Bidirectional associations between eosinophils, basophils, and lymphocytes with atopic dermatitis: A multivariable Mendelian randomization study

The Role of Basophils in Atopic Dermatitis, from Pathogenesis to Therapeutic Perspectives

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by intense pruritus. The principal pathological features include abnormalities in the structure and function of the epidermis, as well as skin inflammation marked by the overexpression of T helper 2 cell (Th2) cytokines. Throughout the progression of AD, various immune cells contribute to its pathogenesis. Basophils, the least abundant granulocytes in the human peripheral circulation, have historically been overlooked. However, the advent of novel research tools has facilitated a renewed focus on the role of basophils in diverse physiological and pathological conditions, including AD. Accordingly, this review will primarily summarize the association between AD and basophils, the alterations observed in basophils among AD patients, and the implications of these changes for AD patients.

Enhanced Siglec-8 and HLA-DR and reduced CRTH2 surface expression highlight a distinct phenotypic signature of circulating eosinophils in atopic dermatitis

Atopic dermatitis and other type 2 immune response diseases are often linked to elevated eosinophil levels in the blood. Although the role of eosinophils in atopic dermatitis pathophysiology is suspected, it remains unclear. The development of new treatments targeting the type 2 response, particularly cytokines involved in eosinophil activation and chemotaxis, makes it necessary to identify potential eosinophil profiles in atopic dermatitis that may respond to these treatments. A prospective study was conducted comparing blood eosinophil phenotypes in patients with moderate to severe atopic dermatitis (n = 19) without recent systemic treatment to healthy individuals (n = 19). The primary outcome was the membranous phenotypic signature of eosinophils, assessed by flow cytometry. Most patients with atopic dermatitis (84%) had early onset in childhood, a severe disease (mean SCORing Atopic Dermatitis of 57.5), and elevated blood eosinophil counts (310 per µL in atopic dermatitis vs 120 in healthy individuals, P < 0.0001). Patients with atopic dermatitis exhibited lower CRTH2 on eosinophils but higher levels of human leukocyte antigen-DR isotype and Siglec-8 compared to healthy individuals. Other surface proteins showed no significant differences. Clustering analysis confirmed increased Siglec-8 in patients with atopic dermatitis. Additionally, patients with atopic dermatitis had higher serum levels of type 2 immune response markers such as eotaxin-2, IL-5, IL-3, and TARC. Circulating eosinophils in patients with atopic dermatitis show a distinct phenotypic profile, suggesting a role in atopic dermatitis pathophysiology and potential involvement in differential treatment responses.

Causal association of allergic diseases, eosinophils, and osteoporosis: A Mendelian randomization study

Background

The association between allergic diseases and osteoporosis remains controversial. We hypothesize that this discrepancy may be due to a mediator that plays a role in the pathogenesis of both allergic diseases and osteoporosis. To test this hypothesis, we used Mendelian randomization (MR) analysis to investigate the relationships among allergic diseases, eosinophils, and osteoporosis.

Method

This study utilized data from publicly available GWAS databases, including 3 allergic diseases: asthma, allergic rhinitis, and eczema. We conducted bidirectional MR analyses on the relationships between allergic diseases and eosinophils (including eosinophil counts and percentage), allergic diseases and osteoporosis, and eosinophils and osteoporosis, respectively. We conducted sensitivity analyses for results with significance, validated the findings using multivariable Mendelian randomization (MVMR) analysis to ensure the reliability of the significant results.

Results

Two-sample MR analysis revealed significant bidirectional causal relationships between the 3 allergic diseases and eosinophils. A unidirectional causal relationship was found between eosinophils and osteoporosis, with eosinophil counts associated with osteoporosis (OR: 1.194; 95% CI 1.064 to 1.339; Pivw <0.001) and eosinophil percentage associated with osteoporosis (OR: 1.187; 95% CI 1.057 to 1.332; Pivw <0.001). Sensitivity analyses indicated no pleiotropy, However, the association between eosinophil percentage and osteoporosis was no longer significant after multivariable (MVMR) analysis. Additionally, no causal effects were observed from allergic diseases to osteoporosis, from osteoporosis to allergic diseases, or from osteoporosis to eosinophils.

