed, including type I ("autoallergy" by means of autoantibodies to self-antigens) and type IIb (autoimmunity). Atopic, autoimmune, and psychiatric disorders are prevalent comorbidities in both children and adults with Chronic Spontaneous Urticaria (CSU). Although malignancies, cardiovascular diseases and other comorbidities have also been reported as associated diseases in patients with CSU, data remain scarce. It is still unknown whether the aforementioned comorbidities share common pathophysiological mechanisms with specific endotypes of CSU. The current review aims to overview current data on comorbidities of CU, and furthermore to comment on the potential linked pathways underlying these diseases.

Decreased peripheral basophil counts in urticaria and mouse model of oxazolone-induced hypersensitivity, the latter suggesting basopenia reflecting migration to skin

A decrease in the number of basophils in the peripheral blood, or basopenia, has been noted, reflecting the activity of chronic spontaneous urticaria (CSU). Infiltration of basophils into the skin has also been reported, but the mechanism of basopenia in CSU has not been clarified. The phenomenon of basopenia during the active phase of urticaria was confirmed, and basophil numbers increased following symptom improvement in 15 out of 17 patients treated with omalizumab and in 13 of 15 patients treated with antihistamines. Our examination by immunostaining also revealed basophil infiltration of the CSU lesions, as in previous reports, but since most of our patients were already taking oral steroids, it was not considered appropriate to examine the relationship between basophil numbers in tissue and peripheral blood. Then, we used mouse model of contact hypersensitivity with a single application of oxazolone, which is known to stimulate basophil infiltration, and investigated basophil counts in the skin, peripheral blood, and bone marrow. In this model, a decrease in peripheral blood basophil numbers was observed one day after challenge, but not after 2 days, reflecting supplementation from the bone marrow. Indeed, when cultured basophils expressing GFP were transplanted into the peripheral blood, GFP-positive basophil numbers in the peripheral blood remained low even after 2 days of challenge. Despite differences among species and models, these results suggest that one reason for the decrease of basophils in the peripheral blood in CSU may involve migration of circulating basophils into the skin.