Conclusions

1.) There is a significant bidirectional potential causal relationship between the 3 allergic diseases (asthma, allergic rhinitis, eczema) and eosinophils. 2.) There is no evidence to support a causal relationship between the 3 allergic diseases and osteoporosis, and vice versa. 3.) There is a unidirectional causal relationship may exist from eosinophil counts to osteoporosis.

Eosinophil-Basophil/Lymphocyte (EB/LR) and Eosinophil-Basophil-Platelet/Lymphocyte (EBP/LR) Ratios Could Serve as Useful Additional Markers for Assessing the Severity of Wasp Allergic Reactions

Wasp venom allergy can trigger severe allergic reactions, and predicting these acute responses remains challenging. This study evaluates the utility of immune system indexes, particularly the eosinophil-basophil/lymphocyte (EB/LR) and eosinophil-basophil-platelet/lymphocyte (EBP/LR) ratios, in assessing the severity of allergic reactions in patients with wasp venom allergy. A total of 61 patients with confirmed wasp venom allergy were categorized according to the Mueller scale, which classifies the severity of allergic reactions. Blood samples were analyzed for total and specific IgE levels alongside a range of hematological and biochemical parameters. This study found significant differences in the EB/LR and EBP/LR indexes between patients with mild (Mueller I-II) and severe (Mueller III-IV) allergic reactions, with higher values indicating more severe responses. However, no significant differences were observed in other immune indexes, such as the platelet-to-lymphocyte ratio, neutrophil-to-lymphocyte ratio, systemic immune-inflammation index, and systemic inflammatory response index, as well as in additional blood parameters. These findings suggest that the EB/LR and EBP/LR ratios may serve as useful markers for predicting the severity of allergic reactions in patients with wasp venom allergy. This is the first study to establish such a link, although further research with larger cohorts is necessary to confirm these results and their potential application in clinical settings.

The Roles of Innate Immune Cells in Atopic Dermatitis

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin condition characterized by recurrent eczematous lesions and severe pruritus. The economic burden and time penalty caused by the relapse of AD reduce patients' life quality.

SUMMARY

AD has complex pathogenesis, including genetic disorders, epidermal barrier dysfunction, abnormal immune responses, microbial dysbiosis of the skin, and environmental factors. Recently, the role of innate immune cells in AD has attracted considerable attention. This review highlighted recent findings on innate immune cells in the onset and progression of AD.

KEY MESSAGES

Innate immune cells play essential roles in the pathogenesis of AD and enough attention should be given for treating AD from the perspective of innate immunity in clinics.

Potential Role of IL-37 in Atopic Dermatitis

Interleukin 37 (IL-37) is a recently discovered member of the IL-1 cytokine family that appears to have anti-inflammatory and immunosuppressive effects in various diseases. IL-37 acts as a dual-function cytokine, exerting its effect extracellularly by forming a complex with the receptors IL-18 α (IL-18Rα) and IL-1R8 and transmitting anti-inflammatory signals, as well as intracellularly by interacting with Smad3, entering the nucleus, and inhibiting the transcription of pro-inflammatory genes. Consequently, IL-37 is linked to IL-18, which plays a role in the pathogenesis of atopic dermatitis (AD), consistent with our studies. Some isoforms of IL-37 are expressed by keratinocytes, monocytes, and other skin immune cells. IL-37 has been found to modulate the skewed T helper 2 (Th2) inflammation that is fundamental to the pathogenesis of AD. This review provides an up-to-date summary of the function of IL-37 in modulating the immune system and analyses its potential role in the pathogenesis of AD. Moreover, it speculates on IL-37's hypothetical value as a therapeutic target in the treatment of AD.

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